Oxidized low-density lipoprotein (oxLDL) has been reported as an inhibitor of hepatitis C virus (HCV) cell entry, making it the only known component of human lipid metabolism with an antiviral effect on HCV. However, several questions remain open, including its effect on full-length cell-culture-grown HCV (HCVcc) of different genotypes or on other steps of the viral replication cycle, its mechanism of action, and whether endogenous oxLDL shares the anti-HCV properties of in vitro-generated oxLDL. We combined molecular virology tools with oxLDL serum measurements in different patient cohorts to address these questions. We found that oxLDL inhibits HCVcc at least as potently as HCV pseudoparticles. There was moderate variation between genotypes, with genotype 4 appearing the most oxLDL sensitive. Intracellular RNA replication and assembly and release of new particles were unaffected. HCV particles entering target cells lost oxLDL sensitivity with time kinetics parallel to anti-SR-BI (scavenger receptor class B type I), but significantly earlier than anti-CD81, suggesting that oxLDL acts by perturbing interaction between HCV and SR-BI. Finally, in chronically HCV-infected individuals, endogenous serum oxLDL levels did not correlate with viral load, but in HCV-negative sera, high endogenous oxLDL had a negative effect on HCV infectivity in vitro. Conclusion: oxLDL is a potent pangenotype HCV entry inhibitor that maintains its activity in the context of human serum and targets an early step of HCV entry.
Transsignaling of interleukin (IL)-6 is a central pathway in the pathogenesis of disorders associated with chronic inflammation, such as Crohn disease, rheumatoid arthritis, and inflammatory colon cancer. Notably, IL-6 also represents an independent risk factor for coronary artery disease (CAD) in humans and is crucially involved in vascular inflammatory processes.
The CC chemokine receptor 7 (CCR7) and its ligands CCL19 and CCL21 essentially contribute to both immunity and tolerance by directing T cells and antigen-presenting dendritic cells (DCs) to and within lymph organs. In the pathogenesis of atherosclerosis, the accumulation of cholesterol in the subendothelial space of the vessel wall represents the initial step of plaque development in which DCs acquire and process low-density lipoprotein cholesterol as antigen in the vessel wall and then migrate to draining lymph nodes and present this antigen to naive T cells. Deletion of CCR7 receptor in murine atherosclerosis not only results in a reduced atherosclerotic plaque content but also leads to a disturbed entry and exit of T cells within the inflamed vessel wall. These observations are consistent with the notion that CCR7-dependent T cell priming in secondary lymphoid organs and CCR7-dependent recirculation of T cells between secondary lymphoid organs and inflamed tissue is pivotal for atherosclerotic plaque development and may represent an interesting target for innovative immune-modulatory therapy.
Elevated levels of acute phase proteins (APP) are often found in patients with cardiovascular diseases. In a previous study, we demonstrated the importance of the IL-6-gp130 axis -as a key regulator of inflammatory acute phase signaling in hepatocytes-for the development of atherosclerosis.
Atherosclerosis is a systemic inflammatory disease characterized by the formation of atherosclerotic plaques. Both innate immunity and adaptive immunity contribute to atherogenesis, but the mode of interaction is poorly understood. Chemokine receptor 7 (CCR7) is critically involved in the transition from innate to adaptive immune activation by coordinating the migration to and positioning of antigen-presenting dendritic cells and T cells in secondary lymphoid organs. More recently, it was shown that CCR7 is also responsible for T-cell migration into inflamed tissues and T-cell egress from these tissues via the afferent lymph. Thus, we investigated the influence of a systemic CCR7 deficiency on atherogenesis in atherosclerosis-prone low-density lipoprotein receptor (ldlr) knockout mice.
Inflammation and vascular remodeling are hallmarks of atherosclerosis, hypertension, and restenosis after angioplasty. Here we investigated the role of the hepatocyte gp130-dependent systemic acute phase response on vascular remodeling after carotid artery ligation. Mice with a hepatocyte-specific gp130 knockout on an apolipoprotein E(-/-) background (gp130-) were compared with control mice (gp130(flox)). Vascular remodeling was induced by permanent ligation of the left common carotid artery. This, in turn, activated the systemic acute phase reaction in gp130(flox) mice, as measured by serum amyloid A plasma levels, which was completely abrogated in gp130- mice (P<0.05). Morphometric analysis of the carotid artery revealed severe neointima formation and media thickening 28 days after ligation in gp130(flox) mice, which was suppressed in gp130- mice (P<0.01). Serial sections from gp130- carotid segments showed significantly less smooth muscle cell (SMC) proliferation and monocyte recruitment (P<0.01). To evaluate the impact of the gp130-dependent systemic acute phase response on SMCs, hepatocytes from gp130(flox) and gp130- mice were stimulated with interleukin 6. Interleukin 6-induced secretion of serum amyloid A was completely abolished in gp130- hepatocytes (P<0.01). Moreover, when stimulated with supernatants from gp130- hepatocytes, SMCs showed significantly less migration and proliferation compared with supernatants from gp130(flox) hepatocytes (P<0.01). Recombinant serum amyloid A induced SMC migration and proliferation (P<0.05) and serum amyloid A injection after carotid artery ligation restored vascular remodeling in gp130- mice (P<0.01). These results imply a critical role for the gp130-dependent systemic acute phase response for vascular inflammation and SMC migration, as well as proliferation, and, subsequently, for vascular remodeling.
The importance of inflammation as a driver of pathology is no longer confined to autoimmune and infectious diseases. In line with convincing experimental data as well as abundant clinical findings the current view of atherosclerosis points to inflammation as a critical regulator of atherosclerotic plaque formation and progression leading to the fatal clinical endpoints myocardial infarction, stroke or sudden cardiac death. The underlying mechanisms have been a matter of intense research during the last decades. In this regard, the interleukin-6 (IL-6) cytokines and their signalling events have been shown to contribute to both, atherosclerotic plaque development and plaque destabilisation via a variety of mechanisms. These involve the release of other pro-inflammatory cytokines, oxidation of lipoproteins by phospholipases, stimulation of acute phase protein secretion, the release of prothrombotic mediators, and the activation of matrix metalloproteinases. Moreover, the formation of reactive oxygen species generated by vascular enzyme systems may play a critical role in the regulation of IL-6 indicating a cross talk between vasoactive substances i.e. angiotensin II or adrenalin and pro-inflammatory cytokines such as IL-6. In this review we will summarise and discuss the underlying molecular and cellular mechanisms how IL-6 as an early and central regulator of inflammation contributes to atherosclerosis and how this knowledge can be integrated into the clinical context.
While the impact of inflammation as the substantial driving force of atherosclerosis has been investigated in detail throughout the years, the influence of negative regulators of pro-atherogenic pathways on plaque development has remained largely unknown. Suppressor of cytokine signaling (SOCS)-1 potently restricts transduction of various inflammatory signals and, thereby modulates T-cell development, macrophage activation and dendritic cell maturation. Its role in atherogenesis, however has not been elucidated so far.
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