The use of an antifibrosis agent to improve muscle recovery after laceration

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Role of microenvironment on muscle stem cell function in health, adaptation, and disease

The role of the cellular microenvironment has recently gained attention in the context of muscle health, adaption, and disease. Emerging evidence supports major roles for the extracellular matrix (ECM) in regeneration and the dynamic regulation of the satellite cell niche. Satellite cells normally reside in a quiescent state in healthy muscle, but upon muscle injury, they activate, proliferate, and fuse to the damaged fibers to restore muscle function and architecture. This chapter reviews the composition and mechanical properties of skeletal muscle ECM and the role of these factors in contributing to the satellite cell niche that impact muscle regeneration. In addition, the chapter details the effects of satellite cell-matrix interactions and provides evidence that there is bidirectional regulation affecting both the cellular and extracellular microenvironment within skeletal muscle. Lastly, emerging methods to investigate satellite cell-matrix interactions will be presented.

Decorin: a potential therapeutic candidate for ligamentum flavum hypertrophy by antagonizing TGF-β1

Ligamentum flavum hypertrophy (LFH) is the main physiological and pathological mechanism of lumbar spinal canal stenosis (LSCS). The specific mechanism for LFH has not been completely clarified. In this study, bioinformatic analysis, human ligamentum flavum (LF) tissues collection and analysis, and in vitro and in vivo experiments were conducted to explore the effect of decorin (DCN) on LFH pathogenesis. Here, we found that TGF-β1, collagen I, collagen III, α-SMA and fibronectin were significantly upregulated in hypertrophic LF samples. The DCN protein expression in hypertrophic LF samples was higher than that in non-LFH samples, but the difference was not significant. DCN inhibited the expression of TGF-β1-induced fibrosis-associated proteins in human LF cells, including collagen I, collagen III, α-SMA, and fibronectin. ELISAs showed that TGF-β1 can upregulate PINP and PIIINP in the cell supernatant, and this effect was inhibited after DCN administration. Mechanistic studies revealed that DCN suppressed TGF-β1-induced fibrosis by blocking the TGF-β1/SMAD3 signaling pathway. In addition, DCN ameliorated mechanical stress-induced LFH in vivo. In summary, our findings indicated that DCN ameliorated mechanical stress-induced LFH by antagonizing the TGF-β1/SMAD3 signaling pathway in vitro and in vivo. These findings imply that DCN is a potential therapeutic candidate for ligamentum flavum hypertrophy.

In vitro analysis of genome-engineered muscle-derived stem cells for autoregulated anti-inflammatory and antifibrotic activity

Traumatic muscle injury leads to chronic and pathologic fibrosis in skeletal muscles, primarily driven through upregulation of transforming growth factor-β1 (TGF-β1). Cell-based therapies, such as injection of muscle-derived stem cells (MDSCs), have shown promise in muscle repair. However, injected MDSCs in injured skeletal muscle can differentiate into myofibroblasts under the influence of TGF-β1, and contribute to the development of fibrosis, limiting their regenerative potential. In this study, we created a "smart" cell-based drug delivery system using CRISPR-Cas9 to genetically engineer MDSCs capable of sensing TGF-β1 and producing an antifibrotic biologic, decorin. These gene-edited smart cells, capable of inhibiting fibrosis in a dose-dependent and autoregulating manner, show anti-inflammatory and antifibrotic properties in vitro, without changing the expression of myogenic and stem cell markers as well as their cell proliferation and myogenic differentiation. Additionally, differentiation down a fibrotic lineage is reduced or eliminated in response to TGF-β1. Our results show that gene editing can be used to successfully create smart stem cells capable of producing biologic drugs with antifibrotic capabilities in a controlled and localized manner. This system provides a tool for cell-based drug delivery as the basis for a novel therapeutic approach for a variety of diseases.

Histological and biochemical evaluation of plasma rich in growth factors treatment for grade II muscle injuries in sheep

The purpose of this study was to perform a histological and biochemical evaluation of the influence of plasma rich in growth factors (PRGF) on muscle regeneration process after a surgically induced grade II muscle laceration. A randomized, single blind, controlled experimental research was conducted including twenty-one adult healthy sheep, randomly divided in three groups (n = 7). A grade II surgical section was performed in the biceps femoris muscle of both hindlimbs. After two days (basal time), intralesional infiltration of autologous PRGF or Saline solution was randomly administered in both hindlimbs. Treatment was repeated once a week. Animal groups were euthanized at 1 (T1), 2 (T2) or 4 (T4) weeks. Histological assessment showed that PRGF intralesional injection induced a significant decrease of inflammatory cells density, significant higher centrally nucleated fibers percentage and significantly smaller fibrotic areas compared to Saline-treated muscles at T1, T2 and T4. Also, lower vascular density, with lower capillaries cross-sectional area, in PRGF group compared to Saline was observed. Biochemical analysis revealed a significant higher expression level of MYOD1, MYF5 and MYOG genes in PRGF groups at T1 compared to Saline treated muscles. At ultrastructural level, PRGF groups presented scarce edema and loss of connective tissue structure, as well as higher mitochondrial density adequately associated to the sarcomere unit in contrast to the Saline group. In conclusion, histological, biochemical, and ultrastructural results showed that PRGF treatment improved muscle regeneration process leading to more mature histological aspect in newly formed muscle tissue after a surgically induced grade II muscle injury.

The Role of Decorin in Autoimmune and Inflammatory Diseases

Decorin is an extracellular matrix protein that belongs to the family of small leucine-rich proteoglycans. As a matrix protein, the first discovered role of decorin is participating in collagen fibril formation. Many other functions of decorin in various biological processes have been subsequently identified. Decorin is involved in an extensive signaling network and can interact with other extracellular matrix components, growth factors, receptor tyrosine kinases, and various proteases. Decorin has been shown to be involved in wound repair, cell cycle, angiogenesis, tumor metastasis, and autophagy. Recent evidence indicates that it also plays a role in immune regulation and inflammatory diseases. This review summarizes the characteristics of decorin in immune and inflammatory diseases, including inflammatory bowel disease (IBD), Sjögren's syndrome (SS), chronic obstructive pulmonary disease (COPD), IgA nephropathy, rheumatoid arthritis (RA), spondyloarthritis (SpA), osteoarthritis, multiple sclerosis (MS), idiopathic inflammatory myopathies (IIM), and systemic sclerosis (SSc) and discusses the potential role in these disorders.

Transcriptome analysis of collagen VI-related muscular dystrophy muscle biopsies

Objective

To define the transcriptomic changes responsible for the histologic alterations in skeletal muscle and their progression in collagen VI‐related muscular dystrophy (COL6‐RD).

Methods

COL6‐RD patient muscle biopsies were stratified into three groups based on the overall level of pathologic severity considering degrees of fibrosis, muscle fiber atrophy, and fatty replacement of muscle tissue. Using microarray and RNA‐Seq, we then performed global gene expression profiling on the same muscle biopsies and compared their transcriptome with age‐ and sex‐matched controls.

Results

COL6‐RD muscle biopsy transcriptomes as a group revealed prominent upregulation of muscle extracellular matrix component genes and the downregulation of skeletal muscle and mitochondrion‐specific genes. Upregulation of the TGFβ pathway was the most conspicuous change across all biopsies and was fully evident even in the mildest/earliest histological group. There was no difference in the overall transcriptional signature between the different histologic groups but polyserial analysis identified relative changes along with COL6‐RD histological severity.

