Identifying age-specific gene signatures of the human cerebral cortex with joint analysis of transcriptomes and functional connectomes.

The human cerebral cortex undergoes profound structural and functional dynamic variations across the lifespan, whereas the underlying molecular mechanisms remain unclear. Here, with a novel method transcriptome-connectome correlation analysis (TCA), which integrates the brain functional magnetic resonance images and region-specific transcriptomes, we identify age-specific cortex (ASC) gene signatures for adolescence, early adulthood and late adulthood. The ASC gene signatures are significantly correlated with the cortical thickness (P-value <2.00e-3) and myelination (P-value <1.00e-3), two key brain structural features that vary in accordance with brain development. In addition to the molecular underpinning of age-related brain functions, the ASC gene signatures allow delineation of the molecular mechanisms of neuropsychiatric disorders, such as the regulation between ARNT2 and its target gene ETF1 involved in Schizophrenia. We further validate the ASC gene signatures with published gene sets associated with the adult cortex, and confirm the robustness of TCA on other brain image datasets. Availability: All scripts are written in R. Scripts for the TCA method and related statistics result can be freely accessed at https://github.com/Soulnature/TCA. Additional data related to this paper may be requested from the authors.

Aryl Hydrocarbon Receptor Nuclear Translocator in Vascular Smooth Muscle Cells Is Required for Optimal Peripheral Perfusion Recovery.

BACKGROUND: Limb ischemia resulting from peripheral vascular disease is a common cause of morbidity. Vessel occlusion limits blood flow, creating a hypoxic environment that damages distal tissue, requiring therapeutic revascularization. Hypoxia-inducible factors (HIFs) are key transcriptional regulators of hypoxic vascular responses, including angiogenesis and arteriogenesis. Despite vascular smooth muscle cells' (VSMCs') importance in vessel integrity, little is known about their functional responses to hypoxia in peripheral vascular disease. This study investigated the role of VSMC HIF in mediating peripheral ischemic responses. METHODS AND RESULTS: We used ArntSMKO mice with smooth muscle-specific deletion of aryl hydrocarbon receptor nuclear translocator (ARNT, HIF-1ß), required for HIF transcriptional activity, in a femoral artery ligation model of peripheral vascular disease. ArntSMKO mice exhibit impaired perfusion recovery despite normal collateral vessel dilation and angiogenic capillary responses. Decreased blood flow manifests in extensive tissue damage and hypoxia in ligated limbs of ArntSMKO mice. Furthermore, loss of aryl hydrocarbon receptor nuclear translocator changes the proliferation, migration, and transcriptional profile of cultured VSMCs. ArntSMKO mice display disrupted VSMC morphologic features and wrapping around arterioles and increased vascular permeability linked to decreased local blood flow. CONCLUSIONS: Our data demonstrate that traditional vascular remodeling responses are insufficient to provide robust peripheral tissue reperfusion in ArntSMKO mice. In all, this study highlights HIF responses to hypoxia in arteriole VSMCs critical for the phenotypic and functional stability of vessels that aid in the recovery of blood flow in ischemic peripheral tissues.

Pharmacological induction of hypoxia-inducible transcription factor ARNT attenuates chronic kidney failure.

Progression of chronic kidney disease associated with progressive fibrosis and impaired tubular epithelial regeneration is still an unmet biomedical challenge because, once chronic lesions have manifested, no effective therapies are available as of yet for clinical use. Prompted by various studies across multiple organs demonstrating that preconditioning regimens to induce endogenous regenerative mechanisms protect various organs from later incurring acute injuries, we here aimed to gain insights into the molecular mechanisms underlying successful protection and to explore whether such pathways could be utilized to inhibit progression of chronic organ injury. We identified a protective mechanism controlled by the transcription factor ARNT that effectively inhibits progression of chronic kidney injury by transcriptional induction of ALK3, the principal mediator of antifibrotic and proregenerative bone morphogenetic protein-signaling (BMP-signaling) responses. We further report that ARNT expression itself is controlled by the FKBP12/YY1 transcriptional repressor complex and that disruption of such FKBP12/YY1 complexes by picomolar FK506 at subimmunosuppressive doses increases ARNT expression, subsequently leading to homodimeric ARNT-induced ALK3 transcription. Direct targeting of FKBP12/YY1 with in vivo morpholino approaches or small molecule inhibitors, including GPI-1046, was equally effective for inducing ARNT expression, with subsequent activation of ALK3-dependent canonical BMP-signaling responses and attenuated chronic organ failure in models of chronic kidney disease, and also cardiac and liver injuries. In summary, we report an organ-protective mechanism that can be pharmacologically modulated by immunophilin ligands FK506 and GPI-1046 or therapeutically targeted by in vivo morpholino approaches.

