The G protein-coupled receptor kinase-2 is a TGFbeta-inducible antagonist of TGFbeta signal transduction

Signaling from the activin/transforming growth factor beta (TGFbeta) family of cytokines is a tightly regulated process. Disregulation of TGFbeta signaling is often the underlying basis for various cancers, tumor metastasis, inflammatory and autoimmune diseases. In this study, we identify the protein G-coupled receptor kinase 2 (GRK2), a kinase involved in the desensitization of G protein-coupled receptors (GPCR), as a downstream target and regulator of the TGFbeta-signaling cascade. TGFbeta-induced expression of GRK2 acts in a negative feedback loop to control TGFbeta biological responses. Upon TGFbeta stimulation, GRK2 associates with the receptor-regulated Smads (R-Smads) through their MH1 and MH2 domains and phosphorylates their linker region. GRK2 phosphorylation of the R-Smads inhibits their carboxyl-terminal, activating phosphorylation by the type I receptor kinase, thus preventing nuclear translocation of the Smad complex, leading to the inhibition of TGFbeta-mediated target gene expression, cell growth inhibition and apoptosis. Furthermore, we demonstrate that GRK2 antagonizes TGFbeta-induced target gene expression and apoptosis ex vivo in primary hepatocytes, establishing a new role for GRK2 in modulating single-transmembrane serine/threonine kinase receptor-mediated signal transduction.     

3D reconstruction of the pelvis from bi-planar radiography

3D personalized models are more and more requested for clinical and biomechanical studies. Techniques based on bi-planar X-rays present the advantage of a low radiation dose for the patient. However, up to now, such techniques have shown limited accuracy in the case of pelvis reconstruction. This study proposes and validates a method providing accurate 3D personalized model of the pelvis from bi-planar X-rays. The algorithm is based on the fast computation of an initial solution followed by local deformations based on 2D anatomical points and contours that are digitized in both radiographs. Results were close to CT-scan reconstructions (mean difference 1.6 mm and differences under 4.3 mm for 95% of the points). Moreover, 3D morphometry of the pelvis could be obtained with an accuracy of 5%. This technique provides 3D patient specific model with a low radiation dose.     

Phagocytic functions of microglial cells in the central nervous system and their importance in two neurodegenerative diseases: multiple sclerosis and Alzheimer’s disease

Microglial cells are the resident phagocytic cells of the central nervous system (CNS). They possess a wide range of receptors allowing them to identify and internalize numerous pathogens. We will discuss here the role of the most important receptors of microglia involved in non-opsonin-dependent phagocytosis (mannose receptor, β-glucan receptor, scavenger receptor) and that of receptors involved in the opsonin-dependent phagocytosis, namely the complement 3 (CR3) and the Fcγ receptors (FcγR). First, the molecular and cellular mechanisms induced when these receptors are conducting a phagocytic event are presented. In the second part, we will discuss the role these receptors may play in multiple sclerosis and Alzheimer’s disease, in the elimination by phagocytosis of myelin and beta amyloid peptide respectively. The first two authors contributed equally to this work.     

Charles-Edouard Brown-Séquard: an eventful life and a significant contribution to the study of the nervous system

This is an account of the life of a 19th-century physiologist who was born in 1817 in Port-Louis (Mauritius Island, formerly 'Ile de France') and died in Paris in 1894. His mother tongue, education and medical training were French, but as the 'Ile de France' had become British a few years before his birth, he was a British citizen and therefore ineligible for a permanent position in a French institution. This explains, partly at least, his eventful life, during which he restlessly wandered during several decades between France, the United States, Great Britain and Mauritius, without ever finding a position that would satisfy him. This difficult period lasted until 1879 when, having finally acquired French nationality, he succeeded Claude Bernard in the chair of experimental medicine at the 'Collège de France'. Some of his contributions to the physiology of the nervous system are analysed: sensory pathways in the spinal cord, vasoconstrictor innervation, nervous inhibition and experimental epilepsy.     

