Gamma secretase (γ-secretase) is an enzymatic transmembrane complex responsible for the cleavage of over 100 substrates, including notch, E-cadherin, amyloid precursor protein, specific cytokine receptors, and other type I transmembrane proteins. Genetic variants in the γ-secretase complex are associated with familial hidradenitis suppurativa (HS), where they are predicted to inactivate enzymatic function. Further, γ-secretase inhibitors cause HS-like pathologies in patients with desmoid tumors. However, it is unclear how modulation of γ-secretase activity in keratinocytes impacts cellular processes and contributes to HS pathophysiology. We explored how the loss of γ-secretase function impacts keratinocyte-mediated inflammatory cytokine and chemokine production and adhesion, two key keratinocyte processes altered in HS. We used pharmacological inhibitors of γ-secretase (SCP0004, nirogacestat, and E2012) that have different mechanisms of action and substrate selectivity (e.g. notch processing). Each inhibitor exhibited both distinct and similar effects on normal human keratinocyte functions. SCP0004 strongly modulated inflammatory cytokine responses. Nirogacestat modulated select chemokines and cytokines, whereas E2012 showed little effect. Conversely, keratinocyte adhesion was reduced by all γ-secretase inhibitors. Thus, γ-secretase inhibitors can drive keratinocyte functions associated with HS development. Future studies elucidating the contribution of specific substrates may inform the mechanisms of drug-induced HS phenotypes.

Cadherins are linked to actin through α- and β -catenin. p120 catenin (p120) also binds to the cadherin cytoplasmic domain and prevents cadherin endocytosis. In mouse epidermis, p120 gene ablation leads to severe skin inflammation and early postnatal lethality. These outcomes have been ascribed to cadherin-independent functions of p120 in RhoA and NFκB inflammatory signaling. However, the downregulation of cadherins in a p120 null background complicates interpretations. We engineered a mouse line in which a di-leucine endocytic motif in the E-cadherin cytoplasmic domain was mutated (EcadLL). Using tissue-level morphometric analyses in parallel to transcriptomics, we find that the EcadLL mutant is epistatic to p120 gene ablation. Mice lacking epidermal p120, but harboring the EcadLL mutant, are viable, fertile, and lack epidermal inflammation and hyperproliferation observed in p120 knock-out epidermis. These findings demonstrate that regulation of cadherin cell surface stability is the essential function of p120 and suggest a role for cadherins in suppressing epidermal inflammatory pathways.

BACKGROUND:Therapeutic options for mild hidradenitis suppurativa (HS) represent a significant gap in the current treatment landscape, with no U.S. Food and Drug Administration-approved therapies for early-stage HS. Topical Janus kinase (JAK) inhibitors (JAKi) are a compelling option due to the known upregulation of inflammatory JAK signalling in HS lesions and the recent success of systemic JAKi for the treatment of moderate-to-severe HS. OBJECTIVES:To assess the clinical efficacy of ruxolitinib in a pilot cohort and to investigate the underlying biologic mechanisms associated with clinical response. METHODS:This was a pilot single-site open-label prospective 24-week clinical trial of topical ruxolitinib (NCT04414514). Men and women with mild HS (Hurley stage I or II), with active inflammatory nodules, were recruited. All participants were observed for 8 weeks to monitor lesion counts (observational phase); active therapy (treatment phase) was then administered for 16 weeks. Topical ruxolitinib 1.5% cream was applied twice daily, covering the entirety of each HS-affected body site. Clinician- and patient-reported outcome measures were recorded throughout the study. Lesional skin punch biopsies were taken at the start and end of treatment for downstream mechanistic RNA sequencing and histological analyses. RESULTS:Ten participants were enrolled in the study; four dropped out before the treatment phase of the trial. Six individuals with Hurley stage I (no tunnels) HS completed the study, five of whom successfully achieved Hidradenitis Suppurativa Clinical Response (HiSCR50) through 16 weeks of therapy. In this interim analysis, differential gene expression and gene set enrichment analyses revealed reduced activation of JAK-dependent interferon, interleukin (IL)-6, IL-2 and epidermal growth factor receptor signalling, and antimicrobial and keratinocyte responses. In contrast, signatures of wound healing and lipid metabolism were increased following JAKi treatment, indicating a return to homeostasis. Histological analyses revealed that clinically responsive patients had significantly reduced epidermal and dermal inflammation. Affected inflammatory infiltrate included neutrophils, T cells and plasma cells, with the predominantly affected cell types specific to the patient. CONCLUSIONS:Collectively, the broad activity of topical ruxolitinib on inflammatory signalling processes resulted in promising efficacy, even with heterogeneity in baseline inflammation, in this pilot cohort. Importantly, topical treatment not only resolved epidermal inflammation, but also cleared deeper inflammatory infiltrate. The observed efficacy provides rationale to further investigate topical JAKi and other novel topical treatments in HS.

