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Extracellular sodium regulates fibroblast growth factor 23 (FGF23) formation

ABSTRACT: Fibroblast growth factor-23 (FGF23) is a bone-derived hormone that has recently received much attention due to its association with the progression of chronic kidney disease, cardiovascular disease, and associated mortality. Extracellular sodium ion concentration ([Na+]) plays a significant role in bone metabolism. Both hyponatremia (low serum [Na+]) and hypernatremia (high serum [Na+]) have been shown to affect bone remodeling. However, nothing is known about the impact of [Na+] on FGF23 production. Here, we show that elevated [Na+] (by +20 mM) suppressed FGF23 formation, whereas low [Na+] (by -20 mM) led to an increase in FGF23 synthesis in the osteoblast-like cell line UMR-106. Similar bidirectional changes in FGF23 were observed when osmolality was altered by mannitol but not by urea, suggesting a role of tonicity in FGF23 formation. Moreover, these changes in FGF23 were inversely proportional to the expression of NFAT5 (nuclear factor of activated T cells-5), a transcription factor responsible for tonicity-mediated cellular adaptations. On the other hand, arginine vasopressin (AVP), which is often responsible for hyponatremia, did not affect FGF23 production. Next, comprehensive and unbiased RNA-seq analysis of UMR-106 cells exposed to low vs. high [Na+] revealed several novel genes involved in cellular adaptation to altered tonicity. Additional analysis of cells with Crisp-Cas9 mediated NFAT5 deletion indicated that NFAT5 controls numerous genes associated with FGF23 synthesis, thereby confirming its role in [Na+]-mediated FGF23 regulation. In line with these findings, in a pilot study, we found that human hyponatremic patients have higher FGF23 levels. Our results suggest that [Na+] is a critical regulator of FGF23 synthesis.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE235694 | GEO | 2023/06/23

REPOSITORIES: GEO

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Project description:We used gene array analysis of cortical bone to identify Phex-dependent gene transcripts regulating Fgf23 production and mineralization in Hyp mice. We discovered that activation of Fgf receptor- and Wnt-pathways contribute to increased Ffg23 gene transcription in Hyp bone. We found evidence in Hyp bone for increased expression of Fgf1, Fgf7, and Egr2 in the Fgf-signaling pathway and decrements in Sost and Cpz and increments in Sfrp1 and 4 in the Wnt-signaling pathway. Moreover, activation of Fgf and Wnt-signaling stimulated, whereas Tgf β inhibited Fgf23 promoter activity in osteoblasts. We also observed reductions in Bmp1, a metalloproteinase that metabolizes the Fgf23 regulatory extracellular matrix protein Dmp1. These findings suggest that elevation of Fgf23 expression in osteocytes is regulated by interactions between cell surface expression of Phex, extracellular matrix proteins and paracrine effects of Fgf and Wnt. Alterations were also found in enzymes regulating the posttranslational processing and stability of Fgf23, including decrements in the glycosyltransferase Galnt3 and the proprotein convertase Pcsk5. In addition, we found that the Pcsk5 and the glycosyltransferase Galnt3 were decreased in Hyp bone, suggesting that reduced post-translational processing of FGF23 may also contribute to increased Fgf23 levels in Hyp mice. With regards to mineralization, we identified additional candidates to explain the intrinsic mineralization defect in Hyp osteoblasts, including increases in the mineralization inhibitors Mgp and Thbs4, as well as increases in local pH altering factors, carbonic anhydrase 12 (Car12) and 3 (Car3) and the sodium-dependent citrate transporter (Slc13a5). These studies demonstrate the complexity of gene expression alterations in bone that accompanies inactivating Phex mutations and identify novel pathways that may coordinate Fgf23 expression and mineralization of extracellular matrix in Hyp bone. We isolated total RNAs from long bones of both WT and Hyp mice at 12 days of age. Since the RNA yields from the long bones are very low, we combined 2 bone samples with same genotype (WT or Hyp) for one RNA extraction. We will compare the difference of the gene expressions between Hyp and WT. We will use 4 samples in each animal condition.

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Extracellular sodium regulates fibroblast growth factor 23 (FGF23) formation

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