Reduction and restoration of mitochondrial dna content after focal cerebral ischemia/reperfusion

Mitochondrial dysfunctions induce PANoptosis and ferroptosis in cerebral ischemia/reperfusion injury: from pathology to therapeutic potential

Ischemic stroke (IS) accounts for more than 80% of the total stroke, which represents the leading cause of mortality and disability worldwide. Cerebral ischemia/reperfusion injury (CI/RI) is a cascade of pathophysiological events following the restoration of blood flow and reoxygenation, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, further aggravate the damage of brain tissue. Paradoxically, there are still no effective methods to prevent CI/RI, since the detailed underlying mechanisms remain vague. Mitochondrial dysfunctions, which are characterized by mitochondrial oxidative stress, Ca²⁺ overload, iron dyshomeostasis, mitochondrial DNA (mtDNA) defects and mitochondrial quality control (MQC) disruption, are closely relevant to the pathological process of CI/RI. There is increasing evidence that mitochondrial dysfunctions play vital roles in the regulation of programmed cell deaths (PCDs) such as ferroptosis and PANoptosis, a newly proposed conception of cell deaths characterized by a unique form of innate immune inflammatory cell death that regulated by multifaceted PANoptosome complexes. In the present review, we highlight the mechanisms underlying mitochondrial dysfunctions and how this key event contributes to inflammatory response as well as cell death modes during CI/RI. Neuroprotective agents targeting mitochondrial dysfunctions may serve as a promising treatment strategy to alleviate serious secondary brain injuries. A comprehensive insight into mitochondrial dysfunctions-mediated PCDs can help provide more effective strategies to guide therapies of CI/RI in IS.

The Ketogenic Diet but not Hydroxycitric Acid Keeps Brain Mitochondria Quality Control and mtDNA Integrity Under Focal Stroke

Mitochondrial dysfunction in the ischemic brain is one of the hallmarks of stroke. Dietary interventions such as the ketogenic diet and hydroxycitric acid supplementation (a caloric restriction mimetic) may potentially protect neurons from mitochondrial damage induced by focal stroke in mice. We showed that in control mice, the ketogenic diet and the hydroxycitric acid did not impact significantly on the mtDNA integrity and expression of genes involved in the maintenance of mitochondrial quality control in the brain, liver, and kidney. The ketogenic diet changed the bacterial composition of the gut microbiome, which via the gut-brain axis may affect the increase in anxiety behavior and reduce mice mobility. The hydroxycitric acid causes mortality and suppresses mitochondrial biogenesis in the liver. Focal stroke modelling caused a significant decrease in the mtDNA copy number in both ipsilateral and contralateral brain cortex and increased the levels of mtDNA damage in the ipsilateral hemisphere. These alterations were accompanied by a decrease in the expression of some of the genes involved in maintaining mitochondrial quality control. The ketogenic diet consumption before stroke protects mtDNA in the ipsilateral cortex, probably via activation of the Nrf2 signaling. The hydroxycitric acid, on the contrary, increased stroke-induced injury. Thus, the ketogenic diet is the most preferred variant of dietetic intervention for stroke protection compared with the hydroxycitric acid supplementation. Our data confirm some reports about hydroxycitric acid toxicity, not only for the liver but also for the brain under stroke condition.

Neuronal Pentraxin 1 Promotes Hypoxic-Ischemic Neuronal Injury by Impairing Mitochondrial Biogenesis via Interactions With Active Bax[6A7] and Mitochondrial Hexokinase II

Mitochondrial dysfunction is a key mechanism of cell death in hypoxic-ischemic brain injury. Neuronal pentraxin 1 (NP1) has been shown to play crucial roles in mitochondria-mediated neuronal death. However, the underlying mechanism(s) of NP1-induced mitochondrial dysfunction in hypoxia-ischemia (HI) remains obscure. Here, we report that NP1 induction following HI and its subsequent localization to mitochondria, leads to disruption of key regulatory proteins for mitochondrial biogenesis. Brain mitochondrial DNA (mtDNA) content and mtDNA-encoded subunit I of complex IV (mtCOX-1) expression was increased post-HI, but not the nuclear DNA-encoded subunit of complex II (nSDH-A). Up-regulation of mitochondrial proteins COXIV and HSP60 further supported enhanced mtDNA function. NP1 interaction with active Bax (Bax6A7) was increased in the brain after HI and in oxygen-glucose deprivation (OGD)-induced neuronal cultures. Importantly, NP1 colocalized with mitochondrial hexokinase II (mtHKII) following OGD leading to HKII dissociation from mitochondria. Knockdown of NP1 or SB216763, a GSK-3 inhibitor, prevented OGD-induced mtHKII dissociation and cellular ATP decrease. NP1 also modulated the expression of mitochondrial transcription factor A (Tfam) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), regulators of mitochondrial biogenesis, following HI. Together, we reveal crucial roles of NP1 in mitochondrial biogenesis involving interactions with Bax[6A7] and mtHKII in HI brain injury.

Aerobic exercise attenuates neurodegeneration and promotes functional recovery - Why it matters for neurorehabilitation & neural repair

Aerobic exercise facilitates optimal neurological function and exerts beneficial effects in neurologic injuries. Both animal and clinical studies have shown that aerobic exercise reduces brain lesion volume and improves multiple aspects of cognition and motor function after stroke. Studies using animal models have proposed a wide range of potential molecular mechanisms that underlie the neurological benefits of aerobic exercise. Furthermore, additional exercise parameters, including time of initiation, exercise dosage (exercise duration and intensity), and treatment modality are also critical for clinical application, as identifying the optimal combination of parameters will afford patients with maximal functional gains. To clarify these issues, the current review summarizes the known neurological benefits of aerobic exercise under both physiological and pathological conditions and then considers the molecular mechanisms underlying these benefits in the contexts of stroke-like focal cerebral ischemia and cardiac arrest-induced global cerebral ischemia. In addition, we explore the key roles of exercise parameters on the extent of aerobic exercise-induced neurological benefits to elucidate the optimal combination for aerobic exercise intervention. Finally, the current challenges for aerobic exercise implementation after stroke are discussed.

Activation of PGC-1α and Mitochondrial Biogenesis Protects Against Prenatal Hypoxic-ischemic Brain Injury

Survivals after prenatal hypoxia-ischemia (HI) usually suffer long-lasting cognitive defects. Reduced blood-oxygen supplies and the following reperfusion cause mitochondrial injury. Damaged mitochondria could be replaced by mitochondrial biogenesis program and peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) is the specific up-regulator. The objective of this study was to determine whether PGC-1α and mitochondrial biogenesis participate in the resistant responses of an immature brain to prenatal HI. We used a pregnant rat model of transient occlusion of uterine perfusion to induce intrauterine HI associated brain injury. SH-SY5Y cells exposed to oxygen-glucose deprivation was used to investigate the HI induced reactions in vitro. PGC-1α and its downstream signaling pathway (NRF-1 and TFAM) were examined by Western blot and quantitative Real-time PCR. Mitochondrial respiratory enzyme COX-IV was investigated by Western blot and immunohistochemistry. Mitochondrial density and morphology was detected by transmission electron microscopy. The hippocampal injury and cognitive function were examined. We found that the intrauterine HI triggered PGC-1α-NRF-1-TFAM pathway in both protein and mRNA levels. COX-IV expression significantly increased after HI injury. Intrauterine HI induced both mitochondrial impairment and mitochondrial biogenesis. Postnatal administration of pioglitazone further promoted PGC-1α and mitochondrial biogenesis, alleviated hippocampal injury, and improved performance in the behavioral tasks after intrauterine HI. Our investigation implicated activation of PGC-1α, and mitochondrial biogenesis is a neuroprotective mechanism against brain injury caused by systemic prenatal HI. Promotion of PGC-1α by pioglitazone might be a potential treatment for protecting against hippocampal injury and cognitive defects after intrauterine HI.

