Abstract: BACKGROUND: Aerobic exercise can suppress liver fibrosis in diabetic mice. However, the specific mechanism is yet to be elucidated.
OBJECTIVE: To investigate the protective effect and mechanism of aerobic exercise on liver fibrosis in db/db mice via the transforming growth factor-β/Smad signaling pathway. 
METHODS: 8-week-old male db/db mice and age-matched m/m mice were randomly divided into m/m control group, m/m+exercise group, db/db control group, and db/db+exercise group, with 10 mice in each group. Mice in the exercise group were subjected to a 12-week aerobic exercise. After the exercise, fasting blood glucose levels were measured in mice, and glucose tolerance and insulin tolerance tests were conducted. Mouse liver was extracted to calculate liver index and mouse eyeballs were taken to collect blood sample and detect biochemical indicators. Masson, oil red O and Hematoxylin-eosin staining were used to detect and analyze the pathological changes in mouse liver tissues. Immunohistochemistry was used to determine the protein expression levels of transforming growth factor-β1 and p-Smad3. Western blot analysis was applied to determine the protein expression levels of transforming growth factor-β1, Smad3, p-Smad3, α-smooth muscle actin, type I collagen and type III collagen.

RESULTS AND CONCLUSION: Compared with the m/m group and m/m+exercise group, body mass, liver mass, liver index, fasting blood glucose, triglycerides, total cholesterol, low-density lipoprotein and creatine kinase levels were significantly increased (P < 0.01), but the high-density lipoprotein level significantly decreased (P < 0.01) in the db/db group; the protein expressions of transforming growth factor-β1, p-Smad3, α-smooth muscle actin, type I collagen and type III collagen significantly increased (P < 0.01) in the db/db group; the area under curve of glucose and insulin tolerance tests significantly increased (P < 0.01) in the db/db group; and pathological staining of the liver in the db/db group showed extensive infiltration of inflammatory cells, increased lipid droplets, and significant fibrosis. In the db/db+exercise group, aerobic exercise could significantly reduce body mass, liver mass, liver index, fasting blood glucose, triglycerides, total cholesterol, low-density lipoprotein and creatine kinase levels (P < 0.05 or P < 0.01), and increase high-density lipoprotein level (P < 0.05). Similarly, a marked decrease was observed in the protein expression levels of transforming growth factor-β1, p-Smad3, α-smooth muscle actin, type I collagen and type III collagen (P < 0.05 or P < 0.01) in the db/db+exercise group. In addition, the area under the curve of glucose tolerance and insulin tolerance tests significantly decreased (P < 0.01, P < 0.05), and pathological changes in liver tissues were significantly improved. In conclusion, aerobic exercise can attenuate liver fibrosis in diabetic mice, which may be related to the regulation of the transforming growth factor-β1/Smad signaling pathway.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: aerobic exercise, transforming growth factor-β, Smad, signaling pathway, db/db, liver fibrosis