At birth, dynamic changes occur in serum components and haemodynamics, such as closure of the ductus arteriosus (DA). A previous study demonstrated that, in full-term human neonates, serum osmolality decreased transiently after birth, but recovered over the next few days. However, the significance of this transient decrease in osmolality has never been addressed. The objective of the present study was to examine the role of changes in serum osmolality after birth in DA closure.
The heart has an intrinsic ability to increase systolic force in response to a rise in ventricular filling (the Frank-Starling law of the heart). It is widely accepted that the length dependence of myocardial activation underlies the Frank-Starling law of the heart. Recent advances in muscle physiology have enabled the identification of the factors involved in length-dependent activation, viz., titin (connectin)-based interfilament lattice spacing reduction and thin filament "on-off" regulation, with the former triggering length-dependent activation and the latter determining the number of myosin molecules recruited to thin filaments. Patients with a failing heart have demonstrated reduced exercise tolerance at least in part via depression of the Frank-Starling mechanism. Recent studies revealed that various mutations occur in the thin filament regulatory proteins, such as troponin, in the ventricular muscle of failing hearts, which consequently alter the Frank-Starling mechanism. In this article, we review the molecular mechanisms of length-dependent activation, and the influence of troponin mutations on the phenomenon.
Patent ductus arteriosus (PDA) is one of the most common congenital cardiovascular defects in children. The Brown-Norway (BN) inbred rat presents a higher frequency of PDA. A previous study reported that 2 different quantitative trait loci on chromosomes 8 and 9 were significantly linked to PDA in this strain. Nevertheless, the genetic or molecular mechanisms underlying PDA phenotypes in BN rats have not been fully investigated yet.
Elastic fiber formation is disrupted with age and by health conditions including aneurysms and atherosclerosis. Despite considerable progress in the understanding of elastogenesis using the planar culture system and genetically modified animals, it remains difficult to restore elastic fibers in diseased vessels. To further study the molecular mechanisms, in vitro three-dimensional vascular constructs need to be established. We previously fabricated vascular smooth muscle cells (SMCs) into three-dimensional cellular multilayers (3DCMs) using a hierarchical cell manipulation technique, in which cells were coated with fibronectin-gelatin nanofilms to provide adhesive nano-scaffolds. Since fibronectin is known to assemble and activate elastic fiber-related molecules, we further optimized culture conditions.
Mutations of ?B-crystallin (Cry?B), a small heat shock protein abundantly expressed in cardiac and skeletal muscles, are known to cause desmin-related myopathies. The Cry?B R120G allele has been linked to a familial desminopathy and, in transgenic mice, causes a sudden death at about 28 weeks of age. To investigate the mechanisms of the sudden cardiac arrest of Cry?B R120G transgenic mice, we prepared protein samples from left ventricular tissues of two different age groups (10 and 28 weeks) and examined Ca(2+) -handling proteins. Expression of sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) 2, phospholamban, ryanodine receptor 2 and calsequestrin 2 was significantly decreased in 28- versus 10-week-old Cry?B R120G transgenic mice. In addition, low heart rate variability, including heart rate, total power and low frequency, was observed and continuous electrocardiogram monitoring revealed cardiac arrhythmias, such as ventricular tachycardia, atrioventricular block and atrial flutter, in 28-week-old Cry?B R120G transgenic mice. In contrast, expression of endoplasmic reticulum (ER) degradation enhancing ?-mannosidase-like protein, inositol requirement 1 and X-box binding protein 1 were increased significantly in 28- versus 10-week-old Cry?BR120G transgenic mice, suggesting that the Cry?BR120G transgenic mice exhibit increased ER stress compared with wild-type mice. Together, the data suggest that the Cry?B R120G dominant variant induces ER stress and impairs Ca(2+) regulation, leading to ageing-related cardiac dysfunction, arrhythmias and decreased autonomic tone with shortened lifespan.