Interpretation

Overall, our study establishes the prominent dysregulation of extracellular matrix genes, TGFβ signaling, and its downstream cellular pathways at the transcriptomic level in COL6‐RD muscle.

Effect of decorin protein administration on rat sciatic nerve injury: an experimental study

INTRODUCTION

Peripheral nerve traumas are common injuries in young adult population. The myriad of techniques and medications have been defined to obtain better recovery but none of them was proved to have superior effect. This study aims to determine the anti-fibrotic effect of the decorin on sciatic nerve injury in order to enhance functional outcome.

MATERIALS AND METHODS

24 12-week-old male Sprague-Dawley rats (350-400 gr) were divided into four groups. The sciatic nerve was dissected and exposed; a full-thickness laceration was created 1.5 cm proximal to the bifurcation point and 1.5 cm distal to where it originated from the lumbosacral plexus. Motor and sensory tests were conducted before and after the operations for evaluating the nerve healing.

RESULTS

There was a statistically significant difference between DCN bolus and PBS bolus group. (p<0.0001, p&lt;0.05) in neuromotor tests. Increase of the latency was significantly lower in DCN bolus and infusion group when compared with the PBS bolus group. (p&lt;0,001). All operated gastrocnemius muscles were atrophic compared with the contralateral side. The differences between the averages in the sciatic functional index, the improvement of the DCN infusion group was 8.6 units better than the PBS group and 4.4 units better than the DCN bolus group. When the amount of stimulation was 10 mV at the proximal segment in electromyography, there was no significant difference between the DCN bolus and sham groups. (p&gt; 0.05, p = 0.6623).

CONCLUSION

Decorin protein reduces the fibrosis and enhances the motor and sensory recovery both clinically and histologically. Despite the high cost, short half-life and production issues, this protein could be administered after the microsurgical repair but more studies are required to overcome the limitations.

Use of Platelet-Rich Plasma Plus Suramin, an Antifibrotic Agent, to Improve Muscle Healing After Injuries

BACKGROUND

The increasing use of platelet-rich plasma (PRP) to treat muscle injuries raises concerns because transforming growth factor-beta (TGF-β) in PRP may promote fibrosis in the injured muscle and thus impair muscle regeneration.

PURPOSE

To investigate whether suramin (a TGF-β inhibitor) can reduce muscle fibrosis to improve healing of the injured muscle after PRP treatment and identify the underlying molecular mechanism.

STUDY DESIGN

Controlled laboratory study.

METHODS

Myoblasts isolated from the gastrocnemius muscle of Sprague Dawley rats were treated with PRP or PRP plus suramin. MTT assays were performed to evaluate cell viability. The expression of fibrosis-associated proteins (such as type I collagen and fibronectin), Smad2, and phosphorylated Smad2 was determined using Western blot analysis and immunofluorescent staining. An anti-TGF-β antibody was employed to verify the role of TGF-β in fibronectin expression. Gastrocnemius muscles were injured through a partial transverse incision and then treated using PRP or PRP plus suramin. Hematoxylin and eosin staining was conducted to evaluate the healing process 7 days after the injury. Immunofluorescent staining was performed to evaluate fibronectin expression. Muscle contractile properties-fast-twitch and tetanic strength-were evaluated through electric stimulation.

RESULTS

PRP plus 25 μg/mL of suramin promoted myoblast proliferation. PRP induced fibronectin expression in myoblasts, but suramin reduced this upregulation. The anti-TGF-β antibody also reduced the upregulation of fibronectin expression in the presence of PRP. The upregulation of phosphorylated Smad2 by PRP was reduced by either the anti-TGF-β antibody or suramin. In the animal study, no significant difference was discovered in muscle healing between the PRP versus PRP plus suramin groups. However, the PRP plus suramin group had reduced fibronectin expression at the injury site. Fast-twitch strength and tetanic strength were significantly higher in the injured muscle treated using PRP or PRP plus suramin.

CONCLUSION

Simultaneous PRP and suramin use reduced fibrosis in the injured muscle and promoted healing without negatively affecting the muscle's contractile properties. The underlying molecular mechanism may be associated with the phosphorylated Smad2 pathway.

CLINICAL RELEVANCE

Simultaneous PRP and suramin use may reduce muscle fibrosis without compromising muscle contractile properties and thus improve muscle healing.

[Proliferative vitreoretinopathy prophylaxis : Mission (im)possible]

BACKGROUND

Proliferative vitreoretinopathy (PVR) is one of the most important complications following vitreoretinal surgery. So far, surgical strategies have been the gold standard in treatment. Pharmacological approaches for prevention and treatment of PVR are under clinical investigation and intervene in different phases of the PVR cascade.

METHODS

The relevant literature as well as own data and experience with PVR are discussed in this review article. The most important aspects of pharmacological approaches for PVR prophylaxis and treatment are explained.

RESULTS

A prophylactic use of systemic prednisone administration as an anti-inflammatory substance showed contradictory results, while there was no additional benefit for intravitreal triamcinolone. Orally administered isotretinoin also seems to be able to minimize the formation of PVR after retinal reattachment surgery, whereas there was no improvement in the success rate in established PVR. Cell proliferation inhibitors have already been extensively studied. The combined intravitreal prophylactic approach of 5‑fluorouracil and low molecular weight heparin was recently further investigated in a multicenter, placebo-controlled study and showed a positive effect in some studies. New preclinical and experimental approaches include the inhibition of growth factors, modulation of integrin activity and the induction of apoptosis.

CONCLUSION

Most clinical studies dealt with an anti-inflammatory or antiproliferative approach. So far, no pharmacological substance has been established for the treatment of PVR but there are promising approaches for prophylaxis.

Hydrogen Sulfide Alleviates Skeletal Muscle Fibrosis via Attenuating Inflammation and Oxidative Stress

The purpose of this study was to investigate the effect of exogenous hydrogen sulfide (H₂S) treatment on skeletal muscle contusion. We established a skeletal muscle contusion model (S group) and an H₂S treated of skeletal muscle contusion model (H₂S group). Gastrocnemius muscles (GMs) were collected at day 1, day 5, day 10, and day 15 after injury, and comprehensive morphological and genetic analyses was conducted. H₂S treatment reduced M1 macrophage (CD68), profibrotic cytokines (TGF-β), pro-inflammatory cytokines (TNF-α, IFN-γ, IL-1β, and IL-6), chemokines (CCL2, CCR2, CCL3, CCL5, CXCL12, and CXCR4), matrix metalloproteinases (MMP-1, MMP-2, MMP-9, and MMP-14) and oxidative stress factor (gp91phox) expression levels, improved M2 macrophage (CD206) level. Thus, exogenous H₂S treatment reduced inflammation and oxidative stress, attenuated skeletal muscle fibrosis, and partly improved skeletal muscle injury.

