IU Indianapolis ScholarWorks :: Browsing by Subject "mitochondria"

Browsing by Subject "mitochondria"

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An expanded population of CD8^dim T cells with features of mitochondrial dysfunction and senescence is associated with persistent HIV-associated Kaposi’s sarcoma under ART
(Frontiers, 2022-09-29) Clutton, Genevieve T.; Weideman, Ann Marie K.; Goonetilleke, Nilu P.; Maurer , Toby; Dermatology, School of Medicine
HIV-associated Kaposi’s sarcoma (KS), which is caused by Kaposi’s sarcoma-associated herpesvirus, usually arises in the context of uncontrolled HIV replication and immunosuppression. However, disease occasionally occurs in individuals with durable HIV viral suppression and CD4 T cell recovery under antiretroviral therapy (ART). The underlying mechanisms associated with this phenomenon are unclear. Suppression of viral infections can be mediated by CD8 T cells, which detect infected cells via their T cell receptor and the CD8 coreceptor. However, CD8 T cells exhibit signs of functional exhaustion in untreated HIV infection that may not be fully reversed under ART. To investigate whether KS under ART was associated with phenotypic and functional perturbations of CD8 T cells, we performed a cross-sectional study comparing HIV-infected individuals with persistent KS under effective ART (HIV+ KS+) to HIV-infected individuals receiving effective ART with no documented history of KS (HIV+ KSneg). A subset of T cells with low cell surface expression of CD8 (“CD8dim T cells”) was expanded in HIV+ KS+ compared with HIV+ KSneg participants. Relative to CD8bright T cells, CD8dim T cells exhibited signs of senescence (CD57) and mitochondrial alterations (PGC-1α, MitoTracker) ex vivo. Mitochondrial activity (MitoTracker) was also reduced in proliferating CD8dim T cells. These findings indicate that an expanded CD8dim T cell population displaying features of senescence and mitochondrial dysfunction is associated with KS disease under ART. CD8 coreceptor down-modulation may be symptomatic of ongoing disease.
Bif-1 Interacts with Prohibitin-2 to Regulate Mitochondrial Inner Membrane during Cell Stress and Apoptosis
(American Society of Nephrology, 2019-05-24) Cho, Sung-Gyu; Xiao, Xiao; Wang, Shixuan; Gao, Hua; Rafikov, Ruslan; Black, Stephen; Huang, Shang; Ding, Han-Fei; Yoon, Yisang; Kirken, Robert A.; Yin, Xiao-Ming; Wang, Hong-Gang; Dong, Zheng; Medicine, School of Medicine
Background Mitochondria are dynamic organelles that undergo fission and fusion. During cell stress, mitochondrial dynamics shift to fission, leading to mitochondrial fragmentation, membrane leakage, and apoptosis. Mitochondrial fragmentation requires the cleavage of both outer and inner membranes, but the mechanism of inner membrane cleavage is unclear. Bif-1 and prohibitin-2 may regulate mitochondrial dynamics. Methods We used azide-induced ATP depletion to incite cell stress in mouse embryonic fibroblasts and renal proximal tubular cells, and renal ischemia-reperfusion to induce stress in mice. We also used knockout cells and mice to determine the role of Bif-1, and used multiple techniques to analyze the molecular interaction between Bif-1 and prohibitin-2. Results Upon cell stress, Bif-1 translocated to mitochondria to bind prohibitin-2, resulting in the disruption of prohibitin complex and proteolytic inactivation of the inner membrane fusion protein OPA1. Bif-1-deficiency inhibited prohibitin complex disruption, OPA1 proteolysis, mitochondrial fragmentation, and apoptosis. Domain deletion analysis indicated that Bif-1 interacted with prohibitin-2 via its C-terminus. Notably, mutation of Bif-1 at its C-terminal tryptophan-344 not only prevented Bif-1/prohibitin-2 interaction but also reduced prohibitin complex disruption, OPA1 proteolysis, mitochondrial fragmentation, and apoptosis, supporting a pathogenic role of Bif-1/prohibitin-2 interaction. In mice, Bif-1 bound prohibitin-2 during renal ischemia/reperfusion injury, and Bif-1-deficiency protected against OPA1 proteolysis, mitochondrial fragmentation, apoptosis and kidney injury. Conclusions These findings suggest that during cell stress, Bif-1 regulates mitochondrial inner membrane by interacting with prohibitin-2 to disrupt prohibitin complexes and induce OPA1 proteolysis and inactivation.
