Visualizing Leukocyte Rolling and Adhesion in Angiotensin II-Infused Mice: Techniques and Pitfalls

Epifluorescence intravital video microscopy (IVM) of blood vessels is an established method to evaluate the activation of immune cells and their ability ...

University Medical Center Mainz

Angiotensin II (ATII), a potent vasoconstrictor, causes hypertension, promotes infiltration of myelomonocytic cells into the vessel wall, and stimulates both vascular and inflammatory cell NADPH oxidases. The predominant source of reactive oxygen species, eg, vascular (endothelial, smooth muscle, adventitial) versus phagocytic NADPH oxidase, and the role of myelomonocytic cells in mediating arterial hypertension have not been defined yet.

Lysozyme M-positive monocytes mediate angiotensin II-induced arterial hypertension and vascular dysfunction.

Endothelial nitric-oxide synthase (eNOS) uncoupling and increased inducible NOS (iNOS) activity amplify vascular oxidative stress. The role of inflammatory myelomonocytic cells as mediators of these processes and their impact on tetrahydrobiopterin availability and function have not yet been defined. Angiotensin II (ATII, 1 mg/kg/day for 7 days) increased Ly6C(high) and CD11b(+)/iNOS(high) leukocytes and up-regulated levels of eNOS glutathionylation in aortas of C57BL/6 mice. Vascular iNOS-dependent NO formation was increased, whereas eNOS-dependent NO formation was decreased in aortas of ATII-infused mice as assessed by electron paramagnetic resonance (EPR) spectroscopy. Diphtheria toxin-mediated ablation of lysozyme M-positive (LysM(+)) monocytes in ATII-infused LysM(iDTR) transgenic mice prevented eNOS glutathionylation and eNOS-derived N(ω)-nitro-L-arginine methyl ester-sensitive superoxide formation in the endothelial layer. ATII increased vascular guanosine triphosphate cyclohydrolase I expression and biopterin synthesis in parallel, which was reduced in monocyte-depleted LysM(iDTR) mice. Vascular tetrahydrobiopterin was increased by ATII infusion but was even higher in monocyte-depleted ATII-infused mice, which was paralleled by a strong up-regulation of dihydrofolate reductase expression. EPR spectroscopy revealed that both vascular iNOS- and eNOS-dependent NO formation were normalized in ATII-infused mice following monocyte depletion. Additionally, deletion as well as pharmacologic inhibition of iNOS prevented ATII-induced endothelial dysfunction. In summary, ATII induces an inflammatory cell-dependent increase of iNOS, guanosine triphosphate cyclohydrolase I, tetrahydrobiopterin, NO formation, and nitro-oxidative stress as well as eNOS uncoupling in the vessel wall, which can be prevented by ablation of LysM(+) monocytes.

Inflammatory monocytes determine endothelial nitric-oxide synthase uncoupling and nitro-oxidative stress induced by angiotensin II.

Heme oxygenase-1 (HO-1) confers protection to the vasculature and suppresses inflammatory properties of monocytes and macrophages. It is unclear how HO-1 determines the extent of vascular dysfunction in mice and humans.

Heme oxygenase-1 suppresses a pro-inflammatory phenotype in monocytes and determines endothelial function and arterial hypertension in mice and humans.

The gut microbiome is essential for physiological host responses and development of immune functions. The impact of gut microbiota on blood pressure and systemic vascular function, processes that are determined by immune cell function, is unknown.

Gut Microbiota Promote Angiotensin II-Induced Arterial Hypertension and Vascular Dysfunction.

Alcoholic cardiomyopathy (ACM) resulting from excess alcohol consumption is an important cause of heart failure (HF). Although it is assumed that the cardiotoxicity of the ethanol (EtOH)-metabolite acetaldehyde (ACA) is central for its development and progression, the exact mechanisms remain obscure. Murine cardiomyocytes (CMs) exposed to ACA or EtOH showed increased superoxide (O2(•-)) levels and decreased mitochondrial polarization, both being normalized by NADPH oxidase (NOX) inhibition. C57BL/6 mice and mice deficient for the ACA-degrading enzyme mitochondrial aldehyde dehydrogenase (ALDH-2(-/-)) were fed a 2% EtOH diet for 5 weeks creating an ACA-overload. 2% EtOH-fed ALDH-2(-/-) mice exhibited a decreased cardiac function, increased heart-to-body and lung-to-body weight ratios, increased cardiac levels of the lipid peroxidation product malondialdehyde (MDA) as well as increased NOX activity and NOX2/glycoprotein 91(phox) (NOX2/gp91(phox)) subunit expression compared to 2% EtOH-fed C57BL/6 mice. Echocardiography revealed that ALDH-2(-/-)/gp91(phox-/-) mice were protected from ACA-overload-induced HF after 5 weeks of 2% EtOH-diet, demonstrating that NOX2-derived O2(•-) contributes to the development of ACM. Translated to human pathophysiology, we found increased gp91(phox) expression in endomyocardial biopsies of ACM patients. In conclusion, ACM is promoted by ACA-driven mitochondrial dysfunction and can be improved by ablation of NOX2/gp91(phox). NOX2/gp91(phox) therefore might be a potential pharmacological target to treat ACM.

