In JoVE (1)

Other Publications (52)

Articles by Isabel Varela-Nieto in JoVE

 JoVE Biology

A Comparative Study of Drug Delivery Methods Targeted to the Mouse Inner Ear: Bullostomy Versus Transtympanic Injection

1Instituto de Investigaciones Biomédicas (IIBm) Alberto Sols CSIC-UAM, 2Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III (ISCIII), 3Instituto de Investigación Sanitaria La Paz (IdiPAZ), 4Facultad de Veterinaria, Universidad Complutense de Madrid, 5Departmento de Otorrino laringología, Hospital Universitario La Paz


JoVE 54951

Other articles by Isabel Varela-Nieto on PubMed

Serum Deprivation Increases Ceramide Levels and Induces Apoptosis in Undifferentiated HN9.10e Cells

Neurochemistry International. Apr, 2002  |  Pubmed ID: 11792463

Sphingolipid metabolites have been involved in the regulation of proliferation, differentiation and apoptosis. While cellular mechanisms of these processes have been extensively analysed in the post-mitotic neurons, little is known about proliferating neuronal precursors. We have taken as a model of neuroblasts the embryonic hippocampal cell line HN9.10e. Apoptosis was induced by serum deprivation and by treatment with N-acetylsphingosine (C2-Cer), a membrane-permeant analogue of the second messenger ceramide. Following C2-Cer addition, cytochrome c was released from mitochondria, [Ca(2+)](i) and caspase-3-like activity increased. Both cytochrome c release and rise of [Ca(2+)](i) occurred before caspase-3 activation and nuclear condensation. The intracellular levels of ceramide peaked at 1h following the serum deprivation. These results indicate that the serum deprivation induces a rise in the intracellular ceramide level, and that increased ceramide concentration leads to calcium dysregulation and release of cytochrome c followed by caspase-3 activation. We show that cytochrome c is released without a loss of mitochondrial transmembrane potential.

Liver Cell Proliferation Requires Methionine Adenosyltransferase 2A MRNA Up-regulation

Hepatology (Baltimore, Md.). Jun, 2002  |  Pubmed ID: 12029623

Regulation of liver cell proliferation is a key event to control organ size during development and liver regeneration. Methionine adenosyltransferase (MAT) 2A is expressed in proliferating liver, whereas MAT1A is the form expressed in adult quiescent hepatocytes. Here we show that, in H35 hepatoma cells, growth factors such as hepatocyte growth factor (HGF) and insulin up-regulated MAT2A expression. HGF actions were time- and dose-response dependent and required transcriptional activity. Mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-phosphate kinase (PI 3-K) pathways were required for both HGF-induced cell proliferation and MAT2A up-regulation. Furthermore, in H35 cells treated with HGF, the inhibition of these pathways was associated with the switch from the expression of fetal liver MAT2A to the adult liver MAT1A isoform. Fetal liver hepatocytes exhibited an identical response pattern. Treatment of H35 hepatoma cells with MAT2A antisense oligonucleotides decreased cell proliferation induced by HGF; this decrease correlated with the decay in MAT2A messenger RNA (mRNA) levels. Finally, growth inhibitors such as transforming growth factor (TGF) beta blocked HGF-induced MAT2A up-regulation while increasing MAT1A mRNA levels in H35 cells. In conclusion, our results show that MAT2A expression not only correlates with liver cell proliferation but is required for this process.

Cochlear Abnormalities in Insulin-like Growth Factor-1 Mouse Mutants

Hearing Research. Aug, 2002  |  Pubmed ID: 12208536

Insulin-like growth factor 1 (IGF-1) modulates inner ear cell proliferation, differentiation and survival in culture. Its function in human hearing was first evidenced by a report of a boy with a homozygous deletion of the Igf-1 gene, who showed severe sensorineural deafness [Woods et al., New Engl. J. Med. 335 (1996) 1363-1367]. To better understand the in vivo role of IGF-1 during inner ear differentiation and maturation, we studied the cochleae of Igf-1 gene knockout mice by performing morphometric stereological analyses, immunohistochemistry and electron microscopy on postnatal days 5 (P5), P8 and P20. At P20, but not at P5, the volumes of the cochlea and cochlear ganglion were significantly reduced in mutant mice, although the reduction was less severe than whole body dwarfism. A significant decrease in the number and average size of auditory neurons was also evident at P20. IGF-1-deficient cochlear neurons showed increased apoptosis, along with altered expression of neurofilament 200 kDa and vimentin. The eighth nerve, the cochlear ganglion and the fibers innervating the sensory cells of the organ of Corti of the P20 mouse mutants presented increased expression of vimentin, whereas the expression of neurofilament was decreased. In addition, the myelin sheath was severely affected in ganglion neurons. In conclusion, IGF-1 deficit in mice severely affects postnatal survival, differentiation and maturation of the cochlear ganglion cells.

Expression and Function of Phospholipase A(2) in Brain

FEBS Letters. Oct, 2002  |  Pubmed ID: 12401195

Phospholipase A(2) (PLA(2)) appears to play a fundamental role in cell injury in the central nervous system. We have investigated PLA(2) expression in the astrocytoma cell line 1231N1, and found that GIVA, GIVB, GIVC and GVI PLA(2) messages are expressed. PLA(2) activity is increased by inflammatory/injury stimuli such as interleukin-1beta and lipopolysaccharide in these cells but with very different time courses. The arachidonic acid liberated is converted to prostaglandin E(2), possibly by cyclooxygenase-2, which is induced by inflammatory stimuli. This cell system emerges as a model to study injury/inflammation-related activation of the new PLA(2) forms GIVB and GIVC.

Programmed Cell Death in the Developing Inner Ear is Balanced by Nerve Growth Factor and Insulin-like Growth Factor I

Journal of Cell Science. Feb, 2003  |  Pubmed ID: 12508109

Nerve growth factor induces cell death in organotypic cultures of otic vesicle explants. This cell death has a restricted pattern that reproduces the in vivo pattern of apoptosis occurring during inner ear development. In this study, we show that binding of nerve growth factor to its low affinity p75 neurotrophin receptor is essential to achieve the apoptotic response. Blockage of binding to p75 receptor neutralized nerve-growth-factor-induced cell death, as measured by immunoassays detecting the presence of cytosolic oligonucleosomes and by TUNEL assay to visualize DNA fragmentation. Nerve growth factor also induced a number of cell-death-related intracellular events including ceramide generation, caspase activation and poly-(ADP ribose) polymerase cleavage. Again, p75 receptor blockade completely abolished all of these effects. Concerning the intracellular pathway, ceramide increase depended on initiator caspases, whereas its actions depended on both initiator and effector caspases, as shown by using site-specific caspase inhibitors. Conversely, insulin-like growth factor I, which promotes cell growth and survival in the inner ear, abolished apoptosis induced by nerve growth factor. Insulin-like growth factor cytoprotective actions were accomplished, at least in part, by decreasing endogenous ceramide levels and activating Akt. Taken together, these results strongly suggest that regulation of nerve-growth-factor-induced apoptosis in the otocysts occurs via p75 receptor binding and is strictly controlled by the interaction with survival signalling pathways.

