Expression of Glutamate Receptor Subtype 3 Is Epigenetically Regulated in Podocytes under Diabetic Conditions

Recent studies suggest a role of epigenetics in the pathogenesis of diabetic kidney disease. However, epigenetic changes occurring specifically in kidney cells is poorly understood.

To examine the epigenetic regulation of genes in podocytes under diabetic conditions, we performed DNA methylation and transcriptomic profiling in podocytes exposed to high glucose conditions.

Comparative analysis of genes with DNA methylation changes and correspondingly altered mRNA expression identified 337 hypomethylated genes with increased mRNA expression and only 2 hypermethyated genes (ESX1 and GRIA3) with decreased mRNA expression. Glutamate ionotropic receptor AMPA type subunit 3 (GRIA3) belongs to the ionotropic class of glutamate receptors that mediate fast excitatory synaptic transmission in the central nervous system. As podocytes have glutamate-containing vesicles and various glutamate receptors mediate important biological effects in podocytes, we further examined GRIA3 expression and its function in podocytes. Real-time PCR and western blots confirmed the suppression of GRIA3 expression in podocytes under high glucose conditions, which were abolished in the presence of a DNA methyltransferase inhibitor. Sites of DNA hypermethylation were also confirmed by bisulfite sequencing of the GRIA3 promoter region. GRIA3 mRNA and protein expression was suppressed in diabetic kidneys of human and mouse models, and knockdown of GRIA3 exacerbated high glucose-induced apoptosis in cultured podocytes.

These results indicate that decreased GRIA3 expression in podocytes in diabetic condition heightens podocyte apoptosis and loss.