| Radon is an inert radioactive gas that exists naturally in the air. In normal background areas, the radioactive dose from radon and its decay products is the main natual dose received by mankind, which account for 50% of the total annual absorbed dose. The levels of radon may be higher in some mines and buildings with the new type building materials. Because of the special characteristics of radon and radon progeny, the basal and secretory cells are the primary target of them. Radon will decay into a series of radon decay products, and the alpha particle emitted from radon progeny in the human respiratory will damage the target cells. Causal association of exposure to radon and lung cancer has been demonstrated in epidemiological studies performed on cohorts of miners. Domestic radon has been identified as the most important environmental risk factor for lung cancer. It was reported that 10% of all lung cancer in general populations could be because of indoor radon. International Agency for Research on Cancer (IARC) have recognized radon as a group I carcinogen. In recent years, the potential hazards posed by exposure to alpha radiation from air radon have been of great concern worldwide. And studies of the mechanisms and the protection from radon and its daughters have been become the focus.In the present study, we firstly established an animal model of radon-exposure to study the pathologies of lung and bronchus of the radon-exposure mice at different time points and different dose groups. The radon-exposure caused various pathologies of lung and bronchus, including hyperemia, hemorrhage, emphysema, edema, exudation and inflammation. However, the degeneration, necrosis and loss of lung epithelial cells were not obvious. There was not significant difference between the two dose groups. After radon-exposure, along with the time, the incidence rates of edema and hyperplasia increased and decreased later. The capillary thrombosis became serious. After 90 days, the shrinks and fibrosis of alveolar occurred. No cancer cells were founded in the study. This study also showed that radon and its daughters absorbed in the respiratory tract would damage on lung and bronchus. The pathological changes in lung were dynamic process, which were caused by the interaction between the external factors (radon and its daughters) and the internal factor of the body. After radon-exposure, the lung and bronchus would experience early acute inflammation, proliferation and pulmonary fibrosis three stages. The pathological procedure of lung after radon-exposure was similar to that induced by the other radiation. Hyperplasia and fibrosis were important responses of the body to the external hazardous. The excessive hyperplasia and fibrosis may be one of the inducements of cancer.During the pathological procedure of lung after radon-exposure, a large number of related genes may be involved in. In the SSH test, two pairs of radon-exposure mice of different stages (<24h and 90 days after exposure with 30 WLM) were used as animal models. The control and the treatment groups acted as testers and drivers for the each other. The differentially expressed cDNA libraries in lung and bronchus of mice exposed to radon were constructed. The obtained forward and reverse cDNA fragments were directly inserted into pGEM-T-easy vector and transformed into E. coli DH5α. The inserts in plasmid were amplified by nested polymerase chain reaction (PCR), and the differentially expressed fragments were sequenced. In the end these sequences were aligned with GeneBank data and the differentially expressed genes were classified based on their function. Finally, in the two screening group (<24h and 90 days post-exposure), there were 89 and 53 ESTs respectively were found to be identified with known genes encoding protein of below: Cytokines and receptor-associated protein; Kinases and related proteins; Other proteins including enzymes, heat shock protein, cytoskeleton proteins, fibronectins, products of oncogene, some hypothetical proteins. Those proteins may be involved in the procedures of apoptosis, cell cycle regulation, tissue fibrosis and intracellular signal transduction.Based on the screening constructed libraries, we took TGF-β, members of MAPK signaling pathway and Akt as the target genes for the further study. We use molecular biology techniques to study the expression of them in the lung and bronchus of radon-exposure mice preliminarily. Within 24h post-exposure, TGF-βprotein in lung and bronchus increased along with the increase of expose dose. After radon-exposure with 60 WLM, TGF-βprotein in lung was higher than the control group, and increased with time-lapse. Less than 24 hours post-exposure, the levels of JNK mRNA, JNK protein and the phosphorylation levels of JNK protein in lung all increased with the dose-increasing. After radon-exposure the JNK mRNA, JNK protein and the phosphorylated JNK protein increased first and reduced later. Within 24 hours after exposure, the expression of p38/MAPK protein in each dose group enhanced than the control group. But the increasing level is lower than the JNK protein. The phosphorylated p38/MAPK protein also increased significantly in the samples exposed to 60 WLM. After exposure, the phosphorylated p38/MAPK protein increased first and reduced later. In different doses and stages after radon-exposure, there was not significant difference in the levels of ERK and p-ERK protein compared with the control group. Within 24 hours after exposure, the levels of Akt protein were stable in different dose groups. However, the phosphorylated Akt protein has increased with the dose increasing. After exposure, the Akt and phosphorylated Akt proteins have increased. The phosphorylated Akt protein increased significantly and maintained for a long time.TGF-βexerts its effects on cell proliferation, differentiation and migration partly through its modulation of extracellular matrix components, such as fibronectin and plasminogen activator inhibitor-1 (PAI-1). TGF-βplays an important role in the radiation-induced pulmonary fibrosis formation, and promotes the synthesis of collagen fibers. After radon-exposure, the regularity of TGF-βprotein expression increased simultaneously with the appearance of pulmonary hyperplasia and fibrosis, indicating that TGF-βplays an important role in the procedure of radon-induced pulmonary fibrosis. The JNK signal pathway can be stimulated by various stresses and took part in cellular growth, development, division, differentiation and apoptosis. As one kind of radioactive factor, radon and its daughters can stimulated the transcription, translation and phosphorylation of JNK protein. The levels of JNK and phosphorylated JNK protein have related with the dose and the time after the radon-exposure. The p38 MAPK signaling pathway plays an important role in inflammation, stress reaction, apoptosis and cell cycle regulation. This study showed that the threshold of p38 activation induced by radon-exposure is relatively high and resistant to the stimulation. Once the dose reaches the threshold, the p38 protein was activated dramatically. The ERK signaling pathway is not involved in radon-induced lung injury process. The activation of Akt protein is closely related to the occurrence and development of tumors. A variety of growth factors, hormones, cytokines, and deletion of PTEN gene, as well as activation of Ras could stimulate the activation of Akt. In this study, phosphorylation level of Akt protein was positively correlated with the dose, and maintained at high levels for a long time, suggesting that pathological changes in lung tissue may be aggravated.TGF-βhas relationship with the members of MAPK family, such as JNK and p38. TGF-βcould transfer signalling through the JNK and p38 signal transduction pathway to the nucleus, and regulate the cell growth, differentiation and apoptosis. In some conditions the MAPK and Akt signaling pathways can be activated sequencely. There are other determinants to activate MAPK cascade at the same time. They need further studies to explore the roles of TGF-β, MAPK cascades and Akt in the pathologies induced by radon-exposure.
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