The PERK Pathway Plays a Neuroprotective Role During the Early Phase of Secondary Brain Injury Induced by Experimental Intracerebral Hemorrhage

Astragaloside IV ameliorated neuroinflammation and improved neurological functions in mice exposed to traumatic brain injury by modulating the PERK-eIF2α-ATF4 signaling pathway

Increasing evidence suggests that endoplasmic reticulum stress (ER stress) and neuroinflammation are involved in the complex pathological process of traumatic brain injury (TBI). However, the pathological mechanisms of their interactions in TBI remain incompletely elucidated. Therefore, investigating and ameliorating neuroinflammation and ER stress post-TBI may represent effective strategies for treating secondary brain injury. Astragaloside IV (AS-IV) has been reported as a potential neuroprotective and anti-inflammatory agent in neurological diseases. This study utilized a mouse TBI model to investigate the pathological mechanisms and crosstalk of ER stress, neuroinflammation, and microglial cell morphology in TBI, as well as the mechanisms and potential of AS-IV in improving TBI. The research revealed that post-TBI, inflammatory factors IL-6, IL-1β, and TNF-α increased, microglial cells were activated, and the specific inhibitor of PERK phosphorylation, GSK2656157, intervened to alleviate neuroinflammation and inhibit microglial cell activation. Post-TBI, levels of ER stress-related proteins (p-PERK, p-eIF2a, ATF4, ATF6, and p-IRE1a) increased. Following AS-IV treatment, neurological dysfunction in TBI mice improved. Levels of p-PERK, p-eIF2a, and ATF4 decreased, along with reductions in inflammatory factors IL-6, IL-1β, and TNF-α. Changes in microglial/macrophage M1/M2 polarization were observed. Additionally, the PERK activator CCT020312 intervention eliminated the impact of AS-IV on post-TBI inflammation and ER stress-related proteins p-PERK, p-eIF2a, and ATF4. These results indicate that AS-IV alleviates neuroinflammation and brain damage post-TBI through the PERK pathway, offering new directions and theoretical insights for TBI treatment.

LncRNA-PEAK1 promotes neuronal apoptosis after intracerebral hemorrhage by miR-466i-5p/caspase 8 axis

Background

At present, the treatment of intracerebral hemorrhage (ICH)-induced secondary brain injury (ISB) is limited, and the curative effect is not good. Long noncoding RNAs (lncRNAs) have been reported to play a role in ISB after ICH. We preliminarily monitored the induction effect of lncRNA-pseudopodium-enriched atypical kinase 1 (PEAK1) on neuronal cell apoptosis after ICH through our previous study and further experimental verification. However, the specific role and mechanism of lncRNA-PEAK1 in neuronal cell apoptosis after ICH have not been reported.

Methods

ICH cell models were established with hemin. Pro-inflammatory cytokines, cell proliferation, and apoptosis were evaluated by enzyme-linked immunosorbent assay, Cell Counting Kit-8 assay, flow cytometry, and terminal deoxynucleotidyl transferase dUTP nick end labeling, respectively. Moreover, lncRNA expression associated with apoptosis was confirmed by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The biological functions of lncRNA-PEAK1, miR-466i-5p, and caspase8 were conducted in vitro. Further, we used bioinformatics, a dual-luciferase reporter assay, and rescue experiments to understand the mechanisms of competitive endogenous RNAs.

Results

qRT-PCR revealed that lncRNA-PEAK1 was markedly upregulated in ICH cell models. LncRNA-PEAK1 knockdown decreased the interleukin-1β and tumor necrosis factor-alpha levels, promoted cell proliferation, weakened cell apoptosis, and downregulated the key molecular protein levels involved in the cell apoptosis pathway. Bioinformatics analysis and dual-luciferase reporter assay revealed that lncRNA bound to miR-466i-5p, and caspase 8 was a target of miR-466i-5p. The mechanistic analysis demonstrated that lncRNA-PEAK1/miR-466i-5p promoted neuronal cell apoptosis by activating the apoptosis pathway through caspase8 after ICH.

Conclusion

Collectively, our investigation identified that the lncRNA-PEAK1/miR-446i-5p/caspase8 axis is closely related to neuronal cell apoptosis after ICH. Additionally, lncRNA-PEAK1 may be a potential target for ICH intervention.

