Hakim Ben Abdallah

Chronic inflammatory skin diseases such as psoriasis and hidradenitis suppurativa are driven by cytokines, including IL-17A and TNF. Although biologics targeting these cytokines have transformed therapy, the transcriptional contributions of individual skin-resident cell types remain unclear, and dermal fibroblasts have been largely overlooked compared with keratinocytes. To address this, we compared the transcriptional responses of primary human dermal fibroblasts and keratinocytes following in vitro stimulation with IL-17A, TNF, or both, using bulk RNA sequencing and Western blotting. Dermal fibroblasts mounted a stronger and broader proinflammatory response than keratinocytes. This was particularly evident in response to TNF and combined TNF/IL-17A stimulation, with enrichment for immune signalling and chemotaxis pathways and robust induction of chemokine genes, including CCL20, CXCL8, and IL6. Keratinocytes primarily upregulated genes associated with epithelial differentiation, barrier function, and protein regulation, including IL36G, S100A7A, and DEFB4A. The heightened fibroblast responsiveness correlated with increased TNF sensitivity and substantially higher TNFR2 (TNFRSF1B) expression and signalling compared with keratinocytes, suggesting a fibroblast-specific mechanism amplifying inflammatory responses. These findings challenge the keratinocyte-centric view of skin inflammation and identify dermal fibroblasts as active contributors and potential therapeutic targets in TNF- and Th17-driven skin diseases.

Chronic inflammatory skin diseases such as psoriasis and hidradenitis suppurativa are driven by cytokines, including IL‐17A and TNF. Although biologics targeting these cytokines have transformed therapy, the transcriptional contributions of individual skin‐resident cell types remain unclear, and dermal fibroblasts have been largely overlooked compared with keratinocytes. To address this, we compared the transcriptional responses of primary human dermal fibroblasts and keratinocytes following in vitro stimulation with IL‐17A, TNF, or both, using bulk RNA sequencing and Western blotting. Dermal fibroblasts mounted a stronger and broader proinflammatory response than keratinocytes. This was particularly evident in response to TNF and combined TNF/IL‐17A stimulation, with enrichment for immune signalling and chemotaxis pathways and robust induction of chemokine genes, including CCL20 , CXCL8 , and IL6 . Keratinocytes primarily upregulated genes associated with epithelial differentiation, barrier function, and protein regulation, including IL36G , S100A7A , and DEFB4A . The heightened fibroblast responsiveness correlated with increased TNF sensitivity and substantially higher TNFR2 ( TNFRSF1B ) expression and signalling compared with keratinocytes, suggesting a fibroblast‐specific mechanism amplifying inflammatory responses. These findings challenge the keratinocyte‐centric view of skin inflammation and identify dermal fibroblasts as active contributors and potential therapeutic targets in TNF‐ and Th17‐driven skin diseases.

Introduction: Hidradenitis suppurativa is a painful inflammatory disease characterised by diverse cutaneous lesions that exhibit distinct clinical morphologies. The study aimed to examine the transcriptome of the various hidradenitis suppurativa lesion types. Methods: Transcriptomic analyses were performed using bulk RNA sequencing to examine the various lesion types, including draining tunnels, inflammatory nodules, non-draining tunnels, non-lesional skin from patients with hidradenitis suppurativa and normal skin from healthy individuals. Results/discussion: Principal component and differential expression analyses revealed that these different lesion types exhibit distinct expression profiles while sharing common transcriptional features. Enrichment analysis of exclusively differentially expressed genes for each lesion type showed increased antigen presentation and cytotoxic T cell response in inflammatory nodules, including genes such as CD8B , HLA-C , and HLA-F. In accordance, cell-type enrichment analysis showed an elevated CD8 ⁺ T cell signature in inflammatory nodules. Gene set variation analysis demonstrated distinct inflammatory pathway signatures in hidradenitis suppurativa lesions, including heightened IL-1 signalling in draining tunnels with significant upregulation of IL1B and its receptor IL1R , but not IL1A. Furthermore , IL17A and IL17F were significantly increased in draining tunnels, inflammatory nodules, and non-draining tunnels, with IL17F showing the highest expression in draining tunnels. MMP3 , MMP8 , and MMP10 were preferentially upregulated in draining tunnels, indicating a role in tunnel activity. Moreover, AQP4 and AQP5 were significantly downregulated in both lesional and non-lesional hidradenitis suppurativa skin, suggesting a possible involvement in preclinical pathogenic events. Conclusion: Distinct molecular signatures specific for each lesion type were identified, which may reflect differences in molecular mechanisms. These findings underscore the importance of distinguishing between lesion types in translational and clinical studies.

Psoriasis, a chronic inflammatory skin disorder characterised by erythematous and scaly plaques, can be both physically and emotionally distressing for patients. Dead Sea climatotherapy (DSC), a treatment modality combining sun exposure, mineral‐rich water and mud therapy during 4 weeks at Ein Gedi, Israel, is used for a small group of patients with psoriasis. This study aimed to investigate the cellular composition of psoriatic skin lesions at relapse after complete clearance from DSC. Skin biopsies from baseline, end of treatment and relapse were collected from eight patients with plaque psoriasis who achieved complete clearance from Dead Sea climatotherapy treatment. These biopsies were subjected to immunohistochemistry, RNA sequencing and quantitative polymerase chain reaction analysis (qPCR). Our findings demonstrate that DSC effectively reduces inflammatory markers to levels comparable to baseline non‐lesional skin in the short term. The differential expression analysis identified several upregulated differentially expressed genes, including OSM, CXCL8, TREM1, CXCL1, CSF3R, BCL2A1 and CXCL2, in relapsed psoriasis skin compared with baseline lesional skin. These findings were confirmed by qPCR analysis. Pathway enrichment analysis indicated a marked upregulation of neutrophil‐associated pathways in relapse skin compared with baseline lesional skin. Immunohistochemical staining for neutrophil markers, such as CD11b, CD15, CD66b, CD207, MPO and NE, showed a non‐significant trend towards enhanced neutrophil infiltration and activation at relapse. In conclusion, while DSC provides short‐term effectiveness in managing psoriasis, the initial relapse phase is associated with neutrophil activation and migration. Thus, targeting neutrophils early in the psoriasis disease course may disturb the evolution of psoriasis, potentially preventing disease chronicity.

