White adipose tissue as endocrine organ and its role in obesity

Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity.