Many brain disorders involve mitochondrial alterations, but owing to the lack of suitable tools, the causal role of mitochondrial dysfunction in pathophysiological processes is difficult to establish. Heterotrimeric guanine nucleotide-binding (G) proteins are key regulators of cell functions, and they can be found within mitochondria. Therefore, we reasoned that the activation of stimulatory mitochondrial G proteins (Gs) could rapidly promote the activity of the organelle and possibly compensate for bioenergetic dysfunction. Here, we show that a mitochondria-targeted recombinant designer receptor exclusively activated by designer drugs (mitoDREADD-Gs) can acutely trigger intramitochondrial signaling to increase mitochondrial membrane potential and oxygen consumption. In vivo activation of mitoDREADD-Gs abolished memory alterations in cannabinoid-treated mice and in two mouse models of Alzheimer's disease and frontotemporal dementia. Thus, mitoDREADD-Gs enables the establishment of causal relationships between mitochondria and biological or disease-related processes and represents an innovative potential therapeutic approach for disorders associated with mitochondrial impairment.

The Acadian variant of Fanconi Syndrome (AVFS) is a rare genetic disorder characterized by renal deficiencies. AVFS is caused by a mutation to NDUFAF6 encoding a complex I assembly factor, and leading to metabolic alterations. We confirmed that fibroblasts derived from AVFS patients have lower complex I activity, mitochondrial membrane potential and cellular respiration. These mitochondrial defects were accompanied by higher levels of 8-hydroxy-2′deoxyguanosine, malondialdehyde and carbonyl, which are markers of oxidative damage to DNA, lipids and proteins, respectively. Thus, we hypothesized that the antioxidant N-Acetyl-L-cysteine (NAC) would reduce oxidative stress and mitochondrial defects in AVFS fibroblasts. Treatment with NAC during 5 days partially restored complex I activity, mitochondrial membrane potential and cellular respiration in AVFS fibroblasts. NAC also prevented oxidative damage in AVFS fibroblasts. This work shows for the first time that the physiopathology of AVFS includes high oxidative stress. It also reveals that NAC and other antioxidant-based strategies might represent an effective pharmacological treatment for AVFS.

Platelets release microvesicles (PMVs) upon activation which retain platelet cargo, including functional mitochondria, and actively participate in intercellular communication. Neutrophils (PMN) play a vital role in the innate immune response and inflammation. Despite growing interest in the transfer of biological material between immune cells, the transfer of mitochondrial content from PMVs to PMN and its resulting effects remain unclear. This study aimed to address this gap in literature by investigating if the increase of mitochondria in PMN could delay cell death and prolong the inflammatory response. We show that PMV mitochondria were found associated with PMN, consequently increasing viability. PMVs induced an increase in ATP production, ETS state and mitochondrial reductase activity in the recipient cell. To confirm the implication of platelet-derived mitochondria in the observed changes of the PMN’s phenotype, PMVs were subjected to freeze-thaw cycles to generate dysfunctional mitochondria which did not affect the cellular respiration of PMN or the mitochondrial reductase activity. Interestingly, dysfunctional PMVs showed significantly more caspase-3 activity in PMN compared to fresh PMVs. Finally, we detected the transfer of active 12-lipoxygenase and cyclooxygenase-1 in the PMN, enzymes found specifically in PMVs. These findings suggest that PMV-derived mitochondria play a key role in enhancing the survival and inflammatory function of PMN in inflammatory conditions. Supported by Research New Brunswick and the Canadian Institutes of Health Research. Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)

