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Giorgio Casari - One of the best experts on this subject based on the ideXlab platform.
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Haploinsufficiency of AFG3L2, the Gene Responsible for Spinocerebellar Ataxia Type 28, Causes Mitochondria-Mediated Purkinje Cell Dark Degeneration
The Journal of Neuroscience, 2009Co-Authors: Francesca Maltecca, Angelo Quattrini, Raffaealla Magnoni, Federica Cerri, Giorgio CasariAbstract:Paraplegin and AFG3L2 are ubiquitous nuclear-encoded mitochondrial proteins that form hetero-oligomeric Paraplegin-AFG3L2 and homo-oligomeric AFG3L2 complexes in the inner mitochondrial membrane, named m -AAA proteases. These complexes ensure protein quality control in the inner membrane, jointly with a chaperone-like activity on the respiratory chain complexes. Despite coassembling in the same complex, mutations of either Paraplegin or AFG3L2 cause two different neurodegenerative disorders. Indeed, mutations of Paraplegin are responsible for a recessive form of hereditary spastic paraplegia, whereas mutations of AFG3L2 have been recently associated to a dominant form of spinocerebellar ataxia (SCA28). In this work, we report that the mouse model haploinsufficient for Afg3l2 recapitulates important pathophysiological features of the human disease, thus representing the first SCA28 model. Furthermore, we propose a pathogenetic mechanism in which respiratory chain dysfunction and increased reactive oxygen species production caused by Afg3l2 haploinsufficiency lead to dark degeneration of Purkinje cells and cerebellar dysfunction.
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Genetic interaction between the m -AAA protease isoenzymes reveals novel roles in cerebellar degeneration
Human Molecular Genetics, 2009Co-Authors: Paola Martinelli, Giorgio Casari, Angelo Quattrini, Federica Cerri, Veronica La Mattina, Andrea Bernacchia, Raffaella Magnoni, Elena I RugarliAbstract:: The mitochondrial m-AAA protease has a crucial role in axonal development and maintenance. Human mitochondria possess two m-AAA protease isoenzymes: a hetero-oligomeric complex, composed of Paraplegin and AFG3L2 (Afg3 like 2), and a homo-oligomeric AFG3L2 complex. Loss of function of Paraplegin (encoded by the SPG7 gene) causes hereditary spastic paraplegia, a disease characterized by retrograde degeneration of cortical motor axons. Spg7(-/-) mice show a late-onset degeneration of long spinal and peripheral axons with accumulation of abnormal mitochondria. In contrast, Afg3l2(Emv66/Emv66) mutant mice, lacking the AFG3L2 protein, are affected by a severe neuromuscular phenotype, due to defects in motor axon development. The role of the homo-oligomeric m-AAA protease and the extent of cooperation and redundancy between the two isoenzymes in adult neurons are still unclear. Here we report an early-onset severe neurological phenotype in Spg7(-/-) Afg3l2(Emv66/+) mice, characterized by loss of balance, tremor and ataxia. Spg7(-/-) Afg3l2(Emv66/+) mice display acceleration and worsening of the axonopathy observed in Paraplegin-deficient mice. In addition, they show prominent cerebellar degeneration with loss of Purkinje cells and parallel fibers, and reactive astrogliosis. Mitochondria from affected tissues are prone to lose mt-DNA and have unstable respiratory complexes. At late stages, neurons contain structural abnormal mitochondria defective in COX-SDH reaction. Our data demonstrate genetic interaction between the m-AAA isoenzymes and suggest that different neuronal populations have variable thresholds of susceptibility to reduced levels of the m-AAA protease. Moreover, they implicate impaired mitochondrial proteolysis as a novel pathway in cerebellar degeneration.
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variable and tissue specific subunit composition of mitochondrial m aaa protease complexes linked to hereditary spastic paraplegia
Molecular and Cellular Biology, 2007Co-Authors: Mirko Koppen, Elena I Rugarli, Giorgio Casari, Metodi D Metodiev, Thomas LangerAbstract:The m-AAA protease, an ATP-dependent proteolytic complex in the mitochondrial inner membrane, controls protein quality and regulates ribosome assembly, thus exerting essential housekeeping functions within mitochondria. Mutations in the m-AAA protease subunit Paraplegin cause axonal degeneration in hereditary spastic paraplegia (HSP), but the basis for the unexpected tissue specificity is not understood. Paraplegin assembles with homologous Afg3l2 subunits into hetero-oligomeric complexes which can substitute for yeast m-AAA proteases, demonstrating functional conservation. The function of a third paralogue, Afg3l1 expressed in mouse, is unknown. Here, we analyze the assembly of Paraplegin into m-AAA complexes and monitor consequences of Paraplegin deficiency in HSP fibroblasts and in a mouse model for HSP. Our findings reveal variability in the assembly of m-AAA proteases in mitochondria in different tissues. Homo-oligomeric Afg3l1 and Afg3l2 complexes and hetero-oligomeric assemblies of both proteins with Paraplegin can be formed. Yeast complementation studies demonstrate the proteolytic activity of these assemblies. Paraplegin deficiency in HSP does not result in the loss of m-AAA protease activity in brain mitochondria. Rather, homo-oligomeric Afg3l2 complexes accumulate, and these complexes can substitute for housekeeping functions of Paraplegin-containing m-AAA complexes. We therefore propose that the formation of m-AAA proteases with altered substrate specificities leads to axonal degeneration in HSP.
