Regeneration Of Injured Skeletal Muscle Research Articles

Matrix metalloproteinase-9 deficiency confers resilience in fibrodysplasia ossificans progressiva in a man and mice.

Single case studies of extraordinary disease resilience may provide therapeutic insight into conditions for which no definitive treatments exist. An otherwise healthy 35-year-old man (patient-R) with the canonical pathogenic ACVR1R206H variant and the classic congenital great toe malformation of fibrodysplasia ossificans progressiva (FOP) had extreme paucity of post-natal heterotopic ossification (HO) and nearly normal mobility. We hypothesized that patient-R lacked a sufficient post-natal inflammatory trigger for HO. A plasma biomarker survey revealed a reduction in total matrix metalloproteinase-9 (MMP-9) compared to healthy controls and individuals with quiescent FOP. Whole exome sequencing identified compound heterozygous variants in MMP-9 (c.59C > T, p.A20V and c.493G > A, p.D165N). Structural analysis of the D165N variant predicted both decreased MMP-9 secretion and activity that were confirmed by enzyme-linked immunosorbent assay and gelatin zymography. Further, human proinflammatory M1-like macrophages expressing either MMP-9 variant produced significantly less Activin A, an obligate ligand for HO in FOP, compared to wildtype controls. Importantly, MMP-9 inhibition by genetic, biologic, or pharmacologic means in multiple FOP mouse models abrogated trauma-induced HO, sequestered Activin A in the extracellular matrix (ECM), and induced regeneration of injured skeletal muscle. Our data suggest that MMP-9 is a druggable node linking inflammation to HO, orchestrates an existential role in the pathogenesis of FOP, and illustrates that a single patient's clinical phenotype can reveal critical molecular mechanisms of disease that unveil novel treatment strategies.

Effects of autoimmune abnormalities on skeletal muscle regeneration after needle puncture in mice.

Regeneration of injured skeletal muscles is supported by the activation of satellite cells, and excessive traumatic injuries may trigger abnormal processes, such as fibrosis. Because the participation of immune cells is crucial during skeletal muscle repair, systemic autoimmune diseases impair their regeneration. This study focused on a traumatic injury by injection and investigated the effect of autoimmune diseases on skeletal muscle regeneration. Male mice of MRL/MpJ-Faslpr/lpr and MRL/MpJ (6-7 months old) were used for autoimmune disease and healthy groups. The abdominal walls punctured by a needle were histologically analyzed at 1, 3, and 8 days postinjection. In both groups, injured skeletal muscle tissues showed necrosis and inflammatory cell infiltrations on day 1, increased cell density at 3 days, and regenerative myotubes with central nuclei without fibrosis at 8 days. Gr-1+ neutrophils at injured skeletal muscle were abundant at 1 day, and then substantially decreased starting from 3 days in both groups. The number of CD3+ T cells was remarkably higher in MRL/MpJ-Faslpr/lpr than that in MRL/MpJ at 1 day, and a similar tendency was observed in B220+ B cells. The numbers of IBA1+ macrophages and bromodeoxyuridine-incorporating cells tended to be higher at 3 days, and those of the latter, mainly proliferating paired-box-7+ satellite cells, showed significance at other time points and negatively correlated with the autoimmune disease indices, such as spleen weights or serum autoantibody level. Thus, this result suggested that injured skeletal muscle by minor trauma is normally regenerated regardless of the effects of autoimmune diseases, although lymphocyte infiltrations during these processes were more severe in MRL/MpJ-Faslpr/lpr.

Myoblast-derived exosomes promote the repair and regeneration of injured skeletal muscle in mice.

