Ultraviolet Irradiation of Skin Alters the Faecal Microbiome Independently of Vitamin D in Mice.

Simon Ghaly,Frances Lloyd,Cynthia Forest,Prue Hart,Lavinia Gordon,Ian Lawrance,Nadeem Kaakoush

doi:10.3390/nu10081069

Abstract

Reduced sunlight exposure has been associated with an increased incidence of Crohn’s disease and ulcerative colitis. The effect of ultraviolet radiation (UVR) on the faecal microbiome and susceptibility to colitis has not been explored. C57Bl/6 female mice were fed three different vitamin D-containing diets for 24 days before half of the mice in each group were UV-irradiated (1 kJ/m2) for each of four days, followed by twice-weekly irradiation of shaved dorsal skin for 35 days. Faecal DNA was extracted and high-throughput sequencing of the 16S RNA gene performed. UV irradiation of skin was associated with a significant change in the beta-diversity of faeces compared to nonirradiated mice, independently of vitamin D. Specifically, members of phylum Firmicutes, including Coprococcus, were enriched, whereas members of phylum Bacteroidetes, such as Bacteroidales, were depleted. Expression of colonic CYP27B1 increased by four-fold and IL1β decreased by five-fold, suggesting a UVR-induced anti-inflammatory effect. UV-irradiated mice, however, were not protected against colitis induced by dextran sodium sulfate (DSS), although distinct faecal microbiome differences were documented post-DSS between UV-irradiated and nonirradiated mice. Thus, skin exposure to UVR alters the faecal microbiome, and further investigations to explore the implications of this in health and disease are warranted.

Highlights

The health of the gastrointestinal tract is dependent on the bidirectional interaction between gut microbial antigens and the intestinal immune system to maintain homeostasis or “physiological inflammation”
C57Bl/6 mice, with an increase in the relative quantities of Bacteroidetes, Firmicutes, Actinobacteria, and Gammaproteobacteria in naïve, noncolitic mice [6]. This group has recently demonstrated reduced global β-diversity in faeces from mice fed diets with high vitamin D content compared to no vitamin D, as well as 40 microbial taxa that were significantly different between the groups [7]
Nonmetric multidimensional scaling (NMDS) plot of the Bray–Curtis resemblance matrix following square-root transformation of relative abundance data showed an outlier control mouse in the D+ultraviolet radiation (UVR)− group which was removed from all further analyses

Summary

Introduction

The health of the gastrointestinal tract is dependent on the bidirectional interaction between gut microbial antigens and the intestinal immune system to maintain homeostasis or “physiological inflammation”. In inflammatory bowel disease (IBD), Crohn’s disease (CD), and ulcerative colitis (UC), there is a dysregulated immune response against luminal antigens leading to uncontrolled inflammation. C57Bl/6 mice, with an increase in the relative quantities of Bacteroidetes, Firmicutes, Actinobacteria, and Gammaproteobacteria in naïve, noncolitic mice [6]. This group has recently demonstrated reduced global β-diversity in faeces from mice fed diets with high vitamin D content compared to no vitamin D, as well as 40 microbial taxa that were significantly different between the groups [7]

Methods

Results

Conclusion