Hormonal Signaling and Follicular Regulation in Normal and Miniature Pigs During Corpus Luteum Regression

Reproductive efficiency in pigs is regulated by hormonal pathways that control follicular development at Day 15 of the estrous cycle, during corpus luteum regression. Miniature pigs are extensively employed as human-relevant models in biomedical research, yet their reproductive characteristics during mid-luteal regression remain inadequately characterized, limiting assessments of their translational reliability. Differences in follicular morphology, hormonal signaling, and vascular development may underlie their lower fertility compared to conventional pigs. In this study, follicular development after corpus luteum formation was compared between conventional pigs and minipigs using histological staining, immunofluorescence, hormonal assays, and transcriptomic profiling. The expression of VEGF, mTOR, LH, FSH, PAPP-A, and apoptosis markers was evaluated across the granulosa and thecal regions. Differential gene expression was analyzed using microarray data followed by GO categorization. Minipigs exhibited smaller follicles, reduced vascularization, and lower VEGF and MMP activity compared to conventional pigs. Expression of LH and PAPP-A was higher in conventional pigs, while minipigs showed relatively elevated E2 and FSH levels. Transcriptomic data revealed greater upregulation of cell-survival- and angiogenesis-related genes in conventional pigs, including genes involved in IGF pathways. Apoptosis and poor extracellular matrix remodeling were more pronounced in minipigs. Minipigs demonstrated impaired follicular remodeling and weaker hormonal signaling after corpus luteum formation, which likely contributed to their reduced reproductive efficiency. Understanding these species differences can guide breeding strategies and fertility management in biomedical and agricultural settings.