The vitamin D3 hormone, 1,25(OH)2D3, regulates fibroblast growth factor 23 (FGF23) production in human skin cells

Summary: Abstract Body: The bone hormone fibroblast growth factor 23 (FGF23) regulates renal phosphate reabsorption and the enzymatic production of active vitamin D3 (1,25(OH)2D3). Therefore, FGF23 production in bone cells is closely regulated by 1,25(OH)2D3 acting via the vitamin D receptor (VDR). Skin cells can produce hydroxyvitamin D3 metabolites from its precursor D3 made through UVB-light exposure. Interestingly, expression of Fgf23 has been found in rodent skin, but its expression, regulation, and role in human skin are unclear. Therefore, we investigated whether hydroxyvitamin D3 metabolites regulate FGF23 in human skin cells. Primary adult and neonatal epidermal keratinocytes (HEKn), melanocytes (HEMn), dermal fibroblasts (HDFn), as well as human melanoma cells, HaCaT, HaCaT VDR KO, and A431 epidermoid cells, were used to assess FGF23 gene expression (qRT-PCR), cellular FGF23 protein (western blot), or secreted FGF23 protein (ELISA) after treatment with hydroxyvitamin D3 metabolites. HaCaT cells treated with recombinant FGF23 were used to explore its function in skin. Human skin cells can synthesize FGF23. Treatment with 1,25(OH)2D3 significantly increased FGF23 mRNA levels in HaCaT and HDFn cells, and moderately in HEKn cells, mediated in part by the VDR. It also moderately enhanced mRNA levels of the FGF23-processing enzyme GALNT3 and stimulated secretion of hormonally active FGF23 from HaCaT cells. Treatment of HaCaT cells with FGF23 increased mRNA levels of the cholesterol- and vitamin D-metabolizing enzymes, CYP11A1 and CYP27A1. In conclusion, human skin cells express and secrete FGF23, which is regulated by 1,25(OH)2D3 acting in part by the VDR. FGF23 affects the expression of cutaneous sterol-metabolizing enzymes Franz Ewendt^{1, 4}, Zorica Janjetovic¹, Tae-Kang Kim¹, Alisa Mobley¹, Anna Brozyna², Senthilkumar Ravichandran¹, Adrian Fabisiak³, Pawel Brzeminski³, Rafal Sicinski³, Gabriele Stangl⁴, Robert Tuckey⁵, Andrzej T. Slominski¹ 1. The University of Alabama at Birmingham, Birmingham, AL, United States. 2. Uniwersytet Mikolaja Kopernika w Toruniu, Torun, Kuyavian-Pomeranian Voivodeship, Poland. 3. Uniwersytet Warszawski, Warsaw, Masovian Voivodeship, Poland. 4. Martin-Luther-Universitat Halle-Wittenberg, Halle (Saale), SA, Germany. 5. The University of Western Australia, Perth, WA, Australia. UV Biology/Injury and Non-melanoma Cancers