Regulation of blood-brain barrier permeability by Salvinorin A via alleviating endoplasmic reticulum stress in brain endothelial cell after ischemia stroke

Inhibition of soluble epoxide hydrolase as a therapeutic approach for blood-brain barrier dysfunction

The blood-brain barrier (BBB) is a protective semi-permeable structure that regulates the exchange of biomolecules between the peripheral blood and the central nervous system (CNS). Due to its specialized tight junctions and low vesicle trafficking, the BBB strictly limits the paracellular passage and transcellular transport of molecules to maintain the physiological condition of brain tissues. BBB breakdown is associated with many CNS disorders. Soluble epoxide hydrolase (sEH) is a hydrolase enzyme that converts epoxy-fatty acids (EpFAs) to their corresponding diols and is involved in the onset and progression of multiple diseases. EpFAs play a protective role in the central nervous system via preventing neuroinflammation, making sEH a potential therapeutic target for CNS diseases. Recent studies showed that sEH inhibition prevented BBB impairment caused by stroke, hemorrhage, traumatic brain injury, hyperglycemia and sepsis via regulating the expression of tight junctions. In this review, the protective actions of sEH inhibition on BBB and potential mechanisms are summarized, and some important questions that remain to be resolved are also addressed.

Nuclear Factor Erythroid 2-Related Factor 2 is Essential for Low-Normobaric Oxygen Treatment-Mediated Blood-Brain Barrier Protection Following Ischemic Stroke

Cerebral ischemia/reperfusion (I/R) injury increases blood-brain barrier (BBB) permeability, leading to hemorrhagic transformation and brain edema. Normobaric oxygen (NBO) is a routine clinical treatment strategy for this condition. However, its neuroprotective effects remain controversial. This study investigated the effect of different NBO concentrations on I/R injury and explores the involvement of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway in the underlying mechanism. A mouse middle cerebral artery occlusion (MCAO) model, and an oxygen and glucose deprivation (OGD) model featuring mouse brain microvascular endothelial cells (ECs) called bEnd.3, were used to investigate the effect of NBO on I/R injury. A reactive oxygen species (ROS) inducer and Nrf2-knockdown by RNA were used to explore whether the Nrf2 pathway mediates the effect of NBO on cerebrovascular ECs. In the early stage of MCAO, 40% O2 NBO exposure significantly improved blood perfusion in the ischemic area and effectively relieved BBB permeability, cerebral edema, cerebral injury, and neurological function after MCAO. In the OGD model, 40% O2 NBO exposure significantly reduced apoptosis, inhibited ROS generation, reduced ER stress, upregulated the expression of tight junction proteins, and stabilized the permeability of ECs. Blocking the Nrf2 pathway nullified the protective effect of 40% O2 NBO on ECs after OGD. Finally, our study confirmed that low concentrations of NBO have a neuroprotective effect on I/R by activating the Nrf2 pathway in ECs.

Knockdown of FOXO4 protects against OGD/R‑induced cerebral microvascular endothelial cell injury and regulates the AMPK/Nrf2/HO‑1 pathway through transcriptional activation of CTRP6

