Impact of Electronic Patient-Reported Outcomes on Unplanned Consultations and Hospitalizations in Patients With Cancer Undergoing Systemic Therapy: Results of a Patient-Reported Outcome Study Compared With Matched Retrospective Data.

BACKGROUND: The evaluation of electronic patient-reported outcomes (ePROs) is increasingly being used in clinical studies of patients with cancer and enables structured and standardized data collection in patients' everyday lives. So far, few studies or analyses have focused on the medical benefit of ePROs for patients. OBJECTIVE: The current exploratory analysis aimed to obtain an initial indication of whether the use of the Consilium Care app (recently renamed medidux; mobile Health AG) for structured and regular self-assessment of side effects by ePROs had a recognizable effect on incidences of unplanned consultations and hospitalizations of patients with cancer compared to a control group in a real-world care setting without app use. To analyze this, the incidences of unplanned consultations and hospitalizations of patients with cancer using the Consilium Care app that were recorded by the treating physicians as part of the patient reported outcome (PRO) study were compared retrospectively to corresponding data from a comparable population of patients with cancer collected at 2 Swiss oncology centers during standard-of-care treatment. METHODS: Patients with cancer in the PRO study (178 included in this analysis) receiving systemic therapy in a neoadjuvant or noncurative setting performed a self-assessment of side effects via the Consilium Care app over an observational period of 90 days. In this period, unplanned (emergency) consultations and hospitalizations were documented by the participating physicians. The incidence of these events was compared with retrospective data obtained from 2 Swiss tumor centers for a matched cohort of patients with cancer. RESULTS: Both patient groups were comparable in terms of age and gender ratio, as well as the distribution of cancer entities and Joint Committee on Cancer stages. In total, 139 patients from each group were treated with chemotherapy and 39 with other therapies. Looking at all patients, no significant difference in events per patient was found between the Consilium group and the control group (odds ratio 0.742, 90% CI 0.455-1.206). However, a multivariate regression model revealed that the interaction term between the Consilium group and the factor "chemotherapy" was significant at the 5% level (P=.048). This motivated a corresponding subgroup analysis that indicated a relevant reduction of the risk for the intervention group in the subgroup of patients who underwent chemotherapy. The corresponding odds ratio of 0.53, 90% CI 0.288-0.957 is equivalent to a halving of the risk for patients in the Consilium group and suggests a clinically relevant effect that is significant at a 2-sided 10% level (P=.08, Fisher exact test). CONCLUSIONS: A comparison of unplanned consultations and hospitalizations from the PRO study with retrospective data from a comparable cohort of patients with cancer suggests a positive effect of regular app-based ePROs for patients receiving chemotherapy. These data are to be verified in the ongoing randomized PRO2 study (registered on ClinicalTrials.gov; NCT05425550). TRIAL REGISTRATION: ClinicalTrials.gov NCT03578731; https://www.clinicaltrials.gov/ct2/show/NCT03578731. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): RR2-10.2196/29271.

TLR2-Dependent Reversible Oxidation of Connexin 43 at Cys260 Modifies Electrical Coupling After Experimental Myocardial Ischemia/Reperfusion.

We have shown previously that during myocardial ischemia/reperfusion (MI/R), toll-like receptor 2 (TLR2) signaling regulates connexin 43 (Cx43) subcellular localization and function and dampens arrhythmia formation. We aimed to identify sites capable of TLR2-dependent redox modification within Cx43. Post-ischemic TLR2-/- or wild-type (WT) mouse hearts were analyzed by OxICAT. Cx43 was mutated to exclude redox modification and transfected into HL-1 cardiomyocytes (CM) that were challenged with a TLR2 agonist. We identified Cys260 of Cx43 to be susceptible to reversible oxidation MI/R; TLR2-/- leads to reduced H2O2 production in post-ischemic isolated mitochondria and subsequently reduced oxidation of Cx43 at Cys260. Cx43 was dephosphorylated in WT, while phosphorylation was preserved in TLR2-/-. Mutation of Cx43 (C260A) and lentiviral transfection in HL-1 CM accelerated pacemaker activity and reduced activity after TLR2 ligand stimulation. We here provide evidence for TLR2-dependent reversible oxidation of Cx43 at Cys260, which led to decreased Cx43 phosphorylation and affected CM pacemaker frequency and intercellular communication.