Structural and functional analysis of coral Hypoxia Inducible Factor.

Tissues of symbiotic Cnidarians are exposed to wide, rapid and daily variations of oxygen concentration. Indeed, during daytime, intracellular O2 concentration increases due to symbiont photosynthesis, while during night, respiration of both host cells and symbionts leads to intra-tissue hypoxia. The Hypoxia Inducible Factor 1 (HIF-1) is a heterodimeric transcription factor used for maintenance of oxygen homeostasis and adaptation to hypoxia. Here, we carried out a mechanistic study of the response to variations of O2 concentrations of the coral model Stylophora pistillata. In silico analysis showed that homologs of HIF-1 α (SpiHIF-1α) and HIF-1ß (SpiHIF-1ß) exist in coral. A specific SpiHIF-1 DNA binding on mammalian Hypoxia Response Element (HRE) sequences was shown in extracts from coral exposed to dark conditions. Then, we cloned the coral HIF-1α and ß genes and determined their expression and transcriptional activity. Although HIF-1α has an incomplete Oxygen-dependent Degradation Domain (ODD) relative to its human homolog, its protein level is increased under hypoxia when tested in mammalian cells. Moreover, co-transfection of SpiHIF-1α and ß in mammalian cells stimulated an artificial promoter containing HRE only in hypoxic conditions. This study shows the strong conservation of molecular mechanisms involved in adaptation to O2 concentration between Cnidarians and Mammals whose ancestors diverged about 1,200-1,500 million years ago.

Identification of a molecular signaling gene-gene regulatory network between GWAS susceptibility genes ADTRP and MIA3/TANGO1 for coronary artery disease.

Coronary artery disease (CAD) is the leading cause of death worldwide. GWAS have identified >50 genomic loci for CAD, including ADTRP and MIA3/TANGO1. However, it is important to determine whether the GWAS genes form a molecular network. In this study, we have uncovered a novel molecular network between ADTRP and MIA3/TANGO1 for the pathogenesis of CAD. We showed that knockdown of ADTRP expression markedly down-regulated expression of MIA3/TANGO1. Mechanistically, ADTRP positively regulates expression of PIK3R3 encoding the regulatory subunit 3 of PI3K, which leads to activation of AKT, resulting in up-regulation of MIA3/TANGO1. Both ADTRP and MIA3/TANGO1 are involved in endothelial cell (EC) functions relevant to atherosclerosis. Knockdown of ADTRP expression by siRNA promoted oxidized-LDL-mediated monocyte adhesion to ECs and transendothelial migration of monocytes, inhibited EC proliferation and migration, and increased apoptosis, which was reversed by expression of constitutively active AKT1 and MIA3/TANGO1 overexpression, while the over-expression of ADTRP in ECs blunted these processes. Knockdown of MIA3/TANGO1 expression also promoted monocyte adhesion to ECs and transendothelial migration of monocytes, and vice versa for overexpression of MIA3/TANGO1. We found that ADTRP negatively regulates the levels of collagen VII and ApoB in HepG2 and endothelial cells, which are downstream regulatory targets of MIA3/TANGOI. In conclusion, we have uncovered a novel molecular signaling pathway for the pathogenesis of CAD, which involves a novel gene-gene regulatory network. We show that ADTRP positively regulates PIK3R3 expression, which leads to activation of AKT and up-regulation of MIA3/TANGO1, thereby regulating endothelial cell functions directly relevant to atherosclerosis.

