Immunolocalization of tenascin-C in vitiligo

Fibroblast: A Novel Target for Autoimmune and Inflammatory Skin Diseases Therapeutics

Fibroblasts are crucial components of the skin structure. They were traditionally believed to maintain the skin's structure by producing extracellular matrix and other elements. Recent research illuminated that fibroblasts can respond to external stimuli and exhibit diverse functions, such as the secretion of pro-inflammatory factors, adipogenesis, and antigen presentation, exhibiting remarkable heterogeneity and plasticity. This revelation positions fibroblasts as active contributors to the pathogenesis of skin diseases, challenging the traditional perspective that views fibroblasts solely as structural entities. Based on their diverse functions, fibroblasts can be categorized into six subtypes: pro-inflammatory fibroblasts, myofibroblasts, adipogenic fibroblasts, angiogenic fibroblasts, mesenchymal fibroblasts, and antigen-presenting fibroblasts. Cytokines, metabolism, and epigenetics regulate functional abnormalities in fibroblasts. The dynamic changes fibroblasts exhibit in different diseases and disease states warrant a comprehensive discussion. We focus on dermal fibroblasts' aberrant manifestations and pivotal roles in inflammatory and autoimmune skin diseases, including psoriasis, vitiligo, lupus erythematosus, scleroderma, and atopic dermatitis, and propose targeting aberrantly activated fibroblasts as a potential therapeutic strategy for inflammatory and autoimmune skin diseases.

Emerging Role of Fibroblasts in Vitiligo: A Formerly Underestimated Rising Star

Vitiligo is a disfiguring depigmentation disorder characterized by loss of melanocytes. Although numerous studies have been conducted on the pathogenesis of vitiligo, the underlying mechanisms remain unclear. Although most studies have focused on melanocytes and keratinocytes, growing evidence suggests the involvement of dermal fibroblasts, residing deeper in the skin. This review aims to elucidate the role of fibroblasts in both the physiological regulation of skin pigmentation and their pathological contribution to depigmentation, with the goal of shedding light on the involvement of fibroblasts in vitiligo. The topics covered in this review include alterations in the secretome, premature senescence, autophagy dysfunction, abnormal extracellular matrix, autoimmunity, and metabolic changes.

Extraciliary OFD1 Is Involved in Melanocyte Survival through Cell Adhesion to ECM via Paxillin

Primary cilia play a significant role in influencing cell fate, including apoptosis in multiple cell types. In the lesional epidermis of vitiligo patients, a reduced number of ciliated cells was observed. Our study also revealed a downregulation of oral-facial digital syndrome type 1 (OFD1) in the affected skin of vitiligo patients. However, it remains unknown whether primary cilia are involved in the control of melanocyte apoptosis. While both intraflagellar transport 88 (IFT88) and retinitis pigmentosa GTPase regulator-interacting protein-1 like (RPGRIP1L) are associated with ciliogenesis in melanocytes, only the knockdown of OFD1, but not IFT88 and RPGRIP1L, resulted in increased melanocyte apoptosis. OFD1 knockdown led to a decrease in the expression of proteins involved in cell-extracellular matrix (ECM) interactions, including paxillin. The OFD1 amino acid residues 601-1012 interacted with paxillin, while the amino acid residues 1-601 were associated with ciliogenesis, suggesting that the OFD1 domains responsible for paxillin binding are distinct from those involved in ciliogenesis. OFD1 knockdown, but not IFT88 knockdown, inhibited melanocyte adhesion to the ECM, a defect that was restored by paxillin overexpression. In summary, our findings indicate that the downregulation of OFD1 induces melanocyte apoptosis, independent of any impairment in ciliogenesis, by reducing melanocyte adhesion to the ECM via paxillin.

