Close Homolog of L1 Deficiency Exacerbated Intestinal Epithelial Barrier Function in Mouse Model of Dextran Sulfate Sodium-Induced Colitis.

The cell adhesion molecule CHL1, which belongs to the immunoglobulin superfamily, functions in a variety of physiological and pathological processes, including neural development, tissue injury, and repair. We previously found that the loss of CHL1 exacerbated the dextran sulfate sodium (DSS)-induced colitis in mice. In the present study, we further addressed the role of CHL1 in mouse model of DSS-induced colitis and its' potential mechanism. Colon tissues were collected from CHL1+/+, CHL1+/-, and CHL1-/- mice after DSS induction to investigate the effects of CHL1 on the development of colitis. The data showed that CHL1 was expressed in intestine tissue, and expression of CHL1 was increased by DSS-induced inflammation. CHL1 deficiency induced more pronounced colitis features, exacerbated inflammation, and damage to colonic tissues in DSS-induced mice. Moreover, colonic tissues of CHL1-/- mice showed a marked increase in neutrophil and macrophage infiltration, be accompanied by more severe damage to intestinal epithelial cells and higher fluorescein isothiocyanate (FITC) leakage. Our results revealed deficiency of CHL1 exacerbated DSS-induced colitis, and this pathogenesis was potentially mediated by disruption of intestinal barrier integrity, indicating that CHL1 may be an attractive therapeutic target for inflammatory bowel diseases (IBDs) in mice.

[Intermittent hypoxic preconditioning relieves fear and anxiety behavior in post-traumatic stress model mice].

Intermittent hypoxia (IH) has preventive and therapeutic effects on hypertension, myocardial infarction, cerebral ischemia and depression, but its effect on post-traumatic stress disorder (PTSD) has not been known. In this study, we used inescapable electric foot shock combined with context recapture to build PTSD mouse model. The levels of fear and anxiety were valued by the open field, the elevated plus maze (EPM) and the fear conditioning tests; the level of spatial memory was valued by Y maze test; the number of Fos positive neurons in hippocampus, amygdala and medial prefrontal cortex was valued by immunohistochemical staining; and the protein expressions of hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and brain derived neurotrophic factor (BDNF) in these brain area were valued by Western blot. The results showed that IH and model (foot shock) had an interaction on percentage of entering open arms (OE%) in EPM and freezing time and the number of fecal pellets in fear conditioning test. IH increased OE% in EPM and reduced the freezing time and the number of fecal pellets in fear conditioning test in PTSD model mice. At the same time, IH reduced the number of Fos positive neurons in the hippocampus, amygdala and medial prefrontal cortex of PTSD model mice, and increased the protein expression levels of HIF-1α, VEGF and BDNF in these brain tissues. In conclusion, IH pretreatment can relieve fear and anxiety behavior in post-traumatic stress model mice, suggesting that IH may be an effective means of preventing PTSD.

[Effects of CHL1 deficiency,a cell adhesion molecule,on the inflammatory bowel disease].

OBJECTIVE: To investigate the effects of deficiency of CHL1 in inflammatory bowel disease (IBD). METHODS: Dextran Sulfate Sodium (DSS)-induced colitis model was used to study the effects of deficiency of CHL1 on the development of IBD. Ten CHL1(+/+) mice in C57/BL6 background were randomly divided into CHL1(+/+) group and DSS-induced CHL1(+/+) group. Ten CHL1(-/-) mice in C57/BL6 background were randomly divided into CHL1(-/-) group and DSS-induced CHL1(-/-) group. DSS-induced CHL1(+/+) group and DSS-induced CHL1(-/-)group were fed with 1.5% DSS for 7 days, and then drinking distilled water for 2 days. CHL1(+/+) group and CHL1(-/-) group as control group were fed with distilled water for 9 days. The changes of weight, survival, fecal blood and the change of colon length in this study were observed. RESULTS: On the 7th day, the weight of DSS-induced CHL1(-/-) group were reduced significantly, and DSS-induced CHL1(-/-) group had extreme mortality on the 9th day. The fecal blood of DSS-induced CHL1(-/-) group also had higher score than that of DSS-induced CHL1(+/+) group. In the DSS-induced CHL1(-/-) group,the length of colon was shortened obviously. CONCLUSIONS: The loss of CHL1 aggravates the development of IBD.

