MiR-21 regulates skeletal muscle atrophy and fibrosis by targeting TGF-beta/SMAD7-SMAD2/3 signaling pathway

Long-term denervation-induced atrophy and fibrosis of skeletal muscle due to denervation leads to poor recovery of muscle function. Studies have shown that the transforming growth factor-β1 (TGF-β1)-Smad signaling pathway plays a central role in muscle atrophy and fibrosis. Recent studies demonstrate the role of microRNAs (miRs) in various pathological conditions, including muscle regeneration. miR-21 has been shown to play a dynamic role in inflammatory responses and in accelerating injury responses to fibrosis. We used both RNA sequencing and quantitative RT-PCR strategies to examine the alternations of miRNAs during denervation-induced gastrocnemius muscle atrophy and fibrosis. Our data showed that MiR-21 was upregulated in denervated gastrocnemius muscle tissue, and TGF-β1treatment increased miR-21 expression. Inhibition of miR-21 reduced gastrocnemius muscle fibrosis and significantly downregulated the expression of p-SMAD2/3 and the fibrosis-associated markers TGF-β1, connective tissue growth factor, alpha smooth muscle actin. Masson's trichrome staining revealed that atrophy and fibrosis in gastrocnemius muscle tissue were reduced in the miR-21 inhibition group compared to the control group. We confirmed that SMAD7 is a direct target of miR-21 using a dual luciferase assay. Furthermore, Immunofluorescence and Western blot analyses revealed that miR-21 inhibition reduced SMAD2/3 phosphorylation and nuclear translocation. While SMAD7-siRNA abolished the effect. Consequently, the discovery that miR-21 regulates the atrophy and fibrosis of the gastrocnemius muscle offers a possible therapeutic approach for their management.

Antibacterial and Anti-inflammatory Effects of Clarithromycin-Loaded Poly(l-Lactide) Membrane in Rabbit Postoperation Model of Chronic Rhinosinusitis

OBJECTIVE

Macrolide antibiotics are often used to prevent infection and inflammation after functional endoscopic sinus surgery for the treatment of chronic rhinosinusitis (CRS). The purpose of this study was to investigate the anti-inflammatory and antibacterial effects of the clarithromycin-loaded poly(-lactide) (CLA-PLLA) membrane and its mechanism.

STUDY DESIGN

Randomized controlled trial.

SETTING

Animal Experiment Center.

METHODS

We compared the difference between poly(l-lactide) (PLLA) and CLA-PLLA membranes by observing the morphology of fibrous scaffolds, measuring water contact angle, tensile strength, and drug release capacity, and evaluating the antimicrobial activity of CLA-PLLA. Twenty-four rabbits were divided into a PLLA group and a CLA-PLLA group after establishing CRS models. Another 5 normal rabbits comprised the control group. After 3 months, we placed the PLLA membrane in the nasal cavity of the PLLA group and the CLA-PLLA membrane in the CLA-PLLA group. Then, 14 days later, we evaluated the histological and ultrastructural changes in the sinus mucosa, protein, and messenger RNA (mRNA) levels of interleukin (IL)-4, IL-8, tumor necrosis factor-α, transforming growth factor-β1, α-smooth muscle actin, and type I collagen.

RESULTS

The CLA-PLLA membrane showed no significant difference in physical performance to the PLLA membrane, which continuously released 95% of the clarithromycin (CLA) for 2 months. The CLA-PLLA membrane had significant bacteriostatic properties that can improve the morphology of mucosal tissues, and inhibit protein and mRNA expression of inflammatory cytokines. In addition, CLA-PLLA also inhibited the expression of fibrosis-associated marker molecules.

CONCLUSION

The CLA-PLLA membrane released CLA slowly and continuously, providing antibacterial, anti-inflammatory, and antifibrotic effects in a rabbit model of postoperative CRS.

Expression profiles of circular RNAs and interaction networks of competing endogenous RNAs in neurogenic bladder of rats following suprasacral spinal cord injury

Background

Neurogenic bladder (NB) following suprasacral spinal cord injury (SSCI) is an interstitial disease with the structural remodeling of bladder tissue and matrix over-deposition. Circular RNAs (circRNAs) are involved in fibrotic disease development through their post-transcriptional regulatory functions. This study aimed to use transcriptome high-throughput sequencing to investigate the process of NB and bladder fibrosis after SSCI.

