Pax3/7 gene function in Oikopleura dioica supports a neuroepithelial-like origin for its house-making Fol territory.

Larvacean tunicates feature a spectacular innovation not seen in other animals - the trunk oikoplastic epithelium (OE). This epithelium produces a house, a large and complex extracellular structure used for filtering and concentrating food particles. Previously we identified several homeobox transcription factor genes expressed during early OE patterning. Among these are two Pax3/7 copies that we named pax37A and pax37B. The vertebrate homologs, PAX3 and PAX7 are involved in developmental processes related to neural crest and muscles. In the ascidian tunicate Ciona intestinalis, Pax3/7 plays a role in the development of cells deriving from the neural plate border, including trunk epidermal sensory neurons and tail nerve cord neurons, as well as in the neural tube closure. Here we have investigated the roles of Oikopleura dioica pax37A and pax37B in the development of the OE, by using CRISPR-Cas9 mutant lines and analyzing scRNA-seq data from wild-type animals. We found that pax37B but not pax37A is essential for the differentiation of cell fields that produce the food concentrating filter of the house: the anterior Fol, giant Fol and Nasse cells. Trajectory analysis supported a neuroepithelial-like or a preplacodal ectoderm transcriptional signature in these cells. We propose that the highly specialized secretory epithelial cells of the Fol region either maintained or evolved neuroepithelial features. This is supported by a fragmented gene regulatory network involved in their development that also operates in ascidian epidermal neurons.

Inhibition of Sesn2 has negative regulatory effects on the myogenic differentiation of C2C12 myoblasts.

Sestrin2 (Sesn2) has been previously confirmed to be a stress-response molecule. However, the influence of Sesn2 on myogenic differentiation remains elusive. This study was conducted to analyze the role of Sesn2 in the myogenic differentiation of C2C12 myoblasts and related aspects in mdx mice, an animal model of Duchenne muscular dystrophy (DMD). Our results showed that knockdown of Sesn2 reduced the myogenic differentiation capacity of C2C12 myoblasts. Predictive analysis from two databases suggested that miR-182-5p is a potential regulator of Sesn2. Further experimental validation revealed that overexpression of miR-182-5p decreased both the protein and mRNA levels of Sesn2 and inhibited myogenesis of C2C12 myoblasts. These findings suggest that miR-182-5p negatively regulates myogenesis by repressing Sesn2 expression. Extending to an in vivo model of DMD, knockdown of Sesn2 led to decreased Myogenin (Myog) expression and increased Pax7 expression, while its overexpression upregulated Myog levels and enhanced the proportion of slow-switch myofibers. These findings indicate the crucial role of Sesn2 in promoting myogenic differentiation and skeletal muscle regeneration, providing potential therapeutic targets for muscular dystrophy.

Development of a local controlled release system for therapeutic proteins in the treatment of skeletal muscle injuries and diseases.

The present study aims to develop and characterize a controlled-release delivery system for protein therapeutics in skeletal muscle regeneration following an acute injury. The therapeutic protein, a membrane-GPI anchored protein called Cripto, was immobilized in an injectable hydrogel delivery vehicle for local administration and sustained release. The hydrogel was made of poly(ethylene glycol)-fibrinogen (PEG-Fibrinogen, PF), in the form of injectable microspheres. The PF microspheres exhibited a spherical morphology with an average diameter of approximately 100 micrometers, and the Cripto protein was uniformly entrapped within them. The release rate of Cripto from the PF microspheres was controlled by tuning the crosslinking density of the hydrogel, which was varied by changing the concentration of poly(ethylene glycol) diacrylate (PEG-DA) crosslinker. In vitro experiments confirmed a sustained-release profile of Cripto from the PF microspheres for up to 27 days. The released Cripto was biologically active and promoted the in vitro proliferation of mouse myoblasts. The therapeutic effect of PF-mediated delivery of Cripto in vivo was tested in a cardiotoxin (CTX)-induced muscle injury model in mice. The Cripto caused an increase in the in vivo expression of the myogenic markers Pax7, the differentiation makers eMHC and Desmin, higher numbers of centro-nucleated myofibers and greater areas of regenerated muscle tissue. Collectively, these results establish the PF microspheres as a potential delivery system for the localized, sustained release of therapeutic proteins toward the accelerated repair of damaged muscle tissue following acute injuries.

