HMB and Liraglutide Synergistically Protect C2C12 Myotubes from Lipotoxic Atrophy via mTOR Signaling

Type 2 diabetes (T2D) is often complicated by sarcopenia, characterized by impaired insulin signaling, lipotoxicity, oxidative stress, and progressive muscle loss. While Liraglutide, a GLP-1R agonist, effectively improves glucose control and reduces lipid burden, its capacity to preserve muscle integrity under diabetic lipotoxic conditions remains limited. This study addresses the critical gap in protecting skeletal muscle from HG+FFA-induced injury, investigating whether β-hydroxy-β-methylbutyrate (HMB) can enhance liraglutide's muscle-protective effects.

Differentiated C2C12 myotubes were exposed to high-glucose plus free fatty acid (HG+FFA) to establish a sublethal lipotoxic model. Cells were then treated with Liraglutide, HMB, or their combination. Researchers assessed cell viability, lipid accumulation, myotube morphology, insulin signaling, glucose uptake, mitochondrial function, reactive oxygen species (ROS), antioxidant gene expression, and atrophy-related signaling. Key markers like atrogin-1 and MuRF1 were evaluated to determine the extent of muscle atrophy.

HG+FFA exposure induced significant lipid droplet accumulation, impaired insulin signaling, and reduced glucose uptake. It also disrupted mitochondrial membrane potential, increased ROS production, suppressed antioxidant gene expression, and promoted an atrophic phenotype marked by increased atrogin-1 and MuRF1 with reduced myogenic markers. Liraglutide alone reduced large lipid droplets and partially improved insulin signaling but showed limited efficacy in preserving myotube morphology. HMB alone had modest effects on lipid accumulation but preserved myotube area. > Notably, combined HMB and Liraglutide treatment more effectively reduced lipid burden, restored insulin signaling and glucose uptake, attenuated mitochondrial dysfunction and oxidative stress, and restored antioxidant gene expression. This combination also preserved MyHC-positive area and myotube diameter while suppressing atrogin-1/MuRF1 activation. These protective effects were largely attenuated by rapamycin, indicating at least partial dependence on mTOR-associated signaling.