Role of Glucocorticoid Receptor and Pregnane X Receptor in Dexamethasone Induction of Rat Hepatic Aryl Hydrocarbon Receptor Nuclear Translocator and NADPH-Cytochrome P450 Oxidoreductase.

The aryl hydrocarbon receptor (AHR) nuclear translocator (ARNT), as the AHR's heterodimerization partner, and NADPH-cytochrome P450 oxidoreductase (POR), as the key electron donor for all microsomal P450s, are independent and indispensable components in the adaptive and toxic responses to polycyclic aromatic hydrocarbons. Expression of both ARNT and POR in rat liver is induced by dexamethasone (DEX), a synthetic glucocorticoid known to activate both the glucocorticoid receptor (GR) and the pregnane X receptor (PXR). To better understand the role of GR and PXR in the in vivo DEX induction of rat hepatic ARNT and POR at the mRNA and protein levels, we studied the following: 1) the effects of DEX doses that activate GR (≥0.1 mg/kg) or PXR (≥10 mg/kg); 2) responses produced by GR- and PXR-selective agonists; 3) the impact of GR antagonism on DEX's inducing effects; and 4) whether biologic responses to DEX are altered in PXR-knockout rats. Our findings are consistent with a role for GR as a key mediator of the induction of rat hepatic ARNT expression by glucocorticoids; a role for PXR in the modulation of ARNT protein levels could not be excluded. Although GR activation may contribute to POR mRNA induction, regulation of POR expression and function by DEX is primarily PXR-mediated. This work suggests that the hepatic expression and function of ARNT and POR may be modulated by exposure to exogenous PXR activators and/or conditions that alter glucocorticoid levels such as stress, steroidal therapies, and diseases of excess or deficiency.

Expression and analyses of the HIF-1 pathway in the lungs of humans with pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is characterized by endothelial dysfunction and structural remodeling of the pulmonary vasculature, mediated initially by reduced oxygen availability in the lungs. Hypoxia inducible factor (HIF), consisting of the functional subunit, HIF­1α, and the constitutively expressed HIF­1ß, is involved in the pathological processes associated with hypoxia. In the current study, the sequences of cDNAs and amino acids of HIF were characterized and analyzed using online bioinformatics tools. To further evaluate whether HIF accounts for the occurrence of PAH, the present study determine the expression and phosphorylation levels of HIF and its associated pathways, including extracellular signal­regulated kinase (Erk)1/2 and phosphoinositide 3­kinase (PI3K)/Akt, in the lungs of patients with PAH by reverse transcription­quantitative polymerase chain reaction and western blotting. The mRNA expression levels of PI3K, Erk2, and HIF­1α in the patients with PAH were significantly higher, compared with those in the control group, by 3.6­fold (P<0.01), 4.06­fold and 2.64­fold (P<0.05), respectively. No significant differences were found in the mRNA and protein levels of Akt between the two groups (P>0.05). The protein levels of phosphorylated (p­)Akt, Erk1/2, p­Erk1/2, HIF­1α and HIF­1ß were significantly increased by 5.89­, 0.5­, 0.59­, 1.46­ and 0.92­fold, respectively, in the patients with PAH, compared with those in the controls group (P<0.01 for p­Akt, Erk1/2; P<0.05 for p­Erk1/2, HIF­1α and HIF­1ß). These findings suggested that the mitogen­activated protein kinase and PI3K/Akt signaling pathways, and HIF­1 may perform a specific function in the pathogenesis of PAH.

Comparative studies of hemolymph physiology response and HIF-1 expression in different strains of Litopenaeus vannamei under acute hypoxia.

