Retinoid‐induced skeletal hyperostosis in disorders of keratinisation

Darier disease: Current insights and challenges in pathogenesis and management

Darier disease is a rare autosomal dominant genodermatosis caused by mutations in the ATP2A2 gene encoding for sarcoendoplasmic reticulum Ca2+ ATPase isoform 2. The skin disease is characterized by a chronic relapsing course with recurrent reddish-brown keratotic papules and plaques located mainly in seborrhoeic areas. Due to chronic inflammation and epidermal barrier defects of the skin, patients often develop severe bacterial and viral superinfections. Therapeutic options are limited, mainly symptomatic and in most cases unsatisfactory in the long term. Patients are advised to avoid aggravating factors such as high temperature, high humidity, UV radiation and mechanical irritation. To prevent superinfection, antiseptics and periodic use of topical corticosteroids are fundamental in treatment. In case of bacterial and viral superinfection, systemic anti-infective therapy is often necessary. Currently, the most effective treatment option for extensive and persistent skin lesions is systemic retinoids, which are thought to mainly target the epidermal compartment (e.g. by reducing hyperkeratosis). One hallmark of Darier disease patients is chronic skin inflammation. We and others have previously reported Th17 cells in the dermal infiltrate of inflamed Darier disease skin. Counteracting inflammation by blocking the IL-23/IL-17 axis improved skin manifestations in a small cohort of previously therapy-resistant patients over 1 year. Furthermore, several other topical treatment options for mild disease as well as various ablative therapies and surgical excision have been proposed to be effective in some patients with hypertrophic skin lesions. This article aims to outline the pathogenesis, clinical features, diagnosis/differential diagnosis and available treatment modalities of Darier disease.

ERK hyperactivation in epidermal keratinocytes impairs intercellular adhesion and drives Grover disease pathology

Grover disease is an acquired epidermal blistering disorder in which keratinocytes lose intercellular connections. While its pathologic features are well defined, its etiology remains unclear, and there is no FDA-approved therapy. Interestingly, Grover disease was a common adverse event in clinical trials for cancer using B-RAF inhibitors, but it remained unknown how B-RAF blockade compromised skin integrity. Here, we identified ERK hyperactivation as a key driver of Grover disease pathology. We leveraged a fluorescent biosensor to confirm that the B-RAF inhibitors dabrafenib and vemurafenib paradoxically activated ERK in human keratinocytes and organotypic epidermis, disrupting cell-cell junctions and weakening epithelial integrity. Consistent with clinical data showing that concomitant MEK blockade prevents Grover disease in patients receiving B-RAF inhibitors, we found that MEK inhibition suppressed ERK and rescued cohesion of B-RAF-inhibited keratinocytes. Validating these results, we demonstrated ERK hyperactivation in patient biopsies from vemurafenib-induced Grover disease and from spontaneous Grover disease, revealing a common etiology for both. Finally, in line with our recent identification of ERK hyperactivation in Darier disease, a genetic disorder with identical pathology to Grover disease, our studies uncovered that the pathogenic mechanisms of these diseases converge on ERK signaling and support MEK inhibition as a therapeutic strategy.

ERK hyperactivation in epidermal keratinocytes impairs intercellular adhesion and drives Grover disease pathology

Grover disease is an acquired dermatologic disorder characterized by pruritic vesicular and eroded skin lesions. While its pathologic features are well-defined, including impaired cohesion of epidermal keratinocytes, the etiology of Grover disease remains unclear and it lacks any FDA-approved therapy. Interestingly, drug-induced Grover disease occurs in patients treated with B-RAF inhibitors that can paradoxically activate C-RAF and the downstream kinase MEK. We recently identified hyperactivation of MEK and ERK as key drivers of Darier disease, which is histologically identical to Grover disease, supporting our hypothesis that they share a pathogenic mechanism. To model drug-induced Grover disease, we treated human keratinocytes with clinically utilized B-RAF inhibitors dabrafenib or vemurafenib and leveraged a fluorescent biosensor to confirm they activated ERK, which disrupted intercellular junctions and compromised keratinocyte sheet integrity. Consistent with clinical data showing concomitant MEK blockade prevents Grover disease in patients receiving B-RAF inhibitors, we found that MEK inhibition suppressed excess ERK activity to rescue cohesion of B-RAF-inhibited keratinocytes. Validating these results, we demonstrated ERK hyperactivation in skin biopsies of vemurafenib-induced Grover disease, but also in spontaneous Grover disease. In sum, our data define a pathogenic role for ERK hyperactivation in Grover disease and support MEK inhibition as a therapeutic strategy.

