Host genotype can influence the composition of the commensal bacterial community in some organisms. Composition, however, is only one parameter describing a microbial community. Here, we test whether a second parameter—abundance of bacteria—is a heritable trait by quantifying the presence of four commensal bacterial strains within 36 gnotobiotic inbred lines of Drosophila melanogaster. We find that D. melanogaster genotype exerts a significant effect on microbial levels within the fly. When introduced as monocultures into axenic flies, three of the four bacterial strains were reliably detected within the fly. The amounts of these different strains are strongly correlated, suggesting that the host regulates commensal bacteria through general, not bacteria-specific, means. While the correlation does not appear to be driven by simple variation in overall gut dimensions, a genetic association study suggests that variation in commensal bacterial load may largely be attributed to physical aspects of host cell growth and development.

Multiple beneficial cardiovascular effects of HDL depend on sphingosine-1-phosphate (S1P). S1P associates with HDL by binding to apolipoprotein M (ApoM). Insulin resistance is a major driver of dyslipidemia and cardiovascular risk. However, the mechanisms linking alterations in insulin signaling with plasma lipoprotein metabolism are incompletely understood. The insulinrepressible FoxO transcription factors mediate key effects of hepatic insulin action on glucose and lipoprotein metabolism. This work tested whether hepatic insulin signaling regulates HDL-S1P, and the underlying molecular mechanisms. We report that insulin resistant, nondiabetic human subjects had decreased HDL-S1P levels, but no change in total plasma S1P. This also occurred in insulin resistant db/db mice, which had low ApoM and a specific reduction of S1P in the HDL fraction, with no change in total plasma S1P. Using mice lacking hepatic FoxOs (L-FoxO1,3,4), we found that hepatic FoxOs were required for ApoM expression. Total plasma S1P levels were similar to controls, but S1P was nearly absent from HDL, and was instead increased in the lipoprotein depleted plasma fraction. This phenotype was restored to normal by rescuing ApoM in L-FoxO1,3,4 mice. Our findings show that insulin resistance in humans and mice is associated with decreased HDL-associated S1P. Hepatic FoxO transcription factors are regulators of the ApoM-S1P pathway.

Bile acids (BAs) comprise heterogenous amphipathic cholesterol-derived molecules that carry out physicochemical and signaling functions. A major site of BA action is the terminal ileum, where enterocytes actively reuptake BAs and express high levels of BA-sensitive nuclear receptors. BA pool size and composition are affected by changes in metabolic health, and vice versa. One of several factors that differentiate BAs is the presence of a hydroxyl group on C12 of the steroid ring. 12α-hydroxylated BAs (12HBAs) are altered in multiple disease settings, but the consequences of 12HBA abundance are incompletely understood. We employed mouse primary ileum organoids to investigate the transcriptional effects of varying 12HBA abundance in BA pools. We identified Slc30a10 as one of the top genes differentially induced by BA pools with varying 12HBA abundance. SLC30A10 is a manganese (Mn) efflux transporter critical for whole-body manganese excretion. We found that BA pools, especially those low in 12HBAs, induce cellular manganese efflux, and that Slc30a10 induction by BA pools is driven primarily by lithocholic acid signaling via the vitamin D receptor. Administration of lithocholic acid or a vitamin D receptor agonist resulted in increased Slc30a10 expression in mouse ileum epithelia. These data demonstrate a previously unknown role for BAs in intestinal control of Mn homeostasis.

Bile acids (BAs) comprise heterogenous amphipathic cholesterol-derived molecules that carry out physicochemical and signaling functions. A major site of BA action is the terminal ileum,

The authors declare no conflicts of interest.Abbreviations: AAV=adeno-associated virus, ApoM=apolipoprotein M, DIO=diet induced obese, FPLC=fast protein liquid chromatography, HDL=high density lipoprotein, HFD=high fat diet, LC-MS/MS=liquid chromatography-mass spectrometry, LDL=low density lipoprotein, LPD=lipoprotein depleted, S1P=sphingosine-1-phosphate, Tbg=thyroxin binding globulin, VLDL=very low density lipoprotein, WTD=western type diet ABSTRACTThe FoxO family of transcription factors play an important role in mediating insulin action on glucose, lipid, and lipoprotein metabolism. Liver-specific triple FoxO knockout mice (L-FoxO1,3,4) have defects in expression of genes related to glucose production, bile acid synthesis, and high density lipoprotein (HDL)-cholesterol uptake. We have now identified Apolipoprotein M (Apom) as a novel transcriptional target of liver FoxO. ApoM is a liver-secreted apolipoprotein that is bound to HDL in the circulation, and it serves as a chaperone for the bioactive lipid, sphingosine-1-phosphate (S1P). Several recent studies have demonstrated that S1P bound to ApoM induces unique effects, compared to S1P bound to albumin. We now show that liver FoxOs are required for ApoM mRNA and protein expression, and that ApoM is a transcriptional target of FoxOs. Moreover, while total plasma S1P levels are similar between control and L-FoxO1,3,4 mice, S1P is nearly absent from HDL in L-FoxO1,3,4 mice, and is instead increased in the lipoprotein depleted fraction. We also observed that leptin receptor deficient db/db mice have low hepatic Apom mRNA, and low levels of ApoM and S1P in HDL, without changes in total plasma S1P. These data demonstrate that FoxO transcription factors are novel regulators of the ApoM-S1P pathway, and indicate a potential link between hepatic insulin action and HDL function. METHODS Mice and diets.All experiments were approved by the Columbia University Institutional Animal Care and Use Committee. L-FoxO1,3,4 mice have been previously described 5,9 . Males at least 12 weeks old were studied, except in studies of 2-day-old pups, which were of mixed sex. For the acute FoxO depletion experiments, adult Foxo1 fl/fl , Foxo3 fl/fl , and Foxo4 fl/Y control mice were transduced with adeno-associated virus (serotype 8) expressing Cre recombinase driven by the hepatocyte-specific Tbg promoter (AAV8.Tbg. Cre) or control virus (AAV.GFP). Mice were injected intravenously with 1×10 11 virus particles/mouse, 4 weeks prior to euthanasia. AAV8.Tbg.Cre was a gift ). For the adenovirus experiments, adult male mice were injected intravenously with murine ApoM adenovirus (Welgen) 0.5 × 10 9 virus particles/gram of body weight, 8 days prior to euthanasia. For the db/db studies, male db/db and db/+ mice were purchased from Jackson Laboratory and were studied when they were 12, 13 or 25 weeks old. For the diet induced obesity studies, male C57BL/6J mice were purchased from Jackson Laboratory when they were 6 weeks old. Mice were fed either a standard chow diet (Purina) or a high fat diet ...