Brief exposure to hypoxia induces bFGF mRNA and protein and protects rat cortical neurons from prolonged hypoxic stress

SARS-CoV-2 Infection to Premature Neuronal Aging and Neurodegenerative Diseases: Is there any Connection with Hypoxia?

The pandemic of coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, has become a global concern as it leads to a spectrum of mild to severe symptoms and increases death tolls around the world. Severe COVID-19 results in acute respiratory distress syndrome, hypoxia, and multi- organ dysfunction. However, the long-term effects of post-COVID-19 infection are still unknown. Based on the emerging evidence, there is a high possibility that COVID-19 infection accelerates premature neuronal aging and increases the risk of age-related neurodegenerative diseases in mild to severely infected patients during the post-COVID period. Several studies correlate COVID-19 infection with neuronal effects, though the mechanism through which they contribute to the aggravation of neuroinflammation and neurodegeneration is still under investigation. SARS-CoV-2 predominantly targets pulmonary tissues and interferes with gas exchange, leading to systemic hypoxia. The neurons in the brain require a constant supply of oxygen for their proper functioning, suggesting that they are more vulnerable to any alteration in oxygen saturation level that results in neuronal injury with or without neuroinflammation. We hypothesize that hypoxia is one of the major clinical manifestations of severe SARS-CoV-2 infection; it directly or indirectly contributes to premature neuronal aging, neuroinflammation, and neurodegeneration by altering the expression of various genes responsible for the survival of the cells. This review focuses on the interplay between COVID-19 infection, hypoxia, premature neuronal aging, and neurodegenerative diseases and provides a novel insight into the molecular mechanisms of neurodegeneration.

Cellular Mechanisms of FGF-Stimulated Tissue Repair

Growth factors belonging to the FGF family play important roles in tissue and organ repair after trauma. In this review, I discuss the regulation by FGFs of the aspects of cellular behavior important for reparative processes. In particular, I focus on the FGF-dependent regulation of cell proliferation, cell stemness, de-differentiation, inflammation, angiogenesis, cell senescence, cell death, and the production of proteases. In addition, I review the available literature on the enhancement of FGF expression and secretion in damaged tissues resulting in the increased FGF supply required for tissue repair.

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

Possible role of proteases in preconditioning of brain cells to pathological conditions

Preconditioning (PC) is one of the most effective strategies to reduce the severity of cell damage, in particular of nervous tissue cells. Although PC mechanisms are studied insufficiently, it is clear that proteases are involved in them, but their role has yet been not studied in detail. In this work, some mechanisms of a potential recruiting of proteases in PC are considered. Our attention is mainly focused on the protease families of caspases and cathepsins and on protease receptors. We present evidence that just these proteins are involved in the PC of brain cells. A hypothesis is proposed that secreted cathepsin B is involved in the realization of PC through activation of PAR2 receptor.

The effects of fibroblast growth factor-2 and pluripotent astrocytic stem cells on cognitive function in a rat model of neonatal hypoxic-ischemic brain injury

OBJECTIVE

This study aimed to determine the effect of pluripotent astrocytic stem cells (PASCs) and fibroblast growth factor-2 (FGF-2) on cognitive function in neonatal rats with hypoxic-ischemic brain injury (HIBI).

METHODS

The study was performed on 7-d-old rats that were randomly divided into four groups. All rats, except those in the sham group, were kept in a hypoxic chamber containing 8% oxygen for 2 h after the ligation of the right carotid artery. Next, 5 d after HIBI was induced, PASCs were administered to the motor cortex, and FGF-2 was administered intraperitoneally to group AF; PASCs were administered to the motor cortex, and salt solution buffered with phosphate was administered intraperitoneally to group A; and fresh cell culture solution (medium) was administered to group M. Immunofluorescence was used to localize the administered PASCs in the brains of rats from groups A and AF. The Morris water maze tank (MWM) test was performed to assess the rats' cognitive functions at week 12. The rats that were administered PASCs were observed for the development of neoplasms and autopsies were performed after 30 months.

RESULTS

PASCs migrated to damaged brain regions surrounding the hippocampus in groups A and AF. The mean platform finding time (PFT) significantly decreased over time in each group on day 1-4 of MWM testing (p < 0.001). On day 2-4, the mean PFT was shortest in group S followed by group AF. In group A, the PFT was significantly longer than in group S on day 3-4 (p = 0.01 and 0.007, respectively). On day 5 of the MWM test, the time spent in the eastern quadrant (which previously contained the platform) was longest in group S followed by groups AF, A, and M; however, the differences between groups were not significant (p = 0.51). After 30 months, none of the rats in groups A or AF had benign or malignant neoplasms.

CONCLUSIONS

Following the administration of PASCs in rats with experimentally induced HIBI, PASCs migrated to the injured brain regions; however, treatment with PASCs did not have a positive effect on cognitive function. The administration of FGF-2 together with PASCs resulted in positive cognitive results, although not at the level of significance.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Efficacious and clinically relevant conditioned medium of human adipose-derived stem cells for therapeutic angiogenesis

Using stem cell-conditioned medium (CM) might be a viable alternative to stem cell transplantation, which is often hampered by low grafting efficiency and potential tumorigenesis, but the concentrations of angiogenic growth factors in CM are too low for therapeutic use and some components of the medium are not for human use. We used three-dimensional (3D) spheroid culture of human adipose-derived stem cells (ADSCs) with clinically relevant medium composed of amino acids, vitamins, glucose, and human serum to produce clinically relevant CM containing angiogenic and/or antiapoptotic factors such as vascular endothelial cell growth factor, fibroblast growth factor 2, hepatocyte growth factor, and chemokine (C-X-C motif) ligand 12. The concentrations of these factors were 23- to 27-fold higher than that in CM produced by conventional monolayer culture. Compared with injection of either monolayer culture CM or human ADSC, injection of spheroid culture CM to an ischemic region in mice significantly enhanced endothelial cell growth, CD34(+)/PTPRC(-) (endothelial progenitor) cell mobilization from bone marrow, and bone marrow cell homing to the ischemic region, resulting in improved blood vessel density, limb salvage, and blood perfusion in a mouse hindlimb ischemia model. The stem cell CM developed in this study will likely be an effective alternative to conventional stem cell transplantation therapy.

