eIF3f depletion impedes mouse embryonic development, reduces adult skeletal muscle mass and amplifies muscle loss during disuse.

KEY POINTS: In muscular cells, eukaryotic initiation factor subunit f (eIF3f) activates protein synthesis by allowing physical interaction between mechanistic target of rapamycin complex 1 (MTORC1) and ribosomal protein S6 kinase 1 (S6K1), although its physiological role in animals is unknown. A knockout approach suggests that homozygous mice carrying a null mutation of the eIF3f gene fail to develop and consequently die at early embryonic stage, whereas heterozygous mice associated with a partial depletion of eIF3f gene grow normally and are phenotypically indistinguishable from wild-type mice. Heterozygous mice express reduced eIF3f mRNA and protein levels in skeletal muscles and show diminished muscle mass associated with a decrease in the protein synthesis rate and an inhibition of the MTORC1 pathway. During hindlimb immobilization, heterozygous eIF3f mice display an exacerbated immobilization-induced muscle atrophy associated with reduced protein synthesis. These results highlight the essential role of eIF3f during embryonic development and its involvement in muscular homeostasis via protein synthesis regulation. ABSTRACT: Eukaryotic translation initiation factor 3, subunit F (eIF3f), a component of eIF3 complex, plays an important role in protein synthesis regulation, although its physiological functions are unknown. We generated and analysed mice carrying a null mutation in the eIF3f gene. We showed that homozygous eIF3f knockout fail to develop and that eIF3f-/- embryos die at an early stage of development but after the pre-implantation stage. However, disrupting one eIF3f allele does not affect growth, viability and fertility of heterozygous mice but, instead, reduces eIF3f mRNA and protein levels in all tissues examined. Although heterozygous mice are phenotypically indistinguishable from wild-type mice, they present a diminished body weight and a lean mass reduction associated with normal body size. Interestingly, skeletal muscles are mainly affected and display an altered cell size without modification of fibre number. Skeletal muscles of heterozygous mice show a deficiency in polysome content, a decrease in protein synthesis rate and an inhibition of the mechanistic target of rapamycin (MTOR) pathway. We then studied the effects of hindlimb immobilization that mimic muscle disuse on heterozygous mice aiming to further explore the involvement of eIF3f in protein synthesis. We found that eIF3f partial depletion amplifies muscle atrophy compared to wild-type mice. Mass and cross-sectional area decreases were associated with reduced MTOR pathway activation and protein synthesis rate. Taken together, our data indicate that eIF3f is essential for mice embryonic development and controls adult skeletal muscle mass via protein synthesis regulation in a MTOR-dependent manner.

Metabolism and Skeletal Muscle Homeostasis in Lung Disease.

There is increased awareness that patients with lung diseases develop muscle dysfunction. Muscle dysfunction is a major contributor to a decreased quality of life in patients with chronic pulmonary diseases. Furthermore, muscle dysfunction exacerbates lung disease outcome, as a decrease in muscle mass and function are associated with increased morbidity, often long after critical illness or lung disease has been resolved. As we are learning more about the role of metabolism in health and disease, we are appreciating more the direct role of metabolism in skeletal muscle homeostasis. Altered metabolism is associated with numerous skeletal muscle pathologies and, conversely, skeletal muscle diseases are associated with significant changes in metabolic pathways. In this review, we highlight the role of metabolism in the regulation of skeletal muscle homeostasis. Understanding the metabolic pathways that underlie skeletal muscle wasting is of significant clinical interest for critically ill patients as well as patients with chronic lung disease, in which proper skeletal muscle function is essential to disease outcome.

Regimen on Dnaja3 haploinsufficiency mediated sarcopenic obesity with imbalanced mitochondrial homeostasis and lipid metabolism.

BACKGROUND: Sarcopenic obesity is characterized by excess fat mass and diminished muscular mass/function. DNAJA3, a mitochondrial co-chaperone protein, plays a crucial role in skeletal muscle development. GMI, an immunomodulatory protein, promotes myogenic differentiation through DNAJA3 activation. This study aims to elucidate the physiological effects of muscular Dnaja3 haploinsufficiency on mitochondrial dysfunction and dysregulated lipid metabolism and to assess the efficacy of GMI in rescuing sarcopenic obesity both in vitro and in vivo. METHODS: We generated mouse strain with Dnaja3 heterozygosity (HSA-Dnaja3f/+) specifically in skeletal muscle. The body weight, body composition, and locomotor activity of WT and HSA-Dnaja3f/+ mice were examined. The isolated skeletal muscles and primary myoblasts from the WT and HSA-Dnaja3f/+ mice, at young or old age, were utilized to study the molecular mechanisms, mitochondrial respiration and ROS level, mitochondrial proteomes, and serological analyses, respectively. To evaluate the therapeutic efficacy of GMI, both short-term and long-term GMI treatment were administrated intraperitoneally to the HSA-Dnaja3f/+ young (4 weeks old) or adult (3 months old) mice for a duration of either 1 or 6 months, respectively. RESULTS: Muscular Dnaja3 heterozygosity resulted in impaired locomotor activity (P < 0.05), reduced muscular cross-sectional area (P < 0.0001), and up-regulation of lipogenesis (ACC2) and pro-inflammation (STAT3) in skeletal muscles (P < 0.05). Primary myoblasts from the HSA-Dnaja3f/+ mice displayed impaired mitochondrial respiration (P < 0.01) and imbalanced mitochondrial ROS levels. A systemic proteomic analysis of the purified mitochondria from the primary myoblasts was conducted to show the abnormalities in mitochondrial function and fatty acid metabolism (P < 0.0001). At age of 13 to 14 months, the HSA-Dnaja3f/+ mice displayed increased body fat mass (P < 0.001), reduced fat-free mass (P < 0.01), and impaired glucose and insulin tolerance (P < 0.01). The short-term GMI treatment improved locomotor activity (P < 0.01) and down-regulated the protein levels of STAT3 (P < 0.05), ACC2, and mitochondrial respiratory complex III (UQCRC2) (P < 0.01) via DNAJA3 activation. The long-term GMI treatment ameliorated fat mass accumulation, glucose intolerance, and systemic inflammation (AST) (P < 0.05) in skeletal muscle, while enhancing thermogenesis (UCP1) (P < 0.01) in eWAT. GMI treatment promoted myogenesis, enhanced oxygen consumption, and ameliorated STAT3 (P < 0.01) through DNAJA3 activation (P < 0.05) in vitro. CONCLUSIONS: Muscular Dnaja3 haploinsufficiency dysregulates mitochondrial function and lipid metabolism then leads to sarcopenic obesity. GMI emerges as a therapeutic regimen for sarcopenic obesity treatment through DNAJA3 activation.

