A double-edged sword with therapeutic potential: an updated role of autophagy in ischemic cerebral injury

ER stress and impaired autophagy flux in neuronal degeneration and brain injury

Autophagy is a highly controlled lysosome-mediated function in eukaryotic cells to eliminate damaged or aged long-lived proteins and organelles. It is required for restoring cellular homeostasis in cell survival under multiple stresses. Autophagy is known to be a double-edged sword because too much activation or inhibition of autophagy can disrupt homeostatic degradation of protein and organelles within the brain and play a role in neuronal cell death. Many factors affect autophagy flux function in the brain, including endoplasmic reticulum (ER) stress, oxidative stress, and aging. Newly emerged research indicates that altered autophagy flux functionality is involved in neurodegeneration of the aged brain, chronic neurological diseases, and after traumatic and ischemic brain injuries. In search to identify neuroprotective agents that may reduce oxidative stress and stimulate autophagy, one particular neuroprotective agent docosahexaenoic acid (DHA) presents unique functions in reducing ER and oxidative stress and modulating autophagy. This review will summarize the recent findings on changes of autophagy in aging, neurodegenerative diseases, and brain injury after trauma or ischemic strokes. Discussion of DHA functions is focused on modulating ER stress and autophagy in regard to its neuroprotection and anti-tumor functions.

Synergism and mechanism of Astragaloside IV combined with Ginsenoside Rg1 against autophagic injury of PC12 cells induced by oxygen glucose deprivation/reoxygenation

The aim of this study was to explore the effect by which the combination of Astragaloside IV (AST IV) and Ginsenoside Rg1 (Rg1) resisted autophagic injury in PC12 cells induced by oxygen glucose deprivation/reoxygenation (OGD/R). We studied the nature of the interaction between AST IV and Rg1 that inhibited autophagy through the Isobologram method, and investigated the synergistic mechanism via the PI3K I/Akt/mTOR and PI3K III/Becline-1/Bcl-2 signaling pathways. Our results showed that, based on the 50% inhibiting concentration (IC50), AST IV combined with Rg1 at a 1:1 ratio resulted in a synergistic effect, whereas the combination of the two had an antagonistic effect on autophagy at ratios of 1:2 and 2:1. Meanwhile, AST IV and Rg1 alone increased cell survival and decreased lactate dehydrogenase (LDH) leakage induced by OGD/R, reduced autophagosomes and the LC3 II positive patch, down-regulated the LC3 II/LC3 I ratio and up-regulated the p62 protein; the 1:1 combination enhanced these effects. Mechanistic study showed that Rg1 and the 1:1 combination increased the phosphorylation of PI3K I, Akt and mTOR; the effects of the combination were greater than those of the drugs alone. AST IV and the 1:1 combination suppressed the expression of PI3K III and Becline-1, and the combination elevated Bcl-2 protein expression; the effects of the combination were better than those of the drugs alone. These results suggest that after 2 h-OGD followed by reoxygenation for 24h, PC12 cells suffer excessive autophagy and damage, which are blocked by AST IV or Rg1; moreover, the combination of AST IV and Rg1 at a 1:1 ratio of their IC50 concentrations has a synergistic inhibition on autophagic injury. The synergistic mechanism may be associated with the PI3K I/Akt/mTOR and PI3K III/Becline-1/Bcl-2 signaling pathways.

Puerarin provides a neuroprotection against transient cerebral ischemia by attenuating autophagy at the ischemic penumbra in neurons but not in astrocytes

Puerarin is an isoflavone derived from the Chinese medical herb of Radix puerariae (kudzu root), and has been widely used in the treatment for ischemic stroke in China. However, its underlying pharmacological mechanisms are still not understood. This study was to investigate the efficacy of puerarin on autophagy in the ischemic penumbra after cerebral stroke. A model of cerebral stroke in Sprague-Dawley rats was prepared by middle cerebral artery occlusion (MCAO); rats were then randomly divided into 5 groups: MCAO+Pue group (rats were treated with puerarin), MCAO+Pue+Tat-Beclin-1 group (rats were administrated with both puerarin and autophagy inducer Tat-Beclin-1), MCAO+Tat-Beclin-1 group (rats were treated with Tat-Beclin-1), MCAO+saline group (rats were administrated with the same volume of physiological saline), and sham surgery group. The autophagy levels in infarct penumbra were evaluated by western blotting, real-time PCR and immunofluorescence 14days after the insult. Meanwhile, the neurological deficit score, brain water content and infarct volume were assessed. The results illustrated that the cerebral infarct volume, cerebral edema and neurological deficiency were significantly alleviated by puerarin treatment. Western blotting and the quantitative PCR revealed that the autophagy level in the penumbra was markedly reduced by puerarin administration. However, these effects of puerarin could be counteracted by Tat-Beclin-1. Additionally, double immunofluorescence showed that neuronal autophagy was markedly attenuated by puerarin treatment, whereas astrocytic autophagy was only mildly reduced. Our study suggests that puerarin could confer a neuroprotection against cerebral ischemia, and this biological function is associated with attenuating autophagy in neurons but not in astrocytes.

Retracted Article: Vitexin mitigates myocardial ischemia reperfusion-induced damage by inhibiting excessive autophagy to suppress apoptosis via the PI3K/Akt/mTOR signaling cascade

Myocardial ischemia reperfusion (MI/R) injury is reported to induce apoptosis and autophagy of myocardial cells and contribute to adverse cardiovascular outcomes.

Prevention of Cyclophilin D-Mediated mPTP Opening Using Cyclosporine-A Alleviates the Elevation of Necroptosis, Autophagy and Apoptosis-Related Markers Following Global Cerebral Ischemia-Reperfusion

The mitochondrial permeability transition pore (mPTP) is a complex channel of the inner membrane, the opening of which leads to mitochondrial swelling and dissipation of mitochondrial membrane potential (MMP). Here, we aimed to evaluate the role of the cyclophilin D (CypD) as a prominent mediator of mPTP, on necroptosis and autophagy as well as apoptosis, beyond the global cerebral ischemia-reperfusion (I/R) injury. We showed that while cerebral I/R injury is accompanied by loss of MMP, mitochondrial swelling and programmed cell death, pretreatment with cyclosporine-A (CsA) as a potent inhibitor of CypD, led to partial but significant reduction in necroptosis markers, RIP1 and RIP3 as well as activity of glutamate-ammonia ligase (GLUL) and glutamate dehydrogenase 1 (GLUD1), downstream enzymes of RIP3. Administration of CsA also partially decreased autophagy associated proteins. Furthermore, we demonstrated that Bax/Bcl-2 ratio as well as caspase-3 activation, as the executioner of apoptosis, noticeably decreased by CsA pretreatment. Taken together, our results suggest that the CypD alongside the apoptosis regulation plays a partial role in inducing necroptosis and autophagy.

Autophagy flux induced by ginsenoside-Rg3 attenuates human prion protein-mediated neurotoxicity and mitochondrial dysfunction

Mitochondrial quality control is a process by which mitochondria undergo successive rounds of fusion and fission with dynamic exchange of components to segregate functional and damaged elements. Removal of mitochondrion that contains damaged components is accomplished via autophagy. In this study, we investigated whether ginsenoside Rg3, an active ingredient of the herbal medicine ginseng that is used as a tonic and restorative agent, could attenuate prion peptide, PrP (106-126)-induced neurotoxicity and mitochondrial damage. To this end, western blot and GFP-LC3B puncta assay were performed to monitor autophagy flux in neuronal cells; LC3B-II protein level was found to increase after Rg3 treatment. In addition, electron microscopy analysis showed that Rg3 enhanced autophagic vacuoles in neuronal cells. By using autophagy inhibitors wortmannin and 3-methyladenine (3MA) or autophagy protein 5 (Atg5) small interfering RNA (siRNA), we demonstrated that Rg3 could protect neurons against PrP (106-126)-induced cytotoxicity via autophagy flux. We found that Rg3 could also attenuate PrP (106-126)-induced mitochondrial damage via autophagy flux. Taken together, our results suggest that Rg3 is a possible therapeutic agent in neurodegenerative disorders, including prion diseases.

