scholarly journals Bcl-xL regulates mitochondrial energetics by stabilizing the inner membrane potential

2011 ◽  
Vol 195 (2) ◽  
pp. 263-276 ◽  
Author(s):  
Ying-bei Chen ◽  
Miguel A. Aon ◽  
Yi-Te Hsu ◽  
Lucian Soane ◽  
Xinchen Teng ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Atp Synthase ◽  
Mitochondrial Membrane ◽  
Ion Flux ◽  
Β Subunit ◽  
Inner Mitochondrial Membrane ◽  
Two Photon Microscopy ◽  
Mitochondrial Atp Synthase ◽  
Large Fluctuations

Mammalian Bcl-xL protein localizes to the outer mitochondrial membrane, where it inhibits apoptosis by binding Bax and inhibiting Bax-induced outer membrane permeabilization. Contrary to expectation, we found by electron microscopy and biochemical approaches that endogenous Bcl-xL also localized to inner mitochondrial cristae. Two-photon microscopy of cultured neurons revealed large fluctuations in inner mitochondrial membrane potential when Bcl-xL was genetically deleted or pharmacologically inhibited, indicating increased total ion flux into and out of mitochondria. Computational, biochemical, and genetic evidence indicated that Bcl-xL reduces futile ion flux across the inner mitochondrial membrane to prevent a wasteful drain on cellular resources, thereby preventing an energetic crisis during stress. Given that F1FO–ATP synthase directly affects mitochondrial membrane potential and having identified the mitochondrial ATP synthase β subunit in a screen for Bcl-xL–binding partners, we tested and found that Bcl-xL failed to protect β subunit–deficient yeast. Thus, by bolstering mitochondrial energetic capacity, Bcl-xL may contribute importantly to cell survival independently of other Bcl-2 family proteins.

ATP synthase activity is required for fructose to protect cultured hepatocytes from the toxicity of cyanide

1993 ◽  
Vol 264 (3) ◽  
pp. C709-C714 ◽  
Author(s):  
J. W. Snyder ◽  
J. G. Pastorino ◽  
A. P. Thomas ◽  
J. B. Hoek ◽  
J. L. Farber
Keyword(s):  
Membrane Potential ◽  
Protective Effect ◽  
Mitochondrial Membrane Potential ◽  
Atp Synthase ◽  
Mitochondrial Membrane ◽  
Cultured Hepatocytes ◽  
Intracellular Acidosis ◽  
Mitochondrial Atp Synthase ◽  
Carbonyl Cyanide

The contributions of the loss of the mitochondrial membrane potential (MMP) and a depletion of ATP to the genesis of lethal injury were evaluated in the killing of cultured hepatocytes by cyanide (CN). The glycolytic production of ATP from fructose (Fru) maintained the MMP and prevented the killing by CN. Inhibition of the mitochondrial ATP synthase by 0.1 micrograms/ml oligomycin (Oligo) reduced ATP stores at the same rate and to the same extent as did 1 mM CN. With Oligo there was no loss of the MMP, and the hepatocytes maintained viability over the 6 h during which CN killed all of the cells. Oligo had no effect on the rate of killing by CN. However, Oligo reversed the protective effect of Fru on CN-induced killing, a result that correlated with the loss of MMP but not with the depletion of ATP. Neither Fru nor Oligo affected the intracellular acidosis achieved with CN alone. Fru also prevented toxicity of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), a result that correlated with the preservation of MMP. Oligo potentiated the toxicity of CCCP. It is concluded that a functioning mitochondrial ATP synthase is required for the production of ATP from Fru to prevent the killing of hepatocytes by CN. The extent of killing correlated closely with changes in the MMP but not with changes in the content of ATP.

scholarly journals ATP Synthase Is Responsible for Maintaining Mitochondrial Membrane Potential in Bloodstream Form Trypanosoma brucei

2006 ◽  
Vol 5 (1) ◽  
pp. 45-53 ◽  
Author(s):  
Silvia V. Brown ◽  
Paul Hosking ◽  
Jinlei Li ◽  
Noreen Williams
Keyword(s):  
Membrane Potential ◽  
Trypanosoma Brucei ◽  
Mitochondrial Membrane Potential ◽  
Atp Synthase ◽  
Mitochondrial Membrane ◽  
Krebs Cycle ◽  
Bloodstream Form ◽  
Β Subunit ◽  
Α Subunit ◽  
Protein Levels

ABSTRACT The mitochondrion of Trypanosoma brucei bloodstream form maintains a membrane potential, although it lacks cytochromes and several Krebs cycle enzymes. At this stage, the ATP synthase is present at reduced, although significant, levels. To test whether the ATP synthase at this stage is important for maintaining the mitochondrial membrane potential, we used RNA interference (RNAi) to knock down the levels of the ATP synthase by targeting the F1-ATPase α and β subunits. RNAi-induced cells grew significantly slower than uninduced cells but were not morphologically altered. RNAi of the β subunit decreased the mRNA and protein levels for the β subunit, as well as the mRNA and protein levels of the α subunit. Similarly, RNAi of α subunit decreased the α subunit transcript and protein levels, as well as the β-subunit transcript and protein levels. In contrast, α and β RNAi knockdown resulted in a 60% increase in the F0 complex subunit 9 protein levels without a significant change in the steady-state transcript levels of this subunit. The F0-32-kDa subunit protein expression, however, remained stable throughout induction of RNAi for α or β subunits. Oligomycin-sensitive ATP hydrolytic and synthetic activities were decreased by 43 and 44%, respectively. Significantly, the mitochondrial membrane potential of α and β RNAi cells was decreased compared to wild-type cells, as detected by MitoTracker Red CMXRos fluorescence microscopy and flow cytometry. These results support the role of the ATP synthase in the maintenance of the mitochondrial membrane potential in bloodstream form T. brucei.

