Autophagy in acute brain injury: feast, famine, or folly?

The effects of apelin-13 in a mouse model of post-traumatic stress disorder

The objective is to investigate the effects of apelin-13 in models of post-traumatic stress disorder (PTSD). Mature male CD1 mice were subjected to the single prolonged stress method to induce PTSD-related behaviors. These behaviors were then evaluated using the elevated plus maze test, Morris water maze test, and open field test. Hippocampal neural cell death was assessed using propidium iodide labeling. The expression of hippocampal autophagy pathway-associated proteins was determined through immunoblotting analysis, and LC3 levels were also measured via quantitative real-time reverse transcription-PCR. The results demonstrate that administration of apelin-13 suppressed PTSD-induced hippocampal neural cell death and alleviated PTSD-related behaviors in mice. Additionally, PTSD led to an up-regulation of LC3 and FoxO3a, and down-regulation of P62, p-PI3K, p-Akt, and p-FoxO3a in the hippocampus. However, these changes were reversed by apelin-13 treatment. These findings support the hypothesis that apelin-13 prevents the development of PTSD-like behavior and inhibits autophagy of neuronal cells in a mouse model of PTSD. Apelin-13 may hold potential as a therapeutic agent for PTSD in clinical applications.

Functional recovery following traumatic brain injury in rats is enhanced by oral supplementation with bovine thymus extract

Traumatic brain injury (TBI) is one of the leading causes of death worldwide. There are currently no effective treatments for TBI, and trauma survivors suffer from a variety of long-lasting health consequences. With nutritional support recently emerging as a vital step in improving TBI patients' outcomes, we sought to evaluate the potential therapeutic benefits of nutritional supplements derived from bovine thymus gland, which can deliver a variety of nutrients and bioactive molecules. In a rat model of controlled cortical impact (CCI), we determined that animals supplemented with a nuclear fraction of bovine thymus (TNF) display greatly improved performance on beam balance and spatial memory tests following CCI. Using RNA-Seq, we identified an array of signaling pathways that are modulated by TNF supplementation in rat hippocampus, including those involved in the process of autophagy. We further show that bovine thymus-derived extracts contain antigens found in neural tissues and that supplementation of rats with thymus extracts induces production of serum IgG antibodies against neuronal and glial antigens, which may explain the enhanced animal recovery following CCI through possible oral tolerance mechanism. Collectively, our data demonstrate, for the first time, the potency of a nutritional supplement containing nuclear fraction of bovine thymus in enhancing the functional recovery from TBI.

HSPB2 facilitates neural regeneration through autophagy for sensorimotor recovery after traumatic brain injury

Autophagy is a promising target for promoting neural regeneration, which is essential for sensorimotor recovery following traumatic brain injury (TBI). Whether neuronal heat shock protein B2 (HSPB2), a small molecular heat shock protein, reduces injury and promotes recovery following TBI remains unclear. In this study, we demonstrated that HSPB2 was significantly increased in the neurons of a TBI mouse model, patients, and primary neuron cultures subjected to oxygen/glucose deprivation and reperfusion treatment. Upon creating a tamoxifen-induced neuron-specific HSPB2 overexpression transgenic mouse model, we found that elevated HSPB2 levels promoted long-term sensorimotor recovery and alleviated tissue loss after TBI. We also demonstrated that HSPB2 enhanced white matter structural and functional integrity, promoted central nervous system (CNS) plasticity, and accelerated long-term neural remodeling. Moreover, we found that autophagy occurred around injured brain tissues in patients, and the pro-regenerative effects of HSPB2 relied on its autophagy-promoting function. Mechanistically, HSPB2 may regulate autophagy possibly by forming the HSPB2/BCL2-associated athanogene 3/sequestosome-1 complex to facilitate the clearance of erroneously accumulated proteins in the axons. Treatment with the autophagy inhibitor chloroquine during the acute stage or delayed induction of HSPB2 remarkably impeded HSPB2's long-term reparative function, indicating the importance of acute-stage autophagy in long-term neuro-regeneration. Our findings highlight the beneficial role of HSPB2 in neuro-regeneration and functional recovery following acute CNS injury, thereby emphasizing the therapeutic potential of autophagy regulation for enhancing neuro-regeneration.

Stimulator of interferon genes (STING) expression in the enteric nervous system and contributions of glial STING in disease

BACKGROUND

Appropriate host-microbe interactions are essential for enteric glial development and subsequent gastrointestinal function, but the potential mechanisms of microbe-glial communication are unclear. Here, we tested the hypothesis that enteric glia express the pattern recognition receptor stimulator of interferon genes (STING) and communicate with the microbiome through this pathway to modulate gastrointestinal inflammation.

METHODS

In situ transcriptional labeling and immunohistochemistry were used to examine STING and IFNβ expression in enteric neurons and glia. Glial-STING KO mice (Sox10CreERT2+/- ;STINGfl/fl ) and IFNβ ELISA were used to characterize the role of enteric glia in canonical STING activation. The role of glial STING in gastrointestinal inflammation was assessed in the 3% DSS colitis model.

RESULTS

Enteric glia and neurons express STING, but only enteric neurons express IFNβ. While both the myenteric and submucosal plexuses produce IFNβ with STING activation, enteric glial STING plays a minor role in its production and seems more involved in autophagy processes. Furthermore, deleting enteric glial STING does not affect weight loss, colitis severity, or neuronal cell proportions in the DSS colitis model.

CONCLUSION

Taken together, our data support canonical roles for STING and IFNβ signaling in the enteric nervous system through enteric neurons but that enteric glia do not use these same mechanisms. We propose that enteric glial STING may utilize alternative signaling mechanisms and/or is only active in particular disease conditions. Regardless, this study provides the first glimpse of STING signaling in the enteric nervous system and highlights a potential avenue of neuroglial-microbial communication.

Mechanisms Underlying Curcumin-Induced Neuroprotection in Cerebral Ischemia

Ischemic stroke is the leading cause of death and disability worldwide, and restoring the blood flow to ischemic brain tissues is currently the main therapeutic strategy. However, reperfusion after brain ischemia leads to excessive reactive oxygen species production, inflammatory cell recruitment, the release of inflammatory mediators, cell death, mitochondrial dysfunction, endoplasmic reticulum stress, and blood-brain barrier damage; these pathological mechanisms will further aggravate brain tissue injury, ultimately affecting the recovery of neurological functions. It has attracted the attention of researchers to develop drugs with multitarget intervention effects for individuals with cerebral ischemia. A large number of studies have established that curcumin plays a significant neuroprotective role in cerebral ischemia via various mechanisms, including antioxidation, anti-inflammation, anti-apoptosis, protection of the blood-brain barrier, and restoration of mitochondrial function and structure, restoring cerebral circulation, reducing infarct volume, improving brain edema, promoting blood-brain barrier repair, and improving the neurological functions. Therefore, summarizing the results from the latest literature and identifying the potential mechanisms of action of curcumin in cerebral ischemia will serve as a basis and guidance for the clinical applications of curcumin in the future.

Restoration of ER proteostasis attenuates remote apoptotic cell death after spinal cord injury by reducing autophagosome overload

The pathogenic mechanisms that underlie the progression of remote degeneration after spinal cord injury (SCI) are not fully understood. In this study, we examined the relationship between endoplasmic reticulum (ER) stress and macroautophagy, hereafter autophagy, and its contribution to the secondary damage and outcomes that are associated with remote degeneration after SCI. Using a rat model of spinal cord hemisection at the cervical level, we measured ER stress and autophagy markers in the axotomized neurons of the red nucleus (RN). In SCI animals, mRNA and protein levels of markers of ER stress, such as GRP78, CHOP, and GADD34, increased 1 day after the injury, peaking on Day 5. Notably, in SCI animals, the increase of ER stress markers correlated with a blockade in autophagic flux, as evidenced by the increase in microtubule-associated protein 2 light chain 3 (LC3-II) and p62/SQSTM1 (p62) and the decline in LAMP1 and LAMP2 levels. After injury, treatment with guanabenz protected neurons from UPR failure and increased lysosomes biogenesis, unblocking autophagic flux. These effects correlated with greater activation of TFEB and improved neuronal survival and functional recovery—effects that persisted after suspension of the treatment. Collectively, our results demonstrate that in remote secondary damage, impairments in autophagic flux are intertwined with ER stress, an association that contributes to the apoptotic cell death and functional damage that are observed after SCI.

Oxygen Sensing and Signaling in Alzheimer's Disease: A Breathtaking Story!