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loss of m aaa protease in mitochondria causes complex i deficiency and increased sensitivity to oxidative stress in hereditary spastic paraplegia
Journal of Cell Biology, 2003Co-Authors: Luigia Atorino, Roberto Marconi, Laura Silvestri, Mirko Koppen, Laura Cassina, Andrea Ballabio, Thomas Langer, Giorgio CasariAbstract:Mmutations in Paraplegin, a putative mitochondrial metallopeptidase of the AAA family, cause an autosomal recessive form of hereditary spastic paraplegia (HSP). Here, we analyze the function of Paraplegin at the cellular level and characterize the phenotypic defects of HSP patients' cells lacking this protein. We demonstrate that Paraplegin coassembles with a homologous protein, AFG3L2, in the mitochondrial inner membrane. These two proteins form a high molecular mass complex, which we show to be aberrant in HSP fibroblasts. The loss of this complex causes a reduced complex I activity in mitochondria and an increased sensitivity to oxidant stress, which can both be rescued by exogenous expression of wild-type Paraplegin. Furthermore, complementation studies in yeast demonstrate functional conservation of the human Paraplegin–AFG3L2 complex with the yeast m-AAA protease and assign proteolytic activity to this structure. These results shed new light on the molecular pathogenesis of HSP and functionally link AFG3L2 to this neurodegenerative disease.
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Molecular basis of inherited spastic paraplegias.
Current Opinion in Genetics & Development, 2001Co-Authors: Giorgio Casari, Elena I RugarliAbstract:Abstract Recently, Paraplegin and spastin have been found to be mutated in two autosomal forms of hereditary spastic paraplegia. Both proteins harbour a common ATPase domain that expresses a chaperone function. Paraplegin is a nuclear-encoded mitochondrial metalloprotease, while the exact role and subcellular localisation of spastin are still unclear.
Thomas Langer - One of the best experts on this subject based on the ideXlab platform.
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m-AAA proteases, mitochondrial calcium homeostasis and neurodegeneration
Cell Research, 2018Co-Authors: Maria Patron, Hans-georg Sprenger, Thomas LangerAbstract:The function of mitochondria depends on ubiquitously expressed and evolutionary conserved m -AAA proteases in the inner membrane. These ATP-dependent peptidases form hexameric complexes built up of homologous subunits. AFG3L2 subunits assemble either into homo-oligomeric isoenzymes or with SPG7 (Paraplegin) subunits into hetero-oligomeric proteolytic complexes. Mutations in AFG3L2 are associated with dominant spinocerebellar ataxia (SCA28) characterized by the loss of Purkinje cells, whereas mutations in SPG7 cause a recessive form of hereditary spastic paraplegia (HSP7) with motor neurons of the cortico-spinal tract being predominantly affected. Pleiotropic functions have been assigned to m -AAA proteases, which act as quality control and regulatory enzymes in mitochondria. Loss of m -AAA proteases affects mitochondrial protein synthesis and respiration and leads to mitochondrial fragmentation and deficiencies in the axonal transport of mitochondria. Moreover m -AAA proteases regulate the assembly of the m itochondrial c alcium u niporter (MCU) complex. Impaired degradation of the MCU subunit EMRE in AFG3L2-deficient mitochondria results in the formation of deregulated MCU complexes, increased mitochondrial calcium uptake and increased vulnerability of neurons for calcium-induced cell death. A reduction of calcium influx into the cytosol of Purkinje cells rescues ataxia in an AFG3L2-deficient mouse model. In this review, we discuss the relationship between the m -AAA protease and mitochondrial calcium homeostasis and its relevance for neurodegeneration and describe a novel mouse model lacking MCU specifically in Purkinje cells. Our results pledge for a novel view on m -AAA proteases that integrates their pleiotropic functions in mitochondria to explain the pathogenesis of associated neurodegenerative disorders.