Cell Death in the Nervous System: Lessons from Insulin and Insulin-like Growth Factors

Molecular Neurobiology. Aug, 2003  |  Pubmed ID: 14514984

Programmed cell death is an essential process for proper neural development. Cell death, with its similar regulatory and executory mechanisms, also contributes to the origin or progression of many or even all neurodegenerative diseases. An understanding of the mechanisms that regulate cell death during neural development may provide new targets and tools to prevent neurodegeneration. Many studies that have focused mainly on insulin-like growth factor-I (IGF-I), have shown that insulin-related growth factors are widely expressed in the developing and adult nervous system, and positively modulate a number of processes during neural development, as well as in adult neuronal and glial physiology. These factors also show neuroprotective effects following neural damage. Although some specific actions have been demonstrated to be anti-apoptotic, we propose that a broad neuroprotective role is the foundation for many of the observed functions of the insulin-related growth factors, whose therapeutical potential for nervous system disorders may be greater than currently accepted.

Growth Factors and Early Development of Otic Neurons: Interactions Between Intrinsic and Extrinsic Signals

Current Topics in Developmental Biology. 2003  |  Pubmed ID: 14674481

Acidic Sphingomyelinase Downregulates the Liver-specific Methionine Adenosyltransferase 1A, Contributing to Tumor Necrosis Factor-induced Lethal Hepatitis

The Journal of Clinical Investigation. Mar, 2004  |  Pubmed ID: 15067322

S-adenosyl-L-methionine (SAM) is synthesized by methionine adenosyltransferases (MATs). Ablation of the liver-specific MAT1A gene results in liver neoplasia and sensitivity to oxidant injury. Here we show that acidic sphingomyelinase (ASMase) mediates the downregulation of MAT1A by TNF-alpha. The levels of MAT1A mRNA as well as MAT I/III protein decreased in cultured rat hepatocytes by in situ generation of ceramide from exogenous human placenta ASMase. Hepatocytes lacking the ASMase gene (ASMase-/-) were insensitive to TNF-alpha but were responsive to exogenous ASMase-induced downregulation of MAT1A. In an in vivo model of lethal hepatitis by TNF-alpha, depletion of SAM preceded activation of caspases 8 and 3, massive liver damage, and death of the mice. In contrast, minimal hepatic SAM depletion, caspase activation, and liver damage were seen in ASMase-/- mice. Moreover, therapeutic treatment with SAM abrogated caspase activation and liver injury, thus rescuing ASMase+/+ mice from TNF-alpha-induced lethality. Thus, we have demonstrated a new role for ASMase in TNF-alpha-induced liver failure through downregulation of MAT1A, and maintenance of SAM may be useful in the treatment of acute and chronic liver diseases.

Jejunal Microvilli Atrophy and Reduced Nutrient Transport in Rats with Advanced Liver Cirrhosis: Improvement by Insulin-like Growth Factor I

BMC Gastroenterology. Jun, 2004  |  Pubmed ID: 15196310

Previous results have shown that in rats with non-ascitic cirrhosis there is an altered transport of sugars and amino acids associated with elongated microvilli. These alterations returned to normal with the administration of Insulin-Like Growth Factor-I (IGF-I). The aims of this study were to explore the evolution of these alterations and analyse the effect of IGF-I in rats with advanced cirrhosis and ascites. Thus, jejunal structure and nutrient transport (D-galactose, L-leucine, L-proline, L-glutamic acid and L-cystine) were studied in rats with ascitic cirrhosis.

Hematotesticular Barrier is Altered from Early Stages of Liver Cirrhosis: Effect of Insulin-like Growth Factor 1

World Journal of Gastroenterology. Sep, 2004  |  Pubmed ID: 15300898

The pathogenesis of hypogonadism in liver cirrhosis is not well understood. Previous results from our laboratory showed that IGF-1 deficiency might play a pathogenetic role in hypogonadism of cirrhosis. The administration of IGF-1 for a short period of time reverted the testicular atrophy associated with advanced experimental cirrhosis. The aim of this study was to establish the historical progression of the described alterations in the testes, explore testicular morphology, histopathology, cellular proliferation, integrity of testicular barrier and hypophyso-gonadal axis in rats with no ascitic cirrhosis.

Trophic Effects of Insulin-like Growth Factor-I (IGF-I) in the Inner Ear

Hearing Research. Oct, 2004  |  Pubmed ID: 15464297

Insulin-like growth factors (IGFs) have a pivotal role during nervous system development and in its functional maintenance. IGF-I and its high affinity receptor (IGF1R) are expressed in the developing inner ear and in the postnatal cochlear and vestibular ganglia. We recently showed that trophic support by IGF-I is essential for the early neurogenesis of the chick cochleovestibular ganglion (CVG). In the chicken embryo otic vesicle, IGF-I regulates developmental death dynamics by regulating the activity and/or levels of key intracellular molecules, including lipid and protein kinases such as ceramide kinase, Akt and Jun N-terminal kinase (JNK). Mice lacking IGF-I lose many auditory neurons and present increased auditory thresholds at early postnatal ages. Neuronal loss associated to IGF-I deficiency is caused by apoptosis of the auditory neurons, which presented abnormally increased levels of activated caspase-3. It is worth noting that in man, homozygous deletion of the IGF-1 gene causes sensory-neural deafness. IGF-I is thus necessary for normal development and maintenance of the inner ear. The trophic actions of IGF-I in the inner ear suggest that this factor may have therapeutic potential for the treatment of hearing loss.

Phosphorylation of Glycosyl-phosphatidylinositol by Phosphatidylinositol 3-kinase Changes Its Properties As a Substrate for Phospholipases

FEBS Letters. Jan, 2005  |  Pubmed ID: 15620691

Phosphatidylinositol 3-kinases (PI3K) phosphorylate the 3-position of the inositol ring of phosphatidylinositol-4,5-bisphosphate to produce phosphatidylinositol-3,4,5-trisphosphate. It is not clear whether PI3K can phosphorylate the inositol group in other biomolecules. We sought to determine whether PI3K was able to use glycosyl-phosphatidylinositol (GPI) as a substrate. This phospholipid may exist either in free form (GPIfree) or forming a lipid anchor (GPIanchor) for the attachment of extracellular proteins to the plasma membrane. We demonstrate the specific PI3K-mediated phosphorylation of the inositol 3-hydroxyl group within both types of GPI by incubating this phospholipid with immunoprecipitated PI3K. The phosphorylated product behaves in HPLC as a derivative of a PI3K lipid product. To our knowledge, this is the first demonstration that PI3K uses lipid substrates other than phosphoinositides. Further, we show that this has potential functional consequences. When GPIfree is phosphorylated, it becomes a poorer substrate for GPI-specific phospholipase D, but a better substrate for phosphatidylinositol-specific phospholipase C. These phosphorylation events may constitute the basis of a previously undescribed signal transduction mechanism.

Regulation of Vertebrate Sensory Organ Development: a Scenario for Growth Hormone and Insulin-like Growth Factors Action

Advances in Experimental Medicine and Biology. 2005  |  Pubmed ID: 16370141

Anti-apoptotic Actions of Insulin-like Growth Factors: Lessons from Development and Implications in Neoplastic Cell Transformation

Current Pharmaceutical Design. 2007  |  Pubmed ID: 17346184

Insulin-like growth factor-I (IGF-I) is widely expressed during development, and is actively involved in the regulation of cell growth, proliferation, and differentiation. Underlying these activities is the capacity of IGF-I to promote survival in a variety of cell types, including those of the nervous system. However, in adult tissues deregulation of the IGF system can cause undesired cell survival and therefore excessive cell proliferation. Here, we review the contribution of IGF-I in developmental processes with a focus on the development of the inner ear, as well as pathological implications resulting from IGF-I deregulation during cancer.

