DAGL-dependent endocannabinoid signalling: roles in axonal pathfinding, synaptic plasticity and adult neurogenesis

Comparative transcriptomics revealed the ecological trap effect of linearly polarized light on Oratosquilla oratoria

Although polarized light can assist many animals in performing special visual tasks, current polarized light pollution (PLP) caused by urban construction has been shown to induce maladaptive behaviors of PL-sensitive animals and change ecological interactions. However, the underlying mechanisms remain unclear. Our previous work hypothesized that linearly polarized light (LPL) is an ecological trap for Oratosquilla oratoria, a common Stomatopoda species in the China Sea. Here we explored the underlying negative effects of artificially LPL on O. oratoria based on comparative transcriptomics. We identified 3616 differentially expressed genes (DEGs) in O. oratoria compound eyes continuous exposed to natural light (NL) and LPL scenarios. In comparison with the NL scenario, a total of 1972 up- and 1644 down- regulated genes were obtained from the O. oratoria compound eyes under LPL scenario, respectively. Furthermore, we performed functional annotation of those DEGs described above and identified 65 DEGs related to phototransduction, reproduction, immunity, and synapse. Based on the functional information, we suspected that continuous LPL exposure could block the light transmission, disrupt the reproductive process, and lead to the progressive failure of the immune response of O. oratoria. In conclusion, this study is the first to systematically describe the negative effects of artificial LPL exposure on O. oratoria at the genetic level, and it can improve the biological conservation theory behind PLP.

Pluripotent Stem Cells as a Preclinical Cellular Model for Studying Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSPs) comprise a family of degenerative diseases mostly hitting descending axons of corticospinal neurons. Depending on the gene and mutation involved, the disease could present as a pure form with limb spasticity, or a complex form associated with cerebellar and/or cortical signs such as ataxia, dysarthria, epilepsy, and intellectual disability. The progressive nature of HSPs invariably leads patients to require walking canes or wheelchairs over time. Despite several attempts to ameliorate the life quality of patients that have been tested, current therapeutical approaches are just symptomatic, as no cure is available. Progress in research in the last two decades has identified a vast number of genes involved in HSP etiology, using cellular and animal models generated on purpose. Although unanimously considered invaluable tools for basic research, those systems are rarely predictive for the establishment of a therapeutic approach. The advent of induced pluripotent stem (iPS) cells allowed instead the direct study of morphological and molecular properties of the patient's affected neurons generated upon in vitro differentiation. In this review, we revisited all the present literature recently published regarding the use of iPS cells to differentiate HSP patient-specific neurons. Most studies have defined patient-derived neurons as a reliable model to faithfully mimic HSP in vitro, discovering original findings through immunological and -omics approaches, and providing a platform to screen novel or repurposed drugs. Thereby, one of the biggest hopes of current HSP research regards the use of patient-derived iPS cells to expand basic knowledge on the disease, while simultaneously establishing new therapeutic treatments for both generalized and personalized approaches in daily medical practice.

Cannabinoid regulation of neurons in the dentate gyrus during epileptogenesis: Role of CB1R-associated proteins and downstream pathways

The hippocampal formation plays a central role in the development of temporal lobe epilepsy (TLE), a disease characterized by recurrent, unprovoked epileptic discharges. TLE is a neurologic disorder characterized by acute long-lasting seizures (i.e., abnormal electrical activity in the brain) or seizures that occur in close proximity without recovery, typically after a brain injury or status epilepticus. After status epilepticus, epileptogenic hyperexcitability develops gradually over the following months to years, resulting in the emergence of chronic, recurrent seizures. Acting as a filter or gate, the hippocampal dentate gyrus (DG) normally prevents excessive excitation from propagating through the hippocampus, and is considered a critical region in the progression of epileptogenesis in pathological conditions. Importantly, lipid-derived endogenous cannabinoids (endocannabinoids), which are produced on demand as retrograde messengers, are central regulators of neuronal activity in the DG circuit. In this review, we summarize recent findings concerning the role of the DG in controlling hyperexcitability and propose how DG regulation by cannabinoids (CBs) could provide avenues for therapeutic interventions. We also highlight possible pathways and manipulations that could be relevant for the control of hyperexcitation. The use of CB compounds to treat epilepsies is controversial, as anecdotal evidence is not always validated by clinical trials. Recent publications shed light on the importance of the DG as a region regulating incoming hippocampal excitability during epileptogenesis. We review recent findings concerning the modulation of the hippocampal DG circuitry by CBs and discuss putative underlying pathways. A better understanding of the mechanisms by which CBs exert their action during seizures may be useful to improve therapies.

Endocannabinoid dysfunction in neurological disease: neuro-ocular DAGLA-related syndrome

The endocannabinoid system is a highly conserved and ubiquitous signalling pathway with broad-ranging effects. Despite critical pathway functions, gene variants have not previously been conclusively linked to human disease. We identified nine children from eight families with heterozygous, de novo truncating variants in the last exon of DAGLA with a neuro-ocular phenotype characterized by developmental delay, ataxia and complex oculomotor abnormality. All children displayed paroxysms of nystagmus or eye deviation accompanied by compensatory head posture and worsened incoordination most frequently after waking. RNA sequencing showed clear expression of the truncated transcript and no differences were found between mutant and wild-type DAGLA activity. Immunofluorescence staining of patient-derived fibroblasts and HEK cells expressing the mutant protein showed distinct perinuclear aggregation not detected in control samples. This report establishes truncating variants in the last DAGLA exon as the cause of a unique paediatric syndrome. Because enzymatic activity was preserved, the observed mislocalization of the truncated protein may account for the observed phenotype. Potential mechanisms include DAGLA haploinsufficiency at the plasma membrane or dominant negative effect. To our knowledge, this is the first report directly linking an endocannabinoid system component with human genetic disease and sets the stage for potential future therapeutic avenues.

How thermal challenges change gene regulation in the songbird brain and gonad: implications for sexual selection in our changing world

In a rapidly warming world, exposure to high temperatures may impact fitness, but the gene regulatory mechanisms that link sublethal heat to sexually selected traits are not well understood, particularly in endothermic animals. Our experiment used zebra finches (Taeniopygia guttata), songbirds that experience extreme temperature fluctuations in their native Australia. We exposed captive males to an acute thermal challenge (43°C) compared with thermoneutral (35°C) and lower (27°C) temperatures. We found significantly more heat dissipation behaviors at 43°C, a temperature previously shown to reduce song production and fertility, and more heat retention behaviors at 27°C. Next, we characterized transcriptomic responses in tissues important for mating effort - the posterior telencephalon, for its role in song production, and the testis, for its role in fertility and hormone production. Differential expression of hundreds of genes in the testes, but few in the brain, suggest the brain is less responsive to extreme temperatures. Nevertheless, gene network analyses revealed that expression related to dopaminergic signaling in the brain co-varied with heat dissipation behaviors, providing a mechanism by which temporary thermal challenges may alter motivational circuits for song production. In both brain and testis, we observed correlations between thermally sensitive gene networks and individual differences in thermoregulatory behavior. Although we cannot directly relate these gene regulatory changes to mating success, our results suggest that individual variation in response to thermal challenges could impact sexually selected traits in a warming world.

AP-4-mediated axonal transport controls endocannabinoid production in neurons

The adaptor protein complex AP-4 mediates anterograde axonal transport and is essential for axon health. AP-4-deficient patients suffer from a severe neurodevelopmental and neurodegenerative disorder. Here we identify DAGLB (diacylglycerol lipase-beta), a key enzyme for generation of the endocannabinoid 2-AG (2-arachidonoylglycerol), as a cargo of AP-4 vesicles. During normal development, DAGLB is targeted to the axon, where 2-AG signalling drives axonal growth. We show that DAGLB accumulates at the trans-Golgi network of AP-4-deficient cells, that axonal DAGLB levels are reduced in neurons from a patient with AP-4 deficiency, and that 2-AG levels are reduced in the brains of AP-4 knockout mice. Importantly, we demonstrate that neurite growth defects of AP-4-deficient neurons are rescued by inhibition of MGLL (monoacylglycerol lipase), the enzyme responsible for 2-AG hydrolysis. Our study supports a new model for AP-4 deficiency syndrome in which axon growth defects arise through spatial dysregulation of endocannabinoid signalling.

