Heparan sulfate mimetics modulate calpain activity during rat Soleus muscle regeneration

Muscular Contribution to Adolescent Idiopathic Scoliosis from the Perspective of Stem Cell-Based Regenerative Medicine

Adolescent idiopathic scoliosis (AIS) is a relatively frequent disease within a range 0.5%-5.0% of population, with higher frequency in females. While a resultant spinal deformity is usually medically benign condition, it produces far going psychosocial consequences, which warrant attention. The etiology of AIS is unknown and current therapeutic approaches are symptomatic only, and frequently inconvenient or invasive. Muscular contribution to AIS is widely recognized, although it did not translate to clinical routine as yet. Muscle asymmetry has been documented by pathological examinations as well as systemic muscle disorders frequently leading to scoliosis. It has been also reported numerous genetic, metabolic and radiological alterations in patients with AIS, which are linked to muscular and neuromuscular aspects. Therefore, muscles might be considered an attractive and still insufficiently exploited therapeutic target for AIS. Stem cell-based regenerative medicine is rapidly gaining momentum based on the tremendous progress in understanding of developmental biology. It comes also with a toolbox of various stem cells such as satellite cells or mesenchymal stem cells, which could be transplanted; also, the knowledge acquired in research on regenerative medicine can be applied to manipulation of endogenous stem cells to obtain desired therapeutic goals. Importantly, paravertebral muscles are located relatively superficially; therefore, they can be an easy target for minimally invasive approaches to treatment of AIS. It comes in pair with a fast progress in image guidance, which allows for precise delivery of therapeutic agents, including stem cells to various organs such as brain, muscles, and others. Summing up, it seems that there is a link between AIS, muscles, and stem cells, which might be worth of further investigations with a long-term goal of setting foundations for eventual bench-to-bedside translation.

IL-4 and SDF-1 Increase Adipose Tissue-Derived Stromal Cell Ability to Improve Rat Skeletal Muscle Regeneration

Skeletal muscle regeneration depends on the satellite cells, which, in response to injury, activate, proliferate, and reconstruct damaged tissue. However, under certain conditions, such as large injuries or myopathies, these cells might not sufficiently support repair. Thus, other cell populations, among them adipose tissue-derived stromal cells (ADSCs), are tested as a tool to improve regeneration. Importantly, the pro-regenerative action of such cells could be improved by various factors. In the current study, we tested whether IL-4 and SDF-1 could improve the ability of ADSCs to support the regeneration of rat skeletal muscles. We compared their effect at properly regenerating fast-twitch EDL and poorly regenerating slow-twitch soleus. To this end, ADSCs subjected to IL-4 and SDF-1 were analyzed in vitro and also in vivo after their transplantation into injured muscles. We tested their proliferation rate, migration, expression of stem cell markers and myogenic factors, their ability to fuse with myoblasts, as well as their impact on the mass, structure and function of regenerating muscles. As a result, we showed that cytokine-pretreated ADSCs had a beneficial effect in the regeneration process. Their presence resulted in improved muscle structure and function, as well as decreased fibrosis development and a modulated immune response.

Human and mouse skeletal muscle stem and progenitor cells in health and disease

The proper functioning of tissues and organs depends on their ability to self-renew and repair. Some of the tissues, like epithelia, renew almost constantly while in the others this process is induced by injury or diseases. The stem or progenitor cells responsible for tissue homeostasis have been identified in many organs. Some of them, such as hematopoietic or intestinal epithelium stem cells, are multipotent and can differentiate into various cell types. Others are unipotent. The skeletal muscle tissue does not self-renew spontaneously, however, it presents unique ability to regenerate in response to the injury or disease. Its repair almost exclusively relies on unipotent satellite cells. However, multiple lines of evidence document that some progenitor cells present in the muscle can be supportive for skeletal muscle regeneration. Here, we summarize the current knowledge on the complicated landscape of stem and progenitor cells that exist in skeletal muscle and support its regeneration. We compare the cells from two model organisms, i.e., mouse and human, documenting their similarities and differences and indicating methods to test their ability to undergo myogenic differentiation.

