A systematic review and critical evaluation of immunohistochemical associations in hidradenitis suppurativa

Hidradenitis Suppurativa from a Multi-Omic Scope

Hidradenitis suppurativa (HS) is recognized as a systemic immune-mediated disease (IMID), sharing genetic and environmental risk factors with other IMIDs such as inflammatory bowel disease and psoriasis. Over time, correlating clinical findings with genetic, proteomic, and metabolomic results has been challenging due to diverse sampling methods, analysis techniques, and the use of variable clinical phenotype descriptions across studies. This review aims to summarize the results from various omics fields to explore the etiopathology of HS. Genetic studies highlight defects in Notch and γ-secretase signaling and inflammasome function. Syndromic HS involves specific mutations in autoinflammatory syndromes such as pyogenic sterile arthritis, pyoderma gangrenosum, and acne (PAPA) and pyoderma gangrenosum, acne, and HS (PASH). Proteomic analyses reveal key inflammatory pathways indicating activation of both innate and adaptive immunity. Additionally, microbiome studies show an increased presence of anaerobes like Prevotella in HS lesions and a decreased presence of commensals such as Staphylococcus epidermidis. Gut microbiota dysbiosis, particularly involving Ruminococcus gnavus and Clostridium ramosum, is associated with HS. Moreover, metabolomic profiling indicates dysregulated tryptophan catabolism and lipid metabolism, with increased 5-lipoxygenase-derived metabolites and odd-chain fatty acids suggesting bacterial involvement. In summary, despite advances, robust associations between genetics, proteomics, microbiome, and metabolomics in HS are still lacking. Integrating these datasets could identify new clinical phenotypes, genetic predispositions, microbial signatures, and therapeutic targets, enhancing personalized treatment strategies and biomarker discovery for HS classification, prognosis, and treatment response.

Deregulated Long Non-Coding RNAs (lncRNA) as Promising Biomarkers in Hidradenitis Suppurativa

Background/Objectives: In recent times, epigenetics alterations in Hidradenitis suppurativa (HS) have been explored and exploited translationally to guide investigation of new therapeutic approaches. On the other hand, long noncoding RNAs (LncRNAs), main regulators of the epigenetic status of the human genome, have been scarcely investigated, notwithstanding their potential relevance in broad pathogenesis comprehension. Here, we aim to explore the methylation pattern of lncRNAs in HS. Methods: In this case-control study, 24 HS patients and age-, sex- and BMI-matched controls were analyzed to characterize the methylome of lncRNA genes in peripheral blood cells. Gene ontology analysis (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, protein-protein interaction (PPI) network, and MCODE analysis were performed. Results: A set of fifteen lncRNA genes exhibited significantly differential methylation patterns, with ten of them showing hypomethylation and five displaying hypermethylation at specific CpG sites. The hypomethylated lncRNA genes were DLEU2, MESTIT1, CASC2, TUG1, KCNQ1DN, PSORS1C3, PCA3, DSCR8, RFPL1S, and PVT1, while the hypermethylated ones were HAR1A, FAM66B, SNHG9, HCG9, and HCP5. These lncRNA genes have been linked to various important biological processes, including cell proliferation, apoptosis, inflammation, chronic inflammatory skin diseases, and wound healing. Their altered methylation status suggests potential roles in regulating these processes, and may contribute to HS pathogenesis and healing mechanisms. Conclusions: This study revealed an interesting dysregulation pattern of definite lncRNAs in the methylome which is linked to both the development of HS and its comorbidities. Epigenetically altered lncRNAs genes could represent useful biomarkers, and could help in guiding innovative treatment strategies.

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.

Baseline clinical, hormonal and molecular markers associated with clinical response to IL-23 antagonism in hidradenitis suppurativa: A prospective cohort study

