Affiliation:
1. Department of Emergency Medicine, Tri‐Service General Hospital National Defense Medical Center Taipei Taiwan
2. Department of Physiology and Biophysics, Graduate Institute of Physiology National Defense Medical Center Taipei Taiwan
3. Graduate Institute of Medical Science National Defense Medical Center Taipei Taiwan
4. Department of Oncology, Lombardi Comprehensive Cancer Center Georgetown University Washington DC USA
5. Department of Bioengineering and Medicine, Institute of Engineering in Medicine University of California San Diego La Jolla California USA
Abstract
ABSTRACTVulnerable atherosclerotic plaque rupture, the leading cause of fatal atherothrombotic events, is associated with an increased risk of mortality worldwide. Peroxisome proliferator–activated receptor delta (PPARδ) has been shown to modulate vascular smooth muscle cell (SMC) phenotypic switching, and, hence, atherosclerotic plaque stability. Melatonin reportedly plays a beneficial role in cardiovascular diseases; however, the mechanisms underlying improvements in atherosclerotic plaque vulnerability remain unknown. In this study, we assessed the role of melatonin in regulating SMC phenotypic switching and its consequential contribution to the amelioration of atherosclerotic plaque vulnerability and explored the mechanisms underlying this process. We analyzed features of atherosclerotic plaque vulnerability and markers of SMC phenotypic transition in high‐cholesterol diet (HCD)–fed apolipoprotein E knockout (ApoE−/−) mice and human aortic SMCs (HASMCs). Melatonin reduced atherosclerotic plaque size and necrotic core area while enhancing collagen content, fibrous cap thickness, and smooth muscle alpha‐actin positive cell coverage on the plaque cap, which are all known phenotypic characteristics of vulnerable plaques. In atherosclerotic lesions, melatonin significantly decreased the synthetic SMC phenotype and KLF4 expression and increased the expression of PPARδ, but not PPARα and PPARγ, in HCD‐fed ApoE−/− mice. These results were subsequently confirmed in the melatonin‐treated HASMCs. Further analysis using PPARδ silencing and immunoprecipitation assays revealed that PPARδ plays a role in the melatonin‐induced SMC phenotype switching from synthetic to contractile. Collectively, we provided the first evidence that melatonin mediates its protective effect against plaque destabilization by enhancing PPARδ‐mediated SMC phenotypic switching, thereby indicating the potential of melatonin in treating atherosclerosis.