Inhibition of atherogenesis in LDLR knockout mice by systemic delivery of adeno-associated virus type 2-hIL-10

Mechanisms and consequences of efferocytosis in advanced atherosclerosis

Throughout atherosclerotic lesion development, intimal macrophages undergo apoptosis, a form of death that usually prevents cellular necrosis. In advanced atherosclerotic lesions, however, these apoptotic macrophages become secondarily necrotic and coalesce over time into a key feature of vulnerable plaques, the necrotic core. This event is critically important, as necrotic core formation in these advanced atheromata is thought to promote plaque disruption and ultimately, acute atherothrombotic vascular disease. Increasing evidence suggests that the mechanism behind postapoptotic macrophage necrosis in advanced atherosclerosis is defective phagocytic clearance or "efferocytosis" of the apoptotic cells. Thus, understanding the cellular and molecular mechanisms of efferocytosis in atherosclerosis and why efferocytosis becomes defective in advanced lesions is an important goal. Molecular-genetic causation studies in mouse models of advanced atherosclerosis have provided evidence that several molecules known to be involved in efferocytosis, including TG2, MFG-E8, complement C1q, Mertk, lysoPC, and Fas, play important roles in the clearance of apoptotic cells in advanced plaques. These and future insights into the molecular mechanisms of defective efferocytosis in advanced atheromata may open the way for novel therapeutic strategies for atherothrombotic vascular disease, the leading cause of death in the industrialized world.

Cervical cancer isolate PT3, super-permissive for adeno-associated virus replication, over-expresses DNA polymerase delta, PCNA, RFC and RPA

BACKGROUND

Adeno-associated virus (AAV) type 2 is an important virus due to its use as a safe and effective human gene therapy vector and its negative association with certain malignancies. AAV, a dependo-parvovirus, autonomously replicates in stratified squamous epithelium. Such tissue occurs in the nasopharynx and anogenitals, from which AAV has been clinically isolated. Related autonomous parvoviruses also demonstrate cell tropism and preferentially replicate in oncogenically transformed cells. Combining these two attributes of parvovirus tropism, squamous and malignant, we assayed if AAV might replicate in squamous cervical carcinoma cell isolates.

RESULTS

Three primary isolates (PT1-3) and two established cervical cancer cell lines were compared to normal keratinocytes (NK) for their ability to replicate AAV. One isolate, PT3, allowed for high levels of AAV DNA replication and virion production compared to others. In research by others, four cellular components are known required for in vitro AAV DNA replication: replication protein A (RPA), replication factor C (RFC), proliferating cell nuclear antigen (PCNA), and DNA polymerase delta (POLD1). Thus, we examined PT3 cells for expression of these components by DNA microarray and real-time quantitative PCR. All four components were over-expressed in PT3 over two representative low-permissive cell isolates (NK and PT1). However, this super-permissiveness did not result in PT3 cell death by AAV infection.

CONCLUSION

These data, for the first time, provide evidence that these four cellular components are likely important for AAV in vivo DNA replication as well as in vitro. These data also suggest that PT3 will be a useful reagent for investigating the AAV-permissive transcriptome and AAV anti-cancer effect.

Human tribbles homologue 2 is expressed in unstable regions of carotid plaques and regulates macrophage IL-10 in vitro

Mammalian orthologues of the Drosophila tribbles protein (Trb1, Trb2 and Trb3) are a recently described family of signalling molecules that regulate gene expression by modulation of protein kinase signalling pathways. In the present study, a screen for mRNA species specifically regulated in vulnerable regions of human atherosclerotic plaque demonstrated the up-regulation of both Trb1 and Trb2, the latter by more than 8-fold. In vitro experiments in primary human monocyte-derived macrophages showed that Trb2 expression was up-regulated by treatment with oxidized LDL (low-density lipoprotein), and that expression of recombinant Trb2 specifically reduced macrophage levels of IL-10 (interleukin-10) mRNA. Our results thus identify Trb2 as a highly regulated gene in vulnerable atherosclerotic lesions, and demonstrate inhibition of macrophage IL-10 biosynthesis as a potential pro-inflammatory consequence of high Trb2 expression, which may contribute to plaque instability.

