Reorganization of Actin Cytoskeleton and Reduction of Cortical Elasticity in Podocytes Lacking Acid Ceramidase: Role of Sphingomyelinase-Like Phosphodiesterase 3b

Abstract

Podocytopathy and associated nephrotic syndrome have been reported in a mouse strain (Asah1fl/fl/Podocre) with a podocyte-specific deletion of α subunit (the main catalytic subunit) of acid ceramidase (AC). Nevertheless, the pathogenic mechanism of podocytopathy in these mice remains poorly understood. Given that sphingomyelinase-like phosphodiesterase 3b (SMPDL3b) has been recently reported to play a vital role in maintaining the actin cytoskeleton and normal function of podocytes, the present study tested whether Asah1 gene deletion-induced podocytopathy is attributed to altered SMPDL3b activity and reorganized actin cytoskeleton in podocytes. By Western blot analysis and SMPDL3b enzyme activity assay, we demonstrated that Asah1 gene knockout remarkably decreased both expression and function of SMPDL3b in podocytes isolated from Asah1fl/fl/Podocre mice compared to podocytes of wild type (WT/WT) mice. As a monoclonal antibody which can bind to and stabilize SMPDL3b on podocytes, rituximab was found to significantly recover SMPDL3b expression and activity in podocytes lacking Asah1 gene. Correspondingly, Asah1 gene deletion reduced podocin expression in podocytes, which was attenuated by rituximab treatment. Phalloidin staining of F-actin showed elevation of cortical actin and reduction of stress fiber in podocytes lacking Asah1 gene. Such actin cytoskeleton redistribution was significantly attenuated by rituximab. Moreover, atom force microscopy was used to study the impact of actin cytoskeleton remodeling on mechanical properties of podocytes. Asah1 gene knockout was found to increase podocyte height but decrease cortical elasticity in these cells. These pathological changes were significantly inhibited by rituximab, suggesting the restoration of actin cytoskeleton in podocytes lacking Asah1 gene by rituximab. In vivo, intraperitoneal injection of rituximab markedly attenuated proteinuria and albuminuria in Asah1fl/fl/Podocre mice compared to control groups. In summary, our findings suggest that alteration of SMPDL3b activity and reorganization of actin cytoskeleton in podocytes may contribute to the pathogenesis of podocytopathy in mice with podocyte-specific Asah1 gene deletion. 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.