Methylene Blue Reduces Acute Cerebral Ischemic Injury via the Induction of Mitophagy

Methylene blue and its potential in the treatment of traumatic brain injury, brain ischemia, and Alzheimer's disease

Traumatic brain injury (TBI) and brain ischemia/reperfusion cause neurodegenerative processes that can continue after the acute stage with the development of severe brain atrophy with dementia. In this case, the long-term neurodegeneration of the brain is similar to the neurodegeneration characteristic of Alzheimer's disease (AD) and is associated with the accumulation of beta amyloid and tau protein. In the pathogenesis of AD as well as in the pathogenesis of cerebral ischemia and TBI oxidative stress, progressive inflammation, glial activation, blood-brain barrier dysfunction, and excessive activation of autophagy are involved, which implies the presence of many targets that can be affected by neuroprotectors. That is, multivariate cascades of nerve tissue damage represent many potential targets for therapeutic interventions. One of such substances that can be used in multi-purpose therapeutic strategies is methylene blue (MB). This drug can have an antiapoptotic and anti-inflammatory effect, activate autophagy, inhibit the aggregation of proteins with an irregular shape, inhibit NO synthase, and bypass impaired electron transfer in the respiratory chain of mitochondria. MB is a well-described treatment for methemoglobinemia, malaria, and encephalopathy caused by ifosfamide. In recent years, this drug has attracted great interest as a potential treatment for a number of neurodegenerative disorders, including the effects of TBI, ischemia, and AD.

Targeting mitophagy for neurological disorders treatment: advances in drugs and non-drug approaches

Mitochondria serve as a vital energy source for nerve cells. The mitochondrial network also acts as a defense mechanism against external stressors that can threaten the stability of the nervous system. However, excessive accumulation of damaged mitochondria can lead to neuronal death. Mitophagy is an essential pathway in the mitochondrial quality control system and can protect neurons by selectively removing damaged mitochondria. In most neurological disorders, dysfunctional mitochondria are a common feature, and drugs that target mitophagy can improve symptoms. Here, we reviewed the role of mitophagy in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, stroke, and traumatic brain injuries. We also summarized drug and non-drug approaches to promote mitophagy and described their therapeutic role in neurological disorders in order to provide valuable insight into the potential therapeutic agents available for neurological disease treatment. However, most studies on mitophagy regulation are based on preclinical research using cell and animal models, which may not accurately reflect the effects in humans. This poses a challenge to the clinical application of drugs targeting mitophagy. Additionally, these drugs may carry the risk of intolerable side effects and toxicity. Future research should focus on the development of safer and more targeted drugs for mitophagy.

Signaling pathways in brain ischemia: Mechanisms and therapeutic implications

Ischemic stroke occurs when the arteries supplying blood to the brain are narrowed or blocked, inducing damage to brain tissue due to a lack of blood supply. One effective way to reduce brain damage and alleviate symptoms is to reopen blocked blood vessels in a timely manner and reduce neuronal damage. To achieve this, researchers have focused on identifying key cellular signaling pathways that can be targeted with drugs. These pathways include oxidative/nitrosative stress, excitatory amino acids and their receptors, inflammatory signaling molecules, metabolic pathways, ion channels, and other molecular events involved in stroke pathology. However, evidence suggests that solely focusing on protecting neurons may not yield satisfactory clinical results. Instead, researchers should consider the multifactorial and complex mechanisms underlying stroke pathology, including the interactions between different components of the neurovascular unit. Such an approach is more representative of the actual pathological process observed in clinical settings. This review summarizes recent research on the multiple molecular mechanisms and drug targets in ischemic stroke, as well as recent advances in novel therapeutic strategies. Finally, we discuss the challenges and future prospects of new strategies based on the biological characteristics of stroke.

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.

Yap1-Usp14 Axis Inhibits Neuronal Mitophagy During Neonatal Hypoxia-Ischemia Encephalopathy by Regulation of Beclin-1 Ubiquitination in Mouse

Neonatal hypoxic-ischemic encephalopathy (HIE) that results from perinatal cerebral hypoxia-ischemia has become one of the leading causes of acute mortality and chronic disability in infants and children. Despite that neuronal mitophagy and subsequent clearance of damaged neurons exert protective effect, the pathogenesis of HIE and effective treatment strategies for intervention of HIE remain poorly understood. Here, we report that ubiquitin-specific protease 14 (Usp14, a deubiquitinating enzyme) is closely associated with HIE progression by its negative regulation in neuronal mitophagy in mouse. The expression of Usp14 is elevated in both an oxygen-glucose deprivation (OGD) mouse neuronal cell line culture model in vitro and a HIE mouse model in vivo. Mechanistically, OGD treatment activates Hippo signaling that enhances Yap1 phosphorylation levels at Ser-127 but inhibits Yap1 protein level, which potentiates Usp14 transcription and leads to the downregulated ubiquitination at Lys-63 of Beclin-1, a key molecule in autophagy, resulting in the suppressed neuronal mitophagy, subsequent failure in the clearance of damaged neurons, and finally possible dysregulation in brain functions. Thus, our results provide with Usp14 as a novel target and treatment strategy for intervention of HIE, which may help diagnose and treat HIE in clinic.

Transcutaneous Electrical Nerve Stimulation (TENS) Alleviates Brain Ischemic Injury by Regulating Neuronal Oxidative Stress, Pyroptosis, and Mitophagy

Background

As a noninvasive treatment, transcutaneous electrical nerve stimulation (TENS) has been utilized to treat various diseases in clinic. However, whether TENS can be an effective intervention in the acute stage of ischemic stroke still remains unclear. In the present study, we aimed to explore whether TENS could alleviate brain infarct volume, reduce oxidative stress and neuronal pyroptosis, and activate mitophagy following ischemic stroke.

Methods

TENS was performed at 24 h after middle cerebral artery occlusion/reperfusion (MCAO/R) in rats for 3 consecutive days. Neurological scores, the volume of infarction, and the activity of SOD, MDA, GSH, and GSH-px were measured. Moreover, western blot was performed to detect the related protein expression, including Bcl-2, Bax, TXNIP, GSDMD, caspase-1, NLRP3, BRCC3, HIF-1α, BNIP3, LC3, and P62. Real-time PCR was performed to detect NLRP3 expression. Immunofluorescence was performed to detect the levels of LC3.

Results

There was no significant difference of neurological deficit scores between the MCAO group and the TENS group at 2 h after MCAO/R operation (P > 0.05), while the neurological deficit scores of TENS group significantly decreased in comparison with MCAO group at 72 h following MACO/R injury (P < 0.05). Similarly, TENS treatment significantly reduced the brain infarct volume compared with the MCAO group (P < 0.05). Moreover, TENS decreased the expression of Bax, TXNIP, GSDMD, caspase-1, BRCC3, NLRP3, and P62 and the activity of MDA as well as increasing the level of Bcl-2, HIF-1α, BNIP3, and LC3 and the activity of SOD, GSH, and GSH-px (P < 0.05).

Conclusions

In conclusion, our results indicated that TENS alleviated brain damage following ischemic stroke via inhibiting neuronal oxidative stress and pyroptosis and activating mitophagy, possibly via the regulation of TXNIP, BRCC3/NLRP3, and HIF-1α/BNIP3 pathways.

Autophagy regulates inflammation in intracerebral hemorrhage: Enemy or friend?

Intracerebral hemorrhage (ICH) is the second-largest stroke subtype and has a high mortality and disability rate. Secondary brain injury (SBI) is delayed after ICH. The main contributors to SBI are inflammation, oxidative stress, and excitotoxicity. Harmful substances from blood and hemolysis, such as hemoglobin, thrombin, and iron, induce SBI. When cells suffer stress, a critical protective mechanism called "autophagy" help to maintain the homeostasis of damaged cells, remove harmful substances or damaged organelles, and recycle them. Autophagy plays a critical role in the pathology of ICH, and its function remains controversial. Several lines of evidence demonstrate a pro-survival role for autophagy in ICH by facilitating the removal of damaged proteins and organelles. However, many studies have found that heme and iron can aggravate SBI by enhancing autophagy. Autophagy and inflammation are essential culprits in the progression of brain injury. It is a fascinating hypothesis that autophagy regulates inflammation in ICH-induced SBI. Autophagy could degrade and clear pro-IL-1β and apoptosis-associated speck-like protein containing a CARD (ASC) to antagonize NLRP3-mediated inflammation. In addition, mitophagy can remove endogenous activators of inflammasomes, such as reactive oxygen species (ROS), inflammatory components, and cytokines, in damaged mitochondria. However, many studies support the idea that autophagy activates microglia and aggravates microglial inflammation via the toll-like receptor 4 (TLR4) pathway. In addition, autophagy can promote ICH-induced SBI through inflammasome-dependent NLRP6-mediated inflammation. Moreover, some resident cells in the brain are involved in autophagy in regulating inflammation after ICH. Some compounds or therapeutic targets that regulate inflammation by autophagy may represent promising candidates for the treatment of ICH-induced SBI. In conclusion, the mutual regulation of autophagy and inflammation in ICH is worth exploring. The control of inflammation by autophagy will hopefully prove to be an essential treatment target for ICH.

