A aterosclerose é uma doença degenerativa crônica dos vasos, com conseqüências clínicas agudas que incluem o infarto do miocárdio e o acidente vascular cerebral, resultantes geralmente da ruptura da placa e trombose. É atualmente reconhecida como de característica inflamatória, iniciada e propagada no contexto da hipercolesterolemia. Um trabalho de nosso grupo utilizou técnicas de phage display para comparar placas ateroscleróticas e carótidas normais objetivando a busca de proteínas alteradas potencialmente envolvidas na patogênese da doença. Diversas semaforinas e plexinas (receptores de semaforinas) foram identificadas dentre elas a plexina B1, que possui alta afinidade por CD100, sugerindo assim uma concentração aumentada de CD100 na placa aterosclerótica. CD100 foi a primeira semaforina descrita no sistema imune e a única até hoje descrita como possuidora de duas formas de funcionalidades distintas, sendo uma de membrana (mCD100) e outra solúvel (sCD100). Neste trabalho demonstramos a expressão da semaforina CD100 em macrófagos e células espumosas em placas ateroscleróticas humanas, assim como seu padrão de expressão ao longo da diferenciação monócito-macrófago-célula espumosa, e sob estímulos distintos. Além disso, identificamos pela primeira vez o receptor que medeia suas atividades nessas células, a plexina B2. Adicionalmente, detectamos também pela primeira vez detectamos a expressão de CD100 em células endoteliais teciduais e cultivadas in vitro, o que sugere um papel significativo da semaforina em fenômenos vasculares. Com base nessas observações e nos resultados de experimentos de bloqueio de adesão constatamos que CD100 pode atuar na fase mais precoce da aterosclerose, como uma molécula de adesão envolvida na ligação entre monócitos e células endoteliais. Verificamos ainda que CD100 diminui a captação de LDLox em macrófagos e células espumosas. Poucos estudos relatam a presença ou possível atividade biológica de CD100 tanto na aterosclerose quanto em macrófagos. Devido às já estabelecidas ações no sistema imune, acreditamos que a expressão diferencial dessa semaforina desempenha um papel amplificador na patogênese da aterosclerose. Posteriormente, essa proteína poderá servir como alvo de inibição da progressão da doença e de suas complicações / Atherosclerosis is a chronic degenerative disease affecting vessels, with acute clinical consequences that include myocardium infarction or stroke, generally resulting from plaque rupture and thrombosis. It is now recognized as an inflammatory disease, initiated and developed in a hipercholesterolemic context. A work in our lab has used phage display techniques to compare atherosclerotic plaques and normal carotids, searching for altered proteins potentially involved in the pathogenesis of the disease. Many semaphorins and plexins (semaphorin receptors) have been identified, among which plexin B1, a high affinity receptor for CD100, suggesting an augmented level of CD100 in the atherosclerotic plaques. CD100 is the first semaphorin described in the immune system, and the only to possess two forms with distinct functionalities, being one associated to the membrane, mCD100, and another soluble form, sCD100. In the present work we have demonstrated CD100 expression in macrophages and foam cells of human atherosclerotic plaques, as well as its pattern of expression along monocyte-macrophage-foam cell differentiation and under distinct stimuli. Furthermore, we have identified for the first time the receptor involved in CD100 activities in these cells, namely plexin B2. Aditionally, we have detected CD100 expression in tissue as well as in in vitro cultured endothelial cells, also for the first time. According to these informations and adhesion blockage experiments we have shown that CD100 may act in the earliest phase of the establishment of atherosclerosis, as an adhesion molecule involved in monocyte-endothelial cell association. We have also verified that CD100 diminishes the intake of oxLDL in macrophages and foam cells. Only a few studies describe the presence or possible biological activity of CD100 in atherosclerosis or macrophages. Since the molecule has been shown to participate in the immune system, we believe that the differential expression of this semaphorin plays an amplifying role in the pathogenesis of atherosclerosis. In the future, this protein could act as an inhibition target of the disease progression as well as its complications

