Metformin ameliorates thymus degeneration of mice by regulating mitochondrial function

•Metformin administration alleviated thymic involution in the D-galactose induced accelerated aging mice.•Metformin restored the thymus mitochondrial membrane potential, ROS, SOD and MDA.•Metformin treatment promoted the expression of thymus mitochondrial mitotic protein Drp1.•Metformin stimulated the expression of FoxN1, Aire, Sox2 expression in the thymus.•Metformin led to the reduction of senescent cells in the thymus.