Keratinocyte-derived anosmin-1, an extracellular glycoprotein encoded by the X-linked Kallmann syndrome gene, is involved in modulation of epidermal nerve density in atopic dermatitis

Abstract 

Background

Epidermal nerve density is increased in atopic dermatitis (AD), suggesting that the hyperinnervation is partly responsible for abnormal itch perception. It is probably controlled by axonal guidance molecules produced by keratinocytes. An extracellular matrix glycoprotein anosmin-1 encoded by KAL1 has chemoattractive or chemorepulsive effects on different neuronal types.

Objective

This study was performed to investigate the roles of anosmin-1 in skin innervation.

Methods

Rat dorsal root ganglion (DRG) neurones were cultured in conditioned medium from control or KAL1-overexpressing cells for neurite outgrowth assay. KAL1 expression in cultured epidermal keratinocytes or human skin was examined by quantitative RT-PCR (qRT-PCR). Anosmin-1 distribution in normal and atopic skin was examined immunohistochemically. The effects of calcium concentrations and cytokines on KAL1 expression in cultured normal human epidermal keratinocytes (NHEK) were analysed by qRT-PCR.

Results

Neurite outgrowth in cultured DRG neurones was inhibited by conditioned medium from KAL1-overexpressing cells, while it was rescued by addition of recombinant fibroblast growth factor receptor 1 for capturing anosmin-1. KAL1 transcripts were expressed in cultured keratinocytes or in normal skin. Anosmin-1 was strongly expressed in the basal cell layer of normal skin, but decreased in atopic skin, concomitant with increases of epidermal nerve fibres. KAL1 expression was downregulated during keratinocyte differentiation. The expression was also upregulated by interleukin-4 (IL-4), IL-13 or transforming growth factor (TGF)-β1. TGF-β1 acted synergistically with IL-13 to enhance KAL1 expression, while interferon-γ inhibited its expression.

Conclusion

Anosmin-1 produced by epidermal keratinocytes in response to calcium concentrations or cytokines may modulate epidermal nerve density in AD.

Abbreviations: AD, atopic dermatitis, DRG, dorsal root ganglion, FGFR1, fibroblast growth factor receptor 1, GnRH, gonadotropin-releasing hormone, IFN-γ, interferon-γ, IL, interleukin, K10, keratin 10, K14, keratin 14, KAL1, Kallmann syndrome 1 sequence, NHEK, normal human epidermal keratinocytes, NGF, nerve growth factor, PBS, phosphate buffered saline, PGP9.5, protein gene product 9.5, RT-PCR, reverse transcription-polymerase chain reaction, SD, standard deviation, Sema3A, semaphorin 3A, STAT6, signal transducer and activator of transcription 6, TGF-β1, transforming growth factor-β1, TNF-α, tumour necrosis factor-α

Keywords: KAL1, Nerve fibres, Calcium, Cytokines, Epidermal keratinocytes, Pruritus