Chronic nSMase inhibition suppresses neuronal exosome spreading and sex-specifically attenuates amyloid pathology in APP knock-in Alzheimer's disease mice

Female biased pathology and cognitive decline in Alzheimer's disease (AD) have been consistently observed with unclear underlying mechanisms. Although brain sphingolipid ceramide is elevated in AD patients, whether and how ceramide may contribute to sex-specific differences in amyloid pathology is unknown. Here we investigated the sex-specific impact of chronic pharmacological inhibition of neutral sphingomyelinase (nSMase), a key enzyme responsible for ceramide metabolism, on in vivo neuron-derived exosome dynamics, Aβ plaque load, and cognitive function in the APPNL-F/NL-F knock-in (APP NL-F) AD mouse model. Our results found sex-specific increase of cortical C20:0 ceramide and brain exosome levels only in APP NL-F but not in age-matched WT mice. Although nSMase inhibition similarly blocks exosome spreading in male and female mice, significantly reduced amyloid pathology was mostly observed in cortex and hippocampus of female APP NL-F mice with only modest effect found on male APP NL-F mice. Consistently, T maze test to examine spatial working memory revealed a female-specific reduction in spontaneous alternation rate in APP NL-F mice, which was fully reversed with chronic nSMase inhibition. Together, our results suggest that disease induced changes in ceramide and exosome pathways contribute to the progression of female-specific amyloid pathology in APP NL-F AD models.

Targeting the CB2 receptor and other endocannabinoid elements to delay disease progression in amyotrophic lateral sclerosis

Cannabinoids form a singular group of plant-derived compounds, endogenous lipids and synthetic derivatives with multiple therapeutic effects exerted by targeting different elements of the endocannabinoid system. One of their therapeutic applications is the preservation of neuronal integrity exerted by attenuating the multiple neurotoxic events that kill neurons in neurodegenerative disorders. In this review, we will address the potential of cannabinoids as neuroprotective agents in amyotrophic lateral sclerosis (ALS), a devastating neurodegenerative disorder characterized by muscle denervation, atrophy and paralysis, and progressive deterioration in upper and/or lower motor neurons. The emphasis will be paid on the cannabinoid type 2 (CB₂ ) receptor, whose activation limits glial reactivity, but the potential of additional endocannabinoid-related targets will be also addressed. The evidence accumulated so far at the preclinical level supports the need to soon move towards the patients and initiate clinical trials to confirm the potential of cannabinoid-based medicines as disease modifiers in ALS. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Elevated exosomal secretion of miR-124-3p from spinal neurons positively associates with disease severity in ALS

MicroRNAs (miRs) are powerful regulators of CNS development and diseases. Plasma and cerebrospinal fluid (CSF) miRs have recently been implicated as potential new sources for biomarker development. Previously we showed that miR-124-3p, an essential miR for neuronal identity, is highly abundant in neuronal exosomes and its expression decreases in spinal cord of ALS model SOD1G93A mice. In the current study, we found a disease associated reduction of miR-124-3p levels specifically in spinal neurons using in situ hybridization. By employing our recently developed exosome reporter mice in combination with sciatic nerve injections, we observed an increased association of miR-124-3p with spinal motor neuron-derived exosomes in SOD1G93A mice, even at the pre-symptomatic stage. Sciatic nerve injection delivered miR-124-3p is also more frequently localized outside of spinal motor neurons in SOD1G93A mice. Subsequent quantitative analysis of miR-124-3p levels in CSF exosomes from ALS patients found a significant correlation between CSF exosomal miR-124-3p levels and disease stage (indicated by the ALSFRS-R score) of (male) ALS patients. These results provide preliminary evidence to support the potential use of CSF exosomal miR-124-3p as a disease stage indicator in ALS.

Neuroprotective effects of the cannabigerol quinone derivative VCE-003.2 in SOD1G93A transgenic mice, an experimental model of amyotrophic lateral sclerosis

