Role of the kisspeptin-KISS1R axis in the pathogenesis of chronic kidney disease and uremic cardiomyopathy.

The prevalence of chronic kidney disease (CKD) is increasing globally, especially in elderly patients. Uremic cardiomyopathy is a common cardiovascular complication of CKD, characterized by left ventricular hypertrophy (LVH), diastolic dysfunction, and fibrosis. Kisspeptins and their receptor, KISS1R, exert a pivotal influence on kidney pathophysiology and modulate age-related pathologies across various organ systems. KISS1R agonists, including kisspeptin-13 (KP-13), hold promise as novel therapeutic agents within age-related biological processes and kidney-related disorders. Our investigation aimed to elucidate the impact of KP-13 on the trajectory of CKD and uremic cardiomyopathy. Male Wistar rats (300-350 g) were randomized into four groups: (I) sham-operated, (II) 5/6 nephrectomy-induced CKD, (III) CKD subjected to a low dose of KP-13 (intraperitoneal 13 µg/day), and (IV) CKD treated with a higher KP-13 dose (intraperitoneal 26 µg/day). Treatments were administered daily from week 3 for 10 days. After 13 weeks, KP-13 increased systemic blood pressure, accentuating diastolic dysfunction's echocardiographic indicators and intensifying CKD-associated markers such as serum urea levels, glomerular hypertrophy, and tubular dilation. Notably, KP-13 did not exacerbate circulatory uremic toxin levels, renal inflammation, or fibrosis markers. In contrast, the higher KP-13 dose correlated with reduced posterior and anterior wall thickness, coupled with diminished cardiomyocyte cross-sectional areas and concurrent elevation of inflammatory (Il6, Tnf), fibrosis (Col1), and apoptosis markers (Bax/Bcl2) relative to the CKD group. In summary, KP-13's influence on CKD and uremic cardiomyopathy encompassed heightened blood pressure and potentially activated inflammatory and apoptotic pathways in the left ventricle.

The kisspeptin-1 receptor antagonist peptide-234 aggravates uremic cardiomyopathy in a rat model.

Uremic cardiomyopathy is characterized by diastolic dysfunction, left ventricular hypertrophy (LVH), and fibrosis. Dysregulation of the kisspeptin receptor (KISS1R)-mediated pathways are associated with the development of fibrosis in cancerous diseases. Here, we investigated the effects of the KISS1R antagonist peptide-234 (P234) on the development of uremic cardiomyopathy. Male Wistar rats (300-350 g) were randomized into four groups: (i) Sham, (ii) chronic kidney disease (CKD) induced by 5/6 nephrectomy, (iii) CKD treated with a lower dose of P234 (ip. 13 µg/day), (iv) CKD treated with a higher dose of P234 (ip. 26 µg/day). Treatments were administered daily from week 3 for 10 days. At week 13, the P234 administration did not influence the creatinine clearance and urinary protein excretion. However, the higher dose of P234 led to reduced anterior and posterior wall thicknesses, more severe interstitial fibrosis, and overexpression of genes associated with left ventricular remodeling (Ctgf, Tgfb, Col3a1, Mmp9), stretch (Nppa), and apoptosis (Bax, Bcl2, Casp7) compared to the CKD group. In contrast, no significant differences were found in the expressions of apoptosis-associated proteins between the groups. Our results suggest that the higher dose of P234 hastens the development and pathophysiology of uremic cardiomyopathy by activating the fibrotic TGF-ß-mediated pathways.

Unravelling the Effects of Syndecan-4 Knockdown on Skeletal Muscle Functions.

The remodelling of the extracellular matrix plays an important role in skeletal muscle development and regeneration. Syndecan-4 is a cell surface proteoglycan crucial for muscle differentiation. Syndecan-4-/- mice have been reported to be unable to regenerate following muscle damage. To investigate the consequences of the decreased expression of Syndecan-4, we have studied the in vivo and in vitro muscle performance and the excitation-contraction coupling machinery in young and aged Syndecan-4+/- (SDC4) mice. In vivo grip force was decreased significantly as well as the average and maximal speed of voluntary running in SDC4 mice, regardless of their age. The maximal in vitro twitch force was reduced in both EDL and soleus muscles from young and aged SDC4 mice. Ca2+ release from the sarcoplasmic reticulum decreased significantly in the FDB fibres of young SDC4 mice, while its voltage dependence was unchanged regardless of age. These findings were present in muscles from young and aged mice as well. On C2C12 murine skeletal muscle cells, we have also found altered calcium homeostasis upon Syndecan-4 silencing. The decreased expression of Syndecan-4 leads to reduced skeletal muscle performance in mice and altered motility in C2C12 myoblasts via altered calcium homeostasis. The altered muscle force performance develops at an early age and is maintained throughout the life course of the animal until old age.