Ductus arteriosus (DA) closure follows constriction and remodeling of the entire vessel wall. Patent ductus arteriosus occurs when the DA does not close after birth, and this condition is currently treated using cyclooxygenase inhibitors. However, the efficacy of cyclooxygenase inhibitors is often limited. Our previous study demonstrated that low-dose thromboxane A2 receptor (TP) stimulation constricted the DA with minimal adverse effects in rat neonates. However, its effect on DA remodeling remains unknown. In this study, we focused on the impact of the exogenous TP stimulation on the DA remodeling, especially intimal thickening. Using DA explants from rat fetuses at embryonic day 19 as a ex vivo model and primary cultured rat DA smooth muscle cells from embryonic day 21 as a in vitro model, we evaluated the effect of TP stimulation on the DA remodeling. The selective TP agonists U46619 and I-BOP promoted neointima formation in the ex vivo DA explants, and TP stimulation increased DA SMC migration in a dose-dependent manner. Both effects were inhibited by the selective TP antagonist SQ29548 or the siRNA against TP. TP stimulation also increased DA SMC proliferation in the presence of 10% fetal bovine serum. LC/MS/MS analysis revealed that TP stimulation increased secretion of several extracellular matrix proteins that may contribute to an increase in neointima formation. In conclusion, we uncovered that exogenous administration of TP agonist promotes neointima formation through the induction of migration and proliferation of DA SMC, which could contribute to DA closure and also to its vasoconstrictive action.
Elastic fiber formation begins in mid-gestation and increases dramatically during the last trimester in the great arteries, providing elasticity and thus preventing vascular wall structure collapse. However, the ductus arteriosus (DA), a fetal bypass artery between the aorta and pulmonary artery, exhibits lower levels of elastic fiber formation, which promotes vascular collapse and subsequent closure of the DA after birth. The molecular mechanisms for this inhibited elastogenesis in the DA, which is necessary for the establishment of adult circulation, remain largely unknown.
Energy of the cardiac muscle largely depends on fatty acid oxidation. It is known that the atrium and ventricle have chamber-specific functions, structures, gene expressions, and pathologies. The left ventricle works as a high-pressure chamber to pump blood toward the body, and its muscle wall is thicker than those of the other chambers, suggesting that energy utilization in each of the chambers should be different. However, a chamber-specific pattern of metabolism remains incompletely understood. Recently, innovative techniques have enabled the comprehensive analysis of metabolites. Therefore, we aimed to clarify differences in metabolic patterns among the chambers. Male C57BL6 mice at 6 wk old were subject to a comprehensive measurement of metabolites in the atria and ventricles by capillary electrophoresis and mass spectrometry. We found that overall metabolic profiles, including nucleotides and amino acids, were similar between the right and left ventricles. On the other hand, the atria exhibited a distinct metabolic pattern from those of the ventricles. Importantly, the high-energy phosphate pool (the total concentration of ATP, ADP, and AMP) was higher in both ventricles. In addition, the levels of lactate, acetyl CoA, and tricarboxylic acid cycle contents were higher in the ventricles. Accordingly, the activities and/or expression levels of key enzymes were higher in the ventricles to produce more energy. The present study provides a basis for understanding the chamber-specific metabolism underlining pathophysiology in the heart.
Endothelial cells (ECs) lining the blood vessels serve a variety of functions and play a central role in the homeostasis of the circulatory system. Since the ductus arteriosus (DA) has different arterial characteristics from its connecting vessels, we hypothesized that ECs of the DA exhibited a unique gene profile involved in the regulation of DA-specific morphology and function. Using a fluorescence-activated cell sorter, we isolated ECs from pooled tissues from the DA or the descending aorta of Wistar rat fetuses at full-term of gestation (F group) or neonates 30 minutes after birth (N group). Using anti-CD31 and anti-CD45 antibodies as cell surface markers for ECs and hematopoietic derived cells, respectively, cDNAs from the CD31-positive and CD45-negative cells were hybridized to the Affymetrix GeneChip® Rat Gene 1.0 ST Array. Among 26,469 gene-level probe sets, 82 genes in the F group and 81 genes in the N group were expressed at higher levels in DA ECs than in aortic ECs (p<0.05, fold change>2.0). In addition to well-known endothelium-enriched genes such as Tgfb2 and Vegfa, novel DA endothelium-dominant genes including Slc38a1, Capn6, and Lrat were discovered. Enrichment analysis using GeneGo MetaCore software showed that DA endothelium-related biological processes were involved in morphogenesis and development. We identified many overlapping genes in each process including neural crest-related genes (Hoxa1, Hoxa4, and Hand2, etc) and the second heart field-related genes (Tbx1, Isl1, and Fgf10, etc). Moreover, we found that regulation of epithelial-to-mesenchymal transition, cell adhesion, and retinol metabolism are the active pathways involved in the network via potential interactions with many of the identified genes to form DA-specific endothelia. In conclusion, the present study uncovered several significant differences of the transcriptional profile between the DA and aortic ECs. Newly identified DA endothelium-dominant genes may play an important role in DA-specific functional and morphologic characteristics.
