Edward D. Tran

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

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 microM). Multiple pathways may be responsible. Since the beta(2)-adrenergic receptor (beta(2)-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 beta(2)-AR. SHR arterioles respond in an attenuated fashion to beta(2)-AR agonists and antagonists. Aorta and heart muscle of control Wistar rats were exposed for 24 h (37 degrees C) to fresh plasma of male Wistar and WKY rats and SHRs with and without doxycycline (30 microM) and EDTA (10 mM) to reduce MMP activity. The density of extracellular and intracellular domains of beta(2)-AR was determined by immunohistochemistry. The density of the extracellular domain of beta(2)-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 beta(2)-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 beta(2)-AR in blood vessels and to the increased arteriolar tone of SHRs compared with normotensive rats.

Enhanced Matrix Metalloproteinase Activity in the Spontaneously Hypertensive Rat: VEGFR-2 Cleavage, Endothelial Apoptosis, and Capillary Rarefaction

Besides an elevated blood pressure, the spontaneously hypertensive rat (SHR) has multiple microvascular complications including endothelial apoptosis with capillary rarefaction. The SHR also has elevated levels of proteolytic (e.g. matrix metalloproteinase, MMP) activity and apoptosis in microvascular cells compared to its normotensive control, but the specific enzymes involved and the molecular mechanism for apoptosis are unknown. We hypothesize that selected MMPs cleave the extracellular domain of vascular endothelial growth factor receptor-2 (VEGFR-2), which in turn causes endothelial apoptosis and capillary rarefaction. Zymographic analysis shows that gelatinase (MMP-2 and MMP-9) and matrilysin (MMP-7) activities are significantly enhanced in SHR plasma. The SHR has lower levels of the extracellular domains of VEGFR-2 in cardiac microvessels. Furthermore, application of plasma from the SHR, or purified MMP-9 and MMP-7 to naïve cells causes cleavage of the extracellular domain of VEGFR-2. The receptor cleavage was blocked by broad-acting MMP inhibitors (GM6001 1 µM, EDTA 10 mM, or doxycycline 11.3 µM). Chronic MMP inhibition (doxycycline, 5.4 mg/kg/day, 24 weeks) attenuated VEGFR-2 cleavage, endothelial apoptosis, and capillary rarefaction in the SHR. These results suggest elevated plasma MMP activities may cleave VEGFR-2, resulting in endothelial apoptosis and capillary rarefaction in the SHR.

An In‐Vivo Analysis of Capillary Stasis and Endothelial Apoptosis in a Model of Hypertension

Objective: Recent evidence suggests endothelial apoptosis may be a mechanism for capillary rarefaction in hypertensives. The objective of this study was to examine the early phase of endothelial apoptosis and capillary blood flow in the spontaneously hypertensive rat (SHR) and the normotensive Wistar‐Kyoto (WKY) rat.

Matrix metalloproteinase activity causes VEGFR-2 cleavage and microvascular rarefaction in rat mesentery.

Please cite this paper as: Tran, Yang, Chen, DeLano, Murfee and Schmid‐Schönbein (2011). Matrix Metalloproteinase Activity Causes VEGFR‐2 Cleavage and Microvascular Rarefaction in Rat Mesentery. Microcirculation 18(3), 228–237.

Constitutive Expression and Enzymatic Cleavage of ICAM-1 in the Spontaneously Hypertensive Rat

Background/Aims: Leukocyte adhesion to the endothelium is abnormal in hypertension. We have recently shown that spontaneously hypertensive rats (SHRs) have circulating leukocytes with enhanced CD18 receptor cleavage. In the current study, we investigate expression levels of its counter receptor, intercellular adhesion molecule (ICAM-1), and its possible proteolytic cleavage in the SHR and control Wistar rat. Methods: ICAM-1 was labeled on tissue sections with two antibodies targeting its extracellular and intracellular domains and evaluated by light absorption measurements. The in situ cleavage of ICAM-1 was assessed by treating vessel sections with matrix metalloproteinase (MMP)-7, MMP-9 and elastase. Results: SHRs showed a significant increase in ICAM-1 expression in liver and kidney compared with Wistar rats. The liver and kidney glomeruli exhibit a discrepancy in label density between intra- and extracellular antibodies, which suggests that enzymatic cleavage may be a factor determining ICAM-1 distribution. MMP-7 and MMP-9, which are elevated in SHR plasma, and elastase, which has elevated activity in SHR neutrophils, cleave the extracellular domain of ICAM-1 when applied to the tissue. Conclusion: ICAM-1 expression in SHRs is upregulated in a tissue-specific manner. Proteolytic cleavage of the extracellular domain of ICAM-1 and accumulation in kidney glomeruli may play a role in the renal involvement of inflammation.

Microvascular cell death in spontaneously hypertensive rats during experimental inflammation.

Objective: Chronic hypertension is associated with an increased risk for tissue injury that may be mediated in part by endothelium and inflammatory cells. To clarify a possible underlying mechanisms, we examined leukocyte migration in the microcirculation and concomitant parenchymal cell death.