Carbohydrates are key components of many microbial cell walls and play a versatile role in immune recognition. In this study, we analyzed the carbohydrate cell wall composition of Cutibacterium acnes strains associated with healthy skin (denoted as CH) and acne-prone skin (denoted as CA) to understand their influence on host immune responses in acne. We identified glucose, mannose, and galactose as the primary monosaccharides, with minor amounts of fucose, N-acetylgalactosamine, and N-acetylglucosamine. Linkage analysis revealed structural variations between CH and CA strains: CH strains showed a balanced and diverse polysaccharide structure, whereas CA strains displayed a more rigid structure with 1→4 and branched 1→6 linkages, potentially contributing to inflammatory properties. Immunostimulatory assays revealed that C acnes carbohydrates induced IL-6 and IL-17 but not IL-1β, highlighting the role of carbohydrate structures in influencing cytokine responses. Treatment with sodium meta-periodate impaired this immunostimulatory activity, indicating that carbohydrate integrity is crucial for immune activation. In addition, analysis of single-cell RNA-sequencing data from acne lesions revealed elevated glycolytic activity in acne lesions in comparison with that in nonlesional skin, suggesting a Warburg-like effect that promotes inflammation. Our findings highlight the role of C acnes polysaccharides in immune modulation and inflammation, suggesting their potential as therapeutic targets for acne treatment.

Introduction/Rationale: Familial pulmonary fibrosis (FPF) represents a subset of idiopathic pulmonary fibrosis cases, but the genetic basis for only a fraction of FPF patients has been determined. We report genetic analyses and phenotypes of a multigenerational cohort with early onset FPF. We further describe an unanticipated skin abnormality not previously reported and strictly linked to affected individuals. Methods: Clinical diagnosis and phenotyping included longitudinal chest computerized tomography, serial pulmonary function testing, thoracic lung biopsies, bronchoalveolar lavage and skin biopsies. Microarray analysis and genome sequencing were used to generate polymorphic profiles of the cohort. Skin punch biopsies were obtained from visually normal skin 4-6 cm below the midclavicular line and processed for histology, immunohistochemistry and isolation of fibroblasts for cell culture. Results: Affected family members displayed atypical parenchymal features as early as age 21, including ground-glass opacities, nodules and early cystic changes suggesting surfactant dysfunction. Progressive fibrosis and respiratory failure led to lung transplantation at age 32, 39 and 46 for three family members with a fourth referred for transplant evaluation at age 32. A fifth family member had mild interstitial changes detected at age 57 concurrent with a diagnosis of lung cancer. Additionally, several family members from previous generations died of FPF. Genetic analysis identified genomic regions on chromosomes 7, 10 and 17 that segregate only to affected family members as well as a rare variant in the SFTPA2 gene present in the affected members but also in several unaffected members. Variants in SFTPA2 have been previously linked to FPF. The variant causes a V187M substitution in the globular domain of the encoded Surfactant Protein A2 (SP-A2). Family members with early onset FPF showed an unusual separation of the skin epidermis, abnormal deposition of elastin as evidenced by pentachrome staining, poor growth of fibroblasts in vitro, and lack of SP-A staining in epithelial cells. Family members with the V187M substitution but without clinical fibrosis did not show the abnormal skin phenotypeConclusion: These results implicate a variant in SFTPA2 as contributing to FPF and suggest other genomic regions may collaborate with this variant to cause disease. We further observed strict linkage of the pulmonary disease in this family with a novel extrapulmonary skin phenotype consisting of epidermal detachment. Further investigation of the role that the specific genetic domains play in the pathogenesis of these abnormalities may lead to new strategies for early identification and intervention.

