Luteinizing hormone activates the Hippo pathway to promote progesterone synthesis in bovine luteal cells

BACKGROUND: Progesterone production by the corpus luteum is essential for embryo implantation and early pregnancy maintenance and is acutely stimulated by luteinizing hormone (LH). While LH signaling through protein kinase A (PKA) is well established, downstream regulatory networks that constrain or shape luteal steroidogenesis remain incompletely defined. Here, we identify a previously unrecognized role for the Hippo signaling pathway in regulating luteal progesterone production. METHODS: Using primary bovine luteal cells isolated from corpora lutea, we examined the relationship between LH/PKA signaling and Hippo signaling pathway activity. Expression, phosphorylation, and subcellular localization of Hippo pathway components were assessed by immunoblotting and nuclear fractionation. Progesterone production was quantified by ELISA. LH-induced transcriptional responses were analyzed using upstream regulator prediction from RNA sequencing. Functional roles of YAP1 and TAZ were evaluated using adenoviral overexpression of constitutively active mutants and siRNA-mediated knockdown. RESULTS: Hippo pathway components were enriched in luteal cells relative to follicular precursors. LH rapidly increased phosphorylation and cytoplasmic sequestration of YAP1 and TAZ in small luteal cells through PKA. Pharmacologic inhibition of LATS1/2 did not alter LH-stimulated progesterone production, suggesting that LH-induced steroidogenesis is not limited by LATS-dependent regulation of YAP1/TAZ. Sustained activation of YAP1 or TAZ suppressed LH-induced progesterone synthesis, whereas depletion of either factor enhanced progesterone output. Consistently, RNA-seq analysis identified YAP1/TAZ, and TEAD transcription factors as inhibited upstream regulators following LH stimulation in small luteal cells. CONCLUSIONS: Our findings support a model in which LH, via PKA and activation of Hippo signaling promotes progesterone synthesis by restraining YAP1/TAZ transcriptional activity in small luteal cells. This work identifies Hippo signaling as an unrecognized regulatory layer in luteal steroidogenesis and highlights YAP1/TAZ as potential therapeutic target for luteal insufficiency and infertility.