Although hair aging affects appearance and hair quality, objective biomarkers linking molecular alterations to clinically relevant mechanical properties of hair remain limited. Here, we investigated the relationships among age, hair tensile resistance, and cortical disulfide bond content. Hair shafts from healthy volunteers (20-40 years vs. > 50 years) were analysed for tensile resistance, which was measured as maximum tensile force, and disulfide bond content was assessed by Raman spectroscopy. In parallel, human scalp hair follicles were stratified according to disulfide bond content and donor age to generate transcriptomic datasets for analysis. We identified follicular gene-expression signatures associated with these parameters. Differential expression analysis revealed a shared gene set associated with reduced disulfide bond content and age, which was subsequently evaluated in ex vivo human hair follicle cultures. Among these candidates, cochlin (COCH) emerged as a prominent candidate gene associated with higher cortical disulfide bond content and enhanced tensile resistance of the hair shaft. Immunohistochemical analysis revealed that COCH predominantly localized to the hair matrix and outer root sheath, supporting a follicle-derived contribution to shaft biochemistry. Together, these findings identify COCH as a promising candidate marker linked to disulfide bond integrity and tensile properties of human hair and establish an integrative framework for connecting follicular gene expression with age-associated changes in hair shaft mechanics.
Ultraviolet (UV) irradiation leads to acute photodamage, photoaging and skin cancers. Post-translational modifications (PTMs) represent a key regulatory layer by modulating protein function, localization and interactions under UV stress. This review discusses the mechanistic involvement of PTMs in UV-induced skin damage and summarizes emerging PTM-related photoprotective strategies. Phosphorylation is a central mediator of UV-induced signal transduction, driving activation of the epidermal growth factor receptor (EGFR) and its downstream signalling pathways. Acetylation exerts distinct regulatory effects: histone acetylation primarily regulates transcription of inflammation-related genes and matrix metalloproteinases (MMPs), while non-histone acetylation modulates cellular senescence and mitochondrial antioxidant defence through modification of key proteins. Ubiquitination regulates protein degradation and, through non-degradative modifications, participates in DNA damage recognition and nucleotide excision repair (NER). Furthermore, other PTMs, including methylation, glycosylation, citrullination, SUMOylation and poly(ADP-ribosyl)ation (PARylation), participate in diverse regulatory processes during UV-induced cutaneous alterations. Experimental and emerging interventions associated with PTMs in UV-induced skin damage range from natural extracts to small-molecule agents and mainly include upstream-level modulation of oxidative stress, metabolic status or key effector protein function, as well as enzyme-level modulation of PTM writers and erasers. Different classes of PTMs contribute to UV-induced skin damage through distinct regulatory mechanisms. Further studies should explore the roles of emerging and less-characterized PTMs and evaluate interventions targeting PTM-regulating enzymes in physiologically relevant skin models.
Cutibacterium acnes is a common skin bacterium that inhabits sebaceous follicles and comprises multiple phylotypes. Healthy skin is colonized by a C. acnes population dominated by phylotypes IA, IB, and II. In acne, this diversity is reduced, with a predominance of phylotype IA. Quantifying C. acnes phylotypes has been challenging due to the lack of specific methods. Here, we developed a droplet digital PCR (ddPCR) assay that separately quantifies phylotype IA and phylotypes IB/II, based on a difference in the hyaluronidase gene. The method was applied to skin swabs from 14 healthy individuals and 14 acne patients. Healthy skin contained nearly equal amounts of IA and IB/II, whereas acne samples showed a 111-fold predominance of IA over IB/II, due to a marked depletion of IB/II, instead of an increase of IA. After 4-6 months of isotretinoin treatment, C. acnes levels decreased drastically, with phylotype IA reduced by 50-fold. Twelve to 15 months after treatment, both phylotypes rebounded, although IB/II recovered only partially. Taken together, this ddPCR method can quantitatively distinguish the acne-dominant phylotype IA from healthy skin-associated phylotypes IB/II, and is thus a useful tool for skin microbiome studies and specifically for assessing C. acnes dysbiosis in acne.