Sirtuin 1 Regulates Mitochondrial Biogenesis and Provides an Endogenous Neuroprotective Mechanism Against Seizure-Induced Neuronal Cell Death in the Hippocampus Following Status Epilepticus

Status epilepticus may decrease mitochondrial biogenesis, resulting in neuronal cell death occurring in the hippocampus. Sirtuin 1 (SIRT1) functionally interacts with peroxisome proliferator-activated receptors and γ coactivator 1α (PGC-1α), which play a crucial role in the regulation of mitochondrial biogenesis. In Sprague-Dawley rats, kainic acid was microinjected unilaterally into the hippocampal CA3 subfield to induce bilateral seizure activity. SIRT1, PGC-1α, and other key proteins involving mitochondrial biogenesis and the amount of mitochondrial DNA were investigated. SIRT1 antisense oligodeoxynucleotide was used to evaluate the relationship between SIRT1 and mitochondrial biogenesis, as well as the mitochondrial function, oxidative stress, and neuronal cell survival. Increased SIRT1, PGC-1α, and mitochondrial biogenesis machinery were found in the hippocampus following experimental status epilepticus. Downregulation of SIRT1 decreased PGC-1α expression and mitochondrial biogenesis machinery, increased Complex I dysfunction, augmented the level of oxidized proteins, raised activated caspase-3 expression, and promoted neuronal cell damage in the hippocampus. The results suggest that the SIRT1 signaling pathway may play a pivotal role in mitochondrial biogenesis, and could be considered an endogenous neuroprotective mechanism counteracting seizure-induced neuronal cell damage following status epilepticus.

Abnormal oxidative metabolism in a quiet genomic background underlies clear cell papillary renal cell carcinoma

While genomic sequencing routinely identifies oncogenic alterations for the majority of cancers, many tumors harbor no discernable driver lesion. Here, we describe the exceptional molecular phenotype of a genomically quiet kidney tumor, clear cell papillary renal cell carcinoma (CCPAP). In spite of a largely wild-type nuclear genome, CCPAP tumors exhibit severe depletion of mitochondrial DNA (mtDNA) and RNA and high levels of oxidative stress, reflecting a shift away from respiratory metabolism. Moreover, CCPAP tumors exhibit a distinct metabolic phenotype uniquely characterized by accumulation of the sugar alcohol sorbitol. Immunohistochemical staining of primary CCPAP tumor specimens recapitulates both the depletion of mtDNA-encoded proteins and a lipid-depleted metabolic phenotype, suggesting that the cytoplasmic clarity in CCPAP is primarily related to the presence of glycogen. These results argue for non-genetic profiling as a tool for the study of cancers of unknown driver.

Resveratrol Promotes Mitochondrial Biogenesis and Protects against Seizure-Induced Neuronal Cell Damage in the Hippocampus Following Status Epilepticus by Activation of the PGC-1α Signaling Pathway

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is known to regulate mitochondrial biogenesis. Resveratrol is present in a variety of plants, including the skin of grapes, blueberries, raspberries, mulberries, and peanuts. It has been shown to offer protective effects against a number of cardiovascular and neurodegenerative diseases, stroke, and epilepsy. This study examined the neuroprotective effect of resveratrol on mitochondrial biogenesis in the hippocampus following experimental status epilepticus. Kainic acid was microinjected into left hippocampal CA3 in Sprague Dawley rats to induce bilateral prolonged seizure activity. PGC-1α expression and related mitochondrial biogenesis were investigated. Amounts of nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (Tfam), cytochrome c oxidase 1 (COX1), and mitochondrial DNA (mtDNA) were measured to evaluate the extent of mitochondrial biogenesis. Increased PGC-1α and mitochondrial biogenesis machinery after prolonged seizure were found in CA3. Resveratrol increased expression of PGC-1α, NRF1, and Tfam, NRF1 binding activity, COX1 level, and mtDNA amount. In addition, resveratrol reduced activated caspase-3 activity and attenuated neuronal cell damage in the hippocampus following status epilepticus. These results suggest that resveratrol plays a pivotal role in the mitochondrial biogenesis machinery that may provide a protective mechanism counteracting seizure-induced neuronal damage by activation of the PGC-1α signaling pathway.

Mitochondrial DNA degradation: A quality control measure for mitochondrial genome maintenance and stress response

Mitochondria play a central role in bioenergetics, and fulfill a plethora of functions in cell signaling, programmed cell death, and biosynthesis of key protein cofactors. Mitochondria harbor their own genomic DNA, which encodes protein subunits of the electron transport chain and a full set of transfer and ribosomal RNAs. Mitochondrial DNA (mtDNA) is essential for cellular and organismal functions, and defects in mitochondrial genome maintenance have been implicated in common human diseases and mitochondrial disorders. mtDNA repair and degradation are known pathways to cope with mtDNA damage; however, molecular factors involved in this process have remained unclear. Such knowledge is fundamental to the understanding of mitochondrial genomic maintenance and pathology, because mtDNA degradation may contribute to the etiology of mtDNA depletion syndromes and to the activation of the innate immune response by fragmented mtDNA. This article reviews the current literature regarding the importance of mitochondrial DNA degradation in mtDNA maintenance and stress response, and the recent progress in uncovering molecular factors involved in mtDNA degradation. These factors include key components of the mtDNA replication machinery, such as DNA polymerase γ, helicase Twinkle, and exonuclease MGME1, as well as a major DNA-packaging protein, mitochondrial transcription factor A (TFAM).

Comparative mRNA and MicroRNA Profiling during Acute Myocardial Infarction Induced by Coronary Occlusion and Ablation Radio-Frequency Currents

The ligation of the left anterior descending coronary artery is the most commonly used experimental model to induce myocardial infarction (MI) in rodents. A high mortality in the acute phase and the heterogeneity of the size of the MI obtained are drawbacks recognized in this model. In an attempt to solve the problem, our group recently developed a new MI experimental model which is based on application of myocardial ablation radio-frequency currents (AB-RF) that yielded MI with homogeneous sizes and significantly reduce acute mortality. In addition, cardiac structural, and functional changes aroused by AB-RF were similar to those seen in animals with MI induced by coronary artery ligation. Herein, we compared mRNA expression of genes that govern post-MI milieu in occlusion and ablation models. We analyzed 48 mRNAs expressions of nine different signal transduction pathways (cell survival and metabolism signs, matrix extracellular, cell cycle, oxidative stress, apoptosis, calcium signaling, hypertrophy markers, angiogenesis, and inflammation) in rat left ventricle 1 week after MI generated by both coronary occlusion and AB-RF. Furthermore, high-throughput miRNA analysis was also assessed in both MI procedures. Interestingly, mRNA expression levels and miRNA expressions showed strong similarities between both models after MI, with few specificities in each model, activating similar signal transduction pathways. To our knowledge, this is the first comparison of genomic alterations of mRNA and miRNA contents after two different MI procedures and identifies key signaling regulators modulating the pathophysiology of these two models that might culminate in heart failure. Furthermore, these analyses may contribute with the current knowledge concerning transcriptional and post-transcriptional changes of AB-RF protocol, arising as an alternative and effective MI method that reproduces most changes seem in coronary occlusion.

A Biophysical Systems Approach to Identifying the Pathways of Acute and Chronic Doxorubicin Mitochondrial Cardiotoxicity

The clinical use of the anthracycline doxorubicin is limited by its cardiotoxicity which is associated with mitochondrial dysfunction. Redox cycling, mitochondrial DNA damage and electron transport chain inhibition have been identified as potential mechanisms of toxicity. However, the relative roles of each of these proposed mechanisms are still not fully understood. The purpose of this study is to identify which of these pathways independently or in combination are responsible for doxorubicin toxicity. A state of the art mathematical model of the mitochondria including the citric acid cycle, electron transport chain and ROS production and scavenging systems was extended by incorporating a novel representation for mitochondrial DNA damage and repair. In silico experiments were performed to quantify the contributions of each of the toxicity mechanisms to mitochondrial dysfunction during the acute and chronic stages of toxicity. Simulations predict that redox cycling has a minor role in doxorubicin cardiotoxicity. Electron transport chain inhibition is the main pathway for acute toxicity for supratherapeutic doses, being lethal at mitochondrial concentrations higher than 200μM. Direct mitochondrial DNA damage is the principal pathway of chronic cardiotoxicity for therapeutic doses, leading to a progressive and irreversible long term mitochondrial dysfunction.

