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Degeneration of olivo-cerebellar circuitry in patients with mitochondrial disease: A neuropathological study
672
Abstracts
drial DNA copy number shows a striking reduction of mitochondrial genomes in these cells. Examination of the spinal cord reveals a dramatic loss of myelinated axons from the posterior columns, a commonly affected region in patients with mitochondrial disease. This area of the cord corresponds to a loss of innervation from degenerative DRG neurons. This study gives us some insight into the pattern and mechanisms of degeneration leading to the clinical phenotype of peripheral neuropathy in mitochondrial disease. Our findings highlight that the main source of abnormality is likely to be the DRG in many of these patients with the presence of severe respiratory chain deficiency.
doi:10.1016/j.mito.2011.03.104
92 Primary oligodendropathy in a patient with Kearns Sayre syndrome Nichola Z. Lax⁎, Amy K. Reeve, Philippa Hepplewhite, Evelyn Jaros, Robert W. Taylor, Doug M. Turnbull, Don J. Mahad Mitochondrial research group, Institute for Ageing and Health, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom Kearns Sayre syndrome (KSS) is predominately a sporadic condition caused by either a large-scale deletion or complex rearrangements of the mitochondrial DNA (mtDNA). It is clinically characterised by progressive external opthalmoplegia, pigmentary retinopathy and an onset before 20 years of age with one of the following features: cerebrospinal fluid protein >1 g/L, cerebellar ataxia or heart block. In addition, abnormalities of the white matter (WM) are well-documented in patients with KSS. Here we present a 40 year old patient harbouring a single deletion of the mtDNA. Our patient demonstrates typical severe spongiform degeneration and demyelination throughout the brain. It is speculated that this alteration is due to a specific vulnerability of oligo dendrocytes in KSS. Fixed and frozen brain tissue was sourced from the Newcastle Brain Tissue Resource. Routine histopathological stains for CFV for identification of neuronal populations, H&E for morphology, Loyez for myelin, and Bielschowsky for axons were applied. Immunohistochemistry was performed with a variety of antibodies using a polymer detection system. Percentage deletion level was performed using quantitative real-time PCR in individual neurons. In addition to severe WM vacuolation within the cerebellum, we detected the presence of an oligodendrocyte deficient lesion. This welldemarcated lesion was defined by preservation of myelinated axons, but with a dramatic loss of oligodendrocytes. There is evidence of poly (ADP-ribose) polymer (PAR) activation and translocation of Apoptosis Inducing Factor (AIF) to the nuclei of cells residing in this region, which suggests a mechanism of oligodendrocyte cell death. Surviving oligodendrocytes are devoid of integral mitochondrial subunits. We also show that the percentage deletion level in this region is high. This work provides strong evidence of primary oligodendrocyte dysfunction and cell death due to a single deletion of the mtDNA and shows some insight into what may be happening in the early stages of white matter degeneration in KSS.
doi:10.1016/j.mito.2011.03.105
93 Degeneration of olivo-cerebellar circuitry in patients with mitochondrial disease: A neuropathological study Nichola Z. Lax⁎, Amy K. Reeve, Philippa Hepplewhite, Charlotte Alston, Evelyn Jaros, Robert W. Taylor, Doug M. Turnbull
Mitochondrial research group, Institute for Ageing and Health, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom Mutations of the mitochondrial DNA (mtDNA) genome and nuclear-encoded mitochondrial maintenance genes lead to neurodegeneration. Consequently, neurological deficits are prominent in patients with mitochondrial disease and can often be the most debilitating symptoms. Despite this known involvement of the central nervous system, our understanding of the mechanisms leading to neural dysfunction and degeneration is limited. The present investigation aims to unravel the neuropathological changes underpinning the clinical symptom of ataxia. Ataxia is a common manifestation of patients with mitochondrial disease with approximately one third of our patients affected. Here we explore some of the neurodegenerative changes occurring in the inferior olivary nucleus and cerebellum of twelve clinically and genetically well-defined patients with a range of mitochondrial defects in relation to ataxia. The results of our analysis show that the cerebellum is particularly vulnerable to defects in mitochondrial function. Using modified stereological techniques, we performed an in depth assessment of neuron loss in the inferior olive, dentate nucleus and Purkinje cell populations. We show that Purkinje cell degeneration is common and often severe, with the presence of multiple microinfarcts generally accompanied by proliferation of Bergmann glia. There is strong evidence of mitochondrial dysfunction in surviving neurons with prominent deficiencies of subunits of mitochondrial complex I. We report evidence of secondary axonal degeneration in white matter tracts of the cerebellum as a consequence of cell loss. The changes seen are in part mutation specific and relate to both mutation load and copy number in individual neurons. This study is the first of this kind to comprehensively evaluate the neuropathological and molecular substrates of ataxia in patients with mitochondrial disease. This extensive neuropathological study will enable us to formulate hypotheses about the mechanisms leading to neuronal cell dysfunction and death in not only our patients with mitochondrial disease, but potentially other neurodegenerative disorders. doi:10.1016/j.mito.2011.03.106
