CAG RNAs induce DNA damage and apoptosis by silencing NUDT16 expression in polyglutamine degeneration.

DNA damage plays a central role in the cellular pathogenesis of polyglutamine (polyQ) diseases, including Huntington's disease (HD). In this study, we showed that the expression of untranslatable expanded CAG RNA per se induced the cellular DNA damage response pathway. By means of RNA sequencing (RNA-seq), we found that expression of the Nudix hydrolase 16 (NUDT16) gene was down-regulated in mutant CAG RNA-expressing cells. The loss of NUDT16 function results in a misincorporation of damaging nucleotides into DNAs and leads to DNA damage. We showed that small CAG (sCAG) RNAs, species generated from expanded CAG transcripts, hybridize with CUG-containing NUDT16 mRNA and form a CAG-CUG RNA heteroduplex, resulting in gene silencing of NUDT16 and leading to the DNA damage and cellular apoptosis. These results were further validated using expanded CAG RNA-expressing mouse primary neurons and in vivo R6/2 HD transgenic mice. Moreover, we identified a bisamidinium compound, DB213, that interacts specifically with the major groove of the CAG RNA homoduplex and disfavors the CAG-CUG heteroduplex formation. This action subsequently mitigated RNA-induced silencing complex (RISC)-dependent NUDT16 silencing in both in vitro cell and in vivo mouse disease models. After DB213 treatment, DNA damage, apoptosis, and locomotor defects were rescued in HD mice. This work establishes NUDT16 deficiency by CAG repeat RNAs as a pathogenic mechanism of polyQ diseases and as a potential therapeutic direction for HD and other polyQ diseases.

Brain-Targeting Delivery of Two Peptidylic Inhibitors for Their Combination Therapy in Transgenic Polyglutamine Disease Mice via Intranasal Administration.

Polyglutamine diseases are a set of progressive neurodegenerative disorders caused by misfolding and aggregation of mutant CAG RNA and polyglutamin protein. To date, there is a lack of effective therapeutics that can counteract the polyglutamine neurotoxicity. Two peptidylic inhibitors, QBP1 and P3, targeting the protein and RNA toxicities, respectively, have been previously demonstrated by us with combinational therapeutic effects on the Drosophila polyglutamine disease model. However, their therapeutic efficacy has never been investigated in vivo in mammals. The current study aims to (a) develop a brain-targeting delivery system for both QBP1 and L1P3V8 (a lipidated variant of P3 with improved stability) and (b) evaluate their therapeutic effects on the R6/2 transgenic mouse model of polyglutamine disease. Compared with intravenous administration, intranasal administration of QBP1 significantly increased its brain-to-plasma ratio. In addition, employment of a chitosan-containing in situ gel for the intranasal administration of QBP1 notably improved its brain concentration for up to 10-fold. Further study on intranasal cotreatment with the optimized formulation of QBP1 and L1P3V8 in mice found no interference on the brain uptake of each other. Subsequent efficacy evaluation of 4-week daily QBP1 (16 µmol/kg) and L1P3V8 (6 µmol/kg) intranasal cotreatment in the R6/2 mice demonstrated a significant improvement on the motor coordination and explorative behavior of the disease mice, together with a full suppression on the RNA- and protein-toxicity markers in their brains. In summary, the current study developed an efficient intranasal cotreatment of the two peptidylic inhibitors, QBP1 and L1P3V8, for their brain-targeting, and such a novel therapeutic strategy was found to be effective on a transgenic polyglutamine disease mouse model.

Size anomaly and alteration of GABAergic enzymes expressions in cerebellum of a valproic acid mouse model of autism.

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficit and repetitive behaviour. In the past few years, increasing clinical evidence has shown that the cerebellum may contribute to the neuropathology of ASD. However, studies in the mechanism for the involvement of the cerebellum in autism remained speculative. Although some have suggested the possibility of a change of glutamate decarboxylases in the cerebellum of autistic patients, this remains controversial and is limited to the alteration in transcriptional level. This study aimed to investigate the cerebellar structure and determine the expression of rate-limiting GABAergic enzymes in GABA signalling of the autism cerebellum. Pregnant C57BL/6 J mice were intraperitoneally injected with a dosage of 500 mg/kg valproic acid (VPA) on embryonic day 10.5 for autistic behavioural induction. This study found that early prenatal exposure to VPA led to tail deformation and decreased cerebellar weight and size. Early adult mouse models with autistic behaviour showed reduced expression of both isoforms of glutamate decarboxylases (GAD) 65 and 67 in the cerebellum. Also, protein expressions of cerebellar type 1 GABA transporter (GAT-1) and GABA transaminase (GABAT) were reduced in VPA mice. It indicated that abnormal GABA production, recycling, and metabolism could alter the excitatory-inhibitory balance in the autistic cerebellum. Thus, our findings provide supporting evidence that cerebellum impairment could be an etiology of environmentally induced autism. Changes in cerebellar structure and the altered GABAergic enzymes in the cerebellum provide targets for future therapeutic studies in idiopathic autism.