SIRT1 Regulates HIV Transcription via Tat Deacetylation

The human immunodeficiency virus (HIV) Tat protein is acetylated by the transcriptional coactivator p300, a necessary step in Tat-mediated transactivation. We report here that Tat is deacetylated by human sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent class III protein deacetylase in vitro and in vivo. Tat and SIRT1 coimmunoprecipitate and synergistically activate the HIV promoter. Conversely, knockdown of SIRT1 via small interfering RNAs or treatment with a novel small molecule inhibitor of the SIRT1 deacetylase activity inhibit Tat-mediated transactivation of the HIV long terminal repeat. Tat transactivation is defective in SIRT1-null mouse embryonic fibroblasts and can be rescued by expression of SIRT1. These results support a model in which cycles of Tat acetylation and deacetylation regulate HIV transcription. SIRT1 recycles Tat to its unacetylated form and acts as a transcriptional coactivator during Tat transactivation

DNA glycosylases: in DNA repair and beyond

The base excision repair machinery protects DNA in cells from the damaging effects of oxidation, alkylation, and deamination; it is specialized to fix single-base damage in the form of small chemical modifications. Base modifications can be mutagenic and/or cytotoxic, depending on how they interfere with the template function of the DNA during replication and transcription. DNA glycosylases play a key role in the elimination of such DNA lesions; they recognize and excise damaged bases, thereby initiating a repair process that restores the regular DNA structure with high accuracy. All glycosylases share a common mode of action for damage recognition; they flip bases out of the DNA helix into a selective active site pocket, the architecture of which permits a sensitive detection of even minor base irregularities. Within the past few years, it has become clear that nature has exploited this ability to read the chemical structure of DNA bases for purposes other than canonical DNA repair. DNA glycosylases have been brought into context with molecular processes relating to innate and adaptive immunity as well as to the control of DNA methylation and epigenetic stability. Here, we summarize the key structural and mechanistic features of DNA glycosylases with a special focus on the mammalian enzymes, and then review the evidence for the newly emerging biological functions beyond the protection of genome integrity

Rising rural body-mass index is the main driver of the global obesity epidemic in adults

Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities(.)(1,2) This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity(3-6). Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017-and more than 80% in some low- and middle-income regions-was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing-and in some countries reversal-of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.Peer reviewe

Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories: a pooled analysis of 2181 population-based studies with 65 million participants

Summary Background Comparable global data on health and nutrition of school-aged children and adolescents are scarce. We aimed to estimate age trajectories and time trends in mean height and mean body-mass index (BMI), which measures weight gain beyond what is expected from height gain, for school-aged children and adolescents. Methods For this pooled analysis, we used a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. We applied a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5–19 years. The model allowed for non-linear changes over time in mean height and mean BMI and for non-linear changes with age of children and adolescents, including periods of rapid growth during adolescence. Findings We pooled data from 2181 population-based studies, with measurements of height and weight in 65 million participants in 200 countries and territories. In 2019, we estimated a difference of 20 cm or higher in mean height of 19-year-old adolescents between countries with the tallest populations (the Netherlands, Montenegro, Estonia, and Bosnia and Herzegovina for boys; and the Netherlands, Montenegro, Denmark, and Iceland for girls) and those with the shortest populations (Timor-Leste, Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala, Bangladesh, Nepal, and Timor-Leste for girls). In the same year, the difference between the highest mean BMI (in Pacific island countries, Kuwait, Bahrain, The Bahamas, Chile, the USA, and New Zealand for both boys and girls and in South Africa for girls) and lowest mean BMI (in India, Bangladesh, Timor-Leste, Ethiopia, and Chad for boys and girls; and in Japan and Romania for girls) was approximately 9–10 kg/m2. In some countries, children aged 5 years started with healthier height or BMI than the global median and, in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall (eg, boys in Austria and Barbados, and girls in Belgium and Puerto Rico) or gaining too much weight for their height (eg, girls and boys in Kuwait, Bahrain, Fiji, Jamaica, and Mexico; and girls in South Africa and New Zealand). In other countries, growing children overtook the height of their comparators (eg, Latvia, Czech Republic, Morocco, and Iran) or curbed their weight gain (eg, Italy, France, and Croatia) in late childhood and adolescence. When changes in both height and BMI were considered, girls in South Korea, Vietnam, Saudi Arabia, Turkey, and some central Asian countries (eg, Armenia and Azerbaijan), and boys in central and western Europe (eg, Portugal, Denmark, Poland, and Montenegro) had the healthiest changes in anthropometric status over the past 3·5 decades because, compared with children and adolescents in other countries, they had a much larger gain in height than they did in BMI. The unhealthiest changes—gaining too little height, too much weight for their height compared with children in other countries, or both—occurred in many countries in sub-Saharan Africa, New Zealand, and the USA for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls. Interpretation The height and BMI trajectories over age and time of school-aged children and adolescents are highly variable across countries, which indicates heterogeneous nutritional quality and lifelong health advantages and risks

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight NCD Risk Factor Collaboration (NCD-RisC)

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions

A function of thymine DNA glycosylase-initiated DNA repair in maintaining epigenome stability