A Network of Growth and Transcription Factors Controls Neuronal Differentation and Survival in the Developing Ear

The International Journal of Developmental Biology. 2007  |  Pubmed ID: 17891717

Inner ear neurons develop from the otic placode and connect hair cells with central neurons in auditory brain stem nuclei. Otic neurogenesis is a developmental process which can be separated into different cellular states that are characterized by a distinct combination of molecular markers. Neurogenesis is highly regulated by a network of extrinsic and intrinsic factors, whose participation in auditory neurogenesis is discussed. Trophic factors include the fibroblast growth factor, neurotrophins and insulin-like peptide families. The expression domains of transcription factor families and their roles in the regulation of intracellular signaling pathways associated with neurogenesis are also discussed. Understanding and defining the key factors and gene networks in the development and function of the inner ear represents an important step towards defeating deafness.

Spatial and Temporal Segregation of Auditory and Vestibular Neurons in the Otic Placode

Developmental Biology. Oct, 2008  |  Pubmed ID: 18674529

The otic placode generates the auditory and vestibular sense organs and their afferent neurons; however, how auditory and vestibular fates are specified is unknown. We have generated a fate map of the otic placode and show that precursors for vestibular and auditory cells are regionally segregated in the otic epithelium. The anterior-lateral portion of the otic placode generates vestibular neurons, whereas the posterior-medial region gives rise to auditory neurons. Precursors for vestibular and auditory sense organs show the same distribution. Thus, different regions of the otic placode correspond to particular sense organs and their innervating neurons. Neurons from contiguous domains rarely intermingle suggesting that the regional organisation of the otic placode dictates positional cues to otic neurons. But, in addition, vestibular and cochlear neurogenesis also follows a stereotyped temporal pattern. Precursors from the anterior-lateral otic placode delaminate earlier than those from its medial-posterior portion. The expression of the proneural genes NeuroM and NeuroD reflects the sequence of neuroblast formation and differentiation. Both genes are transiently expressed in vestibular and then in cochlear neuroblasts, while differentiated neurons express Islet1, Tuj1 and TrkC, but not NeuroM or NeuroD. Together, our results indicate that the position of precursors within the otic placode confers identity to sensory organs and to the corresponding otic neurons. In addition, positional information is integrated with temporal cues that coordinate neurogenesis and sensory differentiation.

RasGRF1 Disruption Causes Retinal Photoreception Defects and Associated Transcriptomic Alterations

Journal of Neurochemistry. Jul, 2009  |  Pubmed ID: 19457086

RasGRF1 null mutant mice display impaired memory/learning and their hippocampus transcriptomic pattern includes a number of differentially expressed genes playing significant roles in sensory development and function. Odour avoidance and auditory brainstem response tests yielded normal results but electroretinographic analysis showed severe light perception impairment in the RasGRF1 knockouts. Whereas no structural alterations distinguished the retinas of wild-type and knockout mice, microarray transcriptional analysis identified at least 44 differentially expressed genes in the retinas of these Knockout animals. Among these, Crb1, Pttg1, Folh1 and Myo7a have been previously related to syndromes involving retina degeneration. Interestingly, over-expression of Folh1 would be expected to result in accumulation of its enzymatic product N-acetyl-aspartate, an event known to be linked to Canavan disease, a human cerebral degenerative syndrome often involving blindness and hearing loss. Consistently, in vivo brain nuclear magnetic resonance spectroscopy identified higher levels of N-acetyl-aspartate in our RasGRF1-/- mice and immunohistochemical analysis detected reduced levels of aspartoacylase, the enzyme which degrades N-acetyl-aspartate. These studies demonstrate for the first time the functional relevance of Ras signalling in mammalian photoreception and warrant further analysis of RasGRF1 Knockout mice as potential models to analyse molecular mechanisms underlying defective photoreception human diseases.

Direct Drug Application to the Round Window: a Comparative Study of Ototoxicity in Rats

Otolaryngology--head and Neck Surgery : Official Journal of American Academy of Otolaryngology-Head and Neck Surgery. Nov, 2009  |  Pubmed ID: 19861195

To assess the validity of inducing ototoxicity in rats by applying a sponge soaked in kanamycin and furosemide on the round window.

Melanin Precursors Prevent Premature Age-related and Noise-induced Hearing Loss in Albino Mice

Pigment Cell & Melanoma Research. Feb, 2010  |  Pubmed ID: 19843244

Strial melanocytes are required for normal development and correct functioning of the cochlea. Hearing deficits have been reported in albino individuals from different species, although melanin appears to be not essential for normal auditory function. We have analyzed the auditory brainstem responses (ABR) of two transgenic mice: YRT2, carrying the entire mouse tyrosinase (Tyr) gene expression-domain and undistinguishable from wild-type pigmented animals; and TyrTH, non-pigmented but ectopically expressing tyrosine hydroxylase (Th) in melanocytes, which generate the precursor metabolite, L-DOPA, but not melanin. We show that young albino mice present a higher prevalence of profound sensorineural deafness and a poorer recovery of auditory thresholds after noise-exposure than transgenic mice. Hearing loss was associated with absence of cochlear melanin or its precursor metabolites and latencies of the central auditory pathway were unaltered. In summary, albino mice show impaired hearing responses during ageing and after noise damage when compared to YRT2 and TyrTH transgenic mice, which do not show the albino-associated ABR alterations. These results demonstrate that melanin precursors, such as L-DOPA, have a protective role in the mammalian cochlea in age-related and noise-induced hearing loss.

RNA Microarray Analysis in Prenatal Mouse Cochlea Reveals Novel IGF-I Target Genes: Implication of MEF2 and FOXM1 Transcription Factors

PloS One. Jan, 2010  |  Pubmed ID: 20111592

Insulin-like growth factor-I (IGF-I) provides pivotal cell survival and differentiation signals during inner ear development throughout evolution. Homozygous mutations of human IGF1 cause syndromic sensorineural deafness, decreased intrauterine and postnatal growth rates, and mental retardation. In the mouse, deficits in IGF-I result in profound hearing loss associated with reduced survival, differentiation and maturation of auditory neurons. Nevertheless, little is known about the molecular basis of IGF-I activity in hearing and deafness.