Oxidative Stress in Hypoxic-Ischemic Encephalopathy: Molecular Mechanisms and Therapeutic Strategies

Hypoxic-ischemic encephalopathy (HIE) is one of the leading causes of morbidity and mortality in neonates. Because of high concentrations of sensitive immature cells, metal-catalyzed free radicals, non-saturated fatty acids, and low concentrations of antioxidant enzymes, the brain requires high levels of oxygen supply and is, thus, extremely sensitive to hypoxia. Strong evidence indicates that oxidative stress plays an important role in pathogenesis and progression. Following hypoxia and ischemia, reactive oxygen species (ROS) production rapidly increases and overwhelms antioxidant defenses. A large excess of ROS will directly modify or degenerate cellular macromolecules, such as membranes, proteins, lipids, and DNA, and lead to a cascading inflammatory response, and protease secretion. These derivatives are involved in a complex interplay of multiple pathways (e.g., inflammation, apoptosis, autophagy, and necrosis) which finally lead to brain injury. In this review, we highlight the molecular mechanism for oxidative stress in HIE, summarize current research on therapeutic strategies utilized in combating oxidative stress, and try to explore novel potential clinical approaches.

Autophagy activation involved in hypoxic-ischemic brain injury induces cognitive and memory impairment in neonatal rats

Hypoxic-ischemic brain injury (HIBI) in neonates can lead to lifelong cognitive and memory impairment, but protective strategies are lacking at present. It has been demonstrated that autophagy plays a critical role in HIBI, while the function of autophagy in cognitive and memory impairment induced by HIBI in neonates has not been tested. In this study, we tested the impact of autophagy on the impairment of cognitive function and memory in HIBI neonatal rats by using a Morris water maze and investigated its possible mechanisms, which were established as HIBI model by ligating the left common carotid artery in neonatal rats, followed by 2-h hypoxia. The expression of microtubule-associated protein 1 light chain 3 (LC3)-II increased in HI group 24 h after HI in neonatal rats, while Sequestosome 1 (P62/SQSTM1), phosphorylated cAMP-response element-binding protein (p-CREB) decreased (compared with the sham group, p < 0.05), which were shown in the same left hippocampus CA3 region by immunofluorescence analysis. Brain injury of neonatal rats was aggravated significantly at 7 day after HI, coinciding with the results of Morris water maze. An autophagy inhibitor, 3-methyladenine (3-MA) pretreatment significantly attenuated the increase of LC3II and the loss of P62/SQSTM1 and p-CREB, ameliorated neuronal death, and improved the results of Morris water maze. Our results demonstrate that HIBI in neonatal rats induced excessive autophagy flux, which aggravated brain injury and induced cognitive and memory impairment during adolescence. Inhibition of autophagy reversed the results partly and improved the function of spatial learning and memory by attenuating the reduction of p-CREB. The use of autophagy modulators in the immature brain would create new opportunities for protective strategies clinically in the future.

Bexarotene targets autophagy and is protective against thromboembolic stroke in aged mice with tauopathy

Stroke is a highly debilitating, often fatal disorder for which current therapies are suitable for only a minor fraction of patients. Discovery of novel, effective therapies is hampered by the fact that advanced age, primary age-related tauopathy or comorbidities typical to several types of dementing diseases are usually not taken into account in preclinical studies, which predominantly use young, healthy rodents. Here we investigated for the first time the neuroprotective potential of bexarotene, an FDA-approved agent, in a co-morbidity model of stroke that combines high age and tauopathy with thromboembolic cerebral ischemia. Following thromboembolic stroke bexarotene enhanced autophagy in the ischemic brain concomitantly with a reduction in lesion volume and amelioration of behavioral deficits in aged transgenic mice expressing the human P301L-Tau mutation. In in vitro studies bexarotene increased the expression of autophagy markers and reduced autophagic flux in neuronal cells expressing P301L-Tau. Bexarotene also restored mitochondrial respiration deficits in P301L-Tau neurons. These newly described actions of bexarotene add to the growing amount of compelling data showing that bexarotene is a potent neuroprotective agent, and identify a novel autophagy-modulating effect of bexarotene.

cPKCγ-Modulated Autophagy in Neurons Alleviates Ischemic Injury in Brain of Mice with Ischemic Stroke Through Akt-mTOR Pathway

We have reported that neuron-specific conventional protein kinase C (cPKC)γ is involved in the development of cerebral hypoxic preconditioning (HPC) and the neuroprotection against ischemic injuries, but its molecular mechanism is unclear. In this study, the adult and postnatal 24 h C57BL/6J wild-type (cPKCγ^+/+) and cPKCγ knockout (cPKCγ^-/-) mice were respectively used to establish the models of middle cerebral artery occlusion (MCAO)-induced ischemic stroke in vivo and oxygen-glucose deprivation (OGD)-treated primarily cultured cortical neurons as cell ischemia in vitro. The results showed that cPKCγ knockout could increase the infarct volume and neuronal cell loss in the peri-infarct region, and enhance the neurological deficits, the impaired coordination, and the reduced muscle strength of mice following 1 h MCAO/1-7 days reperfusion. Meanwhile, cPKCγ knockout significantly increased the conversion of LC3-I to LC3-II and beclin-1 protein expression, and resulted in more reductions in P-Akt, P-mTOR, and P-S6 phosphorylation levels in the peri-infarct region of mice with ischemic stroke. The autophagy inhibitor BafA1 could enhance or reduce neuronal cell loss in the peri-infarct region of cPKCγ^+/+ and cPKCγ^-/- mice after ischemic stroke. In addition, cPKCγ knockout and restoration could aggravate or alleviate OGD-induced neuronal ischemic injury in vitro through Akt-mTOR pathway-mediated autophagy. These results suggested that cPKCγ-modulated neuron-specific autophagy improves the neurological outcome of mice following ischemic stroke through the Akt-mTOR pathway, providing a potential therapeutic target for ischemic stroke.

Epigallocatechin gallate exerts protective effects against myocardial ischemia/reperfusion injury through the PI3K/Akt pathway-mediated inhibition of apoptosis and the restoration of the autophagic flux

Epigallocatechin gallate (EGCG), a polyphenol derived from green tea, exhibits a wide range of biological activities, including antioxidant, atherosclerosis and antitumor activities. In this study, the cardioprotective effects of EGCG on myocardial ischemia/reperfusion (I/R) injury in rats and the underlying mechanisms were investigated. A rat model of I/R injury was established by ligating the left anterior descending coronary artery for 30 min, followed by reperfusion for 2 h. The levels of I/R-induced creatine kinase-MB (CK-MB) and the release of lactate dehydrogenase (LDH), as well as the infarct size, cardiomyocyte apoptosis and cardiac functional impairment were examined and compared. Western blot analysis was carried out to elucidate the potential molecular mechanisms of action of EGCG. The results revealed that EGCG post-conditioning significantly decreased the levels of CK-MB and the release of LDH, reduced the myocardial infarct size, decreased the apoptotic rate and partially preserved heart function. Furthermore, EGCG decreased the expression of cleaved caspase-3 concomitantly with the upregulation of PI3K, and the phosphorylation of Akt and endothelial nitric oxide synthase (eNOS). It also inhibited I/R-induced overautophagy and promoted the clearance of autophagosomes, as evidenced by a decrease in the ratio of microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I, the downregulation of Beclin1, Atg5 and p62, and the upregulation of active cathepsin D. Additionally, we observed an increase in the phosphorylation levels of the mammalian target of rapamycin (mTOR) following treatment with EGCG. Taken together, the findings of this study demonstrate that, EGCG post-conditioning alleviates myocardial I/R injury by inhibiting apoptosis and restoring the autophagic flux, which is associated with several targets of the PI3K/Akt signaling pathway.

