Role of Blood Cell–Associated AT1 Receptors in the Microvascular Responses to Hypercholesterolemia

Prooxidative effects of aspartame on antioxidant defense status in erythrocytes of rats

Since aspartame (L-aspartyl-L-phenylalanine methyl ester, ASP) is one of the most widely used artificial sweeteners, the aim of the present study was to investigate its effects on serum glucose and lipid levels as well as its effects on oxidative/antioxidative status in erythrocytes of rats. The experiment included two groups of animals: the control group was administered with water only, while the experimental group was orally administered with ASP (40 mg/kg b.w.) daily, for a period of six weeks. When compared with the control group, the group administrated with ASP indicated higher values of serum glucose, cholesterol and triglycerides. Significantly increased concentrations of superoxide anion (O2 .-), hydrogen peroxide (H2O2), peroxynitrite (?N??-) and lipid peroxides (LPO) were recorded in the erythrocytes of ASP treated group in comparison to the control group. In the course of chronic ASP administration, the following was observed: the concentration of reduced glutathione (GSH) and the activity of catalase (CAT) increased. Thus, these findings suggest that long-term consumption of ASP leads to hyperglycemia and hyperlipidemia, as well as to oxidative stress in erythrocytes.

Transgenic Mice Overexpressing Human Angiotensin I Receptor Gene Are Susceptible to Stroke Injury

Hypertension is one of the co-morbid conditions for stroke and profoundly increases its incidence. Angiotensin II (AngII) is shown to be at the center stage in driving the renin angiotensin system via activation of angiotensin 1 receptor (AT1R). This makes the AT1R gene one of the candidates whose differential regulation leads to the predisposition to disorders associated with hypertension. A haplotype block of four SNPs is represented primarily by haplotype-I, or Hap-I (TTAA), and haplotype-II, or Hap-II (AGCG), in the promoter of human AT1R (hAT1R) gene. To better understand the physiological role of these haplotypes, transgenic (TG) mice containing Hap-I and Hap-II of the hAT1R gene in a 166-kb bacterial artificial chromosome (BAC) were generated. Mice received injection of endothelin-1 (1 mg/ml) directly in to the striatum and were evaluated for neurologic deficit scores and sacrificed for analysis of infarct volume and mRNA levels of various proteins. Mice containing Hap-I suffered from significantly higher neurological deficits and larger brain infarcts than Hap II. Similarly, the molecular analysis of oxidant and inflammatory markers in brains of mice showed a significant increase (p < 0.05) in NOX-1 (2.3-fold), CRP (4.3-fold), and IL6 (1.9-fold) and a corresponding reduced expression of antioxidants SOD (60%) and HO1 (55%) in Hap-I mice as compared to Hap-II mice. These results suggest that increased expression of hAT1R rendered Hap-I TG mice susceptible to stroke-related pathology, possibly due to increased level of brain inflammatory and oxidative stress markers and a suppressed antioxidant defense system.

Bone marrow angiotensin AT2 receptor deficiency aggravates atherosclerosis development by eliminating macrophage liver X receptor-mediated anti-atherogenic actions

BACKGROUND

Bone marrow (BM) Angiotensin II (Ang II) type 1 (AT1) receptor plays a crucial role in atherosclerosis development; however, the effect of BM Ang II type 2 (AT2) receptor on atherogenesis remains undefined.

METHODS AND RESULTS

We generated BM chimera apoE-deficient (apoE(-/-)) mice whose BM cells were repopulated with AT2-deficient (Agtr2(-/-)) or wild-type (Agtr2(+/+)) cells. After 2 months of a high-cholesterol diet, the atherosclerotic lesion area was significantly increased in the apoE(-/-)/BM-Agtr2(-/-) mice compared with the apoE(-/-)/BM-Agtr2(+/+) mice (51%, P < 0.05), accompanied by an augmented accumulation of lesion macrophages. Although phenotypic polarization in BM-derived macrophages and lipopolysaccharide-induced expression of proinflammatory cytokines in thioglycollate-induced peritoneal macrophages (TGPMs) were not affected by AT2-deficiency, mRNA and protein expression levels of macrophage liver X receptor β (LXRβ) were significantly decreased in Agtr2(-/-) TGPMs compared with Agtr2(+/+) TGPMs. Anti-inflammatory effects of LXR agonist (GW3965) were markedly inhibited in Agtr2(-/-) TGPMs. Furthermore, the expression levels of ATP-binding cassette transporter ABCA1 and CCR7 were much lower in Agtr2(-/-) TGPMs than Agtr2(+/+) TGPMs, accompanied by a significantly reduced cholesterol efflux.

CONCLUSIONS

Our findings demonstrate that BM-AT2 deficiency aggravates atherosclerosis, at least in part, by eliminating the anti-atherogenic properties of macrophages elicited by LXRβ activation.

