Cardiolipin and mitochondrial function in health and disease

Mitochondria and neuroprotection in stroke: Cationic arginine-rich peptides (CARPs) as a novel class of mitochondria-targeted neuroprotective therapeutics

Stroke is the second leading cause of death globally and represents a major cause of devastating long-term disability. Despite sustained efforts to develop clinically effective neuroprotective therapies, presently there is no clinically available neuroprotective agent for stroke. As a central mediator of neurodamaging events in stroke, mitochondria are recognised as a critical neuroprotective target, and as such, provide a focus for developing mitochondrial-targeted therapeutics. In recent years, cationic arginine-rich peptides (CARPs) have been identified as a novel class of neuroprotective agent with several demonstrated mechanisms of action, including their ability to target mitochondria and exert positive effects on the organelle. This review provides an overview on neuronal mitochondrial dysfunction in ischaemic stroke pathophysiology and highlights the potential beneficial effects of CARPs on mitochondria in the ischaemic brain following stroke.

Proteolipid domains form in biomimetic and cardiac mitochondrial vesicles and are regulated by cardiolipin concentration but not monolyso-cardiolipin

Cardiolipin (CL) is an anionic phospholipid mainly located in the inner mitochondrial membrane, where it helps regulate bioenergetics, membrane structure, and apoptosis. Localized, phase-segregated domains of CL are hypothesized to control mitochondrial inner membrane organization. However, the existence and underlying mechanisms regulating these mitochondrial domains are unclear. Here, we first isolated detergent-resistant cardiac mitochondrial membranes that have been reported to be CL-enriched domains. Experiments with different detergents yielded only nonspecific solubilization of mitochondrial phospholipids, suggesting that CL domains are not recoverable with detergents. Next, domain formation was investigated in biomimetic giant unilamellar vesicles (GUVs) and newly synthesized giant mitochondrial vesicles (GMVs) from mouse hearts. Confocal fluorescent imaging revealed that introduction of cytochrome c into membranes promotes macroscopic proteolipid domain formation associated with membrane morphological changes in both GUVs and GMVs. Domain organization was also investigated after lowering tetralinoleoyl-CL concentration and substitution with monolyso-CL, two common modifications observed in cardiac pathologies. Loss of tetralinoleoyl-CL decreased proteolipid domain formation in GUVs, because of a favorable Gibbs-free energy of lipid mixing, whereas addition of monolyso-CL had no effect on lipid mixing. Moreover, murine GMVs generated from cardiac acyl-CoA synthetase-1 knockouts, which have remodeled CL acyl chains, did not perturb proteolipid domains. Finally, lowering the tetralinoleoyl-CL content had a stronger influence on the oxidation status of cytochrome c than did incorporation of monolyso-CL. These results indicate that proteolipid domain formation in the cardiac mitochondrial inner membrane depends on tetralinoleoyl-CL concentration, driven by underlying lipid-mixing properties, but not the presence of monolyso-CL.

Mitochondrial bioenergetics and cardiolipin alterations in myocardial ischemia-reperfusion injury: implications for pharmacological cardioprotection

Mitochondrial dysfunction plays a central role in myocardial ischemia-reperfusion (I/R) injury. Increased reactive oxygen species production, impaired electron transport chain activity, aberrant mitochondrial dynamics, Ca²⁺ overload, and opening of the mitochondrial permeability transition pore have been proposed as major contributory factors to mitochondrial dysfunction during myocardial I/R injury. Cardiolipin (CL), a mitochondria-specific phospholipid, plays a pivotal role in multiple mitochondrial bioenergetic processes, including respiration and energy conversion, in mitochondrial morphology and dynamics as well as in several steps of the apoptotic process. Changes in CL levels, species composition, and degree of oxidation may have deleterious consequences for mitochondrial function with important implications in a variety of pathophysiological conditions, including myocardial I/R injury. In this review, we focus on the role played by CL alterations in mitochondrial dysfunction in myocardial I/R injury. Pharmacological strategies to prevent myocardial injury during I/R targeting mitochondrial CL are also examined.

Mitochondria and aging: A role for the mitochondrial transition pore?

The cellular mechanisms responsible for aging are poorly understood. Aging is considered as a degenerative process induced by the accumulation of cellular lesions leading progressively to organ dysfunction and death. The free radical theory of aging has long been considered the most relevant to explain the mechanisms of aging. As the mitochondrion is an important source of reactive oxygen species (ROS), this organelle is regarded as a key intracellular player in this process and a large amount of data supports the role of mitochondrial ROS production during aging. Thus, mitochondrial ROS, oxidative damage, aging, and aging-dependent diseases are strongly connected. However, other features of mitochondrial physiology and dysfunction have been recently implicated in the development of the aging process. Here, we examine the potential role of the mitochondrial permeability transition pore (mPTP) in normal aging and in aging-associated diseases.

