Gut epithelial barrier dysfunction in lupus triggers a differential humoral response against gut commensals

D-beta-hydroxybutyrate up-regulates Claudin-1 and alleviates the intestinal hyperpermeability in lipopolysaccharide-treated mice

The hyperpermeability of intestinal epithelium is a key contributor to the occurrence and development of systemic inflammation. Although D-beta-hydroxybutyrate (BHB) exhibits various protective effects, whether it affects the permeability of intestinal epithelium in systemic inflammation has not been clarified. In this study, we investigated the effects of BHB on the intestinal epithelial permeability, the epithelial marker E-cadherin and the tight junction protein Claudin-1 in colon in the lipopolysaccharide (LPS)-induced systemic inflammation mouse model. Intraperitoneal injection of LPS was used to induce systemic inflammation and BHB was given by oral administration. The permeability of intestinal epithelium, the morphological changes of colonic epithelium, the distribution and generation of colon E-cadherin, and the Claudin-1 generation and its epithelial distribution in colon were detected. The results confirmed the intestinal epithelial hyperpermeability and inflammatory changes in colonic epithelium, with disturbed E-cadherin distribution in LPS-treated mice. Besides, colon Claudin-1 generation was decreased and its epithelial distribution in colon was weakened in LPS-treated mice. However, BHB treatments alleviated the LPS-induced hyperpermeability of intestinal epithelium, attenuated the colonic epithelial morphological changes and promoted orderly distribution of E-cadherin in colon. Furthermore, BHB up-regulated colon Claudin-1 generation and promoted its colonic epithelial distribution and content in LPS-treated mice. In conclusion, BHB may alleviate the hyperpermeability of intestinal epithelium via up-regulation of Claudin-1 in colon in LPS-treated mice.

Dietary tryptophan and genetic susceptibility expand gut microbiota that promote systemic autoimmune activation

Tryptophan modulates disease activity and the composition of microbiota in the B6.Sle1.Sle2.Sle3 (TC) mouse model of lupus. To directly test the effect of tryptophan on the gut microbiome, we transplanted fecal samples from TC and B6 control mice into germ-free or antibiotic-treated non-autoimmune B6 mice that were fed with a high or low tryptophan diet. The recipient mice with TC microbiota and high tryptophan diet had higher levels of immune activation, autoantibody production and intestinal inflammation. A bloom of Ruminococcus gnavus (Rg), a bacterium associated with disease flares in lupus patients, only emerged in the recipients of TC microbiota fed with high tryptophan. Rg depletion in TC mice decreased autoantibody production and increased the frequency of regulatory T cells. Conversely, TC mice colonized with Rg showed higher autoimmune activation. Overall, these results suggest that the interplay of genetic and tryptophan can influence the pathogenesis of lupus through the gut microbiota.