Mitophagy in Intestinal Epithelial Cells Triggers Adaptive Immunity during Tumorigenesis.

In colorectal cancer patients, a high density of cytotoxic CD8+ T cells in tumors is associated with better prognosis. Using a Stat3 loss-of-function approach in two wnt/ß-catenin-dependent autochthonous models of sporadic intestinal tumorigenesis, we unravel a complex intracellular process in intestinal epithelial cells (IECs) that controls the induction of a CD8+ T cell based adaptive immune response. Elevated mitophagy in IECs causes iron(II)-accumulation in epithelial lysosomes, in turn, triggering lysosomal membrane permeabilization. Subsequent release of proteases into the cytoplasm augments MHC class I presentation and activation of CD8+ T cells via cross-dressing of dendritic cells. Thus, our findings highlight a so-far-unrecognized link between mitochondrial function, lysosomal integrity, and MHC class I presentation in IECs and suggest that therapies triggering mitophagy or inducing LMP in IECs may prove successful in shifting the balance toward anti-tumor immunity in colorectal cancer.

Degradation of the mitochondrial complex I assembly factor TMEM126B under chronic hypoxia.

Cell stress such as hypoxia elicits adaptive responses, also on the level of mitochondria, and in part is mediated by the hypoxia-inducible factor (HIF) 1α. Adaptation of mitochondria towards acute hypoxic conditions is reasonably well understood, while regulatory mechanisms, especially of respiratory chain assembly factors, under chronic hypoxia remains elusive. One of these assembly factors is transmembrane protein 126B (TMEM126B). This protein is part of the mitochondrial complex I assembly machinery. We identified changes in complex I abundance under chronic hypoxia, in association with impaired substrate-specific mitochondrial respiration. Complexome profiling of isolated mitochondria of the human leukemia monocytic cell line THP-1 revealed HIF-1α-dependent deficits in complex I assembly and mitochondrial complex I assembly complex (MCIA) abundance. Of all mitochondrial MCIA members, we proved a selective HIF-1-dependent decrease of TMEM126B under chronic hypoxia. Mechanistically, HIF-1α induces the E3-ubiquitin ligase F-box/WD repeat-containing protein 1A (ß-TrCP1), which in turn facilitates the proteolytic degradation of TMEM126B. Attenuating a functional complex I assembly appears critical for cellular adaptation towards chronic hypoxia and is linked to destruction of the mitochondrial assembly factor TMEM126B.

Mammalian target of rapamycin complex 1 activation sensitizes human glioma cells to hypoxia-induced cell death.

Glioblastomas are characterized by fast uncontrolled growth leading to hypoxic areas and necrosis. Signalling from EGFR via mammalian target of rapamycin complex 1 (mTORC1) is a major driver of cell growth and proliferation and one of the most commonly altered signalling pathways in glioblastomas. Therefore, epidermal growth factor receptor and mTORC1 signalling are plausible therapeutic targets and clinical trials with inhibitors are in progress. However, we have previously shown that epidermal growth factor receptor and mTORC1 inhibition triggers metabolic changes leading to adverse effects under the conditions of the tumour microenvironment by protecting from hypoxia-induced cell death. We hypothesized that conversely mTORC1 activation sensitizes glioma cells to hypoxia-induced cell death. As a model for mTORC1 activation we used gene suppression of its physiological inhibitor TSC2 (TSC2sh). TSC2sh glioma cells showed increased sensitivity to hypoxia-induced cell death that was accompanied by an earlier ATP depletion and an increase in reactive oxygen species. There was no difference in extracellular glucose consumption but an altered intracellular metabolic profile with an increase of intermediates of the pentose phosphate pathway. Mechanistically, mTORC1 upregulated the first and rate limiting enzyme of the pentose phosphate pathway, G6PD. Furthermore, an increase in oxygen consumption in TSC2sh cells was detected. This appeared to be due to higher transcription rates of genes involved in mitochondrial respiratory function including PPARGC1A and PPARGC1B (also known as PGC-1α and -ß). The finding that mTORC1 activation causes an increase in oxygen consumption and renders malignant glioma cells susceptible to hypoxia and nutrient deprivation could help identify glioblastoma patient cohorts more likely to benefit from hypoxia-inducing therapies such as the VEGFA-targeting antibody bevacizumab in future clinical evaluations.