Cardiovascular Research in Friedreich Ataxia: Unmet Needs and Opportunities
(Elsevier, 2022-12) Payne, R. Mark; Pediatrics, School of Medicine
Friedreich Ataxia (FRDA) is an autosomal recessive disease in which a mitochondrial protein, frataxin, is severely decreased in its expression. In addition to progressive ataxia, patients with FRDA often develop a cardiomyopathy that can be hypertrophic. This cardiomyopathy is unlike the sarcomeric hypertrophic cardiomyopathies in that the hypertrophy is associated with massive mitochondrial proliferation within the cardiomyocyte rather than contractile protein overexpression. This is associated with atrial arrhythmias, apoptosis, and fibrosis over time, and patients often develop heart failure leading to premature death. The differences between this mitochondrial cardiomyopathy and the more common contractile protein hypertrophic cardiomyopathies can be a source of misunderstanding in the management of these patients. Although imaging studies have revealed much about the structure and function of the heart in this disease, we still lack an understanding of many important clinical and fundamental molecular events that determine outcome of the heart in FRDA. This review will describe the current basic and clinical understanding of the FRDA heart, and most importantly, identify major gaps in our knowledge that represent new directions and opportunities for research.
Conditional Targeting of the DNA Repair Enzyme hOGG1 into Mitochondria
(2002-11) Rachek, Lyudmila I.; Grishko, Valentina I.; Musiyenko, Sergiy I.; Kelley, Mark R.; LeDoux, Susan P.; Wilson, Glenn L.
Oxidative damage to mitochondrial DNA (mtDNA) has been suggested to be a key factor in the etiologies of many diseases and in the normal process of aging. Although the presence of a repair system to remove this damage has been demonstrated, the mechanisms involved in this repair have not been well defined. In an effort to better understand the physiological role of recombinant 8-oxoguanine DNA glycosylase/apurinic lyase (OGG1) in mtDNA repair, we constructed an expression vector containing the gene for OGG1 downstream of the mitochondrial localization sequence from manganese-superoxide dismutase. This gene construct was placed under the control of a tetracycline-regulated promoter. Transfected cells that conditionally expressed OGG1 in the absence of the tetracycline analogue doxycycline and targeted this recombinant protein to mitochondria were generated. Western blots of mitochondrial extracts from vector- and OGG1-transfected clones with and without doxycycline revealed that removal of doxycycline for 4 days caused an approximate 8-fold increase in the amount of OGG1 protein in mitochondria. Enzyme activity assays and DNA repair studies showed that the doxycycline-dependent recombinant OGG1 is functional. Functional studies revealed that cells containing recombinant OGG1 were more proficient at repairing oxidative damage in their mtDNA, and this increased repair led to increased cellular survival following oxidative stress.
Glucose-independent Acetate Metabolism Promotes Melanoma Cell Survival and Tumor Growth
(American Society for Biochemistry and Molecular Biology, 2016-10-14) Lakhter, Alexander J.; Hamilton, James; Konger, Raymond L.; Brustovetsky, Nickolay; Broxmeyer, Hal E.; Naidu, Samisubbu R.; Microbiology and Immunology, School of Medicine
Tumors rely on multiple nutrients to meet cellular bioenergetics and macromolecular synthesis demands of rapidly dividing cells. Although the role of glucose and glutamine in cancer metabolism is well understood, the relative contribution of acetate metabolism remains to be clarified. We show that glutamine supplementation is not sufficient to prevent loss of cell viability in a subset of glucose-deprived melanoma cells, but synergizes with acetate to support cell survival. Glucose-deprived melanoma cells depend on both oxidative phosphorylation and acetate metabolism for cell survival. Acetate supplementation significantly contributed to maintenance of ATP levels in glucose-starved cells. Unlike acetate, short chain fatty acids such as butyrate and propionate failed to prevent loss of cell viability from glucose deprivation. In vivo studies revealed that in addition to nucleo-cytoplasmic acetate assimilating enzyme ACSS2, mitochondrial ACSS1 was critical for melanoma tumor growth in mice. Our data indicate that acetate metabolism may be a potential therapeutic target for BRAF mutant melanoma.
Identification of TgElp3 as an essential, tail-anchored mitochondrial lysine acetyltransferase in the protozoan pathogen toxoplasma gondii
(2014-07-11) Stilger, Krista L.; Nass, Richard M.; Bauer, Margaret E.; Oxford, G. S.; Queener, Sherry F.; Sullivan, William J., Jr.
