Self-renewal and differentiation of muscle satellite cells are regulated by the Fas-associated death domain

Gene expression profiling of porcine skeletal muscle satellite cells after poly(I:C) stimulation

Porcine satellite cells (PSCs) play a vital role in the construction, development and self-renewal of skeletal muscle. In this study, PSCs were exposed to poly(I:C) stimulation to mimic viral infection during the proliferation and differentiation phases at 0, 12, 24 and 48 hours (h) of the stimulation. The untreated and treated PSCs were analyzed by the RNA-Seq technology. There were 88, 119, 104 and 95 genes being differentially expressed in 0 h vs 12 h treated, 12 h vs 24 h treated, 0 h vs 24 h treated and 24 h vs 48 h untreated comparison libraries, respectively. The GO terms analysis results showed that during the proliferation phase of treated PSCs, the up-regulated genes related to the immune system were highly expressed. In addition, the gene expressions associated with muscle structure development in response to growth factor emerged during the differentiation phase of untreated PSCs. The biological pathways associated with Influenza A, Toll-like receptor and chemokine signaling were revealed in PSCs following poly(I:C) stimulation. The differentially expressed genes were confirmed by quantitative real-time PCR. These findings expanded our understanding of gene expressions and signaling pathways about the infiltrated mechanism of the virus into PSCs.

Myogenic regulatory factors: The orchestrators of myogenesis after 30 years of discovery

Prenatal and postnatal myogenesis share many cellular and molecular aspects. Myogenic regulatory factors are basic Helix-Loop-Helix transcription factors that indispensably regulate both processes. These factors (Myf5, MyoD, Myogenin, and MRF4) function as an orchestrating cascade, with some overlapped actions. Prenatally, myogenic regulatory factors are restrictedly expressed in somite-derived myogenic progenitor cells and their derived myoblasts. Postnatally, myogenic regulatory factors are important in regulating the myogenesis process via satellite cells. Many positive and negative regulatory mechanisms exist either between myogenic regulatory factors themselves or between myogenic regulatory factors and other proteins. Upstream factors and signals are also involved in the control of myogenic regulatory factors expression within different prenatal and postnatal myogenic cells. Here, the authors have conducted a thorough and an up-to-date review of the myogenic regulatory factors since their discovery 30 years ago. This review discusses the myogenic regulatory factors structure, mechanism of action, and roles and regulations during prenatal and postnatal myogenesis. Impact statement Myogenic regulatory factors (MRFs) are key players in the process of myogenesis. Despite a considerable amount of literature regarding these factors, their exact mechanisms of actions are still incompletely understood with several overlapped functions. Herein, we revised what has hitherto been reported in the literature regarding MRF structures, molecular pathways that regulate their activities, and their roles during pre- and post-natal myogenesis. The work submitted in this review article is considered of great importance for researchers in the field of skeletal muscle formation and regeneration, as it provides a comprehensive summary of all the biological aspects of MRFs and advances a better understanding of the cellular and molecular mechanisms regulating myogenesis. Indeed, attaining a better understanding of MRFs could be utilized in developing novel therapeutic protocols for multiple myopathies.

The role of FADD in pancreatic cancer cell proliferation and drug resistance

Pancreatic cancer has one of the poorest patient outcomes and is highly resistant to chemotherapy. Identifying the molecular mechanisms involved in drug resistance is critical in the development of novel strategies to treat pancreatic cancer. The results of the present study demonstrate that Fas-associated death domain protein (FADD), a classical adaptor protein mediating apoptotic stimuli-induced cell death, protects pancreatic cancer cells from drug-induced apoptosis. In contrast to its classical apoptotic roles, it was observed that FADD is required for pancreatic cancer cell proliferation and that it is overexpressed to varying degrees in various types of pancreatic cancer cell. This leads to differing levels of drug resistance in pancreatic cancer cells, where drug resistance is positively correlated with FADD expression. Notably, the results of the present study demonstrate that FADD protects pancreatic cancer cells from drug-induced apoptosis, while RNA interference of FADD sensitizes drug-resistant cells to Adriamycin^®-mediated apoptosis. The results of the present study reveal unexpected roles for FADD in pancreatic cancer cell proliferation and drug resistance.

The beneficial role of proteolysis in skeletal muscle growth and stress adaptation

Muscle atrophy derived from excessive proteolysis is a hallmark of numerous disease conditions. Accordingly, the negative consequences of skeletal muscle protein breakdown often overshadow the critical nature of proteolytic systems in maintaining normal cellular function. Here, we discuss the major cellular proteolysis machinery-the ubiquitin/proteosome system, the autophagy/lysosomal system, and caspase-mediated protein cleavage-and the critical role of these protein machines in establishing and preserving muscle health. We examine how ordered degradation modifies (1) the spatiotemporal expression of myogenic regulatory factors during myoblast differentiation, (2) membrane fusion during myotube formation, (3) sarcomere remodeling and muscle growth following physical stress, and (4) energy homeostasis during nutrient deprivation. Finally, we review the origin and etiology of a number of myopathies and how these devastating conditions arise from inborn errors in proteolysis.

Satellite cells: regenerative mechanisms and applicability in muscular dystrophy

The satellite cells are long regarded as heterogeneous cell population, which is intimately linked to the processes of muscular recovery. The heterogeneous cell population may be classified by specific markers. In spite of the significant amount of variation amongst the satellite cell populations, it seems that their activity is tightly bound to the paired box 7 transcription factor expression, which is, therefore, used as a canonical marker for these cells. Muscular dystrophic diseases, such as Duchenne muscular dystrophy, elicit severe tissue injuries leading those patients to display a very specific pattern of muscular recovery abnormalities. There have been works on the application of precursors cells as a therapeutic alternative for Duchenne muscular dystrophy and initial attempts have proven the cells inefficient; however later endeavours have proposed solutions for the experiments improving significantly the results. The presence of a range of satellite cells populations indicates the existence of specific cells with enhanced capability of muscular recovery in afflicted muscles.