Hypoxic postconditioning promotes mitophagy against transient global cerebral ischemia via PINK1/Parkin-induced mitochondrial ubiquitination in adult rats

Jiawei Bai-Hu-decoction ameliorated heat stroke-induced brain injury by inhibiting TLR4/NF-κB signal and mitophagy of glial cell

ETHNOPHARMACOLOGICAL RELEVANCE

Jiawei Bai-Hu-Decoction (JWBHD), a prescription formulated with seven traditional Chinese medicinal material has demonstrated clinical efficacy in mitigating brain injury among heat stroke (HS) patients.

AIM OF THE STUDY

This study aimed to evaluate the therapeutic efficacy of JWBHD on rat model of HS and to explore its therapeutic mechanisms by integrating network pharmacology and pharmacodynamic methodologies, which major components were analyzed by using UPLC-MS/MS.

MATERIALS AND METHODS

The network pharmacology analysis was firstly conducted to predict the potential active ingredients and therapeutic targets of JWBHD. The anti-HS effectiveness of JWBHD was then evaluated on rats experienced HS. Rat brain tissues were harvested for a comprehensive array of experiments, including Western blot, PCR, H&E staining, Nissl staining, ELISA, transmission electron microscope, flow cytometry and immunofluorescence to validate the protective effects of JWBHD against HS-induced brain damage. Furthermore, the inhibitory effects of JWBHD on TLR4/NF-κB signal and mitophagy of glial were further verified on HS-challenged F98 cell line. Finally, the chemical compositions of the water extract of JWBHD were analyzed by using UPLC-MS/MS.

RESULTS

Network pharmacology has identified fifty core targets and numerous HS-related signaling pathways as potential therapeutic targets of JWBHD. Analysis of protein-protein interaction (PPI) and GO suggests that JWBHD may suppress HS-induced inflammatory signals. In experiments conducted on HS-rats, JWBHD significantly reduced the core temperature, restored blood pressure and alleviated neurological defect. Furthermore, JWBHD downregulated the counts of white blood cells and monocytes, decreased the levels of inflammatory cytokines such as IL-1β, IL-6 and TNF-α in peripheral blood, and suppressed the expression of TLR4 and NF-κB in the cerebral cortex of HS-rats. Besides, JWBHD inhibited the apoptosis of cortical cells and mitigated the damage to the cerebral cortex in HS group. Conversely, overactive mitophagy was observed in the cerebral cortex of HS-rats. However, JWBHD restored the mitochondrial membrane potential and downregulated expressions of mitophagic proteins including Pink1, Parkin, LC3B and Tom20. JWBHD reduced the co-localization of Pink1 and GFAP, a specific marker of astrocytes in the cerebral cortex of HS-rats. In addition, the inhibitory effect of JWBHD on TLR4/NF-κB signaling and overactive mitophagy were further confirmed in F98 cells. Finally, UPLC-MS/MS analysis showed that the main components of JWBHD include isoliquiritigenin, liquiritin, dipotassium glycyrrhizinate, ginsenoside Rb1, ginsenoside Re, etc. CONCLUSIONS: JWBHD protected rats from HS and prevented HS-induced damage in the cerebral cortex by suppressing TLR4/NF-κB signaling and mitophagy of glial.

Role of cardiolipin in regulating and treating atherosclerotic cardiovascular diseases

Cardiovascular diseases, mainly caused by atherosclerosis, are the leading causes of morbidity and mortality worldwide. Despite the discrepancies in clinical manifestations between different abnormalities, atherosclerosis shares similar pathophysiological processes, such as mitochondrial dysfunction. Cardiolipin (CL) is a conserved mitochondria-specific lipid that contributes to the cristae structure of the inner mitochondrial membrane (IMM). Alterations in the CL, including oxidative modification, reduced quantity, and abnormal localization, contribute to the onset and progression of atherosclerosis. In this review, we summarize the knowledge that CL is involved in the pathogenesis of atherosclerosis. On the one hand, CL and its oxidative modification promote the progression of atherosclerosis via several mechanisms, including oxidative stress, apoptosis, and inflammation in response to stress. On the other hand, CL externalizes to the outer mitochondrial membrane (OMM) and acts as the pivotal "eat-me" signal in mitophagy, removing dysfunctional mitochondria and safeguarding against the progression of atherosclerosis. Given the imbalance between proatherogenic and antiatherogenic effects, we provide our understanding of the roles of the CL and its oxidative modification in atherosclerotic cardiovascular diseases, in addition to potential therapeutic strategies aimed at restoring the CL. Briefly, CL is far more than a structural IMM lipid; broader significances of the evolutionarily conserved lipid need to be explored.

PHLDA1 contributes to hypoxic ischemic brain injury in neonatal rats via inhibiting FUNDC1-mediated mitophagy

Hypoxia-ischemia (HI) is one of the main causes of neonatal brain injury. Mitophagy has been implicated in the degradation of damaged mitochondria and cell survival following neonatal brain HI injury. Pleckstrin homology-like domain family A member 1 (PHLDA1) plays vital roles in the progression of various disorders including the regulation of oxidative stress, the immune responses and apoptosis. In the present study we investigated the role of PHLDA1 in HI-induced neuronal injury and further explored the mechanisms underlying PHLDA1-regulated mitophagy in vivo and in vitro. HI model was established in newborn rats by ligation of the left common carotid artery plus exposure to an oxygen-deficient chamber with 8% O2 and 92% N2. In vitro studies were conducted in primary hippocampal neurons subjected to oxygen and glucose deprivation/-reoxygenation (OGD/R). We showed that the expression of PHLDA1 was significantly upregulated in the hippocampus of HI newborn rats and in OGD/R-treated primary neurons. Knockdown of PHLDA1 in neonatal rats via lentiviral vector not only significantly ameliorated HI-induced hippocampal neuronal injury but also markedly improved long-term cognitive function outcomes, whereas overexpression of PHLDA1 in neonatal rats via lentiviral vector aggravated these outcomes. PHLDA1 knockdown in primary neurons significantly reversed the reduction of cell viability and increase in intracellular reactive oxygen species (ROS) levels, and attenuated OGD-induced mitochondrial dysfunction, whereas overexpression of PHLDA1 decreased these parameters. In OGD/R-treated primary hippocampal neurons, we revealed that PHLDA1 knockdown enhanced mitophagy by activating FUNDC1, which was abolished by FUNDC1 knockdown or pretreatment with mitophagy inhibitor Mdivi-1 (25 μM). Notably, pretreatment with Mdivi-1 or the knockdown of FUNDC1 not only increased brain infarct volume, but also abolished the neuroprotective effect of PHLDA1 knockdown in HI newborn rats. Together, these results demonstrate that PHLDA1 contributes to neonatal HI-induced brain injury via inhibition of FUNDC1-mediated neuronal mitophagy.

