Background: Dysbiosis and altered host-bacterial interactions are a common feature of intestinal inflammation. Spontaneous colitis in Interleukin 10 knockout (IL-10 KO) mice seems to be associated to the presence of dysbiosis. We assessed changes in gut commensal microbiota (GCM) and host-bacterial interaction systems (toll like receptors – TLR – and antimicrobial peptides – AMP) during colitis development in IL-10 KO mice.
Methods: Wild type (WT) and IL-10 KO mice were bread under barrier conditions; at 4-wk of age animals were moved to a conventional facility for an additional 8-wk period. Colitis and GCM were assessed in 4-wk-old (WT, n=5; KO, n=6) and 12-wk-old animals (WT, n=4; KO, n=5). GCM was evaluated from stools (pyrosequencing of 16S rDNA). Expression of pro-inflammatory markers (INF-γ, IL-12p40, TNF-α and iNOS), AMPs (regenerating islet-derived 3γ – Reg3γ – and defensin α6/24 – Defα6/24) and TLR2/3/4/5/7 was assessed by RT-qPCR.
Results: In 4-wk-old mice no signs of colitis were observed. GCM was similar in IL-10 KO and WT mice; with a predominance of Firmicutes (WT: 80%, IL-10 KO: 73%) and Bacteroidetes (WT: 17%, IL-10 KO: 25%). 12-wk-old IL-10 KO mice showed signs of colitis (increased relative colonic weight and histopathological scores; 100% incidence) and an up-regulation of pro-inflammatory markers vs. 10-wk-old WT mice. At this time, WT and IL-10 KO mice showed similar adaptive changes of their GCM (Firmicutes: 46% in WT, 30% in IL-10 KO; Bacteroidetes: 50% in WT, 68% in IL-10 KO). However, Verrucomicrobia (genus Akkermansia) increased significantly in IL-10 KO mice (95-fold vs. 3-fold in WT). Similarly, the genus Alistipes (phylum Bacteroidetes) appeared in the WT at detectable levels and increased by 50-fold in IL-10 KO mice. Verrucobacteria (p<0.001) and Alistipes (p<0.01) proportions correlated positively with histopathological scores. 12-wk-old IL-10 KO mice showed a general down-regulation of TLRs (50–75% vs. WT, p<0.001 in all cases), an up-regulation of the AMP Reg3γ (12-fold vs. WT, p<0.001) and a down-regulation of Defα6/24 (0.8-fold vs. WT; p<0.05).
Conclusions: When moved to standard conditions, similar adaptive changes of GCM were observed in WT and IL-10 KO mice, although only IL-10 KO mice developed colitis. Increased proportions of Verrucobacteria and Alistipes were observed in IL-10 KO mice with colitis. Colitic IL-10 KO mice showed also alterations in host-bacterial interaction systems. These observations support the implication of Verrucobacteria and Alistipes in intestinal inflammation, although the cause-effect relationship remains unclear. Dysbiosis and altered host-bacterial interactions might contribute to the development and maintenance of intestinal inflammation.