Fibrotic response induced by angiotensin-II requires NAD(P)H oxidase-induced reactive oxygen species (ROS) in skeletal muscle cells

The role of fibrosis in the pathophysiology of muscular dystrophy

Muscular dystrophy exerts significant and dramatic impacts on affected patients, including progressive muscle wasting leading to lung and heart failure, and results in severely curtailed lifespan. Although the focus for many years has been on the dysfunction induced by the loss of function of dystrophin or related components of the striated muscle costamere, recent studies have demonstrated that accompanying pathologies, particularly muscle fibrosis, also contribute adversely to patient outcomes. A significant body of research has now shown that therapeutically targeting these accompanying pathologies via their underlying molecular mechanisms may provide novel approaches to patient management that can complement the current standard of care. In this review, we discuss the interplay between muscle fibrosis and muscular dystrophy pathology. A better understanding of these processes will contribute to improved patient care options, restoration of muscle function, and reduced patient morbidity and mortality.

Thrown for a loop: fibro-adipogenic progenitors in skeletal muscle fibrosis

Fibro-adipogenic progenitors (FAPs) are key regulators of skeletal muscle regeneration and homeostasis. However, dysregulation of these cells leads to fibro-fatty infiltration across various muscle diseases. FAPs are the key source of extracellular matrix (ECM) deposition in muscle, and disruption to this process leads to a pathological accumulation of ECM, known as fibrosis. The replacement of contractile tissue with fibrotic ECM functionally impairs the muscle and increases muscle stiffness. FAPs and fibrotic muscle form a progressively degenerative feedback loop where, as a muscle becomes fibrotic, it induces a fibrotic FAP phenotype leading to further development of fibrosis. In this review, we summarize FAPs' role in fibrosis in terms of their activation, heterogeneity, contributions to fibrotic degeneration, and role across musculoskeletal diseases. We also discuss current research on potential therapeutic avenues to attenuate fibrosis by targeting FAPs.

Cholic and deoxycholic acids induce mitochondrial dysfunction, impaired biogenesis and autophagic flux in skeletal muscle cells

BACKGROUND

Skeletal muscle is sensitive to bile acids (BA) because it expresses the TGR5 receptor for BA. Cholic (CA) and deoxycholic (DCA) acids induce a sarcopenia-like phenotype through TGR5-dependent mechanisms. Besides, a mouse model of cholestasis-induced sarcopenia was characterised by increased levels of serum BA and muscle weakness, alterations that are dependent on TGR5 expression. Mitochondrial alterations, such as decreased mitochondrial potential and oxygen consumption rate (OCR), increased mitochondrial reactive oxygen species (mtROS) and unbalanced biogenesis and mitophagy, have not been studied in BA-induced sarcopenia.

METHODS

We evaluated the effects of DCA and CA on mitochondrial alterations in C₂C₁₂ myotubes and a mouse model of cholestasis-induced sarcopenia. We measured mitochondrial mass by TOM20 levels and mitochondrial DNA; ultrastructural alterations by transmission electronic microscopy; mitochondrial biogenesis by PGC-1α plasmid reporter activity and protein levels by western blot analysis; mitophagy by the co-localisation of the MitoTracker and LysoTracker fluorescent probes; mitochondrial potential by detecting the TMRE probe signal; protein levels of OXPHOS complexes and LC3B by western blot analysis; OCR by Seahorse measures; and mtROS by MitoSOX probe signals.

RESULTS

DCA and CA caused a reduction in mitochondrial mass and decreased mitochondrial biogenesis. Interestingly, DCA and CA increased LC3II/LC3I ratio and decreased autophagic flux concordant with raised mitophagosome-like structures. In addition, DCA and CA decreased mitochondrial potential and reduced protein levels in OXPHOS complexes I and II. The results also demonstrated that DCA and CA decreased basal, ATP-linked, FCCP-induced maximal respiration and spare OCR. DCA and CA also reduced the number of cristae. In addition, DCA and CA increased the mtROS. In mice with cholestasis-induced sarcopenia, TOM20, OXPHOS complexes I, II and III, and OCR were diminished. Interestingly, the OCR and OXPHOS complexes were correlated with muscle strength and bile acid levels.

CONCLUSION

Our results showed that DCA and CA decreased mitochondrial mass, possibly by reducing mitochondrial biogenesis, which affects mitochondrial function, thereby altering potential OCR and mtROS generation. Some mitochondrial alterations were also observed in a mouse model of cholestasis-induced sarcopenia characterised by increased levels of BA, such as DCA and CA.

Sarcopenia and Cognitive Decline in Older Adults: Targeting the Muscle-Brain Axis

Declines in physical performance and cognition are commonly observed in older adults. The geroscience paradigm posits that a set of processes and pathways shared among age-associated conditions may also serve as a molecular explanation for the complex pathophysiology of physical frailty, sarcopenia, and cognitive decline. Mitochondrial dysfunction, inflammation, metabolic alterations, declines in cellular stemness, and altered intracellular signaling have been observed in muscle aging. Neurological factors have also been included among the determinants of sarcopenia. Neuromuscular junctions (NMJs) are synapses bridging nervous and skeletal muscle systems with a relevant role in age-related musculoskeletal derangement. Patterns of circulating metabolic and neurotrophic factors have been associated with physical frailty and sarcopenia. These factors are mostly related to disarrangements in protein-to-energy conversion as well as reduced calorie and protein intake to sustain muscle mass. A link between sarcopenia and cognitive decline in older adults has also been described with a possible role for muscle-derived mediators (i.e., myokines) in mediating muscle-brain crosstalk. Herein, we discuss the main molecular mechanisms and factors involved in the muscle-brain axis and their possible implication in cognitive decline in older adults. An overview of current behavioral strategies that allegedly act on the muscle-brain axis is also provided.

Mini-review: Angiotensin- converting enzyme 1 (ACE1) and the impact for diseases such as Alzheimer's disease, sarcopenia, cancer, and COVID-19

Ageing has been associated with comorbidities, systemic low-grade of inflammation, and immunosenescence. Hypertension is the most common morbidity and anti-hypertensives are used for more than 50%. Angiotensin-converting enzyme 1 inhibitors (ACEi) and angiotensin II receptor blockers (ARB) control blood pressure but also seem to play a role in comorbidities such as Alzheimer's disease, sarcopenia and cancer. The impact of anti-hypertensives in comorbidities is due to the expression of renin-angiotensin system (RAS) in several tissues and body fluids. Angiotensin-converting enzyme 1 (ACE1) has been linked to oxidative stress, metabolism, and inflammation. The levels and activity of ACE1 are under genetic control and polymorphisms have been correlated with susceptibility to Alzheimer's disease. In addition, some results found that ACEi and ARB users present delayed cognitive decline and reduced risk of dementia. Regarding to sarcopenia, RAS has been linked to the catabolic and anabolic pathways for muscle mass maintenance. In some studies, older adults using ACEi were highly benefited by exercise training. In cancer, RAS and its products have been shown to play a role since their inhibition in animal models modulates tumor microenvironment and improves the delivery of chemotherapy drugs. Clinically, the incidence of colorectal cancer is reduced in patients using ACEi and ARB. During the pandemic COVID-19 it was found that ACE2 receptor plays a role in the entry of SARS-CoV-2 into the host cell. ACE1 genotypes have been linked to an increased risk for COVID-19 and severe disease. In some studies COVID-19 patients taking ARB or ACEi presented better outcome.

Differential Fibrotic Response of Muscle Fibroblasts, Myoblasts, and Myotubes to Cholic and Deoxycholic Acids

Fibrosis is a condition characterized by an increase in the components of the extracellular matrix (ECM). In skeletal muscle, the cells that participate in the synthesis of ECM are fibroblasts, myoblasts, and myotubes. These cells respond to soluble factors that increase ECM. Fibrosis is a phenomenon that develops in conditions of chronic inflammation, extensive lesions, or chronic diseases. A pathological condition with muscle weakness and increased bile acids (BA) in the blood is cholestatic chronic liver diseases (CCLD). Skeletal muscle expresses the membrane receptor for BA called TGR5. To date, muscle fibrosis in CCLD has not been evaluated. This study aims to assess whether BA can induce a fibrotic condition in muscle fibroblasts, myoblasts, and myotubes. The cells were incubated with deoxycholic (DCA) and cholic (CA) acids, and fibronectin protein levels were evaluated by Western blot. In muscle fibroblasts, both DCA and CA induced an increase in fibronectin protein levels. The same response was found in fibroblasts when activating TGR5 with the specific receptor agonist (INT-777). Interestingly, DCA reduced fibronectin protein levels in both myoblasts and myotubes, while CA did not show changes in fibronectin protein levels in myoblasts and myotubes. These results suggest that DCA and CA can induce a fibrotic phenotype in muscle-derived fibroblasts. On the other hand, DCA decreased the fibronectin in myoblasts and myotubes, whereas CA did not show any effect in these cell populations. Our results show that BA has different effects depending on the cell population to be analyzed.

