Primary alterations during the development of hidradenitis suppurativa

Hidradenitis Suppurativa Tunnels: Unveiling a Unique Disease Entity

Hidradenitis suppurativa tunnel structures lined with epithelium within the dermis are unique features of advanced disease stages that significantly impair patients' QOL. The presence of hidradenitis suppurativa tunnels is associated with a decreased likelihood of achieving a clinical response, even when receiving biological therapy. The cellular and molecular mechanisms underlying tunnel formation and pathology are only partially understood, which hampers the development of more effective targeted therapies. Tunnels create a unique microenvironment that drives a vicious cycle of hidradenitis suppurativa inflammation, with tunnel keratinocytes exhibiting an activated phenotype characterized by distinct gene expression signatures. In this review, we summarize the current literature and discuss aspects of the pathophysiology of tunnels, including the role of hair follicle epidermal stem cells in tunnel formation, potential role of fibroblast-mediated epithelial-mesenchymal transition, role of dermal papilla fibroblasts, and aberrant proinflammatory repair response contributing to the observed fibrosis and scarring. Finally, tunnel structures are characterized by unique microbial dysbiosis and an overabundance of Gram-negative anaerobes that are not targeted by current therapeutics. In addition to outlining the possible mechanisms of tunnel formation, we provide perspectives on the translation of current knowledge into more effective treatment approaches for patients with hidradenitis suppurativa tunnels.

Pilot study of topical ruxolitinib demonstrates efficacy and blunting of heterogeneous inflammatory processes in mild hidradenitis suppurativa

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.

Senescence as a molecular target in skin aging and disease

Skin aging represents a multifactorial process influenced by both intrinsic and extrinsic factors, collectively known as the skin exposome. Cellular senescence, characterized by stable cell cycle arrest and secretion of pro-inflammatory molecules, has been implicated as a key driver of physiological and pathological skin aging. Increasing evidence points towards the role of senescence in a variety of dermatological diseases, where the accumulation of senescent cells in the epidermis and dermis exacerbates disease progression. Emerging therapeutic strategies such as senolytics and senomorphics offer promising avenues to target senescent cells and mitigate their deleterious effects, providing potential treatments for both skin aging and senescence-associated skin diseases. This review explores the molecular mechanisms of cellular senescence and its role in promoting age-related skin changes and pathologies, while compiling the observed effects of senotherapeutics in the skin and discussing the translational relevance.

The Inflammatory Landscape of a Whole-Tissue Explant Model of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a relatively common and highly morbid inflammatory skin disease. Due to the relatively limited understanding of HS's pathogenesis, there are currently insufficient treatment options available, and many patients' medical needs are not being met. This is partly due to the historical scarcity of ex vivo assays and animal models that accurately recapitulate the disease. Thus, we have developed a standardised whole-tissue explant model of HS to examine its pathogenic mechanisms and the efficacy of potential treatments within intact human tissue. We measured cytokine protein and RNA within whole tissue maintained in an agar-media solution, finding that IL-6 and IL-8 concentrations trended upwards in both HS explants and healthy controls, while IL-17A, IL-1β, and TNF-α exhibited increases in HS tissue alone. We also show that the explants were responsive to treatment with both dexamethasone and IL-2. Not only do our results show that this model effectively delivers treatments throughout the explants, but they also elucidate which cytokines are related to the explant process regardless of tissue state and which are related to HS tissue specifically, laying the groundwork for future implementations of this model.