Inflammatory response during slow- and fast-twitch muscle regeneration

INTRODUCTION

Skeletal muscles are characterized by their unique ability to regenerate. Injury of a so-called fast-twitch muscle, extensor digitorum longus (EDL), results in efficient regeneration and reconstruction of the functional tissue. In contrast, slow-twitch muscle (soleus) fails to properly reconstruct and develops fibrosis. This study focuses on soleus and EDL muscle regeneration and associated inflammation.

METHODS

We determined differences in the activity of neutrophils and M1 and M2 macrophages using flow cytometry and differences in the levels of proinflammatory cytokines using Western blotting and immunolocalization at different times after muscle injury.

RESULTS

Soleus muscle repair is accompanied by increased and prolonged inflammation, as compared to EDL. The proinflammatory cytokine profile is different in the soleus and ED muscles.

CONCLUSIONS

Muscle repair efficiency differs by muscle fiber type. The inflammatory response affects the repair efficiency of slow- and fast-twitch muscles. Muscle Nerve 55: 400-409, 2017.

Rat Model of Parkes Weber Syndrome

The Parkes Weber syndrome is a congenital vascular malformation, characterized by varicose veins, arterio-venous fistulas and overgrown limbs. No broadly accepted animal model of Parkes Weber syndrome has been described. We created side-to-side arterio-venous fistula between common femoral vessels with proximal non-absorbable ligature on common femoral vein limiting the enlargement of the vein diameter in Wistar rats. Contralateral limb was sham operated. Invasive blood pressure measurements in both iliac and inferior cava veins were performed in rats 30 days after fistula creation. Tight circumference and femoral bone length were measured. Histopathology and morphology of soleus muscle, extensor digitorum longus muscle, and the common femoral vessel were analyzed. 30 days following arterio-venous fistula creation, a statistically significant elevation of blood pressure in common iliac vein and limb overgrowth was observed. Limb enlargement was caused by muscle overgrowth, varicose veins formation and bone elongation. Arterio-venous fistula with proximal outflow limitation led to significant increase of femoral vein circumference and venous wall thickness. Our study indicates that the described rat model mimics major clinical features characteristic for the human Parkes Weber syndrome: presence of arterio-venous fistula, venous hypertension and dilatation, varicose veins formation, and the limb hypertrophy. We reveal that limb overgrowth is caused by bone elongation, muscle hypertrophy, and venous dilatation. The newly established model will permit detailed studies on the mechanisms underlying the disease and on the efficacy of novel therapeutic strategies for the Parkes Weber syndrome treatment.

Activation of p38 signaling increases utrophin A expression in skeletal muscle via the RNA-binding protein KSRP and inhibition of AU-rich element-mediated mRNA decay: implications for novel DMD therapeutics

Several therapeutic approaches are currently being developed for Duchenne muscular dystrophy (DMD) including upregulating the levels of endogenous utrophin A in dystrophic fibers. Here, we examined the role of post-transcriptional mechanisms in controlling utrophin A expression in skeletal muscle. We show that activation of p38 leads to an increase in utrophin A independently of a transcriptional induction. Rather, p38 controls the levels of utrophin A mRNA by extending the half-life of transcripts via AU-rich elements (AREs). This mechanism critically depends on a decrease in the functional availability of KSRP, an RNA-binding protein known to promote decay of ARE-containing transcripts. In vitro and in vivo binding studies revealed that KSRP interacts with specific AREs located within the utrophin A 3' UTR. Electroporation experiments to knockdown KSRP led to an increase in utrophin A in wild-type and mdx mouse muscles. In pre-clinical studies, treatment of mdx mice with heparin, an activator of p38, causes a pronounced increase in utrophin A in diaphragm muscle fibers. Together, these studies identify a pathway that culminates in the post-transcriptional regulation of utrophin A through increases in mRNA stability. Furthermore, our results constitute proof-of-principle showing that pharmacological activation of p38 may prove beneficial as a novel therapeutic approach for DMD.

A Rodent Model to Advance the Field Treatment of Crush Muscle Injury During Earthquakes and Other Natural Disasters

Approximately 170 earthquakes of 6.0 or higher magnitude occur annually worldwide. Victims often suffer crush muscle injuries involving impaired blood flow to the affected muscle and damage to the muscle fiber membrane. Current rescue efforts are directed toward preventing acute kidney injury (AKI), which develops upon extrication and muscle reperfusion. But field-usable, muscle-specific interventions may promote muscle regeneration and prevent or minimize the pathologic changes of reperfusion. Although current rodent crush injury models involve reperfusion upon removal of the crush stimulus, an analysis of their methodological aspects is needed to ensure adequate simulation of the earthquake-related crush injury. The objectives of this systematic review are to (a) describe rodent crush muscle injury models, (b) discuss the benefits and limitations of these models, and (c) offer a recommendation for animal models that would increase our understanding of muscle recovery processes after an earthquake-induced crush muscle injury. The most commonly used rodent model uses a clamping or pressing crush stimulus directly applied to murine hindlimb muscle. This model has increased our understanding of muscle regeneration but its open approach does not adequately represent the earthquake-related crush injury. The model we recommend for developing field-usable, muscle-specific interventions is a closed approach that involves a nonclamping crush stimulus. Findings from studies employing this recommended model may have greater relevance for developing interventions that lessen the earthquake’s devastating impact on individual and community health and quality of life, especially in developing countries.

Cell cycle regulation during proliferation and differentiation of mammalian muscle precursor cells

Proliferation and differentiation of muscle precursor cells are intensively studied not only in the developing mouse embryo but also using models of skeletal muscle regeneration or analyzing in vitro cultured cells. These analyses allowed to show the universality of the cell cycle regulation and also uncovered tissue-specific interplay between major cell cycle regulators and factors crucial for the myogenic differentiation. Examination of the events accompanying proliferation and differentiation leading to the formation of functional skeletal muscle fibers allows understanding the molecular basis not only of myogenesis but also of skeletal muscle regeneration. This chapter presents the basis of the cell cycle regulation in proliferating and differentiating muscle precursor cells during development and after muscle injury. It focuses at major cell cycle regulators, myogenic factors, and extracellular environment impacting on the skeletal muscle.

Glycosaminoglycan mimetics trigger IP3-dependent intracellular calcium release in myoblasts

Glycosaminoglycans (GAG) are sulfated polysaccharides that play an important role in regulating cell functions. GAG mimetics called RGTAs (for ReGeneraTing Agents) have been shown to stimulate tissue repair. In particular they accelerate myogenesis, in part via their heparin-mimetic property towards growth factors. RGTAs also increase activity of calcium-dependent intracellular protease suggesting an effect on calcium cellular homeostasis. This effect was presently investigated on myoblasts in vitro using one member of the RGTA family molecule named OTR4120. We have shown that OTR4120 or heparin induced transient increases of intracellular calcium concentration ([Ca(2+)]i) in pre-fusing myoblasts from both mouse SolD7 cell line and rat skeletal muscle satellite cells grown in primary culture by mobilising sarcoplasmic reticulum store. This [Ca(2+)]i was not mediated by ryanodine receptors but instead resulted from stimulation of the Inositol-3 phosphate-phospholipase C activation pathway. OTR4120-induced calcium transient was not mediated through an ATP, nor a tyrosine kinase, nor an acetylcholine receptor but principally through serotonin 5-HT2A receptor. This original finding shows that the GAG mimetic can induce calcium signal through serotonin receptors and the IP3 pathway may be relevant to its ability to favour myoblast differentiation. It supports a novel and unexpected function of GAGs in the regulation of calcium homeostasis.

Novel glycosaminoglycan mimetic (RGTA, RGD120) contributes to enhance skeletal muscle satellite cell fusion by increasing intracellular Ca2+ and calpain activity