Combined Administration of Andrographolide and Angiotensin- (1-7) Synergically Increases the Muscle Function and Strength in Aged Mice

BACKGROUND

Sarcopenia is a progressive and generalized skeletal muscle disorder characterized by muscle weakness, loss of muscle mass, and decline in the capacity of force generation. Aging can cause sarcopenia. Several therapeutic strategies have been evaluated to prevent or alleviate this disorder. One of them is angiotensin 1-7 [Ang-(1-7)], an anti-atrophic peptide for skeletal muscles that regulates decreased muscle mass for several causes, including aging. Another regulator of muscle mass and function is andrographolide, a bicyclic diterpenoid lactone that decreases the nuclear factor kappa B (NF-κB) signaling and attenuates the severity of some muscle diseases.

OBJECTIVE

Evaluate the effect of combined administration of Ang-(1-7) with andrographolide on the physical performance, muscle strength, and fiber´s diameter in a murine model of sarcopenia by aging.

METHODS

Aged male mice of the C57BL/6J strain were treated with Andrographolide, Ang-(1-7), or combined for three months. The physical performance, muscle strength, and fiber´s diameter were measured.

RESULTS

The results showed that aged mice (24 months old) treated with Ang-(1-7) or Andrographolide improved their performance on a treadmill test, muscle strength, and their fiber´s diameter compared to aged mice without treatment. The combined administration of Ang-(1-7) with andrographolide to aged mice has an enhanced synergically effect on physical performance, muscle strength, and fiber´s diameter.

CONCLUSION

Our results indicated that in aged mice, the effects of andrographolide and Ang-(1-7) on muscle function, strength, and fiber´s diameter are potentiated.

Rewinding sarcopenia: a narrative review on the renin-angiotensin system

BACKGROUND AND AIMS

The purpose of this review was two-fold. First, we aimed to provide an in-depth glance on the relationship between renin-angiotensin system (RAS) dysregulation and sarcopenia. Second, we aimed to touch upon potential treatments of sarcopenia (including RAS blockers, vitamin D, and exercise) in light of the pertinent literature.

METHODS

Currently available research regarding the effects of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers on knee extensor strength, grip strength, chair stand test, gate speed together with the effects of exercise on muscle mass, strength, physical performance, blood pressure and cognitive tests (particularly in older adults) was reviewed.

RESULTS

Although some studies have shown favorable effects of ACEIs on muscle strength and/or physical function tests, some studies have reported no/negative association in between. The favorable impact of exercise on reducing blood pressure is shown, and exercise treatment is widely recommended in the relevant literature. Different types of exercises (aerobic, resistance, dancing, music movement, water-based, golf, knitting activities or multicomponent exercises) have shown improvement in cognitive functions as well.

CONCLUSION

Classical RAS activity results in deleterious effects not only on the cardiovascular but also on the neuromusculoskeletal system. Therefore, treatments targeting inhibition of the classical RAS activity seem to be important in the management of several age-related pathologies, including sarcopenia. As such, ACEIs, vitamin D, exercise, and healthy diet can have prominent effects not only on the modulation of RAS but also on physical and cognitive functions and sarcopenia as well.

Modulation of Intracellular ROS and Senescence-Associated Phenotypes of Xenopus Oocytes and Eggs by Selective Antioxidants

Aging of oocytes and eggs diminishes their reproductive and developmental potential. It has been demonstrated previously that reactive oxygen species (ROS) contribute to accelerated aging of various cells. In the present study, we measured intracellular levels of ROS and investigated effects of several selective antioxidants (AOXs) on the viability and functional activity of aging oocytes and eggs of the African clawed frog Xenopus laevis. The fluorescent cell-permeable dye DCFDA, which is widely employed for ROS detection in cultured mammalian cells, was used to monitor ROS levels in the fresh and bench-aged oocytes and eggs by an optimized protocol. It was found that intracellular ROS contents were increased in frog oocytes and eggs aged for 48 h. It was further demonstrated using selective cell-permeable AOXs targeting different ROS-generating mechanisms, that the major source of ROS in Xenopus oocytes and eggs is the plasma membrane NADPH oxidase, and that mitochondrial generation contributes to the intracellular ROS content to a lesser extent. Targeted inhibition of NADPH oxidase with a natural organic compound apocynin reduced ROS levels significantly in Xenopus oocytes and eggs, maintained their normal phenotype and supported their functional competence. To our knowledge this is the first report concerning beneficial effects of apocynin on the isolated gamete cells, such as oocytes and eggs.

CoQ10 augments candesartan protective effect against tourniquet-induced hind limb ischemia-reperfusion: Involvement of non-classical RAS and ROS pathways

Tourniquet is a well-established model of hind limb ischemia–reperfusion (HLI/R) in rats. Nevertheless, measures should be taken to alleviate the expected injury from ischemia/ reperfusion (I/R). In the present study, 30 adult male Sprague-Dawley rats were randomly divided into 5 groups (n = 6): control, HLI/R, HLI/R given candesartan (1 mg/kg, P.O); HLI/R given Coenzyme Q10 (CoQ10) (10 mg/kg, P.O); HLI/R given candesartan (0.5 mg/kg) and CoQ10 (5 mg/kg). The drugs were administered for 7 days starting one hour after reperfusion. Candesartan and CoQ10 as well as their combination suppressed gastrocnemius content of angiotensin II while they raised angiotensin-converting enzyme 2 (ACE2) activity, angiotensin (1–7) expression, and Mas receptor mRNA level. Consequently, candesartan and/or CoQ10 reversed the oxidative stress and inflammatory changes that occurred following HLI/R as demonstrated by the rise of SOD activity and the decline of MDA, TNF-α, and IL-6 skeletal muscle content. Additionally, candesartan and/or CoQ10 diminished gastrocnemius active caspase-3 level and phospho-p38 MAPK protein expression. Our study proved that CoQ10 enhanced the beneficial effect of candesartan in a model of tourniquet-induced HLI/R by affecting classical and non-classical renin-angiotensin system (RAS) pathway. To our knowledge, this is the first study showing the impact of CoQ10 on skeletal muscle RAS in rats.

Role of Matricellular CCN Proteins in Skeletal Muscle: Focus on CCN2/CTGF and Its Regulation by Vasoactive Peptides

The Cellular Communication Network (CCN) family of matricellular proteins comprises six proteins that share conserved structural features and play numerous biological roles. These proteins can interact with several receptors or soluble proteins, regulating cell signaling pathways in various tissues under physiological and pathological conditions. In the skeletal muscle of mammals, most of the six CCN family members are expressed during embryonic development or in adulthood. Their roles during the adult stage are related to the regulation of muscle mass and regeneration, maintaining vascularization, and the modulation of skeletal muscle fibrosis. This work reviews the CCNs proteins' role in skeletal muscle physiology and disease, focusing on skeletal muscle fibrosis and its regulation by Connective Tissue Growth factor (CCN2/CTGF). Furthermore, we review evidence on the modulation of fibrosis and CCN2/CTGF by the renin-angiotensin system and the kallikrein-kinin system of vasoactive peptides.

The linkage between inflammation and fibrosis in muscular dystrophies: The axis autotaxin-lysophosphatidic acid as a new therapeutic target?

Muscular dystrophies (MDs) are a diverse group of severe disorders characterized by increased skeletal muscle feebleness. In many cases, respiratory and cardiac muscles are also compromised. Skeletal muscle inflammation and fibrosis are hallmarks of several skeletal muscle diseases, including MDs. Until now, several keys signaling pathways and factors that regulate inflammation and fibrosis have been identified. However, no curative treatments are available. Therefore, it is necessary to find new therapeutic targets to fight these diseases and improve muscle performance. Lysophosphatidic acid (LPA) is an active glycerophospholipid mainly synthesized by the secreted enzyme autotaxin (ATX), which activates six different G protein-coupled receptors named LPA₁ to LPA₆ (LPARs). In conjunction, they are part of the ATX/LPA/LPARs axis, involved in the inflammatory and fibrotic response in several organs-tissues. This review recapitulates the most relevant aspects of inflammation and fibrosis in MDs. It analyzes experimental evidence of the effects of the ATX/LPA/LPARs axis on inflammatory and fibrotic responses. Finally, we speculate about its potential role as a new therapeutic pharmacological target to treat these diseases.

