When transcribed DNA is damaged, the transcription and DNA repair machineries must interact to ensure successful DNA repair. The mechanisms of this interaction in the context of chromatin are still ...being elucidated. Here we show that the SIRT6 protein enhances non-homologous end joining (NHEJ) DNA repair by transiently repressing transcription. Specifically, SIRT6 mono-ADP ribosylates the lysine demethylase JHDM1A/KDM2A leading to rapid displacement of KDM2A from chromatin, resulting in increased H3K36me2 levels. Furthermore, we found that through HP1α binding, H3K36me2 promotes subsequent H3K9 tri-methylation. This results in transient suppression of transcription initiation by RNA polymerase II and recruitment of NHEJ factors to DNA double-stranded breaks (DSBs). These data reveal a mechanism where SIRT6 mediates a crosstalk between transcription and DNA repair machineries to promote DNA repair. SIRT6 functions in multiple pathways related to aging, and its novel function coordinating DNA repair and transcription is yet another way by which SIRT6 promotes genome stability and longevity.
DNA double-strand breaks are the most dangerous DNA lesions that may lead to massive loss of genetic information and cell death. Cells repair DSBs using two major pathways: nonhomologous end joining ...(NHEJ) and homologous recombination (HR). Perturbations of NHEJ and HR are often associated with premature aging and tumorigenesis, hence it is important to have a quantitative way of measuring each DSB repair pathway. Our laboratory has developed fluorescent reporter constructs that allow sensitive and quantitative measurement of NHEJ and HR. The constructs are based on an engineered GFP gene containing recognition sites for a rare-cutting I-SceI endonuclease for induction of DSBs. The starting constructs are GFP negative as the GFP gene is inactivated by an additional exon, or by mutations. Successful repair of the I-SceI-induced breaks by NHEJ or HR restores the functional GFP gene. The number of GFP positive cells counted by flow cytometry provides quantitative measure of NHEJ or HR efficiency.
Mitochondrial defects are implicated in aging and in a multitude of age-related diseases, such as cancer, heart failure, Parkinson's disease, and Huntington's disease. However, it is still unclear ...how mitochondrial defects arise under normal physiological conditions. Mitochondrial DNA (mtDNA) deletions caused by direct repeats (DRs) are implicated in the formation of mitochondrial defects, however, mitochondrial DRs show relatively weak (Pearson's r = -0.22, p<0.002; Spearman's ρ = -0.12, p = 0.1) correlation with maximum lifespan (MLS). Here we report a stronger correlation (Pearson's r = -0.55, p<10(-16); Spearman's ρ = -0.52, p<10(-14)) between mitochondrial inverted repeats (IRs) and lifespan across 202 species of mammals. We show that, in wild type mice under normal conditions, IRs cause inversions, which arise by replication-dependent mechanism. The inversions accumulate with age in the brain and heart. Our data suggest that IR-mediated inversions are more mutagenic than DR-mediated deletions in mtDNA, and impose stronger constraint on lifespan. Our study identifies IR-induced mitochondrial genome instability during mtDNA replication as a potential cause for mitochondrial defects.
Rad51 protein, involved in homologous recombination, is overexpressed in a variety of tumors, and its expression is correlated with a poor prognosis. Here we propose to exploit the overexpression of ...Rad51 in cancer cells to design a Rad51 promoter-based anticancer therapy. On average, Rad51 mRNA and protein levels are increased in cancer cells four- and sixfold, respectively. Serendipitously, we discovered that when the Rad51 ORF is replaced with another ORF, the difference in promoter activity between normal and cancer cells increases to an average of 840-fold with a maximum difference of 12,500-fold. This dramatic difference in activity has high therapeutic potential. We demonstrate that the fusion of Rad51 promoter to diphtheria toxin A (DTA) gene kills a variety of cancer cell types, including breast cancer, fibrosarcoma, and cervical cancer cells, with minimal effect on normal breast epithelial cells and normal fibroblasts. Our results suggest that therapies based on the Rad51 promoter will be highly tumor specific and open new avenues for targeting a broad range of cancers.