Effects of Tannic Acid on the Ischemic Brain Tissue of Rats

Many studies of brain ischemia have shown the role played by massive ischemia-induced production of reactive oxygen species, the main mechanism of neuronal death. However, currently, there is no treatment choice to prevent cell death triggered by reactive oxygen species. In our study, we researched the effects of tannic acid, an antioxidant, on the ischemic tissue of rats with induced middle cerebral artery occlusion. The animals were divided into three groups of eight animals. The sham group were only administered 10 % ethanol intraperitoneally, the second group had middle cerebral artery occlusion induced and were given 10 % ethanol intraperitoneally, while the third group had middle cerebral artery occlusion with 10 mg/kg dose tannic acid dissolved in 10 % ethanol administered within half an hour intraperitoneally. The rats were sacrificed 24 h later, and brain tissue was examined biochemically and histopathologically. Biochemical evaluation of brain tissue found that comparing the ischemic group with no treatment with the tannic acid-treated ischemia group; the superoxide dismutase (SOD) levels were higher, malondialdehyde (MDA) levels were lower, and nuclear respiratory factor-1 (NRF-1) was higher in the tannic acid-treated group. Histopathological examination showed that the histopathological results of the tannic acid group were better than the group not given tannic acid. Biochemical and histopathological results showed that tannic acid administration had an antioxidant effect on the negative effects of ischemia in brain tissue.

Presequence-Independent Mitochondrial Import of DNA Ligase Facilitates Establishment of Cell Lines with Reduced mtDNA Copy Number

Due to the essential role played by mitochondrial DNA (mtDNA) in cellular physiology and bioenergetics, methods for establishing cell lines with altered mtDNA content are of considerable interest. Here, we report evidence for the existence in mammalian cells of a novel, low- efficiency, presequence-independent pathway for mitochondrial protein import, which facilitates mitochondrial uptake of such proteins as Chlorella virus ligase (ChVlig) and Escherichia coli LigA. Mouse cells engineered to depend on this pathway for mitochondrial import of the LigA protein for mtDNA maintenance had severely (up to >90%) reduced mtDNA content. These observations were used to establish a method for the generation of mouse cell lines with reduced mtDNA copy number by, first, transducing them with a retrovirus encoding LigA, and then inactivating in these transductants endogenous Lig3 with CRISPR-Cas9. Interestingly, mtDNA depletion to an average level of one copy per cell proceeds faster in cells engineered to maintain mtDNA at low copy number. This makes a low-mtDNA copy number phenotype resulting from dependence on mitochondrial import of DNA ligase through presequence-independent pathway potentially useful for rapidly shifting mtDNA heteroplasmy through partial mtDNA depletion.

Mitochondrial ROS Induces Cardiac Inflammation via a Pathway through mtDNA Damage in a Pneumonia-Related Sepsis Model

We have previously shown that mitochondria-targeted vitamin E (Mito-Vit-E), a mtROS specific antioxidant, improves cardiac performance and attenuates inflammation in a pneumonia-related sepsis model. In this study, we applied the same approaches to decipher the signaling pathway(s) of mtROS-dependent cardiac inflammation after sepsis. Sepsis was induced in Sprague Dawley rats by intratracheal injection of S. pneumoniae. Mito-Vit-E, vitamin E or vehicle was administered 30 minutes later. In myocardium 24 hours post-inoculation, Mito-Vit-E, but not vitamin E, significantly protected mtDNA integrity and decreased mtDNA damage. Mito-Vit-E alleviated sepsis-induced reduction in mitochondria-localized DNA repair enzymes including DNA polymerase γ, AP endonuclease, 8-oxoguanine glycosylase, and uracil-DNA glycosylase. Mito-Vit-E dramatically improved metabolism and membrane integrity in mitochondria, suppressed leakage of mtDNA into the cytoplasm, inhibited up-regulation of Toll-like receptor 9 (TLR9) pathway factors MYD88 and RAGE, and limited RAGE interaction with its ligand TFAM in septic hearts. Mito-Vit-E also deactivated NF-κB and caspase 1, reduced expression of the essential inflammasome component ASC, and decreased inflammatory cytokine IL–1β. In vitro, both Mito-Vit-E and TLR9 inhibitor OND-I suppressed LPS-induced up-regulation in MYD88, RAGE, ASC, active caspase 1, and IL–1β in cardiomyocytes. Since free mtDNA escaped from damaged mitochondria function as a type of DAMPs to stimulate inflammation through TLR9, these data together suggest that sepsis-induced cardiac inflammation is mediated, at least partially, through mtDNA-TLR9-RAGE. At last, Mito-Vit-E reduced the circulation of myocardial injury marker troponin-I, diminished apoptosis and amended morphology in septic hearts, suggesting that mitochondria-targeted antioxidants are a potential cardioprotective approach for sepsis.

Mitochondrial DNA: A disposable genome?

In mammalian cells, mitochondria are the only organelles besides the nucleus that house genomic DNA. The mammalian mitochondrial genome is represented by prokaryotic-type, circular, highly compacted DNA molecules. Today, more than a half-century after their discovery, the biology of these small and redundant molecules remains much less understood than that of their nuclear counterparts. One peculiarity of the mitochondrial genome that emerged in recent years is its disposable nature, as evidenced by cells abandoning a fraction of their mitochondrial DNA (mtDNA) in response to various stimuli with little or no physiological consequence. Here, we review some recent developments in the field of mtDNA biology and discuss emerging questions on the disposability and indispensability of mtDNA.

Propofol prevents neuronal mtDNA deletion and cerebral damage due to ischemia/reperfusion injury in rats

Propofol is a commonly used intravenous anesthetic that has been demonstrated to be neuroprotective against cerebral ischemia-reperfusion (I/R) injury. It remains unclear whether this protective effect has any relationship with the prevention of neuronal mitochondrial deoxyribonucleic acid (mtDNA) deletion. In this study, 81 Wistar rats were randomly divided into three groups (n = 27 each): sham (S group), ischemia/reperfusion (I/R group), or propofol (P group). Cerebral ischemia was induced by clamping the bilateral common carotid arteries for 10 min. A polymerase chain reaction (PCR) was conducted to determine mtDNA deletion. The mitochondrial membrane potential (MMP) changes were detected via microplate reader. The neuronal ultrastructure was visualized via electron microscope. MMP significantly decreased after I/R (P<0.05 compared with the S group). Severe damage to the ultrastructure of neuronal mitochondria was observed in cerebral I/R injury. When propofol (1.0mg/kg/min) was administered intravenously for 1h prior to the induction of I/R, the neuronal structure and MMP were well preserved, and mtDNA deletion was reduced after ischemia/reperfusion injury compared with the I/R group (P<0.05). These data suggested that propofol prevented mtDNA deletion and preserved a normal structure and MMP, which are important for normal mitochondrial function and increase neuronal resistance to I/R injury.

