sirolimus and Machado-Joseph-Disease

Autophagy, the major pathway for protein turnover, is critical to maintain cellular homeostasis and has been implicated in neurodegenerative diseases. The aim of this research was to analyze the expression of autophagy markers in postmortem brains from Machado-Joseph disease (MJD) patients. The expression of autophagy markers in the cerebellum and the oculomotor nucleus from MJD patients and age-matched controls with no signs of neuropathology was inspected postmortem by immunohistochemistry (IHC) and Western blot. Furthermore, autophagy was examined by means of transmission electron microscopy (TEM). Western blot and IHC revealed nuclear accumulation of misfolded ataxin-3 (ATXN3) and the presence of ubiquitin- and p62-positive aggregates in MJD patients as compared to controls. Moreover, the autophagic proteins, autophagy-related gene (Atg) protein (ATG)-7, ATG-12, ATG16L2 and autophagosomal microtubule-associated protein light chain 3 (LC3) were significantly increased in MJD brains relative to controls, while beclin-1 levels were reduced in MJD patients. Increase in the levels of lysosomal-associated membrane protein 2 (LAMP-2) and of the endosomal markers (Rab7 and Rab1A) were observed in MJD patients relatively to controls. In addition, these findings were further confirmed by TEM in brain tissue where large vesicles accumulating electron-dense materials were highly enriched in MJD patients. Postmortem brains with MJD exhibit increased markers of autophagy relative to age-matched control brains, therefore suggesting strong dysregulation of autophagy that may have an important role in the course of MJD pathogenesis.

Topics: Adult; Ataxin-3; Autophagy; Beclin-1; Biomarkers; Cell Adhesion Molecules, Neuronal; Cerebellum; Endosomes; Female; GPI-Linked Proteins; Humans; Lysosomes; Machado-Joseph Disease; Male; Microtubule-Associated Proteins; Middle Aged; Oculomotor Nuclear Complex; Proto-Oncogene Proteins c-myc; Sirolimus; Ubiquitin

A major pathological hallmark in several neurodegenerative disorders, like polyglutamine disorders (polyQ), including Machado-Joseph disease (MJD), is the formation of protein aggregates. MJD is caused by a CAG repeat expansion in the ATXN3 gene, resulting in an abnormal protein, which is prone to misfolding and forms cytoplasmic and nuclear aggregates within neurons, ultimately inducing neurodegeneration. Treatment of proteinopathies with drugs that up-regulate autophagy has shown promising results in models of polyQ diseases. Temsirolimus (CCI-779) inhibits the mammalian target of rapamycin (m-TOR), while lithium chloride (LiCl) acts by inhibiting inositol monophosphatase, both being able to induce autophagy. We have previously shown that chronic treatment with LiCl (10.4 mg/kg) had limited effects in a transgenic MJD mouse model. Also, others have shown that CCI-779 had mild positive effects in a different mouse model of the disease. It has been suggested that the combination of mTOR-dependent and -independent autophagy inducers could be a more effective therapeutic approach. To further explore this avenue toward therapy, we treated CMVMJD135 transgenic mice with a conjugation of CCI-779 and LiCl, both at concentrations known to induce autophagy and not to be toxic. Surprisingly, this combined treatment proved to be deleterious to both wild-type (wt) and transgenic animals, failing to rescue their neurological symptoms and actually exerting neurotoxic effects. These results highlight the possible dangers of manipulating autophagy in the nervous system and suggest that a better understanding of the potential disruption in the autophagy pathway in MJD is required before successful long-term autophagy modulating therapies can be developed.

Topics: Animals; Animals, Genetically Modified; Ataxin-3; Autophagy; Brain; Caenorhabditis elegans; Central Nervous System Agents; Disease Models, Animal; Drug Evaluation, Preclinical; Drug Therapy, Combination; Lithium Compounds; Locomotion; Machado-Joseph Disease; Male; Mice, Inbred C57BL; Motor Activity; Neurotoxicity Syndromes; Sirolimus; TOR Serine-Threonine Kinases

Spinocerebellar ataxia type 3 is a neurodegenerative disorder caused by the expansion of the polyglutamine repeat region within the ataxin-3 protein. The mutant protein forms intracellular aggregates in the brain. However, the cellular mechanisms causing toxicity are still poorly understood and there are currently no effective treatments. In this study we show that administration of a rapamycin ester (cell cycle inhibitor-779, temsirolimus) improves motor performance in a transgenic mouse model of spinocerebellar ataxia type 3. Temsirolimus inhibits mammalian target of rapamycin and hence upregulates protein degradation by autophagy. Temsirolimus reduces the number of aggregates seen in the brains of transgenic mice and decreases levels of cytosolic soluble mutant ataxin-3, while endogenous wild-type protein levels remain unaffected. Temsirolimus is designed for long-term use in patients and therefore represents a possible therapeutic strategy for the treatment of spinocerebellar ataxia type 3. Using this disease model and treatment paradigm, we employed a microarray approach to investigate transcriptional changes that might be important in the pathogenesis of spinocerebellar ataxia type 3. This identified ubiquitin specific peptidase-15, which showed expression changes at both the messenger ribonucleic acid and protein level. Ubiquitin specific peptidase-15 levels were also changed in mice expressing another mutant polyglutamine protein, huntingtin. In total we identified 16 transcripts that were decreased in transgenic ataxin-3 mice that were normalized following temsirolimus treatment. In this mouse model with relatively mild disease progression, the number of transcripts changed was low and the magnitude of these changes was small. However, the importance of these transcriptional alterations in the pathogenesis of spinocerebellar ataxia type 3 remains unclear.

Topics: Animals; Ataxin-3; Autophagy; Cells, Cultured; Disease Models, Animal; Humans; Machado-Joseph Disease; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Nuclear Proteins; Rats; Rats, Sprague-Dawley; Sirolimus; Transcription Factors

The role of autophagy in the degradation of aggregate-prone proteins has been well established. As a result, autophagy upregulation has become an attractive therapeutic strategy for the treatment of proteinopathies, a group of diseases caused by the accumulation of mutant misfolded proteins. We have previously shown that rapamycin attenuates the phenotype in a mouse model of Huntington disease when administered pre-symptomatically and have recently extended this to demonstrate the effectiveness of rapamycin in a transgenic mouse model of spinocerebellar ataxia type 3, a polyglutamine disorder caused by mutations in the ataxin-3 gene. Rapamycin, administered from the initial onset of disease signs, improves motor coordination and results in a decrease in the levels of soluble mutant ataxin-3 and protein aggregates in the brain.

Topics: Animals; Antineoplastic Agents; Ataxin-3; Humans; Huntington Disease; Machado-Joseph Disease; Mice; Nerve Tissue Proteins; Nuclear Proteins; Repressor Proteins; Sirolimus