Toxoplasma gondii, a single-celled eukaryotic pathogen, has infected one-third of the world’s population and is the causative agent of toxoplasmosis. The disease primarily affects immunocompromised individuals such as AIDS, cancer, and transplant patients. The parasites can infect any nucleated cell in warm-blooded vertebrates, but because they preferentially target CNS, heart, and ocular tissue, manifestations of infection often include encephalitis, myocarditis, and a host of neurological and ocular disorders. Toxoplasma can also be transmitted congenitally by a mother who becomes infected for the first time during pregnancy, which may result in spontaneous abortion or birth defects in the child. Unfortunately, the therapy currently available for treating toxoplasmosis exhibits serious side effects and can cause severe allergic reactions. Therefore, there is a desperate need to identify novel drug targets for developing more effective, less toxic treatments. The regulation of proteins via lysine acetylation, a reversible post-translational modification, has previously been validated as a promising avenue for drug development. Lysine acetyltransferases (KATs) are responsible for the acetylation of hundreds of proteins throughout prokaryotic and eukaryotic cells. In Toxoplasma, we identified a KAT that exhibits homology to Elongator protein 3 (TgElp3), the catalytic component of a transcriptional elongation complex. TgElp3 contains the highly conserved radical S-adenosylmethionine and KAT domains but also possesses a unique C-terminal transmembrane domain (TMD). Interestingly, we found that the TMD anchors TgElp3 in the outer mitochondrial membrane (OMM) such that the catalytic domains are oriented towards the cytosol. Our results uncovered the first tail-anchored mitochondrial KAT reported for any species to date. We also discovered a shortened form of Elp3 present in mouse mitochondria, suggesting that Elp3 functions beyond transcriptional elongation across eukaryotes. Furthermore, we established that TgElp3 is essential for parasite viability and that its OMM localization is important for its function, highlighting its value as a potential target for future drug development.
Mitochondria as Target for Tumor Management of Hemangioendothelioma
(Liebert, 2020) Gordillo, Gayle M.; Biswas, Ayan; Singh, Kanhaiya; Sen, Abhishek; Guda, Poornachander R.; Miller, Caroline; Pan, Xueliang; Khanna, Savita; Cadenas, Enrique; Sen, Chandan K.; Surgery, School of Medicine
Aims: Hemangioendothelioma (HE) may be benign or malignant. Mouse hemangioendothelioma endothelial (EOMA) cells are validated to study mechanisms in HE. This work demonstrates that EOMA cells heavily rely on mitochondria to thrive. Thus, a combination therapy, including weak X-ray therapy (XRT, 0.5 Gy) and a standardized natural berry extract (NBE) was tested. This NBE is known to be effective in managing experimental HE and has been awarded with the Food and Drug Administration Investigational New Drug (FDA-IND) number 140318 for clinical studies on infantile hemangioma. Results: NBE treatment alone selectively attenuated basal oxygen consumption rate of EOMA cells. NBE specifically sensitized EOMA, but not murine aortic endothelial cells to XRT-dependent attenuation of mitochondrial respiration and adenosine triphosphate (ATP) production. Combination treatment, selectively and potently, influenced mitochondrial dynamics in EOMA cells such that fission was augmented. This was achieved by lowering of mitochondrial sirtuin 3 (SIRT3) causing increased phosphorylation of AMP-activated protein kinase (AMPK). A key role of SIRT3 in loss of EOMA cell viability caused by the combination therapy was evident when pyrroloquinoline quinone, an inducer of SIRT3, pretreatment rescued these cells. Innovation and Conclusion: Mitochondria-targeting NBE significantly extended survival of HE-affected mice. The beneficial effect of NBE in combination with weak X-ray therapy was, however, far more potent with threefold increase in murine survival. The observation that safe natural products may target tumor cell mitochondria and sharply lower radiation dosage required for tumor management warrants clinical testing.
