TGFbeta1-dependent contraction of fibroblasts is mediated by the PDGFalpha receptor.

PURPOSE

Contraction of fibroblasts and the resultant tractional force is a contributing factor to fibrotic diseases of the eye, such as proliferative vitreoretinopathy (PVR). Transforming growth factor (TGF)-beta is abundant in the eye, and is one of the growth factors thought to contribute to the development of PVR. A second is platelet-derived growth factor (PDGF). In the current study, the relationship between TGFbeta1 and PDGF was investigated at the level of cellular contraction.

METHODS

To study cellular contraction, an in vitro type I collagen gel contraction assay was used with a panel of fibroblast lines that expressed the PDGFalpha receptor (alphaPDGFR) or PDGFbeta receptor (betaPDGFR) or no PDGFRs. The agents tested included rabbit vitreous, TGFbeta1, and PDGF.

RESULTS

Vitreous promoted cellular contraction, and approximately 60% of this activity was eliminated by preincubation of the vitreous with neutralizing TGFbeta antibodies. The alphaPDGFR-expressing cells responded better than cells expressing the betaPDGFR or no PDGFRs. Both of the PDGFR-expressing cell lines contracted in response to PDGF, whereas the best response to TGFbeta1 was observed with cells expressing the alphaPDGFR. Finally, TGFbeta1 promoted the tyrosine phosphorylation of both of the PDGFRs, and the alphaPDGFR was more strongly phosphorylated than the betaPDGFR.

CONCLUSIONS

The results show that the vitreous promotes cellular contraction, that TGFbeta is the major factor responsible, and that at least a portion of the TGFbeta-dependent contraction proceeds through the alphaPDGFR-that is, indirectly. Therefore, the alphaPDGFR is responsible for mediating cellular contraction of multiple growth factors: TGFbeta and members of the PDGF family.