Mitochondrial Damage-Associated Molecular Patterns: From Inflammatory Signaling to Human Diseases

Over the recent years, much has been unraveled about the pro-inflammatory properties of various mitochondrial molecules once they are leaving the mitochondrial compartment. On entering the cytoplasm or the extracellular space, mitochondrial DAMPs (also known as mitochondrial alarmins) can become pro-inflammatory and initiate innate and adaptive immune responses by activating cell surface and intracellular receptors. Current evidence indicates that uncontrolled and excessive release of mitochondrial DAMPs is associated with severity, has prognosis value in human diseases, and contributes to the dysregulated process observed in numerous inflammatory and autoimmune conditions, as well as in ischemic heart disease and cancer. Herein, we review that the expanding research field of mitochondrial DAMPs in innate immune responses and the current knowledge on the association between mitochondrial DAMPs and human diseases.

Mechanisms by Which Dietary Fatty Acids Regulate Mitochondrial Structure-Function in Health and Disease

Mitochondria are the energy-producing organelles within a cell. Furthermore, mitochondria have a role in maintaining cellular homeostasis and proper calcium concentrations, building critical components of hormones and other signaling molecules, and controlling apoptosis. Structurally, mitochondria are unique because they have 2 membranes that allow for compartmentalization. The composition and molecular organization of these membranes are crucial to the maintenance and function of mitochondria. In this review, we first present a general overview of mitochondrial membrane biochemistry and biophysics followed by the role of different dietary saturated and unsaturated fatty acids in modulating mitochondrial membrane structure-function. We focus extensively on long-chain n-3 (ω-3) polyunsaturated fatty acids and their underlying mechanisms of action. Finally, we discuss implications of understanding molecular mechanisms by which dietary n-3 fatty acids target mitochondrial structure-function in metabolic diseases such as obesity, cardiac-ischemia reperfusion injury, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and select cancers.

SIRT3 deficiency exacerbates p53/Parkin‑mediated mitophagy inhibition and promotes mitochondrial dysfunction: Implication for aged hearts

Mitochondrial dynamics have critical roles in aging, and their impairment represents a prominent risk factor for myocardial dysfunction. Mitochondrial deacetylase sirtuin (SIRT)3 contributes greatly to the prevention of redox stress and cell aging. The present study explored the role of SIRT3 on myocardium aging. Western blot analysis demonstrated that SIRT3 expression levels were significantly lower in the myocardia of aged mice compared with young mice. Immunoprecipitation and western blot assays indicated that the activity of mitochondrial manganese superoxide dismutase (MnSOD) and peroxisome proliferator‑activated receptor γ coactivator (PGC)‑1α was reduced in the aged heart. To further explore the association between SIRT3 and myocardial senescence, SIRT3 heart‑specific knockout (SIRT3-/-) mice were used in the present study. The results revealed that obvious features of aging were present in the myocardium of SIRT3-/- mice, including mitochondrial protein dysfunction, enhanced oxidative stress, and energy metabolism dysfunction. SIRT3 deficiency impaired Parkin‑mediated mitophagy by increasing p53‑Parkin binding and blocking the mitochondrial translocation of Parkin in cardiomyocytes. Injection of autophagy agonist CCCP significantly increased the mitochondrial Parkin level in young wild‑type hearts but not in aged hearts; the effect was less pronounced in SIRT3-/- hearts. These data suggest that CCCP‑induced Parkin translocation was reduced in aged and SIRT3-/- hearts. CCCP‑induced mitochondrial clearance, which could be rescued by autophagy antagonist bafilomycin‑A1, was markedly weakened in aged and SIRT3-/- hearts vs. young hearts. SIRT3 deficiency exacerbated p53/Parkin‑mediated mitophagy inhibition and disrupted mitochondrial homeostasis, suggesting that loss of SIRT3 may increase the susceptibility of aged hearts to cardiac dysfunction. Therapeutic activation of SIRT3 and improved mitochondrial function may ameliorate the symptoms of cardiac aging.