The effects of NAD+ on apoptotic neuronal death and mitochondrial biogenesis and function after glutamate excitotoxicity

NAD+ is an essential co-enzyme for cellular energy metabolism and is also involved as a substrate for many cellular enzymatic reactions. It has been shown that NAD+ has a beneficial effect on neuronal survival and brain injury in in vitro and in vivo ischemic models. However, the effect of NAD+ on mitochondrial biogenesis and function in ischemia has not been well investigated. In the present study, we used an in vitro glutamate excitotoxicity model of primary cultured cortical neurons to study the effect of NAD+ on apoptotic neuronal death and mitochondrial biogenesis and function. Our results show that supplementation of NAD+ could effectively reduce apoptotic neuronal death, and apoptotic inducing factor translocation after neurons were challenged with excitotoxic glutamate stimulation. Using different approaches including confocal imaging, mitochondrial DNA measurement and Western blot analysis of PGC-1 and NRF-1, we also found that NAD+ could significantly attenuate glutamate-induced mitochondrial fragmentation and the impairment of mitochondrial biogenesis. Furthermore, NAD+ treatment effectively inhibited mitochondrial membrane potential depolarization and NADH redistribution after excitotoxic glutamate stimulation. Taken together, our results demonstrated that NAD+ is capable of inhibiting apoptotic neuronal death after glutamate excitotoxicity via preserving mitochondrial biogenesis and integrity. Our findings provide insights into potential neuroprotective strategies in ischemic stroke.

Sirt3 protects cortical neurons against oxidative stress via regulating mitochondrial Ca2+ and mitochondrial biogenesis

Oxidative stress is a well-established event in the pathology of several neurobiological diseases. Sirt3 is a nicotinamide adenine nucleotide (NAD+)-dependent protein deacetylase that regulates mitochondrial function and metabolism in response to caloric restriction and stress. This study aims to investigate the role of Sirt3 in H2O2 induced oxidative neuronal injury in primary cultured rat cortical neurons. We found that H2O2 treatment significantly increased the expression of Sirt3 in a time-dependent manner at both mRNA and protein levels. Knockdown of Sirt3 with a specific small interfering RNA (siRNA) exacerbated H2O2-induced neuronal injury, whereas overexpression of Sirt3 by lentivirus transfection inhibited H2O2-induced neuronal damage reduced the generation of reactive oxygen species (ROS), and increased the activities of endogenous antioxidant enzymes. In addition, the intra-mitochondrial Ca2+ overload, but not cytosolic Ca2+ increase after H2O2 treatment, was strongly attenuated after Sirt3 overexpression. Overexpression of Sirt3 also increased the content of mitochondrial DNA (mtDNA) and the expression of mitochondrial biogenesis related transcription factors. All these results suggest that Sirt3 acts as a prosurvival factor playing an essential role to protect cortical neurons under H2O2 induced oxidative stress, possibly through regulating mitochondrial Ca2+ homeostasis and mitochondrial biogenesis.

Neuronal injury from cardiac arrest: aging years in minutes

Cardiac arrest is a leading cause of death and permanent disability. Most victims succumb to the oxidative and inflammatory damage sustained during cardiac arrest/resuscitation, but even survivors typically battle long-term neurocognitive impairment. Although extensive research has delineated the complex mechanisms that culminate in neuronal damage and death, no effective treatments have been developed to interrupt these mechanisms. Of importance, many of these injury cascades are also active in the aging brain, where neurons and other cells are under persistent oxidative and inflammatory stress which eventually damages or kills the cells. In light of these similarities, it is reasonable to propose that the brain essentially ages the equivalent of several years within the few minutes taken to resuscitate a patient from cardiac arrest. Accordingly, cardiac arrest-resuscitation models may afford an opportunity to study the deleterious mechanisms underlying the aging process, on an accelerated time course. The aging and resuscitation fields both stand to gain pivotal insights from one another regarding the mechanisms of injury sustained during resuscitation from cardiac arrest and during aging. This synergism between the two fields could be harnessed to foster development of treatments to not only save lives but also to enhance the quality of life for the elderly.

The influence of low-level laser therapy on parameters of oxidative stress and DNA damage on muscle and plasma in rats with heart failure

In heart failure (HF), there is an imbalance between the production of reactive oxygen species and the synthesis of antioxidant enzymes, causing damage to the cardiovascular function and increased susceptibility to DNA damage. The aim of this study was to evaluate the influence of low-level laser therapy (LLLT) on parameters of oxidative stress and DNA damage in skeletal muscle and plasma of rats with HF. Wistar rats were allocated into six groups: "placebo" HF rats (P-HF, n = 9), "placebo" Sham rats (P-sham, n = 8), HF rats at a dose 3 J/cm(2) of LLLT (3 J/cm(2)-HF, n = 8), sham rats at a dose 3 J/cm(2) of LLLT (3 J/cm(2)-sham, n = 8), HF rats at a dose 21 J/cm(2) of LLLT (21 J/cm(2)-HF, n = 8) and sham rats at a dose 21 J/cm(2) of LLLT (21 J/cm(2)-sham, n = 8). Animals were submitted to a LLLT protocol for 10 days at the right gastrocnemius muscle. Comparison between groups showed a significant reduction in superoxide dismutase (SOD) activity in the 3 J/cm(2)-HF group (p = 0.03) and the 21 J/cm(2)-HF group (p = 0.01) compared to the P-HF group. 2',7'-Dihydrodichlorofluorescein (DCFH) oxidation levels showed a decrease when comparing 3 J/cm(2)-sham to P-sham (p = 0.02). The DNA damage index had a significant increase either in 21 J/cm(2)-HF or 21 J/cm(2)-sham in comparison to P-HF (p = 0.004) and P-sham (p = 0.001) and to 3 J/cm(2)-HF (p = 0.007) and 3 J/cm(2)-sham (p = 0.037), respectively. Based on this, laser therapy appears to reduce SOD activity and DCFH oxidation levels, changing the oxidative balance in the skeletal muscle of HF rats. Otherwise, high doses of LLLT seem to increase DNA damage.

The "fast" and the "slow" modes of mitochondrial DNA degradation

In a living cell, oxidative stress resulting from an external or internal insult can result in mitochondrial DNA (mtDNA) damage and degradation. Here, we show that in HeLa cells, mtDNA can withstand relatively high levels of extracellular oxidant H2O2 before it is damaged to a point of degradation, and that mtDNA levels in these cells quickly recover after removal of the stressor. In contrast, mtDNA degradation in mouse fibroblast cells is induced at eight-fold lower concentrations of H2O2, and restoration of the lost mtDNA proceeds much slower. Importantly, mtDNA levels in HeLa cells continue to decline even after withdrawal of the stressor thus marking the "slow" mode of mtDNA degradation. Conversely, in mouse fibroblasts maximal loss of mtDNA is achieved during treatment, and is already detectable at 5 min after exposure, indicating the "fast" mode. These differences may modulate susceptibility to oxidative stress of those organs, which consist of multiple cell types.

Reperfusion promotes mitochondrial biogenesis following focal cerebral ischemia in rats

Background and Purpose

Reperfusion after transient cerebral ischemia causes severe damage to mitochondria; however, little is known regarding the continuous change in mitochondrial biogenesis during reperfusion. Mitochondrial biogenesis causes an increase in the individual mitochondrial mass of neurons and maintains their aerobic set-point in the face of declining function. The aim of this study was to examine mitochondrial biogenesis in the cortex during reperfusion following focal cerebral ischemia.

Methods

Male Wistar rats were subjected to transient focal cerebral ischemia. The relative amount of cortical mitochondrial DNA was analyzed using quantitative real-time PCR at 0 h, 24 h, 72 h, and 7 d after reperfusion. Three critical transcriptional regulators of mitochondrial biogenesis were measured by semi-quantitative reverse-transcription PCR. The protein expression of cytochrome C oxidase subunits I and IV was detected by Western blotting.

Results

Evidence of increased mitochondrial biogenesis was observed after reperfusion. The cortical mitochondrial DNA content increased after 24 h, peaked after 72 h, and maintained a high level for 7 d. The cortical expression of three critical genes for the transcriptional regulation of mitochondrial biogenesis, namely, peroxisome proliferator-activated receptor coactivator-1α, nuclear respiratory factor-1, and mitochondrial transcription factor A, also increased at 24 h and 72 h. The expression of peroxisome proliferator-activated receptor coactivator-1α returned to the baseline level at 7 d, but two other factors maintained higher levels compared with the controls. Moreover, the expression of cytochrome C oxidase subunits I and IV was increased in the cortex.