Bullous pemphigoid (BP) is the most common subepidermal autoimmune blistering disease, characterized by autoantibodies against BP180 and BP230. Although the NC16A domain of BP180 is the immunodominant epitope, increasing evidence indicates that non-NC16A epitopes also contribute to the clinical heterogeneity of BP. This review summarizes the immunological characteristics and clinical significance of BP180 and BP230 epitopes, and discusses their associations with disease phenotypes, treatment responses, and prognosis. We also outline the pathogenesis and animal models of BP, and highlight the rarity of validated models for non-NC16A epitopes and their limited mechanistic scope. Emerging targeted therapies are critically reviewed in relation to current knowledge of epitope-specific immune responses. Although epitope profiling may eventually contribute to disease stratification and biomarker development, current evidence is insufficient to support routine epitope-guided therapeutic decision-making. Despite current progress, challenges remain in clarifying the pathogenicity of non-NC16A epitopes and establishing standardized detection. Future research should focus on epitope-phenotype correlations and large-cohort studies to promote the development of precision therapy for BP.
Female-pattern hair loss is common in obese women with polycystic ovary syndrome (PCOS), recently proposed as polyendocrine metabolic ovarian syndrome (PMOS) and is often associated with hypertriglyceridemia (TG), although the underlying mechanisms remain unclear. This study investigated how metabolic factors and androgens contribute to hair loss in female mice exposed to a high-fat diet (HFD). A controlled, parallel-group study using 8-week-old female C57BL/6 mice fed either an HFD (60% kcal fat) or a standard diet for 16 weeks. Mice were sacrificed at baseline and 4-week intervals for serial evaluation of metabolic, hormonal and skin changes (n = 6/group/time point). Hair loss was quantified from digital photographs using the ImageJ and further supported by histological examination. Circulating metabolic and hormonal profiles were measured. In dorsal skin, oxidative stress (malondialdehyde, MDA) and androgen-related markers-5-alpha-reductase type II (5αR2), dihydrotestosterone (DHT) and androgen receptor (AR)-were evaluated using immunohistochemistry, Western blot and enzyme-linked immunosorbent assay. From Week 12 onward, HFD-fed mice exhibited greater weight gain, pronounced dorsal hair thinning and elevated TG, insulin and free androgen index (FAI) levels. Skin MDA, 5αR2, DHT and AR levels also progressively increased. In the second experiment, 8-week-old female mice were assigned to four groups (n = 6/group): HFD with N-acetylcysteine (NAC), finasteride, spironolactone, or vehicle administered by oral gavage for 12 weeks. Compared with HFD-vehicle, antioxidant or anti-androgen co-treatment significantly lowered serum TG, tissue MDA and ameliorated hair thinning despite similar weight gain and 5αR2 levels. NAC reduced TG, FAI and decreased tissue MDA, DHT and AR. Finasteride lowered TG, MDA, DHT and AR, whereas spironolactone reduced TG and MDA. HFD-induced obesity exacerbates hair loss in female mice by enhancing oxidative stress and activating androgen signalling in the skin. Targeting these pathways, such as antioxidants and antiandrogens, may mitigate HFD-accelerated hair loss.
Cutaneous antimicrobial peptides (AMPs) are increasingly recognized for their multifaceted roles in skin disease and cancer, and thus application for therapeutic potential. Beyond their contributions to innate defence and the skin's microbiome, AMPs have been implicated in inflammatory skin conditions and cutaneous malignancies. Comprehensive summaries of AMPs' roles in skin cancer and related current clinical developments remain scarce, despite abundant emerging evidence of pro- and anti-tumour properties in other fields. This review provides a comprehensive discussion of AMPs, including dermcidin, psoriasin (S100A7), human cathelicidin (LL-37), RNase-7 and the human β-defensins, in the context of skin cancer research and clinical developments. These AMPs influence skin tumorigenesis through microbiome regulation, innate immune pathways and chronic inflammation, and although the mechanistic details are subject to scrutiny, several AMP-derived therapies, including LL-37 and LTX-315, have been developed for their potential in cutaneous oncology.