Immunological Tolerance, Pregnancy, and Preeclampsia: The Roles of Semen Microbes and the Father

Although it is widely considered, in many cases, to involve two separable stages (poor placentation followed by oxidative stress/inflammation), the precise originating causes of preeclampsia (PE) remain elusive. We have previously brought together some of the considerable evidence that a (dormant) microbial component is commonly a significant part of its etiology. However, apart from recognizing, consistent with this view, that the many inflammatory markers of PE are also increased in infection, we had little to say about immunity, whether innate or adaptive. In addition, we focused on the gut, oral and female urinary tract microbiomes as the main sources of the infection. We here marshall further evidence for an infectious component in PE, focusing on the immunological tolerance characteristic of pregnancy, and the well-established fact that increased exposure to the father's semen assists this immunological tolerance. As well as these benefits, however, semen is not sterile, microbial tolerance mechanisms may exist, and we also review the evidence that semen may be responsible for inoculating the developing conceptus (and maybe the placenta) with microbes, not all of which are benign. It is suggested that when they are not, this may be a significant cause of PE. A variety of epidemiological and other evidence is entirely consistent with this, not least correlations between semen infection, infertility and PE. Our view also leads to a series of other, testable predictions. Overall, we argue for a significant paternal role in the development of PE through microbial infection of the mother via insemination.

Mitochondrial bioenergetics decay in aging: beneficial effect of melatonin

Aging is a biological process characterized by progressive decline in physiological functions, increased oxidative stress, reduced capacity to respond to stresses, and increased risk of contracting age-associated disorders. Mitochondria are referred to as the powerhouse of the cell through their role in the oxidative phosphorylation to generate ATP. These organelles contribute to the aging process, mainly through impairment of electron transport chain activity, opening of the mitochondrial permeability transition pore and increased oxidative stress. These events lead to damage to proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid of the inner mitochondrial membrane, plays a pivotal role in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis and in mitochondrial membrane stability and dynamics. Cardiolipin alterations are associated with mitochondrial bienergetics decline in multiple tissues in a variety of physiopathological conditions, as well as in the aging process. Melatonin, the major product of the pineal gland, is considered an effective protector of mitochondrial bioenergetic function. Melatonin preserves mitochondrial function by preventing cardiolipin oxidation and this may explain, at least in part, the protective role of this compound in mitochondrial physiopathology and aging. Here, mechanisms through which melatonin exerts its protective role against mitochondrial dysfunction associated with aging and age-associated disorders are discussed.

Gynostemma pentaphyllum is neuroprotective in a rat model of cardiopulmonary resuscitation

Asphyxial cardiac arrest (ACA)-induced ischemia results in acute and delayed neuronal cell death. The early reperfusion phase is critical for the outcome. Intervention strategies directed to this period are promising to reduce ACA/resuscitation-dependent impairments. This study focused on the evaluation of the protective potential of an extract from Gynostemma pentaphyllum (GP), a plant used in traditional medicine with antioxidative, glucose lowering and neuroprotective activities, in an ACA rat model. We tested the following parameters: i) Basic systemic parameters such as pCO₂ and blood glucose value within the first 30 min post-ACA; ii) mitochondrial response by determining activities of citrate synthase, respiratory chain complexes I + III and II + III, and the composition of cardiolipin 6 and 24 h post-ACA; iii) neuronal vitality of the CA1 hippocampal region by immunohistochemistry 24 h and 7 days post-ACA; and iv) cognitive function by a novel object recognition test 7 days post-ACA. GP, administered after reaching spontaneous circulation, counteracted the following: i) ACA-mediated increases in arterial CO₂ tension and blood glucose values; ii) transient increase in the activity of the respiratory chain complexes II + III; iii) elevation in cardiolipin content; iv) hippocampal CA1 neurodegeneration, and v) loss of normal novelty-object seeking. The protective effects of GP were accompanied by side effects of the vehicle DMSO, such as the stimulation of citrate synthase activity in control animals, inhibition of cardiolipin synthesis in ACA animals and complex II + III activity in both control and ACA animals. The results emphasize the importance of the early post-resuscitation phase for the neurological outcome after ACA/resuscitation, and demonstrated the power of GP substitution as neuroprotective intervention. Moreover, the results underline the need of a careful handling of the popular vehicle DMSO.

