Dysfunction Of Mitochondrial Complex Research Articles

Sulforaphane ameliorate Arsenic induced cardiotoxicity in rats: Role of PI3k/Akt mediated Nrf2 signaling pathway.

Arsenic (As) toxicity can generate reactive free radicals, which play an important role in the evolution of cardiomyopathy. The aim of this research is to see if sulforaphane (SFN) protects against As-induced heart damage, oxidative stress, and mitochondrial complex dysfunction via the PI3K/Akt/Nrf2 signaling pathway. The rats were placed into four groups, each with eight rats. Group 1: Normal rats (control group); Group 2: Treatment group (5 mg/kg body weight); Group 3: SFN+As-treatment group (80 mg/kg body weight + 5 mg/kg body weight); Group 4: SFN group only (80 mg/kg body weight). The swot will last 4 weeks. At the end of the intermission (28 days), all of the rats starved overnight and killed with cervical decapitation. As administration considerably (p < 0.05) inflated the extent of free radicals (O2-, OH-), lipoid peroxidation (malondialdehyde, 4-hydroxynonenal), lipoid profile (low-density lipoprotein-cholesterol, very low-density lipoprotein-cholesterol (VLDL-C), total cholesterol, triglyceride, and phospholipids), cardiac Troponin (cTnT&I), and Mitochondrial complex III. A noteworthy (p < 0.05) diminish the level of HDL-C, Mitochondrial complex I and II, enzymatic (superoxide dismutase, catalase, and glutathione peroxidase), and nonenzymatic antioxidant (glutathione and total sulfhydryl groups) and PI3k, Akt, and Nrf2 sequence in As treated rats. The western blot, real-time polymerase chain reaction, flowcytometric, and histology studies all corroborated the biochemical findings which revealed significant heart damage in rats. Pretreatment with SFN significantly (p < 0.05) reduced the invitro free radicals, lipid oxidative indicators, mitochondrial complex, lipid profiles, and increased phase II antioxidants in the heart. This result shows that dietary supplementation of SFN protects against As-induced cardiotoxicity via PI3k/Akt/Nrf2 pathway in rats.

Protection against rotenone-induced animal model of Parkinson’s disease: Electrophysiological, behavioral and histological study

Parkinson's disease (PD) is an age-related neurodegenerative disease characterized clinically as a movement disorder. A hallmark feature of PD is the degeneration of the dopamine neurons in the substantia nigra pars compacta and the consequent striatal dopamine deficiency. The lack of dopamine causes the primary symptoms of PD- tremor, slowness of movement, muscle stiffness and balance problems. Research is devoted to the study of systemic compensatory reactions of the rat's brain developing in response to rotenone-induced animal model of PD under the conditions of neuroprotective intervention of Curcumin. This has raising expectations for the development of new neuroprotective therapies for the prevention of PD. Male albino rats were treated with rotenone injections (2.5 mg/ml intraperitoneally) for 21 days.We examined the effects of neuroprotector curcumin (200 mg/kg) on behavior and the electrical activity of hippocampus neurons measured in response to high frequency stimulation (HFS) of entorhinal cortex (EC). In the hippocampus, the excitatory and inhibitory synapses between EC and CA3 pyramidal cells expresses robust forms of short-term plasticity, such as frequency facilitation (post-tetanic potentiation – PTP) and depression (post-tetanic depression – PTD). Motor activity was assessed by cylinder test. The results showed that Rotenone causes significant reduction of neuronal activity, whereas curcumin can improve the motor impairments and electrophysiological parameters and may be beneficial in the treatment of PD. Curcumin significantly prevented rotenone-induced impairment of hippocampal synaptic plasticity, which is likely mediated via dysfunction of mitochondrial complex I. It alleviated the deficits behavior in rats as the rearing frequencies of animals were enhanced.&#x0D; Keywords: Parkinson's disease, rotenone-induced animal model, electrophysiological parameters, deficits behavior.