Litopenaeus vannamei has a high commercial value and is the primary cultured shellfish species globally. In this study, we have compared the hemolymph physiological responses between two L. vannamei strains under acute hypoxia. The results showed that hemocyanin concentration (HC) of strain A6410 was significantly higher than strain Zhengda; Total hemocyte counts (THC) decreased significantly in both strains under hypoxic stress (p < 0.05). We also investigated the temporal and spatial variations of hypoxia inducible factors 1 (HIF-1) by qRT-PCR. The results showed that hypoxia for 12 h increased the expression levels of HIF-1α in tissues of muscle and gill from the two strains (p < 0.05). In the hepatopancreas, the expression levels of HIF-1 increased significantly in strain Zhengda and decreased significantly in strain A6410 (p < 0.05). No significant changes of HIF-1 expression were detected in the same tissues between the two strains under hypoxia for 6 h (p > 0.05), but in the gills and hepatopancreas under hypoxia for 12 h (p < 0.05). Additionally, the expression level of HIF-1 was higher in the strain Zhengda than A6410 in the same tissue under hypoxia for 12 h. It was indicated that the hypoxic tolerance of Litopenaeus vannamei was closely correlated with the expression level of HIF-1, and the higher expression level of HIF-1 to hypoxia, the lower tolerance to hypoxia in the early stage of hypoxia. These results can help to better understand the molecular mechanisms of hypoxic tolerance and speed up the selective breeding process of hypoxia tolerance in L. vannamei.

Induction of WNT11 by hypoxia and hypoxia-inducible factor-1α regulates cell proliferation, migration and invasion.

Changes in cellular oxygen tension play important roles in physiological processes including development and pathological processes such as tumor promotion. The cellular adaptations to sustained hypoxia are mediated by hypoxia-inducible factors (HIFs) to regulate downstream target gene expression. With hypoxia, the stabilized HIF-α and aryl hydrocarbon receptor nuclear translocator (ARNT, also known as HIF-ß) heterodimer bind to hypoxia response elements (HREs) and regulate expression of target genes. Here, we report that WNT11 is induced by hypoxia in many cell types, and that transcription of WNT11 is regulated primarily by HIF-1α. We observed induced WNT11 expression in the hypoxic area of allograft tumors. In addition, in mice bearing orthotopic malignant gliomas, inhibition with bevacizumab of vascular endothelial growth factor, which is an important stimulus for angiogenesis, increased nuclear HIF-1α and HIF-2α, and expression of WNT11. Gain- and loss-of-function approaches revealed that WNT11 stimulates proliferation, migration and invasion of cancer-derived cells, and increases activity of matrix metalloproteinase (MMP)-2 and 9. Since tumor hypoxia has been proposed to increase tumor aggressiveness, these data suggest WNT11 as a possible target for cancer therapies, especially for tumors treated with antiangiogenic therapy.

Identification of differentially expressed three novel transcript variants of mouse ARNT gene.

The aryl hydrocarbon receptor nuclear translocator (ARNT/HIF1-ß) is an obligatory transcriptional partner of the aryl hydrocarbon receptor (AHR) and hypoxia-inducible factor-1α (HIF-1α). It has a basic helix-loop-helix domain that belongs to period-ARNT-single-minded (PAS) protein family. PAS proteins act as heterodimeric transcription factors with ARNT being master dimerization partner. The ARNT-HIF-1α complex is an important transcriptional regulator of the hypoxic response of the tumor cells. Previous studies have reported two transcript variants of the gene produced by alternative splicing in mouse. One transcript variant contains all 22 exons while the other variant lacks exon-E5. In our study, using combinatorial approach comprising bioinformatics tools and molecular biology techniques involving RT-PCR, semi-nested PCR, sequencing and qPCR, we have identified three novel transcript variants of Arnt gene in mouse. All three new transcripts arise as a result of alternative splicing of newly identified exons with exon-E2, replacing reported exon-E1. These transcripts encode for three protein isofoms having different N-termini. The expression of these transcripts was found to be different in different tissues of adult mice. In silico analysis of the upstream region of the new exons revealed three distinct promoter regions designated as PA, PB and PC present upstream of newly identified exons. These promoters possess potential signature sequences for common as well as different transcription factors suggesting complex regulation of Arnt gene. In silico post translational studies of the conceptually translated amino acid sequences of these transcripts show similarity in some of the properties while differ in others. The diversity at N-termini of protein isoforms suggests the possibility of forming different complexes in different tissues and may also be important for unique interactions with partner molecules.

