FIGURE 4.

Scheme of wooden breast syndrome (WB) pathogenesis focusing on mitochondrial clearance and myofiber pathology. In pectoralis major muscles (PM) with no or mild WB, the adaptation to hypoxia by HIF1 signaling induces physiological mitochondrial clearance mediated by mitochondrial fusion, fission, and autophagy/mitophagy, which corresponds with the appearance of myofibers with small vacuoles. At this stage, PM repair appears to occur through the differentiation of myoblasts into myofibers. Alternatively, in the muscles exhibiting severe WB, the acquired resistance to hypoxia alters the regulation of mitochondrial clearance. The accumulated damage in mitochondria exacerbates the various pathological characteristics such as myofibers with rimmed vacuoles, along with their hypertrophy and degeneration. Under severe hypoxia, the regeneration of myofibers fails, which corresponds with the frequent appearance of split fibers and myofibers with small caliber. HIF1, hypoxia-inducible factor 1.