Mitochondrial defects in the respiratory complex I contribute to impaired translational initiation via ROS and energy homeostasis in SMA motor neurons

Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by loss of lower motor neurons, which leads to proximal muscle weakness and atrophy. SMA is caused by reduced survival motor neuron (SMN) protein levels due to biallelic deletions or mutations in the SMN1 gene. When SMN levels fall under a certain threshold, a plethora of cellular pathways are disturbed, including RNA processing, protein synthesis, metabolic defects, and mitochondrial function. Dysfunctional mitochondria can harm cells by decreased ATP production and increased oxidative stress due to elevated cellular levels of reactive oxygen species (ROS). Since neurons mainly produce energy via mitochondrial oxidative phosphorylation, restoring metabolic/oxidative homeostasis might rescue SMA pathology. Here, we report, based on proteome analysis, that SMA motor neurons show disturbed energy homeostasis due to dysfunction of mitochondrial complex I. This results in a lower basal ATP concentration and higher ROS production that causes an increase of protein carbonylation and impaired protein synthesis in SMA motor neurons. Counteracting these cellular impairments with pyruvate reduces elevated ROS levels, increases ATP and SMN protein levels in SMA motor neurons. Furthermore, we found that pyruvate-mediated SMN protein synthesis is mTOR-dependent. Most importantly, we showed that ROS regulates protein synthesis at the translational initiation step, which is impaired in SMA. As many neuropathies share pathological phenotypes such as dysfunctional mitochondria, excessive ROS, and impaired protein synthesis, our findings suggest new molecular interactions among these pathways. Additionally, counteracting these impairments by reducing ROS and increasing ATP might be beneficial for motor neuron survival in SMA patients.

The novel E-subgroup pentatricopeptide repeat protein DEK55 is responsible for RNA editing at multiple sites and for the splicing of nad1 and nad4 in maize

BackgroundPentatricopeptide repeat (PPR) proteins compose a large protein family whose members are involved in both RNA processing in organelles and plant growth. Previous reports have shown that E-subgroup PPR proteins are involved in RNA editing. However, the additional functions and roles of the E-subgroup PPR proteins are unknown.ResultsIn this study, we developed and identified a new maize kernel mutant with arrested embryo and endosperm development, i.e., defective kernel (dek) 55 (dek55). Genetic and molecular evidence suggested that the defective kernels resulted from a mononucleotide alteration (C to T) at + 449 bp within the open reading frame (ORF) of Zm00001d014471 (hereafter referred to as DEK55). DEK55 encodes an E-subgroup PPR protein within the mitochondria. Molecular analyses showed that the editing percentage of 24 RNA editing sites decreased and that of seven RNA editing sites increased in dek55 kernels, the sites of which were distributed across 14 mitochondrial gene transcripts. Moreover, the splicing efficiency of nad1 introns 1 and 4 and nad4 intron 1 significantly decreased in dek55 compared with the wild type (WT). These results indicate that DEK55 plays a crucial role in RNA editing at multiple sites as well as in the splicing of nad1 and nad4 introns. Mutation in the DEK55 gene led to the dysfunction of mitochondrial complex I. Moreover, yeast two-hybrid assays showed that DEK55 interacts with two multiple organellar RNA-editing factors (MORFs), i.e., ZmMORF1 (Zm00001d049043) and ZmMORF8 (Zm00001d048291).ConclusionsOur results demonstrated that a mutation in the DEK55 gene affects the mitochondrial function essential for maize kernel development. Our results also provide novel insight into the molecular functions of E-subgroup PPR proteins involved in plant organellar RNA processing.

Protective Effect of Hemin Against Experimental Chronic Fatigue Syndrome in Mice: Possible Role of Neurotransmitters.

Chronic fatigue syndrome (CFS) is a disorder characterized by persistent and relapsing fatigue along with long-lasting and debilitating fatigue, myalgia, cognitive impairment, and many other common symptoms. The present study was conducted to explore the protective effect of hemin on CFS in experimental mice. Male albino mice were subjected to stress-induced CFS in a forced swimming test apparatus for 21days. After animals had been subjected to the forced swimming test, hemin (5 and 10mg/kg; i.p.) and hemin (10mg/kg) + tin(IV) protoporphyrin (SnPP), a hemeoxygenase-1 (HO-1) enzyme inhibitor, were administered daily for 21days. Various behavioral tests (immobility period, locomotor activity, grip strength, and anxiety) and estimations of biochemical parameters (lipid peroxidation, nitrite, and GSH), mitochondrial complex dysfunctions (complexes I and II), and neurotransmitters (dopamine, serotonin, and norepinephrine and their metabolites) were subsequently assessed. Animals exposed to 10min of forced swimming session for 21days showed a fatigue-like behavior (as increase in immobility period, decreased grip strength, and anxiety) and biochemical alteration observed by increased oxidative stress, mitochondrial dysfunction, and neurotransmitter level alteration. Treatment with hemin (5 and 10mg/kg) for 21days significantly improved the decreased immobility period, increased locomotor activity, and improved anxiety-like behavior, oxidative defense, mitochondrial complex dysfunction, and neurotransmitter level in the brain. Further, these observations were reversed by SnPP, suggesting that the antifatigue effect of hemin is HO-1 dependent. The present study highlights the protective role of hemin against experimental CFS-induced behavioral, biochemical, and neurotransmitter alterations.