Mutant huntingtin fails to directly impair brain mitochondria
(Wiley, 2019) Hamilton, James; Brustovetsky, Tatiana; Brustovetsky, Nickolay; Pharmacology and Toxicology, School of Medicine
Although the mechanisms by which mutant huntingtin (mHtt) results in Huntington's disease (HD) remain unclear, mHtt‐induced mitochondrial defects were implicated in HD pathogenesis. The effect of mHtt could be mediated by transcriptional alterations, by direct interaction with mitochondria, or by both. In the present study, we tested a hypothesis that mHtt directly damages mitochondria. To test this hypothesis, we applied brain cytosolic fraction from YAC128 mice, containing mHtt, to brain non‐synaptic and synaptic mitochondria from wild‐type mice and assessed mitochondrial respiration with a Clark‐type oxygen electrode, membrane potential and Ca2+ uptake capacity with tetraphenylphosphonium (TPP+)‐ and Ca2+‐sensitive electrodes, respectively, and, reactive oxygen species production with Amplex Red assay. The amount of mHtt bound to mitochondria following incubation with mHtt‐containing cytosolic fraction was greater than the amount of mHtt bound to brain mitochondria isolated from YAC128 mice. Despite mHtt binding to wild‐type mitochondria, no abnormalities in mitochondrial functions were detected. This is consistent with our previous results demonstrating the lack of defects in brain mitochondria isolated from R6/2 and YAC128 mice. This, however, could be because of partial loss of mitochondrially bound mHtt during the isolation procedure. Consequently, we increased the amount of mitochondrially bound mHtt by incubating brain non‐synaptic and synaptic mitochondria isolated from YAC128 mice with mHtt‐containing cytosolic fraction. Despite the enrichment of YAC128 brain mitochondria with mHtt, mitochondrial functions (respiration, membrane potential, reactive oxygen species production, Ca2+ uptake capacity) remained unchanged. Overall, our results suggest that mHtt does not directly impair mitochondrial functions, arguing against the involvement of this mechanism in HD pathogenesis.
The Role of Heme Synthesis in Endothelial Mitochondrial Function and Ocular Angiogenesis
(2020-08) Shetty, Trupti; Corson, Timothy W.; Bhatwadekar, Ashay D.; Hoffmann-Longtin, Krista J.; Jerde, Travis J.; Lu, Tao; Sullivan, William J., Jr.
Abnormal blood vessel growth from pre-existing blood vessels, termed pathological angiogenesis, is a common characteristic of vascular diseases like proliferative diabetic retinopathy (PDR) and wet age-related macular degeneration (wet AMD). Retinal detachment, hemorrhage, and loss of vision are only some of the debilitating consequences of advanced pathological angiogenesis. Current therapeutics targeting these blood vessels are ineffective in many patients. We previously identified a novel angiogenesis target, ferrochelatase (FECH), from the heme synthesis pathway, and found that FECH inhibition is antiangiogenic in cell and animal models. Heme synthesis occurs in mitochondria, where FECH inserts Fe2+ into protoporphyrin IX (PPIX) to produce heme. However, the relationship between heme metabolism and angiogenesis is poorly understood. I sought to understand the mechanism of how FECH and thus, heme is involved in endothelial cell function. First, I determined the energetic state of retinal and choroidal endothelial cells, previously uncharacterized. I found that mitochondria in endothelial cells had several functional defects after heme inhibition. FECH loss changed the shape of mitochondria and depleted expression of genes maintaining mitochondrial dynamics. FECH blockade elevated oxidative stress and depolarized mitochondrial membrane potential. Heme depletion had negative effects on cellular metabolism, affecting oxidative phosphorylation and glycolysis. Mitochondrial complex IV of the electron transport chain (cytochrome c oxidase) was decreased in cultured human retinal endothelial cells and in murine retina ex vivo after FECH inhibition. Supplementation with heme partially rescued phenotypes of FECH blockade. Additionally, I discovered that partial loss-of-function Fech mutation in mice caused PPIX accumulation with no change in normal vasculature, as assessed by fundoscopy. These findings provide an unexpected link between mitochondrial heme metabolism and angiogenesis. My studies identify a novel role of a heme synthesis enzyme in blood vessel formation and provide an opportunity to exploit these findings therapeutically for patients with PDR and wet AMD.
Role of Tafazzin in Mitochondrial Function, Development and Disease
(MDPI, 2020-05-23) Chin, Michael T.; Conway, Simon J.; Pediatrics, School of Medicine
Tafazzin, an enzyme associated with the rare inherited x-linked disorder Barth Syndrome, is a nuclear encoded mitochondrial transacylase that is highly conserved across multiple species and plays an important role in mitochondrial function. Numerous studies have elucidated the mechanisms by which Tafazzin affects mitochondrial function, but its effects on development and susceptibility to adult disease are incompletely understood. The purpose of this review is to highlight previous functional studies across a variety of model organisms, introduce recent studies that show an important role in development, and also to provide an update on the role of Tafazzin in human disease. The profound effects of Tafazzin on cardiac development and adult cardiac homeostasis will be emphasized. These studies underscore the importance of mitochondrial function in cardiac development and disease, and also introduce the concept of Tafazzin as a potential therapeutic modality.

Browsing by Subject "mitochondria"

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