Lysosomal Regulation of Gasdermin D Pore Formation in Podocytes Determined by Acid Sphingomyelinase

Abstract

Recent studies have shown that gasdermin D (GSDMD) pore may be involved in inflammasome product release and pyroptosis in podocytes. Nevertheless, the molecular mechanism by which GSDMD pore formation is regulated in these cells remains poorly understood. Given the important role of acid sphingomyelinase (ASM)-ceramide signaling pathway in glomerular inflammation and sclerosis under pathological conditions, the present study tested whether ASM controls lysosome-dependent autophagic degradation of GSDMD-NT and GSDMD pore repair to determine GSDMD pore formation in podocytes. WT/WT, ASM knockout (KO), and ASM overexpression (OE) podocytes were isolated from wild type, Smpd1 (gene code of ASM) gene KO, and podocyte-specific Smpd1 gene OE mice for experiments. We first demonstrated that palmitic acid (PA) as an obesity-related danger factor induced NLRP3 inflammasome activation, GSDMD pore formation on plasma membrane, and IL-1β secretion in podocytes, which was blocked by Smpd1 gene KO but exaggerated by Smpd1 gene OE. Also, it was found that PA-induced pyroptosis was prevented by ASM KO but amplified by ASM OE in podocytes. By confocal microscopy and super-resolution microscopy, we observed that PA treatment enhanced the formation of autophagosomes containing GSDMD-NT but inhibited lysosome-autophagosome interaction in podocytes. Also, FasL-induced lysosome fusion to plasma membrane was reduced by PA. All these pathological changes were remarkably attenuated by ASM KO or amitriptyline but significantly augmented by ASM OE. To further dissect the molecular mechanism by which ASM determines GSDMD pore formation, we examined whether ASM controls lysosomal TRPML1 channel-mediated Ca2+ release to regulate lysosome traffcking and associated lysosomal functions. By GCaMP3 Ca2+ imaging, we found that PA treatment significantly inhibited TRPML1 channel activity in podocytes, which was exaggerated by ASM OE. Correspondingly, PA-induced reduction of lysosome traffcking was more remarkable in ASM OE podocytes compared to WT/WT podocytes. Moreover, PA-induced decrease in lysosome-autophagosome interaction and increase in GSDMD pore formation in podocytes were hindered by ML-SA5 (TRPML1 channel agonist) but enhanced by ML-SI1 (TRPML1 channel inhibitor). In summary, our findings suggest that ASM plays a crucial role in lysosomal regulation of GSDMD pore formation via control of TRPML1 channel activity and lysosome traffcking in podocytes. This study was supported by NIH grants DK054927 and DK120491. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.