The Therapeutic Potential of Mitochondria Transplantation Therapy in Neurodegenerative and Neurovascular Disorders

Neurodegenerative and neurovascular disorders affect millions of people worldwide and account for a large and increasing health burden on the general population. Thus, there is a critical need to identify potential disease-modifying treatments that can prevent or slow the disease progression. Mitochondria are highly dynamic organelles and play an important role in energy metabolism and redox homeostasis, and mitochondrial dysfunction threatens cell homeostasis, perturbs energy production, and ultimately leads to cell death and diseases. Impaired mitochondrial function has been linked to the pathogenesis of several human neurological disorders. Given the significant contribution of mitochondrial dysfunction in neurological disorders, there has been considerable interest in developing therapies that can attenuate mitochondrial abnormalities and proffer neuroprotective effects. Unfortunately, therapies that target specific components of mitochondria or oxidative stress pathways have exhibited limited translatability. To this end, mitochondrial transplantation therapy (MTT) presents a new paradigm of therapeutic intervention, which involves the supplementation of healthy mitochondria to replace the damaged mitochondria for the treatment of neurological disorders. Prior studies demonstrated that the supplementation of healthy donor mitochondria to damaged neurons promotes neuronal viability, activity, and neurite growth and has been shown to provide benefits for neural and extra-neural diseases. In this review, we discuss the significance of mitochondria and summarize an overview of the recent advances and development of MTT in neurodegenerative and neurovascular disorders, particularly Parkinson's disease, Alzheimer's disease, and stroke. The significance of MTT is emerging as they meet a critical need to develop a diseasemodifying intervention for neurodegenerative and neurovascular disorders.

LncRNA TUG1 compromised neuronal mitophagy in cerebral ischemia/reperfusion injury by targeting sirtuin 1

BACKGROUND

Mitophagy protects against cerebral ischemia/reperfusion (CI/R)-induced neuronal apoptosis via mitochondrial clearance. Although taurine-upregulated gene 1 (lncRNA TUG1) has been proposed to be involved in the neuronal apoptosis evoked by CI/R, its specific role in mitophagy during the progression of CI/R injury remains unknown.

METHODS

The CI/R rat model was established using middle cerebral artery occlusion/reperfusion (MCAO/R). Human neuroblastoma cell line SH-SY5Y was subjected to oxygen-glucose deprivation and reoxygenation (OGD/R). Ubiquitination assay, co-immunoprecipitation assay, RNA pull-down, and RNA immunoprecipitation were used to determine the interplay among TUG1, sirtuin 1 (SIRT1), and F-box and WD repeat domain-containing 7 (FBXW7).

RESULTS

The upregulation of the TUG1 level and downregulation of the mitophagy were observed in both MCAO/R-treated rats and OGD/R-treated cells. The administration of si-TUG1 (a siRNA directed against TUG1) potentiated mitophagy and suppressed neuronal apoptosis in OGD/R-treated cells. However, the neuroprotective effect of si-TUG1 was reversed by mitophagy inhibitor or SIRT1 knockdown in vitro. Functionally, TUG1 enhanced FBXW7-mediated SIRT1 ubiquitination by upregulating FBXW7 expression. The overexpression of FBXW7 abrogated the si-TUG1-reinforced mitophagy by decreasing SIRT1 expression, thus aggravating neuronal apoptosis in the OGD/R+si-TUG1-treated cells. In rats with MCAO/R, the interference of TUG1 clearly decreased neuronal apoptosis, lessened the infarct volume, and relieved the neurological deficits.

CONCLUSION

TUG1 knockdown promotes SIRT1-induced mitophagy by suppressing FBXW7-mediated SIRT1 degradation, thus relieving the neuronal apoptosis induced by CI/R injury. LncRNA TUG1 promotes neuronal apoptosis through inhibition of mitophagy. TUG1 decreased SIRT1 expression by promoting FBXW7-mediated SIRT1 ubiquitination. FBXW7/SIRT1 axis mediated the effect of TUG1 on OGD/R-induced neuronal apoptosis by regulating mitophagy.

The critical role of the endolysosomal system in cerebral ischemia

Cerebral ischemia is a serious disease that triggers sequential pathological mechanisms, leading to significant morbidity and mortality. Although most studies to date have typically focused on the lysosome, a single organelle, current evidence supports that the function of lysosomes cannot be separated from that of the endolysosomal system as a whole. The associated membrane fusion functions of this system play a crucial role in the biodegradation of cerebral ischemia-related products. Here, we review the regulation of and the changes that occur in the endolysosomal system after cerebral ischemia, focusing on the latest research progress on membrane fusion function. Numerous proteins, including N-ethylmaleimide-sensitive factor and lysosomal potassium channel transmembrane protein 175, regulate the function of this system. However, these proteins are abnormally expressed after cerebral ischemic injury, which disrupts the normal fusion function of membranes within the endolysosomal system and that between autophagosomes and lysosomes. This results in impaired "maturation" of the endolysosomal system and the collapse of energy metabolism balance and protein homeostasis maintained by the autophagy-lysosomal pathway. Autophagy is the final step in the endolysosomal pathway and contributes to maintaining the dynamic balance of the system. The process of autophagosome-lysosome fusion is a necessary part of autophagy and plays a crucial role in maintaining energy homeostasis and clearing aging proteins. We believe that, in cerebral ischemic injury, the endolysosomal system should be considered as a whole rather than focusing on the lysosome. Understanding how this dynamic system is regulated will provide new ideas for the treatment of cerebral ischemia.

Molecular Mechanisms of the Neuroprotective Effect of Methylene Blue

Methylene blue (MB) is the first fully synthetic compound that had found its way into medicine over 120 years ago as a treatment against malaria. MB has been approved for the treatment of methemoglobinemia, but there are premises for its repurposing as a neuroprotective agent based on the efficacy of this compound demonstrated in the models of Alzheimer's, Parkinson's, and Huntington's diseases, traumatic brain injury, amyotrophic lateral sclerosis, depressive disorders, etc. However, the goal of this review was not so much to focus on the therapeutic effects of MB in the treatment of various neurodegeneration diseases, but to delve into the mechanisms of direct or indirect effect of this drug on the signaling pathways. MB can act as an alternative electron carrier in the mitochondrial respiratory chain in the case of dysfunctional electron transport chain. It also displays the anti-inflammatory and anti-apoptotic effects, inhibits monoamine oxidase (MAO) and nitric oxide synthase (NOS), activates signaling pathways involved in the mitochondrial pool renewal (mitochondrial biogenesis and autophagy), and prevents aggregation of misfolded proteins. Comprehensive understanding of all aspects of direct and indirect influence of MB, and not just some of its effects, can help in further research of this compound, including its clinical applications.

Activation of peripheral TRPM8 mitigates ischemic stroke by topically applied menthol

Background

No reports exist as to neuroprotective effects associated with topical activation of transient receptor potential melastatin 8 (TRPM8), a noted cold receptor. In the present study, we identified whether activating peripheral TRPM8 can be an adjuvant therapy for ischemic stroke.

Methods

Menthol, an agonist of TRPM8, was applied orally or topically to all paws or back of the mouse after middle cerebral artery occlusion (MCAO). We used Trpm8 gene knockout (Trpm8^−/−) mice or TRPM8 antagonist and lidocaine to validate the roles of TRPM8 and peripheral nerve conduction in menthol against ischemic stroke.

