Direct Transcriptional Repression of Zfp423 by Zfp521 Mediates a Bone Morphogenic Protein-Dependent Osteoblast versus Adipocyte Lineage Commitment Switch

Abstract

cOsteoblasts and adipocytes arise from a common mesenchymal precursor cell. The cell fate decision of a mesenchymal precursor cell is under the influence of molecular cues and signaling pathways that lead to the activation or repression of lineage-specific transcription factors. The molecular mechanisms determining osteoblast versus adipocyte lineage specificity in response to bone morphogenic protein (BMP) remain unclear. In this study, we describe the mechanism through which Zfp521 (ZNF521), a regulator of lineage progression in multiple immature cell populations, regulates lineage specification of mesenchymal progenitor cells during BMP-induced differentiation events. In vivo deletion or in vitro knockdown of Zfp521 in mesenchymal precursors resulted in increased expression of the adipocyte determinant factor Zfp423 (ZNF423). This was concurrent with the loss of histone H3K9 methylation and an increase in histone H3K9 acetylation at the Zfp423 promoter, which together are indicative of decreased gene repression. Indeed, we found that Zfp521 occupies and represses the promoter and intronic enhancer regions of Zfp423. Accordingly, conditional deletion of Zfp521 inhibited heterotopic bone formation in response to local injection of BMP2. In contrast, marrow adiposity within BMP2-induced bone was markedly enhanced in Zfp521-deficient mice, suggesting that precursor cells lacking Zfp521 differentiate preferentially into adipocytes instead of osteoblasts in response to BMP2. Consistent with a cell-autonomous role of Zfp521 in mesenchymal precursors, knockdown of Zfp521 in stromal cells prevented BMP2-induced osteoblast marker expression and simultaneously enhanced lipid accumulation and expression of adipocyterelated genes. Taken together, the data suggest that Zfp521 is a cell fate switch critical for BMP-induced osteoblast commitment and identify Zfp521 as the intrinsic repressor of Zfp423 and hence of adipocyte commitment during BMP-induced mesenchymal precursor differentiation. Multipotent mesenchymal precursor cells can differentiate into several cell types, including osteoblasts and adipocytes. Commitment to a lineage appears to be mutually exclusive, so that factors that enhance osteoblastogenesis are often inhibitory to adipogenesis and vice versa. Imbalances between osteoblast and adipocyte commitment is evident in some human diseases, such as age-related osteoporosis (1), where decreased bone formation is accompanied by increased bone marrow fat, or in progressive osseous heteroplasia, where bone formation is initiated within subcutaneous fat (2). Thus, understanding the regulatory mechanisms that alter precursor cell fate is of potential clinical significance.Mesenchymal progenitor cell fate is fine-tuned by transcription factors and signaling pathways, including the bone morphogenic protein (BMP) pathway. Although BMPs were first discovered based on their ability to induce the recruitment and differentiation of mesenchymal precursors into bone-forming osteoblasts (3), BMPs are now known to be important ...

Effect of lipopolysaccharides on adipogenic potential and premature senescence of adipocyte progenitors

“…Ectopic expression of Zfp423 in nonadipogenic NIH-3T3 fibroblasts robustly promoted adipocyte differentiation (29). On contrary, transcriptional repression of Zfp423 by Zfp521 inhibited the commitment of mesenchymal stem cells to preadipocyte lineage (2). In the present study, we showed that the expression of Zfp423 gene was significantly downregulated upon LPS treatment in SV cells, and the downregulation of Zfp423 was not reversed by a NF-B inhibitor.…”

ZNF423: Transcriptional modulation in development and cancer

“…Zfp521 binding at Zfp423 regulatory sequences facilitates transcriptional silencing of its homolog by repressive chromatin modifications. 17 Taken together, these data reveal that transcriptional regulation of ZNF423 is dependent on a variety of signaling pathways and epigenetic modifications, the ramifications of which are still incompletely understood.…”

“…5 In adipocyte differentiation, BMP signaling is thought to indirectly enhance Zfp423 expression by downregulation of its homolog Zfp521. 17 Moreover, in human umbilical vein endothelial cells, BMP9-dependent SMAD1-SMAD5 enrichment was observed at the ZNF423 locus. 19 Recently, 3 independent research groups have presented data on the epigenetic regulation of ZNF423 expression.…”

“…16 In addition to Zfp423 itself, its homolog Zfp521 is recruited to the Zfp423 promoter and intronic enhancer in intron 5 to decrease Zfp423 expression. 17 Furthermore, in multipotent mesenchymal stem cells, Zfp521 physically interacts with Ebf1 and inhibits its transcriptional activity. Ebf1 in turn induces Zfp423 expression in these cells.…”

“…19 Recently, 3 independent research groups have presented data on the epigenetic regulation of ZNF423 expression. 5,17,20 Epigenetic changes, such as DNA methylation and histone modifications, are key regulators of transcription. [21][22][23] Harder et al described a CpG island (CGI) situated between the alternative ZNF423a and ZNF423b promoters (Fig.…”