Role of triadin in the organization of reticulum membrane at the muscle triad.

International audienceThe terminal cisternae represent one of the functional domains of the skeletal muscle sarcoplasmic reticulum (SR). They are closely apposed to plasma membrane invaginations, the T-tubules, with which they form structures called triads. In triads, the physical interaction between the T-tubule-anchored voltage-sensing channel DHPR and the SR calcium channel RyR1 is essential because it allows the depolarization-induced calcium release that triggers muscle contraction. This interaction between DHPR and RyR1 is based on the peculiar membrane structures of both T-tubules and SR terminal cisternae. However, little is known about the molecular mechanisms governing the formation of SR terminal cisternae. We have previously shown that ablation of triadins, a family of SR transmembrane proteins that interact with RyR1, induced skeletal muscle weakness in knockout mice as well as a modification of the shape of triads. Here we explore the intrinsic molecular properties of the longest triadin isoform Trisk 95. We show that when ectopically expressed, Trisk 95 can modulate reticulum membrane morphology. The membrane deformations induced by Trisk 95 are accompanied by modifications of the microtubule network organization. We show that multimerization of Trisk 95 by disulfide bridges, together with interaction with microtubules, are responsible for the ability of Trisk 95 to structure reticulum membrane. When domains responsible for these molecular properties are deleted, anchoring of Trisk 95 to the triads in muscle cells is strongly decreased, suggesting that oligomers of Trisk 95 and microtubules contribute to the organization of the SR terminal cisternae in a triad

In vitro and in vivo intracellular delivery of quantum dots by maurocalcine

International audienceMaurocalcine is a new member of the increasing family of cell penetrating peptides. We report for the first time that this peptide is able to deliver quantum dots inside a variety of cells, both in vitro and in vivo. In vivo, maurocalcine produces intracellular delivery of the nanoparticles without affecting the relative distribution of quantum dots within organs. The data stress out that maurocalcine can be used for intracellular delivery of functionalised nanoparticles in vivo

Mutations in DNAH1, which encodes an inner arm heavy chain dynein, lead to male infertility from multiple morphological abnormalities of the sperm flagella.

International audienceTen to fifteen percent of couples are confronted with infertility and a male factor is involved in approximately half the cases. A genetic etiology is likely in most cases yet only few genes have been formally correlated with male infertility. Homozygosity mapping was carried out on a cohort of 20 North African individuals, including 18 index cases, presenting with primary infertility resulting from impaired sperm motility caused by a mosaic of multiple morphological abnormalities of the flagella (MMAF) including absent, short, coiled, bent, and irregular flagella. Five unrelated subjects out of 18 (28%) carried a homozygous variant in DNAH1, which encodes an inner dynein heavy chain and is expressed in testis. RT-PCR, immunostaining, and electronic microscopy were carried out on samples from one of the subjects with a mutation located on a donor splice site. Neither the transcript nor the protein was observed in this individual, confirming the pathogenicity of this variant. A general axonemal disorganization including mislocalization of the microtubule doublets and loss of the inner dynein arms was observed. Although DNAH1 is also expressed in other ciliated cells, infertility was the only symptom of primary ciliary dyskinesia observed in affected subjects, suggesting that DNAH1 function in cilium is not as critical as in sperm flagellum

Exosomes as a novel way of interneuronal communication.

International audienceExosomes are small extracellular vesicles which stem from endosomes fusing with the plasma membrane; they contain lipids, proteins and RNAs that are able to modify receiving cells. Functioning of the brain relies on synapses, and certain patterns of synaptic activity can change the strength of responses at sparse groups of synapses, to modulate circuits underlying associations and memory. These local changes of the synaptic physiology in one neuron driven by another have, so far, been explained by classical signal transduction modulating transcription, translation and post-translational modifications. We have accumulated in vitro evidence that exosomes released by neurons in a way depending on synaptic activity can be recaptured by other neurons. Some lipids, proteins and RNAs contained in exosomes secreted by emitting neurons could directly modify signal transduction and protein expression in receiving cells. Exosomes may be an ideal mechanism for anterograde and retrograde information transfer across synapses underlying local changes in synaptic plasticity. Exosomes might also participate in the spreading across the nervous system of pathological proteins such as PrPSc (abnormal disease-specific conformation of prion protein), APP (amyloid precursor protein) fragments, phosphorylated tau or α-synuclein

Intermittent Hypoxia Rewires the Liver Transcriptome and Fires up Fatty Acids Usage for Mitochondrial Respiration