Methods

Spinal cord transection at the T10-T11 level was used to construct the SSCI model in rats (10-week-old female Wistar rats, weighing 200 ± 20 g). The bladders were collected without (sham group) and with (SSCI 1-3 groups) NB status. Morphological examination was conducted to assess the extent of bladder fibrosis. Additionally, RNA sequencing was utilized to determine mRNAs and circRNAs expression patterns. The dynamic changes of differentially expressed mRNAs (DEMs) and circRNAs (DECs) in different periods of SSCI were further analyzed.

Results

Bladder weight, smooth muscle cell hypertrophy, and extracellular matrix gradually increased after SSCI. Compared with the sham group, 3,255 DEMs and 1,339 DECs, 3,449 DEMs and 1,324 DECs, 884 DEMs, and 1,151 DECs were detected in the SSCI 1-3 groups, respectively. Specifically, circRNA3621, circRNA0617, circRNA0586, and circRNA4426 were significant DECs common to SSCI 1-3 groups compared with the sham group. Moreover, Gene Ontology (GO) enrichment suggested that inflammatory and chronic inflammatory responses were the key events in NB progression following SSCI. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways enrichment associated with the "Chemokine signaling pathway", the "IL-17 signaling pathway", and the "TGF-beta signaling pathway" suggests their potential involvement in regulating biological processes. The circRNA-miRNA-mRNA interaction networks of DECs revealed rno-circ-2239 (micu2) as the largest node, indicating that the rno-circ-2239-miRNA-mRNA-mediated network may play a critical role in the pathogenesis of SSCI-induced NB.

Conclusions

This study offers a comprehensive outlook on the possible roles of DEMs and DECs in bladder fibrosis and NB progression following SSCI. These findings have the potential to serve as novel biomarkers and therapeutic targets.

The Effect of Electrical Stimulation on Nerve Regeneration Following Peripheral Nerve Injury

Peripheral nerve injuries (PNI) are common and often result in lifelong disability. The peripheral nervous system has an inherent ability to regenerate following injury, yet complete functional recovery is rare. Despite advances in the diagnosis and repair of PNIs, many patients suffer from chronic pain, and sensory and motor dysfunction. One promising surgical adjunct is the application of intraoperative electrical stimulation (ES) to peripheral nerves. ES acts through second messenger cyclic AMP to augment the intrinsic molecular pathways of regeneration. Decades of animal studies have demonstrated that 20 Hz ES delivered post-surgically accelerates axonal outgrowth and end organ reinnervation. This work has been translated clinically in a series of randomized clinical trials, which suggest that ES can be used as an efficacious therapy to improve patient outcomes following PNIs. The aim of this review is to discuss the cellular physiology and the limitations of regeneration after peripheral nerve injuries. The proposed mechanisms of ES protocols and how they facilitate nerve regeneration depending on timing of administration are outlined. Finally, future directions of research that may provide new perspectives on the optimal delivery of ES following PNI are discussed.

Passive Properties of the Wrist and Fingers Following Chronic Hemiparetic Stroke: Interlimb Comparisons in Persons With and Without a Clinical Treatment History That Includes Botulinum Neurotoxin

Background: Neural impairments that follow hemiparetic stroke may negatively affect passive muscle properties, further limiting recovery. However, factors such as hypertonia, spasticity, and botulinum neurotoxin (BoNT), a common clinical intervention, confound our understanding of muscle properties in chronic stroke. Objective: To determine if muscle passive biomechanical properties are different following prolonged, stroke-induced, altered muscle activation and disuse. Methods: Torques about the metacarpophalangeal and wrist joints were measured in different joint postures in both limbs of participants with hemiparetic stroke. First, we evaluated 27 participants with no history of BoNT; hand impairments ranged from mild to severe. Subsequently, seven participants with a history of BoNT injections were evaluated. To mitigate muscle hypertonia, torques were quantified after an extensive stretching protocol and under conditions that encouraged participants to sleep. EMGs were monitored throughout data collection. Results: Among participants who never received BoNT, no significant differences in passive torques between limbs were observed. Among participants who previously received BoNT injections, passive flexion torques about their paretic wrist and finger joints were larger than their non-paretic limb (average interlimb differences = +42.0 ± 7.6SEM Ncm, +26.9 ± 3.9SEM Ncm, respectively), and the range of motion for passive finger extension was significantly smaller (average interlimb difference = -36.3° ± 4.5°SEM; degrees). Conclusion: Our results suggest that neural impairments that follow chronic, hemiparetic stroke do not lead to passive mechanical changes within the wrist and finger muscles. Rather, consistent with animal studies, the data points to potential adverse effects of BoNT on passive muscle properties post-stroke, which warrant further consideration.

