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Mutations in the mitochondrial protease gene AFG3L2 cause dominant hereditary ataxia SCA28

Nature Genetics volume 42, pages 313–321 (2010)Cite this article

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Abstract

Autosomal dominant spinocerebellar ataxias (SCAs) are genetically heterogeneous neurological disorders characterized by cerebellar dysfunction mostly due to Purkinje cell degeneration. Here we show that AFG3L2 mutations cause SCA type 28. Along with paraplegin, which causes recessive spastic paraplegia, AFG3L2 is a component of the conserved m-AAA metalloprotease complex involved in the maintenance of the mitochondrial proteome. We identified heterozygous missense mutations in five unrelated SCA families and found that AFG3L2 is highly and selectively expressed in human cerebellar Purkinje cells. m-AAA–deficient yeast cells expressing human mutated AFG3L2 homocomplex show respiratory deficiency, proteolytic impairment and deficiency of respiratory chain complex IV. Structure homology modeling indicates that the mutations may affect AFG3L2 substrate handling. This work identifies AFG3L2 as a novel cause of dominant neurodegenerative disease and indicates a previously unknown role for this component of the mitochondrial protein quality control machinery in protecting the human cerebellum against neurodegeneration.

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Figure 1: AFG3L2 mutations cause amino acid substitutions in highly conserved regions of the protein.
Figure 2: Complementation studies in S. cerevisiae.
Figure 3: Cytochrome c oxidase enzyme activity and protein levels in yeast cells expressing mutant AFG3L2.
Figure 4: Proteolytic activity of normal and mutant AFG3L2 in yeast.
Figure 5: Molecular modeling of normal and mutant AFG3L2.
Figure 6: Expression of AFG3L2 and paraplegin in human and mouse nervous systems.

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NCBI Reference Sequence

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Acknowledgements

We thank the affected individuals and their families for participating in this study, our colleagues A. Salmaggi and C.P. Trevisan for referring to us the index patients from families MI-A0762 and MI-A0650, respectively, M. Rimoldi for his help in respiratory chain analysis and V. Seveso for her help with blue native electrophoresis. This work was supported by grants from the Italian Ministry of Health (RF2006 ex art. 56/2005/1 “Malattie Neurodegenerative” to F. Taroni), European Commission FP6 Integrated Project EUROSCA (to F. Taroni and S.D.D.), Telethon-UILDM (GUP04009 to F. Taroni), Fondazione Telethon-Italia (GGP07110 to A. Brusco, GGP030406 to M.M.-F. and GGP09301 to F. Taroni and M.M.-F.), Regione Piemonte Ricerca Sanitaria Finalizzata (to A. Brusco), National Organization for Rare Disorders (to A. Brusco), Regione Piemonte (CIPE 2004, project A183 to F. Tempia), Compagnia di San Paolo (to F. Tempia) and Fondazione Cariplo (to P.P.).

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Authors and Affiliations

  1. Unit of Genetics of Neurodegenerative and Metabolic Diseases, Fondazione IRCCS Istituto Neurologico “Carlo Besta”, Milan, Italy

    Daniela Di Bella, Massimo Plumari, Barbara Castellotti, Silvia Baratta, Caterina Mariotti, Cinzia Gellera, Valentina Fracasso, Stefania Magri, Stefano Di Donato & Franco Taroni

  2. Department of Biomolecular Sciences and Biotechnology, University of Milan, Milan, Italy

    Federico Lazzaro, Paolo Plevani & Marco Muzi-Falconi

  3. Department of Genetics, Biology, and Biochemistry, University of Turin, and Unit of Medical Genetics, San Giovanni Battista Hospital, Turin, Italy

    Alfredo Brusco, Claudia Cagnoli & Alessandro Brussino

  4. Unit of Molecular Neuroanatomy, Fondazione IRCCS Istituto Neurologico “Carlo Besta”, Milan, Italy

    Giorgio Battaglia & Adele Finardi

  5. National Institute for Medical Research, London, UK

    Annalisa Pastore

  6. Section of Physiology of the Department of Neuroscience, University of Turin, and Rita Levi Montalcini Center for Brain Repair, National Institute of Neuroscience, Turin, Italy

    Filippo Tempia, Tiziana Sacco & Enrica Boda

  7. Institute of Neurobiology and Molecular Medicine, Consiglio Nazionale delle Ricerche, Rome, Italy

    Marina Frontali & Liana Veneziano

  8. Institute for Genetics and Center for Molecular Medicine Cologne, University of Cologne, Germany

    Florian Bonn & Thomas Langer

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Contributions

D.D.B. and F. Taroni identified the disease gene and characterized the mutations in the cells of affected individuals; D.D.B., F.L., V.F. and S.M. carried out the experiments in yeast; A. Brusco, C.C. and A. Brussino performed preliminary genetic screening and generated AFG3L2 expression plasmid; M.P. and C.G. generated antibodies to AFG3L2 and paraplegin and performed biochemical studies in the cells of affected individuals; A.P. performed molecular modeling of the mutant proteins; G.B. and A.F. performed immunohistochemical studies in human nervous tissue; F. Tempia, T.S. and E.B. performed expression studies in mouse cerebellum; C.M. and S.D.D. made clinical diagnoses and collected clinical data and samples; M.F. and L.V. characterized and contributed data from family RM-DS; F.B. and T.L. provided yeast antibodies, shared unpublished observations and advised on handling of yeast data analysis; C.G., B.C. and S.B. performed preliminary genetic screening and subject selection; B.C. performed quantitative analysis of AFG3L2 gene copy number; F. Taroni, M.M.-F. and P.P. conceived and designed the study and provided financial support; F. Taroni wrote the paper; all others received, edited and approved the manuscript.

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Correspondence to Franco Taroni.

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Di Bella, D., Lazzaro, F., Brusco, A. et al. Mutations in the mitochondrial protease gene AFG3L2 cause dominant hereditary ataxia SCA28. Nat Genet 42, 313–321 (2010). https://doi.org/10.1038/ng.544

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