Factors associated with therapeutic response to adalimumab in hidradenitis suppurativa: evidence from the Belgian patients of the European Registry for Hidradenitis Suppurativa (ERHS-Be)

Hidradenitis suppurativa is an inflammatory skin disease for which adalimumab is an effective treatment in just over half of cases. Few factors associated with therapeutic response, and therefore potentially predictive of response, are known to date. This real-life study retrospectively explores the existence of such factors in a Belgian cohort of 82 patients, using several response scores: the Hidradenitis Suppurativa Clinical Response (HiSCR), the International Hidradenitis Suppurativa Severity Scoring System-55 (iHS4-55), and the dynamic metascore (a combination of the Hurley score, the 2007 version of the Sartorius score, the iHS4 and the HiSCR). Among the factors associated with a good therapeutic response, we find, for example, the "Frictional furunculoid" and "Conglobata" phenotypes, in contrast to the "Scarring folliculitis" phenotype, which is associated with a poorer response to treatment. Other factors associated with a good response to treatment were observed, such as the patient's description of longer flares, or, among others, the presence of inflammatory bowel disease. Subject to our sample size, the window of opportunity for adalimumab, whereby the treatment would be more effective if administered earlier, was not found in this study.

Inflammasomes: emerging therapeutic targets in hidradenitis suppurativa?

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by recurrent inflammatory lesions, which affect skin and hair follicles in intertriginous areas. HS has a multifactorial aetiology resulting in barrier dysfunction associated with aberrant immune activation. There is increased evidence for the role of inflammasomes in the pathophysiology of inflammatory skin diseases, including HS. Inflammasomes are multiprotein complexes activated following exposure to danger signals, including microbial ligands and components of damaged host cells. Inflammasome activation induces many signalling cascades and subsequent cleavage of proinflammatory cytokines - most notably interleukin (IL)-1β - which have a role in HS pathogenesis. Limited immunotherapies are approved for treating moderate-to-severe HS, with variable response rates influenced by disease heterogeneity. Inflammasomes represent attractive targets to suppress multiple inflammatory pathways in HS, including IL-1β and IL-17. This review aims to summarize the role of inflammasomes in HS and to evaluate evidence for inflammasomes as therapeutic targets for HS treatment.

S2k‐Leitlinie zur Therapie der Hidradenitis suppurativa/Acne inversa – Kurzfassung

Die S2k‐Leitlinie der Hidradenitis suppurativa/Acne inversa (HS/AI) soll eine akzeptierte Entscheidungshilfe für die Auswahl/Durchführung einer geeigneten/suffizienten Therapie liefern. Hidradenitis suppurativa/Acne inversa ist eine chronisch‐rezidivierende, entzündliche, potenziell mutilierende Hauterkrankung des terminalen Haartalgdrüsenapparats, mit schmerzhaften, entzündlichen Läsionen in den apokrinen drüsenreichen Körperregionen. Ihre Punktprävalenz in Deutschland ist 0,3%, sie wird mit einer Verspätung von 10,0 ± 9,6 Jahren diagnostiziert. Abnormale Differenzierung der Keratinozyten des Haartalgdrüsenapparats und eine begleitende Entzündung bilden die zentrale pathogenetische Grundlage. Primäre HS/AI‐Läsionen sind entzündliche Knoten, Abszesse und drainierende Tunnel. Rezidive in den letzten 6 Monaten mit mindestens zwei Läsionen an den Prädilektionsstellen verweisen auf eine HS/AI mit einer 97‐prozentigen Genauigkeit. HS/AI‐Patienten leiden an einer deutlichen Einschränkung der Lebensqualität. Zur korrekten Therapieentscheidung sollen Klassifikation und Aktivitätsbewertung mit einem validierten Instrument erfolgen, wie dem International Hidradenitis Suppurativa Severity Scoring System (IHS4). Hidradenitis suppurativa/Acne inversa wird nach der Ausprägung der nachweisbaren Entzündung in zwei Formen eingeteilt: aktive, entzündliche (milde, mittelschwere und schwere nach IHS4) und vorwiegend inaktive, nicht entzündliche (Hurley‐Grad‐I, ‐II und ‐III) HS/AI. Orale Tetrazykline oder eine 5‐tägige intravenöse Therapie mit Clindamycin sind mit der Effektivität von Clindamycin/Rifampicin vergleichbar. Subkutan applizierbares Adalimumab, Secukinumab und Bimekizumab sind für die Therapie der HS/AI zugelassen. Für die vorwiegend nicht entzündliche Erkrankungsform stehen verschiedene operative Verfahren zur Verfügung. Medikamentöse/chirurgische Kombinationen gelten als ganzheitliches Therapieverfahren.