NOX2 amplifies acetaldehyde-mediated cardiomyocyte mitochondrial dysfunction in alcoholic cardiomyopathy.

Vascular inflammation in cardiovascular diseases is recognized to be linked with immune cell activation. Recruitment of immune cells into the vessel wall is an early step in angiotensin II-induced vascular dysfunction and arterial hypertension. Exploring the role of monocytes and macrophages in angiotensin II-induced hypertension and vascular inflammation in mouse models highlights the importance of these pathophysiological processes. Here we describe our routinely used protocols concerning angiotensin II-induced hypertension, assessment of blood pressure, vascular function, and immune cell infiltration.

Assessment of Vascular Dysfunction and Inflammation Induced by Angiotensin II in Mice.

Multicellular interactions of platelets, leukocytes, and the blood vessel wall support coagulation and precipitate arterial and venous thrombosis. High levels of angiotensin II cause arterial hypertension by a complex vascular inflammatory pathway that requires leukocyte recruitment and reactive oxygen species production and is followed by vascular dysfunction. We delineate a previously undescribed, proinflammatory coagulation-vascular circuit that is a major regulator of vascular tone, blood pressure, and endothelial function. In mice with angiotensin II-induced hypertension, tissue factor was up-regulated, as was thrombin-dependent endothelial cell vascular cellular adhesion molecule 1 expression and integrin αMβ2- and platelet-dependent leukocyte adhesion to arterial vessels. The resulting vascular inflammation and dysfunction was mediated by activation of thrombin-driven factor XI (FXI) feedback, independent of factor XII. The FXI receptor glycoprotein Ibα on platelets was required for this thrombin feedback activation in angiotensin II-infused mice. Inhibition of FXI synthesis with an antisense oligonucleotide was sufficient to prevent thrombin propagation on platelets, vascular leukocyte infiltration, angiotensin II-induced endothelial dysfunction, and arterial hypertension in mice and rats. Antisense oligonucleotide against FXI also reduced the increased blood pressure and attenuated vascular and kidney dysfunction in rats with established arterial hypertension. Further, platelet-localized thrombin generation was amplified in an FXI-dependent manner in patients with uncontrolled arterial hypertension, suggesting that platelet-localized thrombin generation may serve as an inflammatory marker of high blood pressure. Our results outline a coagulation-inflammation circuit that promotes vascular dysfunction, and highlight the possible utility of FXI-targeted anticoagulants in treating hypertension, beyond their application as antithrombotic agents in cardiovascular disease.

Platelet-localized FXI promotes a vascular coagulation-inflammatory circuit in arterial hypertension.

Hypertension caused by increased renin-angiotensin system activation is associated with elevated reactive oxygen species production. Previous studies implicate NADPH oxidase (Nox) proteins as important reactive oxygen species sources during renin-angiotensin system activation, with different Nox isoforms being potentially involved. Among these, Nox2 is expressed in multiple cell types, including endothelial cells, fibroblasts, immune cells, and microglia. Blood pressure (BP) is regulated at the central nervous system, renal, and vascular levels, but the cell-specific role of Nox2 in BP regulation is unknown.

Sabine Kossmann

Center for Thrombosis and Hemostasis Mainz,
Center for Cardiology

University Medical Center Mainz

Visualizing Leukocyte Rolling and Adhesion in Angiotensin II-Infused Mice: Techniques and Pitfalls

Sabine Kossmann

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University Medical Center Mainz

Visualizing Leukocyte Rolling and Adhesion in Angiotensin II-Infused Mice: Techniques and Pitfalls

Center for Thrombosis and Hemostasis Mainz,
Center for Cardiology