Role of Oxidative Stress in Hepatic and Extrahepatic Dysfunctions during Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) is a pathology that contains a broad liver dysfunctions spectrum. These alterations span from noninflammatory isolated steatosis until nonalcoholic steatohepatitis (NASH), a more aggressive form of the disease characterized by steatosis, inflammatory status, and varying liver degrees fibrosis. NAFLD is the most prevalent chronic liver disease worldwide. The causes of NAFLD are diverse and include genetic and environmental factors. The presence of NASH is strongly associated with cirrhosis development and hepatocellular carcinoma, two conditions that require liver transplantation. The liver alterations during NAFLD are well described. Interestingly, this pathological condition also affects other critical tissues and organs, such as skeletal muscle and even the cardiovascular, renal, and nervous systems. Oxidative stress (OS) is a harmful state present in several chronic diseases, such as NAFLD. The purpose of this review is to describe hepatic and extrahepatic dysfunctions in NAFLD. We will also review the influence of OS on the physiopathological events that affect the critical function of the liver and peripheral tissues.

Human and Rodent Skeletal Muscles Express Angiotensin II Type 1 Receptors

Abundant evidence reveals that activation of the renin-angiotensin system promotes skeletal muscle atrophy in several conditions including congestive heart failure, chronic kidney disease, and prolonged mechanical ventilation. However, controversy exists about whether circulating angiotensin II (AngII) promotes skeletal muscle atrophy by direct or indirect effects; the centerpiece of this debate is the issue of whether skeletal muscle fibers express AngII type 1 receptors (AT1Rs). While some investigators assert that skeletal muscle expresses AT1Rs, others argue that skeletal muscle fibers do not contain AT1Rs. These discordant findings in the literature are likely the result of study design flaws and additional research using a rigorous experimental approach is required to resolve this issue. We tested the hypothesis that AT1Rs are expressed in both human and rat skeletal muscle fibers. Our premise was tested using a rigorous, multi-technique experimental design. First, we established both the location and abundance of AT1Rs on human and rat skeletal muscle fibers by means of an AngII ligand-binding assay. Second, using a new and highly selective AT1R antibody, we carried out Western blotting and determined the abundance of AT1R protein within isolated single muscle fibers from humans and rats. Finally, we confirmed the presence of AT1R mRNA in isolated single muscle fibers from rats. Our results support the hypothesis that AT1Rs are present in both human and rat skeletal muscle fibers. Moreover, our experiments provide the first evidence that AT1Rs are more abundant in fast, type II muscle fibers as compared with slow, type I fibers. Together, these discoveries provide the foundation for an improved understanding of the mechanism(s) responsible for AngII-induced skeletal muscle atrophy.

Cholic acid and deoxycholic acid induce skeletal muscle atrophy through a mechanism dependent on TGR5 receptor

Skeletal muscle atrophy is characterized by the degradation of myofibrillar proteins, such as myosin heavy chain or troponin. An increase in the expression of two muscle-specific E3 ligases, atrogin-1 and MuRF-1, and oxidative stress are involved in muscle atrophy. Patients with chronic liver diseases (CLD) develop muscle wasting. Several bile acids increase in plasma during cholestatic CLD, among them, cholic acid (CA) and deoxycholic acid (DCA). The receptor for bile acids, TGR5, is expressed in healthy skeletal muscles. TGR5 is involved in the regulation of muscle differentiation and metabolic changes. In this paper, we evaluated the participation of DCA and CA in the generation of an atrophic condition in myotubes and isolated fibers from the muscle extracted from wild-type (WT) and TGR5-deficient (TGR5^-/- ) male mice. The results show that DCA and CA induce a decrease in diameter, and myosin heavy chain (MHC) protein levels, two typical atrophic features in C₂ C₁₂ myotubes. We also observed similar results when INT-777 agonists activated the TGR5 receptor. To evaluate the participation of TGR5 in muscle atrophy induced by DCA and CA, we used a culture of muscle fiber isolated from WT and TGR5^-/- mice. Our results show that DCA and CA decrease the fiber diameter and MHC protein levels, and there is an increase in atrogin-1, MuRF-1, and oxidative stress in WT fibers. The absence of TGR5 in fibers abolished all these effects induced by DCA and CA. Thus, we demonstrated that CS and deoxycholic acid induce skeletal muscle atrophy through TGR5 receptor.

Angiotensin (1-7) Decreases Myostatin-Induced NF-κB Signaling and Skeletal Muscle Atrophy

Myostatin is a myokine that regulates muscle function and mass, producing muscle atrophy. Myostatin induces the degradation of myofibrillar proteins, such as myosin heavy chain or troponin. The main pathway that mediates protein degradation during muscle atrophy is the ubiquitin proteasome system, by increasing the expression of atrogin-1 and MuRF-1. In addition, myostatin activates the NF-κB signaling pathway. Renin–angiotensin system (RAS) also regulates muscle mass. Angiotensin (1-7) (Ang-(1-7)) has anti-atrophic properties in skeletal muscle. In this paper, we evaluated the effect of Ang-(1-7) on muscle atrophy and signaling induced by myostatin. The results show that Ang-(1-7) prevented the decrease of the myotube diameter and myofibrillar protein levels induced by myostatin. Ang-(1-7) also abolished the increase of myostatin-induced reactive oxygen species production, atrogin-1, MuRF-1, and TNF-α gene expressions and NF-κB signaling activation. Ang-(1-7) inhibited the activity mediated by myostatin through Mas receptor, as is demonstrated by the loss of all Ang-(1-7)-induced effects when the Mas receptor antagonist A779 was used. Our results show that the effects of Ang-(1-7) on the myostatin-dependent muscle atrophy and signaling are blocked by MK-2206, an inhibitor of Akt/PKB. Together, these data indicate that Ang-(1-7) inhibited muscle atrophy and signaling induced by myostatin through a mechanism dependent on Mas receptor and Akt/PKB.

The Emerging Roles of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 2 in Skeletal Muscle Redox Signaling and Metabolism

Significance: Skeletal muscle is a crucial tissue to whole-body locomotion and metabolic health. Reactive oxygen species (ROS) have emerged as intracellular messengers participating in both physiological and pathological adaptations in skeletal muscle. A complex interplay between ROS-producing enzymes and antioxidant networks exists in different subcellular compartments of mature skeletal muscle. Recent evidence suggests that nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are a major source of contraction- and insulin-stimulated oxidants production, but they may paradoxically also contribute to muscle insulin resistance and atrophy. Recent Advances: Pharmacological and molecular biological tools, including redox-sensitive probes and transgenic mouse models, have generated novel insights into compartmentalized redox signaling and suggested that NOX2 contributes to redox control of skeletal muscle metabolism. Critical Issues: Major outstanding questions in skeletal muscle include where NOX2 activation occurs under different conditions in health and disease, how NOX2 activation is regulated, how superoxide/hydrogen peroxide generated by NOX2 reaches the cytosol, what the signaling mediators are downstream of NOX2, and the role of NOX2 for different physiological and pathophysiological processes. Future Directions: Future research should utilize and expand the current redox-signaling toolbox to clarify the NOX2-dependent mechanisms in skeletal muscle and determine whether the proposed functions of NOX2 in cells and animal models are conserved into humans.

Apocynin Dietary Supplementation Delays Mouse Ovarian Ageing

Advanced maternal age is associated with higher infertility rates, pregnancy-associated complications, and progeny health issues. The ovary is considered the main responsible for these consequences due to a continuous decay in follicle number and oocyte quality. Intracellular imbalance between oxidant molecules and antioxidant mechanisms, in favour of the former, results in oxidative stress (OS) that is believed to contribute to ovarian ageing. This work is aimed at evaluating whether an age-related increase in ovarian OS, inflammation, and fibrosis may contribute to tissue dysfunction and whether specific antioxidant supplementation with a NADPH oxidase inhibitor (apocynin) could ameliorate them. Mice aged 8–12 weeks (reproductively young) or 38-42 weeks (reproductively aged) were employed. Aged mice were divided into two groups, with one receiving apocynin (5 mM) in the drinking water, for 7 weeks, upon which animals were sacrificed and their ovaries collected. Ovarian structure was similar at both ages, but the ovaries from reproductively aged mice exhibited lipofuscin deposition, enhanced fibrosis, and a significant age-related reduction in primordial and primary follicle number when compared to younger animals. Protein carbonylation and nitration, and markers of OS were significantly increased with age. Moreover, mRNA levels of inflammation markers, collagens, metalloproteinases (MMPs), and tissue inhibitor MMPs (TIMPs) were upregulated. Expression of the antifibrotic miRNA29c-3p was significantly reduced. Apocynin supplementation ameliorated most of the age-related observed changes, sometimes to values similar to those observed in young females. These findings indicate that there is an age-related increase in OS that plays an important role in enhancing inflammation and collagen deposition, contributing to a decline in female fertility. Apocynin supplementation suggests that the imbalance can be ameliorated and thus delay ovarian ageing harmful effects.

