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Y. Song, L. Zhao, Y. Liu, A.M. Laties, R. Wen; Human RPE Cells Do Not Respond to CNTF: Lack of LIF Receptors . Invest. Ophthalmol. Vis. Sci. 2003;44(13):390.
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Purpose: Members of the IL-6 family of cytokines, including CNTF, LIF, and CT-1, rescue photoreceptors in a variety of animal models. Evidence shows that Müller cells are the major responding cells to these cytokines. However, information regarding other retinal cells in response to these cytokines is lacking. We report here that cultured human RPE cells do not respond to CNTF or CT-1, and the lack of response to CNTF or CT-1 is due to the absence of LIF receptor. Methods: Human RPE cells (ARPE-19) were cultured in DMEM supplemented with 10% Fetal Calf Serum at 37° and 5% CO2. Subconfluent cells were serum starved for 3 hours and then treated with 10 ng or 100 ng/ml of CNTF, CT-1, or OSM for 15 minutes. Total protein was collected and immunoblot analysis was performed to examine the amount of phosphorylated STAT3 and Akt. Expression levels of CNTFRα, LIFR, gp130, and OSMR were examined by RT-PCR. Results: No significant increase in either STAT3 or Akt phosphorylation was observed when treated with either CNTF or CT-1, even at 100 ng/ml. In contrast, there was a remarkable increase in phosphorylated STAT3 in OSM treated cells. The increase reached a maximal level at 10 ng/ml; no further increase was seen with 100 ng/ml OSM. In addition, a significant increase in Akt phosphorylation was observed when cells were treated with 10 ng/ml OSM and a further increase was seen with 100 ng/ml OSM. CNTF and CT-1 share LIFR/gp130 receptor complex, while OSM not only uses LIFR/gp130, but also has its own high affinity receptor OSMR, which forms an OSMR/gp130 receptor complex not shared by other members of the IL-6 family. Thus, the lack of response to CNTF and CT-1 could be due to the lack of LIF receptors in these cells. Indeed, results of RT-PCR experiments show no detectable transcription of LIF receptor and CNTFRα, whereas the transcription level of OSMR was comparable to that of gp130. Conclusions: Human RPE cells do not express LIF receptors and thus do not respond to cytokines that bind only to the LIFR/gp130 receptor complex, such as CNTF and CT-1. The presence of OSM receptors, however, allows them to respond to OSM. The relatively high level of OSMR expression in RPE cells suggests a role of OSM in regulating their functions.
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