PROJECT SUMMARY Traumatic brain injury (TBI) is a major health concern in terms of human disability, medical expenses, and lost productivity. In addition to immediate mechanical trauma, secondary neurovascular dysfunction, including cerebral edema, impaired cerebral blood flow, and neuronal cell death, worsens patient outcome in the hours and days after TBI. Acute activation of toll-like receptor 4 (TLR4) on myeloid cells aggravates inflammation and edema after experimental TBI and correlates with poor outcomes after clinical TBI. Activation of myeloid TLR4 increases the polarization of naïve helper T cells (TH0) into pro-inflammatory TH1 and TH17 cells, for weeks after TBI phenotypes. As TH1 and TH17 cells augment T-cell mediated immunity, amplify pro-inflammatory macrophage/microglia activation, and perpetuate neurodegeneration, the identification of novel strategies to reduce post-traumatic inflammation may substantially improve patient outcomes. Endocannabinoids, such as anandamide (N-arachidonoylethanolamide, AEA) and 2-arachidonoylglycerol (2-AG), are arachidonate based lipids that activate the cannabinoid receptors, CB1R and CB2R. CB2R activation restores immune balance, reduces edema, improves vasculature function, and enhances behavioral outcomes, suggesting a protective effect of endocannabinoids after TBI. Of note, activation of the endocannabinoid metabolizing enzyme monoacylglycerol lipase (MAGL), which selectively degrades monoacylglycerols, such as 2-AG, into free fatty acids and glycerol, worsens outcomes after brain injury. However, the role of MAGL remains poorly defined after TBI. Our long-term goal is to define the regulatory mechanisms and functional implications of eCS after TBI, which may establish a mechanistic framework to advance the development of immunomodulatory therapeutics to enhance patient outcomes. Our central hypothesis is that the endocannabinoid metabolizing enzyme, MAGL, is a molecular switch underlying pro-inflammatory activation after TBI. To test our hypothesis, we propose three Specific Aims: Specific Aim 1 will test the hypothesis that myeloid-CB2R activation improves neurovascular function via suppression of MAGL after TBI. Specific Aim 2 will test the hypothesis that myeloid-specific TLR4 regulates MAGL in innate immune activation after TBI. Specific Aim 3 will test the hypothesis that myeloid-specific deletion of MAGL limits myeloid-lymphoid interaction and thus, protects white matter injury (WMI) and chronic behavioral deficits after TBI. Expected outcomes: Our proposed studies have far-reaching translational implications, as demonstration of a key role for myeloid MAGL-CB2R-TLR4 in regulation of inflammation and chronic WMI resolution may result in improved long-term TBI outcomes.