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

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

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>_m = 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

Different thiamine treatments affected glucose metabolism.

<p>(A) Scheme of experimental design. Two groups of mice (Group-1 and Group-2) were treated with a CD, 5 mg/kg, and one group (Group-3) with an HT, 50 mg/kg, to the end of the experiment. The third group of mice (Group-2) was treated with a CD but switched to a TD, 0 mg/kg, for 10 days. After dietary treatment, mice were fasted overnight for 16 hours before being humanely killed (<i>n</i> = 4 per genotype in each treatment). (B) Hepatic glycogen content quantification. (C) Hepatic glucose content quantification. (D) Plasma glucose quantification. For (B–D), CD, TD, and HT indicate diet received by the mice during the final 10 days of treatment. (E) Hepatic glucose-6-phosphate content quantification. (F) Representative western blots of protein expression in enzymes involved in energy metabolism; protein was pooled from 4 mice per genotype. Data shown are mean ± SEM. Data were analyzed by ordinary one-way ANOVA and <i>p</i>-value is stated, and Dunnett’s post hoc test was used to compare to the control (CD) group for (B), (C), and (D). Data were analyzed by unpaired two-tailed Student <i>t</i> test for (E); *<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>. CD, thiamine controlled diet; Glut2, glucose transporter 2; GS, glycogen synthase; GS-p⁶⁴¹, phospho-glycogen synthase at serine 641; HT, high thiamine diet; Oct1, organic cation transporter 1; TD, thiamine deficient diet.</p