Fc-gamma receptor cross-linking by immune complexes induces matrix metalloproteinase-1 in U937 cells via mitogen-activated protein kinase

Genetic variation of matrix metalloproteinase enzyme in HIV-associated neurocognitive disorder

Matrix metalloproteinases (MMPs) play a key role in several diseases such as rheumatoid arthritis, HIV-associated neurological diseases (HAND), multiple sclerosis, osteoporosis, stroke, Alzheimer's disease, certain viral infections of the central nervous system, cancer, and hepatitis C virus. MMPs have been explained with regards to extracellular matrix remodeling, which occurs throughout life and ranges from tissue morphogenesis to wound healing in various processes. MMP are inhibited by endogenous tissue inhibitors of metalloproteinases (TIMPs). Matrix metalloproteases act as an interface between host's attack by Tat protein of HIV-1 virus and extracellular matrix, which causes breaches in the endothelial barriers by degrading ECM. This process initiates the dissemination of virus in tissues which can lead to an increase HIV-1 infection. MMPs are diverse and are highly polymorphic in nature, hence associated with many diseases. The main objective of this review is to study the gene expression of MMPs in HIV-related diseases and whether TIMPs and MMPs could be related with disease progression, HIV vulnerability and HAND. In this review, a brief description on the classification, regulation of MMP and TIMP, the effect of different MMPs and TIMPs gene polymorphisms and its expression on HIV-associated diseases have been provided. Previous studies have shown that MMPs polymorphism (MMP-1, MMP-2 MMP3, and MMP9) plays an important role in HIV vulnerability, disease progression and HAND. Further research is required to explore their role in pathogenesis and therapeutic perspective.

Reduced Atherosclerosis in apoE-inhibitory FcγRIIb-Deficient Mice Is Associated With Increased Anti-Inflammatory Responses by T Cells and Macrophages

OBJECTIVE

Fcγ receptors (FcγRs) are classified as activating (FcγRI, III, and IV) and inhibitory (FcγRII) receptors. We have reported that deletion of activating FcγRs in apolipoprotein E (apoE) single knockout mice attenuated atherosclerosis. In this report, we investigated the hypothesis that deficiency of inhibitory FcγRIIb exacerbates atherosclerosis.

APPROACH AND RESULTS

ApoE-FcγRIIb double knockout mice, congenic to the C57BL/6 (apoE-FcγRIIbB6 (-/-)), were generated and atherosclerotic lesions were assessed. In contrary to our hypothesis, when compared with apoE single knockout mice, arterial lesions were significantly decreased in apoE-FcγRIIbB6 (-/-) male and female mice fed chow or high-fat diets. Chimeric mice generated by transplanting apoE-FcγRIIbB6 (-/-) marrow into apoE single knockout mice also developed reduced lesions. CD4(+) T cells from apoE-FcγRIIbB6 (-/-) mice produced higher levels of interleukin-10 and transforming growth factor-β than their apoE single knockout counterparts. As our findings conflict with a previous report using apoE-FcγRIIb129/B6 (-/-) mice on a mixed genetic background, we investigated whether strain differences contributed to the anti-inflammatory response. Macrophages from FcγRIIb129/B6 (-/-) mice on a mixed genetic background produced more interleukin-1β and MCP-1 (monocyte chemoattractant protein-1) in response to immune complexes, whereas congenic FcγRIIbB6 (-/-) mice generated more interleukin-10 and significantly less interleukin-1β. Interestingly, the expression of lupus-associated slam genes, located in proximity to fcgr2b in mouse chromosome 1, is upregulated only in mixed FcγRIIb129/B6 (-/-) mice.

CONCLUSIONS

Our findings demonstrate a detrimental role for FcγRIIb signaling in atherosclerosis and the contribution of anti-inflammatory cytokine responses in the attenuated lesions observed in apoE-FcγRIIbB6 (-/-) mice. As 129/sv genome-derived lupus-associated genes have been implicated in lupus phenotype in FcγRIIb129/B6 (-/-) mice, our findings suggest possible epistatic mechanism contributing to the decreased lesions.

Fcγ receptors and ligands and cardiovascular disease

Fcγ receptors (FcγRs) classically modulate intracellular signaling on binding of the Fc region of IgG in immune response cells. How FcγR and their ligands affect cardiovascular health and disease has been interrogated recently in both preclinical and clinical studies. The stimulation of activating FcγR in endothelial cells, vascular smooth muscle cells, and monocytes/macrophages causes a variety of cellular responses that may contribute to vascular disease pathogenesis. Stimulation of the lone inhibitory FγcR, FcγRIIB, also has adverse consequences in endothelial cells, antagonizing NO production and reparative mechanisms. In preclinical disease models, activating FcγRs promote atherosclerosis, whereas FcγRIIB is protective, and activating FcγRs also enhance thrombotic and nonthrombotic vascular occlusion. The FcγR ligand C-reactive protein (CRP) has undergone intense study. Although in rodents CRP does not affect atherosclerosis, it causes hypertension and insulin resistance and worsens myocardial infarction. Massive data have accumulated indicating an association between increases in circulating CRP and coronary heart disease in humans. However, Mendelian randomization studies reveal that CRP is not likely a disease mediator. CRP genetics and hypertension warrant further investigation. To date, studies of genetic variants of activating FcγRs are insufficient to implicate the receptors in coronary heart disease pathogenesis in humans. However, a link between FcγRIIB and human hypertension may be emerging. Further knowledge of the vascular biology of FcγR and their ligands will potentially enhance our understanding of cardiovascular disorders, particularly in patients whose greater predisposition for disease is not explained by traditional risk factors, such as individuals with autoimmune disorders.