Decorin expression is associated with predictive diffusion MR phenotypes of anti-VEGF efficacy in glioblastoma

Previous data suggest that apparent diffusion coefficient (ADC) imaging phenotypes predict survival response to anti-VEGF monotherapy in glioblastoma. However, the mechanism by which imaging may predict clinical response is unknown. We hypothesize that decorin (DCN), a proteoglycan implicated in the modulation of the extracellular microenvironment and sequestration of pro-angiogenic signaling, may connect ADC phenotypes to survival benefit to anti-VEGF therapy. Patients undergoing resection for glioblastoma as well as patients included in The Cancer Genome Atlas (TCGA) and IVY Glioblastoma Atlas Project (IVY GAP) databases had pre-operative imaging analyzed to calculate pre-operative ADC_L values, the average ADC in the lower distribution using a double Gaussian mixed model. ADC_L values were correlated to available RNA expression from these databases as well as from RNA sequencing from patient derived mouse orthotopic xenograft samples. Targeted biopsies were selected based on ADC values and prospectively collected during resection. Surgical specimens were used to evaluate for DCN RNA and protein expression by ADC value. The IVY Glioblastoma Atlas Project Database was used to evaluate DCN localization and relationship with VEGF pathway via in situ hybridization maps and RNA sequencing data. In a cohort of 35 patients with pre-operative ADC imaging and surgical specimens, DCN RNA expression levels were significantly larger in high ADC_L tumors (41.6 vs. 1.5; P = 0.0081). In a cohort of 17 patients with prospectively targeted biopsies there was a positive linear correlation between ADC_L levels and DCN protein expression between tumors (Pearson R² = 0.3977; P = 0.0066) and when evaluating different targets within the same tumor (Pearson R² = 0.3068; P = 0.0139). In situ hybridization data localized DCN expression to areas of microvascular proliferation and immunohistochemical studies localized DCN protein expression to the tunica adventitia of blood vessels within the tumor. DCN expression positively correlated with VEGFR1 & 2 expression and localized to similar areas of tumor. Increased ADC_L on diffusion MR imaging is associated with high DCN expression as well as increased survival with anti-VEGF therapy in glioblastoma. DCN may play an important role linking the imaging features on diffusion MR and anti-VEGF treatment efficacy. DCN may serve as a target for further investigation and modulation of anti-angiogenic therapy in GBM.

Role of Myokines in Myositis Pathogenesis and Their Potential to be New Therapeutic Targets in Idiopathic Inflammatory Myopathies

Idiopathic inflammatory myopathies (IIM) represent a heterogeneous group of autoimmune diseases whose treatment is often a challenge. Many patients, even after immunosuppressive therapy, do not respond to treatment, so new alternatives have been sought for this. Therefore, other signaling pathways that could contribute to the pathogenesis of myositis have been investigated, such as the expression of myokines in skeletal muscle in response to the inflammatory process. In this review, we will refer to these muscle cytokines that are overexpressed or downregulated in skeletal muscle in patients with various forms of IIM, thus being able to contribute to the maintenance of the autoimmune process. Some muscle cytokines, through their antagonistic action, may be a helpful contributor to the disease modulation, and thus, they could represent personalized treatment targets. Here, we consider the main myokines involved in the pathogenesis of myositis, expressing our view on the possibility of using them as potential therapeutic targets: interleukins IL-6, IL-15, and IL-18; chemokines CXCL10, CCL2, CCL3, CCL4, CCL5, and CCL20; myostatin; follistatin; decorin; osteonectin; and insulin-like 6. An interesting topic regarding the complex connection between myokines and noninflammatory pathways implied in IIM has also been briefly described, because it is an important scientific approach to the pathogenesis of IIM and can be a therapeutic alternative to be considered, especially for the patients who do not respond to immunosuppressive treatment.

Application of Bone Marrow-Derived Mesenchymal Stem Cells for Muscle Healing After Contusion Injury in Mice

BACKGROUND

Skeletal muscle injuries are very common in sports medicine. Conventional therapies have limited clinical efficacy. New treatment methods should be developed to allow athletes to return to play with better function.

PURPOSE

To evaluate the in vitro differentiation potential of bone marrow-derived mesenchymal stem cells and the in vivo histologic and physiologic effects of mesenchymal stem cell therapy on muscle healing after contusion injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

Bone marrow cells were flushed from both femurs of 5-week-old C57BL/6 mice to establish immortalized mesenchymal stem cell lines. A total of 36 mice aged 8 to 10 weeks were used to develop a muscle contusion model and were divided into 6 groups (6 mice/group) on the basis of the different dosages of IM2 cells to be injected (0, 1.25 × 105, and 2.5 × 105 cells with/without F-127 in 100 μL of phosphate-buffered saline). Histological analysis of muscle regeneration was performed, and the fast-twitch and tetanus strength of the muscle contractions was measured 28 days after muscle contusion injury, after injections of different doses of mesenchymal stem cells with or without the F-127 scaffold beginning 14 days after contusion injury.

RESULTS

The mesenchymal stem cell-treated muscles exhibited numerous regenerating myofibers. All the groups treated with mesenchymal stem cells (1.25 × 105 cells, 2.5 × 105 cells, 1.25 × 105 cells plus F-127, and 2.5 × 105 cells plus F-127) exhibited a significantly higher number of regenerating myofibers (mean ± SD: 111.6 ± 14.77, 133.4 ± 21.44, 221.89 ± 32.65, and 241.5 ± 25.95, respectively) as compared with the control group and the control with F-127 (69 ± 18.79 and 63.2 ± 18.98). The physiologic evaluation of fast-twitch and tetanus strength did not reveal differences between the age-matched uninjured group and the groups treated with various doses of mesenchymal stem cells 28 days after contusion. Significant differences were found between the control group and the groups treated with various doses of mesenchymal stem cells after muscle contusion.

CONCLUSION

Mesenchymal stem cell therapy increased the number of regenerating myofibers and improved fast-twitch and tetanus muscle strength in a mouse model of muscle contusion. However, the rapid decay of transplanted mesenchymal stem cells suggests a paracrine effect of this action. Treatment with mesenchymal stem cells at various doses combined with the F-127 scaffold is a potential therapy for a muscle contusion.

CLINICAL RELEVANCE

Mesenchymal stem cell therapy has an effect on sports medicine because of its effects on myofiber regeneration and muscle strength after contusion injury.

Morphological evaluation of polysaccharide content and collagen composition during cutaneous wound healing in the Sunda porcupine (Hystrix javanica)

Wound healing in the Sunda porcupine is believed to occur quickly, although the wound is large and severe. Wound enclosure involves many processes to restore the lost or damaged skin structure where conjugated polysaccharide-protein and collagen, as the main components deposited in wound tissue to restore it. The aim of this study was to evaluate alteration of polysaccharide contents and collagen in untreated full-thickness wound healing in the thoracodorsal and lumbosacral regions in the Sunda porcupines. Histological analysis was performed by periodic acid Schiff, alcian blue pH 2.5, picrosirius red staining method and Low Vacuum Scanning Electron Microscope (LV-SEM) imaging to obtain the fundamental data of healing process. Wound healing began with re-epithelization followed by progressive wound contraction with 4 overlapping stages in about 30–50 days until the wound closed (21–30 days in thoracodorsal and 30–50 days in lumbosacral). Neutral polysaccharide was more widely distributed compared to the acid polysaccharide in almost all stages of wound healing. The ratio of collagen I to III appeared to be higher in the thoracodorsal region than the lumbosacral region during healing process. LV-SEM imaging showed changes in connective tissue structure in the wound border and granulation tissue which appeared abundant and mixed of thin and thick fiber. In conclusion, cutaneous full thickness wound healing in the Sunda porcupine occurred faster in the thoracodorsal region, which might be correlated to the role of neutral polysaccharide and a high ratio of collagen I to III.

