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Lysophosphatidic acid synergizes with 1,25-dihydroxyvitamin D to promote fibroblast growth factor-23 synthesis via MAPK signaling and induction of the IL12A gene

ABSTRACT: Dysregulated actions of the bone-derived phosphaturic hormone, fibroblast growth factor-23 (FGF23), underlie the pathophysiology of several diseases. FGF23 is synthesized primarily in osteocytes in response to various endogenous molecules; however, the mechanisms governing FGF23 production are incompletely understood. Glycerol-3-phosphate (G3P), a glycolytic by-product originating from the kidney, critically controls skeletal FGF23 synthesis via its conversion in bone to lysophosphatidic acid (LPA), which stimulates osteocyte FGF23 production. The bioactive vitamin D, 1,25-dihydroxyvitamin D (1,25D), also promotes FGF23 production in osteocytes. We herein demonstrated that LPA requires 1,25D action to raise FGF23 levels in mouse bone explants and mice. RNA sequencing of osteocyte-like Ocy454 cells identified differentially expressed genes (DEGs) uniquely induced by LPA/1,25D co-treatment. These unique DEGs were enriched for the ribosome biogenesis pathway. DEGs concurrently induced by individual LPA and 1,25D treatments were enriched for MAPK signaling, and inhibiting this pathway obliterated LPA/1,25D-induced FGF23 production. DEGs following LPA/1,25D co-treatment were enriched for the cytokine-cytokine interaction pathway. Moreover, LPA/1,25D co-treatment, but not individual LPA and 1,25D treatments, rapidly induced the expression of Il12a, the gene encoding the proinflammatory cytokine interleukin-12 alpha-subunit, which responded solely to 1,25D at later times and required MAPK-ERK1/2 signaling. Inhibiting cytokine signaling or knocking down Il12a inhibited, while overexpressing Il12a enhanced LPA/1,25D-induced FGF23 production. However, challenging Ocy454 cells with recombinant bioactive interleukin-12 failed to enhance FGF23 production, suggesting that Il12a plays a non-canonical role. Our results reveal a mechanism of skeletal FGF23 synthesis involving cooperative actions of LPA and 1,25D, advancing our understanding of FGF23 regulation.

ORGANISM(S): Mus musculus

PROVIDER: GSE297103 | GEO | 2026/01/09

REPOSITORIES: GEO

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Project description:Fibroblast growth factor 23 (FGF23), a hormone, mainly produced by osteocytes, regulates phosphate and vitamin D metabolism. By contrast, 1,25-dihydroxyvitamin D3, the active form of vitamin D, has been shown to enhance FGF23 production. While it is likely that osteocytes are heterogenous in terms of gene expression profiles, specific subpopulations of Fgf23-expressing osteocytes have not been identified. Single-cell RNA sequencing (scRNA-seq) technology can characterize the transcriptome of an individual cell. Recently, scRNA-seq has been used for bone tissue analysis. However, owing to technical difficulties associated with isolation of osteocytes, studies using scRNA-seq analysis to characterize FGF23-producing osteocytes are lacking. In this study, we characterized osteocytes secreting FGF23 from murine femurs in response to calcitriol (1,25-dihydroxyvitamin D3) using scRNA-seq. We first detected Dmp1, Mepe, and Phex expression in murine osteocytes by in situ hybridization and used these as marker genes of osteocytes. After decalcification, enzyme digestion, and removal of CD45+ cells, femoral bone cells were subjected to scRNA-seq. We identified cell clusters containing osteocytes using marker gene expression. While Fgf23 expression was observed in some osteocytes isolated from femurs of calcitriol-injected mice, no Fgf23 expression was detected in untreated mice. In addition, the expression of several genes which are known to be changed after 1,25-dihydroxyvitamin D3 treatment such as Ccnd2, Fn1, Igfbp7, Pdgfa, and Timp1 was also affected by calcitriol treatment in Fgf23-expressing osteocytes, but not in those lacking Fgf23 expression, even after calcitriol administration. Furthermore, box-and-whisker plots indicated that Fgf23 expression was observed in osteocytes with higher expression levels of the Fam20c, Dmp1, and Phex genes, whose inactivating mutations have been shown to cause FGF23-related hypophosphatemic diseases. These results indicate that osteocytes are heterogeneous with respect to their responsiveness to 1,25-dihydroxyvitamin D3, and sensitivity to 1,25-dihydroxyvitamin D3 is one of the characteristics of osteocytes with Fgf23 expression. It is likely that there is a subpopulation of osteocytes expressing several genes, including Fgf23, involved in phosphate metabolism.

