H. Kobayashi et al., Identification of link protein during follicle development and cumulus cell cultures in rats, ENDOCRINOL, 140(8), 1999, pp. 3835-3842
Cumulus oocyte complex (COC) expansion is induced through hyaluronic acid p
roduction and accumulation of proteins of the inter-alpha-trypsin inhibitor
family in the gonadotropin-stimulated cumulus cells. Link protein, a glyco
protein found in cartilage, interacts specifically with hyaluronic acid and
stabilizes the binding of proteoglycan monomers to hyaluronic acid to form
aggregates. The aim of this study was to investigate the expression of imm
unoreactive link protein during follicle development in rats and in cumulus
cells in culture by immunohistochemistry and Western blot as well as by sp
ecific enzyme-linked immunosorbent assay. Immunohistochemical analysis reve
aled that the extracellular matrix of cumulus cells that were morphological
ly at a stage of COC expansion were markedly stained for link protein, wher
eas granulosa cells from immature follicles were not stained. Cumulus cells
deposited link protein into the extracellular matrix in an in vitro cultur
e system. The staining intensity was negated by the treatment with hyaluron
idase, suggesting that the link protein is bound to hyaluronic acid. We hav
e identified a 42-kDa immunoreactive link protein in rat ovary during the p
reovulatory period and in COC extracts. Addition of FSH to the medium of cu
mulus cells in culture supplemented with 10% FBS and oocyte-conditioned med
ium resulted in an increased rate of link protein synthesis. This work sugg
ests that the cumulus cells synthesize the link protein that may stabilize
the binding of inter-alpha-trypsin inhibitor or dermatan sulfate proteoglyc
an to hyaluronic acid to make up hyaluronic acid-rich matrix aggregate.