Sex-specific, reciprocal regulation of ERα and miR-22 controls muscle lipid metabolism in male mice.

Control of energy homeostasis and metabolism is achieved by integrating numerous pathways, and miRNAs are involved in this process by regulating expression of multiple target genes. However, relatively little is known about the posttranscriptional processing of miRNAs and a potential role for the precursors they derive from. Here, we demonstrate that mature miRNA-22 is more abundant in muscle from male mice relative to females and that this enables sex-specific regulation of muscular lipid metabolism and body weight by repressing estrogen receptor alpha (ERα) expression. We found that the ERα adjusts its own activity by preventing processing of miR-22 via direct binding to a conserved ERα-binding element within the primary miR-22 precursor. Mutation of the ERα binding site within the pri-miR-22 in vivo eliminates sex-specific differences in miR-22 expression. We reason that the resulting tissue selective negative feedback regulation is essential to establish sex-specific differences in muscle metabolism and body weight development.

A Bak-dependent mitochondrial amplification step contributes to Smac mimetic/glucocorticoid-induced necroptosis.

Necroptosis is a form of programmed cell death that critically depends on RIP3 and MLKL. However, the contribution of mitochondria to necroptosis is still poorly understood. In the present study, we discovered that mitochondrial perturbations play a critical role in Smac mimetic/Dexamethasone (Dexa)-induced necroptosis independently of death receptor ligands. We demonstrate that the Smac mimetic BV6 and Dexa cooperate to trigger necroptotic cell death in acute lymphoblastic leukemia (ALL) cells that are deficient in caspase activation due to absent caspase-8 expression or pharmacological inhibition by the caspase inhibitor zVAD.fmk, since genetic silencing or pharmacological inhibition of RIP3 or MLKL significantly rescue BV6/Dexa-induced necroptosis. In addition, RIP3 or MLKL knockout mouse embryonic fibroblasts (MEFs) are protected from BV6/Dexa/zVAD.fmk-induced cell death. In contrast, antagonistic antibodies against the death receptor ligands TNFα, TRAIL or CD95 ligand fail to rescue BV6/Dexa-triggered cell death. Kinetic studies revealed that prior to cell death BV6/Dexa treatment causes hyperpolarization of the mitochondrial membrane potential (MMP) followed by loss of MMP, reactive oxygen species (ROS) production, Bak activation and disruption of mitochondrial respiration. Importantly, knockdown of Bak significantly reduces BV6/Dexa-induced loss of MMP and delays cell death, but not ROS production, whereas ROS scavengers attenuate Bak activation, indicating that ROS production occurs upstream of BV6/Dexa-mediated Bak activation. Consistently, BV6/Dexa treatment causes oxidative thiol modifications of Bak protein. Intriguingly, knockdown or knockout of RIP3 or MLKL protect ALL cells or MEFs from BV6/Dexa-induced ROS production, Bak activation, drop of MMP and disruption of mitochondrial respiration, demonstrating that these mitochondrial events depend on RIP3 and MLKL. Thus, mitochondria might serve as an amplification step in BV6/Dexa-induced necroptosis. These findings provide new insights into the role of mitochondrial dysfunctions during necroptosis and have important implications for the development of novel treatment approaches to overcome apoptosis resistance in ALL.

Basal autophagy is pivotal for Hodgkin and Reed-Sternberg cells' survival and growth revealing a new strategy for Hodgkin lymphoma treatment.

As current classical Hodgkin lymphoma (cHL) treatment strategies have pronounced side-effects, specific inhibition of signaling pathways may offer novel strategies in cHL therapy. Basal autophagy, a regulated catabolic pathway to degrade cell's own components, is in cancer linked with both, tumor suppression or promotion. The finding that basal autophagy enhances tumor cell survival would thus lead to immediately testable strategies for novel therapies. Thus, we studied its contribution in cHL.We found constitutive activation of autophagy in cHL cell lines and primary tissue. The expression of key autophagy-relevant proteins (e.g. Beclin-1, ULK1) and LC3 processing was increased in cHL cells, even in lymphoma cases. Consistently, cHL cells exhibited elevated numbers of autophagic vacuoles and intact autophagic flux. Autophagy inhibition with chloroquine or inactivation of ATG5 induced apoptosis and reduced proliferation of cHL cells. Chloroquine-mediated inhibition of basal autophagy significantly impaired HL growth in-vivo in NOD SCID γc-/- (NSG) mice. We found that basal autophagy plays a pivotal role in sustaining mitochondrial function.We conclude that cHL cells require basal autophagy for growth, survival and sustained metabolism making them sensitive to autophagy inhibition. This suggests basal autophagy as useful target for new strategies in cHL treatment.

