Monica de Gaetano

M1- and M2-Type Macrophage Responses Are Predictive of Adverse Outcomes in Human Atherosclerosis.

Atherosclerosis is an inflammatory disease caused by endothelial injury, lipid deposition, and oxidative stress. This progressive disease can be converted into an acute clinical event by plaque rupture and thrombosis. In the context of atherosclerosis, the underlying cause of myocardial infarction and stroke, macrophages uniquely possess a dual functionality, regulating lipid accumulation and metabolism and sustaining the chronic inflammatory response, two of the most well-documented pathways associated with the pathogenesis of the disease. Macrophages are heterogeneous cell populations and it is hypothesized that, during the pathogenesis of atherosclerosis, macrophages in the developing plaque can switch from a pro-inflammatory (MΦ1) to an anti-inflammatory (MΦ2) phenotype and vice versa, depending on the microenvironment. The aim of this study was to identify changes in macrophage subpopulations in the progression of human atherosclerotic disease. Established atherosclerotic plaques from symptomatic and asymptomatic patients with existing coronary artery disease undergoing carotid endarterectomy were recruited to the study. Comprehensive histological and immunohistochemical analyses were performed to quantify the cellular content and macrophage subsets of atherosclerotic lesion. In parallel, expression of MΦ1 and MΦ2 macrophage markers were analyzed by real-time PCR and Western blot analysis. Gross analysis and histological staining demonstrated that symptomatic plaques presented greater hemorrhagic activity and the internal carotid was the most diseased segment, based on the predominant prevalence of fibrotic and necrotic tissue, calcifications, and hemorrhagic events. Immunohistochemical analysis showed that both MΦ1 and MΦ2 macrophages are present in human plaques. However, MΦ2 macrophages are localized to more stable locations within the lesion. Importantly, gene and protein expression analysis of MΦ1/MΦ2 markers evidenced that MΦ1 markers and Th1-associated cytokines are highly expressed in symptomatic plaques, whereas expression of the MΦ2 markers, mannose receptor (MR), and CD163 and Th2 cytokines are inversely related with disease progression. These data increase the understanding of atherosclerosis development, identifying the cellular content of lesions during disease progression, and characterizing macrophage subpopulation within human atherosclerotic plaques.

Macrophage PPAR gamma Co-activator-1 alpha participates in repressing foam cell formation and atherosclerosis in response to conjugated linoleic acid

Conjugated linoleic acid (CLA) has the unique property of inducing regression of pre‐established murine atherosclerosis. Understanding the mechanism(s) involved may help identify endogenous pathways that reverse human atherosclerosis. Here, we provide evidence that CLA inhibits foam cell formation via regulation of the nuclear receptor coactivator, peroxisome proliferator‐activated receptor (PPAR)‐γ coactivator (PGC)‐1α, and that macrophage PGC‐1α plays a role in atheroprotection in vivo. PGC‐1α was identified as a hub gene within a cluster in the aorta of the apoE−/− mouse in the CLA‐induced regression model. PGC‐1α was localized to macrophage/foam cells in the murine aorta where its expression was increased during CLA‐induced regression. PGC‐1α expression was also detected in macrophages in human atherosclerosis and was inversely linked to disease progression in patients with the disease. Deletion of PGC‐1α in bone marrow derived macrophages promoted, whilst over expression of the gene inhibited foam cell formation. Importantly, macrophage specific deletion of PGC‐1α accelerated atherosclerosis in the LDLR−/− mouse in vivo. These novel data support a functional role for PGC‐1α in atheroprotection.