Hypoxia augments LPS-induced inflammation and triggers high altitude cerebral edema in mice.

High altitude cerebral edema (HACE) is a life-threatening illness that develops during the rapid ascent to high altitudes, but its underlying mechanisms remain unclear. Growing evidence has implicated inflammation in the susceptibility to and development of brain edema. In the present study, we investigated the inflammatory response and its roles in HACE in mice following high altitude hypoxic injury. We report that acute hypobaric hypoxia induced a slight inflammatory response or brain edema within 24h in mice. However, the lipopolysaccharide (LPS)-induced systemic inflammatory response rapidly aggravated brain edema upon acute hypobaric hypoxia exposure by disrupting blood-brain barrier integrity and activating microglia, increasing water permeability via the accumulation of aquaporin-4 (AQP4), and eventually leading to impaired cognitive and motor function. These findings demonstrate that hypoxia augments LPS-induced inflammation and induces the occurrence and development of cerebral edema in mice at high altitude. Here, we provide new information on the impact of systemic inflammation on the susceptibility to and outcomes of HACE.

Ketogenic diet improves the spatial memory impairment caused by exposure to hypobaric hypoxia through increased acetylation of histones in rats.

Exposure to hypobaric hypoxia causes neuron cell damage, resulting in impaired cognitive function. Effective interventions to antagonize hypobaric hypoxia-induced memory impairment are in urgent need. Ketogenic diet (KD) has been successfully used to treat drug-resistant epilepsy and improves cognitive behaviors in epilepsy patients and other pathophysiological animal models. In the present study, we aimed to explore the potential beneficial effects of a KD on memory impairment caused by hypobaric hypoxia and the underlying possible mechanisms. We showed that the KD recipe used was ketogenic and increased plasma levels of ketone bodies, especially ß-hydroxybutyrate. The results of the behavior tests showed that the KD did not affect general locomotor activity but obviously promoted spatial learning. Moreover, the KD significantly improved the spatial memory impairment caused by hypobaric hypoxia (simulated altitude of 6000 m, 24 h). In addition, the improving-effect of KD was mimicked by intraperitoneal injection of BHB. The western blot and immunohistochemistry results showed that KD treatment not only increased the acetylated levels of histone H3 and histone H4 compared to that of the control group but also antagonized the decrease in the acetylated histone H3 and H4 when exposed to hypobaric hypoxia. Furthermore, KD-hypoxia treatment also promoted PKA/CREB activation and BDNF protein expression compared to the effects of hypoxia alone. These results demonstrated that KD is a promising strategy to improve spatial memory impairment caused by hypobaric hypoxia, in which increased modification of histone acetylation plays an important role.

WIP1 phosphatase is a critical regulator of adipogenesis through dephosphorylating PPARγ serine 112.

WIP1, as a critical phosphatase, plays many important roles in various physiological and pathological processes through dephosphorylating different substrate proteins. However, the functions of WIP1 in adipogenesis and fat accumulation are not clear. Here, we report that WIP1-deficient mice show impaired body weight growth, dramatically decreased fat mass, and significantly reduced triglyceride and leptin levels in circulation. This dysregulation of adipose development caused by the deletion of WIP1 occurs as early as adipogenesis. In contrast, lentivirus-mediated WIP1 phosphatase overexpression significantly increases the adipogenesis of pre-adipocytes via an enzymatic activity-dependent mechanism. PPARγ is a master gene of adipogenesis, and the phosphorylation of PPARγ at serine 112 strongly inhibits adipogenesis; however, very little is known about the negative regulation of this phosphorylation. Here, we show that WIP1 phosphatase plays a pro-adipogenic role by interacting directly with PPARγ and dephosphorylating p-PPARγ S112 in vitro and in vivo.