Dystrophic epidermolysis bullosa (DEB) is a rare, debilitating genodermatosis caused by loss-of-function variants in COL7A1, resulting in type VII collagen (C7) deficiency and defective anchoring fibrils, which are essential for dermal-epidermal adhesion. COL7A1 is a large gene, and C7 is synthesized by both keratinocytes and fibroblasts, and extracellularly secreted, where it forms a supramolecular network that stabilizes the dermal-epidermal junction. Human genotype-phenotype correlations suggest that residual C7 expression (~10% of normal levels) may confer a milder disease phenotype, whereas complete absence results in generalized skin fragility with scarring and systemic complications. Thus, restoring C7 expression remains a central therapeutic objective. Since the discovery of COL7A1, thousands of pathogenic variants have been described, including amino acid substitutions in the triple-helical domain that allow partial C7 function, whereas null alleles are associated with severe phenotypes. Gene- and cell-based strategies have evolved to address the large COL7A1 size and delivery challenges. Ex vivo gene/cell therapies (keratinocytes or fibroblasts engineered to express COL7A1) have demonstrated partial, wound-specific C7 restoration but with durability limitations, as grafted cells may be outcompeted or lose transgene expression over time; select patients show sustained anchoring fibril formation and improved wound healing; however, long-term outcomes remain variable. In vivo topical gene therapy has achieved clinically meaningful wound closure in DEB, illustrating a paradigm shift toward accessible and patient-friendly therapeutic approaches, albeit with real-world considerations on durability and wound recurrence. A multidisciplinary framework integrating EB expert centers, drug-delivery pharmacy services, wound management, and patient-support programs can further enhance treatment access and adherence. General factors such as nutritional status, infection and comorbidities also influence both wound healing and the response to gene therapy. Revertant mosaicism offers a natural gene-therapy substrate: cultured epidermal autografts derived from revertant patches have yielded substantial, yet heterogeneous, epithelization, with outcomes contingent on revertant cell proportion and culture fidelity. Collectively, these advances highlight the emerging potential of gene- and cell-based therapies to achieve durable disease modification in DEB.
Cutaneous lupus erythematosus (CLE) encompasses a heterogeneous group of autoimmune skin manifestations that often overlap clinically with other inflammatory dermatoses, particularly rosacea. While histopathology remains the gold standard, its invasiveness limits routine and longitudinal use. Line-field confocal optical coherence tomography (LC-OCT) is an emerging non-invasive imaging modality capable of providing real-time, near-histological resolution of skin architecture. In this single-center cross-sectional observational study, 45 patients (30 CLE: 16 acute, 5 subacute, 9 chronic; 15 rosacea) underwent LC-OCT imaging of active lesions. Images were independently evaluated using predefined criteria reflecting histopathological features. LC-OCT identified key histopathological correlates of CLE in vivo. Interface dermatitis features (including dermoepidermal junction disruption, basal cell vacuolization and band-like inflammatory infiltrate) were highly prevalent in ACLE and SCLE, while chronic CLE was characterized by epidermal atrophy, hyperkeratosis, fibrosis and adnexal destruction. In contrast, rosacea exhibited a vascular and folliculocentric pattern with frequent peri-adnexal inflammation and Demodex infestation, without interface changes. Interobserver agreement was substantial to excellent for most criteria. In the ACLE versus rosacea comparison, interface dermatitis features like band-like DEJ infiltrate, DEJ disruption, basal vacuolization and apoptotic bodies were associated with ACLE. Conversely, rosacea exhibited a vascular-folliculocentric profile with peri-infundibular infiltrates and Demodex mites. In conclusion, LC-OCT enables non-invasive visualization of disease-specific microarchitectural patterns in CLE, reflecting both inflammatory and chronic remodelling changes. In this pilot study, it shows potential in differentiating CLE from rosacea and may support diagnosis, staging and treatment monitoring in clinical practice. Larger, multicenter studies are required to confirm the role of LC-OCT in the non-invasive diagnosis of CLE.
