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Mitochondrial–cellular interactions can contribute to the patholphysiology of disease
Abstracts g Bioinformatics Laboratory, Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Center, Amsterdam, The Netherlands
Body of Abstract: The X–linked disease Barth syndrome (BTHS) is caused by mutations in TAZ; TAZ is the main determinant of the final acyl chain composition of the mitochondrial-specific phospholipid, cardiolipin. To date, a detailed characterization of endogenous TAZ has only been performed in yeast. Here, we demonstrate that surprisingly, mammalian TAZ associates with the matrix-facing leaflet of the inner mitochondrial membrane, revealing a topological difference between yeast and mammalian cardiolipin remodeling. Intriguingly, heterologously expressed human TAZ can functionally replace yeast taffazin even though it localizes to the opposite side of inner membrane as its yeast ortholog. Finally, we demonstrate that the loss-of function mechanisms for two BTHS alleles are the same in humans as originally defined in a yeast BTHS model. Thus, although TAZ-remodeling of cardiolipin occurs on opposite sides of the inner membrane in yeast and mammals, the biochemical defects caused by each tested pathogenic allele is the same.
S5
Abstract: The pathophysiology of mitochondrial disease not only involves alterations in the structure and physiology of the mitochondrion but also in alterations in the interactions between mitochondria and between mitochondria and the nucleus and the extracellular matrix. Mitochondria interact in high energy tissues via direct contact through inter-mitochondrial junctions (IMJs) and the associated alignment of their cristae. Mitochondria interact with the nucleus likely through regulation of high energy intermediates which modulate transcription via the signal transduction pathways and the epigenome. Mitochondria interact with the extracellular matrix, perhaps via the cytoskeleton. Disruption of mitochondrial function in the heart and muscle can reduce mitochondrial IMJs and/or altered cristae alignment. Alterations in mitochondrial pathogenic tRNA mutation heteroplasmy levels that correspond to phenotypic changes can cause distinct phase changes in the nuclear gene transcriptional profiles. Alterations in extracellular matrix can activate the mitochondrial permeability transmission pore causing cellular dysfunction. Hence, clinically relevant mitochondrial dysfunction can be directly related to dysfunctions inside and outside of the cell. doi:10.1016/j.mito.2015.07.021
doi:10.1016/j.mito.2015.07.019
Small molecule modulators for mitochondrial protein import Presenter: Carla Koehler Carla Koehler UCLA, Department of Chemistry and Biochemistry, Los Angeles, CA 90095-1569, USA Body of Abstract: Mitochondrial dysfunction is a contributing factor in degenerative diseases. Modulation of the mitochondrial protein import pathways can have regulatory effects on mitochondrial function. Studying these pathways by conventional methods such as RNAi in mammalian cells can be difficult because it takes several days to knockdown proteins coupled with an overall loss of mitochondrial function. Therefore, we have developed several approaches to develop small molecule modulators for mitochondrial protein translocation. Here we provide an analysis of results from screens to identify inhibitors of the TOM-TIM23 import pathway. We show that one FDA-approved inhibitor (MB-12) can be used in a strategy to treat patients with primary hyperoxaluria 1. The AGTP11LG170R allele in PH1 results in alanine:glyoxylate aminotransferase (AGT) enzyme being mistargeted from peroxisomes to mitochondria. AGT contains a C-terminal peroxisomal targeting sequence, but mutations generate an N-terminal mitochondrial targeting sequence that directs AGT from peroxisomes to mitochondria. Although AGTP11LG170R is functional, the enzyme must translocate to the peroxisome to detoxify glyoxylate by conversion to alanine. Treatment of cells with MB-12 rescues restores peroxisomal trafficking of AGTP11LG170R. This strategy also works to alter Pink1 trafficking in mitochondria, attenuating the mitophagy pathway. This strategy has been useful in generating a toolbox of small molecule modulators for mitochondrial translocation.
