Interleukin-10 fails to modulate low shear stress-induced neointimal hyperplasia

Treg cells in atherosclerosis

Atherosclerosis involves both innate and adaptive immunity. Here, we provide an overview of the role of regulatory T (Treg) cells in atherosclerotic diseases. Treg cells and their inhibitory cytokines, IL-10 and TGF-β, have been identified in atherosclerotic lesions and to inhibit progression through lipoprotein metabolism modulation. Treg cells have also been found to convert to T follicular helper (Tfh) cells and promote atherosclerosis progression. Treg cell involvement in different stages of atherosclerotic progression and Treg cell-mediated modulation of plaque development occurs via inflammation suppression and atheroma formation has been focused. Moreover, existing knowledge suggests that Treg cells are likely involved in the pathology of other specific circumstances including in-stent restenosis, neointimal hyperplasia, vessel graft failure, and ischemic arterial injury; however, there remain gaps regarding their specific contribution. Hence, advancements in the knowledge regarding Treg cells in diverse aspects of atherosclerosis offer translational significance for the management of atherosclerosis and associated diseases.

IL-19 reduces ligation-mediated neointimal hyperplasia by reducing vascular smooth muscle cell activation

We tested the hypothesis that IL-19, a putative member of the type 2 helper T-cell family of anti-inflammatory interleukins, can attenuate intimal hyperplasia and modulate the vascular smooth muscle cell (VSMC) response to injury. Ligated carotid artery of IL-19 knockout (KO) mice demonstrated a significantly higher neointima/intima ratio compared with wild-type (WT) mice (P = 0.04). More important, the increased neointima/intima ratio in the KO could be reversed by injection of 10 ng/g per day recombinant IL-19 into the KO mouse (P = 0.04). VSMCs explanted from IL-19 KO mice proliferated significantly more rapidly than WT. This could be inhibited by addition of IL-19 to KO VSMCs (P = 0.04 and P < 0.01). IL-19 KO VSMCs migrated more rapidly compared with WT (P < 0.01). Interestingly, there was no type 1 helper T-cell polarization in the KO mouse, but there was significantly greater leukocyte infiltrate in the ligated artery in these mice compared with WT. IL-19 KO VSMCs expressed significantly greater levels of inflammatory mRNA, including IL-1β, tumor necrosis factor α, and monocyte chemoattractant protein-1 in response to tumor necrosis factor α stimulation (P < 0.01 for all). KO VSMCs expressed greater adhesion molecule expression and adherence to monocytes. Together, these data indicate that IL-19 is a previously unrecognized counterregulatory factor for VSMCs, and its expression is an important protective mechanism in regulation of vascular restenosis.

Animal, in vitro, and ex vivo models of flow-dependent atherosclerosis: role of oxidative stress

Atherosclerosis is an inflammatory disease preferentially occurring in curved or branched arterial regions, whereas straight parts of the arteries are protected, suggesting a close relationship between flow and atherosclerosis. However, evidence directly linking disturbed flow to atherogenesis is just emerging, thanks to the recent development of suitable animal models. In this article, we review the status of various animal, in vitro, and ex vivo models that have been used to study flow-dependent vascular biology and atherosclerosis. For animal models, naturally flow-disturbed regions such as branched or curved arterial regions as well as surgically created models, including arterio-venous fistulas, vascular grafts, perivascular cuffs, and complete, incomplete, or partial ligation of arteries, are used. Although in vivo models provide the environment needed to mimic the complex pathophysiological processes, in vitro models provide simple conditions that allow the study of isolated factors. Typical in vitro models use cultured endothelial cells exposed to various flow conditions, using devices such as cone-and-plate and parallel-plate chambers. Ex vivo models using isolated vessels have been used to bridge the gap between complex in vivo models and simple in vitro systems. Here, we review these flow models in the context of the role of oxidative stress in flow-dependent inflammation, a critical proatherogenic step, and atherosclerosis.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Newly developed angiotensin II-infused experimental models in vascular biology

Angiotensin II is a major vasoactive peptide in the renin-angiotensin system (RAS). In vitro evidence demonstrates that this peptide can modulate the function of various adhesion molecules, chemokines, cytokines and growth factors, and ultimately contributes to cell proliferation, hypertrophy and inflammation. Moreover, in vivo studies further support that angiotensin II induces several vascular alterations including sustained elevations of blood pressure, enhanced inflammatory response, increased medial thickness of the aortas, and formation of aortic dissection and aneurysms. Thus, it has been a long time that angiotensin II-induced hypertension, atherosclerosis and abdominal aortic aneurysms emerge as important experimental models with respect to vascular biology. Applications of these models to investigate the vascular diseases have dramatically improved our understanding in the pathogenesis of these diseases. However, the pathophysiology of angiotensin II in vivo remains to be determined in many other vascular diseases where angiotensin II has been implicated as the detrimental factor, at least in part due to the limit availability of animal models. Recently some new exciting experimental models based on angiotensin II infusion have been reported to replicate the human diseases, such as postmenopausal hypertension, preeclampsia, vascular remodeling, vascular aging and neovascularization. In this review, we will focus on the rationales and anticipated applications of these newly developed models, with special emphasis placed on those relevant to the vascular biology. We will also discuss the limitations of the method of chronic angiotensin II infusion and additional approaches to overcome these limitations. These experimental models will provide great opportunity for us to investigate the molecular mechanisms of angiotensin II and evaluate therapeutic approaches, particularly to finely tune the potential role of RAS activation in various vascular events using genetically engineered mice.

