Lower Mitochondrial Respiration Research Articles

Abstract Tu134: Oncostatin M favors cardiomyocyte survival by promoting glycolysis

Introduction: Cardiomyocytes is in high demand of energy and is susceptible to low oxygen environment. Timely switch of energy metabolism after cardiac ischaemia is helpful for cardiomyocyte preservation. We previously identified a critical role of Oncostatin M (OSM) in cardiomyocyte proliferation. Since the level of OSM quickly rises in myocardium after myocardial injury, OSM may play a protective role in early phase after myocardial injury through metabolic regulation. Hypothesis: We hypothesized that Oncostatin M regulates cardiomyocyte energy metabolism to promote its resistance to hypoxia. Methods and Results: We cultivated cardiomyocytes under hypoxic condition observed that in OSM-treated group, the percentage of TUNEL positive cardiomyocytes significantly decreased compared with that in vehicle-treated group. Published RNA sequencing data from OSM-treated neonatal cardiomyocytes revealed alterations in genes related to energy metabolism. Our Seahorse metabolic stress assays demonstrated that OSM-treated cardiomyocytes exhibited higher glycolytic metabolism and lower mitochondrial respiration than vehicle-treated cells. Pyruvate kinase M2 (PKM2), among the regulatory enzymes, was significantly upregulated in OSM-treated cardiomyocytes as was detected via western-blotting. Interestingly, PKM2 has lower catalytic activity compared to its isotype PKM1, suggesting that the augmented glycolysis might be mediated by PKM2. The mutually exclusive splicing of the gene Pkm between exons 9 and 10 led to the switch between PKM1 and PKM2. qPCR results indicated a 1.5-fold increase in Pkm transcripts and a 2-fold increase in the ratio of Pkm2 to Pkm1 , suggesting that OSM concomitantly promoted Pkm transcription as well as alternative splicing of Pkm2 . Furthermore, we performed RNA interference to knock down Stat3 , the canonical downstream signal of OSM, in cardiomyocytesand observed that OSM failed to upregulate Pkm transcription. ChIP-qPCR analysis on cardiomyocyte cell line HL-1 confirmed an increased STAT3 binding signal upstream of Pkm after OSM treatment. Additionally, RIP-qPCR assays revealed a 3-fold increase in PTBP1-binding signal to Pkm transcripts in cardiomyocytes following OSM treatment. Conclusions: Our results suggest that OSM promotes glycolysis and suppresses mitochondrial respiration in cardiomyocytes by upregulates PKM2 through STAT3 mediated transcription of Pkm and PTBP1-mediated alternative splicing of Pkm transcripts.

Metabolism of immune cells in septic shock in children

In septic shock the hyperimmune response and immunosuppression can occur at the same time, being defined as mixed antagonist response syndrome. Under standard conditions, mitochondria supports cellular energy metabolism through the citric cycle and the phosphorylation chain. Both NK and T cells produce an immediate effector response to inflammatory signals using the rapid production of energy in aerobic glycolysis (glucose-lactate]. When the inflammatory signal is eliminated, they return to metabolism in the Krebs cycle. Septic shock in the children was accompanied by immunoparalysis (TNFα <200pg/ml), lower monocyte human antigen (HLA-DR), loss of peripheral non-naive CD4 T cells and low mitochondrial respiration. Children with septic shock had a in hospital mortality rate of 10.8-33.5%, high risk of hospitali­zation in the next 28 days and in the following months with predominantly respiratory infections. The treatment of mitochondrial dysfunction, insufficiently structured, is based on antioxidant medication, but the results await confirmation.

Mitochondrial respiration is lower in the intrauterine growth-restricted fetal sheep heart.