Pathogenic role of modified LDL antibodies and immune complexes in atherosclerosis

There is strong evidence supporting a key role of the adaptive immune response in atherosclerosis, given that both activated Th cells producing predominantly interferon-γ and oxidized LDL (oxLDL) and the corresponding antibodies have been isolated from atheromatous plaques. Studies carried out using immune complexes (IC) prepared with human LDL and rabbit antibodies have demonstrated proatherogenic and pro-inflammatory properties, mostly dependent on the engagement of Fcγ receptors Ⅰ and Ⅱ in macrophages and macrophage-like cell lines. Following the development of a methodology for isolating modified LDL (mLDL) antibodies from serum and isolated IC, it was confirmed that antibodies reacting with oxLDL and advanced glycation end product-modified LDL are predominantly IgG of subtypes 1 and 3 and that mLDL IC prepared with human reagents possesses pro-inflammatory and proatherogenic properties. In previous studies, LDL separated from isolated IC has been analyzed for its modifications, and the reactivity of antibodies isolated from the same IC with different LDL modifications has been tested. Recently, we obtained strong evidence suggesting that the effects of mLDL IC on phagocytic cells are modulated by the composition of the mLDL. Clinical studies have shown that the level of mLDL in circulating IC is a strong predictor of cardiovascular disease (CVD) and, in diabetic patients, other significant complications, such as nephropathy and retinopathy. In conclusion, there is convincing ex vivo and clinical data supporting the hypothesis that, in humans, the humoral immune response to mLDL is pathogenic rather than protective.

Macrophage impairment produced by Fc receptor gamma deficiency plays a principal role in the development of lipoprotein glomerulopathy in concert with apoE abnormalities

BACKGROUND

To obtain a clear understanding of the pathogenesis of lipoprotein glomerulopathy (LPG), we studied the role of the deficiency of Fc receptor gamma chain (FcRγ) for the development of LPG in concert with apolipoprotein E (apoE) abnormalities.

METHODS

We generated apoE and FcRγ double-knockout (FcRγ/apoE-KO) mice, and subsequently introduced several kinds of human recombinant apoE genes. At 21 days after infection, the mice were sacrificed and histologically examined. Peritoneal macrophages were evaluated for their response to modified lipids.

RESULTS

In the FcRγ/apoE-KO mice, the human apoE3-injected mice showed the most drastic LPG-like changes, as well as prominent hypertriglyceridemia. Meanwhile, relative to the human apoE3-injected mice, the FcRγ/apoE-KO mice showed greater lipoprotein deposition and less macrophage infiltration into the mesangial area. Moreover, the peritoneal macrophages in the apoE/FcRγ-KO mice were impaired in lipid uptake and secretion of the cytokines monocyte chemotactic protein-1 and regulated upon activation, normal T-cell expressed and secreted, after the uptake of oxidized low-density lipoprotein.

CONCLUSIONS

These results suggest that the impairment of macrophage function resulting from FcRγ deficiency plays a principal role in the development of LPG in the presence of apoE abnormalities.

The role of Fcγ receptors in atherosclerosis

Atherosclerosis is widely considered to be an immune-mediated process. Fcγ receptors (Fcγ Rs) contribute to the regulation of a multitude of immune and inflammatory responses and are implicated in human atherosclerotic lesions. Major cell types involved in the pathogenesis of atherosclerosis express Fcγ Rs and their proatherogenic ligands such as immune complexes and C-reactive protein, which act to activate Fcγ R signaling pathways. This review summarizes recent significant progress addressing the multifaceted roles of Fcγ Rs in atherogenesis which comes from the studies of Fcγ R-deficient animal models, clinical investigations and in vitro molecular and cellular studies. These new findings help us appreciate the emerging role of Fcγ Rs in atherosclerosis, and suggest Fcγ Rs as a potential therapeutic target for atherosclerosis.

High concentrations of AGE-LDL and oxidized LDL in circulating immune complexes are associated with progression of retinopathy in type 1 diabetes

OBJECTIVE

To determine whether immunocomplexes (ICs) containing advanced glycation end product (AGE)-LDL (AGE-LDL) and oxidized LDL (oxLDL) contribute to the development of retinopathy over a 16-year period in subjects with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Levels of AGE-LDL and oxLDL in ICs were measured in 517 patients of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort. Retinopathy was assessed by stereoscopic fundus photography. Cox proportional hazards models were used to assess the effect of AGE-LDL-ICs and oxLDL-ICs on retinopathy progression.