Heat shock protein (HSP)27 is traditionally described as an intracellular chaperone and signaling molecule, but growing evidence suggests it is released from immune cells where it plays an anti-inflammatory role during atherogenesis. Previously, the O’Brien lab found that overexpression of HSP27 led to augmented HSP27 serum levels in female apolipoprotein E knockout (ApoE-/-) mice, attenuated atherogenesis, and inhibited macrophage foam cell formation via physical binding with scavenger receptor (SR)-A. However, the precise mechanism of atheroprotection remained elusive. This thesis sought to ascertain the mechanism(s) by which HSP27 prevents foam cell formation, and determine if SR-A, a key receptor involved in the uptake of lipid into macrophages, plays an important role in HSP27-mediated atheroprotection. Pre-treatment of human macrophages with recombinant HSP27 (rHSP27) inhibited acytelated low density lipoprotein (acLDL) binding and uptake independent from receptor competition effect. Reduction in uptake was associated with attenuation of expression of SR-A mRNA, total protein, and cell surface expression. To explore the signaling mechanism by which HSP27 modulated SR-A expression it was hypothesized that nuclear factor-kappa B (NF-kB), a major regulator of many atherosclerosis gene programs, is altered by extracellular HSP27. Indeed, rHSP27 markedly activated NF-kB signaling in macrophages. Using an inhibitor of NF-kBsignaling there was an attenuation of rHSP27-induced inhibition of SR-A gene and protein expression, as well as lipid uptake, suggesting that SR-A expression is regulated by NF-kB activation. Lastly, to investigate if SR-A is required for HSP27-mediated atheroprotection in vivo, ApoE-/- and ApoE-/-SR-A-/- mice fed a high fat diet were treated with rHSP25, the mouse orthologue of HSP27, or PBS for 3 weeks. While rHSP25 therapy equally reduced serum cholesterol levels in the mouse cohorts, aortic atherogenesis, assessed using en face and sinus cross-sectional analyses, was attenuated in ApoE-/- mice but not ApoE-/-SR-A-/- mice. In conclusion, rHSP27 inhibits foam cell formation by downregulating SR-A expression. This effect may be associated with NF-kB activation. Reductions in atherosclerotic burden by rHSP27 require SR-A, and are independent of changes in serum cholesterol levels, highlighting the importance of macrophage lipid uptake in atherogenesis. Results presented in this thesis demonstrate that SR-A is a major target for HSP27 atheroprotection in the vessel wall, and provide an impetus for further studies that investigate the potential therapeutic value of HSP27.

Heat shock protein (HSP)27 is traditionally described as an intracellular chaperone and signaling molecule, but growing evidence suggests it is released from immune cells where it plays an anti-inflammatory role during atherogenesis. Previously, the O’Brien lab found that overexpression of HSP27 led to augmented HSP27 serum levels in female apolipoprotein E knockout (ApoE-/-) mice, attenuated atherogenesis, and inhibited macrophage foam cell formation via physical binding with scavenger receptor (SR)-A. However, the precise mechanism of atheroprotection remained elusive. This thesis sought to ascertain the mechanism(s) by which HSP27 prevents foam cell formation, and determine if SR-A, a key receptor involved in the uptake of lipid into macrophages, plays an important role in HSP27-mediated atheroprotection. Pre-treatment of human macrophages with recombinant HSP27 (rHSP27) inhibited acytelated low density lipoprotein (acLDL) binding and uptake independent from receptor competition effect. Reduction in uptake was associated with attenuation of expression of SR-A mRNA, total protein, and cell surface expression. To explore the signaling mechanism by which HSP27 modulated SR-A expression it was hypothesized that nuclear factor-kappa B (NF-kB), a major regulator of many atherosclerosis gene programs, is altered by extracellular HSP27. Indeed, rHSP27 markedly activated NF-kB signaling in macrophages. Using an inhibitor of NF-kBsignaling there was an attenuation of rHSP27-induced inhibition of SR-A gene and protein expression, as well as lipid uptake, suggesting that SR-A expression is regulated by NF-kB activation. Lastly, to investigate if SR-A is required for HSP27-mediated atheroprotection in vivo, ApoE-/- and ApoE-/-SR-A-/- mice fed a high fat diet were treated with rHSP25, the mouse orthologue of HSP27, or PBS for 3 weeks. While rHSP25 therapy equally reduced serum cholesterol levels in the mouse cohorts, aortic atherogenesis, assessed using en face and sinus cross-sectional analyses, was attenuated in ApoE-/- mice but not ApoE-/-SR-A-/- mice. In conclusion, rHSP27 inhibits foam cell formation by downregulating SR-A expression. This effect may be associated with NF-kB activation. Reductions in atherosclerotic burden by rHSP27 require SR-A, and are independent of changes in serum cholesterol levels, highlighting the importance of macrophage lipid uptake in atherogenesis. Results presented in this thesis demonstrate that SR-A is a major target for HSP27 atheroprotection in the vessel wall, and provide an impetus for further studies that investigate the potential therapeutic value of HSP27.

