Abstract
Phagocytosis by glial cells has been shown to play an important role in maintaining brain homeostasis. Microglia are currently considered to be the major phagocytes in the brain parenchyma, and these cells phagocytose a variety of materials, including dead cell debris, abnormally aggregated proteins, and, interestingly, the functional synapses of living neurons. The intracellular signaling mechanisms that regulate microglial phagocytosis have been studied extensively, and several important factors, including molecules known as “find me” signals and “eat me” signals and receptors on microglia that are involved in phagocytosis, have been identified. In addition, recent studies have revealed that astrocytes, which are another major glial cell in the brain parenchyma, also have phagocytic abilities. In this review, we will discuss the roles of microglia and astrocytes in phagocytosis-mediated brain homeostasis, focusing on the characteristics and differences of their phagocytic abilities.
Highlights
Phagocytosis is a dynamic process that consists of several steps
We compared the phagocytic functions of microglia and astrocytes, which have attracted much attention in recent years, from the viewpoint of their different roles in phagocytosis
Whether these differences are because microglia and astrocytes are derived from the mesoderm and ectoderm, respectively, and have different intrinsic cellular characteristics, was not determined but will be interesting to study in the future
Summary
Phagocytosis is a dynamic process that consists of several steps. First, the targets of phagocytosis are recognized by phagocytic receptors or are ingested through nonspecific mechanisms. We outline the main targets of phagocytosis of both cell types, cell debris, amyloid-β (Aβ), and synapses, while comparing the characteristics and molecular mechanniissmmss ooff pphhaaggooccyyttoossiiss iinn mmiiccrroogglliiaa aanndd aassttrrooccyytteess. Knockdown of MEGF10 with siMEGF10 in astrocytes did not impair astrocyte-mediated phagocytosis of apoptotic microglia, whereas knockdown of Axl and Mer tyrosine kinase (Mertk), which are members of the Tyro3-Axl-Mer (TAM) receptor kinase family, was found to impair phagocytosis, which was not consistent with the results in the studies described in the previous paragraph It is unclear whether the different results on the involvement of MEGF10 in phagocytosis are due to different types of cells being phagocytosed or by different experimental methods. These findings indicate that phagocytosis is regulated by chemical signals through receptors and by nonchemical signals
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