Glycosaminoglycans (GAG) are classes of molecules that play an important role in cellular processes. The use of GAG mimetics called regenerating agent (RGTA) represents a tool to investigate the effect of GAG moiety on cellular behavior. A first member of the RGTA family (RG1192), a dextran polymers with defined amounts of sulfate, carboxymethyl, as well as hydrophobic groups (benzylamide), was shown to stimulate skeletal muscle repair after damage and myoblast differentiation. To obtain a comprehensive insight into the mechanism of action of GAG mimetics, we investigated the effect on myoblast differentiation of a novel RGTA, named RGD120, which was devoid of hydrophobic substitution and had ionic charge similar to heparin. Myoblasts isolated from adult rat skeletal muscles and grown in primary cultures were used in this study. We found that chronic treatment with RGD120 increased the growth of adult myoblasts and induced their precocious fusion into myotubes in vitro. It also partially overcame the inhibitory effect of the calpain inhibitor N-acetyl-leu-leu-norleucinal (ALLN) on these events. Western blot and zymography analyses revealed that milli calpain was slightly increased by RGD120 chronic treatment. In addition, using fluorescent probes (Indo-1 and Boc-leu-met-MAC), we demonstrated that RGD120 added to prefusing myoblast cultures accelerates myoblast fusion into myotubes, induced an increase of cytosolic free calcium concentration, and concomitantly an increase of intracellular calpain protease activity. Altogether, these results suggested that the efficiency of RGD120 in stimulating myogenesis might be in part explained through its effect on calcium mobilization as well as on the calpain amount and activity.

A synthetic glycosaminoglycan mimetic (RGTA) modifies natural glycosaminoglycan species during myogenesis

Crucial events in myogenesis rely on the highly regulated spatiotemporal distribution of cell surface heparan sulfate proteoglycans to which are associated growth factors, thus creating a specific microenvironment around muscle cells. Most growth factors involved in control of myoblast growth and differentiation are stored in the extracellular matrix through interaction with specific sequences of glycosaminoglycan oligosaccharides, mainly heparan sulfate (HS). Different HS subspecies revealed by specific antibodies, have been shown to provide spatiotemporal regulation during muscle development. We have previously shown that glycosaminoglycan (GAG) mimetics called RGTA (ReGeneraTing Agent), stimulate muscle precursor cell growth and differentiation. These data suggest an important role of GAGs during myogenesis; however, little is yet known about the different species of GAGs synthesized during myogenesis and their metabolic regulation. We therefore quantified GAGs during myogenesis of C2.7 cells and show that the composition of GAG species was modified during myogenic differentiation. In particular, HS levels were increased during this process. In addition, the GAG mimetic RGTA, which stimulated both growth and differentiation of C2.7 cells, increased the total amount of GAG produced by these cells without significantly altering their rate of sulfation. RGTA treatment further enhanced HS levels and changed its sub-species composition. Although mRNA levels of the enzymes involved in HS biosynthesis were almost unchanged during myogenic differentiation, heparanase mRNA levels decreased. RGTA did not markedly alter these levels. Here we show that the effects of RGTA on myoblast growth and differentiation are in part mediated through an alteration of GAG species and provide an important insight into the role of these molecules in normal or pathologic myogenic processes.

Myogenic and nonmyogenic cells differentially express proteinases, Hsc/Hsp70, and BAG-1 during skeletal muscle regeneration

Skeletal muscle has a remarkable capacity to regenerate after injury. To determine whether changes in the expression of proteinases, 73-kDa constitutive heat shock cognate protein (Hsc70) and stress-inducible 72-kDa heat shock protein (Hsp70) (Hsc/Hsp70), and Bcl-2-associated gene product-1 (BAG-1) contribute to the remodeling response of muscle tissue, tibialis anterior muscles of male Sprague-Dawley rats were injected with 0.75% bupivacaine and removed at 3, 5, 7, 10, 14, 21, or 35 days postinjection (n = 5-7/group). The immunohistochemical analysis of desmin, alpha-actin, and developmental/neonatal myosin heavy chain expressions indicated the presence of myoblasts (days 3-7), inflammatory cells (days 3-7), degenerating myofibers (days 3-7), regenerating myofibers (days 5-10), and growing mature myofibers (days 10-21) in regenerating muscles. Our biochemical analysis documented profound adaptations in proteolytic metabolism characterized by significant increases in the enzyme activities of matrix metalloproteinases 2 and 9 and plasminogen activators (days 3-14), calpains 1 and 2 (days 3-7), cathepsins B and L(days 3-10), and proteasome (days 3-14). Proteasome activity was strongly correlated with proliferating cell nuclear antigen protein level, suggesting that proteasome played a key role in myoblast proliferation. The expression pattern of BAG-1, a regulatory cofactor of Hsc/Hsp70 at the interface between protein folding and proteasomal proteolysis, did not corroborate the changes in proteasome enzyme activity, suggesting that BAG-1 may promote other functions, such as the folding capacity of Hsc/Hsp70. Altogether, the diversity of functions attributed to proteinases in the present study was strongly supported by the relative changes in the proportion of myogenic and nonmyogenic cells over the time course of regeneration.

