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A Parathyroid Hormone/Salt Inducible Kinase Signaling Axis Controls Renal Vitamin D Activation and Organismal Calcium Homeostasis [SK]

ABSTRACT: The renal actions of parathyroid hormone (PTH) promote 1,25-vitamin D generation; however, the signaling mechanisms in renal epithelial cells downstream of the PTH receptor that control vitamin D metabolism remain unknown. Here we demonstrate that Salt Inducible Kinases (SIKs) control renal 1,25-vit D production downstream of PTH signaling via regulating Cyp27b1 expression. As PTH inhibits the cellular activity of SIKs by cAMP-dependent PKA phosphorylation in bone, we hypothesized that SIKs would also work as an essential mediator of PTH doownstream signaling in kidney, thus regulate vitamin D metabolism. Whole tissue and single cell transcriptomics in kidney demonstrates that both PTH and pharmacologic SIK inhibitors regulate a vitamin D gene module in specific proximal tubule cells. Moreover, small molecule SIK inhibitors directly increase 1,25-vit D production and renal Cyp27b1 mRNA expression in mice and in human embryonic stem cell-derived kidney organoids. Global- and kidney-specific Sik2/Sik3 mutant mice show Cyp27b1 upregulation, elevated serum levels of 1,25-vit D, and PTH-independent hypercalcemia. The SIK substrate CRTC2 shows PTH and SIK inhibitor-inducible binding to key Cyp27b1 regulatory enhancers in the kidney, which are also required for SIK inhibitors to increase Cyp27b1 in vivo. Lastly, in a podocyte injury mouse model of chronic kidney disease (CKD) characterized by low 1,25-vit D levels, SIK inhibitor treatment stimulates both renal Cyp27b1 expression and 1,25-vit D production.

ORGANISM(S): Mus musculus

PROVIDER: GSE207733 | GEO | 2023/03/01

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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A Parathyroid Hormone/Salt Inducible Kinase Signaling Axis Controls Renal Vitamin D Activation and Organismal Calcium Homeostasis [SK]

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