Arylhydrocarbon receptor-dependent mIndy (Slc13a5) induction as possible contributor to benzo[a]pyrene-induced lipid accumulation in hepatocytes.

Non-alcoholic fatty liver disease is a growing problem in industrialized and developing countries. Hepatic lipid accumulation is the result of an imbalance between fatty acid uptake, fatty acid de novo synthesis, ß-oxidation and secretion of triglyceride-rich lipoproteins from the hepatocyte. A central regulator of hepatic lipid metabolism is cytosolic citrate that can either be derived from the mitochondrium or be taken up from the blood via the plasma membrane sodium citrate transporter NaCT, the product of the mammalian INDY gene (SLC13A5). mINDY ablation protects against diet-induced steatosis whereas mINDY expression is increased in patients with hepatic steatosis. Diet-induced hepatic steatosis is also enhanced by activation of the arylhyrocarbon receptor (AhR) both in humans and animal models. Therefore, the hypothesis was tested whether the mINDY gene might be a target of the AhR. In accordance with such a hypothesis, the AhR activator benzo[a]pyrene induced the mINDY expression in primary cultures of rat hepatocytes in an AhR-dependent manner. This induction resulted in an increased citrate uptake and citrate incorporation into lipids which probably was further enhanced by the benzo[a]pyrene-dependent induction of key enzymes of fatty acid synthesis. A potential AhR binding site was identified in the mINDY promoter that appears to be conserved in the human promoter. Elimination or mutation of this site largely abolished the activation of the mINDY promoter by benzo[a]pyrene. This study thus identified the mINDY as an AhR target gene. AhR-dependent induction of the mINDY gene might contribute to the development of hepatic steatosis.

Inverse regulation of early and late chondrogenic differentiation by oxygen tension provides cues for stem cell-based cartilage tissue engineering.

BACKGROUND/AIMS: Multipotent stem/stromal cells (MSC) are considered promising for cartilage tissue engineering. However, chondrogenic differentiation of MSC can ultimately lead to the formation of hypertrophic chondrocytes responsible for the calcification of cartilage. To prevent the production of this calcified matrix at the articular site, the late hypertrophic differentiation of MSCs must be carefully controlled. Given that articular cartilage is avascular, we hypothesized that in addition to its stimulatory role in the early differentiation of chondrogenic cells, hypoxia may prevent their late hypertrophic conversion. METHODS: Early and late chondrogenic differentiation were evaluated using human adipose MSC and murine ATDC5 cells cultured under either normoxic (21%O2) or hypoxic (5%O2) conditions. To investigate the effect of hypoxia on late chondrogenic differentiation, the transcriptional activity of hypoxia-inducible factor-1alpha (HIF-1α) and HIF-2α were evaluated using the NoShift DNA-binding assay and through modulation of their activity (chemical inhibitor, RNA interference). Results : Our data demonstrate that low oxygen tension not only stimulates the early chondrogenic commitment of two complementary models of chondrogenic cells, but also inhibits their hypertrophic differentiation. Conclusion : These results suggest that hypoxia can be used as an instrumental tool to prevent the formation of a calcified matrix in MSC-based cartilage tissue engineering.

Hypoxia-inducible factor/MAZ-dependent induction of caveolin-1 regulates colon permeability through suppression of occludin, leading to hypoxia-induced inflammation.