European Scientific, Ethical, and Legal Issues on Human Stem Cell Research and Regenerative Medicine

Stem Cells (Dayton, Ohio). Jun, 2010  |  Pubmed ID: 20533567

A Comparative Study of Age-related Hearing Loss in Wild Type and Insulin-like Growth Factor I Deficient Mice

Frontiers in Neuroanatomy. 2010  |  Pubmed ID: 20661454

Insulin-like growth factor-I (IGF-I) belongs to the family of insulin-related peptides that fulfils a key role during the late development of the nervous system. Human IGF1 mutations cause profound deafness, poor growth and mental retardation. Accordingly, Igf1(-/-) null mice are dwarfs that have low survival rates, cochlear alterations and severe sensorineural deafness. Presbycusis (age-related hearing loss) is a common disorder associated with aging that causes social and cognitive problems. Aging is also associated with a decrease in circulating IGF-I levels and this reduction has been related to cognitive and brain alterations, although there is no information as yet regarding the relationship between presbycusis and IGF-I biodisponibility. Here we present a longitudinal study of wild type Igf1(+/+) and null Igf1(-/-) mice from 2 to 12 months of age comparing the temporal progression of several parameters: hearing, brain morphology, cochlear cytoarchitecture, insulin-related factors and IGF gene expression and IGF-I serum levels. Complementary invasive and non-invasive techniques were used, including auditory brainstem-evoked response (ABR) recordings and in vivo MRI brain imaging. Igf1(-/-) null mice presented profound deafness at all the ages studied, without any obvious worsening of hearing parameters with aging. Igf1(+/+) wild type mice suffered significant age-related hearing loss, their auditory thresholds and peak I latencies augmenting as they aged, in parallel with a decrease in the circulating levels of IGF-I. Accordingly, there was an age-related spiral ganglion degeneration in wild type mice that was not evident in the Igf1 null mice. However, the Igf1(-/-) null mice in turn developed a prematurely aged stria vascularis reminiscent of the diabetic strial phenotype. Our data indicate that IGF-I is required for the correct development and maintenance of hearing, supporting the idea that IGF-I-based therapies could contribute to prevent or ameliorate age-related hearing loss.

RAF Kinase Activity Regulates Neuroepithelial Cell Proliferation and Neuronal Progenitor Cell Differentiation During Early Inner Ear Development

PloS One. Dec, 2010  |  Pubmed ID: 21203386

Early inner ear development requires the strict regulation of cell proliferation, survival, migration and differentiation, coordinated by the concerted action of extrinsic and intrinsic factors. Deregulation of these processes is associated with embryonic malformations and deafness. We have shown that insulin-like growth factor I (IGF-I) plays a key role in embryonic and postnatal otic development by triggering the activation of intracellular lipid and protein kinases. RAF kinases are serine/threonine kinases that regulate the highly conserved RAS-RAF-MEK-ERK signaling cascade involved in transducing the signals from extracellular growth factors to the nucleus. However, the regulation of RAF kinase activity by growth factors during development is complex and still not fully understood.

The Role of Insulin-like Growth Factor-I in the Physiopathology of Hearing

Frontiers in Molecular Neuroscience. 2011  |  Pubmed ID: 21845174

Insulin-like growth factor-I (IGF-I) belongs to the family of polypeptides of insulin, which play a central role in embryonic development and adult nervous system homeostasis by endocrine, autocrine, and paracrine mechanisms. IGF-I is fundamental for the regulation of cochlear development, growth, and differentiation, and its mutations are associated with hearing loss in mice and men. Low levels of IGF-I have been shown to correlate with different human syndromes showing hearing loss and with presbyacusis. Animal models are fundamental to understand the genetic, epigenetic, and environmental factors that contribute to human hearing loss. In the mouse, IGF-I serum levels decrease with aging and there is a concomitant hearing loss and retinal degeneration. In the Igf1(-/-) null mouse, hearing loss is due to neuronal loss, poor innervation of the sensory hair cells, and age-related stria vascularis alterations. In the inner ear, IGF-I actions are mediated by intracellular signaling networks, RAF, AKT, and p38 MAPK protein kinases modulate the expression and activity of transcription factors, as AP1, MEF2, FoxM1, and FoxP3, leading to the regulation of cell cycle and metabolism. Therapy with rhIGF-I has been approved in humans for the treatment of poor linear growth and certain neurodegenerative diseases. This review will discuss these findings and their implications in new IGF-I-based treatments for the protection or repair of hearing loss.

Insulin Receptor Substrate 2 (IRS2)-deficient Mice Show Sensorineural Hearing Loss That is Delayed by Concomitant Protein Tyrosine Phosphatase 1B (PTP1B) Loss of Function

Molecular Medicine (Cambridge, Mass.). 2012  |  Pubmed ID: 22160220

The insulin receptor substrate (IRS) proteins are key mediators of insulin and insulinlike growth factor 1 (IGF-1) signaling. Protein tyrosine phosphatase (PTP)-1B dephosphorylates and inactivates both insulin and IGF-1 receptors. IRS2-deficient mice present altered hepatic insulin signaling and β-cell failure and develop type 2-like diabetes. In addition, IRS2 deficiency leads to developmental defects in the nervous system. IGF1 gene mutations cause syndromic sensorineural hearing loss in humans and mice. However, the involvement of IRS2 and PTP1B, two IGF-1 downstream signaling mediators, in hearing onset and loss has not been studied. Our objective was to study the hearing function and cochlear morphology of Irs2-null mice and the impact of PTP1B deficiency. We have studied the auditory brainstem responses and the cochlear morphology of systemic Irs2⁻/⁻Ptpn1⁺/⁺, Irs2⁺/⁺Ptpn1⁻/⁻ and Irs2⁻/⁻Ptpn1⁻/⁻ mice at different postnatal ages. The results indicated that Irs2⁻/⁻Ptpn1⁺/⁺ mice present a profound congenital sensorineural deafness before the onset of diabetes and altered cochlear morphology with hypoinnervation of the cochlear ganglion and aberrant stria vascularis, compared with wild-type mice. Simultaneous PTP1B deficiency in Irs2⁻/⁻Ptpn1⁻/⁻ mice delays the onset of deafness. We show for the first time that IRS2 is essential for hearing and that PTP1B inhibition may be useful for treating deafness associated with hyperglycemia and type 2 diabetes.

Drug Delivery to the Inner Ear: Strategies and Their Therapeutic Implications for Sensorineural Hearing Loss

Current Drug Delivery. May, 2012  |  Pubmed ID: 22283653

Hearing aids or cochlear implants constitute almost exclusively the treatment options currently available to patients suffering from sensorineural hearing loss and related conditions, such as noise-induced hearing loss, ototoxicity or autoimmune inner ear disease. While some systemic treatments exist, they generally exert adverse secondary effects and their efficacy is hampered by the blood-cochlear barrier that limits drug access to the inner ear. Hence, the new therapies that are being developed for hearing loss focus on strategies for direct drug delivery to the inner ear. The passive and active methods for local delivery can be categorized into two general groups: intratympanic or intracochlear. The intratympanic approach is a non-invasive method that preserves hearing and takes advantage of the permeability of the round window to gain access to the cochlea. However, this technique is limited by not knowing the dose of the drug that reaches the cochlea, (a handicap which might be overcome by the use of tagged drugs). While direct access to the inner ear by intracochlear administration avoids this problem, this method requires surgery. Currently, laboratory animals are being used to explore which therapeutic approaches are best suited to address this problem. These include cochleostomy and the insertion of devices that pump drugs into the inner ear without inducing cochlear damage. In this article, we review the different techniques under evaluation in animal models of deafness, and their potential use for drug delivery and treatment of human inner ear diseases.

AKT Signaling Mediates IGF-I Survival Actions on Otic Neural Progenitors

PloS One. 2012  |  Pubmed ID: 22292041

Otic neurons and sensory cells derive from common progenitors whose transition into mature cells requires the coordination of cell survival, proliferation and differentiation programmes. Neurotrophic support and survival of post-mitotic otic neurons have been intensively studied, but the bases underlying the regulation of programmed cell death in immature proliferative otic neuroblasts remains poorly understood. The protein kinase AKT acts as a node, playing a critical role in controlling cell survival and cell cycle progression. AKT is activated by trophic factors, including insulin-like growth factor I (IGF-I), through the generation of the lipidic second messenger phosphatidylinositol 3-phosphate by phosphatidylinositol 3-kinase (PI3K). Here we have investigated the role of IGF-dependent activation of the PI3K-AKT pathway in maintenance of otic neuroblasts.

