Transcriptional activation of ENPP1 by osterix in osteoblasts and osteocytes

Abstract

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is the main source of extracellular pyrophosphate. Along with tissue-nonspecific alkaline phosphatase (TNAP), ENPP1 plays an important role in balancing bone mineralisation. Although well established in pre-osteoblasts, the regulating mechanisms of ENPP1 in osteoblasts and osteocytes remain largely unknown. Using bioinformatic methods, osterix (Osx), an essential transcription factor in osteoblast differentiation and osteocyte function, was found to have five predicted binding sites on the ENPP1 promoter. ENPP1 and Osx showed a similar expression profile both in vitro and in vivo. Over-expression of Osx in MC3T3-E1 and MLO-Y4 cells significantly up-regulated the expression of ENPP1 (p < 0.05). The consensus Sp1 sequences, located in the proximal ENPP1 promoter, were identified as Osx-regulating sites using promoter truncation experiments and chromatin immunoprecipitation (ChIP) assays. The p38-mitogen-activated protein kinase (MAPK) signalling pathway was demonstrated to be responsible for ENPP1 promoter activation by Osx. Runt-related transcription factor 2 (Runx2) was confirmed to have synergistic effects with Osx in activating ENPP1 promoter. Taken together, these results provided evidence of the regulating mechanisms of ENPP1 transcription in osteoblasts and osteocytes.

A single-cell transcriptome of mesenchymal stromal cells to fabricate bioactive hydroxyapatite materials for bone regeneration

“…During OM induction, the expression of MMP7 was enhanced, while the expression of MMP1 was repressed; these findings indicate that MMP7, instead of MMP1, is involved in OM-induced matrix remodeling. In addition, the expression of ENPP1, which produces an inhibitor of hydroxyapatite crystal formation (pyrophosphate, PPi), is a regulator of the phosphate/PPi ratio [ 66 ], was specifically upregulated by OM. Other bone resorption promotors, including ADAMTS1, MGP and CTSK, were also upregulated to accelerate mineralization remodeling.…”

Sp7 Action in the Skeleton: Its Mode of Action, Functions, and Relevance to Skeletal Diseases

“…Sp7 has been shown to upregulate transcription of various osteoblast-related genes, including Fmod (fibromodulin) [ 29 ], Col1a1 [ 30 , 31 ], Col1a2 [ 32 ], Col5a1 [ 33 ], Col5a3 [ 34 ], Ibsp [ 29 , 35 ], Sost [ 13 , 36 ], Bglap [ 37 ], Zbtb16 [ 38 ], Cx43 [ 39 ], Vegf (vascular endothelial growth factor) [ 40 ], Mmp9 (matrix metalloproteinase 9) [ 41 ], Mmp13 (matrix metalloproteinase 13) [ 42 , 43 ], Zip1 [ 44 ], Ucma (upper zone of growth plate and cartilage matrix associated) [ 45 ], and Enpp1 (pyrophosphatase/phosphodiesterase 1) [ 46 ] (extensively reviewed in [ 47 ]). This series of studies demonstrated that Sp7 bound to the typical GC-box (Sp1-binding sites) or CCAAT sequences around these genes ( Figure 1 ).…”

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

“…Osx can also interact with Runx2 to coordinately activate the expression of the various genes, and their synergistic effects achieve significantly higher expression levels than those obtained with the individual expression vectors. Col1a1, Sost, Ectonucleotide pyrophosphatase/phosphodiesterase 1(Enpp1) and the novel gene unique cartilage matrix-associated protein (Ucma) have been reported to be their coordinated target genes (Ortuno et al, 2013;Lee Y. J. et al, 2015;Pérez-Campo et al, 2016;Gao M. et al, 2018). The interaction of Osx and Runx2 in the regulation of these promoters is mediated by Osx's enhancer regions adjacent to Sp1 and Runx2 DNA-binding sites, thereby synergistically regulating those downstream genes transcription.…”