Antigen-induced immunomodulation in the pathogenesis of atherosclerosis

Atherosclerosis is a chronic inflammatory disorder characterised by the accumulation of monocytes/macrophages, smooth muscle cells, and lymphocytes within the arterial wall in response to the release of proinflammatory molecules. Such accumulation results in the formation of the atherosclerotic plaque, which would eventually evolve to complications such as total artery occlusion, rupture, calcification, or aneurysm. Although the molecular mechanism responsible for the development of atherosclerosis is not completely understood, it is clear that the immune system plays a key role in the development of the atherosclerotic plaque and in its complications. There are multiple antigenic stimuli that have been associated with the pathogenesis of atherosclerosis. Most of these stimuli come from modified self-molecules such as oxidised low-density lipoproteins (oxLDLs), beta2glycoprotein1 (β2GP1), lipoprotein a (LP(a)), heat shock proteins (HSPs), and protein components of the extracellular matrix such as collagen and fibrinogen in the form of advanced glycation-end (AGE) products. In addition, several foreign antigens including bacteria such as Porphyromonas gingivalis and Chlamydia pneumoniae and viruses such as enterovirus and cytomegalovirus have been associated with atherosclerosis as potentially causative or bystander participants, adding another level of complexity to the analysis of the pathophysiology of atherosclerosis. The present review summarises the most important scientific findings published within the last two decades on the importance of antigens, antigen stimulation, and adaptive immune responses in the development of atherosclerotic plaques.

Cytokines and atherosclerosis: a comprehensive review of studies in mice

In the past few years, inflammation has emerged as a major driving force of atherosclerotic lesion development. It is now well-established that from early lesion to vulnerable plaque formation, numerous cellular and molecular inflammatory components participate in the disease process. The most prominent cells that invade in evolving lesions are monocyte-derived macrophages and T-lymphocytes. Both cell types produce a wide array of soluble inflammatory mediators (cytokines, chemokines) which are critically important in the initiation and perpetuation of the disease. This review summarizes the currently available information from mouse studies on the contribution of a specified group of cytokines expressed in atherosclerotic lesions, viz. interleukins (IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IL-12, IL-18, IL-20) and macrophage-associated cytokines [tumour necrosis factor-α (TNF-α); macrophage migration inhibitory factor (MIF); interferon-γ (IFN-γ); colony stimulating factors G-CSF,-M-CSF,-GM-CSF) to atherogenesis. Emphasis is put on the consistency of the effects of these cytokines, i.e. inasmuch an effect depends on the experimental approach applied (overexpression/deletion, strain, gender, dietary conditions, and disease stage). An important outcome of this survey is (i) that only for a few cytokines there is sufficient consistent data allowing classifying them as typically proatherogenic (IL-1, IL-12, IL-18, MIF, IFN-γ, TNF-α, and M-CSF) or antiatherogenic (IL-10) and (ii) that some cytokines (IL-4, IL-6 and GM-CSF) can exert pro- or anti-atherogenic effects depending on the experimental conditions. This knowledge can be used for improved early detection, prevention and treatment of atherosclerosis.

Over-expression of angiotensin II type 2 receptor (agtr2) reduces atherogenesis and modulates LOX-1, endothelial nitric oxide synthase and heme-oxygenase-1 expression

Atherogenesis is associated with inflammation and oxidative stress. Activation of renin-angiotensin system with generation of angiotensin II and type 1 receptor (AT1R) stimulation has been amply reported in atherosclerosis. Since angiotensin II type 2 receptor (AT2R) activity is purported to oppose the effects of AT1R, we hypothesized that AT2R (agtr2) over-expression would inhibit atherogenesis. We prepared recombinant adeno-associated virus type-2 (AAV) carrying AT2R cDNA (AAV/AT2R), and homozygous LDLR-deficient (KO) mice were given AAV/AT2R, AAV/Neo or saline. All mice were placed on a high cholesterol diet. After 18 weeks, AT2R was found to be over-expressed systemically in AAV/AT2R-treated mice. Atherogenesis in aorta was reduced in the AAV/AT2R group by approximately 50% compared to other LDLR KO mice groups. Expression of NADPH oxidase, nitrotyrosine and NF-kappaB was increased in aortic tissues of the LDLR KO mice given saline or AAV/Neo, but not in mice with AT2R upregulation. Expression of endothelial nitric oxide synthase (eNOS) and heme-oxygenase-1 (HO-1) was decreased and that of the lectin-like oxidized-LDL receptor (LOX-1) increased in the LDLR KO mice, but not in the mice with AT2R over-expression. Further, Akt-1 phosphorylation was reduced in the LDLR KO mice, but not in the mice with AT2R over-expression. Thus, AT2R upregulation can reduce atherogenesis, possibly by modulating oxidative stress and the pro-inflammatory cascade, mediated via Akt-1. Over-expression of AT2R may be an important therapeutic approach in atherosclerosis.