The Thymine DNA Glycosylase (TDG) was initially discovered by its ability to excise the deamination products of cytosine and 5-methylcytosine (5-mC), and therefore thought to initiate base excision repair (BER) of the resulting G•U and G•T mismatches. Later, TDG was also found to act in concert with transcription factors in the regulation of gene expression. With its apparently two-sided nature, TDG has riddled researchers for many years and the stimuli and interactions that control TDG function are still under investigation. The aim of my thesis was to dissect the role of TDG in DNA repair with a focus on its regulation by post-translational modification, and to investigate how TDG-initiated BER contributes to epigenetic stability at CpG islands (CGIs) during cell differentiation. Both described functions of TDG, in DNA repair and in the regulation of gene expression, require its post-translational modification and non-covalent interaction with the small ubiquitin-like modifiers, SUMO1 and SUMO2/3. Extensive biochemical studies by our laboratory have shown that SUMOylation of TDG may induce its dissociation from the abasic (AP-) site after base excision. However, in vivo evidence corroborating an involvement of SUMOylation in TDG-dependent BER has been pending and the function of non-covalent SUMO-binding has remained elusive. I thus generated a Fluorescence Resonance Energy Transfer (FRET) system to monitor the interaction between TDG and SUMO1 or SUMO3 in cells. I was able to confirm a modulation of the SUMO1-TDG interaction dynamics in response to DNA damage, whereas the interaction with SUMO3 remained unaffected, suggesting that modification by SUMO3 might regulate TDG function in a context other than DNA repair. To investigate the biological function of TDG genetically, we generated a Tdg knockout mouse. In contrast to any other known DNA glycosylase, deletion of Tdg caused embryonic lethality. Further characterization of MEFs isolated from TDG-proficient and -deficient embryos revealed no evidence for a DNA repair defect, but a significant number of misregulated genes in differentiated Tdg-/- cells, as well as a loss of active histone marks, gain of repressive histone modifications and an accumulation of 5-mC at CGI promoters. A phenotype we did not observe in embryonic stem cells. From these data, we proposed a dual function of TDG in maintaining active chromatin states at promoters in differentiating cells, first by structurally coordinating histone modifying enzymes and second by counteracting errors of the DNA methylation machinery by initiating repair of aberrantly methylated cytosines in CGIs. Consistent with a TDG-dependent engagement of DNA repair at such sites, we found BER factors to associate with these promoters and DNA repair intermediates to accumulate in differentiating cells in a TDG dependent manner. To investigate further how TDG is involved in DNA methylation control, we mapped DNA methylation in the genomes of TDG-proficient and -deficient mouse embryonic stem cells (ESCs), neuronal progenitor cells (NPs) and MEFs and found differential methylation to arise only with differentiation. Further characterization of the resulting differentially methylated regions (DMRs) revealed that those overlapping with a CGI were almost exclusively hypomethylated in TDG-deficient compared to -proficient cells, reflecting a failure to establish methylation at these CGIs during differentiation. In search of the reason for this failure in a 24 h differentiation timecourse, we found global 5-mC levels to rise with differentiation in cells lacking TDG activity, in parallel to the generation of the final products of TET-protein catalyzed 5-mC oxidation, 5-formylcytosine (5-fC) and 5-carboxylcytosine (5- caC), the latter two of which are proposed intermediates of active DNA demethylation and substrates for TDG. Differentiation thus appeared to induce methylation but also the intermediates of active demethylation. We therefore analyzed 5-mC and 5-caC levels at the CGI DMRs and found both to rise with differentiation in wildtype cells, suggesting that the loss of pluripotency induces a cycle of DNA methylation and demethylation specific CGIs. In Tdg knockout cells, though, this induction appeared to fail whereas in cells expressing a catalytically dead mutant TDG (TDG-cat), the cycle of methylation and demethylation was induced but blocked by the inability of TDG-cat to excise 5-caC. Taken together, in collaboration with colleagues from different laboratories I was able to show that differentiation triggers a state of high epigenetic plasticity at these CGIs and that catalytically active TDG is required to maintain an equilibrium of DNA methylation and demethylation. The imbalance of epigenetic marks resulting from knockout of TDG disrupts gene expression programs and the accumulation of aberrations eventually leads to loss of viability on the cellular and on the organismic level

Technical standards in allergen exposure chambers worldwide – an EAACI Task Force Report

Allergen exposure chambers (AECs) can be used for controlled exposure to allergenic and non-allergenic airborne particles in an enclosed environment, in order to (i) characterize the pathological features of respiratory diseases and (ii) contribute to and accelerate the clinical development of pharmacological treatments and allergen immunotherapy for allergic disease of the respiratory tract (such as allergic rhinitis, allergic rhinoconjunctivitis, and allergic asthma). In the guidelines of the European Medicines Agency for the clinical development of products for allergen immunotherapy (AIT), the role of AECs in determining primary endpoints in dose-finding Phase II trials is emphasized. Although methodologically insulated from the variability of natural pollen exposure, chamber models remain confined to supporting secondary, rather than primary, endpoints in Phase III registration trials. The need for further validation in comparison with field exposure is clearly mandated. On this basis, the European Academy of Allergy and Clinical Immunology (EAACI) initiated a Task Force in 2015 charged to gain a better understanding of how AECs can generate knowledge about respiratory allergies and can contribute to the clinical development of treatments. Researchers working with AECs worldwide were asked to provide technical information in eight sections: (i) dimensions and structure of the AEC, (ii) AEC staff, (iii) airflow, air processing, and operating conditions, (iv) particle dispersal, (v) pollen/particle counting, (vi) safety and non-contamination measures, (vii) procedures for symptom assessments, (viii) tested allergens/substances and validation procedures. On this basis, a minimal set of technical requirements for AECs applied to the field of allergology is proposed