Oxygen sensing and homeostasis is indispensable for the maintenance of brain structural and functional integrity. Under low-oxygen tension, the non-diseased brain has the ability to cope with hypoxia by triggering a homeostatic response governed by the highly conserved hypoxia-inducible family (HIF) of transcription factors. With the advent of advanced neuroimaging tools, it is now recognized that cerebral hypoperfusion, and consequently hypoxia, is a consistent feature along the Alzheimer's disease (AD) continuum. Of note, the reduction in cerebral blood flow and tissue oxygenation detected during the prodromal phases of AD, drastically aggravates as disease progresses. Within this scenario a fundamental question arises: How HIF-driven homeostatic brain response to hypoxia "behaves" during the AD continuum? In this sense, the present review is aimed to critically discuss and summarize the current knowledge regarding the involvement of hypoxia and HIF signaling in the onset and progression of AD pathology. Importantly, the promises and challenges of non-pharmacological and pharmacological strategies aimed to target hypoxia will be discussed as a new "hope" to prevent and/or postpone the neurodegenerative events that occur in the AD brain.

Reduction of Autophagosome Overload Attenuates Neuronal Cell Death After Traumatic Brain Injury

Previous studies have shown that alterations in autophagy-related proteins exist extensively after traumatic brain injury (TBI). However, whether autophagy is enhanced or suppressed by TBI remains controversial. In our study, a controlled cortical impact was used to establish a model of moderate TBI in rats. We found that a significant increase in protein levels of LC3-II and SQSTM1 in the injured cortex group. However, there were no significant differences in protein levels of VPS34, Beclin-1, and phosphor-ULK1, which are the promoters of autophagy. Lysosome dysfunction after TBI might lead to autophagosome accumulation. In addition, the highly specific autophagy inhibitor SAR405 administration reduced TBI-induced apoptosis-related protein cleaved caspase-3 and cleaved caspase-9 levels in the ipsilateral cortex, as well as brain edema and neurological defects accessed by mNSS. Furthermore, chloroquine treatment reversed the beneficial effects of SAR405 by increasing the accumulation of autophagosomes. Finally, our data showed that autophagy inhibition by VPS34 gene knockout method attenuated cell death after TBI. Our findings indicate that impaired autophagosome degradation is involved in the pathological reaction after TBI, and the inhibition of autophagy contributes to attenuate neuronal cell death and functional defects.

The Neuroprotective Role of Neuroserpin in Ischemic and Hemorrhagic Stroke

Tissue plasminogen activator (tPA) is commonly used to treat acute ischemic stroke within an appropriate therapeutic window. Its inhibitor, neuroserpin (NSP), is reported to exhibit neuroprotective effects on stroke. This review aims to summarize, from literature, the available evidence, potential mechanisms, and knowledge limitations regarding the neuroprotective role of NSP in stroke. All the available evidence indicates that the regulation of the inflammatory response may play a key role in the mechanisms of NSP, which involve all the constituents of the neuroimmune axis. The neuroinflammatory response triggered by stroke can be reversed by NSP, with complicated mechanisms such as maintenance and reconstruction of the structure and function of the blood-brain barrier (BBB), protection of the cells in the central nervous system, and suppression of cell death in both ischemic and hemorrhagic stroke. Moreover, available evidence strongly suggests a tPA-independent mechanism is involved in NSP. However, there are many important issues that are still unclear and need further investigation, such as the effects of NSP on hemorrhagic stroke, the role of the tPA-independent neuroprotective mechanisms, and the clinical application prospects of NSP. We believe our work will be helpful to further understand the neuroprotective role of NSP.

EGCG treats ICH via up-regulating miR-137-3p and inhibiting Parthanatos

Intracranial hemorrhage (ICH) causes high mortality and disability without effective treatment in the clinical setting. (-)-Epigallocatechin-3-gallate (EGCG) exerts an essential role in the central nervous system and offers a promising therapeutic agent for the treatment of oxidative damage-related diseases. MiR-137 can inhibit the oxidative stress and apoptosis to attenuate neuronal injury. However, the role of EGCG in regulating miR-137-3p and neuronal Parthanatos remains to be unclear. In the present study, we build the ICH mice model to investigate the antioxidant effects of EGCG via upregulating miR-137-3p and inhibiting neuronal Parthanatos. We revealed that EGCG upregulated miR-137-3p and inhibited neuronal Parthanatos, and promoted the functional recovery, alleviated ICH-induced brain injury, and reduced oxidative stress in mice following ICH. However, following the inhibition of miR-137-3p and activation of Parthanatos, EGCG was unable to exert neuroprotective roles. These combined results suggest that EGCG may upregulate miR-137-3p and inhibit neuronal Parthanatos to accelerate functional recovery in mice after ICH, laying the foundation for EGCG to be a novel strategy for the treatment of neuronal injuries related to Parthanatos.

Hydroxysafflor yellow A promotes multiterritory perforating flap survival: an experimental study

The use of perforator flaps is a common surgical technique in wound repair. However, the area surrounding the multiterritory perforating flap often becomes necrotic due to ischemia. Hydroxysafflor yellow A (HSYA), a traditional Chinese medicine extracted from edible safflower, can be used medicinally to promote angiogenesis, inhibit apoptosis, and alleviate oxidative stress and other biological activities. Here, we investigated the effect of HSYA on perforator flap survival and its potential mechanism. Our results demonstrate that HSYA significantly improves the survival area of perforator flaps, increases blood supply, reduces tissue edema, and increases mean vascular density. HSYA treatment promotes angiogenesis and inhibits oxidative stress, apoptosis, and autophagy in perforator flaps, suggesting many potential mechanisms for flap survival.

Assessment of Long-Term Effects of Sports-Related Concussions: Biological Mechanisms and Exosomal Biomarkers

Concussion or mild traumatic brain injury (mTBI) in athletes can cause persistent symptoms, known as post-concussion syndrome (PCS), and repeated injuries may increase the long-term risk for an athlete to develop neurodegenerative diseases such as chronic traumatic encephalopathy (CTE), and Alzheimer's disease (AD). The Center for Disease Control estimates that up to 3.8 million sport-related mTBI are reported each year in the United States. Despite the magnitude of the phenomenon, there is a current lack of comprehensive prognostic indicators and research has shown that available monitoring tools are moderately sensitive to short-term concussion effects but less sensitive to long-term consequences. The overall aim of this review is to discuss novel, quantitative, and objective measurements that can predict long-term outcomes following repeated sports-related mTBIs. The specific objectives were (1) to provide an overview of the current clinical and biomechanical tools available to health practitioners to ensure recovery after mTBIs, (2) to synthesize potential biological mechanisms in animal models underlying the long-term adverse consequences of mTBIs, (3) to discuss the possible link between repeated mTBI and neurodegenerative diseases, and (4) to discuss the current knowledge about fluid biomarkers for mTBIs with a focus on novel exosomal biomarkers. The conclusions from this review are that current post-concussion clinical tests are not sufficiently sensitive to injury and do not accurately quantify post-concussion alterations associated with repeated mTBIs. In the current review, it is proposed that current practices should be amended to include a repeated symptom inventory, a cognitive assessment of executive function and impulse control, an instrumented assessment of balance, vestibulo-ocular assessments, and an improved panel of blood or exosome biomarkers.

Progesterone Attenuates Stress-Induced NLRP3 Inflammasome Activation and Enhances Autophagy following Ischemic Brain Injury

NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome inhibition and autophagy induction attenuate inflammation and improve outcome in rodent models of cerebral ischemia. However, the impact of chronic stress on NLRP3 inflammasome and autophagic response to ischemia remains unknown. Progesterone (PROG), a neuroprotective steroid, shows promise in reducing excessive inflammation associated with poor outcome in ischemic brain injury patients with comorbid conditions, including elevated stress. Stress primes microglia, mainly by the release of alarmins such as high-mobility group box-1 (HMGB1). HMGB1 activates the NLRP3 inflammasome, resulting in pro-inflammatory interleukin (IL)-1β production. In experiment 1, adult male Sprague-Dawley rats were exposed to social defeat stress for 8 days and then subjected to global ischemia by the 4-vessel occlusion model, a clinically relevant brain injury associated with cardiac arrest. PROG was administered 2 and 6 h after occlusion and then daily for 7 days. Animals were killed at 7 or 14 days post-ischemia. Here, we show that stress and global ischemia exert a synergistic effect in HMGB1 release, resulting in exacerbation of NLRP3 inflammasome activation and autophagy impairment in the hippocampus of ischemic animals. In experiment 2, an in vitro inflammasome assay, primary microglia isolated from neonatal brain tissue, were primed with lipopolysaccharide (LPS) and stimulated with adenosine triphosphate (ATP), displaying impaired autophagy and increased IL-1β production. In experiment 3, hippocampal microglia isolated from stressed and unstressed animals, were stimulated ex vivo with LPS, exhibiting similar changes than primary microglia. Treatment with PROG reduced HMGB1 release and NLRP3 inflammasome activation, and enhanced autophagy in stressed and unstressed ischemic animals. Pre-treatment with an autophagy inhibitor blocked Progesterone's (PROG's) beneficial effects in microglia. Our data suggest that modulation of microglial priming is one of the molecular mechanisms by which PROG ameliorates ischemic brain injury under stressful conditions.

