Induced Muscle Injury Research Articles

Satellite cells deficiency and defective regeneration in dynamin 2‐related centronuclear myopathy

Dynamin 2 (DNM2) is a ubiquitously expressed protein involved in many functions related to trafficking and remodeling of membranes and cytoskeleton dynamics. Mutations in the DNM2 gene cause the autosomal dominant centronuclear myopathy (AD-CNM), characterized mainly by muscle weakness and central nuclei. Several defects have been identified in the KI-Dnm2R465W/+ mouse model of the disease to explain the muscle phenotype, including reduction of the satellite cell pool in muscle, but the functional consequences of this depletion have not been characterized until now. Satellite cells (SC) are the main source for muscle growth and regeneration of mature tissue. Here, we investigated muscle regeneration in the KI-Dnm2R465W/+ mouse model for AD-CNM. We found a reduced number of Pax7-positive SCs, which were also less activated after induced muscle injury. The muscles of the KI-Dnm2R465W/+ mouse regenerated more slowly and less efficiently than wild-type ones, formed fewer new myofibers, and did not recover its normal mass 15days after injury. Altogether, our data provide evidence that the muscle regeneration is impaired in the KI-Dnm2R465W/+ mouse and contribute with one more layer to the comprehension of the disease, by identifying a new pathomechanism linked to DNM2 mutations which may be involved in the muscle-specific impact occurring in AD-CNM.

Sensory and Psychological Factors Predict Exercise-Induced Shoulder Injury Responses in a High-Risk Phenotype Cohort

Our prior studies identified a high-risk phenotype (ie, high pain sensitivity variant of the catechol-O-methyltransferase gene (Single Nucleotide Polymorphism [SNP] rs6269) and pain catastrophizing scores) for shoulder pain. The current study identified sensory and psychological predictors of heightened pain responses following exercise-induced shoulder injury. Healthy participants (N = 131) with the SNP rs6269 catechol-O-methyltransferase gene and Pain Catastrophizing Scale scores ≥5 underwent baseline sensory and psychological testing followed by an established shoulder fatigue protocol, to induce muscle injury. Movement-evoked pain, pain intensity, disability, and strength were assessed 24 hours postinjury. Demographic, sensory, and psychological variables were included as predictors in full and parsimonious models for each outcome. The highest variance explained was for the shoulder disability outcome (full model R2 = .20, parsimonious R2 = .13). In parsimonious models, the individual predictors identified were: 1) 1st pulse heat pain sensitivity for isometric shoulder movement-evoked pain and pain intensity; 2) pressure pain threshold for shoulder disability; 3) fear of pain for active shoulder movement-evoked pain and shoulder disability; and 4) depressive symptoms for shoulder strength. Findings indicate specific pain sensitivity and psychological measures may have additional prognostic value for self-reported disability within a high-risk phenotype. These findings should be tested in a clinical cohort for validation. PerspectiveThe current study extends previous work by providing insight regarding how poor shoulder outcomes may develop within a high-risk phenotype. Specifically, 1st pulse heat pain sensitivity and pressure pain threshold were sensory measures, and fear of pain and depressive symptoms were psychological measures, that improved prediction of different shoulder outcomes.

Estrogen modulates the skeletal muscle regeneration process and myotube morphogenesis: morphological analysis in mice with a low estrogen status.

The purpose of this study was to elucidate the functions of estrogen and two estrogen receptors (ERs; ERα and ERβ) in the myoregeneration process and morphogenesis. Cardiotoxin (CTX) was injected into the tibialis anterior (TA) muscles of ovariectomized (OVX) mice to induce muscle injury, and subsequent myoregeneration was morphologically assessed. The diameter of regenerated myotubes in OVX mice was significantly smaller than that in intact mice at all time points of measurement. OVX mice also showed lower muscle recovery rates and slower speeds than did intact mice. ER protein levels showed a predominance of ERβ over ERα in both intact and OVX states. The ERβ level was increased significantly at 7 days after CTX injection in OVX mice and remained at a high level until 14 days. In addition, continuous administration of E2 to OVX mice in which muscle injury was induced resulted in a significantly larger diameter of regenerated myotubes than that in mice that did not receive estrogen. The results indicate that estrogen is an essential factor in the myoregeneration process since estrogen depletion delayed myoregeneration in injured muscles and administration of estrogen under the condition of a low estrogen status rescued delayed myoregeneration. The results strongly suggested that ERβ may be a factor that promotes myoregeneration more than does ERα.

