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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.
- Mutant Ataxin-2 expression in aged animals aggravates neuropathological features associated with Spinocerebellar Ataxia type 2Publication . Afonso, Inês T.; Lima, Patrícia; Conceição, André; Matos, Carlos A; Nóbrega, ClévioSpinocerebellar ataxia type 2 (SCA2) is a rare autosomal, dominantly inherited disease, in which the affected individuals have a disease onset around their third life decade. The molecular mechanisms underlying SCA2 are not yet completely understood, for which we hypothesize that aging plays a role in SCA2 molecular pathogenesis. In this study, we performed a striatal injection of mutant ataxin-2 mediated by lentiviral vectors, in young and aged animals. Twelve weeks post-injection, we analyzed the striatum for SCA2 neuropathological features and specific aging hallmarks. Our results show that aged animals had a higher number of mutant ataxin-2 aggregates and more neuronal marker loss, compared to young animals. Apoptosis markers, cleaved caspase-3, and cresyl violet staining also indicated increased neuronal death in the aged animal group. Additionally, mRNA levels of microtubule-associated protein 1 light-chain 3B (LC3) and sequestosome-1 (SQSTM1/p62) were altered in the aged animal group, suggesting autophagic pathway dysfunction. This work provides evidence that aged animals injected with expanded ataxin-2 had aggravated SCA2 disease phenotype, suggesting that aging plays an important role in SCA2 disease onset and disease progression.
- 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.
- On the role of RNA binding proteins in polyglutamine diseases: from pathogenesis to therapeuticsPublication . Conceição, André; Koppenol, Rebekah; Nóbrega, ClévioPolyglutamine (polyQ) diseases are a group of different neurodegenerative disorders characterized by an abnormal expansion of the trinucleotide cytosine-adenine-guanine (CAG) within coding regions of each disease-associated gene. The abnormal expansion translates into a protein bearing an abnormally long tract of glutamines. The expanded proteins are prone to aggregate, promote aberrant interaction with other proteins and mRNAs and contribute to cellular pathway disruption (Matos et al., 2019). To date, nine different polyQ diseases are described, including among others, Huntington’s disease, and six different spinocerebellar ataxias (SCA). Patients affected by polyQ diseases, suffer a myriad of motor symptoms that include ataxia, dysphagia, tremors, dysarthria, and even dementia. Unfortunately, there is no cure nor treatment able to delay the disease and patients rely only on symptomatic and supportive treatments culminating in premature death (Takahashi et al., 2010).
- The polyglutamine protein ATXN2: from its molecular functions to its involvement in diseasePublication . Gomes da Costa, Rafael; Vieira da Conceição, André Filipe; Albuquerque Andrade de Matos, Carlos Adriano; Nóbrega, ClévioA CAG repeat sequence in the ATXN2 gene encodes a polyglutamine (polyQ) tract within the ataxin-2 (ATXN2) protein, showcasing a complex landscape of functions that have been progressively unveiled over recent decades. Despite significant progresses in the field, a comprehensive overview of the mechanisms governed by ATXN2 remains elusive. This multifaceted protein emerges as a key player in RNA metabolism, stress granules dynamics, endocytosis, calcium signaling, and the regulation of the circadian rhythm. The CAG overexpansion within the ATXN2 gene produces a protein with an extended poly(Q) tract, inducing consequential alterations in conformational dynamics which confer a toxic gain and/or partial loss of function. Although overexpanded ATXN2 is predominantly linked to spinocerebellar ataxia type 2 (SCA2), intermediate expansions are also implicated in amyotrophic lateral sclerosis (ALS) and parkinsonism. While the molecular intricacies await full elucidation, SCA2 presents ATXN2-associated pathological features, encompassing autophagy impairment, RNA-mediated toxicity, heightened oxidative stress, and disruption of calcium homeostasis. Presently, SCA2 remains incurable, with patients reliant on symptomatic and supportive treatments. In the pursuit of therapeutic solutions, various studies have explored avenues ranging from pharmacological drugs to advanced therapies, including cell or gene-based approaches. These endeavours aim to address the root causes or counteract distinct pathological features of SCA2. This review is intended to provide an updated compendium of ATXN2 functions, delineate the associated pathological mechanisms, and present current perspectives on the development of innovative therapeutic strategies.