Tsc1 (hamartin) confers neuroprotection against ischemia by inducing autophagy

Capsaicin protects against testicular torsion injury through mTOR-dependent mechanism

SCOPE

Testicular torsion and subsequent release of reactive oxygen species (ROS) can cause infertility in adults. Oxidative stress following testicular torsion plays an important role in the ýonset and development of apoptotic cell death through dysregulation of the cellular signaling pathways. Anti-inflammatory and antioxidant properties of capsaicin, a bioactive composition present in red peppers, has already been exploited for treatment of the cancer and pain relief. In present work, we evaluated the role of the mammalian target of rapamycin (mTOR) in antioxidant effect of capsaicin against reperfusion injury following testicular torsion.

METHODS

Male Wistar rats weighing 200-220 g were randomly assigned into four major groups: (i) a sham operated group, (ii) a testicular torsion (TT) group, (iii) three groups treated with different doses of capsaicin (TT + 100, 500 and 1000 μg/ml Cap), and (iv) three groups of healthy rats treated with different doses of capsaicin (100, 500 and 1000 μg/ml). Western blotting assay was used to examine the anti-apoptotic effects of capsaicin in testicular cells following torsion. H&E and TUNEL methods were used to evaluate testicular morphology and apoptosis activity.

RESULTS

Compared to control group, phosphorylation of mTOR was significantly increased in the TT groups. Capsaicin administration remarkably decreased the phosphorylation of mTOR at the highest dose (P < 0.05). Capsaicin decreased apoptosis and preserved tubular morphology in testes.

CONCLUSION

Our results showed that antioxidant properties of capsaicin minimizes cell death and reperfusion injury following testicular torsion.

Mesenchymal Stem Cells Protect Against Hypoxia-Ischemia Brain Damage by Enhancing Autophagy Through Brain Derived Neurotrophic Factor/Mammalin Target of Rapamycin Signaling Pathway

Hypoxic-ischemic encephalopathy (HIE) is a serious disease for neonates. However, present therapeutic strategies are not effective enough for treating HIE. Previous study showed that mesenchymal stem cells (MSCs) can exert neuroprotective effects for brain damage, but its mechanism remains elusive. Using in vitro coculture of rat cortical primary neurons and MSCs in HI conditions, we demonstrated that MSCs help increase brain derived neurotrophic factor (BDNF) and autophagy markers (LC3II and Beclin1) in the cultures and decrease cells death (lactate dehydrogenase levels). We demonstrated a similar mechanism using an in vivo rat model of HI in combination with MSCs transplantation. Using a behavioral study, we further showed that MSCs transplantation into the rat brain after HI injury can attenuate behavioral deficits. Finally, we found that the increase in BDNF and autophagy related factors after HI injury combined with MSCs transplantation can be reversed by anti-BDNF treatment and strengthen the point that the protective effects of BDNF work through inhibition of the mammalin target of rapamycin (mTOR) pathway. Collectively, we proposed that coculture/transplantation of MSCs after HI injury leads to increased BDNF expression and a subsequent reduction in mTOR pathway activation that results in increased autophagy and neuroprotection. This finding gives a hint to explore new strategies for treating neonates with HIE. Stem Cells 2018;36:1109-1121.

Role of mTORC1 Controlling Proteostasis after Brain Ischemia

Intense efforts are being undertaken to understand the pathophysiological mechanisms triggered after brain ischemia and to develop effective pharmacological treatments. However, the underlying molecular mechanisms are complex and not completely understood. One of the main problems is the fact that the ischemic damage is time-dependent and ranges from negligible to massive, involving different cell types such as neurons, astrocytes, microglia, endothelial cells, and some blood-derived cells (neutrophils, lymphocytes, etc.). Thus, approaching such a complicated cellular response generates a more complex combination of molecular mechanisms, in which cell death, cellular damage, stress and repair are intermixed. For this reason, animal and cellular model systems are needed in order to dissect and clarify which molecular mechanisms have to be promoted and/or blocked. Brain ischemia may be analyzed from two different perspectives: that of oxygen deprivation (hypoxic damage per se) and that of deprivation of glucose/serum factors. For investigations of ischemic stroke, middle cerebral artery occlusion (MCAO) is the preferred in vivo model, and uses two different approaches: transient (tMCAO), where reperfusion is permitted; or permanent (pMCAO). As a complement to this model, many laboratories expose different primary cortical neuron or neuronal cell lines to oxygen-glucose deprivation (OGD). This ex vivo model permits the analysis of the impact of hypoxic damage and the specific response of different cell types implicated in vivo, such as neurons, glia or endothelial cells. Using in vivo and neuronal OGD models, it was recently established that mTORC1 (mammalian Target of Rapamycin Complex-1), a protein complex downstream of PI3K-Akt pathway, is one of the players deregulated after ischemia and OGD. In addition, neuroprotective intervention either by estradiol or by specific AT2R agonists shows an important regulatory role for the mTORC1 activity, for instance regulating vascular endothelial growth factor (VEGF) levels. This evidence highlights the importance of understanding the role of mTORC1 in neuronal death/survival processes, as it could be a potential therapeutic target. This review summarizes the state-of-the-art of the complex kinase mTORC1 focusing in upstream and downstream pathways, their role in central nervous system and their relationship with autophagy, apoptosis and neuroprotection/neurodegeneration after ischemia/hypoxia.

Remote limb ischemic postconditioning protects against cerebral ischemia-reperfusion injury by activating AMPK-dependent autophagy

Remote limb ischemic postconditioning (RIPoC) is a promising adjunct treatment for cerebral ischemia-reperfusion (IR) injury. However, the underlying mechanisms have not been fully elucidated yet. The present study aims to investigate potential involvement and regulatory mechanisms of autophagy in RIPoC treatment against cerebral IR injury in mice. Mice were subjected to 2 h middle cerebral artery occlusion (MCAO) then treated with vehicle, 3-methyladenine (3-MA, an autophagy inhibitor), or compound C (an AMPK inhibitor) at the onset of reperfusion. RIPoC was carried out by 3 cycles of 10-min occlusion-reperfusion of bilateral femoral artery at the beginning of the reperfusion. Infarct volume, neurological score, and brain water content of the mice were assessed after 12 h reperfusion. Autophagy markers, cell apoptosis markers, and AMPK pathway activity were also evaluated. Our results indicated that RIPoC treatment reduced neurological deficits, brain water content, and infarct volume after IR. Meanwhile, RIPoC was proved to induce autophagy and activate AMPK pathway. Furthermore, the RIPoC-induced autophagy and neuroprotection were abolished by 3-MA and partially blocked by compound C. In conclusion, the present study suggests that RIPoC attenuates cerebral IR injury by activating AMPK-dependent autophagy.

bFGF plays a neuroprotective role by suppressing excessive autophagy and apoptosis after transient global cerebral ischemia in rats

Transient global cerebral ischemia (tGCI) is a cerebrovascular disorder that can cause apoptotic neuronal damage and functional deficits. Basic fibroblast growth factor (bFGF) was reported to be highly expressed in the central nervous system (CNS) and to exert neuroprotective effects against different CNS diseases. However, the effects of bFGF on tGCI have not been studied intensively. This study was conducted to investigate the effect of bFGF and its underlying mechanism in an animal model of tGCI. After intracerebroventricular (i.c.v.) injection of bFGF, functional improvement was observed, and the number of viable neurons increased in the ischemia-vulnerable hippocampal CA1 region. Apoptosis was induced after tGCI and could be attenuated by bFGF treatment via inhibition of p53 mitochondrial translocation. In addition, autophagy was activated during this process, and bFGF could inhibit activation of autophagy through the mTOR pathway. Rapamycin, an activator of autophagy, was utilized to explore the relationship among bFGF, apoptosis, and autophagy. Apoptosis deteriorated after rapamycin treatment, which indicated that excessive autophagy could contribute to the apoptosis process. In conclusion, these results demonstrate that bFGF could exert neuroprotective effects in the hippocampal CA1 region by suppressing excessive autophagy via the mTOR pathway and inhibiting apoptosis by preventing p53 mitochondrial translocation. Furthermore, our results suggest that bFGF may be a promising therapeutic agent to for treating tGCI in response to major adverse events, including cardiac arrest, shock, extracorporeal circulation, traumatic hemorrhage, and asphyxiation.

