Aberrant expression of PDGF ligands and receptors in the tumor prone ovary of follitropin receptor knockout (FORKO) mouse

Abstract

Although PDGF family members play a vital role in cell proliferation, motility and chemotaxis via activation of structurally similar α- and β-receptors, little is known of their function in ovarian regulation and induction of tumorigenesis. Microarray analyses of ovaries from young follitropin receptor knockout (FORKO) mice that are prone to late ovarian tumors upon aging have revealed significant imbalances in PDGF ligands and receptors. We hypothesized that FSH/FSH-R signaling may exert effects partly by regulation of PDGF the family. To further understand their implications for ovarian tumorigenesis, we studied FORKO ovaries and hormonal regulation of the PDGF family members in normal mice, by using RT-PCR, Q-PCR, immunohistochemistry and western blotting. While PDGF-C and PDGFR-α increased, PDGFR-β mRNA and protein decreased significantly in absence of FSH-R signaling. In the normal ovary, PDGFR-α was not affected by gonadotropin (eCG) stimulation but PDGF-C and PDGFR-β decreased. Administration of estradiol decreased PDGF and their receptors. To further probe the differential regulation of PDGF family members by eCG and estradiol, we co-administered eCG with estrogen antagonist, ICI 182780. Increase in PDGFR-α in the absence of estradiol suggests direct effects of FSH signaling. During the estrous cycle in mice PDGF-C, PDGF-D and PDGFR-α mRNA levels were higher at the proestrous. By IHC, we report for the first time the localization of PDGF-C, PDGFR-α and PDGFR-β protein in mouse ovarian compartments including the surface epithelium that is also altered in mutants. Immunostaining of PDGFRs increased as the follicle developed to preantral stage and declined thereafter. Thus, FSH modulates PDGF family members, partly via E2, suggesting that loss of FSH-R signaling causes an imbalance of PDGF family members predisposing the abnormal ovarian follicular environment for inducing tumorigenesis in aging FORKO mice. © 2006 Oxford University Press.