The inhibition of heat shock protein 90 (HSP90), a molecular chaperone, has been proposed to be a potential novel treatment strategy for Coronavirus disease 2019 (COVID-19). In contrast to other studies, our data demonstrated that RGRN-305, a HSP90 inhibitor, exacerbated the cytopathic effect and did not reduce the viral shedding in VeroE6-hTMPRSS2 cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Likewise in a murine model of SARS-CoV-2, transgenic mice treated orally with RGRN-305 exhibited reduced survival by the end of the experiment (day 12) as 14% (1/7) survived compared to 63% (5/8) of those treated with drug-vehicle. Animal weight was not reduced by the RGRN-305 treatment. Interestingly, we demonstrated that inhibition of HSP90 by RGRN-305 significantly dampened the inflammatory response induced by SARS-CoV-2 spike protein in human macrophage-like cells (U937) and human lung epithelial cells (A549). Measured by quantitative real-time PCR, the mRNA expression of the proinflammatory cytokines TNF, IL1B and IL6 were significantly reduced. Together, these data suggest that HSP90 inhibition by RGRN-305 exacerbates the SARS-CoV-2 infection in vitro and reduces the survival of mice infected with SARS-CoV-2, but exhibits strong anti-inflammatory properties. This data shows that while RGRN-305 may be helpful in a ‘cytokine storm’, it has no beneficial impact on viral replication or survival in animals as a monotherapy. Further animal studies with HSP90 inhibitors in combination with an anti-viral drug may provide additional insights into its utility in viral infections and whether HSP90 inhibition may continue to be a potential treatment strategy for COVID-19 disease.

Background: Heat shock protein 90 (HSP90) is an important chaperone supporting the function of many proinflammatory client proteins. Recent studies indicate HSP90 inhibition may be a novel mechanism of action for inflammatory skin diseases; however, this has not been explored in atopic dermatitis (AD).Objectives: Our study aimed to investigate HSP90 as a novel target to treat AD.Methods: Experimental models of AD were used including primary human keratinocytes stimulated with cytokines (TNF/IFNγ or TNF/IL-4) and a mouse model established by MC903 applications.Results: In primary human keratinocytes using RT-qPCR, the HSP90 inhibitor RGRN-305 strongly suppressed the gene expression of Th1- (TNF, IL1B, IL6) and Th2-associated (CCL17, CCL22, TSLP) cytokines and chemokines related to AD. We next demonstrated that topical and oral RGRN-305 robustly suppressed MC903-induced AD-like inflammation in mice by reducing clinical signs of dermatitis (oedema and erythema) and immune cell infiltration into the skin (T cells, neutrophils, mast cells). Interestingly, topical RGRN-305 exhibited similar or slightly inferior efficacy but less weight loss compared with topical dexamethasone. Furthermore, RNA sequencing of skin biopsies revealed that RGRN-305 attenuated MC903-induced transcriptome alterations, suppressing genes implicated in inflammation including AD-associated cytokines (Il1b, Il4, Il6, Il13), which was confirmed by RT-qPCR. Lastly, we discovered using Western blot that RGRN-305 disrupted JAK-STAT signaling by suppressing the activity of STAT3 and STAT6 in primary human keratinocytes, which was consistent with enrichment analyses from the mouse model.Conclusion: HSP90 inhibition by RGRN-305 robustly suppressed inflammation in experimental models mimicking AD, proving that HSP90 inhibition may be a novel mechanism of action in treating AD.

Hidradenitis suppurativa is a chronic inflammatory skin disease with limited treatment options. The poorly understood pathogenesis hinders the development of effective treatments; therefore, a pressing need exists to further elucidate the molecular mechanisms in hidradenitis suppurativa. This study investigated the underlying inflammatory pathways and cell types in hidradenitis suppurativa using transcriptomic approaches with RNA sequencing of lesional and non-lesional skin biopsies from hidradenitis suppurativa, which was jointly analyzed with previously published transcriptomic data from atopic dermatitis and psoriasis patients. The differential expression and pathway enrichment analyses demonstrated the activation of multiple inflammatory processes, including the innate and adaptive immune systems, implicated in the hidradenitis suppurativa pathogenesis. In agreement, hidradenitis suppurativa exhibited a unique and heterogeneous cell type signature involving lymphoid and myeloid cells such as B cells and macrophages. Furthermore, hidradenitis suppurativa displayed increased expression of T_H1/2/17 signatures with no predominant T_H signatures unlike psoriasis (T_H1/17) and atopic dermatitis (T_H2). In summary, our study provides molecular insights into the pathomechanisms in hidradenitis suppurativa, revealing a strong and widespread immune activation, which may benefit from treatment strategies offering a broad immunomodulation of various key inflammatory pathways. Our data not only corroborate previously reported findings but also enhance our understanding of the immune dysregulation in hidradenitis suppurativa, uncovering novel and potential therapeutic targets.