When skeletal muscle is damaged, satellite cells (SCs) are activated to proliferate rapidly and fuse with the damaged muscle fibers to form new muscle fibers, thereby promoting muscle growth and remodeling and repair of trauma. Exosomes from differentiating human skeletal muscle cells trigger myogenesis of stem cells and provide biochemical cues for skeletal muscle regeneration. Therefore, we hypothesized that, when muscles are injured, myoblast-derived exosomes may regulate muscle repair and regeneration. Here, we investigated the underlying mechanism by applying C2C12-derived exosomes to injured mouse skeletal muscles. The expression levels of skeletal muscle regeneration factors paired box 7 and lipid-promoting factor peroxisome proliferator-activated receptor γ were upregulated, whereas the expression levels of fibrosis factors collagen-1 and α-smooth muscle actin decreased. The expression of proliferating cell nuclear antigen was elevated after applying C2C12-derived exosomes to SCs. Application of C2C12-derived exosomes to fibro-adipogenic progenitors resulted in an increase in peroxisome proliferator-activated receptor γ expression and adipogenesis capacity, whereas α-smooth muscle actin expression and fibrosis capacity decreased. Analysis of the transcriptome and proteome of SCs after treatment with exosomes showed the involvement of multiple biological processes, including proliferation and differentiation of SCs, muscle regeneration, skeletal muscle atrophy, and the inflammatory response after muscle injury. Hence, our data suggest that C2C12-derived exosomes can promote the regeneration of skeletal muscle fibers, accelerate the production of fat from damaged muscles, inhibit the fibrosis of damaged muscles, and accelerate injury repair, which is related to exosome-mediated regulation of the proliferation of SCs, differentiation of fibro-adipogenic progenitors, and modulation of SC mRNA expression and protein formation and decomposition.

Effects Of Acute Exercise And Acupuncture Treatment On Collagen Of Skeletal Muscle Extracellular Matrix

PURPOSE: Skeletal muscle ultrastructure and content changes of different collagen types in the rat skeletal muscle extracellular matrix after acute eccentric exercise was measured to elucidate the effects of acupuncture on exercise-induced skeletal muscle damage and remodeling of the skeletal muscle extracellular matrix. METHODS: Eight-week-old Sprague-Dawley rats (n = 96, body wt 220 ± 6.9 g) were randomly assigned to four groups: sedentary control (C), acupuncture control (CA), exercise (E) and acupunctured exercise (EA). Animals were adapted to the environment for 3 days and made to run on a motor-driven treadmill with −16° downhill tracks at a speed of 16 m/min for 90 min. CA and EA rats underwent intervention after exercise. Tissues were collected from the vastus intermedius muscle of the experimental rats immediately, and at 24 hours, 48 hours, 72 hours, and 120 hours after exercise. A transmission electron microscope was used to observe the skeletal muscle ultrastructure, a scanning electron microscope was used to analyze the morphological changes of collagen fibers, and western blotting were used to detect gene and protein expression of type I, II, and IV collagen. All animal experiments were approved by the Animal Welfare and Ethics Committee of Zhengzhou University. RESULTS: Acute eccentric exercise increased collagen fiber expression, whereas acupuncture inhibited it. Scanning electron microscope results revealed that collagen hyperplasia was increased in the skeletal muscle of E rats but not EA rats 120 hours post exercise. mRNA levels of type I and III collagen of E rats were upregulated to a maximal level 24 hours after exercise compared with immediately killed rats (Type I: 3.865 ± 1.181 to 11.651 ± 3.526, p = 0.28; Type III: 1.032 ± 0.270 to 2.657 ± 0.883, p = 0.17). The mRNA levels of type I and III collagen in EA rats significantly increased 48 hours after exercise compared with immediately killed rats (Type I: 1.024 ± 0.359 to 4.537 ± 1.621, p = 0.56; Type III: 0.680 ± 0.251 to 2.334 ± 0.945, p = 0.32). CONCLUSION: Acute eccentric exercise may stimulate increase collagen levels in rat skeletal muscle. Acupuncture altered collagen expression to facilitate the recovery and regeneration of injured skeletal muscle.

Effects Of Acute Exercise And Acupuncture Treatment On Regulation MMPs/TIMPs Balance Of Skeletal Muscle

