Effect of standard and physiological cell culture temperatures on in vitro proliferation and differentiation of primary broiler chicken pectoralis major muscle satellite cells

Culture temperatures for broiler chicken cells are largely based on those optimized for mammalian species, although normal broiler body temperature is typically more than 3°C higher. The objective was to evaluate the effects of simulating broiler peripheral muscle temperature, 41°C, compared with standard temperature, 38°C, on the in vitro proliferation and differentiation of primary muscle-specific stem cells (satellite cells; SC) from the pectoralis major (PM) of broiler chickens. Primary SC cultures were isolated from the PM of 18-day-old Ross 708 × Yield Plus male broilers. SC were plated in triplicate, 1.8-cm2, gelatin-coated wells at 40,000 cells per well. Parallel plates were cultured at either 38°C or 41°C in separate incubators. At 48, 72, and 96 h post-plating, the culture wells were fixed and immunofluorescence-stained to determine the expression of the myogenic regulatory factors Pax7 and MyoD as well as evaluated for apoptosis using a TUNEL assay. After 168 h in culture, plates were immunofluorescence-stained to visualize myosin heavy chain and Pax7 expression and determine myotube characteristics and SC fusion. Population doubling times were not impacted by temperature (p ≥ 0.1148), but culturing broiler SC at 41°C for 96 h promoted a more rapid progression through myogenesis, while 38°C maintained primitive populations (p ≤ 0.0029). The proportion of apoptotic cells increased in primary SC cultured at 41°C (p ≤ 0.0273). Culturing at 41°C appeared to negatively impact fusion percentage (p < 0.0001) and tended to result in the formation of thinner myotubes (p = 0.061) without impacting the density of differentiated cells (p = 0.7551). These results indicate that culture temperature alters primary broiler PM SC myogenic kinetics and has important implications for future in vitro work as well as improving our understanding of how thermal manipulation can alter myogenesis patterns during broiler embryonic and post-hatch muscle growth.

Effects of photobiomodulation therapy on regulation of myogenic regulatory factor mRNA expression in vivo: A systematic review

Non-invasive promotion of myogenic regulatory factors (MRFs), through photobiomodulation therapy (PBMT), may be a viable method of facilitating skeletal muscle regeneration post-injury, given the importance of MRF in skeletal muscle regeneration. The aim of this systematic review was to collate current evidence, identifying key themes and changes in expression of MRF in in vivo models. Web of Science, PubMed, Scopus and Cochrane databases were systematically searched and identified 1459 studies, of which 10 met the inclusion criteria. Myogenic determination factor was most consistently regulated in response to PBMT treatment, and the expression of remaining MRFs was heterogenous. All studies exhibited a high risk of bias, primarily due to lack of blinding in PBMT application and MRF analysis. Our review suggests that the current evidence base for MRF expression from PBMT is highly variable. Future research should focus on developing a robust methodology for determining the effect of laser therapy on MRF expression, as well as long-term assessment of skeletal muscle regeneration.

Research Note: Increased myostatin expression and decreased expression of myogenic regulatory factors in embryonic ages in a quail line with muscle hypoplasia

Genetic selection of quail for a low body weight for more than 80 generations established a low-weight (LW) Japanese quail line that has been previously characterized to have a muscle hypoplasia phenotype. The aim of this study is to investigate the relationship of temporal expression levels of myostatin (Mstn) and myogenic regulatory factors (MRFs) with hypoplastic muscle growth in the LW line. During embryonic day (E) 13 to 15, gain of embryo weight was 2-fold lower (P < 0.001) in the LW line than that in the random bred control (CON). Gains in body weight and pectoralis muscle weight from hatch to posthatch day (P) 28 were also significantly lower (P < 0.01) in the LW line but increased by 4-fold (P < 0.05) during P42 to P75. PCR analysis showed that expression levels of Mstn were greater in the LW at embryonic stage (E12 to E14, P < 0.05), but there was no difference after hatch. In addition, expression levels of Pax7 and myogenin (MyoG) at E12 were 23-fold (P < 0.05) and 3.4-fold (P < 0.05) lesser in the LW line, respectively. At E14, expression of Pax3, Pax7, and MyoG gene was 3.5-fold (P < 0.05), 6.5-fold (P = 0.065), and 4.4-fold (P < 0.01) less than that in the CON. Taken together, high expression levels of Mstn and low expression of MRFs during embryonic stages can be associated with development of muscle hypoplasia and delayed muscle growth in the LW quail line. These data provide evidence that genetic selection for a low body weight resulting in an avian model with muscle hypoplasia has altered the expression profiles of myogenic factors.

