Psychological stress exacerbates vitiligo via dysregulated proteolysis of substance P and MRGPRX2-dependent mast cell activation.

BACKGROUND

The impact of psychological stress on vitiligo progression remains poorly understood.

OBJECTIVE

We investigated the effects of substance P (SP) and its proteolytic fragments (SP1-9 and SP1-7) on mast cell activation and vitiligo exacerbation.

METHODS

Skin specimens were biopsied from patients with active vitiligo, or from mice subjected to chronic restraint stress (CRS). A tyrosinase-related protein (Tyrp)-2180-188 peptide-induced vitiligo model was established in wild-type (WT) and in Mas-related G protein-coupled receptor-B2 (MrgprB2, MRGPRX2 in humans) knockout mice. Cultured keratinocytes (KCs), fibroblasts (FBs), and SH-SY5Y sensory neuronal-like cells were used in this study. The SP+ protein gene product 9.5 (PGP9.5)+ sensory innervation and the mast cell and CD8+ T cell counts were measured via dual immunofluorescence staining. Protein levels of matrix metalloproteinase (MMP)-9 and neprilysin in skin tissue homogenates from vitiligo patients or from CRS-treated vitiligo mice were measured by western blotting. In vitro proteolysis of SP was profiled by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and mast cell activation was assessed via flow cytometry.

RESULTS

Increased SP+PGP9.5+ innervation and mast cells were observed in active vitiligo lesions and CRS-treated mouse skin. Intradermal injection of full-length SP and SP1-9, but not SP1-7, activated mast cells and worsened depigmentation. MrgprB2-/- mice showed reduced melanocyte loss and CD8+ T cell infiltration versus WT. MRGPRX2-silenced mast cells failed to produce IFNγ upon SP stimulation. LC-MS/MS revealed that KCs-derived MMP9, but not FBs-derived neprilysin, preferentially generated the pro-inflammatory SP1-9 fragment.

CONCLUSION

The SP-MRGPRX2 signaling axis represents a critical link between psychological stress and vitiligo progression.