WIP1 Phosphatase Plays a Critical Neuroprotective Role in Brain Injury Induced by High-Altitude Hypoxic Inflammation.

The hypobaric hypoxic environment in high-altitude areas often aggravates the severity of inflammation and induces brain injury as a consequence. However, the critical genes regulating this process remain largely unknown. The phosphatase wild-type p53-induced phosphatase 1 (WIP1) plays important roles in various physiological and pathological processes, including the regulation of inflammation in normoxia, but its functions in hypoxic inflammation-induced brain injury remain unclear. Here, we established a mouse model of this type of injury and found that WIP1 deficiency augmented the release of inflammatory cytokines in the peripheral circulation and brain tissue, increased the numbers of activated microglia/macrophages in the brain, aggravated cerebral histological lesions, and exacerbated the impairment of motor and cognitive abilities. Collectively, these results provide the first in vivo evidence that WIP1 is a critical neuroprotector against hypoxic inflammation-induced brain injury.

miR-210 protects renal cell against hypoxia-induced apoptosis by targeting HIF-1 alpha.

The kidney is vulnerable to hypoxia-induced injury. One of the mechanisms underlying this phenomenon is cell apoptosis triggered by hypoxia-inducible factor-1-alpha (HIF-1α) activation. MicroRNA-210 (miR-210) is known to be induced by HIF-1α and can regulate various pathological processes, but its role in hypoxic kidney injury remains unclear. Here, in both kinds of rat systemic hypoxia and local kidney hypoxia models, we found miR-210 levels were upregulated significantly in injured kidney, especially in renal tubular cells. A similar increase was observed in hypoxia-treated human renal tubular HK-2 cells. We also verified that miR-210 can directly suppress HIF-1α expression by targeting the 3' untranslated region (UTR) of HIF-1α mRNA in HK-2 cells in severe hypoxia. Accordingly, miR-210 overexpression caused significant inhibition of the HIF-1α pathway and attenuated apoptosis caused by hypoxia, while miR-210 knockdown exerted the opposite effect. Taken together, our findings verify that miR-210 is involved in the molecular response in hypoxic kidney lesions in vivo and attenuates hypoxia-induced renal tubular cell apoptosis by targeting HIF-1α directly and suppressing HIF-1α pathway activation in vitro.

Intermittent hypoxia maintains glycemia in streptozotocin-induced diabetic rats.

Increasing studies have shown protective effects of intermittent hypoxia on brain injury and heart ischemia. However, the effect of intermittent hypoxia on blood glucose metabolism, especially in diabetic conditions, is rarely observed. The aim of this study was to investigate whether intermittent hypoxia influences blood glucose metabolism in type 1 diabetic rats. Streptozotocin-induced diabetic adult rats and age-matched control rats were treated with intermittent hypoxia (at an altitude of 3 km, 4 h per day for 3 weeks) or normoxia as control. Fasting blood glucose, body weight, plasma fructosamine, plasma insulin, homeostasis model assessment of insulin resistance (HOMA-IR), pancreas ß-cell mass, and hepatic and soleus glycogen were measured. Compared with diabetic rats before treatment, the level of fasting blood glucose in diabetic rats after normoxic treatment was increased (19.88 ± 5.69 mmol/L vs. 14.79 ± 5.84 mmol/L, p < 0.05), while it was not different in diabetic rats after hypoxic treatment (13.14 ± 5.77 mmol/L vs. 14.79 ± 5.84 mmol/L, p > 0.05). Meanwhile, fasting blood glucose in diabetic rats after hypoxic treatment was also lower than that in diabetic rats after normoxic treatment (13.14 ± 5.77 mmol/L vs. 19.88 ± 5.69 mmol/L, p<0.05). Plasma fructosamine in diabetic rats receiving intermittent hypoxia was significantly lower than that in diabetic rats receiving normoxia (1.28 ± 0.11 vs. 1.39 ± 0.11, p < 0.05), while there were no significant changes in body weight, plasma insulin and ß-cell mass. HOMA-IR in diabetic rats after hypoxic treatment was also lower compared with diabetic rats after normoxic treatment (3.48 ± 0.48 vs. 3.86 ± 0.42, p < 0.05). Moreover, intermittent hypoxia showed effect on the increase of soleus glycogen but not hepatic glycogen. We conclude that intermittent hypoxia maintains glycemia in streptozotocin-induced diabetic rats and its regulation on muscular glycogenesis may play a role in the underlying mechanism.