Tilorone increases glucose uptake in vivo and in skeletal muscle cells by enhancing Akt2/AS160 signaling and glucose transporter levels.

Skeletal muscle plays a major role in whole-body glucose metabolism. Insulin resistance in skeletal muscle is characterized by decreased insulin-stimulated glucose uptake resulting from impaired intracellular trafficking and decreased glucose transporter 4 (GLUT4) expression. In this study, we illustrated that tilorone, a low-molecular-weight antiviral agent, improves glucose uptake in vitro and in vivo. Tilorone increased bone morphogenetic protein (BMP) signaling in C2C12 myoblasts, the transcription of multiple BMPs (BMP2, BMP4, BMP7, and BMP14), Smad4 expression, and the phosphorylation of BMP-mediated Smad1/5/8. The activation of Akt2/AS160 (TBC1D4) signaling, the critical regulator of GLUT4 translocation, was also increased, as well as the levels of GLUT4 and GLUT1, leading to enhanced uptake of the radioactively labeled glucose analog 18 F-fluoro-2-deoxyglucose (18 FDG). However, this excess glucose content did not result in increased ATP formation by mitochondrial respiration; both basal and ATP-linked respiration were diminished, thereby contributing to the induction of AMPK. In differentiated myotubes, AS160 phosphorylation and 18 FDG uptake also increased. Moreover, tilorone administration further increased insulin-stimulated phosphorylation of Akt2 and glucose uptake of myotubes indicating an insulin-sensitizing effect. Importantly, during in vivo experiments, the systemic administration of tilorone resulted in increased 18 FDG uptake of skeletal muscle, liver, and adipose tissue in C57BL/6 mice. Our results provide new perspectives for the treatment of type 2 diabetes, which has a limited number of treatments that regulate protein expression or translocation.

Syndecan-4 affects myogenesis via Rac1-mediated actin remodeling and exhibits copy-number amplification and increased expression in human rhabdomyosarcoma tumors.

Skeletal muscle demonstrates a high degree of regenerative capacity repeating the embryonic myogenic program under strict control. Rhabdomyosarcoma is the most common sarcoma in childhood and is characterized by impaired muscle differentiation. In this study, we observed that silencing the expression of syndecan-4, the ubiquitously expressed transmembrane heparan sulfate proteoglycan, significantly enhanced myoblast differentiation, and fusion. During muscle differentiation, the gradually decreasing expression of syndecan-4 allows the activation of Rac1, thereby mediating myoblast fusion. Single-molecule localized superresolution direct stochastic optical reconstruction microscopy (dSTORM) imaging revealed nanoscale changes in actin cytoskeletal architecture, and atomic force microscopy showed reduced elasticity of syndecan-4-knockdown cells during fusion. Syndecan-4 copy-number amplification was observed in 28% of human fusion-negative rhabdomyosarcoma tumors and was accompanied by increased syndecan-4 expression based on RNA sequencing data. Our study suggests that syndecan-4 can serve as a tumor driver gene in promoting rabdomyosarcoma tumor development. Our results contribute to the understanding of the role of syndecan-4 in skeletal muscle development, regeneration, and tumorigenesis.

Investigation of the Antiremodeling Effects of Losartan, Mirabegron and Their Combination on the Development of Doxorubicin-Induced Chronic Cardiotoxicity in a Rat Model.