Melanocyte-keratinocyte cross-talk in vitiligo

Vitiligo is a common acquired pigmentary disorder that presents as progressive loss of melanocytes from the skin. Epidermal melanocytes and keratinocytes are in close proximity to each other, forming a functional and structural unit where keratinocytes play a pivotal role in supporting melanocyte homeostasis and melanogenesis. This intimate relationship suggests that keratinocytes might contribute to ongoing melanocyte loss and subsequent depigmentation. In fact, keratinocyte dysfunction is a documented phenomenon in vitiligo. Keratinocyte apoptosis can deprive melanocytes from growth factors including stem cell factor (SCF) and other melanogenic stimulating factors which are essential for melanocyte function. Additionally, keratinocytes control the mobility/stability phases of melanocytes via matrix metalloproteinases and basement membrane remodeling. Hence keratinocyte dysfunction may be implicated in detachment of melanocytes from the basement membrane and subsequent loss from the epidermis, also potentially interfering with repigmentation in patients with stable disease. Furthermore, keratinocytes contribute to the autoimmune insult in vitiligo. Keratinocytes express MHC II in perilesional skin and may present melanosomal antigens in the context of MHC class II after the pigmented organelles have been transferred from melanocytes. Moreover, keratinocytes secrete cytokines and chemokines including CXCL-9, CXCL-10, and IL-15 that amplify the inflammatory circuit within vitiligo skin and recruit melanocyte-specific, skin-resident memory T cells. In summary, keratinocytes can influence vitiligo development by a combination of failing to produce survival factors, limiting melanocyte adhesion in lesional skin, presenting melanocyte antigens and enhancing the recruitment of pathogenic T cells.

A decellularized extracellular matrix derived from keratinocytes can suppress cellular senescence induced by replicative and oxidative stresses

Keratinocyte senescence is suppressed on a keratinocyte-derived decellularized ECM (dECM) through the increase of antioxidant activity. Keratinocyte function is also increased on this dECM, suggesting that this dECM is useful to establish epidermal models.

The clinical and pathological effectiveness of microneedling and topical 5-fluorouracil in vitiligo treatment: An association with matrix metalloproteinase 2 immunohistochemical expression

BACKGROUND

The current therapies for vitiligo require long duration with often disappointing outcomes. 5-Fluorouracil (5-FU) is a chemotherapeutic agent approved for topical use in the treatment of several dermatologic conditions. Matrix metalloproteinase 2 (MMP2) is synthesized by keratinocytes during the epidermal remodeling process and has been found to help in melanocyte migration.

AIM

To investigate the efficacy and safety of flexible microneedling followed by application of 5-FU in vitiligo treatment and to evaluate the immunohistochemical expression of MMP2 in involved skin in vitiligo patients before and after treatment.

METHODS

Twenty patients presented with vitiligo were planned to receive one session every 2 weeks for 12 weeks of microneedling followed by 5-FU application. Clinical response to therapy was evaluated by VASI score. Pre- and post-treatment biopsies were taken from vitiliginous patches for MMP2 immunostaining.

RESULTS

Fifteen patients (75%) responded to therapy with observed side effects such as pain, erythema, and hyperpigmentation of margins. The clinical response was more in young patients and those who have short disease duration. MMP2 was significantly increased in post-treatment biopsy compared with the pretreatment one.

CONCLUSIONS

5-Fluorouracil application after microneedling is effective in the treatment of vitiligo with 75% response, 60% patient satisfaction, and tolerable side effects. The improvement in vitiligo patients by microneedling and 5-fluorouracil could be due to upregulation of MMP2 in affected vitiligo specimens.

Value of silicone gel in prevention of cobblestoning following punch minigrafting in vitiligo

Background: Cobblestoning is the most common complication of minipunch grafting.Objective: To assess the value of silicone gel application following minipunch grafting and the histopathological and immunohistochemical changes in cases with cobblestoning.Methods: Minipunch grafting was performed in two similar vitiligo lesions in 27 cases with stable vitiligo. After healing, silicone gel was applied twice daily on one lesion while zinc oxide ointment was applied to the other lesion serving as a control. Four biopsies were taken from each case; normal, vitiliginous skin before treatment and the two treated lesions 3 months after therapy, for histopathology and immunohistochemical staining for MMP9 & tenascin-C.Results: Repigmentation occurred in 19 cases (70.7%). The number of lesions showing excellent and good response was significantly higher on the silicone gel side (p < .001). In 20 cases, cobblestoning either occurred or was absent on both sides. Histopathologically, cobblestoning was similar to hypertrophic scarring. Both markers were elevated after therapy on both sides with no significant difference in percentage change between lesions showing positive and negative cobblestoning.Conclusion: Silicone gel application after minigrating improved the final response with no significant effect on the occurrence of cobblestoning. Cobblestoning resembled hypertrophic scarring histopathologically.

