33 research outputs found
X-linked myotubular myopathy is associated with epigenetic alterations and is ameliorated by HDAC inhibition
X-linked myotubular myopathy (XLMTM) is a fatal neuromuscular disorder caused by loss of function mutations in MTM1. At present, there are no directed therapies for XLMTM, and incomplete understanding of disease pathomechanisms. To address these knowledge gaps, we performed a drug screen in mtm1 mutant zebrafish and identified four positive hits, including valproic acid, which functions as a potent suppressor of the mtm1 zebrafish phenotype via HDAC inhibition. We translated these findings to a mouse XLMTM model, and showed that valproic acid ameliorates the murine phenotype. These observations led us to interrogate the epigenome in Mtm1 knockout mice; we found increased DNA methylation, which is normalized with valproic acid, and likely mediated through aberrant 1-carbon metabolism. Finally, we made the unexpected observation that XLMTM patients share a distinct DNA methylation signature, suggesting that epigenetic alteration is a conserved disease feature amenable to therapeutic intervention
Phosphatase-dead myotubularin ameliorates X-linked centronuclear myopathy phenotypes in mice
Myotubularin MTM1 is a phosphoinositide (PPIn) 3-phosphatase mutated in X-linked centronuclear myopathy (XLCNM; myotubular myopathy). We investigated the involvement of MTM1 enzymatic activity on XLCNM phenotypes. Exogenous expression of human MTM1 in yeast resulted in vacuolar enlargement, as a consequence of its phosphatase activity. Expression of mutants from patients with different clinical progression and determination of PtdIns3P and PtdIns5P cellular levels confirmed the link between vacuolar morphology and MTM1 phosphatase activity, and showed that some disease mutants retain phosphatase activity. Viral gene transfer of phosphatase-dead myotubularin mutants (MTM1(C375S) and MTM1(S376N)) significantly improved most histological signs of XLCNM displayed by a Mtm1-null mouse, at similar levels as wild-type MTM1. Moreover, the MTM1(C375S) mutant improved muscle performance and restored the localization of nuclei, triad alignment, and the desmin intermediate filament network, while it did not normalize PtdIns3P levels, supporting phosphatase-independent roles of MTM1 in maintaining normal muscle performance and organelle positioning in skeletal muscle. Among the different XLCNM signs investigated, we identified only triad shape and fiber size distribution as being partially dependent on MTM1 phosphatase activity. In conclusion, this work uncovers MTM1 roles in the structural organization of muscle fibers that are independent of its enzymatic activity. This underlines that removal of enzymes should be used with care to conclude on the physiological importance of their activity
Genetic Interaction between MTMR2 and FIG4 Phospholipid Phosphatases Involved in Charcot-Marie-Tooth Neuropathies
We previously reported that autosomal recessive demyelinating Charcot-Marie-Tooth (CMT) type 4B1 neuropathy with myelin outfoldings is caused by loss of MTMR2 (Myotubularin-related 2) in humans, and we created a faithful mouse model of the disease. MTMR2 dephosphorylates both PtdIns3P and PtdIns(3,5)P2, thereby regulating membrane trafficking. However, the function of MTMR2 and the role of the MTMR2 phospholipid phosphatase activity in vivo in the nerve still remain to be assessed. Mutations in FIG4 are associated with CMT4J neuropathy characterized by both axonal and myelin damage in peripheral nerve. Loss of Fig4 function in the plt (pale tremor) mouse produces spongiform degeneration of the brain and peripheral neuropathy. Since FIG4 has a role in generation of PtdIns(3,5)P2 and MTMR2 catalyzes its dephosphorylation, these two phosphatases might be expected to have opposite effects in the control of PtdIns(3,5)P2 homeostasis and their mutations might have compensatory effects in vivo. To explore the role of the MTMR2 phospholipid phosphatase activity in vivo, we generated and characterized the Mtmr2/Fig4 double null mutant mice. Here we provide strong evidence that Mtmr2 and Fig4 functionally interact in both Schwann cells and neurons, and we reveal for the first time a role of Mtmr2 in neurons in vivo. Our results also suggest that imbalance of PtdIns(3,5)P2 is at the basis of altered longitudinal myelin growth and of myelin outfolding formation. Reduction of Fig4 by null heterozygosity and downregulation of PIKfyve both rescue Mtmr2-null myelin outfoldings in vivo and in vitro
Vps34 PI 3-kinase inactivation enhances insulin sensitivity through reprogramming of mitochondrial metabolism
Postdoctoral fellowships were from EU Marie Curie (PIEF-GA-2009â252916) and
EMBO (ALTF 753â2010) for SA and EU Marie Curie (PIIF-GA-2009â252846) for C.C. J.