Repetin (RPTN) is a member of the fusion S100 protein family encoded within the epidermal differentiation complex. Although genetic studies have revealed that RPTN is a susceptibility gene for atopic dermatitis (AD), its biological function remains poorly understood. In this study, we investigated the role of RPTN in epidermal homeostasis and inflammatory skin diseases. We examined RPTN expression in normal skin, inflammatory skin diseases, and differentiated normal human keratinocytes (NHKs). Functional analyses were performed using RPTN knockdown (KD) NHK and three-dimensional (3D) skin-equivalent models. Epidermal barrier function was assessed using a lucifer yellow permeability assay, and cytokine-mediated regulation of RPTN expression was evaluated using 3D atopic dermatitis (AD) and psoriasis models. RPTN was primarily expressed in the granular layer of the normal epidermis and increased with keratinocyte differentiation. In the 3D skin-equivalent model, RPTN deficiency impaired epidermal barrier function and induced the expression of differentiation-related genes, including FLG, IVL, TGM1, CLDN1, KLK7, ALOX12, and TCHHL1. Notably, RPTN knockdown significantly increased IL-25 expression. RPTN expression was elevated in chronic atopic dermatitis (AD) lesions and in hypergranular epithelia of psoriasis vulgaris, lichen planus, and epidermolytic ichthyosis. In a 3D AD model, IL-4 and IL-13 significantly induced RPTN expression. These findings indicate that RPTN contributes to maintaining epidermal barrier homeostasis and suggest that it may be associated with regulating inflammatory responses.
ABSTRACT Skin cutaneous melanoma (SKCM) continues to pose significant therapeutic challenges owing to its aggressive nature and evolving resistance mechanisms. This study investigates the under‐characterized role of Hippo pathway effector TEAD4 in SKCM pathogenesis through integrated multiomics analysis of clinical cohorts (TCGA, GEO, immunotherapy cohorts) combined with functional validation in A375 cell models and xenograft systems. Our pan‐cancer analysis identified TEAD4 overexpression as a strong prognostic indicator associated with poor survival and a potential association with inferior immunotherapy response. Functional experiments in A375 cells and xenograft models showed that TEAD4 knockdown impaired proliferation, migration and tumour growth while increasing necroptosis‐related markers. Mechanistic investigation showed that TEAD4 directly binds the COL1A2 promoter and promotes its transcription. In A375 cells, COL1A2 overexpression attenuated TEAD4 knockdown‐induced changes in AKT/mTOR signalling, necroptosis‐related markers and malignant phenotypes. These findings support a TEAD4 and COL1A2 regulatory model associated with SKCM progression, AKT/mTOR pathway activity and necroptosis‐related phenotypes, and suggest TEAD4 as a prognostic factor and potential biomarker associated with immunotherapy outcome that requires further validation.
ABSTRACT Ultraviolet B (UVB) irradiation initiates cutaneous vitamin D‐related photochemistry from 7‐dehydrocholesterol (7‐DHC), which is also the immediate precursor of cholesterol via 7‐dehydrocholesterol reductase (DHCR7). Thus, DHCR7 occupies a branch‐point position linking cholesterol biosynthesis and UVB‐associated vitamin D‐related metabolism. How keratinocytes regulate this metabolic relationship under UVB remains unclear. We examined whether OPN1SW is associated with DHCR7 protein abundance, conditioned medium 25‐hydroxyvitamin D3 [25(OH)D3] (a vitamin D‐related readout) and sterol‐pool responses in UVB‐exposed keratinocytes. A UVB dose that preserved > 80% cell viability, 10 mJ/cm 2 , increased OPN1SW protein abundance and reduced DHCR7 protein abundance in human epidermal keratinocytes and HaCaT cells. These changes were accompanied by increased conditioned medium 25(OH)D3 and a reduced cellular sterol‐pool readout. OPN1SW overexpression increased DHCR7 protein abundance under basal conditions. Under UVB exposure, OPN1SW overexpression attenuated UVB‐associated DHCR7 reduction, attenuated the UVB‐associated increase in conditioned medium 25(OH)D3 and partially preserved the sterol‐pool readout. Conversely, OPN1SW knockdown exacerbated DHCR7 reduction under UVB and was accompanied by higher conditioned medium 25(OH)D3 and a lower sterol‐pool readout. DHCR7 knockdown produced concordant shifts in these readouts, supporting a contributory role for DHCR7. Together, these findings support the presence of a UVB‐responsive OPN1SW‐DHCR7 module that may contribute to keratinocyte adaptation to UVB exposure.
