ECE2021 Oral Communications Oral Communications 6: Calcium and Bone (6 abstracts)
Osteocalcin actives GPRC6A and calcium-sensing receptor modulating intracellular signaling pathways, cell cycle genes, and apoptosis in human parathyroid tumor cells
Chiara Verdelli 1 , Giulia Stefania Tavanti 1 , Irene Forno 2 , Valentina Vaira 3 , Riccardo Maggiore 4 , Gilberto Mari 4 , Leonardo Vicentini 5 , Paolo Dalino Ciaramella 6 , Giovanni Lombardi 7 , 8 & Sabrina Corbetta 9
1Laboratory of Experimental Endocrinology, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy; 2Division of Pathology, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy; 3Division of Pathology, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Department of Pathophysiology and Organ Transplantation, University of Milan, Milan, Italy; 4Endocrine Surgery, IRCCS Ospedale San Raffaele, Milan, Italy; 5Endocrine Surgery, IRCCS Istituto Auxologico, Milan, Italy; 6Endocrinology Unit, ASST Grande Ospedale Metropolitano Niguarda, Milan, Italy; 7Laboratory of Experimental Biochemistry and Molecular Biology, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy; 8University of Physical Education, Department of Athletics, Strength and Conditioning, Poznan, Poland; 9Endocrinology and Diabetology Service, IRCCS Istituto Ortopedico Galeazzi, Department of Biomedical, Surgical and Dental Sciences, University of Milan, Milan, Italy
Parathyroid glands regulate bone metabolism through PTH, while bone modulates parathyroid function through calcium and FGF23. We tested the hypothesis that the matrix protein osteocalcin (OC), secreted by osteoblasts, may modulate parathyroid function. In human parathyroid cells derived from adenomas (PAds), incubation with g-carboxylated OC (GlaOC) or undercarboxylated OC (GluOC) modulated the intracellular signaling pathways: both GlaOC and GluOC inhibited the basal phosphorylated ERK/total ERK ratio (pERK/ERK) and increased the basal phosphorylated AKT/total AKT ratio (pAKT/AKT) and active b-catenin levels. Moreover, GlaOC and GluOC modulated the expression of parathyroid genes: GlaOC increased the expression levels of the PTH gene, modulated the expression of genes involved in cell cycle, increasing CCND1 and reducing CDKN1B/p27 and TP73, and increased the expression of CASR. GluOC also stimulated the transcription of PTH, while it did not exert any effect on the other genes, except by inhibiting MEN1 expression. Of note, GlaOC and GluOC treatments reduced the proportion of apoptotic cells induced by incubation with staurosporin. OC acts through the putative membrane receptor GPRC6A, whose transcripts and proteins were variably detected in human PAds and did not correlate with the expression of CASR. Immunohistochemistry showed specific GPRC6A cytoplasmic staining in some cells and membrane staining in other cells scattered throughout the parenchyma, both in normal and tumor parathyroids. As GPRC6A and CASR share high homology, OC may activate both the receptors. Reducing the CASR expression by treating PAds-derived cells with CASR siRNA, we observed that GlaOC and GluOC modulated the ERK pathway mainly through GPRC6A activation, while CASR activation was involved in the modulation of the AKT and b-catenin pathways. Using HEK293A cells transfected with GPRC6A and with CASR, we further dissected the effects of GlaOC and GluOC on the signalling pathways in presence of different extracellular calcium concentrations ([Ca2+]o), finding that GlaOC and GluOC can activate CASR, that [Ca2+]o is needed to activate CASR by GlaOC and GluOC, and that GlaOC activates GPRC6A also in calcium-free medium as well as in presence of 5.0 mM [Ca2+]o but exerting opposite effects with respect that observed in presence of 1.5 mM [Ca2+]o.
Conclusion
OC can be added to the bone-parathyroid cross-talk; it may modulate the CASR sensitivity to [Ca2+]o of the parathyroid cells, representing a target for potential medical treatment of parathyroid disorders.
Volume 73
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Endocrine Abstracts
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