Premature cell senescence in human skin: Dual face in chronic acquired pigmentary disorders

Although senescence was originally described as an in vitro acquired cellular characteristic, it was recently recognized that senescence is physiologically and pathologically involved in aging and age-related diseases in vivo. The definition of cellular senescence has expanded to include the growth arrest caused by various cellular stresses, including DNA damage, inadequate mitochondria function, activated oncogene or tumor suppressor genes and oxidative stress. While senescence in normal aging involves various tissues over time and contributes to a decline in tissue function even with healthy aging, disease-induced premature senescence may be restricted to one or a few organs triggering a prolonged and more intense rate of accumulation of senescent cells than in normal aging. Organ-specific high senescence rate could lead to chronic diseases, especially in post-mitotic rich tissue. Recently, two opposite acquired pathological conditions related to skin pigmentation were described to be associated with premature senescence: vitiligo and melasma. In both cases, it was demonstrated that pathological dysfunctions are not restricted to melanocytes, the cell type responsible for melanin production and transport to surrounding keratinocytes. Similar to physiological melanogenesis, dermal and epidermal cells contribute directly and indirectly to deregulate skin pigmentation as a result of complex intercellular communication. Thus, despite senescence usually being reported as a uniform phenotype sharing the expression of characteristic markers, skin senescence involving mainly the dermal compartment and its paracrine function could be associated with the disappearance of melanocytes in vitiligo lesions and with the exacerbated activity of melanocytes in the hyperpigmentation spots of melasma. This suggests that the difference may arise in melanocyte intrinsic differences and/or in highly defined microenvironment peculiarities poorly explored at the current state of the art. A similar dualistic phenotype has been attributed to intratumoral stromal cells as cancer-associated fibroblasts presenting a senescent-like phenotype which influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. Here, we present a framework dissecting senescent-related molecular alterations shared by vitiligo and melasma patients and we also discuss disease-specific differences representing new challenges for treatment.

A Parametric Targetability Evaluation Approach for Vitiligo Proteome Extracted through Integration of Gene Ontologies and Protein Interaction Topologies

Vitiligo is a well-known skin disorder with complex etiology. Vitiligo pathogenesis is multifaceted with many ramifications. A computational systemic path was designed to first propose candidate disease proteins by merging properties from protein interaction networks and gene ontology terms. All in all, 109 proteins were identified and suggested to be involved in the onset of disease or its progression. Later, a composite approach was employed to prioritize vitiligo disease proteins by comparing and benchmarking the properties against standard target identification criteria. This includes sequence-based, structural, functional, essentiality, protein-protein interaction, vulnerability, secretability, assayability, and druggability information. The existing information was seamlessly integrated into efficient pipelines to propose a novel protocol for assessment of targetability of disease proteins. Using the online data resources and the scripting, an illustrative list of 68 potential drug targets was generated for vitiligo. While this list is broadly consistent with the research community's current interest in certain specific proteins, and suggests novel target candidates that may merit further study, it can still be modified to correspond to a user-specific environment, either by adjusting the weights for chosen criteria (i.e., a quantitative approach) or by changing the considered criteria (i.e., a qualitative approach).