Hinokitiol protects primary neuron cells against prion peptide-induced toxicity via autophagy flux regulated by hypoxia inducing factor-1

Prion diseases are fatal neurodegenerative disorders that are derived from structural changes of the native PrPc. Recent studies indicated that hinokitiol induced autophagy known to major function that keeps cells alive under stressful conditions. We investigated whether hinokitiol induces autophagy and attenuates PrP (106-126)-induced neurotoxicity. We observed increase of LC3-II protein level, GFP-LC3 puncta by hinokitiol in neuronal cells. Addition to, electron microscopy showed that hinokitiol enhanced autophagic vacuoles in neuronal cells. We demonstrated that hinokitiol protects against PrP (106-126)-induced neurotoxicity via autophagy by using autophagy inhibitor, wortmannin and 3MA, and ATG5 small interfering RNA (siRNA). We checked hinokitiol activated the hypoxia-inducible factor-1α (HIF-1α) and identified that hinokitiol-induced HIF-1α regulated autophagy. Taken together, this study is the first report demonstrating that hinokitiol protected against prion protein-induced neurotoxicity via autophagy regulated by HIF-1α. We suggest that hinokitiol is a possible therapeutic strategy in neuronal disorders including prion disease.

Protection against Experimental Stroke by Ganglioside GM1 Is Associated with the Inhibition of Autophagy

Ganglioside GM1, which is particularly abundant in the central nervous system (CNS), is closely associated with the protection against several CNS disorders. However, controversial findings have been reported on the role of GM1 following ischemic stroke. In the present study, using a rat middle cerebral artery occlusion (MCAO) model, we investigated whether GM1 can protect against ischemic brain injury and whether it targets the autophagy pathway. GM1 was delivered to Sprague-Dawley male rats at 3 doses (25 mg/kg, 50 mg/kg, 100 mg/kg) by intraperitoneal injection soon after reperfusion and then once daily for 2 days. The same volume of saline was given as a control. Tat–Beclin-1, a specific autophagy inducer, was administered by intraperitoneal injection at 24 and 48 hours post-MCAO. Infarction volume, mortality and neurological function were assessed at 72 hours after ischemic insult. Immunofluorescence and Western blotting were performed to determine the expression of autophagy-related proteins P62, LC3 and Beclin-1 in the penumbra area. No significant changes in mortality and physiological variables (heart rate, blood glucose levels and arterial blood gases) were observed between the different groups. However, MCAO resulted in enhanced conversion of LC3-I into LC3-II, P62 degradation, high levels of Beclin-1, a large area infarction (26.3±3.6%) and serious neurobehavioral deficits. GM1 (50 mg/kg) treatment significantly reduced the autophagy activation, neurobehavioral dysfunctions, and infarction volume (from 26.3% to 19.5%) without causing significant adverse side effects. However, this biological function could be abolished by Tat–Beclin-1. In conclusion: GM1 demonstrated safe and robust neuroprotective effects that are associated with the inhibition of autophagy following experimental stroke.

Minocycline induces protective autophagy in vascular endothelial cells exposed to an in vitro model of ischemia/reperfusion-induced injury

Minocycline has been reported to exhibit advantageous effects on ischemic stroke; however, the precise mechanism of minocycline remains to be established. In the present study, human umbilical vein endothelial cells (HUVECs) were subjected to in vitro simulated ischemia/reperfusion conditions to determine the potential effect of minocycline-induced autophagy on HUVEC damage under oxygen-glucose deprivation/reperfusion (OGD/R). The study demonstrated that minocycline enhanced autophagy in a dose-dependent manner in HUVECs exposed to OGD/R, and only low-dose minocycline protected HUVECs from OGD/R-induced damage. Subsequently, 3-methyladenine (3-MA) was added into the culture media and the protective effect of minocycline was abolished. At the same time, it has been observed that simultaneous treatment with 3-MA also inhibited the autophagy activity induced by minocycline. This finding could suggest that autophagy induced by minocycline serves as one of the potential protective mechanism underlying the beneficial effects of minocycline on ischemic injury.

Electroacupuncture protects against ischemic stroke by reducing autophagosome formation and inhibiting autophagy through the mTORC1-ULK1 complex-Beclin1 pathway

In a previous study by our group, we demonstrated that electroacupuncture (EA) activates the class I phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. There is considerable evidence that the downstream mammalian target of rapamycin complex 1 (mTORC1) plays an important role in autophagy following ischemic stroke. The aim of the present study was to determine whether EA exerts a neuroprotective effect through mTORC1-mediated autophagy following ischemia/reperfusion injury. Our results revealed that EA at the LI11 and ST36 acupoints attenuated motor dysfunction, improved neurological deficit outcomes and decreased the infarct volumes. The number of autophagosomes, autolysosomes and lysosomes was decreased following treatment with EA. Simultaneously, the levels of the autophagosome membrane maker, microtubule-associated protein 1 light chain 3 beta (LC3B)II/I, Unc-51-like kinase 1 (ULK1), autophagy related gene 13 Atg13) and Beclin1 (ser14) were decreased, whereas mTORC1 expression was increased in the peri-infarct cortex. These results suggest that EA protects against ischemic stroke through the inhibition of autophagosome formation and autophagy, which is mediated through the mTORC1-ULK complex-Beclin1 pathway.

Bauhinia championii flavone inhibits apoptosis and autophagy via the PI3K/Akt pathway in myocardial ischemia/reperfusion injury in rats

This study aimed to determine the effects of Bauhinia championii flavone (BCF) on myocardial ischemia/reperfusion injury (MI/RI) in rats and to explore potential mechanisms. The MI/RI model in rats was established by ligating the left anterior descending coronary artery for 30 minutes, then reperfusing for 3 hours. BCF at 20 mg/kg was given 20 minutes prior to ischemia via sublingual intravenous injection, with 24 μg/kg phosphoinositide 3-kinase inhibitor (PI3K; wortmannin) as a control. The creatine kinase-MB and nitric oxide content were assessed by colorimetry. The levels of mitochondrial permeability transition pores and tumor necrosis factor alpha were determined by an enzyme-linked immunosorbent assay. Cardiomyocyte apoptosis was detected by the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Additionally, the expression of PI3K, endothelial nitric oxide synthase, caspase-3, and Beclin1 was analyzed by fluorescence quantitative polymerase chain reaction and Western blotting, respectively. Akt and microtubule-associated protein 1 light chain 3-II protein levels were also evaluated. Pretreatment with BCF significantly decreased the levels of creatine kinase-MB, tumor necrosis factor alpha, and mitochondrial permeability transition pores, but increased the nitric oxide content. Furthermore, BCF inhibited apoptosis, downregulated caspase-3, Beclin1, and microtubule-associated protein 1 light chain 3-II, upregulated PI3K, and increased the protein levels of phosphorylated Akt and endothelial nitric oxide synthase. However, all of the previously mentioned effects of BCF were blocked when BCF was coadministered with wortmannin. In conclusion, these observations indicated that BCF has cardioprotective effects against MI/RI by reducing cell apoptosis and excessive autophagy, which might be related to the activation of the PI3K/Akt signaling pathway.