Loss of Tob1 promotes muscle regeneration through muscle stem cell expansion.

Muscle stem cells (MuSCs) play an indispensable role in postnatal muscle growth and hypertrophy in adults. MuSCs also retain a highly regenerative capacity and are therefore considered a promising stem cell source for regenerative therapy for muscle diseases. In this study, we identify tumor-suppressor protein Tob1 as a Pax7 target protein that negatively controls the population expansion of MuSCs. Tob1 protein is undetectable in the quiescent state but is upregulated during activation in MuSCs. Tob1 ablation in mice accelerates MuSC population expansion and boosts muscle regeneration. Moreover, inactivation of Tob1 in MuSCs ameliorates the efficiency of MuSC transplantation in a murine muscular dystrophy model. Collectively, selective targeting of Tob1 might be a therapeutic option for the treatment of muscular diseases, including muscular dystrophy and age-related sarcopenia.

Targeted expression of heme oxygenase-1 in satellite cells improves skeletal muscle pathology in dystrophic mice.

BACKGROUND: Adult muscle-resident myogenic stem cells, satellite cells (SCs), that play non-redundant role in muscle regeneration, are intrinsically impaired in Duchenne muscular dystrophy (DMD). Previously we revealed that dystrophic SCs express low level of anti-inflammatory and anti-oxidative heme oxygenase-1 (HO-1, HMOX1). Here we assess whether targeted induction of HMOX1 affect SC function and alleviates hallmark symptoms of DMD. METHODS: We generated double-transgenic mouse model (mdx;HMOX1Pax7Ind) that allows tamoxifen (TX)-inducible HMOX1 expression in Pax7 positive cells of dystrophic muscles. Mdx;HMOX1Pax7Ind and control mdx mice were subjected to 5-day TX injections (75 mg/kg b.w.) followed by acute exercise protocol with high-speed treadmill (12 m/min, 45 min) and downhill running to worsen skeletal muscle phenotype and reveal immediate effects of HO-1 on muscle pathology and SC function. RESULTS: HMOX1 induction caused a drop in SC pool in mdx;HMOX1Pax7Ind mice (vs. mdx counterparts), while not exaggerating the effect of physical exercise. Upon physical exercise, the proliferation of SCs and activated CD34- SC subpopulation, was impaired in mdx mice, an effect that was reversed in mdx;HMOX1Pax7Ind mice, however, both in vehicle- and TX-treated animals. This corresponded to the pattern of HO-1 expression in skeletal muscles. At the tissue level, necrotic events of selective skeletal muscles of mdx mice and associated increase in circulating levels of muscle damage markers were blunted in HO-1 transgenic animals which showed also anti-inflammatory cytokine profile (vs. mdx). CONCLUSIONS: Targeted expression of HMOX1 plays protective role in DMD and alleviates dystrophic muscle pathology.

Interplay between Pitx2 and Pax7 temporally governs specification of extraocular muscle stem cells.

Gene regulatory networks that act upstream of skeletal muscle fate determinants are distinct in different anatomical locations. Despite recent efforts, a clear understanding of the cascade of events underlying the emergence and maintenance of the stem cell pool in specific muscle groups remains unresolved and debated. Here, we invalidated Pitx2 with multiple Cre-driver mice prenatally, postnatally, and during lineage progression. We showed that this gene becomes progressively dispensable for specification and maintenance of the muscle stem (MuSC) cell pool in extraocular muscles (EOMs) despite being, together with Myf5, a major upstream regulator during early development. Moreover, constitutive inactivation of Pax7 postnatally led to a greater loss of MuSCs in the EOMs compared to the limb. Thus, we propose a relay between Pitx2, Myf5 and Pax7 for EOM stem cell maintenance. We demonstrate also that MuSCs in the EOMs adopt a quiescent state earlier that those in limb muscles and do not spontaneously proliferate in the adult, yet EOMs have a significantly higher content of Pax7+ MuSCs per area pre- and post-natally. Finally, while limb MuSCs proliferate in the mdx mouse model for Duchenne muscular dystrophy, significantly less MuSCs were present in the EOMs of the mdx mouse model compared to controls, and they were not proliferative. Overall, our study provides a comprehensive in vivo characterisation of MuSC heterogeneity along the body axis and brings further insights into the unusual sparing of EOMs during muscular dystrophy.