Role of Cardiolipin in Mitochondrial Signaling Pathways

The phospholipid cardiolipin (CL) is an essential constituent of mitochondrial membranes and plays a role in many mitochondrial processes, including respiration and energy conversion. Pathological changes in CL amount or species composition can have deleterious consequences for mitochondrial function and trigger the production of reactive oxygen species. Signaling networks monitor mitochondrial function and trigger an adequate cellular response. Here, we summarize the role of CL in cellular signaling pathways and focus on tissues with high-energy demand, like the heart. CL itself was recently identified as a precursor for the formation of lipid mediators. We highlight the concept of CL as a signaling platform. CL is exposed to the outer mitochondrial membrane upon mitochondrial stress and CL domains serve as a binding site in many cellular signaling events. During mitophagy, CL interacts with essential players of mitophagy like Beclin 1 and recruits the autophagic machinery by its interaction with LC3. Apoptotic signaling pathways require CL as a binding platform to recruit apoptotic factors such as tBid, Bax, caspase-8. CL required for the activation of the inflammasome and plays a role in inflammatory signaling. As changes in CL species composition has been observed in many diseases, the signaling pathways described here may play a general role in pathology.

Oxygen-Dependent Lipid Profiles of Three-Dimensional Cultured Human Chondrocytes Revealed by MALDI-MSI

Articular cartilage is exposed to a gradient of oxygen levels ranging from 5% at the surface to 1% in the deepest layers. While most cartilage research is performed in supraphysiological oxygen levels (19–21%), culturing chondrocytes under hypoxic oxygen levels (≤8%) promotes the chondrogenic phenotype. Exposure of cells to various oxygen levels alters their lipid metabolism, but detailed studies examining how hypoxia affects lipid metabolism in chondrocytes are lacking. To better understand the chondrocyte’s behavior in response to oxygen, we cultured 3D pellets of human primary chondrocytes in normoxia (20% oxygen) and hypoxia (2.5% oxygen) and employed matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) in order to characterize the lipid profiles and their spatial distribution. In this work we show that chondrocytes cultured in hypoxia and normoxia can be differentiated by their lipid profiles. Among other species, phosphatidylglycerol species were increased in normoxic pellets, whereas phosphatidylinositol species were the most prominent lipids in hypoxic pellets. Moreover, spatial mapping revealed that phospahtidylglyycerol species were less prominent in the center of pellets where the oxygen level is lower. Additional analysis revealed a higher abundance of the mitochondrial-specific lipids, cardiolipins, in normoxic conditions. In conclusion MALDI-MSI described specific lipid profiles that could be used as sensors of oxygen level changes and may especially be relevant for retaining the chondrogenic phenotype, which has important implications for the treatment of bone and cartilage diseases.

Calcium sensing receptor protects high glucose-induced energy metabolism disorder via blocking gp78-ubiquitin proteasome pathway

Diabetic cardiomyopathy (DCM) is a major complication and fatal cause of the patients with diabetes. The calcium sensing receptor (CaSR) is a G protein-coupled receptor, which is involved in maintaining calcium homeostasis, regulating cell proliferation and apoptosis, and so on. In our previous study, we found that CaSR expression, intracellular calcium levels and cardiac function were all significantly decreased in DCM rats; however, the exact mechanism are not clear yet. The present study revealed the protective role of CaSR in myocardial energy metabolism disorder induced by high glucose (HG) as well as the underlying mechanism. Here, we demonstrated that HG decreased the expression of CaSR, mitochondrial fusion proteins (Mfn1, Mfn2), cell gap junction related proteins (Cx43, β-catenin, N-cadherin), and intracellular ATP concentration. In contrast, HG increased extracellular ATP concentration, the expression of gp78, mitochondrial fission proteins (Fis1, Drp1), and the ubiquitination levels of Mfn1, Mfn2 and Cx43. Moreover, CaSR agonist and gp78-siRNA significantly reduced the above changes. Taken together, these results suggest that HG induces myocardial energy metabolism disorder via decrease of CaSR expression, and activation of gp78-ubiquitin proteasome system. In turn, these effects disrupt the structure and function of the mitochondria and the cell gap junction, result in the reduced ATP synthesis and the increased ATP leakage. Stimulation of CaSR significantly attenuates HG-induced abnormal myocardial energy metabolism, suggesting CaSR would be a promising potential therapeutic target for DCM.