Protective effect of let-7 miRNA family in regulating inflammation in diabetes-associated atherosclerosis

The let-7 miRNA family plays a key role in modulating inflammatory responses. Vascular smooth muscle cell (SMC) proliferation and endothelial cell (EC) dysfunction are critical in the pathogenesis of atherosclerosis, including in the setting of diabetes. Here we report that let-7 levels are decreased in diabetic human carotid plaques and in a model of diabetes-associated atherosclerosis, the diabetic ApoE−/− mouse. In vitro platelet-derived growth factor (PDGF)– and tumor necrosis factor-α (TNF-α)–induced vascular SMC and EC activation was associated with reduced let-7 miRNA expression via Lin28b, a negative regulator of let-7 biogenesis. Ectopic overexpression of let-7 in SMCs inhibited inflammatory responses including proliferation, migration, monocyte adhesion, and nuclear factor-κB activation. The therapeutic potential of restoring let-7 levels using a let-7 mimic was tested: in vitro in SMCs using an endogenous anti-inflammatory lipid (lipoxin A4), ex vivo in murine aortas, and in vivo via tail vein injection in a 24-h murine model. Furthermore, we delivered let-7 mimic to human carotid plaque ex vivo and observed significant changes to the secretome in response to let-7 therapy. Restoration of let-7 expression could provide a new target for an anti-inflammatory approach in diabetic vascular disease.

Conjugated Linoleic Acid Targets β2 Integrin Expression To Suppress Monocyte Adhesion

Chronic recruitment of monocytes and their subsequent migration through the activated endothelium contribute to atherosclerotic plaque development. Integrin-mediated leukocyte adhesion is central to this process. Conjugated linoleic acid (CLA) has the unique property of inducing regression of pre-established murine atherosclerosis via modulation of monocyte/macrophage function. Understanding the mechanisms through which CLA mediates its atheroprotective effect may help to identify novel pathways that limit or reverse atherosclerosis. In this study, we identified a novel mechanism through which CLA alters monocyte function. We show that CLA inhibits human peripheral blood monocyte cell adhesion to activated endothelial cells via loss of CD18 expression, the β2 chain of LFA-1 and Mac-1 integrins. In addition, using a static-adhesion assay, we provide evidence that CLA prevents monocytes from binding to ICAM-1 and subsequently reduces the capacity of these cells to polarize. CXCL12–CXCR4 interactions induce a conformational change in β2 integrins, facilitating leukocyte adhesion. In this study, we demonstrate that CLA inhibits CXCR4 expression, resulting in a failure of monocytes to directionally migrate toward CXCL12. Finally, using intravital microscopy, we show that, during CLA-induced regression of pre-established atherosclerosis in ApoE−/− mice, there is reduced leukocyte adhesion and decreased CD18 expression on Gr1+/CD115+ proinflammatory monocytes. In summary, the data presented describe a novel functional role for CLA in the regulation of monocyte adhesion, polarization, and migration.

Conjugated linoleic acid induces an atheroprotective macrophage MΦ2 phenotype and limits foam cell formation

BackgroundAtherosclerosis, the underlying cause of heart attack and strokes, is a progresive dyslipidemic and inflammatory disease where monocyte-derived macrophage cells play a pivotal role. Although most of the mechanisms that contribute to the progression of atherosclerosis have been identified, there is limited information on those governing regression. Conjugated linoleic acid (CLA) is a group of isomers of linoleic acid that differ in the position and/or geometry of their double bonds. We have previously shown that a specific CLA blend (80:20 cis-9,trans-11:trans-10,cis-12-CLA) induces regression of pre-established atherosclerosis in vivo, via modulation of monocyte/macrophage function. However, the exact mechanisms through which CLA mediates this effect remain to be elucidated.MethodsHere, we address if CLA primes monocytes towards an anti-inflammatory MΦ2 macrophage and examine the effect of individual CLA isomers and the atheroprotective blend on monocyte-macrophage differentiation, cytokine generation, foam cell formation and cholesterol metabolism in human peripheral blood monocyte (HPBMC)-derived macrophages.Resultscis-9,trans-11-CLA and the atheroprotective 80:20 CLA blend regulates expression of pro-inflammatory mediators and modulates the inflammatory cytokine profile of macrophages and foam cells. In addition, cis-9,trans-11-CLA and CLA blend primes HPBMCs towards an anti-inflammatory MΦ2 phenotype, characterised by increased scavenger receptor (CD36) and efflux protein (ABCA-1) expression. Furthermore, this altered macrophage phenotype impacts on foam cell formation, inhibiting ox-LDL accumulation and promoting cholesterol efflux via both PPARγ and LXRα dependent pathways.ConclusionThe data increases the understanding of the pathways regulated by CLA in atheroprotection, namely, inhibiting the progressive acquisition of a pro-inflammatory macrophage phenotype.

