Remote Limb Ischemic Preconditioning Protects Rats Against Cerebral Ischemia via HIF-1α/AMPK/HSP70 Pathway

Genipin ameliorates diabetic retinopathy via the HIF-1α and AGEs-RAGE pathways

BACKGROUND

Traditional Chinese medicine (TCM) is useful in disease treatment and prevention. Genipin is an active TCM compound used to treat diabetic retinopathy (DR). In this study, a network pharmacology (NP)-based approach was employed to investigate the therapeutic mechanisms underlying genipin administration in DR.

METHODS

The potential targets of DR were identified using the gene expression omnibus (GEO) database. TCM database screening and NP were used to predict the potential active targets and pathways of genipin in DR. Cell viability was tested in vitro to determine the effects of different doses of glucose and genipin on Human Retinal Microvascular Endothelial Cells (hRMECs). CCK-8, CCK-F, colony formation, CellTiter-Lum, Annexin V-FITC, wound healing, Transwell, tube-forming, reactive oxygen species (ROS), and other assay kits were used to detect the effects of genipin on hRMECs during high levels of glucose. In vivo, a streptozotocin (STZ)-mouse intraocular genipin injection (IOI.) model was used to explore the effects of genipin on diabetes-induced retinal dysfunction. Western blotting was performed to identify the cytokines involved in proliferation, apoptosis, angiogenesis, ROS, and inflammation. The protein expression of the AKT/ PI3K/ HIF-1α and AGEs/ RAGE pathways was also examined.

RESULTS

Approximately 14 types of TCM, and nearly 300 active ingredients, including genipin, were identified. The NP approach successfully identified the HIF-1α and AGEs-RAGE pathways, with the EGR1 and UCP2 genes, as key targets of genipin in DR. In the in vitro and in vivo models, we discovered that high glucose increased cell proliferation, apoptosis, angiogenesis, ROS, and inflammation. However, genipin application regulated cell proliferation and apoptosis, inhibited angiogenesis, and reduced ROS and inflammation in the HRMECs exposed to high glucose. Furthermore, the retinal thickness in the genipin-treated group was lower than that in the untreated group. AKT/ PI3K/ HIF-1α and AGEs/ RAGE signaling was increased by high glucose levels; however, genipin treatment decreased AKT/ PI3K and AGEs/ RAGE pathway expressions. Genipin also increased HIF-1α phosphorylation, oxidative phosphorylation of ATP synthesis, lipid peroxidation, and the upregulation of oxidoreductase. Genipin was found to protect HG-induced hRMECs and the retina of STZ-mice, based on; 1 the inhibition of UCP2 and Glut1 decreased intracellular glucose, and glycosylation; 2 the increased presence of HIF-1α, which increased oxidative phosphorylation and decreased substrate phosphorylation; 3 the increase in oxidative phosphorylation from ATP synthesis increased lipid peroxidation and oxidoreductase activity, and; 4 the parallel effect of phosphorylation and glycosylation on vascular endothelial growth factor (VEGF), MMP9, and Scg3.

CONCLUSION

Based on NP, we demonstrated the potential targets and pathways of genipin in the treatment of DR and confirmed its effective molecular mechanism in vitro and in vivo. Genipin protects cells and tissues from high glucose levels by regulating phosphorylation and glycosylation. The activation of the HIF-1α pathway can also be used to treat DR. Our study provides new insights into the key genes and pathways associated with the prognosis and pathogenesis of DR.

Pink1 deficiency enhances neurological deficits and inflammatory responses after intracerebral hemorrhage in mice

Pink1 (PTEN-induced putative kinase 1) is a protein associated with maintaining mitochondrial function and integrity and has been reported to mediate neurodegeneration and neuroinflammation. While the role of Pink1 in intracerebral hemorrhage (ICH)-related neurological deficits and inflammatory responses is not deciphered. Congenic blood was transfused into the left corpus striatum to construct the ICH model in C57/BL6 wild-type (WT) and Pink1-/- mice. The relative expression of Pink1, monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein (MIP)-2, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, Cd86, nitric oxide synthase 2 (Nos2), Cd206, arginase 1 (Arg-1), and IL-10 was detected with qRT-PCR, Western blotting, or ELISA. Mouse neurological deficit scores (mNSS) and water content were detected, and an open-field test was performed to assay anxiety-like behavior. Remarkably decreased Pink1 expression and increased MIP-2, IL-1β, MCP-1, and TNF-α expression were observed after 12 ​h, 24 ​h, 48 ​h, 72 ​h, and 7 ​d post-ICH induction in the ipsilateral injury hemispheres. Pink1 deficiency could further up-regulate mNSS scores, brain water content, MIP-2, MCP-1, IL-1β, and TNF-α in the ipsilateral injury hemispheres. On the other hand, Pink1 deficiency could decrease the number of center cross, the velocity, and the total distance traveled in open field test. Pink1 deficiency could further up-regulate the mRNA levels of pro-inflammatory (M1) molecules (Cd86, Nos2), and down-regulate the relative expression of anti-inflammatory (M2) molecules (Cd206, Arg-1, and IL-10). Pink1 deficiency deteriorates neurological deficits and inflammatory responses after ICH, which can be considered as a treatment target.

Aerobic Glycolysis Induced by mTOR/HIF-1α Promotes Early Brain Injury After Subarachnoid Hemorrhage via Activating M1 Microglia

M1 microglial activation is crucial for the pathogenesis of early brain injury (EBI) following subarachnoid hemorrhage (SAH), and there is growing evidence that glucose metabolism is frequently involved in microglial activation. However, the molecular mechanism of glycolysis and its role in M1 microglial activation in the context of EBI are not yet fully understood. In this study, firstly, the relationship between aerobic glycolysis and M1 microglial activation as well as SAH-induced EBI was researched in vivo. Then, intervention on mammalian target of rapamycin (mTOR) was performed to investigate the effects on glycolysis-dependent M1 microglial activation and EBI and its relationship with hypoxia-inducible factor-1α (HIF-1α) in vivo. Next, Hif-1α was inhibited to analyze its role in aerobic glycolysis, M1 microglial activation, and EBI in vivo. Lastly, both in vivo and in vitro, mTOR inhibition and Hif-1α enhancement were administered simultaneously, and the combined effects were further confirmed again. The results showed that aerobic glycolysis and M1 microglial polarization were increased after SAH, and glycolytic inhibition could attenuate M1 microglial activation and EBI. Inhibition of mTOR reduced glycolysis-dependent M1 microglial polarization and EBI severity by down-regulating HIF-1α expression, while enhancement had the opposite effects. Blockading HIF-1α had the similar effects as suppressing mTOR, while HIF-1α agonist worked against mTOR antagonist when administered simultaneously. In conclusion, the present study showed new evidence that aerobic glycolysis induced by mTOR/HIF-1α might promote EBI after SAH by activating M1 microglia. This finding provided new insights for the treatment of EBI.

Neuroadaptive Biochemical Mechanisms of Remote Ischemic Conditioning

This review summarizes the currently known biochemical neuroadaptive mechanisms of remote ischemic conditioning. In particular, it focuses on the significance of the pro-adaptive effects of remote ischemic conditioning which allow for the prevention of the neurological and cognitive impairments associated with hippocampal dysregulation after brain damage. The neuroimmunohumoral pathway transmitting a conditioning stimulus, as well as the molecular basis of the early and delayed phases of neuroprotection, including anti-apoptotic, anti-oxidant, and anti-inflammatory components, are also outlined. Based on the close interplay between the effects of ischemia, especially those mediated by interaction of hypoxia-inducible factors (HIFs) and steroid hormones, the involvement of the hypothalamic-pituitary-adrenocortical system in remote ischemic conditioning is also discussed.

Remote ischemic conditioning attenuates oxidative stress and inflammation via the Nrf2/HO-1 pathway in MCAO mice

The protective effects of remote ischemic conditioning (RIC) on acute ischemic stroke have been reported. However, the protective mechanisms of RIC have not been fully elucidated. This study aimed to investigate whether RIC could reduce oxidative stress and inflammatory responses in middle cerebral artery occlusion (MCAO)-reperfusion mice via the nuclear factor-E2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway. C57BL/6 mice were subjected to MCAO and underwent RIC twice daily at 1, 3, and 7 days after MCAO. ML385 was used to specifically inhibit Nrf2 in MCAO mice. Neurological deficit scores, infarct volume, and hematoxylin-eosin (HE) staining were assessed. Oxidative stress levels were assessed based on total antioxidant capacity (TAC), malonaldehyde (MDA), superoxide dismutase (SOD), and glutathione/glutathione disulfide (GSH/GSSG). mRNA levels were detected using real-time polymerase chain reaction (PCR), and protein levels were detected using western blotting and enzyme-linked immunosorbent assay (ELISA). Protein localization was investigated using immunofluorescence staining. RIC significantly reduced infarct volume and improved neurological function and histological changes after MCAO. RIC significantly increased TAC, SOD, and GSH/GSSG levels and decreased MDA levels. RIC significantly increased Nrf2 and HO-1 mRNA levels and decreased Keap1, NLRP3, and Cleaved Caspase-1 mRNA levels. RIC significantly increased Nrf2, HO-1, and NQO1 protein expression and decreased Keap1, NLRP3, Cleaved Caspase-1, Cleaved IL-1β, IL-6, and TNF-α protein expression. RIC promoted the activation and translocation of Nrf2 into the nucleus. The protective effects of RIC were abolished by ML385 treatment. In conclusion, our findings suggest that RIC alleviates oxidative stress and inflammatory responses via the Nrf2/HO-1 pathway, which in turn improves neurobehavioral function. RIC may provide novel therapeutic options for acute ischemic stroke.

