High mobility group box-1 (
HMGB1) and the
toll-like receptor 4 (TLR4) axis is a key mediator of
inflammation. Platelet-derived high mobility group box-1 (
HMGB1) may also play a critical role in
sepsis-mediated
thrombosis resulting in complications like
disseminated intravascular coagulation and
multiple organ failure. While elevated levels of
HMGB1 have been documented in humans and dogs with
systemic inflammatory response syndrome and
sepsis, a better understanding of how platelet agonists and
lipopolysaccharide (LPS) mediate platelet
HMGB1 expression would open doors to novel
therapies for
sepsis-mediated
thrombosis. Herein, we sought to determine if canine platelets express
HMGB1 in the presence or absence of LPS and agonists (
ADP or
thrombin) and if surface expression of
HMGB1 is dependent on platelet TLR4. Canine platelets were unstimulated (resting) or activated with
thrombin or
adenosine diphosphate (
ADP) in the presence or absence of Escherichia coli LPS prior to flow cytometric and western blot analyses for
HMGB1 expression. We also treated canine platelets with or without TLR4 function blocking antibody or its isotype control. We discovered that while
thrombin upregulated both surface and cellular
HMGB1 expression, LPS-mediated activation in the presence of
ADP priming led to upregulation of surface
HMGB1 expression. This expression was found to be most prominent in platelets that had undergone alpha-granule secretion. Inhibition of TLR4 attenuated LPS-induced
HMGB1 expression indicating that exteriorization of
HMGB1 may be dependent on the non-genomic pathway of platelet TLR4. Our findings indicate that upregulation of platelet-derived
HMGB1 occurs as a result of
thrombin or TLR4-mediated activation in dogs. Future studies should explore the translational implication of platelet-derived
HMGB1 as novel therapeutic targets in humans and dogs with
sepsis.