Properties and functions of adipose tissue macrophages in obesity

• Published in: Immunology Vol. 155; no. 4; pp. 407 - 417
• Main Authors: Russo, Lucia, Lumeng, Carey N.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.12.2018; John Wiley and Sons Inc
• Subjects: Adipose tissue; Animal models; Cell activation; Critical components; Dendritic cells; Diabetes mellitus; Diabetes mellitus (non-insulin dependent); Immune system; Inflammation; Insulin; insulin resistance; Leukocytes; Macrophages; Metabolic disorders; Metabolism; MMe; Monocytes; Obesity; Regulatory mechanisms (biology); Review; adipose tissue; macrophages; MMe; inflammation; insulin resistance; obesity
• ISSN: 0019-2805; 1365-2567
• DOI: 10.1111/imm.13002

Summary The expansion of adipose tissue (AT) in obesity is accompanied by the accumulation of immune cells that contribute to a state of low‐grade, chronic inflammation and dysregulated metabolism. Adipose tissue macrophages (ATMs) represent the most abundant class of leukocytes in AT and are involved in the regulation of several regulatory physiological processes, such as tissue remodeling and insulin sensitivity. With progressive obesity, ATMs are key mediators of meta‐inflammation, insulin resistance and impairment of adipocyte function. While macrophage recruitment from blood monocytes is a critical component of the generation of AT inflammation, new studies have revealed a role for ATM proliferation in the early stages of obesity and in sustaining AT inflammation. In addition, studies have revealed a more complex range of macrophage activation states than the previous M1/M2 model, and the existence of different macrophage profiles between human and animal models. This review will summarize the current understanding of the regulatory mechanisms of ATM function in relation to obesity, type 2 diabetes, depot of origin, and to other leukocytes such as AT dendritic cells, with hopes of emphasizing the regulatory nodes that can potentially be targeted to prevent and treat obesity‐related metabolic disorders. Obesity‐driven adipose tissue dysfunction is mechanistically linked to inflammation. Given that adipose tissue macrophages represent the major source of inflammation in this tissue, we discuss the most recent characteristics of these cells providing an overview on ATM heterogeneity, cellular markers and functions. We also focus on the differences between mice and humans as well as the comparison with adipose tissue dendritic cells.