Ischemic A/D transition of mitochondrial complex I and its role in ROS generation.

Mitochondrial complex I (NADH:ubiquinone oxidoreductase) is a key enzyme in cellular energy metabolism and provides approximately 40% of the proton-motive force that is utilized during mitochondrial ATP production. The dysregulation of complex I function--either genetically, pharmacologically, or metabolically induced--has severe pathophysiological consequences that often involve an imbalance in the production of reactive oxygen species (ROS). Slow transition of the active (A) enzyme to the deactive, dormant (D) form takes place during ischemia in metabolically active organs such as the heart and brain. The reactivation of complex I occurs upon reoxygenation of ischemic tissue, a process that is usually accompanied by an increase in cellular ROS production. Complex I in the D-form serves as a protective mechanism preventing the oxidative burst upon reperfusion. Conversely, however, the D-form is more vulnerable to oxidative/nitrosative damage. Understanding the so-called active/deactive (A/D) transition may contribute to the development of new therapeutic interventions for conditions like stroke, cardiac infarction, and other ischemia-associated pathologies. In this review, we summarize current knowledge on the mechanism of A/D transition of mitochondrial complex I considering recently available structural data and site-specific labeling experiments. In addition, this review discusses in detail the impact of the A/D transition on ROS production by complex I and the S-nitrosation of a critical cysteine residue of subunit ND3 as a strategy to prevent oxidative damage and tissue damage during ischemia-reperfusion injury. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.

Mortality of Septic Mice Strongly Correlates With Adrenal Gland Inflammation.

OBJECTIVES: Sepsis and septic shock are commonly present in the ICU and accompanied by significant morbidity, mortality, and cost. The frequency of secondary adrenal insufficiency in sepsis remains open to debate and a challenge to identify and treat appropriately. Animal models of sepsis using genetic or surgical initiation of adrenal insufficiency resulted in increased mortality, but the mechanisms are still unclear. The present study investigates the impact of adrenal inflammation in septic mice challenged with cecal ligation and puncture. DESIGN: Prospective experimental study. SETTING: University laboratory. SUBJECTS: C57BL/6N wild-type mice. INTERVENTIONS: Sepsis, induced by cecal ligation and puncture for 24 and 48 hours. MEASUREMENTS AND MAIN RESULTS: Both septic and control mice were carefully monitored (every 30 min) for up to 48 hours and divided into survivors and nonsurvivors. We observed a significant and massive increase of interleukin-6, interleukin-1ß, and tumor necrosis factor-α in adrenal protein extracts of nonsurvivors compared with sham animals and survivors. This pattern was partly reflected in liver and lung but not in plasma samples. Notably, a significant increase in nonsurvivors compared with survivors was only found for lung interleukin-6. In line with these findings, we detected a higher degree of leukocyte infiltration and hemorrhage in the adrenal glands of deceased mice. Evaluation of the hypothalamic-pituitary-adrenal axis response in these animals revealed an increase of adrenocorticotropic hormone, which was only partly reflected in the corticosterone level. Notably, using the adrenocorticotropic hormone stimulation test, we found an impaired adrenocorticotropic hormone response, particularly in nonsurvivors, which significantly correlated with the number of infiltrated leukocytes. CONCLUSIONS: Cecal ligation and puncture-induced murine sepsis induces a strong inflammatory response in the adrenal glands, which is accompanied by cell death and hemorrhage. Our data suggest that mortality and adrenal incapacitation are associated with the degree of adrenal inflammation, thereby underscoring the importance of adrenal function on survival.

Hodgkin and Reed-Sternberg cells of classical Hodgkin lymphoma are highly dependent on oxidative phosphorylation.