Dissolved oxygen concentration in the medium during cell culture: Defects and improvements.

In vitro cell culture has provided a useful model to study the effects of oxygen on cellular behavior. However, it remains unknown whether the in vitro operations themselves affect the medium oxygen levels and the living states of cells. In addition, a prevailing controversy is whether reactive oxygen species (ROS) production is induced by continuous hypoxia or reoxygenation. In this study, we have measured the effects of different types of cell culture containers and the oxygen environment where medium replacement takes place on the actual oxygen tension in the medium. We found that the deviations of oxygen concentrations in the medium are much greater in 25-cm(2) flasks than in 24-well plates and 35-mm dishes. The dissolved oxygen concentrations in the medium were increased after medium replacement in normoxia, but remained unchanged in glove boxes in which the oxygen tension remained at a low level (11.4, 5.7, and 0.5% O2 ). We also found that medium replacement in normoxia increased the number of ROS-positive cells and reduced the cell viability; meanwhile, medium replacement in a glove box did not produce the above effects. Therefore, we conclude that the use of 25-cm(2) flasks should be avoided and demonstrate that continuous hypoxia does not produce ROS, whereas the reoxygenation that occurs during the harvesting of cells leads to ROS and induces cell death.

Reduced Cerebral Oxygen Content in the DG and SVZ In Situ Promotes Neurogenesis in the Adult Rat Brain In Vivo.

Neurogenesis in the adult brain occurs mainly within two neurogenic structures, the dentate gyrus (DG) of the hippocampus and the sub-ventricular zone (SVZ) of the forebrain. It has been reported that mild hypoxia promoted the proliferation of Neural Stem Cells (NSCs)in vitro. Our previous study further demonstrated that an external hypoxic environment stimulated neurogenesis in the adult rat brain in vivo. However, it remains unknown how external hypoxic environments affect the oxygen content in the brain and result in neurogenesis. Here we use an optical fiber luminescent oxygen sensor to detect the oxygen content in the adult rat brain in situ under normoxia and hypoxia. We found that the distribution of oxygen in cerebral regions is spatiotemporally heterogeneous. The Po2 values in the ventricles (45∼50 Torr) and DG (approximately 10 Torr) were much higher than those of other parts of the brain, such as the cortex and thalamus (approximately 2 Torr). Interestingly, our in vivo studies showed that an external hypoxic environment could change the intrinsic oxygen content in brain tissues, notably reducing oxygen levels in both the DG and SVZ, the major sites of adult neurogenesis. Furthermore, the hypoxic environment also increased the expression of HIF-1α and VEGF, two factors that have been reported to regulate neurogenesis, within the DG and SVZ. Thus, we have demonstrated that reducing the oxygen content of the external environment decreased Po2 levels in the DG and SVZ. This reduced oxygen level in the DG and SVZ might be the main mechanism triggering neurogenesis in the adult brain. More importantly, we speculate that varying oxygen levels may be the physiological basis of the regionally restricted neurogenesis in the adult brain.

Methylene Blue Reduces Acute Cerebral Ischemic Injury via the Induction of Mitophagy.