Fetuses affected by intrauterine growth restriction have an increased risk of developing heart disease and failure in adulthood. Compared with controls, late gestation intrauterine growth-restricted (IUGR) fetal sheep have fewer binucleated cardiomyocytes, reflecting a more immature heart, which may reduce mitochondrial capacity to oxidize substrates. We hypothesized that the late gestation IUGR fetal heart has a lower capacity for mitochondrial oxidative phosphorylation. Left (LV) and right (RV) ventricles from IUGR and control (CON) fetal sheep at 90% gestation were harvested. Mitochondrial respiration (states 1-3, LeakOmy, and maximal respiration) in response to carbohydrates and lipids, citrate synthase (CS) activity, protein expression levels of mitochondrial oxidative phosphorylation complexes (CI-CV), and mRNA expression levels of mitochondrial biosynthesis regulators were measured. The carbohydrate and lipid state 3 respiration rates were lower in IUGR than CON, and CS activity was lower in IUGR LV than CON LV. However, relative CII and CV protein levels were higher in IUGR than CON; CV expression level was higher in IUGR than CON. Genes involved in lipid metabolism had lower expression in IUGR than CON. In addition, the LV and RV demonstrated distinct differences in oxygen flux and gene expression levels, which were independent from CON and IUGR status. Low mitochondrial respiration and CS activity in the IUGR heart compared with CON are consistent with delayed cardiomyocyte maturation, and CII and CV protein expression levels may be upregulated to support ATP production. These insights will provide a better understanding of fetal heart development in an adverse in utero environment. KEY POINTS: Growth-restricted fetuses have a higher risk of developing and dying from cardiovascular diseases in adulthood. Mitochondria are the main supplier of energy for the heart. As the heart matures, the substrate preference of the mitochondria switches from carbohydrates to lipids. We used a sheep model of intrauterine growth restriction to study the capacity of the mitochondria in the heart to produce energy using either carbohydrate or lipid substrates by measuring how much oxygen was consumed. Our data show that the mitochondria respiration levels in the growth-restricted fetal heart were lower than in the normally growing fetuses, and the expression levels of genes involved in lipid metabolism were also lower. Differences between the right and left ventricles that are independent of the fetal growth restriction condition were identified. These results indicate an impaired metabolic maturation of the growth-restricted fetal heart associated with a decreased capacity to oxidize lipids postnatally.

119-OR: Sex and Diabetes Status Interact to Affect Human Skeletal Muscle Mitochondrial Function

People with type 2 diabetes (T2D) have lower cardiorespiratory fitness (CRF)–a predictor of cardiovascular disease, morbidity, and mortality–than those without T2D. The impact of diabetes on CRF is greater in females than males. T2D confers worse CRF, in part, due to impairments in mitochondrial function, but it is unclear to what extent sex and T2D attenuate the expected improvements in mitochondrial function due to exercise training (ExTr). We hypothesized that female sex and T2D decrease mitochondrial response to ExTr. Mitochondrial respiration measures in vastus lateralis of physically inactive overweight adults aged 30-55 years with and without T2D were analyzed pre- and post- ExTr. We found increases in state 3 respiration (p=0.01), state 4 respiration (p=0.0002), and uncoupled respiration (p=0.02) after ExTr in all groups, suggesting a consistent effect of ExTr. Sex and T2D status interact to affect state 3 respiration (p=0.0003), State 4 respiration (p=0.003) and oxidative phosphorylation (P/E) ratio (p=0.0002) (Figure); females with T2D have lower mitochondrial respiration than males with T2D, unlike overweight control participants. Sex and T2D did not statistically interact with ExTr. These findings suggest that differences in muscle mitochondrial function due to T2D and sex persist despite improvements in mitochondrial respiration with ExTr. Disclosure L.Abushamat: None. J.G.Regensteiner: None. R.L.Scalzo: None. I.E.Schauer: None. L.Knaub: None. D.Rafferty: None. E.Clark: None. M.O.Whipple: None. A.G.Huebschmann: None. J.E.B.Reusch: Advisory Panel; Medtronic. Funding American Diabetes Association (1-21-CMF-003 to L.A.); U.S. Department of Veterans Affairs (CX001532)

Lower mitochondrial respiration does not lead to decreased fat oxidation in young African American women without obesity.

The prevalence of type 2 diabetes in African American women (AAW) is nearly twice that of White women. Lower insulin sensitivity and decreased mitochondrial function may be contributing factors. The purpose of this study was to compare fat oxidation in AAW and White women. Participants were 22 AAW and 22 White women, matched for age (18.7-38.3 years) and BMI (< 28 kg/m2). Participants completed two submaximal (50% VO2max) exercise tests with indirect calorimetry and stable isotope tracers to assess total, plasma, and intramyocellular triglyceride fat oxidation. The respiratory quotientduring the exercise test was nearly identical in AAW and White women (0.813 ± 0.008 vs. 0.810 ± 0.008, p=0.83). Although absolute total and plasma fat oxidation was lower in AAW, adjusting for the lower workload in AAW eliminated these racial differences. There was no racial difference in plasma and intramyocellular triglyceride source of fat for oxidation. No racial differences were observed in rates of ex vivo fat oxidation. Exercise efficiency was lower in AAW when adjusted to leg fat free mass. The data suggest that fat oxidation is not lower in AAW compared with White women, but additional studies are needed across exercise intensity, body weight, and age to confirm these results.