Autonomic function may mediate the neuroprotection of remote ischemic postconditioning in stroke: A randomized controlled trial

OBJECTIVES

To evaluate the effect of remote ischemic postconditioning (RIPostC) on the prognosis of acute ischemic stroke(AIS) patients and investigate the mediating role of autonomic function in the neuroprotection of RIPostC.

MATERIALS AND METHODS

132 AIS patients were randomized into two groups. Patients received four cycles of 5-min inflation to a pressure of 200 mmHg(i.e., RIPostC) or patients' diastolic BP(i.e., shame), followed by 5 min of deflation on healthy upper limbs once a day for 30 days. The main outcome was neurological outcome including the National Institutes of Health Stroke Scale (NIHSS), modified Rankin Scale (mRS), and Barthel index(BI). The second outcome measure was autonomic function measured by heart rate variability(HRV).

RESULTS

Compared with the baseline, the post-intervention NIHSS score was significantly reduced in both groups (P<0.001). NIHSS score was significantly lower in the control group than intervention group at day 7.[RIPostC:3(1,5) versus shame:2(1,4); P=0.030]. mRS scored lower in the intervention group compared with the control group at day 90 follow-up(RIPostC:0.5±2.0 versus shame:1.0±2.0;P=0.016). The goodness-of-fit test revealed a significant difference between the generalized estimating equation model of mRS and BI scores of uncontrolled-HRV and controlled-HRV(P<0.05, both). The results of bootstrap revealed a complete mediation effect of HRV between group on mRS[indirect effect: -0.267 (LLCI = -0.549, ULCI = -0.048), the direct effect: -0.443 (LLCI = -0.831, ULCI = 0.118)].

CONCLUSION

This is the first human-based study providing evidence for a mediation role of autonomic function between RIpostC and prognosis in AIS patients. It indicated that RIPostC could improve the neurological outcome of AIS patients. Autonomic function may play a mediating role in this association.

TRIAL REGISTRATION

The clinical trials registration number for this study is NCT02777099 (ClinicalTrials.gov Identifier).

Remote ischemic preconditioning protects against spinal cord ischemia-reperfusion injury in mice by activating NMDAR/AMPK/PGC-1α/SIRT3 signaling

BACKGROUND

To study the protective effects of delayed remote ischemic preconditioning (RIPC) against spinal cord ischemia-reperfusion injury (SCIRI) in mice and determine whether SIRT3 is involved in this protection and portrayed its upstream regulatory mechanisms.

METHODS

In vivo, WT or SIRT3 global knockout (KO) mice were exposed to right upper and lower limbs RIPC or sham ischemia. After 24 h, the abdominal aorta was clamped for 20 min, then re-perfused for 3 days. The motor function of mice, number of Nissl bodies, apoptotic rate of neurons, and related indexes of oxidative stress in the spinal cord were measured to evaluate for neuroprotective effects. The expression and correlation of SIRT3 and NMDAR were detected by WB and immunofluorescence. In vitro, primary neurons were exacted and OGD/R was performed to simulate SCIRI in vivo. Neuronal damage was assessed by observing neuron morphology, detecting LDH release ratio, and flow cytometry to analyze the apoptosis. MnSOD and CAT enzyme activities, GSH and ROS level were also measured to assess neuronal antioxidant capacity. NMDAR-AMPK-PGC-1α signaling was detected by WB to portray upstream regulatory mechanisms of RIPC regulating SIRT3.

RESULTS

Compared to the SCIRI mice without RIPC, mice with RIPC displayed improved motor function recovery, a reduced neuronal loss, and enhanced antioxidant capacity. To the contrary, the KO mice did not exhibit any effect of RIPC-induced neuroprotection. Similar results were observed in vitro. Further analyses with spinal cord tissues or primary neurons detected enhanced MnSOD and CAT activities, as well as increased GSH level but decreased MDA or ROS production in the RIPC + I/R mice or NMDA + OGD/R neurons. However, these changes were completely inhibited by the absence of SIRT3. Additionally, NMDAR-AMPK-PGC-1α signaling was activated to upregulate SIRT3 levels, which is essential for RIPC-mediated neuroprotection.

CONCLUSIONS

RIPC enhances spinal cord ischemia tolerance in a SIRT3-dependent manner, and its induced elevated SIRT3 levels are mediated by the NMDAR-AMPK-PGC-1α signaling pathway. Combined therapy targeting SIRT3 is a promising direction for treating SCIRI.

Remote ischemic conditioning attenuates blood-brain barrier disruption after recombinant tissue plasminogen activator treatment via reducing PDGF-CC

Treatment of acute ischemic stroke with the recombinant tissue plasminogen activator (rtPA) is associated with increased blood-brain barrier (BBB) disruption and hemorrhagic transformation. Remote ischemic conditioning (RIC) has demonstrated neuroprotective effects against acute ischemic stroke. However, whether and how RIC regulates rtPA-associated BBB disruption remains unclear. Here, a rodent model of thromboembolic stroke followed by rtPA thrombolysis at different time points was performed with or without RIC. Brain infarction, neurological outcomes, BBB permeability, and intracerebral hemorrhage were assessed. The platelet-derived growth factor CC (PDGF-CC)/PDGFRα pathway in the brain tissue, PDGF-CC levels in the skeletal muscle and peripheral blood were also measured. Furthermore, impact of RIC on serum PDGF-CC levels were measured in healthy subjects and AIS patients. Our results showed that RIC substantially reduced BBB injury, intracerebral hemorrhage, cerebral infarction, and neurological deficits after stroke, even when rtPA was administrated in a delayed therapeutic time window. Mechanistically, RIC significantly decreased PDGFRα activation in ischemic brain tissue and reduced blood PDGF-CC levels, which partially resulted from PDGF-CC reduction in the skeletal muscle of RIC-applied hindlimbs and platelets. Intravenous or intraventricular recombinant PDGF-CC supplementation abolished RIC protective effects on BBB integrity. Moreover, similar changes of PDGF-CC in serum by RIC were also observed in healthy humans and acute ischemic stroke patients. Together, our study demonstrates that RIC can attenuate rtPA-aggravated BBB disruption after ischemic stroke via reducing the PDGF-CC/PDGFRα pathway and thus supports RIC as a potential approach for BBB disruption prevention or treatment following thrombolysis.

Ferulic acid: An extraordinarily neuroprotective phenolic acid with anti-depressive properties

BACKGROUND

Depression, one of the most common mental illnesses and mood disorder syndromes, can seriously harm physical and mental health. As the pathophysiology of depression remains unclear, there is a need to find novel therapeutic agents. Ferulic acid (FA), a phenolic compound found in various Chinese herbal medicines, has anti-inflammatory and free radical scavenging properties as well as a wide range of therapeutic effects against depression.

PURPOSE

In this review, we appraised preclinical research to fully discuss the anti-depression capacity of FA and discussed FAs' holistic characteristics that can contribute to better management of depression.

STUDY DESIGN

We reviewed the results of in vitro and in vivo experiments using FA to treat depression and explored the possible antidepressant pharmacological mechanisms of FA for the clinical treatment of depression.

METHODS

Electronic databases, including PubMed, Google Scholar, and China National Knowledge Infrastructure, were searched from the beginning of the database creation to December 2021.

RESULTS

Studies on the antidepressant effects of FA show that it may exert such effects through various mechanisms. These include the following: the regulation of monoamine and non-monoamine neurotransmitter levels, inhibition of hypothalamic-pituitary-adrenal axis hyperfunction and neuroinflammation, promotion of hippocampal neurogenesis and upregulation brain-derived neurotrophic factor level, neuroprotection (inhibition of neuroinflammation, oxidative stress, mitochondrial dysfunction, and apoptosis), and downregulation of oxidative stress.

CONCLUSION

Preclinical studies on the antidepressant effects of FA were reviewed in this study, and research on the antidepressant mechanisms of FA was summarized, confirming that FA can exert antidepressant effects through various pharmacological mechanisms. However, more multicenter clinical case-control studies are needed to confirm the clinical efficacy of FA.