Despite the effectiveness of doxorubicin (DOXO) as a chemotherapeutic agent, dose-dependent development of chronic cardiotoxicity limits its application. The angiotensin-II receptor blocker losartan is commonly used to treat cardiac remodeling of various etiologies. The beta-3 adrenergic receptor agonist mirabegron was reported to improve chronic heart failure. Here we investigated the effects of losartan, mirabegron and their combination on the development of DOXO-induced chronic cardiotoxicity. Male Wistar rats were divided into five groups: (i) control; (ii) DOXO-only; (iii) losartan-treated DOXO; (iv) mirabegron-treated DOXO; (v) losartan plus mirabegron-treated DOXO groups. The treatments started 5 weeks after DOXO administration. At week 8, echocardiography was performed. At week 9, left ventricles were prepared for histology, qRT-PCR, and Western blot measurements. Losartan improved diastolic but not systolic dysfunction and ameliorated SERCA2a repression in our DOXO-induced cardiotoxicity model. The DOXO-induced overexpression of Il1 and Il6 was markedly decreased by losartan and mirabegron. Mirabegron and the combination treatment improved systolic and diastolic dysfunction and significantly decreased overexpression of Smad2 and Smad3 in our DOXO-induced cardiotoxicity model. Only mirabegron reduced DOXO-induced cardiac fibrosis significantly. Mirabegron and its combination with losartan seem to be promising therapeutic tools against DOXO-induced chronic cardiotoxicity.

Syndecan-4 in Tumor Cell Motility.

Syndecan-4 (SDC4) is a ubiquitously expressed, transmembrane proteoglycan bearing heparan sulfate chains. SDC4 is involved in numerous inside-out and outside-in signaling processes, such as binding and sequestration of growth factors and extracellular matrix components, regulation of the activity of the small GTPase Rac1, protein kinase C-alpha, the level of intracellular calcium, or the phosphorylation of focal adhesion kinase. The ability of this proteoglycan to link the extracellular matrix and actin cytoskeleton enables SDC4 to contribute to biological functions like cell adhesion and migration, cell proliferation, cytokinesis, cellular polarity, or mechanotransduction. The multiple roles of SDC4 in tumor pathogenesis and progression has already been demonstrated; therefore, the expression and signaling of SDC4 was investigated in several tumor types. SDC4 influences tumor progression by regulating cell proliferation as well as cell migration by affecting cell-matrix adhesion and several signaling pathways. Here, we summarize the general role of SDC4 in cell migration and tumor cell motility.

Deuterium Depletion Inhibits Cell Proliferation, RNA and Nuclear Membrane Turnover to Enhance Survival in Pancreatic Cancer.

The effects of deuterium-depleted water (DDW) containing deuterium (D) at a concentration of 25 parts per million (ppm), 50 ppm, 105 ppm and the control at 150 ppm were monitored in MIA-PaCa-2 pancreatic cancer cells by the real-time cell impedance detection xCELLigence method. The data revealed that lower deuterium concentrations corresponded to lower MiA PaCa-2 growth rate. Nuclear membrane turnover and nucleic acid synthesis rate at different D-concentrations were determined by targeted [1,2-13C2]-D-glucose fate associations. The data showed severely decreased oxidative pentose cycling, RNA ribose 13C labeling from [1,2-13C2]-D-glucose and nuclear membrane lignoceric (C24:0) acid turnover. Here, we treated advanced pancreatic cancer patients with DDW as an extra-mitochondrial deuterium-depleting strategy and evaluated overall patient survival. Eighty-six (36 male and 50 female) pancreatic adenocarcinoma patients were treated with conventional chemotherapy and natural water (control, 30 patients) or 85 ppm DDW (56 patients), which was gradually decreased to preparations with 65 ppm and 45 ppm deuterium content for each 1 to 3 months treatment period. Patient survival curves were calculated by the Kaplan-Meier method and Pearson correlation was taken between medial survival time (MST) and DDW treatment in pancreatic cancer patients. The MST for patients consuming DDW treatment (n = 56) was 19.6 months in comparison with the 6.36 months' MST achieved with chemotherapy alone (n = 30). There was a strong, statistically significant Pearson correlation (r = 0.504, p < 0.001) between survival time and length and frequency of DDW treatment.

Pathomechanisms and therapeutic opportunities in radiation-induced heart disease: from bench to bedside.

