Targeting Dynein Activator, Dctn1, Ameliorates Podocytopathy in Streptozotocin (STZ)-Induced Diabetic Mice

Background: Diabetic nephropathy (DN) is a severe complication of diabetes that contributes to 30-50% of patients developing end stage kidney disease. In our recent work, we showed an upregulation of dynein genes in diabetes. We have since demonstrated that diabetes suppresses AMP-activated protein kinase (AMPK), which activates specificity protein 1 (SP1)-mediated transcription of these dynein genes. Increased dynactin 1 (Dctn1), a dynein subunit that activates the motor protein, promotes trafficking of nephrin to lysosomes for degradation. The upregulation of Dctn1 correlates with a poor renal outcome in human DN, but its exact role in DN pathogenesis has not been defined. We hypothesize that inactivation of dynein via prevention of Dctn1 upregulation can rescue the disruptions to nephrin trafficking that lead to DN. Methods: We generated a conditional transgenic mouse line with tamoxifen-inducible podocyte-specific knockdown of Dctn1 in C57BL/6 mice by crossing tamoxifen-inducible NPHS2-icre mice with Dctn1loxp/ mice. Diabetes was induced by intraperitoneal (IP) injection of Streptozotocin (STZ) in Cre positive wt/wt and wt/loxp mice. Two weeks later, both the diabetic and nondiabetic mice received IP injections of tamoxifen. Co-staining of Cre recombinase and WT1 was performed to confirm a successful flox of Dctn1 in podocytes. The proteinuria of the mice, histology and ultrastructure of the mouse kidney were compared among diabetic and nondiabetic mice with or without podocyte-specific knockdown of Dctn1. Results: Mice withSTZ-induced diabetes showed features of DN, including proteinuria, glomerulosclerosis, and podocytopathy characterized by reduced nephrin protein with upregulated Dctn1. While Dctn1icre, +/- mice did not undergo spontaneous podocytopathy, they showed rescued disruptions to nephrin and podocytes in diabetic mice, as well as the subsequent development of proteinuria and glomerulosclerosis. The knockdown and normalized expression of Dctn1 in diabetic mouse podocytes prevented the loss of nephrin protein and preserved the foot processes and slit diaphragm structure of podocytes. Conclusion: Inactivation of dynein via prevention of Dctn1 upregulation protects STZ-mice from developing DN. By elucidating the protective effect of targeting dynein in diabetes-induced mistrafficking of nephrin, we provided a new therapeutic strategy for DN. Funding: Other NIH Support - NIH 1R01DK136563 (PI: H. Sun); 5K12HD027748 (PI: Bassuk), Private Foundation Support