The Potential Role of Hypoxia-Inducible Factor-1 in the Progression and Therapy of Central Nervous System Diseases

Hypoxia-inducible factor-1 (HIF-1) is a heterodimer protein composed of an oxygenregulated functional subunit, HIF-1α, and a structural subunit, HIF-1β, belonging to the basic helixloop- helix family. Strict regulation of HIF-1 protein stability and subsequent transcriptional activity involves various molecular interactions and is primarily controlled by post-transcriptional modifications. Hypoxia, owing to impaired cerebral blood flow, has been implicated in a range of central nervous system (CNS) diseases by exerting a deleterious effect on brain function. As a master oxygen- sensitive transcription regulator, HIF-1 is responsible for upregulating a wide spectrum of target genes involved in glucose metabolism, angiogenesis, and erythropoiesis to generate the adaptive response to avoid, or at least minimize, hypoxic brain injury. However, prolonged, severe oxygen deprivation may directly contribute to the role-conversion of HIF-1, namely, from neuroprotection to the promotion of cell death. Currently, an increasing number of studies support the fact HIF-1 is involved in a variety of CNS-related diseases, such as intracranial atherosclerosis, stroke, and neurodegenerative diseases. This review article chiefly focuses on the effect of HIF-1 on the pathogenesis and mechanism of progression of numerous CNS-related disorders by mediating the expression of various downstream genes and extensive biological functional events and presents robust evidence that HIF-1 may represent a potential therapeutic target for CNS-related diseases.

HIF‑1α in cerebral ischemia (Review)

Cerebral ischemic injury may lead to a series of serious brain diseases, death or different degrees of disability. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-sensitive transcription factor, which mediates the adaptive metabolic response to hypoxia and serves a key role in cerebral ischemia. HIF-1α is the main molecule that responds to hypoxia. HIF-1α serves an important role in the development of cerebral ischemia by participating in numerous processes, including metabolism, proliferation and angiogenesis. The present review focuses on the endogenous protective mechanism of cerebral ischemia and elaborates on the role of HIF-1α in cerebral ischemia. In addition, it focuses on cerebral ischemia interventions that act on the HIF-1α target, including biological factors, non-coding RNA, hypoxic-ischemic preconditioning and drugs, and expands upon the measures to strengthen the endogenous compensatory response to support HIF-1α as a therapeutic target, thus providing novel suggestions for the treatment of cerebral ischemia.

Immune Modulation as a Key Mechanism for the Protective Effects of Remote Ischemic Conditioning After Stroke

Remote ischemic conditioning (RIC), which involves a series of short cycles of ischemia in an organ remote to the brain (typically the limbs), has been shown to protect the ischemic penumbra after stroke and reduce ischemia/reperfusion (IR) injury. Although the exact mechanism by which this protective signal is transferred from the remote site to the brain remains unclear, preclinical studies suggest that the mechanisms of RIC involve a combination of circulating humoral factors and neuronal signals. An improved understanding of these mechanisms will facilitate translation to more effective treatment strategies in clinical settings. In this review, we will discuss potential protective mechanisms in the brain and cerebral vasculature associated with RIC. We will discuss a putative role of the immune system and circulating mediators of inflammation in these protective processes, including the expression of pro-and anti-inflammatory genes in peripheral immune cells that may influence the outcome. We will also review the potential role of extracellular vesicles (EVs), biological vectors capable of delivering cell-specific cargo such as proteins and miRNAs to cells, in modulating the protective effects of RIC in the brain and vasculature.

Remote but not Distant: a Review on Experimental Models and Clinical Trials in Remote Ischemic Conditioning as Potential Therapy in Ischemic Stroke

Stroke is one of the main causes of neurological disability worldwide and the second cause of death in people over 65 years old, resulting in great economic and social burden. Ischemic stroke accounts for 85% of total cases, and the approved therapies are based on re-establishment of blood flow, and do not directly target brain parenchyma. Thus, novel therapies are urgently needed. In this review, limb remote ischemic conditioning (RIC) is revised and discussed as a potential therapy against ischemic stroke. The review targets both (i) fundamental research based on experimental models and (ii) clinical research based on clinical trials and human interventional studies with healthy volunteers. Moreover, it also presents two approaches concerning RIC mechanisms in stroke: (i) description of the underlying cerebral cellular and molecular mechanisms triggered by limb RIC that promote neuroprotection against stroke induced damage and (ii) the identification of signaling factors involved in inter-organ communication following RIC procedure. Limb to brain remote signaling can occur via circulating biochemical factors, immune cells, and/or stimulation of autonomic nervous system. In this review, these three hypotheses are explored in both humans and experimental models. Finally, the challenges involved in translating experimentally generated scientific knowledge to a clinical setting are also discussed.

MiRNA-34c-5p protects against cerebral ischemia/reperfusion injury: involvement of anti-apoptotic and anti-inflammatory activities

MicroRNAs (miRNAs) are known as important regulators of gene expression and play important roles in diverse biological activities. However, the involvement of miRNAs in cerebral ischemia remains elusive. In the present study, using the middle cerebral artery occlusion (MCAO) model and oxygen-glucose deprivation/reperfusion (OGD/RP)-induced cell injury model, we found that the expression levels of miR-34c-5p were significantly reduced in MCAO rats and OGD/RP cells. Overexpression of miR-34c-5p could improve the increased brain infarction, brain water content and neurological scores in MCAO rats, as well as the abnormal expression of inflammatory cytokines (TNF-α, IL-6, COX-2, iNOS, IL-10) in OGD/RP cells. Moreover, overexpression of miR-34c-5p was found to inhibit the activity of nuclear factor-kappa B (NF-κB) by regulating the expression of nuclear receptor coactivator 1 (NCOA1), and increase the apoptotic rate of cortical neurons by inhibiting the expression of Caspase-3 and Bax and upregulating the expression of Bcl-2. Taken together, our findings demonstrated that miR-34c-5p plays an important role in cerebral ischemia/reperfusion injury, which may be mediated through inflammatory and apoptotic signaling pathways.

Neuroprotective effects and mechanisms of ischemic/hypoxic preconditioning on neurological diseases

As the organ with the highest demand for oxygen, the brain has a poor tolerance to ischemia and hypoxia. Despite severe ischemia/hypoxia induces the occurrence and development of various central nervous system (CNS) diseases, sublethal insult may induce strong protection against subsequent fatal injuries by improving tolerance. Searching for potential measures to improve brain ischemic/hypoxic is of great significance for treatment of ischemia/hypoxia related CNS diseases. Ischemic/hypoxic preconditioning (I/HPC) refers to the approach to give the body a short period of mild ischemic/hypoxic stimulus which can significantly improve the body's tolerance to subsequent more severe ischemia/hypoxia event. It has been extensively studied and been considered as an effective therapeutic strategy in CNS diseases. Its protective mechanisms involved multiple processes, such as activation of hypoxia signaling pathways, anti-inflammation, antioxidant stress, and autophagy induction, etc. As a strategy to induce endogenous neuroprotection, I/HPC has attracted extensive attention and become one of the research frontiers and hotspots in the field of neurotherapy. In this review, we discuss the basic and clinical research progress of I/HPC on CNS diseases, and summarize its mechanisms. Furthermore, we highlight the limitations and challenges of their translation from basic research to clinical application.

Remote Ischemic Postconditioning vs. Physical Exercise After Stroke: an Alternative Rehabilitation Strategy?

There remain debates on neuroprotection and rehabilitation techniques for acute ischemic stroke patients. Therapeutic physical exercise following stroke has shown promise but is challenging to apply clinically. Ischemic conditioning, which has several clinical advantages, is a potential neuroprotective method for stroke rehabilitation that is less understood. In the present study, the rehabilitative properties and mechanisms of physical exercise and remote ischemic postconditioning (RIPostC) after stroke were compared and determined. A total of 248 adult male Sprague-Dawley rats were divided into five groups: (1) sham, (2) stroke, (3) stroke with intense treadmill exercise, (4) stroke with mild treadmill exercise, and (5) stroke with RIPostC. Focal ischemia was evaluated by infarct volume and neurological deficit. Long-term functional outcomes were represented through neurobehavioral function tests: adhesive removal, beam balance, forelimb placing, grid walk, rota-rod, and Morris water maze. To further understand the mechanisms underlying neurorehabilitation and verify the presence thereof, we measured mRNA and protein levels of neuroplasticity factors, synaptic proteins, angiogenesis factors, and regulation molecules, including HIF-1α, BDNF, TrkB, and CREB. The key role of HIF-1α was elucidated by using the inhibitor, YC-1. Both exercise intensities and RIPostC significantly decreased infarct volumes and neurological deficits and outperformed the stroke group in the neurobehavioral function tests. All treatment groups showed significant increases in mRNA and protein expression levels of the target molecules for neurogenesis, synaptogenesis, and angiogenesis, with intermittent further increases in the RIPostC group. HIF-1α inhibition nullified most beneficial effects and indicative molecule expressions, including HIF-1α, BDNF, TrkB, and CREB, in both procedures. RIPostC is equally, or superiorly, effective in inducing neuroprotection and rehabilitation compared to exercise in ischemic rats. HIF-1α likely plays an important role in the efficacy of neuroplasticity conditioning, possibly through HIF-1α/BDNF/TrkB/CREB regulation.

