The glial cells of the retina aid in function and maintenance of the retina. The macroglia, Muller cells and the retinal astrocytes, become reactive following injury or disease in the retina, a response that is characterized by hypertrophy, dedifferentiation, loss of functionality, proliferation, and remodeling of tissue and extracellular matrix (ECM). The microglia which are the resident macrophages, also respond to injury/disease becoming activated, undergoing characteristic molecular and morphological changes, which include regulation of secreted factors, changes in inflammatory response and increased phagocytosis. Reactivity in Muller glia is thought to be the result of secreted signals, such as epidermal growth factor, ciliary neurotrophic factor, and fibroblast growth factor, which are released at the injury site to interact with quiescent glial cells. Furthermore, microglia and macroglia have been shown by some studies to interact following activation. While BMPs are known to be upregulated following injury in the CNS, little information is available concerning their role in reactive gliosis in the retina. We hypothesize that BMP7 indirectly triggers Müller gliosis by activating microglia. Using RT-qPCR, immunofluorescence and western blot, we assessed changes in gliosis markers in the mouse retinal glia following treatment with BMP. Our results showed that BMP7 was able to trigger Müller cell gliosis in the retina in vitro and in vivo. Furthermore, ablation of microglia lead to a subdued gliosis response in the mouse retina following BMP7 exposure. Thus, BMP7 triggers activation of retinal microglia in addition to the Müller glia. IFN-gamma and IL6 could play a role in microglia mediated activation of Muller glia, following exposure to BMP7. We also assessed the role of the Hippo/YAP pathway in the regulation of gliosis in the retina. We demonstrated that YAP was localized to the nucleus of the Müller cells of the retina and was upregulated in IFN-gamma induced gliosis in the mouse retina
