Huntington's disease (HD) is a neuropsychiatric disorder characterized by choreiform movement of the limbs, cognitive disability, psychosis and dementia. It is untreatable, incurable, and ultimately fatal. HD is invariably associated with an abnormally long CAG expansion within the IT15 gene on human chromosome 4. Although the mutant huntingtin protein (mHtt) is ubiquitously expressed in HD patients, cellular degeneration occurs only in neurons within the striatum and cerebral cortex. The Ras homolog Rhes is expressed very selectively in the precise brain areas affected by HD. Recent work using cultured cells suggests that Rhes may be a co-factor with mHtt in cell death. However, there is controversy as to whether cell death underlies the symptoms of HD. We used a validated transgenic mouse model of HD crossed with Rhes knockout mice to show that the behavioral symptoms of HD are regulated by Rhes. HD/Rhes-/- mice showed greatly delayed expression of HD-like symptoms in this in vivo model. Drugs that block or inhibit the actions of Rhes may be useful as the first treatments for HD.

Huntington’s disease (HD) is a heritable, neurodegenerative disorder characterized by motor, cognitive, and psychiatric disturbances. The progressive disease is caused by an unstable CAG expansion within the gene that normally encodes for the huntingtin protein (Htt). The expanded mutant form of Htt (mHtt) is expressed ubiquitously throughout patients’ bodies; however, neuronal degeneration is prominent only in the corpus striatum and, to a lesser extent, the cortex. The Ras homolog Rhes is also preferentially localized to the striatum. The putative co-factor Rhes has been shown to act with mHtt to cause neuronal death. Simvastatin, a lipid lowering drug, and zoledronate, a nitrogen bisphosphonate, act on the mevalonate pathway, which gives both Rhes and its target cells, binding sites. The current study aimed to interrupt the mevalonate pathway and inactivate, via de-prenylation, Rhes in CD-1 mice exposed to 3-nitroproprionic acid, a neurotoxin that mimics HD mitochondrial dysfunction and striatal degeneration. Results suggest that drug treatment does not rescue motor impairments and may potentiate 3-NP damage. The persistent motor deficits are discussed in relation to possible Rhes de-prenylation.

Autism Spectrum Disorder (ASD) is an umbrella term for disorders involving deficits in social interaction, stereotyped behaviours and communication dificulties. A growing area of research has recently focused on motor deficits in ASD, which have been noted in clinical observations and diagnostic criteria since autism was first described. However, motor deficits have traditionally carried little weight in the diagnostic procedure. Until recent changes to diagnostic criteria (Diagnostic and Statistical Manual 5th edition: DSM-5), a comorbid diagnosis of Developmental Coordination Disorder (DCD: a neurodevelopmental disorder affecting motor development) was not possible for those with ASD and motor deficits. This exclusion criterion prompted an investigation of the nature of motor deficits in ASD, questioning whether they are characteristically different from motor deficits in DCD. Previous literature suggested a possible double dissociation in the use of vision and proprioception to guide movement and perception in ASD and DCD, with a reliance on proprioception in ASD, and an over-reliance on vision in DCD. Motor deficits were first investigated by looking at high-level motor skills, and then more basic sensory processing associated with movement to investigate this possible dissociation. There was no significant difference between ASD and DCD on a standardised motor battery (Movement Assessment Battery for Children 2nd edition: MABC-2), with 70% of children with ASD showing motor difficulties within the clinical range on tasks such as timed manual dexterity tasks and balance. Similarly, children with ASD and poor motor skills were indistinguishable from children with DCD on a number of basic motor tasks manipulating visual and proprioceptive cues. These tests included spatial location matching, reaching, goal-directed movements towards proprioceptively-defined targets, and the rubber hand illusion. Children with poor motor skills with a diagnosis of either ASD or DCD seemed to either rely more heavily on visual cues, or behaved in a similar way to typically developing (TD) children. In the spatial location matching task, children with ASD and spared motor skills showed a tendency to give more weight to proprioceptive cues, however too few children with ASD and spared motor skills took part in other tasks to fully investigate cue weighting in this subgroup. Mirroring the overlap in social and motor skills in the clinical groups, a study of the relationship between perceived social and motor ability in a large sample of TD children highlighted the related nature of these developmental domains in typical development. It is concluded that motor deficits in ASD are not ASD-specific but are instead indicative of an additional diagnosis of DCD. This is supported by the recent change to diagnostic criteria.

