In vitro and in vivo evidence for shear-induced activation of latent transforming growth factor-β1

Transforming growth factor-beta 1 (TGF-beta 1) has potent physiologic and pathologic effects on a variety of cell types at subnanomolar concentrations. Platelets contain 40 times as much TGF-beta 1 as other cells and secrete it as an inactive ( latent) form in complex with latency-associated peptide ( LAP), which is disulfide bonded via Cys33 to latent TGF-beta binding protein 1 (LTBP-1). Little is known about how latent TGF-beta 1 becomes activated in vivo. Here we show that TGF-beta 1 released from platelets or fibroblasts undergoes dramatic activation when subjected to stirring or shear forces, providing a potential mechanism for physiologic control. Thioldisulfide exchange appears to contribute to the process based on the effects of thiol-reactive reagents and differences in thiol labeling of TGF-beta 1 before and after stirring or shear. Activation required the presence of LTBP, as TGF-beta 1 contained in complex with only LAP could not be activated by stirring when studied as either a recombinant purified protein complex or in the platelet releasates or sera of mice engineered to contain an LAP C33S mutation. Release and activation of latent TGF-beta 1 in vivo was demonstrated in a mouse model 5 minutes after thrombus formation. These data potentially provide a novel mechanism for in vivo activation of TGF-beta 1. (Blood. 2008; 112: 3650-3660)