Conclusions

These results indicate that reperfusion increased mitochondrial biogenesis following focal cerebral ischemia, and this tendency was exacerbated as the reperfusion time was extended. Reperfusion-induced mitochondrial biogenesis was mediated through up-regulation of critical transcriptional regulators of mitochondrial biogenesis.

Inhibition of cyclophilin D by cyclosporin A promotes retinal ganglion cell survival by preventing mitochondrial alteration in ischemic injury

Cyclosporin A (CsA) inhibits the opening of the mitochondrial permeability transition pore (MPTP) by interacting with cyclophilin D (CypD) and ameliorates neuronal cell death in the central nervous system against ischemic injury. However, the molecular mechanisms underlying CypD/MPTP opening-mediated cell death in ischemic retinal injury induced by acute intraocular pressure (IOP) elevation remain unknown. We observed the first direct evidence that acute IOP elevation significantly upregulated CypD protein expression in ischemic retina at 12 h. However, CsA prevented the upregulation of CypD protein expression and promoted retinal ganglion cell (RGC) survival against ischemic injury. Moreover, CsA blocked apoptotic cell death by decreasing cleaved caspase-3 protein expression in ischemic retina. Of interest, although the expression level of Bcl-xL protein did not show a significant change in ischemic retina treated with vehicle or CsA at 12 h, ischemic damage induced the reduction of Bcl-xL immunoreactivity in RGCs. More importantly, CsA preserved Bcl-xL immunoreactivity in RGCs of ischemic retina. In parallel, acute IOP elevation significantly increased phosphorylated Bad (pBad) at Ser112 protein expression in ischemic retina at 12 h. However, CsA significantly preserved pBad protein expression in ischemic retina. Finally, acute IOP elevation significantly increased mitochondrial transcription factor A (Tfam) protein expression in ischemic retina at 12 h. However, CsA significantly preserved Tfam protein expression in ischemic retina. Studies on mitochondrial DNA (mtDNA) content in ischemic retina showed that there were no statistically significant differences in mtDNA content among control and ischemic groups treated with vehicle or CsA. Therefore, these results provide evidence that the activation of CypD-mediated MPTP opening is associated with the apoptotic pathway and the mitochondrial alteration in RGC death of ischemic retinal injury. On the basis of these observations, our findings suggest that CsA-mediated CypD inhibition may provide a promising therapeutic potential for protecting RGCs against ischemic injury-mediated mitochondrial dysfunction.

Peroxynitrite induced mitochondrial biogenesis following MnSOD knockdown in normal rat kidney (NRK) cells

Superoxide is widely regarded as the primary reactive oxygen species (ROS) which initiates downstream oxidative stress. Increased oxidative stress contributes, in part, to many disease conditions such as cancer, atherosclerosis, ischemia/reperfusion, diabetes, aging, and neurodegeneration. Manganese superoxide dismutase (MnSOD) catalyzes the dismutation of superoxide into hydrogen peroxide which can then be further detoxified by other antioxidant enzymes. MnSOD is critical in maintaining the normal function of mitochondria, thus its inactivation is thought to lead to compromised mitochondria. Previously, our laboratory observed increased mitochondrial biogenesis in a novel kidney-specific MnSOD knockout mouse. The current study used transient siRNA mediated MnSOD knockdown of normal rat kidney (NRK) cells as the in vitro model, and confirmed functional mitochondrial biogenesis evidenced by increased PGC1α expression, mitochondrial DNA copy numbers and integrity, electron transport chain protein CORE II, mitochondrial mass, oxygen consumption rate, and overall ATP production. Further mechanistic studies using mitoquinone (MitoQ), a mitochondria-targeted antioxidant and L-NAME, a nitric oxide synthase (NOS) inhibitor demonstrated that peroxynitrite (at low micromolar levels) induced mitochondrial biogenesis. These findings provide the first evidence that low levels of peroxynitrite can initiate a protective signaling cascade involving mitochondrial biogenesis which may help to restore mitochondrial function following transient MnSOD inactivation.

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MnSOD knockdown in NRK cells results in a transient loss of MnSOD activity, increased nitrotyrosine and mitochondrial superoxide.

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MnSOD knockdown in NRK cells results in a transient induction of mitochondrial biogenesis.

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Nitric oxide synthase inhibition and Mitoquinone blocks mitochondrial biogenesis after MnSOD knockdown.

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Low doses of peroxynitrite induce biogenesis in NRK cells.

Sex differences in mitochondrial biogenesis determine neuronal death and survival in response to oxygen glucose deprivation and reoxygenation

Background

Mitochondrial dysfunction has been linked to neuronal death and a wide array of neurodegenerative diseases. Previously, we have shown sex differences in mitochondria-mediated cell death pathways following hypoxia-ischemia. However, the role of mitochondrial biogenesis in hypoxic-ischemic brain injury between male vs. female has not been studied yet.

Results

Primary cerebellar granule neurons (CGNs), isolated from P7 male and female mice (CD-1) segregated based on visual inspection of sex, were exposed to 2 h of oxygen glucose deprivation (OGD) followed by 6–24 h of reoxygenation (Reox). Mitochondrial membrane potential (ΔΨ_m) and cellular ATP levels were reduced significantly in XX CGNs as compared to XY CGNs. Mitochondrial DNA (mtDNA) content was increased (>2-fold) at 2 h OGD in XY CGNs and remained increased up to 24 h of Reox compared to XX neurons and normoxia controls. The expression of mitochondrial transcription factor A (Tfam), the nuclear respiratory factor-1 (NRF-1) and the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, were up-regulated (2-fold, ***p < 0.001) in XY CGNs but slightly reduced or remained unchanged in XX neurons. Similarly, the TFAM and PGC-1α protein levels and the mitochondrial proteins HSP60 and COXIV were increased in XY neurons only. Supportively, a balanced stimulation of fusion (Mfn 1and Mfn 2) and fission (Fis 1 and Drp 1) genes and enhanced formation of donut-shaped mitochondria were observed in XY CGNs vs. XX neurons (**p < 0.01).

Conclusions

Our results demonstrate that OGD/Reox alters mitochondrial biogenesis and morphological changes in a sex-specific way, influencing neuronal injury/survival differently in both sexes.

Perfusion, hypoperfusion, and ischemia processes: the effect on bodily function

Adequate perfusion is requisite for normal body function. Should perfusion be disrupted, a cascade of events may result that can lead to disruption of function and potentially cell, tissue, organ, and ultimately organism death. Contrary to logic, reperfusion as a modality of treatment is not without issues in the form of reperfusion injury.

Osthole attenuates spinal cord ischemia-reperfusion injury through mitochondrial biogenesis-independent inhibition of mitochondrial dysfunction in rats

BACKGROUND

Osthole, the main bioactive compounds isolated from the traditional Chinese medical herb broad Cnidium monnieri (L.) cusson, has been shown to exert spectrum of pharmacologic activities. The aim of this study was to investigate the potential neuroprotective effects of osthole against spinal cord ischemia-reperfusion injury in rats.

MATERIALS AND METHODS

Osthole was administrated at the concentration of 0.1, 1, 10, 50, or 200 mg/kg (intraperitoneally) 1 h before spinal cord ischemia. The effects on spinal cord injury were measured by spinal cord water content, infarct volume, hematoxylin and eosin staining, and neurologic assessment. Mitochondria were purified from injured spinal cord tissue to determine mitochondrial function.

RESULTS

We found that treatment with osthole (10 and 50 mg/kg) significantly decreased spinal cord water content and infarct volume, preserved normal motor neurons, and improved neurologic functions. These protective effects can be also observed even if the treatment was delayed to 4 h after reperfusion. Osthole treatment preserved mitochondrial membrane potential level, reduced reactive oxygen species production, increased adenosine triphosphate generation, and inhibited cytochrome c release in mitochondrial samples. Moreover, osthole increased mitochondria respiratory chain complex activities in spinal cord tissue, with no effect on mitochondrial DNA content and the expression of mitochondrial-specific transcription factors.