Cerebral ischemia is a type of cerebrovascular disease with high disability and mortality rates. The expression of forkhead box protein O4 (FOXO4) in the brain is increased following traumatic brain injury. To the best of our knowledge, however, the role of FOXO4 as well as its mechanism in cerebral ischemia has not been reported so far. For the establishment of an in vitro cellular injury model, human brain microvascular endothelial HCMEC/D3 cells were induced by oxygen-glucose deprivation/reoxygenation (OGD/R). mRNA and protein expressions of FOXO4 and C1q/tumor necrosis factor-related protein 6 (CTRP6) in OGD/R-induced HCMEC/D3 cells were detected by reverse transcription-quantitative (RT-q)PCR and western blotting. The transfection efficacy of small interfering (si)- and overexpression (Ov)-FOXO4 and si-CTRP6 was assessed using RT-qPCR and western blotting. Cell Counting Kit-8 and TUNEL assay were used to assess viability and apoptosis of HCMEC/D3 cells induced by OGD/R, respectively. A FITC-Dextran assay kit was applied to determine endothelial permeability and immunofluorescence assay was used for the measurement of the tight junction protein zonula occludens-1. The levels of oxidative stress markers and inflammatory cytokines were assessed with corresponding assay kits. The binding sites of transcription factor, FOXO4 and CTRP6 promoter were predicted using HDOCK SERVER. Luciferase reporter assay was used to detect the activity of the CTRP6 promoter while chromatin immunoprecipitation assay was used to evaluate the binding ability of the FOXO4 and CTRP6 promoter. Western blotting was used for the detection of apoptosis- and AMPK/Nrf2/heme oxygenase-1 (HO-1) pathway-associated proteins, along with tight junction proteins. The expression of FOXO4 was increased in OGD/R-induced HCMEC/D3 cells. After interfering with FOXO4 in cells, the viability of the OGD/R-induced HCMEC/D3 cells was increased while apoptosis was decreased. Furthermore, FOXO4 interference improved cellular barrier dysfunction but inhibited oxidative stress and the inflammatory response in HCMEC/D3 cells induced by OGD/R. FOXO4 knockdown regulated CTRP6 transcription in HCMEC/D3 cells. Knockdown of FOXO4 regulated expression of CTRP6 and protected OGD/R-induced HCMEC/D3 cell injury via the AMPK/Nrf2/HO-1 pathway. The present study indicated that FOXO4 knockdown activated CTRP6 to protect against cerebral microvascular endothelial cell injury induced by OGD/R via the AMPK/Nrf2/HO-1 pathway.

Costunolide and parthenolide: Novel blood-brain barrier permeable sesquiterpene lactones to improve barrier tightness

Sesquiterpene lactones - such as those found in chicory - are considered promising bioactive compounds. These small molecules have shown several health benefits for various diseases, including brain disorders. However, it is unknown whether these compounds can cross the blood-brain barrier (BBB), and which could be the effects on brain microvascular endothelial cells. We show that six sesquiterpene lactones evaluated in an in vitro model of the BBB have different capacities to be transported through the barrier. Costunolide presented more than 20 % of transport while lactucin, 11β-13-dihydrolactucin, 11β-13-dihydrolactucopicrin, and parthenolide presented between 10 % and 20 %, whilst almost no transport was detected for lactucopicrin. Furthermore, costunolide and parthenolide reduced P-gp ABC transporter expression alongside an increase in caveolin-1, the main protein of caveolae. Remarkably, these two compounds improved barrier tightness by increasing the expression of both tight and adherens junctions. These findings open a new avenue to explore costunolide and parthenolide as promising compounds for brain therapies.

Gut microbiome plays a vital role in post-stroke injury repair by mediating neuroinflammation

Cerebral stroke is a common neurological disease and often causes severe neurological deficits. With high morbidity, mortality, and disability rates, stroke threatens patients' life quality and brings a heavy economic burden on society. Ischemic cerebral lesions incur pathological changes as well as spontaneous nerve repair following stroke. Strategies such as drug therapy, physical therapy, and surgical treatment, can ameliorate blood and oxygen supply in the brain, hamper the inflammatory responses and maintain the structural and functional integrity of the brain. The gut microbiome, referred to as the "second genome" of the human body, participates in the regulation of multiple physiological functions including metabolism, digestion, inflammation, and immunity. The gut microbiome is not only inextricably associated with dangerous factors pertaining to stroke, including high blood pressure, diabetes, obesity, and atherosclerosis, but also influences stroke occurrence and prognosis. AMPK functions as a hub of metabolic control and is responsible for the regulation of metabolic events under physiological and pathological conditions. The AMPK mediators have been found to exert dual roles in regulating gut microbiota and neuroinflammation/neuronal apoptosis in stroke. In this study, we reviewed the role of the gut microbiome in cerebral stroke and the underlying mechanism of the AMPK signaling pathway in stroke. AMPK mediators in nerve repair and the regulation of intestinal microbial balance were also summarized.