Results

Application of menthol 16% to paw derma attenuated infarct volumes and ameliorated sensorimotor deficits in stroke mice induced by MCAO. The benefits of topically applied menthol were associated with reductions in oxidative stress, neuroinflammation and infiltration of monocytes and macrophages in ischemic brains. Antagonizing TRPM8 or Trpm8 knockout dulls the neuroprotective effects of topically application of menthol against MCAO. Immunohistochemistry analyses revealed significantly higher TRPM8 expression in skin tissue samples obtained from the paws compared with skin from the backs, which was reflected by significantly smaller infarct lesion volumes and better sensorimotor function in mice treated with menthol on the paws compared with the back. Blocking conduction of peripheral nerve in the four paws reversed the neuroprotective effects of topical menthol administrated to paws. On the other hand, oral menthol dosing did not assist with recovery from MCAO in our study.

Conclusion

Our results suggested that activation of peripheral TRPM8 expressed in the derma tissue of limbs with sufficient concentration of menthol is beneficial to stroke recovery. Topical application of menthol on hands and feet could be a novel and simple-to-use therapeutic strategy for stroke patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02553-4.

Facilitating Mitophagy via Pink1/Parkin2 Signaling Is Essential for the Neuroprotective Effect of β-Caryophyllene against CIR-Induced Neuronal Injury

Mitophagy is an important mechanism for maintaining mitochondrial homeostasis through elimination of damaged or dysfunctional mitochondria following cerebral ischemia-reperfusion (CIR) injury. β-Caryophyllene (BCP) is a natural sesquiterpene compound found in the essential oil of plants and has been shown to ameliorate CIR injury. However, whether BCP protects neurons from CIR injury by activating mitophagy is still unclear, and the underlying mechanism remains unknown. In the present study, a mouse neuron HT-22 cell of oxygen-glucose deprivation/reoxygenation (OGD/R) and C57BL/6 male mouse of transient middle artery occlusion followed by 24 h reperfusion (MCAO/R) were established the model of CIR injury. Our results show that BCP remarkably protected against cell death and apoptosis induced by OGD/R, and decreased neurologic injury, infarct volume, and the injury of neurons in CA1 region on MCAO/R mice. In addition, BCP accelerated mitophagy by regulating expression of mitochondrial autophagy marker molecules and the mt-Atp6/Rpl13 ratio (reflecting the relative number of mitochondria), and promoting autophagosome formation compared with OGD/R and MCAO/R groups both in vitro and in vivo. Furthermore, this study revealed that BCP pre-treatment could activate the Pink1/Parkin2 signaling pathway, also with mitophagy activation. To explore the mechanisms, mitochondrial division inhibitor-1 (Mdivi-1) was used to investigate the role of BCP in CIR injury. We found that Mdivi-1 not only decreased BCP-induced facilitation of mitophagy, but also significantly weakened BCP-induced protection against OGD/R and MCAO/R models, which was consistent with levels of Pink1/Parkin2 signaling pathway. Taken together, these results suggest that facilitating mitophagy via Pink1/Parkin2 signaling is essential for the neuroprotective effect of BCP against CIR injury.

Insight into Crosstalk Between Mitophagy and Apoptosis/Necroptosis: Mechanisms and Clinical Applications in Ischemic Stroke

Ischemic stroke is a serious cerebrovascular disease with high morbidity and mortality. As a result of ischemia-reperfusion, a cascade of pathophysiological responses is triggered by the imbalance in metabolic supply and demand, resulting in cell loss. These cellular injuries follow various molecular mechanisms solely or in combination with this disorder. Mitochondria play a driving role in the pathophysiological processes of ischemic stroke. Once ischemic stroke occurs, damaged cells would respond to such stress through mitophagy. Mitophagy is known as a conservatively selective autophagy, contributing to the removal of excessive protein aggregates and damaged intracellular components, as well as aging mitochondria. Moderate mitophagy may exert neuroprotection against stroke. Several pathways associated with the mitochondrial network collectively contribute to recovering the homeostasis of the neurovascular unit. However, excessive mitophagy would also promote ischemia-reperfusion injury. Therefore, mitophagy is a double-edged sword, which suggests that maximizing the benefits of mitophagy is one of the direction of future efforts. This review emphasized the role of mitophagy in ischemic stroke, and highlighted the crosstalk between mitophagy and apoptosis/necroptosis.

Role of Mitophagy in the Pathogenesis of Stroke: From Mechanism to Therapy

Mitochondria can supply adenosine triphosphate (ATP) to the tissue, which can regulate metabolism during the pathologic process and is also involved in the pathophysiology of neuronal injury after stroke. Recent studies have suggested that selective autophagy could play important roles in the pathophysiological process of stroke, especially mitophagy. It is usually mediated by the PINK1/Parkin-independent pathway or PINK1/Parkin-dependent pathway. Moreover, mitophagy may be a potential target in the therapy of stroke because the control of mitophagy is neuroprotective in stroke in vitro and in vivo. In this review, we briefly summarize recent researches in mitophagy, introduce the role of mitophagy in the pathogenesis of stroke, then highlight the strategies targeting mitophagy in the treatment of stroke, and finally propose several issues in the treatment of stroke by targeting mitophagy.

The dual roles of autophagy and the GPCRs-mediating autophagy signaling pathway after cerebral ischemic stroke

Ischemic stroke, caused by a lack of blood supply in brain tissues, is the third leading cause of human death and disability worldwide, and usually results in sensory and motor dysfunction, cognitive impairment, and in severe cases, even death. Autophagy is a highly conserved lysosome-dependent process in which eukaryotic cells removal misfolded proteins and damaged organelles in cytoplasm, which is critical for energy metabolism, organelle renewal, and maintenance of intracellular homeostasis. Increasing evidence suggests that autophagy plays important roles in pathophysiological mechanisms under ischemic conditions. However, there are still controversies about whether autophagy plays a neuroprotective or damaging role after ischemia. G-protein-coupled receptors (GPCRs), one of the largest protein receptor superfamilies in mammals, play crucial roles in various physiological and pathological processes. Statistics show that GPCRs are the targets of about one-fifth of drugs known in the world, predicting potential values as targets for drug research. Studies have demonstrated that nutritional deprivation can directly or indirectly activate GPCRs, mediating a series of downstream biological processes, including autophagy. It can be concluded that there are interactions between autophagy and GPCRs signaling pathway, which provides research evidence for regulating GPCRs-mediated autophagy. This review aims to systematically discuss the underlying mechanism and dual roles of autophagy in cerebral ischemia, and describe the GPCRs-mediated autophagy, hoping to probe promising therapeutic targets for ischemic stroke through in-depth exploration of the GPCRs-mediated autophagy signaling pathway.

Mitochondrial Quality Control: A Pathophysiological Mechanism and Therapeutic Target for Stroke

Stroke is a devastating disease with high mortality and disability rates. Previous research has established that mitochondria, as major regulators, are both influenced by stroke, and further regulated the development of poststroke injury. Mitochondria are involved in several biological processes such as energy generation, calcium homeostasis, immune response, apoptosis regulation, and reactive oxygen species (ROS) generation. Meanwhile, mitochondria can evolve into various quality control systems, including mitochondrial dynamics (fission and fusion) and mitophagy, to maintain the homeostasis of the mitochondrial network. Various activities of mitochondrial fission and fusion are associated with mitochondrial integrity and neurological injury after stroke. Additionally, proper mitophagy seems to be neuroprotective for its effect on eliminating the damaged mitochondria, while excessive mitophagy disturbs energy generation and mitochondria-associated signal pathways. The balance between mitochondrial dynamics and mitophagy is more crucial than the absolute level of each process. A neurovascular unit (NVU) is a multidimensional system by which cells release multiple mediators and regulate diverse signaling pathways across the whole neurovascular network in a way with a high dynamic interaction. The turbulence of mitochondrial quality control (MQC) could lead to NVU dysfunctions, including neuron death, neuroglial activation, blood–brain barrier (BBB) disruption, and neuroinflammation. However, the exact changes and effects of MQC on the NVU after stroke have yet to be fully illustrated. In this review, we will discuss the updated mechanisms of MQC and the pathophysiology of mitochondrial dynamics and mitophagy after stroke. We highlight the regulation of MQC as a potential therapeutic target for both ischemic and hemorrhagic stroke.

Mitochondrial quality control in acute ischemic stroke

Mitochondria play a central role in the pathophysiological processes of acute ischemic stroke. Disruption of the cerebral blood flow during acute ischemic stroke interrupts oxygen and glucose delivery, leading to the dysfunction of mitochondrial oxidative phosphorylation and cellular bioenergetic stress. Cells can respond to such stress by activating mitochondrial quality control mechanisms, including the mitochondrial unfolded protein response, mitochondrial fission and fusion, mitophagy, mitochondrial biogenesis, and intercellular mitochondrial transfer. Collectively, these adaptive response strategies contribute to retaining the integrity and function of the mitochondrial network, thereby helping to recover the homeostasis of the neurovascular unit. In this review, we focus on mitochondrial quality control mechanisms occurring in acute ischemic stroke. A better understanding of how these regulatory pathways work in maintaining mitochondrial homeostasis will provide a rationale for developing innovative neuroprotectants when these mechanisms fail in acute ischemic stroke.

