Elise Dalmas

Krüppel-like factor 4 regulates macrophage polarization

Current paradigms suggest that two macrophage subsets, termed M1 and M2, are involved in inflammation and host defense. While the distinct functions of M1 and M2 macrophages have been intensively studied - the former are considered proinflammatory and the latter antiinflammatory - the determinants of their speciation are incompletely understood. Here we report our studies that identify Krüppel-like factor 4 (KLF4) as a critical regulator of macrophage polarization. Macrophage KLF4 expression was robustly induced in M2 macrophages and strongly reduced in M1 macrophages, observations that were recapitulated in human inflammatory paradigms in vivo. Mechanistically, KLF4 was found to cooperate with Stat6 to induce an M2 genetic program and inhibit M1 targets via sequestration of coactivators required for NF-κB activation. KLF4-deficient macrophages demonstrated increased proinflammatory gene expression, enhanced bactericidal activity, and altered metabolism. Furthermore, mice bearing myeloid-specific deletion of KLF4 exhibited delayed wound healing and were predisposed to developing diet-induced obesity, glucose intolerance, and insulin resistance. Collectively, these data identify KLF4 as what we believe to be a novel regulator of macrophage polarization.

Defining macrophage phenotype and function in adipose tissue.

In obesity, chronic low-grade inflammation is thought to mediate the effects of increased adipose tissue mass on metabolic comorbidity. Of the different cell types that contribute to obesity-induced inflammation in adipose tissue, this review focuses on macrophages and their monocytes precursors. Mechanisms for monocyte recruitment to adipose tissue, and how both monocytes and macrophages are phenotypically modified in this environment in response to increasing fat mass, are considered. The versatile phenotype of adipose tissue macrophages might contribute not only to inflammatory and metabolic alterations, but could also help to maintain adipose tissue homeostasis in the setting of obesity.

CD14dimCD16+ and CD14+CD16+ Monocytes in Obesity and During Weight Loss

Objective—Studies suggest the implication of CD16+ subpopulations (CD14+CD16+, CD14dimCD16+) in inflammatory diseases. We aimed to determine the frequency of these subpopulations during weight loss in obesity and diabetes, conditions associated with changes in systemic inflammation, and we tested the link with subclinical atherosclerosis. Methods and Results—CD14dimCD16+ and CD14+CD16+ frequencies were measured by flow cytometry in lean subjects, obese subjects before and after a hypocaloric diet or gastric surgery, and obese diabetic subjects before and after gastric surgery. Both monocyte subsets were increased in obese subjects, with a significant enrichment of the CD14dimCD16+ subpopulation in obese diabetic patients. Multivariate analysis demonstrated a link between the percentages of CD14dimCD16+ monocytes and glycemia, independent of fat mass. Drastic weight loss led to a sharp decrease of this subset, the variations of which were strongly related to fat mass changes. A reduction of at least 5% of fat mass was sufficient to observe a significant decrease of CD14dimCD16+ monocytes. A diminution of the CD14+CD16+ subset was also observed during weight loss and was associated with a decrease in intima-media thickness. Conclusion—This work demonstrates a major impact of fat mass variations on CD14dimCD16+ monocyte subsets and that the decrease in the CD14+CD16+ subpopulation is linked to a reduction of subclinical atherosclerosis. Clinical Trial Registration—URL: http://clinicaltrials.gov. Unique identifier: NCT00476658.

T cell-derived IL-22 amplifies IL-1β-driven inflammation in human adipose tissue: relevance to obesity and type 2 diabetes.

Proinflammatory cytokines are critically involved in the alteration of adipose tissue biology leading to deterioration of glucose homeostasis in obesity. Here we show a pronounced proinflammatory signature of adipose tissue macrophages in type 2 diabetic obese patients, mainly driven by increased NLRP3-dependent interleukin (IL)-1β production. IL-1β release increased with glycemic deterioration and decreased after gastric bypass surgery. A specific enrichment of IL-17- and IL-22-producing CD4+ T cells was found in adipose tissue of type 2 diabetic obese patients. Coculture experiments identified the effect of macrophage-derived IL-1β to promote IL-22 and IL-17 production by human adipose tissue CD4+ T cells. Reciprocally, adipose tissue macrophages express IL-17 and IL-22 receptors, making them sensitive to IL-17 and IL-22. IL-22 increased IL-1β release by inducing pro-IL-1β transcription through activation of C-Jun pathways in macrophages. In sum, these human data identified IL-1β and the T-cell cytokine IL-22 as key players of a paracrine inflammatory pathway previously unidentified in adipose tissue, with a pathological relevance to obesity-induced type 2 diabetes. These results provide an additional rationale for targeting IL-1β in obesity-linked type 2 diabetes and may have important implications for the conception of novel combined anti-IL-1β and anti-IL-22 immunotherapy in human obesity.

