Suppression of protein degradation by leucine requires its conversion to β-hydroxy-β-methyl butyrate in C2C12 myotubes

β-Hydroxy-β-methyl Butyrate Regulates the Lipid Metabolism, Mitochondrial Function, and Fat Browning of Adipocytes

A growing number of in vivo studies demonstrated that β-hydroxy-β-methyl butyrate (HMB) can serve as a lipid-lowering nutrient. Despite this interesting observation, the use of adipocytes as a model for research is yet to be explored. To ascertain the effects of HMB on the lipid metabolism of adipocytes and elucidate the underlying mechanisms, the 3T3-L1 cell line was employed. Firstly, serial doses of HMB were added to 3T3-L1 preadipocytes to evaluate the effects of HMB on cell proliferation. HMB (50 µM) significantly promoted the proliferation of preadipocytes. Next, we investigated whether HMB could attenuate fat accumulation in adipocytes. The results show that HMB treatment (50 µM) reduced the triglyceride (TG) content. Furthermore, HMB was found to inhibit lipid accumulation by suppressing the expression of lipogenic proteins (C/EBPα and PPARγ) and increasing the expression of lipolysis-related proteins (p-AMPK, p-Sirt1, HSL, and UCP3). We also determined the concentrations of several lipid metabolism-related enzymes and fatty acid composition in adipocytes. The HMB-treated cells showed reduced G6PD, LPL, and ATGL concentrations. Moreover, HMB improved the fatty acid composition in adipocytes, manifested by increases in the contents of n6 and n3 PUFAs. The enhancement of the mitochondrial respiratory function of 3T3-L1 adipocytes was confirmed via Seahorse metabolic assay, which showed that HMB treatment elevated basal mitochondrial respiration, ATP production, H⁺ leak, maximal respiration, and non-mitochondrial respiration. In addition, HMB enhanced fat browning of adipocytes, and this effect might be associated with the activation of the PRDM16/PGC-1α/UCP1 pathway. Taken together, HMB-induced changes in the lipid metabolism and mitochondrial function may contribute to preventing fat deposition and improving insulin sensitivity.

β-Hydroxy-β-Methylbutyric Acid Promotes Repair of Sheep Myoblast Injury by Inhibiting IL-17/NF-κB Signaling

Delayed muscle development and impaired tissue repair are common occurrences in sheep reared for mutton. Therefore, understanding the regulatory mechanisms involved in muscle growth and development is critical for animal production. Skeletal muscle satellite cells (SMSCs) can simulate the proliferation and differentiation of muscle cells and could be induced to differentiate into myoblasts. β-hydroxy-β-methylbutyric acid (HMB) is an additive commonly used in animal production. This study examined the effect of HMB on myoblast injury repair using flow cytometry, EdU assay, RNA sequencing, Western blot, and ELISA. Our results showed that HMB could inhibit IL-17 expression and, in turn, inhibit NF-κB signaling. By acting on the downstream genes of NF-κB pathway IL-6, TNF-α and IL-1β, HMB inhibits the apoptosis and promotes the proliferation of myoblasts. The findings of this study provide insight into the mechanism by which HMB mediates myoblast injury repair in sheep.