Increasing autophagy does not affect neurogenic muscle atrophy

Physiological autophagy plays a crucial role in the regulation of muscle mass and metabolism, while the excessive induction or the inhibition of the autophagic flux contributes to the progression of several diseases. Autophagy can be activated by different stimuli, including cancer, exercise, caloric restriction and denervation. The latter leads to muscle atrophy through the activation of catabolic pathways, i.e. the ubiquitin-proteasome system and autophagy. However, the kinetics of autophagy activation and the upstream molecular pathways in denervated skeletal muscle have not been reported yet. In this study, we characterized the kinetics of autophagic induction, quickly triggered by denervation, and report the Akt/mTOR axis activation. Besides, with the aim to assess the relative contribution of autophagy in neurogenic muscle atrophy, we triggered autophagy with different stimuli along with denervation, and observed that four week-long autophagic induction, by either intermitted fasting or rapamycin treatment, did not significantly affect muscle mass loss. We conclude that: i) autophagy does not play a major role in inducing muscle loss following denervation; ii) nonetheless, autophagy may have a regulatory role in denervation induced muscle atrophy, since it is significantly upregulated as early as eight hours after denervation; iii) Akt/mTOR axis, AMPK and FoxO3a are activated consistently with the progression of muscle atrophy, further highlighting the complexity of the signaling response to the atrophying stimulus deriving from denervation

Skeletal muscle: a significant novel neurohypophyseal hormone-secreting organ

Vasopressin (arg8-vasopressin) and oxytocin are closely relalated hormones, synthesized as pre-hormones in the magnocellular neurons of the paraventricular Q6 and supraoptic nuclei of the hypothalamus. Vasopressin and oxytocin are secreted in response to a variety of physiological stimuli, serving such different functions as controlling water balance, milk ejection, uterine contraction, mood, and parental behavior (Lechan and Toni, 2000; Costa et al., 2014a)

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

Spontaneous physical activity down-regulates Pax7 in cancer cachexia

Emerging evidence suggests that the muscle microenvironment plays a prominent role in cancer cachexia. We recently showed that NF-kB - induced Pax7 overexpression impairs the myogenic potential of muscle precursors in cachectic mice, suggesting that lowering Pax7 expression may be beneficial in cancer cachexia. We evaluated the muscle regenerative potential after acute injury in C26 colon carcinoma tumor-bearing mice and healthy controls. Our analyses confirmed that the delayed muscle regeneration observed in muscles form tumor-bearing mice was associated with a persistent local inflammation and Pax7 overexpression. Physical activity is known to exert positive effects on cachectic muscles. However, the mechanism by which a moderate voluntary exercise ameliorates muscle wasting is not fully elucidated. To verify if physical activity affects Pax7 expression, we hosted control and C26-bearing mice in wheel-equipped cages and we found that voluntary wheel running down-regulated Pax7 expression in muscles from tumor-bearing mice. As expected, down-regulation of Pax7 expression was associated with a rescue of muscle mass and fiber size. Our findings shed light on the molecular basis of the beneficial effect exerted by a moderate physical exercise on muscle stem cells in cancer cachexia. Furthermore, we propose voluntary exercise as a physiological tool to counteract the over-expression of Pax7observed in cancer cachexia

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

Peroxynitrite activates the NLRP3 inflammasome cascade in SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Neuroinflammation, characterized by the appearance of reactive microglial and astroglial cells, is one of the several pathogenic mechanisms of amyotrophic lateral sclerosis (ALS), a fast-progressing and fatal neurodegenerative disease. Cerebrospinal fluid and spinal cord of ALS patients and SOD1 mutant mice show high concentrations of IL-1β. This interleukin, expressed as an inactive precursor, undergoes a proteolytic maturation by caspase1, whose activation, in turn, depends on inflammasomes. Whether and how inflammasome is activated in ALS models is still to be clarified. The mechanism of inflammasome activation was studied in murine microglial cells overexpressing hSOD1(G93A) and verified in the spinal cord of hSOD1(G93A) mice. Murine microglial hSOD1(G93A) cells express all the inflammasome components and LPS activates caspase1 leading to an increase in the secretion of IL-1β. By activating NF-κB, LPS increases ROS and NO levels that spontaneously react to form peroxynitrite, thus leading to protein nitration. Reduction in peroxynitrite levels results in a decrease in caspase1 activity. Protein nitration and caspase1 activity are concomitantly increased in the spinal cord of pre-symptomatic SOD1(G93A) mice. Oxidative/nitrosative stress induces peroxynitrite formation that may be a key trigger of caspase1/inflammasome activation. Peroxynitrite formation may play a critical role in inflammasome activation and might be exploited as potential therapeutic target for ALS