TNF-alpha and shear stress-induced large artery adaptations

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) up-regulation has been associated with both low and high shear-induced arterial remodeling. To address this apparent paradox and to define the biology of TNF-alpha signaling in large arteries, we tested the hypotheses that differential temporal expression of TNF-alpha drives shear-regulated arterial remodeling.

MATERIALS AND METHODS

Both low- and high-shear environments in the same rabbit were surgically created for common carotid arteries. Common carotid arteries (n = 60 total) were harvested after d0, d1, d3, d7, and d14 and analyses included morphology, TNF-alpha, and IL-10 mRNA quantitation. In separate experiments, animals received pegylated soluble TNF-alpha Type 1 receptor (PEG sTNF-RI) or vehicle via either short- or long-term dosing to define the effect of TNF-alpha blockade.

RESULTS

The model yielded a 14-fold shear differential (P < 0.001) with medial thickening under low shear (P = 0.025), and evidence of outward remodeling with high shear (P = 0.007). Low shear immediately up-regulated TNF-alpha expression approximately 50 fold (P < 0.001) at d1. Conversely, high shear-induced delayed and sustained TNF-alpha expression (22-fold at d7, P = 0.012; 23-fold at d14, P = 0.007). Both low and high shear gradually induced IL-10 expression (P = 0.002 and P = 0.004, respectively). Neither short-term (5-day) nor long-term (14-day) blockage of TNF-alpha signaling resulted in treatment-induced changes in the remodeling of low- or high-shear arteries.

CONCLUSIONS

Shear stress differentially and temporally regulates TNF-alpha expression in remodeling large arteries. However, TNF-alpha blockage did not substantially impact the final shear-induced morphology, suggesting that large arteries can remodel in response to flow perturbations independent of TNF-alpha signaling.

Interleukin-10 attenuates the response to vascular injury

BACKGROUND

The inflammatory response to vascular injury is characterized by expression of cytokines, growth factors, and chemokines that conspire to promote vessel remodeling and intimal hyperplasia (IH). Interleukin-10 (IL-10) is a multifunctional cytokine that has several anti-inflammatory properties in vitro. Few studies have evaluated the effects of IL-10 in experimental atherosclerosis. The purpose of the present study was to determine the influence of IL-10 on vascular inflammation and IH following mechanical injury.

METHODS

Wire carotid injury was performed in wild-type (WT) mice with and without IL-10 treatment. Immunohistochemistry, PCR, and ELISA assays were used to examine vessel production of basic fibroblast growth factor (bFGF), monocyte chemotactic protein-1 (MCP-1), and nuclear factor kappa B (NFkappaB). Vessels were morphometrically analyzed for IH.

RESULTS

Carotid injury induced early expression of MCP-1 and bFGF that was abrogated in mice treated with IL-10. Similarly, injury-induced expression of NFkappaB message and protein was attenuated in mice receiving exogenous IL-10. Compared to untreated mice, IL-10 markedly decreased levels of IH. Interestingly, carotid injury in IL-10-deficient mice resulted in an augmented IH response compared to injured WT mice.

CONCLUSIONS

In an in vivo model of direct vascular injury, IL-10 decreased expression of the pro-inflammatory transcription factor, NFkappaB, and the mitogenic chemokine and growth factor, MCP-1 and bFGF, respectively. These observations were associated with IL-10-induced attenuation of IH. Furthermore, endogenous IL-10 appeared to suppress the injury response. In conclusion, exogenously delivered IL-10 may represent a clinically relevant anti-inflammatory strategy for post-injury intimal hyperplasia.

Impact of IL-1β on flow-induced outward arterial remodeling

BACKGROUND

Flow reduction upregulates arterial wall interleukin 1beta (IL-1beta), and IL-1beta independently modulates intimal hyperplasia under low flow conditions. We hypothesized that IL-1beta expression is also augmented under high flow, and outward remodeling occurs by way of IL-1beta-dependent mechanisms.

METHODS

Carotid artery (CA) flow was surgically augmented in rabbits (n = 20). CAs were harvested at 1, 3, 7, and 14 days, and assayed via quantitative reverse transcriptase-polymerase chain reaction. IL-1 receptor I null mice (KO) and wild-type controls underwent unilateral CA ligation and harvest 4 weeks later to assess the impact of increased flow on the contralateral CA (n = 82).

