Hypoxia Induces autophagic cell death through hypoxia-inducible factor 1α in microglia

The Janus face of HIF-1α in ischemic stroke and the possible associated pathways

Stroke is the most devastating disease, causing paralysis and eventually death. Many clinical and experimental trials have been done in search of a new safe and efficient medicine; nevertheless, scientists have yet to discover successful remedies that are also free of adverse effects. This is owing to the variability in intensity, localization, medication routes, and each patient's immune system reaction. HIF-1α represents the modern tool employed to treat stroke diseases due to its functions: downstream genes such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. Its role can be achieved via two downstream EPO and VEGF strongly related to apoptosis and antioxidant processes. Recently, scientists paid more attention to drugs dealing with the HIF-1 pathway. This review focuses on medicines used for ischemia treatment and their potential HIF-1α pathways. Furthermore, we discussed the interaction between HIF-1α and other biological pathways such as oxidative stress; however, a spotlight has been focused on certain potential signalling contributed to the HIF-1α pathway. HIF-1α is an essential regulator of oxygen balance within cells which affects and controls the expression of thousands of genes related to sustaining homeostasis as oxygen levels fluctuate. HIF-1α's role in ischemic stroke strongly depends on the duration and severity of brain damage after onset. HIF-1α remains difficult to investigate, particularly in ischemic stroke, due to alterations in the acute and chronic phases of the disease, as well as discrepancies between the penumbra and ischemic core. This review emphasizes these contrasts and analyzes the future of this intriguing and demanding field.

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

The Role of Oxygen Homeostasis and the HIF-1 Factor in the Development of Neurodegeneration

Understanding the molecular underpinnings of neurodegeneration processes is a pressing challenge for medicine and neurobiology. Alzheimer's disease (AD) and Parkinson's disease (PD) represent the most prevalent forms of neurodegeneration. To date, a substantial body of experimental evidence has strongly implicated hypoxia in the pathogenesis of numerous neurological disorders, including AD, PD, and other age-related neurodegenerative conditions. Hypoxia-inducible factor (HIF) is a transcription factor that triggers a cell survival program in conditions of oxygen deprivation. The involvement of HIF-1α in neurodegenerative processes presents a complex and sometimes contradictory picture. This review aims to elucidate the current understanding of the interplay between hypoxia and the development of AD and PD, assess the involvement of HIF-1 in their pathogenesis, and summarize promising therapeutic approaches centered on modulating the activity of the HIF-1 complex.

Autophagy-related 5 in acute ischemic stroke: Variation and linkage with neurofunction, and survival

OBJECTIVE

Autophagy-related 5 (ATG5) facilitates the pathologic process of acute ischemic stroke (AIS) via multiple ways. This study aimed to identify the association of serum ATG5 with clinical outcomes in AIS patients.

METHODS

Serum ATG5 from 280 AIS patients were detected at admission, Day (D)1, D3, D7, D30, and D90 after admission by enzyme-linked immunosorbent assay. The median (interquartile range) follow-up was 21.1 (5.9-43.9) months. Another 50 healthy controls (HCs) were also enrolled for serum ATG5 determination.

RESULTS

ATG5 was elevated (p < 0.001) (vs. HCs), and positively correlated with hyperlipidemia (p = 0.016), and the national institutes of health stroke scale score (p = 0.001) in AIS patients. Interestingly, ATG5 was increased from admission to D1, but gradually decreased until D90 (p < 0.001). Besides, 85 (30.4%) and 195 (69.6%) AIS patients were assessed as modified Rankin Scale (mRS) >2 and mRS ≤2 at D90, respectively. ATG5 at admission, D1, D3, D30, and D90 was elevated in AIS patients with mRS >2 versus those with mRS ≤2 (all p < 0.050). ATG5 at admission, D1, D3, D7, D30, or D90 was elevated in relapsed (vs. non-relapsed) or died (vs. survived) AIS patients (all p < 0.050). Recurrence-free survival was shortened in AIS patients with high (≥52.0 ng/mL) ATG5 versus those with low (<52.0 ng/mL) ATG5 at admission, D3, D7, and D30 (all p < 0.050); overall survival was shorter in AIS patients with high (vs. low) ATG5 at D7 and D30 (both p < 0.050).

INTERPRETATION

Serum ATG5 elevates at first, thereafter gradually declines, whose elevation associates with neurological dysfunction, recurrence, and death risk in AIS patients.

Regulation of genes involved in the metabolic adaptation of murine microglial cells in response to elevated HIF-1α mediated activation

Microglia cells are activated in response to different stress signals. Several metabolic adaptations underlie microglia activation in the brain. Among these, in conditions like ischemic stroke and, hypoxic stress stimuli activate microglia cells. Hypoxic stress is mediated by HIF-1α. Although HIF-1α has been implicated in the alteration of metabolic pathways, changes in microglia lipid metabolism during M1 activation of microglia induced by elevated HIF-1α levels are yet to be understood. This can also merit interest in the development of novel targets to mitigate chronic inflammation. Our study aims to elucidate the transcriptional regulation of metabolic pathways in microglia cells during HIF-1α mediated activation. To study the adaptations in the metabolic pathways we induced microglia activation, by activating HIF-1α. Here, we show that microglia cells activated in response to elevated HIF-1α require ongoing lipogenesis and fatty acid breakdown. Notably, autophagy is activated during the initial stages of microglia activation. Inhibition of autophagy in activated microglia affects their viability and phagocytic activity. Collectively, our study expands the understanding of the molecular link between autophagy, lipid metabolism, and inflammation during HIF-1α mediated microglial activation that can lead to the development of promising strategies for controlling maladaptive activation states of microglia responsible for neuroinflammation. Together, our findings suggest that the role of HIF-1α in regulating metabolic pathways during hypoxia in microglia is beyond optimization of glucose utilization and distinctly regulates lipid metabolism during pro-inflammatory activation.

Adipose-Derived Mesenchymal Stem Cells Protect Endothelial Cells from Hypoxic Injury by Suppressing Terminal UPR In Vivo and In Vitro

Adipose-derived stem cells (ASCs) have been used as a therapeutic intervention for peripheral artery disease (PAD) in clinical trials. To further explore the therapeutic mechanism of these mesenchymal multipotent stromal/stem cells in PAD, this study was designed to test the effect of xenogeneic ASCs extracted from human adipose tissue on hypoxic endothelial cells (ECs) and terminal unfolded protein response (UPR) in vitro and in an atherosclerosis-prone apolipoprotein E-deficient mice (ApoE-/- mice) hindlimb ischemia model in vivo. ASCs were added to Cobalt (II) chloride-treated ECs; then, metabolic activity, cell migration, and tube formation were evaluated. Fluorescence-based sensors were used to assess dynamic changes in Ca2+ levels in the cytosolic- and endoplasmic reticulum (ER) as well as changes in reactive oxygen species. Western blotting was used to observe the UPR pathway. To simulate an acute-on-chronic model of PAD, ApoE-/- mice were subjected to a double ligation of the femoral artery (DLFA). An assessment of functional recovery after DFLA was conducted, as well as histology of gastrocnemius. Hypoxia caused ER stress in ECs, but ASCs reduced it, thereby promoting cell survival. Treatment with ASCs ameliorated the effects of ischemia on muscle tissue in the ApoE-/- mice hindlimb ischemia model. Animals showed less muscle necrosis, less inflammation, and lower levels of muscle enzymes after ASC injection. In vitro and in vivo results revealed that all ER stress sensors (BIP, ATF6, CHOP, and XBP1) were activated. We also observed that the expression of these proteins was reduced in the ASCs treatment group. ASCs effectively alleviated endothelial dysfunction under hypoxic conditions by strengthening ATF6 and initiating a transcriptional program to restore ER homeostasis. In general, our data suggest that ASCs may be a meaningful treatment option for patients with PAD who do not have traditional revascularization options.

