Heat shock protein 90α couples with the MAPK-signaling pathway to determine meiotic maturation of porcine oocytes.

Heat shock protein 90 (Hsp90) functions as a molecular chaperone in its interaction with clients to influence multiple cellular and physiological processes. However, our current understanding on Hsp90's relationship with mammalian oocyte maturation is still very limited. Here, we aimed to investigate Hsp90's effect on pig oocyte meiotic maturation. Endogenous Hsp90α was constantly expressed at both mRNA and protein levels in porcine maturing oocytes. Addition of 2 µM 17-allylamino-17-demethoxygeldanamycin (17-AAG), the Hsp90 inhibitor, to in vitro mature cumulus-oocyte complexes (COC) significantly decreased Hsp90α protein level (P < 0.05), delayed germinal vesicle breakdown (GVBD) (P < 0.05), and impeded the first polar body (PB1) extrusion (P < 0.01) of porcine oocytes. 2 µM 17-AAG treatment during in vitro maturation also decreased the subsequent development competence as indicated by the lower cleavage (P < 0.001) and higher fragmentation (P < 0.001) rates of parthenotes, whereas no effects on the percentage and average cell number of blastocysts were found. Immunodepletion of Hsp90α by antibody microinjection into porcine oocytes at germinal vesicle and metaphase II stages induced similar defects of meiotic maturation and parthenote development, to that resulted from 2 µM inhibitor 17-AAG. For oocytes treated by 2 µM 17-AAG, the cytoplasm and membrane actin levels were weakened (P < 0.01), and the spindle assembly was disturbed (P < 0.05), due to decreased p-ERK1/2 level (P < 0.05). However, the mitochondrial function and early apoptosis were not affected, as demonstrated by rhodamine 123 staining and Annexin V assays. Our findings indicate that Hsp90α can couple with mitogen-activated protein kinase to regulate cytoskeletal structure and orchestrate meiotic maturation of porcine oocytes.