The role of autophagic and lysosomal pathways in ischemic brain injury

Neferine Protects Against Brain Damage in Permanent Cerebral Ischemic Rat Associated with Autophagy Suppression and AMPK/mTOR Regulation

Neferine is the major alkaloid compound isolated from the seed embryos of lotus. Neferine has many pharmacological effects, such as anti-inflammatory, antioxidative stress, and antiapoptotic effects, and it maintains autophagic balance. The purpose of this study was to explore the mechanism by which neferine attenuates autophagy after permanent cerebral ischemia in rats. We performed permanent cerebral ischemia in rats by middle cerebral artery occlusion (pMCAO) for 12 h with or without administration of neferine or nimodipine, a calcium (Ca²⁺) channel blocker. Neuroprotective effects were determined by evaluating the infarct volume and neurological deficits. Autophagy and its signaling pathway were determined by evaluating the expression of phosphorylated AMP-activated protein kinase alpha (AMPKα), phosphorylated mammalian target of rapamycin (mTOR), beclin-1, microtubule-associated protein 1A/1B-light chain 3 class II (LC3-II), and p62 by western blotting. Autophagosomes were evaluated by transmission electron microscopy. Neferine treatment significantly reduced infarct volumes and improved neurological deficits. Neferine significantly attenuated the upregulation of autophagy-associated proteins such as LC3-II, beclin-1, and p62 as well as autophagosome formation, all of which were induced by pMCAO. Neferine exerted remarkable protection against cerebral ischemia, possibly via the regulation of autophagy mediated by the Ca²⁺-dependent AMPK/mTOR pathway.

Rapamycin Pretreatment Alleviates Cerebral Ischemia/Reperfusion Injury in Dose-Response Manner Through Inhibition of the Autophagy and NFκB Pathways in Rats

Although rapamycin can attenuate cerebral ischemia/reperfusion (I/R) injury, the potential roles of rapamycin on cerebral I/R injury remain largely controversial. The present work aims to evaluate underlying molecular mechanisms of rapamycin pretreatment on I/R injury. In total, 34 Sprague-Dawley rats were randomly grouped to 3 groups: sham group (n = 2), vehicle group (n = 16), and rapamycin-pretreatment group (n = 16). Before the focal cerebral ischemia was induced, those rats in the pretreatment group were intraperitoneally injected rapamycin (1 mg/kg body) for 20 hours, while rats in the vehicle group received same-volume saline. Then, rats in these 2 groups received focal cerebral ischemia for 3 and 6 hours, respectively (n = 8 in each group), which was followed by the application of reperfusion for 4, 24, 72 hours, and 1 week (n = 2 in each group). The results showed that the rapamycin pretreatment improved the memory functions of rats after I/R injury, which was evaluated using a Y-maze test. Rapamycin pretreatment significantly reduced the size of triphenyltetrazolium chloride infarction and decreased the expression of I/R injury markers. Moreover, the expression of LC-3 and NFκB was also significantly reduced after rapamycin pretreatment. Taken together, rapamycin pretreatment may alleviate cerebral I/R injury partly through inhibiting autophagic activities and NFκB pathways in rats.

Time-Course Changes and Role of Autophagy in Primary Spinal Motor Neurons Subjected to Oxygen-Glucose Deprivation: Insights Into Autophagy Changes in a Cellular Model of Spinal Cord Ischemia

Spinal cord ischemia is a severe clinical complication induced by thoracoabdominal aortic surgery, severe trauma, or compression to the spinal column. As one of the most important functional cells in the spinal cord, spinal motor neurons (SMNs) suffer most during the process since they are vulnerable to ischemic injury due to high demands of energy. Previous researches have tried various animal models or organotypic tissue experiments to mimic the process and get to know the pathogenesis and mechanism. However, little work has been performed on the cellular model of spinal cord ischemia, which has been hampered by the inability to obtain a sufficient number of pure primary SMNs for in vitro study. By optimizing the isolation and culture of SMNs, our laboratory has developed an improved culture system of primary SMNs, which allows cellular models and thus mechanism studies. In the present study, by establishing an in vitro model of spinal cord ischemia, we intended to observe the dynamic time-course changes of SMNs and investigate the role of autophagy in SMNs during the process. It was found that oxygen-glucose deprivation (OGD) resulted in destruction of neural networks and decreased cell viability of primary SMNs, and the severity increased with the prolonging of the OGD time. The OGD treatment enhanced autophagy, which reached a peak at 5 h. Further investigation demonstrated that inhibition of autophagy exacerbated the injury, evidencing that autophagy plays a protective role during the process.

