mouse-model-of-coronary-collateral-growth-through-repetitive-ischemia

Mouse Model of Coronary Collateral Growth Through Repetitive Ischemia

Coronary collaterals are a natural bypass in ischemic heart diseases (IHD), and so for many years, coronary collateral growth (CCG) has been a promising ...

Northeast Ohio Medical University

Coronary microvascular dysfunction is prevalent among people with diabetes and is correlated with cardiac mortality. Compromised endothelial-dependent dilation (EDD) is an early event in the progression of diabetes, but its mechanisms remain incompletely understood. Nitric oxide (NO) is the major endothelium-dependent vasodilatory metabolite in the healthy coronary circulation, but this switches to hydrogen peroxide (HO) in coronary artery disease (CAD) patients. Because diabetes is a significant risk factor for CAD, we hypothesized that a similar NO-to-HO switch would occur in diabetes. Vasodilation was measured ex vivo in isolated coronary arteries from wild type (WT) and microRNA-21 (miR-21) null mice on a chow or high-fat/high-sugar diet, and B6.BKS(D)-Lepr/J (db/db) mice using myography. Myocardial blood flow (MBF), blood pressure, and heart rate were measured in vivo using contrast echocardiography and a solid-state pressure sensor catheter. RNA from coronary arteries, endothelial cells, and cardiac tissues was analyzed via quantitative real-time PCR for gene expression, and cardiac protein expression was assessed via western blot analyses. Superoxide was detected via electron paramagnetic resonance. (1) Ex vivo coronary EDD and in vivo MBF were impaired in diabetic mice. (2) Nω-Nitro-L-arginine methyl ester, an NO synthase inhibitor (L-NAME), inhibited ex vivo coronary EDD and in vivo MBF in WT. In contrast, polyethylene glycol-catalase, an HO scavenger (Peg-Cat), inhibited diabetic mouse EDD ex vivo and MBF in vivo. (3) miR-21 was upregulated in diabetic mouse endothelial cells, and the deficiency of miR-21 prevented the NO-to-HO switch and ameliorated diabetic mouse vasodilation impairments. (4) Diabetic mice displayed increased serum NO and HO, upregulated mRNA expression of Sod1, Sod2, iNos, and Cav1, and downregulated Pgc-1α in coronary arteries, but the deficiency of miR-21 reversed these changes. (5) miR-21-deficient mice exhibited increased cardiac PGC-1α, PPARα and eNOS protein and reduced endothelial superoxide. (6) Inhibition of PGC-1α changed the mRNA expression of genes regulated by miR-21, and overexpression of PGC-1α decreased the expression of miR-21 in high (25.5 mM) glucose treated coronary endothelial cells. Diabetic mice exhibit a NO-to-HO switch in the mediator of coronary EDD, which contributes to microvascular dysfunction and is mediated by miR-21. This study represents the first mouse model recapitulating the NO-to-HO switch seen in CAD patients in diabetes.

Mechanism of the switch from NO to HO in endothelium-dependent vasodilation in diabetes.

Coronary collateral growth is a natural bypass for ischemic heart diseases. It offers tremendous therapeutic benefit, but the process of coronary collateral growth isincompletely understood due to limited preclinical murine models that would enable interrogation of its mechanisms and processes via genetic modification and lineage tracing. Understanding the processes by which coronary collaterals develop can unlock new therapeutic strategies for ischemic heart disease.

The essential role for endothelial cell sprouting in coronary collateral growth.

CXCL12/CXCR4 signaling is essential in cardiac development and repair, however, its contribution to aortic valve stenosis (AVS) remains unclear. In this study, we tested the role of endothelial CXCR4 on the development of AVS.

Role of endothelial CXCR4 in the development of aortic valve stenosis.

Heart failure (HF) is a conundrum in that, current therapies only slow the progression of the disease. We posit, if the causal mechanism were targeted, progression of the disease could be stopped and potentially reversed. We hypothesize that insufficient myocardial blood flow (MBF) produces minute areas of ischemia, that lead to an accumulating injury culminating in HF. Accordingly, we determined the relationship between MBF and cardiac work (wall stress-rate product [WSRP]) in control C57Bl6/J mice (Control), mice with transaortic constriction to produce HF (TAC-HF) and HF mice treated with the coronary vasodilator, chromonar (4 weeks of treatment, TAC-Chromonar). MBF and WSRP were measured during norepinephrine infusion in anesthetized mice. In Controls, MBF increased when work/WSRP was increased with norepinephrine, however, when cardiac work was increased in TAC-HF, MBF did not increase. After chromonar treatment, when work increased, MBF increased. Changes in cardiac function paralleled MBF, i.e., decrement in cardiac function occurred in TAC-HF (ejection fraction), but 4 weeks of chromonar treatment reversed this functional decline. We also found in a model of cardiac hypoxia fate-mapping, a 5-fold increase in the number of hypoxic cardiac myocytes (TAC-HF vs Control), which was reversed by chromonar. Capillary densities also followed this trend with a decrease from Control in TAC-HF, which was restored by Chromonar. We propose that a cause of HF is inadequate MBF to meet the metabolic demands of the working heart. Pharmacological coronary vasodilation with chromonar to increase MBF in HF can reverse the functional decline and improve cardiac function.

Article	Year
Mechanism of the switch from NO to HO in endothelium-dependent vasodilation in diabetes. Basic research in cardiology\| PubMed ID: 35024970	2022
The essential role for endothelial cell sprouting in coronary collateral growth. Journal of molecular and cellular cardiology\| PubMed ID: 35074317	2022
Role of endothelial CXCR4 in the development of aortic valve stenosis. Frontiers in cardiovascular medicine\| PubMed ID: 36148060	2022
Does coronary microvascular dysfunction play a role in heart failure with reduced ejection fraction? Journal of molecular and cellular cardiology\| PubMed ID: 39884552	2025

James Gadd

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