Dysfunctional terminal differentiation of satellite cells in the wooden breast muscle of Ross 308 broiler chickens

Muscle satellite cells (MuSCs), defined as skeletal muscle-resident stem cells, serve as the principal cellular mediators of the repair and regeneration processes in impaired skeletal muscle tissue. However, myofibers with degeneration and necrosis in wooden breast (WB) myopathy are still not completely repaired, and this study aims to elucidate the functional changes of MuSCs between normal and WB-affected pectoralis major (PM) muscle of broilers. A total of 100 Ross 308 broilers (42 days old) fed the same diet were randomly selected. Initial identification of normal and WB phenotypes was conducted through behavioral assessments and manual palpation of the PM muscle. Ultimately, PM samples were harvested from 8 chickens per experimental group, classified into normal (NOR), moderate (MOD), and severe (SEV) groups based on necropsy grading. The superficial cranial region of each PM sample was isolated for quantitative analysis of MuSCs functional markers. One-way ANOVA was used to compare differences among groups, with p < 0.05 indicating significant differences. Results showed that breast muscle weight and morphological indices (length, top/middle/bottom heights) of MOD and SEV groups were higher than those of NOR group (P < 0.05). The SEV group exhibited larger myofiber diameter and cross-sectional area but lower fiber density compared to NOR group (P < 0.05). There was higher mitotic activity of MuSCs, populations of MuSCs and myoblasts in severe WB muscle, characterized by elevated BrdU⁺, Pax7⁺, and MyoD⁺ cells (P < 0.05). The mRNA or protein expressions of Myf5, MyoD, MyoG, Myomaker, Myomerger, MSTN, HGF, IGF-1 and IGF-1R were upregulated in SEV group, along with downregulation of MRF4 protein (P < 0.05). Taken together, the proliferation of MuSCs is promoted in WB muscle, while terminal differentiation and fusion were failure, inhibiting the formation of multinucleated myotubes and mature myofibers. These findings elucidate novel mechanistic insights into the pathogenesis of WB myopathy and potential strategies for stem cell-mediated WB prophylaxis in poultry industry.