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- The stress granule protein G3BP1 alleviates spinocerebellar ataxia-associated deficitsPublication . Koppenol, Rebekah; Conceição, André; Afonso, Inês T.; Afonso-Reis, Ricardo; Costa, Rafael G; Tomé, Sandra; Teixeira, Diogo; Pinto-da-Silva, Joana; Codêsso, José Miguel; Brito, David V.C.; Mendonça, Liliana; Marcelo, Adriana; Pereira de Almeida, Luís; Matos, Carlos A; Nóbrega, ClévioKoppenol et al. show that overexpression of G3BP1 in cell models of SCA2 and SCA3 leads to a reduction in ataxin-2 and ataxin-3 aggregation. G3BP1 lentiviral delivery reduces motor deficits and neuropathology in preclinical models, suggesting that G3BP1 may be a potential therapeutic target for polyQ disorders. Polyglutamine diseases are a group of neurodegenerative disorders caused by an abnormal expansion of CAG repeat tracts in the codifying regions of nine, otherwise unrelated, genes. While the protein products of these genes are suggested to play diverse cellular roles, the pathogenic mutant proteins bearing an expanded polyglutamine sequence share a tendency to self-assemble, aggregate and engage in abnormal molecular interactions. Understanding the shared paths that link polyglutamine protein expansion to the nervous system dysfunction and the degeneration that takes place in these disorders is instrumental to the identification of targets for therapeutic intervention. Among polyglutamine diseases, spinocerebellar ataxias (SCAs) share many common aspects, including the fact that they involve dysfunction of the cerebellum, resulting in ataxia. Our work aimed at exploring a putative new therapeutic target for the two forms of SCA with higher worldwide prevalence, SCA type 2 (SCA2) and type 3 (SCA3), which are caused by expanded forms of ataxin-2 (ATXN2) and ataxin-3 (ATXN3), respectively. The pathophysiology of polyglutamine diseases has been described to involve an inability to properly respond to cell stress. We evaluated the ability of GTPase-activating protein-binding protein 1 (G3BP1), an RNA-binding protein involved in RNA metabolism regulation and stress responses, to counteract SCA2 and SCA3 pathology, using both in vitro and in vivo disease models. Our results indicate that G3BP1 overexpression in cell models leads to a reduction of ATXN2 and ATXN3 aggregation, associated with a decrease in protein expression. This protective effect of G3BP1 against polyglutamine protein aggregation was reinforced by the fact that silencing G3bp1 in the mouse brain increases human expanded ATXN2 and ATXN3 aggregation. Moreover, a decrease of G3BP1 levels was detected in cells derived from patients with SCA2 and SCA3, suggesting that G3BP1 function is compromised in the context of these diseases. In lentiviral mouse models of SCA2 and SCA3, G3BP1 overexpression not only decreased protein aggregation but also contributed to the preservation of neuronal cells. Finally, in an SCA3 transgenic mouse model with a severe ataxic phenotype, G3BP1 lentiviral delivery to the cerebellum led to amelioration of several motor behavioural deficits. Overall, our results indicate that a decrease in G3BP1 levels may be a contributing factor to SCA2 and SCA3 pathophysiology, and that administration of this protein through viral vector-mediated delivery may constitute a putative approach to therapy for these diseases, and possibly other polyglutamine disorders.
- Stress granules, RNA-binding proteins and polyglutamine diseases: too much aggregation?Publication . Marcelo, Adriana; Koppenol, Rebekah; Almeida, Luis Pedro; Matos, Carlos A; Nóbrega, ClévioStress granules (SGs) are membraneless cell compartments formed in response to different stress stimuli, wherein translation factors, mRNAs, RNA-binding proteins (RBPs) and other proteins coalesce together. SGs assembly is crucial for cell survival, since SGs are implicated in the regulation of translation, mRNA storage and stabilization and cell signalling, during stress. One defining feature of SGs is their dynamism, as they are quickly assembled upon stress and then rapidly dispersed after the stress source is no longer present. Recently, SGs dynamics, their components and their functions have begun to be studied in the context of human diseases. Interestingly, the regulated protein self-assembly that mediates SG formation contrasts with the pathological protein aggregation that is a feature of several neurodegenerative diseases. In particular, aberrant protein coalescence is a key feature of polyglutamine (PolyQ) diseases, a group of nine disorders that are caused by an abnormal expansion of PolyQ tract-bearing proteins, which increases the propensity of those proteins to aggregate. Available data concerning the abnormal properties of the mutant PolyQ disease-causing proteins and their involvement in stress response dysregulation strongly suggests an important role for SGs in the pathogenesis of PolyQ disorders. This review aims at discussing the evidence supporting the existence of a link between SGs functionality and PolyQ disorders, by focusing on the biology of SGs and on the way it can be altered in a PolyQ disease context.
- From the molecular hallmarks to motor behavior: characterization of a new transgenic mouse model for spinocerebellar ataxia type 2Publication . Afonso, Inês T.; Koppenol, Rebekah; Conceição, André; Paulino, Rodrigo; Mirapalheta, Lourenzo; Matos, Carlos A; Nóbrega, ClévioSpinocerebellar ataxia type 2 (SCA2) is a rare disease with no cure, and therefore patients depend on symptomatic and supportive treatments. It is a highly debilitating disease affecting predominantly the brain with symptoms that include motor and coordination impairment. SCA2 is caused by an abnormal expansion of the CAG triplet in the coding region of the ATXN2 gene. When it has above 33 CAG repeats, it originates a protein with an abnormally expanded glutamine tract. The mutant protein impairs several cellular functions, leading to neuronal degeneration and death. Several rodent models were developed to study the neuropathology and potential therapies for SCA2. However, most of them fail to mimic a complete SCA2 phenotype, taking too long to develop diseaserelated symptoms or failing to display neuronal-associated deficits.