The neuroprotective effect of Chinese herbal medicine for cerebral ischemia reperfusion injury through regulating mitophagy

The incidence of ischemic stroke has been increasing annually with an unfavorable prognosis. Cerebral ischemia reperfusion injury can exacerbate nerve damage. Effective mitochondrial quality control including mitochondrial fission, fusion and autophagy, is crucial for maintaining cellular homeostasis. Several studies have revealed the critical role of mitophagy in Cerebral ischemia reperfusion injury. Cerebral ischemia and hypoxia induce mitophagy, and mitophagy exhibits positive and negative effects in cerebral ischemia reperfusion injury. Studies have shown that Chinese herbal medicine can alleviate Cerebral ischemia reperfusion injury and serve as a neuroprotective agent by inhibiting or promoting mitophagy-mediated pathways. This review focuses on the mitochondrial dynamics and mitophagy-related pathways, as well as the role of mitophagy in ischemia reperfusion injury. Additionally, it discusses the therapeutic potential and benefits of Chinese herbal monomers and decoctions in the treatment of ischemic stroke.

Mitophagy and its regulatory mechanisms in the biological effects of nanomaterials

Mitophagy is a selective cellular process critical for the removal of damaged mitochondria. It is essential in regulating mitochondrial number, ensuring mitochondrial functionality, and maintaining cellular equilibrium, ultimately influencing cell destiny. Numerous pathologies, such as neurodegenerative diseases, cardiovascular disorders, cancers, and various other conditions, are associated with mitochondrial dysfunctions. Thus, a detailed exploration of the regulatory mechanisms of mitophagy is pivotal for enhancing our understanding and for the discovery of novel preventive and therapeutic options for these diseases. Nanomaterials have become integral in biomedicine and various other sectors, offering advanced solutions for medical uses including biological imaging, drug delivery, and disease diagnostics and therapy. Mitophagy is vital in managing the cellular effects elicited by nanomaterials. This review provides a comprehensive analysis of the molecular mechanisms underpinning mitophagy, underscoring its significant influence on the biological responses of cells to nanomaterials. Nanoparticles can initiate mitophagy via various pathways, among which the PINK1-Parkin pathway is critical for cellular defense against nanomaterial-induced damage by promoting mitophagy. The role of mitophagy in biological effects was induced by nanomaterials, which are associated with alterations in Ca2+ levels, the production of reactive oxygen species, endoplasmic reticulum stress, and lysosomal damage.

Cold-inducible RNA binding protein alleviates iron overload-induced neural ferroptosis under perinatal hypoxia insult

Cold-inducible RNA binding protein (CIRBP), a stress response protein, protects cells from mild hypothermia or hypoxia by stabilizing specific mRNAs and promoting their translation. Neurons subjected to hypobaric hypoxia insult trigger various cell death programs. One of these is ferroptosis, a novel non-apoptotic form of programmed cell death, which is characterized by excessive iron ion accumulation and lipid peroxidation. Here, we establish that CIRBP can regulate neuronal ferroptosis both in vivo and in vitro. We observe that hypoxia leads to neuronal death via intracellular ferrous iron overload and impaired antioxidant systems, accompanied by suppressed CIRBP expression. Genetic enrichment of CIRBP in hippocampal neurons CIRBPTg mice bred with Emx1-Cre mice attenuates hypoxia-induced cognitive deficits and neuronal degeneration. Mechanistically, CIRBP alleviates neuronal ferroptosis and intracellular ferrous ion accumulation by binding to the mitochondrial ferritin (FTMT) 3'UTR to stabilize mRNA and promote its translation. Our novel study shows the critical role of CIRBP in the progression of ferroptosis, and provides promising therapeutic target for hypoxia-induced neurological diseases.

SIRT2 regulates apoptosis by inducing mitophagy in sheep cumulus cells

Cumulus cells surrounding oocytes furnish nutritional support crucial for oocyte maturation in vitro, and thereby enhance oocyte quality significantly. Our previous studies affirmed the role of SIRT2 in regulation of mitochondrial function in sheep granulosa cells. However, the effect of SIRT2 action on mitophagy in these cells remain unclear. Here, RNA-seq was used to scrutinize pathways where differentially expressed genes (DEGs) are enriched following SIRT2 knockdown in cumulus cells. Prior to SIRT2 knock down, cumulus cells were treated with the mitophagy inhibitor Mdivi-1. Potential mechanisms by which SIRT2 affects apoptosis via mitophagy were explored. Results indicated that DEGs after SIRT2 knockdown were enriched in various pathways including mitochondria, mitophagy, and apoptosis. The expression levels of CASP3/CASP9 were significantly increased after mitophagy activation (P < 0.01), whereas inhibition of mitophagy had no effect on apoptosis (P > 0.05). Pretreatment of cumulus cells with Mdivi-1 prior to SIRT2 knockdown significantly reduced the expression of mitophagy-related genes, the number of autolysosomes, the expression of CASP3/CASP9, and the levels of Ca2+ and cytochrome C (P < 0.05). In addition, an improvement in mitochondrial morphology and increases in ATP levels and mitochondrial DNA (mtDNA) copy numbers were observed. Interestingly, double knockdown of SIRT2 and MAPK15 was found to reverse increased mitophagy and apoptosis activity caused by SIRT2 knockdown. Our findings indicate that SIRT2 modulate apoptosis in cumulus cells by regulating mitophagy, with MAPK15 likely playing a pivotal role in this process.

Circadian Clock and Hypoxia

The timing of life on Earth is remarkable: between individuals of the same species, a highly similar temporal pattern is observed, with shared periods of activity and inactivity each day. At the individual level, this means that over the course of a single day, a person alternates between two states. They are either upright, active, and communicative or they lie down in a state of (un)consciousness called sleep where even the characteristic of neuronal signals in the brain shows distinctive properties. The circadian clock governs both of these time stamps-activity and (apparent) inactivity-making them come and go consistently at the same approximate time each day. This behavior thus represents the meeting of two pervasive systems: the circadian clock and metabolism. In this article, we will describe what is known about how the circadian clock anticipates daily changes in oxygen usage, how circadian clock regulation may relate to normal physiology, and to hypoxia and ischemia that can result from pathologies such as myocardial infarction and stroke.