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functional evaluation of Paraplegin mutations by a yeast complementation assay
Human Mutation, 2010Co-Authors: Florian Bonn, Thomas Langer, Krishna Pantakani, Moneef Shoukier, Ashraf U MannanAbstract:An autosomal recessive form of hereditary spastic paraplegia (AR-HSP) is primarily caused by mutations in the SPG7 gene, which codes for Paraplegin, a subunit of the hetero-oligomeric m-AAA protease in mitochondria. In the current study, sequencing of the SPG7 gene in the genomic DNA of 25 unrelated HSP individuals/families led to the identification of two HSP patients with compound heterozygous mutations (p.G349S/p.W583C and p.A510V/p.N739KfsX741) in the coding sequence of the SPG7 gene. We used a yeast complementation assay to evaluate the functional consequence of novel SPG7 sequence variants detected in the HSP patients. We assessed the proteolytic activity of hetero-oligomeric m-AAA proteases composed of Paraplegin variant(s) and proteolytically inactive forms of AFG3L2 (AFG3L2E575Q or AFG3L2K354A) upon expression in m-AAA protease-deficient yeast cells. We demonstrate that the newly identified Paraplegin variants perturb the proteolytic function of hetero-oligomeric m-AAA protease. Moreover, commonly occurring silent polymorphisms such as p.T503A and p.R688Q could be distinguished from mutations (p.G349S, p.W583C, p.A510V, and p.N739KfsX741) in our HSP cohort. The yeast complementation assay thus can serve as a reliable system to distinguish a pathogenic mutation from a silent polymorphism for any novel SPG7 sequence variant, which will facilitate the interpretation of genetic data for SPG7. Hum Mutat 31:1–5, 2010. © 2010 Wiley-Liss, Inc.
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variable and tissue specific subunit composition of mitochondrial m aaa protease complexes linked to hereditary spastic paraplegia
Molecular and Cellular Biology, 2007Co-Authors: Mirko Koppen, Elena I Rugarli, Giorgio Casari, Metodi D Metodiev, Thomas LangerAbstract:The m-AAA protease, an ATP-dependent proteolytic complex in the mitochondrial inner membrane, controls protein quality and regulates ribosome assembly, thus exerting essential housekeeping functions within mitochondria. Mutations in the m-AAA protease subunit Paraplegin cause axonal degeneration in hereditary spastic paraplegia (HSP), but the basis for the unexpected tissue specificity is not understood. Paraplegin assembles with homologous Afg3l2 subunits into hetero-oligomeric complexes which can substitute for yeast m-AAA proteases, demonstrating functional conservation. The function of a third paralogue, Afg3l1 expressed in mouse, is unknown. Here, we analyze the assembly of Paraplegin into m-AAA complexes and monitor consequences of Paraplegin deficiency in HSP fibroblasts and in a mouse model for HSP. Our findings reveal variability in the assembly of m-AAA proteases in mitochondria in different tissues. Homo-oligomeric Afg3l1 and Afg3l2 complexes and hetero-oligomeric assemblies of both proteins with Paraplegin can be formed. Yeast complementation studies demonstrate the proteolytic activity of these assemblies. Paraplegin deficiency in HSP does not result in the loss of m-AAA protease activity in brain mitochondria. Rather, homo-oligomeric Afg3l2 complexes accumulate, and these complexes can substitute for housekeeping functions of Paraplegin-containing m-AAA complexes. We therefore propose that the formation of m-AAA proteases with altered substrate specificities leads to axonal degeneration in HSP.
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Translating m-AAA protease function in mitochondria to hereditary spastic paraplegia
Trends in Molecular Medicine, 2006Co-Authors: Elena I Rugarli, Thomas LangerAbstract:Hereditary spastic paraplegia (HSP) is a genetically heterogeneous neurodegenerative disorder that is characterized by progressive and cell-specific axonal degeneration. An autosomal recessive form of the disease is caused by mutations in Paraplegin, which is a conserved subunit of the ubiquitous and ATP-dependent m-AAA protease in mitochondria. The m-AAA protease carries out protein quality control in the inner membrane of the mitochondria, suggesting a pathogenic role of misfolded proteins in HSP. A recent study demonstrates that the m-AAA protease regulates ribosome assembly and translation within mitochondria by controlling proteolytic maturation of a ribosomal subunit. Here, we will discuss implications of the dual role of the m-AAA protease in protein activation and degradation for mitochondrial dysfunction and axonal degeneration.
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the m aaa protease defective in hereditary spastic paraplegia controls ribosome assembly in mitochondria
Cell, 2005Co-Authors: Mark Nolden, Elena I Rugarli, Mirko Koppen, Andrea Bernacchia, Sarah Ehses, Thomas LangerAbstract:Summary AAA proteases comprise a conserved family of membrane bound ATP-dependent proteases that ensures the quality control of mitochondrial inner-membrane proteins. Inactivation of AAA proteases causes pleiotropic phenotypes in various organisms, including respiratory deficiencies, mitochondrial morphology defects, and axonal degeneration in hereditary spastic paraplegia (HSP). The molecular basis of these defects, however, remained unclear. Here, we describe a regulatory role of an AAA protease for mitochondrial protein synthesis in yeast. The mitochondrial ribosomal protein MrpL32 is processed by the m -AAA protease, allowing its association with preassembled ribosomal particles and completion of ribosome assembly in close proximity to the inner membrane. Maturation of MrpL32 and mitochondrial protein synthesis are also impaired in a HSP mouse model lacking the m -AAA protease subunit Paraplegin, demonstrating functional conservation. Our findings therefore rationalize mitochondrial defects associated with m -AAA protease mutants in yeast and shed new light on the mechanism of axonal degeneration in HSP.
Elena I Rugarli - One of the best experts on this subject based on the ideXlab platform.
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alternative splicing of spg7 a gene involved in hereditary spastic paraplegia encodes a variant of Paraplegin targeted to the endoplasmic reticulum
PLOS ONE, 2012Co-Authors: Giuseppe Mancuso, Esther Barth, Pietro Crivello, Elena I RugarliAbstract:BACKGROUND: Hereditary spastic paraplegia defines a group of genetically heterogeneous diseases characterized by weakness and spasticity of the lower limbs owing to retrograde degeneration of corticospinal axons. One autosomal recessive form of the disease is caused by mutation in the SPG7 gene. Paraplegin, the product of SPG7, is a component of the m-AAA protease, a high molecular weight complex that resides in the mitochondrial inner membrane, and performs crucial quality control and biogenesis functions in mitochondria. PRINCIPAL FINDINGS: Here we show the existence in the mouse of a novel isoform of Paraplegin, which we name Paraplegin-2, encoded by alternative splicing of Spg7 through usage of an alternative first exon. Paraplegin-2 lacks the mitochondrial targeting sequence, and is identical to the mature mitochondrial protein. Remarkably, Paraplegin-2 is targeted to the endoplasmic reticulum. We find that Paraplegin-2 exposes the catalytic domains to the lumen of the endoplasmic reticulum. Moreover, endogenous Paraplegin-2 accumulates in microsomal fractions prepared from mouse brain and retina. Finally, we show that the previously generated mouse model of Spg7-linked hereditary spastic paraplegia is an isoform-specific knock-out, in which mitochondrial Paraplegin is specifically ablated, while expression of Paraplegin-2 is retained. CONCLUSIONS/SIGNIFICANCE: These data suggest a possible additional role of AAA proteases outside mitochondria and open the question of their implication in neurodegeneration.
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Genetic interaction between the m -AAA protease isoenzymes reveals novel roles in cerebellar degeneration
Human Molecular Genetics, 2009Co-Authors: Paola Martinelli, Giorgio Casari, Angelo Quattrini, Federica Cerri, Veronica La Mattina, Andrea Bernacchia, Raffaella Magnoni, Elena I RugarliAbstract:: The mitochondrial m-AAA protease has a crucial role in axonal development and maintenance. Human mitochondria possess two m-AAA protease isoenzymes: a hetero-oligomeric complex, composed of Paraplegin and AFG3L2 (Afg3 like 2), and a homo-oligomeric AFG3L2 complex. Loss of function of Paraplegin (encoded by the SPG7 gene) causes hereditary spastic paraplegia, a disease characterized by retrograde degeneration of cortical motor axons. Spg7(-/-) mice show a late-onset degeneration of long spinal and peripheral axons with accumulation of abnormal mitochondria. In contrast, Afg3l2(Emv66/Emv66) mutant mice, lacking the AFG3L2 protein, are affected by a severe neuromuscular phenotype, due to defects in motor axon development. The role of the homo-oligomeric m-AAA protease and the extent of cooperation and redundancy between the two isoenzymes in adult neurons are still unclear. Here we report an early-onset severe neurological phenotype in Spg7(-/-) Afg3l2(Emv66/+) mice, characterized by loss of balance, tremor and ataxia. Spg7(-/-) Afg3l2(Emv66/+) mice display acceleration and worsening of the axonopathy observed in Paraplegin-deficient mice. In addition, they show prominent cerebellar degeneration with loss of Purkinje cells and parallel fibers, and reactive astrogliosis. Mitochondria from affected tissues are prone to lose mt-DNA and have unstable respiratory complexes. At late stages, neurons contain structural abnormal mitochondria defective in COX-SDH reaction. Our data demonstrate genetic interaction between the m-AAA isoenzymes and suggest that different neuronal populations have variable thresholds of susceptibility to reduced levels of the m-AAA protease. Moreover, they implicate impaired mitochondrial proteolysis as a novel pathway in cerebellar degeneration.
