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Item Altered sterol metabolism in budding yeast affects mitochondrial iron–sulfur (Fe-S) cluster synthesis(American Society for Biochemistry and Molecular Biology, 2018-07-06) Ward, Diane M.; Chen, Opal S.; Li, Liangtao; Kaplan, Jerry; Bhuiyan, Shah Alam; Natarajan, Selvamuthu K.; Bard, Martin; Cox, James E.; Microbiology & Immunology, IU School of MedicineErgosterol synthesis is essential for cellular growth and viability of the budding yeast Saccharomyces cerevisiae, and intracellular sterol distribution and homeostasis are therefore highly regulated in this species. Erg25 is an iron-containing C4-methyl sterol oxidase that contributes to the conversion of 4,4-dimethylzymosterol to zymosterol, a precursor of ergosterol. The ERG29 gene encodes an endoplasmic reticulum (ER)-associated protein, and here we identified a role for Erg29 in the methyl sterol oxidase step of ergosterol synthesis. ERG29 deletion resulted in lethality in respiring cells, but respiration-incompetent (Rho- or Rho0) cells survived, suggesting that Erg29 loss leads to accumulation of oxidized sterol metabolites that affect cell viability. Down-regulation of ERG29 expression in Δerg29 cells indeed led to accumulation of methyl sterol metabolites, resulting in increased mitochondrial oxidants and a decreased ability of mitochondria to synthesize iron-sulfur (Fe-S) clusters due to reduced levels of Yfh1, the mammalian frataxin homolog, which is involved in mitochondrial iron metabolism. Using a high-copy genomic library, we identified suppressor genes that permitted growth of Δerg29 cells on respiratory substrates, and these included genes encoding the mitochondrial proteins Yfh1, Mmt1, Mmt2, and Pet20, which reversed all phenotypes associated with loss of ERG29 Of note, loss of Erg25 also resulted in accumulation of methyl sterol metabolites and also increased mitochondrial oxidants and degradation of Yfh1. We propose that accumulation of toxic intermediates of the methyl sterol oxidase reaction increases mitochondrial oxidants, which affect Yfh1 protein stability. These results indicate an interaction between sterols generated by ER proteins and mitochondrial iron metabolism.Item An expanded population of CD8dim T cells with features of mitochondrial dysfunction and senescence is associated with persistent HIV-associated Kaposi’s sarcoma under ART(Frontiers Media, 2022-09-29) Clutton, Genevieve T.; Weideman, Ann Marie K.; Goonetilleke, Nilu P.; Maurer, Toby; Dermatology, School of MedicineHIV-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.Item Association between plasma L-carnitine levels and mitochondrial DNA copy number(Springer Nature, 2023-12-11) Li, Mingyue; Yang, Keming; De Vivo, Immaculata; Eliassen, A. Heather; Qureshi, Abrar A.; Nan, Hongmei; Han, Jiali; Epidemiology, School of Public HealthMitochondria are key cytoplasmic organelles in eukaryotic cells that generate adenosine triphosphate (ATP) through the electron transport chain and oxidative phosphorylation. Mitochondrial DNA (mtDNA) copy number (mtDNAcn) is considered a biomarker for both mitochondrial quantity and function as well as cellular oxidative stress level. Previous epidemiologic findings revealed that weight gain, higher body mass index (BMI), smoking, and high insulinemic potential of lifestyle were associated with lower leukocyte mtDNAcn. Carnitines are a group of compounds that play a critical role in energy production. We quantified the associations of plasma L-carnitine levels with leukocyte mtDNAcn. We then examined the association between mtDNAcn and L-carnitine (HMDB0000062) in 538 U.S. men without cancers, diabetes, or cardiovascular disease at blood collection from the Health Professionals Follow-Up Study (HPFS). We found a significant inverse association between L-carnitine and mtDNAcn (ρ = −0.1, P = 0.02). This implies that the carnitine metabolic pathway may be associated with mitochondrial function and oxidative stress.Item Autophagy in Alcoholic Liver Disease, Self-eating Triggered by Drinking(Elsevier, 2015-09) Wang, Lin; Khambu, Bilon; Zhang, Hao; Yin, Xiao-Ming; Pathology and Laboratory Medicine, School of MedicineMacroautophagy (autophagy) is an evolutionarily conserved mechanism. It is important for normal cellular function and also plays critical roles in the etiology and pathogenesis of a number of human diseases. In alcohol-induced liver disease, autophagy is a protective mechanism against the liver injury caused by alcohol. Autophagy is activated in acute ethanol treatment but could be suppressed in chronic and/or high dose treatment of alcohol. The selective removal of lipid droplets and/or damaged mitochondria is likely the major mode