Isolation of a persistently quiescent muscle satellite cell population.

Although studies have identified characteristics of quiescent satellite cells (SCs), their isolation has been hampered by the fact that the isolation procedures result in the activation of these cells into their rapidly proliferating progeny (myoblasts). Thus, the use of myoblasts for therapeutic (regenerative medicine) or industrial applications (cellular agriculture) has been impeded by the limited proliferative and differentiative capacity of these myogenic progenitors. Here we identify a subpopulation of satellite cells isolated from mouse skeletal muscle using flow cytometry that is highly Pax7-positive, exhibit a very slow proliferation rate (7.7 ± 1.2 days/doubling), and are capable of being maintained in culture for at least 3 mo without a change in phenotype. These cells can be activated from quiescence using a p38 inhibitor or by exposure to freeze-thaw cycles. Once activated, these cells proliferate rapidly (22.7 ± 0.2 h/doubling), have reduced Pax7 expression (threefold decrease in Pax7 fluorescence vs. quiescence), and differentiate into myotubes with a high efficiency. Furthermore, these cells withstand freeze-thawing readily without a significant loss of viability (83.1 ± 2.1% live). The results presented here provide researchers with a method to isolate quiescent satellite cells, allowing for more detailed examinations of the factors affecting satellite cell quiescence/activation and providing a cell source that has a unique potential in the regenerative medicine and cellular agriculture fields.NEW & NOTEWORTHY We provide a method to isolate quiescent satellite cells from skeletal muscle. These cells are highly Pax7-positive, exhibit a very slow proliferation rate, and are capable of being maintained in culture for months without a change in phenotype. The use of these cells by muscle researchers will allow for more detailed examinations of the factors affecting satellite cell quiescence/activation and provide a novel cell source for the regenerative medicine and cellular agriculture fields.

A dual-color PAX7 and MYF5 in vivo reporter to investigate muscle stem cell heterogeneity in regeneration and aging.

Increasing evidence suggests that the muscle stem cell (MuSC) pool is heterogeneous. In particular, a rare subset of PAX7-positive MuSCs that has never expressed the myogenic regulatory factor MYF5 displays unique self-renewal and engraftment characteristics. However, the scarcity and limited availability of protein markers make the characterization of these cells challenging. Here, we describe the generation of StemRep reporter mice enabling the monitoring of PAX7 and MYF5 proteins based on equimolar levels of dual nuclear fluorescence. High levels of PAX7 protein and low levels of MYF5 delineate a deeply quiescent MuSC subpopulation with an increased capacity for asymmetric division and distinct dynamics of activation, proliferation, and commitment. Aging primarily reduces the MYF5Low MuSCs and skews the stem cell pool toward MYF5High cells with lower quiescence and self-renewal potential. Altogether, we establish the StemRep model as a versatile tool to study MuSC heterogeneity and broaden our understanding of mechanisms regulating MuSC quiescence and self-renewal in homeostatic, regenerating, and aged muscles.

Photobiomodulation mitigates Bothrops jararacussu venom-induced damage in myoblast cells by enhancing myogenic factors and reducing cytokine production.