Impaired Ca(2+) reuptake into the sarcoplasmic reticulum (SR) underlies a primary pathogenesis of heart failure in the aging heart. Sarcalumenin (SAR), a Ca(2+)-binding glycoprotein located in the longitudinal SR, regulates Ca(2+) reuptake by interacting with SR Ca(2+)-ATPase (SERCA). Here we found that the expression levels of both SAR and SERCA2 proteins were significantly downregulated in senescent wild-type mice (18-month old) and that downregulation of SAR protein preceded downregulation of SERCA2 protein. The downregulation of SERCA2 protein was greater in senescent SARKO mice than in age-matched senescent wild-type mice, which was at least in part due to progressive degradation of SERCA2 protein in SARKO mice. Senescent SARKO mice exhibited typical findings of heart failure such as increased sympathetic activity, impaired exercise tolerance, and upregulation of biomarkers of cardiac stress. Consequently, cardiac function was progressively decreased in senescent SARKO. We also found that the expression levels of endoplasmic reticulum (ER) stress-related genes such as x-box binding protein 1 (XBP1) were significantly increased in senescent SARKO mice, indicating that senescent SARKO mice exhibited ER stress. Thus we uncovered the important role of SAR in maintaining Ca(2+) transport activity of SERCA2a and cardiac function in the senescent population.
Reducing stress is important in preventing sudden death in patients with cardiovascular disease, as stressful events may cause autonomic imbalance and trigger fatal arrhythmias. Since chewing has been shown to inhibit stress-induced neuronal responses in the hypothalamus, we hypothesized that chewing could ameliorate stress-induced autonomic imbalance and prevent arrhythmias. To test this hypothesis, we analyzed changes in radiotelemetered electrocardiograms in rats that were allowed to chew a wooden stick during a 1-h period of immobilization stress. Chewing significantly reduced the occurrence of ventricular premature beats (VPBs) and complex ventricular ectopy after immobilization and prevented stress-induced prolongation of the QT interval of VPBs throughout the 10-h experimental period. It also prevented prolongation of the QRS complex and fluctuations in the QT interval in normal sinus rhythm beats preceding VPBs during both immobilization and in the poststress period. Fast Fourier transform-based spectral analysis of heart-rate variability further showed that chewing significantly inhibited the stress-induced increase in the power ratio of low-to-high frequency activity (LF/HF: a marker of sympathetic activity) during immobilization and in addition was associated with blunting of the stress-induced increase in plasma noradrenaline observed at the termination of immobilization. Similar suppressive effects on the occurrence of VPBs and the LF/HF were observed in rats that were administered the ?-adrenergic blocker propranolol before immobilization. These results indicate that chewing can ameliorate sympathetic hyperactivity during stress and prevent poststress arrhythmias and suggest that chewing may provide a nonpharmacological and cost-effective treatment option for patients with a high risk of stress-induced fatal arrhythmia.