Hidradenitis suppurativa is a complex inflammatory disease in which predicting therapeutic response remains challenging. IL-23 interacts with sex hormones but the relationships between the two in HS remains uninvestigated. To assess whether baseline clinical, hormonal or molecular markers are associated with clinical response to IL-23 antagonism with risankizumab in hidradenitis suppurativa. Twenty six individuals with Hurley stage 2/3 disease were administered risankizumab 150 mg Week 0, 4, 12. Baseline sex hormones and skin biopsies were taken. Clinical response at Week 16 assessed by the HiSCR, and differences between responders and non-responders assessed. Eighteen of 26 participants achieved HiSCR50 at week 16 (69.2%). Clinical response to IL-23 antagonism was associated with male gender, elevated total serum testosterone and decreased levels of FSH. Stratification by clinical responders/nonresponders identified differentially expressed genes including PLPP4 and MAPK10. Immunohistochemistry identified elevated numbers of CD11c, IL-17A and IL-17F positive cells compared to nonresponders. CD11c + cells significantly correlated with serum levels of total testosterone and inversely correlated with serum FSH. Clinical response to IL-23 antagonism in HS is associated with serum sex hormones, Th17 polarized inflammation in lesional tissue and CD11c + cells. These potential therapeutic biomarkers require further validation in larger cohorts but may suggest potential targeted HS therapy.

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.

Autoantibodies Present in Hidradenitis Suppurativa Correlate with Disease Severity and Promote the Release of Proinflammatory Cytokines in Macrophages

Hidradenitis suppurativa (HS), also known as acne inversa, is a debilitating inflammatory skin disorder that is characterized by nodules that lead to the development of connected tunnels and scars as it progresses from Hurley stages I to III. HS has been associated with several autoimmune diseases, including inflammatory bowel disease and spondyloarthritis. We previously reported dysregulation of humoral immune responses in HS, characterized by elevated serum total IgG, B-cell activation, and antibodies recognizing citrullinated proteins. In this study, we characterized IgG autoreactivity in HS sera and lesional skin compared with those in normal healthy controls using an array-based high-throughput autoantibody screening. The Cy3-labeled anti-human assay showed the presence of autoantibodies against nuclear antigens, cytokines, cytoplasmic proteins, extracellular matrix proteins, neutrophil proteins, and citrullinated antigens. Most of these autoantibodies were significantly elevated in stages II‒III in HS sera and stage III in HS skin lesions compared with those of healthy controls. Furthermore, immune complexes containing both native and citrullinated versions of antigens can activate M1 and M2 macrophages to release proinflammatory cytokines such as TNF-α, IL-8, IL-6, and IL-12. Taken together, the identification of specific IgG autoantibodies that recognize circulating and tissue antigens in HS suggests an autoimmune mechanism and uncovers putative therapeutic targets.

Hidradenitis Suppurativa and Comorbid Disorder Biomarkers, Druggable Genes, New Drugs and Drug Repurposing-A Molecular Meta-Analysis

Chronic inflammation and dysregulated epithelial differentiation, especially of hair follicle keratinocytes, have been suggested as the major pathogenetic pathways of hidradenitis suppurativa/acne inversa (HS). On the other hand, obesity and metabolic syndrome have additionally been considered as an important risk factor. With adalimumab, a drug has already been approved and numerous other compounds are in advanced-stage clinical studies. A systematic review was conducted to detect and corroborate HS pathogenetic mechanisms at the molecular level and identify HS molecular markers. The obtained data were used to confirm studied and off-label administered drugs and to identify additional compounds for drug repurposing. A robust, strongly associated group of HS biomarkers was detected. The triad of HS pathogenesis, namely upregulated inflammation, altered epithelial differentiation and dysregulated metabolism/hormone signaling was confirmed, the molecular association of HS with certain comorbid disorders, such as inflammatory bowel disease, arthritis, type I diabetes mellitus and lipids/atherosclerosis/adipogenesis was verified and common biomarkers were identified. The molecular suitability of compounds in clinical studies was confirmed and 31 potential HS repurposing drugs, among them 10 drugs already launched for other disorders, were detected. This systematic review provides evidence for the importance of molecular studies to advance the knowledge regarding pathogenesis, future treatment and biomarker-supported clinical course follow-up in HS.

Hidradenitis suppurativa: A folliculotropic disease of innate immune barrier dysfunction?

The innate immune system of human skin consists of a multi-layered barrier consisting of cells and soluble effector molecules charged with maintaining homeostasis and responding to insults and infections. It has become increasingly clear that these barrier layers become compromised in skin diseases, especially in disorders of an (auto)inflammatory nature. In the case of hidradenitis suppurativa, great strides have been made in recent years in characterizing the underlying breakdown in homeostatic innate immunity, including an increasing understanding of the central role of the hair follicle in this process. This breakdown appears to occur at multiple levels: the pilosebaceous unit, associated epithelium, the cutaneous microbiome, alteration of immune cell function and local molecular events such as complement activation. This review seeks to summarize, contextualize and analyse critically our current understanding of how these innate immune barriers become dysregulated in the early stage(s) of hidradenitis suppurativa, and to speculate on where potential hidradenitis suppurativa research could be most fruitful.