Early Development of the Vertebrate Inner Ear

Anatomical Record (Hoboken, N.J. : 2007). Nov, 2012  |  Pubmed ID: 23044927

This is a review of the biological processes and the main signaling pathways required to generate the different otic cell types, with particular emphasis on the actions of insulin-like growth factor I. The sensory organs responsible of hearing and balance have a common embryonic origin in the otic placode. Lineages of neural, sensory, and support cells are generated from common otic neuroepithelial progenitors. The sequential generation of the cell types that will form the adult inner ear requires the coordination of cell proliferation with cell differentiation programs, the strict regulation of cell survival, and the metabolic homeostasis of otic precursors. A network of intracellular signals operates to coordinate the transcriptional response to the extracellular input. Understanding the molecular clues that direct otic development is fundamental for the design of novel treatments for the protection and repair of hearing loss and balance disorders.

Autophagy During Vertebrate Development

Cells. Aug, 2012  |  Pubmed ID: 24710484

Autophagy is an evolutionarily conserved catabolic process by which cells degrade their own components through the lysosomal machinery. In physiological conditions, the mechanism is tightly regulated and contributes to maintain a balance between synthesis and degradation in cells undergoing intense metabolic activities. Autophagy is associated with major tissue remodeling processes occurring through the embryonic, fetal and early postnatal periods of vertebrates. Here we survey current information implicating autophagy in cellular death, proliferation or differentiation in developing vertebrates. In developing systems, activation of the autophagic machinery could promote different outcomes depending on the cellular context. Autophagy is thus an extraordinary tool for the developing organs and tissues.

IGF-I Deficiency and Hearing Loss: Molecular Clues and Clinical Implications

Pediatric Endocrinology Reviews : PER. Jul, 2013  |  Pubmed ID: 23957197

Sensorineural hearing loss is a clinical heterogeneous disorder and a significant health-care problem with tremendous socio-economic impact. According to WHO, "Over 5% of the world's population has disabling hearing loss -328 million adults and 32 million children-". In children, early hearing loss affects language acquisition. Hearing deficits are generally associated with the loss of the sensory "hair" cells and/or neurons caused by primary genetic defects or secondary to environmental factors including infections, noise and ototoxic drugs. Hearing loss cannot be reversed and currently the available treatment is limited to hearing aids and cochlear implants. Studies are being conducted to develop alternative treatments combining both preventive and reparative strategies. Human insulin like growth factor (IGF) I deficiency is a rare disease associated with hearing loss, poor growth rates and mental retardation (ORPHA73272, OMIM608747). Similarly, lgf1-/- mice are dwarfs with poor survival rates and congenital profound sensorineural deafness. IGF-I is known to be a neuroprotective agent that maintains cellular metabolism, activates growth, proliferation and differentiation, and limits cell death. Here we will discuss the basic mechanisms underlying IGF-I actions in the auditory system and their clinical implications to pursue novel treatments to ameliorate hearing loss.

Programmed Cell Senescence During Mammalian Embryonic Development

Cell. Nov, 2013  |  Pubmed ID: 24238962

Cellular senescence disables proliferation in damaged cells, and it is relevant for cancer and aging. Here, we show that senescence occurs during mammalian embryonic development at multiple locations, including the mesonephros and the endolymphatic sac of the inner ear, which we have analyzed in detail. Mechanistically, senescence in both structures is strictly dependent on p21, but independent of DNA damage, p53, or other cell-cycle inhibitors, and it is regulated by the TGF-β/SMAD and PI3K/FOXO pathways. Developmentally programmed senescence is followed by macrophage infiltration, clearance of senescent cells, and tissue remodeling. Loss of senescence due to the absence of p21 is partially compensated by apoptosis but still results in detectable developmental abnormalities. Importantly, the mesonephros and endolymphatic sac of human embryos also show evidence of senescence. We conclude that the role of developmentally programmed senescence is to promote tissue remodeling and propose that this is the evolutionary origin of damage-induced senescence.

Treatment with N- and C-terminal Peptides of Parathyroid Hormone-related Protein Partly Compensate the Skeletal Abnormalities in IGF-I Deficient Mice

PloS One. 2014  |  Pubmed ID: 24503961

Insulin-like growth factor-I (IGF-I) deficiency causes growth delay, and IGF-I has been shown to partially mediate bone anabolism by parathyroid hormone (PTH). PTH-related protein (PTHrP) is abundant in bone, and has osteogenic features by poorly defined mechanisms. We here examined the capacity of PTHrP (1-36) and PTHrP (107-111) (osteostatin) to reverse the skeletal alterations associated with IGF-I deficiency. Igf1-null mice and their wild type littermates were treated with each PTHrP peptide (80 µg/Kg/every other day/2 weeks; 2 males and 4 females for each genotype) or saline vehicle (3 males and 3 females for each genotype). We found that treatment with either PTHrP peptide ameliorated trabecular structure in the femur in both genotypes. However, these peptides were ineffective in normalizing the altered cortical structure at this bone site in Igf1-null mice. An aberrant gene expression of factors associated with osteoblast differentiation and function, namely runx2, osteoprotegerin/receptor activator of NF-κB ligand ratio, Wnt3a , cyclin D1, connexin 43, catalase and Gadd45, as well as in osteocyte sclerostin, was found in the long bones of Igf1-null mice. These mice also displayed a lower amount of trabecular osteoblasts and osteoclasts in the tibial metaphysis than those in wild type mice. These alterations in Igf1-null mice were only partially corrected by each PTHrP peptide treatment. The skeletal expression of Igf2, Igf1 receptor and Irs2 was increased in Igf1-null mice, and this compensatory profile was further improved by treatment with each PTHrP peptide related to ERK1/2 and FoxM1 activation. In vitro, PTHrP (1-36) and osteostatin were effective in promoting bone marrow stromal cell mineralization in normal mice but not in IGF-I-deficient mice. Collectively, these findings indicate that PTHrP (1-36) and osteostatin can exert several osteogenic actions even in the absence of IGF-I in the mouse bone.

Loss of Lysophosphatidic Acid Receptor LPA1 Alters Oligodendrocyte Differentiation and Myelination in the Mouse Cerebral Cortex

Brain Structure & Function. Nov, 2015  |  Pubmed ID: 25226845

Lysophosphatidic acid (LPA) is an intercellular signaling lipid that regulates multiple cellular functions, acting through specific G-protein coupled receptors (LPA(1-6)). Our previous studies using viable Malaga variant maLPA1-null mice demonstrated the requirement of the LPA1 receptor for normal proliferation, differentiation, and survival of the neuronal precursors. In the cerebral cortex LPA1 is expressed extensively in differentiating oligodendrocytes, in parallel with myelination. Although exogenous LPA-induced effects have been investigated in myelinating cells, the in vivo contribution of LPA1 to normal myelination remains to be demonstrated. This study identified a relevant in vivo role for LPA1 as a regulator of cortical myelination. Immunochemical analysis in adult maLPA1-null mice demonstrated a reduction in the steady-state levels of the myelin proteins MBP, PLP/DM20, and CNPase in the cerebral cortex. The myelin defects were confirmed using magnetic resonance spectroscopy and electron microscopy. Stereological analysis limited the defects to adult differentiating oligodendrocytes, without variation in the NG2+ precursor cells. Finally, a possible mechanism involving oligodendrocyte survival was demonstrated by the impaired intracellular transport of the PLP/DM20 myelin protein which was accompanied by cellular loss, suggesting stress-induced apoptosis. These findings describe a previously uncharacterized in vivo functional role for LPA1 in the regulation of oligodendrocyte differentiation and myelination in the CNS, underlining the importance of the maLPA1-null mouse as a model for the study of demyelinating diseases.