Low ambient o(2) enhances ureteric bud branching in vitro

Hypoxia exists widely in developing embryos where it may regulate blood vessel formation. VEGF and FGF2 produced in developing renal primordia (metanephroi) stimulate microvessel formation from embryonic thoracic aorta cultured under hypoxic conditions (HC) relative to room air (RA). The aim of the present study was to provide insight into the participation of hypoxia in a process that occurs concomitant with metanephros vascularization in vivo, ureteric bud (UB) branching. To this end, the arborization of the UB and growth of metanephroi were measured in metanephroi grown in serum-free organ culture for two days under RA or HC. When metanephroi were cultured under HC the arborization of UB was stimulated relative to RA. In the presence of anti-VEGF neutralizing antibody (alphamVEGF), or anti-FGF2 neutralizing antibody (alphahFGF2) UB branching was inhibited under both RA and HC. When both alphamVEGF and alphahFGF2 were added, the inhibition was enhanced. Addition of exogenous VEGF or FGF2 to cultures stimulated UB branching under RA and HC and addition of both stimulated it further. These findings provide evidence for roles of hypoxia and metanephric VEGF and FGF2, as regulators not only for vascularization but also for UB bud branching during renal organogenesis.

Transplantation of cord blood mesenchymal stem cells as spheroids enhances vascularization

Despite promising results from the therapeutic use of stem cells for treating ischemic diseases, the poor survival of cells transplanted into ischemic regions is one of the major problems that undermine the efficacy of stem cell therapy. Cord blood mononuclear cells (CBMNCs) are an alternative source of mesenchymal stem cells (MSCs) without disadvantages, such as the painful and invasive harvesting procedure, of MSCs derived from bone marrow or adipose tissue. In the present study, we investigated whether the angiogenic efficacy of cord blood mesenchymal stem cells (CBMSCs) can be enhanced by grafting as spheroids in a mouse hindlimb ischemia model. Human CBMSC (hCBMSC) spheroids were prepared by using the hanging-drop method. Mouse hindlimb ischemia was induced by excising the femoral artery and its branches. After surgery, the animals were divided into no-treatment, dissociated hCBMSC, and spheroid hCBMSC groups (n=8 per group) and received corresponding hCBMSC treatments. After surgery, the ischemic hindlimbs were monitored for 4 weeks, and then, the ischemic hindlimb muscles were harvested for histological analysis. Apoptotic signaling, angiogenesis-related signal pathways, and blood vessel formation were investigated in vitro and/or in vivo. The transplantation of hCBMSCs as spheroids into mouse ischemic hindlimbs significantly improved the survival of the transplanted cells by suppressing apoptotic signaling while activating antiapoptotic signaling. Furthermore, the transplantation of hCBMSCs as spheroids significantly increased the number of microvessels and smooth muscle α-actin-positive vessels in the ischemic limbs of mice, and attenuated limb loss and necrosis. Human CBMNC can be considered an alternative source of MSC, and spheroid-based hCBMSC delivery can be considered a simple and effective strategy for enhancing the therapeutic efficacy of hCBMSCs.

The effect of hypoxia on in vitro prevascularization of a thick soft tissue

Prevascularizing an implantable tissue is one strategy to improve oxygen (O(2)) transport throughout larger tissues upon implantation. This study examined the role of hypoxia both during (i.e., as a stimulus) and after (i.e., mimicking implant conditions) vascularization of an implantable tissue. Tissues consisted of microcarrier beads coated with human umbilical vein endothelial cells embedded in fibrin. The fibrin was covered with a monolayer of normal human lung fibroblasts (NHLFs), or exposed to conditioned media from NHLFs. Capillary networks developed at 20% or 1% O(2) tension for 8 days. In some experiments, tissues were supplemented with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor, whereas in others the tissues prevascularized at 20% O(2) were transferred to 1% O(2) for 8 additional days. Maximal capillary formation occurred in media conditioned by NHLFs at 20% O(2), supplemented with VEGF (concentration >10 pM). Hypoxia (1% O(2)) did not stimulate basic fibroblast growth factor production and decreased in vitro angiogenesis, despite an increase in endogenous VEGF production. Hypoxia also degraded a preformed capillary network within 4 days. Hence, strategies to prevascularize implantable tissues may not require the physical presence of stromal cells, but will likely require fibroblast-derived growth factors in addition to VEGF to maintain capillary growth.

Preconditioning and tolerance against cerebral ischaemia: from experimental strategies to clinical use

Neuroprotection and brain repair in patients after acute brain damage are still major unfulfilled medical needs. Pharmacological treatments are either ineffective or confounded by adverse effects. Consequently, endogenous mechanisms by which the brain protects itself against noxious stimuli and recovers from damage are being studied. Research on preconditioning, also known as induced tolerance, over the past decade has resulted in various promising strategies for the treatment of patients with acute brain injury. Several of these strategies are being tested in randomised clinical trials. Additionally, research into preconditioning has led to the idea of prophylactically inducing protection in patients such as those undergoing brain surgery and those with transient ischaemic attack or subarachnoid haemorrhage who are at high risk of brain injury in the near future. In this Review, we focus on the clinical issues relating to preconditioning and tolerance in the brain; specifically, we discuss the clinical situations that might benefit from such procedures. We also discuss whether preconditioning and tolerance occur naturally in the brain and assess the most promising candidate strategies that are being investigated.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Cerebral preconditioning and ischaemic tolerance

Adaptation is one of physiology's fundamental tenets, operating not only at the level of species, as Darwin proposed, but also at the level of tissues, cells, molecules and, perhaps, genes. During recent years, stroke neurobiologists have advanced a considerable body of evidence supporting the hypothesis that, with experimental coaxing, the mammalian brain can adapt to injurious insults such as cerebral ischaemia to promote cell survival in the face of subsequent injury. Establishing this protective phenotype in response to stress depends on a coordinated response at the genomic, molecular, cellular and tissue levels. Here, I summarize our current understanding of how 'preconditioning' stimuli trigger a cerebroprotective state known as cerebral 'ischaemic tolerance'.