Insights from γ-Secretase: Functional Genetics of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic, relapsing, and remitting inflammatory disease of the skin with significant heritability and racial disposition. The pathogenesis of HS remains enigmatic, but occlusion of the terminal hair follicle and dysregulation of the local innate immune response may contribute to pathogenesis. Genetic predisposition might also contribute to disease susceptibility and phenotypic heterogeneity because mutations in γ-secretase have been found to underlie a minor but characteristic subset of patients with HS. In this review, we synthesized the current data on γ-secretase in HS, evaluated its importance in the context of disease pathobiology, and discussed avenues of future studies.

Histologic progression of acne inversa/hidradenitis suppurativa: Implications for future investigations and therapeutic intervention

Since first recognized in 1839, the pathogenesis of acne inversa (AI) has undergone repeated revisions. Although there is agreement that AI involves occlusion of hair follicles with subsequent inflammation and the formation of tracts, the histologic progression of this disease still requires refinement. The objective of this study was to examine the histologic progression of AI based on the examination of a large cohort of punch biopsies and excisional samples that were examined first by hematoxylin and eosin staining. The most informative of these samples were step‐sectioned and stained by immunohistochemistry for epithelial and inflammatory markers. Based on this examination, the following observations were made: 1) AI arises from the epithelium of the infundibulum of terminal and vellus hairs; 2) These form cysts and epithelial tendrils that extend into soft tissue; 3) Immunohistochemical staining demonstrates the epithelium of AI is disordered with infundibular and isthmic differentiation and de novo expression of stem cell markers; 4) The inflammatory response in AI is heterogeneous and largely due to cyst rupture. The conclusions of this investigation were that AI is an epithelial‐driven disease caused by infiltrative, cyst forming tendrils and most of the inflammation is due to cyst rupture and release of cornified debris and bacteria. Cyst rupture often occurs below the depths of punch biopsy samples indicating their use for analysis may give an incomplete picture of the disease. Finally, our data suggest that unless therapies inhibit tendril development, it is unlikely they will cause prolonged treatment‐induced remission in AI.

Hidradenitis suppurativa is an autoinflammatory keratinization disease: A review of the clinical, histologic, and molecular evidence

The pathogenic model of hidradenitis suppurativa is in the midst of a paradigm shift away from a disorder of primary follicular occlusion to an autoinflammatory keratinization disease. Observational, experimental, and therapeutic evidence supports the concept of hidradenitis suppurativa as a primarily inflammatory disorder, a disorder of autoimmunity, or both, in contrast to the current prevailing paradigm of primary follicular occlusion. The lack of reliable and high-fidelity disease models has limited the available experimental and mechanistic evidence to support or refute one pathogenic model over another. This scholarly review synthesizes the existing clinical, histologic, and molecular data to evaluate the extant evidence supporting the autoinflammatory paradigm and further informing the molecular mechanisms of hidradenitis suppurativa pathogenesis. Follicular hyperkeratosis/occlusion and perifollicular inflammation coexist in histologic specimens, with interleukin 1α demonstrated to stimulate comedogenesis in the infundibulum. pH elevation in occluded body sites alters the microbiome and amplifies existing T-helper cell type 17 immunoresponses. Known metabolic comorbidities and smoking are known to upregulate interleukin 1α in follicular keratinocytes. Identified genetic variants may alter epidermal growth factor receptor signaling, leading to upregulated keratinocyte inflammatory responses. The process of follicular rupture and dermal tunnel formation can be explained as secondary responses to inflammatory activation of fibroblasts and epithelial-mesenchymal transition, with antibody production associated with inflammatory amplification in advanced disease. This review aims to reevaluate and integrate the current clinical, histologic, and molecular data into a pathogenic model of hidradenitis suppurativa. This is essential to advance our understanding of the disease and identify novel therapeutic targets and approaches.

Alterations in innate immunity and epithelial cell differentiation are the molecular pillars of hidradenitis suppurativa

BACKGROUND

The large unmet need of hidradenitis suppurativa/acne inversa (HS) therapy requires the elucidation of disease-driving mechanisms and tissue targeting.