Preventing skeletal muscle atrophy is critical for maintaining quality of life, but it is often a challenging goal for the elderly and patients with severe conditions. We hypothesized that acupuncture in place of exercise training is an alternative non-pharmacological intervention that can help to prevent muscle atrophy. To elucidate the effects of acupuncture on skeletal muscle atrophy caused by hindlimb suspension (HS), we performed acupuncture on mice according to two different methods: acupuncture with electrical stimulation (EA: electroacupuncture) and without electrical stimulation (MA: manual acupuncture). A needle was retained in the gastrocnemius muscle for 30 min every day for 2 weeks in the EA and MA groups. In the EA group, 30 min of repetitive electrical stimulation (1 Hz, 1 ms pulse width, 6.5 mA intensity) was also applied. HS significantly reduced muscle mass and the cross-sectional area of the soleus muscles. This HS-induced reduction was significantly improved in the EA group, although the level of improvement remained insufficient when compared with the control group. We found that the mRNA expression levels of atrogin-1 and MuRF1, which play a principal role in muscle-specific degradation as E3 ubiquitin ligases, were significantly increased in the HS group compared to the control group. EA and MA reduced the HS-induced upregulation of atrogin-1 (p<0.01 in EA and MA) and MuRF1 (p<0.01 in EA) mRNAs. We also found that the expression levels of PI3K, Akt1, TRPV4, adenosine A1 receptor, myostatin, and SIRT1 mRNAs tended to be increased by HS. EA and MA further increased the HS-induced upregulation of Akt1 (p<0.05 in MA) and TRPV4 (p<0.05 in MA) mRNAs. We concluded that acupuncture partially prevented skeletal muscle atrophy. This effect might be due to an increase in protein synthesis and a decrease in protein degradation.
The ductus arteriosus (DA), a fetal arterial connection between the pulmonary artery and the aorta, has a character distinct from the adjacent arteries. We compared the transcriptional profiles of the DA and the aorta of Wistar rat fetuses on embryonic day 19 (preterm) and day 21 (near-term) using DNA microarray analyses. We found that 39 genes were expressed 2.5-fold greater in the DA than in the aorta. Growth hormone (GH) receptor (GHR) exhibited the most significant difference in expression. Then, we found that GH significantly promoted migration of DA smooth muscle cells (SMCs), thus enhancing the intimal cushion formation of the DA explants. GH also regulated the expression of cytoskeletal genes in DA SMCs, which may retain a synthetic phenotype in the smooth muscle-specific cytoskeletal genes. Thus, the present study revealed that GH-GHR signal played a role in the vascular remodeling of the DA.
ATRAP [ANG II type 1 receptor (AT1R)-associated protein] is a molecule which directly interacts with AT1R and inhibits AT1R signaling. The aim of this study was to examine the effects of continuous ANG II infusion on the intrarenal expression and distribution of ATRAP and to determine the role of AT1R signaling in mediating these effects. C57BL/6 male mice were subjected to vehicle or ANG II infusions at doses of 200, 1,000, or 2,500 ng·kg(-1)·min(-1) for 14 days. ANG II infusion caused significant suppression of ATRAP expression in the kidney but did not affect ATRAP expression in the testis or liver. Although only the highest ANG II dose (2,500 ng·kg(-1)·min(-1)) provoked renal pathological responses, such as an increase in the mRNA expression of angiotensinogen and the ?-subunit of the epithelial sodium channel, ANG II-induced decreases in ATRAP were observed even at the lowest dose (200 ng·kg(-1)·min(-1)), particularly in the outer medulla of the kidney, based on immunohistochemical staining and Western blot analysis. The decrease in renal ATRAP expression by ANG II infusion was prevented by treatment with the AT1R-specific blocker olmesartan. In addition, the ANG II-mediated decrease in renal ATRAP expression through AT1R signaling occurred without an ANG II-induced decrease in plasma membrane AT1R expression in the kidney. On the other hand, a transgenic model increase in renal ATRAP expression beyond baseline was accompanied by a constitutive reduction of renal plasma membrane AT1R expression and by the promotion of renal AT1R internalization as well as the decreased induction of angiotensinogen gene expression in response to ANG II. These results suggest that the plasma membrane AT1R level in the kidney is modulated by intrarenal ATRAP expression under physiological and pathophysiological conditions in vivo.
Multipotent Isl1(+) heart progenitors give rise to three major cardiovascular cell types: cardiac, smooth muscle, and endothelial cells, and play a pivotal role in lineage diversification during cardiogenesis. A critical question is pinpointing when this cardiac-vascular lineage decision is made, and how this plasticity serves to coordinate cardiac chamber and vessel growth. The posterior domain of the Isl1-positive second heart field contributes to the SLN-positive atrial myocardium and myocardial sleeves in the cardiac inflow tract, where myocardial and vascular smooth muscle layers form anatomical and functional continuity. Herein, using a new atrial specific SLN-Cre knockin mouse line, we report that bipotent Isl1(+)/SLN(+) transient cell population contributes to cardiac as well as smooth muscle cells at the heart-vessel junction in cardiac inflow tract. The Isl1(+)/SLN(+) cells are capable of giving rise to cardiac and smooth muscle cells until late gestational stages. These data suggest that the cardiac and smooth muscle cells in the cardiac inflow tract share a common developmental origin. This article is part of a special issue entitled, "Cardiovascular Stem Cells Revisited".