Muscle wasting: A review of exercise, classical and non-classical RAS axes

This review identifies how the classical/non‐classical renin‐angiotensin system (RAS) and exercise influence muscle wasting. The classical RAS axis enhances muscle loss through the interaction with NADPH oxidase (NOX), ubiquitin proteasome system (UPS), protein synthesis and fibrosis pathways. The mainstream hypothesis identifies reactive oxygen species (ROS) as the key pathway in muscle, this review recognizes alternative pathways that lead to an increase in muscle wasting through the classical RAS axis. In addition, pathways in which the non‐classical RAS axis and exercise inhibit the classical RAS axis are also explored. The non‐classical RAS axis and exercise have a significant negative impact on ROS production and protein synthesis. The non‐classical RAS axis has been identified in this review to directly affect protein synthesis pathways not by altering the pre‐existing intracellular ROS level, further supporting the idea that muscle wasting caused by the classical RAS system is not entirely due to ROS production. Exercise has been identified to modify the RAS axes making it a therapeutic option.

Impaired Skeletal Muscle Regeneration Induced by Macrophage Depletion Could Be Partly Ameliorated by MGF Injection

Skeletal muscle injury is one of the most common injuries in sports medicine. Our previous study found that macrophage depletion impairs muscle regeneration and that mechano growth factor (MGF) may play an important role in this process. However, whether injection of MGF protects against impaired muscle regeneration after macrophage depletion has not been explored. Therefore, we generated a muscle contusion and macrophage depletion mouse model and injected MGF into the damaged muscle. Comprehensive morphological and genetic analyses were performed on the injured skeletal muscle after macrophage depletion and MGF injection. The results showed that injection of MGF did not exert a protective effect on muscle fiber regeneration; however, it did decrease fibrosis in the contused skeletal muscle after macrophage depletion. Moreover, MGF injection decreased the expression of muscle inflammatory cytokines (TNF-α, IFN-γ, IL-1β, and TGF-β), chemokines (CCL2, CCL5, and CXCR4), oxidative stress factors (gp91phox) and matrix metalloproteinases (MMP-1, MMP-2, MMP-9, MMP-10, and MMP-14). These results suggest that the impairment of skeletal muscle regeneration induced by macrophage depletion could be partly ameliorated by MGF injection and that inflammatory cytokines, oxidative stress factors, chemokines, and MMP may be involved in this process.

Role of Transforming Growth Factor-β in Skeletal Muscle Fibrosis: A Review

Transforming growth factor-beta (TGF-β) isoforms are cytokines involved in a variety of cellular processes, including myofiber repair and regulation of connective tissue formation. Activation of the TGF-β pathway contributes to pathologic fibrosis in most organs. Here, we have focused on examining the evidence demonstrating the involvement of TGF-β in the fibrosis of skeletal muscle particularly. The TGF-β pathway plays a role in different skeletal muscle myopathies, and TGF-β signaling is highly induced in these diseases. In this review, we discuss different molecular mechanisms of TGF-β-mediated skeletal muscle fibrosis and highlight different TGF-β-targeted treatments that target these relevant pathways.

Signals from the Niche: Insights into the Role of IGF-1 and IL-6 in Modulating Skeletal Muscle Fibrosis

Muscle regeneration, characterized by the activation and proliferation of satellite cells and other precursors, is accompanied by an inflammatory response and the remodeling of the extracellular matrix (ECM), necessary to remove cellular debris and to mechanically support newly generated myofibers and activated satellite cells. Muscle repair can be considered concluded when the tissue architecture, vascularization, and innervation have been restored. Alterations in these connected mechanisms can impair muscle regeneration, leading to the replacement of functional muscle tissue with a fibrotic scar. In the present review, we will discuss the cellular mediators of fibrosis and how the altered expression and secretion of soluble mediators, such as IL-6 and IGF-1, can modulate regulatory networks involved in the altered regeneration and fibrosis during aging and diseases.

Losartan Ameliorates Calcium Oxalate-Induced Elevation of Stone-Related Proteins in Renal Tubular Cells by Inhibiting NADPH Oxidase and Oxidative Stress

Calcium oxalate (CaOx) is the most common type of urinary stone. Increase of ROS and NADPH oxidase gives rise to inflammation and injury of renal tubular cells, which promotes CaOx stone formation. Recent studies have revealed that the renin-angiotensin system might play a role in kidney crystallization and ROS production. Here, we investigated the involvement of Ang II/AT1R and losartan in CaOx stone formation. NRK-52E cells were incubated with CaOx crystals, and glyoxylic acid-induced hyperoxaluric rats were treated with losartan. Oxidative stress statuses were evaluated by detection of ROS, oxidative products (8-OHdG and MDA), and antioxidant enzymes (SOD and CAT). Expression of NADPH oxidase subunits (Nox2 and Nox4), NF-κB pathway subunits (p50 and p65), and stone-related proteins such as OPN, CD44, and MCP-1 was determined by Western blotting. The results revealed upregulation of Ang II/AT1R by CaOx treatment. CaOx-induced ROS and stone-related protein upregulation were mediated by the Ang II/AT1R signaling pathway. Losartan ameliorated renal tubular cell expression of stone-related proteins and renal crystallization by inhibiting NADPH oxidase and oxidative stress. We conclude that losartan might be a promising preventive and therapeutic candidate for hyperoxaluria nephrolithiasis.

A need for NAD+ in muscle development, homeostasis, and aging

Skeletal muscle enables posture, breathing, and locomotion. Skeletal muscle also impacts systemic processes such as metabolism, thermoregulation, and immunity. Skeletal muscle is energetically expensive and is a major consumer of glucose and fatty acids. Metabolism of fatty acids and glucose requires NAD+ function as a hydrogen/electron transfer molecule. Therefore, NAD+ plays a vital role in energy production. In addition, NAD+ also functions as a cosubstrate for post-translational modifications such as deacetylation and ADP-ribosylation. Therefore, NAD+ levels influence a myriad of cellular processes including mitochondrial biogenesis, transcription, and organization of the extracellular matrix. Clearly, NAD+ is a major player in skeletal muscle development, regeneration, aging, and disease. The vast majority of studies indicate that lower NAD+ levels are deleterious for muscle health and higher NAD+ levels augment muscle health. However, the downstream mechanisms of NAD+ function throughout different cellular compartments are not well understood. The purpose of this review is to highlight recent studies investigating NAD+ function in muscle development, homeostasis, disease, and regeneration. Emerging research areas include elucidating roles for NAD+ in muscle lysosome function and calcium mobilization, mechanisms controlling fluctuations in NAD+ levels during muscle development and regeneration, and interactions between targets of NAD+ signaling (especially mitochondria and the extracellular matrix). This knowledge should facilitate identification of more precise pharmacological and activity-based interventions to raise NAD+ levels in skeletal muscle, thereby promoting human health and function in normal and disease states.

Blockage of AKAP12 accelerates angiotensin II (Ang II)-induced cardiac injury in mice by regulating the transforming growth factor β1 (TGF-β1) pathway

Hypertension is a multifactorial chronic inflammatory disease that leads to cardiac remodeling. A-kinase anchor protein 12 (AKAP12) is a scaffolding protein that has multiple functions in various biological events, including the regulation of vessel integrity and differentiation of neural barriers in blood. However, the role of AKAP12 in angiotensin II (Ang II)-induced cardiac injury remains unclear. In the present study, Ang II infusion reduced AKAP12 expressions in the hearts of wild-type (WT) mice, and AKAP12 knockout (KO) enhanced the infiltration of inflammatory cells. In addition, AKAP12 deletion accelerated Ang II-induced cardiac histologic alterations and dysfunction. Further, AKAP12^-/- aggravated heart failure by promoting the inflammation, oxidative stress, cellular apoptosis, and autophagy induced by Ang II. Furthermore, AKAP12 KO elevated Ang II-induced cardiac fibrosis, as indicated by the following: (1) Masson trichrome staining showed that Ang II infusion markedly increased fibrotic areas of the WT mouse heart, which was greatly accelerated in AKAP12^-/- mice; (2) immunohistochemistry analysis showed increased expression of transforming growth factor β1 (TGF-β1) and α-smooth muscle actin (α-SMA) in the AKAP12^-/- mouse heart; (3) reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) analysis showed increased expression of fibrosis-related molecules in the AKAP12-deficient mouse heart; and (4) Western blot analysis indicated significantly higher upregulation of p-SMAD2/3 in the AKAP12^-/- mouse heart. In vitro, AKAP12 knockdown in HL-1 cells was responsible for TGF-β1-induced inflammation, the generation of reactive oxygen species (ROS), apoptosis, autophagy, and fibrosis. Furthermore, overexpression of AKAP12 reduced fibrosis triggered by TGF-β1 in cells. Overall, our study suggests that fibrosis induced by Ang II may be alleviated by AKAP12 expression through inactivation of the TGF-β1 pathway.

