Naked mole rats (NMRs) are the longest‐lived rodents yet their stem cell characteristics remain enigmatic. Here, we comprehensively mapped the NMR hematopoietic landscape and identified unique ...features likely contributing to longevity. Adult NMRs form red blood cells in spleen and marrow, which comprise a myeloid bias toward granulopoiesis together with decreased B‐lymphopoiesis. Remarkably, youthful blood and marrow single‐cell transcriptomes and cell compositions are largely maintained until at least middle age. Similar to primates, the primitive stem and progenitor cell (HSPC) compartment is marked by CD34 and THY1. Stem cell polarity is seen for Tubulin but not CDC42, and is not lost until 12 years of age. HSPC respiration rates are as low as in purified human stem cells, in concert with a strong expression signature for fatty acid metabolism. The pool of quiescent stem cells is higher than in mice, and the cell cycle of hematopoietic cells is prolonged. By characterizing the NMR hematopoietic landscape, we identified resilience phenotypes such as an increased quiescent HSPC compartment, absence of age‐related decline, and neotenic traits likely geared toward longevity.
Synopsis
Naked mole‐rats are the longest‐lived rodents but their hematopoietic system and contained self‐renewing stem cell populations remain poorly characterized. Combining surface marker and sequencing analysis, this resource reports the first comprehensive map of the naked mole‐rat blood system, uncovering similarities to their human counterpart during ageing.
A cross‐reactive FACS antibody panel allows for purification of naked mole‐rat stem, progenitor and effector cells from blood, spleen and bone marrow.
Red blood cells are produced in both bone marrow and spleen, exemplifying a neotenic trait.
Enlargement of the myeloid compartment and concomitantly reduced B‐lymphopoiesis in the bone marrow resemble fetal stages of white blood cell production.
CD34 marks the primitive stem and progenitor compartment, similar as in humans.
An enlarged quiescent stem cell pool preserves hematopoiesis during an extended lifespan.
Stem and progenitor cells feature a prolonged cell cycle in vivo, with a low metabolic profile and elevated lipid metabolism.
In‐depth profiling of the naked mole‐rat hematopoietic system by surface marker analysis and single‐cell sequencing uncovers resilience phenotypes and unexpected similarities with humans.
The accumulation of damage caused by oxidative stress has been linked to aging and to the etiology of numerous age-related diseases. The longevity gene, sirtuin 6 (SIRT6), promotes genome stability ...by facilitating DNA repair, especially under oxidative stress conditions. Here we uncover the mechanism by which SIRT6 is activated by oxidative stress to promote DNA double-strand break (DSB) repair. We show that the stress-activated protein kinase, c-Jun N-terminal kinase (JNK), phosphorylates SIRT6 on serine 10 in response to oxidative stress. This post-translational modification facilitates the mobilization of SIRT6 to DNA damage sites and is required for efficient recruitment of poly (ADP-ribose) polymerase 1 (PARP1) to DNA break sites and for efficient repair of DSBs. Our results demonstrate a post-translational mechanism regulating SIRT6, and they provide the link between oxidative stress signaling and DNA repair pathways that may be critical for hormetic response and longevity assurance.
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•JNK phosphorylates SIRT6 at residue S10 in response to oxidative stress•SIRT6 S10 phosphorylation is required for the stimulation of DNA break repair•SIRT6 S10 phosphorylation stimulates SIRT6 mono-ADP ribosylation activity on PARP1
Van Meter et al. show that SIRT6 is phosphorylated by JNK on serine 10 in response to oxidative stress. SIRT6 S10 phosphorylation promotes DNA break repair by stimulating SIRT6 and PARP1 recruitment to DNA break sites.
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.
Background
In TAGS, an international, double-blind, phase 3 trial, trifluridine/tipiracil significantly improved overall survival and progression-free survival compared with placebo in heavily ...pretreated metastatic gastric cancer patients. This paper reports pre-specified quality of life (QoL) outcomes for TAGS.
Methods
Patients were randomized 2:1 to trifluridine/tipiracil (35 mg/m
2
twice daily on days 1–5 and 8–12 of each 28-day cycle) plus best supportive care (BSC) or placebo plus BSC. QoL was evaluated at baseline and at each treatment cycle, using the EORTC QLQ-C30 and EORTC QLQ-STO22 questionnaires; results were considered valid for analysis only if ≥ 10% of patients completed the questionnaires. Key QoL outcomes were mean changes from baseline and time to deterioration in QoL. A post hoc analysis assessed the association between QoL and time to deterioration of Eastern Cooperative Oncology Group performance score (ECOG PS) to ≥ 2.
Results
Of 507 randomized patients, 496 had baseline QoL data available. The analysis cut-off was 6 cycles for trifluridine/tipiracil and 3 cycles for placebo. In both treatment groups, there were no clinically significant deteriorations in the mean QLQ-C30 Global Health Status (GHS) score, or in most subscale scores. In a sensitivity analysis including death and disease progression as events, there was a trend towards trifluridine/tipiracil reducing the risk of deterioration of QoL scores compared with placebo. Deterioration in the GHS score was associated with deterioration in ECOG PS.
Conclusion
QoL was maintained in TAGS, and there was a trend towards trifluridine/tipiracil reducing the risk of QoL deterioration compared with placebo.
Trial registration
ClinicalTrials.gov number: NCT02500043
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.
Persistent DNA damage triggers cellular senescence, which may play an important role in the pathogenesis of cigarette smoke (CS)-induced lung diseases. Both p21(CDKN1A) (p21) and poly(ADP-ribose) ...polymerase-1 (PARP-1) are involved in DNA damage and repair. However, the role of p21-PARP-1 axis in regulating CS-induced lung DNA damage and cellular senescence remains unknown. We hypothesized that CS causes DNA damage and cellular senescence through a p21-PARP-1 axis. To test this hypothesis, we determined the levels of γH2AX (a marker for DNA double-strand breaks) as well as non-homologous end joining proteins (Ku70 and Ku80) in lungs of mice exposed to CS. We found that the level of γH2AX was increased, whereas the level of Ku70 was reduced in lungs of CS-exposed mice. Furthermore, p21 deletion reduced the level of γH2AX, but augmented the levels of Ku70, Ku80, and PAR in lungs by CS. Administration of PARP-1 inhibitor 3-aminobenzamide increased CS-induced DNA damage, but lowered the levels of Ku70 and Ku80, in lungs of p21 knockout mice. Moreover, 3-aminobenzamide increased senescence-associated β-galactosidase activity, but decreased the expression of proliferating cell nuclear antigen in mouse lungs in response to CS. Interestingly, 3-aminobenzamide treatment had no effect on neutrophil influx into bronchoalveolar lavage fluid by CS. These results demonstrate that the p21-PARP-1 pathway is involved in CS-induced DNA damage and cellular senescence.
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.
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