Mice deficient for SIRT6 exhibit a severely shortened lifespan, growth retardation, and highly elevated LINE1 (L1) activity. Here we report that SIRT6-deficient cells and tissues accumulate abundant ...cytoplasmic L1 cDNA, which triggers strong type I interferon response via activation of cGAS. Remarkably, nucleoside reverse-transcriptase inhibitors (NRTIs), which inhibit L1 retrotransposition, significantly improved health and lifespan of SIRT6 knockout mice and completely rescued type I interferon response. In tissue culture, inhibition of L1 with siRNA or NRTIs abrogated type I interferon response, in addition to a significant reduction of DNA damage markers. These results indicate that L1 activation contributes to the pathologies of SIRT6 knockout mice. Similarly, L1 transcription, cytoplasmic cDNA copy number, and type I interferons were elevated in the wild-type aged mice. As sterile inflammation is a hallmark of aging, we propose that modulating L1 activity may be an important strategy for attenuating age-related pathologies.
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•SIRT6 KO mice accumulate L1 cDNA, triggering interferon response via cGAS pathway•Wild-type aged mice accumulate L1 cDNA and display type I interferon response•Reverse-transcriptase inhibitors rescue type I interferon response and DNA damage•Reverse-transcriptase inhibitors extend lifespan and improve health of SIRT6 KO mice
Simon et al. show that LINE1 retrotransposon elements are derepressed in aged and progeroid mice. Cytoplasmic accumulation of LINE1 cDNA copies induced a type I interferon response, through the cGAS DNA sensing pathway, resulting in pathological inflammation. Inhibiting L1 replication significantly improved the health and lifespan of aged mice.
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.
Sirtuin 6 (SIRT6) is a mammalian homolog of the yeast Sir2 deacetylase. Mice deficient for SIRT6 exhibit genome instability. Here, we show that in mammalian cells subjected to oxidative stress SIRT6 ...is recruited to the sites of DNA double-strand breaks (DSBs) and stimulates DSB repair, through both nonhomologous end joining and homologous recombination. Our results indicate that SIRT6 physically associates with polyadenosine diphosphate (ADP)—ribose polymerase 1 (PARP1) and mono-ADP-ribosylates PARP1 on lysine residue 521, thereby stimulating PARP1 poly-ADP-ribosylase activity and enhancing DSB repair under oxidative stress.
Genomic instability is a hallmark of aging tissues. Genomic instability may arise from the inefficient or aberrant function of DNA double-stranded break (DSB) repair. DSBs are repaired by homologous ...recombination (HR) and nonhomologous DNA end joining (NHEJ). HR is a precise pathway, whereas NHEJ frequently leads to deletions or insertions at the repair site. Here, we used normal human fibroblasts with a chromosomally integrated HR reporter cassette to examine the changes in HR efficiency as cells progress to replicative senescence. We show that HR declines sharply with increasing replicative age, with an up to 38-fold decrease in efficiency in presenescent cells relative to young cells. This decline is not explained by a reduction of the number of cells in S/G ₂/M stage as presenescent cells are actively dividing. Expression of proteins involved in HR such as Rad51, Rad51C, Rad52, NBS1, and Sirtuin 6 (SIRT6) diminished with cellular senescence. Supplementation of Rad51, Rad51C, Rad52, and NBS1 proteins, either individually or in combination, did not rescue the senescence-related decline of HR. However, overexpression of SIRT6 in “middle-aged” and presenescent cells strongly stimulated HR repair, and this effect was dependent on mono-ADP ribosylation activity of poly(ADP-ribose) polymerase (PARP1). These results suggest that in aging cells, the precise HR pathway becomes repressed giving way to a more error-prone NHEJ pathway. These changes in the processing of DSBs may contribute to age-related genomic instability and a higher incidence of cancer with age. SIRT6 activation provides a potential therapeutic strategy to prevent the decline in genome maintenance.
Interest is growing in specialty-specific assessments of student candidates based on clinical clerkship performance to assist in the selection process for postgraduate training. The most established ...and extensively used is the emergency medicine (EM) Standardized Letter of Evaluation (SLOE), serving as a substitute for the letter of recommendation. Typically developed by a program's leadership, the group SLOE strives to provide a unified institutional perspective on performance. The group SLOE lacks guidelines to direct its development raising questions regarding the assessments, processes, and standardization programs employ. This study surveys EM programs to gather validity evidence regarding the inputs and processes involved in developing group SLOEs.
A structured telephone interview was administered to assess the input data and processes employed by United States EM programs when generating group SLOEs.
With 156/178 (87.6%) of Accreditation Council of Graduate Medical Education-approved programs responding, 146 (93.6%) reported developing group SLOEs. Issues identified in development include the following: (1) 84.9% (124/146) of programs limit the consensus process by not employing rigorous methodology; (2) several stakeholder groups (nurses, patients) do not participate in candidate assessment placing final decisions at risk for construct under-representation; and (3) clinical shift assessments don't reflect the task-specific expertise of each stakeholder group nor has the validity of each been assessed.
Success of the group SLOE in its role as a summative workplace-based assessment is dependent upon valid input data and appropriate processes. This study of current program practices provides specific recommendations that would strengthen the validity arguments for the group SLOE.
