Improvement of glucocorticoid-impaired thymus function by dihydromyricetin via up-regulation of PPARγ-associated fatty acid metabolism

Abstract

T lymphocytes produced by the thymus are essential mediators of immunity. Accelerated thymic atrophy appears in the patients with administration of glucocorticoids (GCs) which are commonly-used drugs to treat autoimmune and infectious diseases, leading to dysregulation of immunity with manifestation of progressive diminution of new T cell production. However, there is no ideal method to overcome such side effects of GCs. In the current study, we proposed a composition of dexamethasone (DEX) and dihydromyricetin (DMY) derived from a medicinal plant, which could protect from DEX-induced thymus damage and simultaneously enhance the anti-inflammatory effect of DEX. In the current study, we found that DEX-damaged thymic cellularity and architecture, reduced thymocyte numbers, induced thymocyte apoptosis and dropped CD4+ and CD8+ double positive T cell numbers in thymus which was effectively improved by co-treatment with DMY. Quantification of signal joint TCR delta excision circles (TRECs) and Vβ TCR spectratyping analysis were employed to determine the thymus function with indicated treatments. The results showed that DEX-impaired thymus output and decreased TCR cell diversity which was ameliorated by co-treatment with DMY. iTRAQ 2D LC-MS/MS was applied to analyze the proteomic profiling of thymus of mice treated with or without indicated agents, followed by informatics analysis to identify the correlated signaling pathway. After validated by Western blotting and Real-time PCR, we found that PPARγ-associated fatty acid metabolism was increased in the thymic tissues of the animals treated with DMY plus DEX than the animals treated with DEX alone. The agonist and antagonist of PPARγ were further employed to verify the role of PPARγ in the present study. Furthermore, DMY demonstrated a synergistic effect with co-administration of DEX on suppressing inflammation in vivo. Collectively, DMY relieved thymus function damaged by DEX via regulation of PPARγ-associated fatty acid metabolism. Our findings may provide a new strategy on protection of thymus from damage caused by GCs by using appropriate adjuvant natural agents through up-regulation of PPARγ-associated fatty acid metabolism.

Keywords: Dihydromyricetin; Glucocorticoids; PPARγ; Thymus.