Anti-inflammatory drugs and atherosclerosis

PURPOSE OF REVIEW

Inflammation contributes to the formation and progression of atherosclerosis and the therapeutic potential of some anti-inflammatory drugs has been evaluated for possible antiatherosclerotic effects. This review will briefly describe the mechanisms underlying the inflammation-atherosclerosis connection, the effect of various anti-inflammatory therapies on atherosclerotic disease and a sampling of the potential targets and agents under evaluation.

RECENT FINDINGS

Some agents with anti-inflammatory properties appear to have beneficial effects on atherosclerosis or subsequent risk for cardiovascular events, while others have been disappointing. The anti-inflammatory actions of statins have been linked retrospectively with their favorable effects on atherosclerosis progression and clinical outcomes. The cardiovascular safety of COX-2 inhibitors is being assessed prospectively in patients with atherosclerosis. Potential new therapeutic agents targeting other inflammatory mechanisms and oxidative stress are being evaluated in animal models and clinical trials.

SUMMARY

Due to the contributory inflammatory pathways in atherosclerosis, the properties of existing and novel anti-inflammatory agents are being carefully and actively evaluated in cardiovascular disease. Advances in our understanding of both atherosclerosis and the inflammatory contributors may play an important role in future strategies to decrease the incidence of atherosclerotic cardiovascular disease.

Blockade of hypoxia-reoxygenation-mediated collagen type I expression and MMP activity by overexpression of TGF-β1delivered by AAV in mouse cardiomyocytes

Transforming growth factor (TGF)-β1is one of the most pleiotropic and multifunctional peptides known. While the cardioprotective effect of TGF-β1during ischemia is well known, the specific role of TGF-β1in altering the cardiac remodeling process remains unclear. This study was designed to examine the regulation of hypoxia-reoxygenation-mediated collagen type I expression and activity of matrix metalloproteinases (MMPs) by overexpression of TGF-β1in cultured HL-1 mouse cardiomyocytes. TGF-β1was overexpressed in cardiomyocytes by transfection with adeno-associated virus (AAV)/TGF-β1Latentor with AAV/TGF-β1ACT(active TGF-β1). Twenty-four hours of hypoxia followed by 3 h of reoxygenation (H-R) markedly enhanced (pro)collagen type I expression and activity of MMPs concomitant with an increase in reactive oxygen species (ROS) release and LOX-1 expression. Overexpression of TGF-β1reduced these alterations induced by H-R. TGF-β1overexpression also blocked H-R-mediated p38 and p44/42 MAPK activation. Transfection with AAV/TGF-β1ACTwas superior to that with AAV/TGF-β1Latent. These data for the first time demonstrate that H-R induces signals for cardiac remodeling in cardiomyocytes and TGF-β1can modulate, possibly via antioxidant mechanism, these signals. These findings contribute to further understanding of the role of TGF-β1in the cardiac remodeling process.

Deletion of LOX-1 reduces atherogenesis in LDLR knockout mice fed high cholesterol diet

Atherosclerosis is associated with oxidative stress and inflammation, and upregulation of LOX-1, an endothelial receptor for oxidized LDL (oxLDL). Here, we describe generation of LOX-1 knockout (KO) mice in which binding of oxLDL to aortic endothelium was reduced and endothelium-dependent vasorelaxation preserved after treatment with oxLDL (P<0.01 versus wild-type mice). To address whether endothelial functional preservation might lead to reduction in atherogenesis, we crossed LOX-1 KO mice with LDLR KO mice and fed these mice 4% cholesterol/10% cocoa butter diet for 18 weeks. Atherosclerosis was found to cover 61+/-2% of aorta in the LDLR KO mice, but only 36+/-3% of aorta in the double KO mice. Luminal obstruction and intima thickness were significantly reduced in the double KO mice (versus LDLR KO mice). Expression of redox-sensitive NF-kappaB and the inflammatory marker CD68 in LDLR KO mice was increased (P<0.01 versus wild-type mice), but not in the double KO mice. On the other hand, antiinflammatory cytokine IL-10 expression and superoxide dismutase activity were low in the LDLR KO mice (P<0.01 versus wild-type mice), but not in the double KO mice. Endothelial nitric oxide synthase expression was also preserved in the double KO mice. The proinflammatory signal MAPK P38 was activated in the LDLR KO mice, and LOX-1 deletion reduced this signal. In conclusion, LOX-1 deletion sustains endothelial function leading to a reduction in atherogenesis in association with reduction in proinflammatory and prooxidant signals.