Angiotensin II type 1 receptor blockade suppresses light-induced neural damage in the mouse retina

Exposure to light contributes to the development and progression of retinal degenerative diseases. However, the mechanisms underlying light-induced tissue damage are not fully understood. Here, we examined the role of angiotensin II type 1 receptor (AT1R) signaling, which is part of the renin-angiotensin system, in light-induced retinal damage. Light-exposed Balb/c mice that were treated with the AT1R blockers (angiotensin II receptor blockers; ARBs) valsartan, losartan, and candesartan before and after the light exposure exhibited attenuated visual function impairment, compared to vehicle-treated mice. This effect was dose-dependent and observed across the ARB class of inhibitors. Further evaluation of valsartan showed that it suppressed a number of light-induced retinal effects, including thinning of the photoreceptor cell layer caused by apoptosis, shortening of the photoreceptor cell outer segment, and increased levels of reactive oxygen species (ROS). The role of ROS in retinal pathogenesis was investigated further using the antioxidant N-acetyl-l-cysteine (NAC). Treatment of light-exposed mice with NAC before the light exposure suppressed the visual function impairment and photoreceptor cell histological changes due to apoptosis. Moreover, treatment with valsartan or NAC suppressed the induction of c-fos (a component of the AP-1 transcription factor) and the upregulation of fasl (a proapoptotic molecule whose transcript is regulated downstream of AP-1). Our results suggest that AT1R signaling mediates light-induced apoptosis, by increasing the levels of ROS and proapoptotic molecules in the retina. Thus, AT1R blockade may represent a new therapeutic approach for preventing light-induced retinal neural tissue damage.

Angiotensin II type 1 and type 2 receptor expression in circulating monocytes of diabetic and hypercholesterolemic patients over 3-month rosuvastatin treatment

Background

In diabetes, a variety of pro-inflammatory cellular changes has been found in various cell types, including monocytes which are known to be involved in all the phases of atherogenesis. Angiotensin II (Ang II) type 1 receptor (AT₁R) mediates the pro-atherogenic effects of Ang II whereas the type 2 receptor (AT₂R) seems associated with atheroprotection. We sought to investigate the potential changes of AT₁R-AT₂R expression in human monocytes of type 2 diabetic- hypercholesterolemic patients and in hypercholesterolemic subjects, upon clinical treatment with rosuvastatin.

Methods

The AT₁R membrane protein and mRNA AT₁R and AT₂R expression in monocytes were investigated in 10 type 2 diabetic-hypercholesterolemic patients and in 10 hypercholesterolemic subjects, before and after 3-month rosuvastatin treatment. Moreover, the serum cytokine levels of interferon-γ (IFN-γ) and interleukin-4 (IL-4) were detected.

Results

As expected, rosuvastatin was associated with a change in the lipid profile in the two groups. Both the membrane protein (P = 0.008) and the AT₁R mRNA expression (P = 0.038) were significantly reduced during treatment in the absence of AT₂R expression change in diabetic-hypercholesterolemic patients whereas no significant difference was observed in hypercholesterolemic subjects. The serum IL-4 levels were increased during treatment whereas no change was observed in IFN-γ in diabetic-hypercholesterolemic patients. No cytokine change was observed in hypercholesterolemic subjects.

Conclusions

Our study on monocytes of diabetic-hypercholesterolemic patients, showing a reduced AT₁R but not AT₂R expression during rosuvastatin treatment, suggests that statin therapy may modulate favorably the AT₁-AT₂ receptor balance in subjects with coexistent type 2 diabetes.

Leukocyte-dependent responses of the microvasculature to chronic angiotensin II exposure

Angiotensin II (Ang II) contributes to the pathogenesis of hypertension and other cardiovascular diseases. Ang II induces a pro-oxidative, proinflammatory, and prothrombogenic phenotype in vascular endothelial cells. Although the peptide promotes the recruitment of leukocytes and platelets and induces oxidative stress in the microvasculature, it remains unclear whether and how the blood cell recruitment is linked to the production of reactive oxygen species. In this study, we addressed the contributions of Ang II type 1 receptors (AT(1)r) and gp91(phox) to the recruitment of leukocytes and platelets and reactive oxygen species production in venules during chronic (2-week) infusion of Ang II in wild-type (WT) and mutant mice. Intravital video microscopy was used to measure the adhesion and emigration of leukocytes, the adhesion of fluorescently labeled platelets, and dihydrorhodamine oxidation (a measure of oxidative stress) in cremaster muscle postcapillary venules. In WT mice, Ang II infusion induced a time-dependent increase in the adhesion of leukocytes and platelets and enhanced reactive oxygen species production in venules. These changes in blood cell adhesion and reactive oxygen species production were not observed in AT(1)r(-/-) mice, AT(1)r(-/-) bone marrow chimeras (blood cells deficient in AT(1)r), gp91(phox-/-) mice, gp91(phox-/-) chimeras (blood cells or endothelial cells deficient in gp91(phox)), and in WT mice rendered granulocytopenic via intraperitoneal injection of antimouse granulocyte receptor 1 antibody. Thrombocytopenic WT mice (platelets depleted by intraperitoneal injection of rabbit antimouse thrombocyte antiserum) responded similar to WT mice. These findings implicate leukocyte-associated AT(1)r and gp91(phox) in the induction of the pro-oxidative, proinflammatory, and prothrombogenic phenotype assumed by microvessels that is chronically exposed to elevated Ang II.