Driving fibrosis in neuromuscular diseases: Role and regulation of Connective tissue growth factor (CCN2/CTGF)

Connective tissue growth factor or cellular communication network 2 (CCN2/CTGF) is a matricellular protein member of the CCN family involved in several crucial biological processes. In skeletal muscle, CCN2/CTGF abundance is elevated in human muscle biopsies and/or animal models for diverse neuromuscular pathologies, including muscular dystrophies, neurodegenerative disorders, muscle denervation, and muscle overuse. In this context, CCN2/CTGF is deeply involved in extracellular matrix (ECM) modulation, acting as a strong pro-fibrotic factor that promotes excessive ECM accumulation. Reducing CCN2/CTGF levels or biological activity in pathological conditions can decrease fibrosis, improve muscle architecture and function. In this work, we summarize information about the role of CCN2/CTGF in fibrosis associated with neuromuscular pathologies and the mechanisms and signaling pathways that regulate their expression in skeletal muscle.

Pathological features of reinnervated skeletal muscles after crush injury of the sciatic nerve in ob/ob mice

INTRODUCTION/AIMS

Obesity is a factor contributing to suboptimal improvement of motor function in peripheral nerve disorders. In this study we aimed to evaluate the skeletal muscles during denervation and reinnervation after nerve crush injury in leptin-deficient (ob/ob) mice.

METHODS

Experiments were performed on the skeletal muscles of the hindlimbs in 20 male ob/ob mice and controls. Characteristics of the gastrocnemius muscles were evaluated by histological analysis, immunohistological analysis, and Sircol-collagen assay after measurement of body weight and wet weight of the skeletal muscles, and by walking track analysis. The sciatic nerve was denervated by crushing with smooth forceps and reinnervation was evaluated.

RESULTS

Gastrocnemius wet weight was significantly lower in the ob/ob mice than in the control mice. A smaller cross-sectional area of type II fibers and increase of type I fiber grouping of the skeletal muscles was demonstrated in the ob/ob mice. After nerve injury, motor function recovery was equal between the groups but the cross-sectional area of type II fibers was significantly smaller in the ob/ob mice than in control mice at 4 weeks. The denervated muscles showed an increase in collagen deposition in the interstitial space; predominant in the ob/ob mice after nerve injury.

DISCUSSION

The results of this study suggest that fibrosis in the skeletal muscle of obese patients after nerve injury is prominent, which may impair improvement of muscle function after treatment of peripheral nerve disorders.

HDAC4 Knockdown Alleviates Denervation-Induced Muscle Atrophy by Inhibiting Myogenin-Dependent Atrogene Activation

Denervation can activate the catabolic pathway in skeletal muscle and lead to progressive skeletal muscle atrophy. At present, there is no effective treatment for muscle atrophy. Histone deacetylase 4 (HDAC4) has recently been found to be closely related to muscle atrophy, but the underlying mechanism of HDAC4 in denervation-induced muscle atrophy have not been described clearly yet. In this study, we found that the expression of HDAC4 increased significantly in denervated skeletal muscle. HDAC4 inhibition can effectively diminish denervation-induced muscle atrophy, reduce the expression of muscle specific E3 ubiquitin ligase (MuRF1 and MAFbx) and autophagy related proteins (Atg7, LC3B, PINK1 and BNIP3), inhibit the transformation of type I fibers to type II fibers, and enhance the expression of SIRT1 and PGC-1 α. Transcriptome sequencing and bioinformatics analysis was performed and suggested that HDAC4 may be involved in denervation-induced muscle atrophy by regulating the response to denervation involved in the regulation of muscle adaptation, cell division, cell cycle, apoptotic process, skeletal muscle atrophy, and cell differentiation. STRING analysis showed that HDAC4 may be involved in the process of muscle atrophy by directly regulating myogenin (MYOG), cell cycle inhibitor p21 (CDKN1A) and salt induced kinase 1 (SIK1). MYOG was significantly increased in denervated skeletal muscle, and MYOG inhibition could significantly alleviate denervation-induced muscle atrophy, accompanied by the decreased MuRF1 and MAFbx. MYOG overexpression could reduce the protective effect of HDAC4 inhibition on denervation-induced muscle atrophy, as evidenced by the decreased muscle mass and cross-sectional area of muscle fibers, and the increased mitophagy. Taken together, HDAC4 inhibition can alleviate denervation-induced muscle atrophy by reducing MYOG expression, and HDAC4 is also directly related to CDKN1A and SIK1 in skeletal muscle, which suggests that HDAC4 inhibitors may be a potential drug for the treatment of neurogenic muscle atrophy. These results not only enrich the molecular regulation mechanism of denervation-induced muscle atrophy, but also provide the experimental basis for HDAC4-MYOG axis as a new target for the prevention and treatment of muscular atrophy.