mTOR-Related Cell-Clearing Systems in Epileptic Seizures, an Update

Recent evidence suggests that autophagy impairment is implicated in the epileptogenic mechanisms downstream of mTOR hyperactivation. This holds true for a variety of genetic and acquired epileptic syndromes besides malformations of cortical development which are classically known as mTORopathies. Autophagy suppression is sufficient to induce epilepsy in experimental models, while rescuing autophagy prevents epileptogenesis, improves behavioral alterations, and provides neuroprotection in seizure-induced neuronal damage. The implication of autophagy in epileptogenesis and maturation phenomena related to seizure activity is supported by evidence indicating that autophagy is involved in the molecular mechanisms which are implicated in epilepsy. In general, mTOR-dependent autophagy regulates the proliferation and migration of inter-/neuronal cortical progenitors, synapse development, vesicular release, synaptic plasticity, and importantly, synaptic clustering of GABA_A receptors and subsequent excitatory/inhibitory balance in the brain. Similar to autophagy, the ubiquitin–proteasome system is regulated downstream of mTOR, and it is implicated in epileptogenesis. Thus, mTOR-dependent cell-clearing systems are now taking center stage in the field of epilepsy. In the present review, we discuss such evidence in a variety of seizure-related disorders and models. This is expected to provide a deeper insight into the molecular mechanisms underlying seizure activity.

Spermidine Exhibits Protective Effects Against Traumatic Brain Injury

Traumatic brain injury (TBI) causes permanent neurological and cognitive impairments. Effective pharmacological interventions remain elusive. Spermidine is a polyamine compound found in our body that may play a role in brain development and congenital function. In this study, we aimed to investigate the therapeutic potential of spermidine for TBI. We employed experimental closed head injury (CHI) model to evaluate the protective function of spermidine on brain injury. We assessed the neurobehavioral function recovery using Neurologic Severity Score (NSS) and Morris water maze test. At histological level, we evaluated the improvement on brain edema, brain-blood barrier integrity, and cell apoptosis. We also measured inflammatory cytokines and brain injury biomarkers to monitor the treatment outcomes. Last, we correlated the level of spermidine with CHI animal model and TBI patients with different levels of severity. Spermidine administration post-CHI was found effectively to accelerate NSS improvement and shorten latency in maze test. We observed consistent improvements in brain edema, BBB function, and cell death in spermidine-treated group. Inflammatory cytokines and TBI biomarkers, e.g., S100B, MBP and CFAP were reduced significantly in treatment group. Interestingly, inhibiting spermidine synthesis influenced the neurobehavioral recovery in CHI mice. ODC1, a rate-limiting enzyme for spermidine synthesis, was found lower in CHI mice. Serum level of spermidine was significantly lower in TBI patients with severe pathological scores. Spermidine pathway may carry an endogenous role in pathophysiological process of CHI. For the first time, we demonstrated that administrating spermidine may provide a new treatment for TBI.

The Function and Mechanisms of Autophagy in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the most common causes of long-term disability and death worldwide. Autophagy is activated and autophagic flux is impaired following TBI. But the controversial roles and underlying mechanisms of autophagy after TBI are not clear. This chapter will update the current state of knowledge in the process of autophagy, the roles of autophagy in TBI as well as some upstream moleculars and pharmacological regulators of autophagy involved in TBI. We also discuss autophagy mechanism-based preclinical pharmacological intervention. These observations make autophagy an attractive therapeutic target for developing new therapeutic strategies to achieve better outcomes for patients suffering from TBI.

An early neuroprotective effect of atorvastatin against subarachnoid hemorrhage

Atorvastatin has been shown to reduce early brain edema and neuronal death after subarachnoid hemorrhage, but its mechanism is not clear. In this study, rat models of subarachnoid hemorrhage were established by autologous blood injection in the cisterna magna. Rat models were intragastrically administered 20 mg/kg atorvastatin 24 hours before subarachnoid hemorrhage, 12 and 36 hours after subarachnoid hemorrhage. Compared with the controls, atorvastatin treatment demonstrated that at 72 hours after subarachnoid hemorrhage, neurological function had clearly improved; brain edema was remarkably relieved; cell apoptosis was markedly reduced in the cerebral cortex of rats; the number of autophagy-related protein Beclin-1-positive cells and the expression levels of Beclin-1 and LC3 were increased compared with subarachnoid hemorrhage only. The ultrastructural damage of neurons in the temporal lobe was also noticeably alleviated. The similarities between the effects of atorvastatin and rapamycin were seen in all the measured outcomes of subarachnoid hemorrhage. However, these were contrary to the results of 3-methyladenine injection, which inhibits the signaling pathway of autophagy. These findings indicate that atorvastatin plays an early neuroprotective role in subarachnoid hemorrhage by activating autophagy. The experimental protocol was approved by the Animal Ethics Committee of Anhui Medical University, China (904 Hospital of Joint Logistic Support Force of PLA; approval No. YXLL-2017-09) on February 22, 2017.

Eicosapentaenoic acid prevents inflammation induced by acute cerebral infarction through inhibition of NLRP3 inflammasome activation

OBJECTIVE

Acute cerebral infarction (ACI) is the most common type of acute cerebrovascular diseases resulting in high rate of death and disability. Numerous evidences show that inflammation is the leading cause of ischemic brain injury, thus anti-inflammatory therapy is an attractive candidate for ischemic brain damage. Eicosapentaenoic acid (EPA) exerts anti-inflammatory activity in lots of human inflammatory diseases, whereas its effect in ACI is left to elucidate.

METHOD

Nlpr3^-/- mice, Gpr40^-/-; Gpr120^-/- mice and mice with right middle cerebral artery occlusion (MCAO) were used to detect NLR family pyrin domain containing 3 (NLRP3) inflammasome activation by Western Blot and the release of proinflammatory cytokines by ELISA. To estimate the acute ischemic condition in vitro, oxygen-glucose deprivation (OGD) was induced in BV2 microglia cells. Transfection of the shRNA targeting GPR40 and GPR120 mRNA into BV2 cells was also assessed. Apoptosis in ischemic cerebral tissues and BV2 cells was detected by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay and flow cytometry.

RESULT

Here we show that EPA suppresses ACI-induced inflammatory responses through blocking NLRP3 inflammasome activation. In addition, EPA inhibits NLRP3 inflammasome activation through G protein-coupled receptor 40 (GPR40) and GPR120. Importantly, EPA ameliorates ACI-induced apoptosis.

CONCLUSION

EPA exerts beneficial effect on ACI-induced inflammation through blocking NLRP3 inflammasome activation by GPR40 and GPR120. Our findings suggest the potential clinical use of EPA in ACI.

Autophagy in Neurotrauma: Good, Bad, or Dysregulated

Autophagy is a physiological process that helps maintain a balance between the manufacture of cellular components and breakdown of damaged organelles and other toxic cellular constituents. Changes in autophagic markers are readily detectable in the spinal cord and brain following neurotrauma, including traumatic spinal cord and brain injury (SCI/TBI). However, the role of autophagy in neurotrauma remains less clear. Whether autophagy is good or bad is under debate, with strong support for both a beneficial and detrimental role for autophagy in experimental models of neurotrauma. Emerging data suggest that autophagic flux, a measure of autophagic degradation activity, is impaired in injured central nervous systems (CNS), and interventions that stimulate autophagic flux may provide neuroprotection in SCI/TBI models. Recent data demonstrating that neurotrauma can cause lysosomal membrane damage resulting in pathological autophagosome accumulation in the spinal cord and brain further supports the idea that the impairment of the autophagy-lysosome pathway may be a part of secondary injury processes of SCI/TBI. Here, we review experimental work on the complex and varied responses of autophagy in terms of both the beneficial and detrimental effects in SCI and TBI models. We also discuss the existing and developing therapeutic options aimed at reducing the disruption of autophagy to protect the CNS after injuries.

