Histopathologic and transcriptomic phenotypes of a conditional RANKL transgenic mouse thymus

Area of Science:

• Immunology
• Developmental Biology
• Molecular Biology

Background:

• Conventional mouse models have limitations in studying Receptor Activator of NF-κB Ligand (RANKL) signaling.
• Conditional transgenesis allows for spatiotemporal control of gene expression, offering unique research advantages.

Purpose of the Study:

• To develop and characterize a novel conditional mouse model for studying RANKL signaling in thymic medullary epithelial cells (mTECs).
• To investigate the effects of doxycycline-inducible RANKL expression in mTECs on thymus development and immune cell composition.

Main Methods:

• Generation of a K5: RANKL bigenic mouse model with doxycycline-inducible RANKL expression targeted to cytokeratin 5 (K5) positive mTECs.
• Short-term and prolonged doxycycline administration to induce and study transgene expression.
• Flow cytometry analysis of thymocyte and mTEC populations.
• Transcriptomic analysis to identify RANKL-regulated signaling pathways.

Main Results:

• Doxycycline induction specifically increased RANKL expression in mTECs, leading to thymus enlargement and mTEC hyperproliferation.
• Significant alterations in thymocyte populations, including enrichment of CD4+ and CD8+ single positive cells and depletion of double positives.
• Increased numbers of regulatory T cells (Tregs) and Ulex Europaeus Agglutinin 1 (UEA1) positive mTECs.
• Prolonged induction resulted in medullary epithelial hyperplasia, immune cell infiltration, and tissue necrosis.

Conclusions:

• The K5: RANKL conditional mouse model provides a powerful tool to dissect the complex roles of RANKL in thymic physiology and disease.
• RANKL signaling in mTECs is crucial for regulating thymus size, immune cell development, and maintaining thymic architecture.
• This model can aid in understanding and potentially treating immunopathological conditions affecting thymic function.