Hypoxia-inducible factor-1α contributes to brain edema after stroke by regulating aquaporins and glycerol distribution in brain

Brain edema following stroke is a critical clinical problem due to its association with increased morbidity and mortality. Despite its significance, present treatment for brain edema simply provides symptomatic relief due to the fact that molecular mechanisms underlying brain edema remain poorly understood. The present study investigated the role of hypoxia-inducible factor-1α (HIF-1α) and aquaporins (AQP-4 and -9) in regulating cerebral glycerol accumulation and inducing brain edema in a rodent model of stroke. Two-hours of middle cerebral artery occlusion (MCAO) followed by reperfusion was performed in male Sprague-Dawley rats (250-280 g). Anti-AQP-4 antibody, anti-AQP-9 antibody, or 2-Methoxyestradiol (2ME2, an inhibitor of HIF-1α) was given at the time of MCAO. The rats were sacrificed at 1 and 24 hours after reperfusion and their brains were examined. Extracellular and intracellular glycerol concentration of brain tissue was calculated with an enzymatic glycerol assay. The protein expressions of HIF-1α, AQP-4 and AQP-9 were determined by Western blotting. Brain edema was measured by brain water content. Compared to control, edema (p < 0.01), increased glycerol (p < 0.05), and enhanced expressions of HIF-1α, AQP-4, and AQP-9 (p < 0.05) were observed after stroke. With inhibition of AQP-4, AQP-9 or HIF-1α, edema and extracellular glycerol were significantly (p < 0.01) decreased while intracellular glycerol was increased (p < 0.01) 1 hour after stroke. Inhibition of HIF-1α with 2ME2 suppressed (p < 0.01) the expression of AQP-4 and AQP-9. These findings suggest that HIF-1α serves as an upstream regulator of cerebral glycerol concentrations and brain edema via a molecular pathway involving AQP-4 and AQP-9. Pharmacological blockade of this pathway in stroke patients may provide novel therapeutic strategies.     

Characteristics of the transcription factor HIF-1α expression in the rat brain during the development of a depressive state and the antidepressive effects of hypoxic preconditioning

The dynamics of HIF-1α expression during the development of stress-related depression, as well as after hypoxic preconditioning (HP), which has an antidepressant-like effect, were studied in the hippocampus, paraventricular hypothalamic nucleus, and neocortex of rats, using an immunocytochemical method. It has been found that the factor HIF-1α is induced in neurons in response to psychoemotional stress that causes the development of experimental depression in rats in the “learned helplessness” model. The profile of the stress-induced expression of HIF-1α in the hippocampus has a two-wave character: early expression on the first day and the delayed expression 10 days after the stress. No significant change was found in the neocortex. In the hypothalamus, up-regulation of HIF-1α expression was delayed (5–10 days). After HP by a moderate repetitive hypobaric hypoxia, which prevents the development of the depressive state in rats, the post-stress expression of HIF-1α was considerably altered in the brain regions studied. In the hippocampus of HP rats, the peak of the early expression lasted for about 5 days after the stress; we observed a multifold increase in its amplitude. In contrast, the HIF-1α delayed peak was eliminated. A similar but smaller effect of HP was also observed in the hypothalamus. The data obtained indicate that delayed HIF-1α expression in the hippocampus and hypothalamus was apparently involved in the mechanisms of pathogenesis of the depressive pathology. However, strong modifications in early and late post-stress expression of HIF-1α caused by HP obviously play an important role in increasing the brain’s tolerance to severe stresses and protection against the development of stress-induced depressive pathologies.     

BDNF–TrkB signaling in the nucleus accumbens shell of mice has key role in methamphetamine withdrawal symptoms

