Inhibition of Interleukin-10 Signaling Induces Microbiota-dependent Chronic Colitis in Apolipoprotein E Deficient Mice (1)
Inflammatory bowel diseases (IBDs) are widely believed to be due to the breakdown of tolerance to commensal microbiota, resulting in dysregulated immune cell infiltration into the mucosa that drives intestinal pathology. Persistent secretion of proinflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8, and tumor necrosis alpha (TNFa) into the inflamed gut further exacerbates.
Apolipoprotein E (ApoE), is a 34-kDa secreted protein, participates in the transport of plasma lipids by binding to very low-density lipoprotein and chylomicrons. ApoE-deficient (ApoE-KO) mice develop spontaneous atherosclerosis and had become one of the widely used mouse model to study atherosclerosis. In addition, ApoE was shown to mediate the suppression of T cell proliferation and maintain Th1/Th2 balance. ApoE modulates macrophage polarization by favoring the establishment of alternatively activated antiinflammatory M2 macrophages over the proinflammatory M1 macrophages. ApoE also counterregulates the systemic upregulation of proinflammatory cytokines IL-6, IL-12, TNFa, and interferon-gamma (IFNg) in response to lipopolysaccharide (LPS) and polyinosinic polycytidylic acid challenge, which respectively activates the Toll-like receptor (TLR)-4 and TLR3 responses in mice.
Interleukin-10 (IL-10) is a pleiotropic antiinflammatory cytokine that displays inhibitory effects on the functions of Th1 cells, NK cells, and macrophages. IL-10 is required to maintain immune tolerance in the gut and prevent unregulated/aberrant inflammatory responses and their consequent tissue damage.
For the induction of acute colitis,8-week-old male ApoE-KO mice and WT littermates were administered a single injection of IL-10R antibody (1.0 mg/mouse, intraperitoneally) and euthanized after 1 week. Although aIL-10R treatment induced colitis development, the specificity of such phenotype may not be limited to only ApoE-KO mice.
For the induction of chronic colitis, 4-week-old ApoE-KO mice and WT littermates were given 4 weekly intraperitoneal injections of IL-10R antibody and euthanized 1 week after the fourth injection. WT mice are resistant to IL-10R neutralization-induced chronic colitis; WT mice did not display significant changes in the analyzed colitic parameters, except in fecal
Lcn2 in response to aIL-10R treatment.
ApoE-KO mice and their littermates receiving 4 weekly injections aIL-10R were administered a broad-spectrum antibiotic cocktail (1.0 g/L ampicillin; 0.5 g/L neomycin) in the drinking water 2 weeks before the first injection and maintained throughout the duration of the study. The Abx+aIL-10R-treated ApoE-KO mice were able to gain body weight normally over time and were significantly protected from developing colitis as evident by the lack of spleen enlargement and colon thickening. The levels of colonic IFNg and TNFa mRNA in Abx+aIL-10R-treated ApoE-KO mice were significantly mitigated compared with their counterparts without antibiotics treatment.
IL-10KO mice with either WT or ApoE-KO mice (cohoused IL10KO mice are hereafter named as KO/CoH-WT and KO/CoHApoE-KO). After 4 weeks of cohousing, 50% of the KO/CoH-ApoE-KO mice developed rectal prolapse, a severe irreversible form of colitis. KO/CoH-ApoE-KO mice also developed classical symptoms of colitis including lack of body weight gain, splenomegaly, and colomegaly.
ApoE-KO mice harbor an elevated gut microbiotal burden and an altered composition with a notably higher relative abundance of Bacteroidetes. The increase in the members of the gram-negative Bacteroidetes phyla has been suggested to correlate with the risk of colitis. Elevated serum immunoreactivity against flagellin and LPS in aIL-10R-induced colitic ApoE-KO mice suggested increased translocation of bacteria and/or their products that may further drive the disease. Sharing of microbiota between cohoused ApoE-KO and IL-10KO mice accelerated the induction of chronic inflammation in IL-10KO mice, confirming that ApoE-KO mice harbor a transmissible colitogenic microbiota. Both ApoE and IL-10 have been independently demonstrated to promote the establishment of alternatively activated antiinflammatory M2 macrophage while inactivating the proinflammatory M1 macrophage. It is possible that both ApoE and IL-10 may have similar and overlapping functions that are not limited to atherosclerosis, but also apply to other inflammatory processes as well.
Several ApoE mimetic peptides were designed and have been tested to be bioactive in binding lipoprotein and clearing cholesterol from circulation. The antiinflammatory properties of ApoE mimetic peptides were also demonstrated in murine models of multiple sclerosis. ApoE and IL-10 maintain gut microbiota homeostasis and the crosstalk modulates a critical inflammatory axis in IBD and possibly other inflammatory disorders.