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 Role of Increased Connective Tissue Growth Factor in the Pathogenesis of Oral Submucous Fibrosis and its Malignant Transformation-An Immunohistochemical Study

Connective tissue growth factor (CTGF), a matricellular protein of the CCN family of extracellular matrix-associated heparin-binding proteins, is highly expressed in various organ fibrosis and several malignant tumors. Although a few studies have been conducted using CTGF in oral submucous fibrosis (OSF) and oral squamous cell carcinoma, no study has demonstrated its relation with various stages of OSF and its malignant transformation. The present study investigated the possible role of CTGF in the pathogenesis of OSF and its malignant transformation by using immunohistochemistry. Ten formalin-fixed paraffin-embedded tissue blocks, each of Stage 1 OSF, Stage 2 OSF, Stage 3 OSF, Stage 4 OSF, well- differentiated squamous cell carcinoma (WDSCC) with OSF and WDSCC without OSF were stained for CTGF by immunohistochemistry. Ten cases of healthy buccal mucosa (NOM) were included as controls. The present study demonstrated a statistically significant expression of CTGF in the epithelium and connective tissue of OSF and WDSCC with and without OSF cases against its complete absence in NOM. We observed an upregulation of CTGF expression from NOM to various stages of OSF to WDSCC with or without OSF. A gradual upregulation of the CTGF expression in various stages of OSF to WDSCC (with and without OSF) against its complete absence in NOM suggests that CTGF plays an important role in the pathogenesis of OSF and its malignant transformation.

Postoperative placement of an anti-fibrotic poly L-lactide electrospun fibrous membrane after sinus surgery

BACKGROUND

Endoscopic sinus surgery (ESS) is used to treat chronic rhinosinusitis. However, nasal adhesions often develop postoperatively, triggered by chronic inflammation and local fibrosis. A poly L-lactide (PLLA) electrospun microfibrous membrane is a functional biodegradable material that can be placed on the wound surface to protect the wound and prevent adhesions.

METHODS

We divided 24 rabbits randomly into 2 groups, a control operation group (group A) and an operation+PLLA placement group (group B). We investigated the anti-fibrotic effects of the topical biomaterial after sinus surgery. We placed PLLA fibrous membranes in the sinus cavity of group B rabbits after sinus surgery, and then evaluated changes in the mucosa and in the levels of collagen fibers, interleukin 4 (IL-4), IL-8, tumor necrosis factor α (TNF-α), transforming growth factor β1 (TGF-β1), α-smooth muscle actin (α-SMA), and collagen I (Col I), using morphological and molecular biological methods.

RESULTS

PLLA fibrous membranes did not inhibit the synthesis of messenger RNAs (mRNAs) encoding IL-4, IL-8, or TNF-α, or the protein levels, indicating that the membrane did not have an anti-inflammatory effect. However, the membrane inhibited the synthesis of mRNAs encoding TGF-β1, α-SMA, and Col I, and reduced collagen production. Thus, the nanostructured membrane inhibited fibroblast proliferation.

CONCLUSION

The PLLA membrane had anti-fibrotic effects, and may be used to prevent fibrosis and adhesions after ESS in human patients.