Depression is a core symptom of methamphetamine (METH) withdrawal during the first several weeks of abstinence. However, the precise mechanisms underlying METH withdrawal symptoms remain unknown. Brain-derived neurotrophic factor (BDNF) and its specific receptor, tropomyosin-related kinase (TrkB), have a role the in pathophysiology of depression. In this study, we examined the role of BDNF–TrkB signaling in different brain regions of male mice with METH withdrawal symptoms. Repeated METH (3 mg kg⁻¹ per day for 5 days) administration to mice caused a long-lasting depression-like behavior including anhedonia. Western blot analysis showed that BDNF levels in the nucleus accumbens (NAc) of METH-treated mice were significantly higher than those of control mice whereas BDNF levels in other regions, including the prefrontal cortex and hippocampus, were not altered. METH-induced depression-like behavior, behavioral sensitization and dendritic changes in the NAc shell were improved by subsequent subchronic administration of TrkB antagonist ANA-12 (0.5 mg kg⁻¹ per day for 14 days), but not TrkB agonist 7,8-dihydroxyflavone (10 mg kg⁻¹ per day for 14 days). In vivo microdialysis showed that METH (1 mg kg⁻¹)-induced dopamine release in NAc shell of METH-treated mice was attenuated after subsequent subchronic ANA-12 administration. Interestingly, a single bilateral infusion of ANA-12 into the NAc shell, but not NAc core, showed a rapid and long-lasting therapeutic effect. However, ketamine and paroxetine had no effect. These findings suggest that increased BDNF–TrkB signaling in the NAc shell has an important role in the behavioral abnormalities after withdrawal from repeated METH administration, and that TrkB antagonists are potential therapeutic drugs for withdrawal symptoms in METH abusers.     

The TNF-α/NF-κB signaling pathway has a key role in methamphetamine–induced blood–brain barrier dysfunction

Methamphetamine (METH) is a psychostimulant that causes neurologic and psychiatric abnormalities. Recent studies have suggested that its neurotoxicity may also result from its ability to compromise the blood–brain barrier (BBB). Herein, we show that METH rapidly increased the vesicular transport across endothelial cells (ECs), followed by an increase of paracellular transport. Moreover, METH triggered the release of tumor necrosis factor-alpha (TNF-α), and the blockade of this cytokine or the inhibition of nuclear factor-kappa B (NF-κB) pathway prevented endothelial dysfunction. Since astrocytes have a crucial role in modulating BBB function, we further showed that conditioned medium obtained from astrocytes previously exposed to METH had a negative impact on barrier properties also via TNF-α/NF-κB pathway. Animal studies corroborated the in vitro results. Overall, we show that METH directly interferes with EC properties or indirectly via astrocytes through the release of TNF-α and subsequent activation of NF-κB pathway culminating in barrier dysfunction.     

Steroid-induced inflammatory neuropathy in a patient on tumor necrosis factor-α antagonist therapy

We describe a patient on the tumor necrosis factor-α antagonist, adalimumab, for 2 years for rheumatoid arthitis, who developed a rapidly progressive inflammatory neuropathy shortly after starting oral steroids. Adalimumab was stopped at onset of neurologic symptoms. Electrophysiology showed demyelination, which persisted at 6 month follow-up, cerebrospinal fluid analysis showed persistent albuminocytologic dissociation, and magnetic resonance studies revealed enlarged and enhancing nerve roots. Treatment with intravenous immunoglobulins resulted in slow, progressive improvement. Tumor necrosis factor-α antagonists have previously been implicated in acquired demyelinating neuropathies. In this patient, we hypothesize that adalimumab may have caused an initially asymptomatic chronic inflammatory demyelinating polyneuropathy, which became symptomatic shortly after initiation of steroid therapy. This case may raise the issue of the safety of steroids in conjunction with antitumor necrosis factor-α therapy in susceptible patients.     

Scavenger receptor class-A has a central role in cerebral ischemia–reperfusion injury

The innate immune response is involved in the pathophysiology of cerebral ischemia–reperfusion (I/R) injury. Recent evidence suggests that scavenger receptors have a role in the induction of innate immunity. In this study, we examined the role of scavenger receptor A (SR-A) in focal cerebral I/R injury. Both SR-A^−/− mice (n=10) and age-matched wild-type (WT) mice (n=9) were subjected to focal cerebral ischemia (60 minutes), followed by reperfusion (for 24 hours). Infarct size was determined by TTC (triphenyltetrazolium chloride) staining. The morphology of neurons in the brain sections was examined by Nissl''s staining. Activation of intracellular signaling was analyzed by western blot. Cerebral infarct size in SR-A^−/− mice was significantly reduced by 63.9% compared with WT mice after cerebral I/R. In SR-A^−/− mice, there was less neuronal damage in the hippocampus compared with WT mice. Levels of FasL, Fas, FADD, caspase-3 activity, and terminal deoynucleotidyl transferase-mediated 2′-deoxyuridine 5′-triphosphate-biotin nick end labeling-positive apoptotic cells were significantly increased in WT mice after cerebral I/R, but not in SR-A^−/− mice. Cerebral I/R increased nuclear factor-κB activation in WT mice, but not in SR-A^−/− mice. These data suggest that SR-A has a central role in cerebral I/R injury and that suppression of SR-A may be a useful approach for ameliorating brain injury in stroke patients.     