HDAC3 Downregulation Improves Cerebral Ischemic Injury via Regulation of the SDC1-Dependent JAK1/STAT3 Signaling Pathway Through miR-19a Upregulation

Histone deacetylase (HDAC) inhibitors can protect the brain from ischemic injury. This study aimed to identify the regulation of HDAC3 in cerebral ischemic injury. Middle cerebral artery occlusion (MCAO) was performed to establish a mouse model with cerebral ischemic injury, in which expression of HDAC3 and miR-19a was evaluated using RT-qPCR. In MCAO mice with silencing of HDAC3, infarct volume was determined using 2,3,5-triphenyl tetrazolium chloride (TTC) staining, and serum levels of TNF-α, IL-6, and IL-8 were measured using ELISA. An in vitro model was constructed in human umbilical vein endothelial cells (HUVECs) with oxygen-glucose deprivation/reoxygenation (OGD/R), followed by gain- and loss-of-function experiments. Relationships among miR-19a, HDAC3, and syndecan-1 (SDC1) were explored using RIP, ChIP, and dual-luciferase reporter assays. The expression of HDAC3, SDC1, JAK1, and STAT3 along with the extent of JAK1 and STAT3 phosphorylation was measured by Western blot analysis. HUVEC viability, apoptosis, and angiogenesis were assessed by CCK-8, flow cytometry, and angiogenesis assays in vitro separately. We found elevated HDAC3 and downregulated miR-19a expression in the MCAO mice. Decreased TNF-α, IL-6, and IL-8 serum levels were observed in response to silencing of HDAC3. HDAC3 inhibited the expression of miR-19a, which in turn targeted SDC1, leading to JAK1/STAT3 signaling pathway activation. HDAC3 overexpression or miR-19a inhibition repressed HUVEC viability and angiogenesis but enhanced HUVEC apoptosis. Our data unraveled the mechanism whereby HDAC3 inhibition ameliorated cerebral ischemic injury by activating the JAK1/STAT3 signaling pathway through miR-19a-mediated SDC1 inhibition.

Neuroprotective effect of 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline mediated via regulation of antioxidant system and inhibition of inflammation and apoptosis in a rat model of cerebral ischemia/reperfusion

The aim of the study was the assessment of the neuroprotective potential of 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline (DHQ) and its effect on inflammation, apoptosis, and transcriptional regulation of the antioxidant system in cerebral ischemia/reperfusion (CIR) in rats. The CIR rat model was constructed using the bilateral common carotid artery occlusion followed by reoxygenation. DHQ was administered at a dose of 50 mg/kg for three days. Histological staining was performed using hematoxylin and eosin. The level of S100B protein, 8-hydroxy-2-deoxyguanosine, and 8-isoprostane was assessed using an enzyme immunoassay. The intensity of apoptosis was assessed based on the activity of caspases and DNA fragmentation. The activity of enzymes was measured spectrophotometrically, the level of gene transcripts was assessed by real-time PCR. DHQ reduced the histopathological changes and normalized levels of S100B, lactate, pyruvate, and HIF-1 mRNA in the CIR rat model. In addition, DHQ decreased the oxidative stress markers in animals with a pathology. The tested compound also inhibited inflammation by decreasing the activity of myeloperoxidase, expression of interleukins and Nfkb2. DHQ-treated rats with CIR showed decreased caspase activity, DNA fragmentation, and AIF expression. DHQ changed activity of antioxidant enzymes to the control values, decreased the expression of Cat, Gsr, and Nfe2l2, which was overexpressed in CIR, and activated the expression of Sod1, Gpx1, Gsta2, and Foxo1. DHQ showed a neuroprotective effect on CIR in rats. The neuroprotective effect involve mechanisms such as the inhibition of oxidative stress, leading to a reduction in the inflammatory response and apoptosis and the modulation of the antioxidant defense components.

Does remote ischaemic conditioning reduce inflammation? A focus on innate immunity and cytokine response

The benefits of remote ischaemic conditioning (RIC) have been difficult to translate to humans, when considering traditional outcome measures, such as mortality and heart failure. This paper reviews the recent literature of the anti-inflammatory effects of RIC, with a particular focus on the innate immune response and cytokine inhibition. Given the current COVID-19 pandemic, the inflammatory hypothesis of cardiac protection is an attractive target on which to re-purpose such novel therapies. A PubMed/MEDLINE™ search was performed on July 13th 2020, for the key terms RIC, cytokines, the innate immune system and inflammation. Data suggest that RIC attenuates inflammation in animals by immune conditioning, cytokine inhibition, cell survival and the release of anti-inflammatory exosomes. It is proposed that RIC inhibits cytokine release via a reduction in nuclear factor kappa beta (NF-κB)-mediated NLRP3 inflammasome production. In vivo, RIC attenuates pro-inflammatory cytokine release in myocardial/cerebral infarction and LPS models of endotoxaemia. In the latter group, cytokine inhibition is associated with a profound survival benefit. Further clinical trials should establish whether the benefits of RIC in inflammation can be observed in humans. Moreover, we must consider whether uncomplicated MI and elective surgery are the most suitable clinical conditions in which to test this hypothesis.

Remote Limb Ischemic Postconditioning Protects against Ischemic Stroke via Modulating Microglia/Macrophage Polarization in Mice

Aim

The protection against ischemia/reperfusion injury mediated by remote limb ischemic postconditioning (RIPC) shows great clinical value in ischemic stroke therapy, but the particular mechanism of RIPC remains unclear.

Methods

We carried out middle cerebral artery occlusion/reperfusion (MCAO/R) surgery on C57BL/6 male mice. RIPC was generated by 10-minute occlusion followed by the same period of reperfusion of the bilateral hind limb femoral artery and repeated for 3 cycles. Infarct size and neurological score were performed to assess stroke outcomes. Ly6C^hi monocytes were quantified in the blood and brain by flow cytometry. Real-time PCR, ELISA, and immunofluorescence were utilized to detect phenotype of proinflammatory M1 and anti-inflammatory M2 microglia/macrophage. Nuclear factor κB (NF-κB) and peroxisome proliferator-activated receptor γ (PPARγ) levels were detected using Western blot.

Results

At 24 and 72 h after MCAO, RIPC drastically attenuated infarct size and ameliorated the neurological deficits of mice and facilitated transmigration of Ly6C^hi monocytes to the brain postischemia reperfusion. Furthermore, RIPC contributed to increased M2 and reduced M1 microglia/macrophage through inhibiting NF-κB and promoting PPARγ activation.

Conclusion

Our results reveal pharmacological effect of RIPC in promoting microglia/macrophage transferring from M1 to M2 phenotype after MCAO/R in mice, which provides theoretical support for the therapeutic effect of RIPC in ischemic stroke.

The Mechanism of Gastrodin Participating in Improving the Cerebral Ischemia-Reperfusion Injury Through Notch 1 and NF-κB Signaling Pathways

Background: The purpose of this study was to investigate whether Gastrodin can activate the Notch 1 signaling pathway in the ischemic brain area to produce neuroprotective effects against cerebral ischemia-reperfusion injury, and to elucidate the role of Notch 1 and NF-κB signaling pathways in the Gastrodin-induced cerebral ischemic tolerance. Material and methods: The focal cerebral ischemia reperfusion model of middle cerebral artery embolism was established. TTC staining was applied to detect cerebral infarction. Tunel/NeuN immunofluorescence double labeling was employed to detect apoptosis. WB was used to detect the expressions of proteins related to the Notch 1 and NF-κB pathways. Results: Gastrodin can reduce neuron apoptosis in hippocampus after MCAO/R injury. After DAPT blocked Notch 1 signaling, the neuroprotective effects of Gastrodin improving neural function score, reducing cerebral infarction volume, and inhibiting neuronal apoptosis, were all reversed. Compared with the MCAO/R group, DAPT blocking Notch 1 signaling can also improve the neurological score of rats after MCAO/R injury, reduce cerebral infarct volume, and reduce neuronal apoptosis. Gastrodin can activate Notch 1 and NF-κB signaling pathways in cerebral ischemic areas and increase the expression of related proteins. After DAPT inhibited the Notch 1 signaling in the ipsilateral brain region, the phosphorylation level was significantly decreased, indicating that the activity of the NF-κB pathway was regulated by the Notch 1 signaling. Conclusion: Gastrodin-mediated protection against cerebral ischemia-reperfusion injury is related to the activation of Notch 1 signaling and the up-regulation of NF-κB signaling pathway activity in neurons of ischemic brain area.