Histone deacetylase 4 is crucial for proper skeletal muscle development and disease

Epigenetics plays a pivotal role in modulating gene response to physiological or pathological stimuli. Histone Deacetylase inhibitors (HDACi) have been used in the treatment of various cancers1, are ef-fective in several animal models of neurodegenerative diseases, including amyotrophic lateral scle-rosis (ALS), and are currently in clinical trial to promote muscle repair in muscular dystrophies2. However, long-term use of pan-HDAC inhibitors is not tolerated3. The assignment of distinct biologi-cal functions to individual HDACs in skeletal muscle is a prerequisite to improve the efficacy of pharmacological treatments based on HDACi. HDAC4 is a member of class II HDACs that mediates many cellular responses. Clinical reports suggest that inhibition of HDAC4 can be beneficial to cancer cachexia, dystrophic or ALS patients. All the above conditions are characterized by progressive mus-cle wasting and up-regulation of HDAC4 expression in skeletal muscle, suggesting a potential role for this protein in regulating these diseases. To study the role of HDAC4 with a genetic approach, we generated several models of muscle disease in mice lacking HDAC4 in skeletal muscle: cancer ca-chexia, by implanting Lewis lung carcinoma (LLC), muscular dystrophy, by using mdx mice, or ALS, by using SODG93A mice. Lack of HDAC4 worsens skeletal muscle atrophy induced by both LLC and ALS, demonstrated by a reduction in muscle mass and myofibers size. Conversely, dystrophic mice lacking HDAC4 in skeletal muscle show an increased number of necrotic myofibers and run less efficiently than mdx mice. The aggravation of the dystrophic phenotype may be partially due to the impairment in skeletal muscle regeneration observed in mice lacking HDAC4 in skeletal muscle. Our results indi-cate that HDAC4 is necessary for maintaining skeletal muscle homeostasis and function. Current studies aim to investigate the molecular mechanisms underlying the role of HDAC4 in skeletal mus-cle maintenance in response to cancer cachexia, ALS or muscular dystrophy

Histone Deacetylase 4 is crucial for proper skeletal muscle development and disease

Epigenetics plays a pivotal role in modulating gene response to physiological or pathological stimuli. Histone Deacetylase inhibitors (HDACi) have been used in the treatment of various cancers1, are effective in several animal models of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), and are currently in clinical trial to promote muscle repair in muscular dystrophies2. However, long-term use of pan-HDAC inhibitors is not tolerated3. The assignment of distinct biological functions to individual HDACs in skeletal muscle is a prerequisite to improve the efficacy of pharmacological treatments based on HDACi. HDAC4 is a member of class II HDACs that mediates many cellular responses. Clinical reports suggest that inhibition of HDAC4 can be beneficial to cancer cachexia, dystrophic or ALS patients. All the above conditions are characterized by progressive muscle wasting and up-regulation of HDAC4 expression in skeletal muscle, suggesting a potential role for this protein in regulating these diseases. To study the role of HDAC4 with a genetic approach, we generated several models of muscle disease in mice lacking HDAC4 in skeletal muscle: cancer cachexia, by implanting Lewis lung carcinoma (LLC), muscular dystrophy, by using mdx mice, or ALS, by using SODG93A mice. Lack of HDAC4 worsens skeletal muscle atrophy induced by both LLC and ALS, demonstrated by a reduction in muscle mass and myofibers size. Conversely, dystrophic mice lacking HDAC4 in skeletal muscle show an increased number of necrotic myofibers and run less efficiently than mdx mice. The aggravation of the dystrophic phenotype may be partially due to the impairment in skeletal muscle regeneration observed in mice lacking HDAC4 in skeletal muscle. Our results indicate that HDAC4 is necessary for maintaining skeletal muscle homeostasis and function. Current studies aim to investigate the molecular mechanisms underlying the role of HDAC4 in skeletal muscle maintenance in response to cancer cachexia, ALS or muscular dystrophy