The treatment of stroke is limited by a short therapeutic window and a lack of effective clinical drugs. Methylene blue (MB) has been used in laboratories and clinics since the 1890s. Few studies have reported the neuroprotective role of MB in cerebral ischemia-reperfusion injury. However, whether and how MB protects against acute cerebral ischemia (ACI) injury was unclear. In this study, we investigated the effect of MB on this injury and revealed that MB protected against ACI injury by augmenting mitophagy. Using a rat middle cerebral artery occlusion (MCAO) model, we demonstrated that MB improved neurological function and reduced the infarct volume and necrosis after ACI injury. These improvements depended on the effect of MB on mitochondrial structure and function. ACI caused the disorder and disintegration of mitochondrial structure, while MB ameliorated the destruction of mitochondria. In addition, mitophagy was inhibited at 24 h after stroke and MB augmented mitophagy. In an oxygen-glucose deprivation (OGD) model in vitro, we further revealed that the elevation of mitochondrial membrane potential (MMP) by MB under OGD conditions mediated the augmented mitophagy. In contrast, exacerbating the decline of MMP during OGD abolished the MB-induced activation of mitophagy. Taken together, MB promotes mitophagy by maintaining the MMP at a relatively high level, which contributes to a decrease in necrosis and an improvement in neurological function, thereby protecting against ACI injury.

A method for establishing the high-altitude cerebral edema (HACE) model by acute hypobaric hypoxia in adult mice.

BACKGROUND: Exposure to acute hypobaric hypoxia (AHH) during ascent to high altitudes (>3500 m) is one of the main causes of acute mountain sickness (AMS) and high-altitude cerebral edema (HACE). Therefore, the aim of this study was to develop a model of HACE. NEW METHODS: We developed a model of HACE in mice using a decompression chamber with rapid ascent speed. RESULTS: Healthy male C57BL/6 mice were randomly divided into the control group and the AHH group. The AHH group was housed in a decompression chamber (at a velocity of 50 m/s within 5 min to 6000 m). Compared with the controls, brain water content was increased in the early stage (within 24 h) in the AHH group. After 72 h of exposure to AHH, there was a higher BBB permeability observed. In addition, the brain structure showed significant widening of the pericellular spaces and a dilatation of the cortical blood vessels after exposure to AHH, and some of the neurons appeared shrunken with darkly stained pyknotic nuclei, resulting in neuronal structural damage. Further, exposure to AHH also decreased cognitive function in the mice. COMPARISON WITH EXISTING METHODS: At present, there are no simple and rapid mouse models to study this syndrome in terms of its genetic basis, gene polymorphisms and susceptibility. CONCLUSION: Our findings show that AHH can increase BBB permeability and lead to cerebral edema in mice; thus, we provide an effective and stable model of HACE in mice.

Enhanced hypoxia-inducible factor (HIF)-1α stability induced by 5-hydroxymethyl-2-furfural (5-HMF) contributes to protection against hypoxia.

We first reported the role of 5-hydroxymethyl-2-furfural (5-HMF) against hypoxia. Here, we studied the mechanism by using oxygen-dependent degradation domain (ODD)-Luc mice, which are a useful model to probe the stabilization of hypoxia-inducible factor 1α (HIF-1α). Compared with three other compounds that have been reported to have a role in stabilizing HIF-1α, 5-HMF caused stronger bioluminescence, which is indicative of HIF-1α stability in the brain and kidney of ODD-Luc mice. We further demonstrated that the HIF-1α protein accumulated in response to 5-HMF in the brains and kidneys of these mice, as well as in PC12 cells. Additionally, 5-HMF promoted the nuclear translocation of HIF-1α and the transcriptional activity of HIF-1, which was evaluated by detecting vascular endothelial growth factor (VEGF ) mRNA expression. These results suggest that 5-HMF stabilized HIF-1α and increased its activity. Considering the role of proline hydroxylases (PHDs) in negatively regulating HIF-1α stability, we explored whether 5-HMF interacts with the substrates and cofactors of PHDs, such as 2-oxoglutarate (2-OG), Fe(2+) and vitamin C (VC), which affects the activity of PHDs. The result revealed that 5-HMF did not interact with Fe(2+) or 2-OG but interacted with VC. This interaction was confirmed by subsequent experiments, in which 5-HMF entered into cells and reduced the VC content. The enhanced stability of HIF-1α by 5-HMF was reversed by VC supplementation, and the improved survival of mice caused by 5-HMF under hypoxia was abrogated by VC supplementation. Thus, we demonstrated for the first time that 5-HMF increases HIF-1α stability by reducing the VC content, which mediates the protection against hypoxia.