The Effect of Hyperbaric Oxygen Treatment on Myoblasts and Muscles After Contusion Injury

The recommended treatment varies depending on the severity of muscle injuries. The aim of this study was to evaluate the in vitro myoblast proliferation and the in vivo histologic and physiologic effects of hyperbaric oxygen treatment on muscle healing after contusion. Cells from the C2C12 myoblast cell line were exposed to 100% O2 for 25 min then to air for 5 min at 2.5 atmospheres absolute in a hyperbaric chamber for a total treatment duration of 90 min per 48 h at intervals of 2, 4, 6 and 8 days. Cell growth measurements and western blot analysis of myogenin and actin were performed. Then, 18 mice aged 8-10 weeks were used in the muscle contusion model. The histologic and physiologic effects and muscle regeneration after hyperbaric oxygen treatment were evaluated. The myoblast growth rate was significantly higher (p < 0.05) after hyperbaric oxygen treatment. Densitometric evaluation demonstrated a 39% (p < 0.05) and 25% (p < 0.05) increase in myogenin and actin protein levels, respectively, in the cells treated with 1 dose of hyperbaric oxygen. Similarly, the myogenin and actin protein levels increased for samples receiving multiple hyperbaric oxygen treatments when compared with the control. Physiologic evaluation of fast twitch and tetanus strength revealed a significant difference between the control group and the 14-day hyperbaric oxygen group. In conclusion, hyperbaric oxygen treatment increases the myoblast growth rate and myogenin and actin production. Better histologic and physiologic performance were found after hyperbaric oxygen treatment in animal contusion model. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:329-335, 2020.

Curcumin and Nanocurcumin Oral Supplementation Improve Muscle Healing in a Rat Model of Surgical Muscle Laceration

OBJECTIVE

To compare the effects of curcumin and nanocurcumin oral supplementation on the muscle healing rate of an animal model of surgical muscle laceration.

METHODS

Thirty-two male adult rats were randomly divided into sham, control, curcumin, and nanocurcumin groups. Partial transection of the gastrocnemius muscle was made in the right limb of the control and treatment groups. The sham and control groups received normal saline, curcumin group received 500 mg/kg of curcumin and nanocurcumin group received 100 mg curcumin-loaded nanomicelles orally every day. They euthanized two weeks later and the specimens were stained by hematoxylin-eosin (H&E) and Masson's trichrome methods. Aspartate transaminase (AST) and creatine phosphokinase (CPK) were measured in blood samples.

RESULTS

The percentage of collagen fibers in the nanocurcumin group was significantly lesser than the control and curcumin groups (p<0.001). Muscle fiber regeneration in the treatment groups was significantly higher than the control group (p<0.001). The blood vessels of the nanocurcumin group were significantly more than other groups (p<0.001). Plasma AST had a significant difference in the control group compared to the sham and nanocurcumin groups (p=0.026). The plasma CPK level of the control group was also significantly higher than other groups (p<0.001).

CONCLUSION

In conclusion, although oral curcumin supplementation has little effects because of its poor bioavailability, embedding it in nanoparticles could enhance its systemic effects in promoting the muscle healing process.

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

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

Effects of Two Fractions of Swietenia macrophylla and Catechin on Muscle Damage Induced by BothropsVenom and PLA₂

Plant natural products can attenuate the myonecrosis caused by Bothrops snake venom and their phospholipases A₂ (PLA₂). In this study, we evaluated the effects of two fractions (F4 and F6) from Swietenia macrophylla and purified catechin on the muscle damage caused by a myotoxic PLA₂ from Colombian Bothrops asper venom (BaColPLA₂) in mice and by Bothrops marmoratus venom from Brazil in mouse phrenic nerve-diaphragm muscle (PND) preparations in vitro. Male mice were injected with PLA₂ (50 µg) in the absence or presence of F4, F6, and catechin, in the gastrocnemius muscle and then killed 3, 7, 14, and 28 h later for histopathological analysis of myonecrosis, leukocyte infiltration, and the presence of collagen. Fractions F4 and F6 (500 µg) and catechin (90 µg) significantly reduced the extent of necrosis at all-time intervals. These two fractions and catechin also attenuated the leukocyte infiltration on day 3, as did catechin on day 14. There was medium-to-moderate collagen deposition in all groups up to day 7, but greater deposition on days 14 and 28 in the presence of F6 and catechin. Bothrops marmoratus venom (100 µg/mL) caused slight (~25%) muscle facilitation after 10 minutes and weak neuromuscular blockade (~64% decrease in contractile activity after a 120-minute incubation). Pre-incubation of venom with F4 or F6 abolished the facilitation, whereas catechin, which was itself facilitatory, did not. All three fractions attenuated the venom-induced decrease in muscle contractions. These findings indicate that fractions and catechin from S. macrophylla can reduce the muscle damage caused by Bothrops venom and PLA₂. These fractions or their components could be useful for treating venom-induced local damage.

Non-viral, Tumor-free Induction of Transient Cell Reprogramming in Mouse Skeletal Muscle to Enhance Tissue Regeneration

Overexpression of Oct3/4, Klf4, Sox2, and c-Myc (OKSM) transcription factors can de-differentiate adult cells in vivo. While sustained OKSM expression triggers tumorigenesis through uncontrolled proliferation of toti- and pluripotent cells, transient reprogramming induces pluripotency-like features and proliferation only temporarily, without teratomas. We sought to transiently reprogram cells within mouse skeletal muscle with a localized injection of plasmid DNA encoding OKSM (pOKSM), and we hypothesized that the generation of proliferative intermediates would enhance tissue regeneration after injury. Intramuscular pOKSM administration rapidly upregulated pluripotency (Nanog, Ecat1, and Rex1) and early myogenesis genes (Pax3) in the healthy gastrocnemius of various strains. Mononucleated cells expressing such markers appeared in clusters among myofibers, proliferated only transiently, and did not lead to dysplasia or tumorigenesis for at least 120 days. Nanog was also upregulated in the gastrocnemius when pOKSM was administered 7 days after surgically sectioning its medial head. Enhanced tissue regeneration after reprogramming was manifested by the accelerated appearance of centronucleated myofibers and reduced fibrosis. These results suggest that transient in vivo reprogramming could develop into a novel strategy toward the acceleration of tissue regeneration after injury, based on the induction of transiently proliferative, pluripotent-like cells in situ. Further research to achieve clinically meaningful functional regeneration is warranted.

Potential Usefulness of Losartan as an Antifibrotic Agent and Adjunct to Platelet-Rich Plasma Therapy to Improve Muscle Healing and Cartilage Repair and Prevent Adhesion Formation

Postoperative tissue fibrosis represents a major complication in orthopedics. Transforming growth factor beta 1 is a key molecule in the development of postoperative fibrosis. High concentrations of transforming growth factor beta 1 have also been implicated in various diseases. Agents that counteract the actions of transforming growth factor beta 1 have been investigated as potential antifibrotic medications and as adjunct treatment to platelet-rich plasma injections (increased amounts of transforming growth factor beta 1) to improve their effectiveness and/or safety profile. Losartan blocks transforming growth factor beta 1 action and has attracted special interest in orthopedic research that focuses on how to reduce the risk of postoperative fibrosis. [Orthopedics. 2018; 41(5):e591-e597.].

