Project description:Eukaryotic messenger RNAs (mRNAs) possess a 5’-end N7-methyl guanosine (m7G) cap that promotes their translation and stability. However, it was recently demonstrated that eukaryotic mRNAs can also carry a 5' end nicotinamide adenine dinucleotide (NAD+) cap that promotes mRNA decay mediated by the NAD+ decapping enzyme DXO1. However, the dynamic regulation of NAD+ capping in plant remains unknown. Here, we describe the global landscape of NAD+-capped RNAs in Arabidopsis thaliana, and demonstrate that DXO1 is responsible for removal of these 5’-end modifications and facilitates mRNA degradation in plant transcriptomes. We also reveal that in the absence of DXO1 NAD+-capped mRNAs are unstable and processed into smRNAs. Furthermore, we find that Abscisic Acid (ABA) remodel the landscape of RNA cap epitransciptome, and the mRNA lost their NAD+ cap contribute to their stability under ABA. Overall, our results support a link between ABA response and RNA NAD+ capping.
Project description:Eukaryotic messenger RNAs (mRNAs) possess a 5’-end N7-methyl guanosine (m7G) cap that promotes their translation and stability. However, it was recently demonstrated that eukaryotic mRNAs can also carry a 5' end nicotinamide adenine dinucleotide (NAD+) cap that promotes mRNA decay mediated by the NAD+ decapping enzyme DXO1. However, the dynamic regulation of NAD+ capping in plant remains unknown. Here, we describe the global landscape of NAD+-capped RNAs in Arabidopsis thaliana, and demonstrate that DXO1 is responsible for removal of these 5’-end modifications and facilitates mRNA degradation in plant transcriptomes. We also reveal that in the absence of DXO1 NAD+-capped mRNAs are unstable and processed into smRNAs. Furthermore, we find that Abscisic Acid (ABA) remodel the landscape of RNA cap epitransciptome, and the mRNA lost their NAD+ cap contribute to their stability under ABA. Overall, our results support a link between ABA response and RNA NAD+ capping.
Project description:Poly ADP-ribose (PAR) polymerases (PARPs) play fundamental roles in multiple DNA damage recognition and repair pathways. Persistent nuclear PARP activation causes cellular NAD+ depletion and exacerbates cellular aging. However, very little is known about mitochondrial PARP (mtPARP) and PARylation. The existence of mtPARP is controversial, and the biological roles for mtPARP induced mitochondrial PARylation are unclear. Here, we demonstrate the presence of PARP1 and PARylation in purified mitochondria. The addition of the PARP1 substrate NAD+ to isolated mitochondria induces PARylation which is suppressed by PARP inhibitor olaparib treatment. Mitochondrial PARylation was also evaluated by enzymatic labeling of terminal ADP-ribose (ELTA) labeling. To further confirm the presence of mtPARP1, we evaluated mitochondrial nucleoid PARylation by ADP ribose-chromatin affinity purification (ADPr-ChAP) . We observed that NAD+ stimulated PARylation and TFAM occupancy on the mtDNA regulatory region D-loop, inducing mtDNA transcription. These findings suggest that PARP1 is integrally involved in mitochondrial PARylation and NAD+ dependent mtPARP1 activity contributes to mtDNA transcription regulation.
Project description:Eukaryotic mRNAs generally possess an N7 methyl guanosine cap at their 5? end to promote their translation and stability. Here we demonstrate mammalian mRNAs can carry a 5'-end nicotinamide adenine dinucleotide (NAD+) cap. We further demonstrate fungal and mammalian noncanonical DXO family of decapping enzymes can efficiently remove NAD+ caps from mRNAs in vitro and cocrystal structures of DXO with 3´ phosphate NAD+ illuminates the molecular mechanism for the “deNADing” reaction. An NAD+ cap promotes mRNA decay in wild type mammalian cells and confers mRNA stability in the absence of DXO. Importantly, mammalian cells possess a capping mechanism that NAD+ caps a subset of intronic small nucleolar RNAs that are selectively enriched in DXO deficient cells. Our data establish NAD+ as a bona fide mammalian RNA cap and identifies the DXO proteins as potent deNADing enzymes that modulate the levels of NAD+-capped RNAs in cells.