Fast repetitive stretch suppresses denervation-induced muscle fibrosis

BACKGROUND

We aimed to examine the influence of different speeds of stretching on denervation-induced skeletal muscle fibrosis.

METHODS

Stretching was passively applied to rat plantaris muscle denervated by sciatic nerve excision in three different cycles of 0.5, 3, or 12 cycles/min, for 20 min/d for 2 weeks.

RESULTS

Gene analysis results showed greater expression of fibrosis-related factors with fast stretching compared with non-stretched muscle. Laser Doppler blood flow analysis indicated reduced intramuscular blood flow during stretching. Histological analysis demonstrated fibrotic area decreases in 12 cycles/min stretched muscle compared with non-stretched muscle.

CONCLUSIONS

Slower stretching induced greater mRNA expression of collagen and fibroblasts and greater decrement of blood flow. Histologically, faster stretching suppressed fibrosis. These results suggest that fast repetitive stretching of denervated muscle might suppress processes of muscle fibrosis.

Morphological Alteration and TGF-β1 Expression in Multifidus with Lumbar Disc Herniation

BACKGROUND

Lumbar disc herniation (LDH) can cause lumbar nerve root compression, which can lead to denervated atrophy of paraspinal muscles theoretically, however, the conclusions of morphological alteration in multifidus with LDH remain controversial. Transforming growth factor-beta 1 (TGF-β1) plays an essential role in the development of tissue fibrosis and is a molecular marker in the study of muscle fibrosis, but no relevant studies on TGF-β1 expression in multifidus have been reported so far. This study is to observe altered morphology of multifidus in patients with LDH, and to explore the correlation between multifidus fibrosis and TGF-β1 expression.

MATERIALS AND METHODS

46 LDH patients with low back pain combined with unilateral leg radiation pain and/or numbness were selected. Patients were divided into four groups according to their medical histories. Group 1: medical history less than 6 months (15 cases); group 2: a medical history of 6-12 months (10 cases); group 3: a medical history of 12-24 months (13 cases); and group 4: medical history > 24 months (8 cases). Bilateral multifidus specimens were taken from compressed nerve root segments, and morphological changes in multifidus were determined. Multi-parameter changes in TGF-β1 expression in multifidus were observed by immunohistochemistry and immunofluorescence.

RESULTS

HE staining showed that the cross-sectional area (CSA) of multifidus in the involved sides decreased and muscle fibers atrophied. Masson's trichrome staining showed a decrease in the sectional area ratio of myofibers to collagen fibers in the involved side. In groups 1 and 2, there were no significant differences in the aforementioned parameters. In groups 3 and 4, statistically significant differences in the sectional area ratio of myofibers to collagen fibers in both sides were seen (P < 0.05). TGF-β1 expression was significantly enhanced in both muscle cells and the matrix of the involved side, while no expression or a little expression was found in the matrix in the uninvolved side. In group 1, there was no statistically significant difference in TGF-β1 expression in both sides. In the remaining three groups, TGF-β1 expression in the involved sides was higher than were found in the uninvolved sides.

CONCLUSIONS

Nerve root compression by LDH leads to multifidus atrophy, fibrosis, and increased TGF-β1 expression, which might promote multifidus fibrosis.Trials registration All Clinical Trials done in India should preferably be registered with the Clinical Trials Registry of India, set up by the Indian Council of Medical Research (website: http://ctri.nic.in). Authors should provide the CTRI number along with the manuscript.

Exploring the Role of SRC in Extraocular Muscle Fibrosis of the Graves' Ophthalmopathy