Periostin Promotes Fibroblast Migration and Inhibits Muscle Repair After Skeletal Muscle Injury

BACKGROUND

Skeletal muscle injury (SMI) can cause physical disability due to insufficient recovery of the muscle. The development of muscle fibrosis after SMI has been widely regarded as a principal cause of this failure to recover. Periostin (Postn) exacerbates tissue fibrosis in various organs. We investigated whether Postn is involved in the pathophysiology after SMI.

METHODS

Partial laceration injuries of the gastrocnemius were created in wild-type (WT) and Postn knockout (Postn) mice. We examined the expression of the Postn gene before and after SMI. Regeneration and fibrosis of skeletal muscle were evaluated by histological analyses, and recovery of muscle strength was measured by physiological testing. Immunohistochemistry was used to examine the number and proliferative potential of infiltrating fibroblasts in injured muscle. A trans-well migration assay was used to assess the migration capability of fibroblasts. Control immunoglobulin G (IgG) or Postn-neutralizing antibody (Postn-nAb) was injected into injured muscle at 7 and 14 days after injury (dpi). We evaluated the effects of Postn-nAb on muscle repair after SMI.

RESULTS

The expression of Postn was dramatically upregulated after SMI. Compared with WT mice, Postn mice had improved muscle recovery and attenuated fibrosis as well as a significantly reduced number of infiltrating fibroblasts. The proliferative potential of these fibroblasts in WT and Postn mice was comparable at 14 dpi; however, the migration capability of fibroblasts was significantly enhanced in the presence of Postn (mean, 258%; 95% confidence interval, 183% to 334%). Moreover, the administration of Postn-nAb inhibited fibroblast infiltration and promoted muscle repair after SMI.

CONCLUSIONS

Postn exacerbates fibrotic scar formation through the promotion of fibroblast migration into injured muscle after SMI. Treatment with Postn-nAb is effective for attenuating fibrosis and improving muscle recovery after SMI.

CLINICAL RELEVANCE

Our findings may provide a potential therapeutic strategy to enhance muscle repair and functional recovery after SMI.

Platelet-Rich Plasma Releasate Promotes Regeneration and Decreases Inflammation and Apoptosis of Injured Skeletal Muscle

BACKGROUND

Platelet-rich plasma (PRP) contains various cytokines and growth factors that may be beneficial to the healing process of injured muscle. Based on the authors' previous study, PRP releasate can promote proliferation and migration of skeletal muscle cells in vitro, so animal studies are performed to support the use of PRP to treat muscle injury in vivo.

PURPOSE

To investigate the effect of PRP releasate on regeneration of injured muscle, as well as its effect on inflammatory reaction and cell apoptosis, in the early stages of the muscle-healing process.

STUDY DESIGN

Controlled laboratory study.

METHODS

The gastrocnemius muscles of Sprague-Dawley rats were injured by partial transverse incision and then treated with PRP releasate. Hematoxylin and eosin stain was used to evaluate the healing process of injured muscle at 2, 5, and 10 days after injury. TUNEL assay was used to evaluate the cell apoptosis of injured muscle after PRP releasate treatment. Immunohistochemistry was used to stain the CD68-positive cells during the healing process. Muscle contractile properties, including fast-twitch and tetanic strength, were evaluated by electric stimulation.

RESULTS

The results revealed that PRP releasate treatment could enhance the muscle-healing process and decrease CD68-positive cells and apoptotic cells. Furthermore, the tetanic strength was significantly higher in injured muscle treated with PRP releasate.

CONCLUSION

In conclusion, PRP releasate could enhance the healing process of injured muscle and decrease inflammatory cell infiltration as well as cell apoptosis.

CLINICAL RELEVANCE

PRP promotes skeletal muscle healing in association with decreasing inflammation and apoptosis of injured skeletal muscle. These findings provide in vivo evidence to support the use of PRP to treat muscle injury.

The effect of anti-inflammatory and antifibrotic agents on fibroblasts obtained from arthrofibrotic tissue: An in vitro and in vivo study

Objectives

The aims of this study were to determine whether the administration of anti-inflammatory and antifibrotic agents affect the proliferation, viability, and expression of markers involved in the fibrotic development of the fibroblasts obtained from arthrofibrotic tissue in vitro, and to evaluate the effect of the agents on arthrofibrosis prevention in vivo.

Methods

Dexamethasone, diclofenac, and decorin, in different concentrations, were employed to treat fibroblasts from arthrofibrotic tissue (AFib). Cell proliferation was measured by DNA quantitation, and viability was analyzed by Live/Dead staining. The levels of procollagen type I N-terminal propeptide (PINP) and procollagen type III N-terminal propeptide (PIIINP) were evaluated with enzyme-linked immunosorbent assay (ELISA) kits. In addition, the expressions of fibrotic markers were detected by real-time polymerase chain reaction (PCR). Fibroblasts isolated from healthy tissue (Fib) served as control. Further, a rabbit model of joint contracture was used to evaluate the antifibrotic effect of the three different agents.

Results

Dexamethasone maintained the viability and promoted the proliferation of AFib. Diclofenac decreased the viability and inhibited the cell proliferation during the first week of cultivation. However, decorin inhibited AFib proliferation and downregulated the expressions of fibrotic markers. Additionally, decorin could improve the flexion contracture angle and inhibit the deposition of interstitial matrix components in the rabbit joint model.

Conclusion

Decorin decreased the expression of myofibroblast markers in AFib, inhibited the proliferation of AFib, and prevented the initial procedure of arthrofibrosis in vivo, suggesting that decorin could be a promising treatment to inhibit the development of arthrofibrosis.Cite this article: X. Tang, S. Teng, M. Petri, C. Krettek, C. Liu, M. Jagodzinski. The effect of anti-inflammatory and antifibrotic agents on fibroblasts obtained from arthrofibrotic tissue: An in vitro and in vivo study. Bone Joint Res 2018;7:213-222. DOI: 10.1302/2046-3758.73.BJR-2017-0219.R2.

Tackling muscle fibrosis: From molecular mechanisms to next generation engineered models to predict drug delivery

Muscle fibrosis represents the end stage consequence of different diseases, among which muscular dystrophies, leading to severe impairment of muscle functions. Muscle fibrosis involves the production of several growth factors, cytokines and proteolytic enzymes and is strictly associated to inflammatory processes. Moreover, fibrosis causes profound changes in tissue properties, including increased stiffness and density, lower pH and oxygenation. Up to now, there is no therapeutic approach able to counteract the fibrotic process and treatments directed against muscle pathologies are severely impaired by the harsh conditions of the fibrotic environment. The design of new therapeutics thus need innovative tools mimicking the obstacles posed by the fibrotic environment to their delivery. This review will critically discuss the role of in vivo and 3D in vitro models in this context and the characteristics that an ideal model should possess to help the translation from bench to bedside of new candidate anti-fibrotic agents.