Variations in circulating inflammatory factors are related to changes in calorie and carbohydrate intakes early in the course of surgery-induced weight reduction.

BACKGROUND Obesity is considered a low-grade inflammatory state that improves with weight loss. In addition to acute-phase proteins, other cytokines might contribute to systemic inflammation. OBJECTIVE Our objective was to compare serum concentrations of a large panel of inflammation-related factors in obese and normal-weight subjects and to determine kinetic changes induced by caloric restriction. DESIGN The cohort comprised 14 normal-weight women and 51 obese women who were followed over 2 y after Roux-en-Y gastric bypass. Multiplexed proteomics were used to simultaneously assay 27 cytokines and growth factors in serum. RESULTS Concentrations of interleukin (IL)-9, IL-1-receptor antagonist, IL-10, interferon-γ-inducible protein 10, macrophage inflammatory protein 1β, monocyte chemoattractant protein 1, IL-8, RANTES (regulated upon activation, normal T cell expressed and secreted), monokine induced by interferon-γ, and vascular endothelial growth factor were found to be elevated in obesity. IL-10 was further elevated in diabetic obese patients, whereas eotaxin was found to be higher only in diabetic subjects. After surgery, many factors showed a biphasic pattern of variation, decreasing sharply at month 3 before rising back to presurgical values at month 6; these changes closely tracked similar kinetic changes in calorie and carbohydrate intake. After 1 y, an overall reduction in cytokines accompanied the reduction in body mass index and an amelioration in metabolic status. CONCLUSIONS Obesity is associated with elevated circulating concentrations of a large panel of cytokines. Coordinated kinetic changes during weight loss suggest an early influence of calorie and carbohydrate intakes, whereas a longer-term reduction in corpulence might prevail in regulating circulating cytokine concentrations. This trial is registered at clincaltrials.gov as NCT00476658.

Irf5 deficiency in macrophages promotes beneficial adipose tissue expansion and insulin sensitivity during obesity

Accumulation of visceral adipose tissue correlates with elevated inflammation and increased risk of metabolic diseases. However, little is known about the molecular mechanisms that control its pathological expansion. Transcription factor interferon regulatory factor 5 (IRF5) has been implicated in polarizing macrophages towards an inflammatory phenotype. Here we demonstrate that mice lacking Irf5, when placed on a high-fat diet, show no difference in the growth of their epididymal white adipose tissue (epiWAT) but they show expansion of their subcutaneous white adipose tissue, as compared to wild-type (WT) mice on the same diet. EpiWAT from Irf5-deficient mice is marked by accumulation of alternatively activated macrophages, higher collagen deposition that restricts adipocyte size, and enhanced insulin sensitivity compared to epiWAT from WT mice. In obese individuals, IRF5 expression is negatively associated with insulin sensitivity and collagen deposition in visceral adipose tissue. Genome-wide analysis of gene expression in adipose tissue macrophages highlights the transforming growth factor β1 (TGFB1) gene itself as a direct target of IRF5-mediated inhibition. This study uncovers a new function for IRF5 in controlling the relative mass of different adipose tissue depots and thus insulin sensitivity in obesity, and it suggests that inhibition of IRF5 may promote a healthy metabolic state during this condition.

Intima-media thickness in severe obesity: links with BMI and metabolic status but not with systemic or adipose tissue inflammation.