Endogenous Mechanisms of Neuroprotection: To Boost or Not to Boost

Postmitotic cells, like neurons, must live through a lifetime. For this reason, organisms/cells have evolved with self-repair mechanisms that allow them to have a long life. The discovery workflow of neuroprotectors during the last years has focused on blocking the pathophysiological mechanisms that lead to neuronal loss in neurodegeneration. Unfortunately, only a few strategies from these studies were able to slow down or prevent neurodegeneration. There is compelling evidence demonstrating that endorsing the self-healing mechanisms that organisms/cells endogenously have, commonly referred to as cellular resilience, can arm neurons and promote their self-healing. Although enhancing these mechanisms has not yet received sufficient attention, these pathways open up new therapeutic avenues to prevent neuronal death and ameliorate neurodegeneration. Here, we highlight the main endogenous mechanisms of protection and describe their role in promoting neuron survival during neurodegeneration.

The Blood Component Iron Causes Neuronal Apoptosis Following Intracerebral Hemorrhage via the PERK Pathway

PERK signaling pathway plays an important role in neuronal apoptosis after Intracerebral hemorrhage (ICH). ICH can cause the release of blood components into the brain. However, which component in the blood plays a major role still unclear. This study was designed to investigate the activation of the PERK pathway in different blood components after ICH and explore which components have major relationships with neuronal apoptosis. Eighty-five Sprague-Dawley rats were used to establish an ICH model. Western blot (WB) and immunofluorescence (IF) were used to evaluate the expression of the PERK pathway. TUNEL staining, FJC staining and neurological score were used to evaluate neuronal apoptosis and necrosis after ICH. The results showed that protein levels of p-PERK and p-eIF2α were upregulated following ICH with the injection of Fe³⁺ and Fe²⁺ after 48 h. Then, deferoxamine (DFX) was used to study the roles of Fe³⁺ in ICH through the PERK signaling pathway. The results showed that injection of DFX reversed increasing protein levels and prevented neuronal apoptosis. Thus, iron plays an important role in ICH through the PERK signaling pathway. Furthermore, the reduction of iron demonstrates neuroprotective effects in ICH. This suggests that targeting intervention of the iron and PERK pathway could be an effective treatment strategy to improve ICH prognosis.

Neuroprotection Effect of Astragaloside IV from 2-DG-Induced Endoplasmic Reticulum Stress

Objective

Astragaloside IV shows neuroprotective activity, but its mechanism remains unclear. To investigate whether astragaloside IV protects from endoplasmic reticulum stress (ERS), we focus on the regulation of glycogen synthase kinase-3β (GSK-3β) and mitochondrial permeability transition pore (mPTP) by astragaloside IV in neuronal cell PC12.

Methods and Results

PC12 cells treated with different concentrations of ERS inductor 2-deoxyglucose (2-DG) (25-500 μM) showed a significant increase of glucose-regulated protein 78 (GRP 78) and GRP 94 expressions and a decrease of tetramethylrhodamine ethyl ester (TMRE) fluorescence intensity and mitochondrial membrane potential (∆Ψm), with the peak effect seen at 50 μM, indicating that 2-DG induces ERS and the mPTP opening. Similarly, 50 μM of astragaloside IV increased the GSK-3β phosphorylation at Ser9 most significantly. Next, we examined the neuroprotection of astragaloside IV by dividing the PC12 cells into control group, 2-DG treatment group, astragaloside IV plus 2-DG treatment group, and astragaloside IV only group. PC12 cells treated with 50 μM 2-DG for different time courses (0-36 hr) showed a significant increase of Cleaved-Caspase-3 with the peak at 6 hr. 2-DG significantly induced cell apoptosis and increased the green fluorescence intensity of Annexin V-FITC, and these effects were reversed by astragaloside IV. Such a result indicates that astragaloside IV protected neural cell survival from ERS. 2-DG treatment significantly increased the expressions of inositol-requiring ER-to-nucleus signal kinase 1 (IRE1), phosphor-protein kinase R-like ER kinase (p-PERK), but not affect the transcription factor 6 (ATF6) expression. 2-DG treatment significantly decreased the phosphorylation of GSK-3β and significantly reduced the TMRE fluorescence intensity and ∆Ψm, following mPTP open. Astragaloside IV significantly inhibited the above effects caused by 2-DG, except the upregulation of ATF6 protein. Taken together, astragaloside IV significantly inhibited the ERS caused by 2-DG.