HIF-1α Directly Controls WNT7A Expression During Myogenesis.

Herein we unveil that Hypoxia-inducible factor-1α (HIF-1α) directly regulates WNT7A expression during myogenesis. In fact, chromatin immunoprecipitation (ChiP) and site-directed mutagenesis experiments revealed two distinct hypoxia response elements (HREs) that are specific HIF-1α binding sites on the WNT7A promoter. Remarkably, a pharmacological activation of HIF-1α induced WNT7A expression and enhanced muscle differentiation. On the other hand, silencing of WNT7A using CRISPR/Cas9 genome editing blocked the effects of HIF-1α activation on myogenesis. Finally, treatment with prolyl hydroxylases (PHDs) inhibitors improved muscle regeneration in vitro and in vivo in a cardiotoxin (CTX)-induced muscle injury mouse model, paving the way for further studies to test its efficacy on acute and chronic muscular pathologies.

The effect of curcumin supplementation on recovery following exercise-induced muscle damage and delayed-onset muscle soreness: A systematic review and meta-analysis of randomized controlled trials.

curcumin consumption may have a protective effect against exercise-induced muscle damage (EIMD) through stabilization of the cell membrane via inhibition of free radical formation. Evidence supporting a protective role of curcumin after physical activity induced muscle injury in humans, however, it is inconsistent. Medline, Scopus, and Google scholar were systematically searched up to May 2020. The Cochrane Collaboration tool for assessing the risk of bias was used for assessing the quality of studies. Random effects model, weighted mean difference (WMD), and 95% confidence interval (CI) were used for estimating the overall effect. Between-study heterogeneity was assessed using the chi-squared and I2 statistic. The results revealed a significant effect of curcumin supplementation on reducing creatine kinase (CK) (weighted mean difference [WMD] = -48.54 IU.L-1 ; 95% CI: -80.667, -16.420; p = .003) and muscle soreness index decrease (WMD = -0.476; 95% CI: -0.750, -0.202; p = .001). Moreover, a subgroup analysis resulted in a significant decrease in CK concentrations and muscle soreness index, according to follow-ups after exercise, dose of curcumin, duration of studies, exercise type, train status and study design. The current evidence revealed a efficacy of curcumin in reducing CK serum levels and muscle soreness index among adults. Therefore, curcumin may be known as a priority EIMD recovery agent in interventions.

Myofiber Permeability and Force Production of Rat Muscles Following Eccentric Contractions: The Repeated Bout Effect Depends on the Interval

Past eccentric contraction (ECC)-induced muscle injury reduces the severity of symptoms of subsequent muscle injury; this phenomenon is known as a repeated bout effect (RBE). It has been reported that increases in the duration of the interval between the first and second bouts are linked to weakening of the RBE. However, the histology following the attenuation of the RBE remains unclear. We examined the sustained effects of the second bout with regard to myofiber permeability and muscle force. Sixty-four male rats were randomly assigned to eight groups that varied in the number of exercise sessions and the duration of the interval between the first and second bouts: the non-ECC (Control); the single-injury (Post 1st bout); groups that were allowed to recover for 1, 2, and 4 weeks after a single injury (Pre 2nd bout_1w, Pre 2nd bout_2w, and Pre 2nd bout_4w); and groups that were subjected to second injuries 1, 2, and 4 weeks after the first (Post 2nd bout_1w, Post 2nd bout_2w, and Post 2nd bout_4w). The tibialis anterior was electrically stimulated in each ECC group. Twenty-four hours before muscle sampling, Evans blue dye (EBD) (a marker of myofiber damage) was administered. The maximal isometric contraction tension was measured immediately before sampling. The number of EBD-positive (+) fibers was determined via histological analysis. An RBE was revealed by functional examination at the 1- and 2-week and histological examination at the 1-, 2-, and 4-week time points (P < 0.05). In terms of myofiber permeability, prolongation of the interval before the second bout weakened this effect (P < 0.05). Experiments with 1-, 2-, and 4-week intervals indicated that prolongation of the interval before the second bout weakened the RBE with regard to myofiber permeability.

