MicroRNA-26b<SUP>-/-</SUP> 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 five-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-week 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-week WTD. Intriguingly, relative plaque size in the arches of Apoe ^−/−Lysm ^Cre+Mir26b ^fl/fl mice was 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 their 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.