205 - Exposure to Heat Stress Stimulates Cell Prolifearation and Heat Shock Protein Expression in Bovine Primary Satellite Cells

Abstract: Understanding the myogenic and self-renewal capability of satellite cells under heat stress (HS) is fundamental to coping with global warming in the beef cattle industry. Study objectives were to determine transcriptomic changes and proliferation capability of bovine satellite cells (BSCs) under moderate versus acute levels of HS and exposure times. Satellite cells were isolated from four three-month-old Holstein calves (semitendinosus) and cultured with 10% FBS/DMEM. Following 24h of attachment period, BSCs were incubated under the following temperature conditions 1) control (38°C; Con), 2) moderate (39.5°C; MHS) and extreme (41°C; EHS) and for various exposure times (0, 1, 3, 6, 12, 24, and 48 h). Cells were harvested and used for mRNA gene expression via RT-qPCR at each time point. Cell proliferation was measured using the ELISA kit. Data were analyzed by two-way ANOVA and Tukey HSD test. The expression of HSP70 was greatest (P < 0.05) in cells treated EHS at 1 and 3 h. Cells treated EHS overexpressed (P < 0.05) HSPB1 at 3, 6, 12, and 24 h. A similar pattern was observed (P < 0.05) for MyoD expression at 24 h after heat exposure. Contrarily, Myf5 and PAX3 were decreased (P < 0.05) by EHS compared to the Con at 3 h. Cell proliferation rate was enhanced (P < 0.01) in both MHS and EHS treated BSCs compared withthe Con at 48 h. Our results suggest that extreme heat exposure stimulates the HSPs (HSP70 and HSPB1) expression while modulating muscle regeneration by regulating myogenic regulatory factors (MyoD, Myf5) and PAX3. The transcriptional effect peaked after 3h of heat exposure, but the long-term (48h) exposure may activate the proliferation of BSCs.