Protective Effects of Resveratrol Supplementation on Contusion Induced Muscle Injury.

Muscle injuries frequently occur in contact sports events. The current treatment options for soft tissue injuries remain suboptimal and often result in delayed or incomplete recovery of damaged muscles. Resveratrol (RES) is a phenolic phytochemical, well-known for its antioxidant and anti-inflammatory properties. The purpose of this study is to evaluate the potential beneficial effects of RES supplementation on inflammation and regeneration in skeletal muscle after a contusion injury, in comparison to a conventional treatment of nonsteroidal anti-inflammatory drugs (NSAID). After one week of acclimation, forty eight -week-old male ICR mice were randomly divided into the five groups (n=8 per group): 1) normal control (NC), 2) mass-drop injury without any treatment (mass-drop injury, MDI), 3) post-injury NSAID treatment (MDI+ 10mg/kg NSAID), 4) post-injury RES supplementation (MDI+ 25mg/kg/day RES) and 5) post-injury treatment with RES and NSAID (MDI + resveratrol+ NSAID). After muscle contusion injury of the left gastrocnemius muscle, RES or NSAID were orally administered post-injury once a day for 7 days. Results showed that the MDI group had significantly higher serum uric acid (UA), CREA (creatinine), LDH (lactic dehydrogenase) and creatine kinase (CK) than the normal control group. Treatment with resveratrol reduced muscle damage as evidenced by the significantly decreased serum levels of UA, CREA, LDH and CK after contusion-induced muscle injuries in mice. In addition, RES and RES + NSAID groups promoted muscle satellite cell regeneration with increase in desmin protein after injury. Our results suggest that resveratrol combined with NSAID potentially improve muscle recovery and may be a potential candidate for further development as an effective clinical treatment for muscle repair.

The Possible Protective Role of Sesame Oil on Skeletal Muscle Regeneration in Induced Red-Bull Injury: Experimental Study

Background: Energy drinks (Eds), including Red Bull, were introduced to United States markets in 1997. Consumption hasincreased worldwide mainly consumed by athletes and teenagers as they are seeking for increase their energy level. Seasme oil(SO) has been known to have anti-inflammatory and antioxidant properties.Aim: The current study was designed to elucidate study the possible protective role of SO on skeletal muscle regeneration inRed Bull experimentally induced injury.Materials and Methods: Twenty adult albino rats were divided into four groups, control, sham control, RB and RB+SO.Skeletal muscle sections were subjected to histological, morphometric, biochemical and statistical studies.Results: RB induced various histological changes in skeletal muscle in the form of congestion, atypical fibre, multiple fibroblastand dark nuclei. RB also caused a sig increase in area % collagen, area % of caspase3 immunoexpression (IE), count of alphasmooth muscle actin IE(no I SMA) and count of +ve CD34 IE were recorded. Sig increase in the activity of interleukin-6(IL-6)and PI3K and AKT proteins. Concomitant administration with SO improved sig the previously mentioned changes.Conclusion: It can be concluded that SO enhanced skeletal muscle regeneration in RB induced muscle injury expressed as adefinite ameliorating effect to the induced inflammatory and degenerative changes.