Heat shock protein (HSP)27 is traditionally described as an intracellular chaperone and signaling molecule, but growing evidence suggests it is released from immune cells where it plays an anti-inflammatory role during atherogenesis. Previously, the O’Brien lab found that overexpression of HSP27 led to augmented HSP27 serum levels in female apolipoprotein E knockout (ApoE-/-) mice, attenuated atherogenesis, and inhibited macrophage foam cell formation via physical binding with scavenger receptor (SR)-A. However, the precise mechanism of atheroprotection remained elusive. This thesis sought to ascertain the mechanism(s) by which HSP27 prevents foam cell formation, and determine if SR-A, a key receptor involved in the uptake of lipid into macrophages, plays an important role in HSP27-mediated atheroprotection. Pre-treatment of human macrophages with recombinant HSP27 (rHSP27) inhibited acytelated low density lipoprotein (acLDL) binding and uptake independent from receptor competition effect. Reduction in uptake was associated with attenuation of expression of SR-A mRNA, total protein, and cell surface expression. To explore the signaling mechanism by which HSP27 modulated SR-A expression it was hypothesized that nuclear factor-kappa B (NF-kB), a major regulator of many atherosclerosis gene programs, is altered by extracellular HSP27. Indeed, rHSP27 markedly activated NF-kB signaling in macrophages. Using an inhibitor of NF-kBsignaling there was an attenuation of rHSP27-induced inhibition of SR-A gene and protein expression, as well as lipid uptake, suggesting that SR-A expression is regulated by NF-kB activation. Lastly, to investigate if SR-A is required for HSP27-mediated atheroprotection in vivo, ApoE-/- and ApoE-/-SR-A-/- mice fed a high fat diet were treated with rHSP25, the mouse orthologue of HSP27, or PBS for 3 weeks. While rHSP25 therapy equally reduced serum cholesterol levels in the mouse cohorts, aortic atherogenesis, assessed using en face and sinus cross-sectional analyses, was attenuated in ApoE-/- mice but not ApoE-/-SR-A-/- mice. In conclusion, rHSP27 inhibits foam cell formation by downregulating SR-A expression. This effect may be associated with NF-kB activation. Reductions in atherosclerotic burden by rHSP27 require SR-A, and are independent of changes in serum cholesterol levels, highlighting the importance of macrophage lipid uptake in atherogenesis. Results presented in this thesis demonstrate that SR-A is a major target for HSP27 atheroprotection in the vessel wall, and provide an impetus for further studies that investigate the potential therapeutic value of HSP27.

Macrophage-derived foam cells play a predominant role in the deposition of arterial plaques during the early stages of atherosclerosis. The deposition of arterial plaques is known to be effected by several factors, including a person’s dietary habits. The consumption of a high-fat (>60% of calories from fat) meal is known to elevate serum LDL and triglycerides, which have been previously implicated in the formation pf foam cells. One limitation of current research models is that it is not possible to directly measure foam cells in vivo. Thus, the purpose of the present study was to validate the use of blood derived monocytes as a proxy measure of foam cells. In order to complete this objective, we evaluated monocyte oxLDL phagocytosis capacity following consumption of a high-fat meal. Eight men and women participated in the present study and venous blood samples were collected prior to the meal, 1-h, 3-h, and 5-h post-meal. Monocytes (CD14+/16- and CD14+/16+) were evaluated for adhesion molecule expression (CD11a, CD11b, and CD18), scavenger R (CD36) expression, and oxLDL phagocytosis using an image-based flow cytometry method developed in our laboratory for this purpose. Data was statistically analyzed for significance using a single-factor ANOVA with repeated measures and a p < 0.05. Consumption of a high-fat meal caused an increase significant increase in the proportion of pro-inflammatory monocytes (CD14+/16+) and a decrease in classic monocytes (CD14+/16-), with the greatest difference occurring at 5 h post prandial (p = 0.038). We also found that pro-inflammatory monocyte expression of adhesion molecules and CD36 increased in a manner that would promote in vivo movement of monocytes into the subendothelial space. Finally, over the course of the 5 h postprandial period, the majority of oxLDL uptake occurred in pro-inflammatory compared to classic monocytes. These results suggest that consuming a high-fat meal increases the potential of monocytes to become foam cells for at least 5 h postprandial.

Acyl coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the intracellular synthesis of cholesteryl esters (CE). Both ACAT isoforms, ACAT1 and ACAT2, play key roles in the pathophysiology of atherosclerosis and ACAT inhibition retards atherosclerosis in animal models. Rimonabant, a type 1 cannabinoid receptor (CB1) antagonist, produces anti-atherosclerotic effects in humans and animals by mechanisms which are not completely understood. Rimonabant is structurally similar to two other cannabinoid receptor antagonists, AM251 and SR144528, recently identified as potent inhibitors of ACAT. Therefore, we examined the effects of Rimonabant on ACAT using both in vivo cell-based assays and in vitro cell-free assays. Rimonabant dose-dependently reduced ACAT activity in Raw 264.7 macrophages (IC50=2.9±0.38μM) and isolated peritoneal macrophages. Rimonabant inhibited ACAT activity in intact CHO-ACAT1 and CHO-ACAT2 cells and in cell-free assays with approximately equal efficiency (IC50=1.5±1.2μM and 2.2±1.1μM for CHO-ACAT1 and CHO-ACAT2, respectively). Consistent with ACAT inhibition, Rimonabant treatment blocked ACAT-dependent processes in macrophages, oxysterol-induced apoptosis and acetylated-LDL induced foam cell formation. From these results we conclude that Rimonabant is an ACAT1/2 dual inhibitor and suggest that some of the atherosclerotic beneficial effects of Rimonabant are, at least partly, due to inhibition of ACAT.