Davies et al. identify a putative mechanism underlying the childhood neurological disorder AP-4 deficiency syndrome. In the absence of AP-4, an enzyme that makes 2-AG is not transported to the axon, leading to axonal growth defects, which can be rescued by inhibition of 2-AG breakdown.

Regulation of adult neurogenesis by the endocannabinoid-producing enzyme diacylglycerol lipase alpha (DAGLa)

The endocannabinoid system modulates adult hippocampal neurogenesis by promoting the proliferation and survival of neural stem and progenitor cells (NSPCs). This is demonstrated by the disruption of adult neurogenesis under two experimental conditions: (1) NSPC-specific deletion of cannabinoid receptors and (2) constitutive deletion of the enzyme diacylglycerol lipase alpha (DAGLa) which produces the endocannabinoid 2-arachidonoylglycerol (2-AG). However, the specific cell types producing 2-AG relevant to neurogenesis remain unknown. Here we sought to identify the cellular source of endocannabinoids in the subgranular zone of the dentate gyrus (DG) in hippocampus, an important neurogenic niche. For this purpose, we used two complementary Cre-deleter mouse strains to delete Dagla either in neurons, or in astroglia and NSPCs. Surprisingly, neurogenesis was not altered in mice bearing a deletion of Dagla in neurons (Syn-Dagla KO), although neurons are the main source for the endocannabinoids in the brain. In contrast, a specific inducible deletion of Dagla in NPSCs and astrocytes (GLAST-CreERT2-Dagla KO) resulted in a strongly impaired neurogenesis with a 50% decrease in proliferation of newborn cells. These results identify Dagla in NSPCs in the DG or in astrocytes as a prominent regulator of adult hippocampal neurogenesis. We also show a reduction of Daglb expression in GLAST-CreERT2-Dagla KO mice, which may have contributed to the neurogenesis phenotype.

Systematic Analysis of Brain MRI Findings in Adaptor Protein Complex 4-Associated Hereditary Spastic Paraplegia

BACKGROUND AND OBJECTIVES

AP-4-associated hereditary spastic paraplegia (AP-4-HSP: SPG47, SPG50, SPG51, SPG52) is an emerging cause of childhood-onset hereditary spastic paraplegia and mimic of cerebral palsy. This study aims to define the spectrum of brain MRI findings in AP-4-HSP and to investigate radioclinical correlations.

METHODS

We performed a systematic qualitative and quantitative analysis of 107 brain MRI studies from 76 individuals with genetically confirmed AP-4-HSP and correlation with clinical findings including surrogates of disease severity.

RESULTS

We define AP-4-HSP as a disorder of gray and white matter and demonstrate that abnormal myelination is common and that metrics of reduced white matter volume correlate with severity of motor symptoms. We identify a common diagnostic imaging signature consisting of (1) a thin splenium of the corpus callosum, (2) an absent or thin anterior commissure, (3) characteristic signal abnormalities of the forceps minor ("ears of the grizzly sign"), and (4) periventricular white matter abnormalities. The presence of 2 or more of these findings has a sensitivity of ∼99% for detecting AP-4-HSP; the combination of all 4 is found in ∼45% of cases. Compared to other HSPs with a thin corpus callosum, the absent anterior commissure appears to be specific to AP-4-HSP. Our analysis identified a subset of patients with polymicrogyria, underscoring the role of AP-4 in early brain development. These patients displayed a higher prevalence of seizures and status epilepticus, many at a young age.

DISCUSSION

Our findings define the MRI spectrum of AP-4-HSP, providing opportunities for early diagnosis, identification of individuals at risk for complications, and a window into the role of the AP-4 complex in brain development and neurodegeneration.

Cannabinoids and Neurogenesis: The Promised Solution for Neurodegeneration?

The concept of neurons as irreplaceable cells does not hold true today. Experiments and evidence of neurogenesis, also, in the adult brain give hope that some compounds or drugs can enhance this process, helping to reverse the outcomes of diseases or traumas that once were thought to be everlasting. Cannabinoids, both from natural and artificial origins, already proved to have several beneficial effects (e.g., anti-inflammatory, anti-oxidants and analgesic action), but also capacity to increase neuronal population, by replacing the cells that were lost and/or regenerate a damaged nerve cell. Neurogenesis is a process which is not highly represented in literature as neuroprotection, though it is as important as prevention of nervous system damage, because it can represent a possible solution when neuronal death is already present, such as in neurodegenerative diseases. The aim of this review is to resume the experimental evidence of phyto- and synthetic cannabinoids effects on neurogenesis, both in vitro and in vivo, in order to elucidate if they possess also neurogenetic and neurorepairing properties.

Early suppression of the endocannabinoid degrading enzymes FAAH and MAGL alters locomotor development in zebrafish

The fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) enzymes are the predominant catabolic regulators of the major endocannabinoids (eCBs) anadamide (AEA) and 2-arachidonoylglycerol (2-AG), respectively. The expression and roles of eCBs during early embryogenesis remain to be fully investigated. Here, we inhibited FAAH and MAGL in zebrafish embryos during the first 24 h of life and examined motor neuron and locomotor development at 2 and 5 days post fertilization (dpf). Application of the dual FAAH/MAGL inhibitor, JZL195 (2 µmol l−1), resulted in a reduction in primary and secondary motor neuron axonal branching. JZL195 also reduced nicotinic acetylcholine receptor (nAChR) expression at neuromuscular junctions. Application of URB597 (5 µmol l−1), a specific inhibitor of the FAAH enzyme, also decreased primary motor neuron branching but did not affect secondary motor neuron branching and nAChR expression. Interestingly, JZL184 (5 µmol l−1), a specific inhibitor of MAGL, showed no effects on motor neuron branching or nAChR expression. Co-treatment of the enzyme inhibitors with the CB1R inhibitor AM251 confirmed the involvement of CB1R in motor neuron branching. Disruption of FAAH or MAGL reduced larval swimming activity, and AM251 attenuated the JZL195- and URB597-induced locomotor changes, but not the effects of JZL184. Together, these findings indicate that inhibition of FAAH, or augmentation of AEA acting through CB1R during early development, may be responsible for locomotor deficiencies.

FMR1 and Autism, an Intriguing Connection Revisited

Autism Spectrum Disorder (ASD) represents a distinct phenotype of behavioral dysfunction that includes deficiencies in communication and stereotypic behaviors. ASD affects about 2% of the US population. It is a highly heritable spectrum of conditions with substantial genetic heterogeneity. To date, mutations in over 100 genes have been reported in association with ASD phenotypes. Fragile X syndrome (FXS) is the most common single-gene disorder associated with ASD. The gene associated with FXS, FMR1 is located on chromosome X. Accordingly, the condition has more severe manifestations in males. FXS results from the loss of function of FMR1 due to the expansion of an unstable CGG repeat located in the 5'' untranslated region of the gene. About 50% of the FXS males and 20% of the FXS females meet the Diagnostic Statistical Manual 5 (DSM-5) criteria for ASD. Among the individuals with ASD, about 3% test positive for FXS. FMRP, the protein product of FMR1, is a major gene regulator in the central nervous system. Multiple pathways regulated by FMRP are found to be dysfunctional in ASD patients who do not have FXS. Thus, FXS presents the opportunity to study cellular phenomena that may have wider applications in the management of ASD and to develop new strategies for ASD therapy.