OBJECTIVE

Robust characterization of the underlying HS mechanisms and detection of the involved skin compartments.

METHODS

Hidradenitis suppurativa/acne inversa molecular taxonomy and key signalling pathways were studied by whole transcriptome profiling. Dysregulated genes were detected by comparing lesional and non-lesional skin obtained from female HS patients and matched healthy controls using the Agilent array platform. The differential gene expression was confirmed by quantitative real-time PCR and targeted protein characterization via immunohistochemistry in another set of female patients. HS-involved skin compartments were also recognized by immunohistochemistry.

RESULTS

Alterations to key regulatory pathways involving glucocorticoid receptor, atherosclerosis, HIF1α and IL17A signalling as well as inhibition of matrix metalloproteases were detected. From a functional standpoint, cellular assembly, maintenance and movement, haematological system development and function, immune cell trafficking and antimicrobial response were key processes probably being affected in HS. Sixteen genes were found to characterize HS from a molecular standpoint (DEFB4, MMP1, GJB2, PI3, KRT16, MMP9, SERPINB4, SERPINB3, SPRR3, S100A8, S100A9, S100A12, S100A7A (15), KRT6A, TCN1, TMPRSS11D). Among the proteins strongly expressed in HS, calgranulin-A, calgranulin-B and serpin-B4 were detected in the hair root sheath, koebnerisin and connexin-32 in stratum granulosum, transcobalamin-1 in stratum spinosum/hair root sheath, small prolin-rich protein-3 in apocrine sweat gland ducts/sebaceous glands-ducts and matrix metallopeptidase-9 in resident monocytes.

CONCLUSION

Our findings highlight a panel of immune-related drivers in HS, which influence innate immunity and cell differentiation in follicular and epidermal keratinocytes as well as skin glands.

Contribution of fibroblasts to tunnel formation and inflammation in hidradenitis suppurativa/ acne inversa

The precise pathogenic mechanisms in the development, persistence and worsening of hidradenitis suppurativa (HS) remain ill-defined. This chronic inflammatory dermatosis displays a strong Th1 and Th17 inflammatory signature with elevated levels of TNF-α, IL-1β, IL-17 and IFNγ in lesional and perilesional tissue. HS significantly differs to other chronic inflammatory dermatoses due to the development of hypertrophic scarring and dermal tunnels. The development of scarring and tunnels suggests that fibroblastic stromal cells (including myofibroblasts, fibroblasts, pericytes etc) may be involved in the development and progression of disease. Heterogeneous populations of fibroblasts have been identified in other inflammatory disorders and malignancy which contribute to inflammation and present novel therapeutic targets for fibrotic disorders. Findings in HS are consistent with these fibroblast subpopulations and may contribute to tunnel formation, aggressive squamous cell carcinoma and the phenotypic presentation of familial HS variants. We describe the existing knowledge regarding these mechanistic pathways and methods to confirm their involvement in the pathogenesis of HS.

A systematic review and critical evaluation of immunohistochemical associations in hidradenitis suppurativa

Background: Hidradenitis suppurativa (HS) is a chronic inflammatory disease with significant morbidity and impact on quality of life. Our understanding of the pathophysiology is incomplete, impairing efforts to develop novel therapeutic targets. Immunohistochemistry studies have produced conflicting results and no systematic evaluation of study methods and results has been undertaken to date. Methods: This systematic review aimed to collate and describe all reports of immunohistochemical staining in HS. This systematic review was registered with PROSPERO and conducted in line with the PRISMA reporting guidelines. Potential bias was assessed using the NIH Criteria and antibodies used across various studies were tabulated and compared. Results: A total of 22 articles were identified describing results from 494 HS patients and 168 controls. 87 unique immunohistochemical targets were identified. The overall quality of studies was sub-optimal with staining intensity confounded by active treatment. Conflicting data was identified and able to be reconciled through critical evaluation of the study methodology. Conclusions: Keratinocyte hyperplasia with loss of cytokeratin markers co-localizes with inflammation comprising of dendritic Cells, T-lymphocytes and macrophages, which are known to play central roles in inflammation in HS. Primary follicular occlusion as a pathogenic paradigm and the principal driver of HS is not consistent with the findings of this review. Inflammation as a primary driver of disease with secondary hyperkeratosis and follicular occlusion is more consistent with the current published data.