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Projeto de investigação
Astrosomes: Artificial Astrocytes as a Novel Approach to Regulate Neuronal Communication
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Going the extra (synaptic) mile: excitotoxicity as the road toward neurodegenerative diseases
Publication . Armada-Moreira, Adam; Gomes, Joana I.; Pina, Carolina Campos; Savchak, Oksana K.; Gonçalves-Ribeiro, Joana; Rei, Nádia; Pinto, Sara; Morais, Tatiana P.; Martins, Robertta Silva; Ribeiro, Filipa; Sebastião, Ana M; Crunelli, Vincenzo; Vaz, Sandra H.
Excitotoxicity is a phenomenon that describes the toxic actions of excitatory neurotransmitters, primarily glutamate, where the exacerbated or prolonged activation of glutamate receptors starts a cascade of neurotoxicity that ultimately leads to the loss of neuronal function and cell death. In this process, the shift between normal physiological function and excitotoxicity is largely controlled by astrocytes since they can control the levels of glutamate on the synaptic cleft. This control is achieved through glutamate clearance from the synaptic cleft and its underlying recycling through the glutamate-glutamine cycle. The molecular mechanism that triggers excitotoxicity involves alterations in glutamate and calcium metabolism, dysfunction of glutamate transporters, and malfunction of glutamate receptors, particularly N-methyl-D-aspartic acid receptors (NMDAR). On the other hand, excitotoxicity can be regarded as a consequence of other cellular phenomena, such as mitochondrial dysfunction, physical neuronal damage, and oxidative stress. Regardless, it is known that the excessive activation of NMDAR results in the sustained influx of calcium into neurons and leads to several deleterious consequences, including mitochondrial dysfunction, reactive oxygen species (ROS) overproduction, impairment of calcium buffering, the release of pro-apoptotic factors, among others, that inevitably contribute to neuronal loss. A large body of evidence implicates NMDAR-mediated excitotoxicity as a central mechanism in the pathogenesis of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and epilepsy. In this review article, we explore different causes and consequences of excitotoxicity, discuss the involvement of NMDAR-mediated excitotoxicity and its downstream effects on several neurodegenerative disorders, and identify possible strategies to study new aspects of these diseases that may lead to the discovery of new therapeutic approaches. With the understanding that excitotoxicity is a common denominator in neurodegenerative diseases and other disorders, a new perspective on therapy can be considered, where the targets are not specific symptoms, but the underlying cellular phenomena of the disease.
Astrocytes control hippocampal synaptic plasticity through the vesicular-dependent release of D-serine
Publication . Abreu, Daniela Sofia; Gomes, Joana I.; Ribeiro, Filipa; Diógenes, Maria José; Sebastião, Ana M; Vaz, Sandra H.
Astrocytes, the most abundant glial cells in the central nervous system (CNS), sense synaptic activity and respond through the release of gliotransmitters, a process mediated by intracellular Ca2+ level changes and SNARE-dependent mechanisms. Ionotropic N-methyl-D-aspartate (NMDA) receptors, which are activated by glutamate along with D-serine or glycine, play a crucial role in learning, memory, and synaptic plasticity. However, the precise impact of astrocyte-released D-serine on neuronal modulation remains insufficiently characterized. To address this, we have used the dominant negative SNARE (dnSNARE) mouse model, which selectively inhibits SNARE-dependent exocytosis from astrocytes. We recorded field excitatory postsynaptic potentials (fEPSPs) in CA3-CA1 synapses within hippocampal slices obtained from dnSNARE mice and wild-type (Wt) littermates. Our results demonstrate that hippocampal θ-burst long-term potentiation (LTP), a critical form of synaptic plasticity, is impaired in hippocampal slices from dnSNARE mice. Notably, this LTP impairment was rescued upon incubation with D-serine. To further investigate the involvement of astrocytes in D-serine-mediated mechanisms of LTP maintenance, we perfused hippocampal slices with L-serine - a substrate used by both neurons and astrocytes for D-serine production. The enhancement in LTP observed in dnSNARE mice was exclusively associated with D-serine presence, with no effects evident in the presence of L-serine. Additionally, both D- and L-serine reduced basal synaptic strength in the hippocampal slices of both Wt and dnSNARE mice. These results provide compelling evidence that distinct processes underlie the modulation of basal synaptic transmission and LTP through D-serine. Our findings underscore the pivotal contribution of astrocytes in D-serine-mediated processes that govern LTP establishment and basal transmission. This study not only provides essential insights into the intricate interplay between neurons and astrocytes but also emphasizes their collective role in shaping hippocampal synaptic function.
Glutamate transporters in hippocampal LTD/LTP: not just prevention of excitotoxicity
Publication . Gonçalves-Ribeiro, Joana; Pina, Carolina Campos; Sebastião, Ana M; Vaz, Sandra H.
