RRM1 variants cause a mitochondrial DNA maintenance disorder via impaired de novo nucleotide synthesis

Genetic diseases; Mitochondria; Molecular pathologyEnfermedades genéticas; Mitocondrias; Patología molecularMalalties genètiques; Mitocondris; Patologia molecularMitochondrial DNA (mtDNA) depletion/deletions syndromes (MDDS) encompass a clinically and etiologically heterogenous group of mitochondrial disorders caused by impaired mtDNA maintenance. Among the most frequent causes of MDDS are defects in nucleoside/nucleotide metabolism, which is critical for synthesis and homeostasis of the deoxynucleoside triphosphate (dNTP) substrates of mtDNA replication. A central enzyme for generating dNTPs is ribonucleotide reductase, a critical mediator of de novo nucleotide synthesis composed of catalytic RRM1 subunits in complex with RRM2 or p53R2. Here, we report 5 probands from 4 families who presented with ptosis and ophthalmoplegia as well as other clinical manifestations and multiple mtDNA deletions in muscle. We identified 3 RRM1 loss-of-function variants, including a dominant catalytic site variant (NP_001024.1: p.N427K) and 2 homozygous recessive variants at p.R381, which has evolutionarily conserved interactions with the specificity site. Atomistic molecular dynamics simulations indicate mechanisms by which RRM1 variants affect protein structure. Cultured primary skin fibroblasts of probands manifested mtDNA depletion under cycling conditions, indicating impaired de novo nucleotide synthesis. Fibroblasts also exhibited aberrant nucleoside diphosphate and dNTP pools and mtDNA ribonucleotide incorporation. Our data reveal that primary RRM1 deficiency and, by extension, impaired de novo nucleotide synthesis are causes of MDDS.This work was supported by Department of Defense Focused Program Award W81XWH2010807 (to MH), NIH research grant P01 HD32062 (to MH), and NIH grant 35 GM139453 (to JF). MH is supported by the Arturo Estopinan TK2 Research Fund, Nicholas Nunno Foundation, JDM Fund for Mitochondrial Research, Shuman Mitochondrial Disease Fund, the Marriott Mitochondrial Disease Clinic Research Fund from the J. Willard and Alice S. Marriott Foundation, and NIH grant U54 NS078059. Work in Newcastle upon Tyne was supported by the Wellcome Centre for Mitochondrial Research (203105/Z/16/Z), Medical Research Council International Centre for Genomic Medicine in Neuromuscular Disease (MR/S005021/1), UK NIHR Biomedical Research Centre in Age and Age Related Diseases award to the Newcastle upon Tyne Hospitals NHS Foundation, the Lily Foundation, and the UK National Health Service Highly Specialised Service for Rare Mitochondrial Disorders. RWT receives financial support from the Pathological Society. EWS was funded by a Medical Research Council PhD studentship. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant ACI-1548562. JBGC is supported by grant BIO210070 from XSEDE. The authors thank the patients and their families for collaborating in this study and Saba Tadesse for technical support of mitochondrial respiratory chain enzyme activities. We also thank the Genome Technology Center at the Radboud University Medical Center and BGI Copenhagen for WES technical support

Association between serum ferritin and osteocalcin as a potential mechanism explaining the iron-induced insulin resistance

Background Increased iron stores are associated with increased risk of type 2 diabetes, however, the mechanisms underlying these associations are poorly understood. Because a reduction of circulating osteocalcin levels after iron overload have been demonstrated in cell cultures, and osteocalcin is related to glucose and insulin metabolism, the iron-induced osteocalcin reductions could contribute to explain the role of iron metabolism in the development of type 2 diabetes mellitus. Objective To analyzed the associations between serum total and uncarboxylated osteocalcin and adiponectin concentrations with serum ferritin and soluble transferrin receptor (sTfR) in elderly subjects. Design We evaluated a total of 423 subjects from the PREDIMED cohort in a population-based cross-sectional analysis. Extensive clinical, nutritional and laboratory measurements, including total and uncarboxylated osteocalcin, adiponectin, ferritin and sTfR were recorded. Results Serum ferritin was positively correlated with increased glucose and insulin circulating levels but also with HOMA-IR, and was inversely associated with total osteocalcin and adiponectin. A regression analysis revealed that serum ferritin and transferrin receptor levels were significantly associated with a decrease in total and uncarboxylated osteocalcin. Serum sTfR levels were associated with lower uncarboxylated osteocalcin levels in the whole-study subjects and remained significant only in the IFG (impaired fasting glucose) individuals. Conclusions We described, for the first time, an inverse association between serum ferritin and sTfR with osteocalcin and extend previous results on adiponectin, thus supporting that factors related to iron metabolism could contribute to the insulin resistance and the development of type 2 diabetes mellitus

