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.
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.
Background One of the most important unresolved issues in diabetes is the mechanism for the attenuated response to insulin, i.e. insulin resistance. Aims and methods We hypothesize that the mechanism for the insulin resistance is due to uncontrolled protease activity in the plasma, on endothelial cells and in the tissue parenchyma. To examine this hypothesis we use of microzymographic techniques in the microcirculation, plasma zymography, and receptor labeling techniques with antibodies against an extracellular domain of the insulin receptor α. Results The spontaneously hypertensive rat has an enhanced proteolytic activity and significant cleavage of the receptor with attenuated glucose transport. We present evidence for insulin receptor cleavage in a high fat diet and a transgenic model of diabetes. Conclusion These results suggest that cleavage of the extracellular domain of the insulin receptor, a situation that interferes with the ability for insulin to bind and provide an intracellular signal for glucose transport, may be involved in insulin resistance.
A complication of the spontaneously hypertensive rat (SHR) is microvascular rarefaction, defined by the loss of microvessels. However, the molecular mechanisms involved in this process remain incompletely identified. Recent work in our laboratory suggests that matrix metalloproteinases (MMPs) may play a role by cleavage of the vascular endothelial growth factor receptor 2 (VEGFR-2). In order to further delineate the role for MMPs in microvascular rarefaction, the objective of the current study was to examine the relationship in the same tissue between MMP activity, VEGFR-2 cleavage and rarefaction. Using an in-vivo microzymographic technique we show significantly enhanced levels of MMP-1, -1/-9, -7, and -8 activities, but not MMP-2 and-3 activities, along mesenteric microvessels of the SHR compared to its normotensive control, Wistar Kyoto (WKY) rat. Based on immunohistochemical methods, the SHR exhibited a decreased labeling of the extracellular, but not the intracellular, domain of VEGFR-2 along mesenteric microvessels. Chronic MMP inhibition served to attenuate VEGFR-2 cleavage and microvascular network rarefaction in the SHR mesentery. These results spatially link MMP-induced VEGFR-2 cleavage and rarefaction in the mesentery of the SHR and thus support the hypothesis that MMPs serve as regulators of microvascular dysfunction in hypertension.
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.
Glucocorticoid facilitates cell death and microvessel stasis. Immobilized platelets and leukocytes play a central role in capillary stasis, which leads to progression of endothelial apoptosis.
Rationale: Research that applies an unreliable definition for transfusion-related acute lung injury (TRALI) may draw false conclusions about its risk factors and biology. The effectiveness of preventive strategies may decrease as a consequence. However, the reliability of the consensus TRALI definition is unknown.Objectives: To prospectively study the effect of applying two plausible definitions of acute respiratory distress syndrome onset time on TRALI epidemiology. Methods:We studied 316 adults admitted to the intensive care unit and transfused red blood cells within 24 hours of blunt trauma. We identified patients with acute respiratory distress syndrome, and defined acute respiratory distress syndrome onset time two ways: (1) the time at which the first radiographic or oxygenation criterion was met, and (2) the time both criteria were met. We categorized two corresponding groups of TRALI cases transfused in the 6 hours before acute respiratory distress syndrome onset. We used Cohen's kappa to measure agreement between the TRALI cases and implicated blood components identified by the two acute respiratory distress syndrome onset time definitions. In a nested case-control study, we examined potential risk factors for each group of TRALI cases, including demographics, injury severity, and characteristics of blood components transfused in the 6 hours before acute respiratory distress syndrome onset.Measurements and Main Results: Forty-two of 113 patients with acute respiratory distress syndrome were TRALI cases per the first acute respiratory distress syndrome onset time definition and 63 per the second definition. There was slight agreement between the two groups of TRALI cases (k = 0.16; 95% confidence interval, 20.01 to 0.33) and between the implicated blood components (k = 0.15, 95% confidence interval, 0.11-0.20). Age, Injury Severity Score, high plasma-volume components, and transfused plasma volume were risk factors for TRALI when applying the second acute respiratory distress syndrome onset time definition but not when applying the first definition.Conclusions: The epidemiology of TRALI varies when applying two plausible definitions of acute respiratory distress syndrome onset time to severely injured trauma patients. A TRALI definition that standardizes acute respiratory distress syndrome onset time might improve reliability and align efforts to understand epidemiology, biology, and prevention.
One of the key features of cardiovascular complications, such as hypertension or diabetes, is that they often appear at the same time in the same individual together with other forms of co-morbidities. While clinically a recognized phenomenon, no molecular mechanism for such co-morbidities has received universal acceptance. We propose a new hypothesis that provides a molecular basis for co-morbidities in hypertension due to unchecked proteolytic activity and receptor destruction. Testing of the hypothesis in the spontaneously hypertensive rat reveals an unchecked matrix metalloproteinase and serine protease activity in plasma and on several cardiovascular and parenchymal cells. The elevated proteolytic activity causes extracellular cleavage of multiple receptor types, such that cleavage of one receptor type leads to loss of the function carried out by this receptor. Proteolytic cleavage of the extracellular domain of the β2 adrenergic receptor in arteries and arterioles causes vasoconstriction and elevation of the central blood pressure while cleavage of the extracellular domain of the insulin receptor leads to insulin resistance and lack of transmembrane glucose transport. A diverse set of cell dysfunctions in the spontaneously hypertensive rat are accompanied by cleavage of the membrane receptors that are involved in these functions. Chronic inhibition of the unchecked protease activity in the spontaneously hypertensive rat serves to restore the extracellular receptor density and alleviates the corresponding cell dysfunctions. The mild unchecked proteolytic activity in the spontaneously hypertensive rat points towards a chronic autodigestion process as a contributor to the end organ injury encountered in this rat strain. The presence of various soluble receptors, which consist of extracellular fragments of membrane receptors, in the plasma of hypertensive and diabetic patients suggest that the autodigestion process may also be present in man.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.