Mitochondrial Biogenesis, Mitochondrial Dynamics, and Mitophagy in the Maturation of Cardiomyocytes

Pluripotent stem cells (PSCs) can undergo unlimited self-renewal and can differentiate into all the cell types present in our body, including cardiomyocytes. Therefore, PSCs can be an excellent source of cardiomyocytes for future regenerative medicine and medical research studies. However, cardiomyocytes obtained from PSC differentiation culture are regarded as immature structurally, electrophysiologically, metabolically, and functionally. Mitochondria are organelles responsible for various cellular functions such as energy metabolism, different catabolic and anabolic processes, calcium fluxes, and various signaling pathways. Cells can respond to cellular needs to increase the mitochondrial mass by mitochondrial biogenesis. On the other hand, cells can also degrade mitochondria through mitophagy. Mitochondria are also dynamic organelles that undergo continuous fusion and fission events. In this review, we aim to summarize previous findings on the changes of mitochondrial biogenesis, mitophagy, and mitochondrial dynamics during the maturation of cardiomyocytes. In addition, we intend to summarize whether changes in these processes would affect the maturation of cardiomyocytes. Lastly, we aim to discuss unanswered questions in the field and to provide insights for the possible strategies of enhancing the maturation of PSC-derived cardiomyocytes.

Tomatidine provides mitophagy-independent neuroprotection after ischemic injury

Cerebral ischemia is one of the leading causes of human mortality and disability worldwide. The treatment of cerebral ischemia is refractory due to its short therapeutic window and lack of effective clinical drugs. Mitophagy, the autophagic elimination of damaged mitochondria, attenuates neuronal injury in cerebral ischemia, indicating the potential of mitophagy inducers as therapies for cerebral ischemia. We previously determined that, by enhancing autophagy flux, the steroidal alkaloid tomatidine can function as a neuroprotective agent against ischemic injury. However, its effects on mitophagy remain unknown. For this purpose, neuroblastoma cell lines Neuro-2a and SH-SY5Y were subjected to ischemic injury induced by oxygen-glucose deprivation/reperfusion (OGD/R) and then treated with tomatidine. OGD/R induced a general decrease of cellular contents, and this study revealed that tomatidine had no impact on mitophagy. In addition, tomatidine did not affect mitochondrial contents, including translocase of outer mitochondrial membrane 20 and voltage-dependent anion channel 1, in either OGD/R-treated or intact SH-SY5H cells. Our results indicate that tomatidine exhibits its neuroprotective effects by enhancing autophagy, but in a potentially mitophagy-independent manner, and provide insights for further investigation into its mechanism(s) and potential therapeutic use against cerebral ischemia.

Mitochondrial Quality Control in Cerebral Ischemia-Reperfusion Injury

Ischemic stroke is one of the leading causes of death and also a major cause of adult disability worldwide. Revascularization via reperfusion therapy is currently a standard clinical procedure for patients with ischemic stroke. Although the restoration of blood flow (reperfusion) is critical for the salvage of ischemic tissue, reperfusion can also, paradoxically, exacerbate neuronal damage through a series of cellular alterations. Among the various theories postulated for ischemia/reperfusion (I/R) injury, including the burst generation of reactive oxygen species (ROS), activation of autophagy, and release of apoptotic factors, mitochondrial dysfunction has been proposed to play an essential role in mediating these pathophysiological processes. Therefore, strict regulation of the quality and quantity of mitochondria via mitochondrial quality control is of great importance to avoid the pathological effects of impaired mitochondria on neurons. Furthermore, timely elimination of dysfunctional mitochondria via mitophagy is also crucial to maintain a healthy mitochondrial network, whereas intensive or excessive mitophagy could exacerbate cerebral I/R injury. This review will provide a comprehensive overview of the effect of mitochondrial quality control on cerebral I/R injury and introduce recent advances in the understanding of the possible signaling pathways of mitophagy and potential factors responsible for the double-edged roles of mitophagy in the pathological processes of cerebral I/R injury.

Electroacupuncture at GV20‑GB7 regulates mitophagy to protect against neurological deficits following intracerebral hemorrhage via inhibition of apoptosis

The acupuncture penetrating line of Baihui (GV20) to Qubin (GB7) spans the parietal, frontal and temporal lobes. The present study aimed to elucidate the mechanism by which electroacupuncture (EA) at GV20‑GB7 regulates mitophagy in intracerebral hemorrhage (ICH) and whether it serves a neuroprotective role. A whole blood‑induced ICH model was used. Mitophagy‑regulating proteins, including BCL/adenovirus E1B 19 kDa‑interacting protein 3 (BNIP3), PTEN‑induced putative kinase 1 (PINK1), Parkin and apoptosis‑associated proteins were detected by western blotting; autophagy following ICH was evaluated by immunofluorescent techniques; morphological characteristics of mitophagy were observed using transmission electron microscopy; and TUNEL assay was performed to determine the number of apoptotic cells. Immunohistochemistry was used to detect p53 expression. The protective role of EA (GV20‑GB7) via enhanced mitophagy and suppressed apoptosis in ICH was further confirmed by decreased modified neurological severity score. The results showed that EA (GV20‑GB7) treatment upregulated mitochondrial autophagy following ICH and inhibited apoptotic cell death. The mechanism underlying EA (GV20‑GB7) treatment may involve inhibition of p53, an overlapping protein of autophagy and apoptosis. EA (GV20‑GB7) treatment decreased neurobehavioral deficits following ICH but pretreatment with 3‑methyladenine counteracted the beneficial effects of EA (GV20‑GB7) treatment. In conclusion, EA (GV20‑GB7) improved recovery from ICH by regulating the balance between mitophagy and apoptosis.

Mitophagy in Cerebral Ischemia and Ischemia/Reperfusion Injury

Ischemic stroke is a severe cerebrovascular disease with high mortality and morbidity. In recent years, reperfusion treatments based on thrombolytic and thrombectomy are major managements for ischemic stroke patients, and the recanalization time window has been extended to over 24 h. However, with the extension of the time window, the risk of ischemia/reperfusion (I/R) injury following reperfusion therapy becomes a big challenge for patient outcomes. I/R injury leads to neuronal death due to the imbalance in metabolic supply and demand, which is usually related to mitochondrial dysfunction. Mitophagy is a type of selective autophagy referring to the process of specific autophagic elimination of damaged or dysfunctional mitochondria to prevent the generation of excessive reactive oxygen species (ROS) and the subsequent cell death. Recent advances have implicated the protective role of mitophagy in cerebral ischemia is mainly associated with its neuroprotective effects in I/R injury. This review discusses the involvement of mitochondria dynamics and mitophagy in the pathophysiology of ischemic stroke and I/R injury in particular, focusing on the therapeutic potential of mitophagy regulation and the possibility of using mitophagy-related interventions as an adjunctive approach for neuroprotective time window extension after ischemic stroke.

FUNDC1 inhibits NLRP3-mediated inflammation after intracerebral hemorrhage by promoting mitophagy in mice

Inflammation is a fundamental element in secondary brain injury (SBI) besides intracerebral hemorrhage (ICH). Pyrin domain that contains 3 inflammasome (NLRP3) was regarded as a key role of the nod-like receptor family and played an important part in the inflammatory response following ICH-induced injury. FUN14 domain containing 1 (FUNDC1) is a kind of mitophagy receptor, which can eliminate mitochondrial dysfunction after hypoxia and mitochondrial stress. Previous research showed that mitophagy prevents inflammation through inhibiting NLRP3 inflammasome pathway. However, the relationship between FUNDC1 and ICH-induced inflammatory response stays uncertain. In this study, we investigate that FUNDC1 inhibit NLRP3 inflammasome activation by promoting mitophagy, thereby alleviate ICH-induced injury. We established ICH model by injecting tail venous blood into the basal ganglia of C57 mice (healthy, male adult). We injected siRNA to knockdown FUNDC1. In order to deeply seek for the mechanisms of FUNDC1 in ICH-induced injury, FUNDC1 was overexpressed by adeno-associated virus (AAV) and mitophagy was suppressed by specific inhibitor (mdivi-1). The protein level of FUNDC1 was upregulated and got peak at 12h after ICH. We noticed that silencing FUNDC1 can suppress mitophagy, promote NLRP3-mediated inflammation and exacerbate ICH injury. Furthermore, the results indicated that mitophagy participated in the inhibitory effect of FUNDC1 on NLRP3-mediated inflammatory response after ICH. Our results showed that FUNDC1 alleviated ICH-induced inflammation in mice by promoting mitophagy. Those data suggested that FUNDC1 may be a potential target for the treatment of ICH.