of autophagy in reducing liver injury. Understanding the dynamics of the autophagy process and the approach to modulate autophagy could help finding new ways to battle against alcohol-induced liver injury.Item Bone Metabolism: The Role of STAT3 and Reactive Oxygen Species(2013-08-14) Newnum, America Bethanne; Li, Jiliang; Marrs, James; Ji, Julie; Atkinson, SimonSignal Transducers and Activators of Transcription 3 (STAT3), a transcription factor expressed in many cell types, including osteoblasts and osteoclasts, is emerging as a key regulator of bone mass and strength. STAT3 mutations cause a rare human immunodeficiency disease characterized by extremely elevated levels of IgE in serum that have associated craniofacial and skeletal features, such as reduced bone mineral density and recurrent pathological fractures. Our microarray data and immunohistochemical staining using a normal rat model have shown that STAT3 mRNA and protein levels markedly increase in response to mechanical loading. In addition, as indicated by STAT3 phosphorylation in MC3T3-E1 osteoblastic cells, STAT3 activity significantly increases in response to 30 to 90 minutes fluid shear stress. In order to further study the role that STAT3 plays in bone responsiveness to loading, tissue-selective STAT3 knockout (KO) mice, in which inactivation of STAT3 occurs in osteoblasts, were generated by breeding the transgenic mice in which Cre recombinase cDNA was cloned downstream of a 3.6 or 2.3 kb fragment of the rat Col1a1 promoter (Col3.6-Cre and Col2.3-Cre, respectively) with a strain of floxed mice in which the two loxP sites flank exons 18-20 of the STAT3 gene were used. Mice engineered with bone selective inactivation of STAT3 in osteoblasts exhibited significantly lower bone mineral density (7-12%, p<0.05) and reduced ultimate force (21-34%, p<0.01) compared to their age-matched littermate controls. The right ulnae of 16-week-old bone specific STAT3 KO mice and the age-matched control mice were loaded with peak forces of 2.5 N and 2.75 N for female and male mice, respectively, at 2 Hz, 120 cycles/day for 3 consecutive days. Mice with inactivation of STAT3 specific in bone were significantly less responsive to mechanical loading than the control mice as indicated by decreased relative mineralizing surface (rMS/BS, 47-59%, p<0.05) and relative bone formation rate (rBFR/BS, 64-75%, p<0.001). Bone responsiveness was equally decreased in mice in which STAT3 is inactivated either in early osteoblasts (Col3.6-Cre) or in mature osteoblasts (Col2.3-Cre). Accumulating evidence indicates that bone metabolism is significantly affected by activities in mitochondria. For instance, although STAT3 is reported to be involved in bone formation and resorption through regulation of nuclear genes, inactivation of STAT3 is shown to disrupt mitochondrial activities and result in an increased level of reactive oxygen species (ROS). Inactivation of STAT3 suppressed load-driven mitochondrial activity, which led to an elevated level of ROS in cultured primary osteoblasts. Oxidative stress induced by administration of buthionine sulfoximine (BSO) significantly inhibits load-induced bone formation in wild type mice. Taken together, the results support the notion that the loss-of-function mutation of STAT3 in osteoblasts and osteocytes diminishes load-driven bone formation and impairs the regulation of oxidative stress in mitochondria.Item Ca(2+) handling in isolated brain mitochondria and cultured neurons derived from the YAC128 mouse model of Huntington's disease(Wiley, 2015-08) Pellman, Jessica J.; Hamilton, James; Brustovetsky, Tatiana; Brustovetsky, Nickolay; Department of Pharmacology and Toxicology, IU School of MedicineWe investigated Ca(2+) handling in isolated brain synaptic and non-synaptic mitochondria and in cultured striatal neurons from the YAC128 mouse model of Huntington's disease. Both synaptic and non-synaptic mitochondria from 2- and 12-month-old YAC128 mice had larger Ca(2+) uptake capacity than mitochondria from YAC18 and wild-type FVB/NJ mice. Synaptic mitochondria from 12-month-old YAC128 mice had further augmented Ca(2+) capacity compared with mitochondria from 2-month-old YAC128 mice and age-matched YAC18 and FVB/NJ mice. This increase in Ca(2+) uptake capacity correlated with an increase in the amount of mutant huntingtin protein (mHtt) associated with mitochondria from 12-month-old YAC128 mice. We speculate that this may happen because of mHtt-mediated sequestration of free fatty acids thereby increasing resistance of mitochondria to Ca(2+)-induced damage. In experiments with striatal neurons from YAC128 and FVB/NJ mice, brief exposure to 25 or 100 μM glutamate produced transient elevations in