Human Molecular Genetics Advance Access originally published online on March 25, 2009
Human Molecular Genetics 2009 18(12):2149-2165; doi:10.1093/hmg/ddp148
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Loss-of-function mutations in ATP6V0A2 impair vesicular trafficking, tropoelastin secretion and cell survival
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1 Department of Pediatrics 2 Department of Genetics 3 Department of Medicine, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8208, St Louis, MO 63110, USA 4 Department of Pediatrics 5 Laboratory of Pediatrics and Neurology, Radboud University Nijmegen Medical Centre, Nijmegen 6525GA, The Netherlands 6 Institute for Medical Genetics, Charité Universitätsmedizin, Berlin 13353, Germany 7 Development and Disease Research Group, Max Planck Institute for Molecular Genetics, Berlin 14195, Germany 8 Department of Anatomy and Cell Biology, McGill University, Montreal, Canada H3A 2B2 9 Department of Pediatrics, Rhode Island Hospital, Hasbro Children’s Hospital and Brown University School of Medicine, Providence, RI 02903, USA 10 Department of Biochemistry and Experimental Medicine, The Children’s Memorial Health Institute, Warsaw 04730, Poland 11 Princess Al Jawhara Center of Excellence in the Research of Hereditary Disorders, King Abdulaziz University, Jeddah 21486, Saudi Arabia 12 Schneider Children's Medical Center of Israel and Raphael Recanati Genetics Institute, Rabin Medical Center, Beilinson Campus, Petah Tikva 49202, Israel 13 Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel 14 Medical Genetics Program, Eastern Health, St John’s, Canada A1B 3V6 15 The National Centre for Medical Genetics, Our Lady's Children's Hospital, Crumlin, Dublin 12, Ireland 16 Institut für Humangenetik, Universität zu Lübeck, Lübeck 23538, Germany 17 Istanbul Medical Faculty, Medical Genetics Department, Istanbul University, Istanbul 34390, Turkey 18 Service de Génétique Médicale, CHU-Ste-Justine, Montreal, Quebec, Canada 19 Department of Pediatrics, Ankara University School of Medicine, Ankara 06100, Turkey 20 Department of Pediatric Genetics, Cerrahpasa Medical School, Istanbul University, Istanbul 34452, Turkey 21 Centre de Génétique Humaine, Centre Hospitalier Universitaire du Sart-Tilman, Université de Liège, Liège 4000, Belgium
* To whom correspondence should be addressed. Tel: +1 3142862973; Fax: +1 3142862893; Email: urban_z{at}kids.wustl.edu
Received December 5, 2008; Revised February 27, 2009; Accepted March 23, 2009
Autosomal recessive cutis laxa type 2 (ARCL2), a syndrome of growth and developmental delay and redundant, inelastic skin, is caused by mutations in the a2 subunit of the vesicular ATPase H+-pump (ATP6V0A2). The goal of this study was to define the disease mechanisms that lead to connective tissue lesions in ARCL2. In a new cohort of 17 patients, DNA sequencing of ATP6V0A2 detected either homozygous or compound heterozygous mutations. Considerable allelic and phenotypic heterogeneity was observed, with a missense mutation of a moderately conserved residue p.P87L leading to unusually mild disease. Abnormal N- and/or mucin type O-glycosylation was observed in all patients tested. Premature stop codon mutations led to decreased ATP6V0A2 mRNA levels by destabilizing the mutant mRNA via the nonsense-mediated decay pathway. Loss of ATP6V0A2 either by siRNA knockdown or in ARCL2 cells resulted in distended Golgi cisternae, accumulation of abnormal lysosomes and multivesicular bodies. Immunostaining of ARCL2 cells showed the accumulation of tropoelastin (TE) in the Golgi and in large, abnormal intracellular and extracellular aggregates. Pulse–chase studies confirmed impaired secretion and increased intracellular retention of TE, and insoluble elastin assays showed significantly reduced extracellular deposition of mature elastin. Fibrillin-1 microfibril assembly and secreted lysyl oxidase activity were normal in ARCL2 cells. TUNEL staining demonstrated increased rates of apoptosis in ARCL2 cell cultures. We conclude that loss-of-function mutations in ATP6V0A2 lead to TE aggregation in the Golgi, impaired clearance of TE aggregates and increased apoptosis of elastogenic cells.
The authors wish it to be known that, in their opinion, the first three authors should be regarded as joint First Authors. 
These authors belong to the ARCL Debré-type study group.