Caveolae are specialized microdomains on membranes that are critical for signal transduction, cholesterol transport, and endocytosis. Caveolin-1 (CAV1) is a multifunctional protein and a major component of caveolae. Cav1 is directly activated by hypoxia-inducible factor (HIF). HIFs are heterodimers of an oxygen-sensitive α subunit, HIF1α or HIF2α, and a constitutively expressed ß subunit, aryl hydrocarbon receptor nuclear translocator (ARNT). Whole-genome expression analysis demonstrated that Cav1 is highly induced in mouse models of constitutively activated HIF signaling in the intestine. Interestingly, Cav1 was increased only in the colon and not in the small intestine. Currently, the mechanism and role of HIF induction of CAV1 in the colon are unclear. In mouse models, mice that overexpressed HIF1α or HIF2α specifically in intestinal epithelial cells demonstrated an increase in Cav1 gene expression in the colon but not in the duodenum, jejunum, or ileum. HIF2α activated the Cav1 promoter in a HIF response element-independent manner. myc-associated zinc finger (MAZ) protein was essential for HIF2α activation of the Cav1 promoter. Hypoxic induction of CAV1 in the colon was essential for intestinal barrier integrity by regulating occludin expression. This may provide an additional mechanism by which chronic hypoxia can activate intestinal inflammation.

The aryl hydrocarbon receptor promotes IL-10 production by NK cells.

The cytokine IL-10 has an important role in limiting inflammation in many settings, including toxoplasmosis. In the present studies, an IL-10 reporter mouse was used to identify the sources of this cytokine following challenge with Toxoplasma gondii. During infection, multiple cell types expressed the IL-10 reporter but NK cells were a major early source of this cytokine. These IL-10 reporter(+) NK cells expressed high levels of the IL-12 target genes T-bet, KLRG1, and IFN-γ, and IL-12 depletion abrogated reporter expression. However, IL-12 signaling alone was not sufficient to promote NK cell IL-10, and activation of the aryl hydrocarbon receptor (AHR) was also required for maximal IL-10 production. NK cells basally expressed the AHR, relevant chaperone proteins, and the AHR nuclear translocator, which heterodimerizes with the AHR to form a competent transcription factor. In vitro studies revealed that IL-12 stimulation increased NK cell AHR levels, and the AHR and AHR nuclear translocator were required for optimal production of IL-10. Additionally, NK cells isolated from T. gondii-infected Ahr(-/-) mice had impaired expression of IL-10, which was associated with increased resistance to this infection. Taken together, these data identify the AHR as a critical cofactor involved in NK cell production of IL-10.

Interferon-γ-induced intestinal epithelial barrier dysfunction by NF-κB/HIF-1α pathway.

Interferon-γ (IFN-γ) plays an important role in intestinal barrier dysfunction. However, the mechanisms are not fully understood. As hypoxia-inducible factor-1 (HIF-1) is a critical determinant response to hypoxia and inflammation, which has been shown to be deleterious to intestinal barrier function, we hypothesized that IFN-γ induces loss of barrier function through the regulation of HIF-1α activation and function. In this study, we detected the expressions of HIF-1α and tight junction proteins in IFN-γ-treated T84 intestinal epithelial cell line. IFN-γ led to an increase of HIF-1α expression in time- and dose-dependent manners but did not change the expression of HIF-1ß. The IFN-γ-induced increase in HIF-1α was associated with an activation of NF-κB. Treatment with the NF-κB inhibitor, pyrolidinedithiocarbamate (PDTC), significantly suppressed the activation of NF-κB and the expression of HIF-1α. In addition, IFN-γ also increased intestinal epithelial permeability and depletion of tight junction proteins; inhibition of NF-κB or HIF-1α prevented the increase in intestinal permeability and alteration in tight junction protein expressions. Interestingly, we demonstrated that a significant portion of IFN-γ activation NF-kB and modulation tight junction expression is mediated through HIF-1α. Taken together, this study suggested that IFN-γ induced the loss of epithelial barrier function and disruption of tight junction proteins, by upregulation of HIF-1α expression through NF-κB pathway.

Expression of aryl hydrocarbon receptor nuclear translocator enhances cisplatin resistance by upregulating MDR1 expression in cancer cells.