Accumulation of Lewy bodies in dopaminergic neurons is associated to Parkinson disease (PD). The main component of Lewy bodies appears to be aggregates of alpha-synuclein (α-syn). Several mutations of the gene encoding this protein promote its aggregation. Thus, clustering of α-syn is considered a central event in the onset of PD. An old theory also postulates that mitochondrial dysfunction represents another cause of PD pathogenesis. However, the impact of α-syn aggregates on mitochondria remains poorly understood considering the technical difficulties to discriminate between the different forms of α-syn. In this punctum, we describe our recent work in which we used a newly developed optogenetic tool to control the aggregation of α-syn and examine the impact on mitochondria. This work revealed that α-syn aggregates dynamically interact with mitochondria, triggering their depolarization and leading to cardiolipin translocation to the surface of mitochondria and mitophagy. Abbreviations: α-syn: alpha-synuclein; BNIP3L: BCL2/adenovirus E1B 19 kDa protein-interacting protein 3-like; FUNDC1: FUN14 domain-containing protein 1; IMM: inner mitochondrial membrane; LIPA: light-induced protein aggregation; OMM: outer mitochondrial membrane; PD: Parkinson disease; SNc: substantia nigra par compacta.

Accumulation of α-synuclein aggregates in the substantia nigra pars compacta is central in the pathophysiology of Parkinson’s disease, leading to the degeneration of dopaminergic neurons and the manifestation of motor symptoms. Although several PD models mimic the pathological accumulation of α-synuclein after overexpression, they do not allow for controlling and monitoring its aggregation. We recently generated a new optogenetic tool by which we can spatiotemporally control the aggregation of α-synuclein using a light-induced protein aggregation system. Using this innovative tool, we aimed to characterize the impact of α-synuclein clustering on mitochondria, whose activity is crucial to maintain neuronal survival. We observed that aggregates of α-synuclein transiently and dynamically interact with mitochondria, leading to mitochondrial depolarization, lower ATP production, mitochondrial fragmentation and degradation via cardiolipin externalization-dependent mitophagy. Aggregation of α-synuclein also leads to lower mitochondrial content in human dopaminergic neurons and in mouse midbrain. Interestingly, overexpression of α-synuclein alone did not induce mitochondrial degradation. This work is among the first to clearly discriminate between the impact of α-synuclein overexpression and aggregation on mitochondria. This study thus represents a new framework to characterize the role of mitochondria in PD.

The mechanisms that underpin aging are still elusive. In this study, we suggest that the ability of mitochondria to oxidize different substrates, which is known as metabolic flexibility, is involved in this process. To verify our hypothesis, we used honey bees (Apis mellifera carnica) at different ages, to assess mitochondrial oxygen consumption and enzymatic activities of key enzymes of the energetic metabolism as well as ATP5A1 content (subunit of ATP synthase) and adenylic energy charge (AEC). We also measured mRNA abundance of genes involved in mitochondrial functions and the antioxidant system. Our results demonstrated that mitochondrial respiration increased with age and favored respiration through complexes I and II of the electron transport system (ETS) while glycerol-3-phosphate (G3P) oxidation was relatively decreased. In addition, glycolytic, tricarboxylic acid cycle and ETS enzymatic activities increased, which was associated with higher ATP5A1 content and AEC. Furthermore, we detected an early decrease in the mRNA abundance of subunits of NADH ubiquinone oxidoreductase subunit B2 (NDUFB2, complex I), mitochondrial cytochrome b (CYTB, complex III) of the ETS as well as superoxide dismutase 1 and a later decrease for vitellogenin, catalase and mitochondrial cytochrome c oxidase subunit 1 (COX1, complex IV). Thus, our study suggests that the energetic metabolism is optimized with aging in honey bees, mainly through quantitative and qualitative mitochondrial changes, rather than showing signs of senescence. Moreover, aging modulated metabolic flexibility, which might reflect an underpinning mechanism that explains lifespan disparities between the different castes of worker bees.

Mitochondria are the prime source of cellular energy, and are also responsible for important processes such as oxidative stress, apoptosis and Ca2+ homeostasis. Depression is a psychiatric disease characterized by alteration in the metabolism, neurotransmission and neuroplasticity. In this manuscript, we summarize the recent evidence linking mitochondrial dysfunction to the pathophysiology of depression. Impaired expression of mitochondria-related genes, damage to mitochondrial membrane proteins and lipids, disruption of the electron transport chain, higher oxidative stress, neuroinflammation and apoptosis are all observed in preclinical models of depression and most of these parameters can be altered in the brain of patients with depression. A deeper knowledge of the depression pathophysiology and the identification of phenotypes and biomarkers with respect to mitochondrial dysfunction are needed to help early diagnosis and the development of new treatment strategies for this devastating disorder.

