IFN-γ-induced PD-L1 expression on human melanocytes is impaired in vitiligo

Unveiling the Unseen: Exploring Cellular Dynamics in Nonlesional Vitiligo Skin

Vitiligo is a multifactorial disease involving genetic predispositions, intrinsic melanocyte abnormalities, and deregulated immune response. Recent studies show nonlesional skin involvement. Nonlesional melanocytes display mitochondrial dysfunction and increased oxidative stress affecting their adhesion and function and contribute to immune activation. Keratinocytes and fibroblasts display structural and functional abnormalities impairing melanocyte support and differentiation. They also contribute to the altered immune response by secreting proinflammatory chemokines. Despite immune cell infiltration, nonlesional skin remains clinically unaffected, suggesting that regulatory mechanisms maintain immune activation at a subclinical level. This review provides an overview of the cellular alterations in vitiligo nonlesional skin.

Implication of Immunobiological Function of Melanocytes in Dermatology

Melanocytes are essential for regulating pigmentation and providing photoprotection in human skin. Originating from neural crest cells, these cells migrate to the basal layer of the epidermis and hair follicles during embryogenesis. Melanosomes, the specialized, membrane-bound organelles are essential for melanin synthesis. Beyond their role in pigmentation, melanocytes exhibit complex immune functions, expressing a variety of immune-related markers and receptors, such as pattern recognition receptors (PRRs), major histocompatibility complex class II (MHC-II) molecules, CD40, intercellular adhesion molecule 1 (ICAM-1), and programmed death-ligand 1 (PD-L1). These receptors allow melanocytes to detect environmental signals and engage in the innate immune response. Furthermore, melanocytes release various immunomodulatory substances, including proinflammatory cytokines, chemokines, and damage-associated molecular patterns (DAMPs), contributing to immune regulation. The immune functions of melanocytes are significantly influenced by external factors such as ultraviolet radiation (UVR), the microbiome, and oxidative stress. In different skin diseases, these immune functions may vary. For example, vitiligo, a common hypopigmentary disorder, is primarily driven by an autoimmune response targeting melanocytes, giving rise to depigmentation and the appearance of white patches. In contrast, melanoma, a form of skin cancer that arises from melanocytes, is closely linked to UV exposure. This review highlights the diverse immunobiological functions of melanocytes and their implications in dermatology.

Focusing on the Dark Side of the Moon: Involvement of the Nonlesional Skin in Vitiligo

Research over the last decade has revealed that the normally pigmented skin of patients with vitiligo is not normal at all, as evidenced by alterations in cutaneous morphology and modifications in cellular and metabolic functions that ultimately drive immune activation against melanocytes. Furthermore, nonlesional skin is in a state of subclinical inflammation until triggered by internal and/or external exposomal events. Therefore, targeting early processes that drive immune dysregulation in normally pigmented skin may avoid or reduce melanocyte loss. Thus, shifting the focus to nonlesional skin may prevent the appearance of clinical manifestations of the disease rather than treating the lesions.

Vitiligo: From Pathogenesis to Treatment

Recent advances in vitiligo have provided promising treatment options, particularly through understanding the immune-mediated mechanisms leading to depigmentation. The inflammatory components in both vitiligo (non-segmental) and segmental vitiligo have similarities. Both are believed to result from an immune-based destruction of melanocytes by anti-melanocyte-specific cytotoxic T cells. The JAK-STAT pathway is activated with IFN-γ as the crucial cytokine and Th1-associated chemokines such as CXCL9 and CXCL10 recruit immune cells towards vitiligo skin. Nonetheless, clear differences are also present, such as the localized nature of segmental vitiligo, likely due to somatic mosaicism and increased presence of poliosis. The differing prevalence of poliosis suggests that the follicular immune privilege, which is known to involve immune checkpoints, may be more important in vitiligo (non-segmental). Immunomodulatory therapies, especially those targeting the JAK-IFNγ pathway, are currently at the forefront, offering effective inhibition of melanocyte destruction by cytotoxic T cells. Although Janus Kinase (JAK) inhibitors demonstrate high repigmentation rates, optimal results can take several months to years. The influence of environmental UV exposure on repigmentation in patients receiving immunomodulating drugs remains largely underexplored. Nonetheless, the combined effect of phototherapy with JAK inhibitors is impressive and suggests a targeted immune-based treatment may still require additional stimulation of melanocytes for repigmentation. Identifying alternative melanocyte stimulants beyond UV light remains crucial for the future management of vitiligo.