Ischaemic preconditioning: therapeutic implications for stroke?

Ischaemic preconditioning (IPC), also known as ischaemic tolerance (IT), is a phenomenon whereby tissue is exposed to a brief, sublethal period of ischaemia, which activates endogenous protective mechanisms, thereby reducing cellular injury that may be caused by subsequent lethal ischaemic events. The first description of this phenomenon was in the heart, which was reported by Murry and co-workers in 1986. Subsequent studies demonstrated IPC in lung, kidney and liver tissue, whereas more recent studies have concentrated on the brain. The cellular mechanisms underlying the beneficial effects of IPC remain largely unknown. This phenomenon, which has been demonstrated by using various injury paradigms in both cultured neurons and animal brain tissue, may be utilised to identify and characterise therapeutic targets for small-molecule, antibody, or protein intervention. This review will examine the experimental evidence demonstrating the phenomenon termed IPC in models of cerebral ischaemia, the cellular mechanisms that may be involved and the therapeutic implications of these findings.

Oxygen-sensitive {delta}-opioid receptor-regulated survival and death signals: novel insights into neuronal preconditioning and protection

The detrimental effect of severe hypoxia (SH) on neurons can be mitigated by hypoxic preconditioning (HPC), but the molecular mechanisms involved remain unclear, and an understanding of these may provide novel solutions for hypoxic/ischemic disorders (e.g. stroke). Here, we show that the delta-opioid receptor (DOR), an oxygen-sensitive membrane protein, mediates the HPC protection through specific signaling pathways. Although SH caused a decrease in DOR expression and neuronal injury, HPC induced an increase in DOR mRNA and protein levels and reversed the reduction in levels of the endogenous DOR peptide, leucine enkephalin, normally seen during SH, thus protecting the neurons from SH insult. The HPC-induced protection could be blocked by DOR antagonists. The DOR-mediated HPC protection depended on an increase in ERK and Bcl 2 activity, which counteracted the SH-induced increase in p38 MAPK activities and cytochrome c release. The cross-talk between ERK and p38 MAPKs displays a "yinyang" antagonism under the control of the DOR-G protein-protein kinase C pathway. Our findings demonstrate a novel mechanism of HPC neuroprotection (i.e. the intracellular up-regulation of DOR-regulated survival signals).

Development of an ischemic tolerance model in a PC12 cell line

Although ischemic tolerance has been described in a variety of primary cell culture systems, no similar in vitro models have been reported with any cell line. A model of ischemic preconditioning in the rat pheochromocytoma PC12 cell line is described here. When compared to nonpreconditioned cells, preexposure of PC12 cells to 6 hours of oxygen and glucose deprivation (OGD) significantly increased cell viability after 15 hours of OGD 24 hours later. Flow cytometry analysis of cells labeled with specific markers for apoptosis, Annexin V, and Hoechst 33342, and of DNA content, revealed that apoptosis is involved in OGD-induced PC12 cell death and that preconditioning of the cells mainly counteracts the effect of apoptosis. Immunocytochemistry of caspase-3, a central executioner in the apoptotic process, further confirmed the activation of apoptotic pathways in OGD-induced PC12 cell death. This model may be useful to investigate the cellular mechanisms involved in neuronal transient tolerance following ischemia.

Increased expression of epidermal growth factor receptors in the tracheal epithelia after topical mitomycin-C in rabbits

The aim is to examine histopathological changes and expression of epidermal growth factor receptor (EGFR) in tracheal epithelia caused by application of topical mitomycin-C (MMC) in rabbit model after the tracheotomy procedure. The conventional tracheotomy was performed in 16 rabbits. They were randomly divided into two equal groups. The first group was applied MMC at a concentration of 0.4 mg/ml around tracheotomy for 5 min, and the other group was not taken a treatment as a control. The animals were sacrificed at the end of 4 weeks. Their tracheas were evaluated with H&E and Masson's trichrome histochemically, and with antiepidermal growth factor receptor immunohistochemically. Results showed that there was no significant difference between MMC and control group for inflammatory cells (P=0.09). The numbers of fibroblasts and subepithelial tissue thickness in the group exposed to MMC were significantly lower than the control group (P<0.05). In contrast, the percentage of EGFR in the application of MMC group was significantly higher than the control group (P<0.05). The application of topical MMC on airway epithelia after tracheotomy showed significant elevation in the levels of epithelial EGFR expression compared to controls in a rabbit model. The activation of epithelial EGFR may facilitate epithelial healing, but further studies are needed to assess the effect of topical MMC on respiratory epithelia.

Hypoxia Increases Heparanase-Dependent Tumor Cell Invasion, Which Can Be Inhibited by Antiheparanase Antibodies

The β-endoglucuronidase heparanase plays an important role in tumor invasion, a process that is significantly enhanced by hypoxia. We have used a strategy of stable transfection with antisense to derive ovarian carcinoma cell lines that express different levels of heparanase and used these to demonstrate that invasion correlates with heparanase activity. Secreted heparanase activity was increased by reduction, hypoxia, and growth of cells under reduced oxygen (1%) augmented heparanase activity and invasion, both of which are inhibited by treatment with antiheparanase antibodies. This is the first demonstration that heparanase activity may be regulated by microenvironmental redox conditions, which influence invasion, and that invasion can be blocked with specific heparanase-neutralizing antibodies.