Oxygen metabolism abnormality and Alzheimer's disease: An update

Oxygen metabolism abnormality plays a crucial role in the pathogenesis of Alzheimer's disease (AD) via several mechanisms, including hypoxia, oxidative stress, and mitochondrial dysfunction. Hypoxia condition usually results from living in a high-altitude habitat, cardiovascular and cerebrovascular diseases, and chronic obstructive sleep apnea. Chronic hypoxia has been identified as a significant risk factor for AD, showing an aggravation of various pathological components of AD, such as amyloid β-protein (Aβ) metabolism, tau phosphorylation, mitochondrial dysfunction, and neuroinflammation. It is known that hypoxia and excessive hyperoxia can both result in oxidative stress and mitochondrial dysfunction. Oxidative stress and mitochondrial dysfunction can increase Aβ and tau phosphorylation, and Aβ and tau proteins can lead to redox imbalance, thus forming a vicious cycle and exacerbating AD pathology. Hyperbaric oxygen therapy (HBOT) is a non-invasive intervention known for its capacity to significantly enhance cerebral oxygenation levels, which can significantly attenuate Aβ aggregation, tau phosphorylation, and neuroinflammation. However, further investigation is imperative to determine the optimal oxygen pressure, duration of exposure, and frequency of HBOT sessions. In this review, we explore the prospects of oxygen metabolism in AD, with the aim of enhancing our understanding of the underlying molecular mechanisms in AD. Current research aimed at attenuating abnormalities in oxygen metabolism holds promise for providing novel therapeutic approaches for AD.

HIF-1, an important regulator in potential new therapeutic approaches to ischemic stroke

Ischemic stroke is a leading cause of disability and mortality worldwide due to the narrow therapeutic window of the only approved therapies like intravenous thrombolysis and thrombectomy. Hypoxia inducible factor-1α (HIF-1α) is a sensitive regulator of oxygen homeostasis, and its expression is rapidly induced after hypoxia/ischemia. It plays an extensive role in the pathophysiology of stroke by regulating multiple pathways including glucose metabolism, angiogenesis, neuronal survival, neuroinflammation and blood brain barrier regulation. Here, we give a brief overview of the HIF-1α-targeting strategies currently under investigation and summarise recent research on how HIF-1α is regulated in various brain cells, including neurons and microglia, at various stages in ischemic stroke. The roles of HIF-1 in stroke varies with ischemic time and degree of ischemia, are still up for debate. More focus has been placed on prospective HIF-1α targeting drugs, such as HIF-1α activator, HIF-1α stabilizers, and natural compounds. In this review, we have highlighted the regulation of HIF-1α in the novel therapeutic approaches for treatment of stroke.

Microglia autophagy in ischemic stroke: A double-edged sword

Ischemic stroke (IS) is one of the major types of cerebrovascular diseases causing neurological morbidity and mortality worldwide. In the pathophysiological process of IS, microglia play a beneficial role in tissue repair. However, it could also cause cellular damage, consequently leading to cell death. Inflammation is characterized by the activation of microglia, and increasing evidence showed that autophagy interacts with inflammation through regulating correlative mediators and signaling pathways. In this paper, we summarized the beneficial and harmful effects of microglia in IS. In addition, we discussed the interplay between microglia autophagy and ischemic inflammation, as along with its application in the treatment of IS. We believe this could help to provide the theoretical references for further study into IS and treatments in the future.

Microglial autophagy in cerebrovascular diseases

Microglia are considered core regulators for monitoring homeostasis in the brain and primary responders to central nervous system (CNS) injuries. Autophagy affects the innate immune functions of microglia. Recently some evidence suggests that microglial autophagy is closely associated with brain function in both ischemic stroke and hemorrhagic stroke. Herein, we will discuss the interaction between autophagy and other biological processes in microglia under physiological and pathological conditions and highlight the interaction between microglial metabolism and autophagy. In the end, we focus on the effect of microglial autophagy in cerebrovascular diseases.

Nrf2 Pathway and Autophagy Crosstalk: New Insights into Therapeutic Strategies for Ischemic Cerebral Vascular Diseases

Cerebrovascular disease is highly prevalent and has a complex etiology and variable pathophysiological activities. It thus poses a serious threat to human life and health. Currently, pathophysiological research on cerebrovascular diseases is gradually improving, and oxidative stress and autophagy have been identified as important pathophysiological activities that are gradually attracting increasing attention. Many studies have found some effects of oxidative stress and autophagy on cerebrovascular diseases, and studies on the crosstalk between the two in cerebrovascular diseases have made modest progress. However, further, more detailed studies are needed to determine the specific mechanisms. This review discusses nuclear factor erythroid 2-related factor 2 (Nrf2) molecules, which are closely associated with oxidative stress and autophagy, and the crosstalk between them, with the aim of providing clues for studying the two important pathophysiological changes and their crosstalk in cerebrovascular diseases as well as exploring new target treatments.

Netrin-1 in Post-stroke Neuroprotection: Beyond Axon Guidance Cue

BACKGROUND

Stroke, especially ischemic stroke, is a leading disease associated with death and long-term disability with limited therapeutic options. Neuronal death caused by vascular impairment, programmed cell death and neuroinflammation has been proven to be associated with increased stroke severity and poor stroke recovery. In light of this, a development of neuroprotective drugs targeting injured neurons is urgently needed for stroke treatment. Netrin-1, known as a bifunctional molecule, was originally described to mediate the repulsion or attraction of axonal growth by interacting with its different receptors. Importantly, accumulating evidence has shown that netrin-1 can manifest its beneficial functions to brain tissue repair and neural regeneration in different neurological disease models.

OBJECTIVE

In this review, we focus on the implications of netrin-1 and its possibly involved pathways on neuroprotection after ischemic stroke, through which a better understanding of the underlying mechanisms of netrin-1 may pave the way to novel treatments.

METHODS

Peer-reviewed literature was recruited by searching databases of PubMed, Scopus, Embase, and Web of Science till the year 2021.

CONCLUSION

There has been certain evidence to support the neuroprotective function of netrin-1 by regulating angiogenesis, autophagy, apoptosis and neuroinflammation after stroke. Netrin-1 may be a promising drug candidate in reducing stroke severity and improving outcomes.

Hypoxia and Alpha-Synuclein: Inextricable Link Underlying the Pathologic Progression of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease, with typical motor symptoms as the main clinical manifestations. At present, there are about 10 million patients with PD in the world, and its comorbidities and complications are numerous and incurable. Therefore, it is particularly important to explore the pathogenesis of PD and find possible therapeutic targets. Because the etiology of PD is complex, involving genes, environment, and aging, finding common factors is the key to identifying intervention targets. Hypoxia is ubiquitous in the natural environment and disease states, and it is considered to be closely related to the etiology of PD. Despite research showing that hypoxia increases the expression and aggregation of alpha-synuclein (α-syn), the most important pathogenic protein, there is still a lack of systematic studies on the role of hypoxia in α-syn pathology and PD pathogenesis. Considering that hypoxia is inextricably linked with various causes of PD, hypoxia may be a co-participant in many aspects of the PD pathologic process. In this review, we describe the risk factors for PD, and we discuss the possible role of hypoxia in inducing PD pathology by these risk factors. Furthermore, we attribute the pathological changes caused by PD etiology to oxygen uptake disorder and oxygen utilization disorder, thus emphasizing the possibility of hypoxia as a critical link in initiating or promoting α-syn pathology and PD pathogenesis. Our study provides novel insight for exploring the pathogenesis and therapeutic targets of PD.

Redox aspects of cytotoxicity and anti-neuroinflammatory profile of chloroquine and hydroxychloroquine in serum-starved BV-2 microglia

Chloroquine (CQ) and hydroxychloroquine (HCQ) have long been used worldwide to treat and prevent human malarias. However, these 4-aminoquinolines have also shown promising potential in treating chronic illnesses with an inflammatory component, including neurological diseases. Given the current demand for serum avoidance during pharmacological testing and modeling of some pathologies, we compared cytotoxicities of CQ and HCQ in both serum-deprived and -fed murine BV-2 microglia. Furthermore, we assessed the anti-neuroinflammatory potential of both compounds in serum-deprived cells. Under both conditions, CQ showed higher cytotoxicity than HCQ. However, the comparable MTT-assay-derived data measured under different serum conditions were associated with disparate cytotoxic mechanisms of CQ and HCQ. In particular, under serum starvation, CQ mildly enhanced secondary ROS, mitochondrial hyperpolarization, and decreased phagocytosis. However, CQ promoted G1 phase cell cycle arrest and mitochondrial depolarization in serum-fed cells. Under both conditions, CQ fostered early apoptosis. Additionally, we confirmed that both compounds could exert anti-inflammatory effects in microglia through interference with MAPK signaling under nutrient-deprivation-related stress. Nevertheless, unlike HCQ, CQ is more likely to exaggerate intracellular prooxidant processes in activated starved microglia, which are inefficiently buffered by Nrf2/HO-1 signaling pathway activation. These outcomes also show HCQ as a promising anti-neuroinflammatory drug devoid of CQ-mediated cytotoxicity.