The metabolic properties of lymphomas derived from germinal center (GC) B cells have important implications for therapeutic strategies. In this study, we have compared metabolic features of Hodgkin-Reed-Sternberg (HRS) cells, the tumor cells of classical Hodgkin's lymphoma (cHL), one of the most frequent (post-)GC-derived B-cell lymphomas, with their normal GC B cell counterparts. We found that the ratio of oxidative to nonoxidative energy conversion was clearly shifted toward oxidative phosphorylation (OXPHOS)-linked ATP synthesis in HRS cells as compared to GC B cells. Mitochondrial mass, the expression of numerous key proteins of oxidative metabolism and markers of mitochondrial biogenesis were markedly upregulated in cHL cell lines and in primary cHL cases. NFkappaB promoted this shift to OXPHOS. Functional analysis indicated that both cell growth and viability of HRS cells depended on OXPHOS. The high rates of OXPHOS correlated with an almost complete lack of lactate production in HRS cells not observed in other GC B-cell lymphoma cell lines. Overall, we conclude that OXPHOS dominates energy conversion in HRS cells, while nonoxidative ATP production plays a subordinate role. Our results suggest that OXPHOS could be a new therapeutic target and may provide an avenue toward new treatment strategies in cHL.

Metformin reduces hyper-reactivity of platelets from patients with polycystic ovary syndrome by improving mitochondrial integrity.

Polycystic ovary syndrome (PCOS) is associated with decreased fertility, insulin resistance and an increased risk of developing cardiovascular disease. Treating PCOS patients with metformin improves fertility and decreases cardiovascular complications. Given that platelet activation contributes to both infertility and cardiovascular disease development, we assessed platelet reactivity in PCOS patients and the consequences of metformin treatment. Compared to washed platelets from healthy donors, platelets from PCOS patients demonstrated enhanced reactivity and impaired activation of the AMP-activated kinase (AMPK). PCOS platelets also demonstrated enhanced expression of mitochondrial proteins such as the cytochrome c reductase, ATP synthase and the voltage-dependent anion channel-1. However, mitochondrial function was impaired as demonstrated by a decreased respiration rate. In parallel, the phosphorylation of dynamin-related protein-1 (Drp-1) on Ser616 was increased while that on Ser637 decreased. The latter changes were accompanied by decreased mitochondrial size. In insulin-resistant PCOS patients (HOMA-IR> 2) metformin treatment (1.7 g per day for 4 weeks to 6 months) improved insulin sensitivity, restored mitochondrial integrity and function and normalised platelet aggregation. Treatment was without effect in PCOS patients with HOMA-IR< 2. Moreover, treatment of megakaryocytes with metformin enhanced mitochondrial content and in the same cells metformin enhanced the phosphorylation of the Drp-1 on Ser637 via an AMPKα1-dependent mechanism. In conclusion, the improvement of mitochondrial integrity and platelet reactivity may contribute to the beneficial effects of metformin on cardiovascular disease.

Contribution of Ninjurin1 to Toll-like receptor 4 signaling and systemic inflammation.

Nerve injury-induced protein (Ninjurin [Ninj]) 1 is an adhesion molecule originally identified in Schwann cells after nerve injury, whereas it is also expressed in leukocytes, epithelium, endothelium, and various organs, and is induced under inflammatory conditions. Its contribution to inflammation was so far restricted to the nervous system and exclusively attributed to its role during leukocyte migration. We hypothesized a proinflammatory role for Ninj1 also outside the nervous system. To elucidate its impact during inflammation, we analyzed expression levels and its contribution to inflammation in septic mice and studied its effect on inflammatory signaling in vitro. The effect on inflammation was analyzed by genetic (only in vitro) and pharmacologic repression in septic mice (cecal ligation and puncture) and cell culture, respectively. Repression of Ninj1 by an inhibitory peptide or small interfering RNA attenuated LPS-triggered inflammation in macrophages and endothelial cells by modulating p38 phosphorylation and activator protein-1 activation. Inhibition of Ninj1 in septic mice reduced systemic and pulmonary inflammation as well as organ damage, and ameliorated survival after 24 hours. Ninj1 is elevated under inflammatory conditions and contributes to inflammation not only by mediating leukocyte migration, but also by modulating Toll-like receptor 4-dependent expression of inflammatory mediators. We assume that, owing to both mechanisms, inhibition reduces systemic inflammation and organ damage in septic mice. Our data contribute to a better understanding of the complex inflammatory mechanisms and add a novel therapeutic target for inflammatory conditions such as sepsis.

