Atherosclerosis, complex chronic inflammatory disease, has a heterogonous aetiology. Endothelium is critically involved in the pathogenesis of atherosclerosis by producing proinflammatory cytokines, including interleukin-1 beta (IL-1β). However, the mechanism by which IL-1β is released is unknown. Neutrophil elastase (NE; a potent serine protease) has been shown to cleave proIL-1β in vitro. Therefore, I hypothesised that NE induces IL-1β secretion from endothelial cells (ECs).
I found that NE cleaves proIL-1β in ECs and causes significant secretion of mature IL-1β into supernatant. The release is via extracellular vesicles (EVs), associated with a transient increase in intracellular Ca2+. The released IL-1β is significantly attenuated by inhibition of NE, but not caspase-1. Intracellularly, IL-1β is detected within LAMP-1 positive organelles only after NE treatment. Two distinct populations of vesicles, containing IL-1β are found: at early time points, intracellular vesicles (100-200μm), associated with detection of MV shedding enriched of IL-1β; however, at later time points, IL-1β was detected inside ECs in (>200μm) multivesicular bodies (MVBs) containing exosomes.
In a second study, in experimental atherosclerosis, I attempted to manipulate inflammation using omega-3 fatty acids (n3FAs). I hypothesised that docosahexaenoic acid (DHA), the main n3FAs in fish oil, would inhibit inflammation by an IL-1β driven mechanism. I found that DHA significantly decreased high blood pressure and left ventricular mass induced by high fat diet in ApoE-/- mice. Interestingly, this is associated with a reduction in distal vessel atheroma and plasma proinflammatory markers. Locally, DHA also significantly attenuates eNOS and endothelial IL-1β expressions.
This study reveals a hitherto unexplained mechanistic link between NE expression in atherosclerotic plaques and concomitant bioactive IL-1β secretion from ECs, highlighting the possibility of targeting NE to control IL-1β-induced atherosclerosis. It also sheds a light, for the first time, on how DHA can act as an anti-atherogenic agent through its effects upon IL-1 system.