Isotretinoin, the gold-standard treatment for severe acne, effectively targets major pathogenic factors but carries teratogenic risks. Its precise mechanism of action remains incompletely understood. Computational approaches, such as connectivity mapping, can offer insights into a drug's mechanism and identify alternative compounds as potential novel therapeutics for acne. In this study, we investigated the transcriptomic response in nonlesional skin of 18 patients with severe acne prior to isotretinoin therapy (baseline) and after 1, 8, and 20 weeks of therapy and 6 months after therapy. Our analysis revealed that isotretinoin induced significant early and sustained suppression of metabolic pathways, including oxidative phosphorylation, lipid metabolism, and mTORC1 signaling. Immunofluorescence staining in acne patient skin for phosphorylated S6, a downstream marker of mTORC1, corroborated decreased mTORC1 signaling as early as 1 week of therapy. In addition, connectivity mapping identified mTOR inhibitors as top candidates that mimic isotretinoin's transcriptomic signature. These findings enhance our understanding of isotretinoin's mechanism and highlight mTORC1 as a potential target for developing safer, nonteratogenic acne treatments.

Experimental DermatologyVolume 33, Issue 1 e14968 LETTER TO THE EDITOR SLST D1 strains may contribute to skin health George W. Agak, George W. Agak orcid.org/0000-0002-3356-9864 Division of Dermatology, Department of Medicine, University of California, Los Angeles, CA, USASearch for more papers by this authorDiane M. Thiboutot, Diane M. Thiboutot orcid.org/0000-0002-7342-2357 Department of Dermatology, Penn State College of Medicine, Hershey, Pennsylvania, USASearch for more papers by this authorAndrea L. Zaenglein, Andrea L. Zaenglein orcid.org/0000-0002-2507-7130 Department of Dermatology, Penn State College of Medicine, Hershey, Pennsylvania, USASearch for more papers by this authorAmanda M. Nelson, Corresponding Author Amanda M. Nelson [email protected] orcid.org/0000-0001-6375-8706 Department of Dermatology, Penn State College of Medicine, Hershey, Pennsylvania, USA Correspondence Amanda Nelson, Department of Dermatology, Penn State College of Medicine, 500 University Drive, 7801 BMR Building, Hershey, PA 17036, USA. Email: [email protected]Search for more papers by this author George W. Agak, George W. Agak orcid.org/0000-0002-3356-9864 Division of Dermatology, Department of Medicine, University of California, Los Angeles, CA, USASearch for more papers by this authorDiane M. Thiboutot, Diane M. Thiboutot orcid.org/0000-0002-7342-2357 Department of Dermatology, Penn State College of Medicine, Hershey, Pennsylvania, USASearch for more papers by this authorAndrea L. Zaenglein, Andrea L. Zaenglein orcid.org/0000-0002-2507-7130 Department of Dermatology, Penn State College of Medicine, Hershey, Pennsylvania, USASearch for more papers by this authorAmanda M. Nelson, Corresponding Author Amanda M. Nelson [email protected] orcid.org/0000-0001-6375-8706 Department of Dermatology, Penn State College of Medicine, Hershey, Pennsylvania, USA Correspondence Amanda Nelson, Department of Dermatology, Penn State College of Medicine, 500 University Drive, 7801 BMR Building, Hershey, PA 17036, USA. Email: [email protected]Search for more papers by this author First published: 15 November 2023 https://doi.org/10.1111/exd.14968 Letter to the Editor: Response to Commentary by McDowell and Colleagues. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Open Research DATA AVAILABILITY STATEMENT Data Availability Statement: Sequencing data related to the original publication (Nolan et al., 2023) is available at Sequence Read Archive (SRA): PRJNA935688. REFERENCES 1McDowell A, Bruggemann H, Layton AM. Treatment of acne patients with isotretinoin increases β-diversity of a putative health-associated strain of Cutibacterium acnes within the follicular microbiome of responders. Exp Dermatol. 2023. doi:10.1111/exd.14967 10.1111/exd.14967 PubMedWeb of Science®Google Scholar 2Scholz CF, Jensen A, Lomholt HB, Bruggemann H, Kilian M. A novel high-resolution single locus sequence typing scheme for mixed populations of Propionibacterium acnes in vivo. PloS One. 2014; 9(8):e104199. doi:10.1371/journal.pone.0104199 10.1371/journal.pone.0104199 PubMedWeb of Science®Google Scholar 3Ahle CM, Stodkilde K, Poehlein A, et al. Interference and co-existence of staphylococci and Cutibacterium acnes within the healthy human skin microbiome. Commun Biol. 2022; 5(1): 923. doi:10.1038/s42003-022-03897-6 10.1038/s42003-022-03897-6 CASPubMedWeb of Science®Google Scholar 4Nolan ZT, Banerjee K, Cong Z, et al. Treatment response to isotretinoin correlates with specific shifts in Cutibacterium acnes strain composition within the follicular microbiome. Exp Dermatol. 2023; 32(7): 955-964. doi:10.1111/exd.14798 10.1111/exd.14798 CASPubMedWeb of Science®Google Scholar 5McCoy WH, Otchere E, Rosa BA, Martin J, Mann CM, Mitreva M. Skin ecology during sebaceous drought-how skin microbes respond to isotretinoin. J Invest Dermatol. 2019; 139(3): 732-735. doi:10.1016/j.jid.2018.09.023 10.1016/j.jid.2018.09.023 CASPubMedWeb of Science®Google Scholar Volume33, Issue1January 2024e14968 ReferencesRelatedInformation