The identification of molecular pathways in cancer cells is important for understanding the cells' underlying biology and for designing effective cancer therapies. We demonstrate that the expression of aryl hydrocarbon receptor nuclear translocator (ARNT) is critical during the development of cisplatin resistance. The reduced expression of ARNT was correlated with cisplatin-induced cell death in drug-sensitive cells. In addition, suppression of ARNT reversed the characteristics of cisplatin-resistant cells, making these cells cisplatin-sensitive, and significantly enhanced caspase-3 activation, DNA fragmentation, and apoptosis. The inhibition of colony formation, regulated by cisplatin, was more significant in ARNT-knockdown cells than in parental cells. In a xenograft analysis of severe combined immunodeficiency mice, cisplatin also efficiently inhibited ARNT-deficient c4 tumors but not ARNT-containing vT2 tumor formation. Furthermore, the downregulation of multidrug resistance 1 (MDR1) expression and retention of drugs in cells caused by suppression of ARNT, resulting in the resensitization of drug-resistant cells to cisplatin, was observed. When overexpressed, ARNT interacted with Sp1 to enhance the expression of MDR1 through Sp1-binding sites on the MDR1 promoter, resulting in a reversal of the effect of cisplatin on cell death. In addition, ARNT-induced MDR1 expression was inhibited in Sp1-knockdown cells. These results reveal previously unrecognized, multifaceted functions of ARNT in establishing the drug-resistant properties of cancer cells by the upregulation of MDR1, highlighting ARNT's potential as a therapeutic target in an important subset of cancers.

Reciprocal regulation of the basic helix-loop-helix/Per-Arnt-Sim partner proteins, Arnt and Arnt2, during neuronal differentiation.

Basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) transcription factors function broadly in development, homeostasis and stress response. Active bHLH/PAS heterodimers consist of a ubiquitous signal-regulated subunit (e.g., hypoxia-inducible factors, HIF-1α/2α/3α; the aryl hydrocarbon receptor, AhR) or tissue-restricted subunit (e.g., NPAS1/3/4, Single Minded 1/2), paired with a general partner protein, aryl hydrocarbon receptor nuclear translocator (Arnt or Arnt2). We have investigated regulation of the neuron-enriched Arnt paralogue, Arnt2. We find high Arnt/Arnt2 ratios in P19 embryonic carcinoma cells and ES cells are dramatically reversed to high Arnt2/Arnt on neuronal differentiation. mRNA half-lives of Arnt and Arnt2 remain similar in both parent and neuronal differentiated cells. The GC-rich Arnt2 promoter, while heavily methylated in Arnt only expressing hepatoma cells, is methylation free in P19 and ES cells, where it is bivalent with respect to active H3K4me3 and repressive H3K27me3 histone marks. Typical of a 'transcription poised' developmental gene, H3K27me3 repressive marks are removed from Arnt2 during neuronal differentiation. Our data are consistent with a switch to predominant Arnt2 expression in neurons to allow specific functions of neuronal bHLH/PAS factors and/or to avoid neuronal bHLH/PAS factors from interfering with AhR/Arnt signalling.

Endothelial GATA-6 deficiency promotes pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease characterized by pulmonary vasculopathy with elevation of pulmonary artery pressure, often culminating in right ventricular failure. GATA-6, a member of the GATA family of zinc-finger transcription factors, is highly expressed in quiescent vasculature and is frequently lost during vascular injury. We hypothesized that endothelial GATA-6 may play a critical role in the molecular mechanisms underlying endothelial cell (EC) dysfunction in PAH. Here we report that GATA-6 is markedly reduced in pulmonary ECs lining both occluded and nonoccluded vessels in patients with idiopathic and systemic sclerosis-associated PAH. GATA-6 transcripts are also rapidly decreased in rodent PAH models. Endothelial GATA-6 is a direct transcriptional regulator of genes controlling vascular tone [endothelin-1, endothelin-1 receptor type A, and endothelial nitric oxide synthase (eNOS)], pro-inflammatory genes, CX3CL1 (fractalkine), 5-lipoxygenease-activating protein, and markers of vascular remodeling, including PAI-1 and RhoB. Mice with the genetic deletion of GATA-6 in ECs (Gata6-KO) spontaneously develop elevated pulmonary artery pressure and increased vessel muscularization, and these features are further exacerbated in response to hypoxia. Furthermore, innate immune cells including macrophages (CD11b(+)/F4/80(+)), granulocytes (Ly6G(+)/CD45(+)), and dendritic cells (CD11b(+)/CD11c(+)) are significantly increased in normoxic Gata6-KO mice. Together, our findings suggest a critical role of endothelial GATA-6 deficiency in development and disease progression in PAH.