Human-derived exosomes show promise for hair loss treatment but may pose safety concerns, including inflammatory responses and pathogen transmission. Here, we investigated whether plant-derived exosomes, whose isolation can be standardized, and which show lower compositional complexity and no immunogenicity, represent a valid alternative. We isolated and characterized exosome-like nanovesicles from the Ashwagandha plant (Ash-ELNs), which is traditionally used to relieve stress, and pre-clinically explored their hair growth-promoting potential. Multi-omic approaches demonstrated low variations in the content of seven different Ash-ELN preparations, and cellular vesicle uptake was confirmed in human dermal fibroblasts (HDFs). In a scratch assay of human dermal papilla fibroblasts (HDPCs), Ash-ELNs significantly increased the production/secretion of the hair growth promoters VEGF-A, PLGF1, FGF2 and LIF. Application of Ash-ELNs to healthy human microdissected hair follicles significantly prolonged anagen and increased hair shaft production, while hair matrix keratinocyte proliferation and -apoptosis remained unaltered. Ash-ELNs significantly upregulated VEGF-A protein expression in the bulb mesenchyme, corroborating our in vitro results. Finally, Ash-ELNs promoted tubulogenesis in an HDF-human umbilical vein endothelial cell (HUVEC) assay, suggesting VEGF-A-induced angiogenesis as a possible mechanism underlying the anagen promoting effect of Ash-ELN. Thus, Ash-ELN treatment offers a novel adjuvant strategy or non-drug agent to reduce hair shedding.
Psoriasis is a chronic inflammatory skin disorder driven by systemic immune dysregulation and recent studies have implicated the gut-skin axis in its pathogenesis. However, the specific role of individual gut microbes remains poorly understood. In this study, the impact of Prevotella copri (P. copri) on psoriasis development was examined and the underlying mechanisms were investigated. In an imiquimod (IMQ)-induced mouse model, oral administration of P. copri exacerbated skin inflammation, increased epidermal thickness, promoted neutrophil infiltration and aggravated disease severity. In vitro, stimulation with P. copri enhanced keratinocyte proliferation and pro-inflammatory responses, thereby activating co-cultured neutrophils. These effects were associated with activation of the NF-κB signalling pathway, as evidenced by increased phosphorylation of p65 and upregulation of inflammasome components. The inhibition of NF-κB signalling attenuated P. copri-induced keratinocyte hyperproliferation, neutrophil activation and inflammatory cytokine production. Our findings suggest that P. copri promotes psoriasis progression via NF-κB-mediated keratinocyte-neutrophil crosstalk, potentially through a gut-derived systemic inflammatory mechanism. Targeting the gut-skin axis and NF-κB pathway may offer new therapeutic opportunities for psoriasis.
The diagnosis of an ectodermal dysplasia (ED) is often made by dermatologists. Some of the more than 50 distinct ectodermal dysplasias, however, are still largely unknown and their pathogenesis is poorly understood. Since we recently discovered that variants of the Interferon Regulatory Factor 6 (IRF6) gene IRF6 may cause ED, we have further investigated the link between this gene and maldevelopment of tissues originating from the embryonic ectoderm. Disease characterization in two previously reported subjects and one newly identified patient (mosaic status) included systematic clinical and genetic evaluation, assessment of all available patient records and dental radiographs, hearing tests and immunostaining of skin samples. Structural models of native and mutant IRF6 were analysed to elucidate the pathogenesis. IRF6-associated ED, a combination of natal teeth (irregularly), absent sweat glands, hidradenitis suppurativa-like symptoms, onychodysplasia, agenesis of numerous deciduous and permanent teeth, and sensorineural hearing impairment, was linked to amino acid substitutions in a region between the DNA-binding domain and the protein-binding domain of IRF6, which has not yet been assigned a function. Genotype-phenotype correlations from a total of five patients and immunohistochemical data support the assumption that IRF6-associated ED is based on a gain-of-function mechanism. Thus, IRF6 variants are not only the cause of Van der Woude syndrome and popliteal pterygium syndrome, two diseases with cleft lip/palate as common features, but are most likely responsible also for a new, challenging syndrome without orofacial clefting. Our results facilitate accurate and early diagnosis in affected individuals and may pave the way for specific treatment.