Functional Replacement of Murine CXCR2 by Its Human Homologue in the Development of Atherosclerosis in LDLR Knockout Mice

The CXC chemokine receptor CXCR2 has been implicated in the pathogenesis of several chronic diseases including atherosclerosis. To enable animal studies towards understanding the role of human CXCR2 (hCXCR2) in disease development, we previously generated hCXCR2 knockin (hCXCR2(+/+)) mice. We have demonstrated that the phenotype and the acute immune response of the hCXCR2(+/+) mice was identical to that of wild-type mice, indicating that hCXCR2 indeed takes over the function of endogenous mouse CXCR2 (mCXCR2). In the present paper, we extend these findings by studying whether hCXCR2 functionally replaces the role of mCXCR2 in a chronic disease model for atherosclerosis. We first defined which of two well-described atherosclerosis models (ApoE(-/-) or LDLR(-/-) mice) is most suited for this purpose. When expression of mCXCR2 and that of its ligands in atherosclerotic lesions were compared in these mice, increased expression levels were observed only in LDLR(-/-) mice. Further, cultured atherosclerotic aortas from LDLR(-/-) mice did secrete significantly higher levels of CXCR2 ligands compared to aortas from healthy controls. Since these results support the role of CXCR2 in the atherogenesis in the LDLR(-/-) mice, double mutant hCXCR2(+/+)/LDLR(-/-) mice were generated and diet-induced atherosclerosis in these mice was compared to that in LDLR(-/-) mice. Upon an atherogenic diet, the hCXCR2(+/+)/LDLR(-/-) mice developed plaque lesions in a similar manner to those in LDLR(-/-) mice, indicating successful functional replacement of mCXCR2 by hCXCR2 in this disease model. We conclude that hCXCR2(+/+)/LDLR(-/-) mice present an attractive model to study the role of hCXCR2 in atherosclerosis development and for future testing of novel pharmaceuticals designed to antagonize hCXCR2.

Suppression of atherogenesis by delivery of TGFbeta1ACT using adeno-associated virus type 2 in LDLR knockout mice

TGFbeta(1) deficiency has been attributed to the development of atherosclerosis. There is, however, little direct evidence for this concept. To examine this hypothesis, low-density lipoprotein receptor knockout (LDLR(-/-)) mice were injected via tail vein with recombinant adeno-associated virus type 2 (rAAV) carrying a bioactive TGFbeta(1) mutant (AAV/TGFbeta1ACT, n=10) or granulocyte-macrophage-colony stimulating factor (AAV/GM-CSF, n=10, a negative control) or saline (n=9, control), and then put on a high cholesterol diet. At 18 weeks, blood lipids were found to be similarly elevated in all LDLR(-/-) mice. TGFbeta1ACT and GM-CSF (DNA, mRNA, and protein) were highly expressed in the tissues of mice given TGFbeta1ACT or AAV/GM-CSF, respectively, showing sustained transfection following gene delivery by the systemic route. Saline-treated and AAV/GM-CSF-treated LDLR(-/-) mice showed extensive areas of atherosclerotic lesion formation. There was evidence of intense oxidative stress (nitrotyrosine staining), inflammation (CD68 staining), and expression of adhesion molecules and the ox-LDL receptor LOX-1 (gene array analysis) in the atherosclerotic tissues. Importantly, atherosclerotic lesion formation was markedly inhibited in the LDLR(-/-) mice given AAV/TGFbeta1ACT. Expression of adhesion molecules and LOX-1, oxidative stress, and inflammatory response all were inhibited in the mice given AAV/TGFbeta1ACT (P<0.05 vs. saline-treated or GM-CSF-treated LDLR(-/-) mice). These data for the first time demonstrate that systemic delivery of TGFbeta1ACT gene via AAV can inhibit formation of atherosclerotic lesions, possibly via anti-inflammatory and anti-oxidant mechanisms. These findings suggest a novel view of TGFbeta(1) in atherogenesis and a potential new gene therapy for treatment of atherosclerosis.