Posts in Category: Mitochondria

Calcium Signaling and Reactive Oxygen Species in Mitochondria

Calcium Signaling and Reactive Oxygen Species in Mitochondria

Edoardo Bertero, Christoph Maack

Role of mitochondrial Ca2+ uptake for ATP production and reactive oxygen species (ROS) elimination. Ca2+ is released from the sarcoplasmic reticulum (SR) via ryanodine receptors type 2 (RyR2). Mitochondria take up Ca2+ via the mitochondrial Ca2+ uniporter (MCU) and release it via the Na+/Ca2+ Li+ permeable exchanger (NCLX). Slower SR Ca2+ release via inositol 1,4,5-trisphosphate receptors (IP3R) may be taken up into mitochondria via ryanodine receptors type 1 (RyR1). Close contact points between the SR and mitochondria are controlled by SR-located mitofusin 2 (Mfn2) tethering with Mfn2 and Mfn1 on the outer mitochondrial membrane (OMM), respectively, creating microdomains of high [Ca2+] in the vicinity of mitochondria. Another SR/mitochondrial tethering protein is FUN14 domain containing 1 (FUNDC1). In the matrix, Ca2+ activates Krebs cycle dehydrogenases to regenerate the reduced form of NADH (nicotamide adenine dinucleotide), which donates electrons to the respiratory chain. The electron flow produces a proton gradient (ΔpH) that drives ATP production at the F1Fo-ATP synthase (complex V). ATP converts creatine (Cr) to phosphocreatine (PCr) at the mitochondrial creatine kinase (CKm) while in the cytosol, PCr regenerates ADP at cytosolic CK (CKc). Superoxide (.O2−) is generated at complexes I and III of the respiratory chain and transformed to H2O2 by Mn2+-dependent superoxide dismutase (Mn-SOD). H2O2 is eliminated by glutathione peroxidase (GPX) and the peroxiredoxin (PRX)/thioredoxin (TRX) system. Reduced NADPH (nicotinamide adenine dinucleotide phosphate) regenerates glutathione (GSH) from its oxidized form (GSSG) via glutathione reductase (GR) and thioredoxin reductase (TR), respectively. NADPH is regenerated by isocitrate dehydrogenase (IDH), malic enzyme (MEP), and the nicotinamide nucleotide transhydrogenase (NNT). α-KG indicates α-ketoglutarate; IMM, inner mitochondrial membrane; I-V, complexes I-V of the respiratory chain; Q, Q-cycle; SERCA, SR Ca2+ ATPase; and TRXr/TRXo, reduced/oxidized TRX. Stars (*) denote the sites of Ca2+-induced activation. [Powerpoint File]

Calcium Signaling and Reactive Oxygen Species in Mitochondria

Calcium Signaling and Reactive Oxygen Species in Mitochondria

Edoardo Bertero, Christoph Maack

Mitochondrial calcium uniporter architecture and regulation. The mitochondrial Ca2+ uniporter (MCU) is a macromolecular complex composed of a pentamer of pore-forming subunits (MCUa) and several regulatory subunits. MCUa expression alone is not sufficient for reconstituting MCU activity, but coexpression of the essential MCU regulatory element (EMRE) is required. In the presence of low levels of Ca2+ in the intermembrane space (right half of the figure), the 2 paralogous EF-hand proteins MICU1 and MICU2 inhibit Ca2+ uptake. Vice versa, elevated Ca2+ induces structural rearrangements which enable Ca2+ influx into the mitochondrial matrix (left half of the figure). MCU regulator 1 (MCUR1) interacts with both MCUa and EMRE, but not with MICU1/MICU2, and acts as a scaffold factor for uniporter assembly. IMM indicates inner mitochondrial membrane. [Powerpoint File]

Calcium and Excitation-Contraction Coupling in the Heart

Calcium and Excitation-Contraction Coupling in the Heart

David A. Eisner, Jessica L. Caldwell, Kornél Kistamás, Andrew W. Trafford

Structures involved in Ca cycling. A, Schematic diagram. This shows surface membrane, transverse tubule, sarcoplasmic reticulum (SR), and mitochondria, as well as the various channels and transporters mentioned in the text. B, High-resolution transverse section of a ventricular myocyte showing t-tubule network. Reprinted from Jayasinghe et al39 with permission of the publisher. Copyright ©2009, Biophysical Society. C, Cartoon of dyad emphasizing the major proteins involved in Ca cycling. B-AR indicates beta adrenoceptor; MCU, mitochondrial Ca uniporter; NCX, sodium–calcium exchange; NCLX, mitochondrial Na–Ca exchange; PMCA, plasma membrane Ca-ATPase; RyR, ryanodine receptor; and SERCA, sarco/endoplasmic reticulum Ca-ATPase. [Powerpoint File]

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Henry Gewirtz, Vasken Dilsizian

Diagrammatic representation of myocardial cell and potential targets of radiotracer imaging and mapping of the surface renin–angiotensin system. ACE indicates angiotensin-converting enzyme; AGT, angiotensinogen; Ang II, angiotensin II; AT1R, angiotensin II type 1 receptor; and AT2R, angiotensin II type 2 receptor. Reproduced with permission from Schindler and Dilsizian.61 Copyright © 2012, Elsevier. [Powerpoint File]

