Infusion of Vivo-ERp57 morpholino resulted in markedly
reduced expression of ERp57 levels in platelets as well as the
kidney and liver. Platelet aggregation was impaired in
platelets from Vivo-ERp57-exposed mice. To determine the
functional importance of ERp57 secreted from activated
platelet and endothelium in vivo, the kinetics of platelet accumulation
and fibrin formation was evaluated using intravital
microscopy in Vivo-ERp57-treated animals. Both
platelet thrombus formation and fibrin accumulation were
significantly impaired in mice exposed to Vivo-ERp57
morpholino compared to control Vivo-morpholino (Fig. 6).
Our group has further explored the role of ERp57 in
thrombus formation using the laser injury thrombosis
model to determine how isolated deficiency of platelet
ERp57 affects thrombus formation in vivo. We generated
ERp57fl/flPF4Cre-positive mice that did not express ERp57
in their platelets, but expression of PDI, ERp5, and ERp72
was not affected. ERp57fl/flPF4Cre-positive mice had a
prolonged bleeding time, and ERp57fl/flPF4Cre-positive platelets
failed to aggregate in response to a PAR4 agonist. In response
to laser-induced vessel wall injury, platelet thrombus size
in ERp57fl/flPF4Cre-positive mice was reduced by 85% compared
to ERp57fl/flPF4Cre-negative control animals (Fig. 6).
However, fibrin deposition at sites of laser injury was comparable
in the two experimental and control groups (Fig. 6D). A
function blocking antibody directed against ERp57 also inhibited
both platelet accumulation and fibrin formation following
laser-induced injury. These results indicate that under