RESULTS

In unadjusted models, higher baseline levels of AGE-LDL-ICs and oxLDL-ICs significantly predicted progression of diabetic retinopathy outcomes. After adjustment by study-design variables (treatment group, retinopathy cohort, duration of type 1 diabetes, and baseline albumin excretion rate [AER], hemoglobin A(1c) (HbA(1c)), and Early Treatment Diabetic Retinopathy Study [ETDRS] score), one SD increase in IC levels was associated with 47% (hazard ratio [HR] 1.47 [95% CI 1.19-1.81]; AGE-LDL-IC) and 45% (1.45 [1.17-1.80]; oxLDL-IC) increased risk of developing proliferative diabetic retinopathy (PDR) and 37% (1.37 [1.12-1.66]; to both ICs) increased risk of progressing to severe nonproliferative retinopathy. Analyses were stratified by retinopathy cohort because results differed between primary and secondary cohorts. For AGE-LDL-ICs, HR for progression to PDR was 2.38 (95% CI 1.30-4.34) in the primary cohort and attenuated in the secondary cohort (1.29 [1.03-1.62]). Similar results were observed for oxLDL-ICs.

CONCLUSIONS

Increased levels of AGE-LDL and oxLDL in ICs are associated with increased risk for progression to advanced retinopathy in patients with type 1 diabetes, indicating that the antibody response to modified LDL plays a significant role in retinopathy progression.

Monomeric C-reactive protein alters fibrin clot properties on endothelial cells

Elevated plasma levels of C-reactive protein (CRP) are independently associated with increased risk of atherothrombosis. Several lines of evidence suggest that CRP has prothrombogenic effects on injured vessel wall(s) by enhancing tissue factor (TF) expression. Abnormal fibrin formation is correlated with increased thrombotic risk. However, the impact of localized, cell surface-driven in situ tissue factor generation by CRP on clot dynamics and fibrin architecture has not previously been evaluated. We examined the impact of native CRP and modified or monomeric CRP (mCRP) on the fibrin formation and structure in Human Umbilical Vein Endothelial Cells (HUVECs). Fibrin formation and structure were examined using laser scanning confocal microscopy. Incubation with mCRP on the cell surface had faster fibrin polymerization by the analysis of turbidimetry. Confocal microscopy of fibrin clots showed a significantly increased density in the treatment of mCRP compared with native CRP and control in the proximal versus distal relationship to the cell surface. The increased expression and activity of TF on the cell surface was observed by addition of mCRP. Blockage of tissue factor and lipid rafts significantly reduced the density of fibrin network produced by mCRP-stimulated endothelial cells. mCRP changes clot dynamics and alters fibrin architecture by enhancing TF on the endothelial cell surface. These results support the concept that elevated CRP levels may induce fibrinolytic resistance and endothelial dysfunction by altering fibrin clot structure.

Oxidized LDL immune complexes stimulate collagen IV production in mesangial cells via Fc gamma receptors I and III

Diabetic nephropathy is characterized by progressive mesangial expansion. Although we have reported that circulating oxidized LDL-containing immune complexes (oxLDL-IC) are associated with abnormal levels of albuminuria, the underlying mechanisms have not been investigated. In this study, we have studied the effect of oxLDL-IC on collagen IV expression by mesangial cells. We found that oxLDL-IC markedly stimulated collagen IV expression in a concentration- and time-dependent fashion while oxLDL only had moderate effect. We also found that oxLDL-IC stimulated collagen IV expression by engaging Fc gamma receptor (FcγR) I and III, but not FcγRII, and that p38 MAPK, JNK and PKC pathways were involved in collagen IV expression. Furthermore, we found that oxLDL-IC stimulated FcγRI expression, suggesting a positive feedback mechanism involved in oxLDL-IC-stimulated collagen IV expression. Taken together, this study showed that oxLDL-IC stimulated collagen IV in mesangial cells via FcγRI and FcγRIII, and the expression of FcγRI was increased by oxLDL-IC.

The inhibitory FcγRIIb modulates the inflammatory response and influences atherosclerosis in male apoE(-/-) mice

BACKGROUND

Atherosclerosis is widely accepted as an inflammatory disease involving both innate and adaptive immunity. B cells and/or antibodies have previously been shown to play a protective role against atherosclerosis. Aside from their ability to bind to antigens, antibodies can influence inflammatory responses by interacting with various Fcγ receptors on the surface of antigen presenting cells. Although studies in mice have determined that stimulatory Fcγ receptors contribute to atherosclerosis, the role of the inhibitory Fcγ receptor IIb (FcγRIIb) has only recently been investigated.

METHODS AND RESULTS

To determine the importance of FcγRIIb in modulating the adaptive immune response to hyperlipidemia, we generated FcγRIIb-deficient mice on the apoE-deficient background (apoE/FcγRIIb(-/-)). We report that male apoE/FcγRIIb(-/-) mice develop exacerbated atherosclerosis that is independent of lipid levels, and is characterized by increased antibody titers to modified LDL and pro-inflammatory cytokines in the aorta.