Cancer management has undergone significant improvements, which led to increased long-term survival rates among cancer patients. Radiotherapy (RT) has an important role in the treatment of thoracic tumors, including breast, lung, and esophageal cancer, or Hodgkin's lymphoma. RT aims to kill tumor cells; however, it may have deleterious side effects on the surrounding normal tissues. The syndrome of unwanted cardiovascular adverse effects of thoracic RT is termed radiation-induced heart disease (RIHD), and the risk of developing RIHD is a critical concern in current oncology practice. Premature ischemic heart disease, cardiomyopathy, heart failure, valve abnormalities, and electrical conduct defects are common forms of RIHD. The underlying mechanisms of RIHD are still not entirely clear, and specific therapeutic interventions are missing. In this review, we focus on the molecular pathomechanisms of acute and chronic RIHD and propose preventive measures and possible pharmacological strategies to minimize the burden of RIHD.

Syndecan-4 Modulates Cell Polarity and Migration by Influencing Centrosome Positioning and Intracellular Calcium Distribution.

Efficient cell migration requires cellular polarization, which is characterized by the formation of leading and trailing edges, appropriate positioning of the nucleus and reorientation of the Golgi apparatus and centrosomes toward the leading edge. Migration also requires the development of an asymmetrical front-to-rear calcium (Ca2+) gradient to regulate focal adhesion assembly and actomyosin contractility. Here we demonstrate that silencing of syndecan-4, a transmembrane heparan sulfate proteoglycan, interferes with the correct polarization of migrating mammalian myoblasts (i.e., activated satellite stem cells). In particular, syndecan-4 knockdown completely abolished the intracellular Ca2+ gradient, abrogated centrosome reorientation and thus decreased cell motility, demonstrating the role of syndecan-4 in cell polarity. Additionally, syndecan-4 exhibited a polarized distribution during migration. Syndecan-4 knockdown cells exhibited decreases in the total movement distance during directional migration, maximum and vectorial distances from the starting point, as well as average and maximum cell speeds. Super-resolution direct stochastic optical reconstruction microscopy images of syndecan-4 knockdown cells revealed nanoscale changes in the actin cytoskeletal architecture, such as decreases in the numbers of branches and individual branch lengths in the lamellipodia of the migrating cells. Given the crucial importance of myoblast migration during embryonic development and postnatal muscle regeneration, we conclude that our results could facilitate an understanding of these processes and the general role of syndecan-4 during cell migration.

Myoblast Migration and Directional Persistence Affected by Syndecan-4-Mediated Tiam-1 Expression and Distribution.

Skeletal muscle is constantly renewed in response to injury, exercise, or muscle diseases. Muscle stem cells, also known as satellite cells, are stimulated by local damage to proliferate extensively and form myoblasts that then migrate, differentiate, and fuse to form muscle fibers. The transmembrane heparan sulfate proteoglycan syndecan-4 plays multiple roles in signal transduction processes, such as regulating the activity of the small GTPase Rac1 (Ras-related C3 botulinum toxin substrate 1) by binding and inhibiting the activity of Tiam1 (T-lymphoma invasion and metastasis-1), a guanine nucleotide exchange factor for Rac1. The Rac1-mediated actin remodeling is required for cell migration. Syndecan-4 knockout mice cannot regenerate injured muscle; however, the detailed underlying mechanism is unknown. Here, we demonstrate that shRNA-mediated knockdown of syndecan-4 decreases the random migration of mouse myoblasts during live-cell microscopy. Treatment with the Rac1 inhibitor NSC23766 did not restore the migration capacity of syndecan-4 silenced cells; in fact, it was further reduced. Syndecan-4 knockdown decreased the directional persistence of migration, abrogated the polarized, asymmetric distribution of Tiam1, and reduced the total Tiam1 level of the cells. Syndecan-4 affects myoblast migration via its role in expression and localization of Tiam1; this finding may facilitate greater understanding of the essential role of syndecan-4 in the development and regeneration of skeletal muscle.

Astaxanthin: A Potential Mitochondrial-Targeted Antioxidant Treatment in Diseases and with Aging.