TGF-β requires the activation of canonical and non-canonical signalling pathways to induce skeletal muscle atrophy

The transforming growth factor type-beta (TGF-β) induces skeletal muscle atrophy characterised by a decrease in the fibre’s diameter and levels of myosin heavy chain (MHC), also as an increase of MuRF-1 expression. In addition, TGF-β induces muscle atrophy by a mechanism dependent on reactive oxygen species (ROS). TGF-β signals by activating both canonical Smad-dependent, and non-canonical signalling pathways such as ERK1/2, JNK1/2, and p38 MAPKs. However, the participation of canonical and non-canonical signalling pathways in the TGF-β atrophic effect on skeletal muscle is unknown. We evaluate the impact of Smad and MAPK signalling pathways on the TGF-β-induced atrophic effect in C2C12 myotubes. The results indicate that TGF-β activates Smad2/3, ERK1/2 and JNK1/2, but not p38 in myotubes. The pharmacological inhibition of Smad3, ERK1/2 and JNK1/2 activation completely abolished the atrophic effect of TGF-β. Finally, the inhibition of these canonical and non-canonical pathways did not decrease the ROS increment, while the inhibition of ROS production entirely abolished the phosphorylation of Smad3, ERK1/2 and JNK1/2. These results suggest that TGF-β requires Smad3, ERK1/2 and JNK1/2 activation to produce skeletal muscle atrophy. Moreover, the induction of ROS by TGF-β is an upstream event to canonical and non-canonical pathways.

Telmisartan improves vascular remodeling through ameliorating prooxidant and profibrotic mechanisms in hypertension via the involvement of transforming growth factor-β1

Vascular remodeling is a common complication and pathological basis of hypertension. Transforming growth factor‑β1 (TGF‑β1)/small mothers against decapentaplegic 3 (Smad3) is considered a potential therapeutic target for vascular remodeling in hypertension. The present study aimed to demonstrate the antifibrotic effects of telmisartan and examined the potential mechanisms associated with its prevention of vascular remodeling. Spontaneously hypertensive rats (SHRs) were treated with telmisartan (20 mg/kg), and vascular contractility, reactivity and oxidative stress were preliminarily evaluated. Vascular pathological alterations and collagen deposition were assessed using hematoxylin and eosin, and Masson staining, respectively. The profibrotic factors, TGF‑β1 and Smad3 were evaluated using immunofluorescence and immunohistochemistry. The protein levels of TGF‑β1/Smad3, phosphorylated (p‑)Smad3, collagen‑1 and α-smooth muscle actin in the aorta were assessed using western blot analysis. It was found that telmisartan attenuated chronic vasoconstriction and oxidative stress in the SHRs, and improved vascular reactivity. Telmisartan also restored vascular pathological alterations and decreased collagen deposition. In the vascular wall of the SHRs, telmisartan effectively decreased the protein levels of TGF‑β1/Smad3 and p‑Smad3. Taken together, these findings indicated that telmisartan, with its antioxidant effect, prevented vascular remodeling in hypertension through preventing the TGF‑β1/Smad3 signaling pathway.

Skeletal muscle wasting: new role of nonclassical renin-angiotensin system

PURPOSE OF REVIEW

Skeletal muscle can be affected by many physiological and pathological conditions that contribute to the development of muscle weakness, including skeletal muscle loss, inflammatory processes, or fibrosis. Therefore, research into therapeutic treatment alternatives or alleviation of these effects on skeletal muscle is of great importance.

RECENT FINDINGS

Recent studies have shown that angiotensin (1-7) [Ang-(1-7)] - a vasoactive peptide of the nonclassical axis in the renin-angiotensin system (RAS) - and its Mas receptor are expressed in skeletal muscle. Ang-(1-7), through its Mas receptor, prevents or diminishes deleterious effects induced by skeletal muscle disease or injury. Specifically, the Ang-(1-7)-Mas receptor axis modulates molecular mechanisms involved in muscle mass regulation, such as the ubiquitin proteasome pathway, the insulin-like growth factor type 1/Akt (protein kinase B) pathway, or myonuclear apoptosis, and also inflammation and fibrosis pathways.

SUMMARY

Although further research into this topic and the possible side effects of Ang-(1-7) is necessary, these findings are promising, and suggest that the Ang-(1-7)-Mas axis can be considered a possible therapeutic target for treating patients with muscular disorders.

Reactive Oxygen Species/Nitric Oxide Mediated Inter-Organ Communication in Skeletal Muscle Wasting Diseases

SIGNIFICANCE

Cachexia is defined as a complex metabolic syndrome that is associated with underlying illness and a loss of muscle with or without loss of fat mass. This disease is associated with a high incidence with chronic diseases such as heart failure, cancer, chronic obstructive pulmonary disease (COPD), and acquired immunodeficiency syndrome (AIDS), among others. Since there is currently no effective treatment available, cachectic patients have a poor prognosis. Elucidation of the underlying mechanisms is, therefore, an important medical task. Recent Advances: There is accumulating evidence that the diseased organs such as heart, lung, kidney, or cancer tissue secrete soluble factors, including Angiotensin II, myostatin (growth differentiation factor 8 [GDF8]), GDF11, tumor growth factor beta (TGFβ), which act on skeletal muscle. There, they induce a set of genes called atrogenes, which, among others, induce the ubiquitin-proteasome system, leading to protein degradation. Moreover, elevated reactive oxygen species (ROS) levels due to modulation of NADPH oxidases (Nox) and mitochondrial function contribute to disease progression, which is characterized by loss of muscle mass, exercise resistance, and frailty.

CRITICAL ISSUES

Although substantial progress was achieved to elucidate the pathophysiology of cachexia, effectice therapeutic strategies are urgently needed.

FUTURE DIRECTIONS

With the identification of key components of the aberrant inter-organ communication leading to cachexia, studies in mice and men to inhibit ROS formation, induction of anti-oxidative superoxide dismutases, and upregulation of muscular nitric oxide (NO) formation either by pharmacological tools or by exercise are promising approaches to reduce the extent of skeletal muscle wasting. Antioxid. Redox Signal. 26, 700-717.

Macrophage Depletion Impairs Skeletal Muscle Regeneration: the Roles of Pro-fibrotic Factors, Inflammation, and Oxidative Stress

Muscle contusion is one of the most common muscle injuries in sports medicine. Macrophages play complex roles in the regeneration of skeletal muscle. However, the roles of macrophages, especially the mechanisms involved, in the regeneration of muscle contusion are still not fully understood. We hypothesize that the depletion of macrophages impairs skeletal muscle regeneration and that pro-fibrotic factors, inflammation, and oxidative stress may be involved in the process. To test these hypotheses, we constructed a muscle contusion injury and a macrophage depletion model and followed it up with morphological and gene expression analyses. The data showed that fibrotic scars were formed in the muscle of contusion injury, and they deteriorated in the mice of macrophage depletion. Furthermore, the sizes of regenerating myofibers were significantly reduced by macrophage depletion. Pro-fibrotic factors, inflammatory cytokines, chemokines, and oxidative stress-related enzymes increased significantly after muscle injury. Moreover, the expression of these factors was delayed by macrophage depletion. Most of them were still significantly higher in the later stage of regeneration. These results suggest that macrophage depletion impairs skeletal muscle regeneration and that pro-fibrotic factors, inflammation, and oxidative stress may play important roles in the process.

Diabetes-Induced Reactive Oxygen Species: Mechanism of Their Generation and Role in Renal Injury

Diabetes induces the onset and progression of renal injury through causing hemodynamic dysregulation along with abnormal morphological and functional nephron changes. The most important event that precedes renal injury is an increase in permeability of plasma proteins such as albumin through a damaged glomerular filtration barrier resulting in excessive urinary albumin excretion (UAE). Moreover, once enhanced UAE begins, it may advance renal injury from progression of abnormal renal hemodynamics, increased glomerular basement membrane (GBM) thickness, mesangial expansion, extracellular matrix accumulation, and glomerulosclerosis to eventual end-stage renal damage. Interestingly, all these pathological changes are predominantly driven by diabetes-induced reactive oxygen species (ROS) and abnormal downstream signaling molecules. In diabetic kidney, NADPH oxidase (enzymatic) and mitochondrial electron transport chain (nonenzymatic) are the prominent sources of ROS, which are believed to cause the onset of albuminuria followed by progression to renal damage through podocyte depletion. Chronic hyperglycemia and consequent ROS production can trigger abnormal signaling pathways involving diverse signaling mediators such as transcription factors, inflammatory cytokines, chemokines, and vasoactive substances. Persistently, increased expression and activation of these signaling molecules contribute to the irreversible functional and structural changes in the kidney resulting in critically decreased glomerular filtration rate leading to eventual renal failure.

