Activation of bile acid signaling improves metabolic phenotypes in high-fat diet-induced obese mice - PubMed (original) (raw)

Activation of bile acid signaling improves metabolic phenotypes in high-fat diet-induced obese mice

Joseph F Pierre et al. Am J Physiol Gastrointest Liver Physiol. 2016.

Abstract

The metabolic benefits induced by gastric bypass, currently the most effective treatment for morbid obesity, are associated with bile acid (BA) delivery to the distal intestine. However, mechanistic insights into BA signaling in the mediation of metabolic benefits remain an area of study. The bile diversion () mouse model, in which the gallbladder is anastomosed to the distal jejunum, was used to test the specific role of BA in the regulation of glucose and lipid homeostasis. Metabolic phenotype, including body weight and composition, glucose tolerance, energy expenditure, thermogenesis genes, total BA and BA composition in the circulation and portal vein, and gut microbiota were examined. BD improves the metabolic phenotype, which is in accord with increased circulating primary BAs and regulation of enterohormones. BD-induced hypertrophy of the proximal intestine in the absence of BA was reversed by BA oral gavage, but without influencing BD metabolic benefits. BD-enhanced energy expenditure was associated with elevated TGR5, D2, and thermogenic genes, including UCP1, PRDM16, PGC-1α, PGC-1β, and PDGFRα in epididymal white adipose tissue (WAT) and inguinal WAT, but not in brown adipose tissue. BD resulted in an altered gut microbiota profile (i.e., Firmicutes bacteria were decreased, Bacteroidetes were increased, and Akkermansia was positively correlated with higher levels of circulating primary BAs). Our study demonstrates that enhancement of BA signaling regulates glucose and lipid homeostasis, promotes thermogenesis, and modulates the gut microbiota, which collectively resulted in an improved metabolic phenotype.

Keywords: bile acids; bile diversion; energy expenditure; gastric bypass; gut microbiota; mice; obesity.

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Figures

Fig. 1.

BD improves body weight and glucose tolerance. A: BD mouse model. Cholecystoenterostomy is performed, and bile is drained to the distal jejunum (arrow). B: photograph of gallbladder-jejunal anastomosis. C: intraperitoneal glucose tolerance tests (IPGTTs) were performed at 2 wk postsurgery. *BD vs. WMS at 30, 60, 90, and 120 min, P < 0.05. D: area under the curve of IPGTT at 2 wk postsurgery. *BD vs. WMS, P < 0.05; **LFD, WMS, and BD vs. DIO, P < 0.01 (n = 5 per group). BD, bile diversion; DIO, diet-induced obesity; LFD, low-fat diet; WMS, weight-matched animals that underwent sham surgery.

Fig. 2.

BD improves obesity and glucose tolerance. A: BD and WMS animals had reduced body weight (in grams). B: percentage of reduced body weight in BD and WMS groups, n = 10 per group. C: BD reduces epididymal white adipose tissue (eWAT) (weight in grams). The inset photographs represent eWAT of LFD, DIO, WMS, and BD, respectively, collected at 8 wk postsurgery. *WMS and BD vs. DIO, P < 0.001; #BD vs. WMS, P = 0.0015. D: BD reduces eWAT weight (percentage of body weight). *BD and WMS vs. DIO, P < 0.001; #BD vs. WMS, P = 0.0002. E: BD improves fat mass. Whole body fat mass was measured by dual-energy X-ray absorptiometry (see

materials and Methods

). *BD vs. WMS, P < 0.05; ***WMS and BD vs. DIO, P < 0.001. F: IPGTT was performed at 8 wk postsurgery. *BD vs. WMS, P < 0.05; **vs. DIO, P < 0.01, n = 5 per group. G: area under the curve of IPGTT. *BD vs. WMS, P < 0.05; ***BD vs. DIO, P < 0.001, and #WMS vs. DIO, P < 0.05 (n = 5 per group). All values are presented as means ± SE.

Fig. 3.

