Coagulase-Negative Staphylococci Pathogenomics

Coagulase-negative Staphylococci (CoNS) are skin commensal bacteria. Besides their role in maintaining homeostasis, CoNS have emerged as major pathogens in nosocomial settings. Several studies have investigated the molecular basis for this emergence and identified multiple putative virulence factors with regards to Staphylococcus aureus pathogenicity. In the last decade, numerous CoNS whole-genome sequences have been released, leading to the identification of numerous putative virulence factors. Koch’s postulates and the molecular rendition of these postulates, established by Stanley Falkow in 1988, do not explain the microbial pathogenicity of CoNS. However, whole-genome sequence data has shed new light on CoNS pathogenicity. In this review, we analyzed the contribution of genomics in defining CoNS virulence, focusing on the most frequent and pathogenic CoNS species: S. epidermidis, S. haemolyticus, S. saprophyticus, S. capitis, and S. lugdunensis

Endoplasmic reticulum stress induces cardiac dysfunction through architectural modifications and alteration of mitochondrial function in cardiomyocytes

International audienceAims: Endoplasmic reticulum (ER) stress has recently emerged as an important mechanism involved in the pathogenesis of cardiovascular diseases. However, the molecular mechanisms by which ER stress leads to cardiac dysfunction remain poorly understood. Methods and results: In the present study, we evaluated the early cardiac effects of ER stress induced by tunicamycin (TN) in mice. Echocardiographic analysis indicated that TN-induced ER stress led to a significant impairment of the cardiac function. Electron microscopic observations revealed that ultrastructural changes of cardiomyocytes in response to ER stress manifested extensively at the level of the reticular membrane system. Smooth tubules of sarcoplasmic reticulum in connection with short sections of rough endoplasmic reticulum were observed. The presence of rough instead of smooth reticulum was increased at the interfibrillar space, at the level of dyads and in the vicinity of mitochondria. At the transcriptional level, ER stress resulted in a substantial decrease in the expression of the major regulator of mitochondrial biogenesis PGC-1α and of its targets NRF1, Tfam, CS and COXIV. At the functional level, ER stress also induced an impairment of mitochondrial Ca 2+ uptake, an alteration of mitochondrial oxidative phosphorylation and a metabolic remodeling characterized by a shift from fatty acid to glycolytic substrate consumption. Conclusion: Our findings show that ER stress induces cytoarchitectural and metabolic alterations in cardiomyocytes and provide evidences that ER stress could represent a primary mechanism that contributes to the impairment of energy metabolism reported in most cardiac diseases

Mitochondrial AIF Loss Causes Metabolic Reprogramming, Caspase-Independent Cell Death Blockade, Embryonic Lethality, and Perinatal Hydrocephalus

International audienceObjectives: Apoptosis-Inducing Factor (AIF) is a protein involved in mitochondrial electron transport chain assembly/stability and in programmed cell death. The relevant role of this protein is underlined by the fact that mutations altering mitochondrial AIF properties result in acute pediatric mitochondriopathies and tumor metastasis. By generating an original AIF-deficient mouse strain, the present study sought to analyze, in a single paradigm, the cellular and developmental metabolic consequences of AIF loss and the subsequent oxidative phosphorylation (OXPHOS) dysfunction.Methods: We developed a novel AIF-deficient mouse strain and assessed, by molecular and cell biology approaches, the cellular, embryonic, and adult mice phenotypic alterations. Additionally, we carried out ex vivo assays with primary and immortalized AIF knockout mouse embryonic fibroblasts (MEFs) to establish the cell death characteristics and the metabolic adaptive responses provoked by the mitochondrial electron transport chain (ETC) breakdown.Results: AIF deficiency destabilized mitochondrial ETC and provoked supercomplex disorganization, mitochondrial transmembrane potential loss, and high generation of mitochondrial reactive oxygen species (ROS). AIF-/Y MEFs counterbalanced these OXPHOS alterations by mitochondrial network reorganization and a metabolic reprogramming towards anaerobic glycolysis illustrated by the AMPK phosphorylation at Thr172, the overexpression of the glucose assimilation transporter GLUT-4, the subsequent enhancement of glucose uptake, and the anaerobic lactate generation. A late phenotype was characterized by the activation of P53/P21-mediated senescence. Interestingly, about 2% of AIF-/Y MEFs diminished both mitochondrial mass and ROS levels and spontaneously proliferated. These cycling AIF-/Y MEFs were resistant to caspase-independent cell death inducers. The AIF-deficient mouse strain was embryonic lethal between E11.5 and E13.5 with energy loss, proliferation arrest, and increased apoptotic levels. Contrary to AIF-/Y MEFs, the AIF KO embryos were unable to reprogram their metabolism towards anaerobic glycolysis. Heterozygous AIF-/+ females displayed a progressive bone marrow, thymus, and spleen cellular loss. In addition, about 10% of AIF-/+ females developed perinatal hydrocephaly characterized by brain development impairment, meningeal fibrosis, and medullar hemorrhages; those mice died around 5 weeks of age. AIF-/+ with hydrocephaly exhibited loss of ciliated epithelium in the ependymal layer. This phenotype seemed triggered by the ROS excess. Accordingly, it was possible to diminish the occurrence of hydrocephalus AIF-/+ females by supplying dams and newborns with an antioxidant in drinking water.Conclusion: In a single knockout model and at three different levels (cell, embryo, and adult mice) we demonstrated that, by controlling the mitochondrial OXPHOS/metabolism, AIF is a key factor regulating cell differentiation and fate. Additionally, by shedding new light on the pathological consequences of mitochondrial OXPHOS dysfunction, our new findings pave the way for novel pharmacological strategies