In vitro and in vivo evidence that thrombospondin-1 (TSP-1) contributes to stirring- and shear-dependent activation of platelet-derived TGF-beta1.
Thrombospondin 1 (TSP-1), which is contained in platelet alpha-granules and released with activation, has been shown to activate latent TGF-beta1 in vitro, but its in vivo role is unclear as TSP-1-null (Thbs1(-/-)) mice have a much less severe phenotype than TGF-beta1-null (Tgfb1(-/-)) mice. We recently demonstrated that stirring and/or shear could activate latent TGF-beta1 released from platelets and have now studied these methods of TGF-beta1 activation in samples from Thbs1(-/-) mice, which have higher platelet counts and higher levels of total TGF-beta1 in their serum than wild type mice. After either two hours of stirring or shear, Thbs1(-/-) samples demonstrated less TGF-beta1 activation (31% and 54% lower levels of active TGF-beta1 in serum and platelet releasates, respectively). TGF-beta1 activation in Thbs1(-/-) mice samples was normalized by adding recombinant human TSP-1 (rhTSP-1). Exposure of platelet releasates to shear for one hour led to near depletion of TSP-1, but this could be prevented by preincubating samples with thiol-reactive agents. Moreover, replenishing rhTSP-1 to human platelet releasates after one hour of stirring enhanced TGF-beta1 activation. In vivo TGF-beta1 activation in carotid artery thrombi was also partially impaired in Thbs1(-/-) mice. These data indicate that TSP-1 contributes to shear-dependent TGF-beta1 activation, thus providing a potential explanation for the inconsistent in vitro data previously reported as well as for the differences in phenotypes of Thbs1(-/-) and Tgfb1(-/-) mice.
Ahamed
Jasimuddin
J
Laboratory of Blood and Vascular Biology, The Rockefeller University, New York, NY, USA. jahamed@rockefeller.edu
Janczak
Christin A
CA
Wittkowski
Knut M
KM
Coller
Barry S
BS
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002339:Carotid Arteries / Q000473:pathology; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D013058:Mass Spectrometry; D051379:Mice; D018345:Mice, Knockout; D013927:Thrombosis / Q000473:pathology; D019700:Thrombospondin 1 / Q000502:physiology*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism* / Q000502:physiology
D019700:Thrombospondin 1; D053773:Transforming Growth Factor beta1