Abstract
To elucidate the physiological mechanisms by which Tibetan sheep myocardium adapts to chronic hypoxia in high-altitude environments, this study investigated the effects of altitude on Optic Atrophy 1 (OPA1) and Protein Kinase RNA-like Endoplasmic Reticulum Kinase (PERK) expression, mitochondrial morphology, and functional integrity. Utilizing transmission electron microscopy (TEM), enzyme-linked immunosorbent assay (ELISA), immunohistochemistry, and reverse transcription quantitative PCR (RT-qPCR), we analyzed the protein localization and gene/protein expression levels of PERK and OPA1, the activities of malate dehydrogenase (MDH), citrate synthase (CS), and oxidative phosphorylation (OXPHOS) complexes I, II, and IV, as well as mitochondrial ultrastructure in the myocardium of Tibetan sheep inhabiting high-altitude and very-high-altitude environments. Results demonstrated significantly elevated expression levels of OPA1 and PERK proteins and their corresponding genes in very-high-altitude myocardium compared to high-altitude counterparts (P < 0.05), with a strong positive correlation between their protein expressions. Mitochondrial density in very-high-altitude cardiac muscle was markedly reduced (P < 0.05), yet these mitochondria exhibited enhanced fusion-fission dynamics, increased number and density of cristae, and a more compact arrangement (P < 0.05). Concurrently, the activity of MDH and OXPHOS complex IV was significantly higher in very-high-altitude myocardium (P < 0.05), indicative of augmented tricarboxylic acid cycle flux. Furthermore, mitochondria-associated endoplasmic reticulum (ER) membranes were more abundant in very-high-altitude samples. Collectively, these findings suggest that chronic hypoxia drives coordinated upregulation of OPA1 and PERK, remodeling mitochondrial architecture and enhancing metabolic activity. This adaptive response likely underpins the superior energy production capacity of high-altitude Tibetan sheep myocardium, ensuring functional integrity under sustained hypoxic stress.