Growth differentiation factor 15 (GDF15), a distant member of the transforming growth factor (TGF)-β family, is a secreted protein that circulates as a 25-kDa dimer. In humans, elevated GDF15 correlates with weight loss, and the administration of GDF15 to mice with obesity reduces body weight, at least in part, by decreasing food intake. The mechanisms through which GDF15 reduces body weight remain poorly understood, because the cognate receptor for GDF15 is unknown. Here we show that recombinant GDF15 induces weight loss in mice fed a high-fat diet and in nonhuman primates with spontaneous obesity. Furthermore, we find that GDF15 binds with high affinity to GDNF family receptor α-like (GFRAL), a distant relative of receptors for a distinct class of the TGF-β superfamily ligands. Gfral is expressed in neurons of the area postrema and nucleus of the solitary tract in mice and humans, and genetic deletion of the receptor abrogates the ability of GDF15 to decrease food intake and body weight in mice. In addition, diet-induced obesity and insulin resistance are exacerbated in GFRAL-deficient mice, suggesting a homeostatic role for this receptor in metabolism. Finally, we demonstrate that GDF15-induced cell signaling requires the interaction of GFRAL with the coreceptor RET. Our data identify GFRAL as a new regulator of body weight and as the bona fide receptor mediating the metabolic effects of GDF15, enabling a more comprehensive assessment of GDF15 as a potential pharmacotherapy for the treatment of obesity.
The novel findings are that obese subjects have lower levels of IPA, a solely bacterially derived tryptophan derivative, and IPA improved intestinal barrier function in vitro and DIO mice. Reduced plasma IPA levels and reversal by surgery may be a consequence of intestinal indole-producing microbiota but underlying mechanisms warrant further investigation.
The sodium/glucose cotransporters (SGLT1 and SGLT2) transport glucose across the intestinal brush border and kidney tubule. Dual SGLT1/2 inhibition could reduce hyperglycemia more than SGLT2-selective inhibition in patients with type 2 diabetes. However, questions remain about altered gastrointestinal (GI) luminal glucose and tolerability, and this was evaluated in slc5a1 mice or with a potent dual inhibitor (compound 8; SGLT1 = 1.5 ± 0.5 nM 100-fold greater potency than phlorizin; SGLT2 = 0.4 ± 0.2 nM). C-glucose uptake was quantified in slc5a1 mice and in isolated rat jejunum. Urinary glucose excretion (UGE), blood glucose (Sprague-Dawley rats), glucagon-like peptide 1 (GLP-1), and hemoglobin A1c (HbA1c) levels (Zucker diabetic fatty rats) were measured. Intestinal adaptation and rRNA gene sequencing was analyzed in C57Bl/6 mice. The blood C-glucose area under the curve (AUC) was reduced in the absence of SGLT1 by 75% (245 ± 6 vs. 64 ± 6 mg/dl⋅h in wild-type vs. slc5a1 mice) and compound 8 inhibited its transport up to 50% in isolated rat jejunum. Compound 8 reduced glucose excursion more than SGLT2-selective inhibition (e.g., AUC = 129 ± 3 vs. 249 ± 5 mg/dl⋅h for 1 mg/kg compound 8 vs. dapagliflozin) with similar UGE but a lower renal glucose excretion threshold. In Zucker diabetic fatty rats, compound 8 decreased HbA1c and increased total GLP-1 without changes in jejunum SGLT1 expression, mucosal weight, or villus length. Overall, compound 8 (1 mg/kg for 6 days) did not increase cecal glucose concentrations or bacterial diversity in C57BL/6 mice. In conclusion, potent dual SGLT1/2 inhibition lowers blood glucose by reducing intestinal glucose absorption and the renal glucose threshold but minimally impacts the intestinal mucosa or luminal microbiota in chow-fed rodents.