Mitochondrial Complex Dysfunction May Predict Subsequent Development of Heart Failure in Pressure Overload

Mitochondrial Complex Dysfunction May Predict Subsequent Development of Heart Failure in Pressure Overload

Atomic structure of the entire mammalian mitochondrial complex I

Mitochondrial complex I (also known as NADH:ubiquinone oxidoreductase) contributes to cellular energy production by transferring electrons from NADH to ubiquinone coupled to proton translocation across the membrane. It is the largest protein assembly of the respiratory chain with a total mass of 970 kilodaltons. Here we present a nearly complete atomic structure of ovine (Ovis aries) mitochondrial complex I at 3.9 Å resolution, solved by cryo-electron microscopy with cross-linking and mass-spectrometry mapping experiments. All 14 conserved core subunits and 31 mitochondria-specific supernumerary subunits are resolved within the L-shaped molecule. The hydrophilic matrix arm comprises flavin mononucleotide and 8 iron-sulfur clusters involved in electron transfer, and the membrane arm contains 78 transmembrane helices, mostly contributed by antiporter-like subunits involved in proton translocation. Supernumerary subunits form an interlinked, stabilizing shell around the conserved core. Tightly bound lipids (including cardiolipins) further stabilize interactions between the hydrophobic subunits. Subunits with possible regulatory roles contain additional cofactors, NADPH and two phosphopantetheine molecules, which are shown to be involved in inter-subunit interactions. We observe two different conformations of the complex, which may be related to the conformationally driven coupling mechanism and to the active-deactive transition of the enzyme. Our structure provides insight into the mechanism, assembly, maturation and dysfunction of mitochondrial complex I, and allows detailed molecular analysis of disease-causing mutations.

Structure of bacterial respiratory complex I

Complex I (NADH:ubiquinone oxidoreductase) plays a central role in cellular energy production, coupling electron transfer between NADH and quinone to proton translocation. It is the largest protein assembly of respiratory chains and one of the most elaborate redox membrane proteins known. Bacterial enzyme is about half the size of mitochondrial and thus provides its important “minimal” model. Dysfunction of mitochondrial complex I is implicated in many human neurodegenerative diseases. The L-shaped complex consists of a hydrophilic arm, where electron transfer occurs, and a membrane arm, where proton translocation takes place. We have solved the crystal structures of the hydrophilic domain of complex I from Thermus thermophilus, the membrane domain from Escherichia coli and recently of the intact, entire complex I from T. thermophilus (536kDa, 16 subunits, 9 iron–sulphur clusters, 64 transmembrane helices). The 95Å long electron transfer pathway through the enzyme proceeds from the primary electron acceptor flavin mononucleotide through seven conserved Fe–S clusters to the unusual elongated quinone-binding site at the interface with the membrane domain. Four putative proton translocation channels are found in the membrane domain, all linked by the central flexible axis containing charged residues. The redox energy of electron transfer is coupled to proton translocation by the as yet undefined mechanism proposed to involve long-range conformational changes. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.

