Murine T cells expressing high activity of prolyl endopeptidase are susceptible to activation-induced cell death

AbstractProlyl endopeptidase (PEP) is widely distributed and thought to play an important role in the degradation of peptide hormones and neuropeptides, but its biological role is totally unknown. In this study, we examined PEP activity in subpopulations of murine T cells and found that PEP activity was significantly higher in immature thymocytes than in mature thymocytes or in peripheral T cells. Stimulation of murine peripheral T cells time-dependently increased PEP activity. Although murine T cell hybridomas exhibited high PEP activity, the PEP activity was fully inhibited by treatment with PEP inhibitor. The pretreated T cells were found to be resistant to activation-induced cell death (AICD). Similar results were obtained in murine thymocytes as well as in activated peripheral T cells. PEP activity in T cell hybridomas remained unchanged during AICD. These results suggest that T cells expressing high PEP activity are susceptible to ACID

TGF-β type II receptor expression in thymic epithelial cells inhibits the development of Hassall's corpuscles in mice

TGF-βRII signaling prevents the development of Hassall's corpuscle

Keratin 8 is required for the maintenance of architectural structure in thymus epithelium.

Keratins (Ks), the intermediate filament (IF) proteins of epithelia, are coordinately expressed as pairs in a cell-lineage and differentiation manner. Cortical thymic epithelial cells (cTECs) predominantly express the simple epithelium keratin 8/18 (K8/K18) pair, whereas medullary thymic epithelial cells (mTECs) express the stratified epithelium K5/K14 pair, with TECs exhibiting K5 and K8 at the cortico-medullary junction in mature thymus. In the work reported here, we used wild-type (WT) and K8-knockout (K8-null) mice to address the contribution of K8/K18 IFs in the maintenance of the thymic epithelial structure. K8-null thymus maintained the differential cell segregation at the cortex versus the medulla observed in WT thymus, and the distribution of immature thymocytes at the cortex. The K8/K18 loss did not affect thymocyte development. However, it massively perturbed the TEC morphology both at the cortex and the medulla, along with a prominent depletion of cTECs. Such tissue alterations coincided with an increase in apoptosis and a reduced expression of Albatross (Fas-binding factor-1), also known for its capacity to bind K8/18 IFs. In addition, the K8/K18 loss affected the distribution of K5/K14-positive mTECs, but not their differentiation status. Together, the results indicate that K8/K18 IFs constitute key promoters of the thymic epithelium integrity

Altered morphology of mTECs in keratin 8-deficient mice.

<p>Immunofluorescence staining of thymus sections of 7-week-old wild-type FVB/N mice (WT) and K8-deficient FVB/N mice (K8 KO) was performed to detect K5 or K14 (red). K8-null thymus displays a marked reduction in the frequency of K5+ or K14+ cells. Higher magnification of K8 null thymus to show a looser distribution of K5+ or K14+ cells. Data are representative of independent experiments (<i>n = </i>8 in each group). C, cortex; M, medulla. Scale bars = 100 µm.</p

Development of mTECs in keratin 8-deficient mice.

<p>(<b>A</b>) Immunofluorescence staining of thymus sections of 7-week-old wild-type FVB/N mice and K8-deficient FVB/N mice was performed to detect the binding to either UEA-1 or TPA (green) and K5 (red). (<b>B</b>) Thymus sections of both strains were stained for the detection of either CD80 or Aire (green) with p63 (red). Data are representative of independent experiments (<i>n = </i>8 in each group). Scale bars = 100 µm.</p

Keratin 8-deficient mice are absent from keratin 8/18 in thymic cortex.

<p>Immunofluorescence staining of thymus sections of 7-week-old wild-type FVB/N mice (WT) and K8-deficient FVB/N mice (K8 KO) was performed to detect K8 (<b>A</b>) or K18 (<b>B</b>) (green) and K5 (<b>A</b>) or K14 (<b>B</b>) (red). K8-deficient mice are lack of K8/K18 expression in the cortex. Note the altered morphology of K5+ or K14+ mTECs in K8-deficient mice. Data are representative of independent experiments (<i>n = </i>8 in each group). C, cortex; M, medulla. Scale bars = 100 µm. (<b>C</b>) Thymi from wild-type FVB/N mice and K8-deficient FVB/N mice at 5 weeks and 9 weeks of age were weighed. Each point provides the thymus weight of individual animal.</p