The ductus arteriosus (DA), a fetal arterial connection between the main pulmonary artery and the descending aorta, normally closes immediately after birth. The DA is a normal and essential fetal structure. However, it becomes abnormal if it remains patent after birth. Closure of the DA occurs in two phases: functional closure of the lumen within the first hours after birth by smooth muscle constriction, and anatomic occlusion of the lumen over the next several days due to extensive neointimal thickening in human DA. There are several events that promote the DA constriction immediately after birth: (a) an increase in arterial oxygen tension, (b) a dramatic decline in circulating prostaglandinE(2) (PGE(2)), (c) a decrease in blood pressure within the DA lumen, and (d) a decrease in the number of PGE(2) receptors in the DA wall. Anatomical closure of the DA is associated with the formation of intimal thickening, which are characterized by (a) an area of subendothelial deposition of extracellular matrix, (b) the disassembly of the internal elastic lamina and loss of elastic fiber in the medial layer, and (c) migration into the subendothelial space of undifferentiated medial smooth muscle cells. In addition to the well-known vasodilatory role of PGE(2), our findings uncovered the role of PGE(2) in anatomical closure of the DA. Chronic PGE(2)-EP4-cyclic AMP (cAMP)-protein kinase A (PKA) signaling during gestation induces vascular remodeling of the DA to promote hyaluronan-mediated intimal thickening and structural closure of the vascular lumen. A novel target of cAMP, Epac, has an acute promoting effect on smooth muscle cell migration without hyaluronan production and thus intimal thickening in the DA. Both EP4-cAMP downstream targets, Epac and PKA, regulate vascular remodeling in the DA.
Prostaglandin (PG)E(2), which increases intracellular cAMP via activation of adenylyl cyclases (ACs), induces vasodilation and hyaluronan-mediated intimal thickening (IT) in the ductus arteriosus (DA) during late gestation. After birth, however, differential regulation of vasodilation and IT is preferable for treatment of patients with patent DA and DA-dependent congenital cardiac malformations.
We cloned a novel molecule interacting with angiotensin II type 1 receptor, which we named ATRAP (for angiotensin II type 1 receptor-associated protein). Previous in vitro studies showed that ATRAP significantly promotes constitutive internalization of the angiotensin II type 1 receptor and further attenuates angiotensin II-mediated hypertrophic responses in cardiomyocytes. The present study was designed to investigate the putative functional role of ATRAP in cardiac hypertrophy by angiotensin II infusion in vivo. We first examined the effect of angiotensin II infusion on endogenous ATRAP expression in the heart of C57BL/6J wild-type mice. The angiotensin II treatment promoted cardiac hypertrophy, concomitant with a significant decrease in cardiac ATRAP expression, but without significant change in cardiac angiotensin II type 1 receptor expression. We hypothesized that a downregulation of the cardiac ATRAP to angiotensin II type 1 receptor ratio is involved in the pathogenesis of cardiac hypertrophy. To examine this hypothesis, we next generated transgenic mice expressing ATRAP specifically in cardiomyocytes under control of the alpha-myosin heavy chain promoter. In cardiac-specific ATRAP transgenic mice, the development of cardiac hypertrophy, activation of p38 mitogen-activated protein kinase, and expression of hypertrophy-related genes in the context of angiotensin II treatment were completely suppressed, in spite of there being no significant difference in blood pressure on radiotelemetry between the transgenic mice and littermate control mice. These results demonstrate that cardiomyocyte-specific overexpression of ATRAP in vivo abolishes the cardiac hypertrophy provoked by chronic angiotensin II infusion, thereby suggesting ATRAP to be a novel therapeutic target in cardiac hypertrophy.