Mitochondrial complex I and III mRNA levels in bipolar disorder

BackgroundStudies that have focused on the mitochondrial electron transport chain indicate that bipolar disorder (BD) is associated with pathology in mitochondrial function. These pathological processes occur in the brain circuits that regulate affective functions, emotions, and motor behaviors. The present study aimed to determine the relationship between mitochondrial complex dysfunction and BD. MethodsThe BD group included 32 male patients diagnosed with first-episode manic BD. The control group included 35 sociodemographically matched healthy males. Messenger ribonucleic acid (mRNA) was isolated from peripheral blood samples obtained from the patients and control group, and the mRNA levels of the NDUFV1, NDUFV2, and NDUFS1 genes of mitochondrial complex I and the UQCR10 gene of mitochondrial complex III were investigated. ResultsSignificant differences were identified in complex I gene mRNA levels between the BD group (n=32) and the control group (n=35) for the following genes: NDUFV1 (P=0.01), NDUFV2 (P<0.01), and NDUFS1 (P=0.02). The UQCR10 gene (complex III) mRNA level did not differ between the groups (P=0.1). The mRNA levels of the four genes studied were lower at the 3-month follow-up; however, these differences were not significant (P>0.05). LimitationsAll of the BD patients were in manic episodes; thus, we were unable to separately compare these levels with those during depressive and euthymic episodes. ConclusionsThe mRNA levels of all of the genes representing the subunits of mitochondrial complex I (NDUFV1, NDUFV2, and NDUFS1) were significantly higher in the present study's BD patients during manic episodes than in the controls. With the data obtained from further research, biomarkers that could be used for the diagnosis and follow-up of neuropsychiatric disorders may be discovered.

Resveratrol supplementation restores high-fat diet-induced insulin secretion dysfunction by increasing mitochondrial function in islet.

Resveratrol (RSV), a natural compound, is known for its effects on energy homeostasis. Here we investigated the effects of RSV and possible mechanism in insulin secretion of high-fat diet rats. Rats were randomly divided into three groups as follows: NC group (animals were fed ad libitum with normal chow for 8 weeks), HF group (animals were fed ad libitum with high-fat diet for 8 weeks), and HFR group (animals were treated with high-fat diet and administered with RSV for 8 weeks). Insulin secretion ability of rats was assessed by hyperglycemic clamp. Mitochondrial biogenesis genes, mitochondrial respiratory chain activities, reactive oxidative species (ROS), and several mitochondrial antioxidant enzyme activities were evaluated in islet. We found that HF group rats clearly showed low insulin secretion and mitochondrial complex dysfunction. Expression of silent mating type information regulation 2 homolog- 1 (SIRT1) and related mitochondrial biogenesis were significantly decreased. However, RSV administration group (HFR) showed a marked potentiation of glucose-stimulated insulin secretion. This effect was associated with elevated SIRT1 protein expression and antioxidant enzyme activities, resulting in increased mitochondrial respiratory chain activities and decreased ROS level. This study suggests that RSV may increase islet mitochondrial complex activities and antioxidant function to restore insulin secretion dysfunction induced by high-fat diet.

Alteration of mitochondrial function and ultrastructure in the hippocampus of pilocarpine-treated rat

Present studies were carried out to decipher seizure-dependent changes in mitochondrial function and ultrastructure in rat hippocampus after status epilepticus (SE) induced by pilocarpine (PILO). Discernible mitochondrial ultrastructural damage was observed in the hippocampus. Enzyme assay revealed cytochrome oxidase (COX) activity significantly increased 3h after SE, decreased 7 d and 45 d after SE, whereas succinate dehydrogenase (SDH) activity displayed no significant changes. Quantitative real-time PCR and Western blotting showed that COX III (mitochondrial-encoded) mRNA and protein level were significantly increased at 3h, decreased to the control level on 7d and dropped significantly on 45 d; the corresponding expression of COX IV were not changed by PILO at any time tested. The results were also supported by immunohistochemistry. Thus, our results demonstrate that dysfunction of mitochondrial complex IV respiratory enzyme and mitochondrial ultrastructural damage in the hippocampus are associated with prolonged seizure during experimental temporal lobe epilepsy and mitochondria are more vulnerable to epileptic damage.

Peroxisome proliferator-activated receptors γ/mitochondrial uncoupling protein 2 signaling protects against seizure-induced neuronal cell death in the hippocampus following experimental status epilepticus