Mitochondrial genome mutations and neuronal dysfunction of induced pluripotent stem cells derived from patients with Alzheimer's disease.

ObjectivesPatient‐derived induced pluripotent stem cells (iPSCs) are materials that can be used for autologous stem cell therapy. We screened mtDNA mutations in iPSCs and iPSC‐derived neuronal cells from patients with Alzheimer's disease (AD). Also, we investigated whether the mutations could affect mitochondrial function and deposition of β‐amyloid (Aβ) in differentiated neuronal cells.Materials and MethodsmtDNA mutations were measured and compared among iPSCs and iPSC‐derived neuronal cells. The selected iPSCs carrying mtDNA mutations were subcloned, and then their growth rate and neuronal differentiation pattern were analyzed. The differentiated cells were measured for mitochondrial respiration and membrane potential, as well as deposition of Aβ.ResultsMost iPSCs from subjects with AD harbored ≥1 mtDNA mutations, and the number of mutations was significantly higher than that from umbilical cord blood. About 35% and 40% of mutations in iPSCs were shared with isogenic iPSCs and their differentiated neuronal precursor cells, respectively, with similar or different heteroplasmy. Furthermore, the mutations in clonal iPSCs were stable during extended culture and neuronal differentiation. Finally, mtDNA mutations could induce a growth advantage with higher viability and proliferation, lower mitochondrial respiration and membrane potential, as well as increased Aβ deposition.ConclusionThis study demonstrates that mtDNA mutations in patients with AD could lead to mitochondrial dysfunction and accelerated Aβ deposition. Therefore, early screening for mtDNA mutations in iPSC lines would be essential for developing autologous cell therapy or drug screening for patients with AD.

Reduced Mitochondrial Respiration in Hybrid Asexual Lizards.

AbstractThe scarcity of asexual reproduction in vertebrates alludes to an inherent cost. Several groups of asexual vertebrates exhibit lower endurance capacity (a trait predominantly sourced by mitochondrial respiration) compared with congeneric sexual species. Here we measure endurance capacity in five species of Aspidoscelis lizards and examine mitochondrial respiration between sexual and asexual species using mitochondrial respirometry. Our results show reduced endurance capacity, reduced mitochondrial respiration, and reduced phenotypic variability in asexual species compared with parental sexual species, along with a positive relationship between endurance capacity and mitochondrial respiration. Results of lower endurance capacity and lower mitochondrial respiration in asexual Aspidoscelis are consistent with hypotheses involving mitonuclear incompatibility.

AMPK modulation ameliorates dominant disease phenotypes of CTRP5 variant in retinal degeneration

Late-onset retinal degeneration (L-ORD) is an autosomal dominant disorder caused by a missense substitution in CTRP5. Distinctive clinical features include sub-retinal pigment epithelium (RPE) deposits, choroidal neovascularization, and RPE atrophy. In induced pluripotent stem cells-derived RPE from L-ORD patients (L-ORD-iRPE), we show that the dominant pathogenic CTRP5 variant leads to reduced CTRP5 secretion. In silico modeling suggests lower binding of mutant CTRP5 to adiponectin receptor 1 (ADIPOR1). Downstream of ADIPOR1 sustained activation of AMPK renders it insensitive to changes in AMP/ATP ratio resulting in defective lipid metabolism, reduced Neuroprotectin D1(NPD1) secretion, lower mitochondrial respiration, and reduced ATP production. These metabolic defects result in accumulation of sub-RPE deposits and leave L-ORD-iRPE susceptible to dedifferentiation. Gene augmentation of L-ORD-iRPE with WT CTRP5 or modulation of AMPK, by metformin, re-sensitize L-ORD-iRPE to changes in cellular energy status alleviating the disease cellular phenotypes. Our data suggests a mechanism for the dominant behavior of CTRP5 mutation and provides potential treatment strategies for L-ORD patients.

Hypoxia compromises the mitochondrial metabolism of Alzheimer's disease microglia via HIF1.