CONCLUSIONS

These findings suggest that antibodies against atherosclerosis-associated antigens partially protect against atherosclerosis in male apoE(-/-) mice by conveying inhibitory signals through the FcγRIIb that downregulate pro-inflammatory signaling via other immune receptors. These data are the first to describe a significant in vivo effect for FcγRIIb in modulating the cytokine response in the aorta in male apoE(-/-) mice.

The Role of Immune Complexes in Atherogenesis

Atherosclerosis is now recognized as a chronic inflammatory disease and is characterized by features of inflammation at all stages of its development. It also appears to display elements of autoimmunity, and several autoantibodies including those directed against oxidized low-density lipoprotein (ox-LDL) and heat shock proteins (Hsps) have been identified in atherosclerosis. Immune complexes (ICs) may form between these antigens and autoantibodies and via Fc receptor signaling and complement activation may modulate the inflammation in atherosclerosis. Antibody isotype may direct the role that ICs play in atherogenesis, immunoglobulin G (IgG) being potentially pro-atherogenic and immunoglobulin M (IgM) playing a protective role. Therapeutic options targeting complement activation and those which are potentially Fc-receptor mediated have been investigated in animal models, though targeting Fc receptor signaling is an area that needs further investigation.

Delay of LPS-induced acute lung injury resolution by soluble immune complexes is neutrophil dependent

The pathophysiological role of soluble immune complexes (SICXs) and its relationship with neutrophils were investigated in LPS-induced acute lung injury (ALI) animal model (Sprague-Dawley rat) and through the in vitro studies. Results showed that LPS-induced SICX was timely related to changes of tumor necrosis factor alpha and macrophage inflammatory protein 2 (inflammatory cytokines) in bronchoalveolar lavage fluid. In vitro study showed that SICX can bind to Fc gammaR (CD64 and CD32 or CD16) to prevent the apoptosis of neutrophils. The SICX-mediated apoptosis inhibition was extracellular signal-regulated kinase (ERK) or phosphoinositide 3 kinase dependent and was interrupted by PD98059 and LY294002. In vivo, additional amount of SICX exacerbated the lung injury caused by LPS. LPS-induced lung injury and macrophage inflammatory protein 2 release, however, were prevented by CD64 and CD32 blockers (decoy antibodies). In conclusion, excessive amount of SICX in lung can act through Fc gammaRs to protect bronchoalveolar lavage fluid neutrophils from apoptosis that eventually lead to delayed resolution of ALI caused by LPS. Blockade of SICX engagement of CD32 and CD64 (with decoy antibodies) could interrupt SICX-mediated protection of neutrophils and protect lung from LPS-induced injury. The decoy antibodies may therefore have therapeutic utility in ALI.

Susceptibility for ischemic stroke in Korean population is associated with polymorphisms of the Fc gamma receptor IIA

Fc gamma receptor IIA could influence atherogenic processes through the production of superoxide anions, cytokines, and proteolytic enzymes as well as by oxidation of lipoproteins and enhancement of foam cell formation. In this study, we performed an interaction analysis between FCGR2A polymorphisms and ischemic stroke using direct DNA sequencing after the selection of Fc gamma receptor IIA gene based on genome-wide association study. Four of the FCGR2A polymorphisms, rs7511868 [odds ratio (OR) = 3.21; P = 0.027], rs6427595 (OR = 3.12; P = 0.008), rs7512140 (OR = 5.71; P = 0.002), and rs6696854 (OR = 3.65; P = 0.004) were significantly associated with ischemic stroke. These four polymorphisms still showed significant association after stratification analysis using the Mantel-Haenszel method. In the multivariate logistic regression, the adjusted OR estimates for rs6427595, rs7512140, and rs6696854 were 3.04 (P = 0.016), 4.84 (P = 0.015), and 3.80 (P = 0.006), respectively. The diplotype consisting of two homozygous haplotypes (H2 = AAAC) was significantly associated with ischemic stroke (OR = 17.39; P < 0.001). These results suggest that FCGR2A polymorphisms may be associated with a genetic susceptibility to ischemic stroke in a Korean population.

Clinical significance of the humoral immune response to modified LDL

Human low density lipoprotein (LDL) undergoes oxidation and glycation in vivo. By themselves, oxidized LDL (oxLDL) and AGE-LDL have proinflammatory properties and are considered atherogenic. But the atherogenicity of these lipoproteins are significantly increased as a consequence of the formation of immune complexes (IC) involving specific autoantibodies. OxLDL and AGE antibodies have been shown to be predominantly of the IgG1 and IgG3 isotypes. OxLDL antibodies are able to activate the complement system by the classical pathway and to induce FcR-mediated phagocytosis. In vitro and ex vivo studies performed with modified LDL-IC have proven their pro-inflammatory and atherogenic properties. Clinical studies have demonstrated that the levels of circulating modified LDL-IC correlate with parameters indicative of cardiovascular and renal disease in diabetic patients and other patient populations. The possibility that spontaneously formed or induced modified LDL antibodies (particularly IgM oxLDL antibodies) may have a protective effect has been suggested, but the data is unclear and needs to be further investigated.