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variable and tissue specific subunit composition of mitochondrial m aaa protease complexes linked to hereditary spastic paraplegia
Molecular and Cellular Biology, 2007Co-Authors: Mirko Koppen, Elena I Rugarli, Giorgio Casari, Metodi D Metodiev, Thomas LangerAbstract:The m-AAA protease, an ATP-dependent proteolytic complex in the mitochondrial inner membrane, controls protein quality and regulates ribosome assembly, thus exerting essential housekeeping functions within mitochondria. Mutations in the m-AAA protease subunit Paraplegin cause axonal degeneration in hereditary spastic paraplegia (HSP), but the basis for the unexpected tissue specificity is not understood. Paraplegin assembles with homologous Afg3l2 subunits into hetero-oligomeric complexes which can substitute for yeast m-AAA proteases, demonstrating functional conservation. The function of a third paralogue, Afg3l1 expressed in mouse, is unknown. Here, we analyze the assembly of Paraplegin into m-AAA complexes and monitor consequences of Paraplegin deficiency in HSP fibroblasts and in a mouse model for HSP. Our findings reveal variability in the assembly of m-AAA proteases in mitochondria in different tissues. Homo-oligomeric Afg3l1 and Afg3l2 complexes and hetero-oligomeric assemblies of both proteins with Paraplegin can be formed. Yeast complementation studies demonstrate the proteolytic activity of these assemblies. Paraplegin deficiency in HSP does not result in the loss of m-AAA protease activity in brain mitochondria. Rather, homo-oligomeric Afg3l2 complexes accumulate, and these complexes can substitute for housekeeping functions of Paraplegin-containing m-AAA complexes. We therefore propose that the formation of m-AAA proteases with altered substrate specificities leads to axonal degeneration in HSP.
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Translating m-AAA protease function in mitochondria to hereditary spastic paraplegia
Trends in Molecular Medicine, 2006Co-Authors: Elena I Rugarli, Thomas LangerAbstract:Hereditary spastic paraplegia (HSP) is a genetically heterogeneous neurodegenerative disorder that is characterized by progressive and cell-specific axonal degeneration. An autosomal recessive form of the disease is caused by mutations in Paraplegin, which is a conserved subunit of the ubiquitous and ATP-dependent m-AAA protease in mitochondria. The m-AAA protease carries out protein quality control in the inner membrane of the mitochondria, suggesting a pathogenic role of misfolded proteins in HSP. A recent study demonstrates that the m-AAA protease regulates ribosome assembly and translation within mitochondria by controlling proteolytic maturation of a ribosomal subunit. Here, we will discuss implications of the dual role of the m-AAA protease in protein activation and degradation for mitochondrial dysfunction and axonal degeneration.
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intramuscular viral delivery of Paraplegin rescues peripheral axonopathy in a model of hereditary spastic paraplegia
Journal of Clinical Investigation, 2005Co-Authors: Marinella Pirozzi, Angelo Quattrini, Gennaro Andolfi, Giorgia Dina, Maria Chiara Malaguti, Alberto Auricchio, Elena I RugarliAbstract:Degeneration of peripheral motor axons is a common feature of several debilitating diseases including complicated forms of hereditary spastic paraplegia. One such form is caused by loss of the mitochondrial energy-dependent protease Paraplegin. Paraplegin-deficient mice display a progressive degeneration in several axonal tracts, characterized by the accumulation of morphological abnormal mitochondria. We show that adenoassociated virus–mediated (AAV-mediated) intramuscular delivery of Paraplegin halted the progression of neuropathological changes and rescued mitochondrial morphology in the peripheral nerves of Paraplegin-deficient mice. One single injection before onset of symptoms improved the motor performance of Paraplegin-deficient mice for up to 10 months, indicating that the peripheral neuropathy contributes to the clinical phenotype. This study provides a proof of principle that gene transfer may be an effective therapeutic option for patients with Paraplegin deficiency and demonstrates that AAV vectors can be successfully employed for retrograde delivery of an intracellular protein to spinal motor neurons, opening new perspectives for several hereditary axonal neuropathies of the peripheral nerves.
Mirko Koppen - One of the best experts on this subject based on the ideXlab platform.