I.8Reversible formation of TDP-43 assemblies during skeletal muscle regeneration

Skeletal muscle maintenance and repair is dependent on the resident adult muscle stem cell. Following an injury and in diseased muscle, stem cells are engaged to replace or repair damaged tissue, which requires that the stem cells exit quiescence, expand, fuse and rebuild the contractile apparatus. Severe, progressive neuromuscular diseases manifest a constant injury, possibly disrupting the timing of regeneration, and coupled with attempts to continuously regenerate, may contribute to loss of muscle tissue and function. Proteostasis is disrupted in muscle during neuromuscular disease progression and often accompanied by the accumulation of irreversible protein aggregates in the cytoplasm, which are considered cytotoxic. Tar DNA binding Protein 43 (TDP-43), is a common component of these cytotoxic cytoplasmic cellular aggregates, even though TDP-43 is often not mutated. Unexpectedly, we observed cytoplasmic TDP-43 in amyloid assemblies or myo-granules during muscle regeneration following an induced muscle injury in normal mice. Myo-granules appear following an induced injury and dissipate during muscle regeneration. In regenerating muscle, TDP-43 is associated with transcripts encoding sarcomeric structural proteins as well as vasolin containing protein. We propose that cytoplasmic TDP-43-containing assemblies are not cytotoxic but are required for muscle formation, providing protection, transport and localized translation for TDP-43-associated transcripts. The relationship of cytoplasmic TDP-43-containing aggregates in diseased skeletal muscle to myo-granules in normal muscle is not known, however, myo-granules can seed the formation of insoluble amyloid fibrils. Thus, the formation of insoluble cytoplasmic aggregates occurring in progressive neuromuscular diseases may arise from altered myo-granule composition or from aberrant formation or clearance of myo-granules during continuous regeneration occurring in diseased muscle. Determining the relationship between cytotoxic TDP-43-containing cytoplasmic aggregates and myo-granules is essential to better understand disease progression and for the development of new therapies aimed at eliminating or preventing the accumulation of insoluble cytoplasmic aggregates arising during the progression of neuromuscular diseases.

R3hdml regulates satellite cell proliferation and differentiation.

In this study, we identified a previously uncharacterized skeletal satellite cell-secreted protein, R3h domain containing-like (R3hdml). Expression of R3hdml increases during skeletal muscle development and differentiation in mice. Body weight and skeletal muscle mass of R3hdml knockout (KO) mice are lower compared to control mice. Expression levels of cell cycle-related markers, phosphorylation of Akt, and expression of insulin-like growth factor within the skeletal muscle are reduced in R3hdml KO mice compared to control mice. Expression of R3hdml increases during muscle regeneration in response to cardiotoxin (CTX)-induced muscle injury. Recovery of handgrip strength after CTX injection was significantly impaired in R3hdml KO mice, which is rescued by R3hdml. Our results indicate that R3hdml is required for skeletal muscle development, regeneration, and, in particular, satellite cell proliferation and differentiation.

Muscle injury promotes heterotopic ossification by stimulating local bone morphogenetic protein-7 production

BackgroundHeterotopic ossification (HO) is a pathological condition of abnormal bone formation in soft tissue, which causes pain and restricted range of motion in patients. There are two broad categories of HO, hereditary and acquired. Although different types of HO do not use identical mechanistic pathways of pathogenesis, muscle injury appears to be a unifying feature for all types of HO. However, little is known about the mechanisms by which muscle injury facilitates HO formation. Objective and methodThis study aimed to explore the cellular and molecular mechanisms linking muscle injury to HO by using cardiotoxin to induce muscle injury in a bone morphogenetic protein-2 (BMP-2)–induced HO mouse model. ResultsWe found that muscle injury augmented HO formation and that this effect was correlated with BMP signalling activation and upregulation of BMP-7 expression at the early phase of HO progression. We further demonstrated that inhibition of BMP-7 activity in vitro suppressed the osteogenesis-promoting effect of conditioned medium derived from injured muscle tissue and in vivo reduced the volume of HO formation. We also showed that antiinflammatory drug treatment reduced the volume of HO with concomitant reduction in BMP-7 production. ConclusionIn summary, our study has identified BMP-7 as a key osteoinductive factor in injured muscle that facilitates HO formation. The translational potential of this articleOur results provide a candidate mechanistic rationale for the use of antiinflammatory drugs in the prevention of HO.

Systemic and Local Phenotypes of Barium Chloride Induced Skeletal Muscle Injury in Mice.

