James C. Garmey, John A. Schnorr, M. Elizabeth Bruns, David E. Bruns, Regina M. Seaner, James E. Ferguson II, Friederike C. Luking Jayes, Claudia Aguirre, Johannes D. Veldhuis
Biology of Reproduction 62 (2), 334-339, (1 February 2000) https://doi.org/10.1095/biolreprod62.2.334
Parathyroid hormone-related peptide (PTH-rp) and the PTH-rp receptor are expressed in certain cancers as well as in many normal tissues. To evaluate the expression of this Ca2 -regulating hormone and its receptor in porcine ovary, we isolated partial cDNAs encoding homologous PTH-rp and PTH-rp receptor using reverse transcription-polymerase chain reaction (RT-PCR). The cDNA encoding PTH-rp (419 base pairs [bp]) was 92% and 87% homologous to human and rat sequences, respectively, while the PTH-rp receptor clone (167 bp) was 94% and 91% identical to the human and rat genes. Qualitative estimates of PTH-rp mRNA by RT-PCR indicated that the PTH-rp gene is expressed at high levels in the corpus luteum but is undetectable in granulosa and theca cells isolated from small (1–5 mm) and medium-sized (5–8 mm) antral follicles. In contrast, PTH-rp receptor transcripts were most abundant in corpora lutea and theca cells, and least abundant (albeit detectable) in granulosa cells.
Regulation of PTH-rp protein production was assessed in serum-free monolayer cultures of porcine granulosa cells. Transforming growth factor (TGF)-β1 (100 ng/ml) increased PTH-rp concentrations (assayed by two-site immunoradiometric assay of culture media) as well as corresponding PTH-rp mRNA accumulation (assessed by RT-PCR) in a time-dependent manner, with maximal responses of 3- to 5-fold at 96 h. TGF-β1 dose-response studies revealed an ED50 of 0.24–0.38 ng/ml with a maximal effect at 30 ng/ml. Other growth factors and hormones, including insulin, insulin-like growth factor (type I), epidermal growth factor, FSH, estradiol, and interleukin-1, failed to alter PTH-rp secretion.
Biological effects of PTH-rp were evident in purified porcine theca cells. Using the Ca2 -sensitive fluorescent indicator dye, fura-2, and digital imaging videomicroscopy, we found that PTH-rp (1 μM) stimulated intracellular free calcium ion concentrations ([Ca2 ]i) in single porcine theca cells. The [Ca2 ]i elevation was characterized by a slow and prolonged rise. After PTH-rp stimulation, theca cells maintained responsiveness to hormone stimulation by LH, which elicited a typical theca cell [Ca2 ]i response.
Our results allow a hypothesis of a paracrine intrafollicular signaling system involving interaction between theca cell-derived TGF-β and granulosa cell-derived PTH-rp, with feedback by PTH-rp on theca cells. Alternatively, expression of mRNAs encoding PTH-rp and its receptor in corpora lutea suggests that this peptide may play a role in luteal cell function. The precise role of this intraovarian PTH-rp system will require further study.