Renin-angiotensin system in ventilator-induced diaphragmatic dysfunction: Potential protective role of Angiotensin (1-7)

Ventilator-induced diaphragmatic dysfunction is a feared complication of mechanical ventilation that adversely affects the outcome of intensive care patients. Human and animal studies demonstrate atrophy and ultrastructural alteration of diaphragmatic muscular fibers attributable to increased oxidative stress, depression of the anabolic pathway regulated by Insulin-like growing factor 1 and increased proteolysis. The renin-angiotensin system, through its main peptide Angiotensin II, plays a major role in skeletal muscle diseases, mainly increasing oxidative stress and inducing insulin resistance, atrophy and fibrosis. Conversely, its counter-regulatory peptide Angiotensin (1-7) has a protective role in these processes. Recent data on rodent models show that renin-angiotensin system is activated after mechanical ventilation and that infusion of Angiotensin II induces diaphragmatic skeletal muscle atrophy. Given: (A) common pathways shared by ventilator-induced diaphragmatic dysfunction and skeletal muscle pathology induced by renin-angiotensin system, (B) evidences of an involvement of renin-angiotensin system in diaphragm atrophy and dysfunction, we hypothesize that renin-angiotensin system plays an important role in ventilator-induced diaphragmatic dysfunction, while Angiotensin (1-7) can have a protective effect on this pathological process. The activation of renin-angiotensin system in ventilator-induced diaphragmatic dysfunction can be demonstrated by quantification of its main components in the diaphragm of ventilated humans or animals. The infusion of Angiotensin (1-7) in an established rodent model of ventilator-induced diaphragmatic dysfunction can be used to test its potential protective role, that can be further confirmed with the infusion of Angiotensin (1-7) antagonists like A-779. Verifying this hypothesis can help in understanding the processes involved in ventilator-induced diaphragmatic dysfunction pathophysiology and open new possibilities for its prevention and treatment.

Transforming growth factor type beta (TGF-β) requires reactive oxygen species to induce skeletal muscle atrophy

Transforming growth factor beta 1 (TGF-β1) is a classical modulator of skeletal muscle and regulates several processes, such as myogenesis, regeneration, and muscle function in skeletal muscle diseases. Skeletal muscle atrophy, characterised by the loss of muscle strength and mass, is one of the pathological conditions regulated by TGF-β. Atrophy also results in increased myosin heavy chain (MHC) degradation and the expression of two muscle-specific E3 ubiquitin ligases, atrogin-1 and MuRF-1. Reactive oxygen species (ROS) are modulators of muscle wasting, and NAD(P)H oxidase (NOX) is one of the main sources of ROS. While it was recently found that TGF-β1 induces atrophy in skeletal muscle, the underlying mechanism is not fully understood. In this study, the role of NOX-derived ROS in skeletal muscle atrophy induced by TGF-β was assessed. TGF-β1 induced an atrophic effect in C2C12 myotubes, as evidenced by decreased myotube diameter and MHC levels, together with increased MuRF-1 levels. Concomitantly, TGF-β increased NOX-induced ROS contents. Interestingly, NOX inhibition through apocynin and the antioxidant treatment with N-acetyl cysteine (NAC) decreased increased ROS levels in myotubes. Additionally, both apocynin and NAC completely prevented the decreased MHC, decreased myotube diameter, and increased MuRF-1 induced by TGF-β. Injection of TGF-β1 into the tibialis anterior muscle induced atrophy, as observed by decreased fibre diameter and MHC levels, together with increased MuRF-1 levels. Likewise, TGF-β increased the ROS contents in the smaller fibres of skeletal muscle. Additionally, the administration of NAC to mice prevented all atrophic effects and the increase in ROS induced by TGF-β in the tibialis anterior. This is the first study to report that TGF-β has an atrophic effect dependent on NOX-induced ROS in skeletal muscle.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Apocynin inhibits the upregulation of TGF-β1 expression and ROS production induced by TGF-β in skeletal muscle cells

BACKGROUND

Pure apocynin, which can be traditionally isolated and purified from several plant species such as Picrorhiza kurroa Royle ex Benth (Scrophulariaceae), acts as an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) activity inhibiting its production of reactive oxygen species (ROS). Transforming growth factor type beta 1 (TGF-β1) is a growth factor that produces inhibition of myogenesis, diminution of regeneration and induction of atrophy in skeletal muscle. The typical signalling that is activated by TGF-β involves the Smad pathway.

PURPOSE

To evaluate the effect of TGF-β and the effect of apocynin on TGF-β1 expression in skeletal muscle cells.

STUDY DESIGN

Controlled laboratory study. In vitro assays were performed with C2C12 cells incubated with TGF-β1 in presence or absence of apocynin (NOX inhibitor), SB525334 (TGF-β-receptor I inhibitor), or chelerythrine (PKC inhibitor).

METHODS

TGF-β1 and atrogin-1 expression was evaluated by RT-qPCR and/or ELISA; Smad3 phosphorylation by western blot; Smad4 nuclear translocation by indirect immunofluorescence; and ROS levels by DCF probe fluorescent measurements.

RESULTS

We show that myoblasts respond to TGF-β1 by increasing its own gene expression in a time- and dose-dependent fashion which was abolished by SB525334 and siRNA for Smad2/3. TGF-β1 also induced ROS. Remarkably, apocynin inhibited the TGF-β1 induced ROS as well as the autoinduction of TGF-β1 gene expression. We also show that TGF-β-induced ROS production and TGF-β1 expression require PKC activity as indicated by the inhibition using chelerythrine.

CONCLUSION

These results strongly suggest that TGF-β induces its own expression through a TGF-β-receptor/Smad-dependent mechanism and apocynin is able to inhibit this process, suggesting that requires NOX-induced ROS in skeletal muscle cells.

Renin-angiotensin system: an old player with novel functions in skeletal muscle

Skeletal muscle is a tissue that shows the most plasticity in the body; it can change in response to physiological and pathological stimuli. Among the diseases that affect skeletal muscle are myopathy-associated fibrosis, insulin resistance, and muscle atrophy. A common factor in these pathologies is the participation of the renin-angiotensin system (RAS). This system can be functionally separated into the classical and nonclassical RAS axis. The main components of the classical RAS pathway are angiotensin-converting enzyme (ACE), angiotensin II (Ang-II), and Ang-II receptors (AT receptors), whereas the nonclassical axis is composed of ACE2, angiotensin 1-7 [Ang (1-7)], and the Mas receptor. Hyperactivity of the classical axis in skeletal muscle has been associated with insulin resistance, atrophy, and fibrosis. In contrast, current evidence supports the action of the nonclassical RAS as a counter-regulator axis of the classical RAS pathway in skeletal muscle. In this review, we describe the mechanisms involved in the pathological effects of the classical RAS, advances in the use of pharmacological molecules to inhibit this axis, and the beneficial effects of stimulation of the nonclassical RAS pathway on insulin resistance, atrophy, and fibrosis in skeletal muscle.

Angiotensin-(1-7) decreases skeletal muscle atrophy induced by angiotensin II through a Mas receptor-dependent mechanism

Skeletal muscle atrophy is a pathological condition characterized by the loss of strength and muscle mass, an increase in myosin heavy chain (MHC) degradation and increase in the expression of two muscle-specific ubiquitin ligases: atrogin-1 and MuRF-1. Angiotensin II (AngII) induces muscle atrophy. Angiotensin-(1-7) [Ang-(1-7)], through its receptor Mas, produces the opposite effects than AngII. We assessed the effects of Ang-(1-7) on the skeletal muscle atrophy induced by AngII. Our results show that Ang-(1-7), through Mas, prevents the effects induced by AngII in muscle gastrocnemius: the decrease in the fibre diameter, muscle strength and MHC levels and the increase in atrogin-1 and MuRF-1. Ang-(1-7) also induces AKT phosphorylation. In addition, our analysis in vitro using C2C12 myotubes shows that Ang-(1-7), through a mechanism dependent on Mas, prevents the decrease in the levels of MHC and the increase in the expression of the atrogin-1 and MuRF-1, both induced by AngII. Ang-(1-7) induces AKT phosphorylation in myotubes; additionally, we demonstrated that the inhibition of AKT with MK-2206 decreases the anti-atrophic effects of Ang-(1-7). Thus, we demonstrate for the first time that Ang-(1-7) counteracts the skeletal muscle atrophy induced by AngII through a mechanism dependent on the Mas receptor, which involves AKT activity. Our study indicates that Ang-(1-7) is novel molecule with a potential therapeutical use to improve muscle wasting associated, at least, with pathologies that present high levels of AngII.