Skeletal muscle regeneration in mice has traditionally been studied using local freeze burn or snake venom injection models. More recently, a barium chloride (BaCl2)-induced muscle injury model has been established and is gaining popularity due to the relatively simple procedure and accessibility to required reagents. Here we sought to characterize the local and systemic effects of BaCl2-induced muscle injury. For this study, a 1.2% BaCl2 solution was locally administered to the tibialis anterior (TA) muscle and local and systemic phenotypes were analyzed at different timepoints. When 50 μL of the solution was injected unilaterally in the TA muscle, no mortality was observed. However, when 100 μL of the solution was injected, 50% of the mice died within 24 h. Serum analysis of the mice injected with 50 μL of BaCl2 solution at days 1 and 7 revealed changes resembling rhabdomyolysis. At day 1 post-injection of 50 μL of the BaCl2 solution, acute suppurative inflammation was observed in gross examination of the TA muscle, while extensive hemorrhagic necrosis was revealed on histological examination. At day 7, regenerated myofibers with centralized nuclei appeared with the resolution of acute inflammatory infiltration and the muscle tissue displayed molecular signatures consistent with myofiber differentiation. The overall muscle injury and regeneration phenotypes in the BaCl2-induced muscle injury model were similar to those of the well-established freeze burn or snake venom injection models. Taken together, the BaCl2-induced muscle injury model is comparable to conventional muscle injury and regeneration models, with considerations for possible systemic effects.

Negative Impact of Icing Treatment on Qualitative Recovery of Injured Soleus Muscle in Rats

PURPOSE: Although the RICE (Rest, Ice, Compression, and Elevation) treatment has been recognized as the gold standard of first aid treatment for sports injuries, we and the others previously demonstrated that a transient icing treatment immediately after skeletal muscle injury impaired muscle regeneration. However, the information about the influence of icing treatment following skeletal muscle injury remains limited. This study was, therefore, to investigate the impact of icing as a first-aid treatment on qualitative recovery of damaged muscle in terms of fibrosis and myosin heavy chain (MyHC) profile. METHODS: Male Wistar rats (9-10 weeks of age) were randomly assigned to control (Con), injured, and injured with icing groups (Ice). Bupivacaine (BPVC) was injected into slow soleus muscles bilaterally in order to induce muscle injury in the two injury groups. Application of icing treatment (ice pack, 0°C for 20 min) to the icing group was carried out immediately after the BPVC injection. At 3 days-4 weeks after BPVC injection, soleus muscles were removed and analyzed. RESULTS: Compared with the Con group, a significant increase in fibrotic area was observed after 2 weeks following injury in the injured groups, but after 1 week following injury in the Ice group (P < 0.05). This area was also tended to be higher in Ice than in injured animals during 1-4 weeks of recovery period. In addition, the number of Tcf4-positive nuclei, a fibroblast marker, located in interstitial spaces in both injured groups markedly increased 1 week after BPVC injection. The numbers were tended to be more magnified in the Ice group than in the injured group, then their number in both injured groups gradually degreased thereafter. Injury-related de novo appearance of embryonic, neonatal, IId/x, and IIb MyHC isoforms was noted in both injured groups 1 week after BPVC injection. These MyHC isoforms were significantly decreased toward the undetectable level thereafter. However, the embryonic MyHC isoform was still detectable in icing, but not in injured, animals 4 weeks after BPVC injection. CONCLUSIONS: Our results suggested that icing treatment following skeletal muscle injury will have a negative impact on recovery process (fibrosis and normalization of MyHC profile) of regenerating muscle.

The Onset of Exercise‐induced Microvascular Hyperpermeability is Delayed in Diabetic Skeletal Muscle: In Vivo Imaging Using Two‐Photon Laser Scanning Microscopy

