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Genomic and epigenomic 1α,25(OH)2D3 responses in human colonic organoids

ABSTRACT: Background & Aims: Active vitamin D, 1α,25(OH)2D3, is a nuclear hormone with roles in colonic homeostasis and carcinogenesis, yet mechanisms underlying these effects are incompletely understood. Human organoids are an ideal system to study genomic and epigenomic host-environment interactions. Here, we utilize human colonic organoids to measure 1α,25(OH)2D3 responses on genome-wide gene expression and chromatin accessibilityover time. Methods: Human colonic organoids were cultured and treated in triplicate with either 100nM 1α,25(OH)2D3 or vehicle control for 4 and 18 hours (h) for chromatin accessibility, and 6 and 24hfor gene expression. DNA and RNA were extracted for ATAC- and RNA-sequencing, respectively. Differentially accessible peaks were analyzed using DiffBind and EdgeR; differentially expressed genes were analyzed using DESeq2. Motif enrichment was determined using HOMER. Results: At 6h and 24h, 2870 and 2721 differentially expressed genes, respectively (FDR<5%) were identified with overall stronger responses with 1α,25(OH)2D3. Similarly, 1α,25(OH)2D3 treatment led to stronger chromatin accessibility especially at 4h. The vitamin D receptor (VDR) motif was strongly enriched among open chromatin peaks with 1α,25(OH)2D3 treatment accounting for 30.5% and 11% of target sequences at 4h and 18h, respectively (FDR<1%). A number of genes such as CYP24A1, FGF19, MYC, FOS and TGFBR2 showed significant transcriptional and chromatin accessibility responses to 1α,25(OH)2D3 treatment with open chromatin located distant from promoters for some gene regions. Conclusions: Assessment of chromatin accessibility and transcriptional responses to 1α,25(OH)2D3 yielded new observations about vitamin D genome-wide effects in the colon facilitated by application of human colonic organoids. This framework can be applied to study host-environment interactions between individuals and populations in future.

ORGANISM(S): Homo sapiens

PROVIDER: GSE162856 | GEO | 2020/12/09

REPOSITORIES: GEO

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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.

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Genomic and epigenomic 1α,25(OH)2D3 responses in human colonic organoids

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