Role of blood cell-associated angiotensin II type 1 receptors in the cerebral microvascular response to ischemic stroke during angiotensin-induced hypertension

BACKGROUND

Angiotensin II type 1 receptor (AT1R) blockers lower the incidence of ischemic stroke in hypertensive patients and attenuate brain inflammation and injury in animal models. Although AT1R on both blood cells (BC) and vascular endothelial cells (EC) can be activated by angiotensin II (Ang II) to elicit inflammation, little is known about the relative contributions of AT1R expressed on BC and EC to the brain injury responses to ischemia and reperfusion (I/R) in the setting of angiotensin-induced hypertension.

METHODS

The contributions of BC- and EC-associated AT1R to I/R-induced brain inflammation and injury were evaluated using wild type (WT), AT1aR-/-, and bone marrow chimera mice with either a BC+/EC+ (WT→WT) or BC-/EC+ (AT1aR-/-→WT) distribution of AT1aR. The adhesion of leukocytes and platelets in venules, blood brain barrier (BBB) permeability and infarct volume were monitored in postischemic brain of normotensive and Ang II-induced hypertensive mice.

RESULTS

The inflammatory (blood cell adhesion) and injury (BBB permeability, infarct volume) responses were greatly exaggerated in the presence of Ang II-induced hypertension. The Ang II-enhanced responses were significantly blunted in AT1aR-/- mice. A similar level of protection was noted in AT1aR-/- →WT mice for BBB permeability and infarct volume, while less or no protection was evident for leukocyte and platelet adhesion, respectively.

CONCLUSIONS

BC- and EC-associated AT1aR are both involved in the brain injury responses to ischemic stroke during Ang II-hypertension, with EC AT1aR contributing more to the blood cell recruitment response and BC AT1aR exerting a significant influence on the BBB disruption and tissue necrosis elicited by I/R.

LOX-1 and angiotensin receptors, and their interplay

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, water-salt balance and the pathogenesis of cardiovascular diseases. Angiotensin II (Ang II) is the physiologically active mediator and mediates the main pathophysiological actions in RAS. Ang II exerts the effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). Most of the known pathophysiological effects of Ang II are mediated by AT1R activation. The precise physiological function of AT2R is still not clear. Generally, AT2R is considered to oppose the effects of AT1R. Lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) is one of the major receptors responsible for binding, internalizing and degrading ox-LDL. The activation of LOX-1 has been known to be related to many pathophysiological events, including endothelial dysfunction and injury, fibroblast growth, and vascular smooth muscle cell hypertrophy. Many of these alterations are present in atherosclerosis, hypertension, and myocardial ischemia and remodeling. A growing body of evidence suggests the existence of a cross-talk between LOX-1 and Ang II receptors. Their interplays are embodied in the reciprocal regulation of their expression and activity. Their interplays are involved in a series of signals. Recent studies suggests that reactive oxygen species (ROS), nitric oxide (NO), protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) are important signals responsible for their cross-talk. This paper reviews these aspects of dyslipidemia and RAS activation.

Insulin resistance in obesity and metabolic syndrome: is there a connection with platelet l-arginine transport?

OBJECTIVE

Nitric oxide (NO) is a short-lived gaseous messenger with multiple physiological functions including regulation of blood flow, platelet adhesion and aggregation inhibition. NO synthases (NOS) catalyze the conversion of cationic amino acid L-arginine in L-citrulline and NO. Despite an increasing prevalence of obesity and metabolic syndrome (MetS) in the last decades, the exact mechanisms involved in the pathogenesis and cardiovascular complications are not fully understood. We have examined the effects of obesity and MetS on the L-arginine-NO-cGMP pathway in platelets from a population of adolescents.

MATERIALS

A total of twenty six adolescent patients (13 with obesity and 13 with MetS) and healthy volunteers (n=14) participated in this study. Transport of L-arginine, NO synthase (NOS) activity and cGMP content in platelets were analyzed. Moreover, platelet function, plasma levels of L-arginine, metabolic and clinical markers were investigated in these patients and controls.

RESULTS

L-arginine transport (pmol/10(9) cells/min) in platelets via system y(+)L was diminished in obese subjects (20.8±4.7, n=10) and MetS patients (18.4±3.8, n=10) compared to controls (52.3±14.8, n=10). The y(+)L transport system correlated negatively to insulin levels and Homeostasis Model Assessment of Insulin Resistance (HOMA IR) index. No differences in NOS activity and cGMP content were found among the groups. Moreover, plasma levels of L-arginine were not affected by obesity or MetS.

DISCUSSION

Our study provides the first evidence that obesity and MetS lead to a dysfunction of L-arginine influx, which negatively correlates to insulin resistance. These findings could be a premature marker of future cardiovascular complications during adulthood.

A novel role for calpain in the endothelial dysfunction induced by activation of angiotensin II type 1 receptor signaling

RATIONALE

The cytosolic protease calpain has been recently implicated in the vascular remodeling of angiotensin II (Ang II) type 1 receptor (AT(1)R) signaling. The role of Ang II/AT(1)R/calpain signaling on endothelial function, an important and early determinant of vascular pathology, remains though totally unknown. Accordingly, we investigated the role of calpain in the endothelial dysfunction of Ang II.

