LAUSR

Recent studies have reported that intrinsic stiffness of smooth muscle cells (SMCs) plays an important role in contributing to arterial wall stiffness, which led to the concept of smooth muscle cell stiffness syndrome (SMCSS). However, the molecular mechanisms regulating the intrinsic stiffness of SMCs are still poorly understood. The present study tested whether lysosomal acid ceramidase (AC) determines intrinsic stiffness of mouse aortic SMCs via regulation of actin polymerization and integrin recycling. Atom force microscopy was used to study mechanical properties of SMCs. As an injurious adipokine, visfatin was found to reduce SMC height, but elevate cortical stiffness and focal adhesion in SMCs, indicating the augmentation of intrinsic stiffness. Moreover, visfatin-induced elevation of cortical stiffness was associated with increased actin polymerization in peripheral areas of SMCs. These pathological changes were much more remarkable in SMCs from smooth muscle-specific Asah1 gene (gene code of AC) knockout (Asah1fl/fl/SMcre) mice compared to SMCs from WT/WT mice. Super-resolution microscopy showed that multivesicular bodies (MVBs) as integrin degrading organelles were much less interacted or fused with lysosomes in SMCs from Asah1fl/fl/SMcre mice than WT/WT mice upon visfatin stimulation. In contrast, MVB-α5 integrin encounters increased more in SMCs from Asah1fl/fl/SMcre mice compared to SMCs from control littermates, suggesting that AC deficiency increases α5 integrin accumulation in MVB, which may enhance recycling endosome moving to cell membrane. Given the vital role of lysosomal transient receptor potential mucolipin 1 (TRPML1) channel in the regulation of lysosome trafficking and its interaction with MVB, we tested whether this lysosomal channel is disturbed by visfatin. By GCaMP3 Ca2+ imaging and whole-lysosome patch clamp recording, we found that ML-SA5 (TRPML1 channel agonist) induced remarkable lysosomal Ca2+ release in WT/WT SMCs, which was attenuated by visfatin. In SMCs lacking Asah1 gene, however, ML-SA5 induced much less Ca2+ release from lysosomes, which was almost abolished by visfatin. Lysosome trafficking analysis showed that ML-SA5 activation of lysosomal TRPML1 channels markedly increased lysosome movement in SMCs, which was significantly inhibited by visfatin and Asah1 gene deletion. Based on these results, we concluded that lysosomal AC deficiency leads to dysregulation of actin polymerization and integrin recycling in SMCs, which may be a novel molecular mechanism of SMCSS and ultimate arterial wall stiffening during obesity. This study was supported by NIH grants HL057244 and HL075316. This is the full abstract presented at the American Physiology Summit 2023 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.