LRG1 Promotes Apoptosis and Autophagy through the TGFβ-smad1/5 Signaling Pathway to Exacerbate Ischemia/Reperfusion Injury

Leucine-rich α2-glycoprotein1 (LRG1), a pleiotropic protein, plays a pathogenic role in multiple human diseases. However, its pathophysiological function in ischemia/reperfusion injury remains unclear. In this study, we discussed the function and mechanism of LRG1 in acute ischemic stroke from both basic and clinical research points of view. Mice underwent transient middle cerebral artery occlusion (tMCAO) surgery 2 weeks after LRG1 was overexpressed by the delivery of adeno-associated virus (AAV). For wild-type mice, both the protein and the transcript of LRG1 in the brain tissue were elevated after tMCAO. Meanwhile, the serum levels of LRG1 were decreased after tMCAO. The neuronal injury was shown aggravated in the AAV-LRG1 group (AAV-LRG1 mice with tMCAO) through infarction volume, neurological score, HE, and Nissl staining. Meanwhile, LRG1 significantly enhanced apoptosis and autophagy during tMCAO, as detected by caspase3, Bax, Bcl-2, LC3II/LC3I, Beclin1, p62, and a TUNEL assay. Furthermore, by overexpression of LRG1, the protein of ALK1 was upregulated and the TGFβ-smad1/5 signaling pathway was activated upon tMCAO. We also showed that patients with acute cerebral infarction had lower serum levels of LRG1 compared to healthy controls. In addition, LRG1 levels were associated with infarction volume, stroke severity, and prognosis in patients with supratentorial infarction. Taken together, the data from this study revealed that LRG1 promoted apoptosis and autophagy through the TGFβ-smad1/5 signaling pathway by up-regulating ALK1, which exacerbates ischemia/reperfusion injury.

Cardiolipin-Dependent Mitophagy Guides Outcome after Traumatic Brain Injury

Mitochondrial energy production is essential for normal brain function. Traumatic brain injury (TBI) increases brain energy demands, results in the activation of mitochondrial respiration, associated with enhanced generation of reactive oxygen species. This chain of events triggers neuronal apoptosis via oxidation of a mitochondria-specific phospholipid, cardiolipin (CL). One pathway through which cells can avoid apoptosis is via elimination of damaged mitochondria by mitophagy. Previously, we showed that externalization of CL to the mitochondrial surface acts as an elimination signal in cells. Whether CL-mediated mitophagy occurs in vivo or its significance in the disease processes are not known. In this study, we showed that TBI leads to increased mitophagy in the human brain, which was also detected using TBI models in male rats. Knockdown of CL synthase, responsible for de novo synthesis of CL, or phospholipid scramblase-3, responsible for CL translocation to the outer mitochondrial membrane, significantly decreased TBI-induced mitophagy. Inhibition of mitochondrial clearance by 3-methyladenine, mdivi-1, or phospholipid scramblase-3 knockdown after TBI led to a worse outcome, suggesting that mitophagy is beneficial. Together, our findings indicate that TBI-induced mitophagy is an endogenous neuroprotective process that is directed by CL, which marks damaged mitochondria for elimination, thereby limiting neuronal death and behavioral deficits.SIGNIFICANCE STATEMENT Traumatic brain injury (TBI) increases energy demands leading to activation of mitochondrial respiration associated with enhanced generation of reactive oxygen species and resultant damage to mitochondria. We demonstrate that the complete elimination of irreparably damaged organelles via mitophagy is activated as an early response to TBI. This response includes translocation of mitochondria phospholipid cardiolipin from the inner membrane to the outer membrane where externalized cardiolipin mediates targeted protein light chain 3-mediated autophagy of damaged mitochondria. Our data on targeting phospholipid scramblase and cardiolipin synthase in genetically manipulated cells and animals strongly support the essential role of cardiolipin externalization mechanisms in the endogenous reparative plasticity of injured brain cells. Furthermore, successful execution and completion of mitophagy is beneficial in the context of preservation of cognitive functions after TBI.

Nicotinamide adenine dinucleotide emerges as a therapeutic target in aging and ischemic conditions

Nicotinamide adenine dinucleotide (NAD⁺) has been described as central coenzyme of redox reactions and is a key regulator of stress resistance and longevity. Aging is a multifactorial and irreversible process that is characterized by a gradual diminution in physiological functions in an organism over time, leading to development of age-associated pathologies and eventually increasing the probability of death. Ischemia is the lack of nutritive blood flow that causes damage and mortality that mostly occurs in various organs during aging. During the process of aging and related ischemic conditions, NAD⁺ levels decline and lead to nuclear and mitochondrial dysfunctions, resulting in age-related pathologies. The majority of studies have shown that restoring of NAD⁺ using supplementation with intermediates such as nicotinamide mononucleotide and nicotinamide riboside can be a valuable strategy for recovery of ischemic injury and age-associated defects. This review summarizes the molecular mechanisms responsible for the reduction in NAD⁺ levels during ischemic disorders and aging, as well as a particular focus is given to the recent progress in the understanding of NAD⁺ precursor's effects on aging and ischemia.

Effects of bradykinin on the survival of multiterritory perforator flaps in rats

Background

Bradykinin, a vasoactive peptide, has many biological functions. For example, it accelerates angiogenesis. Thus, we studied the effects of bradykinin on the survival of perforator flaps.

Methods

Averagely, 50 male Sprague–Dawley rats were divided into control and bradykinin groups and underwent procedures to the multiterritory perforator flap. Areas of flap survival were tested 7 days later. Flap perfusion was evaluated by laser Doppler imaging. We assessed the extent of autophagy by determining LC3-II/I, Beclin 1, and p62. Flap angiogenesis was assessed by immunohistochemistry and H&E staining. We measured the level of vascular endothelial growth factor (VEGF) protein using western blot. We assessed oxidative stress by measuring the activity of superoxide dismutase (SOD) and malondialdehyde (MDA) levels. The apoptotic index was also evaluated by western blot, and we determined nitric oxide (NO) production using an NO assay kit.

Results

The bradykinin group exhibited significantly larger areas of flap survival, higher blood supply, and more neovascularization. The bradykinin group also had higher SOD activity, higher VEGF expression and NO content, and reduced MDA compared to the control group. Rats treated with bradykinin also had lower levels of apoptosis and autophagy relative to the control group.

Conclusion

Our results suggest that bradykinin promotes the survival of multiterritory perforator flaps by increasing angiogenesis, promoting the release of NO, suppressing apoptosis, reducing oxidative stress, and inhibiting autophagy.

Rapamycin treatment increases hippocampal cell viability in an mTOR-independent manner during exposure to hypoxia mimetic, cobalt chloride

BACKGROUND

Cobalt chloride (CoCl2) induces chemical hypoxia through activation of hypoxia-inducible factor-1 alpha (HIF-1α). Mammalian target of rapamycin (mTOR) is a multifaceted protein capable of regulating cell growth, angiogenesis, metabolism, proliferation, and survival. In this study, we tested the efficacy of a well-known mTOR inhibitor, rapamycin, in reducing oxidative damage and increasing cell viability in the mouse hippocampal cell line, HT22, during a CoCl2-simulated hypoxic insult.

RESULTS

CoCl2 caused cell death in a dose-dependent manner and increased protein levels of cleaved caspase-9 and caspase-3. Rapamycin increased viability of HT22 cells exposed to CoCl2 and reduced activation of caspases-9 and -3. Cells exposed to CoCl2 displayed increased reactive oxygen species (ROS) production and hyperpolarization of the mitochondrial membrane, both of which rapamycin successfully blocked. mTOR protein itself, along with its downstream signaling target, phospho-S6 ribosomal protein (pS6), were significantly inhibited with CoCl2 and rapamycin addition did not significantly lower expression further. Rapamycin promoted protein expression of Beclin-1 and increased conversion of microtubule-associated protein light chain 3 (LC3)-I into LC3-II, suggesting an increase in autophagy. Pro-apoptotic protein, Bcl-2 associated × (Bax), exhibited a slight, but significant decrease with rapamycin treatment, while its anti-apoptotic counterpart, B cell lymphoma-2 (Bcl-2), was to a similar degree upregulated. Finally, the protein expression ratio of phosphorylated mitogen-activated protein kinase (pMAPK) to its unphosphorylated form (MAPK) was dramatically increased in rapamycin and CoCl2 co-treated cells.

CONCLUSIONS

Our results indicate that rapamycin confers protection against CoCl2-simulated hypoxic insults to neuronal cells. This occurs, as suggested by our results, independent of mTOR modification, and rather through stabilization of the mitochondrial membrane with concomitant decreases in ROS production. Additionally, inhibition of caspase-9 and -3 activation and stimulation of protective autophagy reduces cell death, while a decrease in the Bax/Bcl-2 ratio and an increase in pMAPK promotes cell survival during CoCl2 exposure. Together these results demonstrate the therapeutic potential of rapamycin against hypoxic injury and highlight potential pathways mediating the protective effects of rapamycin treatment.

The Role of Autophagy in Subarachnoid Hemorrhage: An Update

BACKGROUND

Autophagy is an extensive self-degradation process for the disposition of cytosolic aggregated or misfolded proteins and defective organelles which executes the functions of pro-survival and pro-death to maintain cellular homeostasis. The pathway plays essential roles in several neurological disorders. Subarachnoid Hemorrhage (SAH) is a devastating subtype of hemorrhagic stroke with high risk of neurological deficit and high mortality. Early brain injury (EBI) plays a role in the poor clinical course and outcome after SAH. Recent studies have paid attention on the role of the autophagy pathway in the development of EBI after SAH. We aim to update the multifaceted roles of autophagy pathway in the pathogenesis of SAH, especially in the phase of EBI.

