Abstract
Background Mouse Müller cells, considered dormant retinal progenitors, respond to retinal injury by undergoing reactive gliosis rather than displaying regenerative responses. Tumor necrosis factor alpha (TNFα) is a key cytokine induced after injury, and implicated in mediating inflammatory and regenerative responses. However, the molecular events driving reactive gliosis and regenerative responses in Müller cells, and the role of TNFα in these processes, remain unclear. In this study, we investigated the effects of TNFα on Müller cell responses following injury. Methods To investigate the involvement of TNFα in retinal injury, adult C57BL/6J mice were subjected to treatment with light (5,000 lux) for 14 consecutive days; induction of TNFα was confirmed by quantitative polymerase chain reaction (qPCR). TNFα effects on Müller-cell proliferation were evaluated via 5-ethynyl-2’-deoxyuridine (EdU) incorporation in culture. TNFα-mediated gene profile changes were examined using Affymetrix microarray, and gene ontology analysis was carried out to define the molecular pathways involved. Gene- and protein-expression changes were further verified by qPCR, western blot, and enzyme linked immunosorbent assay (ELISA). Results We showed that TNFα induced Müller cell proliferation and the expression of inflammatory and proliferation-related genes, including NFKBIA, Leukemia inhibitory factor, Interleukin-6, Janus kinase (Jak) 1, Jak2, Signal transducer and activator of transcription (Stat) 1, Stat2, Mitogen-Activated Protein Kinase (MAPK) 7, and MAP4K4. Blockade of Jak/Stat and MAPK pathways attenuated TNFα-induced Müller cell proliferation. Moreover, we detected TNFα drove A1 phenotype-reactive gliosis, while Wnt attenuated TNFα-mediated induction of A1 phenotype and promoted an A2-like phenotype. Conclusion In Müller cells, TNFα triggered primarily inflammatory and reactive gliosis by activating Jak/Stat and MAPK-pathways without inducing progenitor cell/regeneration-related genes. Wnt signaling suppressed inflammation, and induced proliferation and expression of progenitor-cell genes in Müller cells. These results suggest that reactive gliosis and regenerative responses in Müller cells are regulated by independent mechanisms. Our study provides new insights into regulation of inflammatory and regenerative responses of Müller cells in the injured retina
Neurochemical plasticity of Müller cells after retinal injury: overexpression of GAT-3 may potentiate excitotoxicity