OBJECTIVE

To demonstrate a mechanistic role for calpain in the endothelial dysfunction induced by Ang II/AT(1)R signaling. To establish endothelial-expressed calpains as an important target of AT(1)R signaling.

METHODS AND RESULTS

Subchronic administration of nonpressor doses of Ang II to rats and mice significantly increased vascular calpain activity via AT(1)R signaling. Intravital microscopy studies revealed that activation of vascular expressed calpains causes endothelial dysfunction with increased leukocyte-endothelium interactions and albumin permeability in the microcirculation. Western blot and immunohistochemistry studies confirmed that Ang II/AT(1)R signaling preferentially activates the constitutively expressed μ-calpain isoform and demonstrated a calpain-dependent degradation of IκBα, along with upregulation of nuclear factor κB-regulated endothelial cell adhesion molecules. These physiological and biochemical parameters were nearly normalized following inhibition of AT(1)R or calpain in vivo. RNA silencing studies in microvascular endothelial cells, along with knockout and transgenic mouse studies, further confirmed the role of μ-calpain in the endothelial adhesiveness induced by Ang II.

CONCLUSIONS

This study uncovers a novel role for calpain in the endothelial dysfunction of Ang II/AT(1)R signaling and establishes the calpain system as a novel molecular target of the vascular protective action of renin-angiotensin system inhibition. Our results may have significant clinical implications in vascular disease.

Mechanisms underlying the cerebral microvascular responses to angiotensin II-induced hypertension

Angiotensin II (AngII) and AngII type-1 receptors (AT1r) have been implicated in the pathogenesis of hypertension and ischemic stroke. The objectives of this study was to determine if/how chronic AngII administration affects blood-brain barrier (BBB) function and blood cell adhesion in the cerebral microvasculature. AngII-loaded osmotic pumps were implanted in wild type (WT) and mutant mice. Leukocyte and platelet adhesion were monitored in cerebral venules by intravital microscopy and BBB permeability detected by Evans blue leakage. AngII (two week) infusion increased blood pressure in WT mice. This was accompanied by an increased BBB permeability and a high density of adherent leukocytes and platelets. AT1r (on the vessel wall, but not on blood cells) was largely responsible for the microvascular responses to AngII. Immunodeficient (Rag-1(-/-) ) mice exhibited blunted blood cell recruitment responses without a change in BBB permeability. A similar protection pattern was noted in RANTES(-/-) and P-selectin(-/-) mice, with bone marrow chimeras (blood cell deficiency only) yielding responses comparable to the respective knockouts. These findings implicate AT1r in the microvascular dysfunction associated with AngII-induced hypertension and suggest that immune cells and blood cell-associated RANTES and P-selectin contribute to the blood cell recruitment, but not the BBB failure, elicited by AngII.

Local bone marrow Renin-Angiotensin system and atherosclerosis

Local hematopoietic bone marrow (BM) renin-angiotensin system (RAS) affects the growth, production, proliferation differentiation, and function of hematopoietic cells. Angiotensin II (Ang II), the dominant effector peptide of the RAS, regulates cellular growth in a wide variety of tissues in pathobiological states. RAS, especially Ang II and Ang II type 1 receptor (AT1R), has considerable proinflammatory and proatherogenic effects on the vessel wall, causing progression of atherosclerosis. Recent investigations, by analyzing several BM chimeric mice whose BM cells were positive or negative for AT1R, disclosed that AT1R in BM cells participates in the pathogenesis of atherosclerosis. Therefore, AT1R blocking not only in vascular cells but also in the BM could be an important therapeutic approach to prevent atherosclerosis. The aim of this paper is to review the function of local BM RAS in the pathogenesis of atherosclerosis.

Connecting chronic and recurrent stress to vascular dysfunction: no relaxed role for the renin-angiotensin system

The renin-angiotensin system (RAS) is classically considered to be a protective system for volume balance and is activated during states of volume depletion. Interestingly, one of the major pathways activating the system is the sympathetic nervous system, also the primary mediator of the acute stress response. When one further examines the cells mediating the immune site of the response, which is primarily an inflammatory response leading to defense at a locally injured area, these cells all express the ANG II type 1 receptor (AGTR1). Scattered throughout the literature are reports indicating that acute and chronic stress can activate renin and increase plasma levels of components of the RAS. Moreover, there are reports describing that ANG II can modulate the distribution and function of immune cells. Since the inflammatory response is also implicated to be central in the initiation and progression of vascular damage, we propose in this review that recurrent acute stress and chronic stress can induce a state with inflammation, due to ANG II-mediated activation of inflammatory cells, specifically monocytes and lymphocytes. Such a proposal would explain a lot of the observations regarding RAS components in inflammatory cells. Despite its attractiveness, substantial research in this area would be required to substantiate this hypothesis.