S2k guideline for the treatment of hidradenitis suppurativa / acne inversa - Short version

The S2k guideline on hidradenitis suppurativa/acne inversa (HS/AI) aims to provide an accepted decision aid for the selection/implementation of appropriate/sufficient therapy. HS/AI is a chronic recurrent, inflammatory, potentially mutilating skin disease of the terminal hair follicle-glandular apparatus, with painful, inflammatory lesions in the apocrine gland-rich regions of the body. Its point prevalence in Germany is 0.3%, it is diagnosed with a delay of 10.0 ± 9.6 years. Abnormal differentiation of the keratinocytes of the hair follicle-gland apparatus and accompanying inflammation form the central pathogenetic basis. Primary HS/AI lesions are inflammatory nodules, abscesses and draining tunnels. Recurrences in the last 6 months with at least 2 lesions at the predilection sites point to HS/AI with a 97% accuracy. HS/AI patients suffer from a significant reduction in quality of life. For correct treatment decisions, classification and activity assessment should be done with a validated tool, such as the International Hidradenitis Suppurativa Severity Scoring System (IHS4). HS/AI is classified into two forms according to the degree of detectable inflammation: active, inflammatory (mild, moderate, and severe according to IHS4) and predominantly inactive, non-inflammatory (Hurley grade I, II and III) HS/AI. Oral tetracyclines or 5-day intravenous therapy with clindamycin are equal to the effectiveness of clindamycin/rifampicin. Subcutaneously administered adalimumab, secukinumab and bimekizumab are approved for the therapy of HS/AI. Various surgical procedures are available for the predominantly non-inflammatory disease form. Drug/surgical combinations are considered a holistic therapy method.

The use of biologics and JAK inhibitors in the management of moderate to severe Hidradenitis Suppurativa treatment: a scoping review

This scoping review aims to characterize the use of biologics and Janus Kinase inhibitors (JAKi) in the treatment of Hidradenitis Suppurativa (HS), which is a chronic inflammatory condition. A comprehensive literature search was conducted in PubMed/NCBI, Embase, Web of Science databases, and the Clinicaltrials.gov register. The search included interventional trials assessing the use of biologics or JAKi in HS, with no geographic or time restrictions. Secukinumab and adalimumab were identified as the only two drugs approved by the FDA for treating moderate to severe HS in adults. Several other drug classes showed promising results based on clinical studies reviewed. IL-12/23 inhibitor ustekinumab demonstrated improvements in disease severity scores and HiSCR rates in small trials. IL-17 inhibitors such as brodalumab, bimekizumab, and CJM112 showed preliminary positive responses in early-phase clinical studies and case reports. While evidence was mixed, some TNF-α inhibitors such as infliximab provided benefits according to a randomized controlled trial, though etanercept trials yielded non-significant or inconsistent findings. Larger, well-designed studies are required to further establish their efficacy and safety, but biologics and JAKis show potential as alternative treatment options for moderate to severe HS. The findings of this review contribute to the growing interest among patients and to enhancing the understanding of physician's regarding potential alternative therapeutic options for HS and provide a basis for further research in this field.

Gram-negative anaerobes elicit a robust keratinocytes immune response with potential insights into HS pathogenesis

