Endothelin signaling regulates mineralization and posttranscriptionally regulates SOST in TMOb cells via miR 126-3p

Previously, our laboratory identified ECE-1, encoding endothelin-converting enzyme-1 (ECE-1), as a positional candidate for a pleiotropic quantitative trait locus affecting femoral size, shape, and biomechanical performance. We hypothesized that endothelin-1 (ET-1) signaling promotes osteogenesis. Exposure of immortalized mouse osteoblast (TMOb) cells to big ET-1 increased mineralization. Following big ET-1 treatment, we measured the secretion of insulin-like-growth factor-1 (IGF1), dickkopf-homolog-1 protein 1 (DKK1), and sclerostin (SOST). In each case, big ET-1 signaling changed secretion in a manner that favored increased osteogenic activity. Treatment with ECE-1, endothelin receptor A (EDNRA), or WNT receptor antagonists inhibited the big ET-1-mediated increase in mineralization. In the presence of big ET-1, message levels of Runx2, Igf1, Dkk1, and Sost are uncoupled from protein production, suggesting posttranscriptional regulation. To evaluate the role of big ET-1 in normal bone physiology, we inhibited EDNRA signaling during mineralization in the absence of exogenous ET-1. EDNRA blockade reduced mineralization, decreased IGF1, and increased DKK1 and SOST secretion, responses opposite to those induced by exogenous big ET-1. Pharmacological and siRNA knockdown to inhibit ECE-1 reduced mineralization and IGF1 secretion with decreasing DKK1 and decreasing or stable SOST secretion, suggesting a further, unknown role of ECE-1 in osteoblast maturation. Previously we identified miR 126-3p as a potential ET-1-responsive regulator of SOST in murine cells. Overexpression of miR126-3p increased mineralization in TMOb cells and decreased SOST secretion. Osteoblasts express the ET-1 signaling pathway and ET-1 signaling is necessary for normal osteoblast differentiation and mineralization, acting through regulation of miRs that target osteogenic molecules.