Gallic acid attenuates thymic involution in the D-galactose induced accelerated aging mice

Senescence is an inevitable and complicated phenomenon. Age-associated thymic involution increases the risk of infectious diseases, which results in the immunosenescence and leads to a poor immune function. D-galactose (D-gal) can cause damages that resemble accelerated aging in mice. Gallic acid (GA), as one of the natural phenolic compounds, has been demonstrated to act in antioxidant and anti-tumor effects. In this study, we explored the effects of GA in preventing the age-related thymic involution and the alterations of the forkhead box protein N1 (FoxN1) in D-gal induced accelerated aging mice. The accelerated aging mice model was established by intraperitoneal injection D-gal for eight weeks and given GA with 200, 250, 500 mg/kg body weight per day, respectively, for six weeks. It showed that the D-gal-treated mice developed structural changes in the thymi compared to normal control mice. With supplement of GA, the mice restored the normal thymic anatomy, including the thickening cortex compartment and clearer cortico-medullary junction. The D-gal-treated mice showed a severe reduction in the number of thymocytes, GA mice also displayed the increased numbers of CD4+ T cells through flow cytometric analysis. GA treatment increased the proliferative cells by BrdU incorporation assay and reduced the numbers of apoptotic cells with FITC-12-dUTP labeling (TUNEL). The expression of FoxN1 was also found increased in GA treated mice by immunohistochemistry and quantitative reverse transcriptase PCR (qRT-PCR). Taken together, our results suggested that the administration of GA opposed the involution of thymus via stimulation of FoxN1 expression and proliferation of cells in a dose-dependent manner.