CD105 prevents apoptosis in hypoxic endothelial cells

CD105, a marker of endothelial cells, is abundantly expressed in tissues undergoing angiogenesis and is a receptor for transforming growth factorbeta. The pivotal role of CD105 in the vascular system was demonstrated by the severe vascular defects that occur in CD105-knockout mice, but the exact mechanisms for CD105 regulation of vascular development have not been fully elucidated. In light of the function of CD105 and the importance of hypoxia in neovascularisation, we speculated that CD105 is involved in hypoxia-initiated angiogenesis. Using tissue-cultured human microvascular endothelial cells, we have investigated the effects of hypoxic stress on CD105 gene expression. Hypoxia induced a significant increase in membrane-bound and secreted CD105 protein levels. CD105 mRNA and promoter activity were also markedly elevated, the latter returning to the basal level after 16 hours of hypoxic stress. Hypoxia induced cell cycle arrest at the G0/G1 phases and massive cell apoptosis after 24 hours through a reduction in the Bcl-2 to Bax ratio, downregulation of Bcl-XL and Mcl-1, and upregulation of caspase-3 and caspase-8. The consequence of CD105 upregulation was revealed using an antisense approach and a TUNEL assay. Suppression of CD105 increased cell apoptosis under hypoxic stress in the absence of TGFbeta1. Furthermore, hypoxia and TGFbeta1 synergistically induced apoptosis in the CD105-deficient cells but not in the control cells. We conclude that hypoxia is a potent stimulus for CD105 gene expression in vascular endothelial cells, which in turn attenuates cell apoptosis and thus contributes to angiogenesis.

Fibroblast growth factor 2 promotes microvessel formation from mouse embryonic aorta

To delineate the roles that oxygen and fibroblast growth factors (FGFs) play in the process of angiogenesis from the embryonic aorta, we cultured mouse embryonic aorta explants (thoracic level to lateral vessels supplying the mesonephros and metanephros) in a three-dimensional type I collagen gel matrix. During 8 days of culture under 5% O(2), but not room air, the addition of FGF2 to explants stimulated the formation of Gs-IB(4-)positive, CD31-positive, and Flk-1-positive microvessels in a concentration-dependent manner. FGF2-stimulated microvessel formation was inhibited by sequestration of FGF2 via addition of soluble FGF receptor (FGFR) chimera protein or anti-FGF2 antibodies. FGFR1 and FGFR2 were present on explants. Levels of FGFR1, but not FGFR2, were increased in embryonic aorta cultured under 5% O(2) relative to room air. Our data suggest that low oxygen upregulates FGFR1 expression in embryonic aorta in vitro and renders it more responsive to FGF2.

Ischemic tolerance

A brief period of cerebral ischemia confers transient tolerance to a subsequent ischemic challenge in the brain. This phenomenon of ischemic tolerance has been confirmed in various animal models of forebrain ischemia and focal cerebral ischemia. Since the ischemic tolerance afforded by preceding ischemia can bring about robust protection of the brain, the mechanism of tolerance induction has been extensively studied. It has been elucidated that ischemic tolerance protects neurons, and at the same time, it preserves brain function. Further experiments have shown that metabolic and physical stresses can also induce cross-tolerance to cerebral ischemia, but the protection by cross-tolerance is relatively modest. The underlying mechanism of ischemic tolerance still is not fully understood. Potential mechanisms may be divided into two categories: (1) A cellular defense function against ischemia may be enhanced by the mechanisms inherent to neurons. They may arise by posttranslational modification of proteins or by expression of new proteins via a signal transduction system to the nucleus. These cascades of events may strengthen the influence of survival factors or may inhibit apoptosis. (2) A cellular stress response and synthesis of stress proteins may lead to an increased capacity for health maintenance inside the cell. These proteins work as cellular "chaperones" by unfolding misfolded cellular proteins and helping the cell to dispose of unneeded denatured proteins. Recent experimental data have demonstrated the importance of the processing of unfolded proteins for cell survival and cell death. The brain may be protected from ischemia by using multiple mechanisms that are available for cellular survival. If tolerance induction can be manipulated and accelerated by a drug treatment that is safe and effective enough, it could greatly improve the treatment of stroke.

Redox signaling in vascular angiogenesis

Angiogenesis is thought to be regulated by several growth factors (EGF, TGF-alpha, beta-FGF, VEGF). Induction of these angiogenic factors is triggered by various stresses. For instance, tissue hypoxia exerts its pro-angiogenic action through various angiogenic factors, the most notable being vascular endothelial growth factor, which has been mainly associated with initiating the process of angiogenesis through the recruitment and proliferation of endothelial cells. Recently, reactive oxygen species (ROS) have been found to stimulate angiogenic response in the ischemic reperfused hearts. Short exposure to hypoxia/reoxygenation, either directly or indirectly, produces ROS that induce oxidative stress which is associated with angiogenesis or neovascularization. ROS can cause tissue injury in one hand and promote tissue repair in another hand by promoting angiogenesis. It thus appears that after causing injury to the cells, ROS promptly initiate the tissue repair process by triggering angiogenic response.