Cannabinoid Receptor 1 associates to different molecular complexes during GABAergic neuron maturation

CB₁ cannabinoid receptor is widely expressed in the central nervous system of animals from late prenatal development to adulthood. Appropriate activation and signaling of CB₁ cannabinoid receptors in cortical interneurons are crucial during perinatal/postnatal ages and adolescence, when long-lasting changes in brain activity may elicit subsequent appearance of disorders in the adult brain. Here we used an optimized immunoprecipitation protocol based on specific antibodies followed by shot-gun proteomics to find CB₁ interacting partners in postnatal rat GABAergic cortical neurons in vitro at two different stages of maturation. Besides describing new proteins associated with CB₁ like dihydrolipoyllysine-residue acetyltransferase component of pyruvate dehydrogenase complex (DLAT), fatty acid synthase (FASN), tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein zeta (YWHAZ), voltage-dependent anion channel 1 (VDAC1), myosin phosphatase Rho-interacting protein (MPRIP) or usher syndrome type-1C protein-binding protein 1 (USHBP1), we show that the signaling complex of CB₁ is different between maturational stages. Interestingly, the CB₁ signaling complex is enriched at the more immature stage in mitochondrial associated proteins and metabolic molecular functions, whereas at more mature stage, CB₁ complex is increased in maturation and synaptic-associated proteins. We describe also interacting partners specifically immunoprecipitated with either N-terminal or C-terminal CB₁ directed antibodies. Our results highlight new players that may be affected by altered cannabinoid signaling at this critical window of postnatal cortical development.

CB1 antagonism increases excitatory synaptogenesis in a cortical spheroid model of fetal brain development

The endocannabinoid system (ECS) plays a complex role in the development of neural circuitry during fetal brain development. The cannabinoid receptor type 1 (CB1) controls synaptic strength at both excitatory and inhibitory synapses and thus contributes to the balance of excitatory and inhibitory signaling. Imbalances in the ratio of excitatory to inhibitory synapses have been implicated in various neuropsychiatric disorders associated with dysregulated central nervous system development including autism spectrum disorder, epilepsy, and schizophrenia. The role of CB1 in human brain development has been difficult to study but advances in induced pluripotent stem cell technology have allowed us to model the fetal brain environment. Cortical spheroids resemble the cortex of the dorsal telencephalon during mid-fetal gestation and possess functional synapses, spontaneous activity, an astrocyte population, and pseudo-laminar organization. We first characterized the ECS using STORM microscopy and observed synaptic localization of components similar to that which is observed in the fetal brain. Next, using the CB1-selective antagonist SR141716A, we observed an increase in excitatory, and to a lesser extent, inhibitory synaptogenesis as measured by confocal image analysis. Further, CB1 antagonism increased the variability of spontaneous activity within developing neural networks, as measured by microelectrode array. Overall, we have established that cortical spheroids express ECS components and are thus a useful model for exploring endocannabinoid mediation of childhood neuropsychiatric disease.

Genetic Manipulation of sn-1-Diacylglycerol Lipase and CB1 Cannabinoid Receptor Gain-of-Function Uncover Neuronal 2-Linoleoyl Glycerol Signaling in Drosophila melanogaster

Introduction: In mammals, sn-1-diacylglycerol lipases (DAGL) generate 2-arachidonoylglycerol (2-AG) that, as the major endocannabinoid, modulates synaptic neurotransmission by acting on CB1 cannabinoid receptors (CB₁R). Even though the insect genome codes for inaE, which is a DAGL ortholog (dDAGL), its products and their functions remain unknown particularly because insects lack chordate-type cannabinoid receptors. Materials and Methods: Gain-of-function and loss-of-function genetic manipulations were carried out in Drosophila melanogaster, including the generation of both dDAGL-deficient and mammalian CB₁R-overexpressing flies. Neuroanatomy, dietary manipulations coupled with targeted mass spectrometry determination of arachidonic acid and 2-linoleoyl glycerol (2-LG) production, behavioral assays, and signal transduction profiling for Akt and Erk kinases were employed. Findings from Drosophilae were validated by a CB₁R-binding assay for 2-LG in mammalian cortical homogenates with functionality confirmed in neurons using high-throughput real-time imaging in vitro. Results: In this study, we show that dDAGL is primarily expressed in the brain and nerve cord of Drosophila during larval development and in adult with 2-LG being its chief product as defined by dietary precursor availability. Overexpression of the human CB₁R in the ventral nerve cord compromised the mobility of adult Drosophilae. The causality of 2-LG signaling to CB₁R-induced behavioral impairments was shown by inaE inactivation normalizing defunct motor coordination. The 2-LG-induced activation of transgenic CB₁Rs affected both Akt and Erk kinase cascades by paradoxical signaling. Data from Drosophila models were substantiated by showing 2-LG-mediated displacement of [³H]CP 55,940 in mouse cortical homogenates and reduced neurite extension and growth cone collapsing responses in cultured mouse neurons. Conclusions: Overall, these results suggest that 2-LG is an endocannabinoid-like signal lipid produced by dDAGL in Drosophila.

Cannabinoid receptor subtype influence on neuritogenesis in human SH-SY5Y cells

Human SH-SY5Y neuroblastoma cells stably expressing exogenous CB₁ (CB₁XS) or CB₂ (CB₂XS) receptors were developed to investigate endocannabinoid signaling in the extension of neuronal projections. Expression of cannabinoid receptors did not alter proliferation rate, viability, or apoptosis relative to parental SH-SY5Y. Transcripts for endogenous cannabinoid system enzymes (diacylglycerol lipase, monoacylglycerol lipase, α/β-hydrolase domain containing proteins 6 and 12, N-acyl phosphatidylethanolamine-phospholipase D, and fatty acid amide hydrolase) were not altered by CB₁ or CB₂ expression. Endocannabinoid ligands 2-arachidonoylglycerol (2-AG) and anandamide were quantitated in SH-SY5Y cells, and diacylglycerol lipase inhibitor tetrahydrolipstatin decreased 2-AG abundance by 90% but did not alter anandamide abundance. M3 muscarinic agonist oxotremorine M, and inhibitors of monoacylglycerol lipase and α/β hydrolase domain containing proteins 6 &12 increased 2-AG abundance. CB₁ receptor expression increased lengths of short (<30 μm) and long (>30 μm) projections, and this effect was significantly reduced by tetrahydrolipstatin, indicative of stimulation by endogenously produced 2-AG. Pertussis toxin, Gβγ inhibitor gallein, and β-arrestin inhibitor barbadin did not significantly alter long projection length in CB₁XS, but significantly reduced short projections, with gallein having the greatest inhibition. The rho kinase inhibitor Y27632 increased CB₁ receptor-mediated long projection extension, indicative of actin cytoskeleton involvement. CB₁ receptor expression increased GAP43 and ST8SIA2 mRNA and decreased ITGA1 mRNA, whereas CB₂ receptor expression increased NCAM and SYT mRNA. We propose that basal endogenous production of 2-AG provides autocrine stimulation of CB₁ receptor signaling through Gi/o, Gβγ, and β-arrestin mechanisms to promote neuritogenesis, and rho kinase influences process extension.

Diacylglycerol lipase alpha in astrocytes is involved in maternal care and affective behaviors

Genetic deletion of cannabinoid CB1 receptors or diacylglycerol lipase alpha (DAGLa), the main enzyme involved in the synthesis of the endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG), produced profound phenotypes in animal models of depression-related behaviors. Furthermore, clinical studies have shown that antagonists of CB1 can increase the incidence and severity of major depressive episodes. However, the underlying pathomechanisms are largely unknown. In this study, we have focused on the possible involvement of astrocytes. Using the highly sensitive RNAscope technology, we show for the first time that a subpopulation of astrocytes in the adult mouse brain expresses Dagla, albeit at low levels. Targeted lipidomics revealed that astrocytic DAGLa only accounts for a minor percentage of the steady-state brain 2-AG levels and other arachidonic acid derived lipids like prostaglandins. Nevertheless, the deletion of Dagla in adult mouse astrocytes had profound behavioral consequences with significantly increased depressive-like behavioral responses and striking effects on maternal behavior, corresponding with increased levels of serum progesterone and estradiol. Our findings therefore indicate that lipids from the DAGLa metabolic axis in astrocytes play a key regulatory role in affective behaviors.

