Capacitation suppression by mouse seminal vesicle autoantigen involves a decrease in plasma membrane Ca2+-ATPase (PMCA)-mediated intracellular calcium.
Successful fertilization is tightly regulated by capacitation and decapacitation processes. Without appropriate decapacitation regulation, sperm would undergo a spontaneous acrosome reaction which leads to loss of fertilization ability. Seminal plasma is known to negatively regulate sperm capacitation. However, the suppressive mechanisms still remain unclear. In this study, we demonstrate the decapacitation mechanism of mouse seminal vesicle autoantigen (SVA) might target membrane sphingomyelin (SPM) and regulate plasma membrane Ca(2+)-ATPase (PMCA) activity. The SVA was shown to suppress sperm capacitation induced by a broad panel of capacitation factors (bovine serum albumin (BSA), PAF, and cyclodextrin (CD)). Furthermore, SVA significantly decreased [Ca(2+)](i) and NaHCO(3)-induced [cAMP](i). Cyclic AMP agonists bypassed the SVA's suppressive ability. Importantly, the SVA may regulate PMCA activity which was evidenced by the fact that the SVA decreased the [Ca(2+)](i) and intracellular pH (pH(i)) of sperm; meanwhile, a PMCA inhibitor (carboxyeosin) could reverse SVA's suppression of [Ca(2+)](i). The potential target of the SVA on membrane SPM/lipid rafts was highlighted by the high binding affinity of SPM-SVA (with a K(d) of ~3 µM) which was close to the IC(50) of SVA's suppressive activity. Additionally, treatment of mink lung epithelial cells with the SVA enhanced plasminogen activator inhibitor (PAI)-1 expression stimulated by tumor growth factor (TGF)-β and CD. These observations supported the membrane lipid-raft targeting of SVA. In summary, in this paper, we demonstrate that the decapacitation mechanism of the SVA might target membrane sphingolipid SPM and regulate PMCA activity to lower [Ca(2+)](i), thereby decreasing the [cAMP](i) level and preventing sperm pre-capacitation.
Lu
Shing-Hwa
SH
Department of Urology, National Yang-Ming University School of Medicine, Taipei City Hospital, Taipei, Taiwan.
Yen
Yuan-Kuei
YK
Ling
Thai-Yen
TY
Cheng
Kur-Ta
KT
Shu
Jye-An
JA
Au
Heng-Kien
HK
Huang
Yen-Hua
YH
D000818:Animals; D001324:Autoantigens / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D021962:Membrane Microdomains; D051379:Mice; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism*; D029607:Seminal Vesicle Secretory Proteins / Q000502:physiology*; D013075:Sperm Capacitation; D013107:Sphingolipids / Q000378:metabolism
D001324:Autoantigens; D029607:Seminal Vesicle Secretory Proteins; D013107:Sphingolipids; C085073:seminal vesicle autoantigen; D000242:Cyclic AMP; D053499:Plasma Membrane Calcium-Transporting ATPases; D002118:Calcium