BACKGROUND: Photobiomodulation has exhibited promise in mitigating the local effects induced by Bothrops snakebite envenoming; however, the mechanisms underlying this protection are not yet fully understood. Herein, the effectiveness of photobiomodulation effects on regenerative response of C2C12 myoblast cells following exposure to Bothrops jararacussu venom (BjsuV), as well as the mechanisms involved was investigated. METHODOLOGY/PRINCIPAL FINDINGS: C2C12 myoblast cells were exposed to BjsuV (12.5 µg/mL) and irradiated once for 10 seconds with laser light of 660 nm (14.08 mW; 0.04 cm2; 352 mW/cm2) or 780 nm (17.6 mW; 0.04 cm2; 440 mW/ cm2) to provide energy densities of 3.52 and 4.4 J/cm2, and total energies of 0.1408 and 0.176 J, respectively. Cell migration was assessed through a wound-healing assay. The expression of MAPK p38-α, NF-Кß, Myf5, Pax-7, MyoD, and myogenin proteins were assessed by western blotting analysis. In addition, interleukin IL1-ß, IL-6, TNF-alfa and IL-10 levels were measured in the supernatant by ELISA. The PBM applied to C2C12 cells exposed to BjsuV promoted cell migration, increase the expression of myogenic factors (Pax7, MyF5, MyoD and myogenin), reduced the levels of proinflammatory cytokines, IL1-ß, IL-6, TNF-alfa, and increased the levels of anti-inflammatory cytokine IL-10. In addition, PBM downregulates the expression of NF-kB, and had no effect on p38 MAKP. CONCLUSION/SIGNIFICANCE: These data demonstrated that protection of the muscle cell by PBM seems to be related to the increase of myogenic factors as well as the modulation of inflammatory mediators. PBM therapy may offer a new therapeutic strategy to address the local effects of snakebite envenoming by promoting muscle regeneration and reducing the inflammatory process.

Dynamics of pax7 expression during development, muscle regeneration, and in vitro differentiation of satellite cells in rainbow trout (Oncorhynchus mykiss).

Essential for muscle fiber formation and hypertrophy, muscle stem cells, also called satellite cells, reside beneath the basal lamina of the muscle fiber. Satellite cells have been commonly identified by the expression of the Paired box 7 (Pax7) due to its specificity and the availability of antibodies in tetrapods. In fish, the identification of satellite cells remains difficult due to the lack of specific antibodies in most species. Based on the development of a highly sensitive in situ hybridization (RNAScope®) for pax7, we showed that pax7+ cells were detected in the undifferentiated myogenic epithelium corresponding to the dermomyotome at day 14 post-fertilization in rainbow trout. Then, from day 24, pax7+ cells gradually migrated into the deep myotome and were localized along the muscle fibers and reach their niche in satellite position of the fibres after hatching. Our results showed that 18 days after muscle injury, a large number of pax7+ cells accumulated at the wound site compared to the uninjured area. During the in vitro differentiation of satellite cells, the percentage of pax7+ cells decreased from 44% to 18% on day 7, and some differentiated cells still expressed pax7. Taken together, these results show the dynamic expression of pax7 genes and the follow-up of these muscle stem cells during the different situations of muscle fiber formation in trout.

Pax7 is involved in leucophore formation in goldfish and gene knockout improves the transparency of transparent goldfish.

Lines with few or no pigment cells have been established in fishes, and these lines are useful for bioimaging. The transparent goldfish (tra) line previously established by N-ethyl-N-nitrosourea (ENU) mutagenesis is also suitable for such experiments. However, in the case of tra, leucophores form in the adult fish, making it difficult to observe the organs inside body from outside the body. In this study, we attempted to create a knockout line of the pax7a and pax7b genes, which are thought to be involved in the formation of leucophores, to further improve the transparency of tra strain.Mutations were introduced by microinjection of the CRISPR/Cas9 mixture into single-cell embryos, mutant individuals were found in F0, and the next generation was generated to confirm the mutation patterns. As a result, multiple mutation patterns, including knockout, were obtained. The same pattern of knockout F1 with pax7a and pax7b mutations was crossed to generate a homozygous knockout in F2.In the resulting pax7b-/- (tra) fish but not in pax7a-/- (tra) fish, the number of leucophores was reduced compared to that in tra, and the transparency of the body was improved. It was suggested that pax7b plays an important role in leucophore formation in goldfish. The established transparent pax7b-/- (tra) goldfish line will be a useful model for bioimaging of the body interior.