Angiotensin II-mediated microvascular thrombosis

Hypertension is associated with an increased risk of thrombosis that appears to involve an interaction between the renin-angiotensin system and hemostasis. In this study we determined whether angiotensin II-mediated thrombosis occurs in arterioles and/or venules and assessed the involvement of type 1 (AT₁), type 2 (AT₂), and type 4 (AT₄) angiotensin II receptors, as well as receptors for endothelin 1 and bradykinin 1 and 2 in angiotensin II-enhanced microvascular thrombosis. Thrombus development in mouse cremaster microvessels was quantified after light/dye injury using the time of onset of the thrombus and time to blood flow cessation. Wild-type and AT₁ receptor-deficient mice were implanted with an angiotensin II-loaded ALZET pump for 2 weeks. Angiotensin II administration in both wild-type and ATAT₁ receptor-deficient mice significantly accelerated thrombosis in arterioles. Genetic deficiency and pharmacological antagonism of AT₁ receptors did not alter the thrombosis response to angiotensin II. Isolated murine platelets aggregated in response to low (picomolar) but not high (nanomolar) concentrations of angiotensin II. The platelet aggregation response to angiotensin II depended on AT₁ receptors. Antagonism of AT₂ receptors in vivo significantly prolonged the onset of angiotensin II-enhanced thrombosis, whereas an AT₄ receptor antagonist prolonged the time to flow cessation. Selective antagonism of either endothelin 1 or bradykinin 1 receptors largely prevented both the onset and flow cessation responses to chronic angiotensin II infusion. Our findings indicate that angiotensin II induced hypertension is accompanied by enhanced thrombosis in arterioles, and this response is mediated by a mechanism that involves AT₂, AT₄, bradykinin 1, and endothelin 1 receptor-mediated signaling.

Microvascular responses to cardiovascular risk factors

Hypertension, hypercholesterolemia, diabetes, and obesity are among a growing list of conditions that have been designated as major risk factors for cardiovascular disease (CVD). While CVD risk factors are well known to enhance the development of atherosclerotic lesions in large arteries, there is also evidence that the structure and function of microscopic blood vessels can be profoundly altered by these conditions. The diverse responses of the microvasculature to CVD risk factors include oxidative stress, enhanced leukocyte- and platelet-endothelial cell adhesion, impaired endothelial barrier function, altered capillary proliferation, enhanced thrombosis, and vasomotor dysfunction. Emerging evidence indicates that a low-grade systemic inflammatory response that results from risk factor-induced cell activation and cell-cell interactions may underlie the phenotypic changes induced by risk factor exposure. A consequence of the altered microvascular phenotype and systemic inflammatory response is an enhanced vulnerability of tissues to the deleterious effects of secondary oxidative and inflammatory stresses, such as ischemia and reperfusion. Future efforts to develop therapies that prevent the harmful effects of risk factor-induced inflammation should focus on the microcirculation.

Novel cerebrovascular pathology in mice fed a high cholesterol diet

Background

Hypercholesterolemia causes atherosclerosis in medium to large sized arteries. Cholesterol is less known for affecting the microvasculature and has not been previously reported to induce microvascular pathology in the central nervous system (CNS).

Results

Mice with a null mutation in the low-density lipoprotein receptor (LDLR) gene as well as C57BL/6J mice fed a high cholesterol diet developed a distinct microvascular pathology in the CNS that differs from cholesterol-induced atherosclerotic disease. Microvessel diameter was increased but microvascular density and length were not consistently affected. Degenerative changes and thickened vascular basement membranes were present ultrastructurally. The observed pathology shares features with the microvascular pathology of Alzheimer's disease (AD), including the presence of string-like vessels. Brain apolipoprotein E levels which have been previously found to be elevated in LDLR-/- mice were also increased in C57BL/6J mice fed a high cholesterol diet.

Conclusion

In addition to its effects as an inducer of atherosclerosis in medium to large sized arteries, hypercholesterolemia also induces a microvascular pathology in the CNS that shares features of the vascular pathology found in AD. These observations suggest that high cholesterol may induce microvascular disease in a range of CNS disorders including AD.

Membrane cholesterol is a biomechanical regulator of neutrophil adhesion

OBJECTIVE

The purpose of this study was to evaluate the role of membrane cholesterol on human neutrophil and HL-60 biomechanics, capture, rolling, and arrest to P-selectin- or IL-1-activated endothelium.

METHODS AND RESULTS

Methyl-beta-cyclodextrin (MbetaCD) removed up to 73% and 45% of membrane cholesterol from HL-60 cells and neutrophils, whereas MbetaCD/cholesterol complexes resulted in maximum enrichment of 65% and 40%, respectively, above control levels. Cells were perfused at a venous wall shear rate of 100 s(-1) over adherent P-selectin-coated 1-microm diameter beads, uncoated 10-mum diameter beads, P-selectin-coated surfaces, or activated endothelium. Elevated cholesterol enhanced capture efficiency to 1-microm beads and increased membrane tether growth rate by 1.5- to 2-fold, whereas cholesterol depletion greatly reduced tether formation. Elevated cholesterol levels increased tether lifetime by 17% in neutrophils and adhesion lifetime by 63% in HL-60 cells. Deformation of cholesterol-enriched neutrophils increased the contact time with 10-mum beads by 32% and the contact area by 7-fold. On both P-selectin surfaces and endothelial-cell monolayers, cholesterol-enriched neutrophils rolled more slowly, more stably, and were more likely to firmly arrest. Cholesterol depletion resulted in opposite effects.

