THROMBOSIS AND HEMOSTASIS Platelet TGF- 1 contributions to plasma TGF- 1, cardiac fibrosis, and systolic dysfunction in a mouse model of pressure overload

Circulating platelets contain high concentrations of TGF1 in their -granules and release it on platelet adhesion/activation. We hypothesized that uncontrolled in vitro release of platelet TGF1 may confound measurement of plasma TGF1 in mice and that in vivo release and activation may contribute to cardiac pathology in response to constriction of the transverse aorta, which produces both high shear and cardiac pressure overload. Plasma TGF1 levels in blood collected from C57Bl/6 mice by the standard retrobulbar technique were much higher than those obtained when prostaglandin E1 was added to inhibit release or when blood was collected percutaneously from the left ventricle under ultrasound guidance. Even with optimal blood drawing, plasma TGF1 was lower in mice rendered profoundly thrombocytopenic or mice with selectively low levels of platelet TGF1 because of megakaryocytespecific disruption of their TGF1 gene (Tgfb1flox). Tgfb1flox mice were also partially protected from developing cardiac hypertrophy, fibrosis, and systolic dysfunction in response to transverse aortic constriction. These studies demonstrate that plasma TGF1 levels can be assessed accurately, but it requires special precautions; that platelet TGF1 contributes to plasma levels of TGF1; and that platelet TGF1 contributes to the pathologic cardiac changes that occur in response to aortic constriction. (Blood. 2012;119(4):1064-1074)