GRAPHICAL ABSTRACT

Targeting SERCA2 in organotypic epidermis reveals MEK inhibition as a therapeutic strategy for Darier disease

Mutation of the ATP2A2 gene encoding sarco-endoplasmic reticulum calcium ATPase 2 (SERCA2) was linked to Darier disease more than 2 decades ago; however, there remain no targeted therapies for this disorder causing recurrent skin blistering and infections. Since Atp2a2-knockout mice do not phenocopy its pathology, we established a human tissue model of Darier disease to elucidate its pathogenesis and identify potential therapies. Leveraging CRISPR/Cas9, we generated human keratinocytes lacking SERCA2, which replicated features of Darier disease, including weakened intercellular adhesion and defective differentiation in organotypic epidermis. To identify pathogenic drivers downstream of SERCA2 depletion, we performed RNA sequencing and proteomics analysis. SERCA2-deficient keratinocytes lacked desmosomal and cytoskeletal proteins required for epidermal integrity and exhibited excess MAPK signaling, which modulates keratinocyte adhesion and differentiation. Immunostaining patient biopsies substantiated these findings, with lesions showing keratin deficiency, cadherin mislocalization, and ERK hyperphosphorylation. Dampening ERK activity with MEK inhibitors rescued adhesive protein expression and restored keratinocyte sheet integrity despite SERCA2 depletion or chemical inhibition. In sum, coupling multiomic analysis with human organotypic epidermis as a preclinical model, we found that SERCA2 haploinsufficiency disrupts critical adhesive components in keratinocytes via ERK signaling and identified MEK inhibition as a treatment strategy for Darier disease.

Alitretinoin as a Treatment Modality for Ichthyosis in Women of Childbearing Age: A Case Series and Review of the Literature

BACKGROUND

Acitretin, a synthetic vitamin A derivative, is the most studied and widely used oral retinoid for ichthyoses. Its major disadvantage is the need for contraceptive measures during 3 years after discontinuation. An alternative is needed for women of childbearing age. With alitretinoin, another retinoid, pregnancy is considered safe 1 month after discontinuation.

OBJECTIVES

The aim of this study was to provide evidence for alitretinoin as an alternative for acitretin for ichthyosis in women of childbearing age. Our experience is shared in a case series combined with an overview of the current literature.

METHODS

Nine women of childbearing age (19-31 years, median 21) with different subtypes of ichthyosis (autosomal recessive congenital ichthyosis, (superficial) epidermolytic ichthyosis, erythrokeratoderma variabilis, and epidermolytic epidermal nevi, a mosaic form of epidermolytic ichthyosis) were included and treated with 30 mg alitretinoin during 2-28 months. Severity was measured by Ichthyosis Area Severity Index (IASI) and Investigator Global Assessment (IGA). A literature search in Pubmed using the Mesh terms "alitretinoin," "skin diseases, genetic" and "ichthyosis" was performed.

RESULTS

Significant reduction in the mean scores of IGA, IASI-erythema, IASI-scaling, and IASI-total was seen. Seven patients are still being treated, 1 patient stopped to become pregnant, 1 patient discontinued due to financial reasons. Observed side effects were reversible headache (n = 6), asteatotic eczema (n = 1), "not feeling well" temporarily (n = 1), and easier blistering of the feet (n = 1). The literature search resulted in six case reports and case series about alitretinoin in ichthyosis and ichthyosis syndromes with in total 29 patients. The vast majority of articles (21/29) reported significant improvement or even complete remission of skin symptoms. However, validated outcome measures to support these results were lacking. Side effects (n = 16) were relatively mild, except for benign intracranial hypertension (n = 1) and autoimmune hypothyroidism (n = 1).

CONCLUSION

Our study shows, with validated outcome measures, that alitretinoin is effective to mitigate the symptoms of ichthyosis in women of childbearing age and a suitable alternative to acitretin.

Targeting SERCA2 in organotypic epidermis reveals MEK inhibition as a therapeutic strategy for Darier disease

Mutation of the ATP2A2 gene encoding sarco-endoplasmic reticulum calcium ATPase 2 (SERCA2) was linked to Darier disease more than two decades ago; however, there remain no targeted therapies for this disorder causing recurrent skin blistering and infections. Since Atp2a2 knockout mice do not phenocopy its pathology, we established a human tissue model of Darier disease to elucidate its pathogenesis and identify potential therapies. Leveraging CRISPR/Cas9, we generated human keratinocytes lacking SERCA2, which replicated features of Darier disease, including weakened intercellular adhesion and defective differentiation in organotypic epidermis. To identify pathogenic drivers downstream of SERCA2 depletion, we performed RNA sequencing and proteomic analysis. SERCA2-deficient keratinocytes lacked desmosomal and cytoskeletal proteins required for epidermal integrity and exhibited excess MAP kinase signaling, which modulates keratinocyte adhesion and differentiation. Immunostaining patient biopsies substantiated these findings with lesions showing keratin deficiency, cadherin mis-localization, and ERK hyper-phosphorylation. Dampening ERK activity with MEK inhibitors rescued adhesive protein expression and restored keratinocyte sheet integrity despite SERCA2 depletion or chemical inhibition. In sum, coupling multi-omic analysis with human organotypic epidermis as a pre-clinical model, we found that SERCA2 haploinsufficiency disrupts critical adhesive components in keratinocytes via ERK signaling and identified MEK inhibition as a treatment strategy for Darier disease.