1. Cardiovascular division of Changhua Cristian Hospital, Changhua, Taiwan.
2. School of Medicine, Chung Shan Medical University, Taichung 402, Taiwan.
3. Department of Internal Medicine, Chung Shan Medical University Hospital, Taichung, 402, Taiwan.
4. Institute of Biochemistry and Biotechnology, Chung Shan Medical University, Tai-chung, 402, Taiwan.
5. Department of Biochemistry, School of Medicine, Medical College, Chung Shan Medical University, Taichung, 402, Taiwan.
6. Institute of Medicine, Chung Shan Medical University, Taichung, 402, Taiwan.
7. Clinical Laboratory, Chung Shan Medical University Hospital, Taichung, 402, Taiwan.
8. Department of Health Diet and Industry Management, Chung Shan Medical University, Taichung 402, Taiwan.
9. Department of Medical Research, Chung Shan Medical University Hospital, Taichung, 402, Taiwan.
#: these authors contributed equally as first author.
Ageing is one of the major risk factors of human diseases, including cancer, diabetes, and cardiovascular disease. Mulberry exhibits a wide range of functions, such as anti-oxidant, anti-inflammation, and anti-diabetes. In this study, we investigated the role of mulberry polyphenol extract (MPE) in K-Ras-induced senescence of smooth muscle cells. Forced expression of K-Ras enhanced senescence of smooth muscle A7r5 cells as shown by the elevation of β-galactosidase activity. Treatment with MPE significantly repressed the Ras, phosphorylated ERK, and β-galactosidase level. MPE triggered the association of cyclins with their corresponding cyclin-dependent protein kinases and hyperphosphorylated retinoblastoma (RB). MPE also down-regulated the levels of K-Ras-induced CDK inhibitors. MPE enhanced the phosphorylated AMP-dependent protein kinase (AMPK) and inducible nitric oxide synthase (iNOS) level in the presence of K-Ras. Pretreatment with either L-NAME or AMPK inhibitor reversed the effects of MPE. In addition, L-NAME and AMPK inhibitor repressed the MPE-induced total and phosphorylated 3-hydroxy-3-methylglutaryl coenzyme A (HMG-Co A) level. MPE repressed K-Ras-induced G0/G1 arrest, whereas L-NAME and AMPK inhibitor blocked the effects of MPE. Our results indicated that MPE recovered the K-Ras-induced senescence of vascular smooth muscle cells through iNOS and AMPK-dependent pathway. Our findings suggested that MPE may prevent ageing-induced atherosclerosis.
Keywords: mulberry polyphenol extract, Ras, smooth muscle cell, senescence