Mitochondrial fission and mitophagy are independent mechanisms regulating ischemia/reperfusion injury in primary neurons

Mitochondrial dynamics and mitophagy are constitutive and complex systems that ensure a healthy mitochondrial network through the segregation and subsequent degradation of damaged mitochondria. Disruption of these systems can lead to mitochondrial dysfunction and has been established as a central mechanism of ischemia/reperfusion (I/R) injury. Emerging evidence suggests that mitochondrial dynamics and mitophagy are integrated systems; however, the role of this relationship in the context of I/R injury remains unclear. To investigate this concept, we utilized primary cortical neurons isolated from the novel dual-reporter mitochondrial quality control knockin mice (C57BL/6-Gt(ROSA)26Sortm1(CAG-mCherry/GFP)Ganl/J) with conditional knockout (KO) of Drp1 to investigate changes in mitochondrial dynamics and mitophagic flux during in vitro I/R injury. Mitochondrial dynamics was quantitatively measured in an unbiased manner using a machine learning mitochondrial morphology classification system, which consisted of four different classifications: network, unbranched, swollen, and punctate. Evaluation of mitochondrial morphology and mitophagic flux in primary neurons exposed to oxygen-glucose deprivation (OGD) and reoxygenation (OGD/R) revealed extensive mitochondrial fragmentation and swelling, together with a significant upregulation in mitophagic flux. Furthermore, the primary morphology of mitochondria undergoing mitophagy was classified as punctate. Colocalization using immunofluorescence as well as western blot analysis revealed that the PINK1/Parkin pathway of mitophagy was activated following OGD/R. Conditional KO of Drp1 prevented mitochondrial fragmentation and swelling following OGD/R but did not alter mitophagic flux. These data provide novel evidence that Drp1 plays a causal role in the progression of I/R injury, but mitophagy does not require Drp1-mediated mitochondrial fission.

An updated review of autophagy in ischemic stroke: From mechanisms to therapies

Stroke is a leading cause of mortality and morbidity worldwide. Understanding the underlying mechanisms is important for developing effective therapies for treating stroke. Autophagy is a self-eating cellular catabolic pathway, which plays a crucial homeostatic role in the regulation of cell survival. Increasing evidence shows that autophagy, observed in various cell types, plays a critical role in brain pathology after ischemic stroke. Therefore, the regulation of autophagy can be a potential target for ischemic stroke treatment. In the present review, we summarize the recent progress that research has made regarding autophagy and ischemic stroke, including common signaling pathways, the role of autophagic subtypes (e.g. mitophagy, pexophagy, aggrephagy, endoplasmic reticulum-phagy, and lipophagy) in ischemic stroke, as well as the current methods for autophagy detection and potential therapeutic strategy.

The neuropsychiatric manifestations of COVID-19: Interactions with psychiatric illness and pharmacological treatment

The recent outbreak of the corona virus disease (COVID-19) has had major global impact. The relationship between severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection and psychiatric diseases is of great concern, with an evident link between corona virus infections and various central and peripheral nervous system manifestations. Unmitigated neuro-inflammation has been noted to underlie not only the severe respiratory complications of the disease but is also present in a range of neuro-psychiatric illnesses. Several neurological and psychiatric disorders are characterized by immune-inflammatory states, while treatments for these disorders have distinct anti-inflammatory properties and effects. With inflammation being a common contributing factor in SARS-CoV-2, as well as psychiatric disorders, treatment of either condition may affect disease progression of the other or alter response to pharmacological treatment. In this review, we elucidate how viral infections could affect pre-existing psychiatric conditions and how pharmacological treatments of these conditions may affect overall progress and outcome in the treatment of SARS-CoV-2. We address whether any treatment-induced benefits and potential adverse effects may ultimately affect the overall treatment approach, considering the underlying dysregulated neuro-inflammatory processes and potential drug interactions. Finally, we suggest adjunctive treatment options for SARS-CoV-2-associated neuro-psychiatric symptoms.

Different Roles of Mitochondria in Cell Death and Inflammation: Focusing on Mitochondrial Quality Control in Ischemic Stroke and Reperfusion

Mitochondrial dysfunctions are among the main hallmarks of several brain diseases, including ischemic stroke. An insufficient supply of oxygen and glucose in brain cells, primarily neurons, triggers a cascade of events in which mitochondria are the leading characters. Mitochondrial calcium overload, reactive oxygen species (ROS) overproduction, mitochondrial permeability transition pore (mPTP) opening, and damage-associated molecular pattern (DAMP) release place mitochondria in the center of an intricate series of chance interactions. Depending on the degree to which mitochondria are affected, they promote different pathways, ranging from inflammatory response pathways to cell death pathways. In this review, we will explore the principal mitochondrial molecular mechanisms compromised during ischemic and reperfusion injury, and we will delineate potential neuroprotective strategies targeting mitochondrial dysfunction and mitochondrial homeostasis.

Effect of Methylene Blue on White Matter Injury after Ischemic Stroke

Methylene blue, the FDA-grandfathered drug was proved to be neuroprotective in ischemic stroke in rat. However, the mechanism of the protective effect was unknown. In this study, we used different animal models to investigate the effect of MB administration given within and beyond the therapeutic time window on behavioral deficits and infarct volume and related mechanism about the white matter protection. Middle cerebral artery occlusion and reperfusion (MCAO) and photothrombotic middle cerebral artery occlusion (PT-MCAO) models were used. Behavioral deficits and infarct volume were measured by foot fault test, Garcia neurological score, and TTC staining. Black gold staining and western blot were used to evaluate the brain white matter injury. We found that intraperitoneal administration of MB immediately or 24 h after the MCAO or PT-MCAO surgery reduced infarct volume, improved the neurological deficits, and reduced the white matter injury via myelin basic protein (BMP) protection. These findings suggested that MB relieved the white matter injury besides neuronal protection and has potential therapeutic effects on ischemic stroke.

The Role of Mitophagy in Ischemic Stroke

Mitochondria are important places for eukaryotes to carry out energy metabolism and participate in the processes of cell differentiation, cell information transmission, and cell apoptosis. Autophagy is a programmed intracellular degradation process. Mitophagy, as a selective autophagy, is an evolutionarily conserved cellular process to eliminate dysfunctional or redundant mitochondria, thereby fine-tuning the number of mitochondria and maintaining energy metabolism. Many stimuli could activate mitophagy to regulate related physiological processes, which could ultimately reduce or aggravate the damage caused by stimulation. Stroke is a common disease that seriously affects the health and lives of people around the world, and ischemic stroke, which is caused by cerebral vascular stenosis or obstruction, accounts for the vast majority of stroke. Abnormal mitophagy is closely related to the occurrence, development and pathological mechanism of ischemic stroke. However, the exact mechanism of mitophagy involved in ischemic stroke has not been fully elucidated. In this review, we discuss the process and signal pathways of mitophagy, the potential role of mitophagy in ischemic stroke and the possible signal transduction pathways. It will help deepen the understanding of mitophagy and provide new ideas for the treatment of ischemic stroke.

The Dichotomous Role of Inflammation in the CNS: A Mitochondrial Point of View

Innate immune response is one of our primary defenses against pathogens infection, although, if dysregulated, it represents the leading cause of chronic tissue inflammation. This dualism is even more present in the central nervous system, where neuroinflammation is both important for the activation of reparatory mechanisms and, at the same time, leads to the release of detrimental factors that induce neurons loss. Key players in modulating the neuroinflammatory response are mitochondria. Indeed, they are responsible for a variety of cell mechanisms that control tissue homeostasis, such as autophagy, apoptosis, energy production, and also inflammation. Accordingly, it is widely recognized that mitochondria exert a pivotal role in the development of neurodegenerative diseases, such as multiple sclerosis, Parkinson's and Alzheimer's diseases, as well as in acute brain damage, such in ischemic stroke and epileptic seizures. In this review, we will describe the role of mitochondria molecular signaling in regulating neuroinflammation in central nervous system (CNS) diseases, by focusing on pattern recognition receptors (PRRs) signaling, reactive oxygen species (ROS) production, and mitophagy, giving a hint on the possible therapeutic approaches targeting mitochondrial pathways involved in inflammation.