METHODS

We reviewed early researches related to autophagy and SAH. The following three aspects of contents will be mainly discussed: the process of the autophagy pathway, the role of the autophagy in SAH and the interaction between organelle dysfunction and autophagy pathway after SAH.

RESULTS

Accumulating evidence shows an increased autophagy reaction in response to early stages of SAH. However, others suggest inadequate or excessive autophagy activation can result in cell injury and death. In addition to autophagy, apoptosis and necrosis can occur in neurons simultaneously after SAH, leading to mixed features of cell death morphologies. And it is also known that there is extensive crosstalk between autophagy and apoptosis pathway. Subcellular organelles of neural cells generally participate in the formation and functional parts of autophagy process.

CONCLUSION

Autophagy plays an important role in the SAH-induced brain injury. A better understanding of the interrelationship among autophagy, apoptosis, and necrosis might provide us better therapeutic targets for the treatment of SAH.

STING-mediated type-I interferons contribute to the neuroinflammatory process and detrimental effects following traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) represents a major cause of disability and death worldwide with sustained neuroinflammation and autophagy dysfunction contributing to the cellular damage. Stimulator of interferon genes (STING)-induced type-I interferon (IFN) signalling is known to be essential in mounting the innate immune response against infections and cell injury in the periphery, but its role in the CNS remains unclear. We previously identified the type-I IFN pathway as a key mediator of neuroinflammation and neuronal cell death in TBI. However, the modulation of the type-I IFN and neuroinflammatory responses by STING and its contribution to autophagy and neuronal cell death after TBI has not been explored.

METHODS

C57BL/6J wild-type (WT) and STING^-/- mice (8-10-week-old males) were subjected to controlled cortical impact (CCI) surgery and brains analysed by QPCR, Western blot and immunohistochemical analyses at 2 h or 24 h. STING expression was also analysed by QPCR in post-mortem human brain samples.

RESULTS

A significant upregulation in STING expression was identified in late trauma human brain samples that was confirmed in wild-type mice at 2 h and 24 h after CCI. This correlated with an elevated pro-inflammatory cytokine profile with increased TNF-α, IL-6, IL-1β and type-I IFN (IFN-α and IFN-β) levels. This expression was suppressed in the STING^-/- mice with a smaller lesion volume in the knockout animals at 24 h post CCI. Wild-type mice also displayed increased levels of autophagy markers, LC3-II, p62 and LAMP2 after TBI; however, STING^-/- mice showed reduced LAMP2 expression suggesting a role for STING in driving dysfunctional autophagy after TBI.

CONCLUSION

Our data implicates a detrimental role for STING in mediating the TBI-induced neuroinflammatory response and autophagy dysfunction, potentially identifying a new therapeutic target for reducing cellular damage in TBI.

AC-YVAD-CMK Inhibits Pyroptosis and Improves Functional Outcome after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) refers to bleeding in the brain and is associated with the release of large amount of inflammasomes, and the activation of different cell death pathways. These cell death pathways lead to removal of inactivated and damaged cells and also result in neuronal cell damage. Pyroptosis is a newly discovered cell death pathway that has gained attention in recent years. This pathway mainly depends on activation of caspase-1-mediated cascades to cause cell death. We tested a well-known selective inhibitor of caspase-1, AC-YVAD-CMK, which has previously been found to have neuroprotective effects in ICH mice model, to ascertain its effects on the activation of inflammasomes mediated pyroptosis. Our results showed that AC-YVAD-CMK could reduce caspase-1 activation and inhibit IL-1β production and maturation, but has no effect on NLRP3 expression, an upstream inflammatory complex. AC-YVAD-CMK administration also resulted in reduction in M1-type microglia polarization around the hematoma, while increasing the number of M2-type cells. Furthermore, AC-YVAD-CMK treated mice showed some recovery of neurological function after hemorrhage especially at the hyperacute and subacute stage resulting in some degree of limb movement. In conclusion, we are of the view that AC-YVAD-CMK could inhibit pyroptosis, decrease the secretion or activation of inflammatory factors, and affect the polarization of microglia resulting in improvement of neurological function after ICH.

Oxidized phospholipid signaling in traumatic brain injury

Oxidative stress is a major contributor to secondary injury signaling cascades following traumatic brain injury (TBI). The role of lipid peroxidation in the pathophysiology of a traumatic insult to neural tissue is increasingly recognized. As the methods to quantify lipid peroxidation have gradually improved, so has the understanding of mechanistic details of lipid peroxidation and related signaling events in the injury pathogenesis. While free-radical mediated, non-enzymatic lipid peroxidation has long been studied, recent advances in redox lipidomics have demonstrated the significant contribution of enzymatic lipid peroxidation to TBI pathogenesis. Complex interactions between inflammation, phospholipid peroxidation, and hydrolysis define the engagement of different cell death programs and the severity of injury and outcome. This review focuses on enzymatic phospholipid peroxidation after TBI, including the mechanism of production, signaling roles in secondary injury pathology, and temporal course of production with respect to inflammatory response. In light of the newly identified phospholipid oxidation mechanisms, we also discuss possible therapeutic targets to improve neurocognitive outcome after TBI. Finally, we discuss current limitations in identifying oxidized phospholipids and possible methodologic improvements that can offer a deeper insight into the region-specific distribution and subcellular localization of phospholipid oxidation after TBI.

Emerging Roles of Sonic Hedgehog in Adult Neurological Diseases: Neurogenesis and Beyond

Sonic hedgehog (Shh), a member of the hedgehog (Hh) family, was originally recognized as a morphogen possessing critical characters for neural development during embryogenesis. Recently, however, Shh has emerged as an important modulator in adult neural tissues through different mechanisms such as neurogenesis, anti-oxidation, anti-inflammation, and autophagy. Therefore, Shh may potentially have clinical application in neurodegenerative diseases and brain injuries. In this article, we present some examples, including ours, to show different aspects of Shh signaling and how Shh agonists or mimetics are used to alter the neuronal fates in various disease models, both in vitro and in vivo. Other potential mechanisms that are discussed include alteration of mitochondrial function and anti-aging effect; both are critical for age-related neurodegenerative diseases. A thorough understanding of the protective mechanisms elicited by Shh may provide a rationale to design innovative therapeutic regimens for various neurodegenerative diseases.

Inhibition of autophagy after perforator flap surgery increases flap survival and angiogenesis

BACKGROUND

The survival ratio of multiterritory perforator flap is variable. Therefore, surviving mechanisms are increasingly explored to identify novel therapeutics. The condition of the choke zone is essential for perforator flap survival. In this study, we investigated autophagy in the choke zone after flap surgery.

MATERIALS AND METHODS

The flap model involved a perforator flap with three territories that was located on the right dorsal side of a rat. A total of 36 rats were divided into six groups, including the control, 0 d postoperative (PO), 1, 3, 5, and 7 d PO groups. In addition, 72 rats were divided into three groups, including a control group, a 3-methyladenine (3-MA) group, and a rapamycin group. Skin tissue of rats was used for measuring autophagy proteins, vascular endothelial growth factor (VEGF) expression, and histological examination. On day 7 after surgery, the survival ratio of each flap was determined.

RESULTS

The expression of autophagy and VEGF in the second choke zone (choke II) was increased after flap surgery. Among the three groups, the survival ratio of flaps in the 3-MA group was the highest. Furthermore, the angiogenesis level in the 3-MA group in choke II was the highest among the three groups.

CONCLUSIONS

Autophagy was initiated by surgery in choke II, and VEGF expression in choke II was increased after flap surgery. Inhibiting autophagy after perforator flap surgery is beneficial for flap survival and for promoting angiogenesis in choke II.

The role of autophagy in acute brain injury: A state of flux?

It is established that increased autophagy is readily detectable after various types of acute brain injury, including trauma, focal and global cerebral ischemia. What remains controversial, however, is whether this heightened detection of autophagy in brain represents a homeostatic or pathologic process, or an epiphenomenon. The ultimate role of autophagy after acute brain injury likely depends upon: 1) the degree of brain injury and the overall autophagic burden; 2) the capacity of individual cell types to ramp up autophagic flux; 3) the local redox state and signaling of parallel cell death pathways; 4) the capacity to eliminate damage associated molecular patterns and toxic proteins and metabolites both intra- and extracellularly; and 5) the timing of the pro- or anti-autophagic intervention. In this review, we attempt to reconcile conflicting studies that support both a beneficial and detrimental role for autophagy in models of acute brain injury.