An optimized spectrophotometric assay reveals increased activity of enzymes involved in 2-arachidonoyl glycerol turnover in the cerebral cortex of a rat model of Alzheimer's disease

The endocannabinoid system is implicated in a plethora of neuropsychiatric disorders. However, it is technically challenging to assess the turnover of 2-arachidonoyl glycerol (2-AG), the principal endocannabinoid molecule in the brain. Two recent studies showed that diacylglycerol lipase α (DAGLα), an enzyme chiefly responsible for the cerebral production of 2-AG, also accepts the surrogate chromogenic substrate 4-nitrophenyl butyrate (4-NPB). Here, we aimed to optimize this spectrophotometric assay for ex vivo brain tissue, in particular, rat cerebrocortical homogenates, to measure the activity of the major enzymes responsible for the production and degradation of 2-AG. The initial velocity of 4-NPB hydrolysis was dependent on protein, substrate, and Ca²⁺ concentrations, and was sensitive to the non-selective serine hydrolase inhibitor, methoxy arachidonyl fluorophosphonate, the DAGLα inhibitors, OMDM188, tetrahydrolipstatin, and RHC80267, as well as the monoacylglycerol lipase (MAGL) inhibitor, JZL184, respectively. Next, we tested the usefulness of this assay in ex vivo brain tissue of rat models of human health conditions known to affect cerebrocortical 2-AG production, i.e. pathological stress and sporadic Alzheimer's disease (AD). In rats submitted to chronic restraint stress, cortical CB₁ R density was significantly decreased, as assessed with radioligand binding. Nevertheless, 4-NPB hydrolysis remained at control levels. However, in rats 4 weeks after intracerebroventricular injection with streptozotocin - an established model of sporadic AD -, both CB₁ R levels and 4-NPB hydrolysis and its DAGL- and MAGL-dependent fractions were significantly increased. Altogether, we optimized a simple complementary ex vivo technique for the quantification of DAGL and MAGL activity in brain samples.

Impact of Endocannabinoid System Manipulation on Neurodevelopmental Processes Relevant to Schizophrenia

The neurodevelopmental hypothesis of schizophrenia has received much support from epidemiological and neuropathological studies and provides a framework to explain how early developmental abnormalities might manifest as psychosis in early adulthood. According to this theory, the onset of schizophrenia is likely the result of a complex interplay between a genetic predisposition and environmental factors whose respective influence might contribute to the etiology and progression of the disorder. The two most sensitive windows for neurodevelopment are the prenatal/perinatal and the adolescent windows, both of which are characterized by specific processes impinging upon brain structure and functionality, whose alterations may contribute to the onset of schizophrenia. An increasing number of articles suggest the involvement of the endocannabinoid system in the modulation of at least some of these processes, especially in the prenatal/perinatal window. Thus, it is not surprising that disturbing the physiological role of endocannabinoid signaling in these sensitive windows might alter the correct formation of neuronal networks, eventually predisposing to neuropsychiatric diseases later in life. We review the most recent preclinical studies that evaluated the impact of endocannabinoid system modulation in the two sensitive developmental windows on neurodevelopmental processes that possess a specific relevance to schizophrenia.

Interference with the Cannabinoid Receptor CB1R Results in Miswiring of GnRH3 and AgRP1 Axons in Zebrafish Embryos

The G protein-coupled cannabinoid receptors type 1 (CB1R) and type 2 (CB2R), and their endocannabinoid (eCBs) ligands, have been implicated in several aspects of brain wiring during development. Here we aim to assess whether interfering with CB1R affects development, neuritogenesis and pathfinding of GnRH and AgRP neurons, forebrain neurons that control respectively reproduction and appetite. We pharmacologically and genetically interfered with CB1R in zebrafish strains with fluorescently labeled GnRH3 and the AgRP1 neurons. By applying CB1R antagonists we observed a reduced number of GnRH3 neurons, fiber misrouting and altered fasciculation. Similar phenotypes were observed by CB1R knockdown. Interfering with CB1R also resulted in a reduced number, misrouting and poor fasciculation of the AgRP1 neuron’s axonal projections. Using a bioinformatic approach followed by qPCR validation, we have attempted to link CB1R functions with known guidance and fasciculation proteins. The search identified stathmin-2, a protein controlling microtubule dynamics, previously demonstrated to be coexpressed with CB1R and now shown to be downregulated upon interference with CB1R in zebrafish. Together, these results raise the likely possibility that embryonic exposure to low doses of CB1R-interfering compounds could impact on the development of the neuroendocrine systems controlling sexual maturation, reproduction and food intake.

2-Linoleoylglycerol Is a Partial Agonist of the Human Cannabinoid Type 1 Receptor that Can Suppress 2-Arachidonolyglycerol and Anandamide Activity

Introduction: The cannabinoid type 1 (CB1) receptor and cannabinoid type 2 (CB2) receptor are widely expressed in the body and anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are their best characterized endogenous ligands. The diacylglycerol lipases (diacylglycerol lipase alpha and diacylglycerol lipase beta) not only synthesize essentially all the 2-AG in the body but also generate other monoacylglycerols, including 2-linoleoylglycerol (2-LG). This lipid has been proposed to modulate endocannabinoid (eCB) signaling by protecting 2-AG from hydrolysis. However, more recently, 2-LG has been reported to be a CB1 antagonist. Methods: The effect of 2-LG on the human CB1 receptor activity was evaluated in vitro using a cell-based reporter assay that couples CB1 receptor activation to the expression of the β-lactamase enzyme. Receptor activity can then be measured by a β-lactamase enzymatic assay. Results: When benchmarked against 2-AG, AEA, and arachidonoyl-2'-chloroethylamide (a synthetic CB1 agonist), 2-LG functions as a partial agonist at the CB1 receptor. The 2-LG response was potentiated by JZL195, a drug that inhibits the hydrolysis of monoacylglycerols. The 2-LG response was also fully inhibited by the synthetic CB1 antagonist AM251 and by the natural plant derived antagonist cannabidiol. 2-LG did not potentiate, and only blunted, the activity of 2-AG and AEA. Conclusions: These results support the hypothesis that 2-LG is a partial agonist at the human CB1 receptor and capable of modulating the activity of the established eCBs.

Identification of α,β-Hydrolase Domain Containing Protein 6 as a Diacylglycerol Lipase in Neuro-2a Cells

The endocannabinoid 2-arachidonoylglycerol (2-AG) is involved in neuronal differentiation. This study aimed to identify the biosynthetic enzymes responsible for 2-AG production during retinoic acid (RA)-induced neurite outgrowth of Neuro-2a cells. First, we confirmed that RA stimulation of Neuro-2a cells increases 2-AG production and neurite outgrowth. The diacylglycerol lipase (DAGL) inhibitor DH376 blocked 2-AG production and reduced neuronal differentiation. Surprisingly, CRISPR/Cas9-mediated knockdown of DAGLα and DAGLβ in Neuro-2a cells did not reduce 2-AG levels, suggesting another enzyme capable of producing 2-AG in this cell line. Chemical proteomics revealed DAGLβ and α,β-hydrolase domain containing protein (ABHD6) as the only targets of DH376 in Neuro-2a cells. Biochemical, genetic and lipidomic studies demonstrated that ABHD6 possesses DAGL activity in conjunction with its previously reported monoacylglycerol lipase activity. RA treatment of Neuro-2a cells increased by three-fold the amount of active ABHD6. Our study shows that ABHD6 exhibits significant DAG lipase activity in Neuro-2a cells in addition to its known MAG lipase activity and suggest it is involved in neuronal differentiation.