Tetramethylpyrazine nitrone activates the BDNF/Akt/CREB pathway to promote post-ischaemic neuroregeneration and recovery of neurological functions in rats

BACKGROUND AND PURPOSE

Neuronal regeneration from endogenous precursors is an attractive strategy for the treatment of ischaemic stroke. However, most stroke-generated newborn neurons die over time. Therefore, a drug that is both neuroprotective and pro-neurogenic may be beneficial after stroke. Here, we assessed the neurogenic and oligodendrogenic effects of tetramethylpyrazine nitrone (TBN), a neuroprotective drug candidate for stroke, in a rat model of ischaemic stroke.

EXPERIMENTAL APPROACH

We used Sprague Dawley rats with middle cerebral artery occlusion (MCAO). TBN was administered by tail vein injection beginning at 3 h post ischaemia. Therapeutic effect of TBN was evaluated by neurological behaviour and cerebral infarction. Promotion of neurogenesis and oligodendrogenesis was determined by double immunofluorescent staining and Western blotting analyses. Primary cultures of cortical neurons were used to assess the effect of TBN on neuronal differentiation in vitro.

KEY RESULTS

TBN reduced cerebral infarction, preserved and/or restored neurological function and promoted neurogenesis and oligodendrogenesis in rats after MCAO. In addition, TBN stimulated neuronal differentiation on primary culture of cortical neurons in vitro. Pro-neurogenic effects of TBN were attributed to its activation of the AKT/cAMP responsive element-binding protein through increasing brain-derived neurotrophic factor (BDNF) expression, as shown by the abolition of the effects of TBN by a specific inhibitor of BDNF receptor ANA-12 and by the PI3K inhibitor LY294002.

CONCLUSION AND IMPLICATIONS

As TBN can simultaneously provide neuroprotection and pro-neurogenic effects, it may be a promising treatment for both acute phase neuroprotection and long-term functional recovery after ischaemic stroke.

The Interrelation between Reactive Oxygen Species and Autophagy in Neurological Disorders

Neurological function deficits due to cerebral ischemia or neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD) have long been considered a thorny issue in clinical treatment. Recovery after neurologic impairment is fairly limited, which poses a major threat to health and quality of life. Accumulating evidences support that ROS and autophagy are both implicated in the onset and development of neurological disorders. Notably, oxidative stress triggered by excess of ROS not only puts the brain in a vulnerable state but also enhances the virulence of other pathogenic factors, just like mitochondrial dysfunction, which is described as the culprit of nerve cell damage. Nevertheless, autophagy is proposed as a subtle cellular defense mode against destructive stimulus by timely removal of damaged and cytotoxic substance. Emerging evidence suggests that the interplay of ROS and autophagy may establish a determinant role in the modulation of neuronal homeostasis. However, the underlying regulatory mechanisms are still largely unexplored. This review sets out to afford an overview of the crosstalk between ROS and autophagy and discusses relevant molecular mechanisms in cerebral ischemia, AD, and PD, so as to provide new insights into promising therapeutic targets for the abovementioned neurological conditions.

Preservation of neuronal functions by exosomes derived from different human neural cell types under ischemic conditions

Stem cell-based therapies have been reported in protecting cerebral infarction-induced neuronal dysfunction and death. However, most studies used rat/mouse neuron as model cell when treated with stem cell or exosomes. Whether these findings can be translated from rodent to humans has been in doubt. Here, we used human embryonic stem cell-derived neurons to detect the protective potential of exosomes against ischemia. Neurons were treated with in vitro oxygen-glucose deprivation (OGD) for 1 h. For treatment group, different exosomes were derived from neuron, embryonic stem cell, neural progenitor cell and astrocyte differentiated from H9 human embryonic stem cell and added to culture medium 30 min after OGD (100 μg/mL). Western blotting was performed 12 h after OGD, while cell counting and electrophysiological recording were performed 48 h after OGD. We found that these exosomes attenuated OGD-induced neuronal death, Mammalian target of rapamycin (mTOR), pro-inflammatory and apoptotic signaling pathway changes, as well as basal spontaneous synaptic transmission inhibition in varying degrees. The results implicate the protective effect of exosomes on OGD-induced neuronal death and dysfunction in human embryonic stem cell-derived neurons, potentially through their modulation on mTOR, pro-inflammatory and apoptotic signaling pathways.

Effects of erythropoietin on astrocytes and brain endothelial cells in primary culture during anoxia depend on simultaneous signaling by other cytokines and on duration of anoxia

Studies on animals revealed neuroprotective effects of exogenously applied erythropoietin (EPO) during cerebral ischemia/hypoxia. Yet, application of exogenous EPO in stroke patients often lead to haemorrhagic transformation. To clarify potential mechanism of this adverse effect we explored effects of EPO on viabilities of astrocytes and brain endothelial cells (BECs) in primary culture during anoxia of various durations, in the presence or absence of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1), which are cytokines that are also released from the neurovascular unit during hypoxia. Anoxia (2-48 h) exerted marginal effects on BECs' viability and significant reductions in viability of astrocytes. Astrocyte-conditioned medium did not exert effects and exerted detrimental effects on BECs during 2 h and 24 h anoxia, respectively. This was partially reversed by inhibition of Janus kinase (Jak)2/signal transducer and activator of transcription (STAT)5 activation. Addition of rat recombinant EPO (rrEPO) during 2 h-6h anoxia was protective for astrocytes, but had no effect on BECs. Addition of rrEPO significantly reduced viability of BECs and astrocytes after 48 h anoxia and after 24 h-48 h anoxia, respectively, which was attenuated by inhibition of Jak2/STAT5 activation. Simultaneous addition of rrEPO and VEGFA (1-165) caused marginal effects on BECs, but a highly significant protective effects on astrocytes during 24-48 h anoxia, which were attenuated by inhibition of Jak2/STAT5 activation. Simultaneous addition of EPO, VEGFA 1-165 and Ang1 exerted protective effects on BECs during 24 h-48 h anoxia, which were attenuated by addition of soluble Tie2 receptor. These data revealed that EPO could exert protective, but also injurious effects on BECs and astrocytes during anoxia, which depended on the duration of anoxia and on simultaneous signaling by VEGF and Ang1. If these injurious effects occur in stroke patients, they could enhance vascular damage and haemorrhagic transformation.