PURPOSE: This study investigated MMPs/TIMPs balance in the rat skeletal muscle extracellular matrix after acute eccentric exercise to elucidate the effects of acupuncture on exercise-induced skeletal muscle damage and remodeling of the skeletal muscle extracellular matrix. METHODS: Eight-week-old Sprague-Dawley rats (n = 96, body wt 220 ± 6.9 g) were randomly assigned to four groups: sedentary control (C), acupuncture control (CA), exercise (E) and acupunctured exercise (EA). Animals were made to run on a motor-driven treadmill with −16° downhill tracks at a speed of 16 m/min for 90 minutes. Tissues were collected from the vastus intermedius muscle immediately, and at 24 hours, 48 hours, 72 hours and 120 hours after exercise. Western blotting was used to detect protein expression of matrix metalloproteinases-2 (MMP2), MMP9, tissue inhibitor of metalloproteinases-1 (TIMP1) and TIMP2. All animal experiments were approved by the Animal Welfare and Ethics Committee of Zhengzhou University. RESULTS: The protein expression of MMP2 (EA: 1.330 ± 0.065, E: 1.341 ± 0.120, C: 1.000 ± 0.060) reached the maximal level 24 hours and MMP9 of EA rats (EA: 3.776 ± 1.253, C: 1.000 ± 0.357, P < 0.05) and E rats (E: 5.828 ± 2.151, C: 1.000 ± 0.357, P = 0.016) reached the maximal level at 48 hours and 24 hours respectively. The protein expression of TIMP1 of EA rats (EA: 2.938 ± 0.437, C: 1.000 ± 0.251, P = 0.032) and E rats (E: 1.984 ± 0.077, C: 1.000 ± 0.251, p = 0.059) reached the maximal level at 72 hours and 48 hours respectively. The protein expression of TIMP2 of EA rats (EA: 1.477 ± 0.199, C: 1.000 ± 0.063, p = 0.067) and E rats (E: 1.371 ± 0.081, C: 1.000 ± 0.063, p = 0.074) reached the maximal level immediately after exercise. CONCLUSION: Acupuncture facilitated the recovery and regeneration of injured skeletal muscle by increasing the expression of MM2 and MMP9. TIMP1 and TIMP2 played different roles in inflammation of injured skeletal muscle.

Programmed death-1 promotes contused skeletal muscle regeneration by regulating Treg cells and macrophages

Immune cells are involved in skeletal muscle regeneration. The mechanism by which Treg cells are involved in the regeneration of injured skeletal muscle is still unclear. The purpose of this study was to explore the role of programmed death-1 in contused skeletal muscle regeneration, and to clarify the regulation of programmed death-1 on Treg cell generation and macrophage polarization, in order to deepen our understanding of the relationship between the immune system and injured skeletal muscle regeneration. The results show that programmed death-1 knockdown reduced the number of Treg cells and impaired contused skeletal muscle regeneration compared with those of wild-type mice. The number of pro-inflammatory macrophages in the contused skeletal muscle of programmed death-1 knockout mice increased, and the expression of pro-inflammatory factors and oxidative stress factors increased, while the number of anti-inflammatory macrophages and the expression of anti-inflammatory factors, antioxidant stress factors, and muscle regeneration-related factors decreased. These results suggest that programmed death-1 can promote contused skeletal muscle regeneration by regulating Treg cell generation and macrophage polarization.

Contribution of Extracellular Vesicles in Rebuilding Injured Muscles

Skeletal myofibers are injured due to mechanical stresses experienced during physical activity, or due to myofiber fragility caused by genetic diseases. The injured myofiber needs to be repaired or regenerated to restore the loss in muscle tissue function. Myofiber repair and regeneration requires coordinated action of various intercellular signaling factors—including proteins, inflammatory cytokines, miRNAs, and membrane lipids. It is increasingly being recognized release and transmission of these signaling factors involves extracellular vesicle (EV) released by myofibers and other cells in the injured muscle. Intercellular signaling by these EVs alters the phenotype of their target cells either by directly delivering the functional proteins and lipids or by modifying longer-term gene expression. These changes in the target cells activate downstream pathways involved in tissue homeostasis and repair. The EVs are heterogeneous with regards to their size, composition, cargo, location, as well as time-course of genesis and release. These differences impact on the subsequent repair and regeneration of injured skeletal muscles. This review focuses on how intracellular vesicle production, cargo packaging, and secretion by injured muscle, modulates specific reparative, and regenerative processes. Insights into the formation of these vesicles and their signaling properties offer new understandings of the orchestrated response necessary for optimal muscle repair and regeneration.

MENS-associated increase of muscular protein content via modulation of caveolin-3 and TRIM72.