Myogenic regulatory factors are key players in determining muscle mass and meat quality in Jeju native and Berkshire pigs

BACKGROUND

Meat from Jeju native pigs (JNPs) is highly popular among Korean consumers; however, the production efficiency is limited due to the low adult body weight. In contrast, the Berkshire breed, which has a genetic background closely related to Asian native pigs, gains weight more efficiently.

OBJECTIVES

This study focused on the differential expression of genes related to muscle growth in postnatal myogenesis between Berkshire and JNPs, specifically the myogenic regulatory factor (MRF) genes (MyoD, Pax7, Myf5, Myf6 and MyBPH). The MRF family is primarily involved in the proliferation and development of muscle.

METHODS

Qualitative reverse transcription-polymerase chain reaction and western blot analyses revealed that expression of MyoD and Pax7 was significantly higher in Berkshire pigs than in JNPs. In addition, co-expression of MyoD and Pax7 was observed in myotubes formed in cultured C2C12 cells. ToppCluster was used to elucidate the relationship between biological processes of the MRFs and muscle-related signalling pathways.

RESULTS

MyoD and Pax7 are factors essential for the activation of satellite cell during myogenesis. However, the mRNA and protein levels of MyBPH (which is responsible for meat quality, e.g. water content, colour and tenderness) are significantly higher in both 1-day-old piglets and adult JNPs than in Berkshire pigs.

CONCLUSIONS

This study provides a genetic understanding of myogenesis in the postnatal and adult stages of Berkshire pigs and JNPs. Moreover, these results will help identify marker genes related to muscle mass, growth performance and meat quality in indigenous Korean pig breeds.

Toxoplasma gondii Impairs Myogenesis in vitro, With Changes in Myogenic Regulatory Factors, Altered Host Cell Proliferation and Secretory Profile

Toxoplasma gondii is the causative agent of toxoplasmosis, a parasitic disease with a wide global prevalence. The parasite forms cysts in skeletal muscle cells and neurons, although no evident association with inflammatory infiltrates has been typically found. We studied the impact of T. gondii infection on the myogenic program of mouse skeletal muscle cells (SkMC). The C2C12 murine myoblast cell line was infected with T. gondii tachyzoites (ME49 strain) for 24 h followed by myogenic differentiation induction. T. gondii infection caused a general decrease in myotube differentiation, fusion and maturation, along with decreased expression of myosin heavy chain. The expression of Myogenic Regulatory Factors Myf5, MyoD, Mrf4 and myogenin was modulated by the infection. Infected cultures presented increased proliferation rates, as assessed by Ki67 immunostaining, whereas neither host cell lysis nor apoptosis were significantly augmented in infected dishes. Cytokine Bead Array indicated that IL-6 and MCP-1 were highly increased in the medium from infected cultures, whereas TGF-β1 was consistently decreased. Inhibition of the IL-6 receptor or supplementation with recombinant TGF-β failed to reverse the deleterious effects caused by the infection. However, conditioned medium from infected cultures inhibited myogenesis in C2C12 cells. Activation of the Wnt/β-catenin pathway was impaired in T. gondii-infected cultures. Our data indicate that T. gondii leads SkMCs to a pro-inflammatory phenotype, leaving cells unresponsive to β-catenin activation, and inhibition of the myogenic differentiation program. Such deregulation may suggest muscle atrophy and molecular mechanisms similar to those involved in myositis observed in human patients.