Neural stem cell lineage-specific cannabinoid type-1 receptor regulates neurogenesis and plasticity in the adult mouse hippocampus

Neural stem cells (NSCs) in the adult mouse hippocampus occur in a specific neurogenic niche, where a multitude of extracellular signaling molecules converges to regulate NSC proliferation as well as fate and functional integration. However, the underlying mechanisms how NSCs react to extrinsic signals and convert them to intracellular responses still remains elusive. NSCs contain a functional endocannabinoid system, including the cannabinoid type-1 receptor (CB1). To decipher whether CB1 regulates adult neurogenesis directly or indirectly in vivo, we performed NSC-specific conditional inactivation of CB1 by using triple-transgenic mice. Here, we show that lack of CB1 in NSCs is sufficient to decrease proliferation of the stem cell pool, which consequently leads to a reduction in the number of newborn neurons. Furthermore, neuronal differentiation was compromised at the level of dendritic maturation pointing towards a postsynaptic role of CB1 in vivo. Deteriorated neurogenesis in NSC-specific CB1 knock-outs additionally resulted in reduced long-term potentiation in the hippocampal formation. The observed cellular and physiological alterations led to decreased short-term spatial memory and increased depression-like behavior. These results demonstrate that CB1 expressed in NSCs and their progeny controls neurogenesis in adult mice to regulate the NSC stem cell pool, dendritic morphology, activity-dependent plasticity, and behavior.

Role of the endocannabinoid system in neurological disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that begins in infancy. Although the etiology and pathogenesis are poorly understood, many studies have shown that ASD is closely related to structural and functional defects in the nervous system, especially synaptic transmission. The endocannabinoid (eCB) system is an important regulatory system of the central nervous system that regulates neurotransmission and synaptic plasticity and plays an important role in emotional and social responses and cognitive function. The relationship between eCB system and ASD has attracted increasing attention from scholars. In this review, we discuss the complex lipid signaling network of the eCB system, intracellular transport pathways, abnormal expression and association with various neurological diseases, and direct and indirect evidence for the link between eCB and ASD. Collectively, the findings to date indicate that the eCB system plays a key role in the pathophysiology of ASD and can provide new insights into potential interventions and rehabilitation strategies for ASD.

Cannabinoid signalling in embryonic and adult neurogenesis: possible implications for psychiatric and neurological disorders

Cannabinoid signalling modulates several aspects of brain function, including the generation and survival of neurons during embryonic and adult periods. The present review intended to summarise evidence supporting a role for the endocannabinoid system on the control of neurogenesis and neurogenesis-dependent functions. Studies reporting participation of cannabinoids on the regulation of any step of neurogenesis and the effects of cannabinoid compounds on animal models possessing neurogenesis-dependent features were selected from Medline. Qualitative evaluation of the selected studies indicated that activation of cannabinoid receptors may change neurogenesis in embryonic or adult nervous systems alongside rescue of phenotypes in animal models of different psychiatric and neurological disorders. The text offers an overview on the effects of cannabinoids on central nervous system development and the possible links with psychiatric and neurological disorders such as anxiety, depression, schizophrenia, brain ischaemia/stroke and Alzheimer's disease. An understanding of the mechanisms by which cannabinoid signalling influences developmental and adult neurogenesis will help foster the development of new therapeutic strategies for neurodevelopmental, psychiatric and neurological disorders.

Early life stress alters the developmental trajectory of corticolimbic endocannabinoid signaling in male rats

Early-life stress modulates the development of cortico-limbic circuits and increases vulnerability to adult psychopathology. Given the important stress-buffering role of endocannabinoid (eCB) signaling, we performed a comprehensive investigation of the developmental trajectory of the eCB system and the impact of exposure to early life stress induced by repeated maternal separation (MS; 3 h/day) from postnatal day 2 (PND2) to PND12. Tissue levels of the eCB molecules anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured after MS exposures, as well under basal conditions at juvenile (PND14), adolescent (PND40) and adult (PND70) timepoints in the prefrontal cortex (PFC), amygdala and hippocampus. We also examined the effects of MS on CB₁ receptor binding in these three brain regions at PND40 and PND70. AEA content was found to increase from PND2 into adulthood in a linear manner across all brain regions, while 2-AG was found to exhibit a transient spike during the juvenile period (PND12-14) within the amygdala and PFC, but increased in a linear manner across development in the hippocampus. Exposure to MS resulted in bidirectional changes in AEA and 2-AG tissue levels within the amygdala and hippocampus and produced a sustained reduction in eCB function in the hippocampus at adulthood. CB₁ receptor densities across all brain regions were generally found to be downregulated later in life following exposure to MS. Collectively, these data demonstrate that early life stress can alter the normative ontogeny of the eCB system, resulting in a sustained deficit in eCB function, particularly within the hippocampus, in adulthood.

The Endocannabinoid System across Postnatal Development in Transmembrane Domain Neuregulin 1 Mutant Mice

The use of cannabis is a well-established component risk factor for schizophrenia, particularly in adolescent individuals with genetic predisposition for the disorder. Alterations to the endocannabinoid system have been found in the prefrontal cortex of patients with schizophrenia. Thus, we assessed whether molecular alterations exist in the endocannabinoid signalling pathway during brain development in a mouse model for the schizophrenia risk gene neuregulin 1 (Nrg1). We analysed transcripts encoding key molecules of the endocannabinoid system in heterozygous transmembrane domain Nrg1 mutant mice (Nrg1 TM HET), which is known to have increased sensitivity to cannabis exposure. Tissue from the prelimbic cortex and hippocampus of male and female Nrg1 TM HET mice and wild type-like littermates was collected at postnatal days (PNDs) 7, 10, 14, 21, 28, 35, 49, and 161. Quantitative polymerase chain reaction was conducted to assess mRNA levels of cannabinoid receptor 1 (CB₁R) and enzymes for the synthesis and breakdown of the endocannabinoid 2-arachidonoylglycerol [i.e., diacylglycerol lipase alpha (DAGLα), monoglyceride lipase (MGLL), and α/β-hydrolase domain-containing 6 (ABHD6)]. No sex differences were found for any transcripts in either brain region; thus, male and female data were pooled. Hippocampal and cortical mRNA expression of DAGLα, MGLL, and ABHD6 increased until PND 21-35 and then decreased and stabilised for the rest of postnatal development. Hippocampal CB₁R mRNA expression increased until PND 21 and decreased after this age. Expression levels of these endocannabinoid markers did not differ in Nrg1 TM HET compared to control mice at any time point. Here, we demonstrate dynamic changes in the developmental trajectory of several key endocannabinoid system transcripts in the mouse brain, which may correspond with periods of endocannabinoid system maturation. Nrg1 TM HET mutation did not alter the developmental trajectory of the endocannabinoid markers assessed, suggesting that other mechanisms may be responsible for the exaggerated cannabinoid susceptibility in these mice.