Hypoxia-inducible factor-1ß (HIF-1ß) is upregulated in a HIF-1α-dependent manner in 518A2 human melanoma cells under hypoxic conditions.

Solid tumors include hypoxic areas due to excessive cell proliferation. Adaptation to low oxygen levels is mediated by the hypoxia-inducible factor (HIF) pathway promoting invasion, metastasis, metabolic alterations, chemo-resistance and angiogenesis. The transcription factor HIF-1, the major player within this pathway consists of HIF-1α and HIF-1ß. The alpha subunit is continuously degraded under normoxia and becomes stabilized under reduced oxygen supply. In contrast, HIF-1ß is generally regarded as constitutively expressed and being present in excess within the cell. However, there is evidence that the expression of this subunit is more complex. The aim of this study was to investigate the role of HIF-1ß in human melanoma cells. Among a panel of five different cell lines, in 518A2 cells exposed to the hypoxia-mimetic cobalt chloride HIF-1ß was rapidly elevated on protein level. Knockdown experiments performed under cobalt chloride-exposure and hypoxia revealed that this effect was mediated by HIF-1α. The non-canonical relationship between these subunits was further confirmed by pharmacologic inhibition of HIF-1α and by expression of a dominant-negative HIF mutant. Overexpression of HIF-1α showed a time delay in HIF-1ß induction, thus arguing for HIF-1ß de novo synthesis rather than protein stabilization by heterodimerization. A Hen's egg test-chorioallantoic membrane model of angiogenesis and invasion indicated a local expression of HIF-1ß and implies a biological relevance of these findings. In summary, this study demonstrates the HIF-1α-dependent regulation of HIF-1ß under hypoxic conditions for the first time. The results indicate a novel cell specific mechanism which might prevent HIF-1ß to become a limiting factor.

The alteration of hypoxia inducible factor-1 (HIF-1) and its target genes in mood disorder patients.

Recent studies suggest that the dysfunction of neural plasticity is associated with mood disorders. Hypoxia-inducible factor-1 (HIF-1), which is a transcriptional activator of vascular endothelial growth factor (VEGF), activates the cellular response to hypoxia. HIF-1 is ubiquitously expressed in all cells, including peripheral leukocytes. However, little is known about the role of HIF-1 in mood disorder. In the present study, we investigated the mRNA expression levels of HIF-1 (α and ß) and its target genes (VEGF, GLUT1, PGK1, PFKFB3, and LDHA) in the peripheral white blood cells of patients with major depressive disorder (MDD) and bipolar disorder (BPD). We found increased expression of HIF- 1α and HIF-1ß mRNA, as well as the target genes, VEGF, and PFKFB3 in both MDD and BPD patients in a depressive state compared to healthy control subjects. Furthermore, the mRNA expression levels of GLUT1, PGK1, and LDHA were increased in MDD patients in a depressive state compared to healthy control subjects. We also found increased expression of HIF-1α and LDHA mRNA in MDD patients in a remissive state, whereas the mRNA expression levels of other genes in a remissive state were comparable to those in healthy control subjects. There was no significant difference in mRNA expression levels of the genes examined among patients receiving any type of antidepressant or mood stabilizer. Our data suggest that altered expression of HIF-1 and its target genes mRNA in peripheral blood cells are associated-mainly in a state-dependent manner-with mood disorders (especially with MDD). In addition, altered expression of HIF-1 and its target genes may be associated with the pathophysiology of depression.