doi:10.1016/j.mito.2015.07.020
Mitochondrial–cellular interactions can contribute to the patholphysiology of disease Presenter: Douglas C. Wallace, PhD Douglas C. Wallace Center for Mitochondrial and Epigenomic Medicine, Children’s Hospital of Philadelphia and Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
Day Three — Morning Session Mitochondria-Induced Mayhem: The Role of Other Organelles in Mitochondrial Disease Metabolic stress and ER proteostasis Presenter: Wiep Scheper, PhD Judith van der Harga,d, Anna Nollec,d,e, Susanne LaFleurb,d, Jeroen Hoozemansc,d, Wiep Schepera,c,d,e a Department of Genome Analysis, Academic Medical Center, Amsterdam, The Netherlands b Department of Endocrinolgy, Academic Medical Center, Amsterdam, The Netherlands c Department of Clinical Genetics and Alzheimer Center, VU University Medical Center, Amsterdam, The Netherlands d Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands e Departments of Functional Genomics and Molecular and Cellular Neuroscience, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands Abstract: A key characteristic of many neurodegenerative diseases is a disturbance in the protein homeostasis, or proteostasis, indicated by the massive accumulation of protein aggregates. Disturbance of proteostasis in the endoplasmic reticulum (ER) leads to activation of the unfolded protein response (UPR), a protein quality control mechanism that initially protects the cell against ER stress toxicity. Our lab has demonstrated that the UPR is activated in the brains of patients with diseases characterized by deposits of aggregated hyperphosphorylated tau protein, so-called tauopathies. This includes Alzheimer's disease (AD) and a subset of frontotemporal dementias. In these diseases UPR activation is closely associated with early stages of tau pathology. The strong correlation suggests a functional connection. Studies in cell and animal models support a model where tau phosphorylation is increased upon UPR activation. This still leaves open, what the trigger for UPR activation is in AD and other tauopathies. Decreased glucose metabolism is an established stressor to activate the UPR and interestingly, epidemiologic studies indicate that the metabolic syndrome is a strong risk factor for AD. In addition, (pre)diabetes enhances tau pathology in animal models. Therefore, we investigated UPR activation and tau phosphorylation different models for metabolic stress, including cell models and animal models for hibernation and diabetes mellitus. Our data support a model where tau phosphorylation is increased in response to metabolic stress as part of an adaptive response to restore the energy balance. This is a reversible response that
Body of Abstract: The X–linked disease Barth syndrome (BTHS) is caused by mutations in TAZ; TAZ is the main determinant of the final acyl chain composition of the mitochondrial-specific phospholipid, cardiolipin. To date, a detailed characterization of endogenous TAZ has only been performed in yeast. Here, we demonstrate that surprisingly, mammalian TAZ associates with the matrix-facing leaflet of the inner mitochondrial membrane, revealing a topological difference between yeast and mammalian cardiolipin remodeling. Intriguingly, heterologously expressed human TAZ can functionally replace yeast taffazin even though it localizes to the opposite side of inner membrane as its yeast ortholog. Finally, we demonstrate that the loss-of function mechanisms for two BTHS alleles are the same in humans as originally defined in a yeast BTHS model. Thus, although TAZ-remodeling of cardiolipin occurs on opposite sides of the inner membrane in yeast and mammals, the biochemical defects caused by each tested pathogenic allele is the same.
