Bone morphogenetic proteins and growth and differentiation factors in the human cornea.

PURPOSE To investigate transcription of members of the transforming growth factor (TGF)-beta superfamily and corresponding receptors in human corneal epithelium and stroma. METHODS Transcription of bone morphogenetic proteins (BMP)-2, BMP-3, BMP-4, BMP-5, and BMP-7; growth- differentiation factor (GDF)-5), and BMP receptors (BMPR) types I (BMPR-IA, BMPR-IB) and II (BMPR-II) was investigated by reverse transcription-polymerase chain reaction (RT-PCR) in ex vivo and cultured cells. For verification, PCR fragments were cloned and sequenced. DNA dot blot analysis was performed to estimate the level of transcription. RNA dot blots were performed to determine expression of GDF-5. Expression of BMP receptor proteins was investigated by immunohistochemistry. Single-cell clonal growth proliferation assays were performed using recombinant human GDF-5 and TGF-beta1. RESULTS Transcription of BMP-2, BMP-3, BMP-4, BMP-5, and BMP-7 and receptors of BMPR-IA, BMPR-IB and BMPR-II was detected in ex vivo and cultured epithelium and stroma. The level of transcription was higher in cultured stroma for all factors, but the level for the receptors was higher in cultured epithelium. In contrast GDF-5 was transcribed only in stromal cells, suggesting that this cytokine may be an important mediator between keratocytes and epithelial cells. Furthermore, GDF-5 inhibited proliferation of corneal epithelial and stromal cells. CONCLUSIONS Given the importance of the TGF-beta family during embryonic development, the results suggest that its members may be components of the corneal cytokine network and may participate in the regulation of cellular proliferation and differentiation.