Selective Inhibition of Alpha/Beta-Hydrolase Domain 6 Attenuates Neurodegeneration, Alleviates Blood Brain Barrier Breakdown, and Improves Functional Recovery in a Mouse Model of Traumatic Brain Injury

Abstract

2-arachidonylglycerol (2-AG) is the most abundant endocannabinoid in the central nervous system and is elevated after brain injury. Because of its rapid hydrolysis, however, the compensatory and neuroprotective effect of 2-AG is short-lived. Although inhibition of monoacylglycerol lipase, a principal enzyme for 2-AG degradation, causes a robust increase of brain levels of 2-AG, it also leads to cannabinoid receptor desensitization and behavioral tolerance. Alpha/beta hydrolase domain 6 (ABHD6) is a novel 2-AG hydrolytic enzyme that accounts for a small portion of 2-AG hydrolysis, but its inhibition is believed to elevate the levels of 2-AG within the therapeutic window without causing side effect. Using a mouse model of traumatic brain injury (TBI), we found that post-insult chronic treatment with a selective ABHD6 inhibitor WWL70 improved motor coordination and working memory performance. WWL70 treatment reduced lesion volume in the cortex and neurodegeneration in the dendate gyrus. It also suppressed the expression of inducible nitric oxide synthase and cyclooxygenase-2 and enhanced the expression of arginase-1 in the ipsilateral cortex at 3 and 7 days post-TBI, suggesting microglia/macrophages shifted from M1 to M2 phenotypes after treatment. The blood-brain barrier dysfunction at 3 and 7 days post-TBI was dramatically reduced. Furthermore, the beneficial effects of WWL70 involved up-regulation and activation of cannabinoid type 1 and type 2 receptors and were attributable to the phosphorylation of the extracellular signal regulated kinase and the serine/threonine protein kinase AKT. This study indicates that the fine-tuning of 2-AG signaling by modulating ABHD6 activity can exert anti-inflammatory and neuroprotective effects in TBI.

Performance of Male and Female C57BL/6J Mice on Motor and Cognitive Tasks Commonly Used in Pre-Clinical Traumatic Brain Injury Research

“…Mice prefer to enter a maze arm that was not previously explored, so the test requires the animals to recall which arm was most recently entered. 35 Overall, performance of sham-treated mice was significantly superior to that of animals with severe CCI, as described previously, 34 but there was a statistical main effect of sex, with females having poorer performance (Fig. 5A).…”

“…34,35 The apparatus consisted of three arms at a 120-degree angle to one another with a triangular central zone. Each arm was 36 cm in length, enclosed by walls 16 cm high, and a small visual cue was placed at the distal wall of each arm.…”

Cannabinoids in Neurodegenerative Disorders and Stroke/Brain Trauma: From Preclinical Models to Clinical Applications

“…By contrast, in the neonatal rat brain, the exposure to concussive head trauma induced a moderate increase in the levels of anandamide and other N-acylethanolamines, but not of 2-AG and other 2-monoacylglycerols [43,44]. Further studies demonstrated that these elevations are endogenous responses addressed to limit brain damage, as the inhibition of 2-AG and anandamide hydrolysis reduced brain damage and improved functional deficits in parallel to a reduction of proinflammatory responses in the mouse brain after TBI [45,46]. Similar elevations of anandamide, 2-AG, and Nacylethanolamines have been detected in experimental cerebral ischemia [47][48][49][50].…”

Chemical Probes of Endocannabinoid Metabolism

“…Indeed, ABHD6 has recently been shown to regulate 2-AG degradation and signaling in murine primary neurons and cortical slices (Marrs et al, 2010) and control 2-AG accumulation in the Neuro2A cell line, which lacks MAGL (Hsu et al, 2012). Additionally, ABHD6 inhibition in vivo produced CB1-and CB2-mediated anti-inflammatory and neuroprotective effects in a mouse model of traumatic brain injury (Tchantchou and Zhang, 2012). Human genetics has implicated ABHD12 as a critical regulator of neurologic function; loss-of-function mutations in ABHD12 cause the human neurodegenerative disease PHARC (polyneuropathy, hearing loss, ataxia, retinosis pigmentosa, and cataract) (Fiskerstrand et al, 2010), although whether ABHD12-disruption leads to neuronal death by dysregulation of 2-AG or an alternate mechanism remains to be determined.…”