Emerging evidence suggests that Sirtuin 6 (SIRT6) functions as a longevity assurance gene by promoting genomic stability, regulating metabolic processes and attenuating inflammation. Here, we examine ...the effect of SIRT6 activation on cancer cells. We show that SIRT6 overexpression induces massive apoptosis in a variety of cancer cell lines but not in normal, non-transformed cells. This cell death requires the mono-ADP-ribosyltransferase but not the deacetylase activity of SIRT6 and is mediated by the activation of both the p53 and p73 apoptotic signaling cascades in cancer cells by SIRT6. These results suggest that SIRT6 is an attractive target for pharmacological activation in cancer treatment.
Sirtuin 6 (SIRT6) is a deacylase and mono‐ADP ribosyl transferase (mADPr) enzyme involved in multiple cellular pathways implicated in aging and metabolism regulation. Targeted sequencing of SIRT6 ...locus in a population of 450 Ashkenazi Jewish (AJ) centenarians and 550 AJ individuals without a family history of exceptional longevity identified enrichment of a SIRT6 allele containing two linked substitutions (N308K/A313S) in centenarians compared with AJ control individuals. Characterization of this SIRT6 allele (centSIRT6) demonstrated it to be a stronger suppressor of LINE1 retrotransposons, confer enhanced stimulation of DNA double‐strand break repair, and more robustly kill cancer cells compared with wild‐type SIRT6. Surprisingly, centSIRT6 displayed weaker deacetylase activity, but stronger mADPr activity, over a range of NAD+ concentrations and substrates. Additionally, centSIRT6 displayed a stronger interaction with Lamin A/C (LMNA), which was correlated with enhanced ribosylation of LMNA. Our results suggest that enhanced SIRT6 function contributes to human longevity by improving genome maintenance via increased mADPr activity and enhanced interaction with LMNA.
Synopsis
Two linked missense mutations in the C‐terminus of SIRT6 are enriched in human centenarians. The centenarian SIRT6 allele confers improved genome maintenance including DNA repair and LINE1 retrotransposon silencing.
Two linked missense mutations in the C‐terminus of SIRT6 are enriched in human centenarians and in people older than 75.
A centenarian allele of SIRT6 has reduced deacetylase/enhanced ribosylase activity compared to wild‐type SIRT6.
The centenarian SIRT6 allele enhances genome maintenance, including more efficient DNA double strand break repair and LINE1 retrotransposon suppression.
The centenarian SIRT6 associates more strongly with Lamin A.
A variant of SIRT6 is enriched in human centenarians that show enhanced mono‐ADP ribosylase activity, but a reduced deacetylase activity; leading to the generation of an allele that promotes enhanced DNA repair, suppression of transposable elements, and resistance to oxidative stress.
Abstract Background Emergency medicine (EM) residency programs use nonstandardized criteria to create applicant rank lists. One implicit assumption is that predictive associations exist between an ...applicant's rank and their future performance as a resident. To date, these associations have not been sufficiently demonstrated. Objectives We hypothesized that a strong positive correlation exists between the National Resident Match Program (NRMP) match-list applicant rank, the United States Medical Licensing Examination (USMLE) Step 1 and In-Training Examination (ITE) scores, and the graduating resident rank. Methods A total of 286 residents from five EM programs over a 5-year period were studied. The applicant rank (AR) was derived from the applicant's relative rank list position on each programs' submitted NRMP rank list. The graduation rank (GR) was determined by a faculty consensus committee. GR was then correlated to AR using a Spearman's partial rank correlation. Additional correlations were sought with a ranking of the USMLE Step Score (UR) and the ITE Score (IR). Results Combining data for all five programs, weak positive correlations existed between GR and AR, UR, and IR. The majority of correlations ranged between. When comparing GR and AR, there was a weak correlation of 0.13 ( p = 0.03). Conclusion Our study found only weak correlations between GR and AR, UR, and IR, suggesting that those variables may not be strong predictors of resident performance. This has important implications for EM programs considering the resources devoted to applicant evaluation and ranking.
T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic cancer derived from the malignant transformation of T-cell progenitors. Outcomes remain poor for T-ALL patients who have ...either primary resistance to standard-of-care chemotherapy or disease relapse. Notably, there are currently no targeted therapies available in T-ALL. This lack of next-generation therapies highlights the need for relevant preclinical disease modeling to identify and validate new targets and treatment approaches. Here, we adapted a spontaneously arising, genetically heterogeneous, thymic transplantation-based murine model of T-ALL, recapitulating key histopathological and genetic features of the human disease, to the preclinical testing of targeted and immune-directed therapies. Genetic engineering of the murine
locus aligned the spectrum of
mutations in the mouse model to that of human T-ALL and confirmed aberrant, recombination-activating gene (RAG)-mediated 5'
recombination events as the preferred pathway in murine T-ALL development. Testing of Notch1-targeting therapeutic antibodies demonstrated T-ALL sensitivity to different classes of Notch1 blockers based on Notch1 mutational status. In contrast, genetic ablation of Notch3 did not impact T-ALL development. The T-ALL model was further applied to the testing of immunotherapeutic agents in fully immunocompetent, syngeneic mice. In line with recent clinical experience in T-cell malignancies, programmed cell death 1 (PD-1) blockade alone lacked anti-tumor activity against murine T-ALL tumors. Overall, the unique features of the spontaneous T-ALL model coupled with genetic manipulations and the application to therapeutic testing in immunocompetent backgrounds will be of great utility for the preclinical evaluation of novel therapies against T-ALL.
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