High-fat diet induces follicular hyperkeratinization and predisposes to develop neutrophilic folliculitis in mice.

Abstract Background Neutrophilic folliculitis is an inflammatory condition of hair follicles. In some neutrophilic folliculitis, such as acne and hidradenitis suppurativa, follicular hyperkeratosis is also observed. Neutrophilic folliculitis is often induced and/or exacerbated by high-fat diet (HFD). However, the molecular mechanisms by which HFD affects neutrophilic folliculitis are not fully understood. Objective To elucidate how HFD promotes the development of neutrophilic folliculitis. Methods Mice were fed with HFD, and the skin was subjected to histological, RNA-sequencing and imaging mass spectrometry analyses. Phorbol 12-myristate 13-acetate (PMA) was used as an irritant to the skin to examine the effect of HFD on neutrophil accumulation around the hair follicles. Results Histological analysis revealed follicular hyperkeratosis in the skin of HFD-fed mice. RNA-sequencing analysis showed that genes related to keratinization, especially in upper hair follicular keratinocytes, were significantly upregulated in HFD-fed mice. Application of PMA to the skin induced neutrophilic folliculitis in HFD-fed mice, but not in normal diet (ND)-fed mice. Accumulation of neutrophils in the skin and around hair follicles was dependent on CXCR2 signaling, and CXCL1, a CXCR2 ligand, was produced mainly by hair follicular keratinocytes. Imaging mass spectrometry analysis revealed an increase of fatty acids in the skin, including oleic acids and palmitoleic acids in HFD-fed mice. Application of these fatty acids to the skin induced follicular hyperkeratosis, and caused PMA-induced neutrophilic folliculitis even in ND-fed mice. Conclusion HFD can facilitate the development of neutrophilic folliculitis with the induction of hyperkeratosis of hair follicles and increased neutrophil infiltration around the hair follicles via CXCR2 signaling.