Membranal Expression of Calreticulin Induced by Unfolded Protein Response in Melanocytes: A Mechanism Underlying Oxidative Stress-Induced Autoimmunity in Vitiligo

Calreticulin (CRT), a damage-associated molecular pattern molecule, is reported to translocate from the endoplasmic reticulum to the membrane in melanocytes under oxidative stress. To investigate the potential role of CRT in the pathogenesis of vitiligo, we analyzed the correlation between CRT and ROS in serum and lesions of vitiligo, detected CRT and protein kinase RNA-like endoplasmic reticulum kinase (PERK) expression in vitiligo lesions, and studied the production of CRT and mediators of unfolded protein response (UPR) pathway and then tested the chemotactic migration of CD8+ T cells or CD11c+ CD86+ cells. Initially, we verified the overexpression of CRT in perilesional epidermis that was positively correlated with the disease severity of vitiligo. Furthermore, the PERK branch of UPR was confirmed to be responsible for the overexpression and membranal translocation of CRT in melanocytes under oxidative stress. We also found that oxidative stress-induced membranal translocation of CRT promoted the activation and migration of CD8+ T cells in vitiligo. In addition, dendritic cells from patients with vitiligo were also prone to maturation with the coincubation of melanocytes harboring membranal CRT. CRT could be induced on the membrane of melanocytes through UPR and might play a role in oxidative stress-triggered CD8+ T-cell response in vitiligo.

YY1: a key regulator inhibits gastric cancer ferroptosis and mediating apatinib-resistance

OBJECTIVE

Gastric cancer (GC) stands as a prevalent and deadly global malignancy. Despite its role as a preoperative neoadjuvant therapy, Apatinib's effectiveness is curtailed among GC patients exhibiting elevated YY1 expression. YY1's connection to adverse prognosis, drug resistance, and GC metastasis is established, yet the precise underlying mechanisms remain elusive. This study aims to unravel potential pathogenic pathways attributed to YY1.

DESIGN

Utilizing bioinformatics analysis, we conducted differentially expressed genes, functional annotation, and pathway enrichment analyses, and further validation through cellular and animal experiments.

RESULTS

Higher YY1 expression correlated with diminished postoperative progression-free survival (PFS) and disease-specific survival (DSS) rates in TCGA analysis, identifying YY1 as an independent DSS indicator in gastric cancer (GC) patients. Notably, YY1 exhibited significantly elevated expression in tumor tissues compared to adjacent normal tissues. Bioinformatics analysis revealed noteworthy differentially expressed genes (DEGs), transcriptional targets, factors, and co-expressed genes associated with YY1. LASSO Cox analysis unveiled Transferrin as a prospective pivotal protein regulated by YY1, with heightened expression linked to adverse DSS and PFS outcomes. YY1's role in governing the p53 signaling pathway and ferroptosis in GC cells was further elucidated. Moreover, YY1 overexpression dampened immune cell infiltration within GC tumors. Additionally, YY1 overexpression hindered GC cell ferroptosis and mediated Apatinib resistance via the p53 pathway. Remarkably, IFN-a demonstrated efficacy in reversing Apatinib resistance and immune suppression in GC tissues.

CONCLUSIONS

Our findings underscore the pivotal role of YY1 in driving GC progression and influencing prognosis, thus pinpointing it as a promising therapeutic target to enhance patient outcomes.

Effects of Toll-like receptor 1 and 2 agonist Pam3CSK4 on uveal melanocytes and relevant experimental mouse model

Pam3CSK4 activates Toll-like receptors 2 and 1 (TLR1/2), which recognize mainly molecules from gram-positive pathogens. The effect of Pam3CSK4 on various cytokine and chemokine expression in cultured human uveal melanocytes (UM) has not been studied systematically. The purpose of this study was to investigate the mechanistic expressions of seven cytokines and chemokines of interleukin- (IL-) 6, IL-10, MCP-1 (CCL-2), CXCL-1 (GRO-α), CXCL-8 (IL-8), interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α) in UM. These cytokines are reported to be increased in intraocular fluids or tissues of the patients with endophthalmitis and non-infectious uveitis, as well as in various experimental animal uveitic models in the literature. Flow cytometry was used to measure the effects of Pam3CSK4 on the expression of TLR1/2 in UM. ELISA and Real-time PCR analysis were used to estimate the ability of Pam3CSK4 to elevate these cytokines and chemokines levels in conditioned media and cell lysates of UM, respectively. Flow cytometry measured and compared the phosphorylated MAPK pathway and activated NF-κB signals pathway in UM, treated with and without Pam3CSK4. ELISA analysis tested the effect of various signal inhibitors (ERK1/2, JNK1/2, p38 and NF-κB) on Pam3CSK4-induced IL-6 levels in cultured UM. The role of TLR2 in Pam3CSK4-induced acute anterior uveitis in experimental mouse model was tested in TLR2 knockout (TLR2 KO) mice and their wild-type C57Bl/6 controls. Pam3CSK4 increased the expression of TLR1/2 proteins in cultured UM. Pam3CSK4 significantly elevated the IL-6, MCP-1, CXCL-1, CXCL-8 protein, and mRNA levels in cultured UM, but not IL-10, TNF-α, or IFN-γ. Pam3CSK4 activated NF-κB, ERK, JNK, and p38 expression. Pam3CSK4-induced expression of IL-6 was decreased by NF-κB, ERK, INK, and p38 inhibitors; especially the NF-κB inhibitor, which can completely block the IL-6 stimulation. Intravitreal injection of Pam3CSK4 induced acute anterior uveitis in C57Bl/6 mice, this effect was significantly reduced in TLR2 KO mice. TLR1/2 plays an important role against invading pathogens, especially gram-positive bacteria; but an excessive reaction to molecules from gram-positive bacteria may promote non-infectious uveitis. UM can produce IL-6, MCP-1, CXCL-1, and CXCL-8, and are one of the target cells of TNF-α and IFN-γ. TLR-2 inhibitors might have a beneficial effect in the treatment of certain types of uveitis and other ocular inflammatory-related diseases and warrant further investigation.