The Graves’ disease is an autoimmune disease highly associated with thyroid cancer. The Graves’ ophthalmopathy (GO) is a special Graves’ disease with inflammatory ophthalmopathy being a typical extrathymic complication. GO is caused by the formation of orbital fat and extraocular muscle fibrosis due to the inflammation of orbital connective tissues. Thus, controlling extraocular muscle fibrosis is critical for the prognosis of GO. The objective of this study is to identify and experimentally validate key genes associated with GO and explore their potential function mechanisms especially on extraocular muscle fibrosis. Specifically, we first created a GO mouse model, and performed RNA sequencing on the extraocular muscles of fibrotic GO mice and controls. SRC was identified as the most significant unstudied differentially expressed gene between GO mice and controls. Thus, we conducted a few in vitro analyses to explore the roles and functions of SRC in GO, for which we selected primary cultured orbital fibroblast (OF) as the in vitro cell line model. It is known that myofibroblast (MFB), which expresses α-SMA, is an important target cell in the process of fibrosis. Our experiment suggests that TGF-β can induce the transformation from OF to MFB, however, the transformation was inhibited by silencing the SRC gene in OF. In addition, we also inhibited TGF-β/Smad, NF-κB, and PI3K/Akt signaling pathways to analyze the interaction between these pathways and SRC. In conclusion, the silence of SRC in OF can inhibit the transformation from OF to MFB, which might be associated with the interaction between SRC and a few pathways such as TGF-β/Smad, NF-κB, and PI3K/Akt.

Investigation of expression and influence of CTGF and HO-1 in rats with diabetic retinopathy

The expression and influence mechanism of CTGF and HO-1 in rats with diabetic retinopathy (DR) was investigated. One hundred and thirty male Sprague-Dawley (SD) rats were selected and randomly divided into the control group and DR group, with 65 rats in each group. DR was caused by intraperitoneal injection of streptozotocin in rats in the DR group. There were 55 successful models and 10 failed in the modelling. The successful models were sacrificed at the 2nd, 4th and 6th month, respectively. RT-qPCR technology was used for detection of the expression of CTGF and HO-1 in rat retina in each group, H&E staining for observation of the gradation structure in rat retina and TUNEL method for detection of apoptosis of retinal cells. In the DR group, the retina layers were disordered and a few blood vessels dilated at the 2nd month. In the DR group, the inner membrane of the retina swelled, and the ganglion cells were irregularly arranged at the 4th month. In the DR group, dilatation of the blood vessels was more obvious, the inner membrane edema was more severe, and the arrangement was more irregular at the 6th month. The retinal apoptosis rate of DR rats gradually increased at the 2nd, 4th and 6th month, after which, the CTGF expression gradually increased, but the HO-1 expression gradually decreased in retina in the DR group. However, the mRNA expression of CTGF and HO-1 in the rats at the 2nd, 4th and 6th month in the DR group was higher than that in the control group at the same period. Therefore, CTGF and HO-1 are associated with the occurrence and development of DR in rats and can be considered as targets for the treatment of DR.

Antiapoptosis and Antifibrosis Effects of Qishen Granules on Heart Failure Rats via Hippo Pathway

Qishen granules (QSG) are a famous formula with cardioprotective properties to heart failure (HF). The aim of this study was to investigate the underlying mechanism of QSG on apoptosis and fibrosis in the treatment of HF. HF model was induced by left anterior descending artery ligation on Sprague-Dawley rats. Transcriptome analysis was used to investigate the regulatory pathways of QSG on HF. Interestingly, downregulated genes of QSG were significantly enriched in Hippo pathway which plays a crucial role in regulating cell apoptosis and proliferation. We found that QSG inhibited the expressions of proapoptotic key proteins P-53 and fibrosis-related proteins TGF-β1, SMAD3, and CTGF. Further, we conducted research on the key proteins in the Hippo pathway upstream of CTGF and P-53. The results showed that MST1, P-MST1, P-LATS1, and RASSF1A that exert proapoptotic function were downregulated after QSG intervention. Similarly, P-YAP and P-TAZ, mediating self-degradation and apoptosis, were both observably decreased after QSG administration. Taken together, QSG are shown to be likely to exert cardioprotective effects by inhibiting the progression of apoptosis and fibrosis through Hippo pathway.

Role of hypoxia in skeletal muscle fibrosis: Synergism between hypoxia and TGF-β signaling upregulates CCN2/CTGF expression specifically in muscle fibers

