Normal Aging Modulates the Neurotoxicity of Mutant Huntingtin

Aging likely plays a role in neurodegenerative disorders. In Huntington's disease (HD), a disorder caused by an abnormal expansion of a polyglutamine tract in the protein huntingtin (Htt), the role of aging is unclear. For a given tract length, the probability of disease onset increases with age. There are mainly two hypotheses that could explain adult onset in HD: Either mutant Htt progressively produces cumulative defects over time or “normal” aging renders neurons more vulnerable to mutant Htt toxicity. In the present study, we directly explored whether aging affected the toxicity of mutant Htt in vivo. We studied the impact of aging on the effects produced by overexpression of an N-terminal fragment of mutant Htt, of wild-type Htt or of a β-Galactosidase (β-Gal) reporter gene in the rat striatum. Stereotaxic injections of lentiviral vectors were performed simultaneously in young (3 week) and old (15 month) rats. Histological evaluation at different time points after infection demonstrated that the expression of mutant Htt led to pathological changes that were more severe in old rats, including an increase in the number of small Htt-containing aggregates in the neuropil, a greater loss of DARPP-32 immunoreactivity and striatal neurons as assessed by unbiased stereological counts

Poly(ADP-ribose)polymerase-1 modulates microglial responses to amyloid β

<p>Abstract</p> <p>Background</p> <p>Amyloid β (Aβ) accumulates in Alzheimer's disease (AD) brain. Microglial activation also occurs in AD, and this inflammatory response may contribute to disease progression. Microglial activation can be induced by Aβ, but the mechanisms by which this occurs have not been defined. The nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) regulates microglial activation in response to several stimuli through its interactions with the transcription factor, NF-κB. The purpose of this study was to evaluate whether PARP-1 activation is involved in Aβ-induced microglial activation, and whether PARP-1 inhibition can modify microglial responses to Aβ.</p> <p>Methods</p> <p>hAPP_J20mice, which accumulate Aβ with ageing, were crossed with PARP-1^-/-mice to assess the effects of PARP-1 depletion on microglial activation, hippocampal synaptic integrity, and cognitive function. Aβ peptide was also injected into brain of wt and PARP-1^-/-mice to directly determine the effects of PARP-1 on Aβ-induced microglial activation. The effect of PARP-1 on Aβ-induced microglial cytokine production and neurotoxicity was evaluated in primary microglia cultures and in microglia-neuron co-cultures, utilizing PARP-1^-/-cells and a PARP-1 inhibitor. NF-κB activation was evaluated in microglia infected with a lentivirus reporter gene.</p> <p>Results</p> <p>The hAPP_J20mice developed microglial activation, reduced hippocampal CA1 calbindin expression, and impaired novel object recognition by age 6 months. All of these features were attenuated in hAPP_J20/<it>PARP-1^-/-</it>mice. Similarly, Aβ_1-42injected into mouse brain produced a robust microglial response in wild-type mice, and this was blocked in mice lacking PARP-1 expression or activity. Studies using microglial cultures showed that PARP-1 activity was required for Aβ-induced NF-κB activation, morphological transformation, NO release, TNFα release, and neurotoxicity. Conversely, PARP-1 inhibition increased release of the neurotrophic factors TGFβ and VEGF, and did not impair microglial phagocytosis of Aβ peptide.</p> <p>Conclusions</p> <p>These results identify PARP-1 as a requisite and previously unrecognized factor in Aβ-induced microglial activation, and suggest that the effects of PARP-1 are mediated, at least in part, by its interactions with NF-κB. The suppression of Aβ-induced microglial activation and neurotoxicity by PARP-1 inhibition suggests this approach could be useful in AD and other disorders in which microglial neurotoxicity may contribute.</p

Ciliary Neurotrophic Factor Protects Striatal Neurons against Excitotoxicity by Enhancing Glial Glutamate Uptake

