Mitochondrial cannabinoid receptors gate corticosterone impact on novel object recognition

Corticosteroid-mediated stress responses require the activation of complex brain circuits involving mitochondrial activity, but the underlying cellular and molecular mechanisms are scantly known. The endocannabinoid system is implicated in stress coping, and it can directly regulate brain mitochondrial functions via type 1 cannabinoid (CB1) receptors associated with mitochondrial membranes (mtCB1). In this study, we show that the impairing effect of corticosterone in the novel object recognition (NOR) task in mice requires mtCB1 receptors and the regulation of mitochondrial calcium levels in neurons. Different brain circuits are modulated by this mechanism to mediate the impact of corticosterone during specific phases of the task. Thus, whereas corticosterone recruits mtCB1 receptors in noradrenergic neurons to impair NOR consolidation, mtCB1 receptors in local hippocampal GABAergic interneurons are required to inhibit NOR retrieval. These data reveal unforeseen mechanisms mediating the effects of corticosteroids during different phases of NOR, involving mitochondrial calcium alterations in different brain circuits.

Signaling-specific inhibition of the CB1 receptor for cannabis use disorder: phase 1 and phase 2a randomized trials

Cannabis use disorder (CUD) is widespread, and there is no pharmacotherapy to facilitate its treatment. AEF0117, the first of a new pharmacological class, is a signaling-specific inhibitor of the cannabinoid receptor 1 (CB1-SSi). AEF0117 selectively inhibits a subset of intracellular effects resulting from Δ9-tetrahydrocannabinol (THC) binding without modifying behavior per se. In mice and non-human primates, AEF0117 decreased cannabinoid self-administration and THC-related behavioral impairment without producing significant adverse effects. In single-ascending-dose (0.2 mg, 0.6 mg, 2 mg and 6 mg; n = 40) and multiple-ascending-dose (0.6 mg, 2 mg and 6 mg; n = 24) phase 1 trials, healthy volunteers were randomized to ascending-dose cohorts (n = 8 per cohort; 6:2 AEF0117 to placebo randomization). In both studies, AEF0117 was safe and well tolerated (primary outcome measurements). In a double-blind, placebo-controlled, crossover phase 2a trial, volunteers with CUD were randomized to two ascending-dose cohorts (0.06 mg, n = 14; 1 mg, n = 15). AEF0117 significantly reduced cannabis' positive subjective effects (primary outcome measurement, assessed by visual analog scales) by 19% (0.06 mg) and 38% (1 mg) compared to placebo (P < 0.04). AEF0117 (1 mg) also reduced cannabis self-administration (P < 0.05). In volunteers with CUD, AEF0117 was well tolerated and did not precipitate cannabis withdrawal. These data suggest that AEF0117 is a safe and potentially efficacious treatment for CUD.ClinicalTrials.gov identifiers: NCT03325595 , NCT03443895 and NCT03717272 .

Imaging mitochondrial calcium dynamics in the central nervous system

Mitochondrial calcium handling is a particularly active research area in the neuroscience field, as it plays key roles in the regulation of several functions of the central nervous system, such as synaptic transmission and plasticity, astrocyte calcium signaling, neuronal activity… In the last few decades, a panel of techniques have been developed to measure mitochondrial calcium dynamics, relying mostly on photonic microscopy, and including synthetic sensors, hybrid sensors and genetically encoded calcium sensors. The goal of this review is to endow the reader with a deep knowledge of the historical and latest tools to monitor mitochondrial calcium events in the brain, as well as a comprehensive overview of the current state of the art in brain mitochondrial calcium signaling. We will discuss the main calcium probes used in the field, their mitochondrial targeting strategies, their key properties and major drawbacks. In addition, we will detail the main roles of mitochondrial calcium handling in neuronal tissues through an extended report of the recent studies using mitochondrial targeted calcium sensors in neuronal and astroglial cells, in vitro and in vivo.

Astroglial ER-mitochondria calcium transfer mediates endocannabinoid-dependent synaptic integration

Intracellular calcium signaling underlies the astroglial control of synaptic transmission and plasticity. Mitochondria-endoplasmic reticulum contacts (MERCs) are key determinants of calcium dynamics, but their functional impact on astroglial regulation of brain information processing is unexplored. We found that the activation of astrocyte mitochondrial-associated type-1 cannabinoid (mtCB₁) receptors determines MERC-dependent intracellular calcium signaling and synaptic integration. The stimulation of mtCB₁ receptors promotes calcium transfer from the endoplasmic reticulum to mitochondria through a specific molecular cascade, involving the mitochondrial calcium uniporter (MCU). Physiologically, mtCB₁-dependent mitochondrial calcium uptake determines the dynamics of cytosolic calcium events in astrocytes upon endocannabinoid mobilization. Accordingly, electrophysiological recordings in hippocampal slices showed that conditional genetic exclusion of mtCB₁ receptors or dominant-negative MCU expression in astrocytes blocks lateral synaptic potentiation, through which astrocytes integrate the activity of distant synapses. Altogether, these data reveal an endocannabinoid link between astroglial MERCs and the regulation of brain network functions.

