An Overview for Possible Mechanisms Governing Stress-induced Microglial Activation

Abstract

Stress has been well documented to bring about various clinical disorders, ranging from neurodegeneration, as seen in such conditions as Parkinson disease and Alzheimer disease, to metabolic disorders, including diabetes mellitus. It is also known that dysregulation of immune responses in the brain is closely linked to clinical disorders. In fact, it is accepted that stress associated with daily activities, be it good or not, can affect immunity as well as general health. However, the effects of stress on immune functions, especially brain immune cells, are not fully understood. As for immune cells, three types of glial cells contribute mainly to brain immunity: astrocytes, oligodendrocytes, and microglia. Microglia differ from the others in several aspects: first, they have a monocyte lineage; and second, they originate from the mesoderm, while astrocytes and oligodendrocytes, like neuronal cells, originate from the ectoderm. Thus, microglia are considered to be the central player in exerting immune functions in the brain. In this review, we describe the microglial responses induced by various kinds of stress and propose a possible mechanism by which stress induces microglial activation.