Hypoxia enhances vascular cell proliferation and angiogenesis in vitro via rapamycin (mTOR)-dependent signaling

Angiogenesis and vascular cell proliferation are pivotal in physiological and pathological processes including atherogenesis, restenosis, wound healing, and cancer development. Here we show that mammalian target of rapamycin (mTOR) signaling plays a key role in hypoxia-triggered smooth muscle and endothelial proliferation and angiogenesis in vitro. Hypoxia significantly increased DNA synthesis and proliferative responses to platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) in rat and human smooth muscle and endothelial cells. In an in vitro 3-dimensional model of angiogenesis, hypoxia increased PDGF- and FGF-stimulated sprout formation from rat and mouse aortas. Hypoxia did not modulate PDGF receptor mRNA, protein, or phosphorylation. PI3K activity was essential for cell proliferation under normoxic and hypoxic conditions. Activities of PI3K-downstream target PKB under hypoxia and normoxia were comparable. However, mTOR inhibition by rapamycin specifically abrogated hypoxia-mediated amplification of proliferation and angiogenesis, but was without effect on proliferation under normoxia. Accordingly, hypoxia-mediated amplification of proliferation was further augmented in mTOR-overexpressing endothelial cells. Thus, signaling via mTOR may represent a novel mechanism whereby hypoxia augments mitogen-stimulated vascular cell proliferation and angiogenesis.

Preconditioning-induced neuroprotection is mediated by reactive oxygen species and activation of the transcription factor nuclear factor-kappaB

Preconditioning by a sublethal stimulus induces tolerance to a subsequent, otherwise lethal insult and it has been suggested that reactive oxygen species (ROS) are involved in this phenomenon. In the present study, we determined whether preconditioning activates the transcription factor nuclear factor-kappaB (NF-kappaB) and how this activation contributes to preconditioning-induced inhibition of neuronal apoptosis. Preconditioning was performed by incubating mixed cultures of neurons and astrocytes from neonatal rat hippocampus with xanthine/xanthine oxidase or FeSO4 for 15 min followed by 24 h of recovery which protected the neurons against subsequent staurosporine-induced (200 nM, 24 h) apoptosis. The cellular ROS content increased during preconditioning, but returned to basal levels after removal of xanthine/xanthine oxidase or FeSO4. We detected a transient activation of NF-kappaB 4 h after preconditioning as shown by immunocytochemistry, by a decrease in the protein level of IkappaBalpha as well as by electrophoretic mobility shift assay. Preconditioning-mediated neuroprotection was abolished by antioxidants, inhibitors of NF-kappaB activation and cycloheximide suggesting the involvement of ROS, an activation of NF-kappaB and de novo protein synthesis in preconditioning-mediated rescue pathways. Furthermore, preconditioning increased the protein level of Mn-superoxide dismutase which could be blocked by antioxidants, cycloheximide and kappaB decoy DNA. Our data suggest that inhibition of staurosporine-induced neuronal apoptosis by preconditioning with xanthine/xanthine oxidase or FeSO4 involves an activation of NF-kappaB and an increase in the protein level of Mn-superoxide dismutase.

Potentiation by histamine of synaptically mediated excitotoxicity in cultured hippocampal neurones: a possible role for mast cells

Excessive glutamatergic neurotransmission, particularly when mediated by the N:-methyl-D-aspartate (NMDA) subtype of glutamate receptor, is thought to underlie neuronal death in a number of neurological disorders. Histamine has been reported to potentiate NMDA receptor-mediated events under a variety of conditions. In the present study we have utilized primary hippocampal neurone cultures to investigate the effect of mast cell-derived, as well as exogenously applied, histamine on neurotoxicity evoked by excessive synaptic activity. Exposure of mature cultures for 15 min to an Mg(2+)-free/glycine-containing buffer to trigger synaptic transmission through NMDA receptors, caused a 30-35% neuronal loss over 24 h. When co-cultured with hippocampal neurones, activated mast cells increased excitotoxic injury to 60%, an effect that was abolished in the presence of histaminase. Similarly, addition of histamine during magnesium deprivation produced a concentration-dependent potentiation (+ 60%; EC(50) : 5 microM) of neuronal death which was inhibited by sodium channel blockers and NMDA receptor antagonists, although this effect did not involve known histamine receptors. The histamine effect was further potentiated by acidification of the culture medium. Cultures 'preconditioned' by sublethal (5 min) Mg(2+) deprivation exhibited less neuronal death than controls when exposed to a more severe insult. NMDA receptor activation and the extracellular regulated kinase cascade were required for preconditioning neuroprotection. The finding that histamine potentiates NMDA receptor-mediated excitotoxicity may have important implications for our understanding of conditions where enhanced glutamatergic neurotransmission is observed in conjunction with tissue acidification, such as cerebral ischaemia and epilepsy.

Central nicotinic receptors, neurotrophic factors and neuroprotection

The multiple combinations of nAChR subunits identified in central nervous structures possess distinct pharmacological and physiological properties. A growing number of data have shown that compounds interacting with neuronal nAChRs have, both in vivo and in vitro, the potential to be neuroprotective and that treatment with nAChR agonists elicit long-lasting improving of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Epidemiological and clinical studies suggested also a potential neuroprotective/trophic role of (-)-nicotine in neurodegenerative disease, such as Alzheimer's and Parkinson's disease. Taken together experimental and clinical data largely indicate a neuroprotective/trophic role of nAChR activation involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR antagonists, and by potent nAChR agonists recently found displaying efficacy and/or larger selective affinities than (-)-nicotine for neuronal nAChR subtypes. A neurotrophic factor gene regulation by nAChR signalling has been taken into consideration as possible mechanism involved in neuroprotective/trophic effects by nAChR activation and has evidenced an involvement of the fibroblast growth factor (FGF-2) gene as a target of nAChR signalling. These findings suggested that FGF-2 could be involved, according to the FGF-2 neurotrophic functions, in nAChR mechanisms mediating the neuronal survival, trophism and plasticity.

