Contribution of NLRP3 Inflammasome Activation to Glomerular Injury during Hyperhomocysteinemia with and without Enhanced Exosome Secretion

Abstract

Hyperhomocysteinemia (hHcy) has been demonstrated to activate NLRP3 inflammasome leading to podocyte injury and glomerular sclerosis. However, it remains unknown whether exosome‐mediated secretion of NLRP3 inflammasome products is involved in the development of glomerular injury during hHcy. In the present study, we examined the possible role of increased exosome secretion during NLRP3 activation in the inflammatory response and tested whether without robust release of exosomes, inflammatory response and glomerular injury still occur. Exosome biogenesis inhibitor‐GW4869, lysosome trafficking stimulator‐rapamycin or ASM inhibitor‐amitriptyline were used in mice to answer this question. By nanoparticle tracking analysis, it was found that hHcy significantly increased urinary exosome release in WT/WT mice. In Smpd1trg/Podocre (podocyte‐specific ASM transgenic) mice, this hHcy‐induced increase in urinary exosomes was significantly enhanced. Pretreatments of WT/WT mice and Smpd1trg/Podocre mice with amitriptyline (Ami), GW4869 (GW) and rapamycin (Rap) all prevented increases in urinary exosomes during hHcy. In podocytes isolated from WT/WT mice and Smpd1trg/Podocre mice, similar results were obtained when we measured exosomes released from these cells after different treatments. Confocal microscopy demonstrated that Ami not only prevented hHcy‐induced NLRP3 inflammasome formation and activation in glomeruli, but also decreased exosome release in podocytes of WT/WT mice and Smpd1trg/Podocre mice. However, GW and Rap only blocked exosome‐mediated IL‐1β secretion from podocytes, but had no effect on inflammasome formation or activation in glomeruli during hHcy. However, all 3 treatments attenuated the inflammatory response in glomeruli and associated injury as shown by reduced immune cell aggregation, decreased proteinuria and ameliorated glomerular sclerosis. These results suggest that without enhanced exosome release NLRP3 inflammasome activation in podocytes may not produce local glomerular inflammatory response and associated injury during hHcy.Support or Funding InformationThis study was supported by NIH grants DK54927 and DK102539.