CONCLUSIONS

Increasing membrane cholesterol enhanced membrane tether formation and whole cell deformability, contributing to slower, more stable rolling on P-selectin and increased firm arrest on activated endothelium.

Bone marrow angiotensin AT1 receptor regulates differentiation of monocyte lineage progenitors from hematopoietic stem cells

BACKGROUND

The angiotensin II (Ang II) type 1 (AT(1)) receptor is expressed in bone marrow (BM) cells, whereas it remains poorly defined how Ang II regulates differentiation/proliferation of monocyte-lineage cells to exert proatherogenic actions.

METHODS AND RESULTS

We generated BM chimeric apoE(-/-) mice repopulated with AT(1)-deficient (Agtr1(-/-)) or wild-type (Agtr1(+/+)) BM cells. The atherosclerotic development was significantly reduced in apoE(-/-)/BM-Agtr1(-/-) mice compared with apoE(-/-)/BM-Agtr1(+/+) mice, accompanied by decreased numbers of BM granulocyte/macrophage progenitors (GMP:c-Kit(+)Sca-1(-)Lin(-)CD34(+)CD16/32(+)) and peripheral blood monocytes. Macrophage-colony-stimulating factor (M-CSF)-induced differentiation from hematopoietic stem cells (HSCs:c-Kit(+)Sca-1(+)Lin(-)) to promonocytes (CD11b(high)Ly-6G(low)) was markedly reduced in HSCs from Agtr1(-/-) mice. The expression of M-CSF receptor c-Fms was decreased in HSCs/promonocytes from Agtr1(-/-) mice, accompanied by a marked inhibition in M-CSF-induced phosphorylation of PKC-delta and JAK2. c-Fms expression in HSCs/promonocytes was mainly regulated by TNF-alpha derived from BM CD45(-)CD34(-) stromal cells, and Ang II specifically regulated the TNF-alpha synthesis and release from BM stromal cells.

CONCLUSIONS

Ang II regulates the expression of c-Fms in HSCs and monocyte-lineage cells through BM stromal cell-derived TNF-alpha to promote M-CSF-induced differentiation/proliferation of monocyte-lineage cells and contributes to the proatherogenic action.

Blood cell-derived RANTES mediates cerebral microvascular dysfunction, inflammation, and tissue injury after focal ischemia-reperfusion

BACKGROUND AND PURPOSE

Although chemokines have been implicated in cardiovascular diseases, few studies have addressed the role of these inflammatory mediators in ischemic stroke. This study tested the hypothesis that RANTES (CCL5; regulated on activation, normal T-cell expressed and secreted) mediates the cerebral microvascular dysfunction, inflammation, and tissue injury induced by brain ischemia and reperfusion.

METHODS

After 60-minute middle cerebral artery occlusion and reperfusion, the adhesion of leukocytes and platelets in cerebral venules, infarct volume, and blood-brain barrier permeability were measured in wild-type mice (WT), RANTES-deficient mice (RANTES(-/-)), WT mice transplanted with RANTES(-/-) bone marrow (RANTES>WT), and control bone marrow chimeras (WT>WT). The concentration of RANTES and several cytokines was also measured by enzyme-linked immunosorbent assay and a cytometric bead array.

RESULTS

The enhanced leukocyte and platelet adhesion, increased blood-brain barrier permeability, and tissue infarction elicited in WT and WT>WT mice after middle cerebral artery occlusion and reperfusion were significantly blunted in RANTES(-/-) mice. Similar attenuation of the middle cerebral artery occlusion and reperfusion-induced responses were noted in RANTES>WT chimeras. Although RANTES deficiency did not alter the changes in tissue cytokine levels elicited by middle cerebral artery occlusion and reperfusion, plasma concentrations interleukin-6, interleukin-10, and interleukin-12 were all reduced.

CONCLUSIONS

These findings implicate blood cell-derived RANTES in the microvascular, inflammatory, and tissue injury responses of the brain to ischemia and reperfusion.

Role of bone marrow renin-angiotensin system in the pathogenesis of atherosclerosis

The renin-angiotensin system (RAS) has been considered to be a circulating hormonal system that regulates blood pressure, blood flow, fluid volume and electrolyte balance. A growing body of evidence indicates local effects of an activated RAS, particularly in the cardiac, vascular, and renal systems. It is now well established that RAS, especially angiotensin II (Ang II) and Ang II type 1 receptor (AT1R) pathway, has significant pro-inflammatory actions on the vessel wall, leading to progression of atherosclerosis. Recent reports suggest that an activated RAS has local effects in bone marrow (BM), which contributes to the regulation of normal and malignant hematologic processes. We reported that AT1aR in BM cells participate in the pathogenesis of atherosclerosis by analyzing several BM chimeric mice whose BM cells were positive or negative for AT1aR. These results suggest that blockade of AT1R not only in vascular cells but also in BM could be an important strategy to prevent atherosclerosis. In this review, we overview recent findings on a role of RAS in the pathogenesis of atherosclerosis, and discuss functional contribution of a local RAS in BM to progression and destabilization of atherosclerotic plaque.

