Transcriptomic Analysis of Single Isolated Myofibers Identifies miR-27a-3p and miR-142-3p as Regulators of Metabolism in Skeletal Muscle

Summary: Skeletal muscle is composed of different myofiber types that preferentially use glucose or lipids for ATP production. How fuel preference is regulated in these post-mitotic cells is largely unknown, making this issue a key question in the fields of muscle and whole-body metabolism. Here, we show that microRNAs (miRNAs) play a role in defining myofiber metabolic profiles. mRNA and miRNA signatures of all myofiber types obtained at the single-cell level unveiled fiber-specific regulatory networks and identified two master miRNAs that coordinately control myofiber fuel preference and mitochondrial morphology. Our work provides a complete and integrated mouse myofiber type-specific catalog of gene and miRNA expression and establishes miR-27a-3p and miR-142-3p as regulators of lipid use in skeletal muscle. : Chemello et al. characterize coding mRNAs and non-coding microRNAs expressed by myofibers of hindlimb mouse muscles, identifying complex interactions between these molecules that modulate mitochondrial functions and muscle metabolism. They demonstrate that specific short non-coding RNAs influence the contractile fiber composition of skeletal muscles by modulating muscle metabolism. Keywords: single myofiber, skeletal muscle metabolism, mitochondria, miRNAs, lipid

Age dependent plasticity in endocannabinoid modulation of pain processing through postnatal development

Significant age and experience-dependent remodelling of spinal and supraspinal neural networks occur resulting in altered pain responses in early life. In adults endogenous opioid peptide and endocannabinoid (ECs) pain control systems exist which modify pain responses but the role they play in acute responses to pain and postnatal neurodevelopment is unknown. Here we have studied the changing role of the ECs in brainstem nuclei essential for the control of nociception from birth to adulthood in both rat and human. Using in vivo electrophysiology we show that substantial functional changes occur in the effect of microinjection of ECs receptor agonists and antagonists in the periaqueductal grey (PAG) and rostroventral medulla (RVM), both of which play central roles in the supraspinal control of pain and the maintenance of chronic pain states in adulthood. We show that in immature PAG and RVM the orphan receptor GPR55 is able to mediate profound analgesia which is absent in adults. We show that tissue levels of endocannabinoid neurotransmitters, anandamide and 2-arachidonoylglycerol within the PAG and RVM are developmentally regulated (using mass spectrometry). The expression patterns and levels of ECs enzymes and receptors were assessed using quantitative PCR and immunohistochemistry. In human brainstem we show age-related alterations in the expression of key enzymes and receptors in involved in ECs function using PCR and in situ hybridisation. These data reveal significant changes on ECs that to this point have been unknown and which shed new light into the complex neurochemical changes that permit normal, mature responses to pain

Diazepam actions in the VTA enhance social dominance and mitochondrial function in the nucleus accumbens by activation of dopamine D1 receptors.

Benzodiazepines can ameliorate social disturbances and increase social competition, particularly in high-anxious individuals. However, the neural circuits and mechanisms underlying benzodiazepines' effects in social competition are not understood. Converging evidence points to the mesolimbic system as a potential site of action for at least some benzodiazepine-mediated effects. Furthermore, mitochondrial function in the nucleus accumbens (NAc) has been causally implicated in the link between anxiety and social competitiveness. Here, we show that diazepam facilitates social dominance, ameliorating both the competitive disadvantage and low NAc mitochondrial function displayed by high-anxious rats, and identify the ventral tegmental area (VTA) as a key site of action for direct diazepam effects. We also show that intra-VTA diazepam infusion increases accumbal dopamine and DOPAC, as well as activity of dopamine D1- but not D2-containing cells. In addition, intra-NAc infusion of a D1-, but not D2, receptor agonist facilitates social dominance and mitochondrial respiration. Conversely, intra-VTA diazepam actions on social dominance and NAc mitochondrial respiration are blocked by pharmacological NAc micro-infusion of a mitochondrial complex I inhibitor or an antagonist of D1 receptors. Our data support the view that diazepam disinhibits VTA dopaminergic neurons, leading to the release of dopamine into the NAc where activation of D1-signaling transiently facilitates mitochondrial function, that is, increased respiration and enhanced ATP levels, which ultimately enhances social competitive behavior. Therefore, our findings critically involve the mesolimbic system in the facilitating effects of diazepam on social competition and highlight mitochondrial function as a potential therapeutic target for anxiety-related social dysfunctions

Synaptic Transmission Optimization Predicts Expression Loci of Long-Term Plasticity

Long-term modifications of neuronal connections are critical for reliable memory storage in the brain. However, their locus of expression—pre- or postsynaptic—is highly variable. Here we introduce a theoretical framework in which long-term plasticity performs an optimization of the postsynaptic response statistics toward a given mean with minimal variance. Consequently, the state of the synapse at the time of plasticity induction determines the ratio of pre- and postsynaptic modifications. Our theory explains the experimentally observed expression loci of the hippocampal and neocortical synaptic potentiation studies we examined. Moreover, the theory predicts presynaptic expression of long-term depression, consistent with experimental observations. At inhibitory synapses, the theory suggests a statistically efficient excitatory-inhibitory balance in which changes in inhibitory postsynaptic response statistics specifically target the mean excitation. Our results provide a unifying theory for understanding the expression mechanisms and functions of long-term synaptic transmission plasticity