TLR3 is expressed in human skin and keratinocytes, and given its varied role in skin inflammation, development, and regeneration, we sought to determine the cellular response in normal human keratinocytes to TLR3 activation. We investigated this mechanism by treating primary human keratinocytes with both UVB, an endogenous and physiologic TLR3 activator, and poly(I:C), a synthetic and selective TLR3 ligand. TLR3 activation with either UVB or poly(I:C) altered keratinocyte morphology, coinciding with the key features of epithelial-to-mesenchymal transition: increased epithelial-to-mesenchymal transition gene expression, enhanced migration, and increased invasion properties. These results confirm and extend previous studies demonstrating that in addition to its classical role in the innate immune response, TLR3 signaling also regulates stem cell-like properties and developmental programs.

Current acne therapies center on preventing new lesions in patients with acne. These therapies were historically found to be beneficial yet were chosen without knowledge of the specific changes in the skin that favor lesion development. A major challenge in developing new treatments is the incomplete understanding of nonlesional (NL), acne-prone skin's molecular characteristics. To address this, we compared RNA-sequencing data from NL skin of 49 patients with acne (denoted as NL acne [NLA]) with those from 19 healthy controls with no acne history. We found 77 differentially expressed genes in NLA (log fold change > 1; P < .05), including genes associated with innate immunity and epidermal barrier function. Notably, K RT 6C, K RT 16, S100A8, S100A9, and lactotransferrin were upregulated, and LCE4A, LCE6A, and CTSE were downregulated. Gene set enrichment analysis revealed that metabolic pathways were enriched in NLA skin, whereas keratinization was negatively enriched. To identify compounds that could shift the gene expression signature of NLA skin toward healthy control skin, we performed connectivity mapping with the Library of Integrated Network-Based Signatures. We identified 187 compounds, particularly mTOR inhibitors, that could potentially normalize the gene expression profile of acne-prone skin to that of healthy skin. Our findings indicate that NLA skin has distinct differences in epidermal differentiation, cellular metabolism, and innate immunity that may promote lesion formation and suggest that mTOR inhibitors could restore NLA skin toward a healthier state, potentially reversing the predisposition to lesion development.

Infection at barrier sites, e.g., skin, activates local immune defenses that limit pathogen spread, while preserving tissue integrity. Phenotypically distinct γδ T cell populations reside in skin, where they shape immunity to cutaneous infection prior to onset of an adaptive immune response by conventional αβ CD4+ (TCD4+) and CD8+ (TCD8+) T cells. To examine the mechanisms used by γδ T cells to control cutaneous virus replication and tissue pathology, we examined γδ T cells after infection with vaccinia virus (VACV). Resident γδ T cells expanded and combined with recruited γδ T cells to control pathology after VACV infection. However, γδ T cells did not play a role in control of local virus replication or blockade of systemic virus spread. We identified a unique wound healing signature that has features common to, but also features that antagonize, the sterile cutaneous wound healing response. Tissue repair generally occurs after clearance of a pathogen, but viral wound healing started prior to the peak of virus replication in the skin. γδ T cells contributed to wound healing through induction of multiple cytokines/growth factors required for efficient wound closure. Therefore, γδ T cells modulate the wound healing response following cutaneous virus infection, maintaining skin barrier function to prevent secondary bacterial infection.

