Caspase-1 Inflammasome Activation Mediates Homocysteine-Induced Pyrop-Apoptosis in Endothelial Cells

Abstract

Rationale Endothelial injury is an initial mechanism mediating cardiovascular disease. Objective Here, we investigated the effect of hyperhomocysteinemia (HHcy) on programed cell death in endothelial cells (EC). Methods and Results We established a novel flow-cytometric gating method to define pyrotosis (Annexin V−/Propidium iodide+). In cultured human EC, we found that: 1). Hcy and Lipopolysaccharide (LPS) individually and synergistically induced inflammatory pyroptotic and non-inflammatory apoptotic cell death. 2). Hcy/LPS induced caspase-1 activation prior to caspase-8, -9, -3 activations. 3). Caspase-1/3 inhibitors rescued Hcy/LPS-induced pyroptosis/apoptosis, but caspase-8/9 inhibitors had differential rescue effect. 4). Hcy/LPS induced NLRP3 protein, caused NLRP3-containing inflammasome assembly, caspase-1 activation and IL-1β cleavage/activation. 5). Hcy/LPS elevated intracellular reactive oxidative species (ROS). 6). Intracellular oxidative gradient determined cell death destiny as intermediate intracellular ROS levels are associated with pyroptosis, whereas, high ROS corresponded to apoptosis. 7). Hcy/LPS induced mitochondrial membrane potential collapse and cytochrome-c release, and increased Bax/Bcl-2 ratio which were attenuated by antioxidants and caspase-1 inhibitor. 8). Antioxidants extracellular superoxide dismutase and catalase prevented Hcy/LPS-induced caspase-1 activation, mitochondrial dysfunction and pyroptosis/apoptosis. In cystathionine β-synthase deficient (Cbs−/−) mice, severe HHcy induced caspase-1 activation in isolated lung EC and caspase-1 expression in aortic endothelium, and elevated aortic caspase-1,9 protein/activity and Bax/Bcl-2 ratio in Cbs−/− aorta and HUVEC. Finally, Hcy-induced DNA fragmentation was reversed in caspase-1−/− EC. HHcy-induced aortic endothelial dysfunction was rescued in caspase-1−/− and NLRP3−/− mice. Conclusion HHcy preferentially induces EC pyroptosis via caspase-1-dependent inflammasome activation leading to endothelial dysfunction. We termed caspase-1 responsive pyroptosis and apoptosis as pyrop-apoptosis.

Protective Effects of Microrna-22 Against Endothelial Cell Injury by Targeting NLRP3 Through Suppression of the Inflammasome Signaling Pathway in a Rat Model of Coronary Heart Disease

“…Therefore, it was hypothesized that NLRP3 was a potential target gene of miR-22, which was further confirmed by the results from the dual-luciferase reporter assays. Caspase-1 activation induced EC dysfunction, leading to vascular remodeling and atherosclerosis [26]. Similarly, Li et al also demonstrated that miR-20a over-expression reduced the formation of the NLRP3 inflammasome, including reducing NLRP3 and caspase-1 expression [27], which possibly explains how miR-22 expression is related to NLRP3 and caspase-1 in our study.…”

Lysophospholipid Receptors, as Novel Conditional Danger Receptors and Homeostatic Receptors Modulate Inflammation—Novel Paradigm and Therapeutic Potential

“…This was further validated by the recent reports from our lab, which demonstrated that NLR/ caspase-1 signaling pathway is responsible for inducing endothelial activation and subsequent atherogenesis during early hyperlipidemia [58] and hyperhomocysteinemia [63], for decreasing vascular endothelial growth factor receptor 2 (VEGFR2) mediated angiogenesis in ischemia [64], and for weakening of the progenitor cell mediated vessel repair [3,64]. …”

Group 2 innate lymphoid cells protect lung endothelial cells from pyroptosis in sepsis

“…EC death triggered by lipopolysaccharide (LPS) and tumor necrosis factor α (TNFα) has been determined in septic mice 9,10 . Studies have shown that LPS through activating caspase-1 induces EC pyroptosis 11 , a caspase-1-dependent pro-inflammatory cell death type 12 . Cell pyroptosis, which can be triggered by various pathological stimuli, including infection, is characterized by plasma-membrane pore formation, intracellular content release, and DNA cleavage 12,13 .…”