Overview

Abstract

Adipose tissue has evolved into a highly specialized tissue for storing energy in the form of triglycerides (TGs, also called triacylglycerols, or “fat”). It is heterogeneous in cellular composition, location, and function – reflecting its complex role in normal physiology and disease [1]. It is comprised not only of different types of adipocytes (ranging from white to brown) but also other non-adipocyte cell types (such as stromal vascular and immune cells) to form a true multicellular organ [2]. Unlike other organs, adipose tissue is distributed throughout the body where it exhibits location-specific properties. Furthermore, its functions extend well beyond its role in fat storage to a variety of other processes necessary for physiological homeostasis including energy homeostasis, immune homeostasis, and reproductive function [3]. The heterogeneity of adipose tissue is reflected by the variety of clinical disorders that result from adipose tissue dysfunction [4, 5]. Indeed, both adipose tissue excess (obesity) and deficiency (lipodystrophy) result in profound physiological impairments that promote the metabolic syndrome (see chapter “Metabolic syndrome”) and cardiovascular disease (see chapter “Atherosclerotic heart disease”). Adipose tissue dysfunction or excess also contributes to a myriad of other diseases affecting virtually all organ systems including liver disease, i.e., fatty liver and cirrhosis (see chapter “Cirrhosis”); kidney disease, e.g., diabetic and hypertensive nephropathy (see chapters “Diabetes mellitus” and “Hypertension”); pulmonary disease, e.g., sleep apnea; musculoskeletal disease, i.e., arthritis (see chapters “Osteoarthritis” and “Rheumatoid arthritis”) and back pain; reproductive disease, i.e., infertility; psychological disease, i.e., depression (see chapter “Major depressive disorder”); and even cancer (see chapter “Overview” under the part “Cancer”) [6]. Thus, adipose tissue is not simply an inert tissue for storing fat, but a highly dynamic tissue required for health and survival. By understanding the unique characteristics of adipose tissue, can we begin to exploit its complexities to treat or prevent disease.