Hypoxia-inducible factors HIF-1alpha and HIF-2alpha are decreased in an experimental model of severe respiratory distress syndrome in preterm lambs.

Respiratory distress syndrome (RDS) secondary to preterm birth and surfactant deficiency is characterized by severe hypoxemia, lung injury, and impaired production of nitric oxide (NO) and vascular endothelial growth factor (VEGF). Since hypoxia-inducible factors (HIFs) mediate the effects of both NO and VEGF in part through regulation by prolyl-hydroxylase-containing domains (PHDs) in the presence of oxygen, we hypothesized that HIF-1alpha and -2alpha in the lung are decreased following severe RDS in preterm neonatal lambs. To test this hypothesis, fetal lambs were delivered at preterm gestation (115-day gestation, term = 145 days; n = 4) and mechanically ventilated for 4 h. Lambs developed respiratory failure characterized by severe hypoxemia despite treatment with mechanical ventilation with high inspired oxygen concentrations. Lung samples were compared with nonventilated control animals at preterm (115-day gestation; n = 3) and term gestation (142-day gestation; n = 3). We found that HIF-1alpha protein expression decreased (P < 0.05) and PHD-2 expression increased (P < 0.005) at birth in normal term animals before air breathing. Compared with age-matched controls, HIF-1alpha protein and HIF-2alpha protein expression decreased by 80% and 55%, respectively (P < 0.005 for each) in preterm lambs with RDS. Furthermore, VEGF mRNA was decreased by 40%, and PHD-2 protein expression doubled in RDS lambs. We conclude that pulmonary expression of HIF-1alpha, HIF-2alpha, and the downstream target of their regulation, VEGF mRNA, is impaired following RDS in neonatal lambs. We speculate that early disruption of HIF and VEGF expression after preterm birth and RDS may contribute to long-term abnormalities in lung growth, leading to bronchopulmonary dysplasia.

Grover TR ，Asikainen TM ，Kinsella JP ，Abman SH ，White CW ... -  《AMERICAN JOURNAL OF PHYSIOLOGY-LUNG CELLULAR AND MOLECULAR PHYSIOLOGY》

Effect of preterm birth on hypoxia-inducible factors and vascular endothelial growth factor in primate lungs.

Diminished vascular and alveolar development is characteristic of bronchopulmonary dysplasia (BPD). The low fetal O(2) tension promotes angiogenic responses during ontogenesis, while preterm birth interrupts normal lung growth. Most of the angiogenic responses are governed by hypoxia-inducible factors (HIFs), the expressions of which are unknown in the lungs of preterm primates. Lung tissue was harvested from fetal third-trimester baboons as well as from preterm baboons (67% or 75% of term gestation) treated with mechanical ventilation and either pro re nata (PRN) or 100% O(2). Both groups of preterm animals developed lung hypoplasia similar to human BPD. Expression of HIF-1alpha protein by Western blotting of nuclear extracts of fetal baboon samples differed from that of HIF-2alpha in that both were high at early third trimester, but at term, HIF-1alpha was absent, whereas HIF-2alpha remained unchanged. Moreover, the expression of prolyl hydroxylase domain-containing proteins 2 and 3 (PHD-2 and -3), which degrade HIFs, was increased following term birth. HIF-1alpha was diminished both in 125-day and 140-day BPD models, whereas HIF-2alpha was reduced only in the latter. Surprisingly, vascular endothelial growth factor (VEGF) was enhanced in preterm baboons with BPD as compared with age-matched fetal controls, and there was a negative correlation between HIF-1alpha and/or HIF-2alpha and VEGF in BPD. Moreover, VEGF receptors KDR and/or Flt-1 were decreased in BPD. Preterm birth also prevented the end-gestational increase in the expression of endothelial cell marker platelet-endothelial cell adhesion molecule 1. These results suggest that selective downregulation of HIFs in lungs of preterm neonates may contribute to the pathophysiology of BPD.

Asikainen TM ，Ahmad A ，Schneider BK ，White CW ... -  《-》

Increased activation of the hypoxia-inducible factor pathway in varicose veins.

