Rôle du métabolisme énergétique dans un contexte de vieillissement chez C. elegans

L’incidence constante des maladies liées à l’âge reflète un réel enjeu dans nos sociétés actuelles, principalement lorsqu’il est question des cas de cancers, d’accidents cérébraux et de maladies neurodégénératives. Ces désordres sont liés à l’augmentation de l’espérance de vie et à un vieillissement de la population. Les coûts, estimés en milliards de dollars, représentent des sommes de plus en plus importantes. Bien que les efforts déployés soient importants, aucun traitement n’a encore été trouvé. Les maladies neurodégénératives, telles que la maladie d’Alzheimer, de Parkinson, d’Huntington ou la sclérose latérale amyotrophique (SLA), caractérisées par la dégénérescence d’un type neuronal spécifique à chaque pathologie, représentent un défi important. Les mécanismes de déclenchement de la pathologie sont encore nébuleux, de plus il est maintenant clair que certains de ces désordres impliquent de nombreux gènes impliqués dans diverses voies de signalisation induisant le dysfonctionnement de processus biologiques importants, tel que le métabolisme. Dans nos sociétés occidentales, une problématique, directement lié à notre style de vie s’ajoute. L’augmentation des quantités de sucre et de gras dans nos diètes a amené à un accroissement des cas de diabètes de type II, d’obésité et de maladies coronariennes. Néanmoins, le métabolisme du glucose, principale source énergétique du cerveau, est primordial à la survie de n’importe quel organisme. Lors de ces travaux, deux études effectuées à l’aide de l’organisme Caenorhabditis elegans ont porté sur un rôle protecteur du glucose dans un contexte de vieillissement pathologique et dans des conditions de stress cellulaire. Le vieillissement semble accéléré dans un environnement enrichi en glucose. Cependant, les sujets traités ont démontré une résistance importante à différents stress et aussi à la présence de protéines toxiques impliquées dans la SLA et la maladie de Huntington. Dans un deuxième temps, nous avons démontré que ces effets peuvent aussi être transmis à la génération suivante. Un environnement enrichi en glucose a pour bénéfice de permettre une meilleure résistance de la progéniture, sans pour autant transmettre les effets néfastes dû au vieillissement accéléré.The constant increase of the cases of age-related diseases, including cancers, cerebral accidents and neurodegenerative diseases raises a real problem in our current societies. These disorders are very strongly linked to the increase of life expectancy and to the ageing population. The costs, estimated in billion dollars, requiring vast medical resources and very few treatments exist today. Neuronal diseases, such as the Alzheimer's, Parkinson’s, Huntington’s disease and amyotrophic lateral sclerosis (ALS) are characterized by the degeneration of various types of neurons. This represents an important challenge because besides the lack of understanding the underlying mechanisms related to their pathology, it is now clear that some of these disorders involve several genes and lead to the dysfunction of fundmental biological processes such as metabolism. In western societies lifestyle and dietary practices may contribute to disease. The increased quantities of sugar and fat in western diets are thought to contribute to the rise of metabolic disorders, including Type II diabetes, obesity and coronary diseases. Nevertheless, it is important to understand that the metabolism of glucose, the brain’s main energy source, is essential for survival. In this thesis, two studies using the model organism Caenorhabditis elegans investigated a potential protective role of the glucose in a context of pathological ageing and in conditions of cellular stress. Although ageing seems accelerated in a glucose enriched environment, the test subjects demonstrated an improved resistance to numerous stresses including against toxic proteins involved in the ALS and Huntington's disease. Secondly, it appeared that these effects can be heritably transmitted to successive generations of animals. Thus, a glucose enriched environment allows for increased stress resistance in the offspring, without transmitting the negative effects of accelerated ageing

The Strategic Location of Glycogen and Lactate: From Body Energy Reserve to Brain Plasticity

