Acid Sphingomyelinase Gene Knockout Ameliorates Hyperhomocysteinemic Glomerular Injury in Mice Lacking Cystathionine-β-Synthase

Acid sphingomyelinase (ASM) has been implicated in the development of hyperhomocysteinemia (hHcys)-induced glomerular oxidative stress and injury. However, it remains unknown whether genetically engineering of ASM gene produces beneficial or detrimental action on hHcys-induced glomerular injury. The present study generated and characterized the mice lacking cystathionine β-synthase (Cbs) and Asm mouse gene by cross breeding Cbs(+/-) and Asm(+/-) mice. Given that the homozygotes of Cbs(-/-/)Asm(-/-) mice could not survive for 3 weeks. Cbs(+/-/)Asm(+/+), Cbs(+/-/)Asm(+/-) and Cbs(+/-/)Asm(-/-) as well as their Cbs wild type littermates were used to study the role of Asm(-/-) under a background of Cbs(+/-) with hHcys. HPLC analysis revealed that plasma Hcys level was significantly elevated in Cbs heterozygous (Cbs(+/-)) mice with different copies of Asm gene compared to Cbs(+/+) mice with different Asm gene copies. Cbs(+/-/)Asm(+/+) mice had significantly increased renal Asm activity, ceramide production and O(2.)(-) level compared to Cbs(+/+)/Asm(+/+), while Cbs(+/-/)Asm(-/-) mice showed significantly reduced renal Asm activity, ceramide production and O(2.)(-) level due to increased plasma Hcys levels. Confocal microscopy demonstrated that colocalization of podocin with ceramide was much lower in Cbs(+/-/)Asm(-/-) mice compared to Cbs(+/-/)Asm(+/+) mice, which was accompanied by a reduced glomerular damage index, albuminuria and proteinuria in Cbs(+/-/)Asm(-/-) mice. Immunofluorescent analyses of the podocin, nephrin and desmin expression also illustrated less podocyte damages in the glomeruli from Cbs(+/-/)Asm(-/-) mice compared to Cbs(+/-/)Asm(+/+) mice. In in vitro studies of podocytes, hHcys-enhanced O(2.)(-) production, desmin expression, and ceramide production as well as decreases in VEGF level and podocin expression in podocytes were substantially attenuated by prior treatment with amitriptyline, an Asm inhibitor. In conclusion, Asm gene knockout or corresponding enzyme inhibition protects the podocytes and glomeruli from hHcys-induced oxidative stress and injury.