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Reconstitution of mammalian m-AAA protease complexes with variable subunit composition in yeast mitochondria
2020Co-Authors: Mirko KoppenAbstract:The m-AAA protease, an ATP-dependent proteolytic complex in the mitochondrial inner membrane, controls protein quality and regulates ribosome assembly within mitochondria. Mutations in the human m-AAA protease subunit Paraplegin cause hereditary spastic paraplegia (HSP) characterised by cell-specific axonal degeneration which is also observed in a Paraplegin-deficient mouse model. It has been proposed that Paraplegin mediates proteolytic processing of OPA1 which is essential for mitochondrial morphology and linked to dominant optic atrophy, another neurodegenerative disease in humans. Paraplegin assembles with homologous Afg3l2 subunits into hetero-oligomeric complexes, but the consequences of a loss of Paraplegin for m-AAA protease assembly and function remain unclear. Moreover, a third putative m-AAA protease subunit, termed Afg3l1, is expressed in mice but its role for m-AAA protease activity has not been determined. The assembly status of human AFG3L2 was monitored in Paraplegin-deficient mitochondria from human HSP cells revealing the existence of a homo-oligomeric AFG3L2 complex which was also formed upon heterologous expression in yeast. This AFG3L2 complex is proteolytically active as it could substitute for the yeast m-AAA protease. In related complementation studies in yeast, murine m-AAA protease subunits were found to assemble into several proteolytic complexes with variable subunit composition in the mitochondrial inner membrane. Homo-oligomeric Afg3l1 and Afg3l2 complexes and hetero-oligomeric complexes of both proteins with Paraplegin could be identified. Afg3l1 was established as a bona fide subunit of m-AAA proteases with proteolytic activity. All assemblies have conserved and overlapping substrate specificities as they were able to maintain mitochondrial housekeeping functions in yeast. These results suggest that the lack of Paraplegin does not lead to a complete loss of m-AAA protease activity in affected mitochondria. Instead, m-AAA protease complexes with a different subunit composition could be formed which may substitute for Paraplegin-containing m-AAA proteases. First evidence for different substrate specificities of m-AAA proteases differing in their subunit composition was obtained by reconstitution of OPA1 cleavage in yeast cells harbouring different mammalian m-AAA protease complexes. The efficiency of OPA1 processing was dependent on the subunit composition of mammalian m-AAA proteases. Homo-oligomeric complexes composed of murine Afg3l1, Afg3l2, or human AFG3L2 cleaved OPA1 with higher efficiency than hetero-oligomeric complexes containing Paraplegin. This also confirms OPA1 as a novel potential substrate of the m-AAA protease. Taken together, these findings reveal an unexpected variety of mammalian m-AAA proteases in the inner mitochondrial membrane and may help to understand the pathogenesis and tissue-specificity of HSP due to a loss of Paraplegin.
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variable and tissue specific subunit composition of mitochondrial m aaa protease complexes linked to hereditary spastic paraplegia
Molecular and Cellular Biology, 2007Co-Authors: Mirko Koppen, Elena I Rugarli, Giorgio Casari, Metodi D Metodiev, Thomas LangerAbstract:The m-AAA protease, an ATP-dependent proteolytic complex in the mitochondrial inner membrane, controls protein quality and regulates ribosome assembly, thus exerting essential housekeeping functions within mitochondria. Mutations in the m-AAA protease subunit Paraplegin cause axonal degeneration in hereditary spastic paraplegia (HSP), but the basis for the unexpected tissue specificity is not understood. Paraplegin assembles with homologous Afg3l2 subunits into hetero-oligomeric complexes which can substitute for yeast m-AAA proteases, demonstrating functional conservation. The function of a third paralogue, Afg3l1 expressed in mouse, is unknown. Here, we analyze the assembly of Paraplegin into m-AAA complexes and monitor consequences of Paraplegin deficiency in HSP fibroblasts and in a mouse model for HSP. Our findings reveal variability in the assembly of m-AAA proteases in mitochondria in different tissues. Homo-oligomeric Afg3l1 and Afg3l2 complexes and hetero-oligomeric assemblies of both proteins with Paraplegin can be formed. Yeast complementation studies demonstrate the proteolytic activity of these assemblies. Paraplegin deficiency in HSP does not result in the loss of m-AAA protease activity in brain mitochondria. Rather, homo-oligomeric Afg3l2 complexes accumulate, and these complexes can substitute for housekeeping functions of Paraplegin-containing m-AAA complexes. We therefore propose that the formation of m-AAA proteases with altered substrate specificities leads to axonal degeneration in HSP.