Ciliary neurotrophic factor (CNTF) is a potent neuroprotective cytokine in different animal models of glutamate-induced excitotoxicity, although its action mechanisms are still poorly characterized. We tested the hypothesis that an increased function of glial glutamate transporters (GTs) could underlie CNTF-mediated neuroprotection. We show that neuronal loss induced by in vivo striatal injection of the excitotoxin quinolinic acid (QA) was significantly reduced (by ∼75%) in CNTF-treated animals. In striatal slices, acute QA application dramatically inhibited corticostriatal field potentials (FPs), whose recovery was significantly higher in CNTF rats compared to controls (∼40% vs. ∼7%), confirming an enhanced resistance to excitotoxicity. The GT inhibitor dl-threo-β-benzyloxyaspartate greatly reduced FP recovery in CNTF rats, supporting the role of GT in CNTF-mediated neuroprotection. Whole-cell patch-clamp recordings from striatal medium spiny neurons showed no alteration of basic properties of striatal glutamatergic transmission in CNTF animals, but the increased effect of a low-affinity competitive glutamate receptor antagonist (γ-d-glutamylglycine) also suggested an enhanced GT function. These data strongly support our hypothesis that CNTF is neuroprotective via an increased function of glial GTs, and further confirms the therapeutic potential of CNTF for the clinical treatment of progressive neurodegenerative diseases involving glutamate overflow

STAT3-mediated astrocyte reactivity associated with brain metastasis contributes to neurovascular dysfunction

© 2020 American Association for Cancer Research. Astrocytes are thought to play a pivotal role in coupling neural activity and cerebral blood flow. However, it has been shown that astrocytes undergo morphologic changes in response to brain metastasis, switching to a reactive phenotype, which has the potential to significantly compromise cerebrovascular function and contribute to the neurological sequelae associated with brain metastasis. Given that STAT3 is a key regulator of astrocyte reactivity, we aimed here to determine the impact of STAT3- mediated astrocyte reactivity on neurovascular function in brain metastasis. Rat models of brain metastasis and ciliary neurotrophic factor were used to induce astrocyte reactivity. Multimodal imaging, electrophysiology, and IHC were performed to determine the relationship between reactive astrocytes and changes in the cerebrovascular response to electrical and physiological stimuli. Subsequently, the STAT3 pathway in astrocytes was inhibited with WP1066 to determine the role of STAT3- mediated astrocyte reactivity, specifically, in brain metastasis. Astrocyte reactivity associated with brain metastases impaired cerebrovascular responses to stimuli at both the cellular and functional level and disrupted astrocyte-endothelial interactions in both animal models and human brain metastasis samples. Inhibition of STAT3-mediated astrocyte reactivity in rats with brain metastases restored cerebrovascular function, as shown by in vivo imaging, and limited cerebrovascular changes associated with tumor growth. Together these findings suggest that inhibiting STAT3-mediated astrocyte reactivity may confer significant improvements in neurological outcome for patients with brain metastases and could potentially be tested in other brain tumors

Caractérisation phénotypique et fonctionnelle de l'activation astrocytaire induite par transfert lentiviral du CNTF in vivo: Implications pour la survie neuronale

