Background/Purpose: It has been well established that a close relationship exists between gut inflammation and spondyloarthropathies. Polymorphisms in the receptor for IL23 are associated not only with ankylosing spondylitis (AS) but also with inflammatory bowel disease (IBD). AS and IBD are both associated with elevated concentrations of serum IL23. Moreover, IL23 is active at mucosal surfaces and is produced by the gut, suggesting that the intestinal mucosa could be a key site of IL23 production in spondyloarthropathy. Minicircles are small circular DNA vectors which can be used in vivo to provide for long-term transient expression of transgenes without the risk of immunogenic responses that can be caused by the bacterial backbone in standard plasmids. Recently, Sherlock et al. demonstrated that overexpression of IL23 using minicircle DNA technology in the hepatocytes of mice was sufficient to lead to severe entheseal inflammation with infiltra­tion by macrophages and neutrophils, and expansion of periosteal osteoblasts. Disease features included sacroiliitis, axial enthesi­tis, psoriasis, and aortic root inflammation. However, no gut phenotype was reported. 

Methods: IL23 minicircle DNA vector or empty vector was administered via hydrodynamic injection to adult B10RIII female mice obtained from Jackson Labs (Bar Harbor, ME).   A volume equivalent of 10% body mass (~2mL) was injected IV to the lateral tail vein in 6-8 seconds to facilitate cellular uptake of material.  Mice were monitored daily for signs of arthritis and skin lesions.  Arthritis severity was graded using a 0-4 score per paw for a maximum score of 16. Upon sacrifice (14 and 28 days), serum was collected for cytokine analysis, paw and gut  tissue for histologic assessment (Bolder Biopath, Boulder, CO), skin, entheses and gut tissues for mRNA analysis via RT-PCR.  

Results: IL-23 overexpression using minicircle DNA transfection resulted in a similar rapid and pronounced rheumatic and skin phenotype as previously reported (e.g. development of synovitis, enthesitis, and psoriatic-like skin lesions). In addition, sustained and elevated serum concentration of IL23 is associated with intestinal inflammation. Significant and region specific gut expression of IL23 pathway associated genes IL17A, IL17F & IL22 induced by IL23 overexpression was demonstrated, with maximal expression seen in proximal ileum and lesser expression seen in colon. Furthermore, ileum expression of disease associated genes S100A8 and REG3g were increased with IL23 overexpression versus empty vector control. Histologic analysis also demonstrated region specific gut pathology, with colons displaying none to minimal inflammation and ileums displaying minimal to moderate inflammation with crypt abscesses, mild hyperplasia and inflammatory infiltrates in the lamina propria, characteristic of features seen in IBD. 

Conclusion: These studies demonstrate that minicircle DNA transfection offers a powerful tool for interrogating molecular and tissue specific mechanisms in vivo and provides opportunities to dissect the influence of the IL-23 pathway on the inflammatory gut-joint link seen in spondyloarthropathies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/il23-overexpression-demonstrates-gut-joint-inflammation-link-and-increased-expression-of-spondyloarthopathy-associated-genes-in-vivo/