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Comment |
Endocrine meeting. [P3-252] Characterization of Parathyroid Hormone-2 Receptor in the Rodent Ovary: FSH Regulation and Effects on Granulosa Cell Function.
Mark Paciga, Ted B Usdin. Lab of Genet, NIMH NIH, Bethesda, MD
The parathyroid hormone-2 receptor (PTH2R) is a G-protein coupled receptor with a physiological role that has not been fully elucidated. Although PTH2R is expressed and synthesized at highest levels in the central nervous system, studies from our laboratory have indicated the presence of PTH2R messenger RNA in peripheral endocrine tissues. In the rodent reproductive system PTH2R gene expression was detected over the epithelium of spermatic tubules, Leydig cells and sperm cells within the lumen of the epididymus. PTH2R gene expression was also detected in the placenta and ovary. Based on these observations it is possible that PTH2R and its natural ligand, tuberoinfundibular peptide of 39 residues (TIP39), modulate some function(s) of the reproductive system via endocrine and / or autocrine / paracrine mechanisms. Therefore the objectives of this study were to determine the cellular localization of PTH2R in the rodent ovary, to determine whether ovarian PTH2R mRNA levels are affected by mediators of ovarian physiology, and to determine which aspect of ovarian function the TIP39-PTH2R ligand-receptor system modulates. Immunohistochemical analysis of rodent ovary cryosections indicated that only granulosa cells of pre-ovulatory follicles contained PTH2R-immuno positive cells. Real-time PCR analysis of primary cultures of rat granulosa cells revealed the presence of PTH2R levels under basal culture conditions. Exposure of rat granulosa cell cultures to FSH (48 hours; 100 ng/mL) resulted in a significant increase in PTH2R gene expression compared to control cultures. Similar stimulatory effects of FSH on PTH2R expression was observed in the KK-1 mouse granulosa cell line. KK-1 cells also demonstrated the presence of a functional PTH2R signal transduction pathway as indicated by an increase in cAMP levels in cells incubated with TIP39. Although TIP39 did not alter basal steroid production, FSH-stimulated estradiol accumulation in the culture media of rat primary granulosa cells was significantly reduced by TIP39 (∼7500 pg/mL in control cultures vs. ∼2500 pg/mL in TIP39 treated cultures). The results presented in this study indicate that in the rodent ovary PTH2R is localized to the granulosa cell compartment where its expression is FSH regulated. The observation that TIP39 was able to decrease FSH-stimulated estradiol output by granulosa cells suggests that the TIP39-PTH2R system may affect reproductive function via its effects on steroidogenesis.
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