Astrocytes play an active role in brain function. They provide metabolic and trophic support to neurons and control the entry of metabolites inside brain parenchyma. Through their glutamate transporters GLAST and GLT-1, astrocytes are also responsible of the uptake and recycling of glutamate, the main excitatory neurotransmitter but also a potential neurotoxic agent. Astrocytes become activated in response to various pathological situations. This brain hallmark has been known for a long time, however, its functional consequences are still a matter of debate. Does activation of astrocytes represent a protective and adaptive mechanism to face deleterious conditions or does it play a role in neuronal degeneration? We have developed an in vivo model of astrocytic activation in the rat striatum through lentiviral gene tranfer of Ciliary Neurotrophic Factor (CNTF), an endogenous activator of astrocytes. Using this stable and reproducible model of astrocytes activation, we observed marked alterations in brain energy metabolism, with a shift from glycolysis to the ketone bodies pathway. In addition, CNTF activation of astrocytes induced several changes in glutamate uptake machinery. Astroglial transporters were highly glycosylated and redistributed into raft microdomains. During an excitotoxic process, glutamate handling, energetic supply and neuronal survival were significantly improved. These results underline the beneficial role of activated astrocytes that have a prosurvival phenotype and function towards neurons. This study gives new clues (1) to delineate the role and the interest of activated astrocytes in pathological processes and (2) to characterize the effects of CNTF, which is a therapeutic candidate for several neurodegenerative diseases.Les astrocytes participent activement au fonctionnement cérébral. Ils réalisent des échanges métaboliques et trophiques avec les neurones et exercent un contrôle sur l'entrée des substrats énergétiques dans le parenchyme cérébral. Ils sont aussi res ponsables -par le biais de leurs transporteurs GLAST et GLT-1- de la recapture et du recyclage du glutamate, le principal neurotransmetteur excitateur qui a aussi un potentiel neurotoxique. Les astrocytes répondent à des situations pathologiques variées en devenant réactifs. Ils apparaissent hypertrophiques et surexpriment certaines protéines comme les filaments intermédiaires. Bien que cette modification du phénotype astrocytaire soit connue depuis longtemps, ses conséquences fonctionnelles sont toujours débattues. S'agit-il d'un mécanisme de protection et d'adaptation à des conditions pathologiques ou, au contraire, d'un processus délétère participant à la dégénérescence neuronale ? Nous avons développé un modèle in vivo d'activation astrocytaire en utilisant un lentivirus (lenti-CNTF) pour induire une surexpression dans le striatum de rat du Ciliary Neurotrophic Factor (CNTF), un activateur endogène des astrocytes. Grâce à ce modèle d'activation stable et reproductible des astrocytes, nous avons pu mettre en évidence des modifications profondes du métabolisme énergétique cérébral avec une augmentation de l'utilisation des corps cétoniques au dépend du glucose. Par ailleurs, l'activation astrocytaire par le CNTF induit de nombreux changements dans la machinerie de recapture du glutamate. Les transporteurs astrocytaires sont hyperglycosylés et sont enrichis dans les microdomaines membranaires rafts. En conditions excitotoxiques, la gestion du glutamate, l'apport énergétique et la survie neuronale sont significativement améliorés dans le groupe lenti-CNTF. Ces résultats soulignent le rôle bénéfique des astrocytes activés qui présentent un phénotype et un fonctionnement favorables à la survie des neurones. Cette étude permet à la fois de mieux cerner le rôle et l'intérêt de la réponse astrocytaire dans les processus pathologiques et également de caractériser les effets du CNTF , qui est un candidat thérapeutique pour différentes maladies neurodégénératives

Caractérisation phénotypique et fonctionnelle de l' activation astrocytaire induite par transfert lentiviral du CNTF in vivo (implication pour la survie neuronale)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Imaging and monitoring astrocytes in health and disease

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Targeted Activation of Astrocytes: A Potential Neuroprotective Strategy

International audienceAstrocytes are involved in many key physiological processes in the brain, including glutamatergic transmission, energy metabolism, and blood flow control. They become reactive in response to pathological situations, a response that involves well-described morphological alterations and less characterized functional changes. The functional consequences of astrocyte reactivity seem to depend on the molecular pathway involved and may result in the enhancement of several neuroprotective and neurotrophic functions. We propose that a selective and controlled activation of astrocytes may switch these highly pleiotropic cells into therapeutic agents to promote neuron survival and recovery. This may represent a potent therapeutic strategy for many brain diseases in which neurons would benefit from an increased support from activated astrocytes

Astroglial networking contributes to neurometabolic coupling

International audienceThe strategic position of astrocytic processes between blood capillaries and neurons, provided the early insight that astrocytes play a key role in supplying energy substrates to neurons in an activity-dependent manner. The central role of astrocytes in neurometabolic coupling has been first established at the level of single cell. Since then, exciting recent work based on cellular imaging and electrophysiological recordings has provided new mechanistic insights into this phenomenon, revealing the crucial role of gap junction (GJ)-mediated networks of astrocytes. Indeed, astrocytes define the local availability of energy substrates by regulating blood flow. Subsequently, in order to efficiently reach distal neurons, these substrates can be taken up, and distributed through networks of astrocytes connected by GJs, a process modulated by neuronal activity. Astrocytic networks can be morphologically and/or functionally altered in the course of various pathological conditions, raising the intriguing possibility of a direct contribution from these networks to neuronal dysfunction. The present review upgrades the current view of neuroglial metabolic coupling, by including the recently unravelled properties of astroglial metabolic networks and their potential contribution to normal and pathological neuronal activity