La maladie de Parkinson (MP) est une maladie neurodégénérative caractérisée par une perte dopaminergique (DA) de la voie nigro-striée. Cette dégénérescence des neurones DA, induit un déséquilibre entre les transmissions dopaminergique, GABAergique et glutamatergique au sein des ganglions de la base qui se traduit par des troubles de l'excitabilité neuronale aboutissant à l'apparition des symptômes moteurs et non-moteurs. Nous avons étudié l'effet de la modulation des canaux SK et Kv4 par des toxines issues de venins d'animaux. Pour ce faire, nous avons utilisé deux modèles lésionnels à la 6-hydroxydopamine (6-OHDA): une lésion bilatérale partielle du striatum mimant la phase précoce de la MP pour tester les déficits cognitifs et émotionnels, et une lésion unilatérale totale au niveau de la substance noire mimant la rigidité et la bradykinésie en phase tardive pour tester les déficits moteurs. Nos résultats montrent que le blocage des canaux SK par l'apamine (injection systémique, 0.1-0.3 mg/kg) améliore partiellement et transitoirement les déficits moteurs dans le test du cylindre et la rotation induite par l'apomorphine dans le modèle tardif de la MP. L'AmmTX3 (injection intrastriatale, 0.2-0.4 g), réduit les déficits moteurs et restaure des comportements cognitifs déficitaires (mémoire sociale et spatiale à court terme) et émotionnels (anxiété), après une dégénérescence DA bilatérale et partielle. L'ensemble de ces données suggère que l'inhibition pharmacologique de l'activité des canaux SK par l'apamine et Kv4 par l'AmmTX3, pourrait représenter une voie thérapeutique innovatrice quant au traitement des déficits moteurs, cognitifs et émotionnels de la MP. / Parkinson's disease (PD) is a neurodegenerative disease associated to a loss of dopaminergic nigrostriatal pathway that innervates the basal ganglia (GB). The DA neuron degeneration in PD induces imbalance between dopaminergic transmission, GABAergic and glutamatergic resulting in impaired neuronal excitability leading to the onset of motor and non-motor symptoms. Potassium channels, Kv4 and SK, are extensively involved in the phenomenon of neuronal excitability. We addressed the question of whether further blockade of SK or Kv4 activity could restore normal GB function in vivo. In this aim, we used a neurotoxin, 6-hydroxydopamine (6-OHDA) to produce two lesional models of Parkinson's disease in rats that mimics the cognitive and emotional deficits of the early phase of PD (partial and bilateral striatal lesions) and the motor deficits observed in the late phase of the disease (total unilateral nigral lesion). Apamin from bee venom (systemic injection, 0.1-0.3 mg/kg) and AmmTX3 from scorpion venom (intrastriatal injection, 0.2-0.4 g) were chosen to block SK and Kv4 channels respectively.In a first study, apamin treatment partially reduced motor deficits in the cylinder test and the rotation induced by apomorphine. In the second study, the AmmTX3 also decreased parkinsonian motor deficits. This late toxin restored cognitive behaviors (short-term social and spatial memory) and emotion (anxiety).Taken together, these results underlie the importance of SK channels as modulators of neuronal excitability of Kv4 channels as players of the homeostatic responses, and more importantly, provide potential targets for adjunctive therapies for Parkinson's disease.

