Neutrophil Elastase Promotes Interleukin-1β Secretion from Human Coronary Endothelium

The endothelium is critically involved in the pathogenesis of atherosclerosis by producing pro-inflammatory mediators, including IL-1 beta. Coronary arteries from patients with ischemic heart disease express large amounts of IL-1 beta in the endothelium. However, the mechanism by which endothelial cells (ECs) release IL-1 beta 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-1 beta processing and release. This study tested the hypothesis that NE potentiates the processing and release of IL-1 beta from human coronary endothelium. We found that NE cleaves the pro-isoform of IL-1 beta in ECs and causes significant secretion of bioactive IL-1 beta via extracellular vesicles. This release was attenuated significantly 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-1 beta was detected within LAMP-1-positive multivesicular bodies. The released vesicles contained bioactive IL-1 beta. In vivo, in experimental atherosclerosis, NE was detected in mature atherosclerotic plaques, predominantly in the endothelium, alongside IL-1 beta. This study reveals a novel mechanistic link between NE expression in atherosclerotic plaques and concomitant pro-inflammatory bioactive IL-1 beta secretion from ECs. This could reveal additional potential anti-IL-1 beta therapeutic targets and provide further insights into the inflammatory process by which vascular disease develops.