AMP-activated protein kinase-dependent induction of autophagy by erythropoietin protects against spinal cord injury in rats

AIMS

Autophagy has been regarded as a promising therapeutic target for spinal cord injury (SCI). Erythropoietin (EPO) has been demonstrated to exhibit neuroprotective effects in the central nervous system (CNS); however, the molecular mechanisms of its protection against SCI remain unknown. This study aims to investigate whether the neuroprotective effects of EPO on SCI are mediated by autophagy via AMP-activated protein kinase (AMPK) signaling pathways.

METHODS

Functional assessment and Nissl staining were used to investigate the effects of EPO on SCI. Expressions of proteins were detected by Western blot and immunohistochemistry.

RESULTS

Treatment with EPO significantly reduced the loss of motor neurons and improved the functional recovery following SCI. Erythropoietin significantly enhanced the SCI-induced autophagy through activating AMPK and inactivating mTOR signaling. The inhibitor of AMPK, compound C, could block the EPO-induced autophagy and beneficial action on SCI, whereas the activator of AMPK, metformin, could mimic the effects of EPO. In the in vitro studies, EPO enhanced the hypoxia-induced autophagy in an AMPK-dependent manner.

CONCLUSIONS

The AMPK-dependent induction of autophagy contributes to the neuroprotection of EPO on SCI.

Neuroprotective effects of pifithrin-α against traumatic brain injury in the striatum through suppression of neuroinflammation, oxidative stress, autophagy, and apoptosis

Cortical and hippocampal neuronal damages caused by traumatic brain injury (TBI) are associated with motor and cognitive impairments; however, only little attention paid to the striatal damage. It is known that the p53 tumor-suppressor transcription factor participated in TBI-induced secondary brain damage. We investigated how the p53 inactivator pifithrin (PFT)-α affected TBI-induced striatal neuronal damage at 24 h post-injury. Sprague-Dawley rats subjected to a controlled cortical impact were used as TBI models. We observed that p53 mRNA significantly increased, whereas p53 protein expression was distributed predominantly in neurons but not in glia cells in striatum after TBI. PFT-α improved motor deficit following TBI. PFT-α suppressed TBI-induced striatal glial activation and expression of proinflammatory cytokines. PFT-α alleviated TBI-induced oxidative damage TBI induced autophagy was evidenced by increased protein expression of Beclin-1 and shift of microtubule-associated light chain (LC)3-I to LC3-II, and decreased p62. These effects were reduced by PFT-α. Post-injury PFT-α treatment reduced the number of degenerating (FJC-positive) and apoptotic neurons. Our results suggest that PFT-α may provide neuroprotective effects via p53-dependent or -independent mechanisms depending on the cell type and timing after the TBI and can possibly be developed into a novel therapy to ameliorate TBI-induced neuronal damage.

Neuroserpin restores autophagy and promotes functional recovery after acute spinal cord injury in rats

This study is to reveal the characteristics of autophagy and the effect of neuroserpin (NSP) treatment on autophagy during the process of functional recovery following spinal cord injury (SCI). After the clip compress rat model of SCI had been made, autophagy‑associated proteins, including LC3‑II, beclin‑1 and p62, were evaluated at 2, 4, 24, 72 h, and 168 h in the experimental group, and the sham group as control. Transmission electron microscopy (TEM) was further used for autophagy detection at 4 and 72 h. All the male rats were randomly divided into three groups: Sham, vehicle and NSP group. NSP or an equal volume of saline vehicle was administered via intrathecal injection immediately after SCI. Each group was further divided into subgroups for the following experiments: i)Western blot (LC3‑II and p62); ii) Immunofluorescent double staining (LC3/MAP‑2/DAPI); iii) Nissl staining and Basso Beattie Bresnahan (BBB score) for NSP neuroprotection evaluation. Our results revealed both LC3‑II and p62 expression trended upward at 24, 72 and 168 h after SCI. The LC3‑II peaked at 72 h, while p62 peaked at 24 h. Beclin‑1 dropped significantly at 72 and 168 h. TEM results showed that autophagosomes largely accumulated at 72 h after SCI when compared with the sham group. Western blot analysis showed that LC3‑II and p62 were markedly decreased with NSP treatment at 72 h after injury compared with that of the vehicle‑group. Immunofluorescent double labeling indicated that accumulation of autophagosomes was reduced in the NSP group. Further, post‑SCI treatment with NSP improved the BBB scale and increased the number of anterior horn motor neurons. Together, this study demonstrates that autophagic flux is impaired, meanwhile NSP restores autophagic flux and promotes functional recovery after SCI in rats.

Combination Therapy for Multi-Target Manipulation of Secondary Brain Injury Mechanisms

Traumatic brain injury (TBI) is a major healthcare problem that affects millions of people worldwide. Despite advances in understanding and developing preventative and treatment strategies using preclinical animal models, clinical trials to date have failed, and a 'magic bullet' for effectively treating TBI-induced damage does not exist. Thus, novel pharmacological strategies to effectively manipulate the complex and heterogeneous pathophysiology of secondary injury mechanisms are needed. Given that goal, this paper discusses the relevance and advantages of combination therapies (COMTs) for 'multi-target manipulation' of the secondary injury cascade by administering multiple drugs to achieve an optimal therapeutic window of opportunity (e.g., temporally broad window) and compares these regimens to monotherapies that manipulate a single target with a single drug at a given time. Furthermore, we posit that integrated mechanistic multiscale models that combine primary injury biomechanics, secondary injury mechanobiology/neurobiology, physiology, pharmacology and mathematical programming techniques could account for vast differences in the biological space and time scales and help to accelerate drug development, to optimize pharmacological COMT protocols and to improve treatment outcomes.

Neuroprotective effects of hydrogen sulfide on sodium azide-induced oxidative stress in PC12 cells

Alzheimer's disease (AD) is the most common neurodegenerative disorder, responsible for >50% of all dementia cases. Sodium azide (NaN₃) inhibits cytochrome oxidase by irreversibly binding to the heme cofactor and selectively reducing the complex IV activity, which is present in post-mortem AD brains. Previous data demonstrated that hydrogen sulfide (H₂S), the third endogenous gaseous mediator, exerted protective effects against neuronal damage. Therefore, it was hypothesized that H₂S may be able to scavenge excess reactive oxygen species (ROS), thereby protecting against oxidative stress and cell death. In the present study, it was observed that cell viability decreased in a concentration-dependent manner 12 h after NaN₃ treatment (20, 30 and 50 mmol/l). A decrease in cell viability (to 51±3%) was observed 12 h after treatment with 30 mM NaN₃. NaN₃ treatment also led to decreased mitochondrial membrane potential, increased lipid peroxidation (excessive production of malondialdehyde), and increased the protein expression levels of caspase-3. Pretreatment with H₂S (200 μmol/l) attenuated NaN₃-mediated apoptosis, and the anti-apoptotic action of H₂S was partially dependent on suppressing the production of ROS. The findings of the present study suggested that H₂S exerted a neuroprotective effect against NaN₃-induced neurotoxicity through mechanisms related to anti-oxidation and anti-apoptosis. Therefore, the findings of the present study suggest there may be a promising future for H₂S-based preventions and therapies for neuronal damage following exposure to NaN₃.

Mst-1 deficiency promotes post-traumatic spinal motor neuron survival via enhancement of autophagy flux

The mammalian Ste20-like kinase 1 (Mst-1) is a serine-threonine kinase and a component of the Hippo tumor suppressor pathway, which reacts to pathologically relevant stress and regulates cell death. However, little is known about its role in spinal cord injury. Here, we found that p-Mst-1, the activated form of Mst-1, was induced in the post-traumatic spinal motor neurons. In vivo evidence demonstrated that Mst-1 deficiency promoted post-traumatic spinal motor neuron survival, Basso mouse scale scores, and synapse survival. Moreover, we found that autophagosome formation and autolysosome degradation enhanced by Mst-1 deficiency were crucial to attenuate the death of injured spinal motor neurons. Taken together, our findings demonstrate that Mst-1 deficiency promotes post-traumatic spinal motor neuron survival via enhancement of autophagy flux.

Detrimental effect of Hypoxia-inducible factor-1α-induced autophagy on multiterritory perforator flap survival in rats

Hypoxia-inducible factor-1α (HIF-1α) plays a key role in angiogenesis, improves flap survival, and activates autophagy. The effect of HIF-1α-induced autophagy is still debatable. Thus, we investigated the effect of HIF-1α-induced autophagy on multiterritory perforator flap survival. In this study, 99 male Sprague-Dawley rats received multiterritory perforator flap procedure and were divided into three groups with 33 each. The dimethyloxalylglycine (DMOG) plus 3-methyladenine (3-MA) group received intraperitoneal injection of DMOG (40 mg/kg) and 3-MA (10 mg/kg). The DMOG group and control group received comparative DMOG and saline respectively. On postoperative day (POD) 7, HIF-1α’s activities of flap survival and perfusion improvement were confirmed in DMOG group, however, its positive effects were further enhanced by co-administration of autophagy inhibitor, 3-MA. On POD 1, vascular endothelial growth factor, mean microvascular density and blood perfusion were not affected by HIF-1α up-regulation or autophagy inactivation. However, HIF-1α-induced autophagy augments apoptosis and oxidative stress. The increased level of apoptosis and oxidative stress was reversed by 3-MA and resulted in further flap survival improvement. In conclusion, HIF-1α-induced autophagy has a detrimental effect on multiterritory perforator flap survival and the flap survival was determined by the combined effects of ischemia and reperfusion injury.