Les accidents vasculaires cérébraux (AVC) sont considérés comme la pathologie neurologique la plus sévère en termes de mortalité et d’infirmité. Ils touchent plus de 140 000 personnes chaque année. L’AVC ischémique, qui représente 80% des AVC, est causé par l’occlusion localisée d’un vaisseau conduisant à un arrêt de l’apport en oxygène et en glucose au cerveau. Il est ainsi responsable de déficits moteurs, sensitifs et cognitifs qui peuvent gravement compromettre l’autonomie et la qualité de vie des patients. Les patients qui ont subi un AVC ischémique développent notamment une atrophie musculaire qui se produit principalement dans le membre parétique, mais aussi dans une moindre mesure dans le membre non parétique. Toutefois, les mécanismes moléculaires à l’origine de cette atrophie musculaire sont méconnus. Dans une première étude, l’objectif a été d’identifier les déterminants moléculaires mis en jeu dans l’atrophie musculaire induite par une ischémie cérébrale. Pour répondre à cet objectif, les travaux ont été menés sur un modèle d'ischémie cérébrale chez la souris qui consiste en l’occlusion de l'artère cérébrale moyenne par un monofilament en nylon. Nous avons montré que l’ischémie cérébrale entraînait, 3 jours après son induction, une atrophie musculaire des muscles quadriceps, soleus et tibialis anterior du côté parétique. Cette atrophie musculaire était associée à des déficits moteurs touchant l’équilibre, la coordination, la force musculaire, la posture ou la marche. Au niveau moléculaire, nous avons reporté un déséquilibre de la balance entre la synthèse et la dégradation des protéines musculaires en faveur d’une augmentation de la dégradation dans les muscles parétique et non parétique des souris ischémiées. Nous avons notamment montré que l’expression de la myostatine, un régulateur négatif majeur de la masse musculaire, était significativement augmentée. Dans une seconde étude, l’objectif a été d’identifier une cible d’intervention thérapeutique pour préserver la masse musculaire suite à une ischémie cérébrale. Au vu des résultats obtenus dans la première étude, nous avons ciblé la myostatine. Nous avons montré que l’inhibition de la myostatine entraînait, une meilleure récupération du poids de corps et du poids de divers muscles, 15 jours après une ischémie cérébrale. De plus, l’inhibition de la myostatine tendait à améliorer le comportement moteur des souris ischémiées (équilibre, coordination, force musculaire). En revanche, nous n’avons reporté aucune variation majeure des niveaux en ARNm ou protéines d’acteurs impliqués dans les voies de signalisation Akt/mTOR, Smad2/3, ubiquitine-protéasome et autophagie-lysosome, 15 jours après une ischémie cérébrale. Ces données préliminaires suggèrent que l’inhibition pharmacologique de la myostatine pourrait représenter une stratégie thérapeutique efficace pour limiter la perte de masse musculaire suite à une ischémie cérébrale / Strokes are considered as the most severe neurological disease in terms of mortality and disability. The incidence of stroke in France is estimated at 140 000. Ischemic stroke, which represents about 80% of strokes occur as a result of an obstruction of a blood vessel supplying blood to the brain. Motor, cognitive and sensory deficits are common impacts of stroke and can seriously compromise the autonomy and patient quality of life. Ischemic stroke leads to muscle atrophy, wich occurs primarily in the paretic limb, but also to a lesser extent in the nonparetic limb. However, the molecular mechanisms of muscle atrophy is unknown. In a first study, the purpose was to identify the molecular determinants involved in skeletal muscle atrophy following cerebral ischemia. To meet this objective, the work was carried out on a mouse model of cerebral ischemia, which involves the occlusion of the middle cerebral artery (MCAO) with a nylon monofilament. We have shown that cerebral ischemia leads to skeletal muscle atrophy of quadriceps, soleus and tibialis anterior muscles of the paretic side, 3 days after MCAO. This muscular atrophy was associated with motor deficits in the balance, coordination, muscle strength, posture and walking. From a molecular point of view, we reported an imbalance between the rates of synthesis and degradation of muscle protein, in favour of protein degradation in both paretic and nonparetic muscles. In particular, we showed that the expression of myostatin, a master negative regulator of skeletal muscle mass was significantly increased. In a second study, the purpose was to identify a target for therapeutic intervention in order to maintain muscle mass following cerebral ischemia. In view of the results obtained in the first study, we targeted the myostatin. Our results show that myostatin inhibition increases body weight and muscle mass recovery, 15 days after cerebral ischemia. In addition, myostatin inhibition tends to improve motor behavior (balance, coordination, strength). From a molecular point of view, we reported no major change in mRNA or protein level of actors involved in Akt/mTOR, Smad2/3, autophagy-lysosome and ubiquitin-proteasome pathways, involved in the control of muscle mass, 15 days after cerebral ischemia. These preliminary results strongly suggest that pharmacological inhibitors of myostatin may provide significant therapeutic benefit for muscle atrophy following cerebral ischemia