Oxidative stress is characterized by an imbalance between prooxidant and antioxidant species, leading to macromolecular damage and disruption of redox signaling and cellular control. It is a hallmark of various diseases including metabolic syndrome, chronic fatigue syndrome, neurodegenerative, cardiovascular, inflammatory, and age-related diseases. Several mitochondrial defects have been considered to contribute to the development of oxidative stress and known as the major mediators of the aging process and subsequent age-associated diseases. Thus, mitochondrial-targeted antioxidants should prevent or slow down these processes and prolong longevity. This is the reason why antioxidant treatments are extensively studied and newer and newer compounds with such an effect appear. Astaxanthin, a xanthophyll carotenoid, is the most abundant carotenoid in marine organisms and is one of the most powerful natural compounds with remarkable antioxidant activity. Here, we summarize its antioxidant targets, effects, and benefits in diseases and with aging.

Changes in Redox Signaling in the Skeletal Muscle with Aging.

Reduction in muscle strength with aging is due to both loss of muscle mass (quantity) and intrinsic force production (quality). Along with decreased functional capacity of the muscle, age-related muscle loss is associated with corresponding comorbidities and healthcare costs. Mitochondrial dysfunction and increased oxidative stress are the central driving forces for age-related skeletal muscle abnormalities. The increased oxidative stress in the aged muscle can lead to altered excitation-contraction coupling and calcium homeostasis. Furthermore, apoptosis-mediated fiber loss, atrophy of the remaining fibers, dysfunction of the satellite cells (muscle stem cells), and concomitant impaired muscle regeneration are also the consequences of increased oxidative stress, leading to a decrease in muscle mass, strength, and function of the aged muscle. Here we summarize the possible effects of oxidative stress in the aged muscle and the benefits of physical activity and antioxidant therapy.

Mechanisms and Modulation of Oxidative/Nitrative Stress in Type 4 Cardio-Renal Syndrome and Renal Sarcopenia.

Chronic kidney disease (CKD) is a public health problem and a recognized risk factor for cardiovascular diseases (CVD). CKD could amplify the progression of chronic heart failure leading to the development of type 4 cardio-renal syndrome (T4CRS). The severity and persistence of heart failure are strongly associated with mortality risk in T4CRS. CKD is also a catabolic state leading to renal sarcopenia which is characterized by the loss of skeletal muscle strength and physical function. Renal sarcopenia also promotes the development of CVD and increases the mortality in CKD patients. In turn, heart failure developed in T4CRS could result in chronic muscle hypoperfusion and metabolic disturbances leading to or aggravating the renal sarcopenia. The interplay of multiple factors (e.g., comorbidities, over-activated renin-angiotensin-aldosterone system [RAAS], sympathetic nervous system [SNS], oxidative/nitrative stress, inflammation, etc.) may result in the progression of T4CRS and renal sarcopenia. Among these factors, oxidative/nitrative stress plays a crucial role in the complex pathomechanism and interrelationship between T4CRS and renal sarcopenia. In the heart and skeletal muscle, mitochondria, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, uncoupled nitric oxide synthase (NOS) and xanthine oxidase are major ROS sources producing superoxide anion (O2·-) and/or hydrogen peroxide (H2O2). O2·- reacts with nitric oxide (NO) forming peroxynitrite (ONOO-) which is a highly reactive nitrogen species (RNS). High levels of ROS/RNS cause lipid peroxidation, DNA damage, interacts with both DNA repair enzymes and transcription factors, leads to the oxidation/nitration of key proteins involved in contractility, calcium handling, metabolism, antioxidant defense mechanisms, etc. It also activates the inflammatory response, stress signals inducing cardiac hypertrophy, fibrosis, or cell death via different mechanisms (e.g., apoptosis, necrosis) and dysregulates autophagy. Therefore, the thorough understanding of the mechanisms which lead to perturbations in oxidative/nitrative metabolism and its relationship with pro-inflammatory, hypertrophic, fibrotic, cell death and other pathways would help to develop strategies to counteract systemic and tissue oxidative/nitrative stress in T4CRS and renal sarcopenia. In this review, we also focus on the effects of some well-known and novel pharmaceuticals, nutraceuticals, and physical exercise on cardiac and skeletal muscle oxidative/nitrative stress in T4CRS and renal sarcopenia.

Syndecan-4 influences mammalian myoblast proliferation by modulating myostatin signalling and G1/S transition.