Probing the substrate specificity of four different sialyltransferases using synthetic beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O) (CH(2))7CH3 analogues general activating effect of replacing N-acetylglucosamine by N-propionylglucosamine

The acceptor specificities of ST3Gal III, ST3Gal IV, ST6Gal I and ST6Gal II were investigated using a panel of beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O)(CH(2))(7)CH(3) analogues. Modifications introduced at either C2, C3, C4, C5, or C6 of terminal D-Gal, as well as N-propionylation instead of N-acetylation of subterminal D-GlcN were tested for their influence on the alpha-2,3- and alpha-2,6-sialyltransferase acceptor activities. Both ST3Gal enzymes displayed the same narrow acceptor specificity, and only accept reduction of the Gal C2 hydroxyl function. The ST6Gal enzymes, however, do not have the same acceptor specificity. ST6Gal II seems less tolerant towards modifications at Gal C3 and C4 than ST6Gal I, and prefers beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc (LacdiNAc) as an acceptor substrate, as shown by replacing the Gal C2 hydroxyl group with an N-acetyl function. Finally, a particularly striking feature of all tested sialyltransferases is the activating effect of replacing the N-acetyl function of subterminal GlcNAc by an N-propionyl function.     

The phosphoinositide kinase PIKfyve/Fab1p regulates terminal lysosome maturation in Caenorhabditis elegans

Membrane dynamics is necessary for cell homeostasis and signal transduction and is in part regulated by phosphoinositides. Pikfyve/Fab1p is a phosphoinositide kinase that phosphorylates phosphatidylinositol 3-monophosphate into phosphatidylinositol-3,5-bisphosphate [PtdIns(3,5)P2] and is implicated in membrane homeostasis in yeast and in mammalian cells. These two phosphoinositides are substrates of myotubularin phosphatases found mutated in neuromuscular diseases. We studied the roles of phosphatidylinositol phosphate kinase 3 (PPK-3), the orthologue of PIKfyve/Fab1p, in a multicellular organism, Caenorhabditis elegans. Complete loss of ppk-3 function induces developmental defects characterized by embryonic lethality, whereas partial loss of function leads to growth retardation. At the cellular level, ppk-3 mutants display a striking enlargement of vacuoles positive for lysosome-associated membrane protein 1 in different tissues. In the intestine, RAB-7-positive late endosomes are also enlarged. Membranes of the enlarged lysosomes originate at least in part from smaller lysosomes, and functional and genetic analyses show that the terminal maturation of lysosomes is defective. Protein degradation is not affected in the hypomorphic ppk-3 mutant and is thus uncoupled from membrane retrieval. We measured the level of PtdIns(3,5)P2 and showed that its production is impaired in this mutant. This work strongly suggests that the main function of PPK-3 is to mediate membrane retrieval from matured lysosomes through regulation of PtdIns(3,5)P2.     

The non-linear response of a muscle in transverse compression: assessment of geometry influence using a finite element model

Most recent finite element models that represent muscles are generic or subject-specific models that use complex, constitutive laws. Identification of the parameters of such complex, constitutive laws could be an important limit for subject-specific approaches. The aim of this study was to assess the possibility of modelling muscle behaviour in compression with a parametric model and a simple, constitutive law. A quasi-static compression test was performed on the muscles of dogs. A parametric finite element model was designed using a linear, elastic, constitutive law. A multi-variate analysis was performed to assess the effects of geometry on muscle response. An inverse method was used to define Young's modulus. The non-linear response of the muscles was obtained using a subject-specific geometry and a linear elastic law. Thus, a simple muscle model can be used to have a bio-faithful, biomechanical response.     

Defective membrane remodeling in neuromuscular diseases: insights from animal models

Proteins involved in membrane remodeling play an essential role in a plethora of cell functions including endocytosis and intracellular transport. Defects in several of them lead to human diseases. Myotubularins, amphiphysins, and dynamins are all proteins implicated in membrane trafficking and/or remodeling. Mutations in myotubularin, amphiphysin 2 (BIN1), and dynamin 2 lead to different forms of centronuclear myopathy, while mutations in myotubularin-related proteins cause Charcot-Marie-Tooth neuropathies. In addition to centronuclear myopathy, dynamin 2 is also mutated in a dominant form of Charcot-Marie-Tooth neuropathy. While several proteins from these different families are implicated in similar diseases, mutations in close homologues or in the same protein in the case of dynamin 2 lead to diseases affecting different tissues. This suggests (1) a common molecular pathway underlying these different neuromuscular diseases, and (2) tissue-specific regulation of these proteins. This review discusses the pathophysiology of the related neuromuscular diseases on the basis of animal models developed for proteins of the myotubularin, amphiphysin, and dynamin families. A better understanding of the common mechanisms between these neuromuscular disorders will lead to more specific health care and therapeutic approaches.