Differential Organ Phenotypes After Postnatal Igf1r Gene Conditional Deletion Induced by Tamoxifen in UBC-CreERT2; Igf1r Fl/fl Double Transgenic Mice

Transgenic Research. Apr, 2015  |  Pubmed ID: 25238791

Insulin-like growth factor type 1 receptor (IGF1R) is a ubiquitously expressed tyrosine kinase that regulates cell proliferation, differentiation and survival. It controls body growth and organ homeostasis, but with specific functions depending on developmental time and cell type. Human deficiency in IGF1R is involved in growth failure, microcephaly, mental retardation and deafness, and its overactivation is implicated in oncogenesis. Igf1r-deficient mice die at birth due to growth retardation and respiratory failure. Although multiple Igf1r tissue-specific mutant lines have been analyzed postnatally, using Igf1r-floxed (Igf1r (fl/fl) ) mice mated with diverse cell-type recombinase Cre-expressing transgenics, no mouse models for the study of generalized Igf1r deficiency in adults have been reported. To this end we generated UBC-CreERT2; Igf1r (fl/fl) transgenic mice with an inducible deletion of Igf1r activated by tamoxifen. Tamoxifen administration to 4 week-old prepuberal male mice delayed their growth, producing a distinct impact on organ size 4 weeks later. Whereas testes were smaller, spleen and heart showed an increased organ to body weight ratio. Mosaic Igf1r genomic deletions caused a significant reduction in Igf1r mRNA in all organs analyzed, resulting in diverse phenotypes. While kidneys, spleen and cochlea had unaltered gross morphology, testes revealed halted spermatogenesis, and liver and alveolar lung parenchyma showed increased cell proliferation rates without affecting apoptosis. We demonstrate that UBC-CreERT2 transgenic mice efficiently delete Igf1r upon postnatal tamoxifen treatment in multiple mouse organs, and corroborate that IGF1R function is highly dependent on cell, tissue and organ type.

Folic Acid Deficiency Induces Premature Hearing Loss Through Mechanisms Involving Cochlear Oxidative Stress and Impairment of Homocysteine Metabolism

FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology. Feb, 2015  |  Pubmed ID: 25384423

Nutritional imbalance is emerging as a causative factor of hearing loss. Epidemiologic studies have linked hearing loss to elevated plasma total homocysteine (tHcy) and folate deficiency, and have shown that folate supplementation lowers tHcy levels potentially ameliorating age-related hearing loss. The purpose of this study was to address the impact of folate deficiency on hearing loss and to examine the underlying mechanisms. For this purpose, 2-mo-old C57BL/6J mice (Animalia Chordata Mus musculus) were randomly divided into 2 groups (n = 65 each) that were fed folate-deficient (FD) or standard diets for 8 wk. HPLC analysis demonstrated a 7-fold decline in serum folate and a 3-fold increase in tHcy levels. FD mice exhibited severe hearing loss measured by auditory brainstem recordings and TUNEL-positive-apoptotic cochlear cells. RT-quantitative PCR and Western blotting showed reduced levels of enzymes catalyzing homocysteine (Hcy) production and recycling, together with a 30% increase in protein homocysteinylation. Redox stress was demonstrated by decreased expression of catalase, glutathione peroxidase 4, and glutathione synthetase genes, increased levels of manganese superoxide dismutase, and NADPH oxidase-complex adaptor cytochrome b-245, α-polypeptide (p22phox) proteins, and elevated concentrations of glutathione species. Altogether, our findings demonstrate, for the first time, that the relationship between hyperhomocysteinemia induced by folate deficiency and premature hearing loss involves impairment of cochlear Hcy metabolism and associated oxidative stress.

Targeting Cholesterol Homeostasis to Fight Hearing Loss: a New Perspective

Frontiers in Aging Neuroscience. 2015  |  Pubmed ID: 25688206

Sensorineural hearing loss (SNHL) is a major pathology of the inner ear that affects nearly 600 million people worldwide. Despite intensive researches, this major health problem remains without satisfactory solutions. The pathophysiological mechanisms involved in SNHL include oxidative stress, excitotoxicity, inflammation, and ischemia, resulting in synaptic loss, axonal degeneration, and apoptosis of spiral ganglion neurons. The mechanisms associated with SNHL are shared with other neurodegenerative disorders. Cholesterol homeostasis is central to numerous pathologies including neurodegenerative diseases and cholesterol regulates major processes involved in neurons survival and function. The role of cholesterol homeostasis in the physiopathology of inner ear is largely unexplored. In this review, we discuss the findings concerning cholesterol homeostasis in neurodegenerative diseases and whether it should be translated into potential therapeutic strategies for the treatment of SNHL.

Swept-sine Noise-induced Damage As a Hearing Loss Model for Preclinical Assays

Frontiers in Aging Neuroscience. 2015  |  Pubmed ID: 25762930

Mouse models are key tools for studying cochlear alterations in noise-induced hearing loss (NIHL) and for evaluating new therapies. Stimuli used to induce deafness in mice are usually white and octave band noises that include very low frequencies, considering the large mouse auditory range. We designed different sound stimuli, enriched in frequencies up to 20 kHz ("violet" noises) to examine their impact on hearing thresholds and cochlear cytoarchitecture after short exposure. In addition, we developed a cytocochleogram to quantitatively assess the ensuing structural degeneration and its functional correlation. Finally, we used this mouse model and cochleogram procedure to evaluate the potential therapeutic effect of transforming growth factor β1 (TGF-β1) inhibitors P17 and P144 on NIHL. CBA mice were exposed to violet swept-sine noise (VS) with different frequency ranges (2-20 or 9-13 kHz) and levels (105 or 120 dB SPL) for 30 min. Mice were evaluated by auditory brainstem response (ABR) and otoacoustic emission tests prior to and 2, 14 and 28 days after noise exposure. Cochlear pathology was assessed with gross histology; hair cell number was estimated by a stereological counting method. Our results indicate that functional and morphological changes induced by VS depend on the sound level and frequency composition. Partial hearing recovery followed the exposure to 105 dB SPL, whereas permanent cochlear damage resulted from the exposure to 120 dB SPL. Exposure to 9-13 kHz noise caused an auditory threshold shift (TS) in those frequencies that correlated with hair cell loss in the corresponding areas of the cochlea that were spotted on the cytocochleogram. In summary, we present mouse models of NIHL, which depending on the sound properties of the noise, cause different degrees of cochlear damage, and could therefore be used to study molecules which are potential players in hearing loss protection and repair.