The angiotensin-(1-7)/Mas axis reduces myonuclear apoptosis during recovery from angiotensin II-induced skeletal muscle atrophy in mice

Angiotensin-(1-7) [Ang (1-7)] is a peptide belonging to the non-classical renin-angiotensin system (RAS). Ang (1-7), through its receptor Mas, has an opposite action to angiotensin II (Ang II), the typical peptide of the classical RAS axis. Ang II produces skeletal muscle atrophy, a pathological condition characterised by the loss of strength and muscle mass. A feature of muscle atrophy is the decrease of the myofibrillar proteins produced by the activation of the ubiquitin-proteasome pathway (UPP), evidenced by the increase in the expression of two muscle-specific ubiquitin ligases: atrogin-1 and MuRF-1. In addition, it has been described that Ang II also induces myonuclear apoptosis during muscle atrophy. We assessed the effects of Ang (1-7) and Mas participation on myonuclear apoptosis during skeletal muscle atrophy induced by Ang II. Our results show that Ang (1-7), through Mas, prevents the effects induced by Ang II in the diaphragm muscles and decreases several events associated with apoptosis in the diaphragm (increased apoptotic nuclei, increased expression of caspase-8 and caspase-9, increased caspase-3 activity and increased Bax/Bcl-2 ratio). Concomitantly, Ang (1-7) also attenuates the decrease in fibre diameter and muscle strength, and prevents the increase in atrogin-1 and MuRF-1 during the muscle wasting induced by Ang II. Interestingly, these effects of Ang (1-7) are dependent on the Mas receptor. Thus, we demonstrated for the first time that Ang (1-7) prevents myonuclear apoptosis during the recovery of skeletal muscle atrophy induced by Ang II.

Cellular and molecular actions of CCN2/CTGF and its role under physiological and pathological conditions

CCN family protein 2 (CCN2), also widely known as connective tissue growth factor (CTGF), is one of the founding members of the CCN family of matricellular proteins. Extensive investigation on CCN2 over decades has revealed the novel molecular action and functional properties of this unique signalling modulator. By its interaction with multiple molecular counterparts, CCN2 yields highly diverse and context-dependent biological outcomes in a variety of microenvironments. Nowadays, CCN2 is recognized to conduct the harmonized development of relevant tissues, such as cartilage and bone, in the skeletal system, by manipulating extracellular signalling molecules involved therein by acting as a hub through a web. However, on the other hand, CCN2 occasionally plays profound roles in major human biological disorders, including fibrosis and malignancies in major organs and tissues, by modulating the actions of key molecules involved in these clinical entities. In this review, the physiological and pathological roles of this unique protein are comprehensively summarized from a molecular network-based viewpoint of CCN2 functionalities.

Oxidative stress mediates the conversion of endothelial cells into myofibroblasts via a TGF-β1 and TGF-β2-dependent pathway

During the pathogenesis of systemic inflammation, reactive oxygen species (ROS) circulate in the bloodstream and interact with endothelial cells (ECs), increasing intracellular oxidative stress. Although endothelial dysfunction is crucial in the pathogenesis of systemic inflammation, little is known about the effects of oxidative stress on endothelial dysfunction. Oxidative stress induces several functions, including cellular transformation. A singular process of cell conversion is tendothelial-to-mesenchymal transition, in which ECs become myofibroblasts, thus losing their endothelial properties and gaining fibrotic behavior. However, the participation of oxidative stress as an inductor of conversion of ECs into myofibroblasts is not known. Thus, we studied the role played by oxidative stress in this conversion and investigated the underlying mechanism. Our results show that oxidative stress induces conversion of ECs into myofibroblasts through decreasing the levels of endothelial markers and increasing those of fibrotic and ECM proteins. The underlying mechanism depends on the ALK5/Smad3/NF-κB pathway. Oxidative stress induces the expression and secretion of TGF-β1 and TGF-β2 and p38 MAPK phosphorylation. Downregulation of TGF-β1 and TGF-β2 by siRNA technology abolished the H2O2-induced conversion. To our knowledge, this is the first report showing that oxidative stress is able to induce conversion of ECs into myofibroblasts via TGF-β secretion, emerging as a source for oxidative stress-based vascular dysfunction. Thus, oxidative stress emerges as a decisive factor in inducing conversion of ECs into myofibroblasts through a TGF-β-dependent mechanism, changing the ECs protein expression profile, and converting normal ECs into pathological ones. This information will be useful in designing new and improved therapeutic strategies against oxidative stress-mediated systemic inflammatory diseases.

The Ang-(1-7)/Mas-1 axis attenuates the expression and signalling of TGF-β1 induced by AngII in mouse skeletal muscle

AngII (angiotensin II) induces pathological conditions such as fibrosis in skeletal muscle. In this process, AngII increases ROS (reactive oxygen species) and induces a biphasic phosphorylation of p38 MAPK (mitogen-activated protein kinase). In addition, AngII stimulates the expression and production of TGF (transforming growth factor)-β1 via a mechanism dependent on ROS production mediated by NADPH oxidase (NOX) and p38 MAPK activation. In the present study, we investigated whether Ang-(1-7) [angiotensin-(1-7)], through the Mas-1 receptor, can counteract the signalling induced by AngII in mouse skeletal muscle and cause a decrease in the expression and further activity of TGF-β1 in skeletal muscle cells. Our results show that Ang-(1-7) decreased the expression of TGF-β1 induced by AngII in a dose-dependent manner. In addition, we observed that Ang-(1-7) prevented the increase in TGF-β1 expression induced by AngII, ROS production dependent on NOX and the early phase of p38 MAPK phosphorylation. Interestingly, Ang-(1-7) also prevented the late phase of p38 MAPK phosphorylation, Smad-2 phosphorylation and Smad-4 nuclear translocation, an increase in transcriptional activity, as determined using the p3TP-lux reporter, and fibronectin levels, all of which are dependent on the TGF-β1 levels induced by AngII. We also demonstrated that Ang-(1-7) prevented the increase in TGF-β1, fibronectin and collagen content in the diaphragm of mice infused with AngII. All of these effects were reversed by the administration of A779, indicating the participation of Mas-1. In conclusion, our findings support the hypothesis that Ang-(1-7) decreases the expression and further biological activity of TGF-β1 induced by AngII in vitro and in vivo.

Understanding the process of fibrosis in Duchenne muscular dystrophy

Fibrosis is the aberrant deposition of extracellular matrix (ECM) components during tissue healing leading to loss of its architecture and function. Fibrotic diseases are often associated with chronic pathologies and occur in a large variety of vital organs and tissues, including skeletal muscle. In human muscle, fibrosis is most readily associated with the severe muscle wasting disorder Duchenne muscular dystrophy (DMD), caused by loss of dystrophin gene function. In DMD, skeletal muscle degenerates and is infiltrated by inflammatory cells and the functions of the muscle stem cells (satellite cells) become impeded and fibrogenic cells hyperproliferate and are overactivated, leading to the substitution of skeletal muscle with nonfunctional fibrotic tissue. Here, we review new developments in our understanding of the mechanisms leading to fibrosis in DMD and several recent advances towards reverting it, as potential treatments to attenuate disease progression.