Microcurrent electrical neuromuscular stimulation (MENS) is known as an extracellular stimulus for the regeneration of injured skeletal muscle in sports medicine. However, the effects of MENS-associated increase in muscle protein content are not fully clarified. The purpose of this study was to investigate the effects of MENS on the muscular protein content, intracellular signals, and the expression level of caveolin-3 (Cav-3), tripartite motif-containing 72 (TRIM72) and MM isoenzyme of creatine kinase (CK-MM) in skeletal muscle using cell culture system. C2C12 myotubes on the 7th day of differentiation phase were treated with MENS (intensity: 10-20 microA, frequency: 0.3 Hz, pulse width: 250 ms, stimulation time: 15-120 min). MENS-associated increase in the protein content of myotubes was observed, compared to the untreated control level. MENS upregulated the expression of Cav-3, TRIM72, and CK-MM in myotubes. A transient increase in phosphorylation level of Akt was also observed. However, MENS had no effect on the phosphorylation level of p42/44 extracellular signal-regulated kinase-1/2 and 5'AMP-activated protein kinase. MENS may increase muscle protein content accompanied with a transient activation of Akt and the upregulation of Cav-3 and TRIM72.

Regeneration of injured skeletal muscle after the injury

Muscle injuries are one of the most common traumas occurring in sports. Despite their clinical importance, few clinical studies exist on the treatment of these traumas. Thus, the current treatment recommendations for muscle injuries have either been derived from experimental studies or been tested only empirically. Although non operative treatment should almost always be the 1(st) choice as it results in good functional outcomes in the majority of athletes with muscle injuries, the consequences of failed treatment can be very dramatic, possibly postponing an athlete's return to sports for weeks or even months. Moreover, the recognition of some basic principles of skeletal muscle regeneration and healing processes can considerably help in both avoiding the imminent dangers and accelerating the return to competition. Accordingly, in this review, the authors have summarized the prevailing understanding on the biology of muscle regeneration in hopes of extending these findings to clinical practice in an attempt to propose an evidence-based approach for the diagnosis and optimal treatment of skeletal muscle injuries.

Lack of Heme Oxygenase-1 Induces Inflammatory Reaction and Proliferation of Muscle Satellite Cells after Cardiotoxin-Induced Skeletal Muscle Injury

Heme oxygenase-1 (HO-1, Hmox1) regulates viability, proliferation, and differentiation of many cell types; hence, it may affect regeneration of injured skeletal muscle. Here, we injected cardiotoxin into gastrocnemius muscle of Hmox1+/+ and Hmox1-/- animals and analyzed cellular response after muscle injury, focusing on muscle satellite cells (SCs), inflammatory reaction, fibrosis, and formation of new blood vessels. HO-1 is strongly induced after muscle injury, being expressed mostly in the infiltrating leukocytes (CD45+ cells), including macrophages (F4/80+ cells). Lack of HO-1 augments skeletal muscle injury, evidenced by increased creatinine kinase and lactate dehydrogenase, as well as expression of monocyte chemoattractant protein-1, IL-6, IL-1β, and insulin-like growth factor-1. This, together with disturbed proportion of M1/M2 macrophages, accompanied by enhanced formation of arterioles, may be responsible for shift of Hmox1-/- myofiber size distribution toward larger one. Importantly, HO-1-deficient SCs are prone to activation and have higher proliferation on injury. This effect can be partially mimicked by stimulation of Hmox1+/+ SCs with monocyte chemoattractant protein-1, IL-6, IL-1β, and is associated with increased MyoD expression, suggesting that Hmox1-/- SCs are shifted toward more differentiated myogenic population. However, multiple rounds of degeneration/regeneration in conditions of HO-1 deficiency may lead to exhaustion of SC pool, and the number of SCs is decreased in old Hmox1-/- mice. In summary, HO-1 modulates muscle repair mechanisms preventing its uncontrolled acceleration.

Reduction in skeletal muscle fibrosis of spontaneously hypertensive rats after laceration by microRNA targeting angiotensin II receptor.

