Function Of Respiratory Chain Complexes Research Articles

Regulation of Mitochondrial Respiratory Chain Complex Levels, Organization, and Function by Arginyltransferase 1

Arginyltransferase 1 (ATE1) is an evolutionary-conserved eukaryotic protein that localizes to the cytosol and nucleus. It is the only known enzyme in metazoans and fungi that catalyzes posttranslational arginylation. Lack of arginylation has been linked to an array of human disorders, including cancer, by altering the response to stress and the regulation of metabolism and apoptosis. Although mitochondria play relevant roles in these processes in health and disease, a causal relationship between ATE1 activity and mitochondrial biology has yet to be established. Here, we report a phylogenetic analysis that traces the roots of ATE1 to alpha-proteobacteria, the mitochondrion microbial ancestor. We then demonstrate that a small fraction of ATE1 localizes within mitochondria. Furthermore, the absence of ATE1 influences the levels, organization, and function of respiratory chain complexes in mouse cells. Specifically, ATE1-KO mouse embryonic fibroblasts have increased levels of respiratory supercomplexes I+III2+IVn. However, they have decreased mitochondrial respiration owing to severely lowered complex II levels, which leads to accumulation of succinate and downstream metabolic effects. Taken together, our findings establish a novel pathway for mitochondrial function regulation that might explain ATE1-dependent effects in various disease conditions, including cancer and aging, in which metabolic shifts are part of the pathogenic or deleterious underlying mechanism.

Mitochondrial replacement by genome transfer in human oocytes: Efficacy, concerns, and legality.

BackgroundPathogenic mitochondrial (mt)DNA mutations, which often cause life‐threatening disorders, are maternally inherited via the cytoplasm of oocytes. Mitochondrial replacement therapy (MRT) is expected to prevent second‐generation transmission of mtDNA mutations. However, MRT may affect the function of respiratory chain complexes comprised of both nuclear and mitochondrial proteins.MethodsBased on the literature and current regulatory guidelines (especially in Japan), we analyzed and reviewed the recent developments in human models of MRT.Main findingsMRT does not compromise pre‐implantation development or stem cell isolation. Mitochondrial function in stem cells after MRT is also normal. Although mtDNA carryover is usually less than 0.5%, even low levels of heteroplasmy can affect the stability of the mtDNA genotype, and directional or stochastic mtDNA drift occurs in a subset of stem cell lines (mtDNA genetic drift). MRT could prevent serious genetic disorders from being passed on to the offspring. However, it should be noted that this technique currently poses significant risks for use in embryos designed for implantation.ConclusionThe maternal genome is fundamentally compatible with different mitochondrial genotypes, and vertical inheritance is not required for normal mitochondrial function. Unresolved questions regarding mtDNA genetic drift can be addressed by basic research using MRT.

Peculiarities of Immediate Response of Respiratory Chain Enzymes in Rat Cerebral Cortex to Hypoxia.

We performed a complex study of the dependence of immediate reaction of catalytic subunits in mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX1, and ATP5A) in rat cerebral cortex (the most hypoxia-sensitive tissue) on the severity and duration of hypoxia in vivo and the role of individual resistance of rats to oxygen deficiency in this process. Three types of responses to hypoxia were revealed. The immediate response of mitochondria to oxygen deficiency appeared after its drop by 30-33% relatively to normal atmosphere level. It manifested in up-regulation of NAD-dependent oxidation, i.e., activation of respiratory chain complex I. Further decrease in oxygen concentration by 50% reprogrammed the work of respiratory chain via activation of respiratory chain complex II in parallel with down-regulation of the electron transport function of the respiratory chain complex I. This response was optimal for the expression of adaptation genes and for the formation of immediate tolerance of rats to hypoxia. The greatest drop of oxygen concentration by 60-62% reversed the Krebs cycle promoting recovery of the electron transport function of respiratory chain complex I. Despite this, the energy efficiency of the respiratory chain and the potency to mobilize the rapid adaptation mechanisms degraded due to abnormalities in cytochrome segment of the respiratory chain.