NLRP3 Inflammasome Activation: A Therapeutic Target for Cerebral Ischemia–Reperfusion Injury

Millions of patients are suffering from ischemic stroke, it is urgent to figure out the pathogenesis of cerebral ischemia–reperfusion (I/R) injury in order to find an effective cure. After I/R injury, pro-inflammatory cytokines especially interleukin-1β (IL-1β) upregulates in ischemic brain cells, such as microglia and neuron. To ameliorate the inflammation after cerebral I/R injury, nucleotide-binding oligomerization domain (NOD), leucine-rich repeat (LRR), and pyrin domain-containing protein 3 (NLRP3) inflammasome is well-investigated. NLRP3 inflammasomes are complicated protein complexes that are activated by endogenous and exogenous danger signals to participate in the inflammatory response. The assembly and activation of the NLRP3 inflammasome lead to the caspase-1-dependent release of pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Furthermore, pyroptosis is a pro-inflammatory cell death that occurs in a dependent manner on NLRP3 inflammasomes after cerebral I/R injury. In this review, we summarized the assembly and activation of NLRP3 inflammasome; moreover, we also concluded the pivotal role of NLRP3 inflammasome and inhibitors, targeting the NLRP3 inflammasome in cerebral I/R injury.

Effects of Long-Term Vagus Nerve Electrical Stimulation Therapy on Acute Cerebral Infarction and Neurological Function Recovery in Post MCAO Mice

Background

Vagus nerve stimulation therapy is proven to produce neuroprotective effects against central nervous system diseases and reduce neurological injury, having a positive effect on the recovery of neurological functions in mouse model of stroke.

Objective

This study was aimed at exploring a wider time window for VNS treatment, investigating the long-term behavioral improvement of long-term VNS in mice after pMCAO, and exploring the antiapoptotic properties of VNS and its role in autophagy, all of which may be a permanent deficiency potential mechanism of neuroprotection in hemorrhagic stroke.

Methods

Permanent focal cerebral ischemia and implantation of vagus nerve stimulator were performed through intracavitary occlusion of the right middle cerebral artery (MCA). The vagus nerve stimulation group received five times vagus nerve stimulation from 6 h after surgery for 5 days. Adhesive removal test and NSS neurological score were used to evaluate the neurological deficit of mice. TTC staining of mouse brain tissue was performed one week after surgery in order to assess the area of cerebral infarction. Additionally, frozen sections were stained with Fluoro-Jade B to observe the apoptotic cells in the ischemic penumbra of brain tissue. Finally, Western blot was used to detect the changes in the levels of apoptosis-related proteins such as cleaved-caspase3 and Bcl-2 and autophagy-related proteins such as mTOR, Beclin-1, and LC3-II in brain tissue.

Results

VNS can effectively reduce the behavioral score of pMCAO mice; TTC results showed that VNS could effectively reduce the infarct area after pMCAO (P < 0.05). After VNS intervention of the pMCAO group compared with the pMCAO+VNI group, the FJB-positive cells in the VNS group were significantly decreased (P < 0.05); Western Blot analysis showed that the expression of cleaved-caspase3 in the brain tissue of mice increased after pMCAO (P < 0.05), and the expression of Bcl-2 decreased (P < 0.05). This change could be effectively reversed after VNS intervention (P < 0.05).

Conclusion

VNS could effectively improve the behavioral performance of mice after permanent stroke in addition to significantly reducing the infarct size of the brain tissue. The mechanism may be related to the effective reduction of cell apoptosis and excessive autophagy after pMCAO by VNS.

The dual roles of autophagy and the GPCRs-mediating autophagy signaling pathway after cerebral ischemic stroke

Ischemic stroke, caused by a lack of blood supply in brain tissues, is the third leading cause of human death and disability worldwide, and usually results in sensory and motor dysfunction, cognitive impairment, and in severe cases, even death. Autophagy is a highly conserved lysosome-dependent process in which eukaryotic cells removal misfolded proteins and damaged organelles in cytoplasm, which is critical for energy metabolism, organelle renewal, and maintenance of intracellular homeostasis. Increasing evidence suggests that autophagy plays important roles in pathophysiological mechanisms under ischemic conditions. However, there are still controversies about whether autophagy plays a neuroprotective or damaging role after ischemia. G-protein-coupled receptors (GPCRs), one of the largest protein receptor superfamilies in mammals, play crucial roles in various physiological and pathological processes. Statistics show that GPCRs are the targets of about one-fifth of drugs known in the world, predicting potential values as targets for drug research. Studies have demonstrated that nutritional deprivation can directly or indirectly activate GPCRs, mediating a series of downstream biological processes, including autophagy. It can be concluded that there are interactions between autophagy and GPCRs signaling pathway, which provides research evidence for regulating GPCRs-mediated autophagy. This review aims to systematically discuss the underlying mechanism and dual roles of autophagy in cerebral ischemia, and describe the GPCRs-mediated autophagy, hoping to probe promising therapeutic targets for ischemic stroke through in-depth exploration of the GPCRs-mediated autophagy signaling pathway.

Biological Functions and Regulatory Mechanisms of Hypoxia-Inducible Factor-1α in Ischemic Stroke

Ischemic stroke is caused by insufficient cerebrovascular blood and oxygen supply. It is a major contributor to death or disability worldwide and has become a heavy societal and clinical burden. To date, effective treatments for ischemic stroke are limited, and innovative therapeutic methods are urgently needed. Hypoxia inducible factor-1α (HIF-1α) is a sensitive regulator of oxygen homeostasis, and its expression is rapidly induced after hypoxia/ischemia. It plays an extensive role in the pathophysiology of stroke, including neuronal survival, neuroinflammation, angiogenesis, glucose metabolism, and blood brain barrier regulation. In addition, the spatiotemporal expression profile of HIF-1α in the brain shifts with the progression of ischemic stroke; this has led to contradictory findings regarding its function in previous studies. Therefore, unveiling the Janus face of HIF-1α and its target genes in different type of cells and exploring the role of HIF-1α in inflammatory responses after ischemia is of great importance for revealing the pathogenesis and identifying new therapeutic targets for ischemic stroke. Herein, we provide a succinct overview of the current approaches targeting HIF-1α and summarize novel findings concerning HIF-1α regulation in different types of cells within neurovascular units, including neurons, endothelial cells, astrocytes, and microglia, during the different stages of ischemic stroke. The current representative translational approaches focused on neuroprotection by targeting HIF-1α are also discussed.

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.

The Expression Regulatory Network in the Lung Tissue of Tibetan Pigs Provides Insight Into Hypoxia-Sensitive Pathways in High-Altitude Hypoxia

To adapt to a low-oxygen environment, Tibetan pigs have developed a series of unique characteristics and can transport oxygen more effectively; however, the regulation of the associated processes in high-altitude animals remains elusive. We performed mRNA-seq and miRNA-seq, and we constructed coexpression regulatory networks of the lung tissues of Tibetan and Landrace pigs. HBB, AGT, COL1A2, and EPHX1 were identified as major regulators of hypoxia-induced genes that regulate blood pressure and circulation, and they were enriched in pathways related to signal transduction and angiogenesis, such as HIF-1, PI3K-Akt, mTOR, and AMPK. HBB may promote the combination of hemoglobin and oxygen as well as angiogenesis for high-altitude adaptation in Tibetan pigs. The expression of MMP2 showed a similar tendency of alveolar septum thickness among the four groups. These results indicated that MMP2 activity may lead to widening of the alveolar wall and septum, alveolar structure damage, and collapse of alveolar space with remarkable fibrosis. These findings provide a perspective on hypoxia-adaptive genes in the lungs in addition to insights into potential candidate genes in Tibetan pigs for further research in the field of high-altitude adaptation.