Three-dimensional analysis of mitochondrial crista ultrastructure in a Leigh Syndrome patient by in situ cryo-electron tomography

Mitochondrial diseases produce profound neurological dysfunction via mutations affecting mitochondrial energy production, including the relatively common Leigh Syndrome (LS). We recently described an LS case caused by a pathogenic mutation in USMG5, encoding a small supernumerary subunit of mitochondrial ATP synthase. This protein is integral for ATP synthase dimerization, and patient fibroblasts revealed an almost total loss of ATP synthase dimers. Here, we utilize in situ cryo-electron tomography (cryo-ET) in a clinical case-control study of mitochondrial disease to directly study mitochondria within cultured fibroblasts from an LS patient and a healthy human control subject. Through tomographic analysis of patient and control mitochondria, we find that loss of ATP synthase dimerization caused by the pathogenic mutation causes profound disturbances of mitochondrial crista ultrastructure. Overall, this work supports the crucial role of ATP synthase in regulating crista architecture in the context of human disease

Association between dietary phylloquinone intake and peripheral metabolic risk markers related to insulin resistance and diabetes in elderly subjects at high cardiovascular risk

BACKGROUND: Vitamin K has been related to glucose metabolism, insulin sensitivity and diabetes. Because inflammation underlies all these metabolic conditions, it is plausible that the potential role of vitamin K in glucose metabolism occurs through the modulation of cytokines and related molecules. The purpose of the study was to assess the associations between dietary intake of vitamin K and peripheral adipokines and other metabolic risk markers related to insulin resistance and type 2 diabetes mellitus. METHODS: Cross-sectional and longitudinal assessments of these associations in 510 elderly participants recruited in the PREDIMED centers of Reus and Barcelona (Spain). We determined 1-year changes in dietary phylloquinone intake estimated by food frequency questionnaires, serum inflammatory cytokines and other metabolic risk markers. RESULTS: In the cross-sectional analysis at baseline no significant associations were found between dietary phylloquinone intake and the rest of metabolic risk markers evaluated, with exception of a negative association with plasminogen activator inhibitor-1. After 1-year of follow-up, subjects in the upper tertile of changes in dietary phylloquinone intake showed a greater reduction in ghrelin (-15.0%), glucose-dependent insulinotropic peptide (-12.9%), glucagon-like peptide-1 (-17.6%), IL-6 (-27.9%), leptin (-10.3%), TNF (-26.9%) and visfatin (-24.9%) plasma concentrations than those in the lowest tertile (all p<0.05). CONCLUSION: These results show that dietary phylloquinone intake is associated with an improvement of cytokines and other markers related to insulin resistance and diabetes, thus extending the potential protection by dietary phylloquinone on chronic inflammatory diseases. TRIAL REGISTRATION: http://www.controlled-trials.com as ISRCTN35739639

Association between serum ferritin and osteocalcin as a potential mechanism explaining the iron-induced insulin resistance

Background: Increased iron stores are associated with increased risk of type 2 diabetes, however, the mechanisms underlying these associations are poorly understood. Because a reduction of circulating osteocalcin levels after iron overload have been demonstrated in cell cultures, and osteocalcin is related to glucose and insulin metabolism, the ironinduced osteocalcin reductions could contribute to explain the role of iron metabolism in the development of type 2 diabetes mellitus. Objective: To analyzed the associations between serum total and uncarboxylated osteocalcin and adiponectin concentrations with serum ferritin and soluble transferrin receptor (sTfR) in elderly subjects. Design: We evaluated a total of 423 subjects from the PREDIMED cohort in a population-based cross-sectional analysis. Extensive clinical, nutritional and laboratory measurements, including total and uncarboxylated osteocalcin, adiponectin, ferritin and sTfR were recorded. Results: Serum ferritin was positively correlated with increased glucose and insulin circulating levels but also with HOMA-IR, and was inversely associated with total osteocalcin and adiponectin. A regression analysis revealed that serum ferritin and transferrin receptor levels were significantly associated with a decrease in total and uncarboxylated osteocalcin. Serum sTfR levels were associated with lower uncarboxylated osteocalcin levels in the whole-study subjects and remained significant only in the IFG (impaired fasting glucose) individuals. Conclusions: We described, for the first time, an inverse association between serum ferritin and sTfR with osteocalcin and extend previous results on adiponectin, thus supporting that factors related to iron metabolism could contribute to the insulin resistance and the development of type 2 diabetes mellitus. Trial Registration: Controlled-Trials.com ISRCTN35739639 ,http://www.controlled-trials.com/ISRCTN35739639.