Neuroprotective effects of hydrogen sulfide on sodium azide‑induced autophagic cell death in PC12 cells

Sodium azide (NaN3) is a chemical of rapidly growing commercial importance. It is very acutely toxic and inhibits cytochrome oxidase (COX) by binding irreversibly to the heme cofactor. A previous study from our group demonstrated that hydrogen sulfide (H2S), the third endogenous gaseous mediator identified, had protective effects against neuronal damage induced by traumatic brain injury (TBI). It is well‑known that TBI can reduce the activity of COX and have detrimental effects on the central nervous system metabolism. Therefore, in the present study, it was hypothesized that H2S may provide neuroprotection against NaN3 toxicity. The current results revealed that NaN3 treatment induced non‑apoptotic cell death, namely autophagic cell death, in PC12 cells. Expression of the endogenous H2S‑producing enzymes, cystathionine‑β‑synthase and 3‑mercaptopyruvate sulfurtransferase, decreased in a dose‑dependent manner following NaN3 treatment. Pretreatment with H2S markedly attenuated the NaN3‑induced cell viability loss and autophagic cell death in a dose‑dependent manner. The present study suggests that H2S‑based strategies may have future potential in the prevention and/or therapy of neuronal damage following NaN3 exposure.

Autophagosome maturation mediated by Rab7 contributes to neuroprotection of hypoxic preconditioning against global cerebral ischemia in rats

Autophagy disruption leads to neuronal damage in hypoxic–ischemic brain injury. Rab7, a member of the Rab GTPase superfamily, has a unique role in the regulation of autophagy. Hypoxic preconditioning (HPC) provides neuroprotection against transient global cerebral ischemia (tGCI). However, the underlying mechanisms remain poorly understood. Thus, the current study explored the potential molecular mechanism of the neuroprotective effect of HPC by investigating how Rab7 mediates autophagosome (AP) maturation after tGCI in adult rats. We found that HPC attenuated AP accumulation in the hippocampal CA1 region after tGCI via restoration of autophagic flux. We also confirmed that this HPC-induced neuroprotection was not caused by the increase in lysosomes or the improvement of lysosomal function after tGCI. Electron microscopic analysis then revealed an increase in autolysosomes in CA1 neurons of HPC rats. Moreover, the inhibition of autophagosome-lysosome fusion by chloroquine significantly aggravated neuronal death in CA1, indicating that AP maturation contributes to HPC-induced neuroprotection against neuronal injury after tGCI. Furthermore, the activation of Rab7 was found to be involved in the neuroprotective effect of AP maturation after HPC. At last, the knockdown of ultraviolet radiation resistance-associated gene (UVRAG) in vivo disrupted the interaction between Vps16 and Rab7, attenuated the activation of Rab7, interrupted autophagic flux, and ultimately abrogated the HPC-induced neuroprotection against tGCI. Our results indicated that AP maturation was enhanced by the activation of Rab7 via UVRAG-Vps16 interaction, which further demonstrated the potential neuroprotective role of Rab7 in HPC against tGCI-induced neuronal injury in adult rats.

Inhibition of mTOR signaling Confers Protection against Cerebral Ischemic Injury in Acute Hyperglycemic Rats

Hyperglycemia is known to exacerbate neuronal death resulted from cerebral ischemia. The mechanisms are not fully understood. The mammalian target of rapamycin (mTOR) pathway regulates cell growth, division and apoptosis. Recent studies suggest that activation of mTOR may mediate ischemic brain damage. The objective of the present experiment is to explore whether mTOR mediates ischemic brain damage in acute hyperglycemic animals. Rats were subjected to 10 min of forebrain ischemia under euglycemic, hyperglycemic and rapamycin-treated hyperglycemic conditions. The rat brain samples were collected from the cortex and hippocampi after 3h and 16h of reperfusion. The results showed that hyperglycemia significantly increased neuronal death in the cortex and hippocampus and the exacerbation effect of hyperglycemia was associated with further activation of mTOR under control and/or ischemic conditions. Inhibition of mTOR with rapamycin ameliorated the damage and suppressed hyperglycemia-elevated p-MTOR, p-P70S6K and p-S6. In addition, hyperglycemia per se increased the levels of cytosolic cytochrome c and autophagy marker LC3-II, while rapamycin alleviated these alterations. It is concluded that activation of mTOR signaling may play a detrimental role in mediating the aggravating effect of hyperglycemia on cerebral ischemia.

Vulnerability to a Metabolic Challenge Following Perinatal Asphyxia Evaluated by Organotypic Cultures: Neonatal Nicotinamide Treatment

The hypothesis of enhanced vulnerability following perinatal asphyxia was investigated with a protocol combining in vivo and in vitro experiments. Asphyxia-exposed (AS) (by 21 min water immersion of foetuses containing uterine horns) and caesarean-delivered control (CS) rat neonates were used at P2-3 for preparing triple organotypic cultures (substantia nigra, neostriatum and neocortex). At DIV 18, cultures were exposed to different concentrations of H₂O₂ (0.25-45 mM), added to the culture medium for 18 h. After a 48-h recovery period, the cultures were either assessed for cell viability or for neurochemical phenotype by confocal microscopy. Energy metabolism (ADP/ATP ratio), oxidative stress (GSH/GSSG) and a modified ferric reducing/antioxidant power assay were applied to homogenates of parallel culture series. In CS cultures, the number of dying cells was similar in substantia nigra, neostriatum and neocortex, but it was several times increased in AS cultures evaluated under the same conditions. A H₂O₂ challenge led to a concentration-dependent increase in cell death (>fourfold after 0.25 mM of H₂O₂) in CS cultures. In AS cultures, a significant increase in cell death was only observed after 0.5 mM of H₂O₂. At higher than 1 mM of H₂O₂ (up to 45 mM), cell death increased several times in all cultures, but the effect was still more prominent in CS than in AS cultures. The cell phenotype of dying/alive cells was investigated in formalin-fixed cultures exposed to 0 or 1 mM of H₂O₂, co-labelling for TUNEL (apoptosis), MAP-2 (neuronal phenotype), GFAP (astroglial phenotype) and TH (tyrosine hydroxylase; for dopamine phenotype), counterstaining for DAPI (nuclear staining), also evaluating the effect of a single dose of nicotinamide (0.8 nmol/kg, i.p. injected in 100 μL, 60 min after delivery). Perinatal asphyxia produced a significant increase in the number of DAPI/TUNEL cells/mm³, in substantia nigra and neostriatum. One millimolar of H₂0₂ increased the number of DAPI/TUNEL cells/mm³ by ≈twofold in all regions of CS and AS cultures, an effect that was prevented by neonatal nicotinamide treatment. In substantia nigra, the number of MAP-2/TH-positive cells/mm³ was decreased in AS compared to CS cultures, also by 1 mM of H₂0₂, both in CS and AS cultures, prevented by nicotinamide. In agreement, the number of MAP-2/TUNEL-positive cells/mm³ was increased by 1 mM H₂O₂, both in CS (twofold) and AS (threefold) cultures, prevented by nicotinamide. The number of MAP-2/TH/TUNEL-positive cells/mm³ was only increased in CS (>threefold), but not in AS (1.3-fold) cultures. No TH labelling was observed in neostriatum, but 1 mM of H₂O₂ produced a strong increase in the number of MAP-2/TUNEL-positive cells/mm³, both in CS (>2.9-fold) and AS (>fourfold), decreased by nicotinamide. In neocortex, H₂O₂ increased the number of MAP-2/TUNEL-positive cells/mm³, both in CS and AS cultures (≈threefold), decreased by nicotinamide. The ADP/ATP ratio was increased in AS culture homogenates (>sixfold), compared to CS homogenates, increased by 1 mM of H₂0₂, both in CS and AS homogenates. The GSH/GSSG ratio was significantly decreased in AS, compared to CS cultures. One millimolar of H₂O₂ decreased that ratio in CS and AS homogenates. The present results demonstrate that perinatal asphyxia induces long-term changes in metabolic pathways related to energy and oxidative stress, priming cell vulnerability with both neuronal and glial phenotype. The observed effects were region dependent, being the substantia nigra particularly prone to cell death. Nicotinamide administration in vivo prevented the deleterious effects observed after perinatal asphyxia in vitro, a suitable pharmacological strategy against the deleterious consequences of perinatal asphyxia.