M.H. was a recipient of a doctoral fellowship from Eisai UK Ltd. Work in our laboratories
was supported as follows: BV: MRC [G0700755], BBSRC (BB/I007806/1 and BB/
M013278/1), CRUK (C23338/A15965), the Ludwig Institute for Cancer Research and the
National Institute for Health Research (NIHR) UCL Hospitals Biomedical Research
Centre; J.M.B.: NIH AG039632, GM112524. and the Albert Einstein Diabetes Research
and Training Center Animal Physiology Core DK020541; E.G.: Barry Reed Cancer
Research fund; G.S.: BBSRC (BB/L020874/1) and B.H.F.; S.S.: Anatomical Society of
Great Britain (GT) and a Wellcome Trust Career Development Fellowship 074246/Z04/Z
(S.S.); R.K.S.: Wellcome Trust (WT098498) and M.R.C. (MRC_MC_UU_12012/5); S.A.
T. and L.C.: the Francis Crick Institute, which receives its core funding from CRUK
(FC001187), MRC (FC001187), and the Wellcome Trust (FC001187); Y.-L.C.: the CRUK
Cancer Imaging Centre in association with the MRC and DoH (England) grant C1060/
A10334, C1060/A16464, NHS funding to the NIHR BRC; B.P.: Inserm and the Fondation
pour la recherche médicale
Imaging surface photonic states with a circularly polarized tip
Photon unoccupied states tailored by nanostructures present at
sample surfaces can be probed using a scanning near-field optical
microscope including large detection angles (Chicanne C
Overview on Materials and Technological Developments for the LMJ Cryogenic Target Assembly
Infrared near-field study of a localised absorption in a thin film
We study the conditions to perform micro-spectroscopy with a sub-wavelength lateral
resolution in the wavelength spectral range from 3 to 20 ÎŒm, taking advantage of the infrared
spectral signature of different chemical species. We utilised CLIO, a free electron laser, as the
photon source. The transmitted photons were collected by either fluoride or chalcogenide
glass fibres. Fibre tips were obtained through chemical etching by organic solvents.
Metallisation of the tips permits to achieve lateral resolution of the order of the tip size.
However, parasitic propagation of the light in the film reduces the contrast between irradiated
and non-irradiated zones. We exemplify our set up with near-field infrared spectra obtained for
polymer thin films deposited onto silicon wafers
PI3KC2ÎČ inactivation stabilizes VEâcadherin junctions and preserves vascular integrity
Endothelium protection is critical, because of the impact of vascular leakage and edema on pathological conditions such as brain ischemia. Whereas deficiency of class II phosphoinositide 3âkinase alpha (PI3KC2α) results in an increase in vascular permeability, we uncover a crucial role of the beta isoform (PI3KC2ÎČ) in the loss of endothelial barrier integrity following injury. Here, we studied the role of PI3KC2ÎČ in endothelial permeability and endosomal trafficking in vitro and in vivo in ischemic stroke. Mice with inactive PI3KC2ÎČ showed protection against vascular permeability, edema, cerebral infarction, and deleterious inflammatory response. Loss of PI3KC2ÎČ in human cerebral microvascular endothelial cells stabilized homotypic cellâcell junctions by increasing Rab11âdependent VEâcadherin recycling. These results identify PI3KC2ÎČ as a potential new therapeutic target to prevent aggravating lesions following ischemic stroke