KLF15 regulates slow myosin heavy chain expression through NFATc1 in C2C12 myotubes

Genome-wide chromatin accessibility and selective signals of meat rabbits reveal key Cis-regulatory elements and variants during postnatal development of skeletal muscles in rabbits

BACKGROUND

The development of skeletal muscles is intricately modulated by multiple genetic factors and significantly impacts the economic value of meat rabbits. However, our knowledge of epigenetics in rabbit skeletal muscles remains largely unknown.

RESULTS

In this study, we collected leg skeletal muscles of rabbits and performed assays for transposase-accessible chromatin with high throughput sequencing (ATAC-seq) to detect open chromatin across three developmental stages: birth (D1), weaning (D35), and adulthood (D75). A total of 126,959 accessible chromatin regions (ACRs) were identified across samples, and a broad increase and decrease in chromatin accessibility were found from D1 to D35 and D35 to D75, respectively. Integrative analysis of chromatin accessibility and transcriptome data revealed ACRs that were nearly closed at D1 but highly accessible at D35 and D75 were significantly enriched in skeletal muscle development. Cis-regulation analysis further revealed that genes dominated by enhancers mainly play roles in the neuron development of rabbit skeletal muscles. Moreover, the detection of selection signals of meat rabbits and the footprinting analysis of transcription factor at open chromatin revealed that both base transversion (Chr13:12144967 A-> G) and the dynamics of chromatin accessibility at the PRDM1 binding site might regulate ZSWIM5 during the development of skeletal muscles in rabbits.

CONCLUSIONS

Our study provided a category of potential cis-regulatory elements for understanding the development of skeletal muscles at the tissue level and might facilitate potential insights into growth regulation in rabbits.

Genome-wide association study of myofiber type composition traits in a yellow-feather broiler population

Meat quality is a key factor determining the economic viability of the broiler industry, particularly in native broiler breeds. Skeletal muscles contain a mixture of muscle fibers, each possessing unique physicochemical properties; the composition of myofiber types within these muscles is closely linked to meat quality. However, comprehension of the regulatory mechanisms governing this trait remains limited. Therefore, we conducted a genome-wide association study (GWAS) with a population of 400 yellow-feather broilers to explore genetic variations associated with myofiber-type composition at the genomic level. Whole-genome resequencing was employed to detect genetic variations and immunohistochemistry was used for muscle fiber typing in the sartorius muscle. We identified 1 and 18 single-nucleotide polymorphisms (SNPs) significantly and potentially associated with the proportion of slow muscle fibers, respectively, and 1 and 12 SNPs significantly and potentially associated with the area proportion of slow muscle fibers, respectively. We annotated several candidate genes, including DMD, KLF7, CREB1, EFCAB11, GADD45A, GSTT1, and GSTT1L, which are related to myofiber type composition. We also demonstrated that myofiber composition traits exhibit low-to-medium heritability, indicating potential for enhancement through genetic selection. These findings provide a crucial reference for further studies on the regulatory mechanisms of poultry meat quality and for advancing the breeding of superior-quality broiler chickens.

Krüpple-like factors in cardiomyopathy: emerging player and therapeutic opportunities

Cardiomyopathy, a heterogeneous pathological condition characterized by changes in cardiac structure or function, represents a significant risk factor for the prevalence and mortality of cardiovascular disease (CVD). Research conducted over the years has led to the modification of definition and classification of cardiomyopathy. Herein, we reviewed seven of the most common types of cardiomyopathies, including Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), diabetic cardiomyopathy, Dilated Cardiomyopathy (DCM), desmin-associated cardiomyopathy, Hypertrophic Cardiomyopathy (HCM), Ischemic Cardiomyopathy (ICM), and obesity cardiomyopathy, focusing on their definitions, epidemiology, and influencing factors. Cardiomyopathies manifest in various ways ranging from microscopic alterations in cardiomyocytes, to tissue hypoperfusion, cardiac failure, and arrhythmias caused by electrical conduction abnormalities. As pleiotropic Transcription Factors (TFs), the Krüppel-Like Factors (KLFs), a family of zinc finger proteins, are involved in regulating the setting and development of cardiomyopathies, and play critical roles in associated biological processes, including Oxidative Stress (OS), inflammatory reactions, myocardial hypertrophy and fibrosis, and cellular autophagy and apoptosis, particularly in diabetic cardiomyopathy. However, research into KLFs in cardiomyopathy is still in its early stages, and the pathophysiologic mechanisms of some KLF members in various types of cardiomyopathies remain unclear. This article reviews the roles and recent research advances in KLFs, specifically those targeting and regulating several cardiomyopathy-associated processes.