Ectodysplasin A/Ectodysplasin A Receptor System and Their Roles in Multiple Diseases.

Ectodysplasin A (EDA) is a member of the tumor necrosis factor (TNF) family of ligands that was initially reported to induce the formation of various ectodermal derivatives during normal prenatal development. EDA exerts its biological activity as two splice variants, namely, EDA-A1 and EDA-A2. The former binds to the EDA receptor (EDAR), resulting in the recruitment of the intracellular EDAR-associated death domain (EDARADD) adapter protein and the activation of the NF-κB signaling pathway, while the latter binds to a different receptor, EDA2R, also known as X-linked ectodermal dysplasia receptor (XEDAR). Inactivation mutation of the EDA gene or the genes coding for its receptors can result in hypohidrosis ectodermal dysplasia (HED), a condition that is characterized by oligotrichosis, edentulosis or oligodontia, and oligohidrosis or anhidrosis. Recently, as a new liver factor, EDA is gradually known and endowed with some new functions. EDA levels were observed to be upregulated in several metabolic diseases, such as non-alcoholic fatty liver disease (NAFLD), obesity, and insulin resistance. In addition, EDA and its receptors have been implicated in tumor pathogenesis through the regulation of tumor cell proliferation, apoptosis, differentiation, and migration. Here, we first review the role of EDA and its two-receptor system in various signaling pathways and then discuss the physiological and pathological roles of EDA and its receptors.

High-Dimensional Single-Cell Quantitative Profiling of Skeletal Muscle Cell Population Dynamics during Regeneration.

The interstitial space surrounding the skeletal muscle fibers is populated by a variety of mononuclear cell types. Upon acute or chronic insult, these cell populations become activated and initiate finely-orchestrated crosstalk that promotes myofiber repair and regeneration. Mass cytometry is a powerful and highly multiplexed technique for profiling single-cells. Herein, it was used to dissect the dynamics of cell populations in the skeletal muscle in physiological and pathological conditions. Here, we characterized an antibody panel that could be used to identify most of the cell populations in the muscle interstitial space. By exploiting the mass cytometry resolution, we provided a comprehensive picture of the dynamics of the major cell populations that sensed and responded to acute damage in wild type mice and in a mouse model of Duchenne muscular dystrophy. In addition, we revealed the intrinsic heterogeneity of many of these cell populations.

Global DNA methylation pattern involved in the modulation of differentiation potential of adipogenic and myogenic precursors in skeletal muscle of pigs.

BACKGROUND: Skeletal muscle is a complex and heterogeneous tissue accounting for approximately 40% of body weight. Excessive ectopic lipid accumulation in the muscle fascicle would undermine the integrity of skeletal muscle in humans but endow muscle with marbling-related characteristics in farm animals. Therefore, the balance of myogenesis and adipogenesis is of great significance for skeletal muscle homeostasis. Significant DNA methylation occurs during myogenesis and adipogenesis; however, DNA methylation pattern of myogenic and adipogenic precursors derived from skeletal muscle remains unknown yet. METHODS: In this study, reduced representation bisulfite sequencing was performed to analyze genome-wide DNA methylation of adipogenic and myogenic precursors derived from the skeletal muscle of neonatal pigs. Integrated analysis of DNA methylation and transcription profiles was further conducted. Based on the results of pathway enrichment analysis, myogenic precursors were transfected with CACNA2D2-overexpression plasmids to explore the function of CACNA2D2 in myogenic differentiation. RESULTS: As a result, 11,361 differentially methylated regions mainly located in intergenic region and introns were identified. Furthermore, 153 genes with different DNA methylation and gene expression level between adipogenic and myogenic precursors were characterized. Subsequently, pathway enrichment analysis revealed that DNA methylation programing was involved in the regulation of adipogenic and myogenic differentiation potential through mediating the crosstalk among pathways including focal adhesion, regulation of actin cytoskeleton, MAPK signaling pathway, and calcium signaling pathway. In particular, we characterized a new role of CACNA2D2 in inhibiting myogenic differentiation by suppressing JNK/MAPK signaling pathway. CONCLUSIONS: This study depicted a comprehensive landmark of DNA methylome of skeletal muscle-derived myogenic and adipogenic precursors, highlighted the critical role of CACNA2D2 in regulating myogenic differentiation, and illustrated the possible regulatory ways of DNA methylation on cell fate commitment and skeletal muscle homeostasis.