Role of Neuroinflammation in the Establishment of the Neurogenic Microenvironment in Brain Diseases

In many neurological disorders, neuroinflammation contributes not only to the neuropathogenic process but also regulates hippocampal neurogenesis, which plays a critical role in cognitive and emotional functions. A major challenge is to understand how inflammation establishes the neurogenic niche microenvironment to affect the behavior of neural stem cells (NSCs) and/or neural progenitor cells (NPCs). The present review discusses recent advances of research that address such a critical question. During the past few years, several human postmortem studies have demonstrated that adult neurogenesis declines significantly during aging and neurological disorders, and that infiltration/activation of T cells and activation of microglia in the neurogenic niche may play a critical role in such decline. Neuroinflammation is believed to play a detrimental role in neurodegenerative and regenerative processes. However, the effect of neuroinflammation on neurogenesis appears to be complex, since it depends not only on the various components of inflammatory responses (immune cells and cytokines) present in the microenvironment of neurogenic niches but also on the physiological and differentiation status of NSCs.