Spatiotemporal Expression Inversion of CYP11A1 in the HPO Axis and Its Regulation of Granulosa Cell Proliferation via the PI3K/AKT/mTOR Pathway in Wuding Chickens.

Broodiness in poultry represents a major bottleneck for reproductive performance, governed by complex remodeling of the hypothalamic-pituitary-ovarian (HPO) axis. CYP11A1, the rate-limiting enzyme in steroidogenesis, is essential for hormone synthesis; however, its spatiotemporal dynamics within the HPO axis during reproductive transitions remain unclear. Using the Wuding chicken as a model, this study characterized the expression profile and cellular function of CYP11A1. We identified a distinct "ovary-hypothalamus expression inversion" pattern: CYP11A1 expression exhibited an ovary-dominant pattern during the egg-laying period to support folliculogenesis; however, this shifted to a hypothalamus-dominant pattern during the broodiness period. This inversion indicates its active role in central neurosteroid modulation rather than a passive response to HPO axis regression. In vitro assays in granulosa cells (GCs) demonstrated that CYP11A1 overexpression significantly upregulated AKT1 and mTOR transcription, promoted the G0/G1 to S/G2/M cell cycle transition, and enhanced cell proliferation. Conversely, CYP11A1 knockdown arrested the cell cycle and suppressed the PI3K/AKT/mTOR pathway. Additionally, CYP11A1 coordinated the expression of steroidogenic genes (STAR, HSD3B1), reflecting a coupling between steroid metabolism and cell growth. These findings reveal CYP11A1 as a critical molecular node linking HPO axis remodeling, granulosa cell proliferation, and steroidogenesis, providing a potential target for molecular breeding to mitigate broodiness in indigenous chickens.