Osteoarthritis (OA) is the most prevalent disabling disease, affecting quality of life and contributing to morbidity, particularly during aging. Current treatments for OA are limited to palliation: ...pain management and surgery for end‐stage disease. Innovative approaches and animal models are needed to develop curative treatments for OA. Here, we investigated the naked mole‐rat (NMR) as a potential model of OA resistance. NMR is a small rodent with the maximum lifespan of over 30 years, resistant to a wide range of age‐related diseases. NMR tissues accumulate large quantities of unique, very high molecular weight, hyaluronan (HA). HA is a major component of cartilage and synovial fluid. Importantly, both HA molecular weight and cartilage stiffness decline with age and progression of OA. As increased polymer length is known to result in stiffer material, we hypothesized that NMR high molecular weight HA contributes to stiffer cartilage. Our analysis of biomechanical properties of NMR cartilage revealed that it is significantly stiffer than mouse cartilage. Furthermore, NMR chondrocytes were highly resistant to traumatic damage. In vivo experiments using an injury‐induced model of OA revealed that NMRs were highly resistant to OA. While similarly treated mice developed severe cartilage degeneration, NMRs did not show any signs of OA. Our study shows that NMRs are remarkably resistant to OA, and this resistance is likely conferred by high molecular weight HA. This work suggests that NMR is a useful model to study OA resistance and NMR high molecular weight HA may hold therapeutic potential for OA treatment.
Naked mole‐rats are remarkably resistant to post‐traumatic osteoarthritis. Their cartilage is stiffer than mouse cartilage and better protects chondrocytes from damage. These unique biomechanical properties of the naked mole‐rat cartilage are likely due to abundant high molecular weight hyaluronan present in the naked mole‐rat joints.
The naked mole rat (NMR) is the longest-lived rodent, resistant to multiple age-related diseases including neurodegeneration. However, the mechanisms underlying the NMR’s resistance to ...neurodegenerative diseases remain elusive. Here, we isolated oligodendrocyte progenitor cells (OPCs) from NMRs and compared their transcriptome with that of other mammals. Extracellular matrix (ECM) genes best distinguish OPCs of long- and short-lived species. Notably, expression levels of CD44, an ECM-binding protein that has been suggested to contribute to NMR longevity by mediating the effect of hyaluronan (HA), are not only high in OPCs of long-lived species but also positively correlate with longevity in multiple cell types/tissues. We found that CD44 localizes to the endoplasmic reticulum (ER) and enhances basal ATF6 activity. CD44 modifies proteome and membrane properties of the ER and enhances ER stress resistance in a manner dependent on unfolded protein response regulators without the requirement of HA. HA-independent role of CD44 in proteostasis regulation may contribute to mammalian longevity.
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•CD44 levels correlate with species maximum lifespan in OPCs, liver, skin, and fibroblasts•CD44 enhances basal ATF6 activity and ER stress resistance without the requirement of HA•CD44 localizes to the ER and alters ER proteome and ER membrane properties•CD44-dependent ER stress resistance is mediated by non-canonical activation of ATF6
Through comparative transcriptomics of short- and long-lived mammals, Takasugi et al. identified a correlation between longevity and CD44 levels. CD44 localizes to the ER and enhances basal ATF6 activity and ER stress resistance without HA. This HA-independent role of CD44 in proteostasis regulation may contribute to mammalian longevity.
