Pro and Anti-Mutagenic Function of DNA Damage Tolerance in the Mammalian System

The origin of cancer lies in the genetic code (DNA) and in the cell's (in) ability to keep this error-free. Due to influences from both outside and inside the body, the genetic code of cells can be damaged, and many processes have evolved to repair this damage. Unfortunately, these processes can make mistakes, leaving mutations in the DNA. As the DNA acts as a blueprint (genes) for how the cells should operate and how the machinery of the cells should be made, these mutations can cause disruptions in this process. When mutations happen in genes that are responsible for regulating cell duplication, the cell can lose control of this process. This causes rapid division of these cells, often leading to more mistakes being made and further dysregulating cell division. Finally, this deregulated cell growth can lead to the formation of cancer. Besides the prevention of DNA damage, the best way for a cell to avert turning cancerous is the accurate repair of the damage. The pathways responsible for this are complex, and many questions remain about their exact mode of operation, which proteins are involved, how they are initialized, processed, and what the consequences are. Knowing how these processes work will push forward our understanding of both basic biology, tumorigenesis and benefit cancer therapy with DNA damaging agents. Many of the classical chemotherapeutics work on the principle that tumor cells divide rapidly and that the DNA repair pathways are compromised. By introducing a high amount of DNA damage, these cells will not be able to repair the damage in time and die, while normal cells have more time and are better equipped to remove the damage. By gaining a better understanding of the repair processes, different specific inhibitors or types of damage can be applied to combat cancer more effectively. In this thesis, we investigate a specific activity within the DNA damage response network that prevents the detrimental effect of DNA lesions predominantly during replication. This system, known as DNA damage tolerance (DDT) consists of several pathways. Instead of repairing the damage, DDT tolerates DNA lesions allowing cells to continue DNA replication in the presence of DNA lesions and repair the damage later. We used genetic manipulation to mutate and remove genes to prevent specific DDT pathways from functioning. By studying the consequences of the removal of these pathways on genomic, cellular, and organism levels, we aimed to gather mechanistic insights into the regulation and activities of these specific DDT pathways

The Harris hip score: Do ceiling effects limit its usefulness in orthopedics?: A systematic review

The Harris hip score (HHS), a disease-specific health status scale that is frequently used to measure the outcome of total hip arthroplasty, has never been validated properly. A questionnaire is suitable only when all 5 psychometric properties are of sufficient quality. We questioned the usefulness of the HHS by investigating its content validity. We performed a systematic review based on a literature search in PubMed, Embase, and the Cochrane Library for descriptive studies published in 2007. 54 studies (59 patient groups) met our criteria and were included in the data analysis. To determine the content validity, we calculated the ceiling effect (percentage) for each separate study and we pooled data to measure the weighted mean. A subanalysis of indications for THA was performed to differentiate the populations for which the HHS would be suitable and for which it would not. A ceiling effect of 15% or less was considered to be acceptable. Over half the studies (31/59) revealed unacceptable ceiling effects. Pooled data across the studies included (n = 6,667 patients) suggested ceiling effects of 20% (95%CI: 18-22). Ceiling effects were greater (32%, 95%CI:12-52) in those patients undergoing hip resurfacing arthroplasty. Although the Harris hip score is widely used in arthroplasty research on outcomes, ceiling effects are common and these severely limit its validity in this field of researc

Spatiotemporal regulation of clonogenicity in colorectal cancer xenografts

Cancer evolution is predominantly studied by focusing on differences in the genetic characteristics of malignant cells within tumors. However, the spatiotemporal dynamics of clonal outgrowth that underlie evolutionary trajectories remain largely unresolved. Here, we sought to unravel the clonal dynamics of colorectal cancer (CRC) expansion in space and time by using a color-based clonal tracing method. This method involves lentiviral red-green-blue (RGB) marking of cell populations, which enabled us to track individual cells and their clonal outgrowth during tumor initiation and growth in a xenograft model. We found that clonal expansion largely depends on the location of a clone, as small clones reside in the center and large clones mostly drive tumor growth at the border. These dynamics are recapitulated in a computational model, which confirms that the clone position within a tumor rather than cell-intrinsic features, is crucial for clonal outgrowth. We also found that no significant clonal loss occurs during tumor growth and clonal dispersal is limited in most models. Our results imply that, in addition to molecular features of clones such as (epi-)genetic differences between cells, clone location and the geometry of tumor growth are crucial for clonal expansion. Our findings suggest that either microenvironmental signals on the tumor border or differences in physical properties within the tumor, are major contributors to explain heterogeneous clonal expansion. Thus, this study provides further insights into the dynamics of solid tumor growth and progression, as well as the origins of tumor cell heterogeneity in a relevant model system

DNA damage-induced PARP1 activation confers cardiomyocyte dysfunction through NAD(+) depletion in experimental atrial fibrillation

Atrial fibrillation (AF) is the most common clinical tachyarrhythmia with a strong tendency to progress in time. AF progression is driven by derailment of protein homeostasis, which ultimately causes contractile dysfunction of the atria. Here we report that tachypacing-induced functional loss of atrial cardiomyocytes is precipitated by excessive poly(ADP)-ribose polymerase 1 (PARP1) activation in response to oxidative DNA damage. PARP1-mediated synthesis of ADP-ribose chains in turn depletes nicotinamide adenine dinucleotide (NAD+), induces further DNA damage and contractile dysfunction. Accordingly, NAD+ replenishment or PARP1 depletion precludes functional loss. Moreover, inhibition of PARP1 protects against tachypacing-induced NAD+ depletion, oxidative stress, DNA damage and contractile dysfunction in atrial cardiomyocytes and Drosophila. Consistently, cardiomyocytes of persistent AF patients show significant DNA damage, which correlates with PARP1 activity. The findings uncover a mechanism by which tachypacing impairs cardiomyocyte function and implicates PARP1 as a possible therapeutic target that may preserve cardiomyocyte function in clinical AF

