Immunological regulation of neurogenic niches in the adult brain

In mammals, neurogenesis and oligodendrogenesis are germinal processes that occur in the adult brain throughout life. The subventricular zone (SVZ) and subgranular zone (SGZ) are the main neurogenic regions in the adult brain. Therein, resides a subpopulation of astrocytes that act as neural stem cells (NSCs). Increasing evidence indicates that pro-inflammatory and other immunological mediators are important regulators of neural precursors into the SVZ and the SGZ. There are a number of inflammatory cytokines that regulate the function of NSCs. Some of the most studied include: interleukin-1, interleukin-6, tumor necrosis factor alpha, insulin-like growth factor-1, growth-regulated oncogene-alpha, leukemia inhibitory factor, cardiotrophin-1, ciliary neurotrophic factor, interferon-gamma, monocyte chemotactic protein-1 and macrophage inflammatory protein-1alpha. This plethora of immunological mediators can control the migration, proliferation, quiescence, cell-fate choices and survival of NSCs and their progeny. Thus, systemic or local inflammatory processes represent important regulators of germinal niches in the adult brain. In this review, we summarized the current evidence regarding the effects of pro-inflammatory cytokines involved in the regulation of adult NSCs under in vitro and in vivo conditions. Additionally, we described the role of proinflammatory cytokines in neurodegenerative diseases and some therapeutical approaches for the immunomodulation of neural progenitor cells.