Lipocalin2 deficiency results in colitis exacerbation and tumor development in IL-10 mice by Alistipes overgrowth

Introduction & Aims: Accumulating evidence suggests that the intestinal microbiota plays a key role in the initiation and progression of colitis and furthermore colitis associated cancer (CAC). Host factors promoting or preventing disease are a matter of intense research. The protein Lipocalin2 (Lcn2) is highly upregulated during inflammatory conditions and inhibits bacterial growth by sequestration of siderophore-bound iron. However its impact on gut immunity and on the microbiota during intestinal inflammation remains unclear.

In this study we investigated the functional contribution of Lcn2 in the colon and its influence on the gut microbiota during chronic Interleukin-10 (IL-10) colitis.

Methods: IL-10/Lcn2-double deficient mice were generated and colitis development was investigated over time. The gut microbial composition was analysed by 16S rRNA-sequencing. 5-ethynyl-2'-deoxyuridine (EdU) labelled Alistipes finegoldii were used for short- and longterm mono association studies in IL-10 mice. Bacteria were visualized using click-it chemistry and FISH technology on a LSM confocal microscopy. In vitro, Alistipes finegoldii were grown in an iron supplemented or restricted medium with or without recombinant Lcn2.

Results: Lcn2/IL10 animals showed exacerbated colitis and spontaneous emergence of right-sided tumor formation. Further animals exhibited a profound alteration of microbial community structure and expansion of Alistipes species. In IL-10 mice, Alistipes spp. were capable of mimicking disease in short-term experiments and further resulted in tumor formation when supplied long-term. In vitro, Alistipes were dependent on siderophore-bound iron and growth was inhibited by recombinant Lcn2.

Conclusions: Absence of Lcn2 leads to a marked alteration of the intestinal microbiota and entails the presence of Alistipes spp. in IL10 colitis. Alistipes spp. thrive in an inflamed environment, are dependant on siderophore-bound iron from its environment and can be suppressed by Lcn2. Our data suggest that Lcn2 acts as an antimicrobial protein that limits inflammation and colitis-associated cancer in the IL-10 model of colitis.