Regulation of mitophagy in ischemic brain injury

The selective degradation of damaged or excessive mitochondria by autophagy is termed mitophagy. Mitophagy is crucial for mitochondrial quality control and has been implicated in several neurodegenerative disorders as well as in ischemic brain injury. Emerging evidence suggested that the role of mitophagy in cerebral ischemia may depend on different pathological processes. In particular, a neuroprotective role of mitophagy has been proposed, and the regulation of mitophagy seems to be important in cell survival. For these reasons, extensive investigations aimed to profile the mitophagy process and its underlying molecular mechanisms have been executed in recent years. In this review, we summarize the current knowledge regarding the mitophagy process and its role in cerebral ischemia, and focus on the pathological events and molecules that regulate mitophagy in ischemic brain injury.

Activating cannabinoid receptor 2 alleviates pathogenesis of experimental autoimmune encephalomyelitis via activation of autophagy and inhibiting NLRP3 inflammasome

AIMS

Activation of cannabinoid receptor 2 (CB2R) has been reported to ameliorate the pathogenesis of experimental autoimmune encephalomyelitis (EAE). In this study, we examined whether autophagy is involved in the beneficial effect of CB2R on EAE and explored the mechanism with a focus on inflammasome activation.

METHODS

EAE severity was analyzed with clinical score and histological score stained by hematoxylin and eosin or luxol fast blue in spinal cord. Immunoblot analysis was conducted to detect proteins of NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome-related caspase-1 (Casp-1) and the maturation of interleukin (IL)-1β as well as autophagy-related light chain 3 (LC3), and Beciln 1 both in vivo and in vitro. Reverse transcription and real-time PCR were used to detect mRNA of NLRP3, IL-1β and Casp-1. Autophagy-related gene 5 (ATG5)-specific siRNA was transiently transfected in BV2 microglia, and immunofluorescence staining was carried out to detect the expression of NLRP3, caspase recruitment domain (ASC), and pro-caspase-1.

RESULTS

The current data indicated that deleting CB2R decreased the expression of LC3-II/LC3-I ratio, Beclin 1 and increased caspase-1 activation and IL-1β production in the spinal cord of EAE mice, whereas activation of CB2R with a specific agonist HU-308 induced inverse effects. Further study indicated that HU-308 could promote autophagy and inhibit expression and activation of NLRP3 inflammasome in BV2 microglia. Blocking autophagy by ATG5-specific siRNA dismissed the effort of CB2R in mediating NLRP3 inflammasome in vitro.

CONCLUSION

Collectively, our results demonstrated for the first time that CB2R plays a protective role in EAE through promoting autophagy and inhibiting NLRP3 inflammasome activation.

The antiaging activity and cerebral protection of rapamycin at micro-doses

BACKGROUND AND PURPOSE

The immunosuppressant drug rapamycin was reported to have an antiaging activity, which was attributed to the TORC1 inhibition that inhibits cell proliferation and increases autophagy. However, rapamycin also exhibits a number of harmful adverse effects. Whether rapamycin can be developed into an antiaging agent remains unclear.

METHODS AND RESULTS

We demonstrated that rapamycin at micro-doses (below the TORC1 inhibiting concentration) exhibits a cell-protective activity: (1) It protects cultured neurons against neurotoxin MPP(+) and H2O2. (2) It increases survival time of neuron in culture. (3) It maintains the nonproliferative state of cultured senescent human fibroblasts and prevents cell death induced by telomere dysfunction. (4) In animal models, it decreased the cerebral infarct sizes induced by acute ischemia and dramatically extended the life span of stroke prone spontaneously hypertensive rats (SHR-SPs).

CONCLUSION

We propose that rapamycin at micro-dose can be developed into an antiaging agent with a novel mechanism.

The Effects of Methylene Blue on Autophagy and Apoptosis in MRI-Defined Normal Tissue, Ischemic Penumbra and Ischemic Core

Methylene blue (MB) USP, which has energy-enhancing and antioxidant properties, is currently used to treat methemoglobinemia and cyanide poisoning in humans. We recently showed that MB administration reduces infarct volume and behavioral deficits in rat models of ischemic stroke and traumatic brain injury. This study reports the underlying molecular mechanisms of MB neuroprotection following transient ischemic stroke in rats. Rats were subjected to transient (60-mins) ischemic stroke. Multimodal MRI during the acute phase and at 24 hrs were used to define three regions of interest (ROIs): i) the perfusion-diffusion mismatch salvaged by reperfusion, ii) the perfusion-diffusion mismatch not salvaged by reperfusion, and iii) the ischemic core. The tissues from these ROIs were extracted for western blot analyses of autophagic and apoptotic markers. The major findings were: 1) MB treatment reduced infarct volume and behavioral deficits, 2) MB improved cerebral blood flow to the perfusion-diffusion mismatch tissue after reperfusion and minimized harmful hyperperfusion 24 hrs after stroke, 3) MB inhibited apoptosis and enhanced autophagy in the perfusion-diffusion mismatch, 4) MB inhibited apoptotic signaling cascades (p53-Bax-Bcl2-Caspase3), and 5) MB enhanced autophagic signaling cascades (p53-AMPK-TSC2-mTOR). MB induced neuroprotection, at least in part, by enhancing autophagy and reducing apoptosis in the perfusion-diffusion mismatch tissue following ischemic stroke.

Ischemic conditioning-induced endogenous brain protection: Applications pre-, per- or post-stroke

In the area of brain injury and neurodegenerative diseases, a plethora of experimental and clinical evidence strongly indicates the promise of therapeutically exploiting the endogenous adaptive system at various levels like triggers, mediators and the end-effectors to stimulate and mobilize intrinsic protective capacities against brain injuries. It is believed that ischemic pre-conditioning and post-conditioning are actually the strongest known interventions to stimulate the innate neuroprotective mechanism to prevent or reverse neurodegenerative diseases including stroke and traumatic brain injury. Recently, studies showed the effectiveness of ischemic per-conditioning in some organs. Therefore the term ischemic conditioning, including all interventions applied pre-, per- and post-ischemia, which spans therapeutic windows in 3 time periods, has recently been broadly accepted by scientific communities. In addition, it is extensively acknowledged that ischemia-mediated protection not only affects the neurons but also all the components of the neurovascular network (consisting of neurons, glial cells, vascular endothelial cells, pericytes, smooth muscle cells, and venule/veins). The concept of cerebroprotection has been widely used in place of neuroprotection. Intensive studies on the cellular signaling pathways involved in ischemic conditioning have improved the mechanistic understanding of tolerance to cerebral ischemia. This has added impetus to exploration for potential pharmacologic mimetics, which could possibly induce and maximize inherent protective capacities. However, most of these studies were performed in rodents, and the efficacy of these mimetics remains to be evaluated in human patients. Several classical signaling pathways involving apoptosis, inflammation, or oxidation have been elaborated in the past decades. Newly characterized mechanisms are emerging with the advances in biotechnology and conceptual renewal. In this review we are going to focus on those recently reported methodological and mechanistic discoveries in the realm of ischemic conditioning. Due to the varied time differences of ischemic conditioning in different animal models and clinical trials, it is important to define optimal timing to achieve the best conditioning induced neuroprotection. This brings not only an opportunity in the treatment of stroke, but challenges as well, as data is just becoming available and the procedures are not yet optimized. The purpose of this review is to shed light on exploiting these ischemic conditioning modalities to protect the cerebrovascular system against diverse injuries and neurodegenerative disorders.

