Matrix metalloproteinases cleave the β2-adrenergic receptor in spontaneously hypertensive rats

Abstract

We recently observed the enhanced serine and matrix metalloproteinase (MMP) activity in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) rat and the cleavage of membrane receptors in the SHR by MMPs. We demonstrate in vivo that MMP-7 and MMP-9 injection leads to a vasoconstrictor response in microvessels of rats that is blocked by a specific MMP inhibitor (GM-6001, 1 μM). Multiple pathways may be responsible. Since the β2-adrenergic receptor (β2-AR) is susceptible to the action of endogenous MMPs, we hypothesize that MMPs in the plasma of SHRs are able to cleave the extracellular domain of the β2-AR. SHR arterioles respond in an attenuated fashion to β2-AR agonists and antagonists. Aorta and heart muscle of control Wistar rats were exposed for 24 h (37°C) to fresh plasma of male Wistar and WKY rats and SHRs with and without doxycycline (30 μM) and EDTA (10 mM) to reduce MMP activity. The density of extracellular and intracellular domains of β2-AR was determined by immunohistochemistry. The density of the extracellular domain of β2-AR is reduced in aortic endothelial cells and cardiac microvessels of SHRs compared with that of WKY or Wistar rats. Treatment of the aorta and the heart of control Wistar rats with plasma from SHRs, but not from WKY rats, reduced the number of extracellular domains, but not intracellular domains, of β2-AR in aortic endothelial cells and cardiac microvessels. MMP inhibitors (EDTA and doxycycline) prevented the cleavage of the extracellular domain. Thus MMPs may contribute to the reduced density of the extracellular domain of β2-AR in blood vessels and to the increased arteriolar tone of SHRs compared with normotensive rats.