Protective effect of hypoxia inducible factor-1α gene therapy using recombinant adenovirus in cerebral ischaemia-reperfusion injuries in rats

Context: Hypoxia-inducible factor-1α (HIF-1α)-induced genes can improve blood circulation.Objective: To investigate brain protective effect of recombinant adenovirus-mediated HIF-1α (AdHIF-1α) expression and its mechanism.Materials and methods: Male SD rats were used to establish focal cerebral ischaemia-reperfusion (CIR) injury models and randomly divided into normal, sham, CIR, Ad and AdHIF-1α groups. Ad or AdHIF-1α (10⁸ pfu/10 µL) were administered into lateral ventricle of rats in Ad and AdHIF-1α groups. Modified neurological severity score (mNSS), brain water content (BWC) and cerebral infarct volumes (CIVs) were analyzed, and HE staining was performed using the brain tissues. Furthermore, the expression of caspase-3 and HSP90 was analyzed using qRT-PCR and Western blotting.Results: Compared to CIR (mNSS, 8.52 ± 0.52; CIV, 0.22 ± 0.01) and Ad groups (mNSS, 8.83 ± 0.41; CIV, 0.22 ± 0.02), mNSS and CIV were significantly decreased in AdHIF-1α group (mNSS, 6.03 ± 0.61; CIV, 0.11 ± 0.01) at 72 h (p < 0.05). With prolonged reperfusion time (6 h to 72 h), BWC of all rats increased gradually, although the increase was markedly less in AdHIF-1α group (78.15 ± 0.16 to 87.01 ± 0.31) compared to that in CIR (78.77 ± 0.60 to 89.74 ± 0.34) and Ad groups (78.77 ± 0.35 to 89.71 ± 0.27) (p < 0.01). There were significantly greater pathological changes in the neurons in AdHIF-1α group at 72 h following CIR. Furthermore, expression of caspase-3 (p < 0.01) down-regulated and HSP90 up-regulated (p < 0.05) at mRNA and protein levels in AdHIF-1α group.Discussion and conclusions: HIF‑1α gene therapy is neuroprotective towards the CIR rat model. HIF-1α may be a candidate gene for the treatment of ischaemic brain injury.

Hypoxia Inducible Factor-1α (HIF-1α) Mediates NLRP3 Inflammasome-Dependent-Pyroptotic and Apoptotic Cell Death Following Ischemic Stroke

Stroke is a major cause of death and long-term disability. Recent evidence suggests that hypoxia-inducible factor 1α (HIF-1α), a transcription factor that regulates oxygen levels, plays a key role in neurological outcomes after ischemic stroke. Accordingly, we investigated the mechanism of HIF-1α on pyroptotic and apoptotic cells during ischemia/reperfusion (I/R). Adult Sprague-Dawley rats underwent 2 h of middle cerebral artery occlusion (MCAO). The rats were then exposed to 6 or 24 h of reperfusion, with or without YC-1 (HIF-1α inhibitor, 5 mg/kg). Infarct volumes, along with mRNA and protein quantities of HIF-1α, NLRP3, IL-1β, IL-18, Caspase-1, and co-localization of HIF-1α, and NLRP3, were assessed. We measured apoptotic and pyroptotic cell death, gasdermin D (GSDMD) activation and lactate dehydrogenase (LDH) activity, and the infiltration of neutrophils and macrophages after ischemic stroke. HIF-1α mRNA and NLRP3 inflammasome components were increased after 24 h of reperfusion. YC-1 significantly reduced the mRNA and protein expression of NLRP3, IL-1β, IL-18, and caspase-1; significantly decreased infarction and pyroptotic cell death after 24 h of reperfusion; attenuated the neuroinflammatory response by reducing infiltration of CD68- and MPO-positive cells after 24 h of reperfusion; and reduced apoptotic cell death following ischemic stroke. We found that HIF-1α likely regulates inflammatory responses through the NLRP3 inflammasome complex, thus influencing both apoptotic and pyroptotic cell death after stroke. These findings suggest that future investigations are needed regarding HIF-1α and its role as a potential molecular target in the treatment of acute ischemic stroke.

Role of the neurovascular unit in the process of cerebral ischemic injury

Cerebral ischemic injury exhibits both high morbidity and mortality worldwide. Traditional research of the pathogenesis of cerebral ischemic injury has focused on separate analyses of the involved cell types. In recent years, the neurovascular unit (NVU) mechanism of cerebral ischemic injury has been proposed in modern medicine. Hence, more effective strategies for the treatment of cerebral ischemic injury may be provided through comprehensive analysis of brain cells and the extracellular matrix. However, recent studies that have investigated the function of the NVU in cerebral ischemic injury have been insufficient. In addition, the metabolism and energy conversion of the NVU depend on interactions among multiple cell types, which make it difficult to identify the unique contribution of each cell type. Therefore, in the present review, we comprehensively summarize the regulatory effects and recovery mechanisms of four major cell types (i.e., astrocytes, microglia, brain-microvascular endothelial cells, and neurons) in the NVU under cerebral ischemic injury, as well as discuss the interactions among these cell types in the NVU. Furthermore, we discuss the common signaling pathways and signaling factors that mediate cerebral ischemic injury in the NVU, which may help to provide a theoretical basis for the comprehensive elucidation of cerebral ischemic injury.

Remote ischemic preconditioning-induced neuroprotection in cerebral ischemia-reperfusion injury: Preclinical evidence and mechanisms

Remote ischemic preconditioning (RIPC) is an intrinsic protective phenomenon in which 3 to 4 interspersed cycles of non-fatal regional ischemia followed by reperfusion to the remote tissues protect the vital organs including brain, heart and kidney against sustained ischemia-reperfusion-induced injury. There is growing preclinical evidence supporting the usefulness of RIPC in eliciting neuroprotection against focal and global cerebral ischemia-reperfusion injury. Scientists have explored the involvement of HIF-1α, oxidative stress, apoptotic pathway, Lcn-2, platelets-derived microparticles, splenic response, adenosine A₁ receptors, adenosine monophosphate activated protein kinase and neurogenic pathway in mediating RIPC-induced neuroprotection. The present review discusses the early and late phases of neuroprotection induced by RIPC against cerebral ischemic injury in animals along with the various possible mechanisms.

Remote ischemic postconditioning attenuates damage in rats with chronic cerebral ischemia by upregulating the autophagolysosome pathway via the activation of TFEB

The transcription factor EB (TFEB) is known for its role in lysosomal biogenesis, and it coordinates this process by driving autophagy and lysosomal gene expression during ischemia. In the present study, we aimed to explore the role of the TFEB-regulated autophagolysosome pathway (ALP) in rats with chronic cerebral ischemia (CCI) that were treated with remote ischemic postconditioning (RIPC). A modified 2-vessel occlusion (2-VO) method was utilized to establish the CCI rat model, and the CCI rats were identified by the Morris water maze test and histological staining. After the CCI rats were treated with RIPC, the damage to the rat cortex and hippocampal tissues and the status of the ALP were determined. Western blot analysis and immunofluorescence assays were performed to observe the nuclear translocation of TFEB. The rats were injected with TFEB siRNA via the lateral ventricle to investigate the effect of TFEB siRNA on the RIPC-treated CCI rats. The results suggested that RIPC of the CCI rats alleviated nerve injury, induced TFEB translocation into the nucleus, upregulated autophagy-related protein expression, and activated ALP machinery. Furthermore, TFEB siRNA decreased the levels of TFEB and impaired the neuroprotective effects of RIPC on the CCI rats. Collectively, we highlighted that RIPC attenuates damage in CCI rats via the activation of the TFEB-mediated ALP.

Arginine is neuroprotective through suppressing HIF-1α/LDHA-mediated inflammatory response after cerebral ischemia/reperfusion injury

Neuroinflammation is a secondary response following ischemia stroke. Arginine is a non-essential amino acid that has been shown to inhibit acute inflammatory reaction. In this study we show that arginine treatment decreases neuronal death after rat cerebral ischemia/reperfusion (I/R) injury and improves functional recovery of stroke animals. We also show that arginine suppresses inflammatory response in the ischemic brain tissue and in the cultured microglia after OGD insult. We further provide evidence that the levels of HIF-1α and LDHA are increased after rat I/R injury and that arginine treatment prevents the elevation of HIF-1α and LDHA after I/R injury. Arginine inhibits inflammatory response through suppression of HIF-1α and LDHA in the rat ischemic brain tissue and in the cultured microglia following OGD insult, and protects against ischemic neuron death after rat I/R injury by attenuating HIF-1α/LDHA-mediated inflammatory response. Together, these results indicate a possibility that arginine-induced neuroprotective effect may be through the suppression of HIF-1α/LDHA-mediated inflammatory response in microglia after cerebral ischemia injury.

Remote liver ischaemic preconditioning protects rat brain against cerebral ischaemia-reperfusion injury by activation of an AKT-dependent pathway

NEW FINDINGS

What is the central question of this study? Can remote liver ischaemic preconditioning (RLIPC) protect rat brain against cerebral ischaemia-reperfusion injury? What is the main finding and its importance? Pretreatment with RLIPC reduced cerebral infarct volume, improved neurological outcomes and inhibited neuron apoptosis. RLIPC led to increased phosphorylation of AKT, while inhibition of AKT abolished the effects of RLIPC. Our data suggest that liver ischaemic preconditioning exerts a strong neuroprotective effect against cerebral ischaemia-reperfusion injury by activating an AKT-dependent pathway.