Gene structure, recombinant expression and function characterization of Siniperca chuatsi Fsrp-3

A full-length complementary (c)DNA sequence encoding follistatin-related protein 3 (fsrp-3) was determined from skeletal muscle in Chinese mandarin fish Siniperca chuatsi, its molecular structure was characterised and its function suggested. The putative structure of S. chuatsi Fsrp-3 contains an N-terminal domain and two follistatin domains. Quantitative reverse-transcription (qRT)-PCR assays revealed that fsrp-3 messenger (m)RNA was differentially expressed among assayed tissues and was highly expressed in heart and intestine. fsrp-3 mRNA exhibited increasing expression from the larval to the juvenile stage (500 g). To investigate the potential function of S. chuatsi fsrp-3 in muscle growth, we constructed a Fsrp-3 prokaryotic expression system and injected the purified Fsrp-3 fusion protein into the dorsal muscle. Fsrp-3 administration significantly influenced cross-section area, satellite cell activation frequency and nuclear density of S. chuatsi muscle fibres. Following Fsrp-3 treatment, the expression of myogenic regulatory factors was up-regulated and decline in the expression of myostatin was observed. The study revealed that Fsrp-3 may affect muscle growth by regulating myogenic regulatory factor expression and antagonizing myostatin function to initiate satellite cell activation and differentiation in S. chuatsi.

Spatial and temporal changes in myogenic protein expression by the microenvironment after freeze injury

Skeletal muscle has the remarkable capability to regenerate itself following injury. Adult myogenic stem cells (MSCs) are responsible for the repair and regeneration, and their activity is controlled by intrinsic and extrinsic factors. The aim of this study was to examine and compare the expression levels of Pax3, Pax7, MRF and p38 proteins during the course of regeneration and in different areas of the focal freeze-lesion damaged adult rat TA muscle. Using the focal freeze injury model, immunohistochemistry, laser-capture micro-dissection and Western blot analysis were performed. The results show that (1) in the severely damaged area, the focal freeze-lesion injury significantly activated Pax7 and myogenin expression within 7 days and down-regulated Pax3, MyoD and Myf-5 within 1 or 3 days, and (2) the level of the p38 protein was strongly and transiently up-regulated in the whole muscle on day 7 following injury, whereas the level of the pp38 protein was down-regulated within 3 days in the severely damaged and non-damaged areas. These findings indicate that the temporal (e.g. the time course of regeneration) and spatial (e.g. three zones created by the focal freeze-lesion) cues in a regenerating muscle have a significant impact on the activity of the adult MSCs.

Does skeletal muscle have an 'epi'-memory? The role of epigenetics in nutritional programming, metabolic disease, aging and exercise

Skeletal muscle mass, quality and adaptability are fundamental in promoting muscle performance, maintaining metabolic function and supporting longevity and healthspan. Skeletal muscle is programmable and can ‘remember’ early‐life metabolic stimuli affecting its function in adult life. In this review, the authors pose the question as to whether skeletal muscle has an ‘epi’‐memory? Following an initial encounter with an environmental stimulus, we discuss the underlying molecular and epigenetic mechanisms enabling skeletal muscle to adapt, should it re‐encounter the stimulus in later life. We also define skeletal muscle memory and outline the scientific literature contributing to this field. Furthermore, we review the evidence for early‐life nutrient stress and low birth weight in animals and human cohort studies, respectively, and discuss the underlying molecular mechanisms culminating in skeletal muscle dysfunction, metabolic disease and loss of skeletal muscle mass across the lifespan. We also summarize and discuss studies that isolate muscle stem cells from different environmental niches in vivo (physically active, diabetic, cachectic, aged) and how they reportedly remember this environment once isolated in vitro. Finally, we will outline the molecular and epigenetic mechanisms underlying skeletal muscle memory and review the epigenetic regulation of exercise‐induced skeletal muscle adaptation, highlighting exercise interventions as suitable models to investigate skeletal muscle memory in humans. We believe that understanding the ‘epi’‐memory of skeletal muscle will enable the next generation of targeted therapies to promote muscle growth and reduce muscle loss to enable healthy aging.