Deletion of TECRL promotes skeletal muscle repair by up-regulating EGR2.

Myogenic regeneration relies on the proliferation and differentiation of satellite cells. TECRL (trans-2,3-enoyl-CoA reductase like) is an endoplasmic reticulum protein only expressed in cardiac and skeletal muscle. However, its role in myogenesis remains unknown. We show that TECRL expression is increased in response to injury. Satellite cell-specific deletion of TECRL enhances muscle repair by increasing the expression of EGR2 through the activation of the ERK1/2 signaling pathway, which in turn promotes the expression of PAX7. We further show that TECRL deletion led to the upregulation of the histone acetyltransferase general control nonderepressible 5, which enhances the transcription of EGR2 through acetylation. Importantly, we showed that AAV9-mediated TECRL silencing improved muscle repair in mice. These findings shed light on myogenic regeneration and muscle repair.

Exchange of subtelomeric regions between chromosomes 4q and 10q reverts the FSHD genotype and phenotype.

The most common form of facioscapulohumeral dystrophy (FSHD1) is caused by a partial loss of the D4Z4 macrosatellite repeat array in the subtelomeric region of chromosome 4. Patients with FSHD1 typically carry 1 to 10 D4Z4 repeats, whereas nonaffected individuals have 11 to 150 repeats. The ~150-kilobyte subtelomeric region of the chromosome 10q exhibits a ~99% sequence identity to the 4q, including the D4Z4 array. Nevertheless, contractions of the chr10 array do not cause FSHD or any known disease, as in most people D4Z4 array on chr10 is flanked by the nonfunctional polyadenylation signal, not permitting the DUX4 expression. Here, we attempted to correct the FSHD genotype by a CRISPR-Cas9-induced exchange of the chr4 and chr10 subtelomeric regions. We demonstrated that the induced t(4;10) translocation can generate recombinant genotypes translated into improved FSHD phenotype. FSHD myoblasts with the t(4;10) exhibited reduced expression of the DUX4 targets, restored PAX7 target expression, reduced sensitivity to oxidative stress, and improved differentiation capacity.

Hydrogel/microcarrier cell scaffolds for rapid expansion of satellite cells from large yellow croakers: Differential analysis between 2D and 3D cell culture.

Cell culture meat is based on the scaled-up expansion of seed cells. The biological differences between seed cells from large yellow croakers in the two-dimensional (2D) and three-dimensional (3D) culture systems have not been explored. Here, satellite cells (SCs) from large yellow croakers (Larimichthys crocea) were grown on cell climbing slices, hydrogels, and microcarriers for five days to analyze the biological differences of SCs on different cell scaffolds. The results exhibited that SCs had different cell morphologies in 2D and 3D cultures. Cell adhesion receptors (Itgb1andsdc4) and adhesion spot markervclof the 3D cultures were markedly expressed. Furthermore, myogenic decision markers (Pax7andmyod) were significantly enhanced. However, the expression of myogenic differentiation marker (desmin) was significantly increased in the microcarrier group. Combined with the transcriptome data, this suggests that cell adhesion of SCs in 3D culture was related to the integrin signaling pathway. In contrast, the slight spontaneous differentiation of SCs on microcarriers was associated with rapid cell proliferation. This study is the first to report the biological differences between SCs in 2D and 3D cultures, providing new perspectives for the rapid expansion of cell culture meat-seeded cells and the development of customized scaffolds.

Satellite cells in the growth and maintenance of muscle.

Embryonic skeletal muscle growth is contingent upon a population of somite derived satellite cells, however, the contribution of these cells to early postnatal skeletal muscle growth remains relatively high. As prepubertal postnatal development proceeds, the activity and contribution of satellite cells to skeletal muscle growth diminishes. Eventually, at around puberty, a population of satellite cells escapes terminal commitment, continues to express the paired box transcription factor Pax7, and reside in a quiescent state orbiting the myofiber periphery adjacent to the basal lamina. After adolescence, some satellite cell contributions to muscle maintenance and adaptation occur, however, their necessity is reduced relative to embryonic, early postnatal, and prepubertal growth.