atpif1 regulates Mitochondrial Heme Synthesis In Developing Erythroid Cells

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 163-163
Author(s):  
Dhvanit I Shah ◽  
Naoko Takahasi-Makise ◽  
Iman Schultz ◽  
Eric L Pierce ◽  
Liangtao Li ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Mitochondrial Membrane ◽  
Positional Cloning ◽  
Conflicts Of Interest ◽  
Microcytic Anemia ◽  
Mitochondrial Atpase ◽  
Cluster Assembly ◽  
Inner Mitochondrial Membrane ◽  
Heme Synthesis

Abstract Abstract 163 Iron plays a key role as a cofactor in many fundamental metabolic processes, which require heme synthesis and Fe/S cluster assembly in the mitochondria. Defects in the transport of iron into the mitochondria would lead to anemias due to a deficiency in heme and hemoglobin synthesis. Here we describe a zebrafish genetic mutant, pinotage (pnttq209), which exhibits a profound hypochromic, microcytic anemia. Erythrocytes from pnt mutants have a defect in hemoglobinization and decreased red cell indices (mean corpuscular volume and hemoglobin content, hematocrit, hemoglobin concentration). Through positional cloning, we showed that the mitochondrial ATPase Inhibitory Factor 1 (atpif1), which regulates the inner mitochondrial membrane potential, is the gene disrupted in pnt. The identity of the pnt gene was verified by: (a) decreased atpif1 steady-state mRNA in pnt mutants, (b) phenocopying the anemia with anti-sense atpif1 morpholinos, (c) functional complementation of the anemia with atpif1 cRNA, and (d) a genetic polymorphism in the 3'UTR co-segregating with the mutant phenotype that destabilizes the atpif1 mRNA. Consistent with the conserved function of atpif1 in higher vertebrates, the silencing of the murine ortholog of atpif1 in Friend mouse erythroleukemia (MEL) cells showed a defect in hemoglobinization by o-dianisidine staining and reduction of 59Fe incorporation into heme in 59Fe-metabolically labeled cells. Moreover, Atpif1 knockdown destabilizes their mitochondrial membrane potential and volume. Therefore, the identification of atpif1 in pnt functionally demonstrates the role of atpif1 in regulating the proton motive gradient across the inner mitochondrial membrane for mitochondrial iron incorporation in heme biosynthesis. These results uncover a novel hematopoiesis-related function of atpif1, which will directly contribute to our understanding and potential treatment of human congenital and acquired anemias. Disclosures: No relevant conflicts of interest to declare.

Glucosamine-induced alterations of mitochondrial function in pancreatic β-cells: possible role of protein glycosylation

2004 ◽  
Vol 287 (4) ◽  
pp. E602-E608 ◽  
Author(s):  
Marcello Anello ◽  
Daniela Spampinato ◽  
Salvatore Piro ◽  
Francesco Purrello ◽  
Agata Maria Rabuazzo
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Atp Synthase ◽  
Mitochondrial Function ◽  
Chronic Exposure ◽  
Mitochondrial Membrane ◽  
Protein Glycosylation ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Protein Levels

Chronic exposure of rat pancreatic islets and INS-1 insulinoma cells to glucosamine (GlcN) produced a reduction of glucose-induced (22.2 mM) insulin release that was associated with a reduction of ATP levels and ATP/ADP ratio compared with control groups. To further evaluate mitochondrial function and ATP metabolism, we then studied uncoupling protein-2 (UCP2), F1-F0-ATP-synthase, and mitochondrial membrane potential, a marker of F1-F0-ATP-synthase activity. UCP2 protein levels were unchanged after chronic exposure to GlcN on both pancreatic islets and INS-1 β-cells. Due to the high number of cells required to measure mitochondrial F1-F0-ATP-synthase protein levels and mitochondrial membrane potential, we used INS-1 cells, and we found that chronic culture with GlcN increased F1-F0-ATP-synthase protein levels but decreased glucose-stimulated changes of mitochondrial membrane potential. Moreover, F1-F0-ATP-synthase was highly glycosylated, as demonstrated by experiments with N-glycosidase F and glycoprotein staining. Tunicamycin (an inhibitor of protein N-glycosylation), when added with GlcN in the culture medium, was able to partially prevent all these negative effects on insulin secretion, adenine nucleotide content, mitochondrial membrane potential, and protein glycosylation. Thus we suggest that GlcN-induced pancreatic β-cell toxicity might be mediated by reduced cell energy production. An excessive protein N-glycosylation of mitochondrial F1-F0-ATP-synthase might lead to cell damage and secretory alterations in pancreatic β-cells.

Mitochondrial Membrane Potential and ATP Production in Primary Disorders of ATP Synthase

2004 ◽  
Vol 14 (1-2) ◽  
pp. 7-11 ◽  
Author(s):  
Alena Vojtíšková ◽  
Pavel Ješina ◽  
Martin Kalous ◽  
Vilma Kaplanová ◽  
Josef Houštěk ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Atp Synthase ◽  
Mitochondrial Membrane ◽  
Atp Production
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