Anti-apoptosis effect of traditional Chinese medicine in the treatment of cerebral ischemia-reperfusion injury

Cerebral ischemia, one of the leading causes of neurological dysfunction of brain cells, muscle dysfunction, and death, brings great harm and challenges to individual health, families, and society. Blood flow disruption causes decreased glucose and oxygen, insufficient to maintain normal brain tissue metabolism, resulting in intracellular calcium overload, oxidative stress, neurotoxicity of excitatory amino acids, and inflammation, ultimately leading to neuronal cell necrosis, apoptosis, or neurological abnormalities. This paper summarizes the specific mechanism of cell injury that apoptosis triggered by reperfusion after cerebral ischemia, the related proteins involved in apoptosis, and the experimental progress of herbal medicine treatment through searching, analyzing, and summarizing the PubMed and Web Of Science databases, which includes active ingredients of herbal medicine, prescriptions, Chinese patent medicines, and herbal extracts, providing a new target or new strategy for drug treatment, and providing a reference for future experimental directions and using them to develop suitable small molecule drugs for clinical application. With the research of anti-apoptosis as the core, it is important to find highly effective, low toxicity, safe and cheap compounds from natural plants and animals with abundant resources to prevent and treat Cerebral ischemia/reperfusion (I/R) injury (CIR) and solve human suffering. In addition, understanding and summarizing the apoptotic mechanism of cerebral ischemia-reperfusion injury, the microscopic mechanism of CIR treatment, and the cellular pathways involved will help to develop new drugs.

Endoplasmic Reticulum Stress and the Unfolded Protein Response in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an acute cerebrovascular disease characterized by sudden interruption of blood flow in a certain part of the brain, leading to serious disability and death. At present, treatment methods for ischemic stroke are limited to thrombolysis or thrombus removal, but the treatment window is very narrow. However, recovery of cerebral blood circulation further causes cerebral ischemia/reperfusion injury (CIRI). The endoplasmic reticulum (ER) plays an important role in protein secretion, membrane protein folding, transportation, and maintenance of intracellular calcium homeostasis. Endoplasmic reticulum stress (ERS) plays a crucial role in cerebral ischemia pathophysiology. Mild ERS helps improve cell tolerance and restore cell homeostasis; however, excessive or long-term ERS causes apoptotic pathway activation. Specifically, the protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways are significantly activated following initiation of the unfolded protein response (UPR). CIRI-induced apoptosis leads to nerve cell death, which ultimately aggravates neurological deficits in patients. Therefore, it is necessary and important to comprehensively explore the mechanism of ERS in CIRI to identify methods for preserving brain cells and neuronal function after ischemia.

Endoplasmic Reticulum Stress-Associated Neuronal Death and Innate Immune Response in Neurological Diseases

Neuronal death and inflammatory response are two common pathological hallmarks of acute central nervous system injury and chronic degenerative disorders, both of which are closely related to cognitive and motor dysfunction associated with various neurological diseases. Neurological diseases are highly heterogeneous; however, they share a common pathogenesis, that is, the aberrant accumulation of misfolded/unfolded proteins within the endoplasmic reticulum (ER). Fortunately, the cell has intrinsic quality control mechanisms to maintain the proteostasis network, such as chaperone-mediated folding and ER-associated degradation. However, when these control mechanisms fail, misfolded/unfolded proteins accumulate in the ER lumen and contribute to ER stress. ER stress has been implicated in nearly all neurological diseases. ER stress initiates the unfolded protein response to restore proteostasis, and if the damage is irreversible, it elicits intracellular cascades of death and inflammation. With the growing appreciation of a functional association between ER stress and neurological diseases and with the improved understanding of the multiple underlying molecular mechanisms, pharmacological and genetic targeting of ER stress are beginning to emerge as therapeutic approaches for neurological diseases.