Oxygen Sensing and Signaling in Alzheimer's Disease: A Breathtaking Story!

Oxygen sensing and homeostasis is indispensable for the maintenance of brain structural and functional integrity. Under low-oxygen tension, the non-diseased brain has the ability to cope with hypoxia by triggering a homeostatic response governed by the highly conserved hypoxia-inducible family (HIF) of transcription factors. With the advent of advanced neuroimaging tools, it is now recognized that cerebral hypoperfusion, and consequently hypoxia, is a consistent feature along the Alzheimer's disease (AD) continuum. Of note, the reduction in cerebral blood flow and tissue oxygenation detected during the prodromal phases of AD, drastically aggravates as disease progresses. Within this scenario a fundamental question arises: How HIF-driven homeostatic brain response to hypoxia "behaves" during the AD continuum? In this sense, the present review is aimed to critically discuss and summarize the current knowledge regarding the involvement of hypoxia and HIF signaling in the onset and progression of AD pathology. Importantly, the promises and challenges of non-pharmacological and pharmacological strategies aimed to target hypoxia will be discussed as a new "hope" to prevent and/or postpone the neurodegenerative events that occur in the AD brain.

Cellular and Molecular Effects of SARS-CoV-2 Linking Lung Infection to the Brain

In December 2019, a new viral disease emerged and quickly spread all around the world. In March 2020, the COVID-19 outbreak was classified as a global pandemic and by June 2021, the number of infected people grew to over 170 million. Along with the patients' mild-to-severe respiratory symptoms, reports on probable central nervous system (CNS) effects appeared shortly, raising concerns about the possible long-term detrimental effects on human cognition. It remains unresolved whether the neurological symptoms are caused directly by the SARS-CoV-2 infiltration in the brain, indirectly by secondary immune effects of a cytokine storm and antibody overproduction, or as a consequence of systemic hypoxia-mediated microglia activation. In severe COVID-19 cases with impaired lung capacity, hypoxia is an anticipated subsidiary event that can cause progressive and irreversible damage to neurons. To resolve this problem, intensive research is currently ongoing, which seeks to evaluate the SARS-CoV-2 virus' neuroinvasive potential and the examination of the antibody and autoantibody generation upon infection, as well as the effects of prolonged systemic hypoxia on the CNS. In this review, we summarize the current research on the possible interplay of the SARS-CoV-2 effects on the lung, especially on alveolar macrophages and direct and indirect effects on the brain, with special emphasis on microglia, as a possible culprit of neurological manifestation during COVID-19.

Autophagy in vascular dementia and natural products with autophagy regulating activity

Chronic Cerebral Hypoperfusion(CCH)-induced vascular dementia(VD) is a common neurodegenerative disease which seriously affects the patient's quality of life. Therefore, it is critical to find an effective treatment of VD. Autophagy is a natural regulated mechanism that can remove dysfunctional proteins and organelles, however, over-activation or under-activation can of autophagy can induce the apoptosis of cells. Although autophagy plays a role in the central nervous system is unquestionable, the effects of autophagy in the ischemic brain are still controversial. Some autophagy regulators have been tested, suggesting that both activation and inhibition of autophagy can improve the cognitive function. This article reviews the role of autophagy in CCH-induced VD to discuss whether autophagy has the potential to become a target for drug development and provides several potential compounds for treating vascular dementia.

Electrospun meshes intrinsically promote M2 polarization of microglia under hypoxia and offer protection from hypoxia-driven cell death

In this study, we offer new insights into the contrasting effects of electrospun fiber orientation on microglial polarization under normoxia and hypoxia, and establish for the first time, the intrinsically protective roles of electrospun meshes against hypoxia-induced microglial responses. First, resting microglia were cultured under normoxia on poly(caprolactone) fibers possessing two distinctly different fiber orientations. Matrix-guided differences in cell shape/orientation and differentially expressed Rho GTPases (RhoA, Rac1, Cdc42) were well-correlated with the randomly oriented fibers inducing a pro-inflammatory phenotype and the aligned fibers sustaining a resting phenotype. Upon subsequent hypoxia induction, both sets of meshes offered protection from hypoxia-induced damage by promoting a radical phenotypic switch and beneficially altering the M2/M1 ratio to different extents. Compared to 2D hypoxic controls, meshes significantly suppressed the expression of pro-inflammatory markers (IL-6, TNF-α) and induced drastically higher expression of anti-inflammatory (IL-4, IL-10, VEGF-189) and neuroprotective (Nrf-2) markers. Consistent with this M2 polarization, the expression of Rho GTPases was significantly lower in the mesh groups under hypoxia compared to normoxic culture. Moreover, meshes-particularly with aligned fibers-promoted higher cell viability, suppressed caspase 3/8 and LC-3 expression and promoted LAMP-1 and LAMP-2 expression, which suggested the mitigation of apoptotic/autophagic cell death via a lysosomal membrane-stabilization mechanism. Notably, all protective effects under hypoxia were observed in the absence of additional soluble cues. Our results offer promise for leveraging the intrinsic therapeutic potential of electrospun meshes in degenerative diseases where microglial dysfunction, hypoxia and inflammation are implicated.

Long noncoding RNA H19 act as a competing endogenous RNA of Let-7g to facilitate IEC-6 cell migration and proliferation via regulating EGF

Intestinal mucosal injury is one of the most significant complications of burns. In our previous study, it was found that autophagy could alleviate burn-induced intestinal injury, but the underlying mechanisms are still unclear. Irregular expression of long noncoding RNAs (lncRNAs) is present in many diseases, including burns. However, the relationship between lncRNAs and intestinal mucosal injury requires further elucidation. In this study, we established a burn mice model and detected the expression level of autophagy-related proteins. Then, H19 content after autophagy intervention was tested in vitro and in vivo. The interaction of H19 with Let-7g and that of Let-7g with epidermal growth factor (EGF) were verified by dual-luciferase reporter assays. We found that the expression of the autophagy-associated proteins LC3-II and Beclin-1 was raised in the intestinal tract of the burn mice model. Similarly, the transfection of H19 raised autophagy levels. H19 was elevated after autophagy intervention in vitro and in vivo. H19 overexpression was able to promote IEC-6 cell migration and proliferation. Let-7g was suppressed by the overexpression of H19 and the combination of Let-7g mimic was able to abolish the physiological effect of H19. Moreover, the suppression of Let-7g increased the expression of EGF protein, which heightened IEC-6 cell migration and proliferation. Besides this, dual-luciferase assays revealed that Let-7g was a direct target of H19 as well as the EGF gene. Taken together, autophagy-mediated H19 increases in mouse intestinal tract after severe burn and functions as a sponge to Let-7g to regulate EGF, which suggests that H19 serves as a potential therapeutic target and biomarker for intestinal mucosal injury after burns.

Pharmacodynamic Effects of Standard versus High Caffeine Doses in the Developing Brain of Neonatal Rats Exposed to Intermittent Hypoxia

(1) Background: Caffeine citrate, at standard doses, is effective for reducing the incidence of apnea of prematurity (AOP) and may confer neuroprotection and decrease neonatal morbidities in extremely low gestational age neonates (ELGANs) requiring oxygen therapy. We tested the hypothesis that high-dose caffeine (HiC) has no adverse effects on the neonatal brain. (2) Methods: Newborn rat pups were randomized to room air (RA), hyperoxia (Hx) or neonatal intermittent hypoxia (IH), from birth (P0) to P14 during which they received intraperitoneal injections of LoC (20 mg/kg on P0; 5 mg/kg/day on P1-P14), HiC (80 mg/kg; 20 mg/kg), or equivalent volume saline. Blood gases, histopathology, myelin and neuronal integrity, and adenosine receptor reactivity were assessed. (3) Results: Caffeine treatment in Hx influenced blood gases more than treatment in neonatal IH. Exposure to neonatal IH resulted in hemorrhage and higher brain width, particularly in layer 2 of the cerebral cortex. Both caffeine doses increased brain width in RA, but layer 2 was increased only with HiC. HiC decreased oxidative stress more effectively than LoC, and both doses reduced apoptosis biomarkers. In RA, both caffeine doses improved myelination, but the effect was abolished in Hx and neonatal IH. Similarly, both doses inhibited adenosine 1A receptor in all oxygen environments, but adenosine 2A receptor was inhibited only in RA and Hx. (4) Conclusions: Caffeine, even at high doses, when administered in normoxia, can confer neuroprotection, evidenced by reductions in oxidative stress, hypermyelination, and increased Golgi bodies. However, varying oxygen environments, such as Hx or neonatal IH, may alter and modify pharmacodynamic actions of caffeine and may even override the benefits caffeine.