Abstract P5-21-19: Suppression of breast carcinogenesis and metastasis by targeting glucose metabolism with HJC0152

Abstract Lack of targeted strategies for preventing and treating estrogen receptor (ER)-negative breast cancer (ENBC) is an unmet clinical challenge. ENBCs including triple-negative BCs (TNBC) constitute 30-40% of BC cases and are prone to develop remote metastasis and local recurrence, resulting in the majority of deaths in BC patients. Dysregulated glucose and energy metabolism is critically involved in the development and progression of various cancers via promoting aberrant cell growth, malignant transformation and metastasis. Nevertheless, the potential role of glucose/energy metabolism in ENBC carcinogenesis has sparsely been explored, thus representing a key knowledge gap and a potential avenue for effective targeted therapies. Despite a substantial amount of effort has been made towards anticancer metabolic and biogenetic medications, none has progressed into clinical use, due to their limited potency, specificity or drug properties such as toxicity and poor bioavailability. We recently developed HJC0152, a novel small molecule anticancer agent, using structure- and fragment-based drug design strategies and molecular modeling techniques in our initial attempt to develop non-peptide STAT3 inhibitors for anticancer use. HJC0152 significantly inhibits proliferation of BC cells, induces apoptosis, reduces ER-negative mammary tumor development, suppresses ENBC xenograft tumor growth, and blocks lung metastasis in vivo. Intriguingly, HJC0152 differentially modulates expression of glycolytic enzymes including HK1, PFK-L, PFKFB2, ENO2, PDH, PDK1, PGAM1 and ALDOA in a time-dependent manner. HJC0152 also regulates the transcription of genes involved in glucose and mitochondrial energy metabolism, including the subunits of mitochondrial respiratory chain complexes. Functional assessments further demonstrate that HJC0152 significantly modulates respiratory chain complex function. Via in silico and Unique Polymer Technology (UPT) strategy, we identified a number of putative HJC0152-interacting targets for validation studies. Our findings suggest that HJC0152 is capable of reprogramming/restoring the dysregulated glucose metabolism by inducing specific glycolytic enzyme expression and mitochondrial respiratory chain function, likely via targeting upstream key signal molecule(s) that regulates glucose and energy metabolism, thereby suppressing breast cancer development and progression to metastasis. This work was supported by Grants P50 CA097007, and P30DA028821 (JZ) from the NIH, CPRIT (JZ), John Sealy Memorial Endowment Fund (JZ), DFI Grants from MD Anderson Cancer Center (QS), Holden Family Research Grant in BC Prevention (QS), and NCI PREVENT Program HHSN26100002 (QS). Citation Format: Dong J, Kim H, Xu J, Li D, Zhang Z, Zheng Z, Ye N, Chen H, Zhou J, Shen Q. Suppression of breast carcinogenesis and metastasis by targeting glucose metabolism with HJC0152 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-19.

Stomatin-like Protein 2 Deficiency in T Cells Is Associated with Altered Mitochondrial Respiration and Defective CD4+ T Cell Responses

Stomatin-like protein 2 (SLP-2) is a mostly mitochondrial protein that regulates mitochondrial biogenesis and function and modulates T cell activation. To determine the mechanism of action of SLP-2, we generated T cell-specific SLP-2-deficient mice. These mice had normal numbers of thymocytes and T cells in the periphery. However, conventional SLP-2-deficient T cells had a posttranscriptional defect in IL-2 production in response to TCR ligation, and this translated into reduced CD4(+) T cell responses. SLP-2 deficiency was associated with impaired cardiolipin compartmentalization in mitochondrial membranes, decreased levels of the NADH dehydrogenase (ubiquinone) iron-sulfur protein 3, NADH dehydrogenase (ubiquinone) 1β subcomplex subunit 8, and NADH dehydrogenase (ubiquinone) 1α subcomplex subunit 9 of respiratory complex I, and decreased activity of this complex as well as of complex II plus III of the respiratory chain. In addition, SLP-2-deficient T cells showed a significant increase in uncoupled mitochondrial respiration and a greater reliance on glycolysis. Based on these results, we propose that SLP-2 organizes the mitochondrial membrane compartmentalization of cardiolipin, which is required for optimal assembly and function of respiratory chain complexes. This function, in T cells, helps to ensure proper metabolic response during activation.

