Objectives: To study the role of microRNAs in hypertension-induced vascular pathology before the onset of symptoms of severe cardiovascular disease.
Background: MicroRNAs play a crucial role in cardiovascular disease. However, microRNAs are often studied in full-blown cardiovascular disease models, not during development of cardiovascular pathology.
Methods: Angiotensin II was infused into healthy adult rats, inducing chronic hypertension, and microRNA expression profiles were obtained. The most prominently regulated microRNA, miR-487b, was further investigated, using primary cultures of rat aortic and human umbilical cord arterial cells.
Results: MiR-487b is predicted to target insulin receptor substrate 1 (IRS1). IRS1 plays an important role in both insulin signaling and cell proliferation and survival. IRS1 mRNA and protein levels were downregulated in aortae of hypertensive rats. MiR-487b binds directly to both rat and human IRS1 3'UTR and inhibits reporter gene expression in vitro. In primary rat and human arterial adventitial fibroblasts, inhibition of miR-487b leads to upregulation of IRS1 expression. Upregulation of miR-487b had the opposite effect, confirming direct targeting of IRS1 by miR-487b.
Immunohistochemistry of aortic cross sections and rt/qPCR analyses of the separate aortic wall layers showed that both IRS1 and miR-487b were present mainly in the adventitia and less or not at all in the intima and tunica media. IRS1 expression in adventitial fibroblasts was predominantly nuclear and nuclear IRS1 is known to have antiapoptotic effects. Indeed, inhibition of miR-487b protected adventitial fibroblasts, and also medial smooth muscle cells, against serum starvation–induced apoptosis and increased cell survival.
Conclusions: Angiotensin II-induced hypertension leads to upregulation of miR-487b, which targets IRS1. Via downregulation of IRS1, miR-487b can contribute to cell death and loss of adventitial and medial integrity during hypertension-induced vascular pathology.
MiR-487b is upregulated in the aorta of hypertensive rats, where it inhibits expression of IRS1. MiR-487b inhibits antiapoptotic effects of nuclear IRS1 in adventitial fibroblasts and medial smooth muscle cells, thereby affecting the integrity of the vessel wall. This way, miR-487b can contribute to the development of cardiovascular pathology.
*Department of Surgery and Einthoven Laboratory for Experimental Vascular Medicine, Leiden University Medical Center, Leiden, The Netherlands
†Institute for Molecular Medicine, Renal and Cardiovascular Section, University of Southern Denmark and Odense University Hospital, Odense, Denmark
‡Department of Biomedical Sciences and Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark
§Diabetes NBEs and Obesity Biology, Novo Nordisk A/S, Måløv, Denmark.
Reprints: A. Yaël Nossent, PhD, Department of Surgery, D6-28, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands. E-mail: email@example.com.
Disclosure: The authors received financial support from Birthe and John Meyer Foundation in Denmark, the BioMedical Materials, Dutch Ministry of Economic Affairs, Agriculture and Innovation (BMM-PENT; P1.03), and The Netherlands Organization for Scientific Research (NWO) (Veni 916.12.041). The authors declare no conflicts of interest.
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