Active vitamin D and vitamin D analogs stimulate fibroblast growth factor 23 production in osteocyte-like cells via the vitamin D receptor.

Osteocytes play an important role in the regulation of serum phosphorus by producing fibroblast growth factor 23 (FGF23). FGF23 production is stimulated by 1α,25-dihydroxyvitamin D in osteocytes. However, it is unclear whether vitamin D induces FGF23 production in osteocytes directly. Therefore, we investigated vitamin D-induced FGF23 production in osteocyte-like cells derived from MC3T3-E1 osteocyte progenitor cells. We also investigated differences in the induction of FGF23 by 1α,25-dihydroxyvitamin D and various vitamin D analogs. MC3T3-E1 cells were differentiated into osteocyte-like cells (MCT3-E1-OLCs) by treatment with various agents including ß-glycerophosphate and ascorbic acid. MCT3-E1-OLCs were stimulated with 1α,25-dihydroxyvitamin D3 and subsequent FGF23 gene expression was 2631 ± 605 times higher compared with untreated cells. The expression of FGF23 in MCT3-E1-OLCs transfected with a knockdown sequence against vitamin D receptor (VDR) was significantly decreased compared with that in cells transfected with the control vector. Therefore, the induction of FGF23 in osteocytes by vitamin D may be primarily mediated via VDR. The potential of 25(OH)vitamin D3, paricalcitol, and maxacalcitol to induce FGF23 production was almost the same as that of 1α,25-dihydroxyvitamin D3. However, falecalcitriol and eldecalcitol demonstrated a reduced potential to induce FGF23 compared with 1α,25-dihydroxyvitamin D3. Our results demonstrate that FGF23 induction is different among the analogs of 1α,25-dihydroxyvitamin D3. Therefore, an appropriate vitamin D analog should be chosen for each patient with mineral and bone disorder, considering its effect on FGF23 production.

FGF23 modulates the effects of erythropoietin on gene expression in renal epithelial cells.

BACKGROUND: FGF23 plays an important role in calcium-phosphorus metabolism. Other roles of FGF23 have recently been reported, such as commitment to myocardium enlargement and immunological roles in the spleen. In this study, we aimed to identify the roles of FGF23 in the kidneys other than calcium-phosphorus metabolism. METHODS: DNA microarrays and bioinformatics tools were used to analyze gene expression in mIMCD3 mouse renal tubule cells following treatment with FGF23, erythropoietin and/or an inhibitor of ERK. RESULTS: Three protein-coding genes were upregulated and 12 were downregulated in response to FGF23. Following bioinformatics analysis of these genes, PPARγ and STAT3 were identified as candidate transcript factors for mediating their upregulation, and STAT1 as a candidate for mediating their downregulation. Because STAT1 and STAT3 also mediate erythropoietin signaling, we investigated whether FGF23 and erythropoietin might show interactive effects in these cells. Of the 15 genes regulated by FGF23, 11 were upregulated by erythropoietin; 10 of these were downregulated following cotreatment with FGF23. Inhibition of ERK, an intracellular mediator of FGF23, reversed the effects of FGF23. However, FGF23 did not influence STAT1 phosphorylation, suggesting that it impinges on erythropoietin signaling through other mechanisms. CONCLUSION: Our results suggest cross talk between erythropoietin and FGF23 signaling in the regulation of renal epithelial cells.

Effects of Cyclophosphamide Pulse Therapy on the Clinical and Histopathological Findings, Particularly Crescent Formation, in a Patient with Adult-onset Steroid-refractory Henoch-Schönlein Purpura Nephritis.

A 29-year-old woman was diagnosed with Henoch-Schönlein purpura nephritis (HSPN) based on the presence of purpura and histopathological findings showing crescent formation, mesangial proliferation and IgA deposition in the glomerular mesangium. She was treated with high-dose steroids; however, the nephritic syndrome persisted. Therefore, we diagnosed her with steroid-resistant HSPN and decided to add treatment with cyclosphamide pulse therapy. After one year of treatment, the histopathological findings, including crescent formation and IgA deposition, improved, as confirmed on a renal biopsy, and the patient fulfilled the criteria for complete remission. Cyclophosphamide pulse therapy may be considered an effective treatment for intractable HSPN.