Podocyte-Specific Deletion of Asah1 Gene Produced Podocytopathy without Sclerotic Pathology: A Potential Mouse Model for Steroid-Insensitive Minimal Change Disease

Lysosomal acid ceramidase (AC) has been shown to be critical for the ceramide hydrolysis and thereby regulates lysosome function and related cell function such as autophagy and vesicle/molecular trafficking. Despite that ceramide is involved in the regulation of glomerular function, it remains unknown whether AC activity contributes to the control of podocyte function and whether its deficiency causes glomerular disease. In the present study, we generated a mouse line with podocyte‐specific deletion of α subunit in Asah1 (AC gene code in mouse) gene, a main subunit for its activity in lysosomes using Cre‐Lox recombination technology. This Asah1 fl/fl /Podo Cre mouse colony was characterized by several genetic, molecular and biochemical approaches. AC α subunit was not detectable in podocytes in glomeruli of Asah1 fl/fl /Podo Cre mice, compared with their control littermates ( Asah1 fl/fl /WT and WT/WT mice). Using LC‐MS/MS, remarkable ceramide accumulation was detected in isolated glomeruli of Asah1 fl/fl /Podo Cre mice, but not in their control littermates (increased from 42.99 pg/glomerulus to 237.19 pg/glomerulus). Although Periodic acid‐Schiff staining showed no significant increase in glomerular damage index in Asah1 fl/fl /Podo Cre mice compared with other two types of mice, severe proteinuria and albuminuria were found in Asah1 fl/fl /Podo Cre mice started at 8 weeks old (increased from 28.84 μg/24h/gbw to 181.41 μg/24h/gbw of urinary protein excretion, increased from 1.22 μg/24h/gbw to 10.39 μg/24h/gbw of urinary albumin excretion). Correspondingly, glomerular permeability to albumin was markedly increased by podocyte‐specific deletion of AC α subunit. Moreover, hypoalbuminemia and edema were observed in Asah1 fl/fl /Podo Cre mice when they grew to 12 weeks old. Under transmission electron microscope, Asah1 fl/fl /Podo Cre mice were found to have foot process effacement, vacuolation, and microvillus formation in podocytes. Treatment with dexamethasone (DEX) for 4 weeks failed to reverse podocyte injury and proteinuria in Asah1 fl/fl /Podo Cre mice. Immunohistochemistry showed no changes in α‐dystroglycan, but decreases in β‐dystroglycan in glomeruli of Asah1 fl/fl /Podo Cre mice, compared with their control littermates. These results suggest that lysosomal AC and associated ceramide hydrolysis is essential for the maintenance of podocyte structural and functional integrity and that the defect of AC expression and its function deficiency may result in podocytopathy and related glomerular disease such as steroid‐resistant minimal change disease. Support or Funding Information This study was supported by NIH grants DK54927 to Pin‐Lan Li and DK102539 to Joseph K. Ritter. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .