Human vascular smooth muscle cells utilise chymase for the atypical cleavage and activation of Interleukin-1ß.

BACKGROUND AND AIMS: Atherosclerosis and other cardiovascular diseases (CVD) are well established to be both instigated and worsened by inflammation. Indeed, CANTOS formally proved that targeting the inflammatory cytokine IL-1ß only could reduce both cardiovascular events and death. However, due to the central role of IL-1ß in host defence, blockade increased fatal infections, suggesting targeting key immune mediators over the long natural history of CVD is unsuitable. Thus, discovering alternative mechanisms that generate vascular inflammation may identify more actionable targets. METHODS: We used primary human VSMCs and a combination of biochemical, pharmacological and molecular biological techniques to generate the data. Human carotid atherosclerotic plaques were also assessed histologically. RESULTS: We showed that VSMCs expressed and efficiently processed pro-IL-1ß to the active form after receiving a single stimulus via IL-1R1 or TLR4. Importantly, pro-IL-1ß processing did not utilise inflammasomes or caspases. Unusually, we found that cathepsin C-activated chymase was responsible for cleaving IL-1ß in VSMCs, and provided evidence for chymase expression in cultured VSMCs and in the fibrous cap of human plaques. Chymase also efficiently cleaved and activated recombinant pro-IL-1ß. CONCLUSIONS: Thus, VSMCs are efficient activators of IL-1ß that do not use canonical inflammasomes or caspases. Hence, this alternative pathway could be targeted for long-term treatment of CVDs, as it is not central to everyday host defence.

Thrombin-activated interleukin-1α drives atherogenesis, but also promotes vascular smooth muscle cell proliferation and collagen production.

AIMS: Atherosclerosis is driven by multiple processes across multiple body systems. For example, the innate immune system drives both atherogenesis and plaque rupture via inflammation, while coronary artery-occluding thrombi formed by the coagulation system cause myocardial infarction and death. However, the interplay between these systems during atherogenesis is understudied. We recently showed that coagulation and immunity are fundamentally linked by the activation of interleukin-1α (IL-1α) by thrombin, and generated a novel knock-in mouse in which thrombin cannot activate endogenous IL-1α [IL-1α thrombin mutant (IL-1αTM)]. METHODS AND RESULTS: Here, we show significantly reduced atherosclerotic plaque formation in IL-1αTM/Apoe-/- mice compared with Apoe-/- and reduced T-cell infiltration. However, IL-1αTM/Apoe-/- plaques have reduced vascular smooth muscle cells, collagen, and fibrous caps, indicative of a more unstable phenotype. Interestingly, the reduced atherogenesis seen with thrombin inhibition was absent in IL-1αTM/Apoe-/- mice, suggesting that thrombin inhibitors can affect atherosclerosis via reduced IL-1α activation. Finally, bone marrow chimeras show that thrombin-activated IL-1α is derived from both vessel wall and myeloid cells. CONCLUSIONS: Together, we reveal that the atherogenic effect of ongoing coagulation is, in part, mediated via thrombin cleavage of IL-1α. This not only highlights the importance of interplay between systems during disease and the potential for therapeutically targeting IL-1α and/or thrombin, but also forewarns that IL-1 may have a role in plaque stabilization.