Genomic Variations in Susceptibility to Intracranial Aneurysm in the Korean Population

Genome-wide association studies found genetic variations with modulatory effects for intracranial aneurysm (IA) formations in European and Japanese populations. We aimed to identify the susceptibility of single nucleotide polymorphisms (SNPs) to IA in a Korean population consisting of 250 patients, and 294 controls using the Asian-specific Axiom Precision Medicine Research Array. Twenty-nine SNPs reached a genome-wide significance threshold (5 × 10⁻⁸). The rs371331393 SNP, with a stop-gain function of ARHGAP32 (11q24.3), showed the most significant association with the risk of IA (OR = 43.57, 95% CI: 21.84–86.95; p = 9.3 × 10⁻²⁷). Eight out of 29 SNPs—GBA (rs75822236), TCF24 (rs112859779), OLFML2A (rs79134766), ARHGAP32 (rs371331393), CD163L1 (rs138525217), CUL4A (rs74115822), LOC102724084 (rs75861150), and LRRC3 (rs116969723)—demonstrated sufficient statistical power greater than or equal to 0.8. Two previously reported SNPs, rs700651 (BOLL, 2q33.1) and rs6841581 (EDNRA, 4q31.22), were validated in our GWAS (Genome-wide association study). In a subsequent analysis, three SNPs showed a significant difference in expressions: the rs6741819 (RNF144A, 2p25.1) was down-regulated in the adrenal gland tissue (p = 1.5 × 10⁻⁶), the rs1052270 (TMOD1. 9q22.33) was up-regulated in the testis tissue (p = 8.6 × 10⁻¹⁰), and rs6841581 (EDNRA, 4q31.22) was up-regulated in both the esophagus (p = 5.2 × 10⁻¹²) and skin tissues (1.2 × 10⁻⁶). Our GWAS showed novel candidate genes with Korean-specific variations in IA formations. Large population based studies are thus warranted.

Intermittent fasting is neuroprotective in focal cerebral ischemia by minimizing autophagic flux disturbance and inhibiting apoptosis

Previous studies have demonstrated that autophagy induced by caloric restriction (CR) is neuroprotective against cerebral ischemia. However, it has not been determined whether intermittent fasting (IF), a variation of CR, can exert autophagy-related neuroprotection against cerebral ischemia. Therefore, the neuroprotective effect of IF was evaluated over the course of two weeks in a rat model of focal cerebral ischemia, which was induced by middle cerebral artery occlusion and reperfusion (MCAO/R). Specifically, the role of autophagy modulation as a potential underlying mechanism for this phenomenon was investigated. It was demonstrated that IF reduced infarct volume and brain edema, improved neurobehavioral deficits, and rescued neuronal loss after MCAO/R. Furthermore, neuronal apoptosis was decreased by IF in the rat cortex. An increase in the number of autophagosomes (APs) was demonstrated in the cortices of IF-treated rats, using immunofluorescence staining and transmission electron microscopy. Using immunoblots, an IF-induced increase was detected in microtubule-associated protein 1 light chain 3 (LC3)-II, Rab7, and cathepsin D protein levels, which corroborated previous morphological studies. Notably, IF reduced the accumulation of APs and p62, demonstrating that IF attenuated the MCAO/R-induced disturbance of autophagic flux in neurons. The findings of the present study suggest that IF-induced neuroprotection in focal cerebral ischemia is due, at least in part, to the minimization of autophagic flux disturbance and inhibition of apoptosis.

Electroacupuncture Ameliorates Cerebral Ischemia-Reperfusion Injury by Regulation of Autophagy and Apoptosis

