Stress 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.

In response to different stress stimuli, cells transiently form stress granules (SGs) in order to protect themselves and re-establish homeostasis. Besides these important cellular functions, SGs are now being implicated in different human diseases, such as neurodegenerative disorders and cancer. SGs are ribonucleoprotein granules, constituted by a variety of different types of proteins, RNAs, factors involved in translation and signaling molecules, being capable of regulating mRNA translation to facilitate stress response. However, until now a complete list of the SG components has not been available. Therefore, we aimer at identifying and linting in an open access database all the proteins described so far as components of SGs. The identification was made through an exhaustive search of studies listed in PubMed and double checked. Moreover, for each identified protein several details were also gathered from public databases, such as the molecular function, the cell types in which they were detected, the type of stress stimuli used to induce SG formation and the reference of the study describing the recruitment of the component to SGs. Expression levels in the context of different neurodegenerative diseases were also obtained and are also described in the database. The Mammalian Stress Granules Proteome is available at https://msgp.pt/ , being a new and unique open access online database, the first to list all the protein components of the SGs identified so far. The database constitutes an important and valuable tool for researchers in this research area of growing interest.

Machado-Joseph disease (MJD) is a neurodegenerative disorder, caused by an abnormal expansion of CAG trinucleotide repeats in the disease-causing gene. This mutation leads to an abnormal polyglutamine tract in the protein ataxin-3, resulting in formation of mutant ataxin-3 aggregates. Despite several attempts to develop a therapeutic option for MJD, currently there are no available therapies capable of delaying or stopping disease progression. Recently, our group reported that reducing the expression levels of mutant ataxin-3 lead to a mitigation of several MJD-related behavior and neuropathological abnormalities. Aiming a more rapid translation to the human clinics, in this study we investigate a pharmacological inhibitor of translation - cordycepin - in several preclinical models. We found that cordycepin treatment significantly reduced: i) the levels of mutant ataxin-3; ii) the neuropathological abnormalities in a lentiviral mouse model; iii) the motor and neuropathological deficits in a transgenic mouse model and iv) the number of ubiquitin aggregates in a human neural model. We hypothesize that the effect cordycepin is mediated by the increase of phosphorylated AMPK levels, which is accompanied by a reduction in the global translation levels and by a significant activation of the autophagy pathway. Overall, this study suggests that cordycepin might constitute an effective and safe therapeutic approach for MJD, and probably for the other polyglutamine diseases.