Amyloid precursor protein drives down-regulation of mitochondrial oxidative phosphorylation independent of amyloid beta

Amyloid precursor protein (APP) and its extracellular domain, soluble APP alpha (sAPPα) play important physiological and neuroprotective roles. However, rare forms of familial Alzheimer’s disease are associated with mutations in APP that increase toxic amyloidogenic cleavage of APP and produce amyloid beta (Aβ) at the expense of sAPPα and other non-amyloidogenic fragments. Although mitochondrial dysfunction has become an established hallmark of neurotoxicity, the link between Aβ and mitochondrial function is unclear. In this study we investigated the effects of increased levels of neuronal APP or Aβ on mitochondrial metabolism and gene expression, in human SH-SY5Y neuroblastoma cells. Increased non-amyloidogenic processing of APP, but not Aβ, profoundly decreased respiration and enhanced glycolysis, while mitochondrial DNA (mtDNA) transcripts were decreased, without detrimental effects to cell growth. These effects cannot be ascribed to Aβ toxicity, since higher levels of endogenous Aβ in our models do not cause oxidative phosphorylation (OXPHOS) perturbations. Similarly, chemical inhibition of β-secretase decreased mitochondrial respiration, suggesting that non-amyloidogenic processing of APP may be responsible for mitochondrial changes. Our results have two important implications, the need for caution in the interpretation of mitochondrial perturbations in models where APP is overexpressed, and a potential role of sAPPα or other non-amyloid APP fragments as acute modulators of mitochondrial metabolism

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Characterization of mitochondrial dysfunction in the 7PA2 cell model of Alzheimer's disease

The 7WD4 and 7PA2 cell lines, widely used as cellular models for Alzheimer's disease (AD), have been used to investigate the effects of amyloid-\u3b2 protein precursor overexpression and amyloid-\u3b2 (A\u3b2) oligomer accumulation on mitochondrial function. Under standard culture conditions, both cell lines, compared to Chinese hamster ovary (CHO) control cells, displayed an ~5% decrease of O2 respiration as sustained by endogenous substrates. Functional impairment of the respiratory chain was found distributed among the protein complexes, though more evident at the level of complex I and complex IV. Measurements of ATP showed that its synthesis by oxidative phosphorylation is decreased in 7WD4 and 7PA2 cells by ~25%, this loss being partly compensated by glycolysis (Warburg effect). Compensation proved to be more efficient in 7WD4 than in 7PA2 cells, the latter cell line displaying the highest reactive oxygen species production. The strongest deficit was observed in mitochondrial membrane potential that is almost 40% and 60% lower in 7WD4 and 7PA2 cells, respectively, in comparison to CHO controls. All functional parameters point to a severe bioenergetic impairment of the AD cells, with the extent of mitochondrial dysfunction being correlated to the accumulation of A\u3b2 peptides and oligomers

Biomarkers in Czech workers exposed to 1,3-butadiene: a transitional epidemiologic study

A multiinstitutional, transitional epidemiologic study was conducted with a worker population in the Czech Republic to evaluate the utility of a continuum of non-disease biological responses as biomarkers of exposure to 1,3-butadiene (BD)* in an industrial setting. The study site included two BD facilities in the Czech Republic. Institutions that collaborated in the study were the University of Vermont (Burlington, Vermont, USA); the Laboratory of Genetic Ecotoxicology (Prague, the Czech Republic); Shell International Chemicals, BV (Amsterdam, The Netherlands); the University of North Carolina at Chapel Hill (Chapel Hill, North Carolina, USA); University of Texas Medical Branch at Galveston (Galveston, Texas, USA); Leiden University (Leiden, The Netherlands); and the Health and Safety Laboratory (Sheffield, United Kingdom). Male volunteer workers (83) participated in the study: 24 were engaged in BD monomer production, 34 in polymerization activities, and 25 plant administrative workers served as unexposed control subjects. The BD concentrations experienced by each exposed worker were measured by personal monitor on approximately ten separate occasions for 8-hour workshifts over a 60-day exposure assessment period before biological samples were collected. Coexposures to styrene, benzene, and toluene were also measured. The administrative control workers were considered to be a homogeneous, unexposed group for whom a series of 28 random BD measurements were taken during the exposure assessment period. Questionnaires were administered in Czech to all participants. At the end of the exposure assessment period, blood and urine samples were collected at the plant; samples were. fractionated, cryopreserved, and kept frozen in Prague until they were shipped to the appropriate laboratories for specific biomarker analysis. The following biomarkers were analyzed: * polymorphisms in genes involved in BD metabolism (Prague and Burlington); * urinary concentrations of 1-hydroxy-2-(N-acetylcysteinyl)-3-butene and 2-hydroxy-1-(N-acetylcysteinyl)-3-butene (M2 [refers to an isomeric mixture of both forms]) (Amsterdam); * urinary concentrations of 1,2-dihydroxy-4-(N-acetylcysteinyl)-butane (M1) (Amsterdam); * concentrations of the hemoglobin (Hb) adducts N-(1-[hydroxymethyl]-2-propenyl)valine and N-(2-hydroxy-3-butenyl)valine (HBVal [refers to an isomeric mixture of both forms]) (Amsterdam); * concentrations of the Hb adduct N-(2,3,4-trihydroxybutyl)valine (THBVal) (Chapel Hill); * T cell mutations in the hypoxanthine phosphoribosyltransferase (HPRT) gene (autoradiographic assay in Galveston with slide review in Burlington; cloning assay in Leiden with mutational spectra determined in Burlington); and * chromosomal aberrations by the conventional method and by fluorescence in situ hybridization [FISH]), and cytogenetic changes (sister chromatid exchanges [SCEs] (Prague). All assay analysts were blinded to worker and sample identity and remained so until all work in that laboratory had been completed and reported. Assay results were sent to the Biometry Facility in Burlington for statistical analyses. Analysis of questionnaire data revealed that the three exposure groups were balanced with respect to age and years of residence in the district, but the control group had significantly more education than the other two groups and included fewer smokers. Group average BD exposures were 0.023 mg/m3 (0.010 ppm) for the control group, 0.642 mg/m3 (0.290 ppm) for the monomer group, and 1.794 mg/m3 (0.812 ppm) for the polymer group; exposure levels showed considerable variability between and within individuals. Styrene exposures were significantly higher in the polymer group than in the other two groups. We found no statistically significant differences in the distributions of metabolic genotypes over the three exposure groups; genotype frequencies were consistent with those previously reported for this ethnic and national population. Although some specific genotypes were associated with quantitative differences in urinary metabolite concentrations or Hb adduct dose-response characteristics, none indicated a heightened susceptibility to BD. Concentrations of both the M2 and M1 urinary metabolites and both the HBVal and THBVal Hb adducts were significantly correlated with group and individual mean BD exposure levels; the Hb adducts were more strongly correlated than the urinary metabolites. By contrast, no significant relations were observed between BD exposures and HPRT gene mutations (whether determined by the auto-radiographic or the cloning method) or any of the cytogenetic biomarkers (whether determined by the conventional method or FISH analysis). Neither the mutational nor the cytogenetic responses showed any association with genotypes. The molecular spectrum of HPRT mutations in BD-exposed workers showed a high frequency of deletions; but the same result was found in the unexposed control subjects, which suggests that these were not due to BD exposure. This lack of association between BD exposures and genetic effects persisted even when control subjects were excluded from the analyses or when we conducted regression analyses of individual workers exposed to different levels of B

