Aims/hypothesis: Accumulation of adipose tissue macrophages is considered pivotal in the development of obesity-associated inflammation and insulin resistance. In addition, recent studies suggest an involvement of the intestine as the primary organ in inducing hyperglycaemia and insulin resistance. We have reported that the C-C motif chemokine receptor (CCR) CCR9 is associated with intestinal immunity and has a pathogenic role in various liver diseases. However, its contribution to type 2 diabetes is unknown. In the current study, we aimed to clarify the involvement of CCR9 in the pathology of type 2 diabetes and the potential underlying mechanisms.
Methods: To elucidate how CCR9 affects the development of metabolic phenotypes, we examined the impact of CCR9 deficiency on the pathogenesis of type 2 diabetes using male C57BL/6J (wild-type [WT]) and CCR9-deficient (CCR9 knockout [KO]) mice fed a 60% high-fat diet (HFD) for 12 weeks.
Results: WT and Ccr9KO mice fed an HFD exhibited a comparable weight gain; however, glucose tolerance and insulin resistance were significantly improved in Ccr9KO mice. Moreover, visceral adipose tissue (VAT) and the liver of Ccr9KO mice presented with less inflammation and increased expression of glucose metabolism-related genes than WT mice. Ccr9 and Ccl25 expression were specifically higher in the small intestine but was not altered by HFD feeding and type 2 diabetes development. Accumulation of IFN-γ-producing CD4+ T lymphocytes and increased intestinal permeability in the small intestine was observed in WT mice following HFD feeding, but these changes were suppressed in HFD-fed Ccr9KO mice. Adoptive transfer of gut-tropic CCR9-expressing T lymphocytes partially reversed the favourable glucose tolerance found in Ccr9KO mice via exacerbated inflammation in the small intestine and VAT.
Conclusions/interpretation: CCR9 plays a central role in the pathogenesis of type 2 diabetes by inducing an inflammatory shift in the small intestine. Our findings support CCR9 as a new therapeutic target for type 2 diabetes via the gut-VAT-liver axis.
Keywords: Adipose tissue macrophage; Benign obesity; CCR9; Chemokine receptor; Ectopic fat deposition; Gut permeability; Gut–VAT–liver axis; IFN-γ-producing CD4+ T lymphocytes; Small intestinal inflammation; Type 2 diabetes.