Dynein-mediated trafficking and degradation of nephrin in diabetic podocytopathy

Diabetic nephropathy (DN) is characterized by increased endocytosis and degradation of nephrin, a protein that comprises the molecular sieve of the glomerular filtration barrier, but the key trafficking mechanism that connects the initial endocytic events and the homeostasis of nephrin is unknown. Our work implicates cytoplasmic dynein, a transport complex that is upregulated in DN, plays a critical role in triaging the endocytosed nephrin between recycling and proteolytic pathways. Using Nephroseq platform, our transcription analysis in public DN databases revealed dynein overexpression in human DN and diabetic mouse kidney, correlated with the severity of hyperglycemia and nephropathy. The increased expression of dynein subunits was confirmed in high glucose-treated podocytes and in glomeruli isolated from streptozotocin (STZ)-induced diabetic mice. Using live cell imaging, we illustrated that dynein-mediated post-endocytic sorting of nephrin was upregulated, resulting in accelerated nephrin degradation and disrupted nephrin recycling. In diabetic podocytopathy, Dynll1 is one of the most upregulated dynein components that was recruited to endocytosed nephrin. This was corroborated by observing enhanced Dynll1-nephrin colocalization in podocytes of diabetic patients, as well as dynein-mediated trafficking and degradation of nephrin in STZ-induced diabetic mice. Knockdown of Dynll1 attenuated lysosomal degradation of nephrin and promoted its recycling, suggesting the essential role of Dynll1 in dynein-mediated mistrafficking. Defining the role of dynein-mediated mistrafficking of nephrin in diabetes will not only fill the knowledge gap about the early events of DN, but also inspire novel therapeutics that target a broad spectrum of molecular events involved in the dynein-mediated trafficking. Translational StatementDiabetic nephropathy (DN), the leading cause of end stage kidney disease in the United States, is characterized by a podocytopathy with mistrafficking and depletion of the slit diaphragm protein nephrin, which in turn compromises the podocytes function in maintaining the glomerular filtration barrier. There is a critical need to define the trafficking mechanisms underlying the depletion of nephrin. Our work implicates cytoplasmic dynein, a trafficking complex that connects diabetes-triggered endocytosis with proteolytic pathways. Delineation of the dynein-driven pathogenesis of diabetic podocytopathy will inspire new therapies that potentially target a broad spectrum of molecules involved in dynein-mediated trafficking and degradation pathways.