Increased autophagic degradation contributes to the neuroprotection of hydrogen sulfide against cerebral ischemia/reperfusion injury

Hydrogen sulfide (H₂S), an endogenous gaseous signal molecule, exhibits protective effect against ischemic injury. However, its underlying mechanism is not fully understood. We have recently reported that exogenous H₂S decreases the accumulation of autophagic vacuoles in mouse brain with ischemia/reperfusion (I/R) injury. To further investigate whether this H₂S-induced reduction of autophagic vacuoles is caused by the decreased autophagosome synthesis and/or the increased autophagic degradation inautophagic flux, we performed in vitro and in vivo studies using SH-SY5Y cells for the oxygen and glucose deprivation/reoxygenation (OGD/R) and mice for the cerebral I/R, respectively. NaHS (a donor of H₂S) treatment significantly increased cell viability and reduced cerebral infarct volume. NaHS treatment reduced the OGD/R-induced elevation in LC3-II (an autophagic marker), which was completely reversed by co-treatment with an autophagic flux inhibitor bafilomycin A₁ (BafA1). However, H₂S did not affect the OGD/R-induced increase of the ULK1 self-association and decrease of the ATG13 phosphorylation, which are the critical steps for the initiation of autophagosome formation. Cerebral I/R injury caused an increase in LC3-II, a decrease in p62 and the accumulation of autophagosomes in the cortex and the hippocampus, which were inhibited by NaHS treatment. This H₂S-induced decline of LC3-II in ischemic brain was reversed by BafA1. Moreover, BafA1 treatment abolished the protection of H₂S on the cerebral infarction. Collectively, the neuroprotection of exogenous H₂S against ischemia/hypoxia and reperfusion/reoxygenation injury is mediated by the enhancement of autophagic degradation.

Protective effects of short-term dietary restriction in surgical stress and chemotherapy

Reduced caloric intake including fasting, as well as the dietary composition or the timing of food intake, impact longevity, likely through a modification in the onset or the severity of chronic aging-related diseases such as cancer. As with pre- and post-operative dietary recommendations, evidence-based nutritional advice from healthcare professionals during and after cancer treatment is often vague or conflicting. We hypothesize that preventive dietary recommendations can help in the context of both chronic cancer treatment efficacy and the avoidance of development of secondary malignancies, as well as in the context of protection from the acute stress of surgery. In this perspective review, we will discuss the latest findings on the potential role of short-term dietary restriction in cancer treatment and improvement of surgical outcome.

Is age a key factor contributing to the disparity between success of neuroprotective strategies in young animals and limited success in elderly stroke patients? Focus on protein homeostasis

Neuroprotection strategies to improve stroke outcome have been successful in the laboratory but not in clinical stroke trials, and thus have come under scrutiny by the medical community. Experimental stroke investigators are therefore under increased pressure to resolve this problem. Acute ischemic stroke represents a severe form of metabolic stress that activates many pathological processes and thereby impairs cellular functions. Traditionally, neuroprotection strategies were designed to improve stroke outcome by interfering with pathological processes triggered by ischemia. However, stroke outcome is also dependent on the brain's capacity to restore cellular functions impaired by ischemia, and this capacity declines with age. It is, therefore, conceivable that this age-dependent decline in the brain's self-healing capacity contributes to the disparity between the success of neuroprotective strategies in young animals, and limited success in elderly stroke patients. Here, prosurvival pathways that restore protein homeostasis impaired by ischemic stress should be considered, because their capacity decreases with increasing age, and maintenance of proteome fidelity is pivotal for cell survival. Boosting such prosurvival pathways pharmacologically to restore protein homeostasis and, thereby, cellular functions impaired by ischemic stress is expected to counterbalance the compromised self-healing capacity of aged brains and thereby help to improve stroke outcome.

Protective effect of autophagy in neural ischemia and hypoxia: Negative regulation of the Wnt/β-catenin pathway

Autophagy is a highly conserved process of self-digestion to promote cell survival in response to nutrient starvation and other metabolic stresses. However, whether ischemic-hypoxic (IH) injury-induced autophagy acts as a neuroprotective mechanism or leads to neuroinjury is a subject of debate. It is known that autophagy is regulated by signaling pathways, including the mammalian target of rapamycin pathway. However, in neural IH injury, whether other signaling pathways are involved in the regulation of autophagy remains to be fully elucidated. In the present study, using the autophagy agonist (rampycin), autophagy antagonist [3-methyl adenine (3-MA)] and lysosome antagonist (MHY1485), autophagy was intervened with at oxygen-glucose deprivation (OGD) 6 h, in order to elucidate the regulatory mechanisms of autophagy. Using immunocytochemistry and western blot analysis, the expression levels of stress-related proteins, such as hypoxia-inducible factor-1α (HIF-1α) (a key regulator in hypoxia) and cyclooxygenase 2 (COX2; inflammatory indicator), were analyzed. In addition, the upstream proteins (Wnt1 and Wnt3a), downstream proteins (Dvl2, β-catenin) and target proteins (C-myc and cyclin D) in the Wnt/β-catenin signaling pathway were examined by immunocytochemistry and western blot analysis. The present study revealed that autophagy was activated with the upregulation of autophagic flux in IH injury; it was demonstrated that autophagy had a protective role in IH injury. The Wnt/β-catenin pathway was involved in IH injury regulation, and the upstream proteins in the Wnt/β-catenin signaling pathway were upregulated, whereas downstream proteins were downregulated by the activity of autophagy accordingly.

Chimeric Peptide Tat-HA-NR2B9c Improves Regenerative Repair after Transient Global Ischemia

Transient global ischemia (TGI) is a major public health problem, and it heightens the need of effective treatments. The present study was undertaken to investigate whether recombinant polypeptide Tat-HA-NR2B9c improves spatial learning and memory deficits in rats after TGI. Rats were subjected to 20-min ischemia induced by four-vessel occlusion (4-VO) method and daily injected with Tat-HA-NR2B9c (1.12 mg/kg) for 1 week. Tat-HA-NR2B9c increased CREB activity, upregulated B-cell lymphoma-2 (Bcl-2) expression after treated for 24 h. There was a significant increase in dendrite spine density in hippocampal CA1 region and BrdU-positive cells and BrdU/NeuN-positive cells in the dentate gyrus after Tat-HA-NR2B9c treatment, compared with ischemia group at postischemic day 28. Inhibition of the CREB activation by recombinant lentivirus, LV-CREB133-GFP, abolished the upregulation effects of Tat-HA-NR2B9c on Bcl-2 expression. Moreover, Tat-HA-NR2B9c improved the impaired spatial learning and memory ability in Morris water maze. These results suggest that Tat-HA-NR2B9c substantially ameliorated the TGI-induced loss of dendrite spine in hippocampal CA1, increased neurogenesis in dentate gyrus, and significantly improved cognitive abilities by the CREB pathway in rats after transient global cerebral ischemia. It may be served as a treatment for TGI.