Hyperbaric Oxygen Improves Cerebral Ischemia/Reperfusion Injury in Rats Probably via Inhibition of Autophagy Triggered by the Downregulation of Hypoxia-Inducing Factor-1 Alpha

Ischemic stroke, accompanied with high mortality and morbidity, may produce heavy economic burden to societies and families. Therefore, it is of great significance to explore effective therapies. Hyperbaric oxygen (HBO) is a noninvasive, nondrug treatment method that has been proved able to save ischemic penumbra by improving hypoxia, microcirculation, and metabolism and applied in various ischemic diseases. Herewith, we fully evaluated the effect of HBO on ischemic stroke and investigated its potential mechanism in the rat ischemia/reperfusion(I/R) model. Sixty Sprague-Dawley male rats were randomly divided into three groups—sham group, MCAO group, and MCAO+HBO group. In the latter two groups, the middle cerebral artery occlusion was performed (MCAO) for 2 hours, and then the occlusion was removed in order to establish the ischemic/reperfusion model. Subsequently, HBO was performed immediately after I/R (2 hours per day for 3 days). 72 hours after MCAO, the brain was dissected for our experiment. Finally, the data from three groups were analyzed by one-way analysis of variance (ANOVA) and followed by a Bonferroni test. In this article, we reported that HBO effectively reduced the infarction and edema and improved neurological functions to a certain extent. As shown by western blot analysis, HBO significantly reduced autophagy by regulating autophagy-related proteins (mTOR, p-mTOR, Atg13, LC3B II and LC3B II) in the hippocampus 72 hours after I/R, which was accompanied by inhibiting the expression of hypoxia inducible factor-1α (HIF-1α) in hippocampus. The results suggest that HBO may improve cerebral I/R injury, possibly via inhibiting HIF-1α, the upstream molecule of autophagy, and therefore, subsequently inhibiting autophagy in the rat model of ischemic stroke.

αB-Crystallin Alleviates Endotoxin-Induced Retinal Inflammation and Inhibits Microglial Activation and Autophagy

αB-Crystallin, a member of the small heat shock protein (sHSP) family, plays an immunomodulatory and neuroprotective role by inhibiting microglial activation in several diseases. However, its effect on endotoxin-induced uveitis (EIU) is unclear. Autophagy may be associated with microglial activation, and αB-crystallin is involved in the regulation of autophagy in some cells. The role of αB-crystallin in microglial autophagy is unknown. This study aimed to explore the role of αB-crystallin on retinal microglial autophagy, microglial activation, and neuroinflammation in both cultured BV2 cells and the EIU mouse model. Our results show that αB-crystallin reduced the release of typical proinflammatory cytokines at both the mRNA and protein level, inhibited microglial activation in morphology, and suppressed the expression of autophagy-related molecules and the number of autophagolysosomes in vitro. In the EIU mouse model, αB-crystallin treatment alleviated the release of ocular inflammatory cytokines and the representative signs of inflammation, reduced the apoptosis of ganglion cells, and rescued retinal inflammatory structural and functional damage, as evaluated by optical coherence tomographic and electroretinography. Taken together, these results indicate that αB-crystallin inhibits the activation of microglia and supresses microglial autophagy, ultimately reducing endotoxin-induced neuroinflammation. In conclusion, αB-crystallin provides a novel and promising option for affecting microglial autophagy and alleviating symptoms of ocular inflammatory diseases.

Role of Hypoxia Inducible Factor-1α in Alzheimer's Disease

Amyloid-β (Aβ) peptides and hyperphosphorylated tau protein are the most important pathological markers of Alzheimer's disease (AD). Neuroinflammation and oxidative stress are also involved in the development and pathological mechanism of AD. Hypoxia inducible factor-1α (HIF-1α) is a transcriptional factor responsible for cellular and tissue adaption to low oxygen tension. Emerging evidence has revealed HIF-1α as a potential medicinal target for neurodegenerative diseases. On the one hand, HIF-1α increases AβPP processing and Aβ generation by promoting β/γ-secretases and suppressing α-secretases, inactivates microglia and reduces their activity, contributes to microglia death and neuroinflammation, which promotes AD pathogenesis. On the other hand, HIF-1α could resist the toxic effect of Aβ, inhibits tau hyperphosphorylation and promotes microglial activation. In summary, this review focuses on the potential complex roles and the future perspectives of HIF-1α in AD, in order to provide references for seeking new drug targets and treatment methods for AD.

Prevalence of obstructive sleep apnea in female patients with fibromyalgia

Objectives:

To determine the prevalence of obstructive sleep apnea in female patients with fibromyalgia (FM) presenting to physical therapy outpatient clinics.

Methods:

The 36-item short form health survey (SF-36) questionnaire, Berlin test, and epworth sleepiness scale were administered, along with a polysomnography to 38 female patients. This cross-sectional study comprised diagnosed with FM according to the diagnostic criteria of the American College of Rheumatology, between March 2017 and August 2019, at the Faculty of Medicine Hospital, Çanakkale Onsekiz Mart University, Çanakkale, Turkey.

Results:

Of the participants, 65.9% were found to have obstructive sleep apnea (OSA). Patients with OSA were older and had a higher disease activity score for FM. A strong positive correlation was identified between the apnea-hypopnea index (AHI) and the FA disease activity score. A negative correlation was found between AHI and the subscales of SF-36.

Conclusion:

A clinical assessment of female patients with FM requires a multidisciplinary approach, and patients with excessive daytime sleepiness in particular are recommended to undergo polysomnography. The authors believe that the early detection and treatment of accompanying OSA will contribute not only to the quality of life, but also to the survival of patients with FM.

Epidermal growth factor regulation by autophagy-mediated lncRNA H19 in murine intestinal tract after severe burn

To investigate the regulation of epidermal growth factor (EGF) by autophagy‐mediated long non‐coding RNA (lncRNA) H19 in the intestinal tracts of severely burned mice. C57BL/6J mice received third‐degree burns to 30% of the total body surface area. Rapamycin and 3‐methyladenine (3‐MA) were used to activate and inhibit autophagy, and the changes in LC3 and Beclin1 levels were assessed by Western blotting. The effect of autophagy on lncRNA H19 was detected by qRT‐PCR. Adenovirus‐mediated overexpression of lncRNA H19 in IEC‐6 cells was used to assess the effects of lncRNA H19 on EGF and let‐7g via bioinformatics analysis, Western blotting and qRT‐PCR. let‐7g mimic/inhibitor was used to overexpress/inhibit let‐7g, and qRT‐PCR and Western blotting were used to detect the effects of let‐7g on EGF. The expression levels of LC3‐II, Beclin1 and lncRNA H19 were increased in intestinal tissues and IEC‐6 cells after rapamycin treatment but were reversed after 3‐MA treatment. LC3‐II, Beclin1 and lncRNA H19 levels increased in intestinal tissues after the burn, and these increases were more significant after rapamycin treatment but decreased after 3‐MA treatment. The lncRNA H19 overexpression in IEC‐6 cells resulted in increased and decreased expression levels of EGF and let‐7g, respectively. Furthermore, overexpression and inhibition of let‐7g resulted in decreased and increased expression of EGF, respectively. Taken together, intestinal autophagy is activated after a serious burn, which can increase the transcription level of lncRNA H19. lncRNA H19 may regulate the repair of EGF via let‐7g following intestinal mucosa injury after a burn.