Several skeletal muscle diseases are characterized by fibrosis, the excessive accumulation of extracellular matrix. Transforming growth factor-β (TGF-β) and connective tissue growth factor (CCN2/CTGF) are two profibrotic factors augmented in fibrotic skeletal muscle, together with signs of reduced vasculature that implies a decrease in oxygen supply. We observed that fibrotic muscles are characterized by the presence of positive nuclei for hypoxia-inducible factor-1α (HIF-1α), a key mediator of the hypoxia response. However, it is not clear how a hypoxic environment could contribute to the fibrotic phenotype in skeletal muscle. We evaluated the role of hypoxia and TGF-β on CCN2 expression in vitro. Fibroblasts, myoblasts and differentiated myotubes were incubated with TGF-β1 under hypoxic conditions. Hypoxia and TGF-β1 induced CCN2 expression synergistically in myotubes but not in fibroblasts or undifferentiated muscle progenitors. This induction requires HIF-1α and the Smad-independent TGF-β signaling pathway. We performed in vivo experiments using pharmacological stabilization of HIF-1α or hypoxia-induced via hindlimb ischemia together with intramuscular injections of TGF-β1, and we found increased CCN2 expression. These observations suggest that hypoxic signaling together with TGF-β signaling, which are both characteristics of a fibrotic skeletal muscle environment, induce the expression of CCN2 in skeletal muscle fibers and myotubes.

The Role of Muscle Stem Cells in Regeneration and Recovery after Denervation: A Review

BACKGROUND

Skeletal muscle denervation is a complex clinical problem that still lacks a comprehensive solution. Previous studies have suggested that prolonged periods of denervation lead to a decline in the muscle stem cell population, negatively affecting the ability of muscle to regenerate following reinnervation. Recent advances in the understanding of muscle stem cell biology, along with new techniques that increase the ability to identify and manipulate these cells, provide an opportunity to definitively address the impact of muscle stem cells in recovery from denervation and their potential role in treatment.

METHODS

A comprehensive review of the literature on the biology of muscle denervation, and the effect of denervation injury on muscle stem cell behavior, was performed.

RESULTS

In this review, the authors discuss the current understanding of muscle stem cell biology in the setting of denervation atrophy, review barriers to successful reinnervation, and review options available to patients following denervation injury. The authors also discuss potential use of muscle stem cells in future therapies.

CONCLUSIONS

Although the clinical treatment of prolonged denervation injury has improved in recent years, regeneration of native muscle remains elusive. Muscle stem cells have been demonstrated to be of central importance in muscle regeneration following injury, and may be a powerful tool that provides effective new options for future treatments. Additional work clarifying the effect of denervation injury on satellite cells is needed to determine whether they are a limiting factor in recovery and to demonstrate whether their clinical use as a cell-based therapy in denervation injury can be efficacious.

CTGF/CCN2 from Skeletal Muscle to Nervous System: Impact on Neurodegenerative Diseases

Connective tissue growth factor (CTGF/CCN2) is a matricellular protein that belongs to the CCN family of proteins. Since its discovery, it has been linked to cellular processes such as cell proliferation, differentiation, adhesion, migration, and synthesis of extracellular matrix (ECM) components, among others. The pro-fibrotic role of CTGF/CCN2 has been well-studied in several pathologies characterized by the development of fibrosis. Reduction of CTGF/CCN2 levels in mdx mice, a murine model for Duchenne muscular dystrophy (DMD), decreases fibrosis and improves skeletal muscle phenotype and function. Recently, it has been shown that skeletal muscle of symptomatic hSOD1^G93A mice, a model for Amyotrophic lateral sclerosis (ALS), shows up-regulation of CTGF/CCN2 accompanied by excessive deposition ECM molecules. Elevated levels of CTGF/CCN2 in spinal cord from ALS patients have been previously reported. However, there is no evidence regarding the role of CTGF/CCN2 in neurodegenerative diseases such as ALS, in which alterations in skeletal muscle seem to be the consequence of early pathological denervation. In this regard, the emerging evidence shows that CTGF/CCN2 also exerts non-fibrotic roles in the central nervous system (CNS), specifically impairing oligodendrocyte maturation and regeneration, and inhibiting axon myelination. Despite these striking observations, there is no evidence showing the role of CTGF/CCN2 in peripheral nerves. Therefore, even though more studies are needed to elucidate its precise role, CTGF/CCN2 is starting to emerge as a novel therapeutic target for the treatment of neurodegenerative diseases where demyelination and axonal degeneration occurs.