The therapeutic potential of targeting B cells and anti-oxLDL antibodies in atherosclerosis

While the involvement of T cells in atherosclerosis is nowadays well accepted, little is known about the role of B cells. Obviously, B cells as the source of antibodies, in particular antibodies to oxLDL, have gained a lot of attention in atherosclerosis. In addition, B cells do harbour other functions in adaptive immunity. In this review, we provide an overview of the current knowledge on both the role of B cells and antibodies, i.e., anti-oxLDL antibodies, in atherosclerosis. It appears that B cells and also anti-oxLDL antibodies may comprise pro- and anti-atherogenic effects. Therefore, the establishment of effective therapy, targeting B cells or anti-oxLDL antibodies, warrants further research to unravel these opposite effects.

Anti-oxLDL antibody isotype levels, as potential markers for progressive atherosclerosis in APOE and APOECD40L mice

In humans and animal models of atherosclerosis, antibodies against oxidized LDL have been associated with atherosclerotic lesion development. It has been suggested that IgM anti-oxLDL antibodies are anti-atherogenic, whereas IgG anti-oxLDL antibodies are pro-atherogenic. In this study, we examined the relation between IgM and IgG antibody levels and atherosclerosis severity in APOE(-/-)CD40L(-/-) mice, which are deficient for IgG and develop moderate advanced atherosclerosis, and compared results with mice developing severe (APOE(-/-)) or no atherosclerosis (C57Bl/6). Mice were followed in time for anti-oxLDL antibodies while on high-fat diet or normal chow. Anti-oxLDL antibody levels were determined by ELISA. Results revealed that 24-week-old APOE(-/-)CD40L(-/-) mice had enhanced IgM anti-oxLDL antibody levels when compared with wild-type mice, but similar levels to those of APOE(-/-) mice. As expected, IgG anti-oxLDL antibody levels were almost absent in APOE(-/-)CD40L(-/-) mice. The transition from early to advanced lesions in APOE(-/-) mice was reflected by elevated IgM anti-oxLDL antibody levels. IgM anti-oxLDL levels did not further increase during progression to more advanced lesions. No relation was found between IgG anti-oxLDL levels and atherosclerosis severity. In conclusion, the severity of advanced atherosclerosis in mice is not reflected by IgM and/or IgG anti-oxLDL antibody levels. Furthermore, less advanced atherosclerotic lesion development in APOE(-/-)CD40L(-/-) mice does not seem to be the result of higher levels of protective IgM anti-oxLDL antibodies. Therefore, our study does not support the idea that the previously observed inconsistency in the relation between anti-oxLDL and atherosclerosis severity is due to differences in antibody isotypes.

Atherogenesis and the humoral immune response to modified lipoproteins

Modified forms of LDL are immunogenic and activate both cell-mediated and humoral immune responses. Both types of responses are pro-inflammatory and are probably primary players in the perpetuation of the chronic inflammatory reaction characteristic of atherosclerosis. The immunologic response to modified LDL can be directed to MHC-II-associated peptides in the case of T helper cells, and to a variety of epitopes-modified lysine groups, modified phospholipids, proteins that become associated with oxidized LDL (such as beta2GP1)--in the case of B cell responses. T cell activation is likely to play a major role through cross-activation of macrophages. Humoral responses to modified LDL are pathogenic as a consequence of the formation of antigen-antibody complexes containing modified LDL and IgG antibodies. Those immune complexes induce cholesterol ester accumulation in macrophages and macrophage-like cells, and induce the release of pro-inflammatory cytokines, chemokines, oxygen active radicals, and matrix metalloproteinases from those cells. There is no conclusive evidence supporting a protective role for IgM antibodies in humans, possibly because autoantibodies to modified lipoproteins are predominantly of the IgG isotype.

Immune complexes containing modified lipoproteins are related to the progression of internal carotid intima-media thickness in patients with type 1 diabetes

Modified lipoproteins induce autoimmune responses including the synthesis of autoantibodies with pro-inflammatory characteristics. Circulating modified lipoprotein autoantibodies combine with circulating antigens and form immune complexes (IC). We now report the results of a study investigating the role of circulating IC containing modified lipoproteins in the progression of carotid intima-media thickness (IMT) in patients enrolled in the Epidemiology of Diabetes Interventions and Complications (EDIC) Trial, a follow-up study of the Diabetes Control and Complications Trial (DCCT). This cohort includes 1229 patients with type 1 diabetes in whom B-mode ultrasonography of internal and common carotid arteries was performed in 1994-1996 and in 1998-2000. Conventional CHD risk factors, antibodies against modified forms of LDL and modified lipoprotein IC were determined in 1050 of these patients from blood collected in 1996-1998. Cholesterol and apolipoprotein B content of IC (surrogate markers of modified ApoB-rich lipoproteins) were significantly higher in patients who showed progression of the internal carotid IMT than in those showing no progression, regression or mild progression. Multivariate linear and logistic regression modeling using conventional and non-conventional risk factors showed that the cholesterol content of IC was a significant positive predictor of internal carotid IMT progression. In conclusion these data demonstrate that increased levels of modified ApoB-rich IC are associated with increased progression of internal carotid IMT in the DCCT/EDIC cohort of type 1 diabetes.