The Multiple Roles of Autophagy in Neural Function and Diseases

Autophagy involves the sequestration and delivery of cytoplasmic materials to lysosomes, where proteins, lipids, and organelles are degraded and recycled. According to the way the cytoplasmic components are engulfed, autophagy can be divided into macroautophagy, microautophagy, and chaperone-mediated autophagy. Recently, many studies have found that autophagy plays an important role in neurological diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, neuronal excitotoxicity, and cerebral ischemia. Autophagy maintains cell homeostasis in the nervous system via degradation of misfolded proteins, elimination of damaged organelles, and regulation of apoptosis and inflammation. AMPK-mTOR, Beclin 1, TP53, endoplasmic reticulum stress, and other signal pathways are involved in the regulation of autophagy and can be used as potential therapeutic targets for neurological diseases. Here, we discuss the role, functions, and signal pathways of autophagy in neurological diseases, which will shed light on the pathogenic mechanisms of neurological diseases and suggest novel targets for therapies.

PA2G4/EBP1 ubiquitination by PRKN/PARKIN promotes mitophagy protecting neuron death in cerebral ischemia

Cerebral ischemia induces massive mitochondrial damage, leading to neuronal death. The elimination of damaged mitochondria via mitophagy is critical for neuroprotection. Here we show that the level of PA2G4/EBP1 (proliferation-associated 2G4) was notably increased early during transient middle cerebral artery occlusion and prevented neuronal death by eliciting cerebral ischemia-reperfusion (IR)-induced mitophagy. Neuron-specific knockout of Pa2g4 increased infarct volume and aggravated neuron loss with impaired mitophagy and was rescued by introduction of adeno-associated virus serotype 2 expressing PA2G4/EBP1. We determined that PA2G4/EBP1 is ubiquitinated on lysine 376 by PRKN/PARKIN on the damaged mitochondria and interacts with receptor protein SQSTM1/p62 for mitophagy induction. Thus, our study suggests that PA2G4/EBP1 ubiquitination following cerebral IR-injury promotes mitophagy induction, which may be implicated in neuroprotection.Abbreviations: AAV: adeno-associated virus; ACTB: actin beta; BNIP3L/NIX: BCL2 interacting protein 3 like; CA1: Cornu Ammonis 1; CASP3: caspase 3; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; DMSO: dimethyl sulfoxide; PA2G4/EBP1: proliferation-associated 2G4; FUNDC1: FUN14 domain containing 1; IB: immunoblotting; ICC: immunocytochemistry; IHC: immunohistochemistry; IP: immunoprecipitation; MCAO: middle cerebral artery occlusion; MEF: mouse embryonic fibroblast; OGD: oxygen-glucose deprivation; PRKN/PARKIN: parkin RBR E3 ubiquitin protein ligase; PINK1: PTEN induced kinase 1; RBFOX3/NeuN: RNA binding fox-1 homolog 3; SQSTM1/p62: sequestosome 1; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20: translocase of outer mitochondrial membrane 20; TUBB: tubulin beta class I; WT: wild-type.

The Hypoxia Response Pathway: A Potential Intervention Target in Parkinson's Disease?

Parkinson's disease (PD) is a progressive neurodegenerative disorder for which only symptomatic treatments are available. Both preclinical and clinical studies suggest that moderate hypoxia induces evolutionarily conserved adaptive mechanisms that enhance neuronal viability and survival. Therefore, targeting the hypoxia response pathway might provide neuroprotection by ameliorating the deleterious effects of mitochondrial dysfunction and oxidative stress, which underlie neurodegeneration in PD. Here, we review experimental studies regarding the link between PD pathophysiology and neurophysiological adaptations to hypoxia. We highlight the mechanistic differences between the rescuing effects of chronic hypoxia in neurodegeneration and short-term moderate hypoxia to improve neuronal resilience, termed "hypoxic conditioning". Moreover, we interpret these preclinical observations regarding the pharmacological targeting of the hypoxia response pathway. Finally, we discuss controversies with respect to the differential effects of hypoxia response pathway activation across the PD spectrum, as well as intervention dosing in hypoxic conditioning and potential harmful effects of such interventions. We recommend that initial clinical studies in PD should focus on the safety, physiological responses, and mechanisms of hypoxic conditioning, as well as on repurposing of existing pharmacological compounds. © 2023 International Parkinson and Movement Disorder Society.

Hypoxic postconditioning drives protective microglial responses and ameliorates white matter injury after ischemic stroke

BACKGROUND

Ischemic stroke (IS) is a cerebrovascular disease with high incidence and mortality. White matter repair plays an important role in the long-term recovery of neurological function after cerebral ischemia. Neuroprotective microglial responses can promote white matter repair and protect ischemic brain tissue.

AIMS

The aim of this study was to investigate whether hypoxic postconditioning (HPC) can promote white matter repair after IS, and the role and mechanism of microglial polarization in white matter repair after HPC treatment.

MATERIALS & METHODS

Adult male C57/BL6 mice were randomly divided into three groups: Sham group (Sham), MCAO group (MCAO), and hypoxic postconditioning group (HPC). HPC group were subjected to 45 min of transient middle cerebral artery occlusion (MCAO) immediately followed by 40 min of HPC.

RESULTS

The results showed that HPC reduced the proinflammatory level of immune cells. Furthermore, HPC promoted the transformation of microglia to anti-inflammatory phenotype on the third day after the procedure. HPC promoted the proliferation of oligodendrocyte progenitors and increased the expression of myelination-related proteins on the 14th day. On the 28th day, HPC increased the expression of mature oligodendrocytes, which enhanced myelination. At the same time, the motor neurological function of mice was restored.

DISCUSSION

During the acute phase of cerebral ischemia, the function of proinflammatory immune cells was enhanced, long-term white matter damage was aggravated, and motor sensory function was decreased.

CONCLUSION

HPC promotes protective microglial responses and white matter repair after MCAO, which may be related to the proliferation and differentiation of oligodendrocytes.

Hypoxic Preconditioning Attenuates Neuroinflammation via Inhibiting NF-κB/NLRP3 Axis Mediated by p-MLKL after Transient Global Cerebral Ischemia

Hypoxic preconditioning (HPC) has been reported to alleviate neuronal damage and microglial activation in hippocampal CA1 after transient global cerebral ischemia (tGCI). However, the molecular mechanism is unclear. Recent studies identified that nuclear factor-kappa-B (NF-κB)/oligomerization domain-like receptors protein (NLRP) 3 inflammasome pathway is mainly involved in the activation of microglia and that phosphorylated (p)-mixed lineage kinase domain-like (MLKL) is related to the regulation of NF-κB/NLRP3 axis. Hence, in this study, we set out to investigate whether HPC attenuates neuronal damage and microglial activation through inhibiting NF-κB/NLRP3 axis mediated by p-MLKL after tGCI in CA1 of male rats. We found that HPC decreased NLRP3 inflammasome in microglia and inhibited M1 polarization of microglia in CA1 after tGCI. Mechanistically, HPC inhibited the activation of NF-κB signaling pathway and reduced the mRNA and protein levels of NLRP3 inflammasome after tGCI. Additionally, the knockdown of p-MLKL by short hairpin RNA (shRNA) administration inhibited the activation of the NF-κB signaling pathway and reduced the formation of NLRP3 inflammasome, thus attenuating M1 polarization of microglia and decreasing the release of interleukin 1 beta (IL-1β) and necrosis factor alpha (TNF-α) in CA1 post ischemia. We consider that p-MLKL in microglia may be derived from necroptotic neurons after tGCI. In conclusion, the new finding in this study is that HPC-induced neuroprotection against tGCI through inhibiting NF-κB/NLRP3 pathway mediated by p-MLKL.