BD regulates bile acid homeostasis (at 8 wk postsurgery). A: total bile acids in peripheral circulation. *BD vs. LFD and DIO, P < 0.05; **BD vs. WMS, _P_ < 0.01. _B_: total bile acids in portal vein. **BD vs. DIO, _P_ < 0.01; ***BD vs. LFD and WMS, _P_ < 0.001. _C_: total bile acids in feces. *LFD vs. DIO, WMS, and BD, _P_ < 0.05. _D_: expression of TGR5 (G protein-coupled bile acid receptor 1) in ileum tissue (Western blot). *BD vs. DIO, _P_ = 0.026. _E_: BD increased the relative percentage of circulating primary bile acids. _F_: BD increases the relative percentage of conjugated and unconjugated bile acids. _a_: LFD; _b_: DIO; _c_: WMS, and _d_: BD. The color code starts at the top and turns clockwise showing the bile acids designated by key: left→right, top→bottom. _G_: farnesoid X receptor (FXR) mRNA in the liver (_P_ > 0.05 among groups). H: CYP7A1 mRNA in the liver (WMS vs. LFD, DIO, and BD, P < 0.05). I: small heterodimer partner (SHP) mRNA in the liver. *BD vs. DIO, P = 0.07. All values are presented as means ± SE.

Fig. 3.

Fig. 4.

A: BD increases relative percentage of primary bile acids in the portal vein. B: BD resulted in an increased relative percentage of conjugated and unconjugated bile acids in the portal vein. a: LFD; b: DIO; c: WMS, and d: BD. The color code starts at the top and turns clockwise showing the bile acids designated by key: left→right, top→bottom.

Fig. 5.

BD improves hypertrophy of adipocytes and liver steatosis. Epididymal WAT, inguinal WAT (iWAT), brown adipose tissue (BAT) and liver tissues were collected at 8 wk postsurgery and subjected to lipid and histological examinations and liver metabolic gene analysis. A: histological examinations of eWAT, iWAT, BAT, and liver in LFD (a), DIO (b), WMS (c), and BD (d) mice. B: peroxisome proliferator-activated receptor α (PPARα). *BD vs. DIO and WMS, P < 0.05; **BD vs. LFD, P < 0.01. C: peroxisome proliferator-activated receptor γ coactivator-1β (PGC-1β). *BD vs. WMS, P < 0.05; **BD vs. DIO, P < 0.01. D: fibroblast growth factor 21 (FGF21). **BD vs. WMS, P < 0.01; ***BD vs. LFD and DIO, P < 0.001 (n = 5 per group). All values presented as means ± SE.

Fig. 6.

BD reduces lipid droplets in the liver. Hepatic liver lipid droplet area was assessed in histology sections and normalized to total area. Compared with LFD, DIO resulted in dramatically induced steatosis that was prevented with caloric restriction (WMS) and BD surgery. **DIO vs. DIO, WMS, and BD, P < 0.01.

Fig. 7.

BD enhances expression of proglucagon mRNA in the ileum. BD resulted in an elevated expression of proglucagon, the glucagon-like peptide-1 (GLP-1) precursor gene, compared with other treatment groups. *BD vs. LFD, DIO, and WMS, P < 0.01.

Fig. 8.

BD regulates circulating enterohormones. Sera were collected at 8 wk postsurgery and subjected to enterohormone analysis by the Bio-Plex Pro Mouse Diabetes 8-Plex Assay kit (Bio-Rad). A: circulating GLP-1; *BD vs. all other groups, P < 0.05. B: circulating insulin; *DIO vs. all other groups, P < 0.05. C: circulating leptin; *DIO vs. all other groups, P< 0.05. D: circulating resistin; *DIO vs. all other groups, P < 0.05. E: circulating ghrelin; *WMS vs. DIO, P < 0.05. F: relationship between total bile acids and circulating GLP-1 levels in DIO and BD mice (P < 0.001). G: relationship between total bile acids and circulating insulin levels in DIO and BD mice (P = 0.13); H: relationship between total bile acids and leptin levels in DIO and BD mice (P = 0.05); I: relationship between total bile acids and resistin levels in DIO and BD mice (n = 5, P = 0.05); J: relationship between total bile acids and ghrelin levels in DIO and BD mice (P = 0.54); n = 9 in each group. All values are presented as means ± SE.

Fig. 9.

