Glucocorticoid (GC) sensitivity and GC receptor expression differ in thymocyte subpopulations

Abstract

Positive and negative selection steps in the thymus prevent non-functional or harmful T cells from reaching the periphery. To examine the role of glucocorticoid (GC) hormone and its intracellular receptor (GCR) in thymocyte development we measured the GCR expression in different thymocyte subpopulations of BALB/c mice with or without previous dexamethasone (DX), anti-CD3 mAb, RU-486 and RU-43044 treatment. Four-color labeling of thymocytes allowed detection of surface CD4/CD8/CD69 expression in parallel with intracellular GCR molecules by flow cytometry. Double-positive (DP) CD4+CD8+ thymocytes showed the lowest GCR expression compared to double-negative (DN) CD4-CD8- thymocytes and mature single-positive (SP) cells. DX treatment caused a concentration-dependent depletion of the DP cell population and increased appearance of mature SP cells with reduced GCR levels. GCR antagonists (RU-486 or RU-43044) did not influence the effect of DX on thymocyte composition; however, RU-43044 inhibited the high-dose GC-induced GCR down-regulation in SP and DN cells. GCR antagonists alone did not influence the maturation of thymocytes and receptor numbers. Combined low-dose anti-CD3 mAb and DX treatment caused an enhanced maturation (positive selection) of thymocytes followed by the elevation of CD69+ DP cells. The sensitivity of DP thymocytes with a GCRlow phenotype to GC action and the ineffectiveness of the GCR antagonist treatment may reflect a non-genomic GC action in the thymic selection steps.

Thymic Alterations in EphA4-Deficient Mice

“…EphA4 Ϫ/Ϫ mice are known to have defects in other organ systems that could be supporting disturbing stress that could explain the observed hypocellularity and increased apoptosis. However, the phenotype of EphA4 Ϫ/Ϫ thymi is different of that reported for a stressed mouse, in which no such alterations of the thymic epithelial network are observed (45)(46)(47). Accordingly, mutant thymic stroma grafted in SCID mice is not functional and neonatal EphA4 Ϫ/Ϫ thymus exhibits an altered epithelial microenvironment but normal or almost normal proportion of thymocytes.…”

Sodium Methyldithiocarbamate Causes Thymic Atrophy by an Indirect Mechanism of Corticosterone Up-Regulation

“…The higher dosage of SMD (300 mg/kg × 3), on the other hand, decreased the number of all populations, but depleted DP thymocytes more than others. Thymocytes, especially DP thymocytes, are sensitive to corticosterone (Chow et al, 1997;Berki et al, 2002). Depletion of DP thymocytes has been reported with administration of exogenous corticosterone and dexamethasone, a glucocorticoid receptor (GR) agonist (Screpanti et al, 1989).…”

BAC-mediated transgenic expression of fluorescent autophagic protein Beclin 1 reveals a role for Beclin 1 in lymphocyte development

“…As indicated in Figure 2, Beclin 1-GFP high cells mostly belong to SP and DN subsets, previously shown to have lower sensitivity to dexamethasone-induced cell death compared to DP cells. 27 Interestingly, Beclin 1-GFP high cells treated with dexamethasone exhibited accelerated transition from early to late apoptosis, as determined by approximately twofold increase in the number of late apoptotic/necrotic Annexin V þ 7-AAD þ cells (33.7±4% versus 14.9±4.0%, Po0.001), and reduced numbers of early apoptotic, Annexin V þ 7-AADÀ cells (Figures 4a and b). However, we did not detect any significant difference between Beclin 1-GFP high -and Beclin 1-GFP-negative cells with respect to their sensitivity to two other apoptotic stimuli, anti-Fas and anti-TCR antibodies (Figures 4a and b).…”