BackgroundStatus epilepticus induces subcellular changes that may lead to neuronal cell death in the hippocampus. However, the mechanism of seizure-induced neuronal cell death remains unclear. The mitochondrial uncoupling protein 2 (UCP2) is expressed in selected regions of the brain and is emerged as an endogenous neuroprotective molecule in many neurological disorders. We evaluated the neuroprotective role of UCP2 against seizure-induced hippocampal neuronal cell death under experimental status epilepticus.MethodsIn Sprague–Dawley rats, kainic acid (KA) was microinjected unilaterally into the hippocampal CA3 subfield to induce prolonged bilateral seizure activity. Oxidized protein level, translocation of Bcl-2, Bax and cytochrome c between cytosol and mitochondria, and expression of peroxisome proliferator-activated receptors γ (PPARγ) and UCP2 were examined in the hippocampal CA3 subfield following KA-induced status epilepticus. The effects of microinjection bilaterally into CA3 area of a PPARγ agonist, rosiglitazone or a PPARγ antagonist, GW9662 on UCP2 expression, induced superoxide anion (O2· -) production, oxidized protein level, mitochondrial respiratory chain enzyme activities, translocation of Bcl-2, Bax and cytochrome c, and DNA fragmentation in bilateral CA3 subfields were examined.ResultsIncreased oxidized proteins and mitochondrial or cytosol translocation of Bax or cytochrome c in the hippocampal CA3 subfield was observed 3–48 h after experimental status epilepticus. Expression of PPARγ and UCP2 increased 12–48 h after KA-induced status epilepticus. Pretreatment with rosiglitazone increased UCP2 expression, reduced protein oxidation, O2· - overproduction and dysfunction of mitochondrial Complex I, hindered the translocation of Bax and cytochrome c, and reduced DNA fragmentation in the CA3 subfield. Pretreatment with GW9662 produced opposite effects.ConclusionsActivation of PPARγ upregulated mitochondrial UCP2 expression, which decreased overproduction of reactive oxygen species, improved mitochondrial Complex I dysfunction, inhibited mitochondrial translocation of Bax and prevented cytosolic release of cytochrome c by stabilizing the mitochondrial transmembrane potential, leading to amelioration of apoptotic neuronal cell death in the hippocampus following status epilepticus.

Mitochondrial electron transport chain complex dysfunction in the colonic mucosa in ulcerative colitis

Ulcerative colitis (UC) is characterized by an energy deficiency state of the colonic epithelium. This study evaluated mitochondrial electron transport chain (ETC) complex activity in normal and disease mucosa in patients with UC. Alterations in ETC complexes were also investigated in experimental colitis in mice. Biopsies were obtained from macroscopically normal and diseased colonic mucosa of 43 patients with UC and 35 controls undergoing screening colonoscopy and ETC complex activity was assayed biochemically. ETC complex activities were also assayed in colonic epithelial cells isolated from Swiss albino mice with dextran sodium sulfate (DSS)-induced colitis at various stages of induction of colitis. Mucosal nitrite levels and protein carbonyl content were determined. The activity of Complex II was significantly decreased in colonic biopsies from UC patients compared with controls, while activities of other mitochondrial complex were normal. Complex II activity was equally decreased in diseased and normal mucosa in UC; the degree of reduction did not correlate with clinical, endoscopic, or histological grading of disease activity. In DSS-fed mice, a reduction in activity of Complex IV and Complex II was observed. Activity of other complex was not affected. Administration of aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, attenuated all parameters of colitis as well as the reductions in Complex IV and Complex II activity. Reduction in Complex II activity appears to be a specific change in UC, present in quiescent and active disease. Mitochondrial complex dysfunction occurs in DSS colitis in mice and appears to be mediated by nitric oxide.

Hypothalamic mitochondrial dysfunction associated with anorexia in the anx/anx mouse

The anorectic anx/anx mouse exhibits disturbed feeding behavior and aberrances, including neurodegeneration, in peptidergic neurons in the appetite regulating hypothalamic arcuate nucleus. Poor feeding in infants, as well as neurodegeneration, are common phenotypes in human disorders caused by dysfunction of the mitochondrial oxidative phosphorylation system (OXPHOS). We therefore hypothesized that the anorexia and degenerative phenotypes in the anx/anx mouse could be related to defects in the OXPHOS. In this study, we found reduced efficiency of hypothalamic OXPHOS complex I assembly and activity in the anx/anx mouse. We also recorded signs of increased oxidative stress in anx/anx hypothalamus, possibly as an effect of the decreased hypothalamic levels of fully assembled complex I, that were demonstrated by native Western blots. Furthermore, the Ndufaf1 gene, encoding a complex I assembly factor, was genetically mapped to the anx interval and found to be down-regulated in anx/anx mice. These results suggest that the anorexia and hypothalamic neurodegeneration of the anx/anx mouse are associated with dysfunction of mitochondrial complex I.

