Inhibiting degradation of 2-arachidonoylglycerol as a therapeutic strategy for neurodegenerative diseases.

Endocannabinoids are endogenous lipid signaling mediators that participate in a variety of physiological and pathological processes. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and is a full agonist of G-protein-coupled cannabinoid receptors (CB1R and CB2R), which are targets of Δ9-tetrahydrocannabinol (Δ9-THC), the main psychoactive ingredient in cannabis. While 2-AG has been well recognized as a retrograde messenger modulating synaptic transmission and plasticity at both inhibitory GABAergic and excitatory glutamatergic synapses in the brain, growing evidence suggests that 2-AG also functions as an endogenous terminator of neuroinflammation in response to harmful insults, thus maintaining brain homeostasis. Monoacylglycerol lipase (MAGL) is the key enzyme that degrades 2-AG in the brain. The immediate metabolite of 2-AG is arachidonic acid (AA), a precursor of prostaglandins (PGs) and leukotrienes. Several lines of evidence indicate that pharmacological or genetic inactivation of MAGL, which boosts 2-AG levels and reduces its hydrolytic metabolites, resolves neuroinflammation, mitigates neuropathology, and improves synaptic and cognitive functions in animal models of neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and traumatic brain injury (TBI)-induced neurodegenerative disease. Thus, it has been proposed that MAGL is a potential therapeutic target for treatment of neurodegenerative diseases. As the main enzyme hydrolyzing 2-AG, several MAGL inhibitors have been identified and developed. However, our understanding of the mechanisms by which inactivation of MAGL produces neuroprotective effects in neurodegenerative diseases remains limited. A recent finding that inhibition of 2-AG metabolism in astrocytes, but not in neurons, protects the brain from TBI-induced neuropathology might shed some light on this unsolved issue. This review provides an overview of MAGL as a potential therapeutic target for neurodegenerative diseases and discusses possible mechanisms underlying the neuroprotective effects of restraining degradation of 2-AG in the brain.

Chen C 《-》

Endocannabinoid Metabolism and Traumatic Brain Injury.

Zhu D ，Gao F ，Chen C 《Cells》

Augmentation of 2-arachidonoylglycerol signaling in astrocytes maintains synaptic functionality by regulation of miRNA-30b.

2-Arachidonoylglycerol (2-AG), the most abundant endocannabinoid, displays anti-inflammatory and neuroprotective properties. Inhibition of 2-AG degradation by inactivation of monoacylglycerol lipase (MAGL), a key enzyme degrading 2-AG in the brain, alleviates neuropathology and improves synaptic and cognitive functions in animal models of neurodegenerative diseases. In particular, global inactivation of MAGL by genetic deletion of mgll enhances hippocampal long-term potentiation (LTP) and hippocampus-dependent learning and memory. However, our understanding of the molecular mechanisms by which chronic inactivation of MAGL enhances synaptic activity is still limited. Here, we provide evidence that pharmacological inactivation of MAGL suppresses hippocampal expression of miR-30b, a small non-coding microRNA, and upregulates expression of its targets, including ephrin type-B receptor 2 (ephB2), sirtuin1 (sirt1), and glutamate ionotropic receptor AMPA type subunit 2 (GluA2). Importantly, suppression of miR-30b and increase of its targets by inactivation of MAGL result primarily from inhibition of 2-AG metabolism in astrocytes, rather than in neurons. Inactivation of MAGL in astrocytes prevents miR-30b overexpression-induced impairments in synaptic transmission and long-term potentiation (LTP) in the hippocampus. Suppression of miR-30b expression by inactivation of MAGL is apparently associated with augmentation of 2-AG signaling, as 2-AG induces a dose-dependent decrease in expression of miR-30b. 2-AG- or MAGL inactivation-suppressed expression of miR-30b is not mediated via CB1R, but by peroxisome proliferator-activated receptor γ (PPARγ). This is further supported by the results showing that MAGL inactivation-induced downregulation of miR-30b and upregulation of its targets are attenuated by antagonism of PPARγ, but mimicked by PPARγ agonists. In addition, we observed that 2-AG-induced reduction of miR-30b expression is mediated via NF-kB signaling. Our study provides evidence that 2-AG signaling in astrocytes plays an important role in maintaining the functional integrity of synapses in the hippocampus by regulation of miR-30b expression.