Hidradenitis Suppurativa (HS) is a chronic autoinflammatory skin disease with activated keratinocytes, tunnel formation and a complex immune infiltrate in tissue. The HS microbiome is polymicrobial with an abundance of commensal gram-positive facultative (GPs) Staphylococcus species and gram-negative anaerobic (GNA) bacteria like Prevotella, Fusobacterium and Porphyromonas with increasing predominance of GNAs with disease severity. We sought to define the keratinocyte response to bacteria commonly isolated from HS lesions to probe pathogenic relationships between HS and the microbiome. Type strains of Prevotella nigrescens, Prevotella melaninogenica, Prevotella intermedia, Prevotella asaccharolytica, Fusobacterium nucleatum, as well as Staphylococcus aureus and the normal skin commensal Staphylococcus epidermidis were heat-killed and co-incubated with normal human keratinocytes. RNA was collected and analysed using RNAseq and RT-qPCR. The supernatant was collected from cell culture for protein quantification. Transcriptomic profiles between HS clinical samples and stimulated keratinocytes were compared. Co-staining of patient HS frozen sections was used to localize bacteria in lesions. A mouse intradermal injection model was used to investigate early immune recruitment. TLR4 and JAK inhibitors were used to investigate mechanistic avenues of bacterial response inhibition. GNAs, especially F. nucleatum, stimulated vastly higher CXCL8, IL17C, CCL20, IL6, TNF and IL36γ transcription in normal skin keratinocytes than the GPs S. epidermidis and S. aureus. Using RNAseq, we found that F. nucleatum (and Prevotella) strongly induced the IL-17 pathway in keratinocytes and overlapped with transcriptome profiles of HS patient clinical samples. Bacteria were juxtaposed to activated keratinocytes in vivo, and F. nucleatum strongly recruited murine neutrophil and macrophage migration. Both the TLR4 and pan-JAK inhibitors reduced cytokine production. Detailed transcriptomic profiling of healthy skin keratinocytes exposed to GNAs prevalent in HS revealed a potent, extensive inflammatory response vastly stronger than GPs. GNAs stimulated HS-relevant genes, including many genes in the IL-17 response pathway, and were significantly associated with HS tissue transcriptomes. The close association of activated keratinocytes with bacteria in HS lesions and innate infiltration in murine skin cemented GNA pathogenic potential. These novel mechanistic insights could drive future targeted therapies.

Safety and Effectiveness of Percutaneous Ultrasound-Guided Galvanic Current in Tunnels of Patients with Hidradenitis Suppurativa: A Pilot Study

INTRODUCTION

The recurrent nature of hidradenitis suppurativa (HS), even under maintained systemic treatment, makes it necessary to have effective local treatments; however, the response to these therapies is variable (44-81%). The application of galvanic current (GC) has demonstrated its utility in humans in treating lesions structurally similar to those of HS. With this background, the main objective of this study was to evaluate the efficacy and safety of ultrasound-guided percutaneous GC in inflamed and/or draining tunnels of HS.

METHODS

This was an open study (one-way repeated measures design over time). Patients were evaluated at 4 and 12 weeks after receiving GC. A combined clinical response at week 12 (absence of suppuration/inflammation on examination and clinical interview) was considered the principal variable of efficacy. Adverse effects potentially associated with GC were reported by telephone and at each visit.

RESULTS

Twenty-six patients were included, with a male/female ratio of 5:8. The mean age was 35.84 (13.14) years. At 12 weeks after the administration of GC, a complete response was achieved in 77% (20/26) of the treated lesions. No serious adverse effects were observed, and the mean procedural pain assessed by the numeric rating scale was 0.03 (0.2).

CONCLUSION

GC has proven to be effective and well tolerated in inflamed and draining tunnels of patients with HS.

A Novel Epidermis Model Using Primary Hidradenitis Suppurativa Keratinocytes

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease. Patients can present with inflammatory nodules, abscesses up to fistulas, or sinus tracts in intertriginous body parts. Occlusion of the sebaceous gland unit leads to its rupture, with a subsequent exuberant immune response. Given there is still no causative therapy, to better understand HS and develop novel therapeutic concepts, research activities in the HS field are constantly growing. Primary skin cells, blood cells, and ex vivo explant cultures from HS patients have been previously used as HS cell culture models. In vitro reconstituted epidermal models are established to study inflammatory dermatoses, such as psoriasis or atopic dermatitis. For HS, the exploration of epidermis models would be an excellent addition, e.g., biomarkers or barrier function in testing new topic treatment options. We therefore established a stratified in vitro HS epidermis model based on primary cells from HS lesions. After isolating keratinocytes from lesional skin, we cultured them submerged in a transwell system. To induce differentiation, we then lifted them to the air-liquid interface. Immunohistochemical staining demonstrated that our HS-epidermis model meets the expected differentiation pattern. In addition, we detected the secretion of the inflammatory cytokines interleukin-1β and TNF-α.

