consensus-brain-derived-protein-extraction-protocol-for-study-human

Consensus Brain-derived Protein, Extraction Protocol for the Study of Human and Murine Brain Proteome Using Both 2D-DIGE and Mini 2DE Immunoblotting

Two-dimensional gel electrophoresis (2DE) is a powerful tool to uncover proteome modifications potentially related to different physiological or ...

Inserm UMR 837

Muscleblind-like-1 (MBNL1) is a splicing regulatory factor controlling the fetal-to-adult alternative splicing transitions during vertebrate muscle development. Its capture by nuclear CUG expansions is one major cause for type 1 myotonic dystrophy (DM1). Alternative splicing produces MBNL1 isoforms that differ by the presence or absence of the exonic regions 3, 5, and 7. To understand better their respective roles and the consequences of the deregulation of their expression in DM1, here we studied the respective roles of MBNL1 alternative and constitutive exons. By combining genetics, molecular and cellular approaches, we found that (i) the exon 5 and 6 regions are both needed to control the nuclear localization of MBNL1; (ii) the exon 3 region strongly enhances the affinity of MBNL1 for its pre-mRNA target sites; (iii) the exon 3 and 6 regions are both required for the splicing regulatory activity, and this function is not enhanced by an exclusive nuclear localization of MBNL1; and finally (iv) the exon 7 region enhances MBNL1-MBNL1 dimerization properties. Consequently, the abnormally high inclusion of the exon 5 and 7 regions in DM1 is expected to enhance the potential of MBNL1 of being sequestered with nuclear CUG expansions, which provides new insight into DM1 pathophysiology.

Analysis of exonic regions involved in nuclear localization, splicing activity, and dimerization of Muscleblind-like-1 isoforms.

A prerequisite to dephosphorylation at Ser-Pro or Thr-Pro motifs is the isomerization of the imidic peptide bond preceding the proline. The peptidyl-prolyl cis/trans isomerase named Pin1 catalyzes this mechanism. Through isomerization, Pin1 regulates the function of a growing number of targets including the microtubule-associated tau protein and is supposed to be deregulated Alzheimer's disease (AD). Using proteomics, we showed that Pin1 is posttranslationally modified on more than 5 residues, comprising phosphorylation, N-acetylation, and oxidation. Although Pin1 expression remained constant, Pin1 posttranslational two-dimensional pattern was modified by tau overexpression in a tau-inducible neuroblastoma cell line, in our THY-Tau22 mouse model of tauopathy as well as in AD. Interestingly, in all of these systems, Pin1 modifications were very similar. In AD brain tissue when compared with control, Pin1 is hyperphosphorylated at serine 16 and found in the most insoluble hyperphosphorylated tau fraction of AD brain tissue. Furthermore, in all tau pathology conditions, acetylation of Pin1 may also contribute to the differences observed. In conclusion, Pin1 displays several posttranslational modifications, which are specific in tauopathies and may be useful as biomarker.

Tau pathology modulates Pin1 post-translational modifications and may be relevant as biomarker.

While the spatiotemporal development of Tau pathology has been correlated with occurrence of cognitive deficits in Alzheimer's patients, mechanisms underlying these deficits remain unclear. Both brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor TrkB play a critical role in hippocampus-dependent synaptic plasticity and memory. When applied on hippocampal slices, BDNF is able to enhance AMPA receptor-dependent hippocampal basal synaptic transmission through a mechanism involving TrkB and N-methyl-d-Aspartate receptors (NMDAR). Using THY-Tau22 transgenic mice, we demonstrated that hippocampal Tau pathology is associated with loss of synaptic enhancement normally induced by exogenous BDNF. This defective response was concomitant to significant memory impairments. We show here that loss of BDNF response was due to impaired NMDAR function. Indeed, we observed a significant reduction of NMDA-induced field excitatory postsynaptic potential depression in the hippocampus of Tau mice together with a reduced phosphorylation of NR2B at the Y1472, known to be critical for NMDAR function. Interestingly, we found that both NR2B and Src, one of the NR2B main kinases, interact with Tau and are mislocalized to the insoluble protein fraction rich in pathological Tau species. Defective response to BDNF was thus likely related to abnormal interaction of Src and NR2B with Tau in THY-Tau22 animals. These are the first data demonstrating a relationship between Tau pathology and synaptic effects of BDNF and supporting a contribution of defective BDNF response and impaired NMDAR function to the cognitive deficits associated with Tauopathies.

NMDA receptor dysfunction contributes to impaired brain-derived neurotrophic factor-induced facilitation of hippocampal synaptic transmission in a Tau transgenic model.

THY-Tau22 mice constitute an animal model for tau aggregation, a hallmark in Alzheimer's disease (AD) and Tauopathies. Our previous studies have shown learning and memory deficits and changes in synaptic plasticity in the hippocampus in THY-Tau22 mice that are consistent with the learning impairments seen in AD-patients. However, behavioral disturbances are the most important problems in the management of AD and are major determinants of nursing home placement. Thus, we hypothesized that THY-Tau22 mice would demonstrate, in addition to the cognitive impairments, at least some behavioral and psychological signs and symptoms of dementia (BPSD). We found that 12 months old THY-Tau22 mice, relative to wild-type (WT) littermates display increased depression-like and aggressive behavior, co-occurring with disturbances in nocturnal activity. Moreover, these changes were linked to a decreased hippocampal concentration in serotonin, or 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin. Together these data corroborate the usefulness of the model in preclinical evaluations of therapeutic strategies that aim to reverse cognitive defects and alleviate BPSD in the human disease.

Observations in THY-Tau22 mice that resemble behavioral and psychological signs and symptoms of dementia.

The τ pathology found in Alzheimer disease (AD) is crucial in cognitive decline. Midlife development of obesity, a major risk factor of insulin resistance and type 2 diabetes, increases the risk of dementia and AD later in life. The impact of obesity on AD risk has been suggested to be related to central insulin resistance, secondary to peripheral insulin resistance. The effects of diet-induced obesity (DIO) on τ pathology remain unknown. In this study, we evaluated effects of a high-fat diet, given at an early pathological stage, in the THY-Tau22 transgenic mouse model of progressive AD-like τ pathology. We found that early and progressive obesity potentiated spatial learning deficits as well as hippocampal τ pathology at a later stage. Surprisingly, THY-Tau22 mice did not exhibit peripheral insulin resistance. Further, pathological worsening occurred while hippocampal insulin signaling was upregulated. Together, our data demonstrate that DIO worsens τ phosphorylation and learning abilities in τ transgenic mice independently from peripheral/central insulin resistance.

Article	Year
Analysis of exonic regions involved in nuclear localization, splicing activity, and dimerization of Muscleblind-like-1 isoforms. The Journal of biological chemistry\| PubMed ID: 21454535	2011
Tau pathology modulates Pin1 post-translational modifications and may be relevant as biomarker. Neurobiology of aging\| PubMed ID: 22926167	2013
NMDA receptor dysfunction contributes to impaired brain-derived neurotrophic factor-induced facilitation of hippocampal synaptic transmission in a Tau transgenic model. Aging cell\| PubMed ID: 23082852	2013
Observations in THY-Tau22 mice that resemble behavioral and psychological signs and symptoms of dementia. Behavioural brain research\| PubMed ID: 23247080	2013
Detrimental effects of diet-induced obesity on τ pathology are independent of insulin resistance in τ transgenic mice. Diabetes\| PubMed ID: 23250356	2013

Sabiha Eddarkaoui

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