Microglia in the aging retina.

In the healthy retina, microglial cells represent a self-renewing population of innate immune cells, which constantly survey their microenvironment. Equipped with receptors, a microglial cell detects subtle cellular damage and rapidly responds with activation, migration, and increased phagocytic activity. While the involvement of microglial cells has been well characterized in monogenic retinal disorders, it is still unclear how they contribute to the onset of retinal aging disorders including age-related macular degeneration (AMD). There is evidence, that microglial activation is not solely a secondary manifestation of retinal tissue damage in age-related disorders. Thus, work in the aging rodent and human retina suggests that long-lived and genetically predisposed microglia transform into a dystrophic state, with loss of neuroprotective functions. In this concept, malfunction of aging microglia can trigger a chronic low-grade inflammatory environment that favors the onset and progression of retinal degeneration.