Nobiletin attenuates adverse cardiac remodeling after acute myocardial infarction in rats via restoring autophagy flux

BACKGROUND

Our previous study showed that autophagy flux was impaired with sustained heart ischemia, which exacerbated adverse cardiac remodeling after acute myocardial infarction (AMI). Here we investigated whether Nobiletin, a citrus polymethoxylated flavonoids, could restore the autophagy flux and improve cardiac prognosis after AMI. AMI was induced by ligating left anterior descending (LAD) coronary artery in rats. Nobiletin improved the post-infarct cardiac dysfunction significantly and attenuated adverse cardiac remodeling. Meanwhile, Nobiletin protected H9C2 cells against oxygen glucose deprivation (OGD) in vitro. The impaired autophagy flux due to ischemia was ameliorated after Nobiletin treatment by testing the autophagy substrate, LC3BⅡ and P62 protein level both in vivo and in vitro. GFP-mRFP-LC3 adenovirus transfection also supported that Nobiletin restored the impaired autophagy flux. Specifically, the autophagy flux inhibitor, chloroquine, but not 3 MA, alleviated Nobiletin-mediated protection against OGD. Notably, Nobiletin does not affect the activation of classical upstream autophagy signaling pathways. However, Nobiletin increased the lysosome acidation which also supported that Nobiletin accelerated autophagy flux. Taken together, our findings suggested that Nobiletin restored impaired autophagy flux and protected against acute myocardial infarction, suggesting a potential role of autophagy flux in Nobiletin-mediated myocardial protection.

Recovery from critical illness-induced organ failure: the role of autophagy

Autophagy is a catabolic process by which cells can dispose of damaged content and intracellular microorganisms. Recent evidence implicates autophagy as a crucial repair process necessary to recover from critical illness-induced organ failure. Withholding parenteral nutrition in the acute phase of critical illness activates autophagy and enhances recovery. Several registered drugs have autophagy-stimulating properties, but all lack specificity and none has been investigated in critically ill patients for this purpose.

The role of the endoplasmic reticulum stress response following cerebral ischemia

Background Cornu ammonis 3 (CA3) hippocampal neurons are resistant to global ischemia, whereas cornu ammonis (CA1) 1 neurons are vulnerable. Hamartin expression in CA3 neurons mediates this endogenous resistance via productive autophagy. Neurons lacking hamartin demonstrate exacerbated endoplasmic reticulum stress and increased cell death. We investigated endoplasmic reticulum stress responses in CA1 and CA3 regions following global cerebral ischemia, and whether pharmacological modulation of endoplasmic reticulum stress or autophagy altered neuronal viability . Methods In vivo: male Wistar rats underwent sham or 10 min of transient global cerebral ischemia. CA1 and CA3 areas were microdissected and endoplasmic reticulum stress protein expression quantified at 3 h and 12 h of reperfusion. In vitro: primary neuronal cultures (E18 Wistar rat embryos) were exposed to 2 h of oxygen and glucose deprivation or normoxia in the presence of an endoplasmic reticulum stress inducer (thapsigargin or tunicamycin), an endoplasmic reticulum stress inhibitor (salubrinal or 4-phenylbutyric acid), an autophagy inducer ([4'-(N-diethylamino) butyl]-2-chlorophenoxazine (10-NCP)) or autophagy inhibitor (3-methyladenine). Results In vivo, decreased endoplasmic reticulum stress protein expression (phospho-eIF2α and ATF4) was observed at 3 h of reperfusion in CA3 neurons following ischemia, and increased in CA1 neurons at 12 h of reperfusion. In vitro, endoplasmic reticulum stress inducers and high doses of the endoplasmic reticulum stress inhibitors also increased cell death. Both induction and inhibition of autophagy also increased cell death. Conclusion Endoplasmic reticulum stress is associated with neuronal cell death following ischemia. Neither reduction of endoplasmic reticulum stress nor induction of autophagy demonstrated neuroprotection in vitro, highlighting their complex role in neuronal biology following ischemia.

Dexmedetomidine Protects Mouse Brain from Ischemia-Reperfusion Injury via Inhibiting Neuronal Autophagy through Up-Regulating HIF-1α

Stroke is the leading cause of death in China and produces a heavy socio-economic burden in the past decades. Previous studies have shown that dexmedetomidine (DEX) is neuroprotective after cerebral ischemia. However, the role of autophagy during DEX-mediated neuroprotection after cerebral ischemia is still unknown. In this study, we found that post-conditioning with DEX and DEX+3-methyladenine (3-MA) (autophagy inhibitor) reduced brain infarct size and improved neurological deficits compared with DEX+RAPA (autophagy inducer) 24 h after transient middle cerebral artery artery occlusion (tMCAO) model in mice. DEX inhibited the neuronal autophagy in the peri-ischemic brain, and increased viability and decreased apoptosis of primary cultured neurons in oxygen-glucose deprivation (OGD) model. DEX induced expression of Bcl-1 and p62, while reduced the expression of microtubule-associated protein 1 light chain 3 (LC3) and Beclin 1 in primary cultured neurons through inhibition of apoptosis and autophagy. Meanwhile, DEX promoted the expression of hypoxia-inducible factor-1α (HIF-1α) both in vivo and in vitro, and 2-Methoxyestradiol (2ME2), an inhibitor of HIF-1α, could reverse DEX-induced autophagic inhibition. In conclusion, our study suggests that post-conditioning with DEX at the beginning of reperfusion protects mouse brain from ischemia-reperfusion injury via inhibition of neuronal autophagy by upregulation of HIF-1α, which provides a potential therapeutic treatment for acute ischemic injury.

Pharmacological modulation of autophagy: therapeutic potential and persisting obstacles

Autophagy is central to the maintenance of organismal homeostasis in both physiological and pathological situations. Accordingly, alterations in autophagy have been linked to clinically relevant conditions as diverse as cancer, neurodegeneration and cardiac disorders. Throughout the past decade, autophagy has attracted considerable attention as a target for the development of novel therapeutics. However, such efforts have not yet generated clinically viable interventions. In this Review, we discuss the therapeutic potential of autophagy modulators, analyse the obstacles that have limited their development and propose strategies that may unlock the full therapeutic potential of autophagy modulation in the clinic.

Roles of autophagy and endoplasmic reticulum stress in intracerebral hemorrhage-induced secondary brain injury in rats

OBJECTIVES

This study aimed to evaluate the roles of autophagy and endoplasmic reticulum (ER) stress in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI) in rats.

METHODS

Autophagy inducer (rapamycin) and inhibitor (3-methyladenine), as well as ER stress activator (tunicamycin, TM) and inhibitor (tauroursodeoxycholic acid, TUDCA), were used. Bafilomycin A1, an inhibitor of autophagosome-lysosome fusion, was used to assess autophagic flux.

RESULTS

Autophagy and ER stress were enhanced in the week after ICH. At 6 hours after ICH, autophagy was excessive, while the autophagic flux was damaged at 72 hours and return to be intact at 7 days after ICH. At 6 hours after ICH, ER stress induction by TM could enhance autophagy and lead to caspase 12-mediated apoptosis and neuronal degeneration, which was further aggravated by autophagy induction. At 7 days after ICH, ER stress inhibition by TUDCA still could suppress ICH-induced SBI. And, the effects of TUDCA were enhanced by autophagy induction.

CONCLUSIONS

At 6 hours after ICH, excessive autophagy may participate in ER stress-induced brain injury; at 7 days after ICH, autophagy could enhance the protection of ER stress inhibitor possibly via clearing up the cell rubbish generated due to the early-stage damaged autophagic flux.