The connection between C-reactive protein (CRP) and atherosclerosis lies on three grounds. First, the concentration of CRP in the serum, which is measured by using highly sensitive (a.k.a. 'hs') techniques, correlates with the occurrence of cardiovascular disease. Second, although CRP binds only to Fcγ receptor-bearing cells and, in general, to apoptotic and damaged cells, almost every type of cultured mammalian cells has been shown to respond to CRP treatment. Many of these responses indicate proatherogenic functions of CRP but are being reinvestigated using CRP preparations that are free of endotoxins, sodium azide, and biologically active peptides derived from the protein itself. Third, CRP binds to modified forms of low-density lipoprotein (LDL), and, when aggregated, CRP can bind to native LDL as well. Accordingly, CRP is seen with LDL and damaged cells at the atherosclerotic lesions and myocardial infarcts. In experimental rats, human CRP was found to increase the infarct size, an effect that could be abrogated by blocking CRP-mediated complement activation. In the Apob 100/100 Ldlr -/- murine model of atherosclerosis, human CRP was shown to be atheroprotective, and the importance of CRP-LDL interactions in this protection was noted. Despite all this, at the end, the question whether CRP can protect humans from developing atherosclerosis remains unanswered.

Coronary artery disease (CAD) is caused by atherosclerosis, a chronic inflammatory response to modified lipoproteins. A key pathophysiological event is the lipid-induced transformation of macrophages into lipid-laden foam cells and their accumulation in atherosclerotic plaques. Heritable CAD risk is associated with common genetic variants at over 40 genomic loci; the underlying causal mechanisms remain largely unknown and could affect transcriptional regulation in foam cells. Epigenetic and gene expression changes were measured in primary human macrophages before and after exposure to atherogenic, oxidized low-density lipoprotein—with resultant foam cell formation. This unbiased approach involved open chromatin mapping with formaldehyde-assisted isolation of regulatory elements with enhancer and transcription factor mapping using chromatin immuno-precipitation. Foam cell formation was associated with changes in a subset of open chromatin and enhancer sites that were strongly correlated with expression of nearby genes. OxLDL-regulated enhancers were enriched for several transcription factors—including C/EBP-beta— that have no previously documented role in foam cell formation. OxLDL exposure up-regulated C/EBP-beta expression and increased C/EBP-beta binding across the genome, most prominently around genes involved in inflammatory response pathways. Variants at CAD-associated loci were enriched in the subset of oxLDLregulated open chromatin sites. These included rs72664324 in an oxLDL-induced super-enhancer at the PPAP2B locus. OxLDL increased C/EBP-beta binding at rs72664324. C/EBP-beta binding, enhancer activity and oxLDL-induced upregulation of PPAP2B were stronger with the protective A allele of rs72664324. The PPAP2B protein product LPP3 was expressed in foam cells in human atherosclerotic plaques and was upregulated by oxLDL exposure in macrophages, so increasing the degradation of pro-inflammatory mediators. I also found several other CAD risk candidate genes were regulated by oxLDL: Phosphatase and actin regulator 1 (PHACTR1) and macrophage inducible Ca²⁺ dependent C-type lectin (Mincle). This led us to find a novel expression-quantitative-trait locus for PHACTR1 in macrophages and define new glycolipid ligands for Mincle. Our results demonstrate a genetic mechanism contributing to CAD risk at the PPAP2B locus and highlight the value of integrating gene expression and epigenetic changes to study disease processes involving pathogenic environmental stimuli.

Atherosclerosis, characterized by the build-up of cholesterol, immune cells and cellular debris within arterial walls, is accelerated following myocardial infarction by poorly understood mechanisms. Ubiquitin, a small, well-studied intracellular protein involved in protein turnover via the proteasome pathway, has recently been shown to exert extracellular effects on cardiac myocytes, in vitro, and in mice undergoing myocardial remodeling. This study investigates the potential role of extracellular ubiquitin in atherosclerosis by determining its effects on two critical atherosclerotic processes: the migration of vascular smooth muscles cells and the uptake of modified LDL by monocyte/macrophages in foam cell formation. In the presence of ubiquitin, smooth muscle cell migration was accelerated and foam cell formation was enhanced, suggesting that ubiquitin has an active role in atherosclerosis.

No description available.