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the m aaa protease defective in hereditary spastic paraplegia controls ribosome assembly in mitochondria
Cell, 2005Co-Authors: Mark Nolden, Elena I Rugarli, Mirko Koppen, Andrea Bernacchia, Sarah Ehses, Thomas LangerAbstract:Summary AAA proteases comprise a conserved family of membrane bound ATP-dependent proteases that ensures the quality control of mitochondrial inner-membrane proteins. Inactivation of AAA proteases causes pleiotropic phenotypes in various organisms, including respiratory deficiencies, mitochondrial morphology defects, and axonal degeneration in hereditary spastic paraplegia (HSP). The molecular basis of these defects, however, remained unclear. Here, we describe a regulatory role of an AAA protease for mitochondrial protein synthesis in yeast. The mitochondrial ribosomal protein MrpL32 is processed by the m -AAA protease, allowing its association with preassembled ribosomal particles and completion of ribosome assembly in close proximity to the inner membrane. Maturation of MrpL32 and mitochondrial protein synthesis are also impaired in a HSP mouse model lacking the m -AAA protease subunit Paraplegin, demonstrating functional conservation. Our findings therefore rationalize mitochondrial defects associated with m -AAA protease mutants in yeast and shed new light on the mechanism of axonal degeneration in HSP.
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loss of m aaa protease in mitochondria causes complex i deficiency and increased sensitivity to oxidative stress in hereditary spastic paraplegia
Journal of Cell Biology, 2003Co-Authors: Luigia Atorino, Roberto Marconi, Laura Silvestri, Mirko Koppen, Laura Cassina, Andrea Ballabio, Thomas Langer, Giorgio CasariAbstract:Mmutations in Paraplegin, a putative mitochondrial metallopeptidase of the AAA family, cause an autosomal recessive form of hereditary spastic paraplegia (HSP). Here, we analyze the function of Paraplegin at the cellular level and characterize the phenotypic defects of HSP patients' cells lacking this protein. We demonstrate that Paraplegin coassembles with a homologous protein, AFG3L2, in the mitochondrial inner membrane. These two proteins form a high molecular mass complex, which we show to be aberrant in HSP fibroblasts. The loss of this complex causes a reduced complex I activity in mitochondria and an increased sensitivity to oxidant stress, which can both be rescued by exogenous expression of wild-type Paraplegin. Furthermore, complementation studies in yeast demonstrate functional conservation of the human Paraplegin–AFG3L2 complex with the yeast m-AAA protease and assign proteolytic activity to this structure. These results shed new light on the molecular pathogenesis of HSP and functionally link AFG3L2 to this neurodegenerative disease.
Chantal M E Tallaksen - One of the best experts on this subject based on the ideXlab platform.
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Spastic paraplegia type 7 is associated with multiple mitochondrial DNA deletions
PLOS ONE, 2014Co-Authors: Iselin Marie Wedding, Chantal M E Tallaksen, Jeanette Koht, Gia Tuong Thi Tran, Doriana Misceo, Kaja Kristine Selmer, Asbjørn Holmgren, Eirik Frengen, Laurence A. Bindoff, Charalampos TzoulisAbstract:Spastic paraplegia 7 is an autosomal recessive disorder caused by mutations in the gene encoding Paraplegin, a protein located at the inner mitochondrial membrane and involved in the processing of other mitochondrial proteins. The mechanism whereby Paraplegin mutations cause disease is unknown. We studied two female and two male adult patients from two Norwegian families with a combination of progressive external ophthalmoplegia and spastic paraplegia. Sequencing of SPG7 revealed a novel missense mutation, c.2102A>C, p.H 701P, which was homozygous in one family and compound heterozygous in trans with a known pathogenic mutation c.1454_1462del in the other. Muscle was examined from an additional, unrelated adult female patient with a similar phenotype caused by a homozygous c.1047insC mutation in SPG7. Immunohistochemical studies in skeletal muscle showed mosaic deficiency predominantly affecting respiratory complex I, but also complexes III and IV. Molecular studies in single, microdissected fibres showed multiple mitochondrial DNA deletions segregating at high levels (38–97%) in respiratory deficient fibres. Our findings demonstrate for the first time that Paraplegin mutations cause accumulation of mitochondrial DNA damage and multiple respiratory chain deficiencies. While Paraplegin is not known to be directly associated with the mitochondrial nucleoid, it is known to process other mitochondrial proteins and it is possible therefore that Paraplegin mutations lead to mitochondrial DNA deletions by impairing proteins involved in the homeostasis of the mitochondrial genome. These studies increase our understanding of the molecular pathogenesis of SPG7 mutations and suggest that SPG7 testing should be included in the diagnostic workup of autosomal recessive, progressive external ophthalmoplegia, especially if spasticity is present.