Autophagy and Microglia: Novel Partners in Neurodegeneration and Aging

Autophagy is emerging as a core regulator of Central Nervous System (CNS) aging and neurodegeneration. In the brain, it has mostly been studied in neurons, where the delivery of toxic molecules and organelles to the lysosome by autophagy is crucial for neuronal health and survival. However, we propose that the (dys)regulation of autophagy in microglia also affects innate immune functions such as phagocytosis and inflammation, which in turn contribute to the pathophysiology of aging and neurodegenerative diseases. Herein, we first describe the basic concepts of autophagy and its regulation, discuss key aspects for its accurate monitoring at the experimental level, and summarize the evidence linking autophagy impairment to CNS senescence and disease. We focus on acute, chronic, and autoimmunity-mediated neurodegeneration, including ischemia/stroke, Alzheimer's, Parkinson's, and Huntington's diseases, and multiple sclerosis. Next, we describe the actual and potential impact of autophagy on microglial phagocytic and inflammatory function. Thus, we provide evidence of how autophagy may affect microglial phagocytosis of apoptotic cells, amyloid-β, synaptic material, and myelin debris, and regulate the progression of age-associated neurodegenerative diseases. We also discuss data linking autophagy to the regulation of the microglial inflammatory phenotype, which is known to contribute to age-related brain dysfunction. Overall, we update the current knowledge of autophagy and microglia, and highlight as yet unexplored mechanisms whereby autophagy in microglia may contribute to CNS disease and senescence.

Activation of the ATF6 branch of the unfolded protein response in neurons improves stroke outcome

Impaired function of the endoplasmic reticulum (ER stress) is a hallmark of many human diseases including stroke. To restore ER function in stressed cells, the unfolded protein response (UPR) is induced, which activates 3 ER stress sensor proteins including activating transcription factor 6 (ATF6). ATF6 is then cleaved by proteases to form the short-form ATF6 (sATF6), a transcription factor. To determine the extent to which activation of the ATF6 UPR branch defines the fate and function of neurons after stroke, we generated a conditional and tamoxifen-inducible sATF6 knock-in mouse. To express sATF6 in forebrain neurons, we crossed our sATF6 knock-in mouse line with Emx1-Cre mice to generate ATF6-KI mice. After the ATF6 branch was activated in ATF6-KI mice with tamoxifen, mice were subjected to transient middle cerebral artery occlusion. Forced activation of the ATF6 UPR branch reduced infarct volume and improved functional outcome at 24 h after stroke. Increased autophagic activity at early reperfusion time after stroke may contribute to the ATF6-mediated neuroprotection. We concluded that the ATF6 UPR branch is crucial to ischemic stroke outcome. Therefore, boosting UPR pro-survival pathways may be a promising therapeutic strategy for stroke.

Kelch-like ECH-associated Protein 1-dependent Nuclear Factor-E2–related Factor 2 Activation in Relation to Antioxidation Induced by Sevoflurane Preconditioning

Background

The authors have reported that antioxidative effects play a crucial role in the volatile anesthetic-induced neuroprotection. Accumulated evidence shows that endogenous antioxidation could be up-regulated by nuclear factor-E2–related factor 2 through multiple pathways. However, whether nuclear factor-E2–related factor 2 activation is modulated by sevoflurane preconditioning and, if so, what is the signaling cascade underlying upstream of this activation are still unknown.

Methods

Sevoflurane preconditioning in mice was performed with sevoflurane (2.5%) 1 h per day for five consecutive days. Focal cerebral ischemia/reperfusion injury was induced by middle cerebral artery occlusion. Expression of nuclear factor-E2–related factor 2, kelch-like ECH-associated protein 1, manganese superoxide dismutase, thioredoxin-1, and nicotinamide adenine dinucleotide phosphate quinolone oxidoreductase-1 was detected (n = 6). The antioxidant activities and oxidative product expression were also examined. To determine the role of kelch-like ECH-associated protein 1 inhibition-dependent nuclear factor-E2–related factor 2 activation in sevoflurane preconditioning-induced neuroprotection, the kelch-like ECH–associated protein 1-nuclear factor-E2–related factor 2 signal was modulated by nuclear factor-E2–related factor 2 knockout, kelch-like ECH-associated protein 1 overexpression lentivirus, and kelch-like ECH-associated protein 1 deficiency small interfering RNA (n = 8). The infarct volume, neurologic scores, and cellular apoptosis were assessed.

Results

Sevoflurane preconditioning elicited neuroprotection and increased nuclear factor-E2–related factor 2 nuclear translocation, which in turn up-regulated endogenous antioxidation and reduced oxidative injury. Sevoflurane preconditioning reduced kelch-like ECH-associated protein 1 expression. Nuclear factor-E2–related factor 2 ablation abolished neuroprotection and reversed sevoflurane preconditioning by mediating the up-regulation of antioxidants. Kelch-like ECH-associated protein 1 overexpression reversed nuclear factor-E2–related factor 2 up-regulation and abolished the neuroprotection induced by sevoflurane preconditioning. Kelch-like ECH-associated protein 1 small interfering RNA administration improved nuclear factor-E2–related factor 2 expression and the outcome of mice subjected to ischemia/reperfusion injury.

Conclusions

Kelch-like ECH-associated protein 1 down-regulation–dependent nuclear factor-E2–related factor 2 activation underlies the ability of sevoflurane preconditioning to activate the endogenous antioxidant response, which elicits its neuroprotection.

Ervaoffines E–G, three iboga-type alkaloids featuring ring C cleavage and rearrangement from Ervatamia officinalis

Three novel alkaloids (1–3) reveal the high structural plasticity of ring C in iboga-type alkaloids.

E2-25K SUMOylation inhibits proteasome for cell death during cerebral ischemia/reperfusion

Cerebral ischemia/reperfusion (I/R) causes brain damage accompanied by ubiquitin accumulation and impairment of proteasome activity. In this study, we report that E2-25K, an E2-conjugating enzyme, is SUMOylated during oxidative stress and regulates cerebral I/R-induced damage. Knockdown of E2-25K expression protects against oxygen/glucose deprivation and reoxygenation (OGD/R)-induced neuronal cell death, whereas ectopic expression of E2-25K stimulates it. Compared with the control mice, cerebral infarction lesions and behavioral/neurological disorders are ameliorated in E2-25K knockout mice during middle cerebral artery occlusion and reperfusion. In particular, E2-25K is SUMOylated at Lys14 under oxidative stress, OGD/R and I/R to prompt cell death. Further, E2-25K downregulates the proteasome subunit S5a to impair proteasome complex and thus restrain proteasome activity under oxidative stress. This proteasome inhibitory activity of E2-25K is dependent on its SUMOylation. These results suggest that E2-25K has a crucial role in oxidative stress and cerebral I/R-induced damage through inhibiting proteasome via its SUMOylation.

Global ischemia induces lysosomal-mediated degradation of mTOR and activation of autophagy in hippocampal neurons destined to die

The mammalian target of rapamycin (mTOR) is a key regulator of cell growth, autophagy, translation, and survival. Dysregulation of mTOR signaling is associated with cancer, diabetes, and autism. However, a role for mTOR signaling in neuronal death is not well delineated. Here we show that global ischemia triggers a transient increase in mTOR phosphorylation at S2448, whereas decreasing p-mTOR and functional activity in selectively vulnerable hippocampal CA1 neurons. The decrease in mTOR coincides with an increase in biochemical markers of autophagy, pS317-ULK-1, pS14-Beclin-1, and LC3-II, a decrease in the cargo adaptor p62, and an increase in autophagic flux, a functional readout of autophagy. This is significant in that autophagy, a catabolic process downstream of mTORC1, promotes the formation of autophagosomes that capture and target cytoplasmic components to lysosomes. Inhibitors of the lysosomal (but not proteasomal) pathway rescued the ischemia-induced decrease in mTOR, consistent with degradation of mTOR via the autophagy/lysosomal pathway. Administration of the mTORC1 inhibitor rapamycin or acute knockdown of mTOR promotes autophagy and attenuates ischemia-induced neuronal death, indicating an inverse causal relation between mTOR, autophagy, and neuronal death. Our findings identify a novel and previously unappreciated mechanism by which mTOR self-regulates its own levels in hippocampal neurons in a clinically relevant model of ischemic stroke.

