miR‐664a‐5p promotes experimental membranous nephropathy progression through HIPK2/Calpain1/GSα‐mediated autophagy inhibition

Abstract We previously found that miR‐664a‐5p is specifically expressed in urinary exosomes of idiopathic membranous nephropathy (IMN) patients. Homeodomain‐interacting protein kinase 2 (HIPK2), a nuclear serine/threonine kinase, plays an important role in nephropathy. But the function of these factors and their connection in MN are unclear. To investigate the function and mechanism of miR‐664a‐5p in MN, the miR‐664a‐5p expression in HK‐2 cells, exosomes, podocytes and renal tissues were studied, as well as cell growth and apoptosis of these cells, the binding of miR‐664a‐5p to HIPK2 mRNA, the levels of relative proteins and autophagy. The MN progression in MN mice model was also studied. Albumin increased the miR‐664a‐5p content and apoptosis of HK‐2 cells, which was blocked by miR‐664a‐5p antagomir. miR‐664a‐5p bound to the 3′ UTR of HIPK2 mRNA, resulting in the up‐regulation of Calpain1, GSα shear and the inhibition of autophagy level. Autophagy inhibitor CQ blocked the protective effect of miR‐664a‐5p antagomir, HIPK2 overexpression, Calpain inhibitor SJA6017 on albumin‐mediated injury. MiR‐664a‐5p from albumin‐treated HK‐2 cells could be horizontally transported to podocytes through exosomes. Exosomes from albumin‐treated HK‐2 cells promoted progression of MN mice, AAV‐Anti‐miR‐664‐5p (mouse homology miRNA) could improve them. Albumin increases the miR‐664a‐5p level and causes changes of HIPK2/Calpain1/GSα pathway, which leads to autophagy inhibition and apoptosis up‐regulation of renal tubular epithelial cells. miR‐664a‐5p can horizontally enter podocytes through exosomes resulting in podocytes injury. Targeted inhibition of miR‐664a‐5p can reduce the apoptosis of renal tubule cells and podocytes, and may improve the MN progression.