Project description:Nicotinamide adenine dinucleotide (NAD+) is a critical metabolic co-enzyme which is strongly implicated in the pathogenesis of brain aging and neurodegenerative diseases. Prevention of age-related decline in brain NAD+ levels is an attractive therapeutic strategy for combating age-related neurodegeneration, emphasizing the need to fully understand molecular mechanisms regulating brain NAD+ levels. Previous work has shown that the circadian protein REV-ERBα regulates cellular NAD+ levels in cardiac tissue via control of the NAD+ producing enzyme NAMPT. Whether this pathway regulates brain NAD+ levels, however, is unknown. Here, we show that REV-ERBα controls brain NAD+ levels through a distinct pathway involving suppression of the NAD+ consuming enzyme CD38 in astrocytes. Under basal conditions, REV-ERBα suppresses the transcription factor NFIL3 (E4BP4) which itself provides tonic inhibition of CD38 expression, elevating CD38 levels and keeping NAD+ levels low. Deletion of REV-ERBα, either globally or specifically in astrocytes, led to induction of NFIL3, suppression of CD38, increased NAD+, and mitigated protein aggregation, inflammation, and neurodegeneration in a mouse model of tauopathy. This pathway appears to be unique to the brain, as REV-ERBα deletion does not affect NAMPT expression in the brain, does not suppress CD38 in the liver, and has an opposite effect on NAD+ levels in the brain as in the heart. Our data show that the circadian nuclear receptor REV-ERBα can regulate NAD+ via distinct mechanisms in different tissues and define a REV-ERBα-NFIL3-NAD+ downstream pathway controlling brain NAD+ metabolism and neurodegeneration.
Project description:Cockayne syndrome (CS) is a rare premature aging disease, which in the majority of cases is caused by mutations of the genes encoding the CSA or CSB proteins. CS patients display cachectic dwarfism and severe neurological manifestations and die by 12 years of age on average. The CS proteins are involved in transcription and DNA repair, including a specialized form of DNA repair called transcription-coupled nucleotide excision repair (TC-NER). However, there is also evidence for mitochondrial dysfunction in CS, likely contributing to the severe premature aging phenotype of this disease. Our cross-species transciptomic analysis in CS postmortem brain tissue, CS mouse and C. elegans models showed that mitochondrial dysfunction is indeed a common feature in CS. Interestingly, the restoration of mitochondrial dysfunction through NAD+ supplementation significantly improved lifespan and healthspan in the C. elegans models of CS, highlighting mitochondrial dysfunction as a major driver of the aging features of CS. We proceeded to perform molecular studies on cerebellar samples obtained from CS patients. We found that these patients exhibited molecular signatures of dysfunctional mitochondrial dynamics that can be corrected with NAD+ supplementation in primary cells with depleted CSA or CSB. Our study provides support for the interconnection between two major aging theories, DNA damage and mitochondrial dysfunction. Together these two agents contribute to an accelerated aging program that can be averted by NAD+ supplementation.
Project description:Cockayne syndrome (CS) is a rare premature aging disease, which in the majority of cases is caused by mutations of the genes encoding the CSA or CSB proteins. CS patients display cachectic dwarfism and severe neurological manifestations and die by 12 years of age on average. The CS proteins are involved in transcription and DNA repair, including a specialized form of DNA repair called transcription-coupled nucleotide excision repair (TC-NER). However, there is also evidence for mitochondrial dysfunction in CS, likely contributing to the severe premature aging phenotype of this disease. Our cross-species transciptomic analysis in CS postmortem brain tissue, CS mouse and C. elegans models showed that mitochondrial dysfunction is indeed a common feature in CS. Interestingly, the restoration of mitochondrial dysfunction through NAD+ supplementation significantly improved lifespan and healthspan in the C. elegans models of CS, highlighting mitochondrial dysfunction as a major driver of the aging features of CS. We proceeded to perform molecular studies on cerebellar samples obtained from CS patients. We found that these patients exhibited molecular signatures of dysfunctional mitochondrial dynamics that can be corrected with NAD+ supplementation in primary cells with depleted CSA or CSB. Our study provides support for the interconnection between two major aging theories, DNA damage and mitochondrial dysfunction. Together these two agents contribute to an accelerated aging program that can be averted by NAD+ supplementation.