Conclusion

Our data suggested that astragaloside IV protects PC12 cells from ERS by inactivation of GSK-3β and preventing the mPTP opening. The GRP 78, GRP 94, IRE1, and PERK signaling pathways but not ATF6 are responsible for GSK-3β inactivation and neuroprotection by astragaloside IV.

Chronic PERK induction promotes Alzheimer-like neuropathology in Down syndrome: Insights for therapeutic intervention

A major challenge in neurobiology is the identification of the mechanisms by which protein misfolding leads to cellular toxicity. Many neurodegenerative disorders, in which aberrant protein conformers aggregate into pathological inclusions, present the chronic activation of the PERK branch of the unfolded protein response. The adaptive effects of the PERK pathway include reduction of translation by transient inhibition of eIF2α and antioxidant protein production via induction of Nrf2 transcription factor. In contrast, PERK prolonged activation leads to sustained reduction in protein synthesis and induction of cell death pathways. To further investigate the role of the PERK pathway in neurodegenerative disorders, we focused on Down syndrome (DS), in which aging confers a high risk of Alzheimer disease (AD). By investigating human DS frontal cortices, we found early and sustained PERK activation associated with the induction of eIF2α and ATF4 downstream signals. We also observed that the Nrf2 response is uncoupled from PERK and its antioxidant effects are repressed in a mechanism implicating the transcription repressor Bach1. The pharmacological inhibition of PERK in DS mice reduced eIF2α-related translational repression and promoted Nrf2 nuclear translocation, favoring the rescue of Nrf2/Bach1 imbalance. The further analysis of peripheral cells from living DS individuals provided strong support of the pathological link between PERK and trisomy 21. Our results suggest that failure to regulate the PERK pathway is a peculiar characteristic of DS pathology and it may represent an essential step to promote cellular dysfunction, which actively contributes in the brain to the early development of AD.

Up-regulation of PERK/Nrf2/HO-1 axis protects myocardial tissues of mice from damage triggered by ischemia-reperfusion through ameliorating endoplasmic reticulum stress

Background

Ischemia-reperfusion (I/R) injury, which leads to additionally cardiac tissue damage, is a severe adverse effect of reperfusion therapeutics used for the treatment of acute myocardial infarction. Agents capable of alleviating I/R-induced myocardial injury are urgently needed. In this study, we investigated whether up-regulation of PERK/Nrf2/HO-1 axis provided protective roles for murine myocardium suffering I/R intervention.

Methods

The in vivo I/R model was formed by ligation of the left anterior descending (LAD) coronary artery of C57BL/6J mice. All animals were assigned into the following groups at random: sham, I/R, rAAV9-PERK + I/R, rAAV9-Nrf2 + I/R, rAAV9-HO-1 + I/R, siRNA-HO-1 + rAAV9-PERK + I/R. The ligation of LAD was released after 30 min of ischemia, which was followed by reperfusion of LAD for 4 h. Then the cardiac tissues and blood serum were collected. TUNEL staining, ELISA assay, TTC staining, Western blotting and real-time PCR were used to determine I/R injury-related indicators.

Results

Our results showed that I/R administration triggered cardiomyocytes apoptosis and LDH and CK-MB release, yet overexpression of PERK decreased cellular apoptosis index in the cardiac tissue and reduced levels of LDH and CK-MB in the serum. We further found that the protective actions of PERK against I/R-evoked cardiac damage might be attributed to up-regulation of Nrf2/HO-1 signaling transduction, given that overexpression of Nrf2 and HO-1 ameliorated cardiac cell apoptosis and reduced the size of infarction and ischemia in the myocardial tissue, yet gene silencing of HO-1 invalidated the beneficial roles of PERK overexpression in improving I/R-induced cardiac injury. Then, we investigated whether PERK-activated Nrf2/HO-1 cascade affected endoplasmic reticulum stress (ERS), considering the crucial roles of ERS-associated apoptosis in the development of I/R damage. Our findings indicated that up-regulation of PERK-mediated Nrf2/HO-1 pathway induced the expression reduction of GRP78, CRT, CHOP and caspase-12 both at the transcriptional and translational level.

Conclusions

We, for the first time, discovered that up-regulation of PERK/Nrf2/HO-1 axis improved I/R-induced myocardial injury via reducing ERS-related signal molecules and downstream pro-apoptotic factors.