Epigenetics of muscle disorders

As heritable information apart from the DNA sequence itself, epigenetics represents a higher level of complexity in the regulation of gene expression and allows for a wide range of outputs. Epigenetics is a very powerful tool by which cells quickly fine tune the expressions of genes in response to environmental changes or permanently turn off other genes by inactivating their expression or inhibiting their translation. Muscle tissue varies with its function and location in the body. In mammals there are three types of muscle tissues: cardiac, skeletal, and smooth muscle. The first two are striated and display an orderly arrangement of myofibrils in sarcomeres. In contrast, in smooth muscle, the myofilaments are not aligned into sarcomeres. Smooth and cardiac muscles contract involuntarily under the control of the autonomic nervous system and endocrine and hormonal signals. In contrast, skeletal muscle only contracts voluntarily under the influence of the central nervous system. Several epigenetic mechanisms have been shown to regulate both the development and the responses to external stimuli of all muscle tissues. Regarding histone modifications alone, we should mention the existence of numerous epigenetic markers, such as histone methylation, ubiquitylation, phosphorylation, sumoylation, ribosylation, citrullination and acetylation, which affect chromatin structure and, consequently, gene expression. By limiting the discussion to the epigenetic mechanisms of DNA methylation, histone acetylation and methylation, and noncoding RNAs, we review how these processes regulate aspects of adult muscle remodeling. Indeed, all three types of muscles are subjected to changes in shape, mass, and metabolism in adulthood in response to external input. Epigenetics has been demonstrated to mediate many of these adaptations. In this chapter, we will summarize how epigenetics influences cardiac, skeletal, and smooth muscle cell physiologies, and we will review the epigenetic mechanisms that are altered in motor neuron diseases, muscular dystrophies, and rhabdomyosarcoma (RMS) and highlight the potential usefulness of epigenetic drugs for the treatment of muscle disorders

Histone deacetylase 4 is protective in ALS and modulates the response to oxidative stress

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by motor neuron degeneration, muscle atrophy and weakness, eventually leading to muscle paralysis and death. Several factors account for the development of ALS, including accumulation of oxidative stress in skeletal muscle1. A positive correlation between the expression of the histone deacetylase 4 (HDAC4) and the progression of the disease has been recently reported in ALS patients, suggesting the use of HDAC4 inhibitors as a promising therapeutic approach for the treatment of this neurodegenerative disease2. HDAC4 in skeletal muscle plays a crucial role in the regulation of muscle mass and reinnervation following denervation3. However, the molecular pathways controlled by HDAC4 in ALS onset or progression, as well as in response to oxidativestress in skeletal muscle are not delineated yet. We investigated the role of HDAC4 in ALS by deleting HDAC4 in skeletal muscle of SOD1G93A mice, a mouse model of ALS. Lack of HDAC4 in skeletal muscle anticipated body weight loss and induced more pronounced muscle atrophy in late stage SOD1G93A HDAC4 mKO mice, compared with age-matched SOD1G93A mice, indicating a protective role of HDAC4 in ALS. To study the molecular mechanisms underlying HDAC4 function in response to a chronic denervation, such as in ALS, we cut the sciatic nerve of one limb of HDAC4 mKO mice and analyzed muscles over time. HDAC4 mKO mice did not undergo muscle atrophy for two weeks following denervation, but muscles degenerated at later time points. Moreover, contralateral innervated muscle of HDAC4 mKO mice presented ultrastructural defects in myofiber organization and higher levels of ROS, while alteration of sarcomeric architecture and the molecular responses to oxidative stress were blunted following denervation. From our results, we conclude that HDAC4 protects skeletal muscle in ALS and is important to maintain muscle integrity and oxidative stress response following denervation. Further studies are necessary to delineate the role of HDAC4 in skeletal muscle integrity and in response to chronic denervation