Investigation of hypoxia-inducible factor-1α in hippocampal sclerosis: A postmortem study

Purpose: Hypoxia‐inducible factor‐1α (HIF‐1α) is involved in critical aspects of cell survival in response to hypoxia and regulates vascular endothelial growth factor (VEGF) expression. Previous experimental and human studies in epilepsy show up‐regulation of VEGF following seizures, although expression of HIF‐1α as its potential regulator has not been explored. We used a postmortem (PM) series from patients with epilepsy and hippocampal sclerosis (HS) to investigate patterns of expression of HIF‐1α and VEGF and their potential contribution to neuroprotection. Method: In 33 PMs (17 cases with unilateral HS, 3 with bilateral HS, 3 with No‐HS, and 10 controls), we quantified neuronal immunolabeling for HIF‐1α and VEGF in hippocampal subfields. Key Findings: HIF‐1α‐ and VEGF‐immunopositive hippocampal neurones were observed in HS, No‐HS, and also in control cases; there was no significant difference in overall labeling between epilepsy cases and controls. In positive cases, HIF‐1α and VEGF neuronal labeling localized primarily in CA1, CA4, and CA3 subfields in all groups; significantly more positive neurons were seen in the entorhinal cortex in epilepsy cases (p < 0.05). Labeling lateralized to the side of sclerosis in unilateral HS cases, with significant differences between hemispheres (p < 0.05). There was a trend for high HIF‐1α labeling scores in patients with Dravet syndrome without HS and sudden unexpected death in epilepsy (SUDEP) cases, and lower scores with long seizure‐free periods prior to death. Hippocampal HIF‐1α and VEGF labeling showed a significant correlation. There was neuronal colocalization of HIF‐1α and VEGF. Significance: Regional expression patterns are in keeping with seizure‐related activation of HIF‐1α and VEGF. The prominent expression in non‐HS cases could support an overall neuroprotective effect. Correlation between HIF‐1α and VEGF neuronal immunolabeling supports HIF‐1α–mediated induction of VEGF in epilepsy.     

Brain tumor necrosis factor-α mediates anxiety-like behavior in a mouse model of severe obesity

Although the high prevalence of anxiety in obesity increasingly emerges as significant risk factor for related severe health complications, the underlying pathophysiological mechanisms remain poorly understood. Considering that chronic inflammation is a key component of obesity and is well known to impact brain function and emotional behavior, we hypothesized that it may similarly contribute to the development of obesity-related anxiety. This hypothesis was experimentally tested by measuring whether chronic food restriction, a procedure known to reduce inflammation, or chronic anti-inflammatory treatment with ibuprofen improved anxiety-like behavior and concomitantly decreased peripheral and/or hippocampal inflammation characterizing a model of severe obesity, the db/db mice. In both experiments, reduced anxiety-like behaviors in the open-field and/or elevated plus-maze were selectively associated with decreased hippocampal tumor necrosis factor-α (TNF-α) mRNA expression. Highlighting the causality of both events, chronic central infusion of the TNF-α blocker etanercept was then shown to be sufficient to improve anxiety-like behavior in db/db mice. Lastly, by measuring the impact of ex-vivo etanercept on hippocampal synaptic processes underlying anxiety-like behaviors, we showed that the anxiolytic effect of central TNF-α blockade likely involved modulation of synaptic transmission within the ventral hippocampus. Altogether, these results uphold the role of brain TNF-α in mediating obesity-related anxiety and provide important clues about how it may modulate brain function and behavior. They may therefore help to introduce novel therapeutic strategies to reduce anxiety associated with inflammatory conditions.     