Regulation of fibrosis in muscular dystrophy

The production of force and power are inherent properties of skeletal muscle, and regulated by contractile proteins within muscle fibers. However, skeletal muscle integrity and function also require strong connections between muscle fibers and their extracellular matrix (ECM). A well-organized and pliant ECM is integral to muscle function and the ability for many different cell populations to efficiently migrate through ECM is critical during growth and regeneration. For many neuromuscular diseases, genetic mutations cause disruption of these cytoskeletal-ECM connections, resulting in muscle fragility and chronic injury. Ultimately, these changes shift the balance from myogenic pathways toward fibrogenic pathways, culminating in the loss of muscle fibers and their replacement with fatty-fibrotic matrix. Hence a common pathological hallmark of muscular dystrophy is prominent fibrosis. This review will cover the salient features of muscular dystrophy pathogenesis, highlight the signals and cells that are important for myogenic and fibrogenic actions, and discuss how fibrosis alters the ECM of skeletal muscle, and the consequences of fibrosis in developing therapies.

Identification of satellite cells from anole lizard skeletal muscle and demonstration of expanded musculoskeletal potential

The lizards are evolutionarily the closest vertebrates to humans that demonstrate the ability to regenerate entire appendages containing cartilage, muscle, skin, and nervous tissue. We previously isolated PAX7-positive cells from muscle of the green anole lizard, Anolis carolinensis, that can differentiate into multinucleated myotubes and express the muscle structural protein, myosin heavy chain. Studying gene expression in these satellite/progenitor cell populations from A. carolinensis can provide insight into the mechanisms regulating tissue regeneration. We generated a transcriptome from proliferating lizard myoprogenitor cells and compared them to transcriptomes from the mouse and human tissues from the ENCODE project using XGSA, a statistical method for cross-species gene set analysis. These analyses determined that the lizard progenitor cell transcriptome was most similar to mammalian satellite cells. Further examination of specific GO categories of genes demonstrated that among genes with the highest level of expression in lizard satellite cells were an increased number of genetic regulators of chondrogenesis, as compared to mouse satellite cells. In micromass culture, lizard PAX7-positive cells formed Alcian blue and collagen 2a1 positive nodules, without the addition of exogenous morphogens, unlike their mouse counterparts. Subsequent quantitative RT-PCR confirmed up-regulation of expression of chondrogenic regulatory genes in lizard cells, including bmp2, sox9, runx2, and cartilage specific structural genes, aggrecan and collagen 2a1. Taken together, these data suggest that tail regeneration in lizards involves significant alterations in gene regulation with expanded musculoskeletal potency.

αv integrins on mesenchymal cells regulate skeletal and cardiac muscle fibrosis

Mesenchymal cells expressing platelet-derived growth factor receptor beta (PDGFRβ) are known to be important in fibrosis of organs such as the liver and kidney. Here we show that PDGFRβ+ cells contribute to skeletal muscle and cardiac fibrosis via a mechanism that depends on αv integrins. Mice in which αv integrin is depleted in PDGFRβ+ cells are protected from cardiotoxin and laceration-induced skeletal muscle fibrosis and angiotensin II-induced cardiac fibrosis. In addition, a small-molecule inhibitor of αv integrins attenuates fibrosis, even when pre-established, in both skeletal and cardiac muscle, and improves skeletal muscle function. αv integrin blockade also reduces TGFβ activation in primary human skeletal muscle and cardiac PDGFRβ+ cells, suggesting that αv integrin inhibitors may be effective for the treatment and prevention of a broad range of muscle fibroses.

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

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

The Use of Platelet-Rich and Platelet-Poor Plasma to Enhance Differentiation of Skeletal Myoblasts: Implications for the Use of Autologous Blood Products for Muscle Regeneration

BACKGROUND

Platelet-rich plasma (PRP) has been used to augment tissue repair and regeneration after musculoskeletal injury. However, there is increasing clinical evidence that PRP does not show a consistent clinical effect. Purpose/Hypothesis: This study aimed to compare the effects of the following non-neutrophil-containing (leukocyte-poor) plasma fractions on human skeletal muscle myoblast (HSMM) differentiation: (1) PRP, (2) modified PRP (Mod-PRP), in which transforming growth factor β1 (TGF-β1) and myostatin (MSTN) were depleted, and (3) platelet-poor plasma (PPP). The hypothesis was that leukocyte-poor PRP would lead to myoblast proliferation (not differentiation), whereas certain modifications of PRP preparations would increase myoblast differentiation, which is necessary for skeletal muscle regeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

Blood from 7 human donors was individually processed to simultaneously create leukocyte-poor fractions: PRP, Mod-PRP, PPP, and secondarily spun PRP and Mod-PRP (PRP_ss and Mod-PRP_ss, respectively). Mod-PRP was produced by removing TGF-β1 and MSTN from PRP using antibodies attached to sterile beads, while a second-stage centrifugal spin of PRP was performed to remove platelets. The biologics were individually added to cell culture groups. Analysis for induction into myoblast differentiation pathways included Western blot analysis, reverse-transcription polymerase chain reaction, and immunohistochemistry, as well as confocal microscopy to assess polynucleated myotubule formation.

RESULTS

HSMMs cultured with PRP showed an increase in proliferation but no evidence of differentiation. Western blot analysis confirmed that MSTN and TGF-β1 could be decreased in Mod-PRP using antibody-coated beads, but this modification mildly improved myoblast differentiation. However, cell culture with PPP, PRP_ss, and Mod-PRP_ss led to a decreased proliferation rate but a significant induction of myoblast differentiation verified by increased multinucleated myotubule formation and myosin heavy chain expression (mean 8-fold change in mRNA level; P < .05), which was comparable with 2% horse serum, the positive control.

CONCLUSION

PPP and leukocyte-poor PRP preparations subjected to a second spin to remove the platelets led to induction of myoblast cells into the muscle differentiation pathway, whereas unmodified leukocyte-poor PRP led to myoblast proliferation.

CLINICAL RELEVANCE

These results indicate that traditionally formulated PRP may not be appropriate to induce muscle regeneration. Laboratory evidence suggests that PPP or non-neutrophil-containing PRP_ss, subjected to an additional spin to remove platelets, should be used to stimulate myoblast differentiation, which is necessary for skeletal muscle regeneration. Clinical studies will be required to confirm the effect of these biologics on muscle regeneration.

Effect of mesenchymal stem cells on induced skeletal muscle chemodenervation atrophy in adult male albino rats

The present research was conducted to evaluate the effect of bone marrow derived mesenchymal stem cells (BM-MSCs) as a potential therapeutic tool for improvement of skeletal muscle recovery after induced chemodenervation atrophy by repeated local injection of botulinum toxin-A in the right tibialis anterior muscle of adult male albino rats. Forty five adult Wistar male albino rats were classified into control and experimental groups. Experimental group was further subdivided into 3 equal subgroups; induced atrophy, BM-MSCs treated and recovery groups. Biochemical analysis of serum LDH, CK and Real-time PCR for Bcl-2, caspase 3 and caspase 9 was measured. Skeletal muscle sections were stained with H and E, Mallory trichrome, and Immunohistochemical reaction for Bax and CD34. Improvement in the skeletal muscle histological structure was noticed in BM-MSCs treated group, however, in the recovery group, some sections showed apparent transverse striations and others still affected. Immunohistochemical reaction of Bax protein showed strong positive immunoreaction in the cytoplasm of muscle fibers in the induced atrophy group. BM-MSCs treated group showed weak positive reaction while the recovery group showed moderate reaction in the cytoplasm of muscle fibers. Immunohistochemical reaction for CD34 revealed occasional positive CD34 stained cells in the induced atrophy group. In BM-MSCs treated group, multiple positive CD34 stained cells were detected. However, recovery group showed some positive CD34 stained cells at the periphery of the muscle fibers. Marked improvement in the regenerative capacity of skeletal muscles after BM-MSCs therapy. Hence, stem cell therapy provides a new hope for patients suffering from myopathies and severe injuries.