An introduction to the pathophysiology of aneurysmal subarachnoid hemorrhage

Pathophysiological processes following subarachnoid hemorrhage (SAH) present survivors of the initial bleeding with a high risk of morbidity and mortality during the course of the disease. As angiographic vasospasm is strongly associated with delayed cerebral ischemia (DCI) and clinical outcome, clinical trials in the last few decades focused on prevention of these angiographic spasms. Despite all efforts, no new pharmacological agents have shown to improve patient outcome. As such, it has become clear that our understanding of the pathophysiology of SAH is incomplete and we need to reevaluate our concepts on the complex pathophysiological process following SAH. Angiographic vasospasm is probably important. However, a unifying theory for the pathophysiological changes following SAH has yet not been described. Some of these changes may be causally connected or present themselves as an epiphenomenon of an associated process. A causal connection between DCI and early brain injury (EBI) would mean that future therapies should address EBI more specifically. If the mechanisms following SAH display no causal pathophysiological connection but are rather evoked by the subarachnoid blood and its degradation production, multiple treatment strategies addressing the different pathophysiological mechanisms are required. The discrepancy between experimental and clinical SAH could be one reason for unsuccessful translational results.

Intrathecal Injection of 3-Methyladenine Reduces Neuronal Damage and Promotes Functional Recovery via Autophagy Attenuation after Spinal Cord Ischemia/Reperfusion Injury in Rats

The present study aimed to determine the occurrence of autophagy following ischemia/reperfusion (I/R) injury in the rat spinal cord and whether autophagy inhibition contributes to neural tissue damage and locomotor impairment. A spinal cord I/R model was induced via descending thoracic aorta occlusion for 10 min using systemic hypotension (40 mmHg) in adult male Sprague-Dawley rats. Then, 600 nmol 3-methyladenine (3-MA) or vehicle was intrathecally administered. Ultrastructural spinal cord changes were observed via transmission electron microscopy (TEM) and immunofluorescent double-labeling. Western blots were used to determine the protein expression of microtubule-associated protein light chain 3 (LC3) and Beclin 1. Autophagy was activated after spinal cord I/R injury as demonstrated by significantly increased LC3 and Beclin 1 expression at 3-48 h after injury. Furthermore, TEM images indicated the presence of autophagosomes and autolysosomes in the injured spinal cord. 3-MA significantly decreased LC3 and Beclin 1 expression and the number of LC3-positive cells in spinal cord of I/R versus vehicle groups. Moreover, the 3-MA-treated rats exhibited better neurobehavioral scores compared with control rats. These findings suggest activation of autophagy leading to neuronal cell death in the I/R injured spinal cord. These effects were significantly inhibited by intrathecal 3-MA administration. Thus intrathecal 3-MA administration may represent a novel treatment target following spinal cord I/R injury.

Hippocampus and cerebral cortex present a different autophagic response after oxygen and glucose deprivation in an ex vivo rat brain slice model

AIMS

To evaluate the neuroprotective role of autophagy in the cerebral cortex and hippocampus using an ex vivo animal model of stroke in brain slices.

METHODS

Brain slices were maintained for 30 min in oxygen and glucose deprivation (OGD) followed by 3 h in normoxic conditions to simulate the reperfusion that follows ischaemia in vivo (RL, reperfusion-like). Phagophore formation (Beclin 1 and LC3B) as well as autophagy flux (p62/SQSTM1, Atg5, Atg7 and polyubiquitin) markers were quantified by Western blot and/or qPCR. The release of lactate dehydrogenase (LDH) and glutamate in the medium was used as a measure of the mortality in the absence and in the presence of the autophagy inhibitor 3-methyladenine.

RESULTS

Striking differences in the autophagy markers were observed between the hippocampus and cerebral cortex in normoxic conditions. OGD/RL induced increases both in the phagophore formation and in the autophagy flux in the first three hours in the cerebral cortex that were not observed in the hippocampus. The blocking of autophagy increased the OGD/RL-induced mortality, increased the glutamate release in both the cerebral cortex and hippocampus and abolished the OGD-induced decrease in the polyubiquitinated proteins in the cerebral cortex.

CONCLUSIONS

We conclude that OGD induces a rapid autophagic response in the cerebral cortex that plays a neuroprotective role. Polyubiquitination levels and control of the glutamate release appear to be involved in the neuroprotective role of autophagy.

Autophagy Modulation by Lanthionine Ketimine Ethyl Ester Improves Long-Term Outcome after Central Fluid Percussion Injury in the Mouse

Diffuse axonal injury is recognized as a progressive and long-term consequence of traumatic brain injury. Axonal injury can have sustained negative consequences on neuronal functions such as anterograde and retrograde transport and cellular processes such as autophagy that depend on cytoarchitecture and axon integrity. These changes can lead to somatic atrophy and an inability to repair and promote plasticity. Obstruction of the autophagic process has been noted after brain injury, and rapamycin, a drug used to stimulate autophagy, has demonstrated positive effects in brain injury models. The optimization of drugs to promote beneficial autophagy without negative side effects could be used to attenuate traumatic brain injury and promote improved outcome. Lanthionine ketimine ethyl ester, a bioavailable derivative of a natural sulfur amino acid metabolite, has demonstrated effects on autophagy both in vitro and in vivo. Thirty minutes after a moderate central fluid percussion injury and throughout the survival period, lanthionine ketimine ethyl ester was administered, and mice were subsequently evaluated for learning and memory impairments and biochemical and histological changes over a 5-week period. Lanthionine ketimine ethyl ester, which we have shown previously to modulate autophagy markers and alleviate pathology and slow cognitive decline in the 3 × TgAD mouse model, spared cognition and pathology after central fluid percussion injury through a mechanism involving autophagy modulation.

Stroke injury, cognitive impairment and vascular dementia

The global burden of ischaemic strokes is almost 4-fold greater than haemorrhagic strokes. Current evidence suggests that 25–30% of ischaemic stroke survivors develop immediate or delayed vascular cognitive impairment (VCI) or vascular dementia (VaD). Dementia after stroke injury may encompass all types of cognitive disorders. States of cognitive dysfunction before the index stroke are described under the umbrella of pre-stroke dementia, which may entail vascular changes as well as insidious neurodegenerative processes. Risk factors for cognitive impairment and dementia after stroke are multifactorial including older age, family history, genetic variants, low educational status, vascular comorbidities, prior transient ischaemic attack or recurrent stroke and depressive illness. Neuroimaging determinants of dementia after stroke comprise silent brain infarcts, white matter changes, lacunar infarcts and medial temporal lobe atrophy. Until recently, the neuropathology of dementia after stroke was poorly defined. Most of post-stroke dementia is consistent with VaD involving multiple substrates. Microinfarction, microvascular changes related to blood–brain barrier damage, focal neuronal atrophy and low burden of co-existing neurodegenerative pathology appear key substrates of dementia after stroke injury. The elucidation of mechanisms of dementia after stroke injury will enable establishment of effective strategy for symptomatic relief and prevention. Controlling vascular disease risk factors is essential to reduce the burden of cognitive dysfunction after stroke. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

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Ischaemic injury is common among long-term stroke survivors

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About 25% stroke survivors develop dementia with a much greater proportion developing cognitive impairment

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Risk factors of dementia after stroke include older age, vascular comorbidities, prior stroke and pre-stroke impairment

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Current imaging and pathological studies suggest 70% of dementia after stroke is vascular dementia

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Severe white matter changes and medial temporal lobe atrophy as sequelae after ischaemic injury are substrates of dementia

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Controlling vascular risk factors and prevention strategies related to lifestyle factors would reduce dementia after stroke

G-CSF promotes autophagy and reduces neural tissue damage after spinal cord injury in mice

Granulocyte colony-stimulating factor (G-CSF) was investigated for its capacity to induce autophagy and related neuroprotective mechanisms in an acute spinal cord injury model. To accomplish this goal, we established a mouse spinal cord hemisection model to test the effects of recombinant human G-CSF. The results showed that autophagy was activated after spinal cord injury and G-CSF appears to induce a more rapid activation of autophagy within injured spinal cords as compared with that of non-treated animals. Apoptosis as induced in mechanically injured neurons with G-CSF treatment was enhanced after inhibiting autophagy by 3-methyladenine (3-MA), which partially blocked the neuroprotective effect of autophagy as induced by G-CSF. In addition, G-CSF inhibited the activity of the NF-κB signal pathway in neurons after mechanical injury. We conclude that G-CSF promotes autophagy by inhibiting the NF-κB signal pathway and protects neuronal structure after spinal cord injury. We therefore suggest that G-CSF, which rapidly induces autophagy after spinal cord injury to inhibit neuronal apoptosis, may thus provide an effective auxiliary therapeutic intervention for spinal cord injury.