Congenital deficiency reveals critical role of ISG15 in skin homeostasis

Muhammad Nasir Hayat Malik,Matthias Schefzyk,Syed Fakhar-Ul-Hassnain Waqas,Felix Meissner,Robert Geffers,Sven Schuchardt,Jana Zeitvogel,Lennart M Roesner,Thomas Werfel,Mathias Müsken,Gisa Gerold,Zeinab Abu-Elbaha Gouda,Bernd Auber,Peter Braubach,Ruth Olmer,Sylvia Merkert,Ulrich Martin,Ahmed M Elsaman ,Jiongjia Cheng ,Ahmed Radwan ,Frank Peßler

doi:10.1172/jci141573

Abstract

Ulcerating skin lesions are manifestations of human ISG15 deficiency, a type I interferonopathy. However, chronic inflammation may not be their exclusive cause. We describe two siblings with recurrent skin ulcers that healed with scar formation upon corticosteroid treatment. Both had a homozygous nonsense mutation in the ISG15 gene, leading to unstable ISG15 protein lacking the functional domain. We characterized ISG15–/– dermal fibroblasts, HaCaT keratinocytes, and human induced pluripotent stem cell–derived vascular endothelial cells. ISG15-deficient cells exhibited the expected hyperinflammatory phenotype, but also dysregulated expression of molecules critical for connective tissue and epidermis integrity, including reduced collagens and adhesion molecules, but increased matrix metalloproteinases. ISG15–/– fibroblasts exhibited elevated ROS levels and reduced ROS scavenger expression. As opposed to hyperinflammation, defective collagen and integrin synthesis was not rescued by conjugation-deficient ISG15. Cell migration was retarded in ISG15–/– fibroblasts and HaCaT keratinocytes, but normalized under ruxolitinib treatment. Desmosome density was reduced in an ISG15–/– 3D epidermis model. Additionally, there were loose architecture and reduced collagen and desmoglein expression, which could be reversed by treatment with ruxolitinib/doxycycline/TGF-β1. These results reveal critical roles of ISG15 in maintaining cell migration and epidermis and connective tissue homeostasis, whereby the latter likely requires its conjugation to yet unidentified targets.

Highlights

Monogenic type 1 interferonopathies are a heterogeneous group of auto-inflammatory and autoimmune disorders characterized by persistently elevated levels of type 1 interferons (IFN-I)(1-3)
We noted reduced expression of latent-transforming growth factor beta-binding proteins (LTBP) 1 and 2, which augment stability and secretion of transforming growth factor beta 1 (TGF-β1) [26, 27]. These findings suggested that dysregulation of collagen homeostasis and expression of adhesion molecules might act in concert with oxidative stress and hyperinflammation in the pathogenesis of skin ulcerations in IFN-stimulated gene 15 (ISG15) deficiency
In order to test whether the observed dysregulation in fibroblasts affected other cell types that play critical roles in skin inflammation and homeostasis, we evaluated the effects of ISG15 deficiency in human induced pluripotent stem cells (hiPSC)-derived

Summary

Introduction

Monogenic type 1 interferonopathies are a heterogeneous group of auto-inflammatory and autoimmune disorders characterized by persistently elevated levels of type 1 interferons (IFN-I)(1-3). ISG15 deficiency was the first example of a type 1 interferonopathy due to an inborn defect in the negative feed-back loop involving ISG15 and its downstream effector USP18, where absence of ISG15 protein leads to a secondary loss of USP18 and its ability to downregulate signaling through the IFNAR [8, 11]. Skin lesions were recently documented in several patients [13, 14] This was initially not too surprising since vasculitic skin lesions are common in the monogenic type I interferonopathies SAVI and familial chilblains lupus [3, 15], and in polygenically determined autoimmune diseases with IFN signatures such as juvenile systemic lupus erythematosus [16]. Histological changes in skin lesions of those cases of ISG15 deficiency where tissue biopsies were available did not show bona fide vasculitis [13]

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Conclusion