The transcriptional regulator KLF15 is necessary for myoblast differentiation and muscle regeneration by activating FKBP5

Immunoproteasome subunit PSMB8 promotes skeletal muscle regeneration by regulating macrophage phenotyping switch in mice

Immunoproteasomes regulate the degradation of ubiquitin-coupled proteins and cell differentiation. However, its precise role in skeletal muscle regeneration remains unclear. In this study, we found that expression of the immunoproteasome subunit, PSMB8, increased significantly in young muscles after cardiotoxin-induced injury, whereas its expression was downregulated in injured aged mice. Genetic knockout or pharmacological inhibition of the immunoproteasome subunit, PSMB8, resulted in impaired muscle regeneration and increased interstitial fibrosis. PSMB8 inhibition by short interfering RNA (siRNA) or inhibitor decreased the differentiation ability of myoblasts. There was increased infiltration of inflammatory cells, especially Ly6Chi proinflammatory macrophages, in Psmb8 deficient muscles. In vitro, Psmb8-deficient macrophages expressed higher levels of proinflammatory cytokines and lower levels of anti-inflammatory cytokines after phagocytosis of myoblast debris, which was associated with increased activation of the NF-κB signaling pathway. Inhibition of the NF-κB pathway improves the regeneration ability and attenuates interstitial fibrosis in Psmb8-deficient muscles after injury. The overexpression of Psmb8 by adenovirus could also improve the regenerative ability of aged muscles.NEW & NOTEWORTHY The immunoproteasome subunit, PSMB8, is essential for efficient muscle regeneration and may be a new therapeutic target for age-related muscle atrophy.

FKBP5 as a key regulator of metabolic processes in birds: Insights from chicken pectoral muscle

FK506-binding protein 5 (FKBP5) is a negative regulator of the glucocorticoid response and may play an important role in regulating metabolic homeostasis in birds. However, limited information is available regarding its role in avian species. This study aimed to clarify the spatiotemporal characteristics of chicken FKBP5 and investigate the effects of exogenous stimuli on its expression. Real-time quantitative PCR (RT-qPCR) was utilized to analyze the spatiotemporal expression patterns of FKBP5 in chickens. Additionally, the impact of exogenous stimuli, including fasting, energy restriction, and insulin/pyruvate/glucose injections, on FKBP5 expression in the pectoral muscle was investigated. The results showed that FKBP5 is broadly expressed in various bird tissues, with dominant expression in insulin-sensitive tissues. The FKBP5 levels in birds are dramatically modulated during development in insulin-sensitive tissues, with the highest expression observed in striated muscle and liver at embryonic day 19 (E19) (P < 0.01). The basal level of FKBP5 in the pectoral muscle of broilers is higher than that in Silky chickens. Insulin administration leads to a rapid drop in blood glucose levels in both breeds, with a slower recovery in AA broilers (P < 0.01). However, FKBP5 expression in the pectoral muscle initially shows a slight drop, followed by a sharp increase over time after insulin administration (P < 0.01). Additionally, breed heterogeneity in FKBP5 expression was observed in the pectoral muscle upon insulin stimulation, with broilers showing stronger insulin sensitivity compared to Silky chickens. A 24-hour fasting period downregulated blood glucose levels (P < 0.01) and FKBP5 expression in the pectoral muscle of AA broilers (P < 0.01). A 30% energy restriction over three weeks slightly reduced blood glucose levels (P = 0.075) and significantly decreased FKBP5 levels in the pectoralis muscle of broilers. In addition, pyruvate increased blood glucose and pectoralis FKBP5 transcription levels at 60 min (P < 0.01), whereas glucose increased blood glucose levels but had no effect on FKBP5 expression. Overall analysis showed a negative correlation between FKBP5 expression in the pectoral muscle and blood glucose levels (ρ = -0.405, P < 0.001). In conclusion, FKBP5 is a key player in the metabolic regulation of birds, with its expression being highly dynamic and tissue-specific. Insulin regulates FKBP5 expression in pectoral muscles in a time-dependent manner, while pyruvate increases FKBP5 levels and fasting/energy restriction reduces FKBP5 mRNA expression in the pectoral muscles.

Primary Roles of Branched Chain Amino Acids (BCAAs) and Their Metabolism in Physiology and Metabolic Disorders

Leucine, isoleucine, and valine are collectively known as branched chain amino acids (BCAAs) and are often discussed in the same physiological and pathological situations. The two consecutive initial reactions of BCAA catabolism are catalyzed by the common enzymes referred to as branched chain aminotransferase (BCAT) and branched chain α-keto acid dehydrogenase (BCKDH). BCAT transfers the amino group of BCAAs to 2-ketoglutarate, which results in corresponding branched chain 2-keto acids (BCKAs) and glutamate. BCKDH performs an oxidative decarboxylation of BCKAs, which produces their coenzyme A-conjugates and NADH. BCAT2 in skeletal muscle dominantly catalyzes the transamination of BCAAs. Low BCAT activity in the liver reduces the metabolization of BCAAs, but the abundant presence of BCKDH promotes the metabolism of muscle-derived BCKAs, which leads to the production of glucose and ketone bodies. While mutations in the genes responsible for BCAA catabolism are involved in rare inherited disorders, an aberrant regulation of their enzymatic activities is associated with major metabolic disorders such as diabetes, cardiovascular disease, and cancer. Therefore, an understanding of the regulatory process of metabolic enzymes, as well as the functions of the BCAAs and their metabolites, make a significant contribution to our health.