Antioxidant phytocannabinoids, synthetic compounds targeting the CB₂ receptor, and inhibitors of the endocannabinoid inactivation afforded neuroprotection in SOD1^G93A mutant mice, a model of ALS. These effects may involve the activation of PPAR-γ too. Here, we have investigated the neuroprotective effects in SOD1^G93A mutant mice of the cannabigerol derivative VCE-003.2, which works as neuroprotectant by activating PPAR-γ. Mice were treated with VCE-003.2 from 60 days up to an advanced stage in disease progression (18 weeks), when they were euthanized and used for analysis of neuropathological signs. As expected, SOD1^G93A transgenic mice experienced a progressive weight loss and neurological deterioration, which was associated with a marked loss of spinal cholinergic motor neurons, glial reactivity, and elevations in several biochemical markers (cytokines, glutamate transporters) that indirectly reflect the glial proliferation and activation in the spinal cord. The treatment with VCE-003.2 improved most of these neuropathological signs. It attenuated the weight loss and the anomalies in neurological parameters, preserved spinal cholinergic motor neurons, and reduced astroglial reactivity. VCE-003.2 also reduced the elevations in IL-1β and glial glutamate transporters. Lastly, VCE-003.2 attenuated the LPS-induced generation of TNF-α and IL-1β in cultured astrocytes obtained from SOD1^G93A transgenic newborns, an effect also produced by rosiglitazone, then indicating a probable PPAR-γ activation as responsible of its neuroprotective effects. In summary, our results showed benefits with VCE-003.2 in SOD1^G93A transgenic mice supporting PPAR-γ as an additional neuroprotective target available for cannabinoids in ALS. Such benefits would need to be validated in other ALS models prior to be translated to the clinical level.

Targeting glial cannabinoid CB2 receptors to delay the progression of the pathological phenotype in TDP-43 (A315T) transgenic mice, a model of amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

Cannabinoid CB₂ receptors are up-regulated in reactive microglia in the spinal cord of TDP-43 (A315T) transgenic mice, an experimental model of amyotrophic lateral sclerosis. To determine whether this up-regulation can be exploited pharmacologically, we investigated the effects of different treatments that affect CB₂ receptor function.

EXPERIMENTAL APPROACH

We treated TDP-43 (A315T) transgenic mice with the non-selective agonist WIN55,212-2, alone or combined with selective CB₁ or CB₂ antagonists, as well as with the selective CB₂ agonist HU-308, and evaluated their effects on the pathological phenotype.

KEY RESULTS

WIN55,212-2 had modest beneficial effects in the rotarod test, Nissl staining of motor neurons, and GFAP and Iba-1 immunostainings in the spinal cord, which were mediated in part by CB₂ receptor activation. HU-308 significantly improved the rotarod performance of the transgenic mice, with complete preservation of Nissl-stained motor neurons in the ventral horn. Reactive astrogliosis labelled with GFAP was also attenuated by HU-308 in the dorsal and ventral horns, in which CB₂ receptors colocalize with this astroglial marker. Furthermore, HU-308 reduced the elevated Iba-1 immunostaining in the ventral horn of TDP-43 transgenic mice, but did not affect this immunoreactivity in white matter, in which CB₂ receptors also colocalize with this microglial marker.

CONCLUSIONS AND IMPLICATIONS

Our study shows an important role for glial CB₂ receptors in limiting the progression of the pathological phenotype in TDP-43 (A315T) transgenic mice. Such benefits appear to derive from the activation of CB₂ receptors concentrated in astrocytes and reactive microglia located in spinal dorsal and ventral horns.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Upregulation of CB2 receptors in reactive astrocytes in canine degenerative myelopathy, a disease model of amyotrophic lateral sclerosis

Targeting of the CB₂ receptor results in neuroprotection in the SOD1^G93A mutant mouse model of amyotrophic lateral sclerosis (ALS). The neuroprotective effects of CB₂ receptors are facilitated by their upregulation in the spinal cord of the mutant mice. Here, we investigated whether similar CB₂ receptor upregulation, as well as parallel changes in other endocannabinoid elements, is evident in the spinal cord of dogs with degenerative myelopathy (DM), caused by mutations in the superoxide dismutase 1 gene (SOD1). We used well-characterized post-mortem spinal cords from unaffected and DM-affected dogs. Tissues were used first to confirm the loss of motor neurons using Nissl staining, which was accompanied by glial reactivity (elevated GFAP and Iba-1 immunoreactivity). Next, we investigated possible differences in the expression of endocannabinoid genes measured by qPCR between DM-affected and control dogs. We found no changes in expression of the CB₁ receptor (confirmed with CB₁ receptor immunostaining) or NAPE-PLD, DAGL, FAAH and MAGL enzymes. In contrast, CB₂ receptor levels were significantly elevated in DM-affected dogs determined by qPCR and western blotting, which was confirmed in the grey matter using CB₂ receptor immunostaining. Using double-labelling immunofluorescence, CB₂ receptor immunolabelling colocalized with GFAP but not Iba-1, indicating upregulation of CB₂ receptors on astrocytes in DM-affected dogs. Our results demonstrate a marked upregulation of CB₂ receptors in the spinal cord in canine DM, which is concentrated in activated astrocytes. Such receptors could be used as a potential target to enhance the neuroprotective effects exerted by these glial cells.