Project description:Nicotinamide adenine dinucleotide (NAD+) is a vital small molecule with important redox capacity in oxidative phosphorylation (OXPHOS) and a key co-factor in various enzymatic reactions. The recent identification of the mitochondrial NAD+ transporter SLC25A51 provides strong evidence for a direct regulation of the mitochondrial NAD+ pool. Though the effect of this transporter on glucose metabolism has been described, its contribution to other NAD+-dependent processes such as ADP-ribosylation remains elusive. Here, we report that knockdown of SLC25A51 decreased the NAD+ concentration in mitochondria but increased the NAD+ concentration in the cytoplasm and nucleus. The increase in nuclear and cytoplasmic NAD+ was not due to the upregulation of the salvage pathway, thus pointing towards an overall redistribution of NAD+ from the mitochondria towards the cyto/nuclear compartment. Furthermore, the NAD+ redistribution induced by knockdown or knockout of SLC25A51 resulted, as quantified by immunofluorescence or analyzed by mass-spectrometry, in a loss of mitochondrial ADP-ribosylation and an increase of PARP1-mediated nuclear ADP-ribosylation under basal conditions. Further, MMS/Olaparib induced PARP1 chromatin retention and the sensitivity of triple-negative MDA-MB-436 breast cancer cells to PARP inhibition were both reduced upon knockdown of SLC25A51. In addition, H2O2-induced PARP1-dependent nuclear ADP-ribosylation was prolonged while phosphorylation of H2AX was unexpectedly reduced. Together these results provide evidence that lack of SCL25A51 and subsequently altered NAD+ compartmentalization affects not only mitochondrial and nuclear ADP-ribosylation but also other chromatin associated events.
Project description:Aberrant alternative splicing events (ASEs) are emerging as a new hallmark of aging and are linked to age-related neurodegenerative pathologies such as Alzheimer’s disease (AD). AD brains are characterized by abundant intracellular proteinaceous aggregates, including neurofibrillary tangles (NFTs). Although NAD+ and related metabolites can slow down AD progression, the effects of NAD+ on ASEs in AD remain unclear. This study investigates the relationships between NAD+ metabolism, ASEs and AD or AD-like pathologies including tauopathies using deep-learning AI-based algorithms to predict protein structures and protein-protein interactions as well as experimental tauopathy models including hTau.P301S transgenic mice and transgenic hTau[P301L] Caenorhabditis elegans. Mouse transcriptomic data were mined to detect ASEs that were differentially induced in the presence of NAD+ precursor nicotinamide riboside (NR) with specific focus on the Eva1-C locus. The results reveal that the relative abundance of Eva1-C isoforms is sensitive to both the concentration of NR and to tauopathy genotype. NAD+ abundance/metabolic status modulates ASEs and the expression of EVA1-C isoforms, which in turn regulate the interaction with the key proteins, BAG-1 and HSP70, involved in orchestrating protein homeostasis. Importantly, EVA1-C is dramatically reduced in the postmortem entorhinal cortex and hippocampal neurons from 20 Braak 5/6 AD patients compared to 20 of cognitive normal humans. Thus, this study supports the novel idea that NAD+ metabolism modulates abundance of specific mRNA isoforms, and that ASEs influence disease progression in model tauopathies and potentially AD. These results could facilitate future development of NAD+-based splice-switching therapeutics for AD.
Project description:The macro domain of the histone variant macroH2A1.1 is an evolutionary conserved ADP ribose-binding module of unknown physiological function. We demonstrate that during myogenic differentiation alternative splicing switches the expression of macroH2A1 from the non-ADP ribose binding to the binding isoform. While differentiation commitment is normal in cells lacking macroH2A1.1, we observe two phenotypes: diminished cell fusion correlating with reduced expression of adhesion and migration genes and reduced mitochondrial capacity. While the integrity of the ADP ribose-binding pocket is dispensable for gene regulation and fusion, it is critical to sustain optimal mitochondrial fatty acid oxidation. Rescue experiments using a pharmacological PARP-1 inhibitor and metabolomics support the idea that loss of macroH2A1.1 leads to PARP-1 activation and accelerated NAD+ consumption. As a consequence, the level of nicotinamide mononucleotide, the key metabolite for mitochondrial NAD+ pool regeneration, is reduced and sirtuins fail to maintain mitochondrial proteins in their hypoacetylated and active form. Our results support the idea that chromatin states containing the histone variant macroH2A1.1 contribute to optimal mitochondrial oxidative capacity by channeling the consumption of NAD+ from the nucleus to mitochondria in a manner largely independent on transcriptional regulation.