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Henry Gewirtz, Vasken Dilsizian

Myocyte metabolic pathways outlined for glucose and fatty acid metabolism with focus on the mitochondrion. The electron transport chain (ETC), complexes I–V, is a series of proton pumps. The last of which, complex V, supplies protons to a proton-sensitive ATPase and thereby generates ATP. CPT1,2 indicates carnitine palmitoyltransferase 1,2; FA, fatty acid; PDH, pyruvate dehydrogenase; and TCA, tricarboxylic acid (Krebs cycle). Reproduced with permission from Huss and Kelly.30 Copyright © 2005, American Society for Clinical Investigation. [Powerpoint File]

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Henry Gewirtz, Vasken Dilsizian

Key myocyte organelles and ion channels and their function under conditions of ischemia and reperfusion. Ischemia (left panel) causes influx of Ca2+ and decline in pH, both of which, if not severe, facilitate maintenance of closed mitochondrial permeability transition pore (mPTP). On reperfusion (right panel), key events include restoration of physiological pH, burst of reactive oxygen species (ROS) from mitochondria, release of Ca2+ from the sarcoplasmic reticulum (SR), and opening of mPTP which results in collapse of its Δψ. Reproduced with permission from Hausenloy and Yellon.27 Copyright © 2013, American Society for Clinical Investigation. [Powerpoint File]

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Leo E. Otterbein*, Roberta Foresti*, Roberto Motterlini*

Schematic representation of the heme oxygenase pathway. Heme, either derived from intracellular sources, such as hemoproteins and mitochondria, or from damaged tissues and red blood cell hemolysis (extracellular sources) is used by heme oxygenase enzymes (HO-1 and HO-2) to generate carbon monoxide (CO), biliverdin, and iron. Biliverdin is converted to bilirubin by biliverdin reductase (BVR), whereas iron is stored in the ferritin protein. Although heme oxygenase enzymes were initially localized in the endoplasmic reticulum, recent reports suggest that HO-1 can be found under certain conditions in other cellular compartments such as the nucleus.19 [Powerpoint File]

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Leo E. Otterbein*, Roberta Foresti*, Roberto Motterlini*

Interaction of carbon monoxide (CO) with mitochondria. CO at high concentrations is known to inhibit mitochondrial respiration by competing with oxygen for the binding to cytochrome c oxidase (complex IV). In contrast, controlled delivery of CO gas and CO-releasing moleculess at nontoxic concentrations can protect cardiac tissue by promoting mitochondrial biogenesis, uncoupling activity, and metabolic switch (see text for details). The molecular mechanism(s) underlying these effects remains to be defined. However, the interaction of CO with mitochondrial targets different from cytochrome c oxidase is likely as the electron transport chain contains other heme-complexes that may display distinct sensitivities to CO. ROS indicates reactive oxygen species. [Powerpoint File]

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Leo E. Otterbein*, Roberta Foresti*, Roberto Motterlini*

Heme release and cardiac repair. Ischemia-reperfusion injury leads to the sudden release of cellular contents including heme, mitochondrial DNA, and ATP. These cellular danger-associated molecular patterns (DAMPs) have each been shown to induce heme oxygenase-1 (HO-1). HO-1 expression and the subsequent generation CO, biliverdin (BV), and bilirubin (BR) target a variety of cell types that impact cellular repair and tissue regeneration. [Powerpoint File]

Mitochondrial Metabolism in Aging Heart

Mitochondrial Metabolism in Aging Heart

Edward J. Lesnefsky, Qun Chen, Charles L. Hoppel

Schematic of the interfibrillar mitochondrial defects in the aged heart. ETC indicates electron transport chain; IMM, mitochondrial inner membrane; NADH, nicotinamide adenine dinucleotide; PPL, phospholipid, proposed defect affecting subunit VIIa in complex IV; and Q, ubiquinone; Qo site, ubiquinol-binding site on cytochrome bl with proposed defect in Y132. Illustration credit, Ben Smith. [Powerpoint File]

Mitochondrial Metabolism in Aging Heart

Mitochondrial Metabolism in Aging Heart

Edward J. Lesnefsky, Qun Chen, Charles L. Hoppel

A schematic of a cardiomyocyte to highlight the location of subsarcolemmal (SSM) and interfibrillar mitochondria (IFM). Illustration credit: Ben Smith. [Powerpoint File]