Preconditioning-induced neuroprotection is mediated by reactive oxygen species

The current study was performed to determine the role of reactive oxygen species (ROS) in preconditioning against different forms of neuronal damage. Primary cultures of chick embryonic neurons were treated with either FeSO(4) (100 microM; 15 min) to generate hydroxyl radicals or xanthine/xanthinoxidase (10 microM/0.5 mU ml(-1); 15 min; =X/XO (pre)) to produce superoxide radicals. Both stimuli moderately enhanced ROS formation as measured by fluorescence microscopy. This preconditioning significantly protected the neurons against subsequent glutamate (1 mM)-induced excitotoxic damage, staurosporine (200 nM)-induced neuronal apoptosis and oxidative damage caused by exposure to xanthine/xanthinoxidase (500 microM/5 mU ml(-1); 1 h; =X/XO (dam)). The antioxidants vitamin E (10 microM) and 2-OH-estradiol (1 microM), present during the 15-min preconditioning period, completely abolished the protective effect of X/XO (pre). Furthermore, glutamate, staurosporine or X/XO (dam) markedly enhanced oxygen radical formation. Preceding preconditioning by mild ROS stimulation with X/XO (pre) or Fe(2+) reduced this oxygen radical burst. Again, the effect of X/XO (pre) could be blocked by coadministration of vitamin E or 2-OH-estradiol. However, the FeSO(4)-mediated preconditioning was not abolished by the radical scavengers. To address this phenomenon, the effect of vitamin E and 2-OH-estradiol on Fe(2+)- and X/XO (pre)-induced ROS formation kinetics within the 15 min of preconditioning was monitored. The moderate rise of intracellular ROS content during preconditioning was only reduced permanently by the antioxidants, when the neurons were treated with X/XO (pre), but not when Fe(2+) was used. Thus, an immediate and constant radical scavenging seems to be indispensable to abolish the ROS-induced neuronal preconditioning. The current results indicate that preconditioning by moderate ROS-stimulation protects cultured neurons against different damaging agents and prevents against the subsequent massive oxygen radical formation.

Hypothermia-induced ischemic tolerance

Delayed resistance to ischemic injury can be induced by a variety of conditioning stimuli. This phenomenon, known as delayed ischemic tolerance, is initiated over several hours or a day, and can persist for up to a week or more. The present paper describes recent experiments in which transient hypothermia was used as a conditioning stimulus to induce ischemic tolerance. A brief period of hypothermia administered 6 to 48 hours prior to focal ischemia reduces subsequent cerebral infarction. Hypothermia-induced ischemic tolerance is reversed by 7 days postconditioning, and is blocked by the protein synthesis inhibitor anisomycin. Electrophysiological studies utilizing in vitro brain slices demonstrate that hypoxic damage to synaptic responses is reduced in slices prepared from hypothermia-preconditioned animals. Taken together, these findings indicate that transient hypothermia induces tolerance in the brain parenchyma, and that increased expression of one or more gene products contributes to this phenomenon. Inasmuch as hypothermia is already an approved clinical procedure for intraischemic and postischemic therapy, it is possible that hypothermia could provide a clinically useful conditioning stimulus for limiting injury elicited by anticipated periods of ischemia.

Vascular endothelial growth factor and basic fibroblast growth factor in children with cyanotic congenital heart disease

OBJECTIVE

Vascular endothelial growth factor and basic fibroblast growth factor are potent stimulators of angiogenesis. Children with cyanotic congenital heart disease often experience the development of widespread formation of collateral blood vessels, which may represent a form of abnormal angiogenesis. We undertook the present study to determine whether children with cyanotic congenital heart disease have elevated serum levels of vascular endothelial growth factor and basic fibroblast growth factor.

METHODS

Serum was obtained from 22 children with cyanotic congenital heart disease and 19 children with acyanotic heart disease during cardiac catheterization. Samples were taken from the superior vena cava, inferior vena cava, and a systemic artery. Vascular endothelial growth factor and basic fibroblast growth factor levels were measured in the serum from each of these sites by enzyme-linked immunosorbent assay.

RESULTS

Vascular endothelial growth factor was significantly elevated in the superior vena cava (P =.04) and systemic artery (P =.02) but not in the inferior vena cava (P =.2) of children with cyanotic congenital heart disease compared to children with acyanotic heart disease. The mean vascular endothelial growth factor level, determined by averaging the means of all 3 sites, was also significantly elevated (P =.03). Basic fibroblast growth factor was only significantly elevated in the systemic artery (P =.02).

CONCLUSION

Children with cyanotic congenital heart disease have elevated systemic levels of vascular endothelial growth factor. These findings suggest that the widespread formation of collateral vessels in these children may be mediated by vascular endothelial growth factor.

Effects of hypothermia on hypoxia-induced apoptosis in cultured neurons from developing rat forebrain: comparison with preconditioning

In neuronal cultures from the forebrain of 14-d-old rat embryos, transient hypoxia (95% N2/5% CO2, 37 degrees C) for 6 h has been shown to trigger delayed apoptotic death through sequential changes in protein synthesis, whereas preconditioning by a brief episode of hypoxia can rescue neurons. Because hypothermia has been reported to be neuroprotective, the present study was designed to test the influence of reduced temperature on the consequences of lethal hypoxia in our culture model, and cellular mechanisms involved were compared with those underlying preconditioning effects. After 6 d in vitro, cultures were subjected to hypoxia for 6 h. They were either placed at 32 degrees C concomitantly with hypoxia for 6 h or preconditioned the day before by a 1-h episode of hypoxia. The hypoxic insult decreased cell viability by 38% at 96 h after reoxygenation, and 23% of the neurons showed morphologic features of apoptosis. Both hypothermia and preconditioning prevented neuronal death and reduced apoptosis. Preconditioning led to time-dependent changes in leucine incorporation, with persistent overexpression of the survival proteins Bcl-2 and heat-shock protein 70. It also increased thymidine incorporation, in line with induction of the cofactor for DNA polymerase, proliferating cell nuclear antigen. Hypothermia reduced basal apoptosis and necrosis, but did not affect thymidine incorporation, and abolished hypoxia-associated protein synthesis. Therefore, both treatments were protective against neuronal injury consecutive to hypoxia in developing brain neurons in vitro. Whereas preconditioning activated a program that stimulated the expression of anti-apoptotic gene products and regulatory components of the cell cycle, hypothermia did not trigger active processes, but depressed cell activity, which in turn may impair the apoptotic phenomenon.