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 (CB 1 -SSi). AEF0117 selectively inhibits a subset of intracellular effects resulting from Δ 9 -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 .

The architecture of mitochondria adapts to physiological contexts: while mitochondrial fragmentation is usually associated to quality control and cell death, mitochondrial elongation often enhances cell survival during stress. Understanding how these events are regulated is important to elucidate how mitochondrial dynamics control cell fate. Here, we show that the tyrosine kinase Src regulates mitochondrial morphology. Deletion of Src increased mitochondrial size and reduced cellular respiration independently of mitochondrial mass, mitochondrial membrane potential or ATP levels. Re-expression of Src targeted to the mitochondrial matrix, but not of Src targeted to the plasma membrane, rescued mitochondrial morphology in a kinase activity-dependent manner. These findings highlight a novel function for Src in the control of mitochondrial dynamics.

Cannabis psychoactive and medicinal properties have been known for thousands of years, but it is only recently that we started to understand the cellular mechanisms triggered by phytocannabinoids, such as Δ9-tetrahydrocannabinol and cannabidiol. The discovery of the endocannabinoid system, which includes cannabinoid receptors and cannabinoids produced endogenously in animal cells, allowed a better understanding of the impact of these phytocannabinoids on human health. Early findings suggested that these molecules disrupt mitochondrial functions via direct binding to the organelle membranes and subsequent alterations of their structure and functions. The multiple tools generated after the discovery of the cannabinoid receptors in the early 1990s allowed to show that specific cannabinoids can also modulate mitochondrial activity via activation of cannabinoid receptors localized at the plasma membrane or directly within mitochondrial membranes. Considering that mitochondria are involved in the onset and progression of various diseases, it appears crucial to better understand the mechanisms linking cannabinoids and mitochondria. The aim of this chapter is to provide an overview of the multiple mechanisms triggered by cannabinoids that affects mitochondria.

Recent advances in neuroscience have positioned brain circuits as key units in controlling behavior, implying that their positive or negative modulation necessarily leads to specific behavioral outcomes. However, emerging evidence suggests that the activation or inhibition of specific brain circuits can actually produce multimodal behavioral outcomes. This study shows that activation of a receptor at different subcellular locations in the same neuronal circuit can determine distinct behaviors. Pharmacological activation of type 1 cannabinoid (CB1) receptors in the striatonigral circuit elicits both antinociception and catalepsy in mice. The decrease in nociception depends on the activation of plasma membrane-residing CB1 receptors (pmCB1), leading to the inhibition of cytosolic PKA activity and substance P release. By contrast, mitochondrial-associated CB1 receptors (mtCB1) located at the same terminals mediate cannabinoid-induced catalepsy through the decrease in intra-mitochondrial PKA-dependent cellular respiration and synaptic transmission. Thus, subcellular-specific CB1 receptor signaling within striatonigral circuits determines multimodal control of behavior.

Peroxisome biogenesis disorders (PBDs) are a group of metabolic developmental diseases caused by mutations in one or more genes encoding peroxisomal proteins. Zellweger syndrome spectrum (PBD-ZSS) results from metabolic dysfunction caused by damaged or non-functional peroxisomes and manifests as a multi-organ syndrome with significant morbidity and mortality for which there is no current drug therapy. Mild PBD-ZSS patients can exhibit a more progressive disease course and could benefit from the identification of drugs to improve the quality of life and extend the lifespan of affected individuals. Our study used a high-throughput screen of FDA-approved compounds to identify compounds that improve peroxisome function and biogenesis in human fibroblast cells carrying the mild PBD-ZSS variant, PEX1G843D . Our screen identified the nitrogen oxide donor, S -nitrosoglutathione (GSNO), as a potential therapeutic for this mild form of PBD-ZSS. Further biochemical characterization showed that GSNO enhances both peroxisome number and function in PEX1G843D mutant fibroblasts and leads to increased survival and longer lifespan in an in vivo humanized Drosophila model carrying the PEX1G843D mutation. GSNO is therefore a strong candidate to be translated to clinical trials as a potential therapeutic for mild PBD-ZSS.

