@article {337, title = {Loss of Nardilysin, a Mitochondrial Co-chaperone for α-Ketoglutarate Dehydrogenase, Promotes mTORC1 Activation and Neurodegeneration.}, journal = {Neuron}, volume = {93}, year = {2017}, month = {2017 Jan 04}, pages = {115-131}, abstract = {

We previously identified mutations in Nardilysin (dNrd1) in a forward genetic screen designed to isolate genes whose loss causes neurodegeneration in Drosophila photoreceptor neurons. Here~we show that NRD1 is localized to mitochondria, where it recruits mitochondrial chaperones and assists in the folding of α-ketoglutarate dehydrogenase (OGDH), a rate-limiting enzyme in~the Krebs cycle. Loss of Nrd1 or Ogdh leads to an increase in α-ketoglutarate, a substrate for OGDH,~which in turn leads to mTORC1 activation and a subsequent reduction in autophagy. Inhibition of mTOR activity by rapamycin or partially restoring autophagy delays neurodegeneration in dNrd1 mutant flies. In summary, this study reveals a novel role for NRD1 as a mitochondrial co-chaperone for OGDH and provides a mechanistic link between mitochondrial metabolic dysfunction, mTORC1 signaling, and impaired autophagy in neurodegeneration.

}, keywords = {Animals, Autophagy, Drosophila, Drosophila melanogaster, Drosophila Proteins, Ketoglutarate Dehydrogenase Complex, Ketoglutaric Acids, Lysine, Mechanistic Target of Rapamycin Complex 1, Metalloendopeptidases, Mitochondria, Molecular Chaperones, Multiprotein Complexes, Neurodegenerative Diseases, TOR Serine-Threonine Kinases}, issn = {1097-4199}, doi = {10.1016/j.neuron.2016.11.038}, author = {Yoon, Wan Hee and Sandoval, Hector and Nagarkar-Jaiswal, Sonal and Jaiswal, Manish and Yamamoto, Shinya and Haelterman, Nele A and Putluri, Nagireddy and Putluri, Vasanta and Sreekumar, Arun and Tos, Tulay and Aksoy, Ayse and Donti, Taraka and Graham, Brett H and Ohno, Mikiko and Nishi, Eiichiro and Hunter, Jill and Muzny, Donna M and Carmichael, Jason and Shen, Joseph and Arboleda, Valerie A and Nelson, Stanley F and Wangler, Michael F and Karaca, Ender and Lupski, James R and Bellen, Hugo J} } @article {58, title = {Association of MTOR Mutations With Developmental Brain Disorders, Including Megalencephaly, Focal Cortical Dysplasia, and Pigmentary Mosaicism.}, journal = {JAMA Neurol}, volume = {73}, year = {2016}, month = {2016 07 01}, pages = {836-845}, abstract = {

IMPORTANCE: Focal cortical dysplasia (FCD), hemimegalencephaly, and megalencephaly constitute a spectrum of malformations of cortical development with shared neuropathologic features. These disorders are associated with significant childhood morbidity and mortality.

OBJECTIVE: To identify the underlying molecular cause of FCD, hemimegalencephaly, and diffuse megalencephaly.

DESIGN, SETTING, AND PARTICIPANTS: Patients with FCD, hemimegalencephaly, or megalencephaly (mean age, 11.7 years; range, 2-32 years) were recruited from Pediatric Hospital A. Meyer, the University of Hong Kong, and Seattle Children{\textquoteright}s Research Institute from June 2012 to June 2014. Whole-exome sequencing (WES) was performed on 8 children with FCD or hemimegalencephaly using standard-depth (50-60X) sequencing in peripheral samples (blood, saliva, or skin) from the affected child and their parents and deep (150-180X) sequencing in affected brain tissue. Targeted sequencing and WES were used to screen 93 children with molecularly unexplained diffuse or focal brain overgrowth. Histopathologic and functional assays of phosphatidylinositol 3-kinase-AKT (serine/threonine kinase)-mammalian target of rapamycin (mTOR) pathway activity in resected brain tissue and cultured neurons were performed to validate mutations.

MAIN OUTCOMES AND MEASURES: Whole-exome sequencing and targeted sequencing identified variants associated with this spectrum of developmental brain disorders.

RESULTS: Low-level mosaic mutations of MTOR were identified in brain tissue in 4 children with FCD type 2a with alternative allele fractions ranging from 0.012 to 0.086. Intermediate-level mosaic mutation of MTOR (p.Thr1977Ile) was also identified in 3 unrelated children with diffuse megalencephaly and pigmentary mosaicism in skin. Finally, a constitutional de novo mutation of MTOR (p.Glu1799Lys) was identified in 3 unrelated children with diffuse megalencephaly and intellectual disability. Molecular and functional analysis in 2 children with FCD2a from whom multiple affected brain tissue samples were available revealed a mutation gradient with an epicenter in the most epileptogenic area. When expressed in cultured neurons, all MTOR mutations identified here drive constitutive activation of mTOR complex 1 and enlarged neuronal size.