Background. The therapeutic mechanisms of cerebral ischemia treatment by acupuncture are yet not well addressed. Objective. We investigated the effects of electroacupuncture (EA) at GV26 observing the expression of autophagy-related proteins Beclin-1 and LC3B and proportion of apoptotic cells and Bcl-2 positive cells in MCAO/R model rats. Methods. Sprague-Dawley (SD) male rats were randomly assigned to 7 groups: model groups (M6h, M24h, and M72h), EA treatment groups (T6h, T24h, and T72h), and sham operation group (S). Neurological deficit and cerebral infarction volume were measured to assess the improvement effect, while the expression of Beclin-1 and LC3B and proportion of Tunel-positive and Bcl-2 positive cells were examined to explore EA effect on autophagy and apoptosis. Results. EA significantly decreased neurological deficit scores and the volume of cerebral infarction. Beclin-1 was significantly decreased in T24h, while LC3B-II/LC3B-I ratio markedly reduced in 6th hour. EA groups markedly reduced the number of Tunel positive cells, especially in T24h. Meanwhile, the number of Bcl-2 positive cells obviously increased after EA treatment, especially in T6h and T24h. Conclusions. The alleviation of inadequate autophagy and apoptosis may be a key mechanism involved in the reflex regulation of EA at GV26 to treat cerebral ischemia.

Secondary Release of Exosomes From Astrocytes Contributes to the Increase in Neural Plasticity and Improvement of Functional Recovery After Stroke in Rats Treated With Exosomes Harvested From MicroRNA 133b-Overexpressing Multipotent Mesenchymal Stromal Cells

We previously demonstrated that multipotent mesenchymal stromal cells (MSCs) that overexpress microRNA 133b (miR-133b) significantly improve functional recovery in rats subjected to middle cerebral artery occlusion (MCAO) compared with naive MSCs and that exosomes generated from naive MSCs mediate the therapeutic benefits of MSC therapy for stroke. Here we investigated whether exosomes isolated from miR-133b-overexpressing MSCs (Ex-miR-133b+) exert amplified therapeutic effects. Rats subjected to 2 h of MCAO were intra-arterially injected with Ex-miR-133b+, exosomes from MSCs infected by blank vector (Ex-Con), or phosphate-buffered saline (PBS) and were sacrificed 28 days after MCAO. Compared with the PBS treatment, both exosome treatment groups exhibited significant improvement of functional recovery. Ex-miR-133b+ treatment significantly increased functional improvement and neurite remodeling/brain plasticity in the ischemic boundary area compared with the Ex-Con treatment. Treatment with Ex-miR-133b+ also significantly increased brain exosome content compared with Ex-Con treatment. To elucidate mechanisms underlying the enhanced therapeutic effects of Ex-miR-133b+, astrocytes cultured under oxygen- and glucose-deprived (OGD) conditions were incubated with exosomes harvested from naive MSCs (Ex-Naive), miR-133b downregulated MSCs (Ex-miR-133b-), and Ex-miR-133b+. Compared with the Ex-Naive treatment, Ex-miR-133b+ significantly increased exosomes released by OGD astrocytes, whereas Ex-miR-133b- significantly decreased the release. Also, exosomes harvested from OGD astrocytes treated with Ex-miR-133b+ significantly increased neurite branching and elongation of cultured cortical embryonic rat neurons compared with the exosomes from OGD astrocytes subjected to Ex-Con. Our data suggest that exosomes harvested from miR-133b-overexpressing MSCs improve neural plasticity and functional recovery after stroke with a contribution from a stimulated secondary release of neurite-promoting exosomes from astrocytes.

Chronic cerebral hypoperfusion enhances Tau hyperphosphorylation and reduces autophagy in Alzheimer's disease mice

Cerebral hypoperfusion and impaired autophagy are two etiological factors that have been identified as being associated with the development of Alzheimer’s disease (AD). Nevertheless, the exact relationships among these pathological processes remain unknown. To elucidate the impact of cerebral hypoperfusion in AD, we created a unilateral common carotid artery occlusion (UCCAO) model by occluding the left common carotid artery in both young and old 3xTg-AD mice. Two months after occlusion, we found that ligation increases phospho-Tau (p-Tau) at Serine 199/202 in the hippocampus of 3-month-old AD mice, compared to sham-operated AD mice; whereas, there is no change in the wild type (WT) mice after ligation. Moreover, cerebral hypoperfusion led to significant increase of p-Tau in both the hippocampus and cortex of 16-month-old AD mice and WT mice. Notably, we did not detect any change in Aβ₄₂ level in either young or old AD and WT mice after ligation. Interestingly, we observed a downregulation of LC3-II in the cortex of aged AD mice and WT mice after ligation. Our results suggest that elevated p-Tau and reduced autophagy are major cellular changes that are associated with hypoperfusion in AD. Therefore, targeting p-Tau and autophagy pathways may ameliorate hypoperfusion-induced brain damage in AD.