Chantal Renard

Expression of the Growth Hormone/Insulin-Like Growth Factor Axis during Balb/c Thymus Ontogeny and Effects of Growth Hormone upon ex vivo T Cell Differentiation

Aims: We address the question of the expression and the role of the growth hormone/insulin-like growth factor (GH/IGF) axis in the thymus. Methods: Using RT-qPCR, the expression profile of various components of the somatotrope GH/IGF axis was measured in different thymic cell types and during thymus embryogenesis in Balb/c mice. The effect of GH on T cell differentiation was explored via thymic organotypic culture. Results: Transcription of Gh, Igf1, Igf2 and their related receptors predominantly occurred in thymic epithelial cells (TEC), while a low level of Gh and Igf1r transcription was also evidenced in thymic T cells (thymocytes). Gh, Ghr, Ins2, Igf1, Igf2, and Igfr1 displayed distinct expression profiles depending on the developmental stage. The protein concentrations of IGF-1 and IGF-2 were in accordance with the profile of their gene expression. In fetal thymus organ cultures (FTOC) derived from Balb/c mice, treatment with exogenous GH resulted in a significant increase of double negative CD4–CD8– T cells and CD4+ T cells, together with a decrease in double positive CD4+CD8+ T cells. These changes were inhibited by concomitant treatment with GH and the GH receptor (GHR) antagonist pegvisomant. However, GH treatment also induced a significant decrease in FTOC Gh, Ghr and Igf1 expression. Conclusion: These data show that the thymotropic properties of the somatotrope GH/IGF-1 axis involve an interaction between exogenous GH and GHR expressed by TEC. Since thymic IGF-1 is not increased by GH treatment, the effects of GH upon T cell differentiation could implicate a different local growth factor or cytokine.

Thymic neuroendocrine self-antigens. Role in T-cell development and central T-cell self-tolerance

Abstract: The repertoire of thymic neuroendocrine precursors plays a dual role in T‐cell differentiation as the source of either cryptocrine accessory signals in T‐cell development or neuroendocrine self‐antigens presented by the thymic major histocompatibility complex (MHC) Machinery. Thymic neuroendocrine self‐antigens usually correspond to peptide sequences highly conserved during the evolution of one family. The thymic presentation of some neuroendocrine self‐antigens is not restricted by mhc alleles. Oxytocin (OT) is the dominant peptide of the neurohypophysial family. It is expressed by thymic epithelial and nurse cells (TEC/TNCs) of different species. Ontogenetic studies have shown that the thymic expression of the OT gene precedes the hypothalamic one. Both OT and VP stimulate the phosphorylation of p125FAK and other focal adhesion‐related proteins in murine immature T cells. These early cell activation events could play a role in the promotion of close interactions between thymic stromal cells and developing T cells. It is established that such interactions are fundamental for the progression of thymic T‐cell differentiation. Insulin‐like growth factor 2 (IGF‐2) is the dominant thymic polypeptide of the insulin family. Using fetal thymic organ cultures (FTOCs), the inhibition of thymic IGF‐2‐mediated signaling was shown to block the early stages of T‐cell differentiation. The treatment of FTOCs with an mAb anti‐(pro)insulin had no effect on T‐cell development. In an animal model of autoimmune type 1 diabetes (BB rat), thymic levels of (pro)insulin and IGF‐1 mRNAs were normal both in diabetes‐resistant and diabetes‐prone BB rats. IGF‐2 transcripts were clearly identified in all thymuses from diabetes‐resistant adult (5‐week) and young (2‐ and 5‐days) BB rats. In marked contrast, the IGF‐2 transcripts were absent and the IGF‐2 protein was almost undetectable in ±80% of the thymuses from diabetes‐prone adult and young BB rats. These data show that a defect of the thymic IGF‐2‐mediated tolerogenic function might play an important role in the pathophysiology of autoimmune Type 1 diabetes.

High TMEM45A expression is correlated to epidermal keratinization.

TMEM45A (DERP7, DNAPTP4 or FLJ10134) gene, belonging to the TMEM family encoding predicted transmembrane proteins, is highly expressed in epidermal keratinocytes. To investigate the potential involvement of TMEM45A during the differentiation and keratinization processes, its expression has been characterized in normal human keratinocytes and the protein subcellular localization has been studied in this cell type, both in vitro and in vivo. TMEM45A expression is upregulated with differentiation, either induced by cultured keratinocyte confluence or enhanced Ca2+ concentration in medium. In vivo, TMEM45A mRNA and protein are mostly found in the granular layer of the epidermis. TMEM45A expression is linked to keratinization, as accumulation of the protein is detected in native and reconstructed epidermis as well as in thymic Hassal bodies, but not in non‐keratinized stratified epithelia. At the subcellular level, co‐detection with ER and Golgi markers reveals that TM protein 45A is associated with the Golgi apparatus and more specifically with the trans‐Golgi/trans‐Golgi network in vitro and in granular layer in vivo. The protein is neither related to lysosomes nor transported within corneodesmosin‐containing lamellar bodies. These data demonstrate a strong correlation between TMEM45A expression and epidermal keratinization, indicating the relevance of this gene in this process.

Accumulation of IL-17+ Vγ6+ γδ T cells in pregnant mice is not associated with spontaneous abortion

Pregnancy is an immune paradox. While the immune system is required for embryo implantation, placental development and progression of gestation, excessive inflammation is associated with pregnancy failure. Similarly, the cytokine IL‐17A plays an important role in defence against extracellular pathogens, but its dysregulation can lead to pathogenic inflammation and tissue damage. Although expression of IL‐17 has been reported during pregnancy, the cellular source of this cytokine and its relevance to gestation are not clear.