Developmental Sex Differences in the Metabolism of Cardiolipin in Mouse Cerebral Cortex Mitochondria

Cardiolipin (CL) is a mitochondrial-specific phospholipid. CL content and acyl chain composition are crucial for energy production. Given that estradiol induces CL synthesis in neurons, we aimed to assess CL metabolism in the cerebral cortex (CC) of male and female mice during early postnatal life, when sex steroids induce sex-dimorphic maturation of the brain. Despite the fact that total amount of CL was similar, its fatty acid composition differed between males and females at birth. In males, CL was more mature (lower saturation ratio) and the expression of the enzymes involved in synthetic and remodeling pathways was higher, compared to females. Importantly, the sex differences found in CL metabolism were due to the testosterone peak that male mice experience perinatally. These changes were associated with a higher expression of UCP-2 and its activators in the CC of males. Overall, our results suggest that the perinatal testosterone surge in male mice regulates CL biosynthesis and remodeling in the CC, inducing a sex-dimorphic fatty acid composition. In male's CC, CL is more susceptible to peroxidation, likely explaining the testosterone-dependent induction of neuroprotective molecules such as UCP-2. These differences may account for the sex-dependent mitochondrial susceptibility after perinatal hypoxia/ischemia.

Barth syndrome cardiomyopathy

Barth syndrome (BTHS) is an inherited form of cardiomyopathy, caused by a mutation within the gene encoding the mitochondrial transacylase tafazzin. Tafazzin is involved in the biosynthesis of the unique phospholipid cardiolipin (CL), which is almost exclusively found in mitochondrial membranes. CL directly interacts with a number of essential protein complexes in the mitochondrial membranes including the respiratory chain, mitochondrial metabolite carriers, and proteins, involved in shaping mitochondrial morphology. Here we describe, how in BTHS CL deficiency causes changes in the morphology of mitochondria, structural changes in the respiratory chain, decreased respiration, and increased generation of reactive oxygen species. A large number of cellular and animal models for BTHS have been established to elucidate how mitochondrial dysfunction induces sarcomere disorganization and reduced contractility, resulting in dilated cardiomyopathy in vivo.

Distinct membrane properties are differentially influenced by cardiolipin content and acyl chain composition in biomimetic membranes

Cardiolipin (CL) has a critical role in maintaining mitochondrial inner membrane structure. In several conditions such as heart failure and aging, there is loss of CL content and remodeling of CL acyl chains, which are hypothesized to impair mitochondrial inner membrane biophysical organization. Therefore, this study discriminated how CL content and acyl chain composition influenced select properties of simple and complex mitochondrial mimicking model membranes. We focused on monolayer excess area/molecule (a measure of lipid miscibility), bilayer phase transitions, and microdomain organization. In monolayer compression studies, loss of tetralinoleoyl [(18:2)₄] CL content decreased the excess area/molecule. Replacement of (18:2)₄CL acyl chains with tetraoleoyl [(18:1)₄] CL or tetradocosahexaenoyl [(22:6)₄] CL generally had little influence on monolayer excess area/molecule; in contrast, replacement of (18:2)₄CL acyl chains with tetramyristoyl [(14:0)₄] CL increased monolayer excess area/molecule. In bilayers, calorimetric studies showed that substitution of (18:2)₄CL with (18:1)₄CL or (22:6)₄CL lowered the phase transition temperature of phosphatidylcholine vesicles whereas (14:0)₄CL had no effect. Finally, quantitative imaging of giant unilamellar vesicles revealed differential effects of CL content and acyl chain composition on microdomain organization, visualized with the fluorescent probe Texas Red DHPE. Notably, microdomain areas were decreased by differing magnitudes upon lowering of (18:2)₄CL content and substitution of (18:2)₄CL with (14:0)₄CL or (22:6)₄CL. Conversely, exchanging (18:2)₄CL with (18:1)₄CL increased microdomain area. Altogether, these data demonstrate that CL content and fatty acyl composition differentially target membrane physical properties, which has implications for understanding how CL regulates mitochondrial activity and the design of CL-specific therapeutics.

Nature and Implications of Oxidative and Nitrosative Stresses in Autoimmune Hepatitis

Oxidative and nitrosative stresses can damage cellular membranes, disrupt mitochondrial function, alter gene expression, promote the apoptosis and necrosis of hepatocytes, and increase fibrosis in diverse acute and chronic liver diseases, including autoimmune hepatitis. The objectives of this review are to describe the mechanisms of oxidative and nitrosative stresses in inflammatory liver disease, indicate the pathogenic implications of these stresses in autoimmune hepatitis, and suggest investigational opportunities to develop interventions that counter them. The principal antioxidant defenses, including glutathione production, the activities of antioxidant enzymes, and the release of the nuclear factor erythroid 2-related factor 2, may be inadequate or suppressed by transforming growth factor beta. The generation of reactive oxygen species can intensify nitrosative stress, and this stress may not be adequately modulated by the thioredoxin-thioredoxin reductase system and induce post-translational modifications of proteins that further disrupt hepatocyte function. The unfolded protein response and autophagy may be unable to restore redox stability, meet metabolic demands, and maintain hepatocyte survival. Emerging interventions with highly selective site- and organelle-specific actions may improve outcomes, and they include inhibitors of nicotinamide adenine dinucleotide phosphate oxidase, nitric oxide synthase, and transforming growth factor beta. Pharmacological manipulation of nuclear transcription factors may favor expression of antioxidant genes, and stimulation of chaperone proteins within the endoplasmic reticulum and modulation of autophagy may prevent hepatic fibrosis and enhance cell survival. These interventions constitute investigational opportunities to improve the management of autoimmune hepatitis.