Genetic Alzheimer's disease (AD) risk factors associate with reduced defensive amyloid β plaque-associated microglia (AβAM), but the contribution of modifiable AD risk factors to microglial dysfunction is unknown. In AD mouse models, we observe concomitant activation of the hypoxia-inducible factor 1 (HIF1) pathway and transcription of mitochondrial-related genes in AβAM, and elongation of mitochondria, a cellular response to maintain aerobic respiration under low nutrient and oxygen conditions. Overactivation of HIF1 induces microglial quiescence in cellulo, with lower mitochondrial respiration and proliferation. In vivo, overstabilization of HIF1, either genetically or by exposure to systemic hypoxia, reduces AβAM clustering and proliferation and increases Aβ neuropathology. In the human AD hippocampus, upregulation of HIF1α and HIF1 target genes correlates with reduced Aβ plaque microglial coverage and an increase of Aβ plaque-associated neuropathology. Thus, hypoxia (a modifiable AD risk factor) hijacks microglial mitochondrial metabolism and converges with genetic susceptibility to cause AD microglial dysfunction.

Targeting the mitochondrial trifunctional protein restrains tumor growth in oxidative lung carcinomas.

Metabolic reprogramming is a common hallmark of cancer, but a large variability in tumor bioenergetics exists between patients. Using high-resolution respirometry on fresh biopsies of human lung adenocarcinoma, we identified 2 subgroups reflected in the histologically normal, paired, cancer-adjacent tissue: high (OX+) mitochondrial respiration and low (OX-) mitochondrial respiration. The OX+ tumors poorly incorporated [18F]fluorodeoxy-glucose and showed increased expression of the mitochondrial trifunctional fatty acid oxidation enzyme (MTP; HADHA) compared with the paired adjacent tissue. Genetic inhibition of MTP altered OX+ tumor growth in vivo. Trimetazidine, an approved drug inhibitor of MTP used in cardiology, also reduced tumor growth and induced disruption of the physical interaction between the MTP and respiratory chain complex I, leading to a cellular redox and energy crisis. MTP expression in tumors was assessed using histology scoring methods and varied in negative correlation with [18F]fluorodeoxy-glucose incorporation. These findings provide proof-of-concept data for preclinical, precision, bioenergetic medicine in oxidative lung carcinomas.

Abstract 13357: Dhtkd1 Knock-out Alters Cellular Respiration by Preventing Electron Transport Chain Related Proteins From Entering Into Mitochondria

The metabolite α-aminoadipic acid (2-AAA) has been identified as a predictor of diabetes and atherosclerosis in large human prospective studies. However, the mechanisms linking this metabolite to disease pathophysiology remain unknown. DHTKD1 is a central gene in the 2-AAA pathway, and has been linked to variation in 2-AAA levels in humans and animals. However, little is known about the role of DHTKD1 in cellular metabolism. We hypothesized that DHTKD1 is an important regulator of mitochondrial energy metabolism, with potential involvement in cardiometablic disease. Methods and Results: We investigated the consequences of loss of DHTKD1 function in a human HAP-1 cell line. Treatment with 2-AAA increased mitochondrial respiration in wild-type (WT) cells, but had no effect in DHTKD1 knock-out (KO) cells. DHTKD1 KO cells had significantly lower mitochondrial respiration (Mito Stress Test, Seahorse Analyzer), with no differences in glycolytic function, supporting an important role for DHTKD1 in mitochondrial metabolism. Membrane potential and mitochondrial content were up-regulated in KO compared to WT cells, suggesting a potential compensatory mechanism. We investigated the mechanisms underlying impaired mitochondrial function, and found TOM40 and TIM23, the pivotal proteins required for the movement of proteins into mitochondria, were decreased in DHTKD1 KO cells. Further, DHTKD1 KO resulted in reduced expression of electron transport chain related proteins (NDUF88, SDHB, MTCO1, UQCRC2, ATP5A) in mitochondria, but increased expression in the cytosol, suggesting impaired ability to cross the mitochondrial membrane. Conclusions: Our data suggest that the absence of DHTKD1 leads to less TOM40 and TIM23 expression, preventing key proteins in the electron transport chain from entering into mitochondria, resulting in impaired mitochondrial respiration. These findings highlight the vital role of DHTKD1 in cellular metabolism, and establish DHTKD1-mediated mitochondrial dysfunction as a potential novel pathway in cardiometabolic disease. Elevated 2-AAA observed in individuals prior to onset of diabetes and atherosclerosis may be an early biomarker of dysfunction in this pathway.