Transforming Growth Factor β1 Inhibition Protects from Noise-induced Hearing Loss

Frontiers in Aging Neuroscience. 2015  |  Pubmed ID: 25852546

Excessive exposure to noise damages the principal cochlear structures leading to hearing impairment. Inflammatory and immune responses are central mechanisms in cochlear defensive response to noise but, if unregulated, they contribute to inner ear damage and hearing loss. Transforming growth factor β (TGF-β) is a key regulator of both responses and high levels of this factor have been associated with cochlear injury in hearing loss animal models. To evaluate the potential of targeting TGF-β as a therapeutic strategy for preventing or ameliorating noise-induced hearing loss (NIHL), we studied the auditory function, cochlear morphology, gene expression and oxidative stress markers in mice exposed to noise and treated with TGF-β1 peptidic inhibitors P17 and P144, just before or immediately after noise insult. Our results indicate that systemic administration of both peptides significantly improved both the evolution of hearing thresholds and the degenerative changes induced by noise-exposure in lateral wall structures. Moreover, treatments ameliorated the inflammatory state and redox balance. These therapeutic effects were dose-dependent and more effective if the TGF-β1 inhibitors were administered prior to inducing the injury. In conclusion, inhibition of TGF-β1 actions with antagonistic peptides represents a new, promising therapeutic strategy for the prevention and repair of noise-induced cochlear damage.

C-Raf Deficiency Leads to Hearing Loss and Increased Noise Susceptibility

Cellular and Molecular Life Sciences : CMLS. Oct, 2015  |  Pubmed ID: 25975225

The family of RAF kinases transduces extracellular information to the nucleus, and their activation is crucial for cellular regulation on many levels, ranging from embryonic development to carcinogenesis. B-RAF and C-RAF modulate neurogenesis and neuritogenesis during chicken inner ear development. C-RAF deficiency in humans is associated with deafness in the rare genetic insulin-like growth factor 1 (IGF-1), Noonan and Leopard syndromes. In this study, we show that RAF kinases are expressed in the developing inner ear and in adult mouse cochlea. A homozygous C-Raf deletion in mice caused profound deafness with no evident cellular aberrations except for a remarkable reduction of the K(+) channel Kir4.1 expression, a trait that suffices as a cause of deafness. To explore the role of C-Raf in cellular protection and repair, heterozygous C-Raf (+/-) mice were exposed to noise. A reduced C-RAF level negatively affected hearing preservation in response to noise through mechanisms involving the activation of JNK and an exacerbated apoptotic response. Taken together, these results strongly support a role for C-RAF in hearing protection.

Corrigendum: Transforming Growth Factor β1 Inhibition Protects from Noise-induced Hearing Loss

Frontiers in Aging Neuroscience. 2015  |  Pubmed ID: 26005416

Corrigendum To: Swept-sine Noise-induced Damage As a Hearing Loss Model for Preclinical Assays

Frontiers in Aging Neuroscience. 2015  |  Pubmed ID: 26029100

[This corrects the article on p. 7 in vol. 7, PMID: 25762930.].

Age-regulated Function of Autophagy in the Mouse Inner Ear

Hearing Research. Dec, 2015  |  Pubmed ID: 26235979

Autophagy is a highly conserved catabolic process essential for embryonic development and adult homeostasis. The autophagic machinery supplies energy by recycling intracellular components and facilitates the removal of apoptotic cells. In the inner ear, autophagy has been reported to play roles during early development in the chicken embryo and in the response to otic injury in the adult mouse. However, there are no studies on the expression of the autophagy machinery in the postnatal and adult inner ear. Insulin-like growth factor 1 (IGF-1) is one of the factors that regulate both otic development and cochlear postnatal maturation and function. Here, we hypothesised that autophagy could be one of the processes involved in the cochlear development and functional maturation. We report that autophagy-related genes (ATG) Becn1, Atg4g and Atg5 are expressed in the mouse cochlea, vestibular system and brainstem cochlear nuclei from late developmental stages to adulthood. Atg9 was studied in the mouse cochlea and showed a similar pattern. The presence of autophagic flux was confirmed by decreased sequestosome 1 (SQSTM1/p62) and increased relative levels of microtubule-associated protein light chain 3-II (LC3-II). Inner ear autophagy flux is developmentally regulated and is lower at perinatal stages than in the adult mouse, where an expression plateau is reached at the age of two-months, coinciding with the age at which full functional activity is reached. Expression is maintained in adult mice and declines after the age of twelve months. LC3B labelling showed that autophagy was primarily associated with spiral ganglion neurons. Over time, Igf1 wild type mice showed lower expression of genes coding for IGF-1 high affinity receptor and the family factor IGF-2 than null mice. Parallel analysis of autophagy machinery gene expression showed no significant differences between the genotypes over the lifespan of the null mice. Taken together, these results show that the autophagy machinery expression in the inner ear is regulated with age but is not compromised by the chronic absence of IGF-1. Our data also strongly support that the up-regulation of autophagy machinery genes is concomitant with the functional maturation of the inner ear.

Editorial: Aging, Neurogenesis and Neuroinflammation in Hearing Loss and Protection

Frontiers in Aging Neuroscience. 2015  |  Pubmed ID: 26236234

Long-term Omega-3 Fatty Acid Supplementation Prevents Expression Changes in Cochlear Homocysteine Metabolism and Ameliorates Progressive Hearing Loss in C57BL/6J Mice

The Journal of Nutritional Biochemistry. Dec, 2015  |  Pubmed ID: 26321228

Omega-3 polyunsaturated fatty acids (PUFAs) are essential nutrients well known for their beneficial effects, among others on cognitive development and maintenance, inflammation and oxidative stress. Previous studies have shown an inverse association between high plasma levels of PUFAs and age-related hearing loss, and the relationship between low serum folate and elevated plasma homocysteine levels and hearing loss. Therefore, we used C57BL/6J mice and long-term omega-3 supplementation to evaluate the impact on hearing by analyzing their auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) thresholds. The omega-3 group showed significantly lower ABR hearing thresholds (~25 dB sound pressure level) and higher DPOAE amplitudes in mid-high frequencies when compared to the control group. These changes did not correlate with alterations between groups in plasma homocysteine or serum folate levels as measured by high-performance liquid chromatography and a microbiological method, respectively. Aging in the control group was associated with imbalanced cytokine expression toward increased proinflammatory cytokines as determined by quantitative reverse transcriptase polymerase chain reaction; these changes were prevented by omega-3 supplementation. Genes involved in homocysteine metabolism showed decreased expression during aging of control animals, and only alterations in Bhmt and Cbs were significantly prevented by omega-3 feeding. Western blotting showed that omega-3 supplementation precluded the CBS protein increase detected in 10-month-old controls but also produced an increase in BHMT protein levels. Altogether, the results obtained suggest a long-term protective role of omega-3 supplementation on cochlear metabolism and progression of hearing loss.