International audienceSleep Apnea Syndrome (SAS) is one of the most common chronic diseases, affecting nearly one billion people worldwide. The repetitive occurrence of abnormal respiratory events generates cyclical desaturation-reoxygenation sequences known as intermittent hypoxia (IH). Among SAS metabolic sequelae, it has been established by experimental and clinical studies that SAS is an independent risk factor for the development and progression of non-alcoholic fatty liver disease (NAFLD). The principal goal of this study was to decrypt the molecular mechanisms at the onset of IH-mediated liver injury. To address this question, we used a unique mouse model of SAS exposed to IH, employed unbiased high-throughput transcriptomics and computed network analysis. This led us to examine hepatic mitochondrial ultrastructure and function using electron microscopy, high-resolution respirometry and flux analysis in isolated mitochondria. Transcriptomics and network analysis revealed that IH reprograms Nuclear Respiratory Factor- (NRF-) dependent gene expression and showed that mitochondria play a central role. We thus demonstrated that IH boosts the oxidative capacity from fatty acids of liver mitochondria. Lastly, the unbalance between oxidative stress and antioxidant defense is tied to an increase in hepatic ROS production and DNA damage during IH. We provide a comprehensive analysis of liver metabolism during IH and reveal the key role of the mitochondria at the origin of development of liver disease. These findings contribute to the understanding of the mechanisms underlying NAFLD development and progression during SAS and provide a rationale for novel therapeutic targets and biomarker discovery

Extracellular vesicles from myelodysplastic mesenchymal stromal cells induce DNA damage and mutagenesis of hematopoietic stem cells through miRNA transfer

International audiencePhysiopathology of myelodysplastic syndrome (MDS) remains poorly understood and the role of the microenvironment is increasingly highlighted. Recent studies in mouse models demonstrate that abnormalities of mesenchymal stromal cells (MSC) contribute to the physiopathology of MDS. In particular, genetic deletion of dicer1, a gene encoding a type III RNase essential for the genesis of miRNA, in murine MSC-derived osteoprogenitors led to a pathological microenvironment generating myelodysplastic features in hematopoietic progenitors and ultimately leading to acute myeloid leukemia [1]. In human, there is an increased susceptibility to senescence of the MDS mesenchymal stem cells and defects in the support properties of the growth of hematopoietic stem cells (HSC) [2]. These observations establish a causal relationship between deregulation of the hematopoietic niche and MDS pathogenesis. However, so far only few studies have addressed the mechanisms by microenvironmental MSC and HSC exchange signals that may interfere with miRNA processing, specifically in the human MDS microenvironment

Extracellular vesicles from myelodysplastic mesenchymal stromal cells induce DNA damage and mutagenesis of hematopoietic stem cells through miRNA transfer

International audiencePhysiopathology of myelodysplastic syndrome (MDS) remains poorly understood and the role of the microenvironment is increasingly highlighted. Recent studies in mouse models demonstrate that abnormalities of mesenchymal stromal cells (MSC) contribute to the physiopathology of MDS. In particular, genetic deletion of dicer1, a gene encoding a type III RNase essential for the genesis of miRNA, in murine MSC-derived osteoprogenitors led to a pathological microenvironment generating myelodysplastic features in hematopoietic progenitors and ultimately leading to acute myeloid leukemia [1]. In human, there is an increased susceptibility to senescence of the MDS mesenchymal stem cells and defects in the support properties of the growth of hematopoietic stem cells (HSC) [2]. These observations establish a causal relationship between deregulation of the hematopoietic niche and MDS pathogenesis. However, so far only few studies have addressed the mechanisms by microenvironmental MSC and HSC exchange signals that may interfere with miRNA processing, specifically in the human MDS microenvironment

Extracellular vesicles from myelodysplastic mesenchymal stromal cells induce DNA damage and mutagenesis of hematopoietic stem cells through miRNA transfer

International audiencePhysiopathology of myelodysplastic syndrome (MDS) remains poorly understood and the role of the microenvironment is increasingly highlighted. Recent studies in mouse models demonstrate that abnormalities of mesenchymal stromal cells (MSC) contribute to the physiopathology of MDS. In particular, genetic deletion of dicer1, a gene encoding a type III RNase essential for the genesis of miRNA, in murine MSC-derived osteoprogenitors led to a pathological microenvironment generating myelodysplastic features in hematopoietic progenitors and ultimately leading to acute myeloid leukemia [1]. In human, there is an increased susceptibility to senescence of the MDS mesenchymal stem cells and defects in the support properties of the growth of hematopoietic stem cells (HSC) [2]. These observations establish a causal relationship between deregulation of the hematopoietic niche and MDS pathogenesis. However, so far only few studies have addressed the mechanisms by microenvironmental MSC and HSC exchange signals that may interfere with miRNA processing, specifically in the human MDS microenvironment