Effects of Methylene Blue on Ovarian Torsion-Detorsion Injury in a Rat Model

STUDY OBJECTIVES

Methylene blue (MB) is an antioxidant that ameliorates ischemia-reperfusion injury in several tissues. We analyzed the effects of MB as an inhibitor of torsion-detorsion injury in rat ovaries.

METHODS

Rats were randomly divided into 5 groups. Group 1 was the sham group, in which only laparotomy was performed. Group 2 was the torsion group, with 3 hours of ischemia. Group 3 was the torsion + MB group, with 3 hours of ischemia after MB administration. Group 4 was the torsion-detorsion group, with 3 hours of ischemia and reperfusion. Finally, group 5 was the torsion-detorsion + MB group, with 3 hours of ischemia and MB administration before detorsion/reperfusion. Ovary injuries were histopathologically scored. Malondialdehyde (MDA) and total protein levels in ovarian tissues were determined, and long pentraxin-3 (PTX3) levels were measured in ovarian tissue using an enzyme-linked immunosorbent assay.

RESULTS

In comparing group 4 with group 5 and group 2 with 3, histopathological parameters reflecting injury were significantly increased in groups 4 and 2. Group 3 generated increased MDA levels when compared with group 2 (P < .05). However, there was no significant difference between groups 2 and 3 in terms of plasma PTX3 levels. MDA and PTX3 levels decreased in group 5 in comparison with group 4 for MDA (P < .000) and PTX3 levels (P < .01).

CONCLUSIONS

MB alleviated ischemia-reperfusion ovary injury in our experimental model.

Novel Role of Carbon Monoxide in Improving Neurological Outcome After Cardiac Arrest in Aged Rats: Involvement of Inducing Mitochondrial Autophagy

Background

Dysfunctional mitochondria are associated with neurological injury after cardiac arrest (CA). Although carbon monoxide (CO) has shown various potential therapeutic effects in preclinical tissue injury models, its mechanism of action in CA remains unclear. We sought to investigate the effects of a novel CO‐releasing molecule on cerebral mitochondrial dysfunction and neurological injury after CA.

Methods and Results

Male Sprague‐Dawley rats aged 20 to 22 months were subjected to 6‐minute asphyxia CA before receiving CO treatment. Survival, neurologic deficit scores, neuronal death, mitochondrial function, and autophagy were evaluated after the return of spontaneous circulation. Results showed that CO post‐treatment increased 3‐day survival rate from 25% to 70.83% and reduced neurologic deficit scores. CO also ameliorated CA‐induced neuronal apoptosis and necrosis in the cerebral cortex and improved cerebral mitochondrial function by reducing reactive oxygen species, reversing mitochondrial membrane potential depolarization, and preventing cytochrome C release. Furthermore, CO increased mitochondrial autophagy by inducing mitochondrial accumulation of PINK1 (PTEN‐induced putative kinase 1) and Parkin. Downregulation of PINK1 with genetic silencing siRNA abolished CO‐afforded mitochondrial autophagy.

Conclusions

Taken together, our results indicate, for the first time, that CO treatment confers neuroprotection against ischemic neurological injury after CA possibly by promoting mitochondrial autophagy.

Methylene blue post-treatment improves hypoxia-ischemic recovery in a neonatal rat model

Recent work suggested that methylene blue (MB) has beneficial effects in a variety of neurological disorders, while its role in neonatal hypoxic-ischemic (HI) encephalopathy is still unclear. The current study was designed to investigate the effects of MB on HI-induced brain damage and its underlying mechanisms. The results showed that MB treatment can strongly attenuate HI-induced brain loss and neuronal damage in the cortex and hippocampus of neonatal rats. Further mechanistic analysis suggested that MB treatment was able to significantly reduce blood-brain barrier disruption after HI insult. In addition, MB profoundly inhibited microglia and astrocyte activation and the pro-inflammatory cytokines production in neonatal cortex and hippocampus after HI. Further, MB treatment resulted in dramatic suppression of oxidative damage, as evidenced by robustly decreased DHE and protein carbonyls levels in HI brain. Moreover, MB strongly preserved mitochondrial function by repressing HI-induced mitochondrial fragmentation, and the following neuronal death in cortex and hippocampus. Finally, behavioral tests revealed that MB significantly improved the spatial reference memory and motor coordination of neonatal HI rats. Taken together, these findings demonstrate that the mechanisms behind neuroprotective actions of methylene blue are multifactorial, including suppression of oxidative stress and neuroinflammation, restoration of mitochondrial function, as well as attenuation of blood-brain barrier disruption. Our study might provide further directions for MB as a promising option in neonatal HI encephalopathy therapy.

Mitochondria as a target for neuroprotection: role of methylene blue and photobiomodulation

Mitochondrial dysfunction plays a central role in the formation of neuroinflammation and oxidative stress, which are important factors contributing to the development of brain disease. Ample evidence suggests mitochondria are a promising target for neuroprotection. Recently, methods targeting mitochondria have been considered as potential approaches for treatment of brain disease through the inhibition of inflammation and oxidative injury. This review will discuss two widely studied approaches for the improvement of brain mitochondrial respiration, methylene blue (MB) and photobiomodulation (PBM). MB is a widely studied drug with potential beneficial effects in animal models of brain disease, as well as limited human studies. Similarly, PBM is a non-invasive treatment that promotes energy production and reduces both oxidative stress and inflammation, and has garnered increasing attention in recent years. MB and PBM have similar beneficial effects on mitochondrial function, oxidative damage, inflammation, and subsequent behavioral symptoms. However, the mechanisms underlying the energy enhancing, antioxidant, and anti-inflammatory effects of MB and PBM differ. This review will focus on mitochondrial dysfunction in several different brain diseases and the pathological improvements following MB and PBM treatment.

Modulation of copper-induced antioxidant defense, Cu transport, and mitophagy by hypoxia in the large yellow croaker (Larimichthys crocea)

This study aimed to investigate the effects of hypoxia on Cu-induced antioxidant defense, Cu transport, and mitophagy in the liver of the large yellow croaker. Fish were exposed to hypoxia (3.0 mg L^-1), Cu (120 μg L^-1), and hypoxia (3.0 mg L^-1) plus Cu (120 μg L^-1) for 48 h. Hypoxia exposure increased antioxidant abilities to maintain cellular redox balance. Although Cu exposure alone improved antioxidant defense, Cu transport, and mitophagy, these stress responses could not completely neutralize Cu toxicity, as reflected by the elevated reactive oxygen species (ROS) and lipid peroxidation (LPO) and hepatic vacuoles. When compared with Cu stress alone, hypoxia increased Cu toxicity by inhibiting antioxidant defense, Cu transport, and mitophagy, leading to the increment of mortality, ROS, and LPO, and the deterioration of histological structure. The adverse effects of hypoxia on Cu-induced metal transport and mitophagy might be involved in metal-responsive element-binding transcription factor-1 (MTF-1) and Forkhead box O-3 (FoxO3) signaling pathways, respectively. Overall, hypoxia reduced antioxidant response, Cu transport, and mitophagy in fish exposed to Cu, which contributes to understanding the molecular mechanisms underlying negative effects of hypoxia on Cu toxicity in fish.

Pre-hypoxia exposure inhibited copper toxicity by improving energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea

This study investigated the effects of moderate hypoxia pre-exposure on energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea exposed to Cu. Fish were pre-exposed to either normoxia or hypoxia (~3.0 mg L^-1, 42% O₂ saturation) for 48 h, and subsequently were subjected to either control (without Cu addition) or Cu (168 μg L^-1) under normoxic conditions for another 48 h. Copper exposure under normoxia induced Cu toxicity that increased mortality, the production of reactive oxygen species (ROS) and malondialdehyde, and aberrant hepatic mitochondrial ultrastructure. Interestingly, hypoxia pre-exposure improved energy metabolism, antioxidant ability and mitophagy response, and reduced the Cu content to inhibit Cu toxicity, reflecting the enhanced survival rate and reduced oxidative damage. In these processes, hypoxia-inducible factor-1α (HIF-1α), transcription factors NFE2-related nuclear factor 2 (Nrf2), and forkhead box O-3 (FoxO3) mRNA levels were correlated with expression of genes related to energy metabolism, antioxidant defence and mitophagy, respectively, indicating HIF-1α, Nrf2, and FoxO3 are required for the induction of their respective target genes. Overall, moderate hypoxia pre-exposure was able to generate adaptive responses to mitigate Cu-induced toxicological effects, underlining a central role of hormesis.

