The Role of Intestinal Microbiota in the Pathogenesis of Spondyloarthritis
Haley, Emma K.
2019
- Background: Spondyloarthritis (SpA) is a family of inflammatory rheumatic diseases that variably target the spine, joints, skin and intestine. Overexpression of IL-23 by means of hydrodynamic tail vein injection of IL-23 minicircles (EEV) into adult mice results in a SpA-like disease. The impact of microbiota on inflammatory diseases including SpA has gained much attention over the last few ... read moreyears. In many animal models of arthritis or colitis, disease is absent when animals are raised in a germ-free environment. In other models, short chain fatty acids (SCFA), a product of intestinal bacteria, ameliorate inflammation. To optimize the use of the IL- 23 minicircle model in future studies, we first determined the impact of sex and IL-23 EEV dosage on the development of arthritis. The main focus of this study was manipulation of the intestinal microbiota with antibiotics to determine the impact of microbiota on arthritis development. Methods: We hydrodynamically injected male and female mice at 8-12 weeks of age with 0.5 μg of IL-23 EEV. For the IL-23 EEV dose comparison, 0.5 μg, 0.05 μg, or 0.005 μg were injected. Control mice received no EEV. We monitored the development of disease by measuring clinical arthritis scores, paw swelling, and body weight every other day. Animals were euthanized after two weeks. We harvested skin, joints and colon for histology and gene expression analysis by qPCR. Spleen and colon were weighed, and cell frequencies in the spleen were determined by flow cytometry. Serum IL- 23 levels were measured using a commercial ELISA. Vancomycin (0.5 g/l), Gentamicin (1g/l), a Vancomycin/Gentamicin cocktail, or SCFA mix (67.5mM acetate, 40mM Butyrate, 25.9mM Propionate) were prepared fresh every week and delivered orally in the drinking water. Antibiotics and SCFA were started 2 weeks prior to EEV injection. Fecal samples were collected before antibiotics or SCFA were started and then weekly until euthanasia. DNA was extracted from fecal samples, and bacterial strains were analyzed by qPCR. Results: Male mice developed arthritis within 4-6 days after IL-23 EEV injection. Mice lost ~20% of body over two weeks, developed colitis and had enlarged spleens. Neutrophils, dendritic cells, and macrophages were upregulated in the spleen of male mice injected with IL- 23 EEV. Consistent with the observed clinical phenotype, mice injected with IL-23 EEV had increased expression of TNF, IL-1β, IL-17A, IL-22 in arthritic joints. Female mice developed more severe arthritis than male mice, and the female mice did not lose weight even though they had similar colitis. Interestingly, male mice injected with 0.05 μg IL-23 EEV had more severe arthritis than mice injected with 0.5 μg even though their serum IL-23 levels were only 2% compared with the 0.5 μg group. Vancomycin and Gentamicin treated mice had lower clinical scores than H2O treated mice, but SCFA treated mice had similar arthritis severity to H2O treated mice. H2O, Vancomycin, and Gentamycin treated mice had colitis, but only H2O and Vancomycin treated mice had enlarged spleens. There was a significant decrease in the frequency of macrophages in the spleens of male mice injected with IL-23 EEV treated with Gentamicin compared to H2O treated mice. Also, IL-1b gene expression was significantly decreased in the wrists and skin of Gentamicin treated mice compared to H2O treated mice. Conclusion: Myeloid cells (neutrophils, dendritic cells, and macrophages) are the cell types that result in the enlargement of the spleens seen in our arthritis model. Female mice developed more severe arthritis than males. SCFA treatment does not attenuate arthritis in our murine model, contradictory of what was expected, considering the beneficial results seen from SCFA treatment in other references. Decreased arthritis severity after antibiotic treatment indicates a role of the microbiota in the pathogenesis of SpA. The decreased arthritis severity seen in the Gentamicin treated mice compared to the disease seen in the H2O and Vancomycin treated mice suggests a specific role of gram-negative bacteria in the pathogenesis of SpA.read less
- ID:
- v979vg778
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- TARC Citation Guide EndNote
