MicroRNA-26b-/- augments atherosclerosis, while mimic-loaded nanoparticles reduce atherogenesis.

Aims
Increasing evidence has shown that microRNAs (miRs) play a fundamental role in atherosclerosis, but the exact role of various miRs remains elusive. Preliminary data showed that, with a 5-fold increase, miR-26b was highly expressed in human atherosclerotic plaques compared to healthy vessels. Therefore, we aimed to determine its cell-specific effects on atherosclerosis development and its therapeutic potential.Methods And Results
We examined the role of miR-26b in atherosclerosis by using whole-body Apoe-/-Mir26b-/- and myeloid cell-specific miR-26b-deficient (LysM-Cre) mice on a Western-type diet (WTD). Atherosclerotic plaque size and phenotype, as well as the phenotype and function of bone marrow-derived macrophages (BMDMs) from Apoe-/-Mir26b-/- mice, were investigated. Lipid nanoparticles (LNPs) served as vehicles for miR-26b mimics to restore miR-26b levels in miR-26b-deficient BMDMs in-vitro and in mice in-vivo. Apoe-/-Mir26b-/- mice have a striking 2.8-fold increase in atherosclerotic lesion size in the aortic arch after 12 weeks WTD, compared to control Apoe-/-, while lesions in the aortic root were unaffected. Consistent with a more advanced plaque phenotype, collagen, smooth muscle cell, and necrotic core content were all significantly increased in plaques from Apoe-/-Mir26b-/- mice, whilst the relative macrophage content was significantly reduced. This phenotype could also be observed in Apoe-/-Mir26b-/- mice after 4 weeks WTD. Intriguingly, relative plaque size in the arches of Apoe-/-LysmCre+Mir26bfl/fl mice were increased by 2.5-fold, suggesting a role for myeloid-specific miR-26b in atherosclerosis development. Further highlighting its myeloid-specific effects, Apoe-/-Mir26b-/- BMDMs showed an increase in pro-inflammatory cytokine secretion, which could be rescued by LNPs containing miR-26b mimics. MiR-26b pull-down analysis revealed AnnexinA2 as one of the novel targets playing a key role in these effects, which could be validated in BMDMs in-vitro. Furthermore, in-vivo treatment of Apoe-/-Mir26b-/- mice as well as ex-vivo treatment of human plaques with miR-26b-mimic loaded LNPs demonstrated its therapeutic potential and human relevance, respectively.Conclusion
Overall, our results clearly demonstrate an atheroprotective role of miR-26b by attenuating lesion formation, mainly by suppressing inflammation and stimulating collagen breakdown. Furthermore, the therapeutic potential of miR-26b mimic loaded LNPs could be proven, opening up new avenues for miRNA-based treatment options in the future.