Glycosaminoglycan mimetics (RGTA) modulate adult skeletal muscle satellite cell proliferation in vitro

Muscle regeneration occurs through the activation of satellite cells, which are stimulated to proliferate and to fuse into myofibers that will reconstitute the damaged muscle. We have previously reported that a family of new compounds called "regenerating agents" (RGTAs), which are polymers engineered to mimic heparan sulfates, stimulate in vivo tissue repair. One of these agents, RG1192, a dextran derivative substituted by CarboxyMethyl, Benzylamide, and Sulfate (noted CMBS, RGTA type), was shown to improve greatly the regeneration of rat skeletal muscle after severe crushing, denervation, and acute ischemia. In vitro, these compounds mimic the protecting and stabilizing properties of heparin or heparan sulfates toward heparin-binding growth factors (HBGFs). We hypothesized that RGTA could act by increasing the bioavailability of some HBGF involved in myoblast growth and thus asked whether RGTA would alter the ability of satellite cells to proliferate. Its effect was tested on primary cultures of rat satellite cells. The RG1192 stimulated the proliferation of satellite cells in vitro in a dose-dependent manner. It appeared to be as efficient as natural glycosaminoglycans (GAGs; heparan sulfate, dermatan sulfate, or keratan sulfate) in stimulating satellite cell proliferation but was about 100 times more efficient than heparin. RG1192 stimulated satellite cell proliferation by increasing the potency of fibroblast growth factor 2 and scatter factor-hepatocyte growth factor. It also partially restored myoblast proliferation of satellite cells with chlorate-induced hyposulfation. Taken together, our results explain to some extent the improving effect of RGTA with a CMBS structure, such as the RG1192, on muscle regeneration in vivo by providing support for the hypothesis that RGTA may act by increasing the potency of some HBGFs during the proliferation phase of the regenerating muscle.

Differential changes in protein kinase C associated with regeneration of rat extensor digitorum longus and soleus muscles

We used a model of crush-induced regeneration in rat in order to characterize biochemically and histologically the implication of protein kinase C (PKC) in muscle repair after damage. In this model, slow soleus and fast extensor digitorum longus (EDL) muscle regeneration proceed differently. PKC activity has been assayed in regenerating muscles and their intact contralateral during the first 14 days following crushing. Degeneration (myolysis) occurring shortly after crush was associated with a marked down-regulation of the enzyme in both wound muscles and notable increase in the corresponding contralateral muscles. Muscle fiber reconstruction in EDL was associated with a rise in PKC activity which peaked at day 7 in regenerating muscle where it was twice higher than in intact muscle. At variance, muscle PKC activity in soleus increased slower than that of EDL and reached later intact level. Western blot analysis and immunohistochemical studies of representative members of the three PKC subfamilies were performed. All the isoform tested were much less expressed in regenerating than in control intact muscles suggesting that the overall PKC activity in regenerating muscles was more activable than in controls. We have shown that PKC isoforms were sequentially expressed during regeneration in both muscle types. PKC theta; being present the earliest, then delta, epsilon and alpha and finally zeta, beta and eta. Some isoforms were differentially expressed according muscle type. PKC delta being more expressed in soleus whereas beta and eta appeared earlier in EDL. Histochemical studies have revealed that the isoforms were differently localized in muscle tissue and that fiber regeneration was associated with PKC alpha translocation from sarcoplasma to sarcolemma. Together these data have shown that multiple PKC isoforms are implicated in the regenerative process acting at different in times and location and suggesting that individual isoform may fulfill distinct functions.