Zhu D ，Zhang J ，Gao F ，Hu M ，Hashem J ，Chen C ... -  《-》

Endocannabinoid 2-arachidonoylglycerol protects neurons against β-amyloid insults.

While endocannabinoid modulation of both GABAergic and glutamatergic synaptic transmission and plasticity has been extensively investigated, our understanding of the role of endocannabinoids in protecting neurons from harmful insults remains limited. 2-Arachidonoylglycerol (2-AG), the most abundant endogenous ligand and a full agonist for cannabinoid receptors, exhibits anti-inflammatory and neuroprotective effects via a CB1 receptor (CB1R)-mediated mechanism. However, it is still not clear whether 2-AG is also able to protect neurons from β-amyloid (Aβ)-induced neurodegeneration. Here, we demonstrate that exogenous application of 2-AG significantly protected hippocampal neurons in culture against Aβ-induced neurodegeneration and apoptosis. This neuroprotective effect was blocked by SR141716 (SR-1), a selective CB1R antagonist, but not by SR144528 (SR-2), a selective CB2R antagonist, or capsazepine (CAP), a selective transient receptor potential cation channels, subfamily V, member 1 (TRPV1) receptor antagonist. To determine whether endogenous 2-AG is capable of protecting neurons from Aβ insults, hippocampal neurons in culture were treated with URB602 or JZL184, selective inhibitors of monoacylglycerol lipase (MAGL), the enzyme hydrolyzing 2-AG. MAGL inhibition that elevates endogenous levels of 2-AG also significantly reduced Aβ-induced neurodegeneration and apoptosis. The 2-AG-produced neuroprotective effects appear to be mediated via CB1R-dependent suppression of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and nuclear factor-κB (NF-κB) phosphorylation and cyclooxygenase-2 (COX-2) expression. Our results suggest that elevation of endogenous 2-AG by inhibiting its hydrolysis has potential as a novel efficacious therapeutic approach for preventing, ameliorating or treating Alzheimer's disease.

Chen X ，Zhang J ，Chen C 《-》

Inhibition of 2-arachidonoylglycerol degradation enhances glial immunity by single-cell transcriptomic analysis.

2-Arachidonoylglycerol (2-AG) is the most abundant endogenous cannabinoid. Inhibition of 2-AG metabolism by inactivation of monoacylglycerol lipase (MAGL), the primary enzyme that degrades 2-AG in the brain, produces anti-inflammatory and neuroprotective effects in neurodegenerative diseases. However, the molecular mechanisms underlying these beneficial effects are largely unclear. Hippocampal and cortical cells were isolated from cell type-specific MAGL knockout (KO) mice. Single-cell RNA sequencing was performed by 10 × Genomics platform. Cell Ranger, Seurat (v3.2) and CellChat (1.1.3) packages were used to carry out data analysis. Using single-cell RNA sequencing analysis, we show here that cell type-specific MAGL KO mice display distinct gene expression profiles in the brain. Inactivation of MAGL results in robust changes in expression of immune- and inflammation-related genes in microglia and astrocytes. Remarkably, upregulated expression of chemokines in microglia is more pronounced in mice lacking MAGL in astrocytes. In addition, expression of genes that regulate other cellular functions and Wnt signaling in astrocytes is altered in MAGL KO mice. Our results provide transcriptomic evidence that cell type-specific inactivation of MAGL induces differential expression of immune-related genes and other fundamental cellular pathways in microglia and astrocytes. Upregulation of the immune/inflammatory genes suggests that tonic levels of immune/inflammatory vigilance are enhanced in microglia and astrocytes, particularly in microglia, by inhibition of 2-AG metabolism, which likely contribute to anti-inflammatory and neuroprotective effects produced by inactivation of MAGL in neurodegenerative diseases.

Zhu D ，Zhang J ，Hashem J ，Gao F ，Chen C ... -  《Journal of Neuroinflammation》