Glutamate uptake is a process mediated by sodium-dependent glutamate transporters, preventing glutamate spillover from the synapse. Typically, astrocytes express higher amounts of glutamate transporters, thus being responsible for most of the glutamate uptake; nevertheless, neurons can also express these transporters, albeit in smaller concentrations. When not regulated, glutamate uptake can lead to neuronal death. Indeed, the majority of the studies regarding glutamate transporters have focused on excitotoxicity and the subsequent neuronal loss. However, later studies have found that glutamate uptake is not a static process, evincing a possible correlation between this phenomenon and the efficiency of synaptic transmission and plasticity. In this review, we will focus on the role of the increase in glutamate uptake that occurs during long-term potentiation (LTP) in the hippocampus, as well as on the impairment of long-term depression (LTD) under the same conditions. The mechanism underpinning the modulatory effect of glutamate transporters over synaptic plasticity still remains unascertained; yet, it appears to have a more prominent effect over the N-methyl-D-aspartate receptor (NMDAR), despite changes in other glutamate receptors may also occur.
Multicompartment microreactors prevent excitotoxic dysfunctions in rat primary cortical neurons
Publication . Armada-Moreira, Adam; Coelho, Joana E; Lopes, Luisa V.; Sebastião, Ana M; Städler, Brigitte; Vaz, Sandra H.
Excitotoxicity is a cellular phenomenon that comprises the consequences of toxic actions of excitatory neurotransmitters, such as glutamate. This process is usually related to overproduction of reactive oxygen species (ROS) and ammonia (NH4+ ) toxicity. Platinum nanoparticle (Pt-NP)-based microreactors able to degrade hydrogen peroxide (H2 O2 ) and NH4+ , are previously described as a novel therapeutical approach against excitotoxicity, conferring protection to neuroblasts. Now, it is demonstrated that these microreactors are compatible with rat primary cortical neurons, show high levels of neuronal membrane interaction, and are able to improve cell survival and neuronal activity when neurons are exposed to H2 O2 or NH4+ . Additionally, more complex microreactors are assembled, including enzyme-loaded liposomes containing glutamate dehydrogenase and glutathione reductase, in addition to Pt-NP. The in vitro activity of these microreactors is characterized and they are compared to the Pt-NP-based microreactors in terms of biological activity, concluding that they enhance cell viability similarly or more extensively than the latter. Extracellular electrophysiological recordings demonstrate that these microreactors rescue neuronal functionality lost upon incubation with H2 O2 or NH4+ . This study provides more evidence for the potential application of these microreactors in a biomedical context with more complex cellular environments.
Platinum nanoparticle-based microreactors protect against the behavioral and neurobiological consequences of chronic stress exposure
Publication . Hirata, Rafael Y. S.; Oliveira, Roberto N.; Silva, Mariana S. C. F.; Armada-Moreira, Adam; Vaz, Sandra H.; Ribeiro, Filipa; Sebastião, Ana M; Lemes, Jéssica A.; de Andrade, José S.; Rosário, Bárbara A.; Céspedes, Isabel C.; Viana, Milena B.
Excitotoxicity is described as the exacerbated activation of glutamate AMPA and NMDA receptors that leads to neuronal damage, and ultimately to cell death. Astrocytes are responsible for the clearance of 80-90% of synaptically released glutamate, preventing excitotoxicity. Chronic stress renders neurons vulnerable to excitotoxicity and has been associated to neuropsychiatric disorders, i.e., anxiety. Microreactors containing platinum nanoparticles (Pt-NP) and glutamate dehydrogenase have shown in vitro activity against excitotoxicity. The purpose of the present study was to investigate the in vivo effects of these microreactors on the behavioral and neurobiological effects of chronic stress exposure. Rats were either unstressed or exposed for 2 weeks to an unpredictable chronic mild stress paradigm (UCMS), administered intra-ventral hippocampus with the microreactors (with or without the blockage of astrocyte functioning), and seven days later tested in the elevated T-maze (ETM; Experiment 1). The ETM allows the measurement of two defensive responses, avoidance and escape, in terms of psychopathology respectively related to generalized anxiety and panic disorder. Locomotor activity in an open field was also measured. Since previous evidence shows that stress inhibits adult neurogenesis, we evaluated the effects of the different treatments on the number of cells expressing the marker of migrating neuroblasts doublecortin (DCX) in the dorsal and ventral hippocampus (Experiment 2). Results showed that UCMS induces anxiogenic effects, increases locomotion, and decreases the number of DCX cells in the dorsal and ventral hippocampus, effects that were counteracted by microreactor administration. This is the first study to demonstrate the in vivo efficacy of Pt-NP against the behavioral and neurobiological effects of chronic stress exposure.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/BTM-SAL/32147/2017