Regeneration of injured skeletal muscles is affected by fibrosis, which can be improved by the administration of angiotensin II (AngII) receptor (ATR) blockers in normotensive animals. However, the role of ATR in skeletal muscle fibrosis in hypertensive organisms has not been investigated yet. The tibialis anterior (TA) muscle of spontaneously hypertensive (SHR) and Wistar rats (WR) were lacerated and a lentivector encoding a microRNA targeting AngII receptor type 1 (At1) (Lv-mirAT1a) or control (Lv-mirCTL) was injected. The TA muscles were collected after 30 days to evaluate fibrosis by histology and gene expression by real-time quantitative PCR (RT-qPCR) and Western blot. SHR’s myoblasts were analyzed by RT-qPCR, 48 h after transduction. In the SHR’s TA, AT1 protein expression was 23.5-fold higher than in WR without injury, but no difference was observed in the angiotensin II receptor type 2 (AT2) protein expression. TA laceration followed by suture (LS) produced fibrosis in the SHR (23.3±8.5%) and WR (7.9±1.5%). Lv-mirAT1 treatment decreased At1 gene expression in 50% and reduced fibrosis to 7% 30 days after. RT-qPCR showed that reduction in At1 expression is due to downregulation of the At1a but not of the At1b. RT-qPCR of myoblasts from SHR transduced with Lv-mirAT1a showed downregulation of the Tgf-b1, Tgf-b2, Smad3, Col1a1, and Col3a1 genes by mirAT1a. In vivo and in vitro studies indicate that hypertension overproduces skeletal muscle fibrosis, and AngII-AT1a signaling is the main pathway of fibrosis in SHR. Moreover, muscle fibrosis can be treated specifically by in loco injection of Lv-mirAT1a without affecting other organs.

Levels of S100B protein drive the reparative process in acute muscle injury and muscular dystrophy

Regeneration of injured skeletal muscles relies on a tightly controlled chain of cellular and molecular events. We show that appropriate levels of S100B protein are required for timely muscle regeneration after acute injury. S100B released from damaged myofibers and infiltrating macrophages expands the myoblast population, attracts macrophages and promotes their polarization into M2 (pro-regenerative) phenotype, and modulates collagen deposition, by interacting with RAGE (receptor for advanced glycation end-products) or FGFR1 (fibroblast growth factor receptor 1) depending on the muscle repair phase and local conditions. However, persistence of high S100B levels compromises the regeneration process prolonging myoblast proliferation and macrophage infiltration, delaying M1/M2 macrophage transition, and promoting deposition of fibrotic tissue via RAGE engagement. Interestingly, S100B is released in high abundance from degenerating muscles of mdx mice, an animal model of Duchenne muscular dystrophy (DMD), and blocking S100B ameliorates histopathology. Thus, levels of S100B differentially affect skeletal muscle repair upon acute injury and in the context of muscular dystrophy, and S100B might be regarded as a potential molecular target in DMD.

Human myogenic reserve cells are quiescent stem cells that contribute to muscle regeneration after intramuscular transplantation in immunodeficient mice

Satellite cells, localized within muscles in vivo, are Pax7+ muscle stem cells supporting skeletal muscle growth and regeneration. Unfortunately, their amplification in vitro, required for their therapeutic use, is associated with reduced regenerative potential. In the present study, we investigated if human myogenic reserve cells (MRC) obtained in vitro, represented a reliable cell source for muscle repair. For this purpose, primary human myoblasts were freshly isolated and expanded. After 2 days of differentiation, 62 ± 2.9% of the nuclei were localized in myotubes and 38 ± 2.9% in the mononucleated non-fusing MRC. Eighty percent of freshly isolated human MRC expressed a phenotype similar to human quiescent satellite cells (CD56+/Pax7+/MyoD−/Ki67− cells). Fourteen days and 21 days after cell transplantation in immunodeficient mice, live human cells were significantly more numerous and the percentage of Pax7+/human lamin A/C+ cells was 2 fold higher in muscles of animals injected with MRC compared to those injected with human myoblasts, despite that percentage of spectrin+ and lamin A/C+ human fibers in both groups MRC were similar. Taken together, these data provide evidence that MRC generated in vitro represent a promising source of cells for improving regeneration of injured skeletal muscles.

Emerging roles of ER stress and unfolded protein response pathways in skeletal muscle health and disease