Brain energy metabolism has been the object of intense research in recent years. Pioneering work has identified the different cell types involved in energy production and use. Recent evidence has demonstrated a key role of L-Lactate in brain energy metabolism, producing a paradigm-shift in our understanding of the neuronal energy metabolism. At the center of this shift, is the identification of a central role of astrocytes in neuroenergetics. Thanks to their morphological characteristics, they are poised to take up glucose from the circulation and deliver energy substrates to neurons. Astrocyte neuron lactate shuttle (ANLS) model, has shown that the main energy substrate that astrocytes deliver to neurons is L-Lactate, to sustain neuronal oxidative metabolism. L-Lactate can also be produced from glycogen, the storage form of glucose, which is exclusively localized in astrocytes. Inhibition of glycogen metabolism and the ensuing inhibition of L-Lactate production leads to cognitive dysfunction. Experimental evidence indicates that the role of lactate in cognitive function relates not only to its role as a metabolic substrate for neurons but also as a signaling molecule for synaptic plasticity. Interestingly, a similar metabolic uncoupling appears to exist in peripheral tissues plasma, whereby glucose provides L-Lactate as the substrate for cellular oxidative metabolism. In this perspective article, we review the known information on the distribution of glycogen and lactate within brain cells, and how this distribution relates to the energy regime of glial vs. neuronal cells

Mutant TDP-43 and FUS Cause Age-Dependent Paralysis and Neurodegeneration in C. elegans

Mutations in the DNA/RNA binding proteins TDP-43 and FUS are associated with Amyotrophic Lateral Sclerosis and Frontotemporal Lobar Degeneration. Intracellular accumulations of wild type TDP-43 and FUS are observed in a growing number of late-onset diseases suggesting that TDP-43 and FUS proteinopathies may contribute to multiple neurodegenerative diseases. To better understand the mechanisms of TDP-43 and FUS toxicity we have created transgenic Caenorhabditis elegans strains that express full-length, untagged human TDP-43 and FUS in the worm's GABAergic motor neurons. Transgenic worms expressing mutant TDP-43 and FUS display adult-onset, age-dependent loss of motility, progressive paralysis and neuronal degeneration that is distinct from wild type alleles. Additionally, mutant TDP-43 and FUS proteins are highly insoluble while wild type proteins remain soluble suggesting that protein misfolding may contribute to toxicity. Populations of mutant TDP-43 and FUS transgenics grown on solid media become paralyzed over 7 to 12 days. We have developed a liquid culture assay where the paralysis phenotype evolves over several hours. We introduce C. elegans transgenics for mutant TDP-43 and FUS motor neuron toxicity that may be used for rapid genetic and pharmacological suppressor screening

Transgenerational inheritance of glucose phenotypes requires H3K4me3 components.

<p>(A) N2 animals treated with 2% GE had an increased H3K4me3 mark and this effect was lost in subsequent generations. (B–C) GE delayed late onset paralysis in P0 but not in F1 generation of mTDP-43; <i>set-2(ok952)</i> (B) and mTDP-43; <i>wdr-5.1(ok1417)</i> (C) animals compared to untreated control and this protection was lost in F1 generation. (D–E) Stress resistance was increased in P0 but not in F1 generation of COMPASS (Complex Proteins Associated with Set1) mutants (D) <i>set-2(ok952)</i> and (E) <i>wdr-5.1(ok1417)</i>. (F–G) Total progeny numbers were reduced in P0 but not in F1 generations of (F) <i>set-2</i> and (G) <i>wdr-5.1</i> mutants.</p

Transgenerational inheritance of resistance to oxidative stress.

<p>(A) N2 animals exposed to GE are highly resistant to juglone-induced lethality and this resistance was transmitted to descendent progeny in the F1 and generation, P<0.0001 versus untreated animals. (B–E) Resistance to oxidative stress by GE was lost in the P0 and F1 generations in animals mutant for (B) <i>daf-16</i>, (C) <i>aak-2</i>, or (D) <i>sir-2.1</i>. (E) GE continued to provide resistance to P0 and F1 animals mutant for <i>hif-1</i>, P<0.0001 versus untreated animals. (F) GE increased oxidative stress resistance in P0 N2 animals but this effect was lost in F1 animals treated with <i>daf-16</i>, <i>aak-2</i> or <i>sir-2.1</i> RNAi clones.</p

Heritable Transmission of Stress Resistance by High Dietary Glucose in <i>Caenorhabditis elegans</i>