Expression and Function of hsa-miR-6165 in Human Cell Lines and During the NT2 Cell Neural Differentiation Process

MicroRNAs are small non-coding RNAs that posttranscriptionally regulate mRNA expression. hsa-miR-6165 which was previously discovered in our group is located in the forth intron of p75NTR gene and its function is still under investigation. As P75NTR has diverse cellular functions, some of the complexity of its function could be attributed to the internally located microRNA. Our analysis revealed that treatment of HCT116 cells with 5-azacytidine promoted differential expression of hsa-miR-6165 from its host gene which is consistent with the bioinformatic prediction of an independent promoter for hsa-miR-6165. In addition, hsa-miR-6165 promoter is capable of driving GFP reporter gene in HeLa cells. The putative target gene expression level which was detected using RT-qPCR is inversely proportional to the expression level of hsa-miR-6165 during NT2 cell neural differentiation. Furthermore, hsa-miR-6165 overexpression resulted in significant downregulation of ABLIM-1, PVRL1, and PDK1 target genes, while it attenuates NT2 neural differentiation. Hsa-miR-6165 overexpression in SW480 cells also resulted in significant downregulation of PKD1, DAGLA, and PLXNA2 putative target genes, while it increases the sub-G1 cell population of SW480 and HEK293T cells as detected by flow cytometry. Overall, in this study, we report an independent promoter for hsa-miR-6165 which is active in HeLa cells. Additionally, hsa-miR-6165 targets ABLIM-1, PVRL1, PKD1, PLXNA2, and PDK1 genes, and unlike in HEK293T and SW480 cells, hsa-miR-6165 overexpression does not affect HeLa cells while its downregulation reduces sub-G1 cell population. Our results validate that hsa-miR-6165 affects the cell cycle progression and could increase apoptosis in human cell lines.

Endocannabinoid Turnover

In this review, we consider the biosynthetic, hydrolytic, and oxidative metabolism of the endocannabinoids anandamide and 2-arachidonoylglycerol. We describe the enzymes associated with these events and their characterization. We identify the inhibitor profile for these enzymes and the status of therapeutic exploitation, which to date has been limited to clinical trials for fatty acid amide hydrolase inhibitors. To bring the review to a close, we consider whether point block of a single enzyme is likely to be the most successful approach for therapeutic exploitation of the endocannabinoid system.

Cannabinoid Type-2 Receptor Drives Neurogenesis and Improves Functional Outcome After Stroke

BACKGROUND AND PURPOSE

Stroke is a leading cause of adult disability characterized by physical, cognitive, and emotional disturbances. Unfortunately, pharmacological options are scarce. The cannabinoid type-2 receptor (CB2R) is neuroprotective in acute experimental stroke by anti-inflammatory mechanisms. However, its role in chronic stroke is still unknown.

METHODS

Stroke was induced by permanent middle cerebral artery occlusion in mice; CB2R modulation was assessed by administering the CB2R agonist JWH133 ((6aR,10aR)-3-(1,1-dimethylbutyl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran) or the CB2R antagonist SR144528 (N-[(1S)-endo-1,3,3-trimethylbicyclo-[2.2.1]-heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide) once daily from day 3 to the end of the experiment or by CB2R genetic deletion. Analysis of immunofluorescence-labeled brain sections, 5-bromo-2´-deoxyuridine (BrdU) staining, fluorescence-activated cell sorter analysis of brain cell suspensions, and behavioral tests were performed.

RESULTS

SR144528 decreased neuroblast migration toward the boundary of the infarct area when compared with vehicle-treated mice 14 days after middle cerebral artery occlusion. Consistently, mice on this pharmacological treatment, like mice with CB2R genetic deletion, displayed a lower number of new neurons (NeuN⁺/BrdU⁺ cells) in peri-infarct cortex 28 days after stroke when compared with vehicle-treated group, an effect accompanied by a worse sensorimotor performance in behavioral tests. The CB2R agonist did not affect neurogenesis or outcome in vivo, but increased the migration of neural progenitor cells in vitro; the CB2R antagonist alone did not affect in vitro migration.

CONCLUSIONS

Our data support that CB2R is fundamental for driving neuroblast migration and suggest that an endocannabinoid tone is required for poststroke neurogenesis by promoting neuroblast migration toward the injured brain tissue, increasing the number of new cortical neurons and, conceivably, enhancing motor functional recovery after stroke.

The endocannabinoid system in the baboon (Papio spp.) as a complex framework for developmental pharmacology

INTRODUCTION

The consumption of marijuana (exogenous cannabinoid) almost doubled in adults during last decade. Consumption of exogenous cannabinoids interferes with the endogenous cannabinoid (or "endocannabinoid" (eCB)) system (ECS), which comprises N-arachidonylethanolamide (anandamide, AEA), 2-arachidonoyl glycerol (2-AG), endocannabinoid receptors (cannabinoid receptors 1 and 2 (CB1R and CB2R), encoded by CNR1 and CNR2, respectively), and synthesizing/degrading enzymes (FAAH, fatty-acid amide hydrolase; MAGL, monoacylglycerol lipase; DAGL-α, diacylglycerol lipase-alpha). Reports regarding the toxic and therapeutic effects of pharmacological compounds targeting the ECS are sometimes contradictory. This may be caused by the fact that structure of the eCBs varies in the species studied.

OBJECTIVES

First: to clone and characterize the cDNAs of selected members of ECS in a non-human primate (baboon, Papio spp.), and second: to compare those cDNA sequences to known human structural variants (single nucleotide polymorphisms and haplotypes).

MATERIALS AND METHODS

Polymerase chain reaction-amplified gene products from baboon tissues were transformed into Escherichia coli. Amplicon-positive clones were sequenced, and the obtained sequences were conceptually translated into amino-acid sequences using the genetic code.

RESULTS

Among the ECS members, CNR1 was the best conserved gene between humans and baboons. The phenotypes associated with mutations in the untranslated regions of this gene in humans have not been described in baboons. One difference in the structure of CNR2 between humans and baboons was detected in the region with the only known clinically relevant polymorphism in a human receptor. All of the differences in the amino-acid structure of DAGL-α between humans and baboons were located in the hydroxylase domain, close to phosphorylation sites. None of the differences in the amino-acid structure of MAGL observed between baboons and humans were located in the area critical for enzyme function.

CONCLUSION

The evaluation of the data, obtained in non-human primate model of cannabis-related developmental exposure should take into consideration possible evolutionary-determined species-specific differences in the CB1R expression, CB2R transduction pathway, and FAAH and DAGLα substrate-enzyme interactions.

Regulated endosomal trafficking of Diacylglycerol lipase alpha (DAGLα) generates distinct cellular pools; implications for endocannabinoid signaling

Diacylglycerol lipase alpha (DAGLα) generates the endocannabinoid (eCB) 2-arachidonylglycerol (2-AG) that regulates the proliferation and differentiation of neural stem cells and serves as a retrograde signaling lipid at synapses. Nothing is known about the dynamics of DAGLα expression in cells and this is important as it will govern where 2-AG can be made and released. We have developed a new construct to label DAGLα at the surface of live cells and follow its trafficking. In hippocampal neurons a cell surface pool of DAGLα co-localizes with Homer, a postsynaptic density marker. This surface pool of DAGLα is dynamic, undergoing endocytosis and recycling back to the postsynaptic membrane. A similar cycling is seen in COS-7 cells with the internalized DAGLα initially transported to EEA1 and Rab5-positive early endosomes via a clathrin-independent pathway before being transported back to the cell surface. The internalized DAGLα is present on reticular structures that co-localize with microtubules. Importantly, DAGLα cycling is a regulated process as inhibiting PKC results in a significant reduction in endocytosis. This is the first description of DAGLα cycling between the cell surface and an intracellular endosomal compartment in a manner that can regulate the level of the enzyme at the cell surface.