Skeletal muscle is the most abundant tissue in the human body and can adapt its mass as a consequence of physical activity, metabolism, growth factors, and disease conditions. Skeletal muscle contains an extensive network of endoplasmic reticulum (ER), called sarcoplasmic reticulum, which plays an important role in the regulation of proteostasis and calcium homeostasis. In many cell types, environmental and genetic factors that disrupt ER function cause an accumulation of misfolded and unfolded proteins in the ER lumen that ultimately leads to ER stress. To alleviate the stress and restore homeostasis, the ER activates a signaling network called the unfolded protein response (UPR). The UPR has three arms, which regulate protein synthesis and expression of many ER chaperone and regulatory proteins. However, the role of individual UPR pathways in skeletal muscle has just begun to be investigated. Recent studies suggest that UPR pathways play pivotal roles in muscle stem cell homeostasis, myogenic differentiation, and regeneration of injured skeletal muscle. Moreover, markers of ER stress and the UPR are activated in skeletal muscle in diverse conditions such as exercise, denervation, starvation, high fat diet, cancer cachexia, and aging. Accumulating evidence also suggests that ER stress may have important roles in the pathogenesis of inflammatory myopathies and genetic muscle disorders. The purpose of this review article is to discuss the role and potential mechanisms by which ER stress and the individual arms of the UPR regulate skeletal muscle formation, plasticity, and function in various physiological and pathophysiological conditions.

Macrophage depletion impairs skeletal muscle regeneration: The roles of regulatory factors for muscle regeneration.

Though macrophages are essential for skeletal muscle regeneration, which is a complex process, the roles and mechanisms of the macrophages in the process of muscle regeneration are still not fully understood. The objective of this study is to explore the roles of macrophages and the mechanisms involved in the regeneration of injured skeletal muscle. One hundred and twelve C57BL/6 mice were randomly divided into muscle contusion and macrophages depleted groups. Their gastrocnemius muscles were harvested at the time points of 12 h, 1, 3, 5, 7, 14 d post-injury. The changes in skeletal muscle morphology were assessed by hematoxylin and eosin (HE) stain. The gene expression was analyzed by real-time polymerase chain reaction. The data showed that CL-liposomes treatment did affect the expression of myogenic regulatory factors (MyoD, myogenin) after injury. In addition, CL-liposomes treatment decreased the expression of regulatory factors of muscle regeneration (HGF, uPA, COX-2, IGF-1, MGF, FGF6) and increased the expression of inflammatory cytokines (TGF-β1, TNF-α, IL-1β, RANTES) in the late stage of regeneration. Moreover, there were significant correlations between macrophages and some regulatory factors (such as HGF, uPA) for muscle regeneration. These results suggested that macrophages depletion impairs skeletal muscle regeneration and that the regulatory factors for muscle regeneration may play important roles in this process.

Suppression of Myostatin Stimulates Regenerative Potential of Injured Antigravitational Soleus Muscle in Mice under Unloading Condition.

Effects of myostatin (MSTN)-suppression on the regeneration of injured skeletal muscle under unloading condition were investigated by using transgenic mice expressing a dominant-negative form of MSTN (MSTN-DN). Both MSTN-DN and wild-type (WT) mice were subjected to continuous hindlimb suspension (HS) for 6 weeks. Cardiotoxin (CTX) was injected into left soleus muscle under anesthesia 2 weeks after the initiation of HS. Then, the soleus muscles were excised following 6-week HS (4 weeks after CTX-injection). CTX-injection caused to reduce the soleus fiber cross-sectional area (CSA) in WT mice under both unloading and weight-bearing conditions, but not in MSTN-DN mice. Under unloading condition, CTX-injected muscle weight and fiber CSA in MSTN-DN mice were significantly higher than those in WT mice. CTX-injected muscle had many damaged and regenerating fibers having central nuclei in both WT and MSTN-DN mice. Significant increase in the population of Pax7-positive nuclei in CTX-injected muscle was observed in MSTN-DN mice, but not in WT mice. Evidences indicate that the suppression of MSTN cause to increase the regenerative potential of injured soleus muscle via the increase in the population of muscle satellite cells regardless of unloading conditions.

Minimally Invasive Approach to the Repair of Injured Skeletal Muscle With a Shape-memory Scaffold

Repair of injured skeletal muscle by cell therapies has been limited by poor survival of injected cells. Use of a carrier scaffold delivering cells locally, may enhance in vivo cell survival, and promote skeletal muscle regeneration. Biomaterial scaffolds are often implanted into muscle tissue through invasive surgeries, which can result in trauma that delays healing. Minimally invasive approaches to scaffold implantation are thought to minimize these adverse effects. This hypothesis was addressed in the context of a severe mouse skeletal muscle injury model. A degradable, shape-memory alginate scaffold that was highly porous and compressible was delivered by minimally invasive surgical techniques to injured tibialis anterior muscle. The scaffold controlled was quickly rehydrated in situ with autologous myoblasts and growth factors (either insulin-like growth factor-1 (IGF-1) alone or IGF-1 with vascular endothelial growth factor (VEGF)). The implanted scaffolds delivering myoblasts and IGF-1 significantly reduced scar formation, enhanced cell engraftment, and improved muscle contractile function. The addition of VEGF to the scaffold further improved functional recovery likely through increased angiogenesis. Thus, the delivery of myoblasts and dual local release of VEGF and IGF-1 from degradable scaffolds implanted through a minimally invasive procedure effectively promoted the functional regeneration of injured skeletal muscle.