CONCLUSIONS AND RELEVANCE: In this study, mutations of MTOR were associated with a spectrum of brain overgrowth phenotypes extending from FCD type 2a to diffuse megalencephaly, distinguished by different mutations and levels of mosaicism. These mutations may be sufficient to cause cellular hypertrophy in cultured neurons and may provide a demonstration of the pattern of mosaicism in brain and substantiate the link between mosaic mutations of MTOR and pigmentary mosaicism in skin.

}, keywords = {Adolescent, Adult, Amino Acids, Animals, Cells, Cultured, Cerebral Cortex, Child, Child, Preschool, Developmental Disabilities, Embryo, Mammalian, Female, Gene Expression Regulation, Genetic Association Studies, Humans, Intercellular Signaling Peptides and Proteins, Male, Malformations of Cortical Development, Mechanistic Target of Rapamycin Complex 1, Megalencephaly, Mosaicism, Multiprotein Complexes, Mutation, Nerve Tissue Proteins, Neurons, Rats, Retrospective Studies, TOR Serine-Threonine Kinases, Young Adult}, issn = {2168-6157}, doi = {10.1001/jamaneurol.2016.0363}, author = {Mirzaa, Ghayda M and Campbell, Catarina D and Solovieff, Nadia and Goold, Carleton and Jansen, Laura A and Menon, Suchithra and Timms, Andrew E and Conti, Valerio and Biag, Jonathan D and Adams, Carissa and Boyle, Evan August and Collins, Sarah and Ishak, Gisele and Poliachik, Sandra and Girisha, Katta M and Yeung, Kit San and Chung, Brian Hon Yin and Rahikkala, Elisa and Gunter, Sonya A and McDaniel, Sharon S and Macmurdo, Colleen Forsyth and Bernstein, Jonathan A and Martin, Beth and Leary, Rebecca and Mahan, Scott and Liu, Shanming and Weaver, Molly and Doerschner, Michael and Jhangiani, Shalini and Muzny, Donna M and Boerwinkle, Eric and Gibbs, Richard A and Lupski, James R and Shendure, Jay and Saneto, Russell P and Novotny, Edward J and Wilson, Christopher J and Sellers, William R and Morrissey, Michael and Hevner, Robert F and Ojemann, Jeffrey G and Guerrini, Renzo and Murphy, Leon O and Winckler, Wendy and Dobyns, William B} } @article {70, title = {Recessive Inactivating Mutations in TBCK, Encoding a Rab GTPase-Activating Protein, Cause Severe Infantile Syndromic Encephalopathy.}, journal = {Am J Hum Genet}, volume = {98}, year = {2016}, month = {2016 Apr 07}, pages = {772-81}, abstract = {

Infantile encephalopathies are a group of clinically and biologically heterogeneous disorders for which the genetic basis remains largely unknown. Here, we report a syndromic neonatal encephalopathy characterized by profound developmental disability, severe hypotonia, seizures, diminished respiratory drive requiring mechanical ventilation, brain atrophy, dysgenesis of the corpus callosum, cerebellar vermis hypoplasia, and facial dysmorphism. Biallelic inactivating mutations in TBCK (TBC1-domain-containing kinase) were independently identified by whole-exome sequencing as the cause of this condition in four unrelated families. Matching these families was facilitated by the sharing of phenotypic profiles and WES data in a recently released web-based tool (Geno2MP) that links phenotypic information to rare variants in families with Mendelian traits. TBCK is a putative GTPase-activating protein (GAP) for small GTPases of the Rab family and has been shown to control cell growth and proliferation, actin-cytoskeleton dynamics, and mTOR signaling. Two of the three mutations (c.376C>T [p.Arg126(*)] and c.1363A>T [p.Lys455(*)]) are predicted to truncate the protein, and loss of the major TBCK isoform was confirmed in primary fibroblasts from one affected individual. The third mutation, c.1532G>A (p.Arg511His), alters a conserved residue within the TBC1 domain. Structural analysis implicated Arg511 as a required residue for Rab-GAP function, and in~silico homology modeling predicted impaired GAP function in the corresponding mutant. These results suggest that loss of Rab-GAP activity is the underlying mechanism of disease. In contrast to other disorders caused by dysregulated mTOR signaling associated with focal or global brain overgrowth, impaired TBCK function results in progressive loss of brain volume.

}, keywords = {Adolescent, Alleles, Amino Acid Sequence, Brain Diseases, Child, Child, Preschool, Corpus Callosum, Female, GTPase-Activating Proteins, Humans, Magnetic Resonance Imaging, Male, Molecular Sequence Data, Mutation, Pedigree, Protein Conformation, Protein-Serine-Threonine Kinases, Signal Transduction, TOR Serine-Threonine Kinases}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2016.01.016}, author = {Chong, Jessica X and Caputo, Viviana and Phelps, Ian G and Stella, Lorenzo and Worgan, Lisa and Dempsey, Jennifer C and Nguyen, Alina and Leuzzi, Vincenzo and Webster, Richard and Pizzuti, Antonio and Marvin, Colby T and Ishak, Gisele E and Ardern-Holmes, Simone and Richmond, Zara and Bamshad, Michael J and Ortiz-Gonzalez, Xilma R and Tartaglia, Marco and Chopra, Maya and Doherty, Dan} }