Role of Hypoxia Induced Factor (HIF-1 alpha) in Pulmonary Hypertension in Sickle Cell Disease

Background. Pulmonary hypertension is a leading cause of mortality in sickle cell disease (SCD), however, the mechanisms leading to the development of pulmonary hypertension remain poorly understood. The pathogenesis of SCD revolves around chronic hypoxia and hypoxic events that are mediated through the upregulation of hypoxia-inducible factor-1alpha (HIF-1alpha), a transcriptional factor, that is involved in regulation of several redox sensitive genes including vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF) and ApoE. The objective of this study was to examine the role of HIF-1 and its target genes in SCD-associated pulmonary lung disease.

Methods. In this study, 3 groups of age-matched homo and hemizygous sickle and control C57/Bl6 mice (Jackson Labs) were sacrificed and organs harvested for RNA isolation in Trizol. Using quantitative RT-PCR we assessed the RNA expression of HIF-1 and its target genes, VEGF and PDGF-B from the lungs of homozygous sickle mice and compared these with the C57/BL6 and the hemizygous sickle controls. HPRT was used as the housekeeping gene control.

Results. Homozygous sickle mice demonstrated an upregulation of HIF-1 alpha RNA (almost 2.3 fold) compared with the hemizygous sickle and the C57/Bl6 controls. VEGF RNA expression was elevated ~8.3 to 10.9 fold in sickle mice compared to the two control groups. Interestingly there was a down regulation of PDGF-B expression (0.3 fold) in the sickle mice group compared to the control groups. In contrast, expression of all the HIF-related genes tested was down-regulated in the spleens and brains of sickle mice compared with the respective control tissues.

Discussion. These findings support the possibility that complex molecular pathways, including dysregulation of HIF pathway, may contribute to the development of pulmonary hypertension in sickle cell disease and underscore role of oxidative stress pathways in the onset of disease pathogenesis.