BD induces duodenal proliferation, which was reversed by bile acid administration. A: representative duodenal hematoxylin and eosin-stained duodenum with light photomicrograghs from LFD (a), DIO (b), WMS (c), BD (d), and BD + CDCA [BD mice were fed chenodeoxycholic acid (CDCA, 20 mg/kg) at the fourth week postsurgery for 4 wk] (e). The inset figure shows changes in mucosal thickness. B: representative duodenal immunohistochemical staining of Ki-67 in LFD (a), DIO (b), WMS (c), BD (d), and BD+CDCA (e) mice. The figure shows Ki-67-positive cells per crypt base. C: body weight changes after feeding CDCA (starting at the fourth week postsurgery). There was no statistical difference between BD and BD+CDCA groups (DIO, n = 10, BD, n = 10 and BD+CDCA, n = 5). D: IPGTT was performed at 8 wk postsurgery in BD mice with CDCA (20 mg/kg) for 4 wk (n = 5 per group). All values are presented as means ± SE.

Fig. 10.

BD enhances energy expenditure and promotes thermogenesis. A: energy expenditure: 24-h oxygen consumption (n = 5 per group). B: energy expenditure: day and night oxygen consumption. Daytime, *BD vs. WMS P < 0.05; ***BD vs. DIO, P < 0.001; #WMS vs. DIO, P < 0.05. Nighttime, ***BD vs. DIO and WMS, P < 0.001, n = 5 per group. C: TGR5, type-2 iodothyronine deiodinase (D2), and thermogenic genes in eWAT. **BD vs. TGR5, LFD, and DIO, P < 0.01; D2, **BD vs. LFD, DIO, and WMS, P < 0.01; uncoupling protein 1 (UCP1), *BD vs. DIO, P < 0.05; PGC-1α, **BD vs. LFD and DIO, P < 0.01; PR domain-containing 16 (PRDM16), **BD vs. LFD, DIO, and WMS, P < 0.01; and platelet-derived growth factor receptor-α (PDGFRα), **BD vs. LFD, DIO, and WMS, P < 0.01. D: TGR5, D2, and thermogenic genes in iWAT. *BD vs. TGR5 and LFD, P < 0.05; BD vs. DIO, P < 0.01; D2, **BD vs. DIO, P < 0.01; UCP1, **BD vs. DIO, P < 0.01; BD vs. PGC-1α, LFD, WMS, and DIO, P < 0.01; and BD vs. PDGFRα, LFD, DIO, and WMS, P < 0.01. E: there is no statistical differences among all groups (P < 0.05 except D2, WMS vs. DIO, P < 0.01). All values are presented as means ± SE.

Fig. 10.

Fig. 11.

Primary bile acids promote TGR5 and D2 mRNA expressions in 3T3-L1 adipocytes. A: β-muricholic acid (βMCA), tauro-conjugated chenodeoxycholic acid (TCDCA), cholic acid (CA), and chenodeoxycholic acid (CDCA) promote TGR5 mRNA expression (*P < 0.05, **P < 0.01). B: tauro-conjugated β-muricholic acid (TβMCA) and TCDCA significantly increased expression of D2 mRNA (P < 0.05), whereas TCA increased D2 expression, but not significantly (P = 0.10).

Fig. 12.

BD alters the phyla of the cecal content microbiome. A: cluster analysis of LFD, DIO, WMS, and BD mice (n = 5 per group). B: reconfiguration of the gut microbiota. *The phylum Firmicutes was decreased in BD mice (BD vs. DIO, P = 0.03). **The phylum Batcteroidetes was increased in WMS and BD groups (WMS and BD vs. DIO, P < 0.01 and P < 0.001), and the phylum Verrucomicrobia increased in BD mice (BD vs. DIO, P = 0.02, and BD vs. WMS P < 0.01, n = 5 per group). All values are presented as means ± SE.

Fig. 13.

BD alters the genera of the cecal content microbiome. A: Akkermansia (37%) was significantly increased in the BD group compared with LFD (5%), DIO (20%), and WMS (17%), P < 0.01 (n = 5 per group). B: circulating primary bile acids positively correlated with Akkermansia. The relationship between circulating primary bile acid levels and cecal Akkermansia relative composition was analyzed at 8 wk postsurgery (n = 20).

Fig. 14.

BD increases butyrate in cecal contents. A: total cecal short-chain fatty acids. *BD vs. DIO and WMS, P < 0.05. _B_: cecal acetate. *BD vs. DIO and WMS, _P_ < 0.05. _C_: butyrate. *BD vs. LFD, DIO, and WMS, _P_ < 0.05. _D_: cecal proprionate (_P_ > 0.05 among all groups); (n = 5 in DIO, WMS, and BD groups, n = 3 in the LFD group).

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Activation of bile acid signaling improves metabolic phenotypes in high-fat diet-induced obese mice - PubMed (original) (raw)