Anti-OxLDL IgG blocks OxLDL interaction with CD36, but promotes FcgammaR, CD32A-dependent inflammatory cell adhesion

Generation of antibodies against oxidized-low-density lipoproteins (oxLDL) during atherosclerosis could result in the formation and deposition of oxLDL immune complexes (oxLDL-IC) on the vascular endothelial cells. Inflammatory cells express scavenger receptor (SR such as CD36) and Fcgamma receptor (FcgammaR: CD32A and CD64) that can bind to oxLDL and oxLDL-IC, respectively. Hence, depending on anti-oxLDL IgG titer, circulating monocytes could adhere to endothelium to oxLDL-IC-coated vascular bed via either FcgammaR and/or CD36. In this study, we determined the relative contribution of SR and FcgammaR in mediating monocyte interaction with oxLDL-IC deposited on vascular bed. At saturating levels of anti-oxLDL IgG concentration, monocytic cells adhered to oxLDL-IC and this adhesion is completely blocked by anti-CD32A mAb. Using CHOK1-CD32A-CD36 cells expressing equal levels of CD32A and CD36, it was observed that at lower concentrations of anti-oxLDL IgG, CD32A and CD36 contribute about 75% and 25% of cell adhesion, respectively, while at higher concentrations of anti-oxLDL IgG the adhesion is completely CD32A-dependent. CD32A-dependent adhesion was further confirmed with peripheral blood monocytes and platelets that express 2- to 5-fold higher levels of CD36 compared to CD32A. Further, PBMC adhesion to oxLDL-IC-deposited endothelial cells induced secretion of pro-inflammatory chemokines, MCP-1 and IL-8. Our results demonstrate that anti-oxLDL IgG blocks oxLDL interaction with SR such as CD36, whereas oxLDL-IC formation promotes monocyte adhesion and subsequent chemokine release through FcgammaR. These findings suggest a role for FcgammaR-mediated inflammatory cell activation in the progression of atherosclerosis.

Matrix metalloproteinases, their production by monocytes and macrophages and their potential role in HIV-related diseases

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are a subfamily of metzincins. Matrix metalloproteinases are responsible for much of the turnover of extra-cellular matrix components and are key to a wide range of processes including tissue remodeling and release of biological factors. Imbalance between the MMPs and endogenous tissue inhibitors of metalloproteinases (TIMPs) can result in dysregulation of many biologic processes and lead to the development of malignancy, cardiovascular disease, and autoimmune and inflammatory disorders. MMP production by monocyte/macrophages is dependent on the cell type, state of differentiation, and/or level of activation and whether they are infected, e.g., by HIV-1. MMP expression by HIV-1 infected monocytes and macrophages may alter cellular trafficking and contribute to HIV-associated pathology such as HIV-associated dementia (HAD). This review will provide a classification of the MMP super-family with particular reference to those produced by monocyte/macrophages, describe their regulation and function within the immune system, and indicate their possible roles in the pathogenesis of disease, including HIV-associated dementia.

Pioglitazone inhibits MMP-1 expression in vascular smooth muscle cells through a mitogen-activated protein kinase-independent mechanism

Antidiabetic drug thiazolidinedione (TZD) also has anti-atherogenic effects. Among these effects, inhibition of smooth muscle cell (SMC) migration is considered to be essential. However, the mechanism whereby TZD inhibits SMC migration is not well understood. Since it is known that matrix metalloproteinases (MMPs) play a permissive role for SMC migration, we determined if TZD inhibits the upregulation of MMP-1 expression in SMCs by oxidized LDL (oxLDL), a potent stimulator for atherogenesis. Results showed that oxLDL markedly stimulated MMP-1 secretion, mRNA expression, and MMP-1 promoter activity, but pioglitazone significantly inhibited the oxLDL-upregulated MMP-1 expression. In an attempt to explore the signaling mechanism by which pioglitazone inhibits the oxLDL-upregulated MMP-1 expression, we found that extracellular signal-regulated kinase (ERK) and c-Jun-N-terminal kinase (JNK) pathways were required for the oxLDL-stimulated MMP-1 expression, but pioglitazone failed to antagonize the activation of ERK and JNK by oxLDL. Finally, our AP-1 activity assay showed that pioglitazone inhibited oxLDL-stimulated c-Jun activity. Taken together, the present study indicates that pioglitazone inhibits oxLDL-stimulated MMP-1 expression in VSMCs by inhibiting c-Jun transcriptional activity through a mitogen-activated protein kinase (MAPK)-independent mechanism.

