Podocytopathy and Nephrotic Syndrome in Mice with Podocyte-Specific Deletion of the Asah1 Gene

Abstract

Lysosomal acid ceramidase (Ac) has been shown to be critical for ceramide hydrolysis and regulation of lysosome function and cellular homeostasis. In the present study, we generated a knockout mouse strain (Asah1 fl/fl /Podo Cre ) with a podocyte-specific deletion of the a subunit (main catalytic subunit) of Ac. Although no significant morphologic changes in glomeruli were observed in these mice under light microscope, severe proteinuria and albuminuria were found in these podocyte-specific knockout mice compared with control genotype littermates. Transmission electron microscopic analysis showed that podocytes of the knockout mice had distinctive foot process effacement and microvillus formation. These functional and morphologic changes indicate the development of nephrotic syndrome in mice bearing the Asah1 podocyte-specific gene deletion. Ceramide accumulation determined by liquid chromatographyetandem mass spectrometry was demonstrated in isolated glomeruli of Asah1 fl/fl / Podo Cre mice compared with their littermates. By crossbreeding Asah1 fl/fl /Podo Cre mice with Smpd1 À/À mice, we also produced a double knockout strain, Smpd1 À/À /Asah1 fl/fl /Podo Cre , that also lacks Smpd1, the acid sphingomyelinase that hydrolyzes sphingomyelin to ceramide. These mice exhibited significantly lower levels of glomerular ceramide with decreased podocyte injury compared with Asah1 fl/fl / Podo Cre mice. These results strongly suggest that lysosomal Ac in podocytes is essential for the maintenance of the structural and functional integrity of podocytes.

Role of Sphingolipid Signaling in Glomerular Diseases: Focus on DKD and FSGS

“…Interestingly, high plasma levels of very-long-chain ceramide species were associated with a decreased risk of progression to macroalbuminuria in a subgroup of T1D patients enrolled in the Diabetes Control and Complications Trial (DCCT) and its long-term observational follow-up (EDIC) [ 42 ], which may reflect a regulatory role of ceramides in loss of renal function. On the other hand, podocyte-specific deletion of the main catalytic subunit of acid ceramidase resulted in ceramide accumulation in glomeruli and development of nephrotic syndrome in mice [ 43 ]. Notably, a recent report on urinary sphingolipids from patients with DKD also showed elevated urinary levels of ceramide d18:1/16:0, d18:1/18:0, d18:0/20:0, d18:1/22:0 and d18:1/24:0, which were correlated with urinary albumin [ 44 ].…”

Rotten to the Cortex: Ceramide-Mediated Lipotoxicity in Diabetic Kidney Disease

“…Additionally, promoting the production of anti-apoptotic sphingosine-1-phosphate (S1P) in HEK-293 cells significantly decreased rates of ceramide- or TNFα-induced apoptosis ( 67 ). At the time of this review, Guangbi and colleagues are the first and only group to produce a kidney-targeted in vivo model to study manipulation of renal ceramide metabolism ( 68 ). Specifically, knockout of acid ceramidase in podocytes ( Asah1 fl/fl /Podo Cre ) of healthy mice led to glomerular ceramide accumulation and a concomitant increase in albuminuria, podocyte foot process effacement, and glomerular permeability.…”

The Enigmatic Emerging Role of the C-Maf Inducing Protein in Cancer

“…A ceramide-dependent mechanism of CMIP-induced apoptosis can be hypothesized based on these observations. It is worth noting that ceramide accumulation induced in mouse model by invalidation of the Asah1 gene, encoding the acidic ceramidase, leads to podocytopathy and nephrotic syndrome [ 57 ]. The latter prompts the question of ceramide accumulation as potentially playing a part in the link between CMIP expression and INS.…”