SorLA modulates atheroprotective properties of CLA by regulating monocyte migration

OBJECTIVE We have previously shown that CLA induces regression of pre-established atherosclerotic lesions in apoE(-/-) mice. CLA is a known ligand of peroxisome proliferator activated receptors (PPARs) and it is postulated that CLA mediates its atheroprotective effects through activation of PPARs. Earlier work in our group identified the monocyte/macrophage cell as the primary cellular target of CLA. In this study we identified novel genes regulated by CLA during the regression of atherosclerosis and characterised a role for one of these, SorLA. SorLA is a member of the vacuolar protein sorting 10 protein (Vps10p) domain receptor family, which has structural homology with the LDLR family. METHODS AND RESULTS Expression of SorLA was identified with its Vps10p family member Sort1 by transcriptomic analysis of murine aorta following CLA-induced regression of atherosclerosis. Decreased expression of both receptors was confirmed by real-time PCR in the aorta of CLA-supplemented mice. SorLA protein expression was predominantly localised to monocyte/macrophage cells in the vasculature by immunohistochemistry. CLA and the PPAR-γ agonists, troglitazone, and 15-deoxy-prostaglandin (PG) J(2), decreased protein and RNA expression of SorLA in THP-1 monocytes; while pre-treatment with a PPAR-γ antagonist established a PPAR-γ dependent role for CLA regulation of SorLA. CLA inhibits monocyte migration. Consistent with a role for SorLA in mediating this response, overexpression of SorLA increased migration of THP-1 monocytes to monocyte chemoattractant protein-1 with a coincident increase in UPAR expression. CONCLUSION CLA may mediate its atheroprotective effects in part through reduced expression of SorLA and a resulting inhibition of monocyte migration in vitro.

NR4A Receptors Differentially Regulate NF-κB Signaling in Myeloid Cells

Dysregulation of inflammatory responses is a hallmark of multiple diseases such as atherosclerosis and rheumatoid arthritis. As constitutively active transcription factors, NR4A nuclear receptors function to control the magnitude of inflammatory responses and in chronic inflammatory disease can be protective or pathogenic. Within this study, we demonstrate that TLR4 stimulation using the endotoxin lipopolysaccharide (LPS) rapidly enhances NR4A1–3 expression in human and murine, primary and immortalized myeloid cells with concomitant gene transcription and protein secretion of MIP-3α, a central chemokine implicated in numerous pathologies. Deficiency of NR4A2 and NR4A3 in human and murine myeloid cells reveals that both receptors function as positive regulators of enhanced MIP-3α expression. In contrast, within the same cell types and conditions, altered NR4A activity leads to suppression of LPS-induced MCP-1 gene and protein expression. An equivalent pattern of inflammatory gene regulation is replicated in TNFα-treated myeloid cells. We show that NF-κB is the critical regulator of NR4A1–3, MIP-3α, and MCP-1 during TLR4 stimulation in myeloid cells and highlight a parallel mechanism whereby NR4A activity can repress or enhance NF-κB target gene expression simultaneously. Mechanistic insight reveals that NR4A2 does not require DNA-binding capacity in order to enhance or repress NF-κB target gene expression simultaneously and establishes a role for NF-κB family member Relb as a novel NR4A target gene involved in the positive regulation of MIP-3α. Thus, our data reveal a dynamic role for NR4A receptors concurrently enhancing and repressing NF-κB activity in myeloid cells leading to altered transcription of key inflammatory mediators.