Mucin Muc2 Deficiency and Weaning Influences the Expression of the Innate Defense Genes Reg3β, Reg3γ and Angiogenin-4

Background: Mucin Muc2 is the structural component of the intestinal mucus layer. Absence of Muc2 leads to loss of this layer allowing direct bacterial-epithelial interactions. We hypothesized that absence of the mucus layer leads to increased expression of innate defense peptides. Specifically, we aimed to study the consequence of Muc2 deficiency (Muc2(-/-)) on the expression of regenerating islet-derived protein 3 beta (Reg3 beta), regenerating islet-derived protein 3 gamma (Reg3 gamma), and angiogenin-4 (Ang4) in the intestine shortly before and after weaning. Methods: Intestinal tissues of Muc2(-/-) and wild-type (WT) mice were collected at postnatal day 14 (P14, i.e. pre-weaning) and P28 (i.e. post-weaning). Reg3 beta, Reg3 gamma, and Ang4 expression was studied by quantitative real-time PCR, Western-blot, in situ hybridization, and immunohistochemistry. Results: Reg3 beta and Reg3 gamma were expressed by diverging epithelial cell types; namely enterocytes, Paneth cells, and goblet cells. Additionally, Ang4 expression was confined to Paneth cells and goblet cells. Expression of Reg3 beta, Reg3 gamma, and Ang4 differed between WT and Muc2(-/-) mice before and after weaning. Interestingly, absence of Muc2 strongly increased Reg3 beta and Reg3 gamma expression in the small intestine and colon. Finally, morphological signs of colitis were only observed in the distal colon of Muc2(-/-) mice at P28, where and when expression levels of Reg3 beta, Reg3 gamma, and Ang4 were the lowest. Conclusions: Expression of Reg3 proteins and Ang4 by goblet cells point to an important role for goblet cells in innate defense. Absence of Muc2 results in up-regulation of Reg3 beta and Reg3 gamma expression, suggesting altered bacterial-epithelial signaling and an innate defense response in Muc2(-/-) mice. The inverse correlation between colitis development and Reg3 beta, Reg3 gamma, and Ang4 expression levels might point toward a role for these innate defense peptides in regulating intestinal inflammation.