[Effect of high altitude hypoxia on cognitive flexibility].

OBJECTIVE: To explore the effects of high altitude on cognitive flexibility. METHODS: Simulated hypoxia at an altitude of 3 600 m was performed in a hypobaric chamber. Twenty-three volunteers without hypoxic experience were selected and the mean age was about 25.1 years. The physiological parameters (heart rate, blood pressure and oxygen saturation) were measured. Task switch paradigm was used to explore the cognitive flexibility in each phase, and the changing anxiety state was evaluated simultaneously. RESULTS: Reaction time (RT) switch cost in hypoxia phase showed a significant increase compared with the baseline; anxiety level in hypoxia phase was higher than the adaptation phase; a remarkable negative correlation between anxiety level and RT switch cost was found in adaptation phase, whereas a positive correlation was found in landing phase. CONCLUSION: High altitude (3 600 m) affects cognitive flexibility and anxiety state. Anxiety before the hypoxia exposure improves the cognitive flexibility performance, while anxiety after the hypoxia exposure hampers the performance because of the post-hypoxia effect.

Notch1 mediates postnatal neurogenesis in hippocampus enhanced by intermittent hypoxia.

Notch1 is a transcription factor on the membrane and regulates various stages of neurogenesis. Recently, studies have shown that in vitro neurogenesis is enhanced by hypoxia, and there is cross-coupling between Notch and hypoxia signaling pathways in vitro. However, to date, no data have reported whether Notch1 can be regulated by hypoxia in vivo and mediates hypoxia-induced neurogenesis. To determine causative links between Notch1, neurogenesis and hypoxia, we examined multiple steps of hippocampal neurogenesis followed intermittent hypoxia (IH) in wild type (WT) and Notch1 heterozygous deficient (N+/-) mice. We found that IH increased NSC proliferation, newborn neuron survival and migration, and spine morphogenesis in dentate gyrus of hippocampus, as well as neurogenesis in olfactory bulb in WT mice. However, IH-enhanced neurogenesis was inhibited in N+/- mice. It was shown that Notch1 signaling was activated following IH in WT mice, but not in N+/- mice. Our data indicated that IH, as a novel external stimulus, enhances neurogenesis at multiple stages and that Notch1 is activated by hypoxia in vivo and required for hypoxia-induced neurogenesis. These results suggest IH as a novel therapeutic strategy for degenerative neurological disorders and provide evidence for causative links between Notch1, neurogenesis and hypoxia.

[The effects of autophagy on cell survival under different hypoxia].

OBJECTIVE: To investigate the regulation of different hypoxia on cell survival and autophagy. METHODS: PC12 cells were treated with different hypoxia. The cell survival was measured by MTT assay, expressions of LC3 and p62 were marked for autophagy detected by Western Blot, and the level of reactive oxygen species (ROS) was analyzed by flow cytometry. RESULTS: The cell viability was different under different hypoxia: moderate hypoxia promoted cell viability, and severe hypoxia caused a decrease in cell viability; autophagy marker molecules, p62 and LC3-II expressions were different: moderate hypoxia increased p62 and LC3-II expressions, in contrast, severe hypoxia led to the decrease of p62 and LC3-II expressions; compared to normoxia, moderate hypoxia did not change the levels of ROS, while severe hypoxia increased the levels; 3-MA, the inhibitor of autophagy, elevated the levels of ROS in the three oxygen concentrations, additionally, the increased amplitudes in the moderate and severe hypoxia groups were higher than that in the normoxia group. CONCLUSION: Moderate hypoxia promotes cell survival, severe hypoxia causes the cell death, and the autophagy activity may mediate the effects of different hypoxia.

miR-210 suppresses BNIP3 to protect against the apoptosis of neural progenitor cells.