Mitochondrial Quality Control: Role in Cardiac Models of Lethal Ischemia-Reperfusion Injury

The current standard of care for acute myocardial infarction or 'heart attack' is timely restoration of blood flow to the ischemic region of the heart. While reperfusion is essential for the salvage of ischemic myocardium, re-introduction of blood flow paradoxically kills (rather than rescues) a population of previously ischemic cardiomyocytes-a phenomenon referred to as 'lethal myocardial ischemia-reperfusion (IR) injury'. There is long-standing and exhaustive evidence that mitochondria are at the nexus of lethal IR injury. However, during the past decade, the paradigm of mitochondria as mediators of IR-induced cardiomyocyte death has been expanded to include the highly orchestrated process of mitochondrial quality control. Our aims in this review are to: (1) briefly summarize the current understanding of the pathogenesis of IR injury, and (2) incorporating landmark data from a broad spectrum of models (including immortalized cells, primary cardiomyocytes and intact hearts), provide a critical discussion of the emerging concept that mitochondrial dynamics and mitophagy (the components of mitochondrial quality control) may contribute to the pathogenesis of cardiomyocyte death in the setting of ischemia-reperfusion.

Mitochondria as a therapeutic target for ischemic stroke

Stroke is the leading cause of death and physical disability worldwide. Mitochondrial dysfunction has been considered as one of the hallmarks of ischemic stroke and contributes to the pathology of ischemia and reperfusion. Mitochondria is essential in promoting neural survival and neurological improvement following ischemic stroke. Therefore, mitochondria represent an important drug target for stroke treatment. This review discusses the mitochondrial molecular mechanisms underlying cerebral ischemia and involved in reactive oxygen species generation, mitochondrial electron transport dysfunction, mitochondria-mediated regulation of inflammasome activation, mitochondrial dynamics and biogenesis, and apoptotic cell death. We highlight the potential of mitochondrial transfer by stem cells as a therapeutic target for stroke treatment and provide valuable insights for clinical strategies. A better understanding of the roles of mitochondria in ischemia-induced cell death and protection may provide a rationale design of novel therapeutic interventions in the ischemic stroke.

Mild Acidosis Protects Neurons during Oxygen-Glucose Deprivation by Reducing Loss of Mitochondrial Respiration

Brain ischemia is often accompanied by brain acidosis and this acidosis can affect ischemic neuronal injury. Ischemic neuronal injury is initiated by a decrease in ATP production which mainly relies on mitochondrial oxidative phosphorylation. Ischemia often causes mitochondrial dysfunction, and acidosis has been found to affect mitochondrial function, suggesting that acidosis accompanying ischemia may influence neurons by targeting mitochondrial metabolism. However, the effects of acidosis on mitochondrial energy metabolism during ischemia lacks thorough investigation. Here, we found that mild acidosis significantly reduced neuronal death possibly by slowing the process of ATP deprivation during oxygen-glucose deprivation (OGD), an in vitro ischemic model. The maintaining of neuronal ATP depended on protecting mitochondrial ATP production. Further investigation of mitochondrial function revealed that mild acidosis alleviated OGD-induced collapse of mitochondrial membrane potentials as well as damage to respiratory function, at least in part by reducing impacts on complex I and II activities. Inhibition of complex I activity aggravated neuronal death, which suggests that the contribution of mild acidosis to maintaining complex I activity promoted neuronal survival during OGD. Our findings reveal maintaining mitochondrial respiration as a new possible protective mechanism of mild acidosis during ischemia, on neurons.

Urolithin A-activated autophagy but not mitophagy protects against ischemic neuronal injury by inhibiting ER stress in vitro and in vivo

Aim

Mitochondrial autophagy (mitophagy) clears damaged mitochondria and attenuates ischemic neuronal injury. Urolithin A (Uro‐A) activates mitophagy in mammal cells and Caenorhabditis elegans. We explored neuroprotection of Uro‐A against ischemic neuronal injury.

Methods

Mice were subjected to middle cerebral artery occlusion. The brain infarct and neurological deficit scores were measured. The N2a cells and primary cultured mice cortical neurons were subjected to oxygen‐glucose deprivation and reperfusion (OGD/R). Uro‐A was incubated during OGD/R, and cell injury was determined by MTT and LDH. Autophagosomes were visualized by transfecting mCherry‐microtubule‐associated protein 1 light chain 3 (LC3). The protein levels of LC3‐II, p62, Translocase Of Inner Mitochondrial Membrane 23 (TIMM23), and cytochrome c oxidase subunit 4 isoform 1 (COX4I1) were detected by Western blot. The ER stress markers, activating transcription factor 6 (ATF6) and C/EBP homologous protein (CHOP), were determined by reverse transcription‐polymerase chain reaction (RT‐PCR).

Results

Urolithin A alleviated OGD/R‐induced injury in N2a cells and neurons and reduced ischemic brain injury in mice. Uro‐A reinforced ischemia‐induced autophagy. Furthermore, Uro‐A‐conferred protection was abolished by 3‐methyladenine, suggesting the requirement of autophagy for neuroprotection. However, mitophagy was not further activated by Uro‐A. Instead, Uro‐A attenuated OGD/R‐induced ER stress, which was abolished by 3‐methyladenosine. Additionally, neuroprotection was reversed by ER stress inducer.

Conclusion

Urolithin A protected against ischemic neuronal injury by reinforcing autophagy rather than mitophagy. Autophagy activation by Uro‐A attenuated ischemic neuronal death by suppressing ER stress.

Evaluation of the therapeutic effect of methylene blue on the liver of rats submitted to ischemia and reperfusion

PURPOSE

To analyze the effect of methylene blue (MB) therapy during the liver ischemia-reperfusion injury (I/R) process.

METHODS

Thirty-five male Wistar rats were used, (70%) submitted to partial ischemia (IR) or not (NIR) (30%) were obtained from the same animal. These animals were divided into six groups: 1) Sham (SH), 2) Sham with MB (SH-MB); 3) I/R, submitted to 60 minutes of partial ischemia and 15 minutes of reperfusion; 4) NI/R, without I/R obtained from the same animal of group I/R; 5) I/R-MB submitted to I/R and MB and 6) NI/R-MB, without I/R. Mitochondrial function was evaluated. Osmotic swelling of mitochondria as well as the determination of malondialdehyde (MDA) was evaluated. Serum (ALT/AST) dosages were also performed. MB was used at the concentration of 15mg/kg, 15 minutes before hepatic reperfusion. Statistical analysis was done by the Mann Whitney test at 5%.

RESULTS

State 3 shows inhibition in all ischemic groups. State 4 was increased in all groups, except the I/R-MB and NI/R-MB groups. RCR showed a decrease in all I/R and NI/R groups. Mitochondrial osmotic swelling showed an increase in all I/R NI/R groups in the presence or absence of MB. About MDA, there was a decrease in SH values in the presence of MB and this decrease was maintained in the I/R group. AST levels were increased in all ischemic with or without MB.

CONCLUSIONS

The methylene blue was not able to restore the mitochondrial parameters studied. Also, it was able to decrease lipid peroxidation, preventing the formation of reactive oxygen species.

Mitophagy, a potential therapeutic target for stroke

Mitochondria autophagy, termed as mitophagy, is a mechanism of specific autophagic elimination of mitochondria. Mitophagy controls the quality and the number of mitochondria, eliminating dysfunctional or excessive mitochondria that can generate reactive oxygen species (ROS) and cause cell death. Mitochondria are centrally implicated in neuron and tissue injury after stroke, due to the function of supplying adenosine triphosphate (ATP) to the tissue, regulating oxidative metabolism during the pathologic process, and contribution to apoptotic cell death after stroke. As a catabolic mechanism, mitophagy links numbers of a complex network of mitochondria, and affects mitochondrial dynamic process, fusion and fission, reducing mitochondrial production of ROS, mediated by the mitochondrial permeability transition pore (MPTP). The precise nature of mitophagy’s involvement in stroke, and its underlying molecular mechanisms, have yet to be fully clarified. This review aims to provide a comprehensive overview of the integration of mitochondria with mitophagy, also to introduce and discuss recent advances in the understanding of the potential role, and possible signaling pathway, of mitophagy in the pathological processes of both hemorrhagic and ischemic stroke. The author also provides evidence to explain the dual role of mitophagy in stroke.