94 Altered redox status of coenzyme Q9 reflects mitochondrial electron transport chain defects in C. elegans Valeria Vasta a, Margaret Sedensky a,c,d,⁎, Phil Morgan a,c,d, Sihoun Hahn a,b a Seattle Children's Research Institute, Seattle, WA, United States b Department of Pediatrics, University of Washington, Seattle, WA, United States c Department of Anesthesiology, University of Washington, Seattle, WA, United States; d Seattle Children's Hospital, Seattle, WA, United States Introduction: Coenzyme Q (CoQ) is a mobile electron carrier from complexes I or II to complex III in the mitochondrial electron transport chain (ETC). CoQ may exist in either an oxidized or reduced state; the reduced form (ubiquinol) also functions as an antioxidant. The redox status of CoQ is an important marker for metabolic and oxidative stress associated with diseases such as chronic obstructive pulmonary disease, Parkinson disease and Alzheimer's disease. In patients with probable ETC defects, total muscle CoQ10, and not its redox state, was reported as the best predictor of an enzymatic defect (1). However, no underlying genetic abnormalities in those patients were available. Here, we developed an assay to determine reduced and oxidized CoQ and present proof of principle data for the usefulness of the technique in the characterization of ETC defects. We hypothesized that the redox status of CoQ would vary depending on whether the ETC defect was proximal or distal to CoQ.
Abstracts
drial DNA copy number shows a striking reduction of mitochondrial genomes in these cells. Examination of the spinal cord reveals a dramatic loss of myelinated axons from the posterior columns, a commonly affected region in patients with mitochondrial disease. This area of the cord corresponds to a loss of innervation from degenerative DRG neurons. This study gives us some insight into the pattern and mechanisms of degeneration leading to the clinical phenotype of peripheral neuropathy in mitochondrial disease. Our findings highlight that the main source of abnormality is likely to be the DRG in many of these patients with the presence of severe respiratory chain deficiency.
doi:10.1016/j.mito.2011.03.104
92 Primary oligodendropathy in a patient with Kearns Sayre syndrome Nichola Z. Lax⁎, Amy K. Reeve, Philippa Hepplewhite, Evelyn Jaros, Robert W. Taylor, Doug M. Turnbull, Don J. Mahad Mitochondrial research group, Institute for Ageing and Health, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom Kearns Sayre syndrome (KSS) is predominately a sporadic condition caused by either a large-scale deletion or complex rearrangements of the mitochondrial DNA (mtDNA). It is clinically characterised by progressive external opthalmoplegia, pigmentary retinopathy and an onset before 20 years of age with one of the following features: cerebrospinal fluid protein >1 g/L, cerebellar ataxia or heart block. In addition, abnormalities of the white matter (WM) are well-documented in patients with KSS. Here we present a 40 year old patient harbouring a single deletion of the mtDNA. Our patient demonstrates typical severe spongiform degeneration and demyelination throughout the brain. It is speculated that this alteration is due to a specific vulnerability of oligo dendrocytes in KSS. Fixed and frozen brain tissue was sourced from the Newcastle Brain Tissue Resource. Routine histopathological stains for CFV for identification of neuronal populations, H&E for morphology, Loyez for myelin, and Bielschowsky for axons were applied. Immunohistochemistry was performed with a variety of antibodies using a polymer detection system. Percentage deletion level was performed using quantitative real-time PCR in individual neurons. In addition to severe WM vacuolation within the cerebellum, we detected the presence of an oligodendrocyte deficient lesion. This welldemarcated lesion was defined by preservation of myelinated axons, but with a dramatic loss of oligodendrocytes. There is evidence of poly (ADP-ribose) polymer (PAR) activation and translocation of Apoptosis Inducing Factor (AIF) to the nuclei of cells residing in this region, which suggests a mechanism of oligodendrocyte cell death. Surviving oligodendrocytes are devoid of integral mitochondrial subunits. We also show that the percentage deletion level in this region is high. This work provides strong evidence of primary oligodendrocyte dysfunction and cell death due to a single deletion of the mtDNA and shows some insight into what may be happening in the early stages of white matter degeneration in KSS.
