Proteomic profiling of primary retinal Müller glia cells reveals a shift in expression patterns upon adaptation to in vitro conditions.

Cultured primary retinal Müller glia cells (RMG), a glia cell spanning the entire neuroretina, have recently gained increased attention, especially with respect to their presumed in vivo role in supporting photoreceptor function and survival. Cultured RMG cells, however, are at risk to lose much of their in vivo features. To determine the conditions of isolated primary RMG cells best corresponding with their physiological role in the intact retina, we profiled the respective proteomes of RMG freshly isolated from intact pig eye, as well as from cultured material at different timepoints. Protein samples were separated by high-resolution two-dimensional electrophoresis (2-DE), and isolated proteins were identified by matrix-assisted laser desorption ionization time-of- flight (MALDI-TOF) peptide mass fingerprint. Compared with freshly isolated RMG, the in vitro protein expression patterns remain relatively stable for the first 3 days in culture but change dramatically thereafter. Proteins involved in specific RMG physiological functions, such as glycolysis, transmitter recycling, CO2 siphoning, visual pigment cycle, and detoxification, are either downregulated or absent. In contrast, cytoskeletal proteins, as well as proteins involved in motility and in proliferation, are upregulated during culture. In the present report, we show for the first time, on a systematic level, that profound changes in the RMG proteome reflect transdifferentiation from a multifunctional, highly differentiated glial cell to a dedifferentiated fibroblast-like phenotype in culture.