Publications

Significance The sympathetic nervous system plays a critical role in stimulating heart rate and contractility to increase cardiac output and thereby insure adequate tissue O 2 delivery. Altered sympathetic output contributes to cardiac pathologies, such as sudden cardiac death and heart failure. Our data provide insight into the role of the transcription factor hypoxia-inducible factor 1α (HIF-1α) in the development of sympathetic ganglion neurons and cardiac sympathetic innervation. We found that genetic deletion of HIF-1α resulted in increased cell death and decreased proliferation of neuronal progenitors of the sympathetic system. These findings suggest that dysregulated HIF-1α expression may contribute to cardiac dysfunction and disease associated with defects in the cardiac sympathetic system by affecting the function and survival of sympathetic neurons.

Abstract Using a hypoxia-inducible factor 1 (HIF-1)-dependent luciferase reporter in Hep3B human hepatocellular carcinoma cells, we screened over 3,000 drugs that have been used in clinical trials and identified multiple anthracyclines as inhibitors of HIF-1 activity. Anthracyclines interfered with the ability of HIF-1 to bind to DNA. Daily injection of tumor-bearing mice with anthracyclines at low dose inhibited expression of the luciferase reporter and HIF-1 target genes that encode vascular endothelial growth factor A (VEGFA; ligand of VEGFR2), stromal-derived factor 1 (SDF-1; ligand of CXCR4), and stem cell factor (SCF; ligand of CD117) in tumor tissue. Increased numbers of circulating CXCR4 + /Sca1 + , VEGFR2 + /CD34 + , and VEGFR2 + /CD117 + cells were demonstrated in immunodeficient mice bearing prostate cancer xenografts but not in tumor-bearing mice treated with anthracyclines, which also significantly inhibited angiogenesis in tumor tissue. Our findings indicate that HIF-1 inhibition underlies the anti-angiogenic effect associated with daunorubicin or doxorubicin metronomic therapy and suggest that these drugs may be particularly effective in patients with high levels of HIF-1α in their diagnostic tumor biopsy.

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Increased catalytic activity of CBS (cystathionine β-synthase) was recently shown to mediate vasodilation of the cerebral microcirculation, which is initiated within minutes of the onset of acute hypoxia. To test whether chronic hypoxia was a stimulus for increased CBS expression, U87-MG human glioblastoma and PC12 rat phaeochromocytoma cells were exposed to 1% or 20% O2 for 24–72 h. CBS mRNA and protein expression were increased in hypoxic cells. Hypoxic induction of CBS expression was abrogated in cells transfected with vector encoding shRNA targeting HIF (hypoxia-inducible factor) 1α or 2α. Exposure of rats to hypobaric hypoxia (0.35 atm; 1 atm=101.325 kPa) for 3 days induced increased CBS mRNA, protein and catalytic activity in the cerebral cortex and cerebellum, which was blocked by administration of the HIF inhibitor digoxin. HIF-binding sites, located 0.8 and 1.2 kb 5′ to the transcription start site of the human CBS and rat Cbs genes respectively, were identified by ChIP assays. A 49-bp human sequence, which encompassed an inverted repeat of the core HIF-binding site, functioned as a hypoxia-response element in luciferase reporter transcription assays. Thus HIFs mediate tissue-specific CBS expression, which may augment cerebral vasodilation as an adaptive response to chronic hypoxia.

Chronic hypoxia depolarizes and reduces K + current in pulmonary arterial smooth muscle cells (PASMCs). Our laboratory previously demonstrated that hypoxia-inducible factor-1 (HIF-1) contributed to the development of hypoxic pulmonary hypertension. In this study, electrophysiological parameters were measured in PASMCs isolated from intrapulmonary arteries of mice with one null allele at the Hif1a locus encoding HIF-1α [ Hif1a(+/−)] and from their wild-type [ Hif1a(+/+)] littermates after 3 wk in air or 10% O 2 . Hematocrit and right ventricular wall and left ventricle plus septum weights were measured. Capacitance, K + current, and membrane potential were measured with whole cell patch clamp. Similar to our laboratory's previous results, hypoxia-induced right ventricular hypertrophy and polycythemia were blunted in Hif1a(+/−) mice. Hypoxia increased PASMC capacitance in Hif1a(+/+) mice but not in Hif1a(+/−) mice. Chronic hypoxia depolarized and reduced K + current density in PASMCs from Hif1a(+/+) mice. In PASMCs from hypoxic Hif1a(+/−) mice, no reduction in K + current density was observed, and depolarization was significantly blunted. Thus partial deficiency of HIF-1α is sufficient to impair hypoxia-induced depolarization, reduction of K + current density, and PASMC hypertrophy.

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that controls vascular responses to hypoxia and ischemia. In this study, mice that were heterozygous (HET) for a null allele at the locus encoding the HIF-1alpha subunit (HET mice) and their wild-type (WT) littermates were subjected to a thermal injury involving 10% of the body surface area. HIF-1alpha protein levels were increased in burn wounds of WT but not of HET mice on day 2. The serum levels of stromal-derived factor 1alpha, which binds to CXCR4, were increased on day 2 in WT but not in HET mice. Circulating angiogenic cells were also increased on day 2 in WT but not in HET mice and included CXCR4(+)Sca1(+) cells. Laser Doppler perfusion imaging demonstrated increased blood flow in burn wounds of WT but not HET mice on day 7. Immunohistochemistry on day 7 revealed a reduced number of CD31(+) vessels at the healing margin of burn wounds in HET as compared with WT mice. Vessel maturation was also impaired in wounds of HET mice as determined by the number of alpha-smooth muscle actin-positive vessels on day 21. The remaining wound area on day 14 was significantly increased in HET mice compared with WT littermates. The percentage of healed wounds on day 14 was significantly decreased in HET mice. These data delineate a signaling pathway by which HIF-1 promotes angiogenesis during burn wound healing.

Abstract A major obstacle to using bone marrow cell-based therapies for ischemic cardiovascular disease is that transplanted cells must survive in an ischemic microenvironment characterized by low oxygen, glucose, and pH. We demonstrate that treatment of bone marrow-derived angiogenic cells (BMDACs) with dimethyloxalylglycine, an α-ketoglutarate antagonist that induces hypoxia-inducible factor 1 (HIF-1) activity, results in metabolic reprogramming of these cells, with increased glucose uptake, decreased O2 consumption, increased lactate production, decreased reactive oxygen species, and increased intracellular pH. These effects are dependent on HIF-1, which transactivates target genes encoding metabolic enzymes and membrane transporters. Dimethyloxalylglycine-treated BMDACs have a significant survival advantage under conditions of low O2 and low pH ex vivo and in ischemic tissue. Combined HIF-1α-based gene and cell therapy reduced tissue necrosis even when BMDAC donors and ischemic recipient mice were 17 months old, suggesting that this approach may have therapeutic utility in elderly patients with critical limb ischemia.

Significance Hypoxia (reduced oxygen availability) is a common finding in the tumor microenvironment and plays a critical role in stimulating the metastasis of breast cancer cells from the primary tumor to distant organs, which is closely related to patient mortality. Critical transcriptional responses to reduced O 2 availability are mediated by hypoxia-inducible factors (HIFs). In this study, we demonstrate that hypoxia induces HIF-dependent expression of a disintegrin and metalloproteinase 12 (ADAM12), which clips off the extracellular domain of the membrane-bound heparin-binding epidermal growth factor-like growth factor (HB-EGF). The liberated extracellular domain of HB-EGF binds to the epidermal growth factor receptor, triggering a signal transduction pathway that endows breast cancer cells with increased capability for cell migration and invasion, leading to distant metastasis.