Type XVII collagen coordinates proliferation in the interfollicular epidermis

Type XVII collagen (COL17) is a transmembrane protein located at the epidermal basement membrane zone. COL17 deficiency results in premature hair aging phenotypes and in junctional epidermolysis bullosa. Here, we show that COL17 plays a central role in regulating interfollicular epidermis (IFE) proliferation. Loss of COL17 leads to transient IFE hypertrophy in neonatal mice owing to aberrant Wnt signaling. The replenishment of COL17 in the neonatal epidermis of COL17-null mice reverses the proliferative IFE phenotype and the altered Wnt signaling. Physical aging abolishes membranous COL17 in IFE basal cells because of inactive atypical protein kinase C signaling and also induces epidermal hyperproliferation. The overexpression of human COL17 in aged mouse epidermis suppresses IFE hypertrophy. These findings demonstrate that COL17 governs IFE proliferation of neonatal and aged skin in distinct ways. Our study indicates that COL17 could be an important target of anti-aging strategies in the skin.

Meeting Report of the Pathogenesis of Pemphigus and Pemphigoid Meeting in Munich, September 2016

Autoimmune blistering diseases are a heterogeneous group of about a dozen complex disorders that are characterized by intraepidermal (pemphigus) and subepidermal blistering (pemphigoid diseases and dermatitis herpetiformis). The Pathogenesis of Pemphigus and Pemphigoid Meeting, organized by the Departments of Dermatology in Lübeck and Marburg and the Institute of Anatomy and Cell Biology, Munich, was held in September 2016 in Munich. The meeting brought together basic scientists and clinicians from all continents dedicating their work to autoimmune blistering diseases. Considerable advances have been made in describing incidences and prevalences of these diseases and linking comorbidities with autoantibody reactivities and clinical variants, for example, dipeptidyl peptidase-IV inhibitor-associated noninflammatory bullous pemphigoid. Although new entities are still being described, diagnosis of most autoimmune blistering diseases can now be achieved using standardized and widely available serological test systems. Various experimental mouse models of pemphigus and pemphigoid disease are increasingly being used to understand mechanisms of central and peripheral tolerance and to evaluate more specific treatment approaches for these disorders, such as molecules that target autoreactive T and B cells and anti-inflammatory mediators, that is, dimethyl fumarate, phosphodiesterase 4, and leukotriene B4 inhibitors in pemphigoid disorders, and chimeric antigen receptor T cells in pemphigus. Very recent experimental data about the immunopathology and the determinants of autoantibody formation and keratinocyte susceptibility in pemphigus were discussed. With regard to cellular mechanisms leading to the loss of cell-cell adhesion, new ideas were shared in the field of signal transduction. Major steps were taken to put the various partly contradictory and controversial findings about the effects of pemphigus autoantibodies and other inflammatory mediators into perspective and broaden our view of the complex pathophysiology of this disease. Finally, two investigator-initiated multicenter trials highlighted doxycycline and dapsone as valuable medications in the treatment of bullous pemphigoid.

MOB1-YAP1/TAZ-NKX2.1 axis controls bronchioalveolar cell differentiation, adhesion and tumour formation

Mps One Binder Kinase Activator (MOB)1A/1B are core components of the Hippo pathway. These proteins, which coactivate LArge Tumour Suppressor homologue kinases, are also tumour suppressors. To investigate MOB1A/B's roles in normal physiology and lung cancer, we generated doxycycline (Dox)-inducible, bronchioalveolar epithelium-specific, null mutations of MOB1A/B in mice (SPC-rtTA/(tetO)₇-Cre/Mob1a^flox/flox/Mob1b^-/-; termed luMob1DKO mice). Most mutants (70%) receiving Dox in utero (luMob1DKO (E6.5-18.5) mice) died of hypoxia within 1 h post-birth. Their alveolar epithelial cells showed increased proliferation, impaired YAP1/TAZ-dependent differentiation and decreased surfactant protein production, all features characteristic of human respiratory distress syndrome. Intriguingly, mutant mice that received Dox postnatally (luMob1DKO (P21-41) mice) did not develop spontaneous lung adenocarcinomas, and urethane treatment-induced lung tumour formation was decreased (rather than increased). Lungs of luMob1DKO (P21-41) mice exhibited increased detachment of bronchiolar epithelial cells and decreased numbers of the bronchioalveolar stem cells thought to initiate lung adenocarcinomas. YAP1/TAZ-NKX2.1-dependent expression of collagen XVII, a key hemidesmosome component, was also reduced. Thus, a MOB1-YAP1/TAZ-NKX2.1 axis is essential for normal lung homeostasis and expression of the collagen XVII protein necessary for alveolar stem cell maintenance in the lung niche.

