Decreased miR-146a expression in acute ischemic stroke directly targets the Fbxl10 mRNA and is involved in modulating apoptosis.

BACKGROUND: miR-146a, a strong pro-apoptotic factor in some pathophysiological processes, is reported to be involved in ischemic stroke (IS), though its role remains unclear. Fbxl10 is an active anti-apoptotic factor and a predicted target of miR-146a. We hypothesized that dysregulation of miR-146a contributes to ischemic injury by targeting Fbxl10. METHODS: Circulating miRNAs were detected by miRNA microarray and qRT-PCR. miR-146a targets were predicted using bioinformatics and confirmed with a dual luciferase reporter assay. We used an in vitro ischemic model of oxygen-glucose deprivation and reperfusion (OGD/R) to mimic cerebral ischemia/reperfusion (I/R) conditions. Expression of miR-146a, Fbxl10 and Bcl2l2 mRNAs, and Fbxl10 and Bcl2l2 proteins was verified by qRT-PCR and Western blotting. The effects of miR-146a on neuronal cell apoptosis were evaluated by flow cytometry. RESULTS: A significant reduction in miR-146a expression was observed in acute ischemic stroke (AIS). A dual-luciferase reporter assay showed that Fbxl10, but not Bcl2l2, is a target of miR-146a. Transfection with miR-146a mimics promoted apoptosis in SK-N-SH cells and significantly reduced expression of Fbxl10. Conversely, miR-146a inhibition attenuated OGD/R-induced neuronal cell death and significantly up-regulated Fbxl10 expression. CONCLUSIONS: miR-146a expression was significantly down-regulated in AIS, and Fbxl10 was identified as a target of miR-146a. Moreover, up-regulation of Fbxl10, a miR-146a target, likely protects neurons from ischemic death.

Both ubiquitin ligases FBXW8 and PARK2 are sequestrated into insolubility by ATXN2 PolyQ expansions, but only FBXW8 expression is dysregulated.

The involvement of the ubiquitin-proteasome system (UPS) in the course of various age-associated neurodegenerative diseases is well established. The single RING finger type E3 ubiquitin-protein ligase PARK2 is mutated in a Parkinson's disease (PD) variant and was found to interact with ATXN2, a protein where polyglutamine expansions cause Spinocerebellar ataxia type 2 (SCA2) or increase the risk for Levodopa-responsive PD and for the motor neuron disease Amyotrophic lateral sclerosis (ALS). We previously reported evidence for a transcriptional induction of the multi-subunit RING finger Skp1/Cul/F-box (SCF) type E3 ubiquitin-protein ligase complex component FBXW8 in global microarray profiling of ATXN2-expansion mouse cerebellum and demonstrated its role for ATXN2 degradation in vitro. Now, we documented co-localization in vitro and co-immunoprecipitations both in vitro and in vivo, which indicate associations of FBXW8 with ATXN2 and PARK2. Both FBXW8 and PARK2 proteins are driven into insolubility by expanded ATXN2. Whereas the FBXW8 transcript upregulation by ATXN2- expansion was confirmed also in qPCR of skin fibroblasts and blood samples of SCA2 patients, a FBXW8 expression dysregulation was not observed in ATXN2-deficient mice, nor was a PARK2 transcript dysregulation observed in any samples. Jointly, all available data suggest that the degradation of wildtype and mutant ATXN2 is dependent on FBXW8, and that ATXN2 accumulation selectively modulates FBXW8 levels, while PARK2 might act indirectly through FBXW8. The effects of ATXN2-expansions on FBXW8 expression in peripheral tissues like blood may become useful for clinical diagnostics.

Multilocus loss of DNA methylation in individuals with mutations in the histone H3 lysine 4 demethylase KDM5C.

BACKGROUND: A number of neurodevelopmental syndromes are caused by mutations in genes encoding proteins that normally function in epigenetic regulation. Identification of epigenetic alterations occurring in these disorders could shed light on molecular pathways relevant to neurodevelopment. RESULTS: Using a genome-wide approach, we identified genes with significant loss of DNA methylation in blood of males with intellectual disability and mutations in the X-linked KDM5C gene, encoding a histone H3 lysine 4 demethylase, in comparison to age/sex matched controls. Loss of DNA methylation in such individuals is consistent with known interactions between DNA methylation and H3 lysine 4 methylation. Further, loss of DNA methylation at the promoters of the three top candidate genes FBXL5, SCMH1, CACYBP was not observed in more than 900 population controls. We also found that DNA methylation at these three genes in blood correlated with dosage of KDM5C and its Y-linked homologue KDM5D. In addition, parallel sex-specific DNA methylation profiles in brain samples from control males and females were observed at FBXL5 and CACYBP. CONCLUSIONS: We have, for the first time, identified epigenetic alterations in patient samples carrying a mutation in a gene involved in the regulation of histone modifications. These data support the concept that DNA methylation and H3 lysine 4 methylation are functionally interdependent. The data provide new insights into the molecular pathogenesis of intellectual disability. Further, our data suggest that some DNA methylation marks identified in blood can serve as biomarkers of epigenetic status in the brain.