GFAP and Gliosis: In Müller cells, the upregulation of proteins contributing to the formation of intermediate filaments, including glial fibrillary acidic protein (GFAP), is a hallmark of gliosis; in fact, in the healthy retina GFAP is only minimally expressed by Müller cells, which, on the contrary, dramatically increase GFAP expression in retinal diseases [146].