Oxidative stress in mononuclear cells plays a dominant role in their adhesion to mouse femoral artery after injury

Leukocyte recruitment plays a pivotal role during inflammation after vascular injury. The importance of oxidative stress in vascular injury and its modulation by angiotensin II receptor blockers (olmesartan) have been demonstrated. We examined the contribution of leukocyte-associated oxidative stress in acute-phase leukocyte recruitment and its modulation by olmesartan. Male mice were treated with olmesartan (5 mg/kg per day) or vehicle for 7 days before the transluminal wire injury of the femoral artery. Intravital microscopy of the artery revealed that the mechanical injury increased adherent leukocytes at both 24 hours and 7 days after the injury, which was significantly reduced by olmesartan treatment. Dihydroethidium-associated fluorescence intensity observed in vehicle-treated mice was significantly diminished under olmesartan treatment. Apocynin, a nicotinamide-adenine dinucleotide phosphate oxidase inhibitor, showed a similar inhibitory effect on the leukocyte adhesion. Adoptive transfer of mononuclear cells, harvested from mice after wire injury, but not from those without wire injury, exhibited adhesion to the recipient injured artery. Furthermore, olmesartan treatment of mononuclear cells, but not of injured vasculature, reduced their recruitment to the injured artery. These data indicate that leukocyte recruitment to the mechanically injured artery is mediated by oxidative stress in leukocytes but not in vasculatures. Treatment with olmesartan blocked leukocyte recruitment by antagonizing mononuclear cells-associated oxidative stress.

Critical role of bone marrow angiotensin II type 1 receptor in the pathogenesis of atherosclerosis in apolipoprotein E deficient mice

OBJECTIVE

It is suggested that the angiotensin II (Ang II)-Ang II type 1 receptor (AT1R) pathway plays a pivotal role in the pathogenesis of atherosclerosis. Recently, bone marrow (BM) cells were reported to express AT1R. Here, we investigated the role of AT1R in BM in the pathogenesis of atherosclerosis.

METHODS AND RESULTS

Genetic ablation or pharmacological blockade of AT1R led to a significant reduction and stabilization of atherosclerotic lesions in ApoE-/- mice. To elucidate the role of AT1R in BM, we generated several BM chimeric mice. Ang II promoted atherosclerosis progression in the BM chimeric mice that had AT1aR in BM, regardless of the absence of AT1aR in the recipient vasculature (P<0.05). BM chimeric mice whose BM AT1aR was disrupted showed significantly less atherosclerotic lesions in aorta (P<0.05) and more stable plaque with reduced accumulation of BM-derived cells compared with BM chimeric mice that had AT1aR-positive BM. Most of the BM-derived cells in atheroma were positive for a macrophage marker and expressed matrix metalloproteinase (MMP)-9 and monocyte chemoattractant protein-1.

CONCLUSIONS

Our findings suggest that AT1R in BM plays an important role in the pathogenesis of atherosclerosis.

Platelet-associated NAD(P)H oxidase contributes to the thrombogenic phenotype induced by hypercholesterolemia

Elevated cholesterol levels promote proinflammatory and prothrombogenic responses in venules and impaired endothelium-dependent arteriolar dilation. Although NAD(P)H oxidase-derived superoxide has been implicated in the altered vascular responses to hypercholesterolemia, it remains unclear whether this oxidative pathway mediates the associated arteriolar dysfunction and platelet adhesion in venules. Platelet and leukocyte adhesion in cremasteric postcapillary venules and arteriolar dilation responses to acetylcholine were monitored in wild-type (WT), Cu,Zn-superoxide dismutase transgenic (SOD-TgN), and NAD(P)H oxidase-knockout (gp91(phox-/-)) mice placed on a normal (ND) or high-cholesterol (HC) diet for 2 weeks. HC elicited increased platelet and leukocyte adhesion in WT mice versus ND. Cytosolic subunits of NAD(P)H oxidase (p47phox and p67phox) were expressed in platelets. This was not altered by hypercholesterolemia; however, platelets and leukocytes from HC mice exhibited elevated generation of reactive oxygen species compared to ND mice. Hypercholesterolemia-induced leukocyte recruitment was attenuated in SOD-TgN-HC and gp91(phox-/-)-HC mice. Recruitment of platelets derived from WT-HC mice in venules of SOD-TgN-HC or gp91(phox-/-)-HC recipients was comparable to ND levels. Adhesion of SOD-TgN-HC platelets paralleled the leukocyte response and was attenuated in SOD-TgN-HC recipients, but not in WT-HC recipients. However, gp91(phox-/-)-HC platelets exhibited low levels of adhesion comparable to those of WT-ND in both hypercholesterolemic gp91(phox-/-) and WT recipients. Arteriolar dysfunction was evident in WT-HC mice, compared to WT-ND. Overexpression of SOD or, to a lesser extent, gp91(phox) deficiency restored arteriolar vasorelaxation responses toward WT-ND levels. These findings reveal a novel role for platelet-associated NAD(P)H oxidase in producing the thrombogenic phenotype in hypercholesterolemia and demonstrate that NAD(P)H oxidase-derived superoxide mediates the HC-induced arteriolar dysfunction.

