Neutrophil Elastase promotes Interleukin-1β secretion from Human Coronary Endothelium

The endothelium is critically involved in the pathogenesis of atherosclerosis by producing proinflammatory mediators, including interleukin-1 beta (IL-1β). Coronary arteries from patients with ischaemic heart disease express large amounts of IL-1β in endothelium. However, the mechanism by which endothelial cells (ECs) release IL-1β remains to be elucidated. We investigated neutrophil elastase (NE), a potent serine protease detected in vulnerable areas of human carotid plaques, as a potential ′trigger′ for IL-1β processing and release. This study tested the hypothesis that NE potentiates the processing and release of IL-1β from human coronary endothelium. We found that NE cleaves the pro-isoform of IL-1β in ECs and causes significant secretion of bioactive IL-1β via extracellular vesicles. This release was significantly attenuated by inhibition of neutrophil elastase, but not caspase-1. Transient increases in intracellular Ca2+ levels were observed prior to secretion. Inside ECs, and after NE treatment only, IL-1β was detected within LAMP-1 positive multivesicular bodies (MVBs). The released vesicles contained bioactive IL-1β. In vivo, in experimental atherosclerosis, NE was detected in mature atherosclerotic plaques, predominantly in the endothelium, alongside IL-1β. This study reveals a novel mechanistic link between NE expression in atherosclerotic plaques and concomitant pro-inflammatory bioactive IL-1β secretion from ECs; this could reveal additional potential anti-IL-1β therapeutic targets and provide further insight into the inflammatory process by which vascular disease develops.