Lymphoid Tissue-Resident Alcaligenes Establish an Intracellular Symbiotic Environment by Creating a Unique Energy Shift in Dendritic Cells.

Lymphoid-tissue–resident commensal bacteria (LRCs), including Alcaligenes faecalis, are present in intestinal lymphoid tissue including the Peyer’s patches (PPs) of mammals and modulate the host immune system. Although LRCs can colonize within dendritic cells (DCs), the mechanisms through which LRCs persist in DCs and the symbiotic relationships between LRCs and DCs remain to be investigated. Here, we show an intracellular symbiotic system in which the LRC Alcaligenes creates a unique energy shift in DCs. Whereas DCs showed low mitochondrial respiration when they were co-cultured with Escherichia coli, DCs carrying A. faecalis maintained increased mitochondrial respiration. Furthermore, E. coli induced apoptosis of DCs but A. faecalis did not. Regarding an underlying mechanism, A. faecalis—unlike E. coli—did not induce intracellular nitric oxide (NO) production in DCs due to the low activity of its lipopolysaccharide (LPS). Therefore, A. faecalis, an example of LRCs, may persist within intestinal lymphoid tissue because they elicit little NO production in DCs. In addition, the symbiotic DCs exhibit characteristic physiologic changes, including a low rate of apoptosis and increased mitochondrial respiration.

Mitochondrial TXNRD3 confers drug resistance via redox-mediated mechanism and is a potential therapeutic target in vivo

Alterations in ROS metabolism and redox signaling are often observed in cancer cells and play a significant role in tumor development and drug resistance. However, the mechanisms by which redox alterations impact cellular sensitivity to anticancer drugs remain elusive. Here we have identified the mitochondrial isoform of thioredoxin reductase 3 (mtTXNRD3), through RT-PCR microarray screen, as a key molecule that confers drug resistance to sorafenib and other clinical anticancer agents. High expression of mtTXNRD3 is detected in drug-resistant leukemia and hepatocellular carcinoma cells associated with significant metabolic alterations manifested by low mitochondrial respiration and high glycolysis. Mechanistically, high mtTXNRD3 activity keeps the mitochondrial thioredoxin2 (Trx2) in a reduced stage that in turn stabilizes several key survival molecules including HK2, Bcl-XL, Bcl-2, and MCL-1, leading to increased cell survival and drug resistance. Pharmacological inhibition of thioredoxin reductase by auranofin effectively overcomes such drug resistance in vitro and in vivo, suggesting that targeting this redox mechanism may be a feasible strategy to treat drug-resistant cancer.

Heterogeneity of Metabolic Vulnerability in Imatinib -Resistant Gastrointestinal Stromal Tumor.

Metabolic reprogramming is a hallmark of cancer cells in response to targeted therapy. Decreased glycolytic activity with enhanced mitochondrial respiration secondary to imatinib has been shown in imatinib-sensitive gastrointestional stromal tumors (GIST). However, the role of energy metabolism in imatinib-resistant GIST remains poorly characterized. Here, we investigated the effect of imatinib treatment on glycolysis and oxidative phosphorylation (OXPHOS), as well as the effect of inhibition of these energy metabolisms on cell viability in imatinib-resistant and -sensitive GIST cell lines. We observed that imatinib treatment increased OXPHOS in imatinib-sensitive, but not imatinib-resistant, GIST cells. Imatinib also reduced the expression of mitochondrial biogenesis activators (peroxisome proliferator-activated receptor coactivator-1 alpha (PGC1α), nuclear respiratory factor 2 (NRF2), and mitochondrial transcription factor A (TFAM)) and mitochondrial mass in imatinib-sensitive GIST cells. Lower TFAM levels were also observed in imatinib-sensitive GISTs than in tumors from untreated patients. Using the Seahorse system, we observed bioenergetics diversity among the GIST cell lines. One of the acquired resistant cell lines (GIST 882R) displayed a highly metabolically active phenotype with higher glycolysis and OXPHOS levels compared with the parental GIST 882, while the other resistant cell line (GIST T1R) had a similar basal glycolytic activity but lower mitochondrial respiration than the parental GIST T1. Further functional assays demonstrated that GIST 882R was more vulnerable to glycolysis inhibition than GIST 882, while GIST T1R was more resistant to OXPHOS inhibition than GIST T1. These findings highlight the diverse energy metabolic adaptations in GIST cells that allow them to survive upon imatinib treatment and reveal the potential of targeting the metabolism for GIST therapy.