Unfolded protein response (UPR) integrated signaling networks determine cell fate during hypoxia

During hypoxic conditions, cells undergo critical adaptive responses that include the up-regulation of hypoxia-inducible proteins (HIFs) and the induction of the unfolded protein response (UPR). While their induced signaling pathways have many distinct targets, there are some important connections as well. Despite the extensive studies on both of these signaling pathways, the exact mechanisms involved that determine survival versus apoptosis remain largely unexplained and therefore beyond therapeutic control. Here we discuss the complex relationship between the HIF and UPR signaling pathways and the importance of understanding how these pathways differ between normal and cancer cell models.

Autophagy and inflammation in ischemic stroke

Appropriate autophagy has protective effects on ischemic nerve tissue, while excessive autophagy may cause cell death. The inflammatory response plays an important role in the survival of nerve cells and the recovery of neural tissue after ischemia. Many studies have found an interaction between autophagy and inflammation in the pathogenesis of ischemic stroke. This study outlines recent advances regarding the role of autophagy in the post-stroke inflammatory response as follows. (1) Autophagy inhibits inflammatory responses caused by ischemic stimulation through mTOR, the AMPK pathway, and inhibition of inflammasome activation. (2) Activation of inflammation triggers the formation of autophagosomes, and the upregulation of autophagy levels is marked by a significant increase in the autophagy-forming markers LC3-II and Beclin-1. Lipopolysaccharide stimulates microglia and inhibits ULK1 activity by direct phosphorylation of p38 MAPK, reducing the flux and autophagy level, thereby inducing inflammatory activity. (3) By blocking the activation of autophagy, the activation of inflammasomes can alleviate cerebral ischemic injury. Autophagy can also regulate the phenotypic alternation of microglia through the nuclear factor-κB pathway, which is beneficial to the recovery of neural tissue after ischemia. Studies have shown that some drugs such as resveratrol can exert neuroprotective effects by regulating the autophagy-inflammatory pathway. These studies suggest that the autophagy-inflammatory pathway may provide a new direction for the treatment of ischemic stroke.

Evidence of Hypoxic Glial Cells in a Model of Ocular Hypertension

Purpose

Reoxygenation after hypoxia can increase reactive oxygen species and upregulate autophagy. We determined, for the first time, the impact of elevated IOP on hypoxia induction, superoxide accumulation, and autophagy in a bead model of glaucoma.

Method

Ocular hypertension was achieved with magnetic bead injection into the anterior chamber. Before mice were killed, they were injected with pimonidazole for hypoxia detection and dihydroethidium (DHE) for superoxide detection. Total retinal ganglion cells (RGCs) and optic nerve (ON) axons were quantified, total glutathione (GSH) was measured, and retinal and ON protein and mRNA were analyzed for hypoxia (Hif-1α and Hif-2α), autophagy (LC3 and p62), and SOD2.

Results

With IOP elevation (P < 0.0001), the retina showed significantly (P < 0.001) decreased GSH compared with control, and a significant decrease (P < 0.01) in RGC density compared with control. Pimonidazole-positive Müller glia, microglia, astrocytes, and RGCs were present in the retinas after 4 weeks of ocular hypertension but absent in both the control and after only 2 weeks of ocular hypertension. The ON showed significant axon degeneration (P < 0.0001). The mean intensity of DHE in the ganglion cell layer and ON significantly increased (P < 0.0001). The ratio of LC3-II to LC3-I revealed a significant increase (P < 0.05) in autophagic activity in hypertensive retinas compared with control.

Conclusions

We report a novel observation of hypoxia and a significant decrease in GSH, likely contributing to superoxide accumulation, in the retinas of ocular hypertensive mice. The significant increase in the ratio of LC3-II to LC3-I suggests autophagy induction.

Proteostasis During Cerebral Ischemia

Cerebral ischemia is a complex pathology involving a cascade of cellular mechanisms, which deregulate proteostasis and lead to neuronal death. Proteostasis refers to the equilibrium between protein synthesis, folding, transport, and protein degradation. Within the brain proteostasis plays key roles in learning and memory by controlling protein synthesis and degradation. Two important pathways are implicated in the regulation of proteostasis: the unfolded protein response (UPR) and macroautophagy (called hereafter autophagy). Both are necessary for cell survival, however, their over-activation in duration or intensity can lead to cell death. Moreover, UPR and autophagy can activate and potentiate each other to worsen the issue of cerebral ischemia. A better understanding of autophagy and ER stress will allow the development of therapeutic strategies for stroke, both at the acute phase and during recovery. This review summarizes the latest therapeutic advances implicating ER stress or autophagy in cerebral ischemia. We argue that the processes governing proteostasis should be considered together in stroke, rather than focusing either on ER stress or autophagy in isolation.

HMG-CoA Reductase Inhibitors Attenuate Neuronal Damage by Suppressing Oxygen Glucose Deprivation-Induced Activated Microglial Cells

Ischemic stroke is usually followed by inflammatory responses mediated by microglia. However, the effect of statins on directly preventing posthypoxia microglia inflammatory factors to prevent injury to surrounding healthy neurons is unclear. Atorvastatin and rosuvastatin, which have different physical properties regarding their lipid and water solubility, are the most common HMG-CoA reductase inhibitors (statins) and might directly block posthypoxia microglia inflammatory factors to prevent injury to surrounding neurons. Neuronal damage and microglial activation of the peri-infarct areas were investigated by Western blotting and immunofluorescence after 24 hours in a middle cerebral artery occlusion (MCAO) rat model. The decrease in neurons was in accordance with the increase in microglia, which could be reversed by both atorvastatin and rosuvastatin. The effects of statins on blocking secretions from posthypoxia microglia and reducing the secondary damage to surrounding normal neurons were studied in a coculture system in vitro. BV2 microglia were cultured under oxygen glucose deprivation (OGD) for 3 hours and then cocultured following reperfusion for 24 hours in the upper wells of transwell plates with primary neurons being cultured in the bottom wells. Inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and cyclooxygenase-2 (COX2), which are activated by the nuclear factor-kappa B (NF-κB) signaling pathway in OGD-induced BV2 microglia, promoted decreased release of the anti-inflammatory cytokine IL-10 and apoptosis of neurons in the coculture systems according to ELISA and Western blotting. However, pretreatment with atorvastatin or rosuvastatin significantly reduced neuronal death, synaptic injury, and amyloid-beta (Aβ) accumulation, which might lead to increased low-density lipoprotein receptors (LDLRs) in BV2 microglia. We concluded that the proinflammatory mediators released from postischemia damage could cause damage to surrounding normal neurons, while HMG-CoA reductase inhibitors prevented neuronal apoptosis and synaptic injury by inactivating microglia through blocking the NF-κB signaling pathway.

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.

Innate Immunity Cells and the Neurovascular Unit

Recent studies have clarified many still unknown aspects related to innate immunity and the blood-brain barrier relationship. They have also confirmed the close links between effector immune system cells, such as granulocytes, macrophages, microglia, natural killer cells and mast cells, and barrier functionality. The latter, in turn, is able to influence not only the entry of the cells of the immune system into the nervous tissue, but also their own activation. Interestingly, these two components and their interactions play a role of great importance not only in infectious diseases, but in almost all the pathologies of the central nervous system. In this paper, we review the main aspects in the field of vascular diseases (cerebral ischemia), of primitive and secondary neoplasms of Central Nervous System CNS, of CNS infectious diseases, of most common neurodegenerative diseases, in epilepsy and in demyelinating diseases (multiple sclerosis). Neuroinflammation phenomena are constantly present in all diseases; in every different pathological state, a variety of innate immunity cells responds to specific stimuli, differentiating their action, which can influence the blood-brain barrier permeability. This, in turn, undergoes anatomical and functional modifications, allowing the stabilization or the progression of the pathological processes.

Microglial TLR4-dependent autophagy induces ischemic white matter damage via STAT1/6 pathway

Rationale: Ischemic white matter damage frequently results in myelin loss, accompanied with microglial activation. We previously found that directing microglia towards an anti-inflammatory phenotype provided a beneficial microenvironment and helped maintain white matter integrity during chronic cerebral hypoperfusion. However, the molecular mechanisms underlying microglial polarization remain elusive.