NMDA receptor blockade in the developing cortex induces autophagy-mediated death of immature cortical GABAergic interneurons: An ex vivo and in vivo study in Gad67-GFP mice

In neonates, excitotoxicity is a major process involved in hypoxic-ischemic brain lesions, and several research groups have suggested the use of NMDA antagonists for neuroprotection. However, despite their clinical interest, there is more and more evidence suggesting that, in the immature brain, these molecules exert deleterious actions on migrating GABAergic interneurons by suppressing glutamatergic trophic inputs. Consequently, preventing the side effects of NMDA antagonists would be therapeutically useful. Because macroautophagy is involved in the adaptive response to trophic deprivation, the aim of the present study was to investigate the impact of autophagy modulators on the MK801-induced death of immature GABAergic interneurons and to characterize the crosstalk between autophagic and apoptotic mechanisms in this cell type. Ex vivo, using cortical slices from NMRI and Gad67-GFP mice, we show that blockade of the NMDA receptor results in an accumulation of autophagosomes due to the disruption of the autophagic flux. This effect precedes the activation of the mitochondrial apoptotic pathway, and the degeneration of immature GABAergic neurons present in developing cortical layers II-IV and is prevented by 3-MA, an autophagy inhibitor. In contrast, modulators of autophagy (3-MA, rapamycin) do not interfere with the anti-excitotoxic and neuroprotective effect of MK801 observed in deep layers V and VI. In vivo, 3-MA blocks the rapid increase in caspase-3 cleavage induced by the blockade of NMDA receptors and prevents the resulting long-term decrease in Gad67-GFP neurons in layers II-IV. Together, these data suggest that, in the developing cortex, the suppression of glutamatergic inputs through NMDA receptor inhibition results in the impairment of the autophagic flux and the subsequent switch to apoptotic death of immature GABAergic interneurons. The concomitant inhibition of autophagy prevents this pro-apoptotic action of the NMDA blocker and favors the long-term rescue of GABAergic interneurons without interfering with its neuroprotective actions. The use of autophagy modulators in the developing brain would create new opportunities to prevent the side effects of NMDA antagonists used for neuroprotection or anesthesia.

Autophagy in neuronal cells: general principles and physiological and pathological functions

Autophagy delivers cytoplasmic components and organelles to lysosomes for degradation. This pathway serves to degrade nonfunctional or unnecessary organelles and aggregate-prone and oxidized proteins to produce substrates for energy production and biosynthesis. Macroautophagy delivers large aggregates and whole organelles to lysosomes by first enveloping them into autophagosomes that then fuse with lysosomes. Chaperone-mediated autophagy (CMA) degrades proteins containing the KFERQ-like motif in their amino acid sequence, by transporting them from the cytosol across the lysosomal membrane into the lysosomal lumen. Autophagy is especially important for the survival and homeostasis of postmitotic cells like neurons, because these cells are not able to dilute accumulating detrimental substances and damaged organelles by cell division. Our current knowledge on the autophagic pathways and molecular mechanisms and regulation of autophagy will be summarized in this review. We will describe the physiological functions of macroautophagy and CMA in neuronal cells. Finally, we will summarize the current evidence showing that dysfunction of macroautophagy and/or CMA contributes to neuronal diseases. We will give an overview of our current knowledge on the role of autophagy in aging neurons, and focus on the role of autophagy in four types of neurodegenerative diseases, i.e., amyotrophic lateral sclerosis and frontotemporal dementia, prion diseases, lysosomal storage diseases, and Parkinson's disease.

NH2-truncated human tau induces deregulated mitophagy in neurons by aberrant recruitment of Parkin and UCHL-1: implications in Alzheimer's disease

Disarrangement in functions and quality control of mitochondria at synapses are early events in Alzheimer's disease (AD) pathobiology. We reported that a 20-22 kDa NH2-tau fragment mapping between 26 and 230 amino acids of the longest human tau isoform (aka NH2htau): (i) is detectable in cellular and animal AD models, as well in synaptic mitochondria and cerebrospinal fluids (CSF) from human AD subjects; (ii) is neurotoxic in primary hippocampal neurons; (iii) compromises the mitochondrial biology both directly, by inhibiting the ANT-1-dependent ADP/ATP exchange, and indirectly, by impairing their selective autophagic clearance (mitophagy). Here, we show that the extensive Parkin-dependent turnover of mitochondria occurring in NH2htau-expressing post-mitotic neurons plays a pro-death role and that UCHL-1, the cytosolic Ubiquitin-C-terminal hydrolase L1 which directs the physiological remodeling of synapses by controlling ubiquitin homeostasis, critically contributes to mitochondrial and synaptic failure in this in vitro AD model. Pharmacological or genetic suppression of improper mitophagy, either by inhibition of mitochondrial targeting to autophagosomes or by shRNA-mediated silencing of Parkin or UCHL-1 gene expression, restores synaptic and mitochondrial content providing partial but significant protection against the NH2htau-induced neuronal death. Moreover, in mitochondria from human AD synapses, the endogenous NH2htau is stably associated with Parkin and with UCHL-1. Taken together, our studies show a causative link between the excessive mitochondrial turnover and the NH2htau-induced in vitro neuronal death, suggesting that pathogenetic tau truncation may contribute to synaptic deterioration in AD by aberrant recruitment of Parkin and UCHL-1 to mitochondria making them more prone to detrimental autophagic clearance.

Lipoxin A4 methyl ester alleviates vascular cognition impairment by regulating the expression of proteins related to autophagy and ER stress in the rat hippocampus

Since autophagy and endoplasmic reticulum stress mechanisms are involved in some neurodegenerative and cerebral vascular diseases, we suspected that similar mechanisms might participate in vascular cognitive impairments induced by chronic cerebral hypoperfusion. Lipoxin A

Autophagic marker MAP1LC3B expression levels are associated with carotid atherosclerosis symptomatology

Objectives

The mechanism by which atheroma plaque becomes unstable is not completely understood to date but analysis of differentially expressed genes in stable versus unstable plaques may provide clues. This will be crucial toward disclosing the mechanistic basis of plaque instability, and may help to identify prognostic biomarkers for ischaemic events. The objective of our study was to identify differences in expression levels of 59 selected genes between symptomatic patients (unstable plaques) and asymptomatic patients (stable plaques).

Methods

80 carotid plaques obtained by carotid endarterectomy and classified as symptomatic (>70% stenosis) or asymptomatic (>80% stenosis) were used in this study. The expression levels of 59 genes were quantified by qPCR on RNA extracted from the carotid plaques obtained by endarterectomy and analyzed by means of various bioinformatic tools.

Results

Several genes associated with autophagy pathways displayed differential expression levels between asymptomatic and symptomatic (i.e. MAP1LC3B, RAB24, EVA1A). In particular, mRNA levels of MAP1LC3B, an autophagic marker, showed a 5−fold decrease in symptomatic samples, which was confirmed in protein blots. Immune system−related factors and endoplasmic reticulum-associated markers (i.e. ERP27, ITPR1, ERO1LB, TIMP1, IL12B) emerged as differently expressed genes between asymptomatic and symptomatic patients.

Conclusions

Carotid atherosclerotic plaques in which MAP1LC3B is underexpressed would not be able to benefit from MAP1LC3B−associated autophagy. This may lead to accumulation of dead cells at lesion site with subsequent plaque destabilization leading to cerebrovascular events. Identified biomarkers and network interactions may represent novel targets for development of treatments against plaque destabilization and thus for the prevention of cerebrovascular events.

Anesthetic preconditioning inhibits isoflurane-mediated apoptosis in the developing rat brain

BACKGROUND

We hypothesized that preconditioning (PC) with a short exposure to isoflurane (ISO) would reduce neurodegeneration induced by prolonged exposure to ISO in neonatal rats, as previously shown in neuronal cell culture.