cytosolic Ca(2+) followed by recovery to near resting levels. Following recovery of cytosolic Ca(2+), mitochondrial depolarization with FCCP produced comparable elevations in cytosolic Ca(2+), suggesting similar Ca(2+) release and, consequently, Ca(2+) loads in neuronal mitochondria from YAC128 and FVB/NJ mice. Together, our data argue against a detrimental effect of mHtt on Ca(2+) handling in brain mitochondria of YAC128 mice. We demonstrate that mutant huntingtin (mHtt) binds to brain synaptic and nonsynaptic mitochondria and the amount of mitochondria-bound mHtt correlates with increased mitochondrial Ca(2+) uptake capacity. We propose that this may happen due to mHtt-mediated sequestration of free fatty acids thereby increasing resistance of mitochondria to Ca(2+)-induced damage.Item Cancer and Chemotherapy Contribute to Muscle Loss by Activating Common Signaling Pathways(Frontiers, 2016) Barreto, Rafael; Mandili, Giorgia; Witzmann, Frank A.; Novelli, Francesco; Zimmers, Teresa A.; Bonetto, Andrea; Department of Surgery, IU School of MedicineCachexia represents one of the primary complications of colorectal cancer due to its effects on depletion of muscle and fat. Evidence suggests that chemotherapeutic regimens, such as Folfiri, contribute to cachexia-related symptoms. The purpose of the present study was to investigate the cachexia signature in different conditions associated with severe muscle wasting, namely Colon-26 (C26) and Folfiri-associated cachexia. Using a quantitative LC-MS/MS approach, we identified significant changes in 386 proteins in the quadriceps muscle of Folfiri-treated mice, and 269 proteins differentially expressed in the C26 hosts (p < 0.05; -1.5 ≥ fold change ≥ +1.5). Comparative analysis isolated 240 proteins that were modulated in common, with a large majority (218) that were down-regulated in both experimental settings. Interestingly, metabolic (47.08%) and structural (21.25%) proteins were the most represented. Pathway analysis revealed mitochondrial dysfunctions in both experimental conditions, also consistent with reduced expression of mediators of mitochondrial fusion (OPA-1, mitofusin-2), fission (DRP-1) and biogenesis (Cytochrome C, PGC-1α). Alterations of oxidative phosphorylation within the TCA cycle, fatty acid metabolism, and Ca(2+) signaling were also detected. Overall, the proteomic signature in the presence of both chemotherapy and cancer suggests the activation of mechanisms associated with movement disorders, necrosis, muscle cell death, muscle weakness and muscle damage. Conversely, this is consistent with the inhibition of pathways that regulate nucleotide and fatty acid metabolism, synthesis of ATP, muscle and heart function, as well as ROS scavenging. Interestingly, strong up-regulation of pro-inflammatory acute-phase proteins and a more coordinated modulation of mitochondrial and lipidic metabolisms were observed in the muscle of the C26 hosts that were different from the Folfiri-treated animals. In conclusion, our results suggest that both cancer and chemotherapy contribute to muscle loss by activating common signaling pathways. These data support the undertaking of combination strategies that aim to both counteract tumor growth and reduce chemotherapy side effects.Item Cardiovascular Research in Friedreich Ataxia: Unmet Needs and Opportunities(Elsevier, 2022-07-13) Payne, R. Mark; Pediatrics, School of MedicineFriedreich 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.Item A Case for Hydrogen Sulfide Metabolism as an Oxygen Sensing Mechanism(MDPI, 2021-10-21) Olson, Kenneth R.; Anatomy, Cell Biology and Physiology, School of MedicineThe ability to detect oxygen availability is a ubiquitous attribute of aerobic organisms. However, the mechanism(s) that transduce oxygen concentration or availability into appropriate physiological responses is less clear and often controversial. This review will make the case for oxygen-dependent metabolism of hydrogen sulfide (H2S) and polysulfides, collectively referred to as reactive sulfur species (RSS) as a physiologically relevant O2 sensing mechanism. This hypothesis is based on observations that H2S and RSS metabolism is inversely correlated with O2 tension, exogenous H2S elicits physiological responses identical to those produced by hypoxia, factors that affect H2S production or catabolism also affect tissue responses to hypoxia, and that RSS efficiently regulate downstream effectors of the hypoxic response in a manner consistent with a decrease in O2. H2S-mediated O2 sensing is then compared to the more generally accepted reactive oxygen species (ROS) mediated O2 sensing mechanism and a number of reasons are offered to resolve some of the confusion between the two.Item