Phaseic Acid, an Endogenous and Reversible Inhibitor of Glutamate Receptors in Mouse Brain

Phaseic acid (PA) is a phytohormone regulating important physiological functions in higher plants. Here, we show the presence of naturally occurring (-)-PA in mouse and rat brains. (-)-PA is exclusively present in the choroid plexus and the cerebral vascular endothelial cells. Purified (-)-PA has no toxicity and protects cultured cortical neurons against glutamate toxicity through reversible inhibition of glutamate receptors. Focal occlusion of the middle cerebral artery elicited a significant induction in (-)-PA expression in the cerebrospinal fluid but not in the peripheral blood. Importantly, (-)-PA induction only occurred in the penumbra area, indicting a protective role of PA in the brain. Indeed, elevating the (-)-PA level in the brain reduced ischemic brain injury, whereas reducing the (-)-PA level using a monoclonal antibody against (-)-PA increased ischemic injury. Collectively, these studies showed for the first time that (-)-PA is an endogenous neuroprotective molecule capable of reversibly inhibiting glutamate receptors during ischemic brain injury.

Tetramethylpyrazine nitrone, a multifunctional neuroprotective agent for ischemic stroke therapy

TBN, a novel tetramethylpyrazine derivative armed with a powerful free radical-scavenging nitrone moiety, has been reported to reduce cerebral infarction in rats through multi-functional mechanisms of action. Here we study the therapeutic effects of TBN on non-human primate model of stroke. Thirty male Cynomolgus macaques were subjected to stroke with 4 hours ischemia and then reperfusion. TBN were injected intravenously at 3 or 6 hours after the onset of ischemia. Cerebral infarction was examined by magnetic resonance imaging at 1 and 4 weeks post ischemia. Neurological severity scores were evaluated during 4 weeks observation. At the end of experiment, protein markers associated with the stroke injury and TBN treatment were screened by quantitative proteomics. We found that TBN readily penetrated the blood brain barrier and reached effective therapeutic concentration after intravenous administration. It significantly reduced brain infarction and modestly preserved the neurological function of stroke-affected arm. TBN suppressed over-expression of neuroinflammatory marker vimentin and decreased the numbers of GFAP-positive cells, while reversed down-regulation of myelination-associated protein 2', 3'-cyclic-nucleotide 3'-phosphodiesterase and increased the numbers of NeuN-positive cells in the ipsilateral peri-infarct area. TBN may serve as a promising new clinical candidate for the treatment of ischemic stroke.

Meta-Analysis of Tourette Syndrome and Attention Deficit Hyperactivity Disorder Provides Support for a Shared Genetic Basis

Gilles de la Tourette Sydrome (TS) is a childhood onset neurodevelopmental disorder, characterized phenotypically by the presence of multiple motor and vocal tics. It is often accompanied by multiple psychiatric comorbidities, with Attention Deficit/Hyperactivity Disorder (ADHD) among the most common. The extensive co-occurrence of the two disorders suggests a shared genetic background. A major step toward the elucidation of the genetic architecture of TS was undertaken by the first TS Genome-wide Association Study (GWAS) reporting 552 SNPs that were moderately associated with TS (p < 1E-3). Similarly, initial ADHD GWAS attempts and meta-analysis were not able to produce genome-wide significant findings, but have provided insight to the genetic basis of the disorder. Here, we examine the common genetic background of the two neuropsychiatric phenotypes, by meta-analyzing the 552 top hits in the TS GWAS with the results of ADHD first GWASs. We identify 19 significant SNPs, with the top four implicated genes being TBC1D7, GUCY1A3, RAP1GDS1, and CHST11. TBCD17 harbors the top scoring SNP, rs1866863 (p:3.23E-07), located in a regulatory region downstream of the gene, and the third best-scoring SNP, rs2458304 (p:2.54E-06), located within an intron of the gene. Both variants were in linkage disequilibrium with eQTL rs499818, indicating a role in the expression levels of the gene. TBC1D7 is the third subunit of the TSC1/TSC2 complex, an inhibitor of the mTOR signaling pathway, with a central role in cell growth and autophagy. The top genes implicated by our study indicate a complex and intricate interplay between them, warranting further investigation into a possibly shared etiological mechanism for TS and ADHD.

The Dichotomy of Endoplasmic Reticulum Stress Response in Liver Ischemia-Reperfusion Injury

Endoplasmic reticulum (ER) stress plays critical roles in the pathogenesis of liver ischemia-reperfusion injury (IRI). As ER stress triggers an adaptive cellular response, the question of what determines its functional outcome in liver IRI remains to be defined. In a murine liver partial warm ischemia model, we studied how transient (30 minutes) or prolonged (90 minutes) liver ischemia regulated local ER stress response and autophagy activities and their relationship with liver IRI. Effects of chemical chaperon 4-phenylbutyrate (4-PBA) or autophagy inhibitor 3-methyladenine (3-MA) were evaluated. Our results showed that although the activating transcription factor 6 branch of ER stress response was induced in livers by both types of ischemia, liver autophagy was activated by transient, but inhibited by prolonged, ischemia. Although 3-MA had no effects on liver IRI after prolonged ischemia, it significantly increased liver IRI after transient ischemia. The 4-PBA treatment protected livers from IRI after prolonged ischemia by restoring autophagy flux, and the adjunctive 3-MA treatment abrogated its liver protective effect. The same 4-PBA treatment, however, increased liver IRI and disrupted autophagy flux after transient ischemia. Although both types of ischemia activated 5' adenosine monophosphate-activated protein kinase and inactivated protein kinase B (Akt), prolonged ischemia also resulted in downregulations of autophagy-related gene 3 and autophagy-related gene 5 in ischemic livers. These results indicate a functional dichotomy of ER stress response in liver IRI via its regulation of autophagy. Transient ischemia activates autophagy to protect livers from IRI, whereas prolonged ischemia inhibits autophagy to promote the development of liver IRI.

Autophagy in acute brain injury

Autophagy is an evolutionarily ancient mechanism that ensures the lysosomal degradation of old, supernumerary or ectopic cytoplasmic entities. Most eukaryotic cells, including neurons, rely on proficient autophagic responses for the maintenance of homeostasis in response to stress. Accordingly, autophagy mediates neuroprotective effects following some forms of acute brain damage, including methamphetamine intoxication, spinal cord injury and subarachnoid haemorrhage. In some other circumstances, however, the autophagic machinery precipitates a peculiar form of cell death (known as autosis) that contributes to the aetiology of other types of acute brain damage, such as neonatal asphyxia. Here, we dissect the context-specific impact of autophagy on non-infectious acute brain injury, emphasizing the possible therapeutic application of pharmacological activators and inhibitors of this catabolic process for neuroprotection.