Macropinocytosis of type XVII collagen induced by bullous pemphigoid IgG is regulated via protein kinase C

Macropinocytosis is an endocytic pathway that is involved in the nonselective fluid uptake of extracellular fluid. Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies to type XVII collagen (COL17), which is a component of hemidesmosome. When keratinocytes are treated with BP-IgG, COL17 internalizes into cells by way of the macropinocytosis. We investigated the mechanism of COL17 macropinocytosis using DJM-1 cells, a cutaneous squamous cell carcinoma cell line. First, non-hemidesmosomal COL17 was preferentially depleted by stimulation with the BP-IgG in the DJM-1 cells. To investigate the signaling involved in COL17-macropinocytosis, the inhibition of small GTPase family members Rac1 and Cdc42 was found to strongly repress COL17 internalization; in addition, the Rho inhibitor also partially blocked that internalization, suggesting these small GTPases are involved in signaling to mediate COL17-macropinocytosis. Western blotting using Phostag-SDS-PAGE demonstrated high levels of COL17 phosphorylation in DJM-1 cells under steady-state condition. Treatment with BP-IgG increased the intracellular calcium level within a minute, and induced the overabundant phosphorylation of COL17. The overabundant phosphorylation of COL17 was suppressed by a protein kinase C (PKC) inhibitor. In addition, PKC inhibitor repressed COL17 endocytosis using cell culture and organ culture systems. Finally, the depletion of COL17 was not observed in the HEK293 cells transfected COL17 without intracellular domain. These results suggest that COL17 internalization induced by BP-IgG may be mediated by a PKC pathway. In summary, BP-IgG initially binds to COL17 distributed on the plasma membrane, and COL17 may be internalized by means of a macropinocytic pathway related to the phosphorylation of the intracellular domain by PKC.

Autoantibody Profile Differentiates between Inflammatory and Noninflammatory Bullous Pemphigoid

Bullous pemphigoid (BP) is a major autoimmune blistering skin disorder, in which a majority of the autoantibodies (autoAbs) target the juxtamembranous extracellular noncollagenous 16A domain (NC16A) domain of hemidesmosomal collagen XVII. BP-autoAbs may target regions of collagen XVII other than the NC16A domain; however, correlations between epitopes of BP-autoAbs and clinical features have not been fully elucidated. To address correlations between the clinical features and specific epitopes of BP-autoAbs, we evaluated the epitope profiles of BP-autoAbs in 121 patients. A total of 87 patients showed a typical inflammatory phenotype with erythema and autoAbs targeting the anti-NC16A domain, whereas 14 patients showed a distinct noninflammatory phenotype, in which autoAbs specifically targeted the midportion of collagen XVII, but not NC16A. Interestingly, this group clinically showed significantly reduced erythema associated with scant lesional infiltration of eosinophils. Surprisingly, 7 of the 14 cases (50.0%) received dipeptidyl peptidase-IV inhibitors for the treatment of diabetes. Dipeptidyl peptidase-IV inhibitors were used in 3 of 76 (3.9%) typical cases of BP with autoAbs targeting NC16A; thus, dipeptidyl peptidase-IV inhibitors are thought to be involved in the development of atypical noninflammatory BP. This study shows that the autoAb profile differentiates between inflammatory and noninflammatory BP, and that noninflammatory BP may be associated with dipeptidyl peptidase-IV inhibitors.