Myostatin, a TGF-ß superfamily member, is a negative regulator of muscle growth. Here we describe how myostatin activity is regulated by syndecan-4, a ubiquitous transmembrane heparan sulfate proteoglycan. During muscle regeneration the levels of both syndecan-4 and promyostatin decline gradually after a sharp increase, concurrently with the release of mature myostatin. Promyostatin and syndecan-4 co-immunoprecipitate, and the interaction is heparinase-sensitive. ShRNA-mediated silencing of syndecan-4 reduces C2C12 myoblast proliferation via blocking the progression from G1- to S-phase of the cell cycle, which is accompanied by elevated levels of myostatin and p21(Waf1/Cip1), and decreases in cyclin E and cyclin D1 expression. Our results suggest that syndecan-4 functions as a reservoir for promyostatin regulating the local bioavailability of mature myostatin.

Myostatin propeptide mutation of the hypermuscular Compact mice decreases the formation of myostatin and improves insulin sensitivity.

The TGFß family member myostatin (growth/differentiation factor-8) is a negative regulator of skeletal muscle growth. The hypermuscular Compact mice carry the 12-bp Mstn(Cmpt-dl1Abc) deletion in the sequence encoding the propeptide region of the precursor promyostatin, and additional modifier genes of the Compact genetic background contribute to determine the full expression of the phenotype. In this study, by using mice strains carrying mutant or wild-type myostatin alleles with the Compact genetic background and nonmutant myostatin with the wild-type background, we studied separately the effect of the Mstn(Cmpt-dl1Abc) mutation or the Compact genetic background on morphology, metabolism, and signaling. We show that both the Compact myostatin mutation and Compact genetic background account for determination of skeletal muscle size. Despite the increased musculature of Compacts, the absolute size of heart and kidney is not influenced by myostatin mutation; however, the Compact genetic background increases them. Both Compact myostatin and genetic background exhibit systemic metabolic effects. The Compact mutation decreases adiposity and improves whole body glucose uptake, insulin sensitivity, and 18FDG uptake of skeletal muscle and white adipose tissue, whereas the Compact genetic background has the opposite effect. Importantly, the mutation does not prevent the formation of mature myostatin; however, a decrease in myostatin level was observed, leading to altered activation of Smad2, Smad1/5/8, and Akt, and an increased level of p-AS160, a Rab-GTPase-activating protein responsible for GLUT4 translocation. Based on our analysis, the Compact genetic background strengthens the effect of myostatin mutation on muscle mass, but those can compensate for each other when systemic metabolic effects are compared.

Modulation of Hypercholesterolemia-Induced Oxidative/Nitrative Stress in the Heart.

Hypercholesterolemia is a frequent metabolic disorder associated with increased risk for cardiovascular morbidity and mortality. In addition to its well-known proatherogenic effect, hypercholesterolemia may exert direct effects on the myocardium resulting in contractile dysfunction, aggravated ischemia/reperfusion injury, and diminished stress adaptation. Both preclinical and clinical studies suggested that elevated oxidative and/or nitrative stress plays a key role in cardiac complications induced by hypercholesterolemia. Therefore, modulation of hypercholesterolemia-induced myocardial oxidative/nitrative stress is a feasible approach to prevent or treat deleterious cardiac consequences. In this review, we discuss the effects of various pharmaceuticals, nutraceuticals, some novel potential pharmacological approaches, and physical exercise on hypercholesterolemia-induced oxidative/nitrative stress and subsequent cardiac dysfunction as well as impaired ischemic stress adaptation of the heart in hypercholesterolemia.

Myostatin and IGF-I signaling in end-stage human heart failure: a qRT-PCR study.