Dietary intake of phylloquinone is related to a reduced risk of all-cause mortality: the predimed study

Resumen del trabajo presentado en el 20th International Congress of Nutrition, celebrado en Granada (España) del 15 al 20 de septiembre de 2013.[Background and objectives]: Vitamin K has been associated with a reduced risk of CHD and fatal cancer. Dietary menaquinones intake has been associated with cancer mortality. However, the association between the dietary intake of vitamin K and all-cause mortality has not been evaluated in a Mediterranean population at high cardiovascular risk.[Methods]: A prospective analysis was conducted in 7216 participants in the framework of the PREDIMED cohort (median follow-up: 4.8y). Energy and nutrient intakes were evaluated using a previously validated 137-item food frequency questionnaire. Dietary phylloquinone and menaquinone intake was calculated using the USDA database and previous published Abstracts Ann Nutr Metab 2013;63(suppl 1):1– 1960 921 data, respectively. All-cause mortality was verified by medical records and consultation of National Death Index. Cox proportional hazard models were fitted to assess the relative risk of all-cause mortality.[Results]: At baseline, energy-adjusted dietary phylloquinone intake was associated with a significantly reduced risk of all-cause mortality after controlling for potential confounders (HR: 0.64; 95% CI: 0.43, 0.96). No significant associations were found between quartiles of energy adjusted dietary menaquinones intake and risk of all-cause mortality. In a longitudinal manner, subjects who increase their consumption of vitamin K, phylloquinone or menaquinone, had a lower risk of allcause mortality (HR: 0.58; 95% CI: 0.45, 0.74 and HR: 0.59; 95% CI: 0.45, 0.78, respectively) compared with subjects who decrease their consumption.[Conclusions]: The results showed that an increase of dietary intake of vitamin K is related with a reduced risk of all-cause mortality in a Mediterranean population at high cardiovascular risk

Dietary glycemic index and glycemic load are positively associated with risk of developing metabolic syndrome in middle-aged and elderly adults

© 2015, Copyright the Authors Journal compilation © 2015, The American Geriatrics Society. Objectives To evaluate how glycemic index (GI) and glycemic load (GL) are associated with the metabolic syndrome (MetS) and its features in middle-aged and elderly adults at high cardiovascular risk. Design Prospective, longitudinal, population-based cohort. Setting PREvenciõn con DIeta MEDiterránea study. Participants Men and women (N = 6,606) divided into three age groups (<65, 65-74, ≥75). Measurements Energy and nutrient intake was evaluated using a validated 137-item food frequency questionnaire. MetS and its features were defined in accordance with the criteria of the American Heart Association and National Heart, Lung, and Blood Institute. Results A positive association was observed between GI and MetS prevalence in the youngest and middle age groups for participants without diabetes mellitus, but no relationship was found for those with diabetes mellitus. During the median follow-up of 4.8 years, higher GI and GL were related to greater risk of MetS in the middle age group, independent of the presence of diabetes mellitus. Changes in dietary GI were associated with risk of developing the high fasting glucose component of the MetS in the oldest age category, and changes in dietary GL were associated with risk of developing abdominal obesity, hypertriglyceridemia, low high-density lipoprotein cholesterol, and high blood pressure in the youngest age category. Conclusion Dietary GI and GL have a potential role in the development of MetS and associated clinical features, with particular age-dependent considerations.Funded by: Centro Nacional de Investigaciones Cardiovasculares. Grant Number: 06/2007; Instituto de Salud Carlos III; Fondo de Investigación Sanitaria PI. Grant Number: 07/0473; Ministerio de Ciencia e Innovación. Grant Numbers: AGL-2009–13906-C02, AGL2010–22319-C03; Ministerio de Sanidad-Plan Nacional de Drogas. Grant Number: 2010/087; Fondo de Investigaciones Sanitarias. Grant Number: PI1002658 Fundación Mapfre 2010 Government of the Basque Country. Grant Number: IT386–10 University of the Basque Country. Grant Number: UFI 11/32 Catalan government Miguel Servet. Grant Number: 06/00100Peer Reviewe