Caveolin, a member of the membrane-anchoring protein family, accumulates various growth receptors in caveolae and inhibits their function. Upregulation of caveolin attenuates cellular proliferation and growth. However, the role of caveolin in regulating insulin signals remains controversial. Here, we demonstrate that caveolin potently enhances insulin receptor (IR) signaling when overexpressed in the liver in vivo. Adenovirus-mediated gene transfer was used to overexpress caveolin specifically in the liver of diabetic obese mice, which were generated with a high-fat diet. Expression of molecules involved in IR signaling, such as IR or Akt, remained unchanged after gene transfer. However, hepatic glycogen synthesis was markedly increased with a decrease in phosphoenolpyruvate carboxykinase protein expression. Insulin sensitivity was increased after caveolin gene transfer as determined by decreased blood glucose levels in response to insulin injection and fasting blood glucose levels. Glucose tolerant test performance was also improved. Similar improvements were obtained in KKA(y) genetically diabetic mice. Adenovirus-mediated overexpression of caveolin-3 in hepatic cells also enhanced IR signaling, as shown by increased phosphorylation of IR in response to insulin stimulation and higher glycogen synthesis at baseline. These effects were attributed mostly to increased insulin receptor activity and caveolin-mediated, direct inhibition of protein tyrosine phosphatase 1B, which was increased in obese mouse livers. In conclusion, our results suggest that caveolin is an important regulator of glucose metabolism that can enhance insulin signals.
Ischemic injury of the heart is associated with activation of multiple signal transduction systems including the heterotrimeric G-protein system. Here, we report a role of the ischemia-inducible regulator of G betagamma subunit, AGS8, in survival of cardiomyocytes under hypoxia. Cultured rat neonatal cardiomyocytes (NCM) were exposed to hypoxia or hypoxia/reoxygenation following transfection of AGS8siRNA or pcDNA::AGS8. Hypoxia-induced apoptosis of NCM was completely blocked by AGS8siRNA, whereas overexpression of AGS8 increased apoptosis. AGS8 formed complexes with G-proteins and channel protein connexin 43 (CX43), which regulates the permeability of small molecules under hypoxic stress. AGS8 initiated CX43 phosphorylation in a G betagamma-dependent manner by providing a scaffold composed of G betagamma and CX43. AGS8siRNA blocked internalization of CX43 following exposure of NCM to repetitive hypoxia; however it did not influence epidermal growth factor-mediated internalization of CX43. The decreased dye flux through CX43 that occurred with hypoxic stress was also prevented by AGS8siRNA. Interestingly, the G betagamma inhibitor Gallein mimicked the effect of AGS8 knockdown on both the CX43 internalization and the changes in cell permeability elicited by hypoxic stress. These data indicate that AGS8 is required for hypoxia-induced apoptosis of NCM, and that AGS8-G betagamma signal input increased the sensitivity of cells to hypoxic stress by influencing CX43 regulation and associated cell permeability. Under hypoxic stress, this unrecognized response program plays a critical role in the fate of NCM.
The ductus arteriosus (DA), an essential vascular shunt for fetal circulation, begins to close immediately after birth. Although Ca(2+) influx through several membrane Ca(2+) channels is known to regulate vasoconstriction of the DA, the role of the T-type voltage-dependent Ca(2+) channel (VDCC) in DA closure remains unclear. Here we found that the expression of alpha1G, a T-type isoform that is known to exhibit a tissue-restricted expression pattern in the rat neonatal DA, was significantly up-regulated in oxygenated rat DA tissues and smooth muscle cells (SMCs). Immunohistological analysis revealed that alpha1G was localized predominantly in the central core of neonatal DA at birth. DA SMC migration was significantly increased by alpha1G overexpression. Moreover, it was decreased by adding alpha1G-specific small interfering RNAs or using R(-)-efonidipine, a highly selective T-type VDCC blocker. Furthermore, an oxygenation-mediated increase in an intracellular Ca(2+) concentration of DA SMCs was significantly decreased by adding alpha1G-specific siRNAs or using R(-)-efonidipine. Although a prostaglandin E receptor EP4 agonist potently promoted intimal thickening of the DA explants, R(-)-efonidipine (10(-6) m) significantly inhibited EP4-promoted intimal thickening by 40% using DA tissues at preterm in organ culture. Moreover, R(-)-efonidipine (10(-6) m) significantly attenuated oxygenation-induced vasoconstriction by approximately 27% using a vascular ring of fetal DA at term. Finally, R(-)-efonidipine significantly delayed the closure of in vivo DA in neonatal rats. These results indicate that T-type VDCC, especially alpha1G, which is predominantly expressed in neonatal DA, plays a unique role in DA closure, implying that T-type VDCC is an alternative therapeutic target to regulate the patency of DA.