Angiotensin II type 1 receptor signaling contributes to platelet-leukocyte-endothelial cell interactions in the cerebral microvasculature

Angiotensin II type 1 (AT(1)) receptor signaling has been implicated in cerebral microvascular alterations associated with ischemia, diabetes mellitus, hypercholesterolemia, and atherosclerosis. Platelets, which express AT(1) receptors, also appear to contribute to the thrombogenic and inflammatory responses that are elicited by these pathological conditions. This study assesses the role of AT(1) receptor activation on platelet-leukocyte-endothelial cell interactions elicited in cerebral microvasculature by ischemia and reperfusion. Intravital microscopy was used to monitor the adhesion of platelets and leukocytes that were labeled with different fluorochromes, whereas dihydrorhodamine-123 was used to quantify oxygen radical production in cerebral surface of mice that were either treated with the AT(1) receptor agonist Val-angiotensin II (ANG II) or subjected to bilateral common carotid artery occlusion (BCCAO) followed by reperfusion. ANG II elicited a dose- and time- dependent increase in platelet-leukocyte-endothelial cell interactions in cerebral venules that included rolling platelets, adherent platelets on the leukocytes and the endothelial cells, rolling leukocytes, and adherent leukocytes. All of these interactions were attenuated by treatment with either P-selectin or P-selectin glycoprotein ligand 1 (PSGL-1) antibody. The AT(1) receptor antagonist candesartan and losartan as well as diphenyleneiodonium, an inhibitor of flavoproteins including NAD(P)H oxidase, significantly reduced the platelet-leukocyte-endothelial cell interactions elicited by either ANG II administration or BCCAO/reperfusion. The increased oxygen radical generation elicited by BCCAO/reperfusion was also attenuated by candesartan. These findings are consistent with an AT(1) receptor signaling mechanism, which involves oxygen radical production and ultimately results in P-selectin- and PSGL-1-mediated platelet-leukocyte-endothelial cell interactions in the cerebral microcirculation.

Real-time imaging of mechanically injured femoral artery in mice reveals a biphasic pattern of leukocyte accumulation

Wire injury of an artery has been recognized as a standard model of vascular inflammation and atherosclerosis; however, the mechanism of leukocyte recruitment has not been studied in this model. In this study, we documented the recruitment of leukocytes to the murine femoral artery after a wire injury. A transluminal mechanical injury was generated by insertion of a wire into the femoral artery of male C57BL/6J mice. The mice were anesthetized and ventilated after tracheotomy and protected from hypothermia by a warming lamp. Body temperature and blood pH did not significantly change during the experiment. The interaction between rhodamine 6G-labeled leukocytes and the injured femoral artery was monitored using an epifluorescent microscope, and the images were evaluated using a computer-assisted image analysis program. In the absence of injury, virtually no leukocyte adhesion was observed. In contrast, the number of adherent leukocytes increased 4 and 24 h after injury and declined 72 h after injury. The rolling flux of leukocytes increased 4 h after injury and remained high up to 7 days, but it was faster 72 h after injury. We identified another peak of leukocyte adhesion 7 days after injury. Injection of anti-P-selectin antibody significantly reduced leukocyte adhesion at the early and later phases. In conclusion, we have established a novel experimental system for direct observation of leukocyte recruitment to the injured femoral artery. Our system revealed a previously undetected, unique profile of leukocyte recruitment during vascular injury.

Angiotensin II type 1 receptors and the intestinal microvascular dysfunction induced by ischemia and reperfusion

The acute phase of intestinal ischemia-reperfusion (I/R) injury is mediated by leukocytes and is characterized by oxidative stress and blood cell recruitment. Upregulation of angiotensin II type 1 receptors (AT1-R) has been implicated in the pathogenesis of conditions associated with oxidative stress. The AT1-R-antagonist Losartan (Los) attenuates leukocyte recruitment following I/R. However, the role of AT1-R in intestinal I/R injury and the associated platelet-leukocyte interactions remains unclear. The objective of this study was to define the contribution of AT1-R to I/R-induced blood cell recruitment in intestinal venules. Leukocyte and platelet adhesion were quantified by intravital microscopy in the small bowel of C57Bl/6 [wild-type (WT)] mice exposed to sham operation or 45 min of ischemia and 4 h of reperfusion. A separate WT group received Los for 7 days before gut I/R (WT-I/R + Los). AT1-R bone marrow chimeras that express AT1-R on the vessel wall but not blood cells also underwent I/R. Platelet and leukocyte adhesion as well as AT1-R expression in the gut microvasculature were significantly elevated after I/R. All of these responses were attenuated in the WT-I/R + Los group, compared with untreated I/R mice. A comparable abrogation of I/R-induced blood cell adhesion was noted in AT1-R bone marrow chimeras. I/R-induced platelet adhesion was unaltered in mice overexpressing Cu,Zn-SOD or mice deficient in NAD(P)H oxidase. These data suggest that although gut I/R upregulates endothelial expression of AT1-R, engagement of these angiotensin II receptors on blood cells is more important in eliciting the prothrombogenic and proinflammatory state observed in postischemic gut venules, through a superoxide-independent pathway.