Calcineurin and NFAT4 Induce Chondrogenesis

Abstract

The vertebrate skeleton develops from a template that is initially constructed of cartilage. The formation of this template is controlled by a series of interdependent steps that supply spatial information and morphogenic cues that direct mesenchymal cell condensation and differentiation in a process known as chondrogenesis. Mesenchymal cells derived from the lateral plate mesoderm condense to form the rudiments of the appendicular skeleton. The processes that control the condensation of mesenchyme are poorly understood. Cell-cell adhesion certainly contributes to mesenchymal cell condensation as demonstrated in studies showing that homotypic interactions of N-cadherin are required during chondrogenesis (1, 2). In addition, a number of extracellular signaling molecules have been proposed to regulate chondrogenesis by regulating both condensation and differentiation. WNTs (3), fibroblast growth factors (4), sonic hedgehog (5), and bone morphogenetic proteins (BMPs) 1 (6 -8) all contribute to chondrogenesis. Increasing evidence indicates that BMPs have a central role in this process. For example, loss of function experiments using dominant negative BMP receptors suppresses chondrogenesis during chicken limb development (9, 10). Conversely, overexpression of BMPs or activated BMP receptors dramatically augments chondrogenesis during limb development (10, 11). These data suggest that elucidating pathways that control BMP expression will be vital to understanding chondrogenesis.Intracellular calcium ([Ca 2ϩ ] i ) is a universal intracellular signal that intersects with many signaling molecules to regulate gene expression (12). However, the role of intracellular calcium in chondrogenesis is virtually uncharacterized. Elevations of [Ca 2ϩ ] i activate a number of signaling cascades, including the calcineurin/nuclear factor of activated T-cell (NFAT) pathway (13). Prolonged elevations of [Ca 2ϩ ] i activate the phosphatase calcineurin, through interaction with Ca 2ϩ :calmodulin (14). In turn, calcineurin dephosphorylates a set of substrates, including the transcription factors, NFATs (15). Dephosphorylation of NFATs results in translocation of the protein from the cytoplasm to the nucleus (16). In the nucleus, NFATs activate gene expression in cooperation with other transcriptional regulators (17, 18). NFATs are a family of four transcription factors, NFAT1(p, c2), NFAT2(c, c1), NFAT3, and NFAT4(x,c3). Although well known for their ability to regulate cytokine gene expression in immune cells (15), NFATs are broadly expressed and have essential functions outside of the immune system (18 -21). The transcriptional targets of NFATs outside of immune cells, however, are incompletely characterized. Here we report that elevation of [Ca 2ϩ ] i induce chondrogenesis using a pathway requiring calcineurin, NFAT4, and BMP expression. In this pathway BMP2 expression is induced by activated calcineurin/NFAT. Subsequently, BMP2 induces chondrogenesis through an autocrine loop. were generously provided by Jane Aubin. Cells wer...

FGF18 Represses Noggin Expression and Is Induced by Calcineurin

“…signals stimulate chondrocyte differentiation, and in other work (30), we show that the calcium-dependent pathway requires calcineurin. We showed that, when activated, calcineurin induces BMP2 gene expression and that differentiation in these culture systems proceeds via a BMP-dependent pathway (30).…”

“…We showed that, when activated, calcineurin induces BMP2 gene expression and that differentiation in these culture systems proceeds via a BMP-dependent pathway (30). Calcium-dependent Signaling Induces FGF18 ExpressionTo further characterize the effects of calcium-dependent signals on chondrocyte differentiation and gene expression, we asked whether calcium signaling alters FGF18 gene expression.…”

“…Many cytokines are induced following receptor-dependent calcium signaling. For example, we have shown that elevations of intracellular calcium induce BMP2 gene expression (30). This in turn promotes chondrocyte gene expression and chondrogenesis.…”

Ser/Thr-phosphoprotein phosphatases in chondrogenesis: neglected components of a two-player game

“…Furthermore, NFAT4 activation upregulated BMP-2 expression, which in turn induced chondrogenesis. Since the above changes could be prevented by the CaN inhibitor CsA or the BMP antagonist noggin, the authors concluded that CaN/NFAT4 signalling activates BMP-2 expression and induces in vitro chondrogenesis [66]; thus they provided evidence that the phosphatase involved in the BMP-2 signalling pathway could indeed be CaN, according to the assertions of Tateishi and colleagues [65].…”

Optimalized transient transfection of chondrogenic primary cell cultures

“…Our group previously demonstrated that the changes of intracellular Ca 2+ concentration play an important role in cartilage differentiation [30]. Increased intracellular calcium levels can induce chondrogenesis through the Cn-nuclear factor of activated T-cells (NFAT) signaling pathway and modulate the activity of ERK1/2 [19,31]. The importance of the PPs in the regulation of chondrogenesis is doubtless but the effect of their overactivation and/or overexpression on cartilage differentiation has yet to be clarified.…”