2017 Cardiovascular Research Day Abstract Book

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Impact of miR-33 antagonism on coronary artery atherosclerotic plaque composition in
nonhuman primates
Lei Cai, PhD 1 • Tong Li, MD 1 • Sierra Paxton 1 • Courtney Burkett 1 • Peter Hecker, MS 1 • Ryan Temel
, PhD 1
1CVRC, University of Kentucky
Staff
Introduction: Elevated LDL cholesterol (LDL-C) is a major risk factor for coronary heart disease
(CHD). Statins are used to lower LDL-C and CHD risk but do not completely eliminate CHD events
caused by atherosclerotic lesion rupture. By stimulating macrophage cholesterol efflux and
promoting anti-inflammatory macrophage polarization, antagonism of microRNA-33a (miR-33a) in
mice causes atherosclerotic lesions to acquire a more stable composition. Mouse studies have
limited translational value since mice do not develop coronary artery atherosclerosis and express
only one of the two miR-33 family members found in humans. Since nonhuman primates (NHPs)
have miR-33a and miR-33b and develop coronary artery atherosclerosis, NHPs are the best
preclinical model for determining the therapeutic potential of miR-33 antagonism. We hypothesize
that miR-33a/b antagonism will stabilize coronary artery atherosclerotic plaques of NHPs.
Methods and Results: Male cynomolgus monkeys (n=36) were fed for 20 months a high fat/high
cholesterol diet, which caused severe hypercholesterolemia. At the end of the 20-month
progression phase, the hearts from 12 animals were perfused with formalin under physiological to
preserve the structure of the coronary arteries. The remaining monkeys were switched to a
cholesterol-lowering “chow” diet and treated with either vehicle (n=12) or anti-miR-33 (n=12) for
6 months. LDL-C for both treatment groups was rapidly reduced by the chow diet and returned to
baseline levels by the 3rd month of the regression phase. The anti-miR-33 versus the vehicle group
had a sustained and significant elevation in HDL-C that was linked to a significant increase in
hepatic ABCA1, a miR-33 target. Following dissection and paraffin embedding of the right coronary
arteries (RCA), 5 µm slices were analyzed by histology and immunohistochemistry (IHC). The RCA
atherosclerotic lesions from both the progression and regression groups were characterized by
intimal smooth muscle cell proliferation, collagen deposition, elastin degradation, and medial layer
destruction. While necrotic cores were a common feature, there was a minimal amount of plaque
calcification. Macrophages were found at high levels in the progression group lesions but were
almost absent from the plaques of both the anti-miR-33 and vehicle groups.
Conclusions and Future Directions: The qualitative histology and IHC results show that the
monkeys developed RCA atherosclerotic plaques similar to early fibroatheromas observed in
humans. By quantifying the area occupied by the various plaque components, we will determine
whether antagonism of miR-33a/b allowed the lesions to attain a more stable composition. In
addition, to determine whether anti-miR-33 changes the amount or type of macrophages in lesions,
we will analyze coronary arteries from monkeys subjected to 6 weeks, as opposed to 6 months, of
regression.
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