To investigate whether Type I diabetes (DIA) alters the temporal characteristics of muscle microvascular function and fiber damage incurred by eccentric contraction (ECC)‐induced muscle injury, male Wistar rats (n=53, 10–14 wks old) were randomly assigned to control (CON) or Streptozocin (45 mg/kg, i.p. DIA) groups. Four weeks later (blood glucose, 354±46 mg/dL), the tibialis anterior (TA) muscle of 1 leg was injured by 200 times ECC. Microvascular permeability was assessed by in vivo imaging using two‐photon laser scanning microscopy on 1, 3, 7 and 14 days post‐ECC. The TA microcirculation was visualized after intravenous infusion of fluorescent dye; extravasation of which was quantified to assess microvascular permeability. CON and ECC TA muscles were dissected and frozen after in vivo imaging, and serial cryosections were co‐stained with vascular endothelial growth factor A (VEGFA) antibody and hematoxylin‐eosin. Compared with CON rats, non‐ECC TA microvascular permeability was slightly but significantly enhanced in DIA with higher expression of VEGFA in myocytes. In CON rats, compared with non‐ECC TA, injured myocytes and microvascular hyper‐permeability were observed simultaneously on 1 and 3 days (injured myocyte 48, 73%, extravasation 262, 266 μm3×106xmin, 1, 3 days post‐ECC, respectively) and were repaired by 7 days after ECC (no injured myocytes, regenerated myocyte 29%, extravasation 101 μm3×106xmin). DIA TA exhibited delayed muscle injury onset and microvascular hyper‐permeability from 1 to between 3 and 7 days (injured 8, 81, 35%, extravasation 33, 183, 180 μm3×106xmin, 1, 3, 7 days post‐ECC, respectively). Regenerated myocyte was observed between 7 and 14 days post‐ECC (regenerated 47, 23%, 7, 14 days, respectively, extravasation 105 μm3×106xmin, 14 days post‐ECC). Regenerated cell size was smaller in DIA compared to CON (3214 vs. 1377 μm2, CON vs. DIA 14 days post‐ECC, P&lt;0.01). Percentage of VEGFA‐positive myocytes to injured myocytes was increased in both CON (28%, 43%, 1 and 3 days post‐ECC, respectively) and DIA (44%, 43%, 65%, 1, 3, 7 days post‐ECC) rats with a temporal profile corresponding to that of increased dye extravasation. These results suggest that DIA retards the onset of microvascular hyper‐permeability after ECC thereby delaying skeletal muscle injury and recovery. VEGF may regulate microvascular permeability in both CON and DIA skeletal muscle and therefore play a commanding role in post‐ECC damage and regeneration.Support or Funding InformationThis work was supported by Japan Society for the Promotion of Science KAKENHI Grants JP17K13185, 16700450, 18700526, and 23650403.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Concomitant Muscle Injury Does Not Worsen Traumatic Brain Injury Outcomes in Mice.

Traumatic brain injury (TBI) often involves multitrauma in which concurrent extracranial injury occurs. We previously demonstrated that a long bone fracture exacerbates neuroinflammation and functional outcomes in mice given a TBI. Whether other forms of concomitant peripheral trauma that are common in the TBI setting, such as skeletal muscle injury, have similar effects is unknown. As such, here we developed a novel mouse multitrauma model by combining a closed-skull TBI with a cardiotoxin (CTX)-induced muscle injury to investigate whether muscle injury affects TBI outcomes. Adult male mice were assigned to four groups: sham-TBI + sham-muscle injury (SHAM); sham-TBI + CTX-muscle injury (CTX); TBI + sham-muscle injury (TBI); TBI + CTX-muscle injury (MULTI). Some mice were euthanized at 24 h post-injury to assess neuroinflammation and cerebral edema. The remaining mice underwent behavioral testing after a 30-day recovery period, and were euthanized at 35 days post-injury for post-mortem analysis. At 24 h post-injury, both TBI and MULTI mice had elevated edema, increased expression of GFAP (i.e., a marker for reactive astrocytes), and increased mRNA levels of inflammatory chemokines. There was also an effect of injury on cytokine levels at 35 days post-injury. However, the TBI and MULTI mice did not significantly differ on any of the measures assessed. These initial findings suggest that a concomitant muscle injury does not significantly affect preclinical TBI outcomes. Future studies should investigate the combination of different injury models, additional outcomes, and other post-injury time points.

