19 research outputs found
Organic cation transporter 1 (OCT1) modulates multiple cardiometabolic traits through effects on hepatic thiamine content.
A constellation of metabolic disorders, including obesity, dysregulated lipids, and elevations in blood glucose levels, has been associated with cardiovascular disease and diabetes. Analysis of data from recently published genome-wide association studies (GWAS) demonstrated that reduced-function polymorphisms in the organic cation transporter, OCT1 (SLC22A1), are significantly associated with higher total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride (TG) levels and an increased risk for type 2 diabetes mellitus, yet the mechanism linking OCT1 to these metabolic traits remains puzzling. Here, we show that OCT1, widely characterized as a drug transporter, plays a key role in modulating hepatic glucose and lipid metabolism, potentially by mediating thiamine (vitamin B1) uptake and hence its levels in the liver. Deletion of Oct1 in mice resulted in reduced activity of thiamine-dependent enzymes, including pyruvate dehydrogenase (PDH), which disrupted the hepatic glucose-fatty acid cycle and shifted the source of energy production from glucose to fatty acids, leading to a reduction in glucose utilization, increased gluconeogenesis, and altered lipid metabolism. In turn, these effects resulted in increased total body adiposity and systemic levels of glucose and lipids. Importantly, wild-type mice on thiamine deficient diets (TDs) exhibited impaired glucose metabolism that phenocopied Oct1 deficient mice. Collectively, our study reveals a critical role of hepatic thiamine deficiency through OCT1 deficiency in promoting the metabolic inflexibility that leads to the pathogenesis of cardiometabolic disease
Metformin Is a Substrate and Inhibitor of the Human Thiamine Transporter, THTR-2 (SLC19A3)
RNA Regulations and Functions Decoded by Transcriptome-wide RNA Structure Probing
RNA folds into intricate structures that are crucial for its functions and regulations. To date, a multitude of approaches for probing structures of the whole transcriptome, i.e., RNA structuromes, have been developed. Applications of these approaches to different cell lines and tissues have generated a rich resource for the study of RNA structureâfunction relationships at a systems biology level. In this review, we first introduce the designs of these methods and their applications to study different RNA structuromes. We emphasize their technological differences especially their unique advantages and caveats. We then summarize the structural insights in RNA functions and regulations obtained from the studies of RNA structuromes. And finally, we propose potential directions for future improvements and studies. Keywords: RNA structure probing, RNA structurome, RNA secondary structure, Structureâfunction relationship, RNA regulatio
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Metformin Is a Substrate and Inhibitor of the Human Thiamine Transporter, THTR-2 (SLC19A3).
The biguanide metformin is widely used as first-line therapy for the treatment of type 2 diabetes. Predominately a cation at physiological pH's, metformin is transported by membrane transporters, which play major roles in its absorption and disposition. Recently, our laboratory demonstrated that organic cation transporter 1, OCT1, the major hepatic uptake transporter for metformin, was also the primary hepatic uptake transporter for thiamine, vitamin B1. In this study, we tested the reverse, i.e., that metformin is a substrate of thiamine transporters (THTR-1, SLC19A2, and THTR-2, SLC19A3). Our study demonstrated that human THTR-2 (hTHTR-2), SLC19A3, which is highly expressed in the small intestine, but not hTHTR-1, transports metformin (Km = 1.15 ± 0.2 mM) and other cationic compounds (MPP(+) and famotidine). The uptake mechanism for hTHTR-2 was pH and electrochemical gradient sensitive. Furthermore, metformin as well as other drugs including phenformin, chloroquine, verapamil, famotidine, and amprolium inhibited hTHTR-2 mediated uptake of both thiamine and metformin. Species differences in the substrate specificity of THTR-2 between human and mouse orthologues were observed. Taken together, our data suggest that hTHTR-2 may play a role in the intestinal absorption and tissue distribution of metformin and other organic cations and that the transporter may be a target for drug-drug and drug-nutrient interactions
An ultra low-input method for global RNA structure probing uncovers Regnase-1-mediated regulation in macrophages
To enable diverse functions and precise regulation, an RNA sequence often folds into complex yet distinct structures in different cellular states. Probing RNA in its native environment is essential to uncovering RNA structures of biological contexts. However, current methods generally require large amounts of input RNA and are challenging for physiologically relevant use. Here, we report smartSHAPE, a new RNA structure probing method that requires very low amounts of RNA input due to the largely reduced artefact of probing signals and increased efficiency of library construction. Using smartSHAPE, we showcased the profiling of the RNA structure landscape of mouse intestinal macrophages upon inflammation, and provided evidence that RNA conformational changes regulate immune responses. These results demonstrate that smartSHAPE can greatly expand the scope of RNA structure-based investigations in practical biological systems, and also provide a research paradigm for the study of post-transcriptional regulation
Metformin Is a Substrate and Inhibitor of the Human Thiamine Transporter, THTR‑2 (SLC19A3)
The
biguanide metformin is widely used as first-line therapy for
the treatment of type 2 diabetes. Predominately a cation at physiological
pH’s, metformin is transported by membrane transporters, which
play major roles in its absorption and disposition. Recently, our
laboratory demonstrated that organic cation transporter 1, OCT1, the
major hepatic uptake transporter for metformin, was also the primary
hepatic uptake transporter for thiamine, vitamin B1. In this study,
we tested the reverse, i.e., that metformin is a substrate of thiamine
transporters (THTR-1, SLC19A2, and THTR-2, SLC19A3). Our study demonstrated
that human THTR-2 (hTHTR-2), SLC19A3, which is highly expressed in
the small intestine, but not hTHTR-1, transports metformin (<i>K</i><sub>m</sub> = 1.15 ± 0.2 mM) and other cationic compounds
(MPP<sup>+</sup> and famotidine). The uptake mechanism for hTHTR-2
was pH and electrochemical gradient sensitive. Furthermore, metformin
as well as other drugs including phenformin, chloroquine, verapamil,
famotidine, and amprolium inhibited hTHTR-2 mediated uptake of both
thiamine and metformin. Species differences in the substrate specificity
of THTR-2 between human and mouse orthologues were observed. Taken
together, our data suggest that hTHTR-2 may play a role in the intestinal
absorption and tissue distribution of metformin and other organic
cations and that the transporter may be a target for drug–drug
and drug–nutrient interactions
Estimating net primary production of natural grassland and its spatio-temporal distribution in China
<i>Oct1</i> function modulated thiamine disposition in vivo and in vitro.