Comparative Gene Expression Study of the Vestibular Organ of the Igf1 Deficient Mouse Using Whole-transcript Arrays

Hearing Research. Dec, 2015  |  Pubmed ID: 26341476

The auditory and vestibular organs form the inner ear and have a common developmental origin. Insulin like growth factor 1 (IGF-1) has a central role in the development of the cochlea and maintenance of hearing. Its deficiency causes sensorineural hearing loss in man and mice. During chicken early development, IGF-1 modulates neurogenesis of the cochleovestibular ganglion but no further studies have been conducted to explore the potential role of IGF-1 in the vestibular system. In this study we have compared the whole transcriptome of the vestibular organ from wild type and Igf1(-/-) mice at different developmental and postnatal times. RNA was prepared from E18.5, P15 and P90 vestibular organs of Igf1(-/-) and Igf1(+/+) mice and the transcriptome analysed in triplicates using Affymetrix(®) Mouse Gene 1.1 ST Array Plates. These plates are whole-transcript arrays that include probes to measure both messenger (mRNA) and long intergenic non-coding RNA transcripts (lincRNA), with a coverage of over 28 thousand coding transcripts and over 7 thousands non-coding transcripts. Given the complexity of the data we used two different methods VSN-RMA and mmBGX to analyse and compare the data. This is to better evaluate the number of false positives and to quantify uncertainty of low signals. We identified a number of differentially expressed genes that we described using functional analysis and validated using RT-qPCR. The morphology of the vestibular organ did not show differences between genotypes and no evident alterations were observed in the vestibular sensory areas of the null mice. However, well-defined cellular alterations were found in the vestibular neurons with respect their number and size. Although these mice did not show a dramatic vestibular phenotype, we conducted a functional analysis on differentially expressed genes between genotypes and across time. This was with the aim to identify new pathways that are involved in the development of the vestibular organ as well as pathways that maybe affected by the lack of IGF-1 and be associated to the morphological changes of the vestibular neurons that we observed in the Igf1(-/-) mice.

Public Investment in Biomedical Research in Europe

Lancet (London, England). Oct, 2015  |  Pubmed ID: 26460768

Mild Cognitive Decline. A Position Statement of the Cognitive Decline Group of the European Innovation Partnership for Active and Healthy Ageing (EIPAHA)

Maturitas. Jan, 2016  |  Pubmed ID: 26520249

Mild cognitive impairment (MCI) is a term used to describe a level of decline in cognition which is seen as an intermediate stage between normal ageing and dementia, and which many consider to be a prodromal stage of neurodegeneration that may become dementia. That is, it is perceived as a high risk level of cognitive change. The increasing burden of dementia in our society, but also our increasing understanding of its risk factors and potential interventions, require diligent management of MCI in order to find strategies that produce effective prevention of dementia.

Guidelines for the Use and Interpretation of Assays for Monitoring Autophagy (3rd Edition)

Autophagy. Jan, 2016  |  Pubmed ID: 26799652

Wbp2 is Required for Normal Glutamatergic Synapses in the Cochlea and is Crucial for Hearing

EMBO Molecular Medicine. 03, 2016  |  Pubmed ID: 26881968

WBP2 encodes the WW domain-binding protein 2 that acts as a transcriptional coactivator for estrogen receptor α (ESR1) and progesterone receptor (PGR). We reported that the loss of Wbp2 expression leads to progressive high-frequency hearing loss in mouse, as well as in two deaf children, each carrying two different variants in the WBP2 gene. The earliest abnormality we detect in Wbp2-deficient mice is a primary defect at inner hair cell afferent synapses. This study defines a new gene involved in the molecular pathway linking hearing impairment to hormonal signalling and provides new therapeutic targets.

Frailty in Mouse Ageing: A Conceptual Approach

Mechanisms of Ageing and Development. Dec, 2016  |  Pubmed ID: 27443148

Human life expectancy has increased dramatically in the last century and as a result also the prevalence of a variety of age-related diseases and syndromes. One such syndrome is frailty, which is defined as a combination of organ dysfunctions leading to increased vulnerability to adverse health outcomes. In humans, frailty is associated with various biomarkers of ageing and predicts relevant outcomes such as responses to therapies and progression of health status and mortality. Moreover, it is relatively easy to assess. To foster translation of mechanistic understanding of the ageing process and, importantly, of interventions that may extend healthy lifespan, frailty scales have been reverse translated into mice in recent years. We will review these approaches with a view to identify what is known and what is not known at present about their validity, reproducibility and reliability with a focus on the potential for further improvement.

Autophagy Resolves Early Retinal Inflammation in Igf1-deficient Mice

Disease Models & Mechanisms. Sep, 2016  |  Pubmed ID: 27483352

Insulin-like growth factor-1 (IGF-1) is a growth factor with differentiating, anti-apoptotic and metabolic functions in the periphery, and anti-inflammatory properties in the nervous system. Mice that have mutations in the Igf1 gene, rendering the gene product inactive (Igf1(-/-)), present with age-related visual loss accompanied by structural alterations in the first synapses of the retinal pathway. Recent advances have revealed a crucial role of autophagy in immunity and inflammation. Keeping in mind this close relationship, we aimed to decipher these processes in the context of the defects that occur during ageing in the retina of Igf1(-/-) mice. Tnfa and Il1b mRNAs, and phosphorylation of JNK and p38 MAPK were elevated in the retinas of 6- and 12-month old Igf1(-/-) mice compared to those in age-matched Igf1(+/+) controls. In 6-month-old Igf1(-/-) retinas, increased mRNA levels of the autophagy mediators Becn1, Atg9, Atg5 and Atg4, decreased p62 (also known as SQSTM1) protein expression together with an increased LC3-II:LC3-I ratio reflected active autophagic flux. However, in retinas from 12-month-old Igf1(-/-) mice, Nlrp3 mRNA, processing of the IL1β pro-form and immunostaining of active caspase-1 were elevated compared to those in age-matched Igf1(+/+) controls, suggesting activation of the inflammasome. This effect concurred with accumulation of autophagosomes and decreased autophagic flux in the retina. Microglia localization and status of activation in the retinas of 12-month-old Igf1(+/+) and Igf1(-/-) mice, analyzed by immunostaining of Cd11b and Iba-1, showed a specific distribution pattern in the outer plexiform layer (OPL), inner plexiform layer (IPL) and inner nuclear layer (INL), and revealed an increased number of activated microglia cells in the retina of 12-month-old blind Igf1(-/-) mice. Moreover, reactive gliosis was exclusively detected in the retinas from 12-month-old blind Igf1(-/-) mice. In conclusion, this study provides new evidence in a mouse model of IGF-1 deficiency that autophagy is an adaptive response that might confer protection against persistent inflammation in the retina during ageing.

Long-Term Dietary Folate Deficiency Accelerates Progressive Hearing Loss on CBA/Ca Mice

Frontiers in Aging Neuroscience. 2016  |  Pubmed ID: 27630560

Dietary folic acid deficiency induced early hearing loss in C57BL/6J mice after 2-months, corroborates the epidemiological association previously described between vitamin deficiency and this sensory impairment. However, this strain is prone to early hearing loss, and hence we decided to analyze whether the effects exerted by folate deprivation follow the same pattern in a mouse strain such as CBA/Ca, which is resistant to hearing impairment. Here, we show results of a long-term study on hearing carried out on CBA/Ca mice subjected to dietary folate deprivation. Systemic changes included decreased serum folate levels, hyperhomocysteinemia and signs of anemia in the group fed with folate-deficient (FD) diet. Initial signs of hearing loss were detected in this strain after 8-months of vitamin deficiency, and correlated with histological damage in the cochleae. In conclusion, the data presented reinforce the importance of adequate folic acid levels for the auditory system and suggest that the impact of dietary deficiencies may depend on the genetic background.

Waiting
simple hit counter