Effects of hindlimb suspension and reloading on gastrocnemius and soleus muscle mass and function in geriatric mice

Reloading of atrophied muscles after hindlimb suspension (HLS) can induce muscle injury and prolong recovery after disuse in old rats, especially in fast contracting muscles. Less is known about the responses in mice and whether fast and slow muscles from geriatric mice will respond in a similar fashion to HLS unloading and recovery (HLS + R). Furthermore, while slow muscles undergo atrophy with disuse, they typically are more resistant to sarcopenia than fast contracting muscles. Geriatric (28 mo. of age) male C57BL/6 mice were randomly placed into 3 groups. These included HLS for 14 days n = 9, and HLS followed by 14 days of reloading recovery (HLS + R; n = 9), or normal ambulatory cage controls (n = 9). Control mice were not exposed to unloading. Electrically evoked maximal muscle function was assessed in vivo in anesthetized mice at baseline, after 14 days of HLS or HLS + R. As expected, HLS significantly reduced body weight, wet weight of gastrocnemius and soleus muscles and in vivo maximal force. There were no differences in vivo fatigability of the plantar flexor muscles and overall fiber size. There were only minor fiber type distribution and frequency distribution of fiber sizes that differ between HLS + R and control gastrocnemius and soleus muscles. Soleus muscle wet weight had recovered to control levels after reloading, but type I/IIA fibers in the soleus muscles were significantly smaller after HLS + R than control muscles. In contrast, gastrocnemius muscle wet weight did not recover to control levels after reloading. Plantar flexion muscle force (primarily influenced by the gastrocnemius muscles) did not recover in HLS + R conditions as compared to HLS conditions and both were lower than control force production signaling for apoptosis, autophagy and anabolic markers were not different between control and HLS + R gastrocnemius and soleus muscles in geriatric mice. These results suggest that molecular signaling does not explain attenuated ability to regain muscle wet weight, fiber size or muscle force production after HLS in geriatric mice. It is possible that fluid shifts, reduced blood flow, or shortened muscle fibers which failed to regain control lengths contributed to the attenuation of muscle wet weight after HLS and reloading and this affected force production. Further work is needed to determine if altered/loss of neural activity contributed to the inability of geriatric mice to regain gastrocnemius muscle weight and function after HLS and reloading.

Simvastatin Impairs the Inflammatory and Repair Phases of the Postinjury Skeletal Muscle Regeneration.

Background Recent clinical data have suggested that the chronic use of high-lipophilic statins impairs the regenerative capacity of skeletal muscle. Because this activity of statins is poorly understood, we aimed to investigate the effect of simvastatin (SIM) on postinjury myofibre regeneration. Methods The porcine model was used in this study. The animals were divided into two groups: nontreated (control; n=24) and SIM-treated (40 mg/day; n=24). On the 15th day (day 0) of the experiment, a bupivacaine hydrochloride- (BPVC-) induced muscle injury was established, and the animals were sacrificed in the following days after muscle injury. The degree of regeneration was assessed based on histopathological and immunohistochemical examinations. The presence and degree of extravasation, necrosis, and inflammation in the inflammatory phase were assessed, whereas the repair phase was evaluated based on the numbers of muscle precursor cells (MPCs), myotube and young myofibres. Results In the inflammatory phase, SIM increased the distribution and prolonged the period of extravasation, prolonged the duration of necrosis, and prolonged and enhanced the infiltration of inflammatory cells. In the repair phase, SIM delayed and prolonged the activity of MPCs, delayed myotube formation, and delayed and decreased the formation of young myofibres. Our results indicated that SIM did not improve blood vessel stabilization at the site of the injury, did not exert an anti-inflammatory effect, prolonged and enhanced the inflammatory response, and impaired MPC activity, differentiation, and fusion. Moreover, SIM appeared to reduce M1 macrophage activity, resulting in slower removal of necrotic debris and sustained necrosis. Conclusion This study shows that SIM negatively affects the inflammatory and repair phases of the postinjury muscle regeneration. These findings are unique, strengthen the available knowledge on the side effects of SIM, and provide evidence showing that statin therapy is associated with an increased risk of impairment of the regenerative capacity of muscle.

