Transepithelial Barrier Dysfunction Drives Microbiota Dysbiosis to Initiate Epithelial Clock-driven Inflammation

BACKGROUND: Factors that contribute to inflammatory bowel disease [IBD] pathogenesis include genetic polymorphisms, barrier loss, and microbial dysbiosis. A major knowledge gap exists in the origins of the colitogenic microbiome and its relationship with barrier impairment. Epithelial myosin light chain kinase [MLCK] is a critical regulator of the paracellular barrier, but the effects of MLCK activation on the intraepithelial bacteria [IEB] and dysbiosis are incompletely understood. We hypothesise that MLCK-dependent bacterial endocytosis promotes pathobiont conversion and shapes a colitogenic microbiome. METHODS: To explore this, transgenic [Tg] mice with barrier loss induced by intestinal epithelium-specific expression of a constitutively active MLCK were compared with wild-type [WT] mice. RESULTS: When progeny of homozygous MLCK-Tg mice were separated after weaning by genotype [Tg/Tg, Tg/WT, WT/WT], increased IEB numbers associated with dysbiosis and more severe colitis were present in Tg/Tg and Tg/WT mice, relative to WT/WT mice. Cohousing with MLCK-Tg mice induced dysbiosis, increased IEB abundance, and exacerbated colitis in WT mice. Conversely, MLCK-Tg mice colonised with WT microbiota at birth displayed increased Escherichia abundance and greater colitis severity by 6 weeks of age. Microarray analysis revealed circadian rhythm disruption in WT mice co-housed with MLCK-Tg mice relative to WT mice housed only with WT mice. This circadian disruption required Rac1/STAT3-dependent microbial invasion but not MLCK activity, and resulted in increased proinflammatory cytokines and glucocorticoid downregulation. CONCLUSIONS: The data demonstrate that barrier dysfunction induces dysbiosis and expansion of invasive microbes that lead to circadian disruption and mucosal inflammation. These results suggest that barrier-protective or bacterium-targeted precision medicine approaches may be of benefit to IBD patients.