doi:10.1016/j.mito.2011.03.105
93 Degeneration of olivo-cerebellar circuitry in patients with mitochondrial disease: A neuropathological study Nichola Z. Lax⁎, Amy K. Reeve, Philippa Hepplewhite, Charlotte Alston, Evelyn Jaros, Robert W. Taylor, Doug M. Turnbull
Mitochondrial research group, Institute for Ageing and Health, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom Mutations of the mitochondrial DNA (mtDNA) genome and nuclear-encoded mitochondrial maintenance genes lead to neurodegeneration. Consequently, neurological deficits are prominent in patients with mitochondrial disease and can often be the most debilitating symptoms. Despite this known involvement of the central nervous system, our understanding of the mechanisms leading to neural dysfunction and degeneration is limited. The present investigation aims to unravel the neuropathological changes underpinning the clinical symptom of ataxia. Ataxia is a common manifestation of patients with mitochondrial disease with approximately one third of our patients affected. Here we explore some of the neurodegenerative changes occurring in the inferior olivary nucleus and cerebellum of twelve clinically and genetically well-defined patients with a range of mitochondrial defects in relation to ataxia. The results of our analysis show that the cerebellum is particularly vulnerable to defects in mitochondrial function. Using modified stereological techniques, we performed an in depth assessment of neuron loss in the inferior olive, dentate nucleus and Purkinje cell populations. We show that Purkinje cell degeneration is common and often severe, with the presence of multiple microinfarcts generally accompanied by proliferation of Bergmann glia. There is strong evidence of mitochondrial dysfunction in surviving neurons with prominent deficiencies of subunits of mitochondrial complex I. We report evidence of secondary axonal degeneration in white matter tracts of the cerebellum as a consequence of cell loss. The changes seen are in part mutation specific and relate to both mutation load and copy number in individual neurons. This study is the first of this kind to comprehensively evaluate the neuropathological and molecular substrates of ataxia in patients with mitochondrial disease. This extensive neuropathological study will enable us to formulate hypotheses about the mechanisms leading to neuronal cell dysfunction and death in not only our patients with mitochondrial disease, but potentially other neurodegenerative disorders. doi:10.1016/j.mito.2011.03.106
94 Altered redox status of coenzyme Q9 reflects mitochondrial electron transport chain defects in C. elegans Valeria Vasta a, Margaret Sedensky a,c,d,⁎, Phil Morgan a,c,d, Sihoun Hahn a,b a Seattle Children's Research Institute, Seattle, WA, United States b Department of Pediatrics, University of Washington, Seattle, WA, United States c Department of Anesthesiology, University of Washington, Seattle, WA, United States; d Seattle Children's Hospital, Seattle, WA, United States Introduction: Coenzyme Q (CoQ) is a mobile electron carrier from complexes I or II to complex III in the mitochondrial electron transport chain (ETC). CoQ may exist in either an oxidized or reduced state; the reduced form (ubiquinol) also functions as an antioxidant. The redox status of CoQ is an important marker for metabolic and oxidative stress associated with diseases such as chronic obstructive pulmonary disease, Parkinson disease and Alzheimer's disease. In patients with probable ETC defects, total muscle CoQ10, and not its redox state, was reported as the best predictor of an enzymatic defect (1). However, no underlying genetic abnormalities in those patients were available. Here, we developed an assay to determine reduced and oxidized CoQ and present proof of principle data for the usefulness of the technique in the characterization of ETC defects. We hypothesized that the redox status of CoQ would vary depending on whether the ETC defect was proximal or distal to CoQ.