BACKGROUND: Myostatin (Mstn) is a key regulator of heart metabolism and cardiomyocyte growth interacting tightly with insulin-like growth factor I (IGF-I) under physiological conditions. The pathological role of Mstn has also been suggested since Mstn protein was shown to be upregulated in the myocardium of end-stage heart failure. However, no data are available about the regulation of gene expression of Mstn and IGF-I in different regions of healthy or pathologic human hearts, although they both might play a crucial role in the pathomechanism of heart failure. METHODS: In the present study, heart samples were collected from left ventricles, septum and right ventricles of control healthy individuals as well as from failing hearts of dilated (DCM) or ischemic cardiomyopathic (ICM) patients. A comprehensive qRT-PCR analysis of Mstn and IGF-I signaling was carried out by measuring expression of Mstn, its receptor Activin receptor IIB (ActRIIB), IGF-I, IGF-I receptor (IGF-IR), and the negative regulator of Mstn miR-208, respectively. Moreover, we combined the measured transcript levels and created complex parameters characterizing either Mstn- or IGF-I signaling in the different regions of healthy or failing hearts. RESULTS: We have found that in healthy control hearts, the ratio of Mstn/IGF-I signaling was significantly higher in the left ventricle/septum than in the right ventricle. Moreover, Mstn transcript levels were significantly upregulated in all heart regions of DCM but not ICM patients. However, the ratio of Mstn/IGF-I signaling remained increased in the left ventricle/septum compared to the right ventricle of DCM patients (similarly to the healthy hearts). In contrast, in ICM hearts significant transcript changes were detected mainly in IGF-I signaling. In parallel with these results miR-208 showed mild upregulation in the left ventricle of both DCM and ICM hearts. CONCLUSIONS: This is the first demonstration of a spatial asymmetry in the expression pattern of Mstn/IGF-I in healthy hearts, which is likely to play a role in the different growth regulation of left vs. right ventricle. Moreover, we identified Mstn as a massively regulated gene in DCM but not in ICM as part of possible compensatory mechanisms in the failing heart.

Extracellular deposition of matrilin-2 controls the timing of the myogenic program during muscle regeneration.

Here, we identify a role for the matrilin-2 (Matn2) extracellular matrix protein in controlling the early stages of myogenic differentiation. We observed Matn2 deposition around proliferating, differentiating and fusing myoblasts in culture and during muscle regeneration in vivo. Silencing of Matn2 delayed the expression of the Cdk inhibitor p21 and of the myogenic genes Nfix, MyoD and Myog, explaining the retarded cell cycle exit and myoblast differentiation. Rescue of Matn2 expression restored differentiation and the expression of p21 and of the myogenic genes. TGF-ß1 inhibited myogenic differentiation at least in part by repressing Matn2 expression, which inhibited the onset of a positive-feedback loop whereby Matn2 and Nfix activate the expression of one another and activate myoblast differentiation. In vivo, myoblast cell cycle arrest and muscle regeneration was delayed in Matn2(-/-) relative to wild-type mice. The expression levels of Trf3 and myogenic genes were robustly reduced in Matn2(-/-) fetal limbs and in differentiating primary myoblast cultures, establishing Matn2 as a key modulator of the regulatory cascade that initiates terminal myogenic differentiation. Our data thus identify Matn2 as a crucial component of a genetic switch that modulates the onset of tissue repair.

The compact mutation of myostatin causes a glycolytic shift in the phenotype of fast skeletal muscles.

Myostatin is an important negative regulator of skeletal muscle growth. The hypermuscular Compact (Cmpt) mice carry a 12-bp natural mutation in the myostatin propeptide, with additional modifier genes being responsible for the phenotype. Muscle cellularity of the fast-type tibialis anterior (TA) and extensor digitorum longus (EDL) as well as the mixed-type soleus (SOL) muscles of Cmpt and wild-type mice was examined by immunohistochemical staining of the myosin heavy chain (MHC) proteins. In addition, transcript levels of MHC isoforms were quantified by qPCR. Based on our results, all investigated muscles of Cmpt mice were significantly larger compared with that of wild-type mice, as characterized by fiber hyperplasia of different grades. Fiber hypertrophy was not present in TA; however, EDL muscles showed specific IIB fiber hypertrophy while the (I and IIA) fibers of SOL muscles were generally hypertrophied. Both the fast TA and EDL muscles of Cmpt mice contained significantly more glycolytic IIB fibers accompanied by a decreased number of IIX and IIA fibers; however, this was not the case for SOL muscles. In summary, despite the variances found in muscle cellularity between the different myostatin mutant mice, similar glycolytic shifts were observed in Cmpt fast muscles as in muscles from myostatin knockout mice.