Methods: Hypoperfusion induced white matter damage mice model and lipopolysaccharide (LPS) induced primary cultured microglia were established. Autophagy activation in microglia was detected both in vivo and in vitro by immunofluorescence, Western blot and electron microscopy. Autophagy inhibitors/agonist were administrated to investigate the role of autophagic process in modulating microglial phenotypes. Quantitative real time-polymerase chain reaction and Western blot were carried out to investigate the possible pathway.

Results: We identified rapid accumulation of autophagosomes in primary cultured microglia exposed to LPS and within activated microglia during white matter ischemic damage. Autophagy inhibitors switched microglial function from pro-inflammatory to anti-inflammatory phenotype. Furthermore, we found TLR4, one of the major receptors binding LPS, was most highly expressed on microglia in corpus callosum during white matter ischemic damage, and TLR4 deficiency could mimic the phenomenon in microglial functional transformation, and exhibit a protective activity in chronic cerebral hypoperfusion. Whereas, the anti-inflammatory phenotype of microglia in TLR4 deficiency group was largely abolished by the activation of autophagic process. Finally, our transcriptional analysis confirmed that the up-regulation of STAT1 and down-regulation of STAT6 in microglia exposure to LPS could be reversed by autophagy inhibition.

Conclusion: These results indicated that TLR4-dependent autophagy regulates microglial polarization and induces ischemic white matter damage via STAT1/6 pathway.

Histone methyl-transferases and demethylases in the autophagy regulatory network: the emerging role of KDM1A/LSD1 demethylase

Macroautophagy/autophagy is a physiological mechanism that is essential for the maintenance of cellular homeostasis and stress adaptation. Defective autophagy is associated with many human diseases, including cancer and neurodegenerative disorders. The emerging implication of epigenetic events in the control of the autophagic process opens new avenues of investigation and offers the opportunity to develop novel therapeutic strategies in diseases associated with dysfunctional autophagy-lysosomal pathways. Accumulating evidence reveals that several methyltransferases and demethylases are essential regulators of autophagy, and recent studies have led to the identification of the lysine demethylase KDM1A/LSD1 as a promising drug target. KDM1A/LSD1 modulates autophagy at multiple levels, participating in the transcriptional control of several downstream effectors. This review summarizes our current understanding of the role of KDM1A/LSD1 in the autophagy regulatory network.

ROS is the major player in regulating altered autophagy and lifespan in sin-3 mutants of C. elegans

SIN3, a transcriptional corepressor has been implicated in varied functions both as transcription activator and repressor. Recent studies associated Sin3 with the macroautophagic/autophagic process as a negative regulator of Atg8 and Atg32. Though the role of SIN3 in autophagy is being explored, little is known about the overall effect of SIN3 deletion on the survival of an organism. In this study using a Caenorhabditis elegans sin-3(tm1279);him-5(e1490) strain, we demonstrate that under in vivo conditions SIN-3 differentially modulates autophagy and lifespan. We provide evidence that the enhanced autophagy and decreased lifespan observed in sin-3 deletion mutants is dependent on ROS and intracellular oxidative stress. Inability of the mutant worms to maintain redox balance along with dysregulation of enzymatic antioxidants, depletion of GSH and NADP reserves and elevation of ROS markers compromises the longevity of the worms. It is possible that the enhanced autophagic process observed in sin-3(tm1279);him-5(e1490) worms is required to compensate for oxidative stress generated in these worms.

ABBREVIATIONS

cat: catalase; DCFDA: 2',7'-dichlorodihydrofluoroscein diacetate; GSH: reduced glutathione; GSSG: oxidized glutathione; H2O2: hydrogen peroxide; HDAC: Histone deacetylase; HID: HDAC interacting domain; him-5: high incidence of males; HLH-30: Helix Loop Helix-30; HNE: 4-hydroxyl-2-noneal; LIPL: LIPase Like; MDA: malondialdehyde; NGM: nematode growth medium; PAH: paired amphipathic α-helix; PE: phosphatidylethanolamine; RFU: relative fluorescence unit; ROS: reactive oxygen species; sin-3/SIN3: yeast Switch Independent; SOD: superoxide dismutase; NADP: nicotinamide adenine dinucleotide phosphate; SQST-1: SeQueSTosome related-1; ATG: AuTophaGy related.

Ulk1/FUNDC1 Prevents Nerve Cells from Hypoxia-Induced Apoptosis by Promoting Cell Autophagy

Cell autophagy and cell apoptosis are both observed in the process of hypoxia-induced ischemic cerebral infarction (ICI). Unc-51 like autophagy activating kinase 1 (Ulk1) and FUN14 Domain-containing Protein 1 (FUNDC1) are both involved in the regulation of cell autophagy. This study aimed to investigate the regulatory effects of Ulk1 and FUNDC1 on hypoxia-induced nerve cell autophagy and apoptosis. Cell viability was measured using cell counting kit-8 (CCK-8) assay. Cell apoptosis was detected using Annexin V-PE/7-ADD staining assay. qRT-PCR was used to quantify the mRNA levels of Ulk1 and FUNDC1 in PC-12 cells. Cell transfection was performed to up-regulate the expression of Ulk1. 3-Methyladenine (3-MA) was used as autophagy inhibitor and rapamycin was used as autophagy activator in our experiments. SP600125 was used as c-Jun N-terminal kinase (JNK) inhibitor. Western blotting was performed to analyze the expression levels of key factors that are related to cell autophagy, apoptosis and JNK pathway. We found that hypoxia simultaneously induced apoptosis and autophagy of PC-12 cells. The activation of Ulk1 and FUNDC1 were also found in PC-12 cells after hypoxia induction. Overexpression of Ulk1 promoted the activation of FUNDC1 and prevented PC-12 cells from hypoxia-induced apoptosis. Suppression of Ulk1 had opposite effects. Furthermore, we also found that JNK pathway participated in the effects of Ulk1 overexpression on PC-12 cell apoptosis reduction. To conclude, Ulk1/FUNDC1 played critical regulatory roles in hypoxia-induced nerve cell autophagy and apoptosis. Overexpression of Ulk1 prevented nerve cells from hypoxia-induced apoptosis by promoting cell autophagy.

Role of Hypoxia-Inducible Factors 1α (HIF1α) in SH-SY5Y Cell Autophagy Induced by Oxygen-Glucose Deprivation

Background

HIF-1α plays an important role in hypoxia-ischemia brain damage. Accumulating evidences demonstrates that HIF-1α can contribute to cell autophagy. Oxygen-glucose deprivation (OGD) is a commonly used ischemic model in vitro. Our study was performed to investigate the influences of HIF-1α on autophagy in SH-SY5Y cells under OGD treatment.

Material/Methods

An OGD model was constructed in SH-SY5Y cells. PI method and MTT assay were used to test cell death and viability, respectively. Western blot assay was used to estimate the protein levels of HIF-1α and LC3. Quantitative GFP-LC3 light microscopy autophagy assay was performed for SH-SY5Y cells. 2ME2 and siRNA-HIF-1α were applied to investigate the effects of HIF-1α-knockdown on LC3 expression. Additionally, 3-MA (autophagy inhibitor) and autophagy inducer rapamycin (Rapa) were used to investigate the effects of autophagy on cell survival under OGD condition.

Results

Under OGD, the apoptosis of SH-SY5Ycells was increased while cell viability rate was decreased. The expression of HIF-1α was increased along with the advancement of OGD treatment and achieved the highest level at 24 h. However, inhibiting HIF-1α expression decreased the cell apoptosis and increased cell viability. LC3-II expression was gradually increased with the duration of OGD condition and knockdown of HIF-1α resulted in decreased expression of LC3. Inhibiting autophagy significantly enhanced the viability and reduced the apoptosis of SH-SY5Y cells, while enhancing autophagy showed the opposite effects.

Conclusions

Enhanced expression of HIF-1α may be related to autophagy activation in SH-SY5Y cells, thus contributing to ischemic/hypoxic brain damage.

