Different expressions of mitogen-activated protein kinase (MAPK) family between cumulus and mural granulosa cells

Abstract

Objective: The morphology and function of cumulus granulosa cells are very different from those of mural granulosa ones. In previous studies, apoptosis was higher in mural granulosa cells than in cumulus cells. This may result from the difference of intracellular signal transductions. MAPK family is one of important intracellular signals. To further understand the differences between mural and cumulus granulosa cells, we evaluated and compared their expression of MAPKs. Design: A prospective study. Materials and Methods: Patients (n=3) with male factor caused infertility were stimulated with gonadotropin releasing agonist and human menopausal gonadotropin for follicle development in an in vitro fertilization and embryo transfer treatment program. Thirty-five hours after the human chorionic gonadotropin injection, follicle aspiration was performed. Oocytes and granulosa cells were obtained and cumulus granulosa cells were mechanically separated from the oocyte, immediately after the retrieval. Mural and cumulus granulosa cells were washed with cooled phosphate buffered solution (PBS) containing Na3VO4 and lysed with cold lysis buffer. Whole cell lysates were centrifuged, and lysate supernatant was analyzed by Western blot analysis using antibodies of the MAPK family; extracellular signal-regulated kinase (ERK)1/2, Jun amino-terminal kinase (JNK), and p38 proteins (p38). Results: The expression of total ERK1/2 in the mural cells detected by Western blotting was stronger than that in the cumulus cells. Phospholized or activated ERK1/2 in the mural cells was intensively expressed in comparison with the cumulus cells. The expression of total JNK in the mural cells was stronger than that in the cumulus cells. Phospholized or activated JNK in both mural and cumulus cells showed almost no expression. The expression of total p38 in the mural cells was stronger than that in the cumulus cells. Phospholized or activated p38 in the mural cells was intensively expressed when compared with the cumulus cells. Conclusion: MAPK family in cumulus and mural granulosa cells showed different expressions. MAPK family has an important role in intracellular signaling and is involved in key functions such as cell proliferation, differentiation, cell survival and death. This different expression indicates that granulosa cells of each location in a follicle are using their unique intracellular signal transduction and therefore express their own unique functions including steroidogenesis and production of essential substances for ovulation.