Expressions of hypoxia inducible factor-1 alpha and inducible nitric oxide synthase gene in the development of hypoxic pulmonary hypertension in rats

Zhenhua HE; Aiguo DAI; Xiufeng ZHANG; Xiaowu TAN

ABSTRACT

BACKGROUND:

The dynamic changes of hypoxia inducible factor-1 alpha (HIF-α) and inducible nitric oxide synthase (iNOS) genes in the pulmonary artery wall during the process of hypoxic pulmonary hypertension (HPH) development need to be investigated.

OBJECTIVE:

This study was to observe the gene expressions of HIF-α and iNOS in the pulmonary artery wall at the different hypoxic time points, and to investigate their effects in HPH development.

DESIGN:

Controlled observation animal experiment.

SETTING:

Department of Respiration, Second Hospital Affiliated to Nanhua University.MATERIALS Forty healthy male Wistar rats of clean grade, aged 6-8 weeks, with body mass of (220±10) g were involved in this study. They were randomized into control group (n =8) and hypoxia group (n =32). Four time points, i.e.3, 7, 14, and 21 days after hypoxia were set for the animals in the hypoxia group, 8 rats at each time point.

METHODS:

This study was carried out in the Institute of Oncology, Nanhua University between August 2004 and December 2005. Rats in the hypoixa group were treated according to the method reported by Li et al. Hypoxia treatment was omitted for the rats in the control group. At each time point, the rats were anesthetized, and then a micro-catheter was inserted into the right jugular vein and connected to a multichannel physiologic recorder, which was used for detecting the mean pulmonary arterial pressure (mPAP). The heart of each euthanized rat was taken out, and its right ventricle (RV), and left ventricle and septum (LV+S) were weighted. Right ventrical hypertrophy index (RVHI) reflected right ventricle hypertrophy degree. Right upper lung tissue of rat was harvested for haematoxylin & eosin (HE) staining and elastic fiber staining. Pathological image analysis software was used to determine pulmonary arterial wall area/total vascular area, lumina area/total vascular area, smooth muscle cell density in the media of pulmonary arteriole, and media thickness of pulmonary arteriole, which were used as remodeling indexes of pulmonary arteriole. HIF-1α and iNOS in the pulmonary arteriole were performed in situ hybridization and immunohistochemical detection. The mean absorbance of pulmonary arteriole wall was used as the relative content of mRNA expression and protein level.MAIN OUTCOME

MEASURES:

①Changes in mPAP, RV hypertrophy degree and remodeling indexes of pulmonary arteriole of rats. ② Expressions of HIF-α and iNOS as well as their correlations with mPAP and remodeling indexes of pulmonary arteriole.

RESULTS:

All the 40 Wistar rats were involved in the final analysis. ①At hypoxia 7 days, mPAP was significantly higher than that of control group (P ＜ 0.05). mPAP reached to the high level at hypoxia 14 days, and then maintained at this level. ② At hypoxia 14 days, RVHI was higher than that of control group (P ＜ 0.05). ③ At hypoxia 7 days, pulmonary arteriole wall was thickened, and lumina became narrowed. There were significant differences in pulmonary arterial wall area/total vascular area, lumina area/total vascular area between hypoxia group and control group (P ＜ 0.05). At hypoxia 14 days, smooth muscle cell density in the intima-media of pulmonary arteriole, and intima-media thickness of pulmonary arteriole were significantly increased (P ＜ 0.05). At hypoxia 21 days, lumina was further narrowed, and obvious smooth muscle hyperplasy was found. HIF-1α and iNOS mRNA expression presented weak-positive in the control group; The relative content of HIF-1α mRNA did not significantly alter at hypoxia 3 and 7 days, but was obviously increased at hypoxia 14 days ,and after this, it maintained at high level. iNOS mRNA was markedly higher than that in the control group at hypoxia 3 days, reached its peak at hypoxia 7 days, was close to the level in the control group at hypoxia 14 days, and enhanced again at hypoxia 21 days, but it was still lower than that at hypoxia 3 days. ⑤HIF-α was mainly found in the intima and media, while iNOS was found in the whole layer of vessels. iNOS was weakly expressed in the intima and media of pulmonary vessels in the control group. No obvious difference in iNOS existed at hypoxia 3 days as compared with control group. iNOS was obviously expressed in media and intima at hypoxia 7 days. Vascular media was thickened at hypoxia 14 days, and the expression of iNOS was enhanced. iNOS was not found in the vascular adventitia in the control group, but was found in the vascular adventitia in the hypoxia group. ⑥mPAP was positively correlated with pulmonary vascular remodeling (r =0.976, P ＜ 0.01 ), and HIF-1α mRNA was positively correlated with iNOS protein(r =0.927, P ＜ 0.05).

CONCLUSION:

Both HIF-1α and iNOS exert effects in the process of HPH development of rats, and HIF-1α and iNOS gene expression may be mutually regulated.