Glucose metabolism links astroglial mitochondria to cannabinoid effects

Astrocytes take up glucose from the bloodstream to provide energy to the brain, thereby allowing neuronal activity and behavioural responses^1-5. By contrast, astrocytes are under neuronal control through specific neurotransmitter receptors^5-7. However, whether the activation of astroglial receptors can directly regulate cellular glucose metabolism to eventually modulate behavioural responses is unclear. Here we show that activation of mouse astroglial type-1 cannabinoid receptors associated with mitochondrial membranes (mtCB₁) hampers the metabolism of glucose and the production of lactate in the brain, resulting in altered neuronal functions and, in turn, impaired behavioural responses in social interaction assays. Specifically, activation of astroglial mtCB₁ receptors reduces the phosphorylation of the mitochondrial complex I subunit NDUFS4, which decreases the stability and activity of complex I. This leads to a reduction in the generation of reactive oxygen species by astrocytes and affects the glycolytic production of lactate through the hypoxia-inducible factor 1 pathway, eventually resulting in neuronal redox stress and impairment of behavioural responses in social interaction assays. Genetic and pharmacological correction of each of these effects abolishes the effect of cannabinoid treatment on the observed behaviour. These findings suggest that mtCB₁ receptor signalling can directly regulate astroglial glucose metabolism to fine-tune neuronal activity and behaviour in mice.

Functional Analysis of Mitochondrial CB1 Cannabinoid Receptors (mtCB1) in the Brain

Recent evidence indicates that, besides its canonical localization at cell plasma membranes, the type-1 cannabinoid receptor, CB1 is functionally present at brain and muscle mitochondrial membranes (mtCB1). Through mtCB1 receptors, cannabinoids can directly regulate intramitochondrial signaling and respiration. This new and surprising discovery paves the way to new potential fields of research, dealing with the direct impact of G protein-coupled receptors on bioenergetic processes and its functional implications. In this chapter, we summarize some key experimental approaches established in our laboratories to identify anatomical, biochemical, and functional features of mtCB1 receptors in the brain. In particular, we describe the procedures to obtain reliable and controlled detection of mtCB1 receptors by immunogold electromicroscopy and by immunoblotting methods. Then, we address the study of direct cannabinoid effects on the electron transport system and oxidative phosphorylation. Finally, we present a functional example of the impact of mtCB1 receptors on mitochondrial mobility in cultured neurons. Considering the youth of the field, these methodological approaches will very likely be improved and refined in the future, but this chapter aims at presenting the methods that are currently used and, in particular, at underlining the need of rigorous controls to obtain reliable results. We hope that this chapter might help scientists becoming interested in this new and exciting field of research.

The Armc10/SVH gene: genome context, regulation of mitochondrial dynamics and protection against Aβ-induced mitochondrial fragmentation

Mitochondrial function and dynamics are essential for neurotransmission, neural function and neuronal viability. Recently, we showed that the eutherian-specific Armcx gene cluster (Armcx1-6 genes), located in the X chromosome, encodes for a new family of proteins that localise to mitochondria, regulating mitochondrial trafficking. The Armcx gene cluster evolved by retrotransposition of the Armc10 gene mRNA, which is present in all vertebrates and is considered to be the ancestor gene. Here we investigate the genomic organisation, mitochondrial functions and putative neuroprotective role of the Armc10 ancestor gene. The genomic context of the Armc10 locus shows considerable syntenic conservation among vertebrates, and sequence comparisons and CHIP-data suggest the presence of at least three conserved enhancers. We also show that the Armc10 protein localises to mitochondria and that it is highly expressed in the brain. Furthermore, we show that Armc10 levels regulate mitochondrial trafficking in neurons, but not mitochondrial aggregation, by controlling the number of moving mitochondria. We further demonstrate that the Armc10 protein interacts with the KIF5/Miro1-2/Trak2 trafficking complex. Finally, we show that overexpression of Armc10 in neurons prevents Aβ-induced mitochondrial fission and neuronal death. Our data suggest both conserved and differential roles of the Armc10/Armcx gene family in regulating mitochondrial dynamics in neurons, and underscore a protective effect of the Armc10 gene against Aβ-induced toxicity. Overall, our findings support a further degree of regulation of mitochondrial dynamics in the brain of more evolved mammals.

