Epigenetic Modulation of Human Podocyte Vitamin D Receptor in HIV Milieu

Abstract

HIV has been reported to induce podocyte injury through down regulation of vitamin D receptor (VDR) and activation of renin angiotensin system (RAS); however, the involved mechanism is not clear. Since HIV has been reported to modulate gene expression via epigenetic phenomena, we asked whether epigenetic factors are contributing to down regulation of VDR. Kidney cells in HIV transgenic mice as well as HIV-infected podocytes (HIV/HPs) displayed enhanced expression of SNAIL, a repressor of VDR. To elucidate the mechanism, we studied the effect of HIV on expression of molecules involved in SNAIL repressor complex formation and demonstrated that HIV enhancesexpression of histone deacetylase (HDAC) 1, DNA methyl transferase (DNMT) 3b and DNMT1. 293T cells, when stably transfected with SNAIL (SNAIL/293T), displayed suppressed transcription and translation of VDR. In SNAIL/293T cells, co-immunoprecipitation studies revealed the association of HDAC1, DNMT3b, DNMT1, and mSin3A with SNAIL. Chromatin immunoprecipitation (ChIP) experiments confirmed the presence of the SNAIL repressor complex at the VDR promoter. Consistent with the enhanced DNA methyl transferase expression in HIV/HPs, there was an increased CpG methylation at the VDR promoter. ChIP assay confirmed occurrence of H3K4 trimethylation on SNAIL promoter. Neither VDR agonist (VDA) nor an HDAC inhibitor (HDACI) nor demethylating agent (DAC) individually could optimally upregulate VDR in HIV milieu. However, VDA and HDACI when combined were successful in de-repressing VDR expression. Our findings demonstrate that SNAIL recruits multiple chromatin enzymes to form a repressor complex in HIV milieu which down regulates VDR expression.

Vitamin D receptor deficit induces activation of renin angiotensin system via SIRT1 modulation in podocytes

“…We and other investigators have previously reported down regulation of podocyte VDR expression in adverse milieus both in vitro and in vivo studies (8, 9, 25, 26, 34). We asked whether high glucose milieu would also down regulate SIRT1 and enhance podocyte p53 expression and associated downstream signals.…”

“…Recently, high Ang II states including high glucose and HIV milieus have been reported to cause down regulation of VDR in podocytes (8, 9, 25, 26, 34). High Ang II states down regulate podocyte VDR by multiple mechanisms including enhanced VDR degradation via proteasomal pathway and through transcription of CYP24A via de-repression of co-repressor complexes at CYP24A1 promoter (26).…”

“…Additionally, Ang II as well as conditions associated with high Ang II states such as high glucose and HIV milieus are associated with enhanced podocyte expression of SNAIL (19, 32); the latter is a repressor of transcription of VDR (17, 32). Knocking of VDR in kidney cells has been demonstrated to enhance the activation of renin angiotensin system (RAS) (8,9,25, 26, 34). Thus, it appears that Ang II perpetuates its production through down regulation of VDR in kidney cells.…”

“…It has been shown in patients of colon cancer that vitamin D receptor could not be optimally raised with vitamin D therapy in several instances and these patients did not respond to vitamin D therapy (17). We have recently reported that HIV down regulated podocyte VDR expression thorough CpG methylation at VDR promoter (8). In these studies, Vitamin D could not up regulate podocyte VDR expression optimally; however, use of a demethylating agent in combination with vitamin D could optimally increase podocyte VDR expression in HIV milieu (8).…”

“…We have recently reported that HIV down regulated podocyte VDR expression thorough CpG methylation at VDR promoter (8). In these studies, Vitamin D could not up regulate podocyte VDR expression optimally; however, use of a demethylating agent in combination with vitamin D could optimally increase podocyte VDR expression in HIV milieu (8). We propose that discrepancy in vitamin D clinical trials may be related to the inability of vitamin D in upregulating VDR optimally because of the down regulation as a consequence of epigenetics.…”