Osteoprotegerin Expression and Secretion Are Regulated by Calcium Influx through the L-Type Voltage-Sensitive Calcium Channel

Abstract

Our previous studies showed that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] modulates the activity of the Ca(V1.2) alpha-subunit of the L-type voltage-sensitive calcium channel (VSCC) by two temporally distinct mechanisms. First, 1,25(OH)2D3 rapidly modulates local Ca2+ permeability in the plasma membrane of the proliferating osteoblast. Second, treatment with 1,25(OH)2D3 reduces biosynthesis of Ca(V1.2) such that transcript levels are half of original levels after 24 h. Osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) provide important regulatory mechanisms for controlling osteoclastogenesis and Ca2+ homeostasis. Because they often control Ca2+-activated secretion, we investigated the possibility that L-type VSCCs might regulate basal OPG and RANKL secretion in osteoblasts. We also studied 1,25(OH)2D3 effects on OPG and RANKL expression. To address this, we measured changes in expression and secretion of OPG and RANKL in MC3T3-E1 cells and calvarial organ cultures after treatment with 1,25(OH)2D3, VSCC inhibitors, and inhibitors of Ca2+-regulated signaling. RANKL production was increased in calvarial cultures by 1,25(OH)2D3 but was essentially undetectable in the medium of MC3T3-E1 cells. In contrast, OPG secretion in both systems was significantly reduced after 24 h treatment with 1,25(OH)2D3, by inhibitors of L-type VSCCs and calmodulin-sensitive protein kinases but not by inhibitors of protein kinase A, MAPKs, or other families of VSCCs. OPG secretion was abrogated by transfection with decoy cAMP response element binding sites. Our results suggest that OPG secretion is regulated through calmodulin-sensitive protein kinase signaling that depends on the activity of the L-type VSCC and is mediated through the cAMP response element-binding protein.

Increased Ca2+ signaling through CaV1.2 promotes bone formation and prevents estrogen deficiency–induced bone loss

“…Thus, these data extend previous findings for a Ca V 1.2 role in mandibular development (4) Because these mouse models all employed Cre recombinases that drove Ca V 1.2 TS expression in osteoblast lineages, and not in osteoclasts or their precursors, we conclude that the observed anticatabolic responses resulted from an increase in the Rankl/Opg expression ratio and OPG secretion and consequent extrinsic inhibition of osteoclastogenesis. This is consistent with previous data showing that Ca V 1.2 regulates OPG secretion (27) and the well-defined roles for Ca V 1.2 channels in promoting hormone secretion from endocrine tissue. Moreover, our lacZ expression data showed that Ca V 1.2 is expressed within bone tissue where osteoblast precursor cells reside, and previous RNA-seq data showed no expression of Ca V 1.2 in murine BMMs or during osteoclast differentiation (15) TS suggests a possible therapeutic strategy for osteoporotic or osteopenic conditions.…”

CGRP inhibits osteoprotegerin production in human osteoblast-like cells via cAMP/PKA-dependent pathway

“…Bergh et al (4) have described a model in which the calcium signals generated by the regulatory activity of L-type voltage-sensitive channels can regulate OPG expression and secretion by means of calmodulin-sensitive protein kinase signaling; blocking the activity of these channels reduces the level of OPG expression and secretion in primary calvarial organ (4).…”

Inhibitory actions of mibefradil on steroidogenesis in mouse Leydig cells: involvement of Ca2+ entry via the T-type Ca2+ channel

“…Ca 2+ helps regulate a variety of cellular functions in many different cells, including germ cells and somatic cells in the testis, as well as spermatozoa, in response to endocrine hormones and local regulators [7][8][9][10][11]. Moreover, alteration of the Ca 2+ signalling pathway has a drastic impact on many cellular physiologies [12][13][14][15] [5,6,17], while other studies have argued that voltage-dependent Ca 2+ channels (VDCCs) are also involved [18][19][20]. Recently, mibefradil, a new nondihydropyridine calcium antagonist, has been shown to block the T-type Ca 2+ channel with a high affinity and selectivity in a variety of cell preparations [19][20][21][22].…”