Detection of native, activated Notch receptors in normal human apocrine-bearing skin and in hidradenitis suppurativa

Notch signalling has generated considerable interest as a pathogenetic factor and a drug target in a range of human diseases. The gamma-secretase complex is crucial in the activation of Notch receptors by cleaving the intracellular domain allowing nuclear translocation. In recent years several mutations in gamma-secretase components have been discovered in patients with familial hidradenitis suppurativa (HS). This has led to hypotheses that impaired Notch signalling could be an important driver for HS in general, not only in the monogenic variants. However, no study has examined in situ Notch activation per se in HS, and some reports with conflicting results have instead been based on expression of Notch receptors or indirect measures of Notch target gene expression. In this study we established immunostaining protocols to identify native, activated Notch receptors in human skin tissue. The ability to detect changes in Notch activation was confirmed with an ex vivo skin organ model in which signal was reduced or obliterated in tissue exposed to a gamma-secretase inhibitor. Using these methods on skin biopsies from healthy volunteers and a general HS cohort we demonstrated for the first time the distribution of active Notch signalling in human apocrine-bearing skin. Quantification of activated NOTCH1 & NOTCH2 revealed similar levels in non-lesional and peri-lesional HS to that of healthy controls, thus ruling out a general defect in Notch activation in HS patients. We did find a variable but significant reduction of activated Notch in epidermis of lesional HS with a distribution that appeared related to the extent of surrounding tissue inflammation.

Targeting the NLRP3 inflammasome reduces inflammation in hidradenitis suppurativa skin

BACKGROUND

Treatment for the debilitating disease hidradenitis suppurativa (HS) is inadequate in many patients. Despite an incidence of approximately 1%, HS is often under-recognized and underdiagnosed, and is associated with a high morbidity and poor quality of life.

OBJECTIVES

To gain a better understanding of the pathogenesis of HS, in order to design new therapeutic strategies.

METHODS

We employed single-cell RNA sequencing to analyse gene expression in immune cells isolated from involved HS skin vs. healthy skin. Flow cytometry was used to quantify the absolute numbers of the main immune populations. The secretion of inflammatory mediators from skin explant cultures was measured using multiplex and enzyme-linked immunosorbent assays.

RESULTS

Single-cell RNA sequencing analysis identified a significant enrichment in the frequency of plasma cells, T helper (Th) 17 cells and dendritic cell subsets in HS skin, and the immune transcriptome was distinct and more heterogeneous than healthy skin. Flow cytometry revealed significantly increased numbers of T cells, B cells, neutrophils, dermal macrophages and dendritic cells in HS skin. Genes and pathways associated with Th17 cells, interleukin (IL)-17, IL-1β and the NLRP3 inflammasome were enhanced in HS skin, particularly in samples with a high inflammatory load. Inflammasome constituent genes principally mapped to Langerhans cells and a subpopulation of dendritic cells. The secretome of HS skin explants contained significantly increased concentrations of inflammatory mediators, including IL-1β and IL-17A, and culture with an NLRP3 inflammasome inhibitor significantly reduced the secretion of these, as well as other, key mediators of inflammation.

CONCLUSIONS

These data provide a rationale for targeting the NLRP3 inflammasome in HS using small-molecule inhibitors that are currently being tested for other indications.

