[Structural changes and functional evaluation of the thymus in aging mouse induced by D-galactose]

Objective To explore the structural changes and functional changes of the thymus in aging mouse induced by D-galactose, and to explore a suitable method for establishing an aging mouse model of the thymus. Methods Thymus aging mouse models were established, female C57BL/6 mice were randomly divided into control group, [500 mg/(kg.d)] D-galactose treatment group, and [1000 mg/(kg.d)] D-galactose treatment group, with 8 mice in each group. The mice in the D-galactose treatment group were injected with 500 mg/kg and 1000 mg/kg of D-galactose subcutaneously on the back of the neck every day, while the mice in the control group were injected with the same amount of normal saline every day. After 56 days of continuous administration, the mice were sacrificed to take the thymus to observe the gross thymus morphology and calculate the thymus index. Then the thymus structure were observed by HE staining, and CD4/CD8 positive thymocytes were detected by flow cytometry to evaluate the immune function of the thymus. Later, thymus aging mouse models with different treatment time were established. Female C57BL/6 mice were randomly divided into control group and [1000 mg/(kg.d )] D-galactose treatment group, with 24 mice in each group. The mice were sacrificed after 6 weeks, 9 weeks, and 12 weeks treatment. The structure of thymus was observed by HE staining. The contents of thymosin β4, thymosin α1, and thymopoietin in plasma were determined by ELISA. Results D-galactose treatment can induce mouse thymus senescence, atrophy of thymus, decrease of thymus index, disorder of thymus structure and impaired immune function. In the [1000 mg/(kg.d)] D-galactose treatment group, the atrophy of the thymic medulla of mice was more obvious, with the disappeared cortical and medullary boundary, decreased CD4⁺CD8⁺ thymocytes and increased CD4⁺CD8^- thymocytes. The thymus aging mouse models with different treatment time showed the atrophied thymus, decreased thymus index, constricted thymus medulla, blurred boundary of cortex and medulla, decreased plasma thymosin α1 and impaired thymic secretion function. Thymus senescence was most obvious 12 weeks after D-galactose treatment. Conclusion D-galactose can induce the atrophy of the thymus, the thymus index decreases, consticted thymus medulla and blurred boundary of the cortex and medulla,and result in impaired thymic immune and secretory functions.A subcutaneous injection of 1000 mg/kg D-galactose on the back of the neck every day for 12 consecutive weeks is a suitable method to establish a thymus aging model.