VIP, whose receptor-mediated signalling may be defective in alopecia areata, provides protection from hair follicle immune privilege collapse

Summary

Background

Alopecia areata (AA) is an autoimmune disorder whose pathogenesis involves the collapse of the relative immune privilege (IP) of the hair follicle (HF). Given that vasoactive intestinal peptide (VIP) is an immunoinhibitory neuropeptide released by perifollicular sensory nerve fibres, which plays a role in IP maintenance, it may modulate human HF-IP and thus therapeutically relevant for AA.

Objectives

Do human HFs express VIP receptors, and does their stimulation protect from or restore experimentally induced HF-IP collapse? Is VIP signalling defective in AA HFs?

Methods

First, VIP and VIP receptors (VPAC1, VPAC2) expression in human scalp HFs and AA skin was assessed. In HF organ culture, we then explored whether VIP treatment can restore and/or protect from interferonγ-induced HF-IP collapse, assessing the expression of the key IP markers by quantitative (immuno-)histomorphometry.

Results

Here, we provide the first evidence that VIP receptors are expressed in the epithelium of healthy human HFs at the gene and protein level and that VIP receptor protein expression, but not VIP⁺ nerve fibres, is significantly down-regulated in lesional hair bulbs of AA patients, suggesting defects in VIP receptor-mediated signalling. Moreover, we show that VIP protects the HF from experimentally induced IP collapse in vitro, but does not fully restore it once collapsed.

Conclusions

These pilot data suggest that insufficient VIP receptor-mediated signalling may contribute to impairing HF-IP in AA patients and that VIP is a promising candidate “HF-IP guardian” that may be therapeutically exploited to inhibit the progression of AA lesions

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