Mammalian life depends on two distinct pathways of DNA damage tolerance

DNA damage threatens genomic integrity and instigates stem cell failure. To bypass genotoxic lesions during replication, cells employ DNA damage tolerance (DDT), which is regulated via PCNA ubiquitination and REV1. DDT is conserved in all domains of life, yet its relevance in mammals remains unclear. Here, we show that inactivation of both PCNA-ubiquitination and REV1 results in embryonic and adult lethality, and the accumulation of DNA damage in hematopoietic stem and progenitor cells (HSPCs) that ultimately resulted in their depletion. Our results reveal the crucial relevance of DDT in the maintenance of stem cell compartments and mammalian life in unperturbed conditions

STARD 2015: An Updated List of Essential Items for Reporting Diagnostic Accuracy Studies.

Incomplete reporting has been identified as a major source of avoidable waste in biomedical research. Essential information is often not provided in study reports, impeding the identification, critical appraisal, and replication of studies. To improve the quality of reporting of diagnostic accuracy studies, the Standards for Reporting of Diagnostic Accuracy Studies (STARD) statement was developed. Here we present STARD 2015, an updated list of 30 essential items that should be included in every report of a diagnostic accuracy study. This update incorporates recent evidence about sources of bias and variability in diagnostic accuracy and is intended to facilitate the use of STARD. As such, STARD 2015 may help to improve completeness and transparency in reporting of diagnostic accuracy studies

The effects of COVID-19 on child mental health: Biannual assessments up to April 2022 in a clinical and two general population samples

BACKGROUND: The COVID-19 pandemic has had an acute impact on child mental and social health, but long-term effects are still unclear. We examined how child mental health has developed since the start of the COVID-19 pandemic up to 2 years into the pandemic (April 2022). METHODS: We included children (age 8-18) from two general population samples ( N = 222-1333 per measurement and N = 2401-13,362 for pre-covid data) and one clinical sample receiving psychiatric care ( N = 334-748). Behavioral questionnaire data were assessed five times from April 2020 till April 2022 and pre-pandemic data were available for both general population samples. We collected parent-reported data on internalizing and externalizing problems with the Brief Problem Monitor and self-reported data on Anxiety, Depressive symptoms, Sleep-related impairments, Anger, Global health, and Peer relations with the Patient-Reported Outcomes Measurement Information System (PROMIS®). RESULTS: In all samples, parents reported overall increased internalizing problems, but no increases in externalizing problems, in their children. Children from the general population self-reported increased mental health problems from before to during the pandemic on all six PROMIS domains, with generally worst scores in April 2021, and scores improving toward April 2022 but not to pre-pandemic norms. Children from the clinical sample reported increased mental health problems throughout the pandemic, with generally worst scores in April 2021 or April 2022 and no improvement. We found evidence of minor age effects and no sex effects. CONCLUSIONS: Child mental health in the general population has deteriorated during the first phase of the COVID-19 pandemic, has improved since April 2021, but has not yet returned to pre-pandemic levels. Children in psychiatric care show worsening of mental health problems during the pandemic, which has not improved since. Changes in child mental health should be monitored comprehensively to inform health care and policy

Appropriateness, Reasons and Independent Predictors of Consultations in the Emergency Department (ED) of a Dutch Tertiary Care Center: A Prospective Cohort Study.

OBJECTIVE:Consultations occur frequently in the emergency department (ED) of tertiary care centres and pose a threat for patient safety as they contribute to ED lengths of stay (LOS) and overcrowding. The aim of this study was to investigate reasons and appropriateness of consultations, and the relative impact of specialty and patient characteristics on the probability of a consultation, because this could help to improve efficiency of ED patient care. METHODS:This prospective cohort study included ED patients presenting to a Dutch tertiary care centre in a setting where ED physicians mostly treat self-referred and undifferentiated patients and other specialists treat referred patients. Consultations were defined as appropriate if the reason of consultation corresponded with the final advice, conclusion or policy of the consulted specialty. Multivariable logistic regression analysis was used to assess the relative contribution of specialty and patient characteristics on consultation. RESULTS:In the 344 (24% (95% CI 22 to 26%)) of the 1434 inclusions another specialty was consulted, resulting in a 55% increase of ED LOS. ED physicians more often consulted another specialty with a corrected odds ratio (OR) of 5.6 (4.0 to 7.8), mostly because consultations were mandatory in case of hospitalization or outpatient follow-up. Limited expertise of ED physicians was the reason for consultation in 7% (5 to 9%). The appropriateness of consultations was 84% (81 to 88%), similar between ED physicians and other specialists (P = 0.949). The patient characteristics age, comorbidity, and triage category and complaint predicted consultation. CONCLUSION:In a Dutch tertiary care centre another specialty was consulted in 24% of the patients, mostly for an appropriate reason, and rarely because of lack of expertise. The impact of consultations on ED LOS could be reduced if mandatory consultations are abolished and predictors of a consultation are used to facilitate timely consultation