The effect of hyperammonemia on myostatin and myogenic regulatory factor gene expression in broiler embryos

Myogenesis is facilitated by four myogenic regulatory factors and is significantly inhibited by myostatin. The objective of the current study was to examine embryonic gene regulation of myostatin/myogenic regulatory factors, and subsequent manipulations of protein synthesis, in broiler embryos under induced hyperammonemia. Broiler eggs were injected with ammonium acetate solution four times over 48 h beginning on either embryonic day (ED) 15 or 17. Serum ammonia concentration was significantly higher (P<0.05) in ammonium acetate injected embryos for both ED17 and ED19 collected samples when compared with sham-injected controls. Expression of mRNA, extracted from pectoralis major of experimental and control embryos, was measured using real-time quantitative PCR for myostatin, myogenic regulatory factors myogenic factor 5, myogenic determination factor 1, myogenin, myogenic regulatory factor 4 and paired box 7. A significantly lower (P<0.01) myostatin expression was accompanied by a higher serum ammonia concentration in both ED17 and ED19 collected samples. Myogenic factor 5 expression was higher (P<0.05) in ED17 collected samples administered ammonium acetate. In both ED17 and ED19 collected samples, myogenic regulatory factor 4 was lower (P⩽0.05) in ammonium acetate injected embryos. No significant difference was seen in myogenic determination factor 1, myogenin or paired box 7 expression between treatment groups for either age of sample collection. In addition, there was no significant difference in BrdU staining of histological samples taken from treated and control embryos. Myostatin protein levels were evaluated by Western blot analysis, and also showed lower myostatin expression (P<0.05). Overall, it appears possible to inhibit myostatin expression through hyperammonemia, which is expected to have a positive effect on embryonic myogenesis and postnatal muscle growth.

The effect of nutritional status and myogenic satellite cell age on turkey satellite cell proliferation, differentiation, and expression of myogenic transcriptional regulatory factors and heparan sulfate proteoglycans syndecan-4 and glypican-1

Posthatch satellite cell mitotic activity is a critical component of muscle development and growth. Satellite cells are myogenic stem cells that can be induced by nutrition to follow other cellular developmental pathways, and whose mitotic activity declines with age. The objective of the current study was to determine the effect of restricting protein synthesis on the proliferation and differentiation, expression of myogenic transcriptional regulatory factors myogenic determination factor 1, myogenin, and myogenic regulatory factor 4, and expression of the heparan sulfate proteoglycans syndecan-4 and glypican-1 in satellite cells isolated from 1-d-, 7-wk-, and 16-wk-old turkey pectoralis major muscle (1 d, 7 wk, and 16 wk cells, respectively) by using variable concentrations of Met and Cys. Four Met concentrations-30 (control), 7.5, 3, or 0 mg/L with 3.2 mg/L of Cys per 1 mg/L of Met-were used for culture of satellite cells to determine the effect of nutrition and age on satellite cell behavior during proliferation and differentiation. Proliferation was reduced by lower Met and Cys concentrations in all ages at 96 h of proliferation. Differentiation was increased in the 1 d Met-restricted cells, whereas the 7 wk cells treated with 3 mg/L of Met had decreased differentiation. Reduced Met and Cys levels from the control did not significantly affect the 16 wk cells at 72 h of differentiation. However, medium with no Met or Cys suppressed differentiation at all ages. The expression of myogenic determination factor 1, myogenin, myogenic regulatory factor 4, syndecan-4, and glypican-1 was differentially affected by age and Met or Cys treatment. These data demonstrate the age-specific manner in which turkey pectoralis major muscle satellite cells respond to nutritional availability and the importance of defining optimal nutrition to maximize satellite cell proliferation and differentiation for subsequent muscle mass accretion.