CLD1 Reverses the Ubiquinone Insufficiency of Mutant cat5/coq7 in a Saccharomyces cerevisiae Model System

Ubiquinone (Q_n) functions as a mobile electron carrier in mitochondria. In humans, Q biosynthetic pathway mutations lead to Q₁₀ deficiency, a life threatening disorder. We have used a Saccharomyces cerevisiae model of Q₆ deficiency to screen for new modulators of ubiquinone biosynthesis. We generated several hypomorphic alleles of coq7/cat5 (clk-1 in Caenorhabditis elegans) encoding the penultimate enzyme in Q biosynthesis which converts 5-demethoxy Q₆ (DMQ₆) to 5-demethyl Q₆, and screened for genes that, when overexpressed, suppressed their inability to grow on non-fermentable ethanol—implying recovery of lost mitochondrial function. Through this approach we identified Cardiolipin-specific Deacylase 1 (CLD1), a gene encoding a phospholipase A₂ required for cardiolipin acyl remodeling. Interestingly, not all coq7 mutants were suppressed by Cld1p overexpression, and molecular modeling of the mutant Coq7p proteins that were suppressed showed they all contained disruptions in a hydrophobic α-helix that is predicted to mediate membrane-binding. CLD1 overexpression in the suppressible coq7 mutants restored the ratio of DMQ₆ to Q₆ toward wild type levels, suggesting recovery of lost Coq7p function. Identification of a spontaneous Cld1p loss-of-function mutation illustrated that Cld1p activity was required for coq7 suppression. This observation was further supported by HPLC-ESI-MS/MS profiling of monolysocardiolipin, the product of Cld1p. In summary, our results present a novel example of a lipid remodeling enzyme reversing a mitochondrial ubiquinone insufficiency by facilitating recovery of hypomorphic enzymatic function.

Disturbance of mitochondrial functions provoked by the major long-chain 3-hydroxylated fatty acids accumulating in MTP and LCHAD deficiencies in skeletal muscle

The pathogenesis of the muscular symptoms and recurrent rhabdomyolysis that are commonly manifested in patients with mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiencies is still unknown. In this study we investigated the effects of the major long-chain monocarboxylic 3-hydroxylated fatty acids (LCHFA) accumulating in these disorders, namely 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, on important mitochondrial functions in rat skeletal muscle mitochondria. 3HTA and 3HPA markedly increased resting (state 4) and decreased ADP-stimulated (state 3) and CCCP-stimulated (uncoupled) respiration. 3HPA provoked similar effects in permeabilized skeletal muscle fibers, validating the results obtained in purified mitochondria. Furthermore, 3HTA and 3HPA markedly diminished mitochondrial membrane potential, NAD(P)H content and Ca(2+) retention capacity in Ca(2+)-loaded mitochondria. Mitochondrial permeability transition (mPT) induction probably underlie these effects since they were totally prevented by cyclosporin A and ADP. In contrast, the dicarboxylic analogue of 3HTA did not alter the tested parameters. Our data strongly indicate that 3HTA and 3HPA behave as metabolic inhibitors, uncouplers of oxidative phosphorylation and mPT inducers in skeletal muscle. It is proposed that these pathomechanisms disrupting mitochondrial homeostasis may be involved in the muscle alterations characteristic of MTP and LCHAD deficiencies.

Mitochondrial Proteins Containing Coiled-Coil-Helix-Coiled-Coil-Helix (CHCH) Domains in Health and Disease

Members of the coiled-coil-helix-coiled-coil-helix (CHCH) domain-containing protein family that carry (CX9C) type motifs are imported into the mitochondrion with the help of the disulfide relay-dependent MIA import pathway. These evolutionarily conserved proteins are emerging as new cellular factors that control mitochondrial respiration, redox regulation, lipid homeostasis, and membrane ultrastructure and dynamics. We discuss recent insights on the activity of known (CX9C) motif-carrying proteins in mammals and review current data implicating the Mia40/CHCHD4 import machinery in the regulation of their mitochondrial import. Recent findings and the identification of disease-associated mutations in specific (CX9C) motif-carrying proteins have highlighted members of this family of proteins as potential therapeutic targets in a variety of human disorders.