Neuroprotective Effect of Zishen Huoxue Decoction treatment on Vascular Dementia by activating PINK1/Parkin mediated Mitophagy in the Hippocampal CA1 Region

ETHNOPHARMACOLOGICAL RELEVANCE

Zishen Huoxue Decoction (ZSHXD) is a Traditional Chinese Medicine (TCM) prescription for the treatment of vascular dementia (VD). Although the clinical effects of ZSHXD have been demonstrated, the molecular mechanisms underlying the neuroprotective effects of ZSHXD remain unclear.

AIM OF THE STUDY

To explore whether the neuroprotective effect of Zishen Huoxue Decoction (ZSHXD) treatment is associated with the PINK1/Parkin pathway-mediated mitophagy in hippocampal CA1 region of 2-VO model rats.

MATERIALS AND METHODS

Seventy-two male SD rats were randomly divided into the sham group, model group, Donepezil (0.45 mg/kg) group, ZSHXD low dose group (8.9 g/kg), ZSHXD medium dose group (17.8 g/kg), and ZSHXD high dose group (35.6 g/kg). Two-vessel occlusion (2-VO) rat model is established to evaluate the therapeutic effect of ZSHXD pretreatment. Hematoxylin-eosin (HE) staining is conducted to detect the morphological changes of neurons and the number of normal neurons in the hippocampal CA1 region. Then, the mitochondrial function and structure were reflected by the mitochondrial membrane potential (MMP) levels and transmission electron microscopy (TEM). Meanwhile, the expression of mitophagy related proteins mediated by PINK1/Parkin was detected by western blot (WB). After that, malondialdehyde (MDA) and superoxide dismutase (SOD) levels were measured by Elisa. At last, the apoptosis-related proteins Caspase-3、Bax、Bcl-2 were measured by WB.

RESULTS

The results depict that ZSHXD has dose-dependently improved the cognitive function in 2-VO model rats. It has also been showed that ZSHXD can alleviate neuron damage, rescue the mitochondrial structural injury and dysfunction in hippocampal CA1 region. Besides, ZSHXD has increased the activity of SOD and decreased the activity of MDA. In addition, ZSHXD can inhibit apoptosis with Caspase-3, Bax decreasing and Bcl-2 increasing. Specially, the protection of ZSHXD showed in 2-VO model rats is along with the upregulation of PINK1, Parkin and LC3-Ⅱ/Ⅰ, and downregulation of p62 in the hippocampal CA1 region.

CONCLUSIONS

This study reveals that ZSHXD protects the 2-VO model rats from ischemic injury by activating the PINK1/Parkin-mediated mitophagy in the hippocampal CA1 region.

Delayed CO2 postconditioning promotes neurological recovery after cryogenic traumatic brain injury by downregulating IRF7 expression

AIMS

Few treatments are available in the subacute phase of traumatic brain injury (TBI) except rehabilitation training. We previously reported that transient CO2 inhalation applied within minutes after reperfusion has neuroprotective effects against cerebral ischemia/reperfusion injury. In this study, it was hypothesized that delayed CO2 postconditioning (DCPC) starting at the subacute phase may promote neurological recovery of TBI.

METHODS

Using a cryogenic TBI (cTBI) model, mice received DCPC daily by inhaling 5%/10%/20% CO2 for various time-courses (one/two/three cycles of 10-min inhalation/10-min break) at Days 3-7, 3-14 or 7-18 after cTBI. Beam walking and gait tests were used to assess the effect of DCPC. Lesion size, expression of GAP-43 and synaptophysin, amoeboid microglia number and glia scar area were detected. Transcriptome and recombinant interferon regulatory factor 7 (Irf7) adeno-associated virus were applied to investigate the molecular mechanisms.

RESULTS

DCPC significantly promoted recovery of motor function in a concentration and time-course dependent manner with a wide therapeutic time window of at least 7 days after cTBI. The beneficial effects of DCPC were blocked by intracerebroventricular injection of NaHCO3 . DCPC also increased puncta density of GAP-43 and synaptophysin, and reduced amoeboid microglia number and glial scar formation in the cortex surrounding the lesion. Transcriptome analysis showed many inflammation-related genes and pathways were altered by DCPC, and Irf7 was a hub gene, while overexpression of IRF7 blocked the motor function improvement of DCPC.

CONCLUSIONS

We first showed that DCPC promoted functional recovery and brain tissue repair, which opens a new therapeutic time window of postconditioning for TBI. Inhibition of IRF7 is a key molecular mechanism for the beneficial effects of DCPC, and IRF7 may be a potential therapeutic target for rehabilitation after TBI.

Neuron-secreted NLGN3 ameliorates ischemic brain injury via activating Gαi1/3-Akt signaling

We here tested the potential activity and the underlying mechanisms of neuroligin-3 (NLGN3) against ischemia-reperfusion-induced neuronal cell injury. In SH-SY5Y neuronal cells and primary murine cortical neurons, NLGN3 activated Akt-mTOR and Erk signalings, and inhibited oxygen and glucose deprivation (OGD)/re-oxygenation (OGD/R)-induced cytotoxicity. Akt activation was required for NLGN3-induced neuroprotection. Gαi1/3 mediated NLGN3-induced downstream signaling activation. NLGN3-induced Akt-S6K1 activation was largely inhibited by Gαi1/3 silencing or knockout. Significantly, NLGN3-induced neuroprotection against OGD/R was almost abolished by Gαi1/3 silencing or knockout. In vivo, the middle cerebral artery occlusion (MCAO) procedure induced NLGN3 cleavage and secretion, and increased its expression and Akt activation in mouse brain tissues. ADAM10 (A Disintegrin and Metalloproteinase 10) inhibition blocked MCAO-induced NLGN3 cleavage and secretion, exacerbating ischemic brain injury in mice. Neuronal silencing of NLGN3 or Gαi1/3 in mice also inhibited Akt activation and intensified MCAO-induced ischemic brain injury. Conversely, neuronal overexpression of NLGN3 increased Akt activation and alleviated MCAO-induced ischemic brain injury. Together, NLGN3 activates Gαi1/3-Akt signaling to protect neuronal cells from ischemia-reperfusion injury.