Vitiligo is an autoimmune pigmentary disorder characterized by progressive melanocyte loss and unpredictable activity. Objective of disease activity remains challenging, particularly in lesions with subtle clinical changes Cellular-resolution full-field optical coherence tomography (CRFF-OCT) enables non-invasive, high-resolution, histology-like visualization of skin microstructure. This study evaluated the feasibility of integrating CRFF-OCT with machine learning-assisted quantitative analysis for imaging-based characterization of active and stable vitiligo lesions. Fifty patients with non-segmental vitiligo were prospectively enrolled (2021-2022). CRFF-OCT imaging was performed on lesional, perilesional, and normal-appearing skin within the same anatomical region. Quantitative features describing epidermal structure, dermal-epidermal junction (DEJ) morphology, and pigment-associated reflectivity were extracted. A machine learning-assisted computer-aided detection (CADe) framework incorporating 13 features was developed for image-level classification of lesion activity. CRFF-OCT imaging demonstrated distinct microstructural patterns between active and stable lesions. Basal epidermal pigment-associated reflectivity was significantly lower in stable lesions compared with active lesions (9.94% ± 10.06% vs. 21.84% ± 11.08%), with corresponding differences in lesion-to-normal reflectivity ratios (0.21 vs. 0.56). Quantitative analysis revealed significant differences in epidermal thickness, DEJ associated reflectivity, inter-layer contrast, and reflectivity heterogeneity. Among the 13 extracted features, 9 differed significantly between groups and were incorporated into classification models. The CADe framework achieved a maximum image-level classification accuracy of 80.6% using a support vector machine model. These findings demonstrate the feasibility of CRFF-OCT-based quantitative imaging for objective characterization of vitiligo lesion status and support its potential role in disease activity assessment and longitudinal monitoring.
Bullous pemphigoid (BP) is an autoimmune blistering disease with an increasing incidence in recent years; however, the underlying immune regulatory mechanisms remain largely unclear. As a critical signalling hub linking innate and adaptive immunity, stimulator of interferon genes (STING) has recently been implicated in the pathogenesis of various autoimmune diseases and may regulate tissue inflammation and immune homeostasis through modulation of CD4+ T cell responses. In this study, we found that STING expression was significantly increased in lesional skin tissues from patients with BP compared with healthy controls. Transcriptomic analysis further revealed that differentially expressed genes in peripheral blood CD4+ T cells from BP patients were primarily enriched in the JAK-STAT signalling pathway, T cell activation and differentiation, and type I interferon (IFN-I)-related pathways. Pharmacological inhibition of STING markedly attenuated the aberrant activation of these signalling pathways. Moreover, qRT-PCR analysis confirmed that the mRNA levels of STING1, JAK1, and CXCR5 were significantly elevated in BP patients, whereas treatment with the STING inhibitor C176 suppressed the expression of these molecules. Collectively, our findings suggest that STING may contribute to BP immunopathogenesis by regulating the JAK-STAT signalling axis and promoting abnormal CD4+ T cell activation and differentiation, providing new insights into the molecular mechanisms underlying BP and identifying potential therapeutic targets.
