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.

Chronic binge‐like drinking is a risk factor for age‐related dementia, however, the lasting and irreversible effect of alcohol on the brain remains elusive. Transcriptomic changes in brain cortices revealed pro‐ageing hallmarks upon chronic ethanol exposure and these changes predominantly occur in neurons. The changes are attributed to a prioritized ethyl alcohol oxidation in these cells via the NADPH‐dependent cytochrome pathway. This hijacks the folate metabolism of the 1‐carbon network which supports the pathway choice of DNA repair via the non‐cell cycle‐dependent mismatch repair networks. The lost‐in‐function of such results in the de‐inactivation of the less preferred cell cycle‐dependent homologous recombination (HR) repair, forcing these post‐mitotic cells to re‐engage in a cell cycle‐like process. However, mature neurons are post‐mitotic. Therefore, instead of successfully completing a full round of cell cycle which is necessary for the completion of HR‐mediated repair; these cells are arrested at checkpoints. The resulting persistence of repair intermediates induces and promotes the nuclear accumulation of p21 and cyclin B—a trigger for permanent cell cycle exits and irreversible senescence response. Supplementation of bioactive 5‐methyl tetrahydrofolate simultaneously at times with ethyl alcohol exposure supports the fidelity of the 1‐carbon network and hence the activity of the mismatch repair. This prevents aberrant and irreversible cell cycle re‐entry and senescence events of neurons. Together, our findings offer a direct connection between binge‐drinking behaviour and its irreversible impact on the brain, which makes it a potential risk factor for dementia.

Early changes in astrocyte energy metabolism are associated with late‐onset Alzheimer's disease (LOAD), but the underlying mechanism remains elusive. A previous study suggested an association between a synonymous SNP (rs1012672, C→T) in LRP6 gene and LOAD; and that is indeed correlated with diminished LRP6 gene expression in the frontal cortex region. The authors show that LRP6 is a unique Wnt coreceptor on astrocytes, serving as a bimodal switch that modulates their metabolic landscapes. The Wnt‐LRP6 mediated mTOR‐AKT axis is essential for sustaining glucose metabolism. In its absence, Wnt switches to activate the LRP6‐independent Ca2+‐PKC‐NFAT axis, resulting in a transcription network that favors glutamine and branched chain amino acids (BCAAs) catabolism over glucose metabolism. Exhaustion of these raw materials essential for neurotransmitter biosynthesis and recycling results in compromised synaptic, cognitive, and memory functions; priming for early changes that are frequently found in LOAD. The authors also highlight that intranasal supplementation of glutamine and BCAAs is effective in preserving neuronal integrity and brain functions, proposing a nutrient‐based method for delaying cognitive and memory decline when LRP6 cell surface levels and functions are suboptimal.

Neurite outgrowth is a fundamental process in neurons that produces extensions and, consequently, neural connectivity. Neurite damage and atrophy are observed in various brain injuries and disorders. Understanding the intrinsic pathways of neurite outgrowth is essential for developing strategies to stimulate neurite regeneration.Insulin is a pivotal hormone in the regulation of glucose homeostasis. There is increasing evidence for the neurotrophic functions of insulin, including the induction of neurite outgrowth. However, the associated mechanism remains elusive. Here, we demonstrate that insulin potentiates neurite outgrowth mediated by the small GTPases ADP-ribosylation factor 6 (ARF6) and Ras-related C3 botulinum toxin substrate 1 (Rac1) through the neuronal adaptor FE65. Moreover, insulin enhances atypical protein kinase Cι/λ (PKCι/λ) activation and FE65 phosphorylation at serine 459 (S459) in neurons and mouse brains. In vitro and cellular assays show that PKCι/λ phosphorylated FE65 at S459. Consistently, insulin potentiates FE65 S459 phosphorylation only in the presence of PKCι/λ. Phosphomimetic studies show that an FE65 S459E mutant potently activates ARF6, Rac1, and neurite outgrowth. Notably, this phosphomimetic mutation enhances the FE65-ARF6 interaction, a process that promotes ARF6-Rac1-mediated neurite outgrowth. Likewise, insulin treatment and PKCι/λ overexpression potentiate the FE65-ARF6 interaction. Conversely, PKCι/λ

Loss of mitochondrial homeostasis are evident in Alzheimer's disease (AD)1. However, the underlying mechanisms remain largely elusive. In this study, we report that lncMtDloop, an age-related and conserved long noncoding RNA derived from mitochondrial DNA (mtDNA) D-loop, is crucial for sustaining mitochondrial transcription and homeostasis, and associates with Alzheimer’s pathogenesis. Notably, the level of lncMtDloop expression is diminished in the brains of human AD patients and the 3xTg mouse model, whereas the failure to recruit mitochondrial transcription factor A (TFAM) leads to the deregulated mitochondrial transcription. Restoring lncMtDloop expression not only significantly improves mitochondrial transcription, morphology and function, but also enhances mitophagy, ameliorates AD-like pathology, which these subcellular effects extend to a dramatic reversal of deficits in synaptic and cognitive behaviors of the 3xTg mouse model. Collectively, our findings show the decreased lncMtDloop expression potentiates AD risk, thereby revealing an unexpected mitochondrial mechanism contributing to AD pathogenesis and opens a new door for therapeutic intervention.