J Hepatol. 2023 Feb 03. pii: S0168-8278(23)00077-6. [Epub ahead of print]
White adipose tissue (WAT) is critical in regulating systemic energy homeostasis in combination with the liver. Although each organ has its specialised functions, they must work coordinately through tightly regulated crosstalks to regulate whole-body metabolism. Adipose tissues and the liver are relatively resilient and can adapt to energy surplus by facilitating triglyceride (TG) storage up to a certain threshold level without significant metabolic disturbances. However, lipid storage in WAT beyond a "personalised" adiposity threshold becomes dysfunctional, including metabolic inflexibility, progressive inflammation, and aberrant adipokine secretion. Moreover, the failure of adipose tissue to store and mobilise lipids results in systemic knock-on lipid overload, particularly in the liver. Factors contributing to hepatic lipid overload include lipids released from WAT, dietary fat intake, and enhanced de novo hepatic lipogenesis (DNL). In contrast, extrahepatic mechanisms counteracting toxic hepatic lipid overload entail coordinated compensation by oxidising the surplus of fatty acids in brown adipose tissue and storing fatty acids as triglycerides in white adipose tissue. Failure of these integrated homeostatic mechanisms leads to quantitative increase and qualitative alterations in the lipidome of the liver. Initially, the hepatocytes preferentially accumulate TG species leading to a relatively "benign" non-alcoholic fatty liver (NAFL). However, with time, inflammatory responses ensue, progressing into more severe conditions such as non-alcoholic steatohepatitis (NASH), hepatic cirrhosis, and hepatocellular carcinoma, in some individuals without an early prognostic clue. Here we highlight the pathogenic importance of obesity-induced "adipose tissue failure", resulting in decreased adipose tissue functionality (i.e. fat storage capacity and metabolic flexibility), promoting NAFL/NASH development and progression.
Keywords: Adipokines; Adipose tissue biology; Cytokines; Fatty acid flux; Inflammation; Metabolic flexibility; NAFLD