Contact allergen (PPD and DNCB)-induced keratinocyte sensitization is partly mediated through a low molecular weight hyaluronan (LMWHA)/TLR4/NF-κB signaling axis

Allergic contact dermatitis (ACD) is caused by topical exposure to chemical allergens. Keratinocytes play a key role in innate immunity, as well as in ACD progression. The transmembrane Toll-like receptor 4 (TLR4), strongly implicated in skin inflammation, has the ability to bind Damage Associated Molecular Patterns (DAMPs), like Low Molecular Weight Hyaluronan (LMWHA). Previously, we had determined that p-phenylenediamine (PPD) and 2,4-dinitrochlorobenzene (DNCB) modulate keratinocyte HA deposition in a manner correlated to their sensitization. In the present study, we aimed to investigate putative co-operation of HA and TLR4 in the process of PPD and DNCB-induced keratinocyte activation. Contact sensitizers were shown to significantly increase the expression of Hyaluronan Synthases (HAS) and TLR4 in NCTC2544 human keratinocytes, as demonstrated by western blot and Real-Time PCR. These data, in correlation to earlier shown enhanced HA degradation suggest that the contact sensitizers facilitate HA turnover of keratinocytes and increase the release of pro-inflammatory, LMWHA fragments. Treatment with exogenous LMWHA enhanced TLR4, HAS levels and Nuclear factor-kappa beta (NF-κΒ) activation. PPD, DNCB and LMWHA-effects were shown to be partly executed through TLR4 downstream signaling as shown by Real-Time, western blot, siRNA and confocal microscopy approaches. Specifically, PPD and DNCB stimulated the activation of the TLR4 downstream mediator NF-κB. Therefore, the shown upregulation of TLR4 expression is suggested to further facilitate the release of endogenous, bioactive HA fragments and sustain keratinocyte activation. In conclusion, keratinocyte contact allergen-dependent sensitization is partly mediated through a LMWHA/TLR4/ NF-κB signaling axis.

The convergence theory for vitiligo: A reappraisal

Vitiligo is characterized by progressive loss of skin pigmentation. The search for aetiologic factors has led to the biochemical, the neurologic and the autoimmune theory. The convergence theory was then proposed several years ago to incorporate existing theories of vitiligo development into a single overview of vitiligo aetiology. The viewpoint that vitiligo is not caused only by predisposing mutations, or only by melanocytes responding to chemical/radiation exposure, or only by hyperreactive T cells, but rather results from a combination of aetiologic factors that impact melanocyte viability, has certainly stood the test of time. New findings have since informed the description of progressive depigmentation. Understanding the relative importance of such aetiologic factors combined with a careful selection of the most targetable pathways will continue to drive the next phase in vitiligo research: the development of effective therapeutics. In that arena, it is likewise important to acknowledge that pathways affected in some patients may not be altered in others. Taken together, the convergence theory continues to provide a comprehensive viewpoint of vitiligo aetiology. The theory serves to intertwine aetiologic pathways and will help to define pathways amenable to disease intervention in individual patients.

Biomarkers of disease activity in vitiligo: A systematic review

The pathophysiology of vitiligo is complex although recent research has discovered several markers which are linked to vitiligo and associated with disease activity. Besides providing insights into the driving mechanisms of vitiligo, these findings could reveal potential biomarkers. Activity markers can be used to monitor disease activity in clinical trials and may also be useful in daily practice. The aim of this systematic review was to document which factors have been associated with vitiligo activity in skin and blood. A second goal was to determine how well these factors are validated in terms of sensitivity and specificity as biomarkers to determine vitiligo activity. Both in skin (n=43) as in blood (n=66) an adequate number of studies fulfilled the predefined inclusion criteria. These studies used diverse methods and investigated a broad range of plausible biomarkers. Unfortunately, sensitivity and specificity analyses were scarce. In skin, simple histopathology with or without supplemental CD4 and CD8 stainings can still be considered as the gold standard, although more recently chemokine (C-X-C motif) ligand (CXCL) 9 and NLRP1 have demonstrated a good and possibly even better association with progressive disease. Regarding circulating biomarkers, cytokines (IL-1β, IL-17, IFN-γ, TGF-β), autoantibodies, oxidative stress markers, immune cells (Tregs), soluble CDs (sCD25, sCD27) and chemokines (CXCL9, CXCL10) are still competing. However, the two latter may be preferable as both chemokines and soluble CDs are easy to measure and the available studies display promising results. A large multicenter study could make more definitive statements regarding their sensitivity and specificity.