A negative feedback loop of H19/miR‐675/EGR1 is involved in diabetic nephropathy by downregulating the expression of the vitamin D receptor

Aim We aimed to explore the regulatory relationship among the long noncoding RNA H19, micorRNA‐675 (miR‐675), the vitamin D (VD) receptor (VDR), and the early growth response protein 1 (EGR1) in the pathogenesis of diabetic nephropathy (DN) among patients with diabetes mellitus (DM). Methods Expression levels of H19, miR‐675, VDR, and EGR in patients or CIHP‐1/HEK 293 cells were measured via quantitative reverse‐transcription polymerase chain reaction and western blot analysis. Computational analysis and luciferase assays were performed to determine EGR1 as a target gene of miR‐675. Results The relative expression of miR‐675 was higher in the presence of H19, whereas the expression of both VDR and EGR1 messenger RNA was decreased in the presence of H19 or miR‐675. However, relative expression of H19 and miR‐675 was increased, whereas VDR expression was suppressed upon the treatment of 1,25‐dihydroxyvitamin D3 or EGR1. VDR was identified as a target gene of miR‐675. The H19 promoter and EGR1 increased the luciferase activity of cells transfected with wild‐type VDR. Compared with DM patients free of DN, the levels of H19 and miR‐675 were increased in the DN(+) group, whereas the levels of VDR and EGR1 were decreased. Conclusion In summary, the above results indicate the presence of a negative feedback loop in the pathological mechanism of DN, where H19 downregulates the expression of VDR by upregulating the expression of miR‐675, whereas reduced VDR expression subsequently reduced the expression of EGR1. Moreover, reduced EGR1 expression inhibits H19 expression, thus forming a negative feedback loop required to maintain the homeostasis of VDR and to reduce the incidence of DN. In this study, we first suggested that a negative feedback loop of H19/miR‐675/EGR1 is involved in the development of diabetic nephropathy (DN). We found that microRNA‐675 (miR‐675) is located within the chromosome segment of H19, whereas the increase in H19 expression also upregulated the expression of both miR‐675‐5p and miR‐675‐3p. Furthermore, vitamin D (VD) receptor (VDR) was reported as a target gene of miR‐675 in human cells, whereas the activation of the VD signaling pathway could promote the expression of early growth response protein 1, a transcription factor of H19. VDR plays an important role in podocyte apoptosis and DN. Therefore, H19 may serve as a novel biomarker for DN.