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

Abstract

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 O2.− level compared to Cbs+/+/Asm+/+, while Cbs+/−/Asm−/− mice showed significantly reduced renal Asm activity, ceramide production and O2.− 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 O2.− 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.

Acid sphingomyelinase-ceramide system in steatohepatitis: A novel target regulating multiple pathways

“…This resistance to alcohol-mediated ER stress was observed despite an increase in plasma Hcy to levels similar to those found in alcohol-fed wild type littermates, regardless of whether alcohol was administered orally or intragastrically, suggesting that resistance to alcohol-induced ER stress in the absence of ASMase is independent of hyperhomocysteinemia (Baulies et al, unpublished observations) [6]. Consistent with these findings, Boini et al recently showed that ASMase ablation prevented Hcy-induced glomerular injury in CBS +/À mice, a genetic model of hyperhomocysteinemia and increased plasma Hcy levels [118,119]. In this model, ASMase silencing prevented Hcy-induced ceramide generation, indicating that ASMase activation by Hcy is a major pathway of glomerular ceramide generation.…”

Coronary Endothelial Dysfunction Induced by Nucleotide Oligomerization Domain-Like Receptor Protein with Pyrin Domain Containing 3 Inflammasome Activation During Hypercholesterolemia: Beyond Inflammation

“…We further explored the molecular mechanisms mediating the production of these novel effects of Nlrp3 inflammasome in ECs. The production of ROS was shown to be one of the major early factors mediating death factor-induced endothelial injury (5,6,40,49,50). NADPH oxidase-derived ROS associated with ceramide-enriched membrane raft clustering (21,47,52) were found to primarily contribute to the death factor or adipokine visfatin-mediated endothelial dysfunction (13,17,46,48,52,53).…”

Role of Mitochondria in Alcoholic Liver Disease

“…In this regard, findings in mice deficient in cystathionine β-synthase have shown that the link between hyperhomocysteinemia and the subsequent glomerular injury is dependent on acid sphingomyelinase (ASMase)-mediated ceramide generation [77•]. Moreover, exogenous ASMase has been shown to directly induce ER stress in isolated hepatocytes by disrupting ER Ca 2+ homeostasis, while the effects upon the addition of homocysteine in causing ER stress were modest and required suprapharmacological doses [63•].…”