Parkin-mediated mitophagy protects against aluminum trichloride-induced hippocampal apoptosis in mice via the mtROS-NLRP3 pathway

Aluminum is a neurotoxic food contaminant. Aluminum trichloride (AlCl3) causes hippocampal mitochondrial damage, leading to hippocampal injury. Damaged mitochondria can release mitochondrial reactive oxygen species (mtROS) and activate nucleotide-binding oligomerization domain-like receptor-containing 3 (NLRP3) inflammasomes and apoptosis. E3 ubiquitin ligase PARK2 (Parkin)-mediated mitophagy can attenuate mitochondrial damage. However, the role of mitophagy in AlCl3-induced mice hippocampal damage and its regulatory mechanism remain elusive. First, C57BL/6 N mice were treated with 0, 44.825, 89.65, and 179.3 mg/kg body weight AlCl3 drinking water for 90 d. Apoptosis, NLRP3-inflammasome activation and mitochondrial damage were increased in AlCl3-induced hippocampal damage. In addition, Parkin-mediated mitophagy peaked in the middle-dose group and was slightly attenuated in the high-dose group. Subsequently, we used wild-type and Parkin knockout (Parkin-/-) mice to investigate the AlCl3-induced hippocampal damage. The results showed that Parkin-/- inhibited mitophagy, and aggravated AlCl3-induced mitochondrial damage, NLRP3-inflammasome activation, apoptosis and hippocampal damage. Finally, we administered MitoQ (mtROS inhibitor) and MCC950 (NLRP3 inhibitor) to AlCl3-treated Parkin-/- mice to investigate the mechanism of Parkin-mediated mitophagy. The results showed that inhibition of mtROS and NLRP3 attenuated hippocampal NLRP3-inflammasome activation, apoptosis, and damage in AlCl3-treated Parkin-/- mice. These findings indicate that Parkin-mediated mitophagy protects against AlCl3-induced hippocampal apoptosis in mice via the mtROS-NLRP3 pathway.

Targeting neuronal mitophagy in ischemic stroke: an update

Cerebral ischemia is a neurological disorder associated with complex pathological mechanisms, including autophagic degradation of neuronal mitochondria, or termed mitophagy, following ischemic events. Despite being well-documented, the cellular and molecular mechanisms underlying the regulation of neuronal mitophagy remain unknown. So far, the evidence suggests neuronal autophagy and mitophagy are separately regulated in ischemic neurons, the latter being more likely activated by reperfusional injury. Specifically, given the polarized morphology of neurons, mitophagy is regulated by different neuronal compartments, with axonal mitochondria being degraded by autophagy in the cell body following ischemia-reperfusion insult. A variety of molecules have been associated with neuronal adaptation to ischemia, including PTEN-induced kinase 1, Parkin, BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (Bnip3), Bnip3-like (Bnip3l) and FUN14 domain-containing 1. Moreover, it is still controversial whether mitophagy protects against or instead aggravates ischemic brain injury. Here, we review recent studies on this topic and provide an updated overview of the role and regulation of mitophagy during ischemic events.

Hypoxic postconditioning restores mitophagy against transient global cerebral ischemia via Parkin-induced posttranslational modification of TBK1

Hypoxic postconditioning (HPC) has been reported to enhance Parkin-catalyzed mitochondrial ubiquitination to restore mitophagy in hippocampal CA1 against transient global cerebral ischemia (tGCI). However, the molecular mechanism leading ubiquitinated mitochondria to final clearance during HPC-mediated mitophagy after tGCI is unclear. This study aims to investigate whether HPC restores mitophagy after tGCI through Parkin-induced K63-linked poly-ubiquitination (K63-Ub) to activate tumor necrosis factor associated factor family member associated nuclear factor κB activator -binding kinase 1 (TBK1) in CA1 of male rats. We found that HPC maintained TBK1 expression, promoted p62 and TBK1 phosphorylation in mitochondria, and enhanced their recruitments to mitochondria in CA1 after tGCI. However, these effects were partially abolished by TBK1 inhibitor BX795. K63-Ub of mitochondrial TBK1 was disturbed at 26 h of reperfusion after tGCI, which was reversed by HPC. The maintenance of K63-Ub of mitochondrial TBK1 induced by HPC was counteracted under Parkin knockdown with AAV-mediated Prkn small-interfering RNA, accompanied by the suppression on TBK1 activation and the reduction of mitochondrial p62 phosphorylation. This innovative study indicated that HPC maintained K63-Ub of TBK1 in a Parkin-dependent manner to promote TBK1 phosphorylation, and then phosphorylated TBK1 activated p62 to restore mitophagy, thereby alleviating neuronal damage in CA1 after tGCI.

Stabilization of nuclear β-catenin by inhibiting KDM2A mediates cerebral ischemic tolerance

Hypoxic postconditioning (HPC) with 8% oxygen increases nuclear accumulation of β-catenin through activating the classical Wnt pathway, thereby alleviating transient global cerebral ischemia (tGCI)-induced neuronal damage in the hippocampal CA1 subregion of adult rats. However, little is understood about the regulatory mechanism of nuclear β-catenin in HPC-mediated cerebral ischemic tolerance. Although lysine(K)-specific demethylase 2A (KDM2A) has been known as a crucial regulator of nuclear β-catenin destabilization, whether it plays an important role through modulating nuclear β-catenin in cerebral ischemic tolerance induced by HPC remains unknown. In this study, we explored the molecular mechanism of stabilizing nuclear β-catenin by inhibiting KDM2A-mediated demethylation in the HPC-offered neuroprotection against tGCI. In addition, we confirmed that nuclear methylated-β-catenin in CA1 decreased and nuclear β-catenin turnover increased after tGCI, which were reversed by HPC. The administration with methyltransferase inhibitor AdOx abrogated HPC-induced methylation and stabilization of nuclear β-catenin in CA1, as well as the neuroprotection against tGCI. Notably, HPC downregulated the expression of KDM2A in CA1 and reduced the interaction between KDM2A and β-catenin in the nucleus after tGCI. The knockdown of KDM2A with small-interfering RNA could upregulate nuclear methylated-β-catenin and stabilize β-catenin, thereby increasing survivin in CA1 and improving the cognitive function of rats after tGCI. Opposite results were observed by the administration of KDM2A-carried adenovirus vector. Furthermore, we demonstrated that KDM2A mediates the demethylation of nuclear β-catenin through jumonji C (JmjC) domain of KDM2A in HEK-293T and SH-SY5Y cells. Our data support that the inhibition of KDM2A-mediated demethylation of nuclear β-catenin contributes to HPC-induced neuroprotection against tGCI.

