HDAC4 preserves skeletal muscle structure following long-term denervation by mediating distinct cellular responses

BACKGROUND: Denervation triggers numerous molecular responses in skeletal muscle, including the activation of catabolic pathways and oxidative stress, leading to progressive muscle atrophy. Histone deacetylase 4 (HDAC4) mediates skeletal muscle response to denervation, suggesting the use of HDAC inhibitors as a therapeutic approach to neurogenic muscle atrophy. However, the effects of HDAC4 inhibition in skeletal muscle in response to long-term denervation have not been described yet. METHODS: To further study HDAC4 functions in response to denervation, we analyzed mutant mice in which HDAC4 is specifically deleted in skeletal muscle. RESULTS: After an initial phase of resistance to neurogenic muscle atrophy, skeletal muscle with a deletion of HDAC4 lost structural integrity after 4 weeks of denervation. Deletion of HDAC4 impaired the activation of the ubiquitin-proteasome system, delayed the autophagic response, and dampened the OS response in skeletal muscle. Inhibition of the ubiquitin-proteasome system or the autophagic response, if on the one hand, conferred resistance to neurogenic muscle atrophy; on the other hand, induced loss of muscle integrity and inflammation in mice lacking HDAC4 in skeletal muscle. Moreover, treatment with the antioxidant drug Trolox prevented loss of muscle integrity and inflammation in in mice lacking HDAC4 in skeletal muscle, despite the resistance to neurogenic muscle atrophy. CONCLUSIONS: These results reveal new functions of HDAC4 in mediating skeletal muscle response to denervation and lead us to propose the combined use of HDAC inhibitors and antioxidant drugs to treat neurogenic muscle atrophy

Effects of Diet-Induced Obesity on Extracellular Matrix Remodeling During Skeletal Muscle Regeneration

THE EFFECT OF DIET-INDUCED OBESITY ON EXTRACELLULAR MATRIX REMODELING DURING SKELETAL MUSCLE REGENERATION Michelle A. Tedrowe, Lemuel A. Brown, Richard A. Perry Jr., Megan E. Rosa, Jacob L. Brown, David E. Lee, Nicholas P. Greene, Tyrone A. Washington. University of Arkansas, Fayetteville, Arkansas Skeletal muscle has the ability to regenerate from damage; however, recent studies have reported a negative effect of obesity on skeletal muscle regenerative capacity. The extracellular matrix (ECM) contributes to skeletal muscle structure acting as a scaffold for skeletal muscle. Additionally, skeletal muscle serves as a reservoir for proteins and growth factors that promote regeneration. Optimal skeletal muscle regeneration includes inflammation, ECM remodeling, and myofiber growth. Disruption to any of these processes can negatively affect skeletal muscle regeneration. PURPOSE: The purpose of this study was to determine how diet-induced obesity (DIO) affects ECM remodeling during skeletal muscle regeneration. METHODS: Fifty-six male C57BL/6J mice were randomly assigned to two groups; lean diet (10% fat) and high fat diet (HFD) (60% fat). Within those two groups, mice were randomly assigned to either a PBS (uninjured) group or a bupivacaine (injured) group. Bupivacaine is a myotoxin which induces injury to skeletal muscle. Both groups received injections into the tibialis anterior (TA). Three or 28 days post-bupivacaine injection, the TAs were extracted and PCR reaction was done to quantify ECM-related gene expression (i.e. Collagen-I, Collagen-III, Fibronectin, TGF-β, MMP-2, MMP-9, and TIMP-I). RESULTS: There was no difference in Collagen III:I gene expression 3 days post-injection in the lean group (p\u3e0.05). However, there was a 3 fold increase (p0.05). Three and 28 days post injection there was a main effect of injury to increase MMP-2 gene expression (pCONCLUSION: Obesity altered ECM composition during skeletal muscle regeneration. This could negatively impact the ability of obese muscle to recovery form injury. These findings suggest that an altered composition could lead to a change in exercise prescription for this specific population. This work was supported by a grant from the American Biosciences Institute and a Student Undergraduate Research Fellowship Grant