Changes in synaptic plasticity and expression of glutamate receptor subunits in the CA1 and CA3 areas of the hippocampus after transient global ischemia

Excess glutamate release from the presynaptic membrane has been thought to be the major cause of ischemic neuronal death. Although both CA1 and CA3 pyramidal neurons receive presynaptic glutamate input, transient cerebral ischemia induces CA1 neurons to die while CA3 neurons remain relatively intact. This suggests that changes in the properties of pyramidal cells may be the main cause related to ischemic neuronal death. Our previous studies have shown that the densities of dendritic spines and asymmetric synapses in the CA1 area are increased at 12h and 24h after ischemia. In the present study, we investigated changes in synaptic structures in the CA3 area and compared the expression of glutamate receptors in the CA1 and CA3 hippocampal regions of rats after ischemia. Our results demonstrated that the NR2B/NR2A ratio became larger after ischemia although the expression of both the NR2B subunit (activation of apoptotic pathway) and NR2A subunit (activation of survival pathway) decreased in the CA1 area from 6h to 48h after reperfusion. Furthermore, expression of the GluR2 subunit (calcium impermeable) of the AMPA receptor class significantly decreased while the GluR1 subunit (calcium permeable) remained unchanged at the same examined reperfusion times, which subsequently caused an increase in the GluR1/GluR2 ratio. Despite these notable differences in subunit expression, there were no obvious changes in the density of synapses or expression of NMDAR and AMPAR subunits in the CA3 area after ischemia. These results suggest that delayed CA1 neuronal death may be related to the dramatic fluctuation in the synaptic structure and relative upregulation of NR2B and GluR1 subunits induced by transient global ischemia.

Drp-1, a potential therapeutic target for brain ischaemic stroke

BACKGROUND AND PURPOSE

The resistance of CA3 neurons to ischaemia and the ischaemic tolerance conferred by ischaemic preconditioning (IPC) are two well-established endogenous neuroprotective mechanisms. Elucidating the molecules involved may help us find new therapeutic targets. Thus, we determined whether dynamin-related protein 1 (Drp-1) is involved in these processes.

EXPERIMENTAL APPROACH

In vivo, we subjected rats to either 10 min severe global ischaemia using a four-vessel occlusion (4-VO) model or 2 min IPC before the onset of 4-VO. In vitro, we performed oxygen glucose deprivation (OGD) studies in rat hippocampal neurons. Drp-1 was silenced or inhibited by siRNA or pharmacological inhibitor Mdivi1. To assess whether mitochondrial Drp-1 alters neuronal vulnerability to ischaemic injury, various approaches were used including western blot, immunohistochemistry, immunofluorescence staining and electron microscopy. Hippocampal function was assessed using an open-field test.

KEY RESULTS

Mitochondrial dynamin-related protein 1 (mtDrp-1) was selectively induced by ischaemia in hippocampal CA3 neurons. In hippocampal CA1 neurons, mtDrp-1 was not affected by ischaemia but significantly up-regulated by IPC. Suppression of Drp-1 increased the vulnerability of cells to OGD and global ischaemia. Inhibition of Drp-1 in vivo resulted in loss of acquisition and encoding of spatial information, and also prevented ischaemia-induced mitophagy in CA3. Thus mitochondrial-mediated injury was amplified and resistance to ischaemic injury lost.

CONCLUSIONS AND IMPLICATIONS

Our findings that Drp-1 increases the resistance of neurons of hippocampal CA3 affected by global ischaemia and contributes to the tolerance conferred by IPC highlight Drp-1 as a potential therapeutic target for brain ischaemic stroke.

Quantitative MS-based enzymology of caspases reveals distinct protein substrate specificities, hierarchies, and cellular roles

Proteases constitute the largest enzyme family, yet their biological roles are obscured by our rudimentary understanding of their cellular substrates. There are 12 human caspases that play crucial roles in inflammation and cell differentiation and drive the terminal stages of cell death. Recent N-terminomics technologies have begun to enumerate the diverse substrates individual caspases can cleave in complex cell lysates. It is clear that many caspases have shared substrates; however, few data exist about the catalytic efficiencies (kcat/KM) of these substrates, which is critical to understanding their true substrate preferences. In this study, we use quantitative MS to determine the catalytic efficiencies for hundreds of natural protease substrates in cellular lysate for two understudied members: caspase-2 and caspase-6. Most substrates are new, and the cleavage rates vary up to 500-fold. We compare the cleavage rates for common substrates with those found for caspase-3, caspase-7, and caspase-8, involved in apoptosis. There is little correlation in catalytic efficiencies among the five caspases, suggesting each has a unique set of preferred substrates, and thus more specialized roles than previously understood. We synthesized peptide substrates on the basis of protein cleavage sites and found similar catalytic efficiencies between the protein and peptide substrates. These data suggest the rates of proteolysis are dominated more by local primary sequence, and less by the tertiary protein fold. Our studies highlight that global quantitative rate analysis for posttranslational modification enzymes in complex milieus for native substrates is critical to better define their functions and relative sequence of events.

Trophic factors deprivation induces long-term protection of neurons against excitotoxic damage

One of the strategies to induce tolerance of neurons to toxic injury is preconditioning. Preconditioning is caused by a weak damage of cells, which become more resistant to subsequent, more severe damage. We found that preconditioning by deprivation of trophic factors, or deprivation of trophic factor and glucose effectively protects neurons against subsequent toxic effects of glutamate. Deprivation of trophic factors plays a decisive role in the development of resistance, regardless of whether it has been combined with glucose deprivation or not. Neuronal protection is achieved when the deprivation lasts from 30 min to two hours and is kept for a period of from one to five days. Preconditioning is accompanied neuronal secretion of cathepsin B occurs. We suggest that this phenomenon is associated with a more general process of exocytosis of lysosomes triggered by deprivation of trophic factors.

miR-455 inhibits neuronal cell death by targeting TRAF3 in cerebral ischemic stroke

Ischemic stroke is one of the leading causes of brain disease, with high morbidity, disability, and mortality. MicroRNAs (miRNAs) have been identified as vital gene regulators in various types of human diseases. Accumulating evidence has suggested that aberrant expression of miRNAs play critical roles in the pathologies of ischemic stroke. Yet, the precise mechanism by which miRNAs control cerebral ischemic stroke remains unclear. In the present study, we explored whether miR-455 suppresses neuronal death by targeting TRAF3 in cerebral ischemic stroke. The expression levels of miR-455 and TRAF3 were detected by quantitative real-time polymerase chain reaction and Western blot. The role of miR-455 in cell death caused by oxygen-glucose deprivation (OGD) was assessed using Cell Counting Kit-8 (CCK-8) assay. The influence of miR-455 on infarct volume was evaluated in mouse brain after middle cerebral artery occlusion (MCAO). Bioinformatics softwares and luciferase analysis were used to find and confirm the targets of miR-455. The results showed that the expression levels of miR-455 significantly decreased in primary neuronal cells subjected to OGD and mouse brain subjected to MCAO. In addition, forced expression of miR-455 inhibited neuronal death and weakened ischemic brain infarction in focal ischemia-stroked mice. Furthermore, TRAF3 was proved to be a direct target of miR-455, and miR-455 could negatively suppress TRAF3 expression. Biological function analysis showed that TRAF3 silencing displayed the neuroprotective effect in ischemic stroke and could enhance miR-455-induced positive impact on ischemic injury both in vitro and in vivo. Taken together, miR-455 played a vital role in protecting neuronal cells from death by downregulating TRAF3 protein expression. These findings may represent a novel latent therapeutic target for cerebral ischemic stroke.

