Syndecan-4 expression is associated with follicular atresia in mouse ovary

Ovarian granulosa cells synthesize heparan sulfate proteoglycans (HSPGs), that have anticoagulant properties. Moreover, HSPGs greatly increase in the granulosa cells during follicular atresia. However, the species of ovarian HSPGs have not yet been identified. Syndecan-4 (ryudocan, amphiglycan) is a membrane-spanning HSPG and a member of the syndecan family. Herein, we demonstrate that syndecan-4 is expressed in the granulosa cells of type 4-5b follicles and, most intensely, in those of the atretic follicles in the mouse ovary, as revealed by in situ hybridization. There is no relationship between syndecan-4 expression and age or sexual cycle stage. Compared with syndecan-4 expression, syndecan-1 and -3 are expressed more abundantly in postovulatory follicles and the corpora lutea, but less in the type 4-5b follicles and much less in the atretic follicles. Immunohistochemistry also demonstrates syndecan-4 expression in atretic follicles with apoptosis. The present study has revealed the distinct modes of expression of the syndecan family members, and the association of syndecan-4 expression and apoptosis in ovarian atretic follicles.