HIF-1α ODD polypeptides increased the expression of HIF1 and VEGF in hypoxic rat cortical neuron

To investigate the effect of HIF-1α ODD polypeptides on the expression of HIF-1α and VEGF in primary rat cortical neuron in hypoxia. Primary cultured neurons were exposed to hypoxia for 2, 4, and 8 h. Tat-ODD fusion polypeptide was added before hypoxia in the experimental groups. The expression of HIF-1α and VEGF was detected by Western blot and real time PCR. The levels of HIF-1α and VEGF peaked at 4 h then declined in hypoxia. The expression of HIF-1α and VEGF was increased by tat-ODD fusion polypeptide. tat-ODD fusion polypeptide might improve HIF1 adaptation to hypoxia by increased expression of HIF-1α and VEGF.     

Interleukin-1α polymorphism has influence on late-onset sporadic Parkinson’s disease in Taiwan

Summary Inflammatory events may contribute to the pathogenesis of Parkinson’s disease (PD) and interleukin 1 (IL-1) may exert both neurotoxic and neuroprotective effects. We conducted a case-control study in a cohort of 493 PD cases and 388 ethnically matched controls to investigate the association of IL-1α C-889T and IL-1β C-511T polymorphisms with the risk of PD. No significant difference in the genotype distribution of the analyzed polymorphisms was found between PD and controls. However, after stratification by age, individuals over 70 years of age carrying IL-1α-889 C/T genotype demonstrated a significant decrease in risk of developing PD (OR = 0.44; 95% CI = 0.22–0.88, p = 0.021) and the decrease is strengthened by IL-1β-511 T-carrying genotype (OR = 0.28; 95% CI = 0.11–0.71, p = 0.008). Our data suggest that IL-1α, acting synergistically with IL-1β, plays role in PD susceptibility among Taiwanese people older than 70 years of age.     

Transplantation of neural stem cells expressing hypoxia-inducible factor-1α (HIF-1α) improves behavioral recovery in a rat stroke model

We explored the possibility that hypoxia-inducible factor-1α (HIF-1α) might contribute to the therapeutic effect of neural stem cell (NSC) transplantation in cerebral ischemia. The relative efficacy of modified NSC to promote behavioral recovery was investigated in a rat model of stroke induced by a transient middle cerebral artery occlusion (MCAO). A recombinant adenovirus (Ad-HIF-1α) was engineered to express HIF-1α. Control NSC infected with control adenovirus (NSC-Ad), recombinant adenovirus Ad-HIF-1α, or NSC infected by Ad-HIF-1α (NSC-Ad-HIF-1α), were used for intraventricular transplantion into rat brain 24 hours after MCAO. Neurological deficits were assessed over 4 weeks using the modified neurological severity scale (NSS) score. Long-term in vivo expression of HIF-1α was demonstrated by Western blotting and immunocytochemistry, and derivatives of nestin-positive transplanted cells contributed to both neuronal (neurofilament-positive) and astroglial (glial fibrillary acidic protein-positive) lineages. All animals showed functional improvement. Improvement was accelerated in animals receiving either NSC-Ad or Ad-HIF-1α, while improvement at all times between 7 days and 28 days post MCAO was significantly greater in animals transplanted with NSC-Ad-HIF-1α than for other treated animals. NSC-Ad-HIF-1α cells also increased the number of factor VIII-positive cells in the region of ischemic injury, indicating that HIF-1α expression can promote angiogenesis. Gene-modified NSC expressing HIF-1α have therapeutic potential in ischemic stroke.     

Tumor necrosis factor-α expression in muscles of polymyositis and dermatomyositis

We evaluated the expression of tumor necrosis factor-α (TNF-α) mRNA in muscle biopsy specimens from patients with polymyositis (PM) and dermatomyositis (DM) to clarify its role in the pathogenesis of PM and DM. We performed non-radioactive in situ hybridization studies for TNF-α combined with immunohistochemistry for cell type-specific markers on muscles from ten PM and five DM patients. TNF-α-positive infiltrating cells present in the endomysium and perimysium were found in all PM and DM muscles. The frequency of TNF-α-positive cells against total infiltrating cells was similar among PM and DM (27.1 ± 7.4% in PM and 28.5 ± 13.6% in DM). However, TNF-α/CD8-positive lymphocytes and TNF-α-positive macrophages invading the non-necrotic muscle fiber were observed only in PM but not in DM. TNF-α was more highly expressed in PM and DM than was previously thought, and it was suggested that TNF-α plays a role in muscle fiber degeneration in PM. Received: 9 June 1999 / Revised, accepted: 25 October 1999     

Does calcium deposition play a role in the stability of atheroma? Location may be the key

