SUMMARY Fibroblast growth factor-21 (FGF21) is a circulating hepatokine that beneficially affects carbohydrate and lipid metabolism. Here we report that FGF21 is also an inducible, fed-state autocrine factor in adipose tissue that functions in a feed-forward loop to regulate the activity of peroxisome proliferator-activated receptor γ (PPARγ), a master transcriptional regulator of adipogenesis. FGF21-knockout (KO) mice display defects in PPARγ signaling including decreased body fat and attenuation of PPARγ-dependent gene expression. Moreover, FGF21-KO mice are refractory to both the beneficial insulin-sensitizing effects and the detrimental weight gain and edema side effects of the PPARγ agonist rosiglitazone. This loss of function in FGF21-KO mice is coincident with a marked increase in the sumoylation of PPARγ, which reduces its transcriptional activity. Adding back FGF21 prevents sumoylation and restores PPARγ activity. Collectively, these results reveal FGF21 as a key mediator of the physiologic and pharmacologic actions of PPARγ.

Fibroblast growth factor-21 (FGF21) is a hormone secreted by the liver during fasting that elicits diverse aspects of the adaptive starvation response. Among its effects, FGF21 induces hepatic fatty acid oxidation and ketogenesis, increases insulin sensitivity, blocks somatic growth and causes bone loss. Here we show that transgenic overexpression of FGF21 markedly extends lifespan in mice without reducing food intake or affecting markers of NAD+ metabolism or AMP kinase and mTOR signaling. Transcriptomic analysis suggests that FGF21 acts primarily by blunting the growth hormone/insulin-like growth factor-1 signaling pathway in liver. These findings raise the possibility that FGF21 can be used to extend lifespan in other species.DOI: http://dx.doi.org/10.7554/eLife.00065.001

We demonstrate that adrenomedullin (AM) is produced and secreted from cultured murine monocyte/ macrophage cell line (RAW 264.7) as well as mouse peritoneal macrophage. Immunoreactive (IR) AM secreted from RAW 264.7 cells was chromatographically identified to be native AM. To elucidate the regulation mechanism of AM production in macrophage, we examined the effects of various substances inducing differentiation or activation of monocyte/macrophage. Phorbol ester (TPA), retinoic acid (RA), lipopolysaccharide (LPS), and interferon-␥ (IFN-␥) increased AM production 1.5-7-fold in RAW 264.7 cells in a dose-as well as time-dependent manner. By LPS stimulation, the AM mRNA level in RAW 264.7 cells was augmented up to 7-fold after 14 h incubation. RA exerted a synergistic effect when administered with TPA, LPS, or IFN-␥, whereas IFN-␥ completely suppressed AM production in RAW 264.7 cells stimulated with LPS. Dexamethasone, hydrocortisone, estradiol, and transforming growth factor-␤ dosedependently suppressed AM production in RAW 264.7 cells. AM production was also investigated in mouse peritoneal macrophage. Primary mouse macrophage secreted IR-AM at a rate similar to that of RAW 264.7 cells, and its production was enhanced 9-fold by LPS stimulation. AM was found to increase basal secretion of tumor necrosis factor ␣ (TNF-␣) from RAW 264.7 cells, whereas AM suppressed the secretion of TNF-␣ and interleukin-6 from that stimulated with LPS. Thus, macrophage should be recognized as one of the major sources of AM circulating in the blood. Especially in cases of sepsis and inflammation, AM production in macrophage is augmented, and the secreted AM is deduced to function as a modulator of cytokine production. Adrenomedullin (AM)1 is a potent vasorelaxant peptide originally isolated from extracts of human pheochromocytoma by monitoring the elevating activity of platelet cAMP (1). AM shows slight homology with calcitonin gene-related peptide (CGRP) and has a potent and long-lasting depressor effect when injected intravenously into anesthetized rats (1, 2). We have shown that cultured endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) produce and secrete AM into culture medium (3, 4). The production and secretion of AM in VSMC and EC were augmented by interleukin-1 (IL-1), tumor necrosis factor ␣ (TNF-␣), and lipopolysaccharide (LPS) (5, 6), which are known to be major factors inducing septic shock (7-9). In the in vivo study, intravenous administration of LPS into rats actually elevated plasma AM concentration 20-fold and augmented AM gene expression in blood vessels, lung, and intestine (10). Plasma AM levels were also remarkably increased in patients with septic shock compared with those in healthy volunteers (11,12). These data suggest the possibility that AM contributes to induction of refractory hypotension in septic shock. On the other hand, macrophages are activated by exposure to stimuli of foreign bodies such as LPS and then start to produce and secrete various cytokines, such as IL-1 and TNF-␣. These da...

The Na+‐taurocholate cotransporting polypeptide (NTCP/SLC10A1) is believed to be pivotal for hepatic uptake of conjugated bile acids. However, plasma bile acid levels are normal in a subset of NTCP knockout mice and in mice treated with myrcludex B, a specific NTCP inhibitor. Here, we elucidated which transport proteins mediate the hepatic uptake of conjugated bile acids and demonstrated intestinal sensing of elevated bile acid levels in plasma in mice. Mice or healthy volunteers were treated with myrcludex B. Hepatic bile acid uptake kinetics were determined in wild‐type (WT), organic anion transporting polypeptide (OATP) knockout mice (lacking Slco1a/1b isoforms), and human OATP1B1‐transgenic mice. Effects of fibroblast growth factor 19 (FGF19) on hepatic transporter mRNA levels were assessed in rat hepatoma cells and in mice by peptide injection or adeno‐associated virus–mediated overexpression. NTCP inhibition using myrcludex B had only moderate effects on bile acid kinetics in WT mice, but completely inhibited active transport of conjugated bile acid species in OATP knockout mice. Cholesterol 7α‐hydroxylase Cyp7a1 expression was strongly down‐regulated upon prolonged inhibition of hepatic uptake of conjugated bile acids. Fgf15 (mouse counterpart of FGF19) expression was induced in hypercholanemic OATP and NTCP knockout mice, as well as in myrcludex B–treated cholestatic mice, whereas plasma FGF19 was not induced in humans treated with myrcludex B. Fgf15/FGF19 expression was induced in polarized human enterocyte‐models and mouse organoids by basolateral incubation with a high concentration (1 mM) of conjugated bile acids. Conclusion: NTCP and OATPs contribute to hepatic uptake of conjugated bile acids in mice, whereas the predominant uptake in humans is NTCP mediated. Enterocytes sense highly elevated levels of (conjugated) bile acids in the systemic circulation to induce FGF15/19, which modulates hepatic bile acid synthesis and uptake. (Hepatology 2017;66:1631–1643).

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