Metformin ameliorates thymus degeneration of mice by regulating mitochondrial function

As the main lymphoid organ, the thymus degenerates with age. The loss of thymic epithelial cells is mainly related to thymus degeneration and reduced T cells development. As an insulin sensitizer, metformin is a first-line drug for the treatment of diabetes and has been shown to prolong the lifespan of mice, but the mechanism is still unclear. In this study, we explored the therapeutic effect of metformin on thymus degeneration in the accelerated aging mice, which was established by intraperitoneal injection D-galactose (120 mg/kg/day) for eight weeks. Metformin was intragastrically given with 100 or 300 mg/kg body weight per day, respectively, for six weeks. Histological examination showed that metformin administration could alleviate thymus atrophy caused by D-galactose. In addition, metformin therapy increased mitochondrial membrane potential, with a reduction in mitochondrial reactive oxygen species, MDA and SOD levels, and restored mitochondrial balance through enhanced expression of dynamin-related protein 1 (Drp1). Furthermore, metformin altered T lymphocyte subsets and cellular senescent cells; the expression of FoxN1, Aire and Sox2 of thymic epithelial cells also increased. Thus, metformin presented a positive effect on thymic degeneration through improving mitochondrial function. Taken together, these findings revealed an unexpected complexity in the anti-aging of this widely used drug.