S5
Abstract: The pathophysiology of mitochondrial disease not only involves alterations in the structure and physiology of the mitochondrion but also in alterations in the interactions between mitochondria and between mitochondria and the nucleus and the extracellular matrix. Mitochondria interact in high energy tissues via direct contact through inter-mitochondrial junctions (IMJs) and the associated alignment of their cristae. Mitochondria interact with the nucleus likely through regulation of high energy intermediates which modulate transcription via the signal transduction pathways and the epigenome. Mitochondria interact with the extracellular matrix, perhaps via the cytoskeleton. Disruption of mitochondrial function in the heart and muscle can reduce mitochondrial IMJs and/or altered cristae alignment. Alterations in mitochondrial pathogenic tRNA mutation heteroplasmy levels that correspond to phenotypic changes can cause distinct phase changes in the nuclear gene transcriptional profiles. Alterations in extracellular matrix can activate the mitochondrial permeability transmission pore causing cellular dysfunction. Hence, clinically relevant mitochondrial dysfunction can be directly related to dysfunctions inside and outside of the cell. doi:10.1016/j.mito.2015.07.021
doi:10.1016/j.mito.2015.07.019
Small molecule modulators for mitochondrial protein import Presenter: Carla Koehler Carla Koehler UCLA, Department of Chemistry and Biochemistry, Los Angeles, CA 90095-1569, USA Body of Abstract: Mitochondrial dysfunction is a contributing factor in degenerative diseases. Modulation of the mitochondrial protein import pathways can have regulatory effects on mitochondrial function. Studying these pathways by conventional methods such as RNAi in mammalian cells can be difficult because it takes several days to knockdown proteins coupled with an overall loss of mitochondrial function. Therefore, we have developed several approaches to develop small molecule modulators for mitochondrial protein translocation. Here we provide an analysis of results from screens to identify inhibitors of the TOM-TIM23 import pathway. We show that one FDA-approved inhibitor (MB-12) can be used in a strategy to treat patients with primary hyperoxaluria 1. The AGTP11LG170R allele in PH1 results in alanine:glyoxylate aminotransferase (AGT) enzyme being mistargeted from peroxisomes to mitochondria. AGT contains a C-terminal peroxisomal targeting sequence, but mutations generate an N-terminal mitochondrial targeting sequence that directs AGT from peroxisomes to mitochondria. Although AGTP11LG170R is functional, the enzyme must translocate to the peroxisome to detoxify glyoxylate by conversion to alanine. Treatment of cells with MB-12 rescues restores peroxisomal trafficking of AGTP11LG170R. This strategy also works to alter Pink1 trafficking in mitochondria, attenuating the mitophagy pathway. This strategy has been useful in generating a toolbox of small molecule modulators for mitochondrial translocation.
doi:10.1016/j.mito.2015.07.020
Mitochondrial–cellular interactions can contribute to the patholphysiology of disease Presenter: Douglas C. Wallace, PhD Douglas C. Wallace Center for Mitochondrial and Epigenomic Medicine, Children’s Hospital of Philadelphia and Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
Day Three — Morning Session Mitochondria-Induced Mayhem: The Role of Other Organelles in Mitochondrial Disease Metabolic stress and ER proteostasis Presenter: Wiep Scheper, PhD Judith van der Harga,d, Anna Nollec,d,e, Susanne LaFleurb,d, Jeroen Hoozemansc,d, Wiep Schepera,c,d,e a Department of Genome Analysis, Academic Medical Center, Amsterdam, The Netherlands b Department of Endocrinolgy, Academic Medical Center, Amsterdam, The Netherlands c Department of Clinical Genetics and Alzheimer Center, VU University Medical Center, Amsterdam, The Netherlands d Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands e Departments of Functional Genomics and Molecular and Cellular Neuroscience, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands Abstract: A key characteristic of many neurodegenerative diseases is a disturbance in the protein homeostasis, or proteostasis, indicated by the massive accumulation of protein aggregates. Disturbance of proteostasis in the endoplasmic reticulum (ER) leads to activation of the unfolded protein response (UPR), a protein quality control mechanism that initially protects the cell against ER stress toxicity. Our lab has demonstrated that the UPR is activated in the brains of patients with diseases characterized by deposits of aggregated hyperphosphorylated tau protein, so-called tauopathies. This includes Alzheimer's disease (AD) and a subset of frontotemporal dementias. In these diseases UPR activation is closely associated with early stages of tau pathology. The strong correlation suggests a functional connection. Studies in cell and animal models support a model where tau phosphorylation is increased upon UPR activation. This still leaves open, what the trigger for UPR activation is in AD and other tauopathies. Decreased glucose metabolism is an established stressor to activate the UPR and interestingly, epidemiologic studies indicate that the metabolic syndrome is a strong risk factor for AD. In addition, (pre)diabetes enhances tau pathology in animal models. Therefore, we investigated UPR activation and tau phosphorylation different models for metabolic stress, including cell models and animal models for hibernation and diabetes mellitus. Our data support a model where tau phosphorylation is increased in response to metabolic stress as part of an adaptive response to restore the energy balance. This is a reversible response that