Attenuation of Obesity‐Induced Glomerular Inflammatory Response by Inhibition of Exosome Biogenesis and Release without Changes in NLRP3 Inflammasome Activation in Podocytes

Abstract

Obesity has been reported to induce NLRP3 inflammasome activation in podocytes, leading to podocyte injury and glomerular dysfunction. The present study tested whether exosome biogenesis and lysosome function are involved in the regulation of exosome release from podocytes during obesity and whether obesity still induces glomerular inflammatory response without robust release of exosomes. By nanoparticle tracking analysis, increased urinary exosome excretion was found in WT/WT mice fed with high‐fat diet (HFD), which was exaggerated by podocyte‐specific overexpression of Smpd1 gene (Smpd1 is the gene code of mouse acid sphingomyelinase) in Smpd1trg/Podocre mice. Exosome biogenesis inhibitor‐GW4869, lysosome function enhancer‐rapamycin, and acid sphingomyelinase inhibitor‐amitriptyline were found to inhibit the elevation of urinary exosome excretion during obesity in both WT/WT and Smpd1trg/Podocre mice. We also isolated podocytes from WT/WT and Smpd1trg/Podocre mice for in vitro studies. Visfatin as a pro‐inflammatory adipokine enhanced exosome release from podocytes, which was exaggerated by Smpd1 gene overexpression. Correspondingly, pre‐treatment of cells with GW4869, rapamycin, and amitriptyline blocked the increase in exosome release induced by visfatin. By confocal microscopy, we observed HFD‐induced NLRP3 inflammasome activation in glomeruli, which was enhanced by podocyte‐specific Smpd1 gene overexpression but attenuated by amitriptyline. Moreover, HFD‐induced immune cell infiltration into glomeruli and glomerular sclerotic changes were worsen by podocyte‐specific Smpd1 gene overexpression but inhibited by all 3 treatments. However, GW4869 and rapamycin had no effects on NLRP3 inflammasome in podocytes, but only amitriptyline suppressed NLRP3 inflammasome activation. It is concluded that exosome release from podocytes during obesity contributes to the inflammatory response in glomeruli, which is regulated by exosome biogenesis and lysosome function. Without robust release of exosomes, NLRP3 inflammasome activation may not induce glomerular inflammatory response during obesity.