Hidradenitis suppurativa (HS) is a complex inflammatory skin condition affecting 0.1-4% of the population that leads to permanent scarring in the axilla, inframammary region, groin, and buttocks. Its complex pathogenesis involves genetics, innate and adaptive immunity, microbiota, and environmental stimuli. Specific populations have a higher incidence of HS, including females and Black individuals and those with associated comorbidities. HS registries and biobanks have set standards for the documentation of clinical data in the context of clinical trials and outcomes research, but collection, documentation, and reporting of these important clinical and demographic variables are uncommon in HS laboratory research studies. Standardization in the laboratory setting is needed because it helps to elucidate the factors that contribute mechanistically to HS symptoms and pathophysiology. The purpose of this article is to begin to set the stage for standardized reporting in the laboratory setting. We discuss how clinical guidelines can inform laboratory research studies, and we highlight what additional information is necessary for the use of samples in the wet laboratory and interpretation of associated mechanistic data. Through standardized data collection and reporting, data harmonization between research studies will transform our understanding of HS and lead to novel discoveries that will positively impact patient care.

Innate lymphoid cells (ILCs) are a diverse population of lymphocytes classified into natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and ILCregs, broadly following the cytokine secretion and transcription factor profiles of classical T cell subsets. Nonetheless, the ILC lineage does not have rearranged antigen-specific receptors and possesses distinct characteristics. ILCs are found in barrier tissues such as the skin, lungs, and intestines, where they play a role between acquired immune cells and myeloid cells. Within the skin, ILCs are activated by the microbiota and, in turn, may influence the microbiome composition and modulate immune function through cytokine secretion or direct cellular interactions. In particular, ILC3s provide epithelial protection against extracellular bacteria. However, the mechanism by which these cells modulate skin health and homeostasis in response to microbiome changes is unclear. To better understand how ILC3s function against microbiota perturbations in the skin, we propose a role for these cells in response to Cutibacterium acnes, a predominant commensal bacterium linked to the inflammatory skin condition, acne vulgaris. In this article, we review current evidence describing the role of ILC3s in the skin and suggest functional roles by drawing parallels with ILC3s from other organs. We emphasize the limited understanding and knowledge gaps of ILC3s in the skin and discuss the potential impact of ILC3-microbiota crosstalk in select skin diseases. Exploring the dialogue between the microbiota and ILC3s may lead to novel strategies to ameliorate skin immunity.

BACKGROUND Hidradenitis suppurativa (HS) is a debilitating inflammatory skin disease characterized by painful nodules, drainage and scarring in skin folds. Injectable adalimumab is the only drug approved by the US Food and Drug Administration for the treatment of HS. Although systemic Janus kinase (JAK) inhibitors show promise, serious side-effects have been reported. There are no highly effective topical treatments for HS; furthermore, the contribution of epidermal keratinocytes to the intense inflammation has largely been unexplored. OBJECTIVES We investigated the role of keratinocytes and epidermal immune cells in HS inflammation at all Hurley stages of disease severity. We aimed to determine whether ruxolitinib can mitigate inflammation from keratinocytes and to develop a better understanding of how topical therapeutics might benefit patients with HS. METHODS We used skin samples from 87 patients with HS (Hurley stages I-III) and 39 healthy controls to compare keratinocyte- and immune cell-driven epidermal inflammation, in addition to the response of lesional HS keratinocytes to treatment with interferon (IFN)-γ and ruxolitinib. We used haematoxylin and eosin staining, immunohistochemistry, immunoblotting and quantitative reverse-transcription polymerase chain reaction assessments in whole skin, isolated epidermis, and cultured keratinocytes from healthy controls and both nonlesional and lesional HS skin to identify and define epidermal and keratinocyte-mediated inflammation in HS and how this may be targeted by therapeutics. RESULTS HS lesional keratinocytes autonomously secreted high levels of chemokines, such as CCL2, CCL3 and CXCL3, which recruited neutrophils, CD8 T cells, and natural killer cells to the epidermis. Keratinocytes were the dominant source of tumour necrosis factor-α and interleukin (IL)-6 in HS lesions with little to no contribution from underlying dermal immune cells. In the presence of IFN-γ, which is dependent on immune cell infiltrate in vivo, keratinocytes expressed increased levels of additional cytokines including IL-1β, IL-12, IL-23 and IL-36γ. The JAK inhibitor ruxolitinib mitigated the expression of inflammatory cytokines and chemokines in HS lesional keratinocytes, thus providing a rationale for future study as a topical treatment for HS. CONCLUSIONS This study demonstrates that keratinocytes actively recruit immune cells to HS epidermis and interactions between these cells drive a broad inflammatory profile in HS epidermis. Targeting epidermal inflammation in HS with novel topical formulations may be highly efficacious with reduced systemic side-effects.