Cumulus-associated α2-macroglobulin derivative retains proconceptive glycodelin-C in the human cumulus matrix

BACKGROUNDGlycodelin-C is a glycodelin isoform isolated from the cumulus matrix. It stimulates spermatozoa-zona pellucida binding. Here, we report the isolation and characterization of a novel glycodelin interacting protein (GIP) from human cumulus matrix.METHODSGIP was purified by liquid chromatograph and identified by mass spectrometry. The interaction of GIP with glycodelin, matrix molecule and spermatozoa were investigated. RESULTS Mass spectrometry analysis suggested that GIP contained the N-terminal region of α2-macroglobulin, confirmed by western blot with anti-α2-macroglobulin antibody. GIP bound to native but not deglycosylated glycodelin-C in native gel electrophoresis, suggesting that the binding was glycosylation-dependent. GIP did not bind to capacitated and uncapacitated human spermatozoa. The cumulus cells could convert exogenous labeled α2-macroglobulin into GIP in vitro. GIP interacted with hyaluronic acid, a major component of the cumulus matrix. Glycodelin-C bound to hyaluronic acid-coated agarose beads in the presence of GIP. Human spermatozoa acquired the hyaluronic acid-GIP-bound glycodelin-C during incubation in vitro. CONCLUSION The hyaluronic acid-GIP complex formed in the cumulus matrix retains and concentrates glycodelin-C in the cumulus matrix for displacing sperm-bound glycodelin-A and-F and stimulating the zona binding activity of the spermatozoa traversing through the cumulus mass.