Regeneration of injured skeletal muscle in heat shock transcription factor 1-null mice

The purpose of this study was to investigate a role of heat shock transcription factor 1 (HSF1)-mediated stress response during regeneration of injured soleus muscle by using HSF1-null mice. Cardiotoxin (CTX) was injected into the left muscle of male HSF1-null and wild-type mice under anesthesia with intraperitoneal injection of pentobarbital sodium. Injection of physiological saline was also performed into the right muscle. Soleus muscles were dissected bilaterally 2 and 4 weeks after the injection. The relative weight and fiber cross-sectional area in CTX-injected muscles of HSF1-null, not of wild-type, mice were less than controls with injection of physiological saline 4 weeks after the injury, indicating a slower regeneration. Injury-related increase of Pax7-positive muscle satellite cells in HSF1-null mice was inhibited versus wild-type mice. HSF1-deficiency generally caused decreases in the basal expression levels of heat shock proteins (HSPs). But the mRNA expression levels of HSP25 and HSP90α in HSF1-null mice were enhanced in response to CTX-injection, compared with wild-type mice. Significant up-regulations of proinflammatory cytokines, such as interleukin (IL) -6, IL-1β, and tumor necrosis factor mRNAs, with greater magnitude than in wild-type mice were observed in HSF1-deficient mouse muscle. HSF1 and/or HSF1-mediated stress response may play a key role in the regenerating process of injured skeletal muscle. HSF1 deficiency may depress the regenerating process of injured skeletal muscle via the partial depression of increase in Pax7-positive satellite cells. HSF1-deficiency-associated partial depression of skeletal muscle regeneration might also be attributed to up-regulation of proinflammatory cytokines.

Regeneration of injured soleus muscle in heat shock transcription factor 1‐null mice

Heat shock transcription factor 1 (HSF1) mediates stress response, and up‐regulates heat shock proteins (HSPs) in mammalian skeletal muscles. The purpose of this study was to investigate the effects of HSF1‐deficiency on the regeneration of inured skeletal muscle. Cardiotoxin was injected into the left soleus muscle of mice. Soleus muscles were dissected bilaterally 2 and 4 weeks after the treatment. HSF1‐deffiency retarded both the recovery of muscle protein content and fiber size, which were decreased by cardiotoxin injection. Injury‐related‐up‐regulation of HSPs in HSF1‐null mice was depressed, compared with wild type mice. HSF1‐associated stress response may play a key role in the regeneration of injured skeletal muscle. This study was supported, in part, by KAKENHI (22240071, 24650411, 24650407) from Japan Society for the Promotion of Science and the Science Research Promotion and the Promotion and Mutual Aid Corporation for Private Schools of Japan.

Treatment of skeletal muscle injury: a review.

Skeletal muscle injuries are the most common sports-related injuries and present a challenge in primary care and sports medicine. Most types of muscle injuries would follow three stages: the acute inflammatory and degenerative phase, the repair phase and the remodeling phase. Present conservative treatment includes RICE (rest, ice, compression, elevation), nonsteroidal anti-inflammatory drugs (NSAIDs) and physical therapy. However, if use improper, NSAIDs may suppress an essential inflammatory phase in the healing of injured skeletal muscle. Furthermore, it remains controversial whether or not they have adverse effects on the healing process or on the tensile strength. However, several growth factors might promote the regeneration of injured skeletal muscle, many novel treatments have involved on enhancing complete functional recovery. Exogenous growth factors have been shown to regulate satellite cell proliferation, differentiation and fusion in myotubes in vivo and in vitro, TGF-β1 antagonists behave as inhibitors of TGF-β1. They prevent collagen deposition and block formation of muscle fibrosis, so that a complete functional recovery can be achieved.