Vitamin D receptors distribution and MAPK activation in cigarette smoke induced emphysema rats

Abstract

Rat model was used in this study in order to investigate subcellular vitamin D receptors (VDR) distribution and mitogen activated protein kinase (MAPK) alteration in the lungs of emphysema development after cigarette smoke exposure for 7 days (acute) and 14 days (subacute). Thirty male Wistar rats were randomly divided into 3 groups per each time point; 1) control (air exposed), 2) no-filter (smoke exposed without cigarette filter) and 3) filter (smoke exposed with cigarette filter) (n=5 per group). Each rat was daily and constantly exposed to 6 cigarettes smoke for 7 or 14 days. After 24 hours of the last exposure, rats were euthanized by intraperitoneal injection with overdose sodium pentobarbital. The left lung was collected for pathological examination and immunohistochemistry. The right lung was salvaged for determination of VDR distribution and cascade proteins of MAPK pathway. Results on day 7th of cigarette smoke exposure showed declining trend of cytoplasmic VDR in both cigarette smoke groups whereas nuclear VDR only observed in no-filter group. MAPK cascade proteins such as p-ERK, p-JNK and p-p38 were increased in no-filter group while only p-JNK was found in both subcellular areas of filter group. This was consistent with pathological finding that alveolar macrophage and peribronchiolar epithelium proliferation significantly increased (p<0.05) in no-filter group after 7 days smoke exposure. Furthermore, tracheal epithelial change and lung parenchymal infiltration tended to increase in both cigarette smoked groups. For 14 days of cigarette smoke exposure, the results demonstrated decrease cytoplasmic VDR in both cigarette smoked groups in the way same as in 7 days period but only nuclear VDR was significantly (p<0.05) decreased especially in filter groups. In addition, both p-ERK and p-JNK of MAPK cascades in cytoplasm and nucleus were activated in both cigarette smoked groups. On the other hand, cytoplasmic p-p38 was prone to increase only in filter group but not nuclear p-p38 in both groups. These proteins outcomes were consistence with histopathological changes observed in both no-filter and filter groups on 14 days exposure that exhibited significantly (p<0.05) increased of alveolar macrophages, tracheal epithelial cell changes and peribronchiolar epithelial cell proliferation. Lung parenchymal infiltration had tended to increase after exposed to both cigarette smoke types. Immunohistochemistry showed the reduction trend of VDR in both cigarette smoke groups on 7 days and significantly decreased (p<0.05) on 14 days in filter group. In conclusion, this study demonstrated that the second-hand smoker model for 7 and 14 days of cigarette smoke exposure with or without filter. The similar tendencies of VDR depletion and MAPK activation in both cigarette smoke types confirmed that there was no benefit of using cigarette filter to prevent damaging proteins as well as protect cells undergone 14 days smoke exposure. The histological changes of early emphysema pathogenesis and the severity of disease found in this study suggested the best way to prevent chronic respiratory diseases is to quit smoking.