Endothelin‐1 inhibits human osteoblastic cell differentiation: Influence of connexin‐43 expression level

Abstract

Gap junctional intercellular communication (GJIC) permits coordinated cellular activities during developmental and differentiation processes. In bone, the involvement of the gap junctional protein, connexin-43 (Cx43), and of GJIC in osteoblastic differentiation and mineralization of the extracellular matrix has been previously demonstrated. Former studies have shown that endothelin-1 (ET-1) was also implicated in the control of osteoblastic proliferation and differentiation. However, depending on the cellular models, ET-1 has been shown to decrease or increase osteoblastic differentiation markers. As no data were available on the ET-1 effect on GJIC and Cx43 expression in osteoblastic cells, we analyzed here the possible crosstalk between Cx43 and ET-1 in a human cell line (hFOB 1.19) which displays different Cx43 expression levels and phenotypes when cultured at 33.5 or 39 degrees C. The presence of ET-1 (10(-8) M) for 2-12 days of culture did not significantly alter the proliferation rate of hFOB cells whatever their phenotype. In contrast, ET-1 induced a differential inhibitory effect on the biochemical differentiation markers (alkaline phosphatase activity and osteocalcin expression) with a significant reduction in the differentiated phenotype at 39 degrees C, whereas no effects were measured at 33.5 degrees C. The inhibitory effect was linked to a decrease of GJIC and of Cx43 both at transcriptional and protein levels. Altogether, our results suggest that Cx43 expression level could influence the action of ET-1 on human osteoblastic cell differentiation. Our data also indicate that the gap junctional protein could play a pivotal role in the response of osteoblasts to mitogenic factors implicated in bone pathologies.

Effect of endothelin-1 on osteoblastic differentiation is modified by the level of connexin43: comparative study on calvarial osteoblastic cells isolated from Cx43+/−and Cx43+/+ mice

“…The peptide is also partially able to reduce the differentiation state in cultured Cx43 +/− OB cells as confirmed by ALP activity and the synthesis level of OCN. These results validate and complete our previous study of the hFOB1.19 cell model (Niger et al 2008) since the mitogenic effect of this peptide has been clearly shown on primary murine OB cells. Under the present experimental conditions, ET-1 treatment significantly decreases Cx43 transcript and protein levels together, leading to an uncoupling effect.…”

“…Other lines of evidence indicate a physiopathological role of ET-1 in several diseases of human bones, such as Paget's disease (Tarquini et al 1998;Pirzer et al 2005) and prostate-cancerinduced OB metastases (Jimeno and Carducci 2004). Moreover, we have demonstrated, in a human cell line, that the Cx43 level alters the ET-1 effects on OB differentiation (Niger et al 2008), as shown for other modulators such as PTH (Donahue et al 1995;Chung et al 2006).…”

“…However, given the absence of mitogenic effect in our previous cellular model (Niger et al 2008), we have used primary culture of OB cells from the calvaria of Cx43 +/− mice and from their littermates to study the influence of Cx43 on the inhibiting action of ET-1. In addition, no data are available from Cx43 +/− mice regarding bone mineral density (BMD) to allow this mouse to be considered as a useful physiological model of intermediate phenotype.…”

Gap junctions and hemichannels in signal transmission, function and development of bone

“…Several studies suggest that Cx43 expression and GJIC modulate the transcriptional activity of osteoblast-specific promoters [79–86]. Expression of Cx43 increases during osteoblastic differentiation [84] and inhibition of GJIC delays their ability to differentiate and form mineralized matrix [79].…”

Endothelins and their receptors in cancer: Identification of therapeutic targets

“…In human ovarian cancer cells, ET-1 decreased gap junctional communication by inducing phosphorylation of Cx43 [35]. Cx43 expression also was implicated in the actions of ET-1 on human osteoblastic cell differentiation, suggesting that Cx43/ET-1 play a role in the response of osteoblasts to mitogenic factors in bone pathologies, including cancer [36,37]. For further information on the role of endothelins in bone remodeling, which may have particular relevance in prostate and breast cancers, the reader is referred to published reviews [38,39].…”