Differential effectiveness of tyrosine kinase inhibitors in 2D/3D culture according to cell differentiation, p53 status and mitochondrial respiration in liver cancer cells

Sorafenib and Regorafenib are the recommended first- and second-line therapies in patients with advanced hepatocellular carcinoma (HCC). Lenvatinib and Cabozantinib have shown non-inferior antitumoral activities compared with the corresponding recommended therapies. The clinical trials have established recommended doses for each treatment that lead different blood concentrations in patients for Sorafenib (10 µM), Regorafenib (1 µM), Lenvatinib (0.1 µM), and Cabozantinib (1 µM). However, very low response rates are observed in patients attributed to intrinsic resistances or upregulation of survival signaling. The aim of the study was the comparative dose–response analysis of the drugs (0–100 µM) in well-differentiated (HepG2, Hep3B, and Huh7), moderately (SNU423), and poorly (SNU449) differentiated liver cancer cells in 2D/3D cultures. Cells harbors wild-type p53 (HepG2), non-sense p53 mutation (Hep3B), inframe p53 gene deletion (SNU423), and p53 point mutation (Huh7 and SNU449). The administration of regular used in vitro dose (10 µM) in 3D and 2D cultures, as well as the dose–response analysis in 2D cultures showed Sorafenib and Regorafenib were increasingly effective in reducing cell proliferation, and inducing apoptosis in well-differentiated and expressing wild-type p53 in HCC cells. Lenvatinib and Cabozantinib were particularly effective in moderately to poorly differentiated cells with mutated or lacking p53 that have lower basal oxygen consumption rate (OCR), ATP, and maximal respiration capacity than observed in differentiated HCC cells. Sorafenib and Regorafenib downregulated, and Lenvatinib and Cabozantinib upregulated epidermal growth factor receptor (EGFR) and mesenchymal–epithelial transition factor receptor (c-Met) in HepG2 cells. Conclusions: Sorafenib and Regorafenib were especially active in well-differentiated cells, with wild-type p53 and increased mitochondrial respiration. By contrast, Lenvatinib and Cabozantinib appeared more effective in moderately to poorly differentiated cells with mutated p53 and low mitochondrial respiration. The development of strategies that allow us to deliver increased doses in tumors might potentially enhance the effectiveness of the treatments.

Mitochondrial Dysfunction is Associated With an Immune Paralysis Phenotype in Pediatric Sepsis.

Immune dysregulation is a defining feature of sepsis, but the role for mitochondria in the development of immunoparalysis in pediatric sepsis is not known. We sought to determine if mitochondrial dysfunction measured in peripheral blood mononuclear cells (PBMCs) is associated with immunoparalysis and systemic inflammation in children with sepsis. Prospective observational study. Single-academic pediatric intensive care unit (PICU). One hundred sixty-one children with sepsis/septic shock and 18 noninfected PICU controls. Mitochondrial respiration in PBMCs, markers of immune function, and plasma cytokines were measured on days 1 to 2 (T1), 3 to 5 (T2), and 8 to 14 (T3) after sepsis recognition, and once for controls. Immunoparalysis was defined as whole-blood ex vivo lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-α) ≤200 pg/mL or monocyte human leukocyte antigen-DR ≤30%. Mitochondrial respiration was lower in children with versus without immunoparalysis measured at the same timepoint. Mitochondrial respiration measured early (at T1 and T2) was also lower in those with immunoparalysis at T2 and T3, respectively. Although most patients with immunoparalysis exhibited low mitochondrial respiration, this metabolic finding was not specific to the immunoparalysis phenotype. Plasma cytokines, including IL-8, IL-10, TNF-α, and MCP-1, were highest in the subset of sepsis patients with immune paralysis or low mitochondrial respiration at T1. Children with sepsis had lower PBMC mitochondrial respiration when immunoparalysis was present compared with those without immunoparalysis. The subsets with immune paralysis and low mitochondrial respiration exhibited the highest levels of systemic inflammation.