Diabetic rats are unable to elicit cardioprotection by isoflurane: role of mitochondrial dysfunction

We investigated whether differences in mitochondrial genome play a role in anesthetic-induced preconditioning (APC) in the diabetic heart model with “swapped” mitochondria. These rats have identical nuclear genome, but some bear Wistar (T2DNmtWistar) while others bear Fawn Hooded Hypertensive (T2DNmtFHH) mitochondrial genome. The production of reactive oxygen species (ROS) and changes in flavoproteins (FPs) fluorescence were monitored from ventricular myocytes in the presence of 1 MAC isoflurane by laser scanning confocal microscopy. Opening of mitochondrial permeability transition pore (mPTP) was detected by tetramethylrhodamine dye. During isoflurane, ROS were increased by 165% and 107% in T2DNmtFHH and T2DNmtWistar cardiomyocytes, respectively. In addition, isoflurane induced oxidation of mitochondrial FPs in T2DNmtFHH by 94% and by 35% in T2DNmtWistar myocytes. Compared to respective controls, APC increased the mPTP opening time in T2DNmtWistar but not in T2DNmtFHH myocytes. Our findings suggest that mitochondrial genome-related differences in the function of respiratory chain complexes have an impact on anesthetic sensitivity of the mitochondria. This in part could explain that APC protection against mPTP opening is compromised in T2DNmtFHH but not in T2DNmtWistar cardiomyocytes. Supported by P01GM066730 (ZJB) from the NIH, Bethesda, MD.

Simultaneous detection of mitochondrial respiratory chain activity and reactive oxygen in digitonin-permeabilized cells using flow cytometry.

Increased mitochondrial generation of reactive oxygen intermediates (ROI) due to defective respiratory chain activity has been implicated in physiological processes such as apoptosis, in the pathogenesis of mitochondrial diseases, and as part of the normal aging process. Established methods addressing activity of the respiratory chain complexes have been limited to bulk assays for single parameters. This study describes a flow cytometry-based method and its validation for the detection of respiratory chain function in single cells permeabilized by digitonin. Flow cytometry was used to measure mitochondrial membrane potential (DeltaPsi(m)) and reactive oxygen generation under differing conditions of respiration. This was brought about by the addition of substrates and inhibitors to digitonin-permeabilized cells. This method was validated by measurement of oxygen consumption and ATP production and by confocal microscopy. Activity of the respiratory chain complexes assessed by DeltaPsi(m) responded to substrates and inhibitors as predicted from assessment by oxygen consumption and ATP synthesis. In addition, the flow cytometry method allows the simultaneous assessment of mitochondrial ROI generation. This was confirmed by the localization of the ROI probe, carboxy-DCF, to the same site as the mitochondrial probe observed by confocal microscopy. This method allows the functional integrity of the respiratory chain complexes to be studied at the single-cell level, thus addressing the relationship between disordered function of respiratory chain complexes and mitochondrial ROI generation.

Simultaneous detection of mitochondrial respiratory chain activity and reactive oxygen in digitonin-permeabilized cells using flow cytometry

Increased mitochondrial generation of reactive oxygen intermediates (ROI) due to defective respiratory chain activity has been implicated in physiological processes such as apoptosis, in the pathogenesis of mitochondrial diseases, and as part of the normal aging process. Established methods addressing activity of the respiratory chain complexes have been limited to bulk assays for single parameters. This study describes a flow cytometry-based method and its validation for the detection of respiratory chain function in single cells permeabilized by digitonin.Flow cytometry was used to measure mitochondrial membrane potential (DeltaPsi(m)) and reactive oxygen generation under differing conditions of respiration. This was brought about by the addition of substrates and inhibitors to digitonin-permeabilized cells. This method was validated by measurement of oxygen consumption and ATP production and by confocal microscopy.Activity of the respiratory chain complexes assessed by DeltaPsi(m) responded to substrates and inhibitors as predicted from assessment by oxygen consumption and ATP synthesis. In addition, the flow cytometry method allows the simultaneous assessment of mitochondrial ROI generation. This was confirmed by the localization of the ROI probe, carboxy-DCF, to the same site as the mitochondrial probe observed by confocal microscopy.This method allows the functional integrity of the respiratory chain complexes to be studied at the single-cell level, thus addressing the relationship between disordered function of respiratory chain complexes and mitochondrial ROI generation.