Effects of rapamycin on cerebral oxygen supply and consumption during reperfusion after cerebral ischemia

Activation of the mammalian target of rapamycin (mTOR) leads to cell growth and survival. We tested the hypothesis that inhibition of mTOR would increase infarct size and decrease microregional O2 supply/consumption balance after cerebral ischemia-reperfusion. This was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1h and reperfusion for 2h with and without rapamycin (20mg/kg once daily for two days prior to ischemia). Regional cerebral blood flow was determined using a C(14)-iodoantipyrine autoradiographic technique. Regional small-vessel arterial and venous oxygen saturations were determined microspectrophotometrically. The control ischemic-reperfused cortex had a similar blood flow and O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex. Rapamycin significantly increased cerebral O2 consumption and further reduced O2 supply/consumption balance in the reperfused area. This was associated with an increased cortical infarct size (13.5±0.8% control vs. 21.5±0.9% rapamycin). We also found that ischemia-reperfusion increased AKT and S6K1 phosphorylation, while rapamycin decreased this phosphorylation in both the control and ischemic-reperfused cortex. This suggests that mTOR is important for not only cell survival, but also for the control of oxygen balance after cerebral ischemia-reperfusion.

Tissue kallikrein promotes survival and β-catenin degradation in SH-SY5Y cells under nutrient stress conditions via autophagy

Previous studies by our group showed that tissue kallikrein (TK) exerts neuroprotective effects during cerebral ischemia. Autophagy is an important adaptive response to cellular stress during nutrient deprivation, and β-catenin in known to repress autophagy. The present study investigated the possible involvement of autophagy and β-catenin signaling in the protective effects of TK under nutrient deprivation-induced stress conditions. TK was shown to promote the survival and inhibit the death of SH-SY5Y cells under serum starvation and enhanced autophagic activity in a concentration-dependent manner, as indicated by augmented light chain (LC)3-II levels and Beclin-1 expression. The autophagy inhibitors 3-methyladenine and NH4Cl abolished the protective effects of TK. Of note, although serum starvation alone and TK treatment increased p62 protein levels and mRNA expression, incubation with the lysosome inhibitor NH4Cl increased the accumulation of LC3-II and p62 protein, indicating normal autophagic flux. It was also observed that β-catenin expression was significantly downregulated by TK treatment. TK stimulated the interaction between LC3 and β-catenin, and NH4Cl abolished the effects of TK on β-catenin levels in serum-starved cells, suggesting the autophagic degradation of β-catenin, which may have led to the enhancement of autophagy. In conclusion, the findings of the present study demonstrated that TK promoted cell survival and β-catenin degradation in serum-starved SH-SY5Y cells via increasing autophagy, which indicated the therapeutic potential of TK under nutrient deprivation-associated stress conditions.

Vascular mTOR-dependent mechanisms linking the control of aging to Alzheimer's disease

Aging is the strongest known risk factor for Alzheimer's disease (AD). With the discovery of the mechanistic target of rapamycin (mTOR) as a critical pathway controlling the rate of aging in mice, molecules at the interface between the regulation of aging and the mechanisms of specific age-associated diseases can be identified. We will review emerging evidence that mTOR-dependent brain vascular dysfunction, a universal feature of aging, may be one of the mechanisms linking the regulation of the rate of aging to the pathogenesis of Alzheimer's disease. 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.

Possible role of proteases in preconditioning of brain cells to pathological conditions

Preconditioning (PC) is one of the most effective strategies to reduce the severity of cell damage, in particular of nervous tissue cells. Although PC mechanisms are studied insufficiently, it is clear that proteases are involved in them, but their role has yet been not studied in detail. In this work, some mechanisms of a potential recruiting of proteases in PC are considered. Our attention is mainly focused on the protease families of caspases and cathepsins and on protease receptors. We present evidence that just these proteins are involved in the PC of brain cells. A hypothesis is proposed that secreted cathepsin B is involved in the realization of PC through activation of PAR2 receptor.

mTOR pathway inhibition prevents neuroinflammation and neuronal death in a mouse model of cerebral palsy

BACKGROUND AND PURPOSE

Mammalian target of rapamycin (mTOR) pathway signaling governs cellular responses to hypoxia and inflammation including induction of autophagy and cell survival. Cerebral palsy (CP) is a neurodevelopmental disorder linked to hypoxic and inflammatory brain injury however, a role for mTOR modulation in CP has not been investigated. We hypothesized that mTOR pathway inhibition would diminish inflammation and prevent neuronal death in a mouse model of CP.

METHODS

Mouse pups (P6) were subjected to hypoxia-ischemia and lipopolysaccharide-induced inflammation (HIL), a model of CP causing neuronal injury within the hippocampus, periventricular white matter, and neocortex. mTOR pathway inhibition was achieved with rapamycin (an mTOR inhibitor; 5mg/kg) or PF-4708671 (an inhibitor of the downstream p70S6kinase, S6K, 75 mg/kg) immediately following HIL, and then for 3 subsequent days. Phospho-activation of the mTOR effectors p70S6kinase and ribosomal S6 protein and expression of hypoxia inducible factor 1 (HIF-1α) were assayed. Neuronal cell death was defined with Fluoro-Jade C (FJC) and autophagy was measured using Beclin-1 and LC3II expression. Iba-1 labeled, activated microglia were quantified.

RESULTS

Neuronal death, enhanced HIF-1α expression, and numerous Iba-1 labeled, activated microglia were evident at 24 and 48 h following HIL. Basal mTOR signaling, as evidenced by phosphorylated-S6 and -S6K levels, was unchanged by HIL. Rapamycin or PF-4,708,671 treatment significantly reduced mTOR signaling, neuronal death, HIF-1α expression, and microglial activation, coincident with enhanced expression of Beclin-1 and LC3II, markers of autophagy induction.

CONCLUSIONS

mTOR pathway inhibition prevented neuronal death and diminished neuroinflammation in this model of CP. Persistent mTOR signaling following HIL suggests a failure of autophagy induction, which may contribute to neuronal death in CP. These results suggest that mTOR signaling may be a novel therapeutic target to reduce neuronal cell death in CP.

PAK2 is an effector of TSC1/2 signaling independent of mTOR and a potential therapeutic target for Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is caused by inactivating mutations in either TSC1 or TSC2 and is characterized by uncontrolled mTORC1 activation. Drugs that reduce mTOR activity are only partially successful in the treatment of TSC, suggesting that mTOR-independent pathways play a role in disease development. Here, kinome profiles of wild-type and Tsc2^−/− mouse embryonic fibroblasts (MEFs) were generated, revealing a prominent role for PAK2 in signal transduction downstream of TSC1/2. Further investigation showed that the effect of the TSC1/2 complex on PAK2 is mediated through RHEB, but is independent of mTOR and p21RAC. We also demonstrated that PAK2 over-activation is likely responsible for the migratory and cell cycle abnormalities observed in Tsc2^−/− MEFs. Finally, we detected high levels of PAK2 activation in giant cells in the brains of TSC patients. These results show that PAK2 is a direct effector of TSC1-TSC2-RHEB signaling and a new target for rational drug therapy in TSC.