Venous hypoxia has been postulated to contribute to varicose vein (VV) formation. Direct measurements of vein wall oxygen tension have previously demonstrated that the average minimum oxygen tensions were significantly lower in VVs compared with non-varicose veins (NVVs). Hypoxia-inducible factors (HIFs) are nuclear transcriptional factors that regulate the expression of several genes of oxygen homeostasis. This study aimed to investigate if hypoxia was associated with VVs by assessing the expression of HIF-1α, HIF-2α, HIF target genes, and upstream HIF regulatory enzymes in VVs and NVVs, and their regulation by hypoxia. VVs and NVVs were surgically retrieved and immediately snap-frozen or used for organ culture preparation. The relative expression of HIF-1α, HIF-2α, HIF target genes, and HIF regulatory enzymes in VVs and NVVs was analyzed with quantitative polymerase chain reaction (Q-PCR) and Western blot. VV and NVV organ ex vivo cultures were exposed to 16 hours of normoxia, hypoxia (oxygen tension 1%), or the hypoxia mimetic dimethyloxallyl glycine (DMOG) 1 mM in normoxia. The vein organ cultures were then analyzed for HIF-1α, HIF-2α, and their target gene expression with Q-PCR and Western blot. HIF-1α and HIF-2α mRNA were significantly upregulated in VVs compared with NVVs (89.8 ± 18.6 vs 10.4 ± 7.2 and 384.9 ± 209.4 vs 8.1 ± 4.2, respectively). HIF target gene mRNA expression was also significantly elevated in VVs compared with NVVs, namely glucose transporter-1 (GLUT-1; 8.7 ± 2.1 vs 1.0 ± 0.3), carbonic anhydrase-9 (CA9; 8.5 ± 2.1 vs 2.8 ± 1.2), vascular endothelial growth factor (VEGF; 7.5 ± 2.1 vs 0.9 ± 0.2), and BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP-3; 4.5 ± 0.7 vs 1.4 ± 0.3). The upregulation of HIF-1α, HIF-2α, and HIF target genes in VVs was also reflected at protein level. Of the HIF regulatory enzymes, the expression of prolyl-hydroxylase domain (PHD)-2 and PHD-3 was found to be elevated in VVs compared with NVVs. Exposure of VV and NVV organ cultures to hypoxia or DMOG was associated with increases in HIF-1α and HIF-2α protein and HIF target gene expression compared with normoxia only. The study concluded, we believe for the first time, an increased activation of the HIF pathway, with upregulation of the expression of HIF-1α and HIF-2α transcription factors, and HIF target genes, in VVs compared with NVVs. Exposure of VVs and NVVs to hypoxic conditions was associated with increased expression of HIF-1α and HIF-2α protein and HIF target genes. The data suggest that the HIF pathway may be associated with several pathophysiologic changes in the VV wall, and that hypoxia may be a feature contributing to VV pathogenesis.

Lim CS ，Kiriakidis S ，Paleolog EM ，Davies AH ... -  《-》

Increased prolyl 4-hydroxylase expression and differential regulation of hypoxia-inducible factors in the aged rat brain.

Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors that mediate the adaptive response of mammalian cells and tissues to changes in tissue oxygenation. In the present study, we show an age-dependent decline in cortical HIF-1alpha accumulation and activation of HIF target genes in response to hypoxia. This inducible response is significantly attenuated in the cerebral cortex of 18-mo-old Fischer 344 rat yet virtually absent in the cerebral cortex of 24-mo-old Fischer 344 rat. This attenuated HIF-1alpha response had no effect on mRNA upregulation of HIF-independent genes in the aged cortex. We have provided evidence that this absent HIF-1alpha response is directly correlated with an increase in the expression of the HIF regulatory enzyme, prolyl 4-hydroxylase (PHD). In addition, our study shows that cortical HIF-2alpha expression in senescent normoxic controls is also significantly greater than that of younger normoxic controls, despite no difference in HIF-2alpha mRNA levels. The posttranslational regulation of HIF-2alpha under normoxic conditions seems to be attenuated in the aged rat brain, which is an in vivo demonstration of differential regulation of HIF-1alpha and HIF-2alpha.

Ndubuizu OI ，Chavez JC ，LaManna JC 《-》

Placental HIFs as markers of cerebral hypoxic distress in fetal mice.

Trollmann R ，Strasser K ，Keller S ，Antoniou X ，Grenacher B ，Ogunshola OO ，Dötsch J ，Rascher W ，Gassmann M ... -  《AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY》