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During obesity, macrophages infiltrate the visceral adipose tissue and promote inflammation that contributes to type II diabetes. Evidence suggests that the rewiring of cellular metabolism can regulate macrophage function. However, the metabolic programs that characterize adipose tissue macrophages (ATM) in obesity are poorly defined. Here, we demonstrate that ATM from obese mice exhibit metabolic profiles characterized by elevated glycolysis and oxidative phosphorylation, distinct from ATM from lean mice. Increased activation of HIF-1α in ATM of obese visceral adipose tissue resulted in induction of IL-1β and genes in the glycolytic pathway. Using a hypoxia-tracer, we show that HIF-1α nuclear translocation occurred both in hypoxic and non-hypoxic ATM suggesting that both hypoxic and pseudohypoxic stimuli activate HIF-1α and its target genes in ATM during diet-induced obesity. Exposure of macrophages to the saturated fatty acid palmitate increased glycolysis and HIF-1α expression, which culminated in IL-1β induction thereby simulating pseudohypoxia. Using mice with macrophage-specific targeted deletion of HIF-1α, we demonstrate the critical role of HIF-1α-derived from macrophages in regulating ATM accumulation, and local and systemic IL-1β production, but not in modulating systemic metabolic responses. Collectively, our data identify enhanced glycolysis and HIF-1α activation as drivers of low-grade inflammation in obesity.

Obesity is a major public health burden worldwide and is characterized by chronic low-grade inflammation driven by the cooperation of the innate immune system and dysregulated metabolism in adipose tissue and other metabolic organs. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a central regulator of inflammatory cell function that coordinates inflammation, apoptosis and necroptosis in response to inflammatory stimuli. Here we show that genetic polymorphisms near the human RIPK1 locus associate with increased RIPK1 gene expression and obesity. We show that one of these single nucleotide polymorphisms is within a binding site for E4BP4 and increases RIPK1 promoter activity and RIPK1 gene expression in adipose tissue. Therapeutic silencing of RIPK1 in vivo in a mouse model of diet-induced obesity dramatically reduces fat mass, total body weight and improves insulin sensitivity, while simultaneously reducing macrophage and promoting invariant natural killer T cell accumulation in adipose tissue. These findings demonstrate that RIPK1 is genetically associated with obesity, and reducing RIPK1 expression is a potential therapeutic approach to target obesity and related diseases.

International audience; Abdominal aortic aneurysms (AAA) are characterized by matrix remodeling, elastin degradation, absence of nitric oxide (NO) signaling, and inflammation, influencing smooth muscle cell (SMC) phenotype and gene expression. Little is known about the biomolecular release and intrinsic biomechanics of human AAA-SMCs. NO delivery could be an attractive therapeutic strategy to restore lost functionality of AAA-SMCs by inhibiting inflammation and cell stiffening. We aim to establish the differences in phenotype and gene expression of adult human AAA-SMCs from healthy SMCs. Based on our previous study which showed benefits of optimal NO dosage delivered via S-Nitrosoglutathione (GSNO) to healthy aortic SMCs, we tested whether such benefits would occur in AAA-SMCs. The mRNA expression of three genes involved in matrix degradation (ACE, ADAMTS5 and ADAMTS8) was significantly downregulated in AAA-SMCs. Total protein and glycosaminoglycans synthesis were higher in AAA-SMCs than healthy-SMCs (p < 0.05 for AAA-vs. healthy-SMC cultures) and was enhanced by GSNO and 3D cultures (p < 0.05 for 3D vs. 2D cultures; p < 0.05 for GSNO vs. non-GSNO cases). Elastin gene expression, synthesis and deposition, desmosine crosslinker levels, and lysyl oxidase (LOX) functional activity were lower, while cell proliferation, iNOS, LOX and fibrillin-1 gene expressions were higher in AAA-SMCs (p < 0.05 between respective cases), with differential benefits from GSNO exposure. GSNO and 3D cultures reduced MMPs −2, −9, and increased TIMP-1 release in AAA-SMC cultures (p < 0.05 for GSNO vs. non-GSNO cultures). AAA-SMCs were inherently stiffer and had smoother surface than healthy SMCs (p < 0.01 in both cases), but GSNO reduced stiffness (~25%; p < 0.01) and increased roughness (p < 0.05) of both cell types. In conclusion, exogenously-delivered NO offers an attractive strategy by providing therapeutic benefits to AAA-SMCs.

Abdominal aortic aneurysms (AAA) are characterized by extensive extracellular matrix (ECM) fragmentation and inflammation. However, the mechanisms by which these events are coupled thereby fueling focal vascular damage are undefined. Here we report through single-cell RNA-sequencing of diseased aorta that the neuronal guidance cue netrin-1 can act at the interface of macrophage-driven injury and ECM degradation. Netrin-1 expression peaks in human and murine aneurysmal macrophages. Targeted deletion of netrin-1 in macrophages protects mice from developing AAA. Through its receptor neogenin-1, netrin-1 induces a robust intracellular calcium flux necessary for the transcriptional regulation and persistent catalytic activation of matrix metalloproteinase-3 (MMP3) by vascular smooth muscle cells. Deficiency in MMP3 reduces ECM damage and the susceptibility of mice to develop AAA. Here, we establish netrin-1 as a major signal that mediates the dynamic crosstalk between inflammation and chronic erosion of the ECM in AAA., Abdominal aortic aneurysms (AAA) are characterized by extensive extracellular matrix degradation. Here Hadi et al. identify a netrin-1/neogenin-based crosstalk between macrophages and vascular smooth muscle cells (VSMCs), leading to the secretion of the matrix metalloproteinase MMP-3 by VSMCs and subsequent matrix degradation in AAA lesions.

Objective: To determine whether monocyte-platelet aggregates (MPA) correlate with aortic aneurysm (AA) prevalence and severity. BACKGROUND: Inflammation and intraluminal thrombus are key hallmarks of complex AA. While monocytes fuel inflammation in AA, the contribution of platelets is unknown. We hypothesized that increased platelet activity yields to MPA that drive AA development and indicate disease severity. Methods: Blood was collected from 49 symptomatic patients admitted for aneurysm repair procedures (8 thoracic and 41 abdominal) and 36 matched controls. All subjects were on aspirin monotherapy. Platelet responsiveness to agonists was characterized by light transmission aggregometry. Flow cytometry analysis allowed leukocytes (CD45+)/monocytes (CD14+)-platelet (CD61+) aggregates (LPA/MPA) measurements in the blood and profiled MPA in post-surgical aneurysm tissues. Results: Platelet aggregation in response to ADP (57% vs. 35% aggregation, pin situ in AA sac, platelets and tissue macrophage activation was characterized. Compared to the non-diseased part of the aorta, diseased section had significantly higher platelet infiltration (7.0% vs 1.2% CD61+ cells, p=0.006) and interaction with CD68+ tissue macrophages (8.3% vs. 0.7%, CD61+ macrophages p=0.03). Notably, macrophages highly expressed the adhesion protein, ICAM-1, in the diseased part (39.6 vs 3.3% in the non-diseased section, p Conclusions: Our data highlights MPA as a novel mediator valuable to predict AA prevalence and severity.

Objective— Abdominal aortic aneurysms (AAAs), dilations of the infrarenal aorta, are characterized by inflammation and oxidative stress. We previously showed increased levels of peroxiredoxin-1 (PRDX-1) in macrophages cultured from AAA patients. The purpose of the study was to determine which subpopulation of macrophages is present in AAAs and is involved in upregulation of PRDX-1 in aneurysmal disease. Methods and Results— This study used immunohistochemistry with antibodies against CD68 and mannose receptor (MR) to determine the subtype of macrophages in AAA tissue samples (n=33); laser capture microdissection to isolate each subtype; and quantitative–reverse transcriptase-polymerase chain reaction, Western blot, and ELISA to assess PRDX-1 mRNA and PRDX-1protein levels in both types. Proinflammatory CD68 + MR − macrophages predominated in adventitial tissue, whereas the intraluminal thrombus contained CD68 + MR + macrophages. The presence of lipids and iron-containing deposits confirmed their phagocytic phenotype. Laser capture microdissection-isolated CD68 + MR − and CD68 + MR + macrophages, characterized by quantitative–reverse transcriptase-polymerase chain reaction ( TNF , IL1B , MRC1 , and CCL18 ) and Western blot (stabilin and hemoglobin), validated the microdissected subtypes. PRDX-1 expression was colocalized with CD68 + MR − macrophages. PRDX-1 mRNA and PRDX-1 protein were both more abundant in CD68 + MR − than CD68 + MR + macrophages in AAA. Conclusion— These findings suggest that the proteins or mRNAs expressed by the proinflammatory CD68 + MR − macrophages may contribute to aneurysmal pathology.