Enzymatic Dysfunction of Mitochondrial Complex I of the Candida albicansgoa1Mutant Is Associated with Increased Reactive Oxidants and Cell Death

We have previously shown that deletion of GOA1 (growth and oxidant adaptation) of Candida albicans results in a loss of mitochondrial membrane potential, ATP synthesis, increased sensitivity to oxidants and killing by human neutrophils, and avirulence in a systemic model of candidiasis. We established that translocation of Goa1p to mitochondria occurred during peroxide stress. In this report, we show that the goa1Δ (GOA31), compared to the wild type (WT) and a gene-reconstituted (GOA32) strain, exhibits sensitivity to inhibitors of the classical respiratory chain (CRC), including especially rotenone (complex I [CI]) and salicylhydroxamic acid (SHAM), an inhibitor of the alternative oxidase pathway (AOX), while potassium cyanide (KCN; CIV) causes a partial inhibition of respiration. In the presence of SHAM, however, GOA31 has an enhanced respiration, which we attribute to the parallel respiratory (PAR) pathway and alternative NADH dehydrogenases. Interestingly, deletion of GOA1 also results in a decrease in transcription of the alternative oxidase gene AOX1 in untreated cells as well as negligible AOX1 and AOX2 transcription in peroxide-treated cells. To explain the rotenone sensitivity, we measured enzyme activities of complexes I to IV (CI to CIV) and observed a major loss of CI activity in GOA31 but not in control strains. Enzymatic data of CI were supported by blue native polyacrylamide gel electrophoresis (BN-PAGE) experiments which demonstrated less CI protein and reduced enzyme activity. The consequence of a defective CI in GOA31 is an increase in reactive oxidant species (ROS), loss of chronological aging, and programmed cell death ([PCD] apoptosis) in vitro compared to control strains. The increase in PCD was indicated by an increase in caspase activity and DNA fragmentation in GOA31. Thus, GOA1 is required for a functional CI and partially for the AOX pathway; loss of GOA1 compromises cell survival. Further, the loss of chronological aging is new to studies of Candida species and may offer an insight into therapies to control these pathogens. Our observation of increased ROS production associated with a defective CI and PCD is reminiscent of mitochondrial studies of patients with some types of neurodegenerative diseases where CI and/or CIII dysfunctions lead to increased ROS and apoptosis.

In PDE3B KO mice, White Adipose Tissue (WAT) Exhibits Characteristics of “Good Fat”, i.e., Brown Adipose Tissue (BAT): I. Alterations in Mitochondrial Biogenesis and Function

To study effects of cyclic nucleotides on energy homeostatic mechanisms, mice were generated by targeted inactivation of the Pde3b gene, which encodes Cyclic Nucleotide Phosphodiesterase 3B (PDE3B), an enzyme that catalyzes hydrolysis of cAMP and cGMP. In PDE3B‐KO mice, adipose tissue mass is reduced and epididymal white adipose tissue (EWAT) exhibits characteristics of BAT, including changes in morphology, and increased expression of genes related to BAT differentiation, mitochondrial biogenesis, and energy dissipation, including PPARγ coactivator‐1 alpha (PGC‐1α? and uncoupling protein 1 (UCP1). Mitochondria were isolated and studied by electron microscopic and proteomics techniques and functional assays. In KO EWAT, mitochondria are larger than WT mitochondria and uncoupled, with dysfunction of mitochondrial complex I, consuming less oxygen (using glutamate and malate as substrate) and generating less ATP than WT mitochondria. Proteomic patterns in KO mitochondria predict increased fatty acid β‐oxidation and decreased oxidative damage. In WAT to BAT differentiation, PDE3B is a critical molecular switch, inducing UCP1 to promote mitochondria uncoupling and inhibiting complex I to generate less oxidative stress. In KO mice, the presence of 'good fat' may compensate for hepatic insulin resistance.

Iptakalim ameliorates MPP+‐induced astrocyte mitochondrial dysfunction by increasing mitochondrial complex activity besides opening mitoKATP channels

In addition to the established role of the mitochondrion in energy metabolism, regulation of cell death has been regarded as a major function of this organelle. Our previous studies have demonstrated that iptakalim (IPT), a novel ATP-sensitive potassium channel (K(ATP) channel) opener, protects against 1-methyl-4-phenyl-pyridinium ion (MPP+)-induced astrocyte apoptosis via mitochondria and mitogen-activated protein kinase signal pathways. The present study aimed to investigate whether IPT can protect astrocyte mitochondria against MPP+-induced mitochondrial dysfunction. We showed that treatment with IPT could ameliorate the inhibitory effect of MPP+ on mitochondrial respiration and ATP production by using mitochondrial complex I-supported substrates. IPT could also inhibit the increased production of mitochondrial reactive oxygen species (ROS) and the release of cytochrome c from mitochondria induced by MPP+. However, mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel blocker 5-hydroxydecanoate (5-HD) could partly abolish all of the above effects of IPT. Because mitochondrial complex dysfunction impairs mitochondrial respiration and ATP production, a further experiment was undertaken to study the effects of IPT on the activity of mitochondrial complex (COX) I and COX IV. It was found that IPT inhibited the decrease in mitochondrial COX I and COX IV activity induced by MPP+, but 5-HD failed to abolish these effects. Taken together, these findings suggest that IPT may protect astrocyte mitochondrial function by regulating complex activity in addition to opening mitoK(ATP) channels.

Pael‐R transgenic mice crossed with parkin deficient mice displayed progressive and selective catecholaminergic neuronal loss

Parkin, a ubiquitin ligase, is responsible for autosomal recessive juvenile parkinsonism (AR-JP). We identified parkin-associated endothelin receptor-like receptor (Pael-R) as a substrate of parkin, whose accumulation is thought to induce unfolded protein response (UPR) -mediated cell death, leading to dopaminergic neurodegeneration. To create an animal model of AR-JP, we generated parkin knockout/Pael-R transgenic (parkin-ko/Pael-R-tg) mice. parkin-ko/Pael-R-tg mice exhibited early and progressive loss of dopaminergic as well as noradrenergic neurons without formation of inclusion bodies, recapitulating the pathological features of AR-JP. Evidence of activation of UPR and up-regulation of dopamine and its metabolites were observed throughout the lifetime. Moreover, complex I activity of mitochondria isolated from parkin-ko/Pael-R-tg mice was significantly reduced later in life. These findings suggest that persistent induction of unfolded protein stress underlies chronic progressive catecholaminergic neuronal death, and that dysfunction of mitochondrial complex I and oxidative stress might be involved in the progression of Parkinson's disease. parkin-ko/Pael-R-tg mice represents an AR-JP mouse model displaying chronic and selective loss of catecholaminergic neurons.

Molecular pathways of programmed cell death in experimental Parkinson's disease

Dysfunction of mitochondrial complex I leads to degeneration of dopaminergic neurons of the substantia nigra pars compacta, as seen in Parkinson's disease, through activation of mitochondria-dependent programmed cell death pathways. In this scenario, complex I blockade increases the soluble pool of cytochrome c in the mitochondrial intermembrane space through oxidative mechanisms, whereas activation of pro-cell death protein Bax triggers neuronal death by permeabilizing the outer mitochondrial membrane and releasing cytochrome c into the cytosol. Targeting either Bax transcriptional or post-translational activation results in a marked attenuation of dopaminergic cell death caused by complex I inhibition.

Two molecular pathways initiate mitochondria-dependent dopaminergic neurodegeneration in experimental Parkinson's disease

Dysfunction of mitochondrial complex I is associated with a wide spectrum of neurodegenerative disorders, including Parkinson's disease (PD). In rodents, inhibition of complex I leads to degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNpc), as seen in PD, through activation of mitochondria-dependent apoptotic molecular pathways. In this scenario, complex I blockade increases the soluble pool of cytochrome c in the mitochondrial intermembrane space through oxidative mechanisms, whereas activation of pro-cell death protein Bax is actually necessary to trigger neuronal death by permeabilizing the outer mitochondrial membrane and releasing cytochrome c into the cytosol. Activation of Bax after complex I inhibition relies on its transcriptional induction and translocation to the mitochondria. How complex I deficiency leads to Bax activation is currently unknown. Using gene-targeted mice, we show that the tumor suppressor p53 mediates Bax transcriptional induction after PD-related complex I blockade in vivo, but it does not participate in Bax mitochondrial translocation in this model, either by a transcription-independent mechanism or through the induction of BH3-only proteins Puma or Noxa. Instead, Bax mitochondrial translocation in this model relies mainly on the JNK-dependent activation of the BH3-only protein Bim. Targeting either Bax transcriptional induction or Bax mitochondrial translocation results in a marked attenuation of SNpc dopaminergic cell death caused by complex I inhibition. These results provide further insight into the pathogenesis of PD neurodegeneration and identify molecular targets of potential therapeutic significance for this disabling neurological illness.