Work

Extracellular Granzyme B Promotes Melanocytorrhagy, Melanocyte Senescence and Aberrant Epidermal Differentiation in Vitiligo and Is Therapeutically Targetable

Year: 2026

Type: preprint

Abstract: Background Vitiligo is an acquired depigmenting disorder characterised by melanocyte loss. While immune responses against melanocytes are implicated in its pathogenesis, melanocyte detachment, melanocyte senescence and aberrant epidermal differentiation are increasingly characterised as additional pathological features. Granzyme B (GzmB), classically recognised as an intracellular effector of perforin-dependent cytotoxicity, is increased in vitiligo lesions; however, its extracellular contribution to vitiligo pathology remains unclear. Objectives To determine whether extracellular GzmB contributes to depigmentation and epidermal pathological features relevant to vitiligo, and to define its cellular source and underlying mechanisms. Methods Human vitiligo skin samples, murine depigmentation models and cultured human epidermal cells were analysed. The functional effects of extracellular GzmB were examined by subcutaneous administration of recombinant GzmB in mice. A rhododendrol (RD)-induced leukoderma model was used to evaluate the disease relevance of GzmB and the therapeutic effect of topical GzmB inhibition with VTI-1002. Results GzmB-positive cells were markedly increased in active vitiligo lesions and were predominantly associated with tryptase-positive cells, with limited co-distribution with CD8 or perforin. Vitiligo lesions also showed melanocyte detachment, increased p16 INK4A -positive melanocytes and aberrant keratinocyte differentiation. These pathological features were recapitulated in vivo by extracellular GzmB administration, accompanied by focal depigmentation. In cultured melanocytes, GzmB exerted no cytotoxic effects but reduced attachment strength and induced a senescence-associated phenotype characterised by decreased extracellular matrix- and adhesion-related gene expression, increased p16 INK4A level, elevated senescence-associated β-galactosidase activity and activation of transforming growth factor-β/SMAD signalling. In keratinocytes, extracellular GzmB promoted aberrant differentiation associated with activation of p53 signalling. Topical inhibition of GzmB in RD-induced leukoderma attenuated depigmentation progression, melanocyte detachment, melanocyte senescence and abnormal epidermal differentiation. Conclusions Extracellular GzmB promotes depigmentation associated with inducing melanocyte detachment, melanocyte senescence and aberrant keratinocyte differentiation. These findings identify extracellular GzmB as a previously underrecognised pathogenic mediator and potential therapeutic target in vitiligo-associated depigmentation. What is already known about this topic? Vitiligo is an acquired depigmenting disorder characterised by melanocyte loss. Although autoreactive immune responses are implicated in vitiligo, melanocyte detachment, melanocyte senescence and keratinocyte abnormalities are increasingly recognised as additional pathological features that may also contribute to depigmentation. Granzyme B is increased in vitiligo lesions, but whether extracellular granzyme B contributes to disease pathology independently of classical perforin-dependent cytotoxicity has not been tested. What does this study add? In active vitiligo lesions, granzyme B was increased and predominantly distributed to perforin-negative, tryptase-positive mast cells. Extracellular granzyme B induced focal depigmentation, melanocyte detachment, melanocyte senescence and aberrant keratinocyte differentiation. Pharmacological inhibition of extracellular granzyme B attenuated depigmentation progression and associated pathological changes in a rhododendrol-induced vitiligo-like mouse model. What is the translational message? Granzyme B contributes to melanocyte loss via extracellular mechanisms beyond classical intracellular cytotoxicity. These findings support topical inhibition of extracellular granzyme B as a potential local therapeutic strategy for active vitiligo. Abstract figure Abbreviated abstract (Teaser Text) In vitiligo, mast cell-associated extracellular granzyme B promotes depigmentation accompanied by melanocyte detachment, melanocyte senescence and aberrant keratinocyte differentiation. Topical granzyme B inhibition attenuates depigmentation and associated pathological changes in a rhododendrol-induced vitiligo-like mouse model, identifying extracellular granzyme B as a potential therapeutic target for depigmenting skin disease.

Source: bioRxiv (Cold Spring Harbor Laboratory)

DOI: 10.64898/2026.09.19.752829