Mechanisms of dermatologic toxicities to immune checkpoint inhibitor cancer therapies

The discovery of immune checkpoint inhibition (ICI) sparked a revolution in the era of targeted anticancer therapy. While monoclonal antibodies targeting the CTLA-4 and PD-1 axes have improved survival in patients with advanced cancers, these immunotherapies are associated with a wide spectrum of dermatologic immune-related adverse events (irAEs). Several publications have addressed the clinical and histopathologic classification of these skin-directed irAEs, their impact on antitumor immunity and survival, and the critical role of supportive oncologic dermatology in their management. Here, we review the current understanding of the mechanistic drivers of immune-related skin toxicities with a focus on inflammatory, immunobullous, melanocyte/pigment-related reactions. We detail the specific immune-based mechanisms that may underlie different cutaneous reactions. We also discuss potential mechanisms as they relate to non-cutaneous irAEs and potential overlap with cutaneous irAEs, techniques to study differences in immune-related versus de novo skin reactions, and how treatment of these adverse events impacts cancer treatment, patient quality of life, and overall survival. An improved understanding of the mechanistic basis of cutaneous irAEs will allow us to develop and utilize blood-based biomarkers that could help ultimately predict onset and/or severity of these irAEs and to implement rational mechanistic-based treatment strategies that are targeted to the irAEs while potentially avoiding abrogating anti-tumor effect of ICIs.

The delicate relation between melanocytes and skin immunity: A game of hide and seek

Melanocytes exhibit a complex and intriguing relationship with the skin immune response, leading to several clinical conditions. In some disorders, inappropriate melanocyte destruction (e.g., vitiligo, halo naevi) is problematic, while in others, immune tolerance should be broken (melanoma). Important parts of the dysregulated pathways have been unraveled in pigment disorders, ranging from upregulated interferon (IFN)-γ signaling to memory T cells, regulatory T cells, and immune checkpoints. Although a network of many factors is involved, targeting key players such as IFN-γ or checkpoint inhibitors (e.g., programmed death-ligand 1 (PD-L1)] can shift the balance and lead to impressive outcomes. In this review, we focus on the immunological mechanisms of the most common inflammatory disorders where the interaction of the immune system with melanocytes plays a crucial role. This can provide new insights into the current state of melanocyte research.

Networks of CD8+ T Cell Response Activation in Melanoma and Vitiligo

Melanoma is an aggressive skin cancer derived from melanocyte, which shows high response rate to cancer immunotherapy, such as immune checkpoint inhibitors (ICIs). Vitiligo is an autoimmune skin disease resulting from the destruction of melanocytes by autoreactive CD8+ T cells. Vitiligo induced by cancer immunotherapy is a favorable prognostic factor in patients with melanoma, and growing evidence supports the fact that melanocyte/melanoma-shared antigen (MSA)-specific CD8+ T cells infiltrated in the tumor (melanoma) and skin (vitiligo) microenvironment play pivotal roles in the prognosis of both diseases. Thus, cellular communications that promote MSA-specific CD8+ T cells recruitment, proliferation, and effector functions are now seen as key targets to enhance the efficacy of current therapies for both diseases. Here, we discussed recent advancements in illustrating immune signaling pathways and immune cell types that regulate migration, proliferation, and function of MSA-specific CD8+ T cells in melanoma and vitiligo; and future immunotherapeutic approaches that may enhance clinical outcomes of both diseases.