METHODS

We randomly divided 7-day-old Sprague-Dawley rats into 3 groups: control, 1.5% ISO, and PC + 1.5% ISO. The control group was exposed to carrier gas (30% oxygen balanced in nitrogen) for 30 minutes and then to carrier gas again for 6 hours the following day. The 1.5% ISO group was exposed to carrier gas for 30 minutes and then to 1.5% ISO for 6 hours the following day. The PC + 1.5% ISO group was preconditioned with a 30-minute 1.5% ISO exposure and then exposed to 1.5% ISO for 6 hours the following day. Blood and brain samples were collected 2 hours after the exposures for determination of neurodegenerative biomarkers, including caspase-3, S100β, caspase-12, and an autophagy biomarker Beclin-1.

RESULTS

Prolonged exposure to ISO significantly increased cleaved caspase-3 expression in the cerebral cortex of 7-day-old rats compared with the group preconditioned with ISO and the controls using Western blot assays. However, significant differences were not detected for other markers of neuronal injury.

CONCLUSIONS

The ISO-mediated increase in cleaved caspase-3 in the postnatal day 7 rat brain is ameliorated by PC with a brief anesthetic exposure, and differences were not detected in other markers of neuronal injury.

DRAM1 protects neuroblastoma cells from oxygen-glucose deprivation/reperfusion-induced injury via autophagy

DNA damage-regulated autophagy modulator protein 1 (DRAM1), a multi-pass membrane lysosomal protein, is reportedly a tumor protein p53 (TP53) target gene involved in autophagy. During cerebral ischemia/reperfusion (I/R) injury, DRAM1 protein expression is increased, and autophagy is activated. However, the functional significance of DRAM1 and the relationship between DRAM1 and autophagy in brain I/R remains uncertain. The aim of this study is to investigate whether DRAM1 mediates autophagy activation in cerebral I/R injury and to explore its possible effects and mechanisms. We adopt the oxygen-glucose deprivation and reperfusion (OGD/R) Neuro-2a cell model to mimic cerebral I/R conditions in vitro, and RNA interference is used to knock down DRAM1 expression in this model. Cell viability assay is performed using the LIVE/DEAD viability/cytotoxicity kit. Cell phenotypic changes are analyzed through Western blot assays. Autophagy flux is monitored through the tandem red fluorescent protein-Green fluorescent protein-microtubule associated protein 1 light chain 3 (RFP-GFP-LC3) construct. The expression levels of DRAM1 and microtubule associated protein 1 light chain 3II/I (LC3II/I) are strongly up-regulated in Neuro-2a cells after OGD/R treatment and peaked at the 12 h reperfusion time point. The autophagy-specific inhibitor 3-Methyladenine (3-MA) inhibits the expression of DRAM1 and LC3II/I and exacerbates OGD/R-induced cell injury. Furthermore, DRAM1 knockdown aggravates OGD/R-induced cell injury and significantly blocks autophagy through decreasing autophagosome-lysosome fusion. In conclusion, our data demonstrate that DRAM1 knockdown in Neuro-2a cells inhibits autophagy by blocking autophagosome-lysosome fusion and exacerbated OGD/R-induced cell injury. Thus, DRAM1 might constitute a new therapeutic target for I/R diseases.

Dual role of autophagy in lipopolysaccharide-induced preodontoblastic cells

Odontoblasts derive from neural crest-derived odontogenic mesenchymal cells, and they are an important barrier of defense for the host. Survival and immunity of odontoblasts play important roles in protecting the dentin-pulp structure. Autophagy can eliminate damaged organelles and recycle cellular components to facilitate cellular homeostasis. Autophagy can be activated with external stressors, such as starvation, hypoxia, and infection. In this study, the role of autophagy in inflamed odontoblasts was explored, and its possible mechanism was investigated. Cell viability was not affected by mild lipopolysaccharide (LPS) stimulation, and autophagy was activated during this process. Immunofluorescence of light chain 3 confirmed that autophagy was induced with LPS treatment. Early-stage autophagy inhibition resulted in down-regulated cell viability, contrary to the up-regulated cell viability at late-stage autophagy inhibition. Western blot suggested that p-Akt and survivin were not activated in the early stage, and they gradually increased and peaked in the late stage. Meanwhile, autophagy was down-regulated through the Akt/mTOR/survivin pathway in the late stage. Thus, autophagy has a dual role in inflamed odontoblasts, which indicates its importance in maintaining the microenvironment homeostasis of odontoblasts. Autophagy was induced as a survival mechanism in the early stage, and it decreased through the Akt/mTOR/survivin signaling pathway in the late stage.

Autophagy: a double-edged sword for neuronal survival after cerebral ischemia

Evidence suggests that autophagy may be a new therapeutic target for stroke, but whether activation of autophagy increases or decreases the rate of neuronal death is still under debate. This review summarizes the potential role and possible signaling pathway of autophagy in neuronal survival after cerebral ischemia and proposes that autophagy has dual effects.

Autophagy suppression by exercise pretreatment and p38 inhibition is neuroprotective in cerebral ischemia

Autophagy is a degradative mechanism for cellular proteins and organelles, but its role in the nervous system is still not clear. In the present study, we found that exercise pretreatment and p38 inhibition had influence on autophagic process after cerebral ischemia, contributing to their neuroprotective effects. We examined the levels of p62 and phosphorylated ERK1/2 as an autophagic marker and cell-survival marker respectively after cerebral ischemic injury. The brain infarction volume after ischemia was measured as well. Both treadmill training pretreatment and p38 inhibition decreased the degradation of p62, promoted the phosphorylation of ERK1/2, and alleviated the brain infarction, indicating that these treatments could provide neuroprotection in cerebral ischemic injury via autophagy suppression.

Diabetes and the brain: oxidative stress, inflammation, and autophagy

Diabetes mellitus is a common metabolic disorder associated with chronic complications including a state of mild to moderate cognitive impairment, in particular psychomotor slowing and reduced mental flexibility, not attributable to other causes, and shares many symptoms that are best described as accelerated brain ageing. A common theory for aging and for the pathogenesis of this cerebral dysfunctioning in diabetes relates cell death to oxidative stress in strong association to inflammation, and in fact nuclear factor κB (NFκB), a master regulator of inflammation and also a sensor of oxidative stress, has a strategic position at the crossroad between oxidative stress and inflammation. Moreover, metabolic inflammation is, in turn, related to the induction of various intracellular stresses such as mitochondrial oxidative stress, endoplasmic reticulum (ER) stress, and autophagy defect. In parallel, blockade of autophagy can relate to proinflammatory signaling via oxidative stress pathway and NFκB-mediated inflammation.

Stimulation of autophagic activity in human glioma cells by anti-proliferative ardipusilloside I isolated from Ardisia pusilla

AIMS

Ardipusilloside I (ADS-I), a triterpenoid saponin isolated from Ardisia pusilla A.DC (Myrsinaceae), has been recently tested for cancer treatment including brain cancer. However, the mechanism of its action remains elusive. The present study was to investigate the role of autophagy activation in the anti-tumor activities of ADS-I in human glioma cells.

MAIN METHODS

The tetrazolium dye (MTT) colorimetric assay was used for the measurement of cell proliferation in cultured glioma cells, transmission electron microscopy (TEM) for the examination of autophagic activity, flow cytometric analysis for the determination of cell cycle and apoptotic cells, and immunocytochemistry and Western blot for protein expression of microtubule-associated protein light-chain 3 (LC3) and Beclin 1.