Endotoxin induces fibrosis in vascular endothelial cells through a mechanism dependent on transient receptor protein melastatin 7 activity

The pathogenesis of systemic inflammatory diseases, including endotoxemia-derived sepsis syndrome, is characterized by endothelial dysfunction. It has been demonstrated that the endotoxin lipopolysaccharide (LPS) induces the conversion of endothelial cells (ECs) into activated fibroblasts through endothelial-to-mesenchymal transition mechanism. Fibrogenesis is highly dependent on intracellular Ca2+ concentration increases through the participation of calcium channels. However, the specific molecular identity of the calcium channel that mediates the Ca2+ influx during endotoxin-induced endothelial fibrosis is still unknown. Transient receptor potential melastatin 7 (TRPM7) is a calcium channel that is expressed in many cell types, including ECs. TRPM7 is involved in a number of crucial processes such as the conversion of fibroblasts into activated fibroblasts, or myofibroblasts, being responsible for the development of several characteristics of them. However, the role of the TRPM7 ion channel in endotoxin-induced endothelial fibrosis is unknown. Thus, our aim was to study whether the TRPM7 calcium channel participates in endotoxin-induced endothelial fibrosis. Using primary cultures of ECs, we demonstrated that TRPM7 is a crucial protein involved in endotoxin-induced endothelial fibrosis. Suppression of TRPM7 expression protected ECs from the fibrogenic process stimulated by endotoxin. Downregulation of TRPM7 prevented the endotoxin-induced endothelial markers decrease and fibrotic genes increase in ECs. In addition, TRPM7 downregulation abolished the endotoxin-induced increase in ECM proteins in ECs. Furthermore, we showed that intracellular Ca2+ levels were greatly increased upon LPS challenge in a mechanism dependent on TRPM7 expression. These results demonstrate that TRPM7 is a key protein involved in the mechanism underlying endotoxin-induced endothelial fibrosis.

Andrographolide attenuates skeletal muscle dystrophy in mdx mice and increases efficiency of cell therapy by reducing fibrosis

Background

Duchenne muscular dystrophy (DMD) is characterized by the absence of the cytoskeletal protein dystrophin, muscle wasting, increased transforming growth factor type beta (TGF-β) signaling, and fibrosis. At the present time, the only clinically validated treatments for DMD are glucocorticoids. These drugs prolong muscle strength and ambulation of patients for a short term only and have severe adverse effects. Andrographolide, a bicyclic diterpenoid lactone, has traditionally been used for the treatment of colds, fever, laryngitis, and other infections with no or minimal side effects. We determined whether andrographolide treatment of mdx mice, an animal model for DMD, affects muscle damage, physiology, fibrosis, and efficiency of cell therapy.

Methods

mdx mice were treated with andrographolide for three months and skeletal muscle histology, creatine kinase activity, and permeability of muscle fibers were evaluated. Fibrosis and TGF-β signaling were evaluated by indirect immunofluorescence and Western blot analyses. Muscle strength was determined in isolated skeletal muscles and by a running test. Efficiency of cell therapy was determined by grafting isolated skeletal muscle satellite cells onto the tibialis anterior of mdx mice.

Results

mdx mice treated with andrographolide exhibited less severe muscular dystrophy than untreated dystrophic mice. They performed better in an exercise endurance test and had improved muscle strength in isolated muscles, reduced skeletal muscle impairment, diminished fibrosis and a significant reduction in TGF-β signaling. Moreover, andrographolide treatment of mdx mice improved grafting efficiency upon intramuscular injection of dystrophin-positive satellite cells.

Conclusions

These results suggest that andrographolide could be used to improve quality of life in individuals with DMD.

Increases in reactive oxygen species enhance vascular endothelial cell migration through a mechanism dependent on the transient receptor potential melastatin 4 ion channel

A hallmark of severe inflammation is reactive oxygen species (ROS) overproduction induced by increased inflammatory mediators secretion. During systemic inflammation, inflammation mediators circulating in the bloodstream interact with endothelial cells (ECs) raising intracellular oxidative stress at the endothelial monolayer. Oxidative stress mediates several pathological functions, including an exacerbated EC migration. Because cell migration critically depends on calcium channel-mediated Ca(2+) influx, the molecular identification of the calcium channel involved in oxidative stress-modulated EC migration has been the subject of intense investigation. The transient receptor potential melastatin 4 (TRPM4) protein is a ROS-modulated non-selective cationic channel that performs several cell functions, including regulating intracellular Ca(2+) overload and Ca(2+) oscillation. This channel is expressed in multiple tissues, including ECs, and contributes to the migration of certain immune cells. However, whether the TRPM4 ion channel participates in oxidative stress-mediated EC migration is not known. Herein, we investigate whether oxidative stress initiates or enhances EC migration and study the role played by the ROS-modulated TRPM4 ion channel in oxidative stress-mediated EC migration. We demonstrate that oxidative stress enhances, but does not initiate, EC migration in a dose-dependent manner. Notably, we demonstrate that the TRPM4 ion channel is critical in promoting H2O2-enhanced EC migration. These results show that TRPM4 is a novel pharmacological target for the possible treatment of severe inflammation and other oxidative stress-mediated inflammatory diseases.

Reducing CTGF/CCN2 slows down mdx muscle dystrophy and improves cell therapy

In Duchenne muscular dystrophy (DMD) and the mdx mouse model, the absence of the cytoskeletal protein dystrophin causes defective anchoring of myofibres to the basal lamina. The resultant myofibre degeneration and necrosis lead to a progressive loss of muscle mass, increased fibrosis and ultimately fatal weakness. Connective tissue growth factor (CTGF/CCN-2) is critically involved in several chronic fibro-degenerative diseases. In DMD, the role of CTGF might extend well beyond replacement fibrosis secondary to loss of muscle fibres, since its overexpression in skeletal muscle could by itself induce a dystrophic phenotype. Using two independent approaches, we here show that mdx mice with reduced CTGF availability do indeed have less severe muscular dystrophy. Mdx mice with hemizygous CTGF deletion (mdx-Ctgf+/-), and mdx mice treated with a neutralizing anti-CTGF monoclonal antibody (FG-3019), performed better in an exercise endurance test, had better muscle strength in isolated muscles and reduced skeletal muscle impairment, apoptotic damage and fibrosis. Transforming growth factor type-β (TGF-β), pERK1/2 and p38 signalling remained unaffected during CTGF suppression. Moreover, both mdx-Ctgf+/- and FG-3019 treated mdx mice had improved grafting upon intramuscular injection of dystrophin-positive satellite cells. These findings reveal the potential of targeting CTGF to reduce disease progression and to improve cell therapy in DMD.

Defective homocysteine metabolism: potential implications for skeletal muscle malfunction

Hyperhomocysteinemia (HHcy) is a systemic medical condition and has been attributed to multi-organ pathologies. Genetic, nutritional, hormonal, age and gender differences are involved in abnormal homocysteine (Hcy) metabolism that produces HHcy. Homocysteine is an intermediate for many key processes such as cellular methylation and cellular antioxidant potential and imbalances in Hcy production and/or catabolism impacts gene expression and cell signaling including GPCR signaling. Furthermore, HHcy might damage the vagus nerve and superior cervical ganglion and affects various GPCR functions; therefore it can impair both the parasympathetic and sympathetic regulation in the blood vessels of skeletal muscle and affect long-term muscle function. Understanding cellular targets of Hcy during HHcy in different contexts and its role either as a primary risk factor or as an aggravator of certain disease conditions would provide better interventions. In this review we have provided recent Hcy mediated mechanistic insights into different diseases and presented potential implications in the context of reduced muscle function and integrity. Overall, the impact of HHcy in various skeletal muscle malfunctions is underappreciated; future studies in this area will provide deeper insights and improve our understanding of the association between HHcy and diminished physical function.

Transforming growth factor type beta 1 increases the expression of angiotensin II receptor type 2 by a SMAD- and p38 MAPK-dependent mechanism in skeletal muscle

Excessive deposition of extracellular matrix (ECM) proteins, a condition known as fibrosis, is a hallmark of Duchenne muscular dystrophy. Among the factors that trigger muscle fibrosis are transforming growth factor beta (TGF-β) and angiotensin II (Ang-II). Ang-II belongs to the renin-angiotensin system, and its biological effects are exerted by Ang-II receptors type 1 and type 2 (AT-1 and AT-2, respectively). This study aims to determine the effect of TGF-β1 on the expression of AT-1 and AT-2 receptor in skeletal muscle. C2 C12 myoblasts exposed to TGF-β1 showed a dose-dependent increase in AT-2 expression but with no effect on AT-1 levels. Injection of TGF-β1 in the skeletal muscle of mice increased the levels of AT-2 and ECM protein but unchanged AT-1 levels. We also detected higher expression levels of AT-2 receptor in dystrophic skeletal muscle of mdx mice than in normal mice. The induction of AT-2 was mediated by the canonical TGF-β pathway because under the inhibitory conditions of the kinase activity of TGFβ receptor I or the knockdown of Smad2/3 levels, TGF-β-induced AT-2 receptor increase was strongly inhibited. Furthermore, we demonstrated that p38MAPK activity in response to TGF-β is also required for AT-2 increase as evaluated by a p38MAPK inhibitor. Our results show that the levels of AT-2 but not AT-1 receptor are modulated by the pro-fibrotic factor TGF-β1 in myoblasts and mouse skeletal muscle. This finding suggests that AT-2 might be involved in the physiopathology of fibrosis in dystrophic skeletal muscle.