L-theanine induces skeletal muscle fiber type transformation by activation of prox1/CaN signaling pathway in C2C12 myotubes

The aim of this study was to investigate the effect and mechanism of L-theanine (LT) on muscle fiber type transformation in C2C12 myotubes. Our data showed that LT exhibited significantly higher slow oxidative muscle fiber expression and lower glycolytic fibers expression. In addition, LT significantly increased the activities of malate dehydrogenase (MDH) and succinic dehydrogenase (SDH), and decreased lactate dehydrogenase (LDH) activity, the calcineurin (CaN) activity and the protein expressions of nuclear factor of activated T cell 1 (NFATc1), prospero-related homeobox1 (prox1), and calcineurin A (CnA) were significantly increased. However, inhibition of CaN activity by cyclosporine A (CsA) abolished LT-induced increase of slow oxidative muscle fiber expression and decrease of glycolytic fibers expression. Moreover, inhibition of prox1 expression by prox1-siRNA disrupted LT-induced activation of CaN signaling pathway and muscle fiber type transformation. Taken together, these results indicated that LT could promote skeletal muscle fiber type transformation from type II to type I via activation of prox1/CaN signaling pathway.

Elevated ASCL1 activity creates de novo regulatory elements associated with neuronal differentiation

Background

The pro-neural transcription factor ASCL1 is a master regulator of neurogenesis and a key factor necessary for the reprogramming of permissive cell types to neurons. Endogenously, ASCL1 expression is often associated with neuroblast stem-ness. Moreover, ASCL1-mediated reprogramming of fibroblasts to differentiated neurons is commonly achieved using artificially high levels of ASCL1 protein, where ASCL1 acts as an “on-target” pioneer factor. However, the genome-wide effects of enhancing ASCL1 activity in a permissive neurogenic environment has not been thoroughly investigated. Here, we overexpressed ASCL1 in the neuronally-permissive context of neuroblastoma (NB) cells where modest endogenous ASCL1 supports the neuroblast programme.

Results

Increasing ASCL1 in neuroblastoma cells both enhances binding at existing ASCL1 sites and also leads to creation of numerous additional, lower affinity binding sites. These extensive genome-wide changes in ASCL1 binding result in significant reprogramming of the NB transcriptome, redirecting it from a proliferative neuroblastic state towards one favouring neuronal differentiation. Mechanistically, ASCL1-mediated cell cycle exit and differentiation can be increased further by preventing its multi-site phosphorylation, which is associated with additional changes in genome-wide binding and gene activation profiles.

Conclusions

Our findings show that enhancing ASCL1 activity in a neurogenic environment both increases binding at endogenous ASCL1 sites and also results in additional binding to new low affinity sites that favours neuronal differentiation over the proliferating neuroblast programme supported by the endogenous protein. These findings have important implications for controlling processes of neurogenesis in cancer and cellular reprogramming.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08495-8.

Growth Hormone(s), Testosterone, Insulin-Like Growth Factors, and Cortisol: Roles and Integration for Cellular Development and Growth With Exercise

Hormones are largely responsible for the integrated communication of several physiological systems responsible for modulating cellular growth and development. Although the specific hormonal influence must be considered within the context of the entire endocrine system and its relationship with other physiological systems, three key hormones are considered the "anabolic giants" in cellular growth and repair: testosterone, the growth hormone superfamily, and the insulin-like growth factor (IGF) superfamily. In addition to these anabolic hormones, glucocorticoids, mainly cortisol must also be considered because of their profound opposing influence on human skeletal muscle anabolism in many instances. This review presents emerging research on: (1) Testosterone signaling pathways, responses, and adaptations to resistance training; (2) Growth hormone: presents new complexity with exercise stress; (3) Current perspectives on IGF-I and physiological adaptations and complexity these hormones as related to training; and (4) Glucocorticoid roles in integrated communication for anabolic/catabolic signaling. Specifically, the review describes (1) Testosterone as the primary anabolic hormone, with an anabolic influence largely dictated primarily by genomic and possible non-genomic signaling, satellite cell activation, interaction with other anabolic signaling pathways, upregulation or downregulation of the androgen receptor, and potential roles in co-activators and transcriptional activity; (2) Differential influences of growth hormones depending on the "type" of the hormone being assayed and the magnitude of the physiological stress; (3) The exquisite regulation of IGF-1 by a family of binding proteins (IGFBPs 1-6), which can either stimulate or inhibit biological action depending on binding; and (4) Circadian patterning and newly discovered variants of glucocorticoid isoforms largely dictating glucocorticoid sensitivity and catabolic, muscle sparing, or pathological influence. The downstream integrated anabolic and catabolic mechanisms of these hormones not only affect the ability of skeletal muscle to generate force; they also have implications for pharmaceutical treatments, aging, and prevalent chronic conditions such as metabolic syndrome, insulin resistance, and hypertension. Thus, advances in our understanding of hormones that impact anabolic: catabolic processes have relevance for athletes and the general population, alike.