Haptoglobin interacts with Apolipoprotein e and beta-amyloid and influences their crosstalk

Beta-amyloid accumulation in brain is a driving force for Alzheimer's disease pathogenesis. Apolipoprotein E (ApoE) represents a critical player in beta-amyloid homeostasis, but its role in disease progression is controversial. We previously reported that the acute-phase protein haptoglobin binds ApoE and impairs its function in cholesterol homeostasis. The major aims of this study were to characterize the binding of haptoglobin to beta-amyloid, and to evaluate whether haptoglobin affects ApoE binding to beta-amyloid. Haptoglobin is here reported to form a complex with beta-amyloid as shown by immunoblotting experiments with purified proteins, or by its immunoprecipitation in brain tissues from patients with Alzheimer's disease. The interaction between ApoE and beta-amyloid was previously shown to be crucial for limiting beta-amyloid neurotoxicity and for promoting its clearance. We demonstrate that haptoglobin, rather than impairing ApoE binding to beta-amyloid, promotes to a different extent the formation of the complex between beta-amyloid and ApoE2 or ApoE3 or ApoE4. Our data suggest that haptoglobin and ApoE functions in brain should be evaluated taking into account their mutual interaction with beta-amyloid. Hence, the risk of developing Alzheimer's disease might not only be linked to the different ApoE isoforms, but also rely on the level of critical ligands, such as haptoglobin

Mitochondrial respiratory states and rates: Building blocks of mitochondrial physiology (Part 1)

Supporting co-authors: Bakker BM, Bernardi P, Boetker HE, Borsheim E, Borutaitė V, Bouitbir J, Calbet JA, Calzia E, Chaurasia B, Clementi E, Coker RH, Collin A, Das AM, De Palma C, Dubouchaud H, Durham WJ, Dyrstad SE, Engin AB, Fornaro M, Gan Z, Garlid KD, Garten A, Gourlay CW, Granata C, Haas CB, Haavik J, Haendeler J, Hand SC, Hepple RT, Hickey AJ, Hoel F, Jang DH, Kainulainen H, Khamoui AV, Klingenspor M, Koopman WJH, Kowaltowski AJ, Krajcova A, Lane N, Lenaz G, Malik A, Markova M, Mazat JP, Menze MA, Methner A, Neuzil J, Oliveira MT, Pallotta ML, Parajuli N, Pettersen IKN, Porter C, Pulinilkunnil T, Ropelle ER, Salin K, Sandi C, Sazanov LA, Silber AM, Skolik R, Smenes BT, Soares FAA, Sokolova I, Sonkar VK, Swerdlow RH, Szabo I, Trifunovic A, Thyfault JP, Valentine JM, Vieyra A, Votion DM, Williams C, Zischka HAs the knowledge base and importance of mitochondrial physiology to human health expand, the necessity for harmonizing nomenclature concerning mitochondrial respiratory states and rates has become increasingly apparent. Clarity of concept and consistency of nomenclature are key trademarks of a research field. These trademarks facilitate effective transdisciplinary communication, education, and ultimately further discovery. Peter Mitchell’s chemiosmotic theory establishes the link between vectorial and scalar energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theory and nomenclature for mitochondrial physiology and bioenergetics. Herein, we follow IUPAC guidelines on general terms of physical chemistry, extended by considerations on open systems and irreversible thermodynamics. We align the nomenclature and symbols of classical bioenergetics with a concept-driven constructive terminology to express the meaning of each quantity clearly and consistently. In this position statement, in the frame of COST Action MitoEAGLE, we endeavour to provide a balanced view on mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately support the development of databases of mitochondrial respiratory function in species, tissues, and cells.We thank M. Beno for management assistance. Supported by COST Action CA15203 MitoEAGLE and K-Regio project MitoFit (E.G.).N