Expert consensus on priority research gaps in dietary and lifestyle factors in hidradenitis suppurativa: a Delphi consensus study

Hidradenitis suppurativa (HS) is a debilitating systemic inflammatory disease with limited treatment options. Although management through dietary and lifestyle changes is a primary interest of the HS patient community, there is lack of consensus regarding recommendations due to the paucity of evidence. To establish the priority research gaps on this topic, we performed and moderated a Delphi consensus study by integrating expert opinions and the relevant literature. Based on a literature review, research questions on dietary and lifestyle interventions in HS were constructed. HS dietary and lifestyle research questions were sent to an expert panel, consisting of 22 international members, including dermatologists, dietitians, pharmacists, and endocrinologists. Voting on the research questions was conducted using a modified Delphi technique. The primary outcome measure was whether participants could reach consensus on the priority of each research question in the HS dietary and lifestyle factors. After three rounds of surveys investigating the relationships between HS and various diet and lifestyle factors, "BMI", "Obesity", and "Smoking", reached consensus as high priority research questions. Low research priorities per consensus included "effects of iron supplements", "effects of magnesium supplements", "alcohol consumption" and "limiting Brewer's yeast intake. Smoking and obesity were identified as important research questions, concurrent to the literature indicating their association with more significant impact on disease activity. By shedding light on high priority research questions, our study provides a roadmap for further research on dietary and lifestyle modifications in HS and will help determine evidence-based lifestyle and dietary recommendations for patients with HS.

The genetic aspects of hidradenitis suppurativa

Genetic aspects have a substantial role in hidradenitis suppurativa (HS) pathogenesis. A positive family history of HS occurs in about one-third of HS cases and is significantly higher in patients with early onset of the disease. Recent twin studies have shown a high heritability in HS, fortifying the importance of genetic factors in disease pathogenesis. Based on existing knowledge on the genomics of HS, the disease can be categorized as familial HS, sporadic, syndromic HS, and "HS plus" associated with other syndromes. In familial HS, autosomal dominant transmission is proposed, and monogenic inheritance is rare. This monogenic trait is related to mutations of γ-secretase component genes and Notch signaling or defects in inflammasome function. With newly discovered gene mutations, such as those related to innate and adaptive immunity, skin microbiome, inflammasome, epidermal homeostasis, and keratinization pathway, we can define HS as a polygenic, multifactorial, autoinflammatory disease. To fully elucidate the genetic aspects of HS, we need extensive, long-term global collaborations.

The PI3K-Akt-mTOR and Associated Signaling Pathways as Molecular Drivers of Immune-Mediated Inflammatory Skin Diseases: Update on Therapeutic Strategy Using Natural and Synthetic Compounds

The dysregulated phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway has been implicated in various immune-mediated inflammatory and hyperproliferative dermatoses such as acne, atopic dermatitis, alopecia, psoriasis, wounds, and vitiligo, and is associated with poor treatment outcomes. Improved comprehension of the consequences of the dysregulated PI3K/Akt/mTOR pathway in patients with inflammatory dermatoses has resulted in the development of novel therapeutic approaches. Nonetheless, more studies are necessary to validate the regulatory role of this pathway and to create more effective preventive and treatment methods for a wide range of inflammatory skin diseases. Several studies have revealed that certain natural products and synthetic compounds can obstruct the expression/activity of PI3K/Akt/mTOR, underscoring their potential in managing common and persistent skin inflammatory disorders. This review summarizes recent advances in understanding the role of the activated PI3K/Akt/mTOR pathway and associated components in immune-mediated inflammatory dermatoses and discusses the potential of bioactive natural products, synthetic scaffolds, and biologic agents in their prevention and treatment. However, further research is necessary to validate the regulatory role of this pathway and develop more effective therapies for inflammatory skin disorders.

New Insight into the Molecular Pathomechanism and Immunomodulatory Treatments of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is an immune-mediated inflammatory disorder characterized by deep-seated nodules, abscesses, sinus tracts and scars localized in the intertriginous areas. It is accompanied by pain, malodourous secretion and a dramatically decreased quality of life. Although the pathogenesis has not been entirely elucidated, the primary event is follicular hyperkeratosis of the pilosebaceous apocrine unit. Since the registration of the tumor necrosis factor-alpha inhibitor Adalimumab in 2015, several cytokines have been implicated in the pathomechanism of HS and the research of novel therapeutic targets has been intensified. We provide an update on the inflammatory cytokines with a central role in HS pathogenesis and the most promising target molecules of future HS management.