Vitamin C regulates skeletal muscle post-injury regeneration by promoting myoblast proliferation through its direct interaction with the Pax7 protein.

Previous studies have shown that vitamin C (VC), an essential vitamin for the human body, can promote the differentiation of muscle satellite cells (MuSCs) in vitro and play an important role in skeletal muscle post-injury regeneration. However, the molecular mechanism of VC regulating MuSC proliferation has not been elucidated. In this study, the role of VC in promoting MuSC proliferation and its molecular mechanism were explored using cell molecular biology and animal experiments. The results showed that VC accelerates the progress of skeletal muscle post-injury regeneration by promoting MuSC proliferation in vivo. VC can also promote skeletal muscle regeneration in the case of atrophy. Using the C2C12 myoblast murine cell line, we observed that VC also stimulated cell proliferation. In addition, after an in vitro study establishing the occurrence of a physical interaction between VC and Pax7, we observed that VC also upregulated the total and nuclear Pax7 protein levels. This mechanism increased the expression of Myf5 (Myogenic Factor 5), a Pax7 target gene. This study establishes a theoretical foundation for understanding the regulatory mechanisms underlying VC-mediated MuSC proliferation and skeletal muscle regeneration. Moreover, it develops the application of VC in animal muscle nutritional supplements and treatment of skeletal muscle-related diseases.

MyoD Over-Expression Rescues GST-bFGF Repressed Myogenesis.

During embryogenesis, basic fibroblast growth factor (bFGF) is released from neural tube and myotome to promote myogenic fate in the somite, and is routinely used for the culture of adult skeletal muscle (SKM) stem cells (MuSC, called satellite cells). However, the mechanism employed by bFGF to promote SKM lineage and MuSC proliferation has not been analyzed in detail. Furthermore, the question of if the post-translational modification (PTM) of bFGF is important to its stemness-promoting effect has not been answered. In this study, GST-bFGF was expressed and purified from E.coli, which lacks the PTM system in eukaryotes. We found that both GST-bFGF and commercially available bFGF activated the Akt-Erk pathway and had strong cell proliferation effect on C2C12 myoblasts and MuSC. GST-bFGF reversibly compromised the myogenesis of C2C12 myoblasts and MuSC, and it increased the expression of Myf5, Pax3/7, and Cyclin D1 but strongly repressed that of MyoD, suggesting the maintenance of myogenic stemness amid repressed MyoD expression. The proliferation effect of GST-bFGF was conserved in C2C12 over-expressed with MyoD (C2C12-tTA-MyoD), implying its independence of the down-regulation of MyoD. In addition, the repressive effect of GST-bFGF on myogenic differentiation was almost totally rescued by the over-expression of MyoD. Together, these evidences suggest that (1) GST-bFGF and bFGF have similar effects on myogenic cell proliferation and differentiation, and (2) GST-bFGF can promote MuSC stemness and proliferation by differentially regulating MRFs and Pax3/7, (3) MyoD repression by GST-bFGF is reversible and independent of the proliferation effect, and (4) GST-bFGF can be a good substitute for bFGF in sustaining MuSC stemness and proliferation.

The effects of resistance training on denervated myofibers, senescent cells, and associated protein markers in middle-aged adults.

