Estudio funcional del receptor de glucocorticoides en desarrollo y reparación epitelial

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The glucocorticoid receptor (GR) plays a crucial role in epidermal morphogenesis during embryonic development, as demonstrated by analyzing genetically modified mouse models of GR gain- and loss-of-function. Eyelid formation constitutes a useful model to study epithelial development, as it requires coordinated regulation of keratinocyte proliferation, apoptosis and migration. We have analyzed this biological process in GR-/- embryos during ontogeny. Our data demonstrate that GR deficiency results in delayed and impaired eyelid closure, as illustrated by increased keratinocyte proliferation and apoptosis along with impaired differentiation in GR-/- eyelid epithelial cells. These defects are due, at least in part, to the lack of antagonism between GR and epidermal growth factor receptor (EGFR) signaling, causing sustained activation of the MAPK/AP-1 pathway and the upregulation of keratin K6 at embryonic stage E18.5. Additionally, we demonstrate that GR regulates epithelial cell migration in vitro by interfering with EGFR-mediated signaling. Overall, GR/EGFR antagonism appears as a major mechanism regulating ocular epithelial development. Cutaneous wound healing is a complex process starting after an injury aimed to repair the tissue damage and restore skin homeostasis. There are three phases in this process that require a coordinated interaction among diverse cell types with precise kinetics: inflammation, re-epithelization and tissue remodelling. It is well known that glucocorticoid (GC) treatment delays wound healing, which is one of the most common secondary adverse effects associated to GC therapeutic use. We have assessed the specific contribution of the GC receptor (GR) in wound healing using mice with keratinocyte-restricted constitutive expression of the wt or the transactivation-defective mutant form of GR (K5-GR and K5-GR-TR transgenic mice1). This approach allows us to compare the DNA-binding-dependent and –independent mechanisms of GR action in vivo. K5-GR wounds healed slower than WT as assessed by wound closure kinetics at days (d) 4 and 8 after injury, showing reduced granulocyte/macrophage recruitment as well as diminished TNF- and IL-6 expression. The mRNA levels of IL-1, KGF, and TGF-1 were repressed by GR whereas TGF-3 was up-regulated. The re-epithelialization rate, determined by keratinocyte proliferation and migration, was reduced in K5-GR wounds relative to WT, along with impaired formation of the granulation tissue. In contrast, K5-GR-TR mice showed delayed healing at d4 but re-established the skin breach at d8 concomitantly with a minor repression of pro-inflammatory cytokines and growth factors than K5-GR mice. Our data indicate that keratinocyte-targeted overexpression of either GR or GR-TR is sufficient to delay wound healing at early stages. The differential regulation by GR and GR-TR of several cytokines and growth factors with a major role in wound repair may account for distinct kinetics of healing impairment elicited by this hormone receptor.
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