Sarcalumenin (SAR), a Ca(2+)-binding protein located in the longitudinal sarcoplasmic reticulum (SR), regulates Ca(2+) reuptake into the SR by interacting with cardiac sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a (SERCA2a). We have previously demonstrated that SAR deficiency induced progressive heart failure in response to pressure overload, despite mild cardiac dysfunction in sham-operated SAR knockout (SARKO) mice (26). Since responses to physiological stresses often differ from those to pathological stresses, we examined the effects of endurance exercise on cardiac function in SARKO mice. Wild-type (WT) and SARKO mice were subjected to endurance treadmill exercise training ( approximately 65% of maximal exercise ability for 60 min/day) for 12 wk. After exercise training, maximal exercise ability was significantly increased by 5% in WT mice (n = 6), whereas it was significantly decreased by 37% in SARKO mice (n = 5). Cardiac function assessed by echocardiographic examination was significantly decreased in accordance with upregulation of biomarkers of cardiac stress in SARKO mice after training. After training, expression levels of SERCA2a protein were significantly downregulated by 30% in SARKO hearts, whereas they were significantly upregulated by 59% in WT hearts. Consequently, SERCA2 activity was significantly decreased in SARKO hearts after training. Furthermore, the expression levels of other Ca(2+)-handling proteins, including phospholamban, ryanodine receptor 2, calsequestrin 2, and sodium/calcium exchanger 1, were significantly decreased in SARKO hearts after training. These results indicate that SAR plays a critical role in maintaining cardiac function under physiological stresses, such as endurance exercise, by regulating Ca(2+) transport activity into the SR. SAR may be a primary target for exercise-related adaptation of the Ca(2+) storage system in the SR to preserve cardiac function.
Mitsugumin 53 (MG53) is a muscle-specific RBCC/TRIM family member predominantly localized on small vesicles underneath the plasma membrane. Upon cell-surface lesion MG53 recruits the vesicles to the repair site in an oxidation-dependent manner and MG53-knockout mice develop progressive myopathy associated with defective membrane repair. In this report, we focus on MG53-knockout cardiomyocytes showing abnormal action potential profile and a reduced K+ current density. In cDNA expression experiments using cultured cells, KV2.1-mediated currents were remarkably increased by MG53 without affecting the total and cell-surface levels of channel expression. In imaging analysis MG53 seemed to facilitate the mobility of KV2.1-containing endocytic vesicles with acidic pH. However, similar effects on the current density and vesicular mobility were not observed in the putative dominant-negative form of MG53. Our data suggest that MG53 is involved in a constitutive cycle of certain cell-surface proteins between the plasma membrane and endosome-like vesicles in striated muscle, and also imply that the vesicular dynamics are essential for the quality control of KV2.1 in cardiomyocytes.
Patent ductus arteriosus (PDA) is a common life-threatening complication among premature infants. Although cyclooxygenase inhibitors are frequently used to treat PDA, as they inhibit the synthesis of prostaglandin E(2), the most potent vasodilator in the ductus arteriosus (DA), their efficacy is often limited. As thromboxane A(2) (TXA(2)) induces vascular contraction via the TXA(2) receptor (TP), we hypothesized that TP stimulation would promote DA closure.
Aortic aneurysm is a common but life-threatening disease among the elderly, for which no effective medical therapy is currently available. Activation of prostaglandin E(2) (PGE(2)) is known to increase the expression of matrix metalloproteinase (MMP) and the release of inflammatory cytokines, and may thus exacerbate abdominal aortic aneurysm (AAA) formation. We hypothesized that selective blocking of PGE(2), in particular, EP4 prostanoid receptor signaling, would attenuate the development of AAA.
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