Denervated myofibers and senescent cells are hallmarks of skeletal muscle aging. However, sparse research has examined how resistance training affects these outcomes. We investigated the effects of unilateral leg extensor resistance training (2 days/week for 8 weeks) on denervated myofibers, senescent cells, and associated protein markers in apparently healthy middle-aged participants (MA, 55 ± 8 years old, 17 females, 9 males). We obtained dual-leg vastus lateralis (VL) muscle cross-sectional area (mCSA), VL biopsies, and strength assessments before and after training. Fiber cross-sectional area (fCSA), satellite cells (Pax7+), denervated myofibers (NCAM+), senescent cells (p16+ or p21+), proteins associated with denervation and senescence, and senescence-associated secretory phenotype (SASP) proteins were analyzed from biopsy specimens. Leg extensor peak torque increased after training (p < .001), while VL mCSA trended upward (interaction p = .082). No significant changes were observed for Type I/II fCSAs, NCAM+ myofibers, or senescent (p16+ or p21+) cells, albeit satellite cells increased after training (p = .037). While >90% satellite cells were not p16+ or p21+, most p16+ and p21+ cells were Pax7+ (>90% on average). Training altered 13 out of 46 proteins related to muscle-nerve communication (all upregulated, p < .05) and 10 out of 19 proteins related to cellular senescence (9 upregulated, p < .05). Only 1 out of 17 SASP protein increased with training (IGFBP-3, p = .031). In conclusion, resistance training upregulates proteins associated with muscle-nerve communication in MA participants but does not alter NCAM+ myofibers. Moreover, while training increased senescence-related proteins, this coincided with an increase in satellite cells but not alterations in senescent cell content or SASP proteins. These latter findings suggest shorter term resistance training is an unlikely inducer of cellular senescence in apparently healthy middle-aged participants. However, similar study designs are needed in older and diseased populations before definitive conclusions can be drawn.

Cordyceps sinensis accelerates stem cell recruitment to human skeletal muscle after exercise.

Cordyceps sinensis is a parasitic fungus known to induce immune responses. The impact of Cordyceps supplementation on stem cell homing and expansion to human skeletal muscle after exercise remains unexplored. In this study, we examined how pre-exercise Cordyceps supplementation influences cell infiltration, CD34+ cell recruitment, and Pax7+ cell expansion in human skeletal muscle after high-intensity interval exercise (HIIE) on a cycloergometer. A randomized, double-blind, placebo-controlled crossover study was conducted with 14 young adults (age: 24 ± 0.8 years). A placebo (1 g cornstarch) and Cordyceps (1 g Cordyceps sinensis) were administered before exercise (at 120% maximal aerobic power). Multiple biopsies were taken from the vastus lateralis for muscle tissue analysis before and after HIIE. This exercise regimen doubled the VEGF mRNA in the muscle at 3 h post-exercise (P = 0.006). A significant necrotic cell infiltration (+284%, P = 0.05) was observed 3 h after HIIE and resolved within 24 h. This response was substantially attenuated by Cordyceps supplementation. Moreover, we observed increases in CD34+ cells at 24 h post-exercise, notably accelerated by Cordyceps supplementation to 3 h (+51%, P = 0.002). This earlier response contributed to a four-fold expansion in Pax7+ cell count, as demonstrated by immunofluorescence double staining (CD34+/Pax7+) (P = 0.01). In conclusion, our results provide the first human evidence demonstrating the accelerated resolution of exercise-induced muscle damage by Cordyceps supplementation. This effect is associated with earlier stem cell recruitment into the damaged sites for muscle regeneration.

Unlocking the Potential of Obestatin: A Novel Peptide Intervention for Skeletal Muscle Regeneration and Prevention of Atrophy.

Obestatin is derived from the same gene as that of ghrelin and their functions were perceived to be antagonistic. Recent developments have shown that although they are known to have contradictory functions, effect of obestatin on skeletal muscle regeneration is similar to that of ghrelin. Obestatin works through a receptor called GPR39, a ghrelin and motilin family receptor and transduces signals in skeletal muscle similar to that of ghrelin. Not only there is a similarity in the receptor family, but also obestatin targets similar proteins and transcription factors as that of ghrelin (for example, FoxO family members) for salvaging skeletal muscle atrophy. Moreover, like ghrelin, obestatin also works by inducing the transcription of Pax7 which is required for muscle stem cell mobilisation. Hence, there are quite some evidences which points to the fact that obestatin can be purposed as a peptide intervention to prevent skeletal muscle wasting and induce myogenesis. This review elaborates these aspects of obestatin which can be further exploited and addressed to bring obestatin as a clinical intervention towards preventing skeletal muscle atrophy and sarcopenia.