Long-term selection of chickens for body weight alters muscle satellite cell behaviors

Muscle satellite cells (SC) are resident stem-like cells that play an integral role in skeletal muscle growth and repair. Understanding how SC maintain their identities and dynamic properties is critical to animal growth. However, the genetic and environmental factors governing SC behaviors and the underpinning mechanisms remain unknown. To explore whether genetic selection influences SC behaviors, we used 2 lines of chickens selected for over 50 generations with over a 10-fold difference in body weight at 56 d of age-the Virginia high weight selection (HWS) and low weight selection (LWS) lines. To study these 2 lines, we performed both in vivo and in vitro experiments. In vivo, we studied the abundance of SC in normal physiological settings and tested their functional roles in muscle regeneration using a muscle injury model. In vitro, we isolated SC from chicken skeletal muscle and assayed their ability to proliferate and differentiate under cultured conditions. Immunohistochemical staining of breast muscle (pectoralis major) revealed that muscle fibers from HWS chickens possessed more SC than those from LWS. Further analysis showed that the SC pool from HWS muscles contained a higher percentage of activated SC compared to that of LWS. When isolated SC from HWS and LWS muscles were cultured, HWS SC exhibited greater abilities to proliferate and differentiate than those SC from LWS. To test whether the observed in vitro differences in SC properties could be confirmed in vivo, we subjected chicken breast muscle to barium chloride to induce muscle injury and regeneration. Consistent with in vitro data, breast muscle in HWS chicken experienced a faster and more robust recovery than that of LWS, as evidenced by quicker regeneration and larger muscle fiber size. Taken together, these findings suggest divergent selection for body weight not only results in correlated responses in SC number, but also changes SC growth kinetics. Further dissection of the molecular mechanism will aid the identification of the target molecules for growth intervention in chickens.

Aligned Nanofibrillar Scaffolds for Controlled Delivery of Modified mRNA.

RNA-based vector delivery is a promising gene therapy approach. Recent advances in chemical modification of mRNA structure to form modified mRNA (mmRNA or cmRNA or modRNA) have substantially improved their stability and translational efficiency within cells. However, mmRNA conventionally delivered in solution can be taken up nonspecifically or become cleared away prematurely, which markedly limits the potential benefit of mmRNA therapy. To address this limitation, we developed mmRNA-incorporated nanofibrillar scaffolds that could target spatially localized delivery and temporally controlled release of the mmRNA both in vitro and in vivo. To establish the efficacy of mmRNA therapy, mmRNA encoding reporter proteins such as green fluorescence protein or firefly luciferase (Fluc) was loaded into aligned nanofibrillar collagen scaffolds. The mmRNA was released from mmRNA-loaded scaffolds in a transient and temporally controlled manner and induced transfection of human fibroblasts in a dose-dependent manner. In vitro transfection was further verified using mmRNA encoding the angiogenic growth factor, hepatocyte growth factor (HGF). Finally, scaffold-based delivery of HGF mmRNA to the site of surgically induced muscle injury in mice resulted in significantly higher vascular regeneration after 14 days, compared to implantation of Fluc mmRNA-releasing scaffolds. After transfection with Fluc mmRNA-releasing scaffold in vivo, Fluc activity was detectable and localized to the muscle region, based on noninvasive bioluminescence imaging. Scaffold-based local mmRNA delivery as an off-the-shelf form of gene therapy has broad translatability for treating a wide range of diseases or injuries.

Glycerol-induced injury as a new model of muscle regeneration.

Skeletal muscle regenerates efficiently following injuries and diseases. However, muscle regeneration is compromised in several conditions by adipocyte infiltration and excessive collagen deposition. Adipocyte infiltration is a characteristic feature of sarcopenia, diabetes, cachexia, muscular dystrophies and advanced cases of Duchenne muscular dystrophy (DMD), while excessive collagen deposition is a hallmark of muscular dystrophies and severe muscle injuries, such as lacerations, contusions and strains. Muscle adipogenesis and fibrosis are major causes of muscle weakness that impairs muscle function. Therefore, it is essential to develop an appropriate injury model to understand the mechanisms of adipocyte formation and fibrosis during muscle regeneration. This will help to advance our knowledge regarding the events that occur in dystrophic muscle diseases and develop innovative therapies for such pathological conditions. To date, several experimental injury models have been used to investigate skeletal muscle regeneration. Intramuscular injection of glycerol has been used as a new model to induce muscle injury and regeneration. It was reported that degenerative changes following glycerol-induced injury resemble those seen in DMD suggesting a similarity in their mechanism. The objective of the current review is to provide an overview of the current knowledge of using glycerol as a new model to induce muscle injury and regeneration.