ABSTRACT

Remote limb ischaemic preconditioning has been shown to have beneficial effects in protecting brains against ischaemia-reperfusion (I/R) injury. However, little is known regarding the effect of remote liver ischaemic conditioning (RLIPC). We therefore investigated the effect of RLIPC on brain tissues suffering from I/R injury. Rats were randomly assigned to a sham group, a control group or a RLIPC group. Rats in all groups except for the sham group received middle cerebral artery occlusion (MCAO) for 1 h, followed by 48 h of reperfusion. For the RLIPC rats, four cycles of 5 min of liver ischaemia (portal vein, hepatic arterial and venous trunk occlusion) with 5 min intermittent reperfusion were carried out before cerebral ischaemia. Infarct volume was assessed after 48 h of reperfusion. Blood samples were taken for serum lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) tests. Morphological changes of cortical tissue and cellular apoptosis were determined. Right cortex tissues were taken for western blotting measurements. Our data demonstrate that RLIPC reduced cerebral I/R injury, decreased the volume of the MCAO-evoked infarct region, decreased serum levels of LDH and CK-MB, and reduced neurological deficits and apoptosis after I/R injury. Moreover, rats receiving RLIPC showed increased cortical AKT phosphorylation, but protein phosphorylation level was unchanged in the survivor activating factor enhancement (SAFE) signalling pathway. Accordingly, inhibition of AKT with wortmannin abolished the neuroprotective action of liver preconditioning. Our study showed for the first time that liver ischaemic preconditioning effectively protects brain against cerebral I/R injury by activating an AKT-dependent pathway.

RIPC provides neuroprotection against ischemic stroke by suppressing apoptosis via the mitochondrial pathway

Ischemic stroke is a common disease with high morbidity and mortality. Remote ischemic preconditioning (RIPC) can stimulate endogenous protection mechanisms by inducing ischemic tolerance to reduce subsequent damage caused by severe or fatal ischemia to non-ischemic organs. This study was designed to assess the therapeutic properties of RIPC in ischemic stroke and to elucidate their underlying mechanisms. Neurobehavioral function was evaluated with the modified neurological severity score (mNSS) test and gait analysis. PET/CT was used to detect the ischemic volume and level of glucose metabolism. The protein levels of cytochrome c oxidase-IV (COX-IV) and heat shock protein 60 (HSP60) were tested by Western blotting. TUNEL and immunofluorescence staining were used to analyze apoptosis and to observe the nuclear translocation and colocalization of apoptosis-inducing factor (AIF) and endonuclease G (EndoG) in apoptotic cells. Transmission electron microscopy (TEM) was used to detect mitochondrial-derived vesicle (MDV) production and to assess mitochondrial ultrastructure. The experimental results showed that RIPC exerted significant neuroprotective effects, as indicated by improvements in neurological dysfunction, reductions in ischemic volume, increases in glucose metabolism, inhibition of apoptosis, decreased nuclear translocation of AIF and EndoG from mitochondria and improved MDV formation. In conclusion, RIPC alleviates ischemia/reperfusion injury after ischemic stroke by inhibiting apoptosis via the endogenous mitochondrial pathway.

Expression of heat shock protein 70 and Annexin A1 in serum of patients with acutely severe traumatic brain injury

Trends of early expression levels of heat shock protein 70 (Hsp70) and Annexin A1 (ANXA1) in serum of patients with acutely severe traumatic brain injury and the effects on clinical prognosis were investigated. Eighty-four patients with severe traumatic brain injury admitted to Binzhou Center Hospital from June 2014 to July 2017 were selected as the experimental group. Glasgow coma scale and acute physiology and chronic health evaluation II (APACHE II) score were obtained after admission. A further 75 healthy subjects were selected as the control group. Serum expression of Hsp70 and ANXA1 in the two groups was detected by enzyme-linked immunosorbent assay on the 1st, 2nd, 3rd and 4th day after admission. The receiver operating characteristic (ROC) curve was used to analyze the diagnostic value of Hsp70 and ANXA1 for the death of patients with acutely severe traumatic brain injury. Compared with the control group, expression of Hsp70 in the experimental group was significantly increased on the 1st, 2nd, 3rd and 4th day after admission (P<0.05), while expression of ANXA1 was significantly decreased (P<0.05). Expression levels of serum Hsp70 in the experimental group reached the peak on the 3rd day after admission, and the difference was statistically significant compared with the 1st, 2nd and 4th day (P<0.05). Expression of ANXA1 was the lowest on the 3rd day, and the difference was statistically significant compared with the 1st, 2nd and 4th day (P<0.05). The ROC curve analysis showed that the area under the curve of serum Hsp70 and ANXA1 was, respectively, 0.721 (95% CI: 0.611-0.829) and 0.684 (95% CI: 0.569-0.799). In conclusion, Hsp70 and ANXA1 may be involved in the occurrence and progression of acutely severe traumatic brain injury. The detection of serum Hsp70 and ANXA1 has certain diagnostic value for the death of patients with acutely severe traumatic brain injury.

Role of the Janus kinase 2/signal transducers and activators of transcription 3 pathway in the protective effect of remote ischemia preconditioning against cerebral ischemia-reperfusion injury in rats

Remote ischemia preconditioning (RIPC) is a convenient and effective method for alleviating cerebral ischemia-reperfusion injury (CIRI). However, to date, the underlying mechanism has not been fully elucidated. The aim of this research was to explore the protective mechanism of RIPC on the brain after CIRI. Four groups of rats were included in this experiment: the sham group, the middle cerebral artery occlusion (MCAO) group, the RIPC group, and the AG490 group. As an inhibitor of Janus kinase 2 (JAK2), AG490 was used after MCAO in the AG490 group to explore the role of JAK2/signal transducers and activators of transcription 3 (STAT3) after CIRI. Brain tissue was collected for evaluation after 2 h of ischemia and 24 h of reperfusion. ELISA for interleukin (IL)-6, IL-1β and tumor necrosis factor-α, western blot for phosphorylated-JAK2 and phosphorylated-STAT3, the neurological severity score and Longa scoring system for neurological deficit evaluation, triphenyltetrazolium chloride staining for cerebral infarction, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining for apoptotic cells in the brain tissue were performed. Neurological function in the RIPC group was notably better than that in the MCAO group. There were smaller infarction sizes and fewer apoptotic cells in the ischemic area in the RIPC group than in the MCAO group. In the RIPC group, the expression levels of IL-1β, tumor necrosis factor-α, IL-6, and phosphorylated-JAK2 and phosphorylated-STAT3 were significantly lower than those in the MCAO group. The findings in the RIPC and AG490 groups were similar. The inflammatory response and apoptosis are two important processes involved in brain dysfunction after CIRI. The JAK2/STAT3 signaling pathway has an underlying relationship with these two processes. These findings suggest that RIPC can alleviate the damage to brain tissue by CIRI by regulating the JAK2/STAT3 signaling pathway negatively.

Remote ischemic conditioning: a promising therapeutic intervention for multi-organ protection

Despite decades of formidable exploration, multi-organ ischemia-reperfusion injury (IRI) encountered, particularly amongst elderly patients with clinical scenarios, such as age-related arteriosclerotic vascular disease, heart surgery and organ transplantation, is still an unsettled conundrum that besets clinicians. Remote ischemic conditioning (RIC), delivered via transient, repetitive noninvasive IR interventions to distant organs or tissues, is regarded as an innovative approach against IRI. Based on the available evidence, RIC holds the potential of affording protection to multiple organs or tissues, which include not only the heart and brain, but also others that are likely susceptible to IRI, such as the kidney, lung, liver and skin. Neuronal and humoral signaling pathways appear to play requisite roles in the mechanisms of RIC-related beneficial effects, and these pathways also display inseparable interactions with each other. So far, several hurdles lying ahead of clinical translation that remain to be settled, such as establishment of biomarkers, modification of RIC regimen, and deep understanding of underlying minutiae through which RIC exerts its powerful function. As this approach has garnered an increasing interest, herein, we aim to encapsulate an overview of the basic concept and postulated protective mechanisms of RIC, highlight the main findings from proof-of-concept clinical studies in various clinical scenarios, and also to discuss potential obstacles that remain to be conquered. More well designed and comprehensive experimental work or clinical trials are warranted in future research to confirm whether RIC could be utilized as a non-invasive, inexpensive and efficient adjunct therapeutic intervention method for multi-organ protection.