Keratinocytes and immune cells in the epidermis are key drivers of inflammation in hidradenitis suppurativa providing a rationale for novel topical therapies

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.

B-cell-derived transforming growth factor-β may drive the activation of inflammatory macrophages and contribute to scarring in hidradenitis suppurativa

Lesional HS skin was analysed using RNA-sequencing to assess the predicted functional interplay between B cells and macrophages. Our findings support the idea that TGF-beta plays a key role in HS pathogenesis. It is likely that the development of tunnels and scarring in HS is closely related to a chronic activation of TGF-beta signalling.

Dysregulated CD38 expression in blood and skin immune cells of patients with hidradenitis suppurativa

Background

Hidradenitis suppurativa (HS) is a multifactorial, inflammatory skin disease. Increased systemic inflammatory comorbidities and serum cytokines highlight systemic inflammation as a feature of HS. However, the specific immune cell subsets contributing to systemic and cutaneous inflammation have not been resolved.

Objective

Identify features of peripheral and cutaneous immune dysregulation.

Methods

Here, we generated whole-blood immunomes by mass cytometry. We performed a meta-analysis of RNA-seq data, immunohistochemistry, and imaging mass cytometry to characterize the immunological landscape of skin lesions and perilesions from patients with HS.

Results

Blood from patients with HS exhibited lower frequencies of natural killer cells, dendritic cells, and classical (CD14+CD16-) and nonclassical (CD14-CD16+) monocytes, as well as higher frequencies of Th17 cells and intermediate (CD14+CD16+) monocytes than blood from healthy controls. Classical and intermediate monocytes from patients with HS had increased expression of skin-homing chemokine receptors. Furthermore, we identified a CD38+ intermediate monocyte subpopulation that was more abundant in the immunome of blood from patients with HS. Meta-analysis of RNA-seq data found higher CD38 expression in lesional HS skin than in perilesional skin, and markers of classical monocyte infiltration. Imaging mass cytometry showed that CD38+ classical monocytes and CD38+ monocyte-derived macrophages were more abundant in lesional HS skin.

Conclusion

Overall, we report targeting CD38 may be worth pursuing in clinical trials.

Key Messages

3.Monocyte subsets express markers of activation in circulation and HS lesionsTargeting CD38 may be a viable strategy for treating systemic and cutaneous inflammation in patients with HS.

Capsule Summary

4.Dysregulated immune cells in patients with HS express CD38 and may be targeting by anti-CD38 immunotherapy.

New Data on the Features of Skin Barrier in Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a Th1/17-driven inflammatory skin disease of the apocrine gland-rich (AGR) skin regions, where keratinocytes seem to be the crucial drivers of the initial pathogenic steps. However, the possible role of permeability barrier alteration in activating keratinocytes during HS development has not been clarified. We compared the major permeability barrier elements of non-lesional HS (HS-NL; n = 10) and lesional HS (HS-L; n = 10) skin with healthy AGR regions (n = 10) via RT-qPCR and immunohistochemistry. Stratum corneum components related to cornified envelope formation, corneocyte desquamation and (corneo)desmosome organization were analyzed along with tight junction molecules and barrier alarmins. The permeability barrier function was also investigated with transepidermal water loss (TEWL) measurements (n = 16). Junction structures were also visualized using confocal microscopy. At the gene level, none of the investigated molecules were significantly altered in HS-NL skin, while 11 molecules changed significantly in HS-L skin versus control. At the protein level, the investigated molecules were similarly expressed in HS-NL and AGR skin. In HS-L skin, only slight changes were detected; however, differences did not show a unidirectional alteration, as KRT1 and KLK5 were detected in decreased levels, and KLK7, KRT6 and DSG1 in increased levels. No significant differences in TEWL or the expression of junction structures were assessed. Our findings suggest that the permeability barrier is not significantly damaged in HS skin and permeability barrier alterations are not the driver factors of keratinocyte activation in this disease.