High energy Gallium Arsenide laser does not facilitate collagen alteration in muscle skeletal extracellular matrix: experimental study

Abstract Introduction: Low intensity laser therapy has proven effective in treating different tissues, reducing inflammation, preventing the formation of fibrous tissue, and promoting muscle regeneration. Objective: To evaluate the effect of low intensity laser therapy, seven days after the injury, and verify whether the radiated energy chosen influences the formation of fibrous tissue. Methods: Thirty Wistar rats, adult male, average body weight 210-340 g were used. The animals were randomized into three groups: control group, untreated injured group (L), and injured and treated group (LT). After anesthetizing the animals, muscle injury was induced by freezing (cryoinjury) in the central region of the tibialis anterior muscle belly (TA) on the left hind limb, through an iron rod previously immersed in liquid nitrogen. A Gallium Arsenide laser, wavelength 904 nm was used. The applications were initiated 24 hours after injury, daily, for five days, at two points in the lesion area. After 7 days, the animals were euthanized; the TA muscle of the left hind limb was removed and frozen in liquid nitrogen and the obtained histological sections were subjected to Sirius Red staining. Results: Histological analysis showed no significant difference in relation to the area of fibrosis in the LT and L groups. Conclusion: The results suggest that the energy density of 69 J/cm² and final energy (4.8 joules) did not promote alterations in the area of collagen in the skeletal muscle extracellular matrix.

The Combined Use of Losartan and Muscle-Derived Stem Cells Significantly Improves the Functional Recovery of Muscle in a Young Mouse Model of Contusion Injuries

BACKGROUND

Although muscle injuries tend to heal uneventfully in most cases, incomplete functional recovery commonly occurs as a result of scar tissue formation at the site of injury, even after treatment with muscle-derived stem cells (MDSCs).

HYPOTHESIS

The transplantation of MDSCs in the presence of a transforming growth factor β1 (TGF-β1) antagonist (losartan) would result in decreased scar tissue formation and enhance muscle regeneration after contusion injuries in a mouse model.

STUDY DESIGN

Controlled laboratory study.

METHODS

An animal model of muscle contusion was developed using the tibialis anterior muscle in 48 healthy mice at 8 to 10 weeks of age. After sustaining muscle contusion injuries, the mice were divided into 4 groups: (1) saline injection group (control group; n = 15), (2) MDSC transplantation group (MDSC group; n = 15), (3) MDSC transplantation plus oral losartan group (MDSC/losartan group; n = 15), and (4) healthy uninjured group (healthy group; n = 3). Losartan was administrated systemically beginning 3 days after injury and continued until the designated endpoint (1, 2, or 4 weeks after injury). MDSCs were transplanted 4 days after injury. Muscle regeneration and fibrotic scar formation were evaluated by histology, and the expression of follistatin, MyoD, Smad7, and Smad2/3 were analyzed by immunohistochemistry and reverse transcription polymerase chain reaction analysis. Functional recovery was measured via electrical stimulation of the peroneal nerve.

RESULTS

When compared with MDSC transplantation alone, MDSC/losartan treatment resulted in significantly decreased scar formation, an increase in the number of regenerating myofibers, and improved functional recovery after muscle contusions. In support of these findings, the expression levels of Smad7 and MyoD were significantly increased in the group treated with both MDSCs and losartan.

CONCLUSION

When compared with MDSCs alone, the simultaneous treatment of muscle contusions with MDSCs and losartan significantly reduced scar formation, increased the number of regenerating myofibers, and improved the functional recovery of muscle; these effects were caused, at least in part, by the losartan-mediated upregulation of Smad7 and MyoD. Increased levels of Smad7 and MyoD together reduced the deposition of scar tissue (via the inhibition of TGF-β1 by Smad7) and committed the transplanted MDSCs toward a myogenic lineage (via Smad7-regulated MyoD expression).

CLINICAL RELEVANCE

The study findings contribute to the development of biological treatments to accelerate and improve the quality of muscle healing after injury.

Contractile function recovery in severely injured gastrocnemius muscle of rats treated with either oleic or linoleic acid

NEW FINDINGS

What is the central question of this study? Oleic and linoleic acids modulate fibroblast proliferation and myogenic differentiation in vitro. However, their in vivo effects on muscle regeneration have not yet been examined. We investigated the effects of either oleic or linoleic acid on a well-established model of muscle regeneration after severe laceration. What is the main finding and its importance? We found that linoleic acid increases fibrous tissue deposition and impairs muscle regeneration and recovery of contractile function, whereas oleic acid has the opposite effects in severely injured gastrocnemius muscle, suggesting that linoleic acid has a harmful effect and oleic acid a potential therapeutic effect on muscle regeneration. Oleic and linoleic acids control fibroblast proliferation and myogenic differentiation in vitro; however, there was no study in skeletal muscle in vivo. The aim of this study was to evaluate the effects of either oleic or linoleic acid on the fibrous tissue content (collagen deposition) of muscle and recovery of contractile function in rat gastrocnemius muscle after being severely injured by laceration. Rats were supplemented with either oleic or linoleic acid for 4 weeks after laceration [0.44 g (kg body weight)^-1 day^-1 ]. Muscle injury led to an increase in oleic-to-stearic acid and palmitoleic-to-palmitic acid ratios, suggesting an increase in Δ⁹ desaturase activity. Increased fibrous tissue deposition and reduced isotonic and tetanic specific forces and resistance to fatigue were observed in the injured muscle. Supplementation with linoleic acid increased the content of eicosadienoic (20:2, n-6) and arachidonic (20:4, n-6) acids, reduced muscle mass and fibre cross-sectional areas, increased fibrous tissue deposition and further reduced the isotonic and tetanic specific forces and resistance to fatigue induced by laceration. Supplementation with oleic acid increased the content of docosahexaenoic acid (22:6, n-3) and abolished the increase in fibrous tissue area and the decrease in isotonic and tetanic specific forces and resistance to fatigue induced by muscle injury. We concluded that supplementation with linoleic acid impairs muscle regeneration and increases fibrous tissue deposition, resulting in impaired recovery of contractile function. Oleic acid supplementation reduced fibrous tissue deposition and improved recovery of contractile function, attenuating the tissue damage caused by muscle injury.