Glutamine Synthetase Promotes Radiation Resistance via Facilitating Nucleotide Metabolism and Subsequent DNA Damage Repair

Radiation resistance is a critical problem in radiotherapy for cancer. Radiation kills tumor cells mainly through causing DNA damage. Thus, efficiency of DNA damage repair is one of the most important factors that limits radiotherapy efficacy. Glutamine physiologically functions to generate protein and nucleotides. Here, we study the impact of glutamine metabolism on cancer therapeutic responses, in particular under irradiation-induced stress. We show that radiation-resistant cells possessed low glycolysis, mitochondrial respiration, and TCA cycle but high glutamine anabolism. Transcriptome analyses revealed that glutamine synthetase (GS), an enzyme catalyzing glutamate and ammonia to glutamine, was responsible for the metabolic alteration. ChIP and luciferase reporter assays revealed that GS could be transcriptionally regulated by STAT5. Knockdown of GS delayed DNA repair, weakened nucleotide metabolism, and enhanced radiosensitivity both invitro and invivo. Our data show that GS links glutamine metabolism to radiotherapy response through fueling nucleotide synthesis and accelerating DNA repair.

Astaxanthin attenuates the increase in mitochondrial respiration during the activation of hepatic stellate cells

Upon liver injury, quiescent hepatic stellate cells (qHSCs) transdifferentiate to myofibroblast-like activated HSCs (aHSCs), which are primarily responsible for the accumulation of extracellular matrix proteins during the development of liver fibrosis. Therefore, aHSCs may exhibit different energy metabolism from that of qHSCs to meet their high energy demand. We previously demonstrated that astaxanthin (ASTX), a xanthophyll carotenoid, prevents the activation of HSCs. The objective of this study was to determine if ASTX can exert its antifibrogenic effect by attenuating any changes in energy metabolism during HSC activation. To characterize the energy metabolism of qHSCs and aHSCs, mouse primary HSCs were cultured on uncoated plastic dishes for 7 days for spontaneous activation in the presence or absence of 25 μM ASTX. qHSCs (1 day after isolation) and aHSCs treated with or without ASTX for 7 days were used to determine parameters related to mitochondrial respiration using a Seahorse XFe24 Extracellular Flux analyzer. aHSCs had significantly higher basal respiration, maximal respiration, ATP production, spare respiratory capacity and proton leak than those of qHSCs. However, ASTX prevented most of the changes occurring during HSC activation and improved mitochondrial cristae structure with decreased cristae junction width, lumen width and the area in primary mouse aHSCs. Furthermore, qHSCs isolated from ASTX-fed mice had lower mitochondrial respiration and glycolysis than control qHSCs. Our findings suggest that ASTX may exert its antifibrogenic effect by attenuating the changes in energy metabolism during HSC activation.

When organelles signal better together

Calcium Signaling Wolfram syndrome is caused by loss-of-function mutations in the endoplasmic reticulum (ER) protein WFS1. However, patients show symptoms typically associated with mitochondrial dysfunction, such as diabetes and optic atrophy. Angebault et al. found that patient fibroblasts had reduced mitochondria-ER contact sites, decreased mitochondrial calcium (Ca2+) uptake, and lower mitochondrial respiration than control fibroblasts. WFS1 deficiency destabilized the Ca2+ sensor NCS1, and reconstituting NCS1 in patient fibroblasts restored mitochondrial respiration and Ca2+ signaling. Sci. Signal. 11 , eaaq1380 (2018).

Mitochondrial Respiration is Associated with Lower Energy Expenditure and Lower Aerobic Capacity in African American Women.

ObjectiveReasons for the higher obesity prevalence in African American women (AAW) compared to Caucasian women (CW) are unknown. Energy expenditure and maximal aerobic capacity (VO2max) are lower in AAW. We hypothesized these differences are explained by skeletal muscle characteristics, particularly mitochondrial content and function.MethodsMultivariate regression analyses were used to examine the relationships between energy expenditure (resting and during a hyperinsulinemic-euglycemic clamp) and VO2max vs. body composition, physical activity, and skeletal muscle mitochondrial measurements in AAW and CW.ResultsIn AAW, VO2max was lower (p<0.0001). Body-composition-adjusted energy expenditure during the clamp was lower in AAW (p<0.002). Physical activity was similar in both groups. After adjusting for mitochondrial respiration, racial differences in energy expenditure and VO2max were no longer present. Another novel finding was that a thermogenic response to the clamp was observed in CW (+53±22 kcal/d; p<0.03) but not in AAW (−19±24 kcal/d; p=0.43).ConclusionsAAW and CW show differences in adjusted energy expenditure and aerobic capacity that are largely accounted for by differences in skeletal muscle mitochondrial oxidative characteristics. Further research is needed to determine if lower mitochondrial respiration and lower thermogenesis are risk factors for obesity in AAW.