ODDD-Linked Cx43 Mutants Reduce Endogenous Cx43 Expression and Function in Osteoblasts and Inhibit Late Stage Differentiation

Abstract

ABSTRACT:Introduction: Bone development and modeling requires precise gap junctional intercellular communication (GJIC). Oculodentodigital dysplasia (ODDD) is an autosomal dominant human disease caused by mutations in the gene (GJA1) encoding the gap junction protein, connexin43 (Cx43). The disease is characterized by craniofacial bone deformities and limb abnormalities. It is our hypothesis that Cx43 mutation causes osteoblast dysfunction, which may contribute to the bone phenotype of ODDD. Materials and Methods:We expressed human and mouse ODDD-linked Cx43 mutants in MC3T3-E1 cells and primary mouse osteoblasts by retroviral infection and evaluated their in vitro differentiation as an index of osteoblast function. We compared these findings to the differentiation of osteoblasts isolated from a mouse model of ODDD that harbors a germ line Cx43 mutation and exhibits craniofacial and limb defects mimicking human ODDD. We determined the differentiation status of osteoblasts by analyzing alkaline phosphatase activity and the expression levels of osteoblast markers including bone sialoprotein and osteocalcin. Results: We showed that ODDD-linked Cx43 mutants are loss-of-function and dominant-negative to coexpressed Cx43 and, furthermore, greatly inhibit functional GJIC in osteoblasts. Surprisingly, the mutants had only a minor effect on osteoblast differentiation when introduced into lineage committed cells. In contrast, osteoblasts isolated from the ODDD mouse model exhibited impaired late stage differentiation. Conclusions: Expression of human and mouse ODDD-linked Cx43 mutants failed to significantly impair differentiation in cells predisposed to the osteoblast lineage; however, germ line reduction of Cx43-based GJIC leads to impaired osteoblast differentiation, which may account for the bone phenotypes observed in ODDD patients.

Cell–cell communication in the osteoblast/osteocyte lineage

“…Despite these similarities, the cellular bases of the low bone mass in ODDD mouse models are still not totally clear. In contrast to Gja1 deletion, which severely impairs osteoblast differentiation and mineralization potential [30], the presence of ODDD mutant does not lead to major functional abnormalities of committed osteoblastic cells [42], suggesting that the dominant negative effect of the mutant Cx43 may not be sufficient to disrupt full osteoblast differentiation. However, earlier steps of osteogenesis could be affected by a dominant negative Cx43 mutant that may also interfere with the function of other connexins.…”

Oogenesis defects in a mutant mouse model of oculodentodigital dysplasia

“…Jrt /+ mice including osteoblasts, mammary epithelium and cardiomyocytes (McLachlan et al, 2008;Plante and Laird, 2008;Manias et al, 2008) (see Table 2). …”

A Dominant Loss-of-Function GJA1 (Cx43) Mutant Impairs Parturition in the Mouse1

“…G60S also severely impaired Cx43-mediated GJIC in various tissues of the mutant mice [19,21]. In the present study, we sought to determine the effect of this disease-linked Cx43 mutation on myometrium function.…”