Cell aging and caloric restriction: improvement of SA-βG assay, establishment of an aging model, and the role of niacin

• Main Authors: Nae-Cherng Yang, 楊乃成
• Other Authors: Miao-Lin Hu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/40917218181904603519

博士 === 國立中興大學 === 食品科學系 === 92 === According to many yeast-based studies, a gene silence theory was proposed recently. The theory is interesting because it can explain how caloric restriction (CR) can extend lifespan. However, two different regulation mechanisms, i.e., the NAD+-fluctuation model and the nicotinamide (NAM)-depletion model for the aging theory are debated in the literature. To date, more and more evidence has shown that the NAM-depletion mechanism is favored in the yeast. However, it remains to be answered as to whether mammalian cells also possess the same mechanisms as does the yeast. For revealing the question, we established a cell-aging model using human foreskin fibroblast Hs68 cells. The availability of model was validated by comparing anti cell-aging ability of two agents of 2-deoxyglucose, a caloric restriction mimic, and DHEA, a nutritional supplement for anti-aging commercially but without sufficient evidence. We also investigated the specificity of the senescence associated β-galactosidase (SA-βG) assay as a marker for cell aging and developed a new quantitative method for determining SA-βG activity using fluorescein di-β-D-galactopyranoside (FDG) as a substrate. Using the aging-cell model, we further studied the effects of NAM and nicotinic acid (NA) on the aging of Hs68 cells, and the NAD+ level or NAD+/NADH ratio fluctuation corresponding to the cells cultured in the mediums with different glucose concentrations (the low glucose medium can be considered as caloric restriction). The results showed NAM could retard senescence of human foreskin fibroblast Hs68 cells. In addition, the cellular NAD+ levels as well as NAD+/NADH ratios increased in the glucose (calorie)-restricted cells. These results were different from that of yeast studies, as reported in the literature, because the NAD+ levels or NAD+/NADH ratios would not change in the glucose-restricted yeast. The results illustrated that the NAM-depletion model could not be applied to Hs68 cells and it appeared to support the NAD+-fluctuation model but also raised several questions regarding the interpretation of the model. In conclusion, our results on Hs68 cell aging are different from those on yeast as reported in the literature, suggesting that the aging mechanims of the two cells systems may be different.