<div><p>Glucose is a major energy source and is a key regulator of metabolism but excessive dietary glucose is linked to several disorders including type 2 diabetes, obesity and cardiac dysfunction. Dietary intake greatly influences organismal survival but whether the effects of nutritional status are transmitted to the offspring is an unresolved question. Here we show that exposing <i>Caenorhabditis elegans</i> to high glucose concentrations in the parental generation leads to opposing negative effects on fecundity, while having protective effects against cellular stress in the descendent progeny. The transgenerational inheritance of glucose-mediated phenotypes is dependent on the insulin/IGF-like signalling pathway and components of the histone H3 lysine 4 trimethylase complex are essential for transmission of inherited phenotypes. Thus dietary over-consumption phenotypes are heritable with profound effects on the health and survival of descendants.</p></div

Parental exposure to glucose provides transgenerational protection against neurodegeneration.

<p>(A–B) GE reduces TDP-43 mediated age-dependent (A) paralysis, P<0.0001 versus untreated animals and (B) neurodegeneration in P0 animals and their F1 descendants, *P<0.0001 versus untreated animals.</p

Heritable diminution of progeny from glucose exposure in the parental generation.

<p>(A) In parental P0 generation animals, glucose enrichment (GE) decreased the average number of progeny of wild type N2 and <i>hif-1</i> mutant worms compared to untreated controls. GE had no effect on <i>daf-16</i>, <i>aak-2</i> or <i>sir-2.1</i> mutants. **P<0.01 versus untreated <i>hif-1</i> controls, ****P<0.0001 versus untreated N2 controls (B) F1 generation N2 and <i>hif-1</i> descendants had reduced progeny numbers compared to F1 descendants from untreated P0 controls. *P<0.05, ***P<0.001 (C) N2 worms in the F2 generation from P0 parents exposed to GE also had reduced progeny numbers. *P<0.05 (D) F3 generation descendants from GE treated P0 parents had comparable progeny numbers compared to animals descendent from untreated P0 parents.</p

Rescue of ATXN3 neuronal toxicity in Caenorhabditis elegans by chemical modification of endoplasmic reticulum stress

Polyglutamine expansion diseases are a group of hereditary neurodegenerative disorders that develop when a CAG repeat in the causative genes is unstably expanded above a certain threshold. The expansion of trinucleotide CAG repeats causes hereditary adult-onset neurodegenerative disorders, such as Huntington's disease, dentatorubral–pallidoluysian atrophy, spinobulbar muscular atrophy and multiple forms of spinocerebellar ataxia (SCA). The most common dominantly inherited SCA is the type 3 (SCA3), also known as Machado–Joseph disease (MJD), which is an autosomal dominant, progressive neurological disorder. The gene causatively associated with MJD is ATXN3. Recent studies have shown that this gene modulates endoplasmic reticulum (ER) stress. We generated transgenic Caenorhabditis elegans strains expressing human ATXN3 genes in motoneurons, and animals expressing mutant ATXN3-CAG89 alleles showed decreased lifespan, impaired movement, and rates of neurodegeneration greater than wild-type ATXN3-CAG10 controls. We tested three neuroprotective compounds (Methylene Blue, guanabenz and salubrinal) believed to modulate ER stress and observed that these molecules rescued ATXN3-CAG89 phenotypes. Furthermore, these compounds required specific branches of the ER unfolded protein response (UPRER), reduced global ER and oxidative stress, and polyglutamine aggregation. We introduce new C. elegans models for MJD based on the expression of full-length ATXN3 in a limited number of neurons. Using these models, we discovered that chemical modulation of the UPRER reduced neurodegeneration and warrants investigation in mammalian models of MJD

TDP-43 and FUS transgene constructs.

<p>(A) Full-length wild type human TDP-43 and the clinical mutation A315T were cloned into a vector for expression in motor neurons by the <i>unc-47</i> promoter and injected into <i>C. elegans</i>. (B) Full-length wild type human FUS and the clinical mutation S57Δ were cloned into the <i>unc-47</i> expression vector and injected into <i>C. elegans</i>. RRM (RNA Recognition Motif), Q/G/S/Y (Glutamine-Glycine-Serine-Tyrosine-rich region), R/G (Arginine-Glycine-rich region), NLS (Nuclear localization signal).</p