Requirement of MEF2A, C, and D for skeletal muscle regeneration

Regeneration of adult skeletal muscle following injury occurs through the activation of satellite cells, an injury-sensitive muscle stem cell population that proliferates, differentiates, and fuses with injured myofibers. Members of the myocyte enhancer factor 2 (MEF2) family of transcription factors play essential roles in muscle differentiation during embryogenesis, but their potential contributions to adult muscle regeneration have not been systematically explored. To investigate the potential involvement of MEF2 factors in muscle regeneration, we conditionally deleted the Mef2a, c, and d genes, singly and in combination, within satellite cells in mice, using tamoxifen-inducible Cre recombinase under control of the satellite cell-specific Pax7 promoter. We show that deletion of individual Mef2 genes has no effect on muscle regeneration in response to cardiotoxin injury. However, combined deletion of the Mef2a, c, and d genes results in a blockade to regeneration. Satellite cell-derived myoblasts lacking MEF2A, C, and D proliferate normally in culture, but cannot differentiate. The absence of MEF2A, C, and D in satellite cells is associated with aberrant expression of a broad collection of known and unique protein-coding and long noncoding RNA genes. These findings reveal essential and redundant roles of MEF2A, C, and D in satellite cell differentiation and identify a MEF2-dependent transcriptome associated with skeletal muscle regeneration.

Muscle stem cells in developmental and regenerative myogenesis

PURPOSE OF REVIEW

Skeletal muscle development serves as a paradigm for cell lineage specification and cell differentiation. Adult skeletal muscle has high regenerative capacity, with satellite cells the primary source of this capability. The present review describes recent findings on developmental and adult myogenesis with emphasis on emerging distinctions between various muscle groups and stages of myogenesis.

RECENT FINDINGS

Muscle progenitors of the body are derived from multipotent cells of the dermomyotome and express the transcription factors Pax3 and Pax7. These cells self-renew or induce expression of myogenic regulatory factors (MRFs) and differentiate. The roles of Pax3, Pax7 and specific myogenic regulatory factor progenitor populations in trunk and limb myogenesis have been identified through cell ablation in the mouse. Various head muscles and associated satellite cells have differing developmental origins, and rely on distinct combinations of transcriptional regulators, than trunk and limb muscles. Several genetic and sorting protocols demonstrate that satellite cells are heterogeneous with some possessing stem cell properties; the relative roles of lineage and niche in these properties are being explored. Although cellular mechanisms of developmental, postnatal and adult regenerative myogenesis are thought to be similar, recent studies reveal distinct genetic requirements for embryonic, fetal, postnatal and adult regenerative myogenesis.

SUMMARY

Genetic determinants of formation or repair of various muscles during different stages of myogenesis are unexpectedly diverse. Future studies should illuminate these differences, as well as mechanisms that underlie stem cell properties of satellite cells.

Reduced differentiation potential of primary MyoD-/- myogenic cells derived from adult skeletal muscle

To gain insight into the regeneration deficit of MyoD-/- muscle, we investigated the growth and differentiation of cultured MyoD-/- myogenic cells. Primary MyoD-/- myogenic cells exhibited a stellate morphology distinct from the compact morphology of wild-type myoblasts, and expressed c-met, a receptor tyrosine kinase expressed in satellite cells. However, MyoD-/- myogenic cells did not express desmin, an intermediate filament protein typically expressed in cultured myoblasts in vitro and myogenic precursor cells in vivo. Northern analysis indicated that proliferating MyoD-/- myogenic cells expressed fourfold higher levels of Myf-5 and sixfold higher levels of PEA3, an ETS-domain transcription factor expressed in newly activated satellite cells. Under conditions that normally induce differentiation, MyoD-/- cells continued to proliferate and with delayed kinetics yielded reduced numbers of predominantly mononuclear myocytes. Northern analysis revealed delayed induction of myogenin, MRF4, and other differentiation-specific markers although p21 was upregulated normally. Expression of M-cadherin mRNA was severely decreased whereas expression of IGF-1 was markedly increased in MyoD-/- myogenic cells. Mixing of lacZ-labeled MyoD-/- cells and wild-type myoblasts revealed a strict autonomy in differentiation potential. Transfection of a MyoD-expression cassette restored cytomorphology and rescued the differentiation deficit. We interpret these data to suggest that MyoD-/- myogenic cells represent an intermediate stage between a quiescent satellite cell and a myogenic precursor cell.