[Coronary heart disease and lipoprotein (a): relationship with other lipid cardiovascular risk factors]

BACKGROUND

Lipoprotein (Lp) (a) is considered a risk factor for early coronary heart disease (CHD), and a discriminant cutoff of Lp(a) concentration has been suggested.

METHODS

Serum Lp(a) concentrations have been determined by enzymoimmunoassay in 66 men with CHD and in 100 healthy control men. Serum cholesterol, serum triglycerides, high density lipoprotein (HDL)-cholesterol, and apoprotein (apo) A-I were also determined.

RESULTS

Serum Lp(a) concentration was 21.7 +/- 16.9 mg/dl (mean +/- SD) in patients and 12.5 +/- 12.5 mg/dl in controls (p less than 0.001). Serum cholesterol was 5.63 +/- 1.22 mmol/l and 5.29 +/- 1.00 mmol/l (p less than 0.05) respectively; serum triglycerides were 1.99 +/- 1.23 mmol/l and 1.29 +/- 0.61 mmol/l (p less than 0.001) respectively; HDL-cholesterol was 0.97 +/- 0.27 mmol/l and 1.07 +/- 0.30 mmol/l (p less than 0.05) respectively; and apo A-I was 94 +/- 15 mg/dl and 144 +/- 41 mg/dl (p less than 0.001) respectively. Lp(a) concentrations were not correlated with other well-recognized cardiovascular risk lipidic factors, nor influenced by age either body mass index. Using 20 mg/dl as discriminant Lp(a) concentration between patients and controls, a ratio 2:1 in patients with respect to controls has been observed and exceeded some more when the threshold level was put on 30 mg/dl. A subset of normocholesterolemic and normotriglyceridemic patients (n = 17) and controls (n = 49) had serum Lp(a) concentration of 22.7 +/- 16.3 mg/dl and 9.1 +/- 8.2 mg/dl (p less than 0.001) respectively.

CONCLUSIONS

Increased concentration of Lp(a) constitutes an independent risk factor for CHD. On the other hand, Lp(a) concentrations of 20 mg/dl or 30 mg/dl as risk threshold levels are well-defined.

[Evaluation of the use of digoxin in a primary care emergency service]

Digoxin is a widely used drug. Previous studies suggest a high prevalence of inadequate use, subtherapeutic levels and high toxicity rates. The aim of the present study was to evaluation the use of digoxin in our area. 50 consecutive patients who attended our emergency service and who were receiving digoxin on a chronic basis were prospectively evaluated. There were 37 females and males, with age 78.1 +/- 8.6 years. We found that digoxin was not indicated in 12% of cases. Only 48% had digoxin plasma levels within the therapeutic range. When plasma levels were considered in association with clinical and electrocardiographic findings, 12% of patients were undertreated and 6% had digitalis toxicity. There was no relation between the digoxin plasma level and the dosage schedule, the ECG findings, the renal function, the use of other drugs or the anthropometric data. Emphasis is made on the need to individualize digoxin therapy and to measure plasma levels in particular cases.

Differences of postextrasystolic behavior of left ventricular and aortic pressures between fixed and dynamic left ventricular outflow tract stenosis

The dynamic behavior of fixed LV outflow tract stenosis partly resembles that of OCM. To analyze their differences we studied basal and postextrasystolic (post-PVC) peak-to-peak LV aortic gradients, aortic systolic pressure, and pulse pressure in 14 OCM and in 36 pure VAS without two-dimensional echocardiographic findings of OCM. Fifteen mild VAS had basal gradients similar to those of OCM (39 +/- 17 mm Hg vs 24 +/- 16 mm Hg). Patients with OCM show a post-PVC gradient (109 +/- 41 mm Hg) similar to that of VAS (110 +/- 50 mm Hg). However, the latter were departing from much higher gradients (VAS 72 +/- 30 mm Hg vs OCM 24 +/- 16 mm Hg). Decrement of post-PVC aortic systolic pressure and pulse pressure were frequent in both groups, but decrement of pulse pressure greater than 5 mm Hg were more frequent in OCM. We concluded that (1) post-PVC increased aortic gradients and decreased aortic systolic pressure occurred in both VAS and OCM; (2) post-PVC decreased aortic pulse pressure might occur in VAS; and (3) association of post-PVC gradient increment greater than 75 percent and pulse pressure decrement greater than 5 mm Hg are strongly suggestive of OCM.