Biallelic Mutations in MRPS34 Lead to Instability of the Small Mitoribosomal Subunit and Leigh Syndrome

The synthesis of all 13 mitochondrial DNA (mtDNA)-encoded protein subunits of the human oxidative phosphorylation (OXPHOS) system is carried out by mitochondrial ribosomes (mitoribosomes). Defects in the stability of mitoribosomal proteins or mitoribosome assembly impair mitochondrial protein translation, causing combined OXPHOS enzyme deficiency and clinical disease. Here we report four autosomal-recessive pathogenic mutations in the gene encoding the small mitoribosomal subunit protein, MRPS34, in six subjects from four unrelated families with Leigh syndrome and combined OXPHOS defects. Whole-exome sequencing was used to independently identify all variants. Two splice-site mutations were identified, including homozygous c.321+1G>T in a subject of Italian ancestry and homozygous c.322−10G>A in affected sibling pairs from two unrelated families of Puerto Rican descent. In addition, compound heterozygous MRPS34 mutations were identified in a proband of French ancestry; a missense (c.37G>A [p.Glu13Lys]) and a nonsense (c.94C>T [p.Gln32∗]) variant. We demonstrated that these mutations reduce MRPS34 protein levels and the synthesis of OXPHOS subunits encoded by mtDNA. Examination of the mitoribosome profile and quantitative proteomics showed that the mitochondrial translation defect was caused by destabilization of the small mitoribosomal subunit and impaired monosome assembly. Lentiviral-mediated expression of wild-type MRPS34 rescued the defect in mitochondrial translation observed in skin fibroblasts from affected subjects, confirming the pathogenicity of MRPS34 mutations. Our data establish that MRPS34 is required for normal function of the mitoribosome in humans and furthermore demonstrate the power of quantitative proteomic analysis to identify signatures of defects in specific cellular pathways in fibroblasts from subjects with inherited disease

Cure de cystocèle par prothèse vaginale libre de faible grammage : résultats à 6 ans

International audienc

Benzodiazepine dependence: Focus on withdrawal syndrome

Benzodiazepines are potentially addictive drugs: psychological and physical dependence can develop within a few weeks or years of regular or repeated use. The socioeconomic costs of the present high level of long-term benzodiazepine use are considerable. These consequences could be minimised if prescriptions for long-term benzodiazepines were decreased. However, many physicians continue to prescribe benzodiazepines and patients wishing to withdraw receive little advice or support. Particular care should be taken in prescribing benzodiazepines for vulnerable patients such as elderly persons, pregnant women, children, alcohol- or drug-dependent patients and patients with comorbid psychiatric disorders. The following update gives recent research results on the withdrawal pathophysiology and practical information in order to treat or prevent benzodiazepine withdrawal syndrome.N. Authier, D. Balayssac, M. Sautereau, A. Zangarelli, P. Courty, A.A. Somogyi, B. Vennat, P.-M. Llorca and A. Eschalie

Energy restriction only slightly influences protein metabolism in obese rats, whatever the level of protein and its source in the diet

International audienceBACKGROUND: High protein (HP) diets during energy restriction have been studied extensively regarding their ability to reduce body fat and preserve lean body mass, but little is known about their effects on protein metabolism in lean tissues. OBJECTIVE: To determine the effects of energy restriction and protein intake on protein anabolism and catabolism in rats. METHODS: For 5 weeks, 56 male Wistar rats were fed an obesity induction (OI) diet. They were then subjected to a 40% energy restriction using the OI diet or a balanced HP diet for 3 weeks, whereas a control group was fed the OI diet ad libitum (n ¼ 8 per group). HP-restricted rats were divided into five groups differing only in terms of their protein source: total milk proteins, casein (C), whey (W), a mix of 50% C and W, and soy (n ¼ 8). The animals were then killed in the postprandial state and their body composition was determined. Protein synthesis rates were determined in the liver, gastrocnemius and kidney using a subcutaneous 13 C valine flooding dose. mRNA levels were measured for key enzymes involved in the three proteolysis pathways. RESULTS: Energy restriction, but not diet composition, impacted weight loss and adiposity, whereas lean tissue mass (except in the kidney) was not influenced by diet composition. Levels of neoglucogenic amino acids tended to fall under energy restriction (Po0.06) but this was reversed by a high level of protein. The postprandial protein synthesis rates in different organs were similar in all groups. By contrast, mRNA levels encoding proteolytic enzymes rose under energy restriction in the muscle and kidney, but this was counteracted by a HP level. CONCLUSIONS: In adult obese rats, energy restriction but not diet composition affected fat pads and had little impact on protein metabolism, despite marked effects on proteolysis in the kidney and muscle. INTRODUCTION Weight management strategies are designed to reduce body fat while causing no major reduction in lean tissue. The different strategies proposed 1,2 involve varying levels of energy restriction and modifications to the energy nutrient content of diets, such as limiting the consumption of fat or carbohydrate (CHO) and increasing the protein content. 3,4 Proteins have been the focus of particular study because of their satiating effect that might both reduce energy intake 5 and increase subject compliance with a diet. 6,7 In addition, a protein-rich diet may minimize the loss of lean body mass that is observed under a low-calorie diet. 8,9 The type of protein source may also exert an influence, as reported in rodent models. 10,11 The effects of energy restriction on anabolic and catabolic fluxes are poorly understood and the findings available, which differ regarding numerous parameters (model, duration, degree of restrictions), are not comparable. In humans, one study recently showed that muscle protein synthesis was decreased after moderate energy restriction. 12 Other data have been obtained in rats and revealed contrasting effects of energy restriction on muscle protein anabolism, depending the type of muscle (soleus