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Targeting Fibroblast growth factor-23 (FGF23) responsive pathways in the control of renal phosphate and vitamin D metabolism

ABSTRACT: FGF23 is a bone-derived hormone that mediates renal phosphate reabsorption and 1,25(OH)2 vitamin D metabolism via its required co-receptor alpha-Klotho (KL). The functional pathways guiding this hormone’s activity in kidney have not been studied extensively, and whether using other factors with overlapping signaling profiles to produce FGF23-like responses is unclear. To map FGF23-related genes, gene array and single-cell RNA sequencing were utilized on wild type mouse kidneys. After identifying Heparin-binding EGF-like growth factor (HBEGF) as an up-regulated gene in response to FGF23 delivery, KL-null and phosphate-deficient diet fed mouse models and in vitro experiments were utilized to further test HBEGF bioactivity in kidney. Gene array demonstrated that HBEGF was significantly up-regulated following FGF23 delivery to wild type (WT) mice. Next, mice injected with HBEGF had phenotypes consistent with partial FGF23-mimetic activity including robust induction of EGR1, and increased CYP24A1 mRNAs. Single cell RNA sequencing showed overlapping HBEGF and EGFR expression in the proximal tubule (PT), and KL expression in PT and distal tubule (DT) segments. In KL-null mice devoid of canonical FGF23 signaling, HBEGF injections significantly increased EGR1 and CYP24A, and correction of basally-elevated CYP27B1 was observed. In addition, mice placed on a phosphate deficient diet to suppress FGF23 had endogenously increased CYP27B1 mRNA, which was rescued in mice receiving HBEGF. In HEK293 renal epithelial cells, HBEGF and FGF23 increased CYP24A1 mRNA. Targeting pathways known to be downstream of FGF23 in kidney may help to control renal phosphate handling in diseases of altered FGF23 bioactivity.

ORGANISM(S): Mus musculus

PROVIDER: GSE138992 | GEO | 2020/10/01

REPOSITORIES: GEO

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Project description:Human kidney was obtained from the University of Wisconsin Madison Organ Procurement Program from a deceased 69 year old female patient and the cortex was dissected from 3 different cortex locations. Associated publication abstract: Targeted genomic deletions identify diverse enhancer functions and generate a kidney-specific, endocrine-deficient Cyp27b1 pseudo-null mouse Vitamin D3 is terminally bioactivated in the kidney to 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) via cytochrome P450 family 27 subfamily B member 1 (CYP27B1), whose gene is regulated by parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and 1,25(OH)2D3. Our recent genomic studies in the mouse have revealed a complex kidney-specific enhancer module within the introns of adjacent methyltransferase like 1 (Mettl1) and Mettl21b that mediate basal and PTH induced expression of Cyp27b1 and FGF23- and 1,25(OH)2D3-mediated repression. Gross deletion of these segments in mice has severe consequences on Cyp27b1 regulation and skeletal phenotype, but does not affect Cyp27b1 expression in non-renal target cells (NRTCs). Here, we report a bimodal activity in the Mettl1 intronic enhancer with components responsible for PTH-mediated Cyp27b1 induction and 1,25(OH)2D3-mediated repression and additional activities, including FGF23 repression, within the Mettl21b enhancers. Deletion of both submodules eliminated basal Cyp27b1 expression and regulation in the kidney, leading to systemic and skeletal phenotypes similar to those of Cyp27b1-null mice. However, basal expression and lipopolysaccharide-induced regulation of Cyp27b1 in NRTCs was unperturbed. Importantly, dietary normalization of calcium, phosphate, PTH, and FGF23 rescued the skeletal phenotype of this mutant mouse, creating an ideal in vivo model to study non-renal 1,25(OH)2D3 production in health and disease. Finally, we confirmed a conserved chromatin landscape in human kidney that is similar to that in mouse. These findings define a finely balanced homeostatic mechanism involving PTH and FGF23 together with protection from 1,25(OH)2D3 toxicity that is responsible for both adaptive vitamin D metabolism and mineral regulation.

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Targeting Fibroblast growth factor-23 (FGF23) responsive pathways in the control of renal phosphate and vitamin D metabolism

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