A novel live cell assay to measure diacylglycerol lipase α activity

Diacylglycerol lipase α (DAGLα) hydrolyses DAG to generate the principal endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG) in the central nervous system. DAGLα dependent cannabinoid (CB) signalling has been implicated in numerous processes including axonal growth and guidance, adult neurogenesis and retrograde signalling at the synapse. Recent studies have implicated DAGLα as an emerging drug target for several conditions including pain and obesity. Activity assays are critical to the drug discovery process; however, measurement of diacylglycerol lipase (DAGL) activity using its native substrate generally involves low-throughput MS techniques. Some relatively high-throughput membrane based assays utilizing surrogate substrates have been reported, but these do not take into account the rate-limiting effects often associated with the ability of a drug to cross the cell membrane. In the present study, we report the development of a live cell assay to measure DAGLα activity. Two previously reported DAGLα surrogate substrates, p-nitrophenyl butyrate (PNPB) and 6,8-difluoro-4-methylumbelliferyl octanoate (DiFMUO), were evaluated for their ability to detect DAGLα activity in live cell assays using a human cell line stably expressing the human DAGLα transgene. Following optimization, the small molecule chromogenic substrate PNPB proved to be superior by providing lower background activity along with a larger signal window between transfected and parental cells when compared with the fluorogenic substrate DiFMUO. The assay was further validated using established DAGL inhibitors. In summary, the live cell DAGLα assay reported here offers an economical and convenient format to screen for novel inhibitors as part of drug discovery programmes and compliments previously reported high-throughput membrane based DAGL assays.

Protein purification and cloning of diacylglycerol lipase from rat brain

Diacylglycerol (DG) lipase, which hydrolyses 1-stearoyl-2-arachidonyl-sn-glycerol to produce an endocannabinoid, 2-arachidonoylglycerol, was purified from the soluble fraction of rat brain lysates. DG lipase was purified about 1,200-fold by a sequential column chromatographic procedure. Among proteins identified by mass spectrometry analysis in the partially purified DG lipase sample, only DDHD domain containing two (DDHD2), which was formerly regarded as a phospholipase A1, exhibited significant DG lipase activity. Rat DDHD2 expressed in Chinese hamster ovary cells showed similar enzymatic properties to partially purified DG lipase from rat brain. The source of DG lipase activity in rat brain was immunoprecipitated using anti-DDHD2 antibody. Thus, we concluded that the DG lipase activity in the soluble fraction of rat brain is derived from DDHD2. DDHD2 is distributed widely in the rat brain. Immunohistochemical analysis revealed that DDHD2 is expressed in hippocampal neurons, but not in glia.

Differential Pharmacological Regulation of Sensorimotor Gating Deficit in CB1 Knockout Mice and Associated Neurochemical and Histological Alterations

The endocannabinoid system has been widely involved in the pathophysiology of sensorimotor gating deficits. This study aimed to evaluate the pharmacological modulation of the sensorimotor gating impairment induced by cannabinoid CB1 receptor (CB1r) deletion. For this purpose, the prepulse inhibition (PPI) paradigm was used to evaluate the effect of two antipsychotics drugs (risperidone and haloperidol) and a psychostimulant (methylphenidate) on the preattentional deficit presented by CB1KO mice. Furthermore, the effects of the CB1r antagonist AM251 on PPI were evaluated in WT mice. Real-time PCR and immunohistochemical studies were carried out to analyze dopamine transporter (DAT) and α-2C adrenergic receptor (ADRA2C) gene expressions and the distribution of parvalbumin (PV) and cholecystokinin-8 (CCK) immunoreactive (ir) cortical neurons, respectively. Neither risperidone nor haloperidol significantly modified the PPI of WT and CB1KO mice, whereas methylphenidate improved the preattentional deficit of CB1KO mice. In addition, treatment with AM251 (3 mg/kg; i.p.) significantly decreased the PPI of WT animals. The administration of methylphenidate increased DAT and ADRA2C gene expressions in CB1KO mice without producing any effect in WT animals. Immunohistochemical studies revealed that there were no significant changes in CCK immunolabeling between WT and CB1KO mice, whereas the radial distribution of PV-ir neurons was abnormal in CB1KO mice. These data further support the important role of CB1r in sensorimotor gating regulation and the therapeutic usefulness of methylphenidate for the treatment of psychiatric disorders with associated preattentional deficits.

Postnatal ethanol exposure alters levels of 2-arachidonylglycerol-metabolizing enzymes and pharmacological inhibition of monoacylglycerol lipase does not cause neurodegeneration in neonatal mice

The consumption of ethanol by pregnant women may cause neurological abnormalities, affecting learning and memory processes in children, and are collectively described as fetal alcohol spectrum disorders. However, the molecular mechanisms underlying these changes are still poorly understood. In our previous studies, we found that ethanol treatment of postnatal day 7 (P7) mice significantly enhances the anandamide levels but not the 2-arachidonylglycerol (2-AG) levels and induces widespread neurodegeneration, but the reason for the lack of significant effects of ethanol on the 2-AG level is unknown. In this study, we examined developmental changes in diacylglycerol lipase-α, β (DAGL-α and β) and monoacylglycerol lipase (MAGL). We found that the levels of these proteins were significantly higher in adult brains compared to those detected early in brain development. Next, we examined the influence of P7 ethanol treatment on these enzymes, finding that it differentially altered the DAGL-α protein and mRNA levels but consistently enhanced those of the DAGL-β. Interestingly, the ethanol treatment enhanced MAGL protein and mRNA levels. Inhibition of MAGL with KML29 failed to induce neurodegeneration in P7 mice. Collectively, these findings suggest that ethanol significantly activates DAGL-β and MAGL in the neonatal brain, resulting in no net change in 2-AG levels.

Targeted pharmacological treatment of autism spectrum disorders: fragile X and Rett syndromes

Autism spectrum disorders (ASDs) are genetically and clinically heterogeneous and lack effective medications to treat their core symptoms. Studies of syndromic ASDs caused by single gene mutations have provided insights into the pathophysiology of autism. Fragile X and Rett syndromes belong to the syndromic ASDs in which preclinical studies have identified rational targets for drug therapies focused on correcting underlying neural dysfunction. These preclinical discoveries are increasingly translating into exciting human clinical trials. Since there are significant molecular and neurobiological overlaps among ASDs, targeted treatments developed for fragile X and Rett syndromes may be helpful for autism of different etiologies. Here, we review the targeted pharmacological treatment of fragile X and Rett syndromes and discuss related issues in both preclinical studies and clinical trials of potential therapies for the diseases.

Endocannabinoid signalling and the deteriorating brain

Ageing is characterized by the progressive impairment of physiological functions and increased risk of developing debilitating disorders, including chronic inflammation and neurodegenerative diseases. These disorders have common molecular mechanisms that can be targeted therapeutically. In the wake of the approval of the first cannabinoid-based drug for the symptomatic treatment of multiple sclerosis, we examine how endocannabinoid (eCB) signalling controls--and is affected by--normal ageing and neuroinflammatory and neurodegenerative disorders. We propose a conceptual framework linking eCB signalling to the control of the cellular and molecular hallmarks of these processes, and categorize the key components of endocannabinoid signalling that may serve as targets for novel therapeutics.

The Potential of Inhibitors of Endocannabinoid Metabolism for Drug Development: A Critical Review

The endocannabinoids anandamide and 2-arachidonoylglycerol are metabolised by both hydrolytic enzymes (primarily fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL)) and oxygenating enzymes (e.g. cyclooxygenase-2, COX-2). In the present article, the in vivo data for compounds inhibiting endocannabinoid metabolism have been reviewed, focussing on inflammation and pain. Potential reasons for the failure of an FAAH inhibitor in a clinical trial in patients with osteoarthritic pain are discussed. It is concluded that there is a continued potential for compounds inhibiting endocannabinoid metabolism in terms of drug development, but that it is wise not to be unrealistic in terms of expectations of success.