Trypsin is the major serine protease responsible for intestinal protein digestion. An inhibitor, camostat (CS), reduced weight gain, hyperglycemia, and dyslipidemia in obese rats; however, the mechanisms for these are largely unknown. We reasoned that CS creates an apparent dietary protein restriction, which is known to increase hepatic fibroblast growth factor 21 (FGF21). Therefore, metabolic responses to CS and a gut-restricted CS metabolite, FOY-251, were measured in mice. Food intake, body weight, blood glucose, branched-chain amino acids (LC/MS), hormone levels (ELISA), liver pathology (histology), and transcriptional changes (qRT-PCR) were measured in ob/ob, lean and diet-induced obese (DIO) C57BL/6 mice. In ob/ob mice, CS in chow (9–69 mg/kg) or FOY-251 (46 mg/kg) reduced food intake and body weight gain to a similar extent as pair-fed mice. CS decreased blood glucose, liver weight, and lipidosis and increased FGF21 gene transcription and plasma levels. In lean mice, CS increased liver FGF21 mRNA and plasma levels. Relative to pair feeding, FOY-251 also increased plasma FGF21 and induced liver FGF21 and integrated stress response (ISR) transcription. In DIO mice, FOY-251 (100 mg/kg po) did not alter peak glucose levels but reduced the AUC of the glucose excursion in response to an oral glucose challenge. FOY-251 increased plasma FGF21 levels. In addition to previously reported satiety-dependent (cholecystokinin-mediated) actions, intestinal trypsin inhibition engages non-satiety-related pathways in both leptin-deficient and DIO mice. This novel mechanism improves metabolism by a liver-integrated stress response and increased FGF21 expression levels in mice. NEW & NOTEWORTHY Trypsin inhibitors, including plant-based consumer products, have long been associated with metabolic improvements. Studies in the 1980s and 1990s suggested this was due to satiety hormones and caloric wasting by loss of protein and fatty acids in feces. This work suggests an entirely new mechanism based on the lower amounts of digested protein available in the gut. This apparent protein reduction may cause beneficial metabolic adaptation by the intestinal-liver axis to perceived nutrient stress.
GDF-15 is a secreted circulating polypeptide that regulates systemic energy balance. GDF-15 agonists may have therapeutic potential as anorectic agents in obesity and type 2 diabetes. The receptor for GDF-15, Gfral, is expressed on specific neurons in the area postrema (AP) of the hindbrain, and is necessary for the effect of GDF-15 on food intake. Given the role of the AP in vagal control of gastric motility, we sought to investigate the potential effects of GDF-15 on gastric emptying. Food intake reduction by GDF-15 was confirmed in C57Bl/6N mice using BioDAQ continuous food consumption monitoring. Animals were treated sc with recombinant His-tagged human GDF-15 prior to initiation of the dark cycle; GDF-15 treated mice showed significant reduction in food intake relative to vehicle treated controls (12 hour cumulative food intake: 3nmol/kg, -19.9±10.5%; 10nmol/kg, -58.0±10.0%; P<0.0001, n=8). Gastric emptying was assessed using an oral acetaminophen (AAP) absorption test over 90 minute using LC/MS detection. This method was validated using known inhibitor of gastric emptying, Exendin-4 as a positive control; 7.2nmol/kg Exendin-4 significantly reduced integrated AAP absorption by -44.7±5.1% (P<0.01, n=8). In this assay, GDF-15 caused a significant dose-dependent inhibition of gastric emptying, reducing acetaminophen AUC levels by -18.1±10.6% at 1nmol/kg, and by -36.0±9.9% at 10nmol/kg, relative to vehicle treated control mice (P<0.01, n=8). Comparable results were obtained in an independent repetition of the study. We extended the results obtained in mice to SD rats, where we similarly observed a significant reduction in gastric emptying following GDF-15 treatment. Hence, GDF-15 appears to reduce gastric emptying rate in both mouse and rat, potentially contributing to the food intake suppression mechanism of action. Disclosure S.A. Hinke: Employee; Self; Janssen Research & Development. C.R. Cavanaugh: Employee; Self; Janssen Research & Development. T. Kirchner: None. W. Lang: None. R. Meng: None. N.H. Wallace: None. J. Liu: None. K.E. D'Aquino: Employee; Self; Janssen Research & Development. Employee; Spouse/Partner; Janssen Research & Development. G. Ho: None. M.M. Rankin: Employee; Self; Janssen Research & Development. S. Wang: None. J.A. Chavez: None. S.M. Nelson: None. J. Furman: Employee; Self; Janssen Research & Development. S. Mullican: Employee; Self; Janssen Research & Development. S.M. Rangwala: Employee; Self; Janssen Research & Development. A.R. Nawrocki: Employee; Self; Janssen Pharmaceuticals, Inc..
The importance of noncodoing RNAs is being appreciated more. These participate in regulation of all aspects of nucleic acids biology and also have structural and catalytic roles. Noncoding RNAs are assembled from motifs, A‐form helices and unstructured single strands. We are using molecular dynamics (MD) to understand the basis of stability of RNA motifs and their junctions to other motifs and helices.The stability of the sarcin/ricin domain (SRD) RNA motif is being studied in a dumbbell RNA in which a G/C‐rich and a A/U‐rich A‐form helix capped with a tetraloop flank the SRD domain. RNA melting is being observed using adaptively biased and replica exchange methods to explore the free energy profile as the dumbbell melts. We have found that more conformations can be explored more rapidly when the negative charges of the RNA are not completely neutralized by the cations. Artificial cations with less than unit charge allow multiple runs with different degree of neutralization. We are comparing the conformations explored under these conditions with those seen in a standard net neutralized system.
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