KEY FINDINGS

ADS-I significantly inhibited the proliferation of both U373 and T98G glioma cells in cultures in a dose-dependent manner. The cytotoxic activity of ADS-I against glioma cell growth was associated not only with the induction of cell cycle arrest at G2/M phase and cell apoptosis in flow cytometric analysis, but also with the activation of autophagy, indicated by the formation of autophagosomes and up-regulated expression of both autophagic protein Beclin 1 and LC3 in glioma cells. Additionally, the treatment with chloroquine, an autophagy inhibitor, reduced ADS-1-mediated cell death.

SIGNIFICANCE

These data suggest that the anti-proliferative activity of ADS-I in human glioma cells is associated with the activation of autophagy in addition to cell cycle arrest and apoptosis, and the antagonistic effect of chloroquine suggests an important role of autophagy in ADS-I-mediated cell death against tumor growth.

AMP-activated protein kinase is involved in induction of protective autophagy in astrocytes exposed to oxygen-glucose deprivation

AMP-activated kinase (AMPK) acts as the intracellular ATP depletion sensor, which detects and limits increases in the AMP/ATP ratio. AMPK may be significantly activated under stress conditions that deplete cellular ATP levels such as ischemia/hypoxia or glucose deprivation. Recent studies strongly suggest that AMPK participates in autophagy regulation, but it is not known whether AMPK activated by ischemia regulates autophagy in astrocytes and the consequence of autophagy activation in ischemic astrocytes are unclear. We have investigated the contribution of AMPK to autophagy activation in rat primary astrocyte cultures subjected to ischemia-simulating conditions (combined oxygen glucose deprivation, OGD) and its potential effects on astrocyte damage induced by OGD (1-12 h). The evidence supports the conclusion that AMPK activation at early stages of OGD is involved in induction of protective autophagy in astrocytes. Inhibition of AMPK, either by siAMPKα1 or by compound C, significantly attenuated the expression of autophagy-related proteins and decrease of astrocyte viability following OGD. The findings provide additional data about the role of AMPK in ischemic astrocytes and downstream responses that may be involved in OGD-induced protective autophagy.

Ischemic preconditioning provides neuroprotection by induction of AMP-activated protein kinase-dependent autophagy in a rat model of ischemic stroke

Accumulating evidence suggests that ischemic preconditioning (IPC) increases cerebral tolerance to the subsequent ischemic exposure. However, the underlying mechanisms are still not fully understood. In the present study, we tested the hypothesis that AMP-activated protein kinase (AMPK)-dependent autophagy contributed to the neuroprotection of IPC in rats with permanent cerebral ischemia. Male Sprague-Dawley rats were pretreated with vehicle, compound C (an AMPK inhibitor), or 3-methyladenine (3-MA, an autophagy inhibitor) and then were subjected to IPC induced by a 10-min middle cerebral artery occlusion. Afterward, the brain AMPK activity and autophagy biomarkers were measured. At 24 h after IPC, permanent cerebral ischemia was induced in these rats, and infarct volume, neurological deficits as well as cell apoptosis were evaluated 24 h later. We demonstrated that IPC activated AMPK and induced autophagy in the brain, which was accompanied by a reduction of infract volume, neurological deficits, and cell apoptosis after cerebral ischemia. Meanwhile, the IPC-induced autophagy was inhibited by compound C while the neuroprotection of IPC was abolished by compound C or 3-MA. These findings suggest that AMPK-mediated autophagy contributes to the neuroprotection of IPC, highlighting AMPK as a therapeutic target for stroke prevention and treatment.

Extracellular visfatin has nicotinamide phosphoribosyltransferase enzymatic activity and is neuroprotective against ischemic injury

AIM

Visfatin, a novel adipokine, is predominantly produced by visceral adipose tissue and exists in intracellular and extracellular compartments. The intracellular form of visfatin is proved to be nicotinamide phosphoribosyltransferase (NAMPT) and exhibits neuroprotection through maintaining intracellular NAD(+) pool. However, whether extracellular form of visfatin has NAMPT activity and the effect of extracellular visfatin in cerebral ischemia are unknown.

METHODS AND RESULTS

Plasma concentrations of visfatin, NAD(+) , and ATP were increased in mice upon cerebral ischemia. Cultured glia, but not neuron, was able to secrete visfatin. Oxygen-glucose deprivation (OGD) stress increased the secretion of visfatin from glia. Extracellular recombinant mouse wild-type visfatin, but not mouse H247A-mutant enzymatic-dead visfatin, had NAMPT enzymatic function in vitro. Treatment of wild-type visfatin, but not H247A-mutant enzymatic-dead visfatin, significantly attenuated detrimental effect of OGD on the cell viability and apoptosis in both cultured mouse neuron and glia. Treatment of neutralizing antibody, abolished the protective effect of extracellular visfatin on cell viability, but failed to block the antiapoptotic effect of extracellular visfatin. At last, we observed that plasma visfatin concentrations decreased in 6-month-old but not 3-month-old SHR-SP compared with that in age-matched Wistar-Kyoto rats. Inhibition of NAMPT enzymatic function of visfatin (by FK866) accelerated the occurrence of stroke in SHR-SP.

CONCLUSIONS

Extracellular visfatin has NAMPT enzymatic activity and maybe be neuroprotective just as intracellular visfatin in cerebral ischemic injury.

Autophagic effect of programmed cell death 5 (PDCD5) after focal cerebral ischemic reperfusion injury in rats

Former studies indicated that programmed cell death 5 (PDCD5) protein could accelerate the process of apoptosis in response to some stimuli in various kinds of cells via the intrinsic or extrinsic pathway. In this study, we aimed to demonstrate for the first time that protein level of PDCD5 are related to autophagic activity after focal ischemic brain injury in rats. One hundred and twenty-five Sprague-Dawley rats (male) were randomly divided into the following groups: Sham operated, Middle Cerebral Artery Occlusion/Reperfusion (MCAO), MCAO+Control siRNA and MCAO+PDCD5 siRNA. Outcome measurements include neurobehavioral outcomes, brain infarct volume, brain water content, BBB disruption, MRI and double fluorescence labeling. Western blot and histopathophysiological techniques were used to measure the expression of PDCD5 and some pro-autophagic proteins such as Beclin 1 and the LC3-II/LC3-I ratio. The study found that decreased PDCD5 expression via intracerebroventricular injection of PDCD5 siRNA significantly improved the neurobehavioral outcome, reduced the infarct ratio, cerebral edema and BBB disruption. These results were associated with decreased expression of Beclin 1 and the LC3-II/LC3-I ratio in the penumbra area. Rapamycin, an inducer of autophagy, partially weakened the effect of PDCD5 siRNA. In conclusion, this study suggested that PDCD5 was a key regulator of autophagy that might play an important role following MCAO injury.

Involvement of autophagy in hypoxic-excitotoxic neuronal death

Neuronal autophagy is increased in numerous excitotoxic conditions including neonatal cerebral hypoxia-ischemia (HI). However, the role of this HI-induced autophagy remains unclear. To clarify this role we established an in vitro model of excitotoxicity combining kainate treatment (Ka, 30 µM) with hypoxia (Hx, 6% oxygen) in primary neuron cultures. KaHx rapidly induced excitotoxic death that was completely prevented by MK801 or EGTA. KaHx also stimulated neuronal autophagic flux as shown by a rise in autophagosome number (increased levels of LC3-II and punctate LC3 labeling) accompanied by increases in lysosomal abundance and activity (increased SQSTM1/p62 degradation, and increased LC3-II levels in the presence of lysosomal inhibitors) and fusion (shown using an RFP-GFP-LC3 reporter). To determine the role of the enhanced autophagy we applied either pharmacological autophagy inhibitors (3-methyladenine or pepstatinA/E64) or lentiviral vectors delivering shRNAs targeting Becn1 or Atg7. Both strategies reduced KaHx-induced neuronal death. A prodeath role of autophagy was also confirmed by the enhanced toxicity of KaHx in cultures overexpressing BECN1 or ATG7. Finally, in vivo inhibition of autophagy by intrastriatal injection of a lentiviral vector expressing a Becn1-targeting shRNA increased the volume of intact striatum in a rat model of severe neonatal cerebral HI. These results clearly show a death-mediating role of autophagy in hypoxic-excitotoxic conditions and suggest that inhibition of autophagy should be considered as a neuroprotective strategy in HI brain injuries.

