Abstract 16461: Hyperhomocysteinemia Promotes Inflammatory Pyroptosis and Apoptosis via Caspase-1-Inflammasome Signaling in Endothelial Cells
Rationale: Hyperhomocysteinemia (HHcy) is an independent risk factor for cardiovascular disease. HHcy accelerates atherosclerosis and induces endothelial damage.
Objective: To examine whether caspase-1-inflammasome pathway senses elevated homocysteine (Hcy) levels and activates programmed cell death (pyroptosis & apoptosis) in endothelial cells.
Methods and Results: Apoptosis was examined in HHcy mice deficient with cystathionine β-synthase (CBS) gene and added a zinc-inducible human CBS transgene to rescue the neonatal lethality of CBS deficiency (Tg-hCBS Cbs-/-, plasma Hcy ∼150 µM), in primary mouse aortic endothelial cells (MAEC) from caspase-1 deficient mice (Casp1-/-) and in cultured human umbilical vein endothelial cells (HUVEC). Pyroptosis and apoptosis were assessed in HUVEC. We found that HHcy induced caspase-1 expression and apoptosis in aortic endothelium in Tg-hCBS Cbs-/- mice, which was eliminated in Hcy-treated MAEC isolated from Casp1-/- mice. In HUVEC, Hcy (100∼500µM) promoted cell death in a dose sensitive manner. Hcy and lipopolysaccharide (LPS) synergistically induced two distinct programmed cell death forms, inflammatory pyroptosis and noninflammatory apoptosis. Caspase-1 inhibitor suppressed Hcy-induced activation of caspase-9 and -3, suggesting higher hierarchy of caspase-1. Hcy-induced pyroptosis and apoptosis are reversed by caspase-1, -9 and -3 inhibitors, and by antioxidants superoxide dismutase (SOD) and catalase. Further, HHcy increased activated forms of caspase-1 and -9, apoptotic protein Bax levels, and Bax/Bcl2 ratio in aortic from Tg-hCBS Cbs-/- mice. Finally, Hcy and LPS synergistically increased the production of reactive oxygen species, pro-caspase-1 assembling in inflammasome, Bax/Bcl2 ratio, induced mitochondrion membrane potential (Δψm) collapse, and promoted cytochome c release from mitochondria to cytosol in HUVEC, which were all reversed by either caspase-1 inhibitor or SOD plus catalase. Taken together, HHcy promotes inflammatory pyroptosis and mitochondrion-dependence apoptosis via caspase-1-inflammasome signaling in endothelial cells. This implicates the compatibility of caspase-1 in endothelial cell death and inflammation which contribute to atherosclerosis.
- © 2012 by American Heart Association, Inc.