Enhanced Exosome Release and Inhibited TRPML1 Channel Activity in Podocytes from Mice with Podocyte‐Restricted Deletion of Asah1 Gene

Abstract

The ceramide hydrolysis by lysosomal acid ceramidase (AC) has been reported to regulate lysosome function, which determines the degradation of multivesicular bodies. In this regard, we found that urinary exosome excretion was remarkably increased in podocyte‐specific AC gene knockout (Asah1fl/fl/Podocre) mice. Given the importance of transient receptor potential mucolipin 1 (TRPML1) channel‐mediated Ca2+ release to lysosome function and its regulation by sphingolipids, the present study tested a hypothesis that podocyte‐specific Asah1 gene deletion inhibits TRPML1 channel activity, leading to lysosome dysfunction and exosome release from podocytes. It was found that exosomes released from Asah1fl/fl/Podocre podocytes were remarkably higher than WT/WT podocytes as detected by nanoparticle tracking analysis. Super‐resolution microscopy showed less fusion of multivesicular bodies and lysosomes in Asah1fl/fl/Podocre podocytes compared with WT/WT podocytes. Using GCaMP3 Ca2+ imaging, it was found that ML‐SA1 as a specific cell‐permeable TRPML1 inducer remarkably increased Ca2+ release from lysosomes by 7.35 folds in WT/WT podocytes. Pre‐treatment of podocytes with carmofur, a specific AC inhibitor almost totally blocked ML‐SA1‐induced Ca2+ release in WT/WT podocytes. In Asah1fl/fl/Podocre podocytes, however, ML‐SA1 was found to have no effects on TRPML1 channel‐mediated Ca2+ release, but sphingosine as an AC product of ceramide hydrolysis remarkably increased TRPML1 channel‐mediated Ca2+ release in both WT/WT podocytes (5.42 folds) and Asah1fl/fl/Podocre podocytes (4.52 folds). Using whole‐lysosome patch clamp recording, we detected ML‐SA1‐induced Ca2+ currents in a dose‐dependent manner through the membrane of lysosomes isolated from WT/WT podocytes. Compared to WT/WT podocytes, intact lysosomes isolated from Asah1fl/fl/Podocre podocytes had evidently blunted opening of TRPML1 channels in response to its agonist, ML‐SA1. AC associated sphingolipids, sphingomyelin, ceramide and sphingosine had different effects on TRPML1 channel activity in WT/WT podocytes, with inhibition by sphingomyelin, no effect from ceramide, but enhancement by sphingosine (2.25 folds). In Asah1fl/fl/Podocre podocytes, sphingosine remained to increase ML‐SA1‐induced TRPML1 channel‐mediated Ca2+ release (3.96 folds). These results suggest that the AC deficiency decreases TRPML1 channel activity due to reduction of sphingosine production, which may contribute to lysosome dysfunction and enhanced exosome release.Support or Funding InformationThis study was supported by NIH grants DK54927, DK120491, and HL057244.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.