OBJECTIVE Obesity is associated with cardiovascular risk and a low-grade inflammatory state in both blood and adipose tissue (AT). Whether inflammation contributes to vascular alteration remains an open question. To test this hypothesis, we measured arterial intima-media thickness (IMT), which reflects subclinical atherosclerosis, in severely obese subjects and explored associations with systemic inflammation and AT inflammation. RESEARCH DESIGN AND METHODS IMT of the carotid artery (C-IMT) and IMT of the femoral artery (F-IMT) were measured in 132 nonobese (control) subjects (BMI 22.3 kg/m2; mean age 44.8 years) and 232 subjects who were severely obese without diabetes (OB/ND; n = 146; BMI 48.3 kg/m2; age 38.2 years) or severely obese with type 2 diabetes (OB/D; n = 86; BMI 47.0; age 49.4 years). In 57 OB/ND subjects, circulating soluble E-selectin, matrix metalloproteinase 9, myeloperoxidase, soluble intracellular adhesion molecule 1, soluble vascular cell adhesion molecule 1, tissue plasminogen activator inhibitor 1, cystatin C, cathepsin S, and soluble CD14 were measured in serum. AT macrophages were quantified by CD68 immunochemistry. RESULTS Both C-IMT and F-IMT increased in OB/ND and OB/D patients. In OB/ND patients, age was the sole independent determinant of IMT. No significant association was found with circulating inflammation-related molecules, number of CD68+ cells, or the presence of crown-like structures in visceral or subcutaneous AT of OB/ND patients. CONCLUSIONS IMT increased with severe obesity but was not influenced by the degree of systemic inflammation or AT macrophage accumulation.

A role for interleukin-22 in the alleviation of metabolic syndrome.

Increasing evidence points to a role for the immune system in the regulation of metabolism. Two new studies in mice indicate treatment with interleukin-22 restores mucosal immunity in diabetes and alleviates metabolic disease, resulting in improved glycemic control.

Adipose tissue adaptive response to trans-10,cis-12–conjugated linoleic acid engages alternatively activated M2 macrophages

In mice, nutritional supplementation with the trans‐10,cis‐12 isomer of linoleic acid (t10,c12‐CLA) promotes lipoatrophy, hyperinsulinemia, and macrophage infiltration in white adipose tissue (WAT). We explored the dynamics of these interrelated responses over 2 consecu‐five 7 d periods of t10,c12‐CLA administration and withdrawal. t10,c12‐CLA down‐regulated lipogenic and lipolytic gene expression and increased collagen deposition, but with no evidence of cross‐linking. An abundant CD45+ cell infiltrate, comprising prominently CD206+CD11c‐ macrophages, was found in WAT in association with an anti‐inflammatory gene signature. Infiltration of natural killer (NK) and dendritic cells contributed to WATs innate immune response to t10,d12‐CLA. Less abundant adaptive immune cells colonized WAT, including B, NK T, γδ T, and αβ T cells. By contrast, T‐regulatory cell abundance was not affected. Interruption of treatment allowed recovery of WAT mass and normalization of insulinemia, coincident with regain of WAT homeostasis owing to a coordinated reversion of genic, structural, and immune deregulations. These data revealed a striking resilience of WAT after a short‐term metabolic injury induced by t10,d2‐CLA which relies on alternatively activated M2 macrophage engagement. In addition, the temporal links between variations in WAT alterations and insulinemia upon t10,c12‐CLA manipulation strengthen the view that WAT dysfunctional status is critically involved in altered glucose homeostasis.—Pini, M., Touch, S., Poirier, H., Dalmas, E., Niot, I., Rouault, C., Druart, C., Delzenne, N., Clément, K., André, S., Guerre‐Millo, M. Adipose tissue adaptive response to trans‐10,cis‐12‐conjugated linoleic acid engages alternatively activated M2 macrophages. FASEB J. 30, 241‐251 (2016). www.fasebj.org

Macrophages and Inflammation

Adipose tissue has been under focus in the last decades, and pivotal concepts have emerged from the studies of its complex biology. White adipose tissue is composed of mature adipocytes, precursors (preadipocytes), endothelial cells, macrophages, and other immune cells. The phenotype, amount, and biology of each adipose tissue component are profoundly altered in human obesity. Low-grade inflammation both at the local and systemic levels characterizes obesity and appears to have a key role in mediating the consequence of increased adipose tissue mass on metabolic and vascular comorbidities. Among the different cell types contributing to inflammation, this chapter focuses on the mechanisms and consequences of macrophage accumulation in obese adipose tissue. While differences probably exist between rodent models and human cases, macrophage cells have a very complex phenotype able to change with weight modification. It is not fully established whether macrophages exert a rather beneficial or deleterious role in the adipose tissue. In any case, the presence of these cells modifies the biology of adipose specialized cells such as preadipocytes and adipocytes. This chapter reviews the current knowledge regarding the contribution of monocytes/macrophages in development and maintenance of obesity and related complications both in mouse and human situations.