Editors' choice: CB₂ receptors are upregulated in activated astrocytes recruited at the damaged spinal cord in dogs with degenerative myelopathy, a canine model of amyotrophic lateral sclerosis.

Changes in endocannabinoid receptors and enzymes in the spinal cord of SOD1(G93A) transgenic mice and evaluation of a Sativex(®) -like combination of phytocannabinoids: interest for future therapies in amyotrophic lateral sclerosis

AIMS

Cannabinoids afford neuroprotection in SOD1(G93A) mutant mice, an experimental model of amyotrophic lateral sclerosis (ALS). However, these mice have been poorly studied to identify alterations in those elements of the endocannabinoid system targeted by these treatments. Moreover, we studied the neuroprotective effect of the phytocannabinoid-based medicine Sativex(®) in these mice.

METHODS

First, we analyzed the endocannabinoid receptors and enzymes in the spinal cord of SOD1(G93A) transgenic mice at a late stage of the disease. Second, 10-week-old transgenic mice were daily treated with an equimolecular combination of Δ(9) -tetrahydrocannabinol- and cannabidiol-enriched botanical extracts (20 mg/kg for each phytocannabinoid).

RESULTS

We found a significant increase of CB2 receptors and NAPE-PLD enzyme in SOD1(G93A) transgenic males and only CB2 receptors in females. Pharmacological experiments demonstrated that the treatment of these mice with the Sativex(®) -like combination of phytocannabinoids only produced weak improvements in the progression of neurological deficits and in the animal survival, particularly in females.

CONCLUSIONS

Our results demonstrated changes in endocannabinoid signaling, in particular a marked up-regulation of CB2 receptors, in SOD1(G93A) transgenic mice, and provide support that Sativex(®) may serve as a novel disease-modifying therapy in ALS.

Motor effects of the non-psychotropic phytocannabinoid cannabidiol that are mediated by 5-HT1A receptors

The broad presence of CB1 receptors in the basal ganglia, mainly in GABA- or glutamate-containing neurons, as well as the presence of TRPV1 receptors in dopaminergic neurons and the identification of CB2 receptors in some neuronal subpopulations within the basal ganglia, explain the powerful motor effects exerted by those cannabinoids that can activate/block these receptors. By contrast, cannabidiol (CBD), a phytocannabinoid with a broad therapeutic profile, is generally presented as an example of a cannabinoid compound with no motor effects due to its poor affinity for the CB1 and the CB2 receptor, despite its activity at the TRPV1 receptor. However, recent evidence suggests that CBD may interact with the serotonin 5-HT1A receptor to produce some of its beneficial effects. This may enable CBD to directly influence motor activity through the well-demonstrated role of serotonergic transmission in the basal ganglia. We have investigated this issue in rats using three different pharmacological and neurochemical approaches. First, we compared the motor effects of various i.p. doses of CBD with the selective 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; i.p.). Second, we investigated whether the motor effects of CBD are sensitive to 5-HT1A receptor blockade in comparison with CB1 receptor antagonism. Finally, we investigated whether CBD was able to potentiate the effect of a sub-effective dose of 8-OH-DPAT. Our results demonstrated that: (i) only high doses of CBD (>10 mg/kg) altered motor behavior measured in a computer-aided actimeter; (ii) these alterations were restricted to vertical activity (rearing) with only modest changes in other parameters; (iii) similar effects were produced by 8-OH-DPAT (1 mg/kg), although this agonist affected exclusively vertical activity, with no effects on other motor parameters, and it showed always more potency than CBD; (iv) the effects of 8-OH-DPAT (1 mg/kg) and CBD (20 mg/kg) on vertical activity were reversed by the 5-HT1A receptor antagonist WAY-100,635 (0.5 mg/kg; i.p.); (v) the effects of CBD (20 mg/kg) on vertical activity were not reversed by the CB1 receptor antagonist rimonabant (0.1 mg/kg; i.p.); (vi) the effect of 8-OH-DPAT on vertical activity was associated with an increase in serotonin content in the basal ganglia, a neurochemical change not produced by CBD (20 mg/kg); and (vii) CBD at a dose of 20 mg/kg was able to enhance motor effects of a sub-effective dose of 8-OH-DPAT (0.1 mg/kg), producing the expected changes in serotonergic transmission in the basal ganglia. Collectively, these results suggest that CBD may influence motor activity, in particular vertical activity, and that this effect seems to be dependent on its ability to target the 5-HT1A receptor, a mechanism of action that has been proposed to account for its anti-emetic, anxiolytic and antidepressant effects.