Expression of transforming growth factor-beta s and their receptors by human retinal glial cells.
To help test the hypothesis that transforming growth factor beta (TGF-beta) may serve an autocrine function in the retina, we asked whether human Müller (glial) cells in culture express TGF-beta receptors, contain transcripts for various isoforms of this cytokine, and release TGF-beta s into the medium. Using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique with specific primers for TGF-beta 1, -beta 2 and -beta 3 precursors and for TGF-beta type I and type II receptors, we searched for mRNA transcripts expressed by cultured human Müller cells. Also, an ELISA assay allowed quantification of the levels of various TGF-beta s in medium exposed to these glial cells. Human Müller cells in culture express transcripts for both type I and type II TGF-beta receptors and also for TGF-beta 1 and TGF-beta 2. In conditioned medium, the concentration of TGF-beta 1 in the mature form was below detectable levels, and the total TGF-beta 1 was relatively low (mean = 252 pg/ml in confluent cultures). In contrast, the mean levels of mature (55 pg/ml) and total (2530 pg/ml) TGF-beta 2 were markedly higher. Our observations that cultured Müller cells contain mRNA coding for the TGF-beta 2 precursor, release TGF-beta 2 into the medium and express transcripts for both type I and type II TGF-beta receptors are consistent with the idea that this cytokine serves an autocrine function for these glia in the retina.