NF-κB Specifically Activates BMP-2 Gene Expression in Growth Plate Chondrocytes in Vivo and in a Chondrocyte Cell Line in Vitro

Abstract

In long bones, morphogenesis is followed by an extended period of growth. Longitudinal growth occurs at the growth plate by endochondral ossification, a process in which cartilage is formed and then remodeled into bone (1, 2). The multistep process of chondrogenesis involves: 1) the aggregation of mesenchymal cells into prechondrogenic condensations, 2) differentiation of the condensed prechondrogenic mesenchyme into small immature chondrocytes, and 3) chondrocyte maturation followed by ossification, starting in the center of the element.Bone morphogenetic proteins (BMPs) 1 play an important role in skeletal development (3-5). At the early stage of bone development, BMP-2 and BMP-4 are expressed in specific areas of the limb bud 3 and misexpression of noggin, a glycoprotein that blocks actions of BMP-2 and BMP-4, prior to the onset of chondrogenesis leads to the total absence of skeletal elements (6), suggesting that BMP signaling is absolutely required for prechondrogenic condensations. At the late stage, BMP-2, expressed in the growth plate of long bone, accelerates longitudinal bone growth by stimulating growth plate chondrocyte proliferation and hypertrophy (7,8).To understand the regulatory mechanism of BMP-2 gene, we have previously characterized the BMP-2 promoter and identified control elements in osteoblasts and chondrocytes in BMP-2 gene (9). BMP-2 autoregulates its own expression through its proximal promoter (10) in a similar fashion that the decapentaplegic (dpp) gene is regulated in drosophila. dpp is a drosophila homologue of BMP-2. In drosophila, expression of dpp is regulated by dorsal, a homologue of mammalian NF-B (11, 12). In chick embryo, overexpression of a mutated form of I-B␣ protein, which blocks NF-B activation, leads to abnormality in limb bud development, and changes in downstream signals include BMP-4 (13). These findings suggest that NF-B may participate in the regulatory process of the BMP-2 gene.NF-B is a group of transcription factors including five members, p65, c-Rel, RelB, p50, and p52. They form homodimers or heterodimers to regulate expression of a variety of genes and are involved in many biological functions (14). It has been demonstrated previously that NF-B family members p50 and p52 are absolutely required for osteoclast development and p50/p52 double knock-out (dKO) mice failed to form osteoclasts and developed severe osteopetrosis (15).The role of NF-B in BMP-2 gene expression and functions of NF-B in other bone cells, such as chondrocytes, have not been reported. In the present studies, we have examined the regulatory mechanism of BMP-2 by NF-B in chondrocytes in vitro and in vivo. We searched the Ϫ2712/ϩ165 region of BMP-2 gene and found two putative NF-B response elements. Using different experimental approaches, we demonstrate that these NF-B response elements are functional in chondrocytes and NF-B positively regulates BMP-2 gene transcription through these response elements. We also show that in growth plate chondrocytes of 2-week-old NF-B p50/p52 dKO mice, BMP-...

Oxidized Low Density Lipoprotein Induces Bone Morphogenetic Protein-2 in Coronary Artery Endothelial Cells via Toll-like Receptors 2 and 4

“…Further, NF-B has been reported to activate BMP-2 expression in osteoblasts as well as in chondrocytes (36). We found that oxLDL induces rapid and sustained NF-B phosphorylation in human CAECs, and inhibition of NF-B reduces BMP-2 expression.…”

Regulation of Bone Morphogenetic Protein-2 Expression in Endothelial Cells

“…Indeed, NF-〉 binding sites appear to be present in the promoter region of the rat BMP-2 gene, and a recent study reported that NF-〉 binds an NF-〉 response element in the 5Ј flanking region of the BMP-2 gene in mouse chondrocytes. 26 Interestingly, we found that this NF-〉 binding site is located in an evolutionary, highly conserved region of the BMP-2 promoter ( Figure 1C), which provides an explanation for the similar upregulation of BMP-2 expression in human and rat endothelial cells by TNF-␣ ( Figures 1A and 1D). The in vivo significance of the regulation of vascular BMP-2 expression by TNF-␣ and NF-〉 is supported by the lower level of BMP-2 expression in vessels of TNF-␣-deficient mice ( Figure 1G).…”

Anemonin attenuates osteoarthritis progression through inhibiting the activation of IL‐1β/NF‐κB pathway

“…Although the reasons for the accelerated chondrocyte hypertrophy are not fully clarified, NF‐κB signalling has been found to be involved in it 43. NF‐κB pathway could inhibit the chondrogenic differentiation of mesenchymal cells by down‐regulating SOX9 44.…”