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prevalence of hereditary ataxia and spastic paraplegia in southeast norway a population based study
Brain, 2009Co-Authors: Anne Kjersti Erichsen, Jeanette Koht, Asbjorg Straypedersen, Michael Abdelnoor, Chantal M E TallaksenAbstract:A population-based, cross-sectional study was performed in southeast Norway, between January 2002 and February 2008, to identify subjects with hereditary ataxia and hereditary spastic paraplegia, and to estimate the prevalence of these disorders. Patients were recruited through colleagues, families, searches in computerized hospital archives and the National Patients’ Association for Hereditary Ataxia and Spastic Paraplegia. Strict criteria were used for inclusion of familial and isolated subjects. A project neurologist examined all index subjects and clinical and genetic data were registered. The source population on January 1, 2008 was 2.63 million and the prevalence day was set as February 1, 2008. One hundred seventy-one subjects from 87 unrelated families with hereditary ataxia and 194 subjects from 65 unrelated families with hereditary spastic paraplegia were included. The total prevalence was estimated at 13.9/100 000. Hereditary ataxia prevalence in the region was estimated at 6.5/100 000: 4.2/100 000 for autosomal-dominant and 2.3/100 000 for autosomal recessive, 0.15/100 000 for Friedreich's ataxia and 0.4/100 000 for ataxia telangiectasia. Hereditary spastic paraplegia prevalence was 7.4/100 000: 5.5/100 000 for autosomal dominant-hereditary spastic paraplegia, 0.6/100 000 for autosomal recessive-hereditary spastic paraplegia and 1.3/100 000 for isolated subjects. Marked differences were found in the frequencies of hereditary ataxia subtypes compared with other countries, while those of the most common autosomal dominant-hereditary spastic paraplegia genotypes, SPG4, SPG3 and SPG31, were similar to those previously reported. Clear variations between age groups and counties were observed, but no gender differences. Mean age on prevalence day was 48 years, mean age at onset was 24 years. We present the largest population study performed on hereditary ataxia and hereditary spastic paraplegia prevalence and report a higher prevalence than expected. Better inclusion criteria and multiple search strategies may explain the observed differences.
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mutation analysis of the Paraplegin gene spg7 in patients with hereditary spastic paraplegia
Neurology, 2006Co-Authors: N Elleuch, Christel Depienne, A Benomar, A Ouvrard M Hernandez, X Ferrer, B Fontaine, D Grid, Chantal M E Tallaksen, R Zemmouri, Giovanni StevaninAbstract:Background: Mutations in the SPG7 gene, which encodes Paraplegin, are responsible for an autosomal recessive hereditary spastic paraplegia (HSP). Objective: To screen the SPG7 gene in a large population of HSP families compatible with autosomal recessive transmission. Methods: The authors analyzed 136 probands with pure or complex HSP for mutations in the SPG7 using denaturation high-performance liquid chromatography and direct sequencing. Results: The authors identified 47 variants including 6 mutations, 27 polymorphisms, and 14 changes with unknown effects. In one family from Morocco, compound c.850_851delTTinsC and c.1742_1744delTGG heterozygous mutations were shown to be causative. This family had complex HSP with cerebellar impairment. Progression of the disease was rapid, resulting in a severe disease after 8 years of duration. Also detected were 20 families with one heterozygous mutation that was not found in a large control population. The mutations produced highly defective proteins in four of these families, suggesting that they were probably causative. Direct sequencing of all exons and reverse transcription PCR experiments demonstrated the absence of a second mutation. However, the p.Ala510Val missense substitution previously described as a polymorphism was shown to be significantly associated with HSP, suggesting that it had a functional effect. Conclusion: SPG7 mutations account for less than 5% of hereditary spastic paraplegia (HSP) families compatible with autosomal recessive inheritance. Cerebellar signs or cerebellar atrophy on brain imaging were the most frequent additional features in patients with SPG7 HSP. Rare nucleotide variants in SPG7 are frequent, complicating routine diagnosis.
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recent advances in hereditary spastic paraplegia
Current Opinion in Neurology, 2001Co-Authors: Chantal M E Tallaksen, Alexandra Durr, Alexis BriceAbstract:: The hereditary spastic paraplegias are a group of rare disorders that are characterized by great clinical and genetic heterogeneity. There has been an exponential increase in the number of HSP loci mapped in recent years, with nine out of the 17 loci reported during the past 2 years. Eight loci have now been identified for the autosomal-dominant form, and seven of these are associated with pure HSP. Spastic paraplegia-4 remains the most frequent locus, and is usually associated with a pure phenotype. Although the corresponding spastin gene was only recently identified, over 50 mutations have been described to date, which renders molecular diagnosis difficult. Five loci are known for autosomal-recessive HSP, and four of these are associated with complex forms, all with different phenotypes. Two genes have been identified: Paraplegin and sacsin. Finally, three loci have been identified in X-linked HSP, two of which are complex forms. The genes that encode L1 and PLP were the first to be identified in HSP disorders. Surprisingly, the five genes encode proteins of different families, making understanding and diagnosis of HSP even more difficult. The discovery of new genes should hopefully help to clarify the pathophysiology of these disorders.