Mitofusin-2 mediates cannabidiol-induced neuroprotection against cerebral ischemia in rats

Cannabidiol (CBD) reportedly exerts protective effects against many psychiatric disorders and neurodegenerative diseases, but the mechanisms are poorly understood. In this study, we explored the molecular mechanism of CBD against cerebral ischemia. HT-22 cells or primary cortical neurons were subjected to oxygen-glucose deprivation insult followed by reoxygenation (OGD/R). In both HT-22 cells and primary cortical neurons, CBD pretreatment (0.1, 0.3, 1 μM) dose-dependently attenuated OGD/R-induced cell death and mitochondrial dysfunction, ameliorated OGD/R-induced endoplasmic reticulum (ER) stress, and increased the mitofusin-2 (MFN2) protein level in HT-22 cells and primary cortical neurons. Knockdown of MFN2 abolished the protective effects of CBD. CBD pretreatment also suppressed OGD/R-induced binding of Parkin to MFN2 and subsequent ubiquitination of MFN2. Overexpression of Parkin blocked the effects of CBD in reducing MFN2 ubiquitination and reduced cell viability, whereas overexpressing MFN2 abolished Parkin's detrimental effects. In vivo experiments were conducted on male rats subjected to middle cerebral artery occlusion (MCAO) insult, and administration of CBD (2.5, 5 mg · kg-1, i.p.) dose-dependently reduced the infarct volume and ER stress in the brains. Moreover, the level of MFN2 within the ischemic penumbra of rats was increased by CBD treatment, while the binding of Parkin to MFN2 and the ubiquitination of MFN2 was decreased. Finally, short hairpin RNA against MFN2 reversed CBD's protective effects. Together, these results demonstrate that CBD protects brain neurons against cerebral ischemia by reducing MFN2 degradation via disrupting Parkin's binding to MFN2, indicating that MFN2 is a potential target for the treatment of cerebral ischemia.

P‑hydroxybenzyl alcohol ameliorates neuronal cerebral ischemia‑reperfusion injury by activating mitochondrial autophagy through SIRT1

Mitochondrial autophagy serves a key role in clearing damaged mitochondria. P‑hydroxybenzyl alcohol (pHBA) can improve neuronal injury induced by cerebral ischemia‑reperfusion (I/R). However, the mechanism of pHBA improving I/R damage through the mitochondrial pathway remains unclear. A rat model of middle cerebral artery occlusion and reperfusion (MCAO/R) was used in the present study. The rats were treated with sirtuin 1 (SIRT1) inhibitor EX527 and pHBA for 7 days, followed by reperfusion. At 24 h after reperfusion, the infarct size was calculated and the severity of nerve damage was evaluated. Hematoxylin and eosin and Nissl staining revealed cellular changes in the ischemic penumbra. Changes in mitochondrial structure were observed using electron microscopy. Mitochondrial function was evaluated by detecting mitochondrial membrane potential (MMP), mitochondrial permeability transition pore (mPTP) and ATP levels using commercially available kits. In addition, the ischemic penumbra tissues were used for immunofluorescence staining for p62 and LC3 proteins. The expression of SIRT1 and mitochondrial autophagy‑related proteins, PTEN‑induced kinase 1 (PINK1) and Parkin, were detected by western blotting. Finally, apoptosis was analyzed by TUNEL staining and the expression of apoptosis‑related proteins (Bax, Bcl‑2 and Caspase‑3) by western blotting. The results suggested that postoperative pHBA treatment may reduce the size of cerebral infarction and damage to the nervous system, and may improve cell damage in the ischemic penumbra of MCAO/R rats. Compared with rats in the untreated MCAO/R group, the mitochondrial structure of the pHBA‑treated group was improved, the levels of MMP and ATP were increased, and the degree of opening of mPTP was decreased. Simultaneously, immunofluorescence and western blotting results showed that compared with the MCAO/R group, the number of LC3‑ and TUNEL‑positive cells increased, the number of p62‑positive cells decreased, SIRT1 and autophagy protein (PINK1, Parkin and LC3 II/I) expression levels increased and p62 expression decreased in the pHBA group. However, these improvements were blocked by treatment with EX527. In summary, results from the present study suggested that pHBA may improve neuronal injury in the ischemic penumbra of MCAO/R rats through SIRT1‑activated mitochondrial autophagy and mitochondrial‑mediated neuronal apoptosis.

Apelin-13 facilitates mitochondria homeostasis via mitophagy to prevent against airway oxidative injury in asthma

Oxidative stress is a major mediator in the pathogenesis of allergens-induced asthma. Mitochondria damage and dysfunction is considered to be closely related with oxidative stress. Apelin-13 is a novel multifunctional protein with anti-inflammatory and anti-oxidative properties in neuroinflammation and ischemia-reperfusion injury. However, its role in mitochondria homeostasis under asthma-associated airway oxidative injury and the potential mechanisms have not been elucidated. A murine model of asthma was established by house dust mite (HDM) allergen sensitization and challenge. The mice were received Apelin-13 protein through intraperitoneal administration before HDM challenge. Airway inflammation, histopathological changes and oxidative stress were examined. The regulatory effects of Apelin-13 on mitochondria function were evaluated using airway epithelial BEAS-2B cells, including mitochondria membrane potential (MMP), mitophagy and the possible signaling pathway. The HDM-challenged mice group exhibited robust inflammation and apoptosis in airway epithelium compared to the control group. The airway impairment in asthmatic mice was partly lessened after Apelin-13 administration. Meanwhile, protein expressions of mitophagy-related markers PINK1, Parkin, Tomm20 and LC3 were significantly increased in the lungs of Apelin-13-treated asthmatic mice. In vitro, Apelin-13 treatment significantly improved MMP levels and reduced ROS production in BEAS-2B cells exposed to HDM, accompanied with the increase of cell viability. Furthermore, Apelin-13 was found to promote the activation of PINK1/Parkin signaling in BEAS-2B cells, thereby increasing mitophagy activity and facilitating mitochondria homeostasis. These results demonstrate that Apelin-13 acts as a regulator of mitochondria homeostasis by driving mitophagy to protect against HDM allergen-induced airway oxidative injury. Apelin-13 may serve as a promising protective agent for treating asthma.

The inhibition of PGAM5 suppresses seizures in a kainate-induced epilepsy model via mitophagy reduction

Background

Epilepsy is a common neurological disease, and excessive mitophagy is considered as one of the major triggers of epilepsy. Mitophagy is a crucial pathway affecting reactive oxygen species. Phosphoglycerate mutase 5 (PGAM5) is a protein phosphatase present in mitochondria that regulates many biological processes including mitophagy and cell death. However, the mechanism of PGAM5 in epilepsy remains unclear. The purpose of the present study was to examine whether PGAM5 affects epilepsy through PTEN-induced putative kinase 1 (PINK1)-mediated mitophagy.