RESULTS

The rabbit model led to an immediate 36% increase in contralateral flow (P = .01) with an 80% increase at 14 days (P = .016) with subsequent positive remodeling. High flow induced IL-1beta messenger RNA expression (114-fold at 1 day, P < .05), with levels remaining elevated through 14 days (61-fold, P < .05). In murine experiments, CA ligation resulted in a 44% increase in contralateral flow. Wild-type and KO animals responded with equivalent 83% and 78% increases in luminal area (P = .87).

CONCLUSIONS

Positive and negative perturbations of arterial blood flow induce IL-1beta in a time-dependent fashion. However, as opposed to intimal hyperplasia after flow reduction, positive arterial remodeling in response to increased flow occurs via IL-1beta independent mechanisms.

Improved analysis of the vascular response to arterial ligation using a multivariate approach

Ligation of the murine common carotid artery induces a reproducible remodeling response. The contribution of individual genes can be determined by comparison of the phenotypes of genetically modified mice. Although studies have shown the response to carotid artery ligation is influenced by many factors, individual analyses typically only consider a single factor, the presence of a gene of interest. Because of this limitation, measurements of the response to ligation show large variation, making the determination of significant difference between test groups difficult. In this study, we examine the hypothesis that the variation in the response to ligation is due to non-genetic factors in addition to genetic factors. Distance from the ligature, a variable common to all arterial ligation experiments, is an important source of variation and a significant predictor of the remodeling response. We find that the use of statistical regression is an improved analysis technique, as it allows the simultaneous consideration of multiple variables. We demonstrate this by showing improved sensitivity and novel findings in the analysis of the remodeling response in mice genetically mutant for the osteopontin gene. We conclude regression analysis provides a simple way to improve both comparative power and description of vascular remodeling.

Flow-Induced Vascular Remodeling in the Mouse

Objective— Vascular remodeling of the carotid artery with intima-media thickness (IMT) is an important predictive factor for human cardiovascular disease. We characterized a mouse model of vascular remodeling.

Methods and Results— The left external and internal carotid branches were ligated so that left carotid blood flow was reduced to flow via the occipital artery. In response to partial ligation of the left carotid artery (LCA), blood flow significantly decreased (−90%) in the LCA and increased (+70%) in the right carotid artery (RCA). Morphometry showed that both RCA and LCA underwent outward remodeling that was maximal at one week. Remodeling was greater in the RCA with predominantly increased lumen and very little increase in media or adventitia. In the LCA there was a dramatic increase in media with adventitia growth and intima formation. Correlation analysis indicated that the outward remodeling was more likely due to primary changes in the vessel wall rather than to changes in the lumen, such as shear stress. Mechanistic studies suggested roles for macrophage infiltration, upregulation of matrix metalloproteinase (MMP)-9, extracellular matrix reorganization, and vascular smooth muscle cell proliferation in LCA remodeling.

Conclusions— The mouse model described here may be useful to define genetic determinants of IMT and identify new targets for therapy based on vascular remodeling.

Cellular IL-10 is more effective than viral IL-10 in decreasing venous thrombosis

BACKGROUND

Systemic administration of cellular interleukin-10 (cIL-10) and gene transfection of viral interleukin-10 (vIL-10) at thrombus induction decreases vein wall inflammation. Only cIL-10, despite sharing an 84% amino acid sequence homology with vIL-10, decreases thrombosis through mechanisms yet to be determined.

METHODS

C57BL/6 mice (Mus musculus, n99) were studied. Inferior vena caval thrombosis was created by inferior vena caval ligation and the animals were sacrificed and evaluated at days 2 and 6 after ligation. At thrombus induction groups received intravenous 0.25 microg of cIL-10, 0.25 microg of vIL-10, or saline (untreated controls). Evaluations included thrombus mass and vein wall leukocyte counts, protein levels, and reverse-transcription polymerase chain reaction mRNA levels of P- and E-selectin, monocyte chemotactic protein-1, and IL-10. Groups were compared by analysis of variance and t tests.

RESULTS

Less thrombus was noted at both days 2 and 6 in animals treated with cIL-10. At day 2 only, vein wall leukocyte counts revealed a significant decrease in neutrophils in cIL-10 animals versus controls, with no significant differences for vIL-10 animals. In cIL-10-treated animals, P-selectin protein levels were decreased at day 6, along with a decreased thrombus mass, without significant differences in E-selectin, monocyte chemotactic protein-1, or IL-10 protein levels. vIL-10 treated animals showed increased E-selectin mRNA and thrombus mass versus controls on day 6.

CONCLUSIONS

cIL-10 is more antithrombotic/anti-inflammatory than vIL-10. This may be the result of cIL-10 decreasing P-selectin protein expression and vIL-10 increasing E-selectin mRNA levels.