Native and modified C-reactive protein bind different receptors on human neutrophils

Native C-reactive protein (CRP) is a planar pentamer of identical subunits expressed at high serum levels during the acute phase of inflammation. At inflammatory sites, an isomeric form termed modified CRP (mCRP) is expressed and reveals neoantigenic epitopes associated with modified monomeric CRP subunits. mCRP cannot assume the native pentameric conformation but rather forms a nonpentameric aggregate of monomers. While native CRP inhibits neutrophil movement in vitro and in vivo, the effect of mCRP on neutrophil movement has not been reported. To model the biological function and biochemical interaction of mCRP on neutrophils, in vitro chemotaxis and binding experiments were performed using mCRP. Reported here, mCRP effectively inhibited fMLP-induced chemotaxis similar to native CRP. Additionally, mCRP increased binding of labeled native CRP to neutrophils. This increased binding occurred by direct protein-protein interaction of the C-terminus thereby implicating the CRP(199-206) sequence. Binding of mCRP to neutrophils was blocked by anti-CD16 monoclonal antibody whereas native CRP was not. These results suggest that modified forms of CRP inhibit chemotaxis, a function similar to native CRP, but that mCRP and native molecule bind different receptors on human neutrophils.

Up-regulation of matrix metalloproteinase-1 expression in U937 cells by low-density lipoprotein-containing immune complexes requires the activator protein-1 and the Ets motifs in the distal and the proximal promoter regions

We reported previously that low-density lipoprotein (LDL)-containing immune complexes (LDL-IC) stimulated matrix metalloproteinase-1 (MMP-1) expression in U937 histiocytes through Fc gamma receptor (FcgammaR)-mediated extracellular signal-regulated kinase pathway. The present study has explored the transcriptional mechanisms involved in the stimulation. Deletion analysis showed that LDL-IC stimulated MMP-1 promoter activity in cells transfected with the Construct 1 that contained a 4,334-bp MMP-1 promoter fragment, but had no effect in cells transfected with other constructs that had shorter MMP-1 promoter (2685-bp or less), suggesting that cis-acting elements located between -4334 and -2685 are required for the promoter stimulation. The mutation study further indicated that the activator protein-1 (AP-1) (-3471) or Ets (-3836) motifs in this distal region were essential for the LDL-IC-stimulated MMP-1 expression. Moreover, although above deletion analysis showed that LDL-IC did not stimulate MMP-1 promoter activity in cells transfected with constructs that contained the proximal AP-1 (-72) and Ets (-88) in the promoter fragments that are 2685-bp or less, the mutations of the -72 AP-1 or the -88 Ets motif in the construct 1 abolished the stimulation of MMP-1 expression by LDL-IC, suggesting that a long promoter sequence is required for the -72 AP-1 and -88 Ets motifs to be involved in the stimulation. Finally, electrophoretic mobility shift assay showed that LDL-IC stimulated the activities of transcription factors AP-1 and Ets. In conclusion, the present study shows that both the distal and proximal AP-1 and Ets motifs are required for LDL-IC-stimulated MMP-1 expression in U937 histiocytes.

Autoimmune response to advanced glycosylation end-products of human LDL

Advanced glycosylation end-products (AGEs) are believed to play a significant role in the development of vascular complications in diabetic patients. One such product, AGE-LDL, has been shown to be immunogenic. In this report, we describe the isolation and characterization of human AGE-LDL antibodies from the sera of seven patients with Type 1 diabetes by affinity chromatography using an immobilized AGE-LDL preparation that contained primarily the AGE N epsilon (carboxymethyl)lysine (CML, 14.6 mmol/mol lysine), and smaller amounts of N epsilon (carboxyethyl)lysine (CEL, 2.7 mmol/mol lysine). The isolated antibodies were predominantly IgG of subclasses 1 and 3, and considered proinflammatory because of their ability to promote Fc gamma R-mediated phagocytosis and to activate complement. We determined dissociation constants (Kd) for the purified antibodies. The average Kd values (4.76 +/- 2.52 x 10(-9) mol/l) indicated that AGE-LDL antibodies are of higher avidity than oxidized LDL antibodies measured previously (Kd = 1.53 +/- 07 x 10(-8) ml/l), but of lower avidity than rabbit polyclonal LDL antibodies (Kd = 9.34 x 10(-11)). Analysis of the apolipoprotein B-rich lipoproteins isolated with polyethylene glycol-precipitated antigen-antibody complexes from the same patients showed the presence of both CML and CEL, thus confirming that these two modifications are recognized by human autoantibodies. A comparative study of the reactivity of purified AGE-LDL antibodies with CML-LDL and CML-serum albumin showed no cross-reactivity.

Clinical, biochemical, and immunohistochemical features of necrobiotic xanthogranulomatosis

AIMS

To describe the clinical features of two patients with paraproteinaemia and necrobiotic xanthogranulomatosis together with detailed immunohistochemistry of the lesions in one.

METHODS

The clinical history and results of biochemical investigations of the patients were retrieved from the files. Immunohistochemistry was used to investigate the expression of macrophage and mast cell markers, amyloid A and P, S-100 protein, and apolipoprotein AI and B in xanthogranulomatous skin lesions from patient 2. In addition, protein A-sepharose chromatography was used to separate serum from patient 2 and apolipoprotein B and the IgG paraprotein were measured in the fractions eluted.