BACKGROUND: Rupture of vulnerable atheromatous plaque in the carotid and coronary arteries often leads to stroke and heart attack respectively. The role of calcium deposition and its contribution to plaque stability is controversial. This study uses both an idealized and a patient-specific model to evaluate the effect of a calcium deposit on the stress distribution within an atheromatous plaque. METHODS: Using a finite-element method, structural analysis was performed on an idealized plaque model and the location of a calcium deposit within it was varied. In addition to the idealized model, in vivo high-resolution MR imaging was performed on 3 patients with carotid atheroma and stress distributions were generated. The individual plaques were chosen as they had calcium at varying locations with respect to the lumen and the fibrous cap. RESULTS: The predicted maximum stress was increased by 47.5% when the calcium deposit was located in the thin fibrous cap in the model when compared with that in a model without a deposit. The result of adding a calcium deposit either to the lipid core or remote from the lumen resulted in almost no increase in maximal stress. CONCLUSION: Calcification at the thin fibrous cap may result in high stress concentrations, ultimately increasing the risk of plaque rupture. Assessing the location of calcification may, in the future, aid in the risk stratification of patients with carotid stenosis.     

Death receptors on reactive astrocytes: a key role in the fine tuning of brain inflammation?

Immune responses protect the CNS against pathogens. However, the fact that there is little dispensable tissue in the brain makes regulation necessary to avoid disastrous immune-mediated damage. Astrocytes respond vigorously to any brain injury (e.g., tumor, stroke, AD, MS, HIV) and are postulated to play an important role in the fine tuning of brain inflammation. The authors propose that astrocytes use death receptors to modulate pro- and anti-inflammatory effects.     

Possible role of transforming growth factor-β in relapsing-remitting multiple sclerosis

Abstract

Cerebrospinal fluid (CSFJ and serum levels of transforming growth factor (TGFJ-f3 and soluble intercellular adhesion molecule-1 (sICAM-l) were evaluated in ten patients with definite multiple sclerosis (MS) of the relapsing-remitting type. CSF TGF-β levels of MS patients in remission were significantly (p < 0.01) higher than of MS patients in active phase and there was a significant inverse correlation (p < 0.05) between TGF-β and sICAM-l levels in the CSF of patients in both remitting and relapsing type. This is consistent with a possible down-regulation of TGF-β on ICAM-l expression and suggests a possible synthesis in the central nervous system of TGF-β. [Neural Res 1997; 19: 599-600]     

Transforming growth factor-α mediates estrogen-induced upregulation of glutamate transporter GLT-1 in rat primary astrocytes

Glutamate transporter-1 (GLT-1) plays a central role in preventing excitotoxicity by removing excess glutamate from the synaptic clefts. 17β-Estradiol (E2) and tamoxifen (TX), a selective estrogen receptor (ER) modulator, afford neuroprotection in a range of experimental models. However, the mechanisms that mediate E2 and TX neuroprotection have yet to be elucidated. We tested the hypothesis that E2 and TX enhance GLT-1 function by increasing transforming growth factor (TGF)-α expression and, thus, attenuate manganese (Mn)-induced impairment in astrocytic GLT-1 expression and glutamate uptake in rat neonatal primary astrocytes. The results showed that E2 (10 nM) and TX (1 μM) increased GLT-1 expression and reversed the Mn-induced reduction in GLT-1, both at the mRNA and protein levels. E2/TX also concomitantly reversed the Mn-induced inhibition of astrocytic glutamate uptake. E2/TX activated the GLT-1 promoter and attenuated the Mn-induced repression of the GLT-1 promoter in astrocytes. TGF-α knockdown (siRNA) abolished the E2/TX effect on GLT-1 expression, and inhibition of epidermal growth factor receptor (TGF-α receptor) suppressed the effect of E2/TX on GLT-1 expression and GLT-1 promoter activity. E2/TX also increased TGF-α mRNA and protein levels with a concomitant increase in astrocytic glutamate uptake. All ERs (ER-α, ER-β, and G protein-coupled receptor 30) were involved in mediating E2 effects on the regulation of TGF-α, GLT-1, and glutamate uptake. These results indicate that E2/TX increases GLT-1 expression in astrocytes via TGF-α signaling, thus offering an important putative target for the development of novel therapeutics for neurological disorders.