Structural and molecular dysfunctions in granulosa cells: A key contributor to porcine follicular atresia

The physiological function and metabolism of granulosa cells (GCs) are highly regulated processes that coordinate cells specification and morphogenesis to produce related cytokines and secretions that are closely associated with follicular development. However, there is no comprehensive understanding of the molecular functions of GCs in follicular atresia. Here, we investigated follicular morphological features, fibrosis, vascular changes, and immune cell distribution. Additionally, we analyzed the correlation between solute carrier transport proteins (SLCs) and amino acids, and characterized the levels of key enzymes in glucose metabolism. Morphological results showed that atretic follicles had increased gradual fibrosis in the stroma, decreased density of the inner microvasculature, lysis of the basement membrane, and collapse of GCs in the follicular antrum. Further results showed that CD68 macrophages and CD163 macrophages were initially distributed in the stroma of the healthy follicles. When the follicle was atretic, the spatiotemporal distribution of CD68 macrophages gradually migrated from the theca cells to the periphery of the collapsed GCs layer in the follicular antrum. Moreover, SLC39A14 and SLC16A1 were most significantly expressed in the GCs of healthy follicles (P < 0.01), and this correlation was positively associated with amino acids content. The results also showed that the key enzymes of glucose-related pathways (glycolysis (ALDOC, ENO1, HK1), pyruvate metabolism (LDHA, PDHA1), and tricarboxylic acid cycle (IDH1, OGDA, SDHB, CS) were significantly downregulated in GCs of atretic follicles by proteomic analysis (P < 0.05). These results revealed morphological changes and associated molecular events during follicular atresia, which may offer a new perspective on the underlying mechanisms of follicular atresia.