Microglia-Targeted Pharmacotherapy in Retinal Neurodegenerative Diseases

Microglial cells, members of the monocytic lineage, represent the resident immunocompetent cells of the central nervous system including the retina with its peculiarities like a double blood retinal barrier. Microglial cells invade the retina in response to naturally occurring neuronal death during embryonic development and remodelling. Resident microglial cells are extremely sensitive to changes in their microenvironment arising from either traumatic or chronic neurodegeneration, inproper wiring, hereditary diseases or infection and become rapidly activated. In their activated state, the cells undergo drastic morphological changes, upregulate a variety of receptors and secrete soluble factors, which contribute to recognition and phagocytotic cleareance of dying or malfunctioning neurons. In this review, we aim to summarise the current knowledge of microglial involvement in experimentally induced or naturally occurring retinal neurodegenerations with emphasising on mechanisms of microglia activation. Expanding on the mechanisms, we shall discuss on approaches to pharmacologically interfere with the microglial activation and neurophagy. The protagonistic role of these cells in the outcome of certain diseases may help designing microglial targeted treatments with potential benefit for neuronal survival and regeneration in clinically relevant conditions.