Glycemic index in the management of Obesity and Metabolic syndrome

La obesitat y la síndrome metabòlica (SMet) són una de les principals causes de mortalitat arreu del món. L’índex glucémic (IG) i la càrrega glucémica (CG) han estat associades a un augment del risc de desenvolupar obesitat, diabetis tipus 2, SMet i malalties cardiovasculars. Actualment la evidència científica suggereix possibles beneficis de l’IG/CG per a la prevenció i tractament de la obesitat i la SMet. El nostre objectiu va ser analitzar la associació entre IG/CG de la dieta i el risc de desenvolupar SMet i els seus components, a més a més de analitzar la relació entre l’IG/CG i marcadors d’inflamació perifèrics. Per altra banda, vam analitzar la efectivitat d’una dieta de alt IG/CG contra una dieta baixa amb IG/CG i una dieta baixa en greix sobre la pèrdua de pes i la millora del perfil metabòlic, a través de la modulació d’uns mecanismes relacionats amb la sacietat, la inflamació i altres marcadors metabòlics. Aquesta tesi ha estat realitzada en el marc de l’estudi PREDIMED, un assaig clínic nutricional, multicèntric i aleatoritzat; i de l’estudi GLYNDIET, un assaig clínic en paral•lel, aleatoritzat i controlat de 6 mesos de duració. Els resultats obtinguts mostren com les dietes amb alt IG/CG podrien jugar un paper important en el desenvolupament de la SMet i alguns dels seus components. A més, el consum d’aquestes dietes també podria modular alguns marcadors cardiometabolics que contribuirien al guany de pes i al desenvolupament de malalties cardiovasculars. Finalment, vam observar com el consum d’una dieta amb baix IG i un moderat contingut de carbohidrats era més efectiva per la pèrdua de pes i la millora de la sensibilitat i resistència a la insulina que una dieta de alt IG i un moderat contingut de carbohidrats o una dieta baix en greix.La obesidad y el síndrome metabólico (SMet) son una de las principales causas de la mortalidad a nivel mundial. El índice glucémico (IG) i la carga glucémica (CG) han estado asociados a un mayor riesgo de obesidad, diabetes tipo 2, SMet y enfermedades cardiovasculares. Actualmente la evidencia científica sugiere posibles beneficios del IG/CG para la prevención y tratamiento de la obesidad y SMet. Nuestro objetivo fue analizar la asociación entre el IG/CG de la dieta y el riesgo de desarrollar SMet i sus componentes, además de analizar la relación del IG/CG y marcadores de inflamación periféricos. Por otro lado, analizamos la efectividad de una dieta de alto IG/CG contra una dieta baja en IG/CG y una dieta baja en grasa sobre la pérdida de peso i la mejora del perfil metabólico, a través de la modulación de mecanismos relacionados con la saciedad, la inflamación y otros marcadores metabólicos. Esta tesis se ha realizado dentro del marco del estudio PREDIMED, una ensayo clínico nutricional, multicéntrico i aleatorizado; y el estudio GLYNDIET, un ensayo clínico en paralelo, aleatorizado y controlado de 6 meses de duración. Los resultados obtenidos muestran como las dietas de alto IG/CG podrían jugar un papel importante en el desarrollo del SMet y alguno de sus componentes. Además, el consumo de estas dietas también podría modular algunos marcadores cardiometabólicos que contribuyen a la ganancia de peso y al desarrollo de enfermedades cardiovasculares. Finalmente, observamos como el consumo de una dieta de bajo IG y una moderada cantidad de carbohidratos era más efectiva para la pérdida de peso y la mejora de la sensibilidad y la resistencia a la insulina que una dieta de alto IG y una moderada cantidad de carbohidratos o una dieta baja en grasa.Obesity and Metabolic Syndrome (MetS) are one of the main causes of disability and death worldwide. It has been proposed that high glycemic index (GI) and high glycemic load (GL) diets are associated with increased risks of obesity, type 2 diabetes mellitus, MetS and cardiovascular disease. To date, evidence suggests possible benefits of the GI/GL for the prevention and management of obesity and MetS. We aimed to analyze the association between dietary GI and GL and the risk of to develop MetS and its features, as well as, the relationship between dietary GI and GL, peripheral adipokines and inflammatory markers. Also, we aimed to analyze the effectiveness of a high GI/GL diet versus a low-GI/GL and a low-fat diet in body weight loss and the improvement of metabolic profile, through the modulation of some mechanisms related to satiety, inflammation and other metabolic risk markers. This thesis has been conducted in the framework of the PREDIMED Study, multicenter randomized nutrition trial, and the GLYNDIET study, a 6-month randomized, parallel, controlled clinical trial. Our results suggest that high dietary GI and GL have a potential role in the development of MetS and some of its components. The consumption of diets with high-GI foods or high dietary GL may also modulate some cardiometabolic markers thus contributing to weight gain and cardiovascular disease. Finally, we found that a moderate-CH low-GI diet may be more effective for weight loss than a moderate-CH high-GI diet or a conventional low-fat diet. The metabolic benefits observed for insulin resistance and sensitivity in those subjects following a low-GI diet, and the tendency to improve other inflammatory and associated metabolic risk markers, also indicate that low-GI diets are better tools for managing obesity and its associated comorbidities