Figure 3.

Activation of latent TGF-β1 by Mf contraction is integrin mediated. Cultured rat lung Mfs express β3 (A), β1 (B), and αvβ5 integrin (C), as shown by confocal micrographs produced from immunostaining. (D) TMLC were seeded directly on 7-d-old Mf cultures 2 h before adding modulators of integrin binding for an additional 2 h; this was followed by another 1-h incubation in the absence or presence of 0.5 U/ml thrombin. Integrin binding was stimulated with Mn²⁺ and inhibited using RGD peptides, LAP–TGF-β1 (LAPβ1) decapeptide, and integrin function-blocking antibodies; scrambled DGR peptide was used as control. The broken line shows basal latent TGF-β1 activation by Mfs; the dotted line demonstrates active TGF-β1 levels after inducing contraction with thrombin only. Results are expressed as a percentage of nonstimulated control (BSA) corrected for TMLC baseline reporter activity. (E) Controls were performed to test the effect of integrin modulators on TMLC reporter activity with and without stimulation by TGF-β1 and 0.5 U/ml thrombin. Error bars represent the SD of the mean. Bar, 10 μm.