Mitochondrial respiratory chain complexes as sources and targets of thiol-based redox-regulation.

The respiratory chain of the inner mitochondrial membrane is a unique assembly of protein complexes that transfers the electrons of reducing equivalents extracted from foodstuff to molecular oxygen to generate a proton-motive force as the primary energy source for cellular ATP-synthesis. Recent evidence indicates that redox reactions are also involved in regulating mitochondrial function via redox-modification of specific cysteine-thiol groups in subunits of respiratory chain complexes. Vice versa the generation of reactive oxygen species (ROS) by respiratory chain complexes may have an impact on the mitochondrial redox balance through reversible and irreversible thiol-modification of specific target proteins involved in redox signaling, but also pathophysiological processes. Recent evidence indicates that thiol-based redox regulation of the respiratory chain activity and especially S-nitrosylation of complex I could be a strategy to prevent elevated ROS production, oxidative damage and tissue necrosis during ischemia-reperfusion injury. This review focuses on the thiol-based redox processes involving the respiratory chain as a source as well as a target, including a general overview on mitochondria as highly compartmentalized redox organelles and on methods to investigate the redox state of mitochondrial proteins. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

Measuring interference of drug-like molecules with the respiratory chain: toward the early identification of mitochondrial uncouplers in lead finding.

The electron transport chain (ETC) couples electron transfer between donors and acceptors with proton transport across the inner mitochondrial membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate (ATP). Proton transfer is based on the activity of complex I-V proteins in the ETC. The overall electrical activity of these proteins can be measured by proton transfer using Solid Supported Membrane technology. We tested the activity of complexes I, III, and V in a combined assay, called oxidative phosphorylation assay (oxphos assay), by activating each complex with the corresponding substrate. The oxphos assay was used to test in-house substances from different projects and several drugs currently available on the market that have reported effects on mitochondrial functions. The resulting data were compared to the influence of the respective compounds on mitochondria as determined by oxygen consumption and to data generated with an ATP depletion assay. The comparison shows that the oxidative phosphorylation assay provides both a rapid approach for detecting interaction of compounds with respiratory chain proteins and information on their mode of interaction. Therefore, the oxphos assay is a useful tool to support structure activity relationship studies by allowing early identification of mitotoxicity and for analyzing the outcome of phenotypic screens that are susceptible to the generation of mitotoxicity-related artifacts.

Unmasking a temperature-dependent effect of the P. anserina i-AAA protease on aging and development.

Different molecular pathways involved in maintaining mitochondrial function are of fundamental importance to control cellular homeostasis. Mitochondrial i-AAA protease is part of such a surveillance system and PaIAP is the putative ortholog in the fungal aging model Podospora anserina. Here we investigated the role of PaIAP in aging and development. Deletion of the gene encoding PaIAP resulted in a specific phenotype. When incubated at 27°C, spore germination and fruiting body formation are not different from that of the corresponding wild-type strain. Unexpectedly, the lifespan of the deletion strain is strongly increased. In contrast, cultivation at an elevated temperature of 37°C leads to impairments in spore germination and fruiting body formation, and to a reduced lifespan. The higher PaIAP abundance in wild-type strains of the fungus grown at elevated temperature and the phenotype of the deletion strain unmasks a temperature-related role of the protein. The protease appears to be part of a molecular system that has evolved to allow survival under changing temperatures as they characteristically occur in nature.

Three-dimensional structure of the KdpFABC complex of Escherichia coli by electron tomography of two-dimensional crystals.

The KdpFABC complex (Kdp) functions as a K+ pump in Escherichia coli and is a member of the family of P-type ATPases. Unlike other family members, Kdp has a unique oligomeric composition and is notable for segregating K+ transport and ATP hydrolysis onto separate subunits (KdpA and KdpB, respectively). We have produced two-dimensional crystals of the KdpFABC complex within reconstituted lipid bilayers and determined its three-dimensional structure from negatively stained samples using a combination of electron tomography and real-space averaging. The resulting map is at a resolution of 2.4 nm and reveals a dimer of Kdp molecules as the asymmetric unit; however, only the cytoplasmic domains are visible due to the lack of stain penetration within the lipid bilayer. The sizes of these cytoplasmic domains are consistent with Kdp and, using a pseudo-atomic model, we have described the subunit interactions that stabilize the Kdp dimer within the larger crystallographic array. These results illustrate the utility of electron tomography in structure determination of ordered assemblies, especially when disorder is severe enough to hamper conventional crystallographic analysis.

