Protease-activated receptor 4 deficiency increases mortality, intracranial bleeding, and blood-brain barrier impairment following traumatic brain injury in mice

Abstract

Background: Protease-activated receptors (PARs), comprising PAR1 to PAR4, play a critical role in hemostasis and are considered potential therapeutic targets. Clinical trials have evaluated the safety and dosage of PAR4 antagonists, and a pathogenic role of PAR4 has been demonstrated in animal models of coagulopathies, including hemorrhagic brain injury. However, there is a lack of studies regarding the acute effects of PAR4 deficiency (PAR4-/-) following experimental traumatic brain injury (TBI). Objectives: To determine the role of PAR4 in cerebral hemostasis after TBI. Methods: Adult male PAR4-/- and genetically background-matched wild-type C57BL/6 mice (BL6; N = 22 each) were subjected to the controlled cortical impact model of TBI. We analyzed physiological and neurological parameters as well as (immuno-)histology and gene expression. Results: PAR4-/- mice exhibited increased mortality and body weight loss within 24 hours after TBI compared with BL6 mice. TBI-induced neurological deficits were similar between PAR4-/- and BL6 mice. Notably, PAR4-/- mice exhibited subdural hematoma, increased intracerebral hemorrhage, and blood-brain barrier leakage compared with BL6 mice. Severely impaired hemostasis was not associated with significant changes in brain lesion size or in the inflammatory activation of microglia and astrocytes in surviving mice. Conclusion: Our results demonstrate a crucial role for PAR4 in cerebral hemostasis following experimental TBI in mice and suggest that particular caution is warranted in the therapeutic management of PAR4-targeted treatment of coagulopathies.