Developing cardiac and skeletal muscle share fast-skeletal myosin heavy chain and cardiac troponin-I expression

Skeletal muscle derived stem cells (MDSCs) transplanted into injured myocardium can differentiate into fast skeletal muscle specific myosin heavy chain (sk-fMHC) and cardiac specific troponin-I (cTn-I) positive cells sustaining recipient myocardial function. We have recently found that MDSCs differentiate into a cardiomyocyte phenotype within a three-dimensional gel bioreactor. It is generally accepted that terminally differentiated myocardium or skeletal muscle only express cTn-I or sk-fMHC, respectively. Studies have shown the presence of non-cardiac muscle proteins in the developing myocardium or cardiac proteins in pathological skeletal muscle. In the current study, we tested the hypothesis that normal developing myocardium and skeletal muscle transiently share both sk-fMHC and cTn-I proteins. Immunohistochemistry, western blot, and RT-PCR analyses were carried out in embryonic day 13 (ED13) and 20 (ED20), neonatal day 0 (ND0) and 4 (ND4), postnatal day 10 (PND10), and 8 week-old adult female Lewis rat ventricular myocardium and gastrocnemius muscle. Confocal laser microscopy revealed that sk-fMHC was expressed as a typical striated muscle pattern within ED13 ventricular myocardium, and the striated sk-fMHC expression was lost by ND4 and became negative in adult myocardium. cTn-I was not expressed as a typical striated muscle pattern throughout the myocardium until PND10. Western blot and RT-PCR analyses revealed that gene and protein expression patterns of cardiac and skeletal muscle transcription factors and sk-fMHC within ventricular myocardium and skeletal muscle were similar at ED20, and the expression patterns became cardiac or skeletal muscle specific during postnatal development. These findings provide new insight into cardiac muscle development and highlight previously unknown common developmental features of cardiac and skeletal muscle. © 2012 Clause et al

Denervation does not induce muscle atrophy through oxidative stress

Denervation leads to the activation of the catabolic pathways, such as the ubiquitin-proteasome and autophagy, resulting in skeletal muscle atrophy and weakness. Furthermore, denervation induces oxidative stress in skeletal muscle, which is thought to contribute to the induction of skeletal muscle atrophy. Several muscle diseases are characterized by denervation, but the molecular pathways contributing to muscle atrophy have been only partially described. Our study delineates the kinetics of activation of oxidative stress response in skeletal muscle following denervation. Despite the denervation-dependent induction of oxidative stress in skeletal muscle, treatments with anti-oxidant drugs do not prevent the reduction of muscle mass. Our results indicate that, although oxidative stress may contribute to the activation of the response to denervation, it is not responsible by itself of oxidative damage or neurogenic muscle atrophy

Three-Dimensional Human iPSC-Derived Artificial Skeletal Muscles Model Muscular Dystrophies and Enable Multilineage Tissue Engineering

Summary: Generating human skeletal muscle models is instrumental for investigating muscle pathology and therapy. Here, we report the generation of three-dimensional (3D) artificial skeletal muscle tissue from human pluripotent stem cells, including induced pluripotent stem cells (iPSCs) from patients with Duchenne, limb-girdle, and congenital muscular dystrophies. 3D skeletal myogenic differentiation of pluripotent cells was induced within hydrogels under tension to provide myofiber alignment. Artificial muscles recapitulated characteristics of human skeletal muscle tissue and could be implanted into immunodeficient mice. Pathological cellular hallmarks of incurable forms of severe muscular dystrophy could be modeled with high fidelity using this 3D platform. Finally, we show generation of fully human iPSC-derived, complex, multilineage muscle models containing key isogenic cellular constituents of skeletal muscle, including vascular endothelial cells, pericytes, and motor neurons. These results lay the foundation for a human skeletal muscle organoid-like platform for disease modeling, regenerative medicine, and therapy development. : Maffioletti et al. generate human 3D artificial skeletal muscles from healthy donors and patient-specific pluripotent stem cells. These human artificial muscles accurately model severe genetic muscle diseases. They can be engineered to include other cell types present in skeletal muscle, such as vascular cells and motor neurons. Keywords: skeletal muscle, pluripotent stem cells, iPS cells, myogenic differentiation, tissue engineering, disease modeling, muscular dystrophy, organoid