Mechanism of thiazolidinedione-dependent cell death in Jurkat T cells.

Thiazolidinediones are synthetic agonists for the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) and are therapeutically used as insulin sensitizers. Besides therapeutical benefits, potential side effects such as the induction of cell death by thiazolidinediones deserve consideration. Although PPARgamma-dependent and -independent cell death in response to thiazolidinediones has been described, we provide evidence supporting a new mechanism to account for thiazolidinedione-initiated but PPARgamma-independent cell demise. In Jurkat T cells, ciglitazone and troglitazone provoked rapid and dose-dependent cell death, whereas rosiglitazone did not alter cell viability. We found induction of apoptosis by troglitazone, whereas ciglitazone caused necrosis. Because preincubation with the reactive oxygen species (ROS) scavengers manganese (III) tetrakis(4-benzoic acid) porphyrin and vitamin C significantly inhibited ciglitazone- and partially troglitazone-mediated cell death, we suggest that ROS contribute to cytotoxicity. Assuming that ROS originate from mitochondria, studies in submitochondrial particles demonstrated that all thiazolidinediones inhibited complex I of the mitochondrial respiratory chain. However, only ciglitazone and troglitazone lowered complex II activity as well. Pharmacological inhibition of complexes I and II documented that complex II inhibition in Jurkat cells caused massive apoptotic cell death, whereas inhibition of complex I provoked only marginally apoptosis after 4-h treatment. Therefore, inhibition of complex II by ciglitazone and troglitazone is the main trigger of cell death. ATP depletion by ciglitazone, in contrast to troglitazone, is responsible for induction of necrosis. Our results demonstrate that despite their similar molecular structure, thiazolidinediones differently affect cell death, which might help to explain some adverse effects occurring during thiazolidinedione-based therapies.

Mitochondrial dysfunction, peroxidation damage and changes in glutathione metabolism in PARK6.

Oxidative stress and protein aggregation are biochemical hallmarks of Parkinson's disease (PD), a frequent sporadic late-onset degenerative disorder particularly of dopaminergic neurons in the substantia nigra, resulting in impaired spontaneous movement. PARK6 is a rare autosomal-recessively inherited disorder, mimicking the clinical picture of PD with earlier onset and slower progression. Genetic data demonstrated PARK6 to be caused by mutations in the protein PINK1, which is localized to mitochondria and has a serine-threonine kinase domain. To study the effect of PINK1 mutations on oxidative stress, we used primary fibroblasts and immortalized lymphoblasts from three patients homozygous for G309D-PINK1. Oxidative stress was evident from increases in lipid peroxidation and in antioxidant defenses by mitochondrial superoxide dismutase and glutathione. Elevated levels of glutathione reductase and glutathione-S-transferase were also observed. As a putative cause of oxidation, a mild decrease in complex I activity and a trend to superoxide elevation were detectable. These data indicate that PINK1 function is critical to prevent oxidative damage and that peripheral cells may be useful for studies of progression and therapy of PARK6.

The Redox-Bohr group associated with iron-sulfur cluster N2 of complex I.

Proton pumping respiratory complex I (NADH:ubiquinone oxidoreductase) is a major component of the oxidative phosphorylation system in mitochondria and many bacteria. In mammalian cells it provides 40% of the proton motive force needed to make ATP. Defects in this giant and most complicated membrane-bound enzyme cause numerous human disorders. Yet the mechanism of complex I is still elusive. A group exhibiting redox-linked protonation that is associated with iron-sulfur cluster N2 of complex I has been proposed to act as a central component of the proton pumping machinery. Here we show that a histidine in the 49-kDa subunit that resides near iron-sulfur cluster N2 confers this redox-Bohr effect. Mutating this residue to methionine in complex I from Yarrowia lipolytica resulted in a marked shift of the redox midpoint potential of iron-sulfur cluster N2 to the negative and abolished the redox-Bohr effect. However, the mutation did not significantly affect the catalytic activity of complex I and protons were pumped with an unchanged stoichiometry of 4 H(+)/2e(-). This finding has significant implications on the discussion about possible proton pumping mechanism for complex I.