Project description:Fibroblast growth factor 23 (FGF23) is produced and secreted by osteocytes and is essential for maintaining phosphate homeostasis. One of the main regulators of FGF23, 1,25-dihydroxyvitamin D (1,25(OH)2D3), is primarily synthesized in the kidney from 25-hydroxyvitamin D (25(OH)D) by 1α-hydroxylase (encoded by CYP27B1). Hitherto, it is unclear whether osteocytes can convert 25(OH)D and thereby allow for 1,25(OH)2D3 to induce FGF23 production and secretion locally. Here, we differentiated MC3T3-E1 cells towards osteocyte-like cells expressing and secreting FGF23. Treatment with 10-6 M 25(OH)D resulted in conversion of 25(OH)D to 150 pmol/L 1,25(OH)2D3 and increased FGF23 expression and secretion but the converted amount of 1,25(OH)2D3 was insufficient to trigger an FGF23 response, so the effect on FGF23 was most likely directly caused by 25(OH)D. Interestingly, combining phosphate with 25(OH)D resulted in a synergistic increase in FGF23 expression and secretion, likely due to activation of additional signaling pathways by phosphate. Blockage of the vitamin D receptor (VDR) only partially abolished the effects of 25(OH)D or 25(OH)D combined with phosphate on Fgf23, while completely inhibiting the upregulation of cytochrome P450 family 24 subfamily A member 1 (Cyp24a1), encoding for 24-hydroxylase. RNA sequencing and in silico analyses showed that this could potentially be mediated by the nuclear receptors Retinoic Acid Receptor b (RARB) and Estrogen Receptor 2 (ESR2). Taken together, we demonstrate that osteocytes are able to convert 25(OH)D to 1,25(OH)2D3, but this is insufficient for FGF23 activation, implicating a direct effect of 25(OH)D in the regulation of FGF23, which occurs at least partially independent from its cognate vitamin D receptor Moreover, phosphate and 25(OH)D synergistically increase expression and secretion of FGF23, which warrants investigating consequences in patients receiving a combination of vitamin D analogues and phosphate supplements. These observations help us to further understand the complex relations between, phosphate, vitamin D and FGF23.

Project description:Osteocytes are derived from osteoblast lineage cells that become progressively embedded in mineralized bone. Development of the osteocytogenic cell line IDG-SW3 has enabled a temporal and mechanistic investigation of this process. Through RNA-seq analyses, we show that while substantial changes in gene expression occur during the osteoblast to osteocyte transition, the majority of the transcriptome remains qualitatively osteoblast-like. Genes either up-regulated or expressed uniquely in the osteocyte include local and systemic factors such as Sost and Fgf23 as well as genes implicated in neuronal, muscle, vascular, or regulatory function. As assessed by ChIP-seq, numerous changes in epigenetic histone modifications also occur during osteocytogenesis; these are largely qualitative rather than quantitative. Specific epigenetic changes correlate with altered gene expression patterns that are observed during the transition. These genomic changes likely influence the highly restricted transcriptomic response to 1,25(OH)2D3 that occurs during differentiation. VDR binding in osteocytes revealed an extensive cistrome co-occupied by RXR and located predominantly at sites distal to regulated genes. Although sites of VDR binding were apparent near many 1,25(OH)2D3-regulated genes, the expression of others adjacent to VDR binding sites were unaffected; lack of VDR binding was particularly prevalent at down-regulated genes. Interestingly, 1,25(OH)2D3 was found to induce the Boc and Cdon co-receptors that are active in hedgehog signaling in osteocytes. We conclude that osteocytogenesis is accompanied by changes in gene expression that may be driven by both genetic and epigenetic components. These changes are likely responsible for the osteocyte phenotype and may contribute to reduced sensitivity to 1,25(OH)2D3. ChIP-seq was performed on differentiated IDGSW3 cells at day 35 for VDR and RXR following 3 hour vehicle or 1,25(OH)2d3 treatment in biological replicate. ChIP-seq was also performed for H3K4me1, H3K4me2, H3K4me3, H3K27Ac, H4K5Ac, H3K9Ac, H4K20me1, H3K36me3, or H3K9me3 at day 3 and day 35 of differentiation in the basal condition.

Project description:Osteocytes are derived from osteoblast lineage cells that become progressively embedded in mineralized bone. Development of the osteocytogenic cell line IDG-SW3 has enabled a temporal and mechanistic investigation of this process. Through RNA-seq analyses, we show that while substantial changes in gene expression occur during the osteoblast to osteocyte transition, the majority of the transcriptome remains qualitatively osteoblast-like. Genes either up-regulated or expressed uniquely in the osteocyte include local and systemic factors such as Sost and Fgf23 as well as genes implicated in neuronal, muscle, vascular, or regulatory function. As assessed by ChIP-seq, numerous changes in epigenetic histone modifications also occur during osteocytogenesis; these are largely qualitative rather than quantitative. Specific epigenetic changes correlate with altered gene expression patterns that are observed during the transition. These genomic changes likely influence the highly restricted transcriptomic response to 1,25(OH)2D3 that occurs during differentiation. VDR binding in osteocytes revealed an extensive cistrome co-occupied by RXR and located predominantly at sites distal to regulated genes. Although sites of VDR binding were apparent near many 1,25(OH)2D3-regulated genes, the expression of others adjacent to VDR binding sites were unaffected; lack of VDR binding was particularly prevalent at down-regulated genes. Interestingly, 1,25(OH)2D3 was found to induce the Boc and Cdon co-receptors that are active in hedgehog signaling in osteocytes. We conclude that osteocytogenesis is accompanied by changes in gene expression that may be driven by both genetic and epigenetic components. These changes are likely responsible for the osteocyte phenotype and may contribute to reduced sensitivity to 1,25(OH)2D3. Two sets of IDG-SW3 differentitiation mRNA-seq experiments are presented here in biological triplicate. One a differentiation time course in the basal condition at days 3, 7, 14, 21, 28, 35. The second experiment is IDG-SW3 cells differentiated to day 3 or day 35 and treated with vehicle or 100nM 1,25(OH)2D3 for 24 hours prior to mRNA isolation and sequencing.

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Lysophosphatidic acid synergizes with 1,25-dihydroxyvitamin D to promote fibroblast growth factor-23 synthesis via MAPK signaling and induction of the IL12A gene

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