Circular RNA Cdr1as Modulates Macrophage-Mediated Cardiac Reparative Function

Mechanisms of macrophage switching from proinflammatory to anti-inflammatory phenotypes are not well understood. Circular RNAs, a new class of noncoding RNAs, are implicated in immune modulation. We recently identified circ-cdr1as as a regulator of macrophage phenotype in bone marrow-derived macrophages; however, its role in immunomodulation during cardiovascular injury remains unknown.

Cell-specific expression levels of circ-cdr1as were determined in the mouse hearts postmyocardial infarction. Circ-cdr1as was overexpressed in fluorescently labeled bone marrow-derived macrophages and injected into the ischemic myocardium immediately following myocardial infarction. The effect of AAV9 (adeno-associated virus-serotype 9)-mediated systemic delivery of circ-Cdr1as on postmyocardial infarction cardiac function and structure was determined. Downstream mechanisms were studied using gain and loss-of-function strategies.

Cardiac cell-specific expression analysis showed significant downregulation of circ-cdr1as only in macrophages and cardiomyocytes. Overexpression of circ-cdr1as in bone marrow-derived macrophages, injected into the ischemic myocardium, retained their anti-inflammatory phenotype and significantly improved left ventricular functions and reduced infarct size. Systemic delivery of AAV9-circ-cdr1as showed similar cardiac reparative activity. Mechanistically, circ-cdr1as directly binds and sponges microRNA-7 and increases the expression of target KLF4 (Kruppel-like factor 4). Loss and gain of function studies show that modulation of microRNA 7 and KLF recapitulates macrophage phenotypic changes.

Circ-cdr1as plays a crucial role in regulating the anti-inflammatory phenotype of macrophages through modulation of microRNA 7 and its target gene KLF4. Therefore, circ-cdr1as holds potential as an anti-inflammatory regulator in tissue inflammation postcardiac injury.