Investigating the cellular foundations of breast muscle myopathies in broiler chickens

The genetic selection for high growth rate, breast muscle yield, and feed efficiency in modern broilers has been a double-edged sword. While it has resulted in the desired traits, it has also led to broiler myopathies. Recent omics studies have shown that hypoxia may be a potential factor that damages the myofiber niche and compromises muscle repair processes. The objective of this study was to optimize isolation protocols for primary broiler satellite cells (SCs) and fibroadipogenic progenitors (FAPs) and to characterize SCs proliferation and differentiation under hypoxia. The study first focused on the optimization of isolation procedures and culture conditions for primary broiler SCs. Simple and cost-effective preplating techniques were used to purify SCs, which may improve the fidelity of follow-on experiments. In addition, myogenic differentiation potential was maximized under optimal conditions with different types and concentrations of serum and chicken embryo extract. This dissertation further demonstrated the effects of hypoxia on the differentiation and metabolism of SCs. Satellite cells were exposed to hypoxia conditions for 48 h and normoxia recovery. Hypoxia improved SCs proliferation by maintaining Pax7 and reducing Myod1 and myogenin while reducing myogenic differentiation. The cell proliferation was not rescued by 24 h normoxia recovery, whereas myogenic potential was recovered. In addition, hypoxia-activated AMPK and upregulated proteins involved in lipid metabolism and cellular stress, with decreased mitochondrial activity and increased lipid accumulation in myotubes, which indicates that the balance between fatty acid uptake and oxidation was disrupted. Several differentially expressed genes were also identified across myogenic differentiation under hypoxia with targeted RNA sequencing. Lastly, we established an isolation protocol for broiler FAPs for the first time. Through the comparative analysis between FAPs and preadipocytes, the induction of adipogenic differentiation and morphology of adipocytes derived from muscle and adipose tissues are similar. However, fatty acid methyl ester and targeted RNA sequencing data revealed a distinct separation between FAPs and preadipocytes throughout adipogenic differentiation. In conclusion, these data provide valuable insight into the biology of SCs and FAPs and the effects of hypoxia on SC proliferation and differentiation to better understand broiler myopathies.