Glucocorticoids delay age-associated thymic involution through directly affecting the thymocytes.

Area of Science:

• Immunology
• Endocrinology
• Aging Research

Background:

• Age-associated thymic involution, a reduction in thymus size and thymocyte number post-puberty, is poorly understood.
• Endogenous glucocorticoids (GCs) are implicated in immune system regulation, but their specific role in thymic involution is unclear.

Purpose of the Study:

• To investigate the role of endogenous GCs in age-associated thymic involution.
• To determine if GCs directly affect thymocytes and influence T-cell homeostasis in aging.

Main Methods:

• Utilized transgenic mice with enhanced GC sensitivity in T-cell lineage via a GC-receptor transgene.
• Compared thymocyte numbers, cycling status, and apoptosis in transgenic and wild-type mice at various ages.
• Assessed peripheral T-cell populations (CD4+, CD8+) and CD4/CD8 ratios in aged mice.

Main Results:

• Transgenic mice exhibited delayed thymic involution, starting after 6 months of age, indicating GCs delay this process.
• Higher thymocyte numbers in aged transgenic mice correlated with increased cycling of double-negative and single-positive thymocytes.
• GCs differentially regulated thymocytes and peripheral T cells, suppressing T-cell numbers and decreasing the CD4/CD8 ratio in aged transgenic mice.

Conclusions:

• Endogenous GCs, acting directly on thymocytes, delay age-associated thymic involution.
• GCs play a differential role in regulating thymic cellularity versus peripheral T-cell populations.
• These findings highlight novel functions of GCs in thymic involution and T-cell homeostasis during aging.