CONCLUSIONS

All these findings demonstrate the neuroprotective effect of osthole in spinal cord ischemia-reperfusion injury model and suggest that oshtole-induced neuroprotection was mediated by mitochondrial biogenesis-independent inhibition of mitochondrial dysfunction.

The maintenance of mitochondrial DNA integrity--critical analysis and update

DNA molecules in mitochondria, just like those in the nucleus of eukaryotic cells, are constantly damaged by noxious agents. Eukaryotic cells have developed efficient mechanisms to deal with this assault. The process of DNA repair in mitochondria, initially believed nonexistent, has now evolved into a mature area of research. In recent years, it has become increasingly appreciated that mitochondria possess many of the same DNA repair pathways that the nucleus does. Moreover, a unique pathway that is enabled by high redundancy of the mitochondrial DNA and allows for the disposal of damaged DNA molecules operates in this organelle. In this review, we attempt to present a unified view of our current understanding of the process of DNA repair in mitochondria with an emphasis on issues that appear controversial.

Oxidative stress, its role in the pathogenesis of chronic heart failure, and potential methods of correction

For many years, cardiovascular disease (CVD) remains the leading cause of death worldwide. According to the World Health Organization estimates, CVD accounts for 57% of all-cause mortality in Russia. Recently, research efforts have been concentrated on the search for new CVD markers which can improve the diagnostics and treatment of this large disease group, associated with poor prognosis. The markers of oxidative stress (OS) and antioxidant enzyme activity have been considered as potential pathogenetic mechanisms in the CVD development. The potential of statins, as medications with a wide range of pleiotropic – in particular, antioxidant – effects, for the effective management of chronic heart failure (CHF) has been extensively investigated. There is an ongoing discussion whether statins could be used for the treatment of nonischemic CHF.

Pre-B-cell colony-enhancing factor exerts a neuronal protection through its enzymatic activity and the reduction of mitochondrial dysfunction in in vitro ischemic models

Pre-B-cell colony-enhancing factor (PBEF) is known as a rate-limiting enzyme that converts nicotinamide (NAM) to NMN in the salvage pathway of mammalian NAD⁺ biosynthesis. Previously we found PBEF is exclusively expressed in neurons in the mouse brain; heterozygous PBEF knockout (Pbef⁺/⁻) mice have larger ischemic lesion than wild type mice in photothrombosis-induced ischemia. For the mechanistic study of neuronal protective role of PBEF, we used in vitro oxygen-glucose deprivation (OGD) and glutamate excitotoxicity models of primary cultured neurons in current study. Our results showed that the treatments of neurons with NAM and NAD⁺, the substrate and downstream product of PBEF, respectively, significantly reduced neuronal death after OGD and glutamate excitotoxicity, while treatment of neurons treated with FK866, a PBEF inhibitor, increased neuronal death after OGD. Furthermore, over-expression of human PBEF reduced glutamate excitotoxicity, while over-expression of human PBEF mutants (i.e. H247A and H247E) without enzymatic activity had no effect on neuronal death. We further tested the effect of PBEF on mitochondrial function and biogenesis. Our results show that addition of NAD⁺ and NAM increased mitochondrial biogenesis in neurons after OGD. Over-expression of PBEF in neurons reduced mitochondrial membrane potential depolarization following glutamate stimulation, while over-expression of H247A and H247E did not affect mitochondrial membrane potential depolarization. We conclude that PBEF has a neuroprotective effect in ischemia through its enzymatic activity for NAD⁺ production that can ameliorate mitochondrial dysfunction.

Effect of polyphenols on oxidative stress and mitochondrial dysfunction in neuronal death and brain edema in cerebral ischemia

Polyphenols are natural substances with variable phenolic structures and are elevated in vegetables, fruits, grains, bark, roots, tea, and wine. There are over 8000 polyphenolic structures identified in plants, but edible plants contain only several hundred polyphenolic structures. In addition to their well-known antioxidant effects, select polyphenols also have insulin-potentiating, anti-inflammatory, anti-carcinogenic, anti-viral, anti-ulcer, and anti-apoptotic properties. One important consequence of ischemia is neuronal death and oxidative stress plays a key role in neuronal viability. In addition, neuronal death may be initiated by the activation of mitochondria-associated cell death pathways. Another consequence of ischemia that is possibly mediated by oxidative stress and mitochondrial dysfunction is glial swelling, a component of cytotoxic brain edema. The purpose of this article is to review the current literature on the contribution of oxidative stress and mitochondrial dysfunction to neuronal death, cell swelling, and brain edema in ischemia. A review of currently known mechanisms underlying neuronal death and edema/cell swelling will be undertaken and the potential of dietary polyphenols to reduce such neural damage will be critically reviewed.

p53-TIGAR axis attenuates mitophagy to exacerbate cardiac damage after ischemia

Inhibition of tumor suppressor p53 is cardioprotective against ischemic injury and provides resistance to subsequent cardiac remodeling. We investigated p53-mediated expansion of ischemic damage with a focus on mitochondrial integrity in association with autophagy and apoptosis. p53(-/-) heart showed that autophagic flux was promoted under ischemia without a change in cardiac tissue ATP content. Electron micrographs revealed that ischemic border zone in p53(-/-) mice had 5-fold greater numbers of autophagic vacuoles containing mitochondria, indicating the occurrence of mitophagy, with an apparent reduction of abnormal mitochondria compared with those in WT mice. Analysis of autophagic mediators acting downstream of p53 revealed that TIGAR (TP53-induced glycolysis and apoptosis regulator) was exclusively up-regulated in ischemic myocardium. TIGAR(-/-) mice exhibited the promotion of mitophagy followed by decrease of abnormal mitochondria and resistance to ischemic injury, consistent with the phenotype of p53(-/-) mice. In p53(-/-) and TIGAR(-/-) ischemic myocardium, ROS production was elevated and followed by Bnip3 activation which is an initiator of mitophagy. Furthermore, the activation of Bnip3 and mitophagy due to p53/TIGAR inhibition were reversed with antioxidant N-acetyl-cysteine, indicating that this adaptive response requires ROS signal. Inhibition of mitophagy using chloroquine in p53(-/-) or TIGAR(-/-) mice exacerbated accumulation of damaged mitochondria to the level of wild-type mice and attenuated cardioprotective action. These findings indicate that p53/TIGAR-mediated inhibition of myocyte mitophagy is responsible for impairment of mitochondrial integrity and subsequent apoptosis, the process of which is closely involved in p53-mediated ventricular remodeling after myocardial infarction.

Activation of calcium/calmodulin-dependent protein kinase IV and peroxisome proliferator-activated receptor γ coactivator-1α signaling pathway protects against neuronal injury and promotes mitochondrial biogenesis in the hippocampal CA1 subfield after transient global ischemia

Delayed neuronal cell death occurs in the vulnerable CA1 subfield of the hippocampus after transient global ischemia (TGI). We demonstrated previously, based on an experimental model of TGI, that the significantly increased content of oxidized proteins in hippocampal CA1 neuron was observed as early as 30 min after TGI, followed by augmentation of PGC-1α expression at 1 hr, as well as up-regulation of mitochondrial uncoupling protein 2 (UCP2) and superoxide dismutases 2 (SOD2). Using the same animal model, the present study investigated the role of calcium/calmodulin-dependent protein kinase IV (CaMKIV) and PGC-1α in delayed neuronal cell death and mitochondrial biogenesis in the hippocampus. In Sprague-Dawley rats, significantly increased expression of nuclear CaMKIV was noted in the hippocampal CA1 subfield as early as 15 min after TGI. In addition, the index of mitochondrial biogenesis, including a mitochondrial DNA-encoded polypeptide, cytochrome c oxidase subunit 1 (COX1), and mitochondrial number significantly increased in the hippocampal CA1 subfield 4 hr after TGI. Application bilaterally into the hippocampal CA1 subfield of an inhibitor of CaMKIV, KN-93, 30 min before TGI attenuated both CaMKIV and PGC-1α expression, followed by down-regulation of UCP2 and SOD2, decrease of COX1 expression and mitochondrial number, heightened protein oxidation, and enhanced hippocampal CA1 neuronal damage. This study provides correlative evidence for the neuroprotective cascade of CaMKIV/PGC-1α which implicates at least in part the mitochondrial antioxidants UCP2 and SOD2 as well as mitochondrial biogenesis in ischemic brain injury.

Cerebral expression of DNA repair protein, Ku70, and its association with cell proliferation following cerebral hypoxia-ischemia in neonatal rats

We hypothesized that increased Ku70 expression could be involved in recovery following cerebral hypoxia-ischemia. We investigated the progression of cerebral alterations in Ku70 expression at different time points (24 h, 72 h, 1 week, 4 weeks and 8 weeks) after hypoxia-ischemia (right carotid artery occlusion plus 1.5h of hypoxia) in neonatal rats. To determine whether in addition to its known role of DNA repair, Ku70 was associated with cell death or cell proliferation we performed double staining for Ku70 and DNA fragmentation or bromodeoxyuridine, respectively. The results show that Ku70 expression was increased in the infarct core and peri-infarct regions at 24h following hypoxia-ischemia. The increased Ku70 expression was transient in the infarct core with a loss of Ku70 positive cells over days. In contrast, in the peri-infarct region the expression of Ku70 remained increased at chronic times 8 weeks following the insult. Cells positive for DNA fragmentation were not co-localized with cells positive for Ku70 after an insult. However, most of the cells positive for bromodeoxyuridine indicative of cell proliferation were positive for Ku70 in the peri-infarct region at 8 weeks after the insult. Considering the roles of Ku70 in DNA repair or inhibiting apoptosis and its co-localization within cells that had undergone proliferation, Ku70 may be considered a potential novel target to enhance recovery following hypoxia-ischemia.

Quantitative detection of the expression of mitochondrial cytochrome c oxidase subunits mRNA in the cerebral cortex after experimental traumatic brain injury

Secondary brain damage plays a critical role in the outcome of patients with traumatic brain injury (TBI). The multiple mechanisms underlying secondary brain damage, including posttraumatic cerebral ischemia, glutamate excitotoxicity, oxidative stress, calcium overload and inflammation, are associated with increased mortality and morbidity after head injury. TBI is documented to have detrimental effects on mitochondria, such as alterations in glucose utilization and the depression of mitochondrial oxidative phosphorylation. Studies on mitochondrial metabolism have provided evidence for dysfunction of the cytochrome oxidase complex of the electron transport chain (complex IV) after TBI. A growing body of evidence indicates that cytochrome c oxidase is vital for mitochondrial oxidative phosphorylation. Therefore, this study aimed to detect the expression of cytochrome c oxidase (CO) mRNA in a rat weight-dropping trauma model and to clarify the differences between injured cortex (IC) and contralateral cortex (CC) after TBI. A total of forty-four rats were randomly assigned to 7 groups: control groups (n=4), sham-operated group (n=20), 6 h, 1 d, 3 d, 5 d and 7 d postinjury groups (n=4 for each group). The group consisted of sham-operated animals underwent parietal craniotomy without TBI. The rats in postinjury groups were subjected to TBI. The rats of control group were executed immediately without TBI or craniotomy after anesthesia. The brain-injured and sham-operated animals were killed on 6 h, 1 d, 3 d, 5 d and 7 d, respectively. Tissue sections from IC and CC were obtained and the expression of cytochrome c oxidase I, II, and III (CO I, II, III) mRNA, three mitochondrial encoded subunits of complex IV, were assessed by Real-time quantitative PCR. A reduction of CO I, II, and III mRNA expression was detected from IC and reduced to the lowest on 3 d. By contrast, the mRNA expression from CC suggested a slight elevation. The differences may indicate the degree of metabolic and physiologic dysfunction. Our results will better define the roles of gene expression and metabolic function in long-term prognosis and outcome after TBI. With a considerable understanding of post-injury mitochondrial dysfunction, therapeutic interventions targeted to the mitochondria may prevent secondary brain damage that leads to long-term cell death and neurobehavioral disability.

Mitochondrial oxidative stress and dysfunction in myocardial remodelling

Recent experimental and clinical studies have suggested that oxidative stress is enhanced in myocardial remodelling and failure. The production of oxygen radicals is increased in the failing heart, whereas normal antioxidant enzyme activities are preserved. Mitochondrial electron transport is an enzymatic source of oxygen radical generation and can be a therapeutic target against oxidant-induced damage in the failing myocardium. Chronic increases in oxygen radical production in the mitochondria can lead to a catastrophic cycle of mitochondrial DNA (mtDNA) damage as well as functional decline, further oxygen radical generation, and cellular injury. Reactive oxygen species induce myocyte hypertrophy, apoptosis, and interstitial fibrosis by activating matrix metalloproteinases. These cellular events play an important role in the development and progression of maladaptive myocardial remodelling and failure. Therefore, oxidative stress and mtDNA damage are good therapeutic targets. Overexpression of the genes for peroxiredoxin-3 (Prx-3), a mitochondrial antioxidant, or mitochondrial transcription factor A (TFAM), could ameliorate the decline in mtDNA copy number in failing hearts. Consistent with alterations in mtDNA, the decrease in mitochondrial function was also prevented. Therefore, the activation of Prx-3 or TFAM gene expression could ameliorate the pathophysiological processes seen in mitochondrial dysfunction and myocardial remodelling. Inhibition of oxidative stress and mtDNA damage could be novel and effective treatment strategies for heart failure.

Rapidly increased neuronal mitochondrial biogenesis after hypoxic-ischemic brain injury

BACKGROUND AND PURPOSE

Mitochondrial biogenesis is regulated through the coordinated actions of both nuclear and mitochondrial genomes to ensure that the organelles are replenished on a regular basis. This highly regulated process has been well defined in skeletal and heart muscle, but its role in neuronal cells, particularly when under stress or injury, is not well understood. In this study, we report for the first time rapidly increased mitochondrial biogenesis in a rat model of neonatal hypoxic/ischemic brain injury (H-I).

METHODS

Postnatal day 7 rats were subjected to H-I induced by unilateral carotid artery ligation followed by 2.5 hours of hypoxia. The relative amount of brain mitochondrial DNA (mtDNA) was measured semiquantitatively using long fragment PCR at various time points after H-I. HSP60 and COXIV proteins were detected by Western blot. Expression of three genes critical for the transcriptional regulation of mitochondrial biogenesis, peroxisome proliferator-activated receptor coactivator-1 (PGC-1), nuclear respiratory factor-1 (NRF-1), and mitochondrial transcription factor A (TFAM), were examined by Western blot and RT-PCR.

RESULTS

Brain mtDNA content was markedly increased 6 hours after H-I, and continued to increase up to 24 hours after H-I. Paralleling the temporal change in mtDNA content, mitochondrial number and proteins HSP60 and COXIV, and citrate synthase activity were increased in neurons in the cortical infarct border zone after H-I. Moreover, cortical expression of NRF-1 and TFAM were increased 6 to 24 hours after H-I, whereas PGC-1 was not changed.

CONCLUSIONS

Neonatal H-I brain injury rapidly induces mitochondrial biogenesis, which may constitute a novel component of the endogenous repair mechanisms of the brain.

