Cannabinoid receptor type-2 stimulation, blockade, and deletion alter the vascular inflammatory responses to traumatic brain injury

BACKGROUND: Immunomodulatory therapies have been identified as interventions for secondary injury after traumatic brain injury (TBI). The cannabinoid receptor type-2 (CB(2)R) is proposed to play an important, endogenous role in regulating inflammation. The effects of CB(2)R stimulation, blockade, and deletion on the neurovascular inflammatory responses to TBI were assessed. METHODS: Wild-type C57BL/6 or CB(2)R knockout mice were randomly assigned to controlled cortical impact (CCI) injury or to craniotomy control groups. The effects of treatment with synthetic, selective CB(2)R agonists (0-1966 and JWH-133), a selective CB(2)R antagonist, or vehicle solution administered to CCI groups were assessed at 1-day after injury. Changes in TNF-α, intracellular adhesion molecule (ICAM-1), inducible nitric oxide synthase (iNOS), macrophage/microglial ionized calcium-binding adaptor molecule, and blood-brain-barrier (BBB) permeability were assessed using ELISA, quantitative RT-PCR, immunohistochemistry, and fluorometric analysis of sodium fluorescein uptake. CB(2)R knockouts and wild-type mice with CCI injury were treated with a CB(2)R agonist or vehicle treatment. RESULTS: TNF-α mRNA increased at 6 hours and 1 to 3 days after CCI; a CB(2)R antagonist and genetic knockout of the CB(2)R exacerbated TNF-α mRNA expression. Treatment with a CB(2)R agonist attenuated TNF-α protein levels indicating post-transcriptional mechanisms. Intracellular adhesion molecule (ICAM-1) mRNA was increased at 6 hours, and at 1 to 2 days after CCI, reduced in mice treated with a CB(2)R agonist, and increased in CB(2)R knockout mice with CCI. Sodium fluorescein uptake was increased in CB(2)R knockouts after CCI, with and without a CB(2)R agonist. iNOS mRNA expression peaked early (6 hours) and remained increased from 1 to 3 days after injury. Treatment with a CB(2)R agonist attenuated increases in iNOS mRNA expression, while genetic deletion of the CB(2)R resulted in substantial increases in iNOS expression. Double label immunohistochemistry confirmed that iNOS was expressed by macrophage/microglia in the injured cortex. CONCLUSION: Findings demonstrate that the endogenous cannabinoid system and CB(2)R play an important role in regulating inflammation and neurovascular responses in the traumatically injured brain. CB(2)R stimulation with two agonists (0-1966 and JWH-133) dampened post-traumatic inflammation, while blockade or deletion of the CB(2)R worsened inflammation. Findings support previous evidence that modulating the CB(2)R alters infiltrating macrophages and activated resident microglia. Further investigation into the role of the CB(2)R on specific immune cell populations in the injured brain is warranted.