Subcellular specificity of cannabinoid effects in striatonigral circuits

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

An ErbB2/c-Src axis links bioenergetics with PRC2 translation to drive epigenetic 2 reprogramming and mammary tumourigenesis

Dysregulation of histone modifications promotes carcinogenesis by altering transcription. Breast cancers frequently overexpress the histone methyltransferase EZH2, the catalytic subunit of Polycomb Repressor Complex 2 (PRC2). However, the role of EZH2 in this setting is unclear due to the context-dependent functions of PRC2 and the heterogeneity of breast cancer. Moreover, the mechanisms underlying PRC2 overexpression in cancer are obscure. Here, using multiple models of breast cancer driven by the oncogene ErbB2, we show that the tyrosine kinase c-Src links energy sufficiency with PRC2 overexpression via control of mRNA translation. By stimulating mitochondrial ATP production, c-Src suppresses energy stress, permitting sustained activation of the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which increases the translation of mRNAs encoding the PRC2 subunits Ezh2 and Suz12. We show that Ezh2 overexpression and activity are pivotal in ErbB2-mediated mammary tumourigenesis. These results reveal the hitherto unknown c-Src/mTORC1/PRC2 axis, which is essential for ErbB2-driven carcinogenesis

Impact des phosphorylations sur tyrosine sur le métabolisme mitochondrial (régulation et impacts fonctionnels des phosphorylations induites par la Src kinase)

La mitochondrie est une organelle très importante vu son implication dans plusieurs processus cellulaires. Elle produit notamment la majeure partie de l'énergie qui est consommée par la cellule, grâce aux processus d'oxydation phosphorylante (OXPHOS). La phosphorylation des enzymes impliquées dans les OXPHOS apparait comme une voie de régulation importante de la production énergétique. L'objectif de ce thèse était donc de comprendre comment les phosphorylations, et plus particulièrement, les phosphorylations sur tyrosine induites par la Src kinase influencent les OXPHOS. Il a donc été démontré qu'il existe, à l'intérieur des mitochondries, des voies de régulation de ces processus de phosphorylation induits par la Src kinase. Ces processus pouvant induire la phosphorylation de plusieurs enzymes mitochondriales, notamment plusieurs sous-unités des complexes du système des électrons et ainsi, grandement influencer les OXPHOS. Il a aussi été démontré que la Src kinase semble aussi présente dans les mitochondries de cellules cancéreuses, induisant la phosphorylation d'une sous-unité de la NADH-oxidoréductase et une augmentation du métabolisme énergétique mitochondrial. Cette régulation des OXPHOS dans les cellules cancéreuses par la Src kinase pourrait participer à l'établissement du phénotype hautement prolifératif de ces cellules.Mitochondria are implicated in several key cellular processes. They are producing most part of the energy that is consumed by the cell via oxidative phosphorylation processes (OXPHOS). Phosphorylation of different components implicated in OXPHOS are known to constitute an important regulation pathway of energetic production. The objective of this thesis was to understand how tyrosine phosphorylation induced by the Src kinase could influence OXPHOS. First, it was shown that Src kinase mediated phosphorylation can be regulated directly in mitochondria, inducing phosphorylation of several mitochondrial proteins and different effects on OXPHOS. I also demonstrated that Src kinase is also present in mitochondria of cancer cells where it can lead to phosphorylation of NADH-oxidoreductase. This phosphorylation site is associated with increase of OXPHOS which could be implicated in the establishment of global phenotype of cancer cells.BORDEAUX2-Bib. électronique (335229905) / SudocSudocFranceF

Connecting Dots between Mitochondrial Dysfunction and Depression

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

Alpha-synuclein aggregates trigger cardiolipin externalization and mitophagy

ABSTRACTAccumulation 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

Sirtuin 5 protects mitochondria from fragmentation and degradation during starvation

During starvation, intra-mitochondrial sirtuins, NAD(+) sensitive deacylating enzymes that modulate metabolic homeostasis and survival, directly adjust mitochondrial function to nutrient availability; concomitantly, mitochondria elongate to escape autophagic degradation. However, whether sirtuins also impinge on mitochondrial dynamics is still uncharacterized. Here we show that the mitochondrial Sirtuin 5 (Sirt5) is essential for starvation induced mitochondrial elongation. Deletion of Sirt5 in mouse embryonic fibroblasts increased levels of mitochondrial dynamics of 51kDa protein and mitochondrial fission protein 1, leading to mitochondrial accumulation of the pro-fission dynamin related protein 1 and to mitochondrial fragmentation. During starvation, Sirt5 deletion blunted mitochondrial elongation, resulting in increased mitophagy. Our results indicate that starvation induced mitochondrial elongation and evasion from autophagic degradation requires the energy sensor Sirt5