Integrin alpha5 is expressed on human luteinizing granulosa cells during corpus luteum formation, and its expression is enhanced by human chorionic gonadotrophin in vitro.

We previously reported that human granulosa cells (GC) express integrin alpha6beta1, in large follicles and early corpus luteum (CL). In this study, we examined the expression of integrin alpha5 and fibronectin (FN) by immunohistochemistry. Integrin alpha5 was undetectable on human GC in preovulatory follicles, but it was intensely expressed on luteinizing GC of CL in the early luteal phase, and it was weakly expressed on large luteal cells (LL) in the midluteal phase. FN was similarly expressed between GC/LL. Thus, integrin alpha5 and FN were stage-specifically expressed on/between luteinizing GC in the early luteal phase. Next we examined the effect of human chorionic gonadotrophin (HCG) on expression of integrin alpha5 on luteinizing GC in vitro. GC obtained from preovulatory follicles were cultured for 3 days without (control) or with HCG (1 IU/ml), and expression of integrin alpha5 was examined by flow cytometry. Although the positivity rate did not differ, the mean relative fluorescence intensity was 3.4-fold higher in the HCG-treated group (n = 8, P < 0.01). These findings indicate that integrin alpha5 is rapidly expressed on GC during luteinization, probably under LH stimulation, and suggest that integrin alpha5 is involved in CL formation via interaction with its ligand FN.