Intestinal and Limb Ischemic Preconditioning Provides a Combined Protective Effect in the Late Phase, But not in the Early Phase, Against Intestinal Injury Induced by Intestinal Ischemia-Reperfusion in Rats

Intestinal ischemia/reperfusion (I/R) injury is associated with high morbidity and mortality. This study aimed to compare the protective efficacy of intestinal ischemic preconditioning (IIPC) and limb ischemic preconditioning (LIPC) against intestinal I/R injury and investigate their combined protective effect and the underlying mechanism. Male Sprague-Dawley rats were pretreated with IIPC, LIPC, or IIPC plus LIPC (combined), and intestinal I/R or sham operation was performed. The animals were sacrificed at 2 and 24 h after reperfusion and then blood and tissue samples were harvested for further analyses. In additional groups of animals, a 7-day survival study was conducted. The results showed that ischemic preconditioning (IPC) improved the survival rate and attenuated intestinal edema, injury, and apoptosis. IPC decreased the levels of tumor necrosis factor-α, interleukin -6, malondialdehyde and myeloperoxidase, and increased the activity of superoxide dismutase in serum and intestine after the I/R event. IPC downregulated the expression of Toll-like receptor-4 (TLR4) and nuclear factor-kappa B (NF-κB). The effect of combined pretreatment was better than that of single pretreatment in the late phase (24 h), but not in the early phase (2 h). The study demonstrated that IPC could significantly attenuate intestinal injury induced by intestinal I/R via inhibiting inflammation, oxidative stress, and apoptosis. IIPC and LIPC conferred no synergy in protecting I/R-induced intestinal injury in the early phase, but combined preconditioning had clearly stronger protection in the late phase, which was associated with the inhibition of the activated TLR4/NF-κB signaling pathway. It suggested that LIPC or combined preconditioning could potentially be applied in the clinical settings of surgical patient care.

Hypoxia preconditioned renal tubular epithelial cell-derived extracellular vesicles alleviate renal ischaemia-reperfusion injury mediated by the HIF-1α/Rab22 pathway and potentially affected by microRNAs

We previously found that hypoxia induced renal tubular epithelial cells (RTECs) release functional extracellular vesicles (EVs), which mediate the protection of remote ischaemic preconditioning (RIPC) for kidney ischaemia-reperfusion (I/R) injury. We intend to investigate whether the EVs were regulated by hypoxia-inducible factor 1α (HIF-1α) and Rab22 during RIPC. We also attempted to determine the potentially protective cargo of the EVs and reveal their underlying mechanism. Hypoxia preconditioning (HPC) of human kidney 2 (HK2) cells was conducted at 1% oxygen (O₂) for different amounts of time to simulate IPC in vitro. EVs were isolated and then quantified. HIF-1α- and Rab22-inhibited HK2 cells were used to investigate the role of the HIF-1α/Rab22 pathway in HPC-induced EV production. Both normoxic and HPC EVs were treated in vivo to assess the protective effect of I/R injury. Moreover, microRNA (miRNA) sequencing analysis and bioinformatics analysis was performed. We revealed that the optimal conditions for simulating IPC in vitro was no more than 12 h under the 1% O₂ culture circumstance. HPC enhanced the production of EVs, and the production of EVs was regulated by the HIF-1α/Rab22 pathway during HPC. Moreover, HPC EVs were found to be more effective at attenuating mice renal I/R injury. Furthermore, 16 miRNAs were upregulated in HPC EVs. Functional and pathway analysis indicated that the miRNAs may participate in multiple processes and pathways by binding their targets to influence the biochemical results during RIPC. We demonstrated that HIF-1α/Rab22 pathway mediated RTEC-derived EVs during RIPC. The HPC EVs protected renal I/R injury potentially through differentially expressed miRNAs. Further study is needed to verify the effective EV-miRNAs and their underlying mechanism.

Remote ischemic preconditioning attenuates intestinal mucosal damage: insight from a rat model of ischemia-reperfusion injury

Background

Remote ischemic preconditioning (RIPC) is a phenomenon, whereby repeated, non-lethal episodes of ischemia to an organ or limb exert protection against ischemia–reperfusion (I/R) injury in distant organs. Despite intensive research, there is still an apparent lack of knowledge concerning the RIPC-mediated mechanisms, especially in the intestine. Aim of this study was to evaluate possible protective effects RIPC on intestinal I/R injury.

Methods

Thirty rats were randomly assigned to four groups: I/R; I/R + RIPC; Sham; Sham + RIPC. Animals were anesthetized and the superior mesenteric artery was clamped for 30 min, followed by 60 min of reperfusion. RIPC-treated rats received 3 × 5 min of bilateral hindlimb I/R prior to surgery, sham groups obtained laparotomy without clamping. After I/R injury serum/tissue was analyzed for: Mucosal damage, Caspase-3/7 activity, expression of cell stress proteins, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) production, Hypoxia-inducible factor-1α (HIF-1α) protein expression and matrix metalloproteinase (MMP) activity.

Results

Intestinal I/R resulted in increased mucosal injury (P < 0.001) and elevated Caspase-3/7 activity (P < 0.001). RIPC significantly reduced the histological signs of intestinal I/R injury (P < 0.01), but did not affect Caspase-3/7 activity. Proteome profiling suggested a RIPC-mediated regulation of several cell stress proteins after I/R injury: Cytochrome C (+ 157%); Cited-2 (− 39%), ADAMTS1 (+ 74%). Serum concentrations of H₂O₂ and MDA remained unchanged after RIPC, while the reduced intestinal injury was associated with increased HIF-1α levels. Measurements of MMP activities in serum and intestinal tissue revealed an attenuated gelatinase activity at 130 kDa within the serum samples (P < 0.001) after RIPC, while the activity of MMPs within the intestinal tissue was not affected by I/R injury or RIPC.

Conclusions

RIPC ameliorates intestinal I/R injury in rats. The underlying mechanisms may involve HIF-1α protein expression and a decreased serum activity of a 130 kDa factor with gelatinase activity.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1885-4) contains supplementary material, which is available to authorized users.

Ferulic Acid Exerts Anti-apoptotic Effects against Ischemic Injury by Activating HSP70/Bcl-2- and HSP70/Autophagy-Mediated Signaling after Permanent Focal Cerebral Ischemia in Rats

This study assessed the anti-apoptotic effects of the administration of ferulic acid (FrA) in rats 30 min before middle cerebral artery occlusion (MCAo) followed by 3 d of ischemia and the involvement of 70 kDa heat shock protein (HSP70)-mediated signaling in the penumbral cortex. Our results demonstrated that FrA pretreatment at doses of 80 mg/kg (FrA-80 mg) and 100 mg/kg (FrA-100 mg) effectively ameliorated neurological functions and reduced the numbers of cytochrome c-, cleaved caspase-3-, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells in the penumbral cortex 3 d after ischemia. Moreover, FrA-80 mg and FrA-100 mg pretreatment markedly upregulated cytosolic HSP70, Beclin-1, microtubule-associated protein 1 light chain 3 (LC3) A/B-II and autophagy-related protein 5 (Atg5) expression; cytosolic and mitochondrial X-linked inhibitor of apoptosis (XIAP) expression and the Bcl-2/Bax ratio. FrA pretreatment downregulated cytosolic cytochrome c, apoptosis-inducing factor (AIF), procathepsin B, and cathepsin B expression and mitochondrial and cytosolic second mitochondria-derived activator of caspase/direct inhibitor of apoptosis protein-binding protein with a low isoelectric point (Smac/DIABLO) expression in the penumbral cortex. Pretreatment with VER155008, a HSP70 family inhibitor, significantly inhibited the effects of FrA-100 mg on the expression of the aforementioned proteins expression in the penumbral cortex. FrA-80 mg and FrA-100 mg pretreatment exerts neuroprotective effects against caspase-dependent and -independent apoptosis through activating HSP70/Bcl-2- and HSP70/autophagy-induced signaling pathways. Furthermore, the HSP70/Bcl-2- and HSP70/autophagy-induced anti-apoptotic effects of FrA pretreatment can be attributed to the regulation of Bax/cytochrome c/Smac/DIABLO/XIAP/ caspase-3- (or Bax/AIF-) and Beclin-1/LC3A/B-II/Atg5-mediated signaling, respectively, in the penumbral cortex 3 d after permanent MCAo.

Diel cycling hypoxia enhances hypoxia-tolerance in rainbow trout (Oncorhynchus mykiss): evidence of physiological and metabolic plasticity

Many fish naturally encounter a daily cycle of hypoxia but it is unclear whether this exposure hardens hypoxia-intolerant fish to future hypoxia or leads to accumulated stress and death. Rainbow trout (Oncorhynchus mykiss) is a putatively hypoxia-sensitive species found in rivers and estuaries that may routinely experience hypoxic events. Trout were exposed to 1 of 4 135h treatments in a swim-tunnel respirometer: 1) air-saturated control (20.7 kPa PO2); 2) diel cycling O2 (20.7-4.2 kPa over 24h); 3) acute hypoxia (130h at 20.7 kPa PO2 followed by 5h at 4.2 kPa PO2); 4) the mean oxygen tension (12.4 kPa PO2) experienced by the diel cycled fish. Some responses were similar in diel O2 cycled and mean PO2-treated fish but overall exposure to ecologically-representative diel hypoxia cycles improved hypoxia tolerance. Diel hypoxia-induced protective responses included increased inducible HSP70 concentration and mean corpuscular hemoglobin concentration, as well as reduced plasma cortisol. Acclimation to diel hypoxia allowed metabolic rates to decline during hypoxia, reduced oxygen debt following subsequent exposures, and allowed fish to return to an anabolic phenotype. The data demonstrate that acute diel cycling hypoxia improves hypoxia tolerance in previously intolerant fish through the activation of cellular protective mechanisms and a reduction in metabolic O2 requirements.