Long-lived rodents have become an attractive model for the studies on aging. To understand evolutionary paths to long life, we prepare chromosome-level genome assemblies of the two longest-lived ...rodents, Canadian beaver (Castor canadensis) and naked mole rat (NMR, Heterocephalus glaber), which were scaffolded with in vitro proximity ligation and chromosome conformation capture data and complemented with long-read sequencing. Our comparative genomic analyses reveal that amino acid substitutions at “disease-causing” sites are widespread in the rodent genomes and that identical substitutions in long-lived rodents are associated with common adaptive phenotypes, e.g., enhanced resistance to DNA damage and cellular stress. By employing a newly developed substitution model and likelihood ratio test, we find that energy and fatty acid metabolism pathways are enriched for signals of positive selection in both long-lived rodents. Thus, the high-quality genome resource of long-lived rodents can assist in the discovery of genetic factors that control longevity and adaptive evolution.
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•Improved genome assemblies of the naked mole rat and Canadian beaver•Substitutions at disease-causing sites could be adaptive•Unique substitutions in long-lived rodents support stress resistance•Genome resource for studies of long-lived rodents
Zhou et al. generate “chromosome-level” genome assemblies for the Canadian beaver and naked mole rat. They characterize genome features and identify common substitutions in long-lived rodents that support enhanced tolerance of cells to DNA damage. The study also provides a valuable genome resource for aging research.
OBJECTIVES/GOALS: The major objective of this project is two points. First, is to repeat and confirm previous observations that there is elevated cytosolic Line1 DNA in the cytoplasm of cells derived ...from old mice compared to young. Second is to identify which Line1s in the genome are contributing to this free DNA and test if targeting them rescues the age-related phenotype. METHODS/STUDY POPULATION: This project will focus on data collected from both tissues and primary cells derived from multiple tissues. Using cellular/tissue fractionation kits, we isolate specifically from the cytoplasm. This specificity is confirmed by western blotting. Measurement of the Line1 levels is measured by quantitative PCR. Subsequently, these cytoplasmic samples are sent off for sequencing in order to quantify the length of the free DNA in the cytoplasm and to identify which Line1 genomic families the cytosolic DNA originates. Additionally, FISH is utilized to visualize Line1 DNA in the cytoplasm of aged versus young cells RESULTS/ANTICIPATED RESULTS: We anticipate this research to confirm the hypothesis that extranuclear Line1 DNA accumulates with age in both tissues and primary fibroblasts. Additionally, we expect to be able to determine which specific families of genomic Line1 is driving this extranuclear DNA, which would suggest the active retrotransopable elements that are directly involved in this aging related phenotype. Assuming successful identification of such families, we can then target and silence these specific elements to determine not only if cytoplasmic Line1 in aged mice decreases, but additionally if the healthspan and/or lifespan of these mice improves DISCUSSION/SIGNIFICANCE: Dereoressed Line1s have been shown to be involved in detrimental phenotypes, including autoimmune disease, cancer, and inflammaging. Targeting retrotransposons, either directly through degradation of transcriptional product of LINE1s or indirectly by improving function of regulators, will be crucial in ablating aging phenotypes
Descriptions of karyotypes of many animal species are currently available. In addition, there has been a significant increase in the number of sequenced genomes and an ever-improving quality of ...genome assembly. To close the gap between genomic and cytogenetic data we applied fluorescent in situ hybridization (FISH) and Hi-C technology to make the first full chromosome-level genome comparison of the guinea pig (Cavia porcellus), naked mole-rat (Heterocephalus glaber), and human. Comparative chromosome maps obtained by FISH with chromosome-specific probes link genomic scaffolds to individual chromosomes and orient them relative to centromeres and heterochromatic blocks. Hi-C assembly made it possible to close all gaps on the comparative maps and to reveal additional rearrangements that distinguish the karyotypes of the three species. As a result, we integrated the bioinformatic and cytogenetic data and adjusted the previous comparative maps and genome assemblies of the guinea pig, naked mole-rat, and human. Syntenic associations in the two hystricomorphs indicate features of their putative ancestral karyotype. We postulate that the two approaches applied in this study complement one another and provide complete information about the organization of these genomes at the chromosome level.
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