RESULTS

Monocytes/macrophages comprised the major cellular component of the lesion, and unusually for xanthomata, areas of collagen necrosis were also seen. Activated mast cells were present at the margins of macrophage clusters and adjacent to areas of collagen necrosis. Serum paraprotein was bound to low density lipoproteins as judged by protein A-sepharose chromatography, and was also located within macrophagic foam cells of the lesion on immunohistochemistry.

CONCLUSIONS

These observations demonstrate many features similar to atherosclerosis including collagen necrosis and mast cell activation.

Proatherogenic and proinflammatory properties of immune complexes prepared with purified human oxLDL antibodies and human oxLDL

Immune complexes (IC) prepared with human low density lipoprotein (LDL) and rabbit LDL antibodies induce foam cell transformation of human macrophages and activate the release of proinflammatory mediators by human macrophages and THP-1 cells. Because the affinity of human oxidized LDL (oxLDL) antibodies is lower than that of rabbit antibodies, IC formed with human antibodies could have limited pathogenic potential. Immune complexes prepared with human oxidized LDL (oxLDL) and purified human oxLDL antibodies (predominantly of the IgG1 and IgG3 isotypes) were presented to THP-1 cells using two protocols previously described in studies of the properties of LDL-IC prepared with rabbit antibodies. OxLDL/human oxLDL antibody IC immobilized by adsorption to red blood cells (RBC) induced the release of significantly higher levels of TNF from THP-1 cells (872-313 pg/ml) than oxLDL adsorbed to RBC (461-75.6 pg/ml) and caused a higher degree of cholesterol ester accumulation in the same cells (5.4-0.77 in cells incubated with IC-coated RBC vs 1.99-1.16 in oxLDL-coated RBC). Insoluble IC prepared with oxLDL/human oxLDL antibody were even more effective in promoting intracellular accumulation of cholesterol in THP-1 cells (total cholesterol = 53.8-13.5 and cholesterol esters = 24.0-7.2 mg/l in THP-1 cells incubated with insoluble IC (200 micrograms) vs total cholesterol = 32.4-8.2 and cholesterol esters = 7.7 +/- 2.8 micrograms/l in THP-1 cells incubated with an identical concentration of oxLDL) and also induced the release of TNF. Thus we have demonstrated that IC prepared with human oxLDL and human oxLDL antibodies have the same atherogenic and proinflammatory properties as IC prepared with human LDL and rabbit LDL antibodies. This strongly supports the concept that modified LDL-IC present in circulation and/or tissues play an important pathogenic role in arteriosclerosis.

IFN-gamma pretreatment augments immune complex-induced matrix metalloproteinase-1 expression in U937 histiocytes

We reported recently that immune complexes (ICs) induced matrix metalloproteinase-1 (MMP-1) expression in U937 histiocytes. The present study was undertaken to determine the effect of pretreatment of U937 cells with interferon-gamma (IFN-gamma) on IC-induced MMP-1 expression. Our flow cytometry studies showed that IFN-gamma upregulated the surface expression of FcgammaRI, but not FcgammaRII. Results also showed that pretreatment of the cells with IFN-gamma augmented LDL-containing IC (LDL-IC)-induced MMP-1 secretion in a dose- and time-dependent manner. Furthermore, Northern blot analysis revealed that IFN-gamma pretreatment led to a marked increase in MMP-1 mRNA. Finally, we demonstrated that PD98059 was able to block LDL-IC-induced MMP-1 secretion, regardless of whether the cells were pretreated with IFN-gamma or not, suggesting that IFN-gamma pretreatment did not alter the essential role of the ERK signaling pathway in LDL-IC-induced MMP-1 expression. In conclusion, the present study has demonstrated that IFN-gamma pretreatment augments LDL-IC-induced MMP-1 expression in U937 cells, thus elucidating an immune mechanism potentially involved in plaque destabilization.

Quercetin inhibits matrix metalloproteinase-1 expression in human vascular endothelial cells through extracellular signal-regulated kinase

Studies have shown that intake of quercetin was inversely associated with mortality from coronary heart disease. Since recent studies documented that disruption of atherosclerotic plaques is the key event triggering acute myocardial infarction, and vascular endothelium-derived matrix metalloproteinase-1 (MMP-1) contributes to plaque destabilization, we examined the effect of quercetin on MMP-1 expression in human vascular endothelial cells. Our results showed that quercetin significantly inhibited basal and oxidized LDL (oxLDL)-stimulated MMP-1 expression. Our data also indicated that extracellular signal-regulated kinase (ERK) mediated the basal and oxLDL-stimulated expression of MMP-1, and quercetin is a potent inhibitor of ERK, suggesting that quercetin may inhibit MMP-1 expression by blocking the ERK pathway. Finally, we showed that quercetin stimulated tissue inhibitor of metalloproteinase-1 expression in oxLDL- and PMA-treated cells. In conclusion, the present study demonstrated for the first time that quercetin inhibited MMP-1 expression in vascular endothelial cells, suggesting that quercetin might contribute to plaque stabilization.