Autophagy maturation associated with CD 38‐mediated regulation of lysosome function in mouse glomerular podocytes

Podocytes are highly differentiated glomerular epithelial cells that contribute to the glomerular barrier function of kidney. A role for autophagy has been proposed in maintenance of their cellular integrity, but the mechanisms controlling autophagy in podocytes are not clear. The present study tested whether CD 38‐mediated regulation of lysosome function contributes to autophagic flux or autophagy maturation in podocytes. Podocytes were found to exhibit a high constitutive level of LC 3‐II, a robust marker of autophagosomes ( AP s), suggesting a high basal level of autophagic activity. Treatment with the m TOR inhibitor, rapamycin, increased LC 3‐II and the content of both AP s detected by Cyto‐ID Green staining and autophagolysosomes ( APL s) measured by acridine orange staining and colocalization of LC 3 and Lamp1. Lysosome function inhibitor bafilomycin A1 increased AP s, but decreased APL s content under both basal and rapamycin‐induced conditions. Inhibition of CD 38 activity by nicotinamide or silencing of CD 38 gene produced the similar effects to that bafilomycin A1 did in podocytes. To explore the possibility that CD 38 may control podocyte autophagy through its regulation of lysosome function, the fusion of AP s with lysosomes in living podocytes was observed by co‐transfection of GFP ‐ LC 3B and RFP ‐Lamp1 expression vectors. A colocalization of GFP ‐ LC 3B and RFP ‐Lamp1 upon stimulation of rapamycin became obvious in transfected podocytes, which could be substantially blocked by nicotinamide, CD 38 sh RNA , and bafilomycin. Moreover, blockade of the CD 38‐mediated regulation by PPADS completely abolished rapamycin‐induced fusion of AP s with lysosomes. These results indicate that CD 38 importantly control lysosomal function and influence autophagy at the maturation step in podocytes.