Expression of Calcium‐Sensing Receptor in Quail Granulosa Explants: A Key to Survival During Folliculogenesis

Abstract

This study investigated the potential role of the calcium-sensing receptor (CaR) in mediating survival of granulosa cells (GCs) in follicles of the Japanese quail (Coturnix coturnix japonica). Immunoreactivity of CaR was shown in GCs of quail preovulatory follicles as well as in the remnants of the GC layer after ovulation. Conversely, the CaR could not be detected by immunocytochemistry in the granulosa of smaller undifferentiated follicles. The presence of CaR in follicles destined to ovulate was confirmed by immunoblot and the receptor was identified as a protein of 115-125 kDa. Addition of different CaR agonists to granulosa explants in culture for 24 hr caused inhibition of apoptosis elicited by gonadotropin withdrawal on its own or in combination with C 8 -ceramide addition. Furthermore, R-568, a specific, positive allosteric modulator of CaR, not only inhibited apoptosis but also increased GC number per viewing field in cultured granulosa explants. This observation could be attributed not to a rise in GC proliferation but to a more compact tissue structure, including a distinct distribution pattern of connexin-43 gap junction proteins. Incubation in the presence of LY294002, a specific phosphatidylinositol-3 kinase inhibitor, increased GC apoptosis, indicating that this pathway is involved in GC survival signaling. However, LY294002-induced apoptosis was considerably attenuated by incubation with R-568, indicating that other pathways might be major contributors to the survival mediated by CaR agonists. We provide direct evidence for the presence of CaR in preovulatory granulosa explants and suggest a pivotal role for CaR in follicle selection. Anat Rec,

The Calcium-Sensing Receptor as a Regulator of Cellular Fate in Normal and Pathological Conditions

“…Phosphorylation of ERK regulates cell growth and differentiation through phosphorylation and activation of nuclear TFs, such as Elk-1. In agreement with these downstream effects, stimulation of the CaSR in many model systems, including smooth muscle cells, epithelial cells and granulosa cells, results in an increased cell number and/or increased survival [5,10,49,53,61]. Finally, CaSR signaling also has been implicated in regulating colonic epithelial cell differentiation and keratinocyte differentiation through the activation of E-cadherin signaling in a Rhodependent manner with filamin A involvement (Fig.…”

“…Over the past decade, the CaSR has been identified as a novel molecular player in the determination of cellular fate with a fundamental impact on proliferation, apoptosis and differentiation in a diverse array of tissues [2][3][4][5][6][7][8][9][10]. The CaSR coordinates these activities through regulation of a myriad of signaling pathways, including EGFR signaling, MAPK cascades and Ecadherin signaling [3,36,37,47,[50][51][52][62][63][64].…”

“…Incubation of horse oocytes in the presence of calcium in combination with the calcimimetic R-467 results in significantly increased numbers of oocytes in metaphase II, and this is attenuated by pre-treatment with the CaSR antagonist NPS-2390 [88]. Furthermore, the CaSR is not only expressed in the germ line, but also in the surrounding somatic cells where activation has been proposed to play a role in follicle survival [10].…”

“…levels, regulating diverse processes such as hormone secretion, gene expression, ion channel activity, inflammation, and control of cellular fate. Here, we will review the recent findings regarding the physiological effects of CaSR activity on the regulation of cellular fate, particularly in the context of proliferation, differentiation and apoptosis [2][3][4][5][6][7][8][9][10]. We will discuss how CaSR signaling determines cellular fate during normal development and how dysregulated signaling might promote the pathogenesis of many diseases, ranging from proliferative to neurodegenerative and vascular diseases.…”

Parameters for calcium metabolism in women with polycystic ovary syndrome who undergo clomiphene citrate stimulation: a prospective cohort study

“…Moreover, it has been shown, in a small sample size, that PCOS-associated signs of hyperandrogenism were alleviated after administration of high doses of vitamin D (22). Recently, serum calcium levels have been suggested to play a possible role in follicle selection, as calcium receptors have been found to be expressed in preovulatory granulosa explants (23). It has also been mentioned that higher vitamin D levels in serum and follicular fluid would be associated with increased clinical pregnancy rates in women who undergo in vitro fertilization (24).…”