HO‑1 alleviates cholesterol‑induced oxidative stress through activation of Nrf2/ERK and inhibition of PI3K/AKT pathways in endothelial cells

Heme oxygenase‑1 (HO‑1), as an inducible and cytoprotective enzyme, has a protective effect against cellular oxidative stress. In the present study, cholesterol was used to induce lipid overload and increase reactive oxygen species (ROS), leading to oxidative stress in EA.hy926 cells. In the present study, western blotting and immunofluorescence analysis were used to detect the expression level of important molecules in the metabolism process of cholesterol. It was confirmed that cholesterol stimulation upregulated the expression of HO‑1 in a time‑dependent manner via the activation and translocation of nuclear factor erythroid 2‑related factor 2 (Nrf2), activation of the mitogen‑activated protein kinase (MAPK)/extracellular signal‑regulated kinase (ERK) signaling pathway and increasing intercellular Ca2+ ([Ca2+]i) concentration. The results showed that increasing the expression of HO‑1 decreased activation of the phosphoinositide 3‑kinase (PI3K)/AKT signaling pathway and inhibited the expression of c‑Myc. It was confirmed that cholesterol‑mediated oxidative damage in vascular endothelial cells induced an increase in the expression of HO‑1 via the activation of Nrf2 and the MAPK/ERK signaling pathway, and increasing the [Ca2+]i concentration. The overexpression of HO‑1 alleviated oxidative damage through inhibition of the PI3K/AKT signaling pathway and downregulation of the expression of c‑Myc.

HO-1/EBP interaction alleviates cholesterol-induced hypoxia through the activation of the AKT and Nrf2/mTOR pathways and inhibition of carbohydrate metabolism in cardiomyocytes

Heme oxygenase-1 (HO-1) is an inducible and cytoprotective enzyme that provides a defense against oxidant damage. The present study screened 137 HO-1/interacting proteins using a profound co-immunoprecipitation (Co-IP) coupled with proteomics, and profiled the global HO-1 interactome network, including oxidative phosphorylation, endoplasmic reticulum and transport vesicle functions. Among these molecules, we observed that a novel interactor, emopamil-binding protein (EBP), is closely related to the cholesterol metabolism process. This study demonstrated that cholesterol promotes excessive oxidative stress and alters the energy metabolism in cardiomyocytes, further triggering numerous cardiovascular diseases. We observed that cholesterol caused the overexpression of EBP and HO-1 by the activation of AKT and Nrf2/mTOR pathways. In addition, HO-1 and EBP performed a myocardial protective function. The overexpression of HO-1 alleviated the cholesterol-induced excessive oxidative stress status by inhibition of the carbohydrate metabolism. Notably, we also confirmed that the loss of partial HO-1 activity aggravated the oxidative damage and cardiac systolic function induced by a high-fat diet in HO-1 heterozygous (HO-1^+/−) mice. These findings indicate that the HO-1/EBP interaction plays a protective role in alleviating the dysfunction of oxidative stress and cardiac systolic function induced by cholesterol stimulation.

Botulinum toxin injection causes hyper-reflexia and increased muscle stiffness of the triceps surae muscle in the rat

Botulinum toxin is used with the intention of diminishing spasticity and reducing the risk of development of contractures. Here, we investigated changes in muscle stiffness caused by reflex activity or elastic muscle properties following botulinum toxin injection in the triceps surae muscle in rats. Forty-four rats received injection of botulinum toxin in the left triceps surae muscle. Control measurements were performed on the noninjected contralateral side in all rats. Acute experiments were performed, 1, 2, 4, and 8 wk following injection. The triceps surae muscle was dissected free, and the Achilles tendon was cut and attached to a muscle puller. The resistance of the muscle to stretches of different amplitudes and velocities was systematically investigated. Reflex-mediated torque was normalized to the maximal muscle force evoked by supramaximal stimulation of the tibial nerve. Botulinum toxin injection caused severe atrophy of the triceps surae muscle at all time points. The force generated by stretch reflex activity was also strongly diminished but not to the same extent as the maximal muscle force at 2 and 4 wk, signifying a relative reflex hyperexcitability. Passive muscle stiffness was unaltered at 1 wk but increased at 2, 4, and 8 wk (P < 0.01). These data demonstrate that botulinum toxin causes a relative increase in reflex stiffness, which is likely caused by compensatory neuroplastic changes. The stiffness of elastic elements in the muscles also increased. The data are not consistent with the ideas that botulinum toxin is an efficient antispastic medication or that it may prevent development of contractures.