Neurotrophic effects of central nicotinic receptor activation

A growing number of data have shown that compounds interacting with neuronal nicotinic acetylcholine receptors (nAChRs) have, both in vivo and in vitro, the potential to be neuroprotective and that treatment with nAChR agonists elicit long-lasting improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Epidemiological and clinical studies suggested also a potential neuroprotective/trophic role of (-)-nicotine in neurodegenerative disease, such as Alzheimer's disease and Parkinson's disease. This neuroprotective/trophic role of nAChR activation has been mainly mediated by alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR antagonists, and by potent nAChR agonists recently found displaying efficacy and/or larger selective affinities than (-)-nicotine for neuronal nAChR subtypes. A neurotrophic factor gene regulation by nAChR signalling has been taken into consideration as a possible mechanism involved in neuroprotective/trophic effects of nAChR activation and has given evidence that the fibroblast growth factor (FGF-2) gene is a target for nAChR signalling. These findings suggested that FGF-2 could be involved, in view of its neurotrophic functions, in nAChR mechanisms mediating neuronal survival, trophism and plasticity.

Hypoxia-induced bFGF gene expression is mediated through the JNK signal transduction pathway

Although the synthesis of angiogenic factors in hypoxic regions of solid tumors is recognized as one of the critical steps in tumor growth and metastasis, the signal transduction pathway involved in hypoxic induction of basic fibroblast growth factor (bFGF) gene expression is still obscure. In the study described here, we investigated the intracellular responses to hypoxia and the mechanisms triggering the initiation of angiogenic activity in drug-resistant human breast carcinoma MCF-7/ADR cells. Northern blots showed an increase in the level of c-jun, c-fos, and bFGF mRNA during hypoxia. Gel mobility-shift analysis of nuclear extracts from hypoxia-exposed cells showed an increase in AP-1 binding activity. In addition, hypoxic treatment strongly activated c-Jun N-terminal kinase 1 (JNK1), leading to phosphorylation and activation of c-Jun. Expression of a dominant negative mutant of JNK1 suppressed hypoxia-induced JNK1 activation as well as bFGF gene expression. Taken together, hypoxia-induced bFGF gene expression is mediated through the stress-activated protein kinase (SAPK) signal transduction pathway.

HIF-1alpha and p53 promote hypoxia-induced delayed neuronal death in models of CNS ischemia

Brain ischemia is a cause of substantial morbidity and mortality during the later decades of life. In light of this, many studies have used in vitro and in vivo models of acute necrosis to test candidate therapeutic agents. More recently, the existence of a genetically programmed component of ischemic death has become widely accepted. We have used molecular genetic approaches to investigate the potential link between hypoxia-induced gene transcription and the delayed death of ischemic neurons. Hypoxia-induced gene expression is an evolutionarily conserved response comprising both transcriptional activation and posttranscriptional and posttranslational stabilization events. Members of the PER-ARNT-SIM (PAS) family of basic helix-loop-helix transcription factors have been shown to regulate hypoxic transcripts in nonneuronal cultured lines. However, evidence for ischemic activation of PAS proteins within the neuronal compartment or possible involvement in neuronal death is lacking. The tumor-suppressor protein p53 is a known transcriptional activator within the central nervous system that is clearly involved in the pathologic response to ischemia. This article will provide data that implicate the coordinate activities of p53 and the PAS protein HIF-1alpha in driving ischemia-induced delayed neuronal death. Background regarding mechanisms of ischemic neuronal death will also be provided with special attention paid to the role of de novo gene expression in promoting this pathologic sequence. The identification of the HIF-1alpha/p53-mediated signaling pathway in neurons highlights a novel target toward which anti-ischemic neuroprotective drug discovery can be applied.

Evidence from cultured rat cortical neurons of differences in the mechanism of ischemic preconditioning of brain and heart

Ca2+ influx and activation of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) during nonlethal ischemic preconditioning have been implicated in the protection of the heart against subsequent lethal ischemic injury. Thus, we determined if Ca2+ influx, PKC and MAPK also mediate ischemic preconditioning-induced protection in neurons. Preconditioning by exposure of E18 rat cortical cultures to 90 min of nonlethal oxygen-glucose deprivation (OGD) 24 h prior to 180-240 min of lethal OGD was neuroprotective. Exposure to nominally free Ca2+, or blockade of the alpha-amino-hydroxy-5-methyl-isoxazolepropionate (AMPA) receptor with CNQX did not eliminate protection. MAPK activity did not change and PKC activity decreased by 50% relative to normal baseline levels at 0 and 24 h following preconditioning. The sustained decrease in PKC activity was not due to a loss of enzyme as determined from immunoblots using pan and epsilon-, beta- and zeta-specific PKC antibodies. Neuroprotection was maintained with pharmacological inhibition of PKC activity by staurosporine, chelerythrine and calphostin C and MAPK activity by PD 98059 during preconditioning, indicating that activation of these enzymes during preconditioning was not necessary for protection. Therefore, in contrast to cardiac tissue, ischemic preconditioning of neurons does not require activation of PKC and MAP kinase, and protection is maintained with substantial removal of extracellular Ca2+ or blockade of the AMPA receptor.

