M2 Macrophages in the Metabolic Organs and in the Neuroendocrine System

Abstract

Metabolism is a principle of the living organism. It is a complex network of enzymatic and nonenzymatic biochemical transformation processes to sustain life that produce, degrade, and convert vital materials for the organism, generate energy, and eliminate nonfunctional or toxic materials [1, 2]. The proper function of this complex network requires regulatory mechanisms that integrate and synchronize this plethora of processes [1, 3]. In the simplest cellular organisms, robust factors control metabolism, such as substrate availability and the chemical environment that determine the activity of the metabolic pathways. The growing complexity of metabolic networks, however, requires more sophisticated regulatory mechanisms: the endocrine organs and the nervous system become upstream-acting regulators of the metabolism, and signaling modules and complex interactions evolve between the metabolic organs and the neuroendocrine system. Macrophages reside within the metabolic organs and the neuroendocrine system, where they have direct effects on metabolism. Macrophages aid the development of metabolic organs such as the adipose tissue and the liver, and also shape the function of metabolic cells. This trait of macrophages has mostly been studied in metabolic diseases and in the context of M1 activation. We know how suppression of M1 activation would affect metabolism; however, little is known about the physiological function of M2 macrophages in the metabolic organs and in metabolic regulation.