Abstract
Similar to obesity, aging is associated with visceral adiposity and insulin resistance. Inflammation in adipose tissue, mainly evidenced by increased accumulation and proinflammatory polarization of T cells and macrophages, has been well-documented in obesity and may contribute to the associated metabolic dysfunctions including insulin resistance. Studies show that increased inflammation, including inflammation in adipose tissue, also occurs in aging, so-called “inflamm-aging.” Aging-associated inflammation in adipose tissue has some similarities but also differences compared to obesity-related inflammation. In particular, conventional T cells are elevated in adipose tissue in both obesity and aging and have been implicated in metabolic functions in obesity. However, the changes and also possibly functions of regulatory T cells (Treg) in adipose tissue are different in aging and obesity. In this review, we will summarize recent advances in research on the changes of these immune cells in adipose tissue with aging and obesity and discuss their possible contributions to metabolism and the potential of these immune cells as novel therapeutic targets for prevention and treatment of metabolic diseases associated with aging or obesity.
Highlights
Reviewed by: Wenxian Fu, University of California, San Diego, United States Meilian Liu, University of New Mexico Health Sciences Center, United States
We focus on changes in T lymphocytes in adipose tissue in aging and the potential roles of adipose tissue T cells in metabolic functions
Data are not consistent about the roles of invariant natural killer T (iNKT) in adipose tissue inflammation and insulin resistance associated with obesity, which were recently discussed in other review articles [61,62,63] and are not included in this review
Summary
Aging is commonly accompanied by obesity, especially abdominal/visceral adiposity that leads to numerous health problems such as insulin resistance, metabolic syndrome, cardiovascular disease, and disability [11, 12]. Alterations in adipose tissue are major contributors to age-associated metabolic dysfunctions and other health issues [5, 14, 15].There are two types of adipose tissue depots: [1] brown adipose tissue, composed of brown adipocytes, which contain numerous mitochondria and lipid droplets and function as the site of adaptive thermogenesis [16]; [2] white adipose tissue, which includes visceral adipose depots and subcutaneous adipose depots and acts as the prime location where metabolic energy is stored in the form of triglycerides during periods of nutritional excess [17]. After the middle age, the ability of subcutaneous fat depots to store lipids declines [19], leading to relocation of excess fat to visceral fat depots, causing visceral adiposity [20] This excessive lipid accumulation in visceral fat depots, along with the surrounding tissue microenvironment, may drive adipose tissue inflammation. We focus on changes in T lymphocytes in adipose tissue in aging and the potential roles of adipose tissue T cells in metabolic functions
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