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

SIGNIFICANCE

Mitochondria, vital cellular power plants to generate energy, are involved in immune responses. Mitochondrial damage-associated molecular patterns (DAMPs) are molecules that are released from mitochondria to extracellular space during cell death and include not only proteins but also DNA or lipids. Mitochondrial DAMPs induce inflammatory responses and are critically involved in the pathogenesis of various diseases.

RECENT ADVANCES

Recent studies elucidate the molecular mechanisms by which mitochondrial DAMPs are released and initiate immune responses by use of genetically modulated cells or animals. Importantly, the levels of mitochondrial DAMPs in patients are often associated with severity and prognosis of human diseases, such as infection, asthma, ischemic heart disease, and cancer.

CRITICAL ISSUES

Although mitochondrial DAMPs can represent proinflammatory molecules in various experimental models, their roles in human diseases may be multifunctional and complex. It remains unclear where and how mitochondrial DAMPs are liberated into extracellular spaces and exert their biological functions particularly in vivo. In addition, while mitochondria can secrete several types of DAMPs during cell death, the interaction of each mitochondrial DAMP (e.g., synergistic effects) remains unclear.

FUTURE DIRECTIONS

Regulation of mitochondrial DAMP-mediated immune responses may be important to alter the progression of human diseases. In addition, measuring mitochondrial DAMPs in patients may be clinically useful as biomarkers to predict prognosis or response to therapies. Further studies of the mechanisms by which mitochondrial DAMPs impact the initiation and progression of diseases may lead to the development of therapeutics specifically targeting this pathway. Antioxid.

Renal 2',3'-Cyclic Nucleotide 3'-Phosphodiesterase Is an Important Determinant of AKI Severity after Ischemia-Reperfusion

A positional isomer of 3',5'-cAMP, 2',3'-cAMP, is produced by kidneys in response to energy depletion, and renal 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) metabolizes 2',3'-cAMP to 2'-AMP; 2',3'-cAMP is a potent opener of mitochondrial permeability transition pores (mPTPs), which can stimulate autophagy. Because autophagy protects against AKI, it is conceivable that inhibition of CNPase protects against ischemia-reperfusion (IR) -induced AKI. Therefore, we investigated renal outcomes, mitochondrial function, number, area, and autophagy in CNPase-knockout (CNPase(-/-)) versus wild-type (WT) mice using a unique two-kidney, hanging-weight model of renal bilateral IR (20 minutes of ischemia followed by 48 hours of reperfusion). Analysis of urinary purines showed attenuated metabolism of 2',3'-cAMP to 2'-AMP in CNPase(-/-) mice. Neither genotype nor IR affected BP, heart rate, urine volume, or albumin excretion. In WT mice, renal IR reduced (14)C-inulin clearance (index of GFR) and increased renal vascular resistance (measured by transit time nanoprobes) and urinary excretion of kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin. IR did not affect these parameters in CNPase(-/-) mice. Histologic analysis revealed that IR induced severe damage in kidneys from WT mice, whereas histologic changes were minimal after IR in CNPase(-/-) mice. Measurements of renal cardiolipin levels, citrate synthase activity, rotenone-sensitive NADH oxidase activity, and proximal tubular mitochondrial and autophagosome area and number (by transmission electron microscopy) indicted accelerated autophagy/mitophagy in injured CNPase(-/-) mice. We conclude that CNPase deletion attenuates IR-induced AKI, in part by accelerating autophagy with targeted removal of damaged mitochondria.

Exercise and Weight Loss Improve Muscle Mitochondrial Respiration, Lipid Partitioning, and Insulin Sensitivity After Gastric Bypass Surgery

Both Roux-en-Y gastric bypass (RYGB) surgery and exercise can improve insulin sensitivity in individuals with severe obesity. However, the impact of RYGB with or without exercise on skeletal muscle mitochondria, intramyocellular lipids, and insulin sensitivity index (SI) is unknown. We conducted a randomized exercise trial in patients (n = 101) who underwent RYGB surgery and completed either a 6-month moderate exercise (EX) or a health education control (CON) intervention. SI was determined by intravenous glucose tolerance test. Mitochondrial respiration and intramyocellular triglyceride, sphingolipid, and diacylglycerol content were measured in vastus lateralis biopsy specimens. We found that EX provided additional improvements in SI and that only EX improved cardiorespiratory fitness, mitochondrial respiration and enzyme activities, and cardiolipin profile with no change in mitochondrial content. Muscle triglycerides were reduced in type I fibers in CON, and sphingolipids decreased in both groups, with EX showing a further reduction in a number of ceramide species. In conclusion, exercise superimposed on bariatric surgery-induced weight loss enhances mitochondrial respiration, induces cardiolipin remodeling, reduces specific sphingolipids, and provides additional improvements in insulin sensitivity.

