The primary aim of this investigation was to explore the impact of different temporal stress conditions on the regulators associated with skeletal muscle
hypertrophy in bovine myocytes. Bovine satellite cells (BSCs) were extracted from three-month-old Holstein bull calves and subjected to myogenic differentiation under three thermal treatments: 38 °C (control; CON), 39.5 °C (moderate heat stress; MHS), and 41 °C (extreme heat stress; EHS) for a duration of 3 or 48 h. Exposure to EHS resulted in elevated (P < 0.01) expression levels of
heat shock protein (HSP)20, HSP27, HSP70, and HSP90, along with increased (P < 0.01)
protein levels. Moreover, cells exposed to MHS and EHS exhibited enhanced (P < 0.01) gene expression of myoblast determination
protein 1 (MyoD), while
myogenin (MyoG) was overexpressed (P < 0.01) in cells exposed to EHS. These findings suggest that heat exposure can potentially induce myogenic differentiation through the modulation of
myogenic regulatory factors. Furthermore, our investigations revealed that exposure to EHS upregulated (P < 0.01)
myosin heavy chain (MHC) I expression, whereas MHC IIA (P < 0.01) and IIX (P < 0.01) expression were increased; P < 0.01) under MHS conditions. These observations suggest that the temperature of the muscle may alter the proportion of muscle fiber types. Additionally, our data indicated that EHS activated (P < 0.01) the expression of
insulin-like growth factor 1 (IGF-1) and triggered the activation of the Akt/mTOR/S6KB1 pathway, a known anabolic pathway associated with cellular
protein synthesis. Consequently, these altered signaling pathways contributed to enhanced
protein synthesis and increased myotube size. Overall, the results obtained from our current study revealed that extreme heat exposure (41 °C) may promote skeletal muscle
hypertrophy by regulating
myogenic regulatory factors and IGF-1-mediated mTOR pathway in bovine myocytes.