RESUMEN
Background: Mitchell syndrome is a rare, neurodegenerative disease caused by an ACOX1 gain-of-function mutation (c.710A>G; p.N237S), with fewer than 20 reported cases. Affected patients present with leukodystrophy, seizures, and hearing loss. ACOX1 serves as the rate-limiting enzyme in peroxisomal beta-oxidation of very long-chain fatty acids. The N237S substitution has been shown to stabilize the active ACOX1 dimer, resulting in dysregulated enzymatic activity, increased oxidative stress, and glial damage. Mitchell syndrome lacks a vertebrate model, limiting insights into the pathophysiology of ACOX1-driven white matter damage and neuroinflammatory insults. Methods: We report a patient presenting with rapidly progressive white matter damage and neurological decline, who was eventually diagnosed with an ACOX1 N237S mutation through whole genome sequencing. We developed a zebrafish model of Mitchell syndrome using transient ubiquitous overexpression of the human ACOX1 N237S variant tagged with GFP. We assayed zebrafish behavior, oligodendrocyte numbers, expression of white matter and inflammatory transcripts, and analysis of peroxisome counts. Results: The patient experienced progressive leukodystrophy and died 2 years after presentation. The transgenic zebrafish showed a decreased swimming ability, which was restored with the reactive microglia-targeted antioxidant dendrimer-N-acetyl-cysteine conjugate. The mutants showed no effect on oligodendrocyte counts but did display activation of the integrated stress response (ISR). Using a novel SKL-targeted mCherry reporter, we found that mutants had reduced density of peroxisomes. Conclusions: We developed a vertebrate (zebrafish) model of Mitchell syndrome using transient ubiquitous overexpression of the human ACOX1 N237S variant. The transgenic mutants exhibited motor impairment and showed signs of activated ISR, but interestingly, there were no changes in oligodendrocyte counts. However, the mutants exhibited a deficiency in the number of peroxisomes, suggesting a possible shared mechanism with the Zellweger spectrum disorders.
RESUMEN
Synovial sarcoma is a soft tissue malignancy with a poor prognosis; many patients will die from this disease within 10 years of diagnosis, despite treatment. Gene expression profiling and immunohistochemistry studies have identified oncogenes that are highly expressed in synovial sarcoma. Included in this group are receptor tyrosine kinases such as epidermal growth factor receptor, insulin-like growth factor receptor 1, fibroblast growth factor receptor 3, KIT, and HER2. Inhibitors of these growth-promoting receptors are likely to inhibit proliferation of synovial sarcoma; however, the effect of receptor tyrosine kinase inhibitors on synovial sarcoma is largely unknown. We assessed the ability of the following receptor tyrosine kinase inhibitors to halt proliferation and induce apoptosis in synovial sarcoma monolayer and three dimensional spheroid in vitro models: gefitinib (Iressa), NVP-AEW541, imatinib mesylate (Gleevec), SU5402, PRO-001, trastuzumab (Herceptin), and 17-allylamino-17-demethoxygeldanamycin (17-AAG). Gefitinib, NVP-AEW541, and imatinib inhibited proliferation only at relatively high concentrations, which are not clinically applicable. 17-AAG, which destabilizes multiple receptor tyrosine kinases and other oncoproteins through heat shock protein 90 inhibition, prevented proliferation and induced apoptosis in synovial sarcoma monolayer models at concentrations achievable in human serum. 17-AAG treatment was also associated with receptor tyrosine kinase degradation and induction of apoptosis in synovial sarcoma spheroid models. 17-AAG was more effective than doxorubicin, particularly in the spheroid models. Here we provide in vitro evidence that 17-AAG, a clinically applicable drug with known pharmacology and limited toxicity, inhibits synovial sarcoma proliferation by inducing apoptosis, and thus has potential as a systemic therapy for this disease.