The insights into molecular pathways of hypoxia-inducible factor in the brain

The objectives of this present work were to review recent developments on the role of hypoxia-inducible factor (HIF) in the survival of cells under normoxic versus hypoxic and inflammatory brain conditions. The dual nature of HIF effects appears well established, based on the accumulated evidence of HIF playing both the role of adaptive factor and mediator of cell demise. Cellular HIF responses depend on pathophysiological conditions, developmental phase, comorbidities, and administered medications. In addition, HIF-1α and HIF-2α actions may vary in the same tissues. The multiple roles of HIF in stem cells are emerging. HIF not only regulates expression of target genes and thereby influences resultant protein levels but also contributes to epigenetic changes that may reciprocally provide feedback regulations loops. These HIF-dependent alterations in neurological diseases and its responses to treatments in vivo need to be examined alongside with a functional status of subjects involved in such studies. The knowledge of HIF pathways might be helpful in devising HIF-mimetics and modulating drugs, acting on the molecular level to improve clinical outcomes, as exemplified here by clinical and experimental data of selected brain diseases, occasionally corroborated by the data from disorders of other organs. Because of complex role of HIF in brain injuries, prospective therapeutic interventions need to differentially target HIF responses depending on their roles in the molecular mechanisms of neurologic diseases.

Cardioprotection and improvement in endothelial-dependent vasodilation during late-phase of whole body hypoxic preconditioning in spontaneously hypertensive rats via VEGF and endothelin-1

The present study was designed to investigate the effect of late phase of whole body hypoxic preconditioning on endothelial-dependent vasorelaxation and cardioprotection from ischemia-reperfusion injury in spontaneously hypertensive rats (SHR). Hypoxic preconditioning was performed by subjecting rats to four episodes of alternate exposure to low O₂ (8%) and normal air O₂ of 10 min each. After 24 h, the mesenteric arteries and hearts were isolated to determine the vascular function and cardioprotection from ischemia-reperfusion (I/R) injury on the Langendorff apparatus. There was a significant impairment in acetylcholine-induced relaxation in norepinephrine precontracted arteries (endothelium-dependent function) and increase in I/R-induced myocardial injury in SHR in comparison to Wistar Kyoto rats (WKY). However, hypoxic preconditioning significantly restored endothelium-dependent relaxation in SHR and attenuated I/R injury in both SHR and WKY. Hypoxic preconditioning also led to an increase in the levels of endothelin-1 (not endothelin-2 or -3), vascular endothelial growth factor-A (VEGF-A) and HIF-1α levels. Pretreatment with bevacizumab (anti-VEGF-A) and bosentan (endothelin receptor blocker) significantly attenuated hypoxic preconditioning-induced restoration of endothelium-dependent relaxation and cardioprotection from I/R injury. These interventions also attenuated the levels of VEGF-A and HIF-1α without modulating the endothelin-1 levels. It may be concluded that an increase in the endothelin-1 levels with a subsequent increase in HIF-1α and VEGF expression may possibly contribute in improving endothelium-dependent vasorelaxation and protecting hearts from I/R injury in SHR during late phase of whole body hypoxic preconditioning.

RLIPostC protects against cerebral ischemia through improved synaptogenesis in rats

OBJECTIVE

Remote limb ischemic post-conditioning (RLIPostC) has been shown to be neuroprotective in cerebral ischemia, whereas the effect of RLIPostC on synaptogenesis remains elusive. In the present study, we investigated the effects of RLIPostC on synaptogenesis in an experimental stroke rat model.

METHODS

Sprague-Dawley rats were subjected to left middle cerebral artery occlusion (MCAO) and were randomly divided into a control group, an RLIPostC group and a sham group. The RLIPostC group received three cycles of RLIPostC treatment immediately after reperfusion (ten minutes ischemia and ten minutes reperfusion in bilateral femoral artery). The neurological function was assessed by neurological deficit scores and the foot fault test at days 7 and 14 after MCAO. At day 14 after MCAO, the infarct volume and oedema were determined by cresyl violet (CV) staining and by measuring brain water content, respectively. Synaptogenesis was evaluated by western blotting and immunofluorescence staining.

RESULTS

Our results showed that RLIPostC treatment significantly promoted the recovery of behavioural function, reduced infarct volume and brain oedema, and increased the expressions of SYN1, PSD95 and GAP43.

CONCLUSIONS

These results confirmed that RLIPostC treatment for cerebral ischemia was safe and effective. A possible molecular mechanism of the beneficial effects of RLIPostC treatment may be the promotion of synaptogenesis.

S100A11 protects against neuronal cell apoptosis induced by cerebral ischemia via inhibiting the nuclear translocation of annexin A1

The subcellular location of annexin A1 (ANXA1) determines the ultimate fate of neurons after ischemic stroke. ANXA1 nuclear translocation is involved in neuronal apoptosis after cerebral ischemia, and extracellular ANXA1 is also associated with regulation of inflammatory responses. As the factors and mechanism that influence ANXA1 subcellular translocation remain unclear, studies aiming to determine and clarify the role of ANXA1 as a cell fate ‘regulator’ within cells are critically needed. In this study, we found that intracerebroventricular injection of the recombinant adenovirus vector Ad-S100A11 (carrying S100A11) strongly improved cognitive function and induced robust neuroprotective effects after ischemic stroke in vivo. Furthermore, upregulation of S100A11 protected against neuronal apoptosis induced by oxygen-glucose deprivation and reoxygenation (OGD/R) in vitro. Surprisingly, S100A11 overexpression markedly decreased ANXA1 nuclear translocation and subsequently alleviated OGD/R-induced neuronal apoptosis. Notably, S100A11 exerted its neuroprotective effect by directly binding ANXA1. Importantly, S100A11 directly interacted with ANXA1 through the nuclear translocation signal (NTS) of ANXA1, which is essential for ANXA1 to import into the nucleus. Consistent with our previous studies, ANXA1 nuclear translocation after OGD/R promoted p53 transcriptional activity, induced mRNA expression of the pro-apoptotic Bid gene, and activated the caspase-3 apoptotic pathway, which was almost completely reversed by S100A11 overexpression. Thus, S100A11 protects against cell apoptosis by inhibiting OGD/R-induced ANXA1 nuclear translocation. This study provides a novel mechanism whereby S100A11 protects against neuronal cells apoptosis, suggesting the potential for a previously unidentified treatment strategy in minimizing apoptosis after ischemic stroke.

Pentose phosphate pathway activation via HSP27 phosphorylation by ATM kinase: A putative endogenous antioxidant defense mechanism during cerebral ischemia-reperfusion

Molecular mechanism underlying ischemic stroke remains poorly understood. We previously reported glucose 6-phosphate dehydrogenase (G6PD) activity in pentose phosphate pathway (PPP) is activated via heat shock protein 27 (HSP27) phosphorylation at serine 85 (S85) by ataxia telangiectasia mutated (ATM) kinase during cerebral ischemia. This mechanism seems to be endogenous antioxidative system. To determine whether this system also works during reperfusion, we performed comparative metabolic analysis of reperfusion effect on metabolism in rat cortex using middle cerebral artery occlusion (MCAO). Metabolic profiling using gas-chromatography/mass-spectrometry analysis showed changes in metabolic state that depended on reperfusion time. Enrichment analysis showed PPP was significantly upregulated during ischemia-reperfusion. Significant increases in fructose 6-phosphate and ribulose 5-phosphate after reperfusion also suggested enhancement of PPP. In relation to PPP, ischemia-reperfusion induced an increase of up to 69-fold in HSP27 transcripts after 24-h reperfusion. Immunoblotting showed gradual increase in HSP27 protein and marked increase in HSP27 phosphorylation (S85) that were time-dependent (4.5-fold after 24-h reperfusion). G6PD activity was significantly elevated after 1-h MCAO (20%), reduced after 1-h reperfusion, increased gradually thereafter and significantly elevated after 24-h reperfusion. The NADPH/NAD⁺ ratio displayed similar increasing pattern. Intracerebroventricular injection of ATM kinase inhibitor (KU-55933) significantly reduced HSP27 phosphorylation and G6PD activity, significantly increased protein carbonyl, and resulted in increase in infarct size (100%) 24-h after reperfusion following 90-min MCAO. Consequently, G6PD activation via HSP27 phosphorylation by ATM kinase may be part of endogenous antioxidant defense neuroprotection mechanism that is activated during ischemia-reperfusion. These findings have important implications for treatment of stroke.