ABSTRACT
BACKGROUND: The Notch pathway is essential for proper epidermal differentiation during embryonic skin development. Moreover, skin specific loss of Notch signaling in the embryo results in skin barrier defects accompanied by a B-lymphoproliferative disease. However, much less is known about the consequences of loss of Notch signaling after birth. METHODOLOGY AND PRINCIPAL FINDINGS: To study the function of Notch signaling in the skin of adult mice, we made use of a series of conditional gene targeted mice that allow inactivation of several components of the Notch signaling pathway specifically in the skin. We demonstrate that skin-specific inactivation of Notch1 and Notch2 simultaneously, or RBP-J, induces the development of a severe form of atopic dermatitis (AD), characterized by acanthosis, spongiosis and hyperkeratosis, as well as a massive dermal infiltration of eosinophils and mast cells. Likewise, patients suffering from AD, but not psoriasis or lichen planus, have a marked reduction of Notch receptor expression in the skin. Loss of Notch in keratinocytes induces the production of thymic stromal lymphopoietin (TSLP), a cytokine deeply implicated in the pathogenesis of AD. The AD-like associated inflammation is accompanied by a myeloproliferative disorder (MPD) characterized by an increase in immature myeloid populations in the bone marrow and spleen. Transplantation studies revealed that the MPD is cell non-autonomous and caused by dramatic microenvironmental alterations. Genetic studies demontrated that G-CSF mediates the MPD as well as changes in the bone marrow microenvironment leading to osteopenia. SIGNIFICANCE: Our data demonstrate a critical role for Notch in repressing TSLP production in keratinocytes, thereby maintaining integrity of the skin and the hematopoietic system.
Subject(s)
Dermatitis, Atopic/physiopathology , Myeloproliferative Disorders/physiopathology , Receptors, Notch/physiology , Signal Transduction/physiology , Skin/physiopathology , Animals , Cytokines/metabolism , Dermatitis, Atopic/genetics , Dermatitis, Atopic/mortality , Flow Cytometry , Granulocyte Colony-Stimulating Factor/genetics , Granulocyte Colony-Stimulating Factor/metabolism , Humans , Immunoglobulins , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Nude , Mice, Transgenic , Models, Biological , Myeloproliferative Disorders/genetics , Myeloproliferative Disorders/mortality , Receptor, Notch1/genetics , Receptor, Notch1/physiology , Receptor, Notch2/genetics , Receptor, Notch2/physiology , Receptors, Cytokine/genetics , Receptors, Cytokine/metabolism , Receptors, Notch/genetics , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction/genetics , Skin/metabolism , Skin/pathology , Survival Analysis , Survival Rate , Thymic Stromal LymphopoietinABSTRACT
Integrity and preservation of a transparent cornea are essential for good vision. The corneal epithelium is stratified and nonkeratinized and is maintained and repaired by corneal stem cells. Here we demonstrate that Notch1 signaling is essential for cell fate maintenance of corneal epithelium during repair. Inducible ablation of Notch1 in the cornea combined with mechanical wounding show that Notch1-deficient corneal progenitor cells differentiate into a hyperplastic, keratinized, skin-like epithelium. This cell fate switch leads to corneal blindness and involves cell nonautonomous processes, characterized by secretion of fibroblast growth factor-2 (FGF-2) through Notch1(-/-) epithelium followed by vascularization and remodeling of the underlying stroma. Vitamin A deficiency is known to induce a similar corneal defect in humans (severe xerophthalmia). Accordingly, we found that Notch1 signaling is linked to vitamin A metabolism by regulating the expression of cellular retinol binding protein 1 (CRBP1), required to generate a pool of intracellular retinol.
Subject(s)
Cell Lineage , Epithelium, Corneal/cytology , Receptor, Notch1/metabolism , Signal Transduction , Vitamin A/metabolism , Wound Healing , Animals , Cell Differentiation , Cell Movement , Corneal Stroma/pathology , Epidermal Cells , Epithelium, Corneal/pathology , Keratins/metabolism , Meibomian Glands/abnormalities , Mice , Models, Biological , Receptor, Notch1/deficiency , Retinol-Binding Proteins/metabolism , Retinol-Binding Proteins, Cellular , Stem Cells/cytologyABSTRACT
Notch genes encode evolutionarily conserved large, single transmembrane receptors, which regulate many cell fate decisions and differentiation processes during fetal and postnatal life. Multiple Notch receptors and ligands are expressed in both developing and adult epidermis and hair follicles. Proliferation and differentiation of these two ectodermal-derived structures have been proposed to be controlled in part by the Notch pathway. Whether Notch signaling is involved in postnatal hair homeostasis is currently unknown. Here, we investigate and compare the role of the Notch1 receptor during embryonic hair follicle development and postnatal hair homeostasis using Cre-loxP based tissue specific and inducible loss-of-function approaches. During embryonic development, tissue-specific ablation of Notch1 does not perturb formation and patterning of hair follicle placodes. However, Notch1 deficient hair follicles invaginate prematurely into the dermis. Embryonic as well as postnatal inactivation of Notch1 shortly after birth or in adult mice results in almost complete hair loss followed by cyst formation. The first hair cycle of Notch1 deficient mice is characterized by shortened anagen and a premature entry into catagen. These data show that Notch1 is essential for late stages of hair follicle development during embryogenesis as well as for post-natal hair follicle development and hair homeostasis.
