High fat/high salt diet intake promotes Th17 activation in the small intestine in males but not females

Abstract

Previous studies have identified Th17 to be highly pathogenic during immune dysregulation. We have previously shown that chronic high fat diet (HFD) led to significant kidney medullary interstitial fibrosis and aortic hypertrophy compared to normal diet intake. Numerous studies have identified a connection between high fat and high salt diets and an increase in pathogenic Th17 cells. Although little is understood about Th17 activation in the gut and kidney when high fat and high salt diets are combined (HF/HS). Furthermore, little is known about whether there are sex differences in dietary immune responses. We hypothesized that chronic HF/HS diet compared to normal diet (ND) intake can exaggerate Th17 activation and reduce regulatory T cells (Treg) in the gut and kidney compared to ND in a sex dependent manner. The gut comprises the largest site of immune cells in the body and are ideally located for mediating immune responses to dietary challenges, thus we focused on the gut as well as the kidney. We immunophenotyped T cells with flow cytometry through cytokine production and transcriptional markers from 10-week-old C57Bl6/J mice provided ND (10% fat, 0.4% salt) or HF/HS (45% fat, 4% salt) diet for 10 weeks. Small intestines, colons, and kidneys were collected and isolated to single cell suspensions and stimulated for two hours before fluorescent antibody staining for flow cytometric analysis. Results are reported as percentage of CD4+ TCRb+. We first examined baseline immune cell (CD45+) and T cell populations (CD4+) and found no statistical differences between ND and HF/HS. After gating on CD4+ TCRb+ T cells, we gated on IL-17A+ IFNg- cells as our Th17 population. In the small intestine of male mice, we found a significant increase of Th17 cells in the HF/HS group compared to ND mice (ND: 7.05 1.12, HF/HS: 18.32 2.13, p=0.0009). However, in the colon and kidney, we found no significant difference in Th17 cells in the HF/HS and ND groups (Kidney: ND: 1.060.08, HF/HS: 1.140.13, p=0.5967; Colon: ND: 2.87 0.48, HF/HS: 4.83 0.83, p=0.0610). In the colon, we found significantly decreased frequencies of effector Tregs (FoxP3+ RORgt+) with HF/HS compared to ND (ND: 12.95 1.30, HF/HS: 6.400.72, p=0.0023). There were no significant differences in effector Tregs in the small intestine and kidney (Small Intestine: ND: 8.941.26, HF/HS: 7.080.78, p=0.2378; Kidney: ND:0.47 0.19, HF/HS: 0.43 0.20, p=0.9057). We found no significant differences between ND and HF/HS groups in all tissue sources and T cell phenotypes in female mice (Th17: Small Intestine: ND: 18.20 3.86, HF/HS: 16.361.90, p=0.6983; Colon: ND: 3.611.23, HF/HS: 3.020.71, p= 0.6886; Kidney: ND: 27.484.44, HF/HS: 18.963.11, p=0.1666; Treg: Small Intestine: ND: 9.581.20, HF/HS: 8.63 1.07, p=0.5762; Colon: ND: 5.701.14, HF/HS: 4.63 0.61, p=0.4237; Kidney: ND:0.84 0.31, HF/HS: 0.31 0.04, p=0.1505). In conclusion, HF/HS diet induced increased small intestinal Th17 cells and decreased colonic effector Tregs in male mice and not in female mice. These results indicate that a dietary challenge promotes a pathogenic environment in the gut in a sex-specific manner.