Antiapoptotic Effect of Gene Therapy with Recombinant Adenovirus Vector Containing Hypoxia-inducible Factor-1α after Cerebral Ischemia and Reperfusion in Rats

Background:

Mounting evidence has demonstrated that hypoxia-inducible factor-1α (HIF-1α) could attenuate brain injuries after cerebral ischemia and reperfusion (CIR). However, few reports have addressed the therapeutic efficacies of a recombinant adenovirus vector containing HIF-1α (AdHIF-1α) gene after ischemia and reperfusion. The aim of this study was to examine the antiapoptotic and neuroprotective effects of AdHIF-1α gene for cerebral injuries after ischemia and reperfusion in rats.

Methods:

From February to December 2016, male Sprague-Dawley rats were randomly divided into normal, sham, CIR, AdHIF-1α, and recombinant adenovirus (Ad) groups. Middle cerebral artery occlusion model was established by Longa's method and reperfusion resumed at 2 h postocclusion. AdHIF-1α solution, Ad solution, and phosphate-buffered saline were injected into the right lateral ventricle of rats in AdHIF-1α, Ad, and CIR groups. Brain tissue sections were observed under fluorescent microscope to confirm the definite expression of recombinant adenovirus in Ad and AdHIF-1α groups. The expressions of HIF-1α protein were analyzed by immunohistochemical staining at 6 h, 24 h, and 72 h postreperfusion. Brain water content and neurological deficit scores were evaluated at 6 h, 24 h, and 72 h postreperfusion. Pathological brain injuries were examined after hematoxylin and eosin stain and nerve cell apoptosis was measured after terminal-deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) stain at 72 h postreperfusion. Comparisons were conducted with one-way analysis of variance by post hoc Scheffe's test among different experimental groups.

Results:

Green fluorescent protein was successfully expressed in brain tissue of Ad and AdHIF-1α groups from 24 h to 21 days postinjection. As detected by immunohistochemical staining, the expressions of HIF-1α protein were obviously enhanced in AdHIF-1α group than those in CIR and Ad groups at 24 h and 72 h postreperfusion, respectively. There were significant reductions of brain water content (78.83% ± 0.34% vs. 83.21% ± 0.50% and 83.35% ± 0.32%; 84.13% ± 0.24% vs. 89.76% ± 0.34% and 89.70% ± 0.18%; respectively; all P < 0.05) and neurological deficit scores (2.90 ± 0.74 vs. 3.50 ± 0.52 and 3.60 ± 0.53 at 24 h; 2.40 ± 0.84 vs. 3.60 ± 0.52 and 3.50 ± 0.53 at 72 h; respectively; all P < 0.05) in AdHIF-1α group versus CIR and Ad groups at 24 h and 72 h postreperfusion, respectively. The pathologic changes of AdHIF-1α group were milder than those in CIR and Ad groups at 72 h postreperfusion. The percentage of TUNEL-positive cells in cerebral subcortex decreased significantly in AdHIF-1α group versus CIR and Ad groups at 72 h postreperfusion (P < 0.05).

Conclusion:

AdHIF-1α has an obvious neuroprotective effect on ischemia and reperfusion in rat brains possibly through inhibiting the apoptosis of nerve cells.

Cell Death Mechanisms in Stroke and Novel Molecular and Cellular Treatment Options

As a result of ischemia or hemorrhage, blood supply to neurons is disrupted which subsequently promotes a cascade of pathophysiological responses resulting in cell loss. Many mechanisms are involved solely or in combination in this disorder including excitotoxicity, mitochondrial death pathways, and the release of free radicals, protein misfolding, apoptosis, necrosis, autophagy and inflammation. Besides neuronal cell loss, damage to and loss of astrocytes as well as injury to white matter contributes also to cerebral injury. The core problem in stroke is the loss of neuronal cells which makes recovery difficult or even not possible in the late states. Acute treatment options that can be applied for stroke are mainly targeting re-establishment of blood flow and hence, their use is limited due to the effective time window of thrombolytic agents. However, if the acute time window is exceeded, neuronal loss starts due to the activation of cell death pathways. This review will explore the most updated cellular death mechanisms leading to neuronal loss in stroke. Ischemic and hemorrhagic stroke as well as subarachnoid hemorrhage will be debated in the light of cell death mechanisms and possible novel molecular and cellular treatment options will be discussed.

LncRNA UCA1 attenuates autophagy-dependent cell death through blocking autophagic flux under arsenic stress

Arsenic (As) is a naturally toxin which exists ubiquitously in foods and various environment media, incurring diverse toxicities and health problems. Previous studies have shown that oxidative stress, genotoxic damage and pro-apoptotic pathways are ascribed to As-associated detrimental effects. Meanwhile, epigenetic regulations (such as miRNAs and histone modifications) were also reported to contribute to As-induced adverse effects. Nonetheless, whether long non-coding RNAs (LncRNAs) are indispensable for the regulation of As-induced biological outcomes are nearly unknown. In this study, we identified that a lncRNA UCA1 was markedly induced by As treatment in human hepatocytes. Functional assessments revealed that UCA1 played a critical role in protecting hepatocytes from As-induced autophagy inhibition. Furthermore, through RNA-seq assay, oxidative stress induced growth inhibitor 1 (OSGIN1) was uncovered to be the most responsive target downstream of UCA1, and miR-184 acted as an intermediate for the regulation of UCA1 on the level of OSGIN1 through a competing endogenous RNAs (ceRNAs) mechanism. Further mechanistic investigations demonstrated that UCA1/OSGIN1 signaling contributed to As-induced autophagic flux blockage through activating mTOR/p70S6 K cascade, resulting in compromised cell death. Collectively, our study deciphered a lncRNA-dictated molecular mechanism responsible for As toxicity: UCA1 leads a protective role against As-induced cell death through blocking autophagic flux.

Protective effect of autophagy in neural ischemia and hypoxia: Negative regulation of the Wnt/β-catenin pathway

Autophagy is a highly conserved process of self-digestion to promote cell survival in response to nutrient starvation and other metabolic stresses. However, whether ischemic-hypoxic (IH) injury-induced autophagy acts as a neuroprotective mechanism or leads to neuroinjury is a subject of debate. It is known that autophagy is regulated by signaling pathways, including the mammalian target of rapamycin pathway. However, in neural IH injury, whether other signaling pathways are involved in the regulation of autophagy remains to be fully elucidated. In the present study, using the autophagy agonist (rampycin), autophagy antagonist [3-methyl adenine (3-MA)] and lysosome antagonist (MHY1485), autophagy was intervened with at oxygen-glucose deprivation (OGD) 6 h, in order to elucidate the regulatory mechanisms of autophagy. Using immunocytochemistry and western blot analysis, the expression levels of stress-related proteins, such as hypoxia-inducible factor-1α (HIF-1α) (a key regulator in hypoxia) and cyclooxygenase 2 (COX2; inflammatory indicator), were analyzed. In addition, the upstream proteins (Wnt1 and Wnt3a), downstream proteins (Dvl2, β-catenin) and target proteins (C-myc and cyclin D) in the Wnt/β-catenin signaling pathway were examined by immunocytochemistry and western blot analysis. The present study revealed that autophagy was activated with the upregulation of autophagic flux in IH injury; it was demonstrated that autophagy had a protective role in IH injury. The Wnt/β-catenin pathway was involved in IH injury regulation, and the upstream proteins in the Wnt/β-catenin signaling pathway were upregulated, whereas downstream proteins were downregulated by the activity of autophagy accordingly.

Autophagy, Endoplasmic Reticulum Stress and the Unfolded Protein Response in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke that is followed by primary and secondary brain injury. As a result of the injury, cell metabolism is disrupted and a series of stress responses are activated, such as endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), leading to the re-establishment of cell homeostasis or cell death. As an important mechanism of cell homeostasis, autophagy has been widely studied, and the associations between autophagy, ER stress, and the UPR have also been demonstrated. Whether these mechanisms are beneficial or detrimental remains a matter of controversy, but there is no doubt as to their vital functions. An understanding of the mechanisms of injury and recovery after ICH is crucial to develop therapeutic strategies. In this review, we summarize the related studies and highlight the roles of autophagy, ER stress, and the UPR in disease, especially in ICH. We also provide an overview of therapeutic approaches that target autophagy, and we discuss the prospects for modulating autophagy, ER stress, and UPR mechanisms in ICH therapy.