Epidermal growth factor promotes a neural phenotype in thymic epithelial cells and enhances neuropoietic cytokine expression.

Abstract

Abstract. Neural crest-derived cells populate the thymus, and their coexistence with epithelial cells is required for proper organ development and T cell education function. We show here that epidermal growth factor (EGF), a major epithelial cell growth-enhancing agent, has a morphogenetic action to promote the expression of a neuronal phenotype (e.g., neurofilament expression) in cultured thymic epithelial cells that are characterized by a cytokeratin-positive epithelial cell background. The proliferation of such neurodifferentiated cells is also enhanced by EGF. Furthermore, the growth factor enhances cells that express the genes encoding the preprotachykinin A-generated neuropeptides and the bipotential neuropoietic and lymphopoietic cytokines ciliary neurotrophic factor and interleukin-6. These cytokines also enhance the neuronal phenotype of thymic epithelial cells. Therefore, EGF appears to be a composite autocrine/paracrine neuromodulator in thymic stroma. This suggests that EGF may regulate thymus-dependent immune functions by promoting neuronal gene expression in neural crest-derived cells.M ULTIPLE cell interactions control developmental cell fate and morphogenesis. The morphogenetic process of the thymus is an example in which the variety of phenotypes resulting from T lymphoid cell developmental pathways and the acquisition of either the ability to react to external antigens or the tolerance against self-antigens arise through the action of instructive and/or selective differentiation signals generated by the thymic stroma in close association with precursor and differentiating lymphoid cells (8,47,51). A striking aspect of the thymic stroma is the coexistence of cell types arising from distinct cell lineages represented mainly by the endoderm of the third pharyngeal pouch, the ectoderm of the third branchial cleft and cells from the corresponding region of the neural crest (35, 36). The interaction of neuroectoderm-derived cells with other epithelial cells is necessary for both the organ morphogenic and the T cell differentiation processes. Indeed, ablation of the cephalic neural crest in chicken embryos results in thymic aplasia/ hypoplasia (4, 7). The further fate and specific functions of neural crest-derived cells within the thymic stroma remain unclear, although the presence of neural crest-derived cells in thymic medulla and the expression of a number of neuronal markers and neuropeptides in both thymic epithelium in vivo (14,18,20,42) and thymic stromal cell cultures (50) have been described. Cytokeratin-harboring thymic nurse epithelial cells also express most of these neuron and neuroendocrine markers and neuropeptides (19).The coexistence of epithelial and neural cells within the thymic stroma raises the question as to the nature of the regulatory signals that determine the development and survival of the neuronal component. EGF is a likely candidate as a soluble regulatory signal. Indeed, in addition to being a potent growth factor for several epithelial cell types (10), EGF and its recep...

Use of Cultured Thymic Tissues for the Regeneration of the Thymus

“…They noted that EGF promoted the expression of a neuronal phenotype in TEC culture, in addition to enhancing cells that express cytokines. This cytokine is essential for thymocyte proliferation, suggesting that EGF plays an important role in the up-regulation of neuronal expression in cells derived from the neural crest [90]. Similar effects using EGF and TGF-· have also been reported [71].…”

“…In addition, and more significant, is that plasticity appears to extend beyond the development of clearly distinguishable epithelial cell types also studied The secretion of IL-6 in response to EGF stimulation was studied by Screpanti et al [90]. They noted that EGF promoted the expression of a neuronal phenotype in TEC culture, in addition to enhancing cells that express cytokines.…”

“…Nerve growth factor enhances IL-6 gene expression and these two are synergistic in enhancing neurofilament and synapsin expression [88]. Substance P stimulates the production of IL-2 [89], whereas the addition of EGF to TEC cultures triggers neurofilament expression in addition to cytokine expression [90]. The presence of neuropeptides, neurotransmitters, hormones and cytokines are seemingly interrelated to the modulation of one another, to the direct and indirect maturation of thymocytes and the establishment of innervation following disruption to the tissue or involution.…”

2-Aminopurine Unravels a Role for pRB in the Regulation of Gene Expression by Transforming Growth Factor β

“…Cell Cycle Analysis-Cell cycle analysis was performed as described previously (33). Briefly, 1 ϫ 10 6 cells for each sample were fixed in 70% cold ethanol for 30 min at 4°C and, after washes in cold phosphatebuffered saline, treated with RNase (0.5 mg/ml) and stained with 40 g/ml propidium iodide.…”

Epidermal Growth Factor Modulates Fetal Thymocyte Growth and Differentiation

“…Fetal thymus organ cultures (FTOCs) allow these stages to be investigated, because after 7 to 12 days in vitro, starting with 13-to 15-day thymuses, the colonized intact organs develop mimicking almost entirely the in vivo situation up to delivery (Ceredig, 1988), which occurs around 20 days of fetal life. We used this technique to investigate a possible role for epidermal growth factor (EGF) in the thymus, because functional EGF receptors had been demonstrated on the membrane of the epithelial components of thymic stroma (Le et al, 1991), and a few cells in the adult thymus were shown by immunohistochemistry to express the EGF molecule itself (Screpanti et al, 1995).…”