MicroRNA-24 regulates macrophage behavior and retards atherosclerosis

Our recent studies have highlighted membrane type-1 matrix metalloproteinase (MMP)-14 as a selective marker for an invasive subset of macrophages potentially related to atherosclerotic plaque progression. Moreover, colony stimulating factors (CSF) may exert divergent effects on macrophage MMP expression, possibly through microRNAs. We, therefore, aim to identify and test the pathophysiological role of microRNAs, which modulate macrophage MMP-14 expression in atherosclerotic plaque progression.

Compared with macrophage CSF-differentiated macrophages, granulocyte/macrophage CSF-matured macrophages exhibited reduced MMP-14 mRNA levels but increased protein expression and activity, which resulted in heightened macrophage invasion. MicroRNA-24, identified to target MMP-14, was accordingly increased in macrophage CSF compared with granulocyte/macrophage CSF macrophages. Silencing microRNA-24 in macrophage CSF macrophages significantly increased MMP-14 expression and enhanced their invasive capacity, mimicking granulocyte/macrophage CSF macrophages, and suggesting that granulocyte/macrophage CSF modulates MMP-14 protein expression and subsequent macrophage invasion in a microRNA-24-dependent manner. In human coronary atherosclerotic plaques, increased MMP-14 protein expression in foam cell macrophages was associated with lesions exhibiting histological characteristics associated with an unstable phenotype. Furthermore, microRNA-24 expression in these atherosclerotic plaques was inversely related to MMP-14 protein expression. Moreover, stable plaques contained higher microRNA-24 levels than unstable plaques, and microRNA-24 colocalized with foam cell macrophages that exhibited low MMP-14 protein expression. Finally, in atherosclerotic mice (apolipoprotein E-deficient), microRNA-24 inhibition increased plaque size and macrophage MMP-14 expression.

Taken together, our data demonstrates that downregulation of microRNA-24 promotes an invasive macrophage subset and plays a novel regulatory role in MMP-14 proteolytic activity and, therefore, plaque stability, highlighting its therapeutic potential.