Objective: Gut microbiota may promote positive energy balance; however, germfree mice can be either resistant or susceptible to diet-induced obesity (DIO) depending on the type of dietary intervention. We here sought to identify the dietary constituents that determine the susceptibility to body fat accretion in germfree (GF) mice.
Methods: GF and specific pathogen free (SPF) male C57BL/6N mice were fed high-fat diets either based on lard or palm oil for 4 wks. Mice were metabolically characterized at the end of the feeding trial. FT-ICR-MS and UPLC-TOF-MS were used for cecal as well as hepatic metabolite profiling and cecal bile acids quantification, respectively. Hepatic gene expression was examined by qRT-PCR and cecal gut microbiota of SPF mice was analyzed by high-throughput 16S rRNA gene sequencing.
Results: GF mice, but not SPF mice, were completely DIO resistant when fed a cholesterol-rich lard-based high-fat diet, whereas on a cholesterol-free palm oil-based high-fat diet, DIO was independent of gut microbiota. In GF lard-fed mice, DIO resistance was conveyed by increased energy expenditure, preferential carbohydrate oxidation, and increased fecal fat and energy excretion. Cecal metabolite profiling revealed a shift in bile acid and steroid metabolites in these lean mice, with a significant rise in 17β-estradiol, which is known to stimulate energy expenditure and interfere with bile acid metabolism. Decreased cecal bile acid levels were associated with decreased hepatic expression of genes involved in bile acid synthesis. These metabolic adaptations were largely attenuated in GF mice fed the palm-oil based high-fat diet. We propose that an interaction of gut microbiota and cholesterol metabolism is essential for fat accretion in normal SPF mice fed cholesterol-rich lard as the main dietary fat source. This is supported by a positive correlation between bile acid levels and specific bacteria of the order Clostridiales (phylum Firmicutes) as a characteristic feature of normal SPF mice fed lard.
Conclusions: In conclusion, our study identified dietary cholesterol as a candidate ingredient affecting the crosstalk between gut microbiota and host metabolism.
Keywords: ANOVA, analysis of variance; Abcg5, ATP-binding cassette sub-family G member 5; Abcg8, ATP-binding cassette sub-family G member 8; Actb, beta actin; Akr1d1, aldo-keto-reductase family member 1; BMR, basal metabolic rate; CA, cholic acid; CD, control diet; CDCA, chenodeoxycholic acid; CIDEA, cell death inducing DFFA-like effector; COX4, cytochrome c oxidase subunit 4; Cyp27a1, cholesterol 27 alpha-hydroxylase; Cyp7a1, cholesterol 7 alpha-hydroxylase; DCA, deoxycholic acid; DEE, daily energy expenditure; DIO, diet-induced obesity; Dhcr7, 7-dehydrocholesterol reductase; Diet-induced obesity resistance; Eef2, eukaryotic elongation factor 2; Energy balance; FT-ICR-MS, Fourier transform-Ion Cyclotron Resonance-Mass Spectrometry; FT-IR, Fourier transform-infrared spectroscopy; GF, germfree; GUSB, beta-glucuronidase; Germfree; HDCA, hyodeoxycholic acid; HP, heat production; High-fat diet; Hmgcr, 3-hydroxy-3-methylglutaryl Coenzyme A reductase; Hmgcs, 3-hydroxy-3-methylglutaryl Coenzyme A synthase 1; Hprt1, hypoxanthine guanine phosphoribosyl transferase; Hsd11b1, hydroxysteroid (11-β) dehydrogenase 1; Hsp90, heat shock protein 90; LHFD, high-fat diet based on lard; Ldlr, low density lipoprotein receptor; MCA, muricholic acid; Nr1h2, nuclear receptor subfamily 1, group H, member 2 (liver X receptor β); Nr1h3, nuclear receptor subfamily 1, group H, member 3 (liver X receptor α); Nr1h4, nuclear receptor subfamily 1, group H, member 4 (farnesoid X receptor α); PHFD, high-fat diet based on palm oil; PRDM16, PR domain containing 16; SPF, specific pathogen free; Srebf1, sterol regulatory element binding transcription factor 1; TCA, taurocholic acid; TMCA, Tauromuricholic acid; Tf2b, transcription factor II B; UCP1, uncoupling protein 1; UDCA, ursodeoxycholic acid; UPLC-TOF-MS, ultraperformance liquid chromatography-time of flight-mass spectrometry; qPCR, quantitative real-time polymerase chain reaction.