Study On The Establishment Of Skin Photoaging Model In SD Rat And The Histological Expressions Of P38MAPK Pathway

Objective:To explore the method of establishing skin photoaging model in Sprague-Dawley(SD) rat and to investigate the evaluation standards. Meanwhile, to test how p38 MAPK signal pathway expresses in photoaging histologically and investigate their meaning.Methods:The SD rats were randomly divided into normal control group,low-dose group,medium-dose group and high-dose group,8 rats in each group.The dorsal skin of rats in three model groups were irradiated with simulated solar light combined ultraviolet-A and ultraviolet-B everyday for 10 weeks. 1)low-dose group were irradiated 10min/d.2)medium-dose group started with 10min/d, then increased 10 min every 2 weeks and maintained at 20min/d.3)high-dose group started with 10min/d, then increased 10 min every 2 weeks and maintained at 30min/d. After irradiation, visible changes, wrinkle grading, histological and ultrastructural features,biochemical indicators such as MDA,Hyp and SOD were detected to estimate the extent of modeling. Immunohistochemistry was conducted among the successfully established group and the control group to detect expressions of p38 MAPK,MMP-1 and Hsp27,using image analysis system to analyse the mean density.Results:After 10 weeks’ irradiation, the animal skin of high-dose group became coarse and lack of elasticity.Visible deep wrinkles were observed. Histological alterations included epidermis thickening, hyperplasia of glands, elastosis and loss of collagen. Meanwhile, increasing number of senescent and apoptotic cells and structure destruction of dermis were seen in ultrastructure. Compared with those of the control group, there was a statistical significant increase in the content of MDA, a decrease in the content of Hyp in skin tissue of high-dose group(P ?0.05). While SOD activity had no obvious difference. As a result,high-dose group was considered as the successfully established one. IHC showed p38 MAPK expressed,under photoaged condition,in cytoplasm of keratinocyte,glands,and among fibers in upper layer of dermis.MMP-1 expressed in cytoplasm of keratinocyte and fibroblast,and also among fibers in upper layer of dermis.Hsp27 expressed mainly in epidermis and partly in upper dermis.The mean density of high-dose group was statistically significant higher than that in control group.Conclusion:These typical features in high-dose group demonstrate that increasing dose of irradiation and 10 weeks’ term could be more stable and efficient ways to establish photoaging animal model. Moreover, p38 MAPK and its related factors had increased expressions in histological way,which demonstrates p38 MAPK signal pathways may play crucial roles in photoaging development and damage repair response.