HDAC4 regulates skeletal muscle regeneration via soluble factors

Skeletal muscle possesses a high ability to regenerate after an insult or in pathological conditions, relying on satellite cells, the skeletal muscle stem cells. Satellite cell behavior is tightly regulated by the surrounding microenvironment, which provides multiple signals derived from local cells and systemic factors. Among epigenetic mechanisms, histone deacetylation has been proved to affect muscle regeneration. Indeed, pan-histone deacetylase inhibitors were found to improve muscle regeneration, while deletion of histone deacetylase 4 (HDAC4) in satellite cells inhibits their proliferation and differentiation, leading to compromised muscle regeneration. In this study, we delineated the HDAC4 function in adult skeletal muscle, following injury, by using a tissue-specific null mouse line. HDAC4 resulted crucial for skeletal muscle regeneration by mediating soluble factors that influence muscle-derived cell proliferation and differentiation. These findings add new biological functions to HDAC4 in skeletal muscle that need considering when administering histone deacetylase inhibitors

The Contributions of Skeletal Muscle PKC Theta to Diet-Induced Obesity

Protein Kinase C- Theta (PKCθ) is a gene predominantly expressed in hematopoietic cells and skeletal muscle. In skeletal muscle, PKCθ regulates fat metabolism and insulin sensitivity. PKCθ activity increases in response to high levels of diacylglycerol in the cell, a common outcome of chronic high fat diet consumption and obesity. PKCθ is associated with skeletal muscle metabolic dysfunction, which may exacerbate weight gain and metabolic disease. The purpose of this study was to test the hypothesis that the selective deletion of PKCθ from skeletal muscle protects against diet-induced obesity. Mice lacking PKCθ in skeletal muscle were created using Cre-Lox recombination. At weaning, control (PKCθSkM+/+) and knockout (PKCθSkM-/-) mice were randomly assigned to regular or high fat diet (RD or HFD, respectively) groups. Mouse weights were taken weekly for 15 weeks. During the 15-week diet intervention, male PKCθSkM+/+ mice on a HFD became obese. Male PKCθSkM-/- mice consuming a HFD showed attenuated weight gain, which was similar to mice on a RD. This trend was not present for female mice, in which weight changed to a similar magnitude independent of diet and genotype. In conclusion, PKC-θ in the skeletal muscle may contribute to the regulation of diet-induced obesity. It is unclear whether these affects are sex specific

Vitamin D supplementation does not improve human skeletal muscle contractile properties in insufficient young males

Vitamin D may be a regulator of skeletal muscle function, although human trials investigating this hypothesis are limited to predominantly elderly populations. We aimed to assess the effect of oral vitamin D3 in healthy young males upon skeletal muscle function

Human skeletal muscle derived microvesicles induce apoptosis in highly metastatic prostate cancer cells

The human skeletal muscle is a highly vascularised tissue that contributes approximately 40% of the total body mass. These two factors make it a prime target for secondary cancer metastases. Surprisingly, malignant cancers rarely metastasize to the skeletal muscle. Only 1.6% of all soft tissue sarcomas (muscle) examined are metastatic in origin. Various researchers over the years have therefore tried to elucidate the cellular and molecular mechanisms contributing to this rarity of secondary metastasis but they still remain obscure. Although some have postulated high levels of lactic acid or reported factors such as adenosine released by the skeletal muscle cell to create a toxic environment for secondary tumour development, the role of skeletal muscle microvesicles (MVs) on tumour cells is yet to be reported. In previous work we showed MVs capable of fusing with target cells. In this study, we show that MVs derived from human skeletal muscle cells (HSkMC) have a cytotoxic effect (inducing 30% apoptosis) upon interaction with highly metastatic prostate cancer cells (PC3M). We therefore postulate that HSkMC MVs and possibly exosomes may contain certain protein factor(s) that could be the cause of the cytotoxic effect observed on targeted tumour cells.Peer reviewedFinal Accepted Versio