Ischemic tolerance in murine cortical cell culture: critical role for NMDA receptors

Murine cortical cultures containing both neurons and glia (days in vitro 13-15) were exposed to periods of oxygen-glucose deprivation (5-30 min) too brief to induce neuronal death. Cultures "preconditioned" by sublethal oxygen-glucose deprivation exhibited 30-50% less neuronal death than controls when exposed to a 45-55 min period of oxygen-glucose deprivation 24 hr later. This preconditioning-induced neuroprotection was specific in that neuronal death induced by exposure to excitotoxins or to staurosporine was not attenuated. Neuroprotection was lost if the time between the preconditioning and severe insult were decreased to 7 hr or increased to 72 hr and was blocked if the NMDA antagonist 100 microM 3-((D)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid was applied during the preconditioning insult. This was true even if the duration of preconditioning was increased as far as possible (while still remaining sublethal). A similar preconditioning effect was also produced by sublethal exposure to high K+, glutamate, or NMDA but not to kainate or trans-1-aminocyclopentane-1, 3-dicarboxylic acid.

Effect of preceding in vivo sublethal ischemia on the evoked potentials during secondary in vitro hypoxia evaluated with gerbil hippocampal slices

We investigated the mechanism of 'ischemic tolerance phenomenon' by characterizing the physiological events, modified by preceding sublethal ischemia, during secondary hypoxia. Slices from brains after pretreatment of sublethal forebrain ischemia were subjected to a 70% reduction of PO2 (threshold hypoxia). Although evoked potentials disappeared completely in five of eight slices from sham-operated brain, they were sustained in 28/32 slices from pretreated brains. This study indicates that the maintenance of membrane function might be the mechanism of ischemic tolerance.

A comparative study of ethanol, hypoglycemia, hypoxia and neurotrophic factor interactions with fetal rat hippocampal neurons: a multi-factor in vitro model developmental ethanol effects

Fetal alcohol syndrome (FAS) is characterized by numerous central nervous system anomalies, with the hippocampus being particularly vulnerable to developmental ethanol exposure. In addition to direct ethanol neurotoxicity, other conditions resulting from maternal ethanol consumption, such as hypoglycemia and hypoxia, may also contribute to FAS. The present study used a tissue culture system to model multiple conditions which may relate to in vivo FAS, and assessed their relative neurotoxicity with MTT assays. Gestational day 18 rat hippocampal cultures were exposed to varying ethanol concentrations, glucose withdrawal-induced hypoglycemic (gwHG, 16 h) or acute hypoxic (aHP, 2 h) conditions alone, as well as to co-treatments with ethanol and gwHG or aHP. Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) have previously been shown to ameliorate ethanol-, hypoglycemia- and hypoxia-induced neurotoxicity. Therefore, their neuroprotective potential, along with ciliary neurotrophic factor (CNTF), was examined. Neuronal viability was reduced dose-dependently by ethanol, alone or with hypoglycemia or hypoxia. Ethanol + gwHG or aHP was not uniformly additive. NGF treatment provided the most extensive neuroprotection, being effective against ethanol (200 and 400 mg/dl), gwHG, and aHP, alone and combined. BDNF afforded similar protection, but not against ethanol + gwHG. CNTF protected only against aHP. CNTF + BDNF, previously shown to act synergistically, protected against ethanol + aHP up to 800 mg/dl ethanol, but not, paradoxically, against ethanol alone, gwHG, or ethanol + gwHG, all conditions BDNF alone protected against. This study demonstrated that several neurotrophic factors are capable of mitigating neurotoxicity associated with ethanol, hypoglycemia and hypoxia.

Ischemic tolerance in hippocampal CA1 neurons studied using contralateral controls

We induced ischemic tolerance unilaterally in gerbil hippocampus using the contralateral hippocampus as control. Ischemia for 2 min of right common carotid occlusion was reversible but sufficient to cause heat-shock protein 70 production in CA1 neurons. This pretreatment given four days prior to occlusion of both common carotids for 5 min, but not at longer preceding intervals, induced tolerance in right CA1 neurons. Neuroprotection was still evident two months after the 5 min occlusion. Adenosine triphosphate content and immunoreactive microtubule associate protein 2 in the hippocampus showed that the 5 min ischemic insult was essentially equal in both hemispheres. Repetitive pretreatments at two day intervals caused almost complete protection of CA1 neurons against subsequent 5 min ischemia, while a single pretreatment showed 80% protection. However, the increase in heat-shock protein 70 with repeated pretreatments was not significantly more than with one pretreatment. We concluded that true ischemic tolerance was induced by ischemic stress itself, was long-lasting, was not due to mitigation of subsequent ischemia, and was augmented by repetition without further increase of heat-shock protein 70.

Induction of tolerance in rat cortical neurons: hypoxic preconditioning

Sublethal ischemia leads to increased tolerance against subsequent prolonged cerebral ischemia in vivo. In the present study we modeled preconditioning mechanisms in a neuronal-enriched culture. Damage was significantly reduced (up to 72%) with 1.5 h of oxygen-glucose deprivation 48-72 h before 3 h oxygen-glucose deprivation. Tolerance was also elicited by Na+-K+-ATPase inhibition. No damage was observed when astroglial or endothelial cells were exposed to hypoxia for 3 and 6 h, respectively. We conclude that hypoxic preconditioning is a robust neuronal phenomenon in vitro with a similar temporal pattern and selective cellular vulnerability as the ischemic tolerance phenomenon shown in vivo.

Lipopolysaccharide pre-treatment induces resistance against subsequent focal cerebral ischemic damage in spontaneously hypertensive rats

Ischemic tolerance was induced in spontaneously hypertensive rats (SHR) by injection of a single dose of lipopolysaccharide (LPS) (0.9 mg/kg, i.v.) 1-7 days prior to permanent middle cerebral artery occlusion (MCAO). Infarct volume, evaluated 24 h after MCAO, was significantly reduced by LPS administration 2, 3 or 4 days prior to MCAO (22.8, 25.9 and 20.5%, respectively). The beneficial effect of LPS pre-treatment was completely nullified by concurrent administration of TNFbp. On this basis, the tolerance to ischemia induced by LPS is likely to be mediated by TNF-alpha.