Muscle growth differences in Lijiang pigs revealed by ATAC-seq multi-omics

As one of the largest tissues in the animal body, skeletal muscle plays a pivotal role in the production and quality of pork. Consequently, it is of paramount importance to investigate the growth and developmental processes of skeletal muscle. Lijiang pigs, which naturally have two subtypes, fast-growing and slow-growing, provide an ideal model for such studies by eliminating breed-related influences. In this study, we selected three fast-growing and three slow-growing 6-month-old Lijiang pigs as subjects. We utilized assay for transposase-accessible chromatin with sequencing (ATAC-seq) combined with genomics, RNA sequencing, and proteomics to screen for differentially expressed genes and transcription factors linked to increased longissimus dorsi muscle volume in Lijiang pigs. We identified 126 genes through ATAC-seq, including PPARA, TNRC6B, NEDD1, and FKBP5, that exhibited differential expression patterns during muscle growth. Additionally, we identified 59 transcription factors, including Foxh1, JunB, Mef2 family members (Mef2a/b/c/d), NeuroD1, and TEAD4. By examining open chromatin regions (OCRs) with significant genetic differentiation, genes such as SAV1, CACNA1H, PRKCG, and FGFR4 were found. Integrating ATAC-seq with transcriptomics and transcriptomics with proteomics, we identified differences in open chromatin regions, transcription, and protein levels of FKBP5 and SCARB2 genes in fast-growing and slow-growing Lijiang pigs. Utilizing multi-omics analysis with R packages, we jointed ATAC-seq, transcriptome, and proteome datasets, identifying enriched pathways related to glycogen metabolism and skeletal muscle cell differentiation. We pinpointed genes such as MYF6 and HABP2 that exhibit strong correlations across these diverse data types. This study provides a multi-faceted understanding of the molecular mechanisms that lead to differences in pig muscle fiber growth.

Novel Candidate Genes Involved in an Initial Stage of White Striping Development in Broiler Chickens

White striping (WS) is a myopathy characterized by the appearance of white stripes parallel to the muscle fibers in the breast of broiler chickens, composed of adipose and connective tissues. This condition causes economic losses and, although common, its etiology remains poorly understood. Hence, the objective was to identify genes and biological mechanisms involved in the early stages of WS using a paternal broiler line that grows slightly slower than commercial ones, at 35 days of age, through the RNA sequencing of the pectoralis major muscle. Thirty genes were differentially expressed between normal and WS-affected chickens, with 23 upregulated and 7 downregulated in the affected broilers. Of these, 14 genes are novel candidates for WS and are implicated in biological processes related to muscle development (CEPBD, DUSP8, METTL21EP, NELL2, and UBE3D), lipid metabolism (PDK4, DDIT4, FKBP5, DGAT2, LIPG, TDH, and RGCC), and collagen (COL4A5 and COL4A6). Genes related to changes in muscle fiber type and the processes of apoptosis, autophagy, proliferation, and differentiation are possibly involved with the initial stage of WS development. In contrast, the genes linked to lipid metabolism and collagen may have their expression altered due to the progression of the myopathy.

KLF15 maintains contractile phenotype of vascular smooth muscle cells and prevents thoracic aortic dissection by interacting with MRTFB

Thoracic aortic dissection (TAD) is a highly dangerous cardiovascular disorder caused by weakening of the aortic wall, resulting in a sudden tear of the internal face. Progressive loss of the contractile apparatus in vascular smooth muscle cells (VSMCs) is a major event in TAD. Exploring the endogenous regulators essential for the contractile phenotype of VSMCs may aid the development of strategies to prevent TAD. Krüppel-like factor 15 (KLF15) overexpression was reported to inhibit TAD formation; however, the mechanisms by which KLF15 prevents TAD formation and whether KLF15 regulates the contractile phenotype of VSMCs in TAD are not well understood. Therefore, we investigated these unknown aspects of KLF15 function. We found that KLF15 expression was reduced in human TAD samples and β-aminopropionitrile monofumarate-induced TAD mouse model. Klf15KO mice are susceptible to both β-aminopropionitrile monofumarate- and angiotensin II-induced TAD. KLF15 deficiency results in reduced VSMC contractility and exacerbated vascular inflammation and extracellular matrix degradation. Mechanistically, KLF15 interacts with myocardin-related transcription factor B (MRTFB), a potent serum response factor coactivator that drives contractile gene expression. KLF15 silencing represses the MRTFB-induced activation of contractile genes in VSMCs. Thus, KLF15 cooperates with MRTFB to promote the expression of contractile genes in VSMCs, and its dysfunction may exacerbate TAD. These findings indicate that KLF15 may be a novel therapeutic target for the treatment of TAD.

The kruppel-like factor (KLF) family, diseases, and physiological events

The Kruppel-Like Factor family of regulatory proteins, which has 18 members, is transcription factors. This family contains zinc finger proteins, regulates the activation and suppression of transcription, and binds to DNA, RNA, and proteins. Klfs related to the immune system are Klf1, Klf2, Klf3, Klf4, Klf6, and Klf14. Klfs related to adipose tissue development and/or glucose metabolism are Klf3, Klf7, Klf9, Klf10, Klf11, Klf14, Klf15, and Klf16. Klfs related to cancer are Klf3, Klf4, Klf5, Klf6, Klf7, Klf8, Klf9, Klf10, Klf11, Klf12, Klf13, Klf14, Klf16, and Klf17. Klfs related to the cardiovascular system are Klf4, Klf5, Klf10, Klf13, Klf14, and Klf15. Klfs related to the nervous system are Klf4, Klf7, Klf8, and Klf9. Klfs are associated with diseases such as carcinogenesis, oxidative stress, diabetes, liver fibrosis, thalassemia, and the metabolic syndrome. The aim of this review is to provide information about the relationship of Klfs with some diseases and physiological events and to guide future studies.