Genetic activation of Nrf2 reduces cutaneous symptoms in a murine model of Netherton syndrome

The Role of KEAP1-NRF2 System in Atopic Dermatitis and Psoriasis

The Kelch-like erythroid cell-derived protein with cap‘n’collar homology-associated protein 1 (KEAP1)-nuclear factor erythroid-2-related factor 2 (NRF2) system, a thiol-based sensor-effector apparatus, exerts antioxidative and anti-inflammatory effects and maintains skin homeostasis. Thus, NRF2 activation appears to be a promising treatment option for various skin diseases. However, NRF2-mediated defense responses may deteriorate skin inflammation in a context-dependent manner. Atopic dermatitis (AD) and psoriasis are two common chronic inflammatory skin diseases caused by a defective skin barrier, dysregulated immune responses, genetic predispositions, and environmental factors. This review focuses on the role of the KEAP1-NRF2 system in the pathophysiology of AD and psoriasis and the therapeutic approaches that utilize this system.

Loricrin at the Boundary between Inside and Outside

Cornification is a specialized mode of the cell-death program exclusively allowed for terrestrial amniotes. Recent investigations suggest that loricrin (LOR) is an important cornification effector. As the connotation of its name (“lorica” meaning an armor in Latin) suggests, the keratin-associated protein LOR promotes the maturation of the epidermal structure through organizing covalent cross-linkages, endowing the epidermis with the protection against oxidative injuries. By reviewing cornification mechanisms, we seek to classify ichthyosiform dermatoses based on their function, rather than clinical manifestations. We also reviewed recent mechanistic insights into the Kelch-like erythroid cell-derived protein with the cap “n” collar homology-associated protein 1/nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway in skin health and diseases, as LOR and NRF2 coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of cross-talking between keratinocytes and epidermal resident leukocytes, dissecting an LOR immunomodulatory function.

Human Tissue Kallikreins-Related Peptidases Are Targets for the Treatment of Skin Desquamation Diseases

Human tissue Kallikrein-related peptidases (hKLKs) are serine proteases distributed in several tissues that are involved in several biological processes. In skin, many are responsible for skin desquamation in the Stratum Corneum (SC) of the epidermis, specially hKLK5, hKLK7, hKLK6, hKLK8, and hKLK14. In SC, hKLKs cleave proteins of corneodesmosomes, an important structure responsible to maintain corneocytes attached. As part of skin desquamation, hKLKs are also involved in skin diseases with abnormal desquamation and inflammation, such as Atopic Dermatitis (AD), psoriasis, and the rare disease Netherton Syndrome (NS). Many studies point to hKLK overexpression or overactive in skin diseases, and they are also part of the natural skin inflammation process, through the PAR2 cleavage pathway. Therefore, the control of hKLK activity may offer successful treatments for skin diseases, improving the quality of life in patients. Diseases like AD, Psoriasis, and NS have an impact on social life, causing pain, itchy and mental disorders. In this review, we address the molecular mechanisms of skin desquamation, emphasizing the roles of human tissue Kallikrein-related peptidases, and the promising therapies targeting the inhibition of hKLKs.

The Epidermis: Redox Governor of Health and Diseases

A functional epithelial barrier necessitates protection against dehydration, and ichthyoses are caused by defects in maintaining the permeability barrier in the stratum corneum (SC), the uppermost protective layer composed of dead cells and secretory materials from the living layer stratum granulosum (SG). We have found that loricrin (LOR) is an essential effector of cornification that occurs in the uppermost layer of SG (SG1). LOR promotes the maturation of corneocytes and extracellular adhesion structure through organizing disulfide cross-linkages, albeit being dispensable for the SC permeability barrier. This review takes psoriasis and AD as the prototype of impaired cornification. Despite exhibiting immunological traits that oppose each other, both conditions share the epidermal differentiation complex as a susceptible locus. We also review recent mechanistic insights on skin diseases, focusing on the Kelch-like erythroid cell-derived protein with the cap "n" collar homology-associated protein 1/NFE2-related factor 2 signaling pathway, as they coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of thiol-mediated crosstalk between keratinocytes and leukocytes in the epidermis that was put forward earlier.

Netherton Syndrome: Case Report and Review of the Literature

Netherton syndrome (NS) is a rare genodermatosis with an autosomal recessive pattern of inheritance caused by pathogenic variants in the SPINK5 gene. It is characterized by a triad consisting of atopic diathesis, ichthyosis linearis circumflexa, and hair shaft abnormalities. Ichthyosis linearis circumflexa can be confused with atopic dermatitis leading to a delayed diagnosis. Furthermore, difficulty in making the differential diagnosis with other atopiform, erythrodermic, and ichthyosiform entities that exhibit hair shaft abnormalities represent a challenge. Trichoscopy is an accessible and noninvasive auxiliary diagnostic tool in these cases; the hair shaft abnormalities found in NS are bamboo, golf tee, and matchstick hairs. Identification of a pathogenic variant in the SPINK5 gene through genetic testing is necessary to confirm the diagnosis. Multiple treatment options are available including topical therapy with emollients, corticosteroids, calcineurin inhibitors, antiseptics, and narrowband UVB phototherapy. Systemic treatments comprehend intravenous immunoglobulins, and advances in the understanding of the pathophysiology of NS have led to more directed therapies with biologics such as infliximab, ixekizumab, secukinumab, ustekinumab, and dupilumab. Treatments currently under investigation include inhibitors of kallikrein 5, cathelicidins, drugs activating the transcription factor nuclear factor erythroid-derived 2-like 2, and gene therapy using autologous keratinocytes induced with a lentiviral vector encoding SPINK5.

First person – Sukalp Muzumdar

First Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping early-career researchers promote themselves alongside their papers. Sukalp Muzumdar is first author on ‘Genetic activation of Nrf2 reduces cutaneous symptoms in a murine model of Netherton syndrome’, published in DMM. Sukalp conducted the research described in this article while a PhD student in the lab of Prof. Dr Sabine Werner and PD Dr Matthias Schäfer at ETH Zurich, Zurich, Switzerland. He is now a postdoctoral fellow in the lab of Jesse Gillis at Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA, investigating the mechanisms behind rare diseases and exploring avenues for novel treatments.