Differential regulation of myofibrillar proteins in skeletal muscles of septic mice

Sepsis elicits skeletal muscle atrophy as a result of decreased total protein synthesis and/or increased total protein degradation. It is unknown how and whether sepsis differentially affects the expression of specific myofibrillar proteins in respiratory and limb muscles. In this study, we measured the effects of sepsis myofibrillar mRNAs and their corresponding protein levels in the diaphragm (DIA) and tibialis anterior (TA) muscles in a murine cecal ligation and perforation (CLP) model of sepsis. Male mice (C57/BL6j) underwent CLP-induced sepsis. Sham-operated mice were subjected to the same surgical procedures, except for CLP. Mice were euthanized 24, 48, or 96 h postsurgery. Transcript and protein levels of autophagy-related genes, ubiquitin E3 ligases, and several myofibrillar genes were quantified. Sepsis elicited transient fiber atrophy in the DIA and prolonged atrophy in the TA. Atrophy was coincident with increased autophagy and ubiquitin E3 ligase expression. Myosin heavy chain isoforms decreased at 24 h in the DIA and across the time-course in the TA, myosin light chain isoforms decreased across the time-course in both muscles, and troponins T and C as well as tropomyosin decreased after 24 and 48 h in both the DIA and TA. α-Actin and troponin I were unaffected by sepsis. Sepsis-induced decreases in myofibrillar protein levels coincided with decreased mRNA expressions of these proteins, suggesting that transcriptional inhibition is involved. We hypothesize that sepsis-induced muscle atrophy is mediated by decreased transcription and enhanced degradation of specific myofibrillar proteins, including myosin heavy and light chains, troponin C, troponin T, and tropomyosin.

Krüppel-Like Factors in Metabolic Homeostasis and Cardiometabolic Disease

Members of the Krüppel-like factor (KLF) family of transcription factors, which are characterized by the presence of three conserved Cys₂/His₂ zinc-fingers in their C-terminal domains, control a wide variety of biological processes. In particular, recent studies have revealed that KLFs play diverse and essential roles in the control of metabolism at the cellular, tissue and systemic levels. In both liver and skeletal muscle, KLFs control glucose, lipid and amino acid metabolism so as to coordinate systemic metabolism in the steady state and in the face of metabolic stresses, such as fasting. The functions of KLFs within metabolic tissues are also important contributors to the responses to injury and inflammation within those tissues. KLFs also control the function of immune cells, such as macrophages, which are involved in the inflammatory processes underlying both cardiovascular and metabolic diseases. This review focuses mainly on the physiological and pathological functions of KLFs in the liver and skeletal muscle. The involvement of KLFs in inflammation in these tissues is also summarized. We then discuss the implications of KLFs' control of metabolism and inflammation in cardiometabolic diseases.

PAX3+ skeletal muscle satellite cells retain long-term self-renewal and proliferation

INTRODUCTION

Different populations of satellite cells (SCs) have been identified, but their functional difference remains unclear.

METHODS

We used cell-surface markers and paired box transcription factor 3 (Pax3)/paired box transcription factor 7 (Pax7) expression to separate SC populations. In addition, self-renewal, proliferation, and differentiation abilities of each population were analyzed.

RESULTS

Pax3⁺ /Pax7^- SCs exhibited higher proliferation ability characterized by forming clusters of myogenic colonies with more self-renewing cells after several passages, while Pax3^- /Pax7⁺ SCs had faster differentiation. The myotubes derived from Pax3⁺ /Pax7^- SCs tended to express slow-myosin heavy chain and exhibited rhythmic contraction, while myotubes originating from Pax3^- /Pax7⁺ SCs primarily formed fast-myosin heavy chains characterized by transitory contraction.

CONCLUSIONS

Pax3⁺ /Pax7^- SCs exhibited the ability of long-term self-renewal and proliferation, whereas Pax3^- /Pax7⁺ SCs demonstrated faster differentiation. Muscle Nerve 54: 943-951, 2016.