In Silico and In Vivo Experiments Reveal M-CSF Injections Accelerate Regeneration Following Muscle Laceration

Numerous studies have pharmacologically modulated the muscle milieu in the hopes of promoting muscle regeneration; however, the timing and duration of these interventions are difficult to determine. This study utilized a combination of in silico and in vivo experiments to investigate how inflammation manipulation improves muscle recovery following injury. First, we measured macrophage populations following laceration injury in the rat tibialis anterior (TA). Then we calibrated an agent-based model (ABM) of muscle injury to mimic the observed inflammation profiles. The calibrated ABM was used to simulate macrophage and satellite stem cell (SC) dynamics, and suggested that delivering macrophage colony stimulating factor (M-CSF) prior to injury would promote SC-mediated injury recovery. Next, we performed an experiment wherein 1 day prior to injury, we injected M-CSF into the rat TA muscle. M-CSF increased the number of macrophages during the first 4 days post-injury. Furthermore, treated muscles experienced a swifter increase in the appearance of PAX7⁺ SCs and regenerating muscle fibers. Our study suggests that computational models of muscle injury provide novel insights into cellular dynamics during regeneration, and further, that pharmacologically altering inflammation dynamics prior to injury can accelerate the muscle regeneration process.

The extracellular matrix regulates the effect of decorin and transforming growth factor beta-2 (TGF-β2) on myoblast migration

Muscular injuries that destroy the basal lamina result in poor functional recovery of skeletal muscle. This is due, in part, to the deposition of structural fibrotic proteins such as fibronectin and collagen by fibroblasts and other cells. Transforming growth factor-β (TGF-β) promotes fibrosis, whereas the proteoglycan decorin is known to act as an anti-fibrotic agent, in part via the binding and neutralization of TGF-β. We have previously established that decorin can alter the migratory response of skeletal muscle myoblasts to the extracellular matrix (ECM) factor collagen, but not fibronectin. We have also shown that TGF-β reduces myoblast migration. In the current study we demonstrate that decorin can dramatically alter the inhibitory role of TGF-β on human myoblast migration and go on to shown that the extracellular matrix can significantly modify this effect. Decorin and TGF-β2 in combination were observed to significantly increase the rate of human myoblast migration, despite the inhibitory effect of TGF-β2 on its own. Furthermore, in the presence of fibronectin, TGF-β2 and decorin no longer acted synergistically to promote migration; while in the presence of collagen I, TGF-β2 failed to inhibit migration. These studies show, for the first time, that decorin can alter the bioactivity of TGF-β2 on human myoblast migration and emphasize the crucial regulatory role of the extracellular matrix in determining the response of skeletal muscle myoblasts to migratory cues.

Decorin reduces hypertrophic scarring through inhibition of the TGF-β1/Smad signaling pathway in a rat osteomyelitis model

Chronic osteomyelitis is a bone infection that results in hypertrophic scarring of the soft tissue surrounding the infected bone. This scarring can create functional problems and its treatment is challenging. The aim of the present study was to evaluate the efficacy of decorin in treating scar formation in osteomyelitis and the underlying mechanism of its action. A rat osteomyelitis model was used, and animals were divided into three groups, as follows: Group A (control), group B (osteomyelitis model) and group C (decorin-treated). X-ray scans, hematoxylin and eosin (H&E) staining and Masson's trichrome staining were performed to observe changes in femur and muscle tissue. In order to assess the role of the transforming growth factor β1 (TGF-β1)/Smad signaling pathway in scar formation in osteomyelitis, alterations in muscle tissue morphology and in the activation of key members of the TGF-β1/Smad signaling pathway were investigated in groups A and B. According to the results of H&E staining, evident fibrosis in muscle tissue were observed at days 14 and 28 in group B. Simultaneously, the expression levels of key members of the TGF-β1/Smad signaling pathway were increased. Subsequent to treatment with decorin in group C, scarring was reduced, and significant downregulation of collagen I, TGF-β1, phosphorylated (p)Smad2 and pSmad3 protein expression levels was observed at days 14 and 28 compared with the osteomyelitis group. In conclusion, these results suggest that activation of TGF-β1 may serve an important role in the formation of scars in osteomyelitis and that decorin can reduce scar formation in an osteomyelitis rat model through inhibition of the TGF-β1/Smad signaling pathway.

Muscle injuries and strategies for improving their repair

Satellite cells are tissue resident muscle stem cells required for postnatal skeletal muscle growth and repair through replacement of damaged myofibers. Muscle regeneration is coordinated through different mechanisms, which imply cell-cell and cell-matrix interactions as well as extracellular secreted factors. Cellular dynamics during muscle regeneration are highly complex. Immune, fibrotic, vascular and myogenic cells appear with distinct temporal and spatial kinetics after muscle injury. Three main phases have been identified in the process of muscle regeneration; a destruction phase with the initial inflammatory response, a regeneration phase with activation and proliferation of satellite cells and a remodeling phase with maturation of the regenerated myofibers. Whereas relatively minor muscle injuries, such as strains, heal spontaneously, severe muscle injuries form fibrotic tissue that impairs muscle function and lead to muscle contracture and chronic pain. Current therapeutic approaches have limited effectiveness and optimal strategies for such lesions are not known yet. Various strategies, including growth factors injections, transplantation of muscle stem cells in combination or not with biological scaffolds, anti-fibrotic therapies and mechanical stimulation, may become therapeutic alternatives to improve functional muscle recovery.

Effects of icing or heat stress on the induction of fibrosis and/or regeneration of injured rat soleus muscle

The effects of icing or heat stress on the regeneration of injured soleus muscle were investigated in male Wistar rats. Bupivacaine was injected into soleus muscles bilaterally to induce muscle injury. Icing (0 °C, 20 min) was carried out immediately after the injury. Heat stress (42 °C, 30 min) was applied every other day during 2-14 days after the bupivacaine injection. Injury-related increase in collagen deposition was promoted by icing. However, the level of collagen deposition in heat-stressed animals was maintained at control levels throughout the experimental period and was significantly lower than that in icing-treated animals at 15 and 28 days after bupivacaine injection. Furthermore, the recovery of muscle mass, protein content, and muscle fiber size of injured soleus toward control levels was partially facilitated by heat stress. These results suggest that, compared with icing, heat stress may be a beneficial treatment for successful muscle regeneration at least by reducing fibrosis.

Mesenchymal stem cells in regenerative rehabilitation

[Purpose] Regenerative medicine and rehabilitation contribute in many ways to a specific plan of care based on a patient’s medical status. The intrinsic self-renewing, multipotent, regenerative, and immunosuppressive properties of mesenchymal stem cells offer great promise in the treatment of numerous autoimmune, degenerative, and graft-versus-host diseases, as well as tissue injuries. As such, mesenchymal stem cells represent a therapeutic fortune in regenerative medicine. The aim of this review is to discuss possibilities, limitations, and future clinical applications of mesenchymal stem cells. [Subjects and Methods] The authors have identified and discussed clinically and scientifically relevant articles from PubMed that have met the inclusion criteria. [Results] Direct treatment of muscle injuries, stroke, damaged peripheral nerves, and cartilage with mesenchymal stem cells has been demonstrated to be effective, with synergies seen between cellular and physical therapies. Over the past few years, several researchers, including us, have shown that there are certain limitations in the use of mesenchymal stem cells. Aging and spontaneous malignant transformation of mesenchymal stem cells significantly affect the functionality of these cells. [Conclusion] Definitive conclusions cannot be made by these studies because limited numbers of patients were included. Studies clarifying these results are expected in the near future.