Parsing the players: 2-arachidonoylglycerol synthesis and degradation in the CNS

The endogenous cannabinoid signalling system, composed of endogenous cannabinoids, cannabinoid receptors and the enzymes that synthesize and degrade the endogenous cannabinoids, is much more complex than initially conceptualized. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and plays a major role in CNS development and synaptic plasticity. Over the past decade, many key players in 2-AG synthesis and degradation have been identified and characterized. Most 2-AG is synthesized from membrane phospholipids via sequential activation of a phospholipase Cβ and a diacylglycerol lipase, although other pathways may contribute in specialized settings. 2-AG breakdown is more complicated with at least eight different enzymes participating. These enzymes can either degrade 2-AG into its components, arachidonic acid and glycerol, or transform 2-AG into highly bioactive signal molecules. The implications of the precise temporal and spatial control of the expression and function of these pleiotropic metabolizing enzymes have only recently come to be appreciated. In this review, we will focus on the primary organization of the synthetic and degradative pathways of 2-AG and then discuss more recent findings and their implications, with an eye towards the biological and therapeutic implications of manipulating 2-AG synthesis and metabolism.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Chronic exposure to WIN55,212-2 affects more potently spatial learning and memory in adolescents than in adult rats via a negative action on dorsal hippocampal neurogenesis

Several epidemiological studies show an increase in cannabis use among adolescents, especially in Morocco for being one of the major producers in the world. The neurobiological consequences of chronic cannabis use are still poorly understood. In addition, brain plasticity linked to ontogeny portrays adolescence as a period of vulnerability to the deleterious effects of drugs. The aim of this study was to investigate the behavioral neurogenic effects of chronic exposure to the cannabinoid agonist WIN55,212-2 during adolescence, by evaluating the emotional and cognitive performances, and the consequences on neurogenesis along the dorso-ventral axis of the hippocampus in adult rats. WIN55,212 was administered intraperitoneally (i.p.) once daily for 20 days to adolescent (27-30 PND) and adult Wistar rats (54-57 PND) at the dose of 1mg/kg. Following a 20 day washout period, emotional and cognitive functions were assessed by the Morris water maze test and the two-way active avoidance test. Twelve hours after, brains were removed and hippocampal neurogenesis was assessed using the doublecortin (DCX) as a marker for cell proliferation. Our results showed that chronic WIN55,212-2 treatment significantly increased thigmotaxis early in the training process whatever the age of treatment, induced spatial learning and memory deficits in adolescent but not adult rats in the Morris water maze test, while it had no significant effect in the active avoidance test during multitrial training in the shuttle box. In addition, the cognitive deficits assessed in adolescent rats were positively correlated to a decrease in the number of newly generated neurons in dorsal hippocampus. These data suggest that long term exposure to cannabinoids may affect more potently spatial learning and memory in adolescent compared to adult rats via a negative action on hippocampal plasticity.

Endocannabinoid signalling in neuronal migration

The endocannabinoid (eCB) system consists of several endogenous lipids, their target CB1 and CB2 receptors and enzymes responsible for their synthesis and degradation. The most abundant eCB in the central nervous system (CNS), 2-arachidonoyl glycerol (2-AG), triggers a broad range of signalling events by acting on CB1, the most abundant G protein-coupled receptor in the CNS. The eCB system regulates many physiological processes including neurogenesis, axon guidance and synaptic plasticity. Recent studies have highlighted an additional important role for eCB signalling in neuronal migration, which is crucial to achieve the complex architecture and efficient wiring of the CNS. Indeed, eCB signalling controls migration both pre- and post-natally, regulating interneuron positioning in the developing cortex and hippocampus and the polarised motility of stem cell-derived neuroblasts. While these effects may contribute to cognitive deficits associated with cannabis consumption, they also provide potential opportunities for endogenous stem cell-based neuroregenerative strategies.

Lipoprotein lipase (LPL) is associated with neurite pathology and its levels are markedly reduced in the dentate gyrus of Alzheimer's disease brains

Lipoprotein lipase (LPL) is involved in regulation of fatty acid metabolism, and facilitates cellular uptake of lipoproteins, lipids and lipid-soluble vitamins. We evaluated LPL distribution in healthy and Alzheimer’s disease (AD) brain tissue and its relative levels in cerebrospinal fluid. LPL immunostaining is widely present in different neuronal subgroups, microglia, astrocytes and oligodendroglia throughout cerebrum, cerebellum and spinal cord. LPL immunoreactivity is also present in leptomeninges, small blood vessels, choroid plexus and ependymal cells, Schwann cells associated with cranial nerves, and in anterior and posterior pituitary. In vitro studies have shown presence of secreted LPL in conditioned media of human cortical neuronal cell line (HCN2) and neuroblastoma cells (SK-N-SH), but not in media of cultured primary human astrocytes. LPL was present in cytoplasmic and nuclear fractions of neuronal cells and astrocytes in vitro. LPL immunoreactivity strongly associates with AD-related pathology, staining diffuse plaques, dystrophic and swollen neurites, possible Hirano bodies and activated glial cells. We observed no staining associated with neurofibrillary tangles or granulovacuolar degeneration. Granule cells of the dentate gyrus and the associated synaptic network showed significantly reduced staining in AD compared to control tissue. LPL was also reduced in AD CSF samples relative to those in controls.

Fascin regulates the migration of subventricular zone-derived neuroblasts in the postnatal brain

After birth, stem cells in the subventricular zone (SVZ) generate neuroblasts that migrate along the rostral migratory stream (RMS) to become interneurons in the olfactory bulb (OB). This migration is a fundamental event controlling the proper integration of new neurons in a pre-existing synaptic network. Many regulators of neuroblast migration have been identified; however, still very little is known about the intracellular molecular mechanisms controlling this process. Here, we show that the actin-bundling protein fascin is highly upregulated in mouse SVZ-derived migratory neuroblasts. Fascin-1ko mice display an abnormal RMS and a smaller OB. Bromodeoxyuridine labeling experiments show that lack of fascin significantly impairs neuroblast migration, but does not appear to affect cell proliferation. Moreover, fascin depletion substantially alters the polarized morphology of rat neuroblasts. Protein kinase C (PKC)-dependent phosphorylation of fascin on Ser39 regulates its actin-bundling activity. In vivo postnatal electroporation of phosphomimetic (S39D) or nonphosphorylatable (S39A) fascin variants followed by time-lapse imaging of brain slices demonstrates that the phospho-dependent modulation of fascin activity ensures efficient neuroblast migration. Finally, fluorescence lifetime imaging microscopy studies in rat neuroblasts reveal that the interaction between fascin and PKC can be modulated by cannabinoid signaling, which controls neuroblast migration in vivo. We conclude that fascin, whose upregulation appears to mark the transition to the migratory neuroblast stage, is a crucial regulator of neuroblast motility. We propose that a tightly regulated phospho/dephospho-fascin cycle modulated by extracellular signals is required for the polarized morphology and migration in neuroblasts, thus contributing to efficient neurogenesis.

The endocannabinoid system in normal and pathological brain ageing

The role of endocannabinoids as inhibitory retrograde transmitters is now widely known and intensively studied. However, endocannabinoids also influence neuronal activity by exerting neuroprotective effects and regulating glial responses. This review centres around this less-studied area, focusing on the cellular and molecular mechanisms underlying the protective effect of the cannabinoid system in brain ageing. The progression of ageing is largely determined by the balance between detrimental, pro-ageing, largely stochastic processes, and the activity of the homeostatic defence system. Experimental evidence suggests that the cannabinoid system is part of the latter system. Cannabinoids as regulators of mitochondrial activity, as anti-oxidants and as modulators of clearance processes protect neurons on the molecular level. On the cellular level, the cannabinoid system regulates the expression of brain-derived neurotrophic factor and neurogenesis. Neuroinflammatory processes contributing to the progression of normal brain ageing and to the pathogenesis of neurodegenerative diseases are suppressed by cannabinoids, suggesting that they may also influence the ageing process on the system level. In good agreement with the hypothesized beneficial role of cannabinoid system activity against brain ageing, it was shown that animals lacking CB1 receptors show early onset of learning deficits associated with age-related histological and molecular changes. In preclinical models of neurodegenerative disorders, cannabinoids show beneficial effects, but the clinical evidence regarding their efficacy as therapeutic tools is either inconclusive or still missing.