Mitochondria in Ischemic Stroke: New Insight and Implications

Stroke is the leading cause of death and adult disability worldwide. Mitochondrial dysfunction has been regarded as one of the hallmarks of ischemia/reperfusion (I/R) induced neuronal death. Maintaining the function of mitochondria is crucial in promoting neuron survival and neurological improvement. In this article, we review current progress regarding the roles of mitochondria in the pathological process of cerebral I/R injury. In particular, we emphasize on the most critical mechanisms responsible for mitochondrial quality control, as well as the recent findings on mitochondrial transfer in acute stroke. We highlight the potential of mitochondria as therapeutic targets for stroke treatment and provide valuable insights for clinical strategies.

Neuroprotective Effects of Radix Scrophulariae on Cerebral Ischemia and Reperfusion Injury via MAPK Pathways

Ischemic stroke is a clinically common cerebrovascular disease whose main risks include necrosis, apoptosis and cerebral infarction, all caused by cerebral ischemia and reperfusion (I/R). Ischemia and reperfusion-induced injury or apoptosis inhibition in human brain tissue may exert an irreplaceable protective effect on ischemic nerves. This process has particular significance for the treatment of stroke patients. However, the development of neuroprotective drugs remains challenging. Radix Scrophulariae, traditionally considered a valuable medicine, has been discovered to have neuroprotective effects. To explore the neuroprotective effects of an aqueous extract of Radix Scrophulariae (RSAE) on cerebral ischemia/reperfusion and their underlying mechanisms, oxygen-glucose deprivation and reperfusion (OGD/R)-induced PC12 cells were used, and a middle cerebral artery occlusion/reperfusion (MCAO/R) mouse model was established. In vitro results showed that 12.5 μg/mL RSAE markedly improved cell viability; inhibited LDH leakage; increased SOD, GSH-Px and CAT enzyme activity; stabilized the mitochondrial membrane potential; and reduced OGD-induced cell injury and apoptosis. Additionally, in vivo results preliminarily suggested that in MCAO/R model mice, RSAE treatments attenuated infarct volume; reduced brain water content and nitric oxide (NO) and malondialdehyde (MDA) concentrations; inhibited I/R-induced neurological deficits; reduced the levels of lactate dehydrogenase (LDH) leakage release; improved antioxidant capacity by upregulating SOD, GSH-Px and CAT enzyme activity; and reduced neuronal apoptosis, necrosis and loss of neurons. Moreover, it was found that RSAE upregulated the expression of Bcl-2 and downregulated the expression of Bax. In addition, the phosphorylation levels of MAPK signal pathways were elucidated via western blot analysis and immunohistochemical evaluation. In summary, this study investigated the neuroprotective effects and potential mechanisms of RSAE on focal cerebral I/R injury in mice. Radix Scrophulariae has been previously identified as a potential neuroprotective natural plant. Hence, our results may offer insight into discovering new active compounds or drugs for the treatment of ischemic stroke. Many new natural active chemicals in this extract may be discovered by chemical separation and identification and may provide new insights into therapeutic targets in stroke patients.

Methylene blue offers neuroprotection after intracerebral hemorrhage in rats through the PI3K/Akt/GSK3β signaling pathway

Inflammation and apoptosis are two key factors contributing to secondary brain injury after intracerebral hemorrhage (ICH). In the present study, we explored the neuroprotective role of methylene blue (MB) in ICH rats and studied the potential mechanisms involved. Rats were subjected to local injection of collagenase IV in the striatum or sham surgery. We observed that MB treatment could exert a neuroprotective effect on ICH by promoting neurological scores, decreasing the brain water content, alleviating brain-blood barrier disruption, and improving the histological damages in the perihematomal areas. Furthermore, we demonstrated that the various mechanisms underlying MB's neuroprotective effects linked to inhibited apoptosis and inhibited neuroinflammation. In addition, wortmannin, a selective inhibitor of phosphoinositide 3-kinase (PI3K), could reverse the antiapoptotic and anti-inflammatory effects of MB, which suggested that the PI3K-Akt pathway played an important role. In conclusion, these data suggested that MB could inhibit apoptosis and ameliorate neuroinflammation after ICH, and its neuroprotective effects might be exerted via the activation of the PI3K/Akt/GSK3β pathway.

Mitophagy is activated in brain damage induced by cerebral ischemia and reperfusion via the PINK1/Parkin/p62 signalling pathway

This study examined the course of mitophagy following cerebral ischemia with reperfusion and the role of the PTEN-induced kinase 1 (PINK1)/Parkin/p62 signalling pathway. The middle cerebral artery of male Sprague-Dawley rats was occluded for 90 min and was followed by different time-points of reperfusion. Cerebral infarct areas were detected by 2,3,5-triphenyl tetrazolium chloride staining, while brain damage was observed by haematoxylin and eosin staining. Levels of LC3, Beclin1 and LAMP-1 were estimated by western blots. LC3B location was observed in various cells in the neurovascular unit. In addition, PINK1 accumulation in damaged mitochondria and Parkin/p62 mitochondrial translocation were investigated by double immunofluorescence staining. Finally, the levels of PINK1, Parkin and p62 expression in mitochondrial fractions were estimated by western blots. Cerebral ischemia with different time-points of reperfusion resulted in infarct in the territory of the middle cerebral artery accompanied by overall brain damage. In addition, we found up-regulation of LC3B, Beclin1, and LAMP-1, as well as mitophagy activation after reperfusion, with peak expression of these proteins at 24 h after reperfusion. Electron microscopy and immunofluorescence indicated that LC3B was primarily located in neurons, although lower levels of expression were found in astrocytes and even less in vascular endothelial cells. Moreover, significant increases in PINK1 accumulation in the outer membrane of mitochondria and increased Parkin/p62 mitochondrial translocation were shown at 24 h after reperfusion. These findings suggest that the PINK1/Parkin/p62 signalling pathway was involved in the pathophysiological processes following ischemia and reperfusion.

From Mitochondrial Function to Neuroprotection-an Emerging Role for Methylene Blue

Methylene blue (MB) is a well-established drug with a long history of use, owing to its diverse range of use and its minimal side effect profile. MB has been used classically for the treatment of malaria, methemoglobinemia, and carbon monoxide poisoning, as well as a histological dye. Its role in the mitochondria, however, has elicited much of its renewed interest in recent years. MB can reroute electrons in the mitochondrial electron transfer chain directly from NADH to cytochrome c, increasing the activity of complex IV and effectively promoting mitochondrial activity while mitigating oxidative stress. In addition to its beneficial effect on mitochondrial protection, MB is also known to have robust effects in mitigating neuroinflammation. Mitochondrial dysfunction has been identified as a seemingly unifying pathological phenomenon across a wide range of neurodegenerative disorders, which thus positions methylene blue as a promising therapeutic. In both in vitro and in vivo studies, MB has shown impressive efficacy in mitigating neurodegeneration and the accompanying behavioral phenotypes in animal models for such conditions as stroke, global cerebral ischemia, Alzheimer's disease, Parkinson's disease, and traumatic brain injury. This review summarizes recent work establishing MB as a promising candidate for neuroprotection, with particular emphasis on the contribution of mitochondrial function to neural health. Furthermore, this review will briefly examine the link between MB, neurogenesis, and improved cognition in respect to age-related cognitive decline.

Advances in stroke pharmacology

Stroke occurs when a cerebral blood vessel is blocked or ruptured, and it is the major cause of death and adult disability worldwide. Various pharmacological agents have been developed for the treatment of stroke either through interrupting the molecular pathways leading to neuronal death or enhancing neuronal survival and regeneration. Except for rtPA, few of these agents have succeeded in clinical trials. Recently, with the understanding of the pathophysiological process of stroke, there is a resurrection of research on developing neuroprotective agents for stroke treatment, and novel molecular targets for neuroprotection and neurorestoration have been discovered to predict or offer clinical benefits. Here we review the latest major progress of pharmacological studies in stroke, especially in ischemic stroke; summarize emerging potential therapeutic mechanisms; and highlight recent clinical trials. The aim of this review is to provide a panorama of pharmacological interventions for stroke and bridge basic and translational research to guide the clinical management of stroke therapy.