Lipoxins Protect Against Inflammation in Diabetes-Associated Atherosclerosis

Increasing evidence points to the fact that defects in the resolution of inflammatory pathways predisposes individuals to the development of chronic inflammatory diseases, including diabetic complications such as accelerated atherosclerosis. The resolution of inflammation is dynamically regulated by the production of endogenous modulators of inflammation, including lipoxin A4 (LXA₄). Here, we explored the therapeutic potential of LXA₄ and a synthetic LX analog (Benzo-LXA₄) to modulate diabetic complications in the streptozotocin-induced diabetic ApoE^-/- mouse and in human carotid plaque tissue ex vivo. The development of diabetes-induced aortic plaques and inflammatory responses of aortic tissue, including the expression of vcam-1, mcp-1, il-6, and il-1β, was significantly attenuated by both LXA₄ and Benzo-LXA₄ in diabetic ApoE^-/- mice. Importantly, in mice with established atherosclerosis, treatment with LXs for a 6-week period, initiated 10 weeks after diabetes onset, led to a significant reduction in aortic arch plaque development (19.22 ± 2.01% [diabetic]; 12.67 ± 1.68% [diabetic + LXA₄]; 13.19 ± 1.97% [diabetic + Benzo-LXA₄]). Secretome profiling of human carotid plaque explants treated with LXs indicated changes to proinflammatory cytokine release, including tumor necrosis factor-α and interleukin-1β. LXs also inhibited platelet-derived growth factor-stimulated vascular smooth muscle cell proliferation and transmigration and endothelial cell inflammation. These data suggest that LXs may have therapeutic potential in the context of diabetes-associated vascular complications.

Protective Effect of let-7 miRNA Family in Regulating Inflammation in Diabetes-Associated Atherosclerosis

The let-7 miRNA family plays a key role in modulating inflammatory responses. Vascular smooth muscle cell (SMC) proliferation and endothelial cell (EC) dysfunction are critical in the pathogenesis of atherosclerosis, including in the setting of diabetes. Here we report that let-7 levels are decreased in diabetic human carotid plaques and in a model of diabetes-associated atherosclerosis, the diabetic ApoE^-/- mouse. In vitro platelet-derived growth factor (PDGF)- and tumor necrosis factor-α (TNF-α)-induced vascular SMC and EC activation was associated with reduced let-7 miRNA expression via Lin28b, a negative regulator of let-7 biogenesis. Ectopic overexpression of let-7 in SMCs inhibited inflammatory responses including proliferation, migration, monocyte adhesion, and nuclear factor-κB activation. The therapeutic potential of restoring let-7 levels using a let-7 mimic was tested: in vitro in SMCs using an endogenous anti-inflammatory lipid (lipoxin A₄), ex vivo in murine aortas, and in vivo via tail vein injection in a 24-h murine model. Furthermore, we delivered let-7 mimic to human carotid plaque ex vivo and observed significant changes to the secretome in response to let-7 therapy. Restoration of let-7 expression could provide a new target for an anti-inflammatory approach in diabetic vascular disease.