Browsing by Subject "Tricarboxylic acid cycle"

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    Investigation into Tissue-Specific Mechanisms of Mitochondrial Dysfunction: Models of SUCLA2 Deficiency and a Screen for Potential Genetic Modifiers
    (2023-11) Lancaster, Makayla S.; Graham, Brett H.; Kim, Jungsu; Hoffman-Longtin, Krista; White, Kenneth E.
    With no currently effective treatments available, mitochondrial diseases are one of the most common forms of inherited multisystem disease. Primary disorders of the mitochondria affect an estimated 1 in 4,300 people with typical onset in early childhood. Mitochondrial disorders are classically defined by defects in the mitochondrial powerhouse, or respiratory chain (RC). Therefore, they are uniquely complex as the proteins within the RC are encoded by two separate genomes – nuclear DNA (nDNA) and mitochondrial DNA (mtDNA). The mitochondrial genome encodes 13 protein genes within the RC, with the remaining mitochondrial proteome being nuclear encoded. Therefore, mitochondrial disorders result from pathogenic variants within either genome. While mitochondrial disorders can affect multiple tissue symptoms, organs with high energy demand, such as the brain and skeletal muscle, are most typically affected; thus, mitochondrial disease typically manifests as an encephalomyopathy. A wide range of symptoms, including developmental delay, seizures, strokes, and sensorineural hearing loss have been associated with mitochondrial dysfunction. In short, however, investigation into the pathogenic mechanisms of mitochondrial disorders has proven difficult due to the wide clinical and genetic heterogeneity associated with the disorders. Therefore, this project seeks to investigate pathways of mitochondrial dysfunction using two genetic approaches. First, reverse genetics tools are used to generate tissue-specific mouse models of succinyl-CoA synthetase deficiency, which is a known cause of mitochondrial disease in humans. In parallel, forward genetics is used to screen for variation in mitochondrial phenotypes in a genetically diverse population of mice to identify potential genetic modifiers of mitochondrial function and health. Using both forward and reverse genetics approaches, these studies will allow for the investigation into tissue-specific mitochondrial pathogenesis in novel mouse models, as well as broadly characterize tissue-specific mitochondrial function in vivo. Taken together, both genetic approaches are used to broaden understanding of tissue-specific mitochondrial function in health and disease.
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    Succinyl-CoA Synthetase Dysfunction as a Mechanism of Mitochondrial Encephalomyopathy: More than Just an Oxidative Energy Deficit
    (MDPI, 2023-06-27) Lancaster, Makayla S.; Graham, Brett H.; Medical and Molecular Genetics, School of Medicine
    Biallelic pathogenic variants in subunits of succinyl-CoA synthetase (SCS), a tricarboxylic acid (TCA) cycle enzyme, are associated with mitochondrial encephalomyopathy in humans. SCS catalyzes the interconversion of succinyl-CoA to succinate, coupled to substrate-level phosphorylation of either ADP or GDP, within the TCA cycle. SCS-deficient encephalomyopathy typically presents in infancy and early childhood, with many patients succumbing to the disease during childhood. Common symptoms include abnormal brain MRI, basal ganglia lesions and cerebral atrophy, severe hypotonia, dystonia, progressive psychomotor regression, and growth deficits. Although subunits of SCS were first identified as causal genes for progressive metabolic encephalomyopathy in the early 2000s, recent investigations are now beginning to unravel the pathomechanisms underlying this metabolic disorder. This article reviews the current understanding of SCS function within and outside the TCA cycle as it relates to the complex and multifactorial mechanisms underlying SCS-related mitochondrial encephalomyopathy.