MiR-210 is a hypoxia-inducible factor (HIF)-1 target gene and is the most consistently and predominantly upregulated miRNA in response to hypoxia in various cancer cell lines. Our recent study shows that hypoxia increased miR-210 expression in neural progenitor cells (NPCs) in a time-dependent manner. However, the role of miR-210 in NPCs remains unknown. Following the identification of the miR-210 putative target genes, we demonstrated that the Bcl-2 adenovirus E1B 19kDa-interacting protein 3 (BNIP3), which is regulated by HIF-1 and activates cell death, is regulated by miR-210 in NPCs under hypoxia. Moreover, the over-expression of miR-210 decreased apoptosis in NPCs, and the inhibition of miR-210 expression remarkably increased the number of TUNEL-positive NPCs by 30% in response to hypoxia. Importantly, miR-210 mimics reduced both BNIP3 protein expression and the translocation of AIF into the nucleus, which reduced cell death, whereas miR-210 inhibitors reversed this process, leading to cell death during hypoxia. Taken together, we report a novel feedback loop of BNIP3 regulation in NPCs under hypoxia. HIF-1 is activated under hypoxia and then induces the expression of both BNIP3 and miR-210. The upregulation of miR-210 then directly suppresses BNIP3 expression to maintain the survival of NPCs under hypoxia. This negative feedback regulation might partially contribute to protection against hypoxia-induced cell death via the inhibition of AIF nuclear translocation.

FHL family members suppress vascular endothelial growth factor expression through blockade of dimerization of HIF1α and HIF1ß.

Four and a half LIM domain (FHL) proteins belong to a family of LIM-only proteins that have been implicated in the development and progression of various types of cancers. However, the role of FHL proteins in tumor angiogenesis remains to be elucidated. Herein, we demonstrate that FHL1-3 decrease the promoter activity and expression of vascular endothelial growth factor (VEGF), the key regulator of angiogenesis in cancer growth and progression as well as an important target gene of the transcription factor hypoxia-inducible factor 1 (HIF1α/HIF1ß). FHL1-3 interacted with HIF1α both in vitro and in vivo. A single LIM domain of FHL1 was sufficient for its interaction with HIF1α. FHL1 interacted with the HIF1α region containing basic helix-loop-helix (bHLH) motif and PER-ARNT-SIM domain, both of which aid in dimerization with HIF1ß and DNA binding. FHL1-3 inhibited HIF1 transcriptional activity and HIF1-mediated VEGF expression in a hypoxia-independent manner. Moreover, FHL1 blocked HIF1α-HIF1ß heterodimerization and HIF1α recruitment to the VEGF promoter. These data suggest that FHL proteins are involved in negative regulation of VEGF possibly by interfering with the dimerization and DNA binding of HIF1 subunits and may play an important role in tumor angiogenesis.

DNA demethylation regulates the expression of miR-210 in neural progenitor cells subjected to hypoxia.

Several studies have identified a set of hypoxia-regulated microRNAs, among which is miR-210, whose expression is highly induced by hypoxia in various cancer cell lines. Recent studies have highlighted the importance of miR-210 and its transcriptional regulation by the transcription factor hypoxia-inducible factor-1 (HIF-1). We report here that the expression of miR-210 was highly induced in neural progenitor cells (NPCs) subjected to hypoxia. Specifically, treating hypoxic NPCs with the DNA demethylating agent 5-aza-2'-deoxycytidine significantly increased the expression of miR-210, even under normoxia; however, the activity of hypoxia-inducible factor-1 was unaffected. Further analysis of the miR-210 sequence revealed that it is embedded in a CpG island. Bisulfite sequencing of the miR-210 CpG island from NPCs grown under hypoxic conditions showed 24% CpG methylation in NPCs exposed to 20% O(2) , 18% in NPCs exposed to 3% O(2) , and 12% in NPCs exposed to 0.3% O(2) . In addition, the activity of DNA methyltransferases (DNMTs) in NPCs decreased after exposure to hypoxia. Specifically, the expression of DNMT3b decreased significantly after exposure to 0.3% O(2) . Thus, these results demonstrate that DNA demethylation regulates miR-210 expression in NPCs under both normoxia and hypoxia.