Macrophages play a crucial role in the pathogenesis of atherosclerosis, but the molecular mechanisms remain poorly understood. Here we show that microRNA-34a (miR-34a) is a key regulator of macrophage cholesterol efflux and reverse cholesterol transport by modulating ATP-binding cassette transporters ATP-binding cassette subfamily A member 1 (ABCA1) and ATP-binding cassette subfamily G member 1 (ABCG1). miR-34a also regulates M1 and M2 macrophage polarization via liver X receptor a. Furthermore, global loss of miR-34a reduces intestinal cholesterol or fat absorption by inhibiting cytochrome P450 enzymes CYP7A1 and sterol 12a-hydroxylase (CYP8B1). Consistent with these findings, macrophage-selective or global ablation of miR-34a markedly inhibits the development of atherosclerosis. Finally, therapeutic inhibition of miR-34a promotes atherosclerosis regression and reverses diet-induced metabolic disorders. Our studies outline a central role of miR-34a in regulating macrophage cholesterol efflux, inflammation, and atherosclerosis, suggesting that miR-34a is a promising target for treatment of cardiometabolic diseases.
Ischemic heart diseases (IHD) cause millions of deaths around the world annually. While surgical and pharmacological interventions are commonly used to treat patients with IHD, their efficacy varies from patient to patient and is limited by the severity of the disease. One promising, at least theoretically, approach for treating IHD is induction of coronary collateral growth (CCG). Coronary collaterals are arteriole-to-arteriole anastomoses that can undergo expansion and remodeling in the setting of coronary disease when the disease elicits myocardial ischemia and creates a pressure difference across the collateral vessel that creates unidirectional flow. Well-developed collaterals can restore blood flow in the ischemic area of the myocardium and protect the myocardium at risk. Moreover, such collaterals are correlated to reduced mortality and infarct size and better cardiac function during occlusion of coronary arteries. Therefore, understanding the process of CCG is highly important as a potentially viable treatment of IHD. While there are several excellent review articles on this topic, this review will provide a unified overview of the various aspects related to CCG as well as an update of the advancements in the field. We also call for more detailed studies with an interdisciplinary approach to advance our knowledge of CCG. In this review, we will describe growth of coronary collaterals, the various factors that contribute to CCG, animal models used to study CCG, and the cardioprotective effects of coronary collaterals during ischemia. We will also discuss the impairment of CCG in metabolic syndrome and the therapeutic potentials of CCG in IHD.
Introduction
Coronary microvascular dysfunction is characterized by impaired endothelial‐dependent vasodilation. These impairments are seen in diabetic cardiomyopathy (DCM), coronary artery disease (CAD) and ischemia with non‐obstructive coronary artery (INOCA), Takotsubo cardiomyopathy, myocardial infarction with non‐obstructive coronary artery disease (MINOCA), and heart failure with preserved ejection fraction (HFpEF), but detailed mechanisms have yet to be elucidated.
Methods
microRNA‐21 (miR‐21) global and conditional knockout mice were used to study how miR‐21 regulates coronary microcirculation in pathological conditions like DCM. Both genetic (db/db) and diet‐induced diabetic models were used. Coronary arteries were isolated, and endothelial‐dependent vasodilation was assessed using myography (DMT). In vivo myocardial blood flow (MBF) under stress was measured by contrast echocardiography or doppler after the treatment with different dosages of norepinephrine. Quantitative polymerase chain reaction (qPCR) was performed for gene expression analysis. Trichrome staining and histology were performed for structural changes of the hearts.
Results
Our preliminary data show that miR‐21 is upregulated in DCM and the deficiency of miR‐21 restores the endothelial‐dependent vasodilation in isolated diabetic coronary arterioles and coronary blood flow under stress in DCM through the mechanism that miR‐21 prevents the mediator of coronary vasodilation switching from NO to H2O2 in diabetes.
Conclusions
miR‐21 regulates microvascular dysfunction in DCM. Further genetic profiling will elucidate the pathways and mechanisms converging with miR‐21 to regulate microvascular function.
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