Rapamycin induces of protective autophagy in vascular endothelial cells exposed to oxygen-glucose deprivation

The protective potential of rapamycin has been reported in a few experimental models of brain ischemia, both in vivo and in vitro. Although the precise cellular processes underlying the neuroprotective effects of rapamycin in experimental models of stroke remain unknown, the current experimental data suggest that the mechanism of action of the drug may result from the mTOR-mediated autophagy induction. However, it is unclear whether the activation of autophagy acts as a pro-death or pro-survival factor in vascular endothelial cells in ischemic brain damage. It seems to be very important, since stroke affects not only neurons and astrocytes but also microvessels. In the present study, we used human umbilical vein endothelial cells (HUVEC) subjected to ischemia-simulating conditions (combined oxygen and glucose deprivation, OGD) for 6h to determine potential effect of rapamycin-induced autophagy on HUVEC damage. The drug at concentrations of 100 and 1000nM increased the expression of Beclin 1 and LC3-II together with a significant increase in the p62 degradation in ischemic HUVEC. Treatment with rapamycin in OGD significantly increased the cell viability, indicating that the drug exerts cytoprotective effect. The inhibition of Beclin 1 by siRNAs significantly attenuated the expression of autophagy-related proteins and reduced HUVEC viability following OGD and rapamycin treatment. Our findings demonstrated that toxicity of simulated ischemia conditions were enhanced in HUVEC when autophagy was blocked, and that rapamycin effectively prevented OGD-evoked damage by induction of protective autophagy via inhibition of the mTOR pathway.

Platelet-derived microparticles are implicated in remote ischemia conditioning in a rat model of cerebral infarction

AIM

Remote ischemic preconditioning protects against ischemic organ damage by giving short periods of subcritical ischemia to a remote organ. We tested the hypothesis that remote ischemic conditioning can attenuate cerebral stroke in a rat middle cerebral artery occlusion (MCAO) model by microparticles (MPs).

METHODS AND RESULTS

MPs were extracted from healthy rats that underwent hindlimb ischemia-reperfusion preconditioning (RIPC), and were transfused into rats that had undergone MCAO without RIPC. The transfusion resulted in an increase in platelet-derived MPs in blood and reduction in infarction area, confirmed by both 2-3-5-triphenyltetrazolium chloride staining and magnetic resonance imaging, albeit to a lesser degree than RIPC itself. Behavioral tests (modified Neurological Severity Score [mNSS]) were calculated to judge the behavioral change. However, no significant difference was observed after MP transfusion in 24 h or the following consecutive 9 days.

CONCLUSIONS

RIPC induces an increase in MPs, and platelet-derived MPs may confer at least part of the remote protective effect against cerebral ischemic-reperfusion injury.

The involvement of autophagy pathway in exaggerated ischemic brain damage in diabetic mice

BACKGROUND

Patients with Diabetes are at greater risk for ischemic stroke and usually suffer more severe ischemic brain damage than nondiabetic patients. However, the underlying mechanism of the exaggerated injury is not well defined.

AIMS

Macroautophagy (hereafter called autophagy in this report) plays a key role in cellular homeostasis and may contribute to cell death as well. Our aim was to determine whether autophagy was involved in the enhanced susceptibility of diabetic brain cells to ischemic injury and explore it as a possible target for the treatment of stroke in a diabetic condition.

RESULTS

A type II diabetic mouse model generated by combined administration of streptozotocin and nicotinamide showed enlarged infarct volume, increased cell death and excessive blood-brain barrier (BBB) disruption compared with nondiabetic stroke mice. After ischemic stroke, both diabetic and nondiabetic mice showed enhanced autophagosome formation and autophagic flux as demonstrated by increased expression of autophagy signals Beclin 1, microtubule-associated protein light-chain II (LC3-II), and decreased autophagy-specific substrate p62. The increased autophagic activity was significantly higher in diabetic stroke mice than that in nondiabetic stroke mice. The autophagy inhibitor 3-methyladenine (3-MA) attenuated the exaggerated brain injury and improved functional recovery.

CONCLUSIONS

These data suggest that autophagy contributes to exacerbated brain injury in diabetic condition, and autophagy-mediated cell death may be a therapeutic target in diabetic stroke.

Curcumin induces autophagy via activating the AMPK signaling pathway in lung adenocarcinoma cells

Curcumin is a major yellow pigment and active component of turmeric widely used as dietary spice and herbal medicine. This compound has been reported to be a promising antitumor agent, although the underlying molecular mechanisms are not fully understood yet. In this study, we reported that curcumin inhibited growth of lung adenocarcinoma cells, but had no cytotoxic activity to IMR-90 normal lung fibroblast cells. Curcumin induced autophagy in the A549 human lung adenocarcinoma cell line, evidenced by LC3 immunofluorescence analysis and immunoblotting assays on LC3 and SQSTM1. Moreover, the autophagy inhibitor 3-MA partly blocked the inhibitory effect of curcumin on the growth of A549 cells. Curcumin markedly increased the phosphorylation of AMP-activated protein kinase (AMPK) and acetylCoA carboxylase in A549 cells. At last, pharmacological blockade of the AMPK signaling pathway by compound C and genetic disruption of the AMPK signaling pathway with siRNA-mediated AMPKα1 knockdown impaired the autophagy-inducing effect of curcumin. Collectively, our data suggests that curcumin induces autophagy via activating the AMPK signaling pathway and the autophagy is important for the inhibiting effect of curcumin in lung adenocarcinoma cells.

Autophagy and cathepsin L are involved in the antinociceptive effect of DMBC in a mouse acetic acid-writhing model

AIM

2-(3',5'-Dimethoxybenzylidene) cyclopentanone (DMBC) is a novel synthetic compound with antinociceptive activities. The aim of this study was to investigate the roles of the autophagic-lysosomal pathway in the antinociceptive effect of DMBC in a mouse acetic acid-writhing model.

METHODS

Mouse acetic acid-writhing test and hotplate test were used to assess the antinociceptive effects of DMBC, 3-MA (autophagy inhibitor) and Clik148 (cathepsin L inhibitor). The drugs were administered peripherally (ip) or centrally (icv).

RESULTS

Peripheral administration of 3-MA (7.5-30 mg/kg) or Clik148 (10-80 mg/kg) produced potent antinociceptive effect in acetic acid-writhing test. Central administration of 3-MA or Clik148 (12.5-50 nmol/L) produced comparable antinociceptive effect in acetic acid-writhing test. Peripheral administration of DMBC (25-50 mg/kg) produced potent antinociceptive effects in both acetic acid-writhing and hotplate tests. Furthermore, the antinociceptive effect produced by peripheral administration of DMBC (50 mg/kg) in acetic acid-writhing test was antagonized by low doses of 3-MA (3.75 mg/kg) or Clik148 (20 mg/kg) peripherally administered, but was not affected by 3-MA or Clik148 (25 nmol/L) centrally administered.

CONCLUSION

Activation of central autophagy and cathepsin L is involved in nociception in mice, whereas peripheral autophagy and cathepsin L contributes, at least in part, to the antinociceptive effect of DMBC in mice.