Glucocorticoid Receptor Regulates Overlapping and Differential Gene Subsets in Developing and Adult Skin

Abstract

We have previously shown that the glucocorticoid receptor (GR) is required for skin homeostasis and epidermal barrier competence. To understand the transcriptional program by which GR regulates skin development, we performed a microarray analysis using the skin of GR(-/-) and GR(+/+) mice of embryonic d 18.5 and identified 442 differentially expressed genes. Functional clustering demonstrated overrepresentation of genes involved in ectoderm/epidermis development. We found strong repression of genes encoding proteins associated with the later stages of epidermal differentiation, such as several small proline-rich proteins (Sprrs) and corneodesmosin (Cdsn). This, together with the up-regulation of genes induced earlier during epidermal development, including the epithelial-specific gene transcripts E74-like factor 5 (Elf5) and keratin 77 (Krt77), fits with the phenotype of defective epidermal differentiation observed in the GR(-/-) mice. We also found down-regulation of the antimicrobial peptide defensin β 1 (Defb1) and FK506-binding protein 51 (Fkbp51). Skin developmental expression profiling of these genes and studies in cultured keratinocytes from GR(-/-) and wild type embryos demonstrated that gene regulation occurred in a cell-autonomous manner. To investigate the consequences of GR loss in adult epidermis, we generated mice with inducible inactivation of GR restricted to keratinocytes (K14-cre-ER(T2)//GR(loxP/loxP) mice). K14-cre-ER(T2)//GR(loxP/loxP) mice featured thickened skin with increased keratinocyte proliferation and impaired differentiation. Whereas Krt77 and Elf5 expression remained unaffected by loss of GR in adult epidermis, Fkbp51, Sprr2d, and Defb1 were strongly repressed. Importantly, we have identified both Fkbp51 and Defb1 as direct transcriptional targets of GR, and we have shown that GR-mediated regulation of these genes occurs in both developing and adult epidermis. We conclude that both overlapping and differential GR targets are regulated in developing vs. adult skin.

Glucocorticoid receptors, epidermal homeostasis and hair follicle differentiation

“…14 The timing of GC synthesis is in agreement with the expression pattern of GR in skin during mouse development; Nr3c1 mRNA peaks at the transition E14.5 to E16.5, correlating with the mRNA changes of the GR-regulated genes identified during skin development. 36 This is in agreement with previous studies reporting GR mRNA upregulation in fetal rat epidermis in late gestation. 37 Recently, the histopathological and molecular characterization of mice with general ablation of GR has shed light into the physiological role of this transcription factor during epidermal development.…”

“…37 Recently, the histopathological and molecular characterization of mice with general ablation of GR has shed light into the physiological role of this transcription factor during epidermal development. 36,38 The epidermis of GR -/-E18.5 embryos exhibited an immature appearance with abnormal proliferating cells defects to death. 26 Even mild defects in skin development may have consequences in the adult age leading to increased susceptibility to skin infections and inflammation.…”

“…38 Besides, the gene expression changes detected in cultured keratinocytes upon Dex treatment showed some discrepancies relative to GR -/-MPKs. 36,39 These differences may be explained by culture conditions as well as by the Dex dose and kinetics. 35,36,39 Although the use of cultured cells provides relevant information, it seems reasonable to assume that the in vitro studies using MPKs do not fully recapitulate skin physiology.…”

“…36,39 These differences may be explained by culture conditions as well as by the Dex dose and kinetics. 35,36,39 Although the use of cultured cells provides relevant information, it seems reasonable to assume that the in vitro studies using MPKs do not fully recapitulate skin physiology. The generation of a mouse model with keratinocyte-restricted constitutive GR inactivation will allow for study of the epithelial contribution of GR in skin development and disease.…”

“…36 Some of the major constituents of the cornified envelope including several genes encoding for the small proline rich proteins (Sprrs) and corneodesmosin (Cdsn), as well as genes involved in epidermal terminal differentiation (Ptgs1 and Bcl6 ) were strongly downregulated. Also, Krt77 and the epithelial-specific transcription factor Elf5, two genes expressed at relatively high levels during earlier stages of epidermal development were highly upregulated in the GR-deficient skin.…”