Mitochondrial Metabolism in Aging Heart

Mitochondrial Metabolism in Aging Heart

Edward J. Lesnefsky, Qun Chen, Charles L. Hoppel

A schematic of a cardiomyocyte to show defects present in global and mitochondrial metabolism with age in concert with mechanisms of mitochondria-driven cellular injury. The aged heart exhibits impaired fatty acid oxidation (FAO) and preserved oxidation of glucose. Aging leads to defects in the electron transport chain that involve complexes III (CIII) and IV (CIV). Monoamine oxidase (MAO) and p66shc are significant sources of oxidants. There is a decrease in cardiolipin (CL). Antioxidant contents are relatively unchanged although a decrease in matrix antioxidant capacity leads to mitochondrial damage. Age-related damage enhances the production of reactive oxygen species (ROS) that lead to mitochondrial and cell damage. In addition, effector mechanisms of age-induced mitochondrial damage discussed include an increased susceptibility to mitochondrial permeability transition pore opening (MPTP; MPTP Opening in the Aged Heart: Relationship With ROS Production section), impaired mitochondrial dynamics favoring fusion over fission (Mitochondrial Fission and Fusion section), likely impaired mitophagy (Mitochondrial Biogenesis, Dynamics, and Removal section), and enhanced oxidant-derived signaling to activate cell death programs (Mitochondrial Metabolism–Based Signaling in Response to ROS Production section). Illustration credit: Ben Smith. ETC indicates electron transport chain. [Powerpoint File]

Moving Forwards by Blocking Back-Flow: The Yin and Yang of MI Therapy

Moving Forwards by Blocking Back-Flow: The Yin and Yang of MI Therapy

Victoria R. Pell, Edward T. Chouchani, Michael P. Murphy, Paul S. Brookes, Thomas Krieg

Respiratory Complex I and II Yin-Yang during ischemia and reperfusion. Under normoxic conditions, both complex I (red) and complex II (blue) work in the forward direction (dashed gray line indicates direction of electron flow), taking electrons from NADH and succinate, respectively, and reducing ubiquinone (Q) to ubiquinol (QH2). Electrons are eventually passed down the respiratory chain to O2, and complex I pumps protons to generate a transmembrane ΔpH. During ischemia, QH2 generated by complex I working forward, is oxidized by complex II working in reverse. In this Yin-Yang formation, fumarate acts as an electron acceptor, resulting in accumulation of succinate. This process allows complex I to continue pumping protons during ischemia. At reperfusion, the rapid consumption of accumulated succinate generates too much QH2 for the reoxygenated terminal respiratory chain to handle (dotted line). Coupled with residual acidic pH from ischemia, this drives reverse electron transfer in complex I, resulting in the generation of significant amounts of reactive oxygen species (ROS). [Powerpoint File]

Mechanisms of Sudden Cardiac Death: Oxidants and Metabolism

Mechanisms of Sudden Cardiac Death: Oxidants and Metabolism

Kai-Chien Yang, John W. Kyle, Jonathan C. Makielski, Samuel C. Dudley Jr

Oxidative phosphorylation and reactive oxygen species (ROS) production in mitochondria. The diagrams of the mitochondrial inner membrane show key components of the electron transport chain (ETC) above, and channels and transporters (below). Reducing equivalents nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2) produced from the tricarboxylic acid (TCA) cycle feed electrons to the ETC along the mitochondrial inner membrane. The electrons flow through the ETC with the following sequence: complex I and II→coenzyme Q [Q]→complex III→cytochrome C [Cyt C]→complex IV→O2, during which coupled redox reactions drive H+ across the inner membrane, forming the proton gradient and the negative mitochondrial membrane potential (ΔΨm=−150 to −180 mV). The free energy stored in the proton gradient and ΔΨm then drive H+ through the mitochondrial ATP synthase (complex V), converting ADP to ATP. An estimated 0.1% to 1% of the electrons leak prematurely to O2 at complexes I, II, or III, resulting in the formation of superoxide (O2•−). Multiple important mitochondrial channels located on the inner membrane including mitochondrial KATP channels (mito-KATP), the mitochondrial Na+/Ca2+ exchanger (mito-NCX), the inner membrane anion channel (IMAC), the permeability transition pore (PTP), and the mitochondrial calcium uniporter (MCU) also contribute to the regulation of mitochondrial function, myocardial ROS, and cellular cation homeostasis. [Powerpoint File]

Mitochondrial Reactive Oxygen Species at the Heart of the Matter: New Therapeutic Approaches for Cardiovascular Diseases

Mitochondrial Reactive Oxygen Species at the Heart of the Matter: New Therapeutic Approaches for Cardiovascular Diseases

Opher S. Kornfeld, Sunhee Hwang, Marie-Hélène Disatnik, Che-Hong Chen, Nir Qvit, Daria Mochly-Rosen

Targeting reactive oxygen species (ROS) using scavengers. A, General ROS scavengers (purple symbol) target and reduce both pathological (red) and physiological (green) ROS. These ROS scavengers do not have localization specificity and must be administered at stoichiometric (at least 1:1) amounts. In addition, ROS scavengers may get oxidized (red symbol) and instead exert an opposite effect than intended. B, Mitochondria-targeted antioxidants (eg, SS31, MitoQ, SkQ, and mCat; see text for details) aim at ROS-producing sites. Whereas some, such as SS31 (orange symbol), do not have to be administered at stoichiometric doses; they may still reduce both pathological and pathological ROS. The electron transport machinery (complexes I–IV) and cytochrome c are depicted in the inner mitochondrial membrane/matrix interface. CL indicates cardiolipin. [Powerfile File]