C-Src kinase is localized in several subcellular compartments, including mitochondria where it is involved in the regulation of organelle functions and overall metabolism. Surprisingly, the characterization of the intramitochondrial Src interactome has never been fully determined. Using in vitro proximity-dependent biotin identification (BioID) coupled to mass spectrometry, we identified 51 candidate proteins that may interact directly or indirectly with c-Src within the mitochondrial matrix. Pathway analysis suggests that these proteins are involved in a large array of mitochondrial functions such as protein folding and import, mitochondrial organization and transport, oxidative phosphorylation, tricarboxylic acid cycle and metabolism of amino and fatty acids. Among these proteins, we identified 24 tyrosine phosphorylation sites in 17 mitochondrial proteins (AKAP1, VDAC1, VDAC2, VDAC3, LonP1, Hsp90, SLP2, PHB2, MIC60, UBA1, EF-Tu, LRPPRC, ACO2, OAT, ACAT1, ETFβ and ATP5β) as potential substrates for intramitochondrial Src using in silico prediction of tyrosine phospho-sites. Interaction of c-Src with SLP2 and ATP5β was confirmed using coimmunoprecipitation. This study suggests that the intramitochondrial Src could target several proteins and regulate different mitochondrial functions.

Mitochondria are the only organelles that contain their own genetic material (mtDNA). Mitochondria are involved in several key physiological functions, including ATP production, Ca2+ homeostasis, and metabolism of neurotransmitters. Since these organelles perform crucial processes to maintain neuronal homeostasis, mitochondrial dysfunctions can lead to various neurodegenerative diseases. Several mitochondrial proteins involved in ATP production are encoded by mtDNA. Thus, any mtDNA alteration can ultimately lead to mitochondrial dysfunction and cell death. Accumulation of mutations, deletions, and rearrangements in mtDNA has been observed in animal models and patients suffering from Parkinson's disease (PD). Also, specific inherited variations associated with mtDNA genetic groups (known as mtDNA haplogroups) are associated with lower or higher risk of developing PD. Consequently, mtDNA alterations should now be considered important hallmarks of this neurodegenerative disease. This review provides an update about the role of mtDNA alterations in the physiopathology of PD.

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 (mtCB(1)) 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 mtCB(1) 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 mtCB(1) receptor signalling can directly regulate astroglial glucose metabolism to fine-tune neuronal activity and behaviour in mice.

In insect, pyruvate is generally the predominant oxidative substrate for mitochondria. This metabolite is transported inside mitochondria via the mitochondrial pyruvate carrier (MPC), but whether and how this transporter controls mitochondrial oxidative capacities in insects is still relatively unknown. Here, we characterize the importance of pyruvate transport as a metabolic control point for mitochondrial substrate oxidation in two genotypes of an insect model, Drosophila melanogaster, differently expressing MPC1, an essential protein for the MPC function. We evaluated the kinetics of pyruvate oxidation, mitochondrial oxygen consumption, metabolic profile, activities of metabolic enzymes, and climbing abilities of wild-type (WT) flies and flies harboring a deficiency in MPC1 (MPC1def). We hypothesized that MPC1 deficiency would cause a metabolic reprogramming that would favor the oxidation of alternative substrates. Our results show that the MPC1def flies display significantly reduced climbing capacity, pyruvate-induced oxygen consumption, and enzymatic activities of pyruvate kinase, alanine aminotransferase, and citrate synthase. Moreover, increased proline oxidation capacity was detected in MPC1def flies, which was associated with generally lower levels of several metabolites, and particularly those involved in amino acid catabolism such as ornithine, citrulline, and arginosuccinate. This study therefore reveals the flexibility of mitochondrial substrate oxidation allowing Drosophila to maintain cellular homeostasis.