MORG1 And ING4 Regulated Hypoxia-inducible Factor-α Prolyl Hydroxylases During The Development Of Hypoxic Pulmonary Hypertension

Background Hypoxia-inducible factor (HIF) functions as a master regulater of O2 homeostasis by playing critical roles in organism, it is also a transcriptional regulator which plays a key role during the development of hypoxia-induced pulmonary hypertension (HPH). The oxygen sensor PHDs, which catalyse hydroxylation of specific prolyl residues in the regulatory HIF-a subunits, play a central role in the regulation of the HIF stabilization and transcription activity.Activity of PHDs is regulated by many factors. ING4 may interact with PHD2, then co-regulate the HIF-1αand its target genes, resulting in the occurrence and development of hypoxic pulmonary hypertension. PHD3 may require MORG1 which acting as a molecular scaffold for maximal activity.Objective To investigate the dynamic levels of MORG1 and ING4 in HPH rats and COPD patients,study the reciprocal regulation between MORG1,ING4,PHDs and HIF-1α. To clarify the role of MORG1 and ING4 in regulating PHDs during the development of HPH and provide theoretical basis of mechanisms and remedies for COPD.Methods The study consisted of two parts. 1) Models of chronic HPH rats were duplicated by anoxia (respired mixted gases containing 10?? , 8 hours per day for 21 days intermittently). After anoxia for 3d, 7d, 14d and 21d, mean pulmonary artery pressure (mPAP), was measured by right-heart catheterization, right ventricular hypertrophy index (RVHI) was calculated by the ratio of right ventricle to the left ventricle plus septum, and hypoxic pulmonary vascular remodeling (HPVR) was observed with morphmetric analysis by microscope. RT-PCR and in situ hybridization were used to determine the expression of mRNA. Immunohistochemistry and western blots were adopted to determine the expression of protein levels. 2) Small pulmonary arterial remodeling was observed in COPD and the control patients by morphometric analysis. The expression of MORG1, ING4, PHDs, and HIF-1αin lung tissue was examined in COPD patients and the control by in situ hybridization and immunohistochemistry.Results mPAP increased significantly after 7 d of hypoxia (P<0.05, compared with group C), reaching its peak after 14 d of hypoxia, and then remained. Pulmonary artery remodeling developed significantly after 14 d of hypoxia. HIF-1α? protein was poorly positive in control, markedly up-regulated after 3d and 7d of hypoxia(P<0.05, compared with group C), and then declined slightly after 14d and 21d of hypoxia. HIF-1αmRNA increased just a little after 14d of hypoxia (P<0.05, compared with group C). PHD1, PHD2 mRNA and protein was positive in group C. PHD2 mRNA and protein were up-regulated after 3d of hypoxia(P<0.05, compared with group C), reaching its peak after 14d of hypoxia while PHD1 protein declined after 14d of hypoxia(P<0.05, compared with group C) without statistic mRNA changing. PHD3 mRNA and protein were detected at low level in control, markedly up-regulated after 3d of hypoxia(P<0.05, compared with group C), and then PHD3 mRNA kept ??igh level while PHD3 protein declined after 14d of hypoxia(P<0.05, compared with H7). ING4 protein was barely positive in C group,then increased after 3d and 7d of hypoxia,reaching its peak after 14d of hypoxia (compared with C group P < 0.05).ING4mRNA reached its peak after 7d of hypoxia,and has a statistical significance compared with C group. MORG1 protein markedly up-regulated after 3d and 7d of hypoxia(P<0.05, compared with group C), reaching its peak after 14d of hypoxia . MORG1mRNA kept at high level after 21d of hypoxia (compared with C group P < 0.05). Linear correlation analysis showed that MORG1 protein were positively correlated with mPAP,RVHI,WA %,HIF-1αprotein,PHD3 protein. In COPD subject, HIF-αmRNA and proteins increased significantly, PHD1 protein decreased without mRNA change. PHD2 mRNA and protein increased significantly. PHD3 mRNA increased without protein change.ING4 mRNA and protein decreased significantly.MORG1 mRNA and protein increased significantly.Conclusion PHDs showed Relative selectivity in hydroxylate HIF-1αin rat lung after hypoxia exposure. PHD2 and PHD3 would be induced by hypoxia and this may via elevated HIF-α, which suggested that a hypoxic up-regulation of PHD acts via feedback mechanism to attenuate hypoxia induced responses. ING4 may interact with PHD2, then co-regulate the HIF-1αand its target genes, resulting in the occurrence and development of hypoxic pulmonary hypertension. PHD3 may require Morg1 which acting as a molecular scaffold for maximal activity.