Critical role of calpain I in mitochondrial release of apoptosis-inducing factor in ischemic neuronal injury

Loss of mitochondrial membrane integrity and release of apoptogenic factors are a key step in the signaling cascade leading to neuronal cell death in various neurological disorders, including ischemic injury. Emerging evidence has suggested that the intramitochondrial protein apoptosis-inducing factor (AIF) translocates to the nucleus and promotes caspase-independent cell death induced by glutamate toxicity, oxidative stress, hypoxia, or ischemia. However, the mechanism by which AIF is released from mitochondria after neuronal injury is not fully understood. In this study, we identified calpain I as a direct activator of AIF release in neuronal cultures challenged with oxygen-glucose deprivation and in the rat model of transient global ischemia. Normally residing in both neuronal cytosol and mitochondrial intermembrane space, calpain I was found to be activated in neurons after ischemia and to cleave intramitochondrial AIF near its N terminus. The truncation of AIF by calpain activity appeared to be essential for its translocation from mitochondria to the nucleus, because neuronal transfection of the mutant AIF resistant to calpain cleavage was not released after oxygen-glucose deprivation. Adeno-associated virus-mediated overexpression of calpastatin, a specific calpain-inhibitory protein, or small interfering RNA-mediated knockdown of calpain I expression in neurons prevented ischemia-induced AIF translocation. Moreover, overexpression of calpastatin or knockdown of AIF expression conferred neuroprotection against cell death in neuronal cultures and in hippocampal CA1 neurons after transient global ischemia. Together, these results define calpain I-dependent AIF release as a novel signaling pathway that mediates neuronal cell death after cerebral ischemia.

Effect of high-fat enteral nutrition on hepatocyte injury in response to hemorrhagic shock in the rat

BACKGROUND

High-fat enteral nutrition reduces the inflammatory response following hemorrhagic shock in the rat.

AIMS

We hypothesized that this intervention might also ameliorate the remote organ injury to the liver associated with this model.

METHODS

Male Sprague-Dawley rats were either starved or fed low-fat or high-fat isocaloric isonitrogenous feed prior to nonlethal hemorrhagic shock induced by a 40% reduction in the blood volume. Animals were sacrificed at 90 minutes or 24 hours after injury. Liver cell damage was assessed by histology and long polymerase chain reaction (PCR) to detect mitochondrial DNA damage. Stress protein expression was measured by Western blot and mRNA expression by real-time PCR and immunohistochemistry.

RESULTS

Animals fed a low-fat diet had the same severity of liver injury as starved animals and increased expression of stress proteins. Animals fed a high-fat diet had minimal liver injury, no evidence of mitochondrial DNA damage, and significantly lower expression of stress proteins. This effect is associated with preservation of hepatocellular morphology, attenuation of mitochondrial DNA damage, and a reduced stress protein response to injury.

CONCLUSIONS

High-fat enteral nutrition protects the liver from the remote effects of hemorrhagic shock, but the mechanism of this effect is not yet known.

Promoter region methylation and reduced expression of thrombospondin-1 after oxygen-glucose deprivation in murine cerebral endothelial cells

Angiogenesis is induced in response to ischemia. Thrombospondin-1 (TSP-1) is a potent angiostatic factor. Silencing of TSP-1 expression may contribute to the postischemic angiogenesis. Upregulation of TSP-1, in contrast, may terminate the postischemic angiogenesis. A possible mechanism that silences TSP-1 expression is the DNA methylation of its promoter region. DNA methylation has been reported following cerebral ischemia. The present study aimed to explore whether methylation of the promoter region of TSP-1 regulates its expression after oxygen-glucose deprivation (OGD) in murine cerebral endothelial cells (CECs) in vitro. Sublethal OGD increased the extent of methylation of the promoter region of TSP-1 with a concurrent decrease in TSP-1 mRNA and protein expression in CECs. After reoxygenation, demethylation of the TSP-1 promoter region led to the restoration of TSP-1 mRNA and protein expression. The extent of methylation of the promoter region of TSP-1 was inversely correlated with the extent of TSP-1 gene expression at mRNA and protein levels after OGD. Oxygen-glucose deprivation-induced reduction in the TSP-1 mRNA level was not accompanied by a change in mRNA stability. These findings raise the possibility that OGD downregulation of TSP-1 expression is at least in part due to methylation of its promoter region.

Mitochondrial oxidative stress, DNA damage, and heart failure

Recent experimental and clinical studies have suggested that oxidative stress is enhanced in heart failure. The production of oxygen radicals is increased in the failing heart, whereas antioxidant enzyme activities are preserved as normal. Mitochondrial electron transport is an enzymatic source of oxygen radical generation and also a target of oxidant-induced damage. Chronic increases in oxygen radical production in the mitochondria can lead to a catastrophic cycle of mitochondrial DNA (mtDNA) damage as well as functional decline, further oxygen radical generation, and cellular injury. Reactive oxygen species induce myocyte hypertrophy, apoptosis, and interstitial fibrosis by activating matrix metalloproteinases. These cellular events play an important role in the development and progression of maladaptive cardiac remodeling and failure. Therefore, mitochondrial oxidative stress and mtDNA damage are good therapeutic targets. Overexpression of mitochondrial transcription factor A (TFAM) could ameliorate the decline in mtDNA copy number and preserve it at a normal level in failing hearts. Consistent with alterations in mtDNA, the decrease in oxidative capacities was also prevented. Therefore, the activation of TFAM expression could ameliorate the pathophysiologic processes seen in myocardial failure. Inhibition of mitochondrial oxidative stress and mtDNA damage could be novel and potentially very effective treatment strategies for heart failure.

Structural patterns of injured mitochondria in human oedematous cerebral cortex

PRIMARY OBJECTIVE

Cerebral cortical biopsies of 37 patients with clinical diagnosis of congenital malformations, brain trauma and tumours were studied to establish mitochondrial morphological alterations.

METHODS AND PROCEDURES

Cortical biopsies obtained in the surgical room were immediately processed by conventional technique for transmission electron microscopy.

RESULTS

Three injured mitochondrial morphological patterns were found: swollen clear, (SCM), swollen dense (SDM) and dark degenerated (DDM) mitochondria. SCM were predominantly found in traumatic brain oedema. SDM and DDM were frequently observed in sustained permanent ischaemia induced by brain tumours, vascular anomaly and congenital hydrocephalus. SCM exhibited low electron dense mitochondrial matrix, enlarged intracristal space and continuity of outer and inner mitochondrial membranes. SDM showed high electron dense matrix and swollen intact or fragmented cristae. DDM displayed overall high electron density of matrix and mitochondrial membranes.

CONCLUSION

The injured mitochondrial patterns are related with nerve cell death and considered markers of lethal nerve cell injury.

Transient injury to rat lung mitochondrial DNA after exposure to hyperoxia and inhaled nitric oxide

The effect of hyperoxia alone and in combination with inhaled nitric oxide (NO) on the integrity of lung mitochondrial DNA (mtDNA) in vivo was evaluated in Fischer 344 rats. PCR amplification of lung mtDNA using two sets of primers spanning 10.1 kb of the mtDNA revealed that inhalation of 20 ppm of NO in conjunction with hyperoxia (>95% O2) reduced the amplification of mtDNA templates by 10 +/- 1% and 26 +/- 3% after 24 h of exposure. The ability of mtDNA to amplify was not compromised in rats exposed to 80% O2, even in the presence of 20 ppm of inhaled NO. Surprisingly, exposure to >95% O2 alone for either 24 or 48 h did not compromise the integrity of mtDNA templates compared with air-exposed controls, despite evidence of genomic DNA injury. Interestingly, inhaling NO alone for 48 h increased mtDNA amplification by 12 +/- 2% to 21 +/- 7%. Injury to the lung mtDNA after exposure to >95% O2 plus 20 ppm of NO was transient as rats allowed to recover in room air after exposure displayed increased amplification, with levels exceeding controls by 20 +/- 3% to 29 +/- 4%. Increased amplification was not due to cellular proliferation or increased mitochondrial number. Moreover, the ratio of pulmonary mtDNA to genomic DNA remained the same between treatment groups. The results indicate that hyperoxia fails to induce significant injury to mtDNA, and whereas inhalation of NO with hyperoxia results in mtDNA damage, the lesions are rapidly repaired during recovery.