Methods

After the knockdown of PGAM5 expression by the adeno-associated virus, an epilepsy model was created by kainic acid. Next, the seizure activity was recorded by local field potentials before evaluating the level of mitochondrial autophagy marker proteins. Lastly, the ultrastructure of mitochondria, neuronal damage and oxidative stress levels were further observed.

Results

A higher PGAM5 level was found in epilepsy, and its cellular localization was in neurons. The interactions between PGAM5 and PINK1 in epilepsy were further found. After the knockdown of PGAM5, the level of PINK1 and light chain 3B was decreased and the expression of the translocase of the inner mitochondrial membrane 23 and translocase of the outer mitochondrial membrane 20 were both increased. Knockdown of PGAM5 also resulted in reduced neuronal damage, decreased malondialdehyde levels, decreased reactive oxygen species production and increased superoxide dismutase activity. In addition, the duration of spontaneous seizure-like events (SLEs), the number of SLEs and the time spent in SLEs were all reduced in the epilepsy model after inhibition of PGAM5 expression.

Conclusion

Inhibition of PGAM5 expression reduces seizures via inhibiting PINK1-mediated mitophagy.

RhoA signaling increases mitophagy and protects cardiomyocytes against ischemia by stabilizing PINK1 protein and recruiting Parkin to mitochondria

Mitophagy, a mitochondria-specific form of autophagy, removes dysfunctional mitochondria and is hence an essential process contributing to mitochondrial quality control. PTEN-induced kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin are critical molecules involved in stress-induced mitophagy, but the intracellular signaling mechanisms by which this pathway is regulated are unclear. We tested the hypothesis that signaling through RhoA, a small GTPase, induces mitophagy via modulation of the PINK1/Parkin pathway as a protective mechanism against ischemic stress. We demonstrate that expression of constitutively active RhoA as well as sphingosine-1-phosphate induced activation of endogenous RhoA in cardiomyocytes result in an accumulation of PINK1 at mitochondria. This is accompanied by translocation of Parkin to mitochondria and ubiquitination of mitochondrial proteins leading to recognition of mitochondria by autophagosomes and their lysosomal degradation. Expression of RhoA in cardiomyocytes confers protection against ischemia, and this cardioprotection is attenuated by siRNA-mediated PINK1 knockdown. In vivo myocardial infarction elicits increases in mitochondrial PINK1, Parkin, and ubiquitinated mitochondrial proteins. AAV9-mediated RhoA expression potentiates these responses and a concurrent decrease in infarct size is observed. Interestingly, induction of mitochondrial PINK1 accumulation in response to RhoA signaling is neither mediated through its transcriptional upregulation nor dependent on depolarization of the mitochondrial membrane, the canonical mechanism for PINK1 accumulation. Instead, our results reveal that RhoA signaling inhibits PINK1 cleavage, thereby stabilizing PINK1 protein at mitochondria. We further show that active RhoA localizes at mitochondria and interacts with PINK1, and that the mitochondrial localization of RhoA is regulated by its downstream effector protein kinase D. These findings demonstrate that RhoA activation engages a unique mechanism to regulate PINK1 accumulation, induce mitophagy and protect against ischemic stress, and implicates regulation of RhoA signaling as a potential strategy to enhance mitophagy and confer protection under stress conditions.

LncRNA-Profile-Based Screening of Extracellular Vesicles Released from Brain Endothelial Cells after Oxygen–Glucose Deprivation

Brain microvascular endothelial cells (BMECs) linked by tight junctions play important roles in cerebral ischemia. Intercellular signaling via extracellular vesicles (EVs) is an underappreciated mode of cell–cell crosstalk. This study aims to explore the potential function of long noncoding RNAs (lncRNAs) in BMECs’ secreted EVs. We subjected primary human and rat BMECs to oxygen and glucose deprivation (OGD). EVs were enriched for RNA sequencing. A comparison of the sequencing results revealed 146 upregulated lncRNAs and 331 downregulated lncRNAs in human cells and 1215 upregulated lncRNAs and 1200 downregulated lncRNAs in rat cells. Next, we analyzed the genes that were coexpressed with the differentially expressed (DE) lncRNAs on chromosomes and performed Gene Ontology (GO) and signaling pathway enrichment analyses. The results showed that the lncRNAs may play roles in apoptosis, the TNF signaling pathway, and leukocyte transendothelial migration. Next, three conserved lncRNAs between humans and rats were analyzed and confirmed using PCR. The binding proteins of these three lncRNAs in human astrocytes were identified via RNA pulldown and mass spectrometry. These proteins could regulate mRNA stability and translation. Additionally, the lentivirus was used to upregulate them in human microglial HMC3 cells. The results showed NR_002323.2 induced microglial M1 activation. Therefore, these results suggest that BMECs’ EVs carry the lncRNAs, which may regulate gliocyte function after cerebral ischemia.

Ligustilide ameliorates hippocampal neuronal injury after cerebral ischemia reperfusion through activating PINK1/Parkin-dependent mitophagy

BACKGROUND

Mitophagy plays a critical role in cerebral ischemia/reperfusion by timely removal of dysfunctional mitochondria. In mammals, PINK1/Parkin is the most classic pathway mediating mitophagy. And the activation of PINK1/Parkin mediated mitophagy exerts neuroprotective effects during cerebral ischemia reperfusion injury (CIRI). Ligustilide (LIG) is a natural compound extracted from ligusticum chuanxiong hort and angelica sinensis (Oliv.) diels that exerts neuroprotective activity after cerebral ischemia reperfusion injury (CIRI). However, it still remains unclear whether LIG could attenuates cerebral ischemia reperfusion injury (CIRI) through regulating mitophagy mediated by PINK1/Parkin.

PURPOSE

To explore the underlying mechanism of LIG on PINK1/Parkin mediated mitophagy in the hippocampus induced by ischemia reperfusion.

METHODS

This research used the middle cerebral artery occlusion and reperfusion (MCAO/R) animal model and oxygen-glucose deprivation and reperfusion (OGD/R) as in vitro model. Neurological behavior score, 2, 3, 5-triphenyl tetrazolium chloride (TTC) staining and Hematoxylin and Eosin (HE) Staining were used to detect the neuroprotection of LIG in MCAO/R rats. Also, the levels of ROS, mitochondrial membrane potential (MMP) and activities of Na⁺-K⁺-ATPase were detected to reflect mitochondrial function. Moreover, transmission electron microscope (TEM) and fluorescence microscope were used to observe mitophagy and the western blot was performed to explore the changes in protein expression in PINK1/Parkin mediated mitophagy. Finally, exact mechanism between neuroprotection of LIG and mitophagy mediated by PINK1/Parkin was explored by cell transfection.

