MD-1 Deficiency Mitigates Atherosclerosis by Inhibiting NLRP3 Inflammasome Activation via cGAS-STING Dependent Pathway in Macrophages.

MD-1 plays significant roles in various pathological processes closely associated with cardiovascular diseases through its functions in different cell types. However, the critical effects and molecular mechanisms mediated by MD-1 in macrophages involved in the development of atherosclerosis remain elusive. In this study, we observed that the expression of MD-1 was upregulated in atherosclerotic plaques derived from human carotid arteries, as analysed through the Gene Expression Omnibus database. Additionally, MD-1 expression was elevated in the aortas of hyperlipidemic ApoE-deficient mice and in oxidised low-density lipoprotein-stimulated bone marrow-derived macrophages, as demonstrated by RT-PCR and western blot analyses. Furthermore, MD-1 expression exhibited strong co-localisation with macrophages, as confirmed by double immunofluorescence staining. Notably, MD-1-/-ApoE-/- mice subjected to a high-fat diet displayed a significant reduction in atherosclerotic plaques throughout the entire aorta, aortic root, and brachiocephalic arteries. Moreover, the plaques in MD-1-/-ApoE-/- mice were more stable, characterised by a decreased necrotic core size, reduced macrophage infiltration, and lower lipid deposition, alongside an increased accumulation of collagen and smooth muscle cells. Bone marrow transplantation from MD-1-/-ApoE-/- mice to ApoE-/- mice markedly attenuated the development of atherosclerosis. This attenuation was associated with an enhanced anti-inflammatory macrophage phenotype and a reduction in pro-inflammatory macrophage polarisation. Similar effects of MD-1 ablation on macrophage behaviour were also observed in vitro. Mechanistically, MD-1 deficiency inhibited the cyclic GMP-AMP synthase-stimulator of interferon genes-TANK-binding kinase 1-IRF3 pathway, thereby attenuating NLRP3 inflammasome activation in macrophages. However, the use of the STING agonist DMXAA counteracted the effects of MD-1 deficiency on macrophage polarisation. Our findings reveal MD-1 promotes pro-inflammatory (M1-like) macrophage polarisation in atherosclerosis by inhibiting NLRP3 inflammasome activation via a cGAS-STING dependent pathway. These results suggest that MD-1 neutralisation could be a potential therapeutic strategy for atherosclerosis management.