<p>(A) Scheme: deletion of <i>Oct1</i> reduces hepatic uptake of thiamine and increases plasma thiamine levels. (B) Plasma thiamine levels (<i>n</i> = 6 per genotype on a control diet; <i>n</i> = 7 per genotype on a TD). (C) Survival curves for mice on TDs (<i>n</i> = 7 for <i>Oct1</i><sup><i>+/+</i></sup> mice and <i>n</i> = 9 for <i>Oct1</i><sup><i>-/-</i></sup> mice). Animals were euthanized once the humane end points (body condition score of 2 or less or 15% body weight loss) were reached during the treatment (Gehan-Breslow-Wilcoxon test and log-rank test were used for analysis). (D) Representative graph of thiamine uptake in cells stably expressing EV, hOCT1-Ref, hOCT1-420Del, and hOCT1-420Del+G465R; a total of 25 nM thiamine was included in the uptake buffer. Representative graph of thiamine kinetics in cells expressing hOCT1-Ref and hOCT1-420Del; concentrations ranged from 25 nM to 2 mM; uptake was performed for 4 minutes. <i>n</i> = 3 replicated wells; two separate experiments were performed for the in vitro studies. (E) The area under the plasma concentration-time curve of thiamine. A single intraperitoneal injection of 2 mg/kg thiamine (with 4% <sup>3</sup>H-thiamine) was administered to four groups of mice (<i>Oct1</i><sup><i>+/+</i></sup> mice treated with control shRNA, <i>n</i> = 6; <i>Oct1</i><sup><i>+/+</i></sup> mice treated with <i>Oct1</i> shRNA, <i>n</i> = 6; <i>Oct1</i><sup><i>-/-</i></sup> mice treated with control shRNA, <i>n</i> = 3 and <i>Oct1</i><sup><i>-/-</i></sup> mice treated with <i>Oct1</i> shRNA, <i>n</i> = 3) Data are normalized to <i>Oct1</i><sup><i>+/+</i></sup> mice treated with control shRNA. Data shown are mean ± SEM. Data were analyzed by unpaired two-tailed Student <i>t</i> test; *<i>p</i> < 0.05, **<i>p</i> < 0.01, and ***<i>p</i> < 0.001. Underlying data are provided in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2002907#pbio.2002907.s012" target="_blank">S1 Data</a>. AUC, area under the curve; EV, empty vector; hOCT1-Ref, human OCT1 reference; hOCT1-420Del, human OCT1 with methinone<sub>420</sub> deletion; hOCT1-420Del+G465R, human OCT1 with mutation in glycine<sub>465</sub>-to-arginine in addition to 420Del; <i>Oct1</i>, organic cation transporter 1; shRNA, short hairpin RNA; TD, thiamine deficient diet.</p
<i>Oct1</i> deletion altered energy homeostasis in vivo.
<p>Beginning at 5 weeks, mice were treated with a thiamine control diet. (A) Representative images of ORO and PAS staining of mouse livers (<i>n</i> = 3 per genotype); scale bars = 100 μm. Quantified hepatic triglyceride (<i>n</i> = 4 per genotype) and glycogen levels (<i>n</i> = 10 per genotype) in mice fasted 16 hours overnight. (B) Body weight of mice from ages 4 to 14 weeks (<i>n</i> = 12–24 per genotype at each time point). (C) Representative images for body composition measured by DEXA (<i>n</i> = 6 per genotype). Percent of total body fat and percent of fat in the region is indicated by the green square (<i>n</i> = 6 per genotype). (D) Representative images and weights of epididymal fat pads (<i>n</i> = 14 per genotype). (E) Body composition of 12-week-old mice measured by EchoMRI before CLAMS (<i>n</i> = 12 per genotype). (F) Respiratory O<sub>2</sub> consumption normalized by total body weight for 96 hours and calculated AUC (<i>n</i> = 12 per genotype). (G) Energy expenditure normalized by total body weight for 96 hours and calculated AUC (<i>n</i> = 12 per genotype). Data shown are mean ± SEM. Data were analyzed by unpaired two-tailed Student <i>t</i> test; *<i>p</i> < 0.05, **<i>p</i> < 0.01, and ***<i>p</i> < 0.001. Underlying data are provided in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2002907#pbio.2002907.s012" target="_blank">S1 Data</a>. AUC, area under the curve; CLAMS, comprehensive laboratory animal monitoring system; DEXA, dual-energy X-ray absorptiometry; <i>Oct1</i>, organic cation transporter 1; ORO, Oil Red-O; O<sub>2</sub>, oxygen; PAS, Periodic-Acid Schiff’s; TG, triglyceride; VO<sub>2</sub>, oxygen consumption.</p