RESULTS

The results show that LIG improved mitochondrial functions by mitophagy enhancement in vivo and vitro to alleviate CIRI. Whereas, mitophagy enhanced by LIG under CIRI is abolished by PINK1 deficiency and midivi-1, a mitochondrial division inhibitor which has been reported to have the function of mitophagy, which could further aggravate the ischemia-induced brain damage, mitochondrial dysfunction and neuronal injury.

CONCLUSION

LIG could ameliorate the neuronal injury against ischemia stroke by promoting mitophagy via PINK1/Parkin. Targeting PINK1/Parkin mediated mitophagy with LIG treatment might be a promising therapeutic strategy for ischemia stroke.

Dengzhan Xixin injection derived from a traditional Chinese herb Erigeron breviscapus ameliorates cerebral ischemia/reperfusion injury in rats via modulation of mitophagy and mitochondrial apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Dengzhan Xixin injection (DX), a preparation of extracts from traditional Chinese medicine Erigeron breviscapus (Vaniot) Hand.-Mazz., has been widely used in clinical treatment of cerebral ischemia sequelae in China for a long history. However, its underlying mechanisms remain unclear.

AIM OF THE STUDY

The objective of this present study aimed to investigate the therapeutic effects of DX on cerebral ischemia/reperfusion (I/R) injury in a rat model. Meanwhile, its underlying molecular mechanisms on mitochondrial protection were further interpreted.

MATERIALS AND METHODS

The major components of DX were detected by high-performance liquid chromatography analysis. The model of cerebral I/R injury was established by middle cerebral artery occlusion (MCAO) in SD rats. We firstly performed neurobehavioral score, the regional cerebral blood flow (rCBF) assay, and TTC, HE and Nissl staining for evaluating the effects of DX on I/R injury. And then, the cortical levels of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), adenosine triphosphate (ATP) and mitochondrial membrane potential (MMP) were determined by commercial kits. Whereafter, real time-PCR and transmission electron microscopy were employed to investigate the relative copy number of mitochondrial DNA (mtDNA) and neuronal ultrastructure changes, respectively. Further, the potential interactions of major components in DX with mitophagy/apoptosis-related proteins were predicted by Schrodinger molecular docking. The expression of mitophagy-related proteins LC3, p62, TOM20, PINK1 and Parkin was estimated by western blot and immunofluorescence analyses. Furthermore, TUNEL staining and western blot were used to detect the apoptotic phenomenon and the protein expression of Bax, Bcl-2, Cytochrome c (Cyto-c) and cleaved Caspase-3.

RESULTS

DX mainly contains scutellarin, 3,4-O-dicaffeoylquinic acid, 3,5-O-dicaffeoylquinic acid, 4,5-O-dicaffeoylquinic acid, caffeic acid and 5-O-caffeoylquinic acid. Compared with the model group, DX could remarkably relieve ischemia-provoked neurological deficit, rCBF deficiency and cerebral infarction. Pathological changes and neuronal loss in a MCAO model of rats were memorably ameliorated by DX administration. Meanwhile, DX reduced the surged ROS and MDA, while increased the level of SOD. Notably, DX treatment conversed the collapse of ATP and MMP, along with decreased in the relative copy number of mtDNA, contributing to the maintaining of mitochondrial ultrastructure via the increased number of autophagy lysosomes. The representative ingredients in DX had a potential bind with the active sites of mitophagy/apoptosis-related proteins. DX stimulated the protein expression of LC3, PINK1 and Parkin, while reduced the levels of p62 and TOM20. In addition, DX confined TUNEL-positive cell rate with the decreased expressions of Bax, Cyto-c and cleaved Caspase-3 as well as the increased Bcl-2 level.

CONCLUSIONS

We demonstrated that the protection of DX against brain ischemia could attribute to alleviating mitochondrial damage by upregulating mitophagy and inhibiting mitochondria-mediated apoptosis.

Induction of Mitochondrial Fragmentation and Mitophagy after Neonatal Hypoxia-Ischemia

Hypoxia-ischemia (HI) leads to immature brain injury mediated by mitochondrial stress. If damaged mitochondria cannot be repaired, mitochondrial permeabilization ensues, leading to cell death. Non-optimal turnover of mitochondria is critical as it affects short and long term structural and functional recovery and brain development. Therefore, disposal of deficient mitochondria via mitophagy and their replacement through biogenesis is needed. We utilized mt-Keima reporter mice to quantify mitochondrial morphology (fission, fusion) and mitophagy and their mechanisms in primary neurons after Oxygen Glucose Deprivation (OGD) and in brain sections after neonatal HI. Molecular mechanisms of PARK2-dependent and -independent pathways of mitophagy were investigated in vivo by PCR and Western blotting. Mitochondrial morphology and mitophagy were investigated using live cell microscopy. In primary neurons, we found a primary fission wave immediately after OGD with a significant increase in mitophagy followed by a secondary phase of fission at 24 h following recovery. Following HI, mitophagy was upregulated immediately after HI followed by a second wave at 7 days. Western blotting suggests that both PINK1/Parkin-dependent and -independent mechanisms, including NIX and FUNDC1, were upregulated immediately after HI, whereas a PINK1/Parkin mechanism predominated 7 days after HI. We hypothesize that excessive mitophagy in the early phase is a pathologic response which may contribute to secondary energy depletion, whereas secondary mitophagy may be involved in post-HI regeneration and repair.

Mitochondrial Quality Control in Cardiac-Conditioning Strategies against Ischemia-Reperfusion Injury

Mitochondria are the central target of ischemic preconditioning and postconditioning cardioprotective strategies, which consist of either the application of brief intermittent ischemia/reperfusion (I/R) cycles or the administration of pharmacological agents. Such strategies reduce cardiac I/R injury by activating protective signaling pathways that prevent the exacerbated production of reactive oxygen/nitrogen species, inhibit opening of mitochondrial permeability transition pore and reduce apoptosis, maintaining normal mitochondrial function. Cardioprotection also involves the activation of mitochondrial quality control (MQC) processes, which replace defective mitochondria or eliminate mitochondrial debris, preserving the structure and function of the network of these organelles, and consequently ensuring homeostasis and survival of cardiomyocytes. Such processes include mitochondrial biogenesis, fission, fusion, mitophagy and mitochondrial-controlled cell death. This review updates recent advances in MQC mechanisms that are activated in the protection conferred by different cardiac conditioning interventions. Furthermore, the role of extracellular vesicles in mitochondrial protection and turnover of these organelles will be discussed. It is concluded that modulation of MQC mechanisms and recognition of mitochondrial targets could provide a potential and selective therapeutic approach for I/R-induced mitochondrial dysfunction.