Pathogenic variants in the AFG3L2 proteolytic domain cause SCA28 through haploinsufficiency and proteostatic stress-driven OMA1 activation

Susanna Tulli, Andrea Del Bondio, Valentina Baderna, Davide Mazza, Franca Codazzi, Tyler Mark Pierson, Alessandro Ambrosi, Dagmar Nolte, Cyril Goizet, Camilo Toro, Jonathan Baets, Tine Deconinck, Peter Dejonghe, Paola Mandich, Giorgio Casari, Francesca Maltecca

Research output: Contribution to journalArticle

Abstract

Background: Spinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date. Methods: We derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2 +/â ' HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2 â '/â ' murine fibroblasts. Results: We found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells. Conclusion: Our data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2 +/- cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants.

Original languageEnglish
JournalJournal of Medical Genetics
DOIs
Publication statusPublished - Jan 1 2019

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Haploinsufficiency
Mitochondrial Dynamics
Fibroblasts
Clustered Regularly Interspaced Short Palindromic Repeats
Spinocerebellar ataxia 28
HEK293 Cells
Mitochondrial Proteins
Neurodegenerative Diseases
Quality Control
Proteins
Pharmacology
Calcium
T-Lymphocytes
Phenotype

Keywords

  • cell biology
  • genetics
  • mitochondria
  • molecular genetics
  • movement disorders (other than parkinsons)

ASJC Scopus subject areas

  • Genetics
  • Genetics(clinical)

Cite this

Pathogenic variants in the AFG3L2 proteolytic domain cause SCA28 through haploinsufficiency and proteostatic stress-driven OMA1 activation. / Tulli, Susanna; Del Bondio, Andrea; Baderna, Valentina; Mazza, Davide; Codazzi, Franca; Pierson, Tyler Mark; Ambrosi, Alessandro; Nolte, Dagmar; Goizet, Cyril; Toro, Camilo; Baets, Jonathan; Deconinck, Tine; Dejonghe, Peter; Mandich, Paola; Casari, Giorgio; Maltecca, Francesca.

In: Journal of Medical Genetics, 01.01.2019.

Research output: Contribution to journalArticle

Tulli, Susanna ; Del Bondio, Andrea ; Baderna, Valentina ; Mazza, Davide ; Codazzi, Franca ; Pierson, Tyler Mark ; Ambrosi, Alessandro ; Nolte, Dagmar ; Goizet, Cyril ; Toro, Camilo ; Baets, Jonathan ; Deconinck, Tine ; Dejonghe, Peter ; Mandich, Paola ; Casari, Giorgio ; Maltecca, Francesca. / Pathogenic variants in the AFG3L2 proteolytic domain cause SCA28 through haploinsufficiency and proteostatic stress-driven OMA1 activation. In: Journal of Medical Genetics. 2019.
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abstract = "Background: Spinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date. Methods: We derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2 +/{\^a} ' HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2 {\^a} '/{\^a} ' murine fibroblasts. Results: We found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells. Conclusion: Our data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2 +/- cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants.",
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AU - Tulli, Susanna

AU - Del Bondio, Andrea

AU - Baderna, Valentina

AU - Mazza, Davide

AU - Codazzi, Franca

AU - Pierson, Tyler Mark

AU - Ambrosi, Alessandro

AU - Nolte, Dagmar

AU - Goizet, Cyril

AU - Toro, Camilo

AU - Baets, Jonathan

AU - Deconinck, Tine

AU - Dejonghe, Peter

AU - Mandich, Paola

AU - Casari, Giorgio

AU - Maltecca, Francesca

PY - 2019/1/1

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N2 - Background: Spinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date. Methods: We derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2 +/â ' HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2 â '/â ' murine fibroblasts. Results: We found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells. Conclusion: Our data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2 +/- cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants.

AB - Background: Spinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date. Methods: We derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2 +/â ' HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2 â '/â ' murine fibroblasts. Results: We found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells. Conclusion: Our data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2 +/- cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants.

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KW - genetics

KW - mitochondria

KW - molecular genetics

KW - movement disorders (other than parkinsons)

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