Autophagy in Spinocerebellar Ataxia Type 3: From Pathogenesis to Therapeutics

Machado-Joseph disease (MJD) or spinocerebellar ataxia 3 (SCA3) is a rare, inherited, monogenic, neurodegenerative disease, and the most common SCA worldwide. MJD/SCA3 causative mutation is an abnormal expansion of the triplet CAG at exon 10 within the ATXN3 gene. The gene encodes for ataxin-3, which is a deubiquitinating protein that is also involved in transcriptional regulation. In normal conditions, the ataxin-3 protein polyglutamine stretch has between 13 and 49 glutamines. However, in MJD/SCA3 patients, the size of the stretch increases from 55 to 87, contributing to abnormal protein conformation, insolubility, and aggregation. The formation of aggregates, which is a hallmark of MJD/SCA3, compromises different cell pathways, leading to an impairment of cell clearance mechanisms, such as autophagy. MJD/SCA3 patients display several signals and symptoms in which the most prominent is ataxia. Neuropathologically, the regions most affected are the cerebellum and the pons. Currently, there are no disease-modifying therapies, and patients rely only on supportive and symptomatic treatments. Due to these facts, there is a huge research effort to develop therapeutic strategies for this incurable disease. This review aims to bring together current state-of-the-art strategies regarding the autophagy pathway in MJD/SCA3, focusing on evidence for its impairment in the disease context and, importantly, its targeting for the development of pharmacological and gene-based therapies.

The contractile action of palytoxin in the isolated rabbit urinary bladder

Palytoxin at 10(-10)-10(-7) M caused contractions of the detrusor muscle from rabbit urinary bladder in a concentration-dependent manner. The response to palytoxin was markedly inhibited by indomethacin (a cyclooxygenase inhibitor) or nordihydroguaiaretic acid (a lipoxygenase inhibitor) at 10(-5) M. Indomethacin and nordihydroguaiaretic acid also inhibited the response to arachidonic acid at 10(-3) M. A Ca2+-free medium with EGTA or nifedipine at 10(-5) M, nearly abolished the responses to palytoxin and arachidonic acid. Tetrodotoxin, phentolamine, atropine and chlorpheniramine (all at 10(-5) M) had a slight or no inhibitory effect on the response to palytoxin. These results suggested that in the rabbit bladder, the contractile effect of palytoxin is mainly dependent on an increase in metabolites of arachidonic acid.