Role Of Hepatic Or Intestinal Epithelial PHD2/HIF-1α Signaling Pathway In Alteration Of High-fat-diet Induced Gut Microbiota In Mice

BackgroundA high-fat diet changes the structure of the gut microbiota and disrupts the microecological balance in the intestinal tract.Through the gut-liver axis pathway,the gut microbiota affects the process of metabolic diseases such as nonalcoholic fatty liver disease caused by a high-fat diet.In recent years,exercise has gradually become an important means of chronic metabolic liver disease and inflammatory bowel disease.Blood redistribution during exercise reduces visceral and gastrointestinal blood flow.The decrease in blood supply leads to a decrease in the partial pressure of oxygen between tissues and an increase in the expression of hypoxia inducible factor.Under normoxia,theαsubunit of HIF-1 is degraded by the prolyl hydroxylase（PHD）pathway.A high-fat diet increases the incidence of intestinal inflammatory bowel disease and nonalcoholic steatohepatitis.When the liver and intestine become inflamed,the environment in which hepatocytes and intestinal epithelial cells are located is aggravated by hypoxia.This study hypothesized that the PHD2/HIF-1αsignaling pathway was involved in regulating the gut microbiota structure in mice fed a high-fat diet.MethodsThe Cre-Lox P system was used to construct hepatocyte-specific Hif1a knockout mice(Hif1a^LKO),hepatocyte-specific Phd2 knockout mice(Phd2^LKO),intestinal epithelial cell-specific Hif1a knockout mice(Hif1a^VKO)and Phd2 gene knockout mice(Phd2^VKO).The second part of the hepatocyte-specific high-fat diet group(HFD-Hif1a^flox/flox,HFD-Hif1a^LKO,HFD-Phd2^flox/flox,HFD-Phd2^LKO)was fed a 60%high-fat diet for 8 weeks,and the control group(CON-Hif1a^flox/flox,CON-Hif1a^LKO,CON-Phd2^flox/flox,CON-Phd2^LKO)was fed normal chow for 8 weeks（n=8/group）.The third part high-fat diet group(HFD-Hif1a^flox/flox,HFD-Hif1a^VKO,HFD-Phd2^flox/flox,HFD-Phd2^VKO)was fed a 60%high-fat diet for 12 weeks,and the control group(CON-Hif1a^flox/flox,CON-Hif1a^VKO),CON-Phd2^flox/flox,CON-Phd2^VKO)was fed common feed for 12 weeks（n=8/group）.By recording the weight changes of mice,analyzing serum biochemical indexes,liver function and other indexes,and performing fecal microbiota sequencing,we explored the effect of the PHD2/HIF-1αsignaling pathway in hepatocytes and intestinal epithelial cells on the intestinal microbiota of high-fat diet mice.This research protocol has been reviewed by the Scientific Research Ethics Committee of Shanghai Institute of Physical Education（No.102772020DW005）.ResultsThe first part of the study found that the relative body weight changes of all mice after high-fat diet modeling increased significantly（P<0.010）,and the relative body weight changes of the HFD-Hif1a^LKO group and HFD-Phd2-group were significantly higher than those of the HFD-Hif1a^flox/flox group and HFD-Phd2^flox/flox mice（P<0.001）.Liver-specific deletion of Phd2 affects gut microbiota alpha diversity in mice fed a high-fat diet.After modeling a high-fat diet,the Firmicutes/Bacteroidetes（F/B）ratios increased（P<0.010）in all mice.Compared with the mice in the HFD-Hif1a^flox/flox group,the structure and abundance of the intestinal microbiota of the mice in the HFD-Hif1a^LKO group did not change significantly.Compared with HFD-Phd2^flox/flox mice,HFD-Phd2^LKO mice had increased ALB（P=0.002）and ALT concentrations（P=0.012）.After 8 weeks of high-fat feeding,the abundance of Lactobacillus decreased in the 8W-Phd2^LKO group compared with the 8 W-Phd2^flox/flox group（P=0.0174）.Liver-specific deletion of Hif1a had no significant effect on the structure of gut microbiota,and changes in the expression of PHD2 in liver affected the abundance of individual gut microbiota.The second part of the study found that the relative body weight change of HFD-Hif1a^VKO mice was significantly higher than that of HFD-Hif1a^flox/flox mice after high-fat diet modeling（P=0.011）.IEC-specific deletion of Hif1a affects gut microbiota beta diversity in mice fed a high-fat diet.After high-fat diet modeling,the F/B values of both groups were significantly increased（P<0.010）.After feeding on a high-fat diet,compared with the HFD-Hif1a^flox/flox group,the abundance of Desulfobacterota decreased in the HFD-Hif1a^VKO group（P=0.031）,while the abundance of Actinobacteriota increased（P=0.031）.At the genus level,Dubosiella（P=0.035）,Coriobacteriaceae＿UCG-002（P=0.022）,Faecalibaculum（P=0.040）and Enterorhabdus（P=0.024）and other bacterial abundances increased.The abundance of Bacteroides and Lactococcus increased in HFD-Phd2^VKO mice compared with HFD-Phd2^flox/flox mice after a high-fat diet（P=0.041）.The abundance of unclassified＿f＿Oscillospiraceae（P=0.046）and Lachnospiraceae＿UCG-006 decreased（P=0.010）,while the phylum level and community distribution of intestinal microbiota in the two groups of mice were not significantly different.HIF-1αin intestinal epithelial cells is involved in the structural changes of gut microbiota caused by high-fat diet,and the deletion of intestinal epithelial cell-specific Phd2 gene has no significant effect on the overall structure of gut microbiota.ConclusionThis study found that PHD2 in the hepatocytes and HIF-1αin intestinal epithelial cells were mainly involved in the changes in gut microbiota structure in mice fed a high-fat diet.The PHD2/HIF-1αsignaling pathway may play different regulatory roles in liver and intestinal epithelial cells during high-fat diet-induced changes in the gut microbiota structure in mice.