Type VII collagen (COL7), a major component of anchoring fibrils, is essential for dermal-epidermal adhesion and pathogenic variants in COL7A1, encoding COL7, cause dystrophic epidermolysis bullosa (DEB). In normal skin, COL7 is localised just beneath the lamina densa. In contrast, previous immunoelectron microscopy (IEM) studies of DEB skin with residual COL7 expression demonstrated aberrant localisation of COL7 above the lamina densa and hemidesmosomes of epidermal basal keratinocytes, possibly reflecting impaired secretion of defective COL7. However, conventional microscopy techniques lack sufficient spatial resolution to clearly visualise individual protein distributions and resolve this finding. Here, we revisit the abnormal localisation of COL7 using two higher-resolution approaches: structured illumination microscopy (SIM) and expansion microscopy (ExM). In normal human skin, the COL7 NC1 domain colocalised with type IV collagen (COL4), a surrogate marker of the lamina densa and was consistently detected beneath integrin α6 (ITGA6), a hemidesmosomal marker. In DEB skin with residual COL7 expression, COL7 was detected above ITGA6 within basal keratinocytes, recapitulating previous IEM observations. SIM quantitatively confirmed significant BMZ disorganisation in DEB, whereas ExM showed a consistent but non-significant trend, likely due to variability in expansion factors. These findings demonstrate that high-resolution fluorescence imaging can reproduce classic IEM observations of COL7 mislocalisation, suggesting its potential as a more accessible complementary approach for morphologic assessment of DEB.
Resiniferatoxin (RTX) is a key tool for modelling pain-induced white hair because it induces an acute pain-related stress response. However, the specific dosage, injection method, and localization of white hair formation remain unclear. We aimed to investigate RTX application to establish a more stable mouse model of pain-induced stress-associated premature greying using a multidimensional approach. The effects of sex, age, RTX dose, depilation, and injection method on white hair location and area were investigated. Melanin granules and tyrosine-related protein 2 (TRP2)-positive cells in hair follicles were detected using histological and immunofluorescence analyses. RTX at 90 μg/kg induced the largest and most stable white hair area without inducing mortality. Male mice exhibited a higher proportion of white hair area compared to females. The proportion of white hair area was higher in 4-week-old male mice than in other age groups. Total and central activity distance ratios decreased in the open-field tests. Weight gain slowed significantly. Haematoxylin and eosin and Fontana-Masson staining revealed fewer melanin granules in the hair follicles and root areas of white hair. Immunofluorescence analysis showed a reduced TRP2-positive cell count in white hair follicles. A model of pain-induced hair depigmentation in 4-week-old male C57BL/6J mice was established by intraperitoneal injection of RTX at 90 μg/kg. Wax hair removal on day 14 accelerated white hair formation, resulting in a stable white hair area with reduced melanin granules in the follicles.
Chronic exposure to ultraviolet B (UVB) radiation induces excessive reactive oxygen species (ROS) production in dermal fibroblasts, leading to cellular senescence and skin photoaging. Ageing skin is characterised by disruption of the immune microenvironment, including impaired macrophage polarisation and reduced M2 macrophage activity. However, the contribution of M2 macrophages to fibroblast photoaging remains incompletely understood. Here, we investigated whether M2 macrophages attenuate UVB-induced fibroblast senescence through ectonucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2)-dependent lysophosphatidic acid (LPA)signalling. UVB-induced L929 fibroblasts were treated with conditioned media derived from polarised RAW264.7 macrophages, with or without ENPP2 silencing. UVB exposure induced marked senescence, oxidative stress, and mitophagy impairment, whereas conditioned medium from M2 macrophages significantly alleviated these effects compared with M1-derived conditioned medium. Notably, ENPP2 depletion in M2 macrophages substantially reduced these protective effects. M2 macrophage-derived conditioned medium contained elevated LPA levels and restored UVB-suppressed LPAR1 and LPAR3 expression in fibroblasts. Pharmacological inhibition of LPAR1/3 attenuated the protective effects of M2 macrophages, while exogenous LPA supplementation restored these effects under ENPP2-deficient conditions. These changes were associated with enhanced PINK1/Parkin-related mitophagy signalling and reduced oxidative stress. Collectively, these findings identify M2 macrophage-derived ENPP2/LPA signalling as a critical paracrine mechanism that mitigates UVB-induced fibroblast photoaging.