Islet β-cell failure in type 2 diabetes--Within the network of toxic lipids

Obesity-related type 2 diabetes develops in individuals with the onset of β-cell dysfunction. Pancreatic islet lipotoxicity is now recognized as a primary reason for the onset and progression of the disease. Such dysfunction is reflected by the aberrant secretory capacity and detrimental loss of β-cell mass and survival. Elevated circulating serum fatty acid levels and disordered lipid metabolism management are particularly interesting in the search for biologically relevant triggers of β-cell demise. Herein, we review various types of toxic lipid metabolites that may play a significant role in pancreatic islet failure. The lipotoxic effect on β-cells depends on the type of lipid mediator (e.g., long-chain fatty acids, diacylglycerols, ceramides, phospholipids), cellular location of its action (e.g., endoplasmic reticulum, mitochondria), and associated-organelle conditions (e.g., membranes, vesicles). We also discuss various aspects of lipid action in β-cells, including effects on metabolic pathways, stress responses (e.g., oxidative stress, endoplasmic reticulum stress, and autophagy), and gene expression.

Oxidative stress, cardiolipin and mitochondrial dysfunction in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is today considered the most common form of chronic liver disease, affecting a high proportion of the population worldwide. NAFLD encompasses a large spectrum of liver damage, ranging from simple steatosis to steatohepatitis, advanced fibrosis and cirrhosis. Obesity, hyperglycemia, type 2 diabetes and hypertriglyceridemia are the most important risk factors. The pathogenesis of NAFLD and its progression to fibrosis and chronic liver disease is still unknown. Accumulating evidence indicates that mitochondrial dysfunction plays a key role in the physiopathology of NAFLD, although the mechanisms underlying this dysfunction are still unclear. Oxidative stress is considered an important factor in producing lethal hepatocyte injury associated with NAFLD. Mitochondrial respiratory chain is the main subcellular source of reactive oxygen species (ROS), which may damage mitochondrial proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid located at the level of the inner mitochondrial membrane, plays an important role in several reactions and processes involved in mitochondrial bioenergetics as well as in mitochondrial dependent steps of apoptosis. This phospholipid is particularly susceptible to ROS attack. Cardiolipin peroxidation has been associated with mitochondrial dysfunction in multiple tissues in several physiopathological conditions, including NAFLD. In this review, we focus on the potential roles played by oxidative stress and cardiolipin alterations in mitochondrial dysfunction associated with NAFLD.

Mitochondrial reactive oxygen species: a double edged sword in ischemia/reperfusion vs preconditioning

Reductions in the blood supply produce considerable injury if the duration of ischemia is prolonged. Paradoxically, restoration of perfusion to ischemic organs can exacerbate tissue damage and extend the size of an evolving infarct. Being highly metabolic organs, the heart and brain are particularly vulnerable to the deleterious effects of ischemia/reperfusion (I/R). While the pathogenetic mechanisms contributing to I/R-induced tissue injury and infarction are multifactorial, the relative importance of each contributing factor remains unclear. However, an emerging body of evidence indicates that the generation of reactive oxygen species (ROS) by mitochondria plays a critical role in damaging cellular components and initiating cell death. In this review, we summarize our current understanding of the mechanisms whereby mitochondrial ROS generation occurs in I/R and contributes to myocardial infarction and stroke. In addition, mitochondrial ROS have been shown to participate in preconditioning by several pharmacologic agents that target potassium channels (e.g., ATP-sensitive potassium (mKATP) channels or large conductance, calcium-activated potassium (mBKCa) channels) to activate cell survival programs that render tissues and organs more resistant to the deleterious effects of I/R. Finally, we review novel therapeutic approaches that selectively target mROS production to reduce postischemic tissue injury, which may prove efficacious in limiting myocardial dysfunction and infarction and abrogating neurocognitive deficits and neuronal cell death in stroke.