Interleukin-23 (IL-23), an IL-12 family cytokine, plays pivotal roles in pro-inflammatory T helper 17 cell responses linked to autoimmune and inflammatory diseases. Despite intense therapeutic targeting, structural and mechanistic insights into receptor complexes mediated by IL-23, and by IL-12 family members in general, have remained elusive. We determined a crystal structure of human IL-23 in complex with its cognate receptor, IL-23R, and revealed that IL-23R bound to IL-23 exclusively via its N-terminal immunoglobulin domain. The structural and functional hotspot of this interaction partially restructured the helical IL-23p19 subunit of IL-23 and restrained its IL-12p40 subunit to cooperatively bind the shared receptor IL-12Rβ1 with high affinity. Together with structural insights from the interaction of IL-23 with the inhibitory antibody briakinumab and by leveraging additional IL-23:antibody complexes, we propose a mechanistic paradigm for IL-23 and IL-12 whereby cognate receptor binding to the helical cytokine subunits primes recruitment of the shared receptors via the IL-12p40 subunit.
Local ROCK inhibition prevents and reverses intestinal fibrosis by diminishing MRTF and p38 MAPK activation and increasing autophagy in fibroblasts. Overall, our results show that local ROCK inhibition is promising for counteracting fibrosis as an add-on therapy for CD.
The promising results seen in studies of secondary bile acids in experimental colitis suggest that they may represent an attractive and safe class of drugs for the treatment of inflammatory bowel diseases (IBD). However, the exact mechanism by which bile acid therapy confers protection from colitogenesis is currently unknown. Since the gut microbiota plays a crucial role in the pathogenesis of IBD, and exogenous bile acid administration may affect the community structure of the microbiota, we examined the impact of the secondary bile acid ursodeoxycholic acid (UDCA) and its taurine or glycine conjugates on the fecal microbial community structure during experimental colitis. Daily oral administration of UDCA, tauroursodeoxycholic acid (TUDCA), or glycoursodeoxycholic acid (GUDCA) equally lowered the severity of dextran sodium sulfate-induced colitis in mice, as evidenced by reduced body weight loss, colonic shortening, and expression of inflammatory cytokines. Illumina sequencing demonstrated that bile acid therapy during colitis did not restore fecal bacterial richness and diversity. However, bile acid therapy normalized the colitis-associated increased ratio of Firmicutes to Bacteroidetes. Interestingly, administration of bile acids prevented the loss of Clostridium cluster XIVa and increased the abundance of Akkermansia muciniphila, bacterial species known to be particularly decreased in IBD patients. We conclude that UDCA, which is an FDA-approved drug for cholestatic liver disorders, could be an attractive treatment option to reduce dysbiosis and ameliorate inflammation in human IBD.IMPORTANCE Secondary bile acids are emerging as attractive candidates for the treatment of inflammatory bowel disease. Although bile acids may affect the intestinal microbial community structure, which significantly contributes to the course of these inflammatory disorders, the impact of bile acid therapy on the fecal microbiota during colitis has not yet been considered. Here, we studied the alterations in the fecal microbial abundance in colitic mice following the administration of secondary bile acids. Our results show that secondary bile acids reduce the severity of colitis and ameliorate colitis-associated fecal dysbiosis at the phylum level. This study indicates that secondary bile acids might act as a safe and effective drug for inflammatory bowel disease.
Butyricicoccus is a mucosa-associated bacterial genus under-represented in colonic mucosa of patients with active UC, whose activity inversely correlates with CLDN1 expression. Butyrate and B. pullicaecorum conditioned medium reduce CLDN1 expression, supporting its use as a pharmabiotic preserving epithelial TJ integrity.
Ulcerative colitis (UC) is characterized by increased epithelial cell death and subsequent breakdown of the intestinal epithelial barrier, which perpetuates chronic intestinal inflammation. Since fecal bile acid dysmetabolism is associated with UC and tauroursodeoxycholic acid (TUDCA) has been shown to improve murine colitis, we evaluated the effect of TUDCA on intestinal epithelial cell death in a mouse model of UC-like barrier dysfunction elicited by dextran sulfate sodium (DSS). We identified the prevention of colonic caspase-3 induction, a key proapoptotic marker which was also over-activated in UC, as the earliest event resulting in a clear clinical benefit. Whereas vehicle-treated mice showed a cumulative mortality of 40%, all TUDCA-treated mice survived the DSS experiment during a 14-day follow-up period. In line with a barrier protective effect, TUDCA decreased bacterial translocation to the spleen and stimulated mucin production. Similarly, TUDCA inhibited lipopolysaccharide-induced intestinal permeability and associated enterocyte apoptosis. The anti-apoptotic effect was confirmed in vitro by a dose-dependent inhibition of both receptor-dependent (using tumor necrosis factor and Fas ligand) and receptor-independent (staurosporine) caspase-3 induction in HT29 colonic epithelial cells. These data imply that caspase-3 activation is an early marker of colitis that is prevented by TUDCA treatment. These data, together with the previously reported beneficial effect in colitis, suggest that TUDCA could be an add-on strategy to current immunosuppressive treatment of UC patients.
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