Role of PCK1 Gene on Oil Tea-Induced Glucose Homeostasis and Type 2
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Hu et al. Nutrition & Metabolism (2019) 16:12 https://doi.org/10.1186/s12986-019-0337-8 RESEARCH Open Access Role of PCK1 gene on oil tea-induced glucose homeostasis and type 2 diabetes: an animal experiment and a case-control study Qiantu Hu1†, Huafeng Chen2†, Yanli Zuo3†, Qin He2, Xuan He2, Steve Simpson Jr4,5, Wei Huang2, Hui Yang2, Haiying Zhang1,6* and Rui Lin1,2,6* Abstract Background: Oil tea is a type of traditional tea beverage used for treating various ailments in minority population in Guangxi, China. Our previous study showed oil tea improved glucose and lipid levels in type 2 diabetic mice. Yet, the underling molecular mechanisms are still not understood. This study aimed at assessing the effect of oil tea on glucose homeostasis and elucidating the molecular mechanisms underlying the oil tea-induced antidiabetic effects. Methods: Twenty seven db/db mice were gavaged with saline, metformin and oil tea for 8 weeks with measurement of biochemical profiles. A real-time2 (RT2) profiler polymerase chain reaction (PCR) array comprising 84 genes involved in glucose metabolism was measured and validated by quantitative PCR (qPCR). The association between the candidate genes and type 2 diabetes were further analyzed in a case-control study in the Chinese minority population. Results: Oil tea treatment facilitated glucose homeostasis by decreasing fasting blood glucose and total cholesterol, and improving glucose tolerance. Suppressing phosphoenolpyruvate carboxykinase 1 (PCK1) expression was observed in the oil tea treatment group and the expression was significantly correlated with fasting blood glucose levels. Target prediction and functional annotation by WEB-based GEne SeT AnaLysis Toolkit (WebGestalt) revealed that PCK1 mainly involved in the glycolysis/gluconeogenesis pathway among the top Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathways. Both rs707555 and rs2071023 in PCK1 were significantly associated with type 2 diabetes in the minority population of Guangxi. Conclusion: Our findings indicated oil tea improved glucose homeostasis via down-regulation of PCK1 and PCK1 may be a genetic marker for the treatment of type 2 diabetes. Keywords: Fasting blood glucose, Glucose tolerance, Glycolysis/gluconeogenesis pathway, Oil tea, PCK1,RT2 profiler PCR array, SNP, Type 2 diabetes * Correspondence: [email protected]; [email protected] †Qiantu Hu, Huafeng Chen and Yanli Zuo contributed equally to this work. 1Center for Genomic and Personalized Medicine, Guangxi Medical University, 22 Shuangyong Road, Nanning 530021, Guangxi, China Full list of author information is available at the end of the article © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Hu et al. Nutrition & Metabolism (2019) 16:12 Page 2 of 12 Background added, and the mixture boiled for 1 min and the result- Oil tea is a unique beverage and an important dietary ing decoction retained. This process was repeated twice, component in the minority areas of Guangxi Province, whereupon the mixed decoction was called oil tea. The China. Oil tea is rich in polyphenol, caffeine, 6-gingerol oil tea decoction then was concentrated by a rotary and several minerals [1], and is the most popular vacuum evaporator (IKA Works, Germany) and stored traditional beverage used for treating various ailments in at − 80 °C until use. Guangxi [2]. Green tea and ginger, as the main ingredi- ents of oil tea, individually have exhibited various bio- Animal model and experimental design logical activities, including anticancer effects, antioxidative The experimental procedures were approved by the effects, and antidiabetic effects [3–5]. Previously, our Animal Ethics Committee of Guangxi Center for Disease study showed oil tea treatment improved hyperglycemia, Prevention and Control (Approval No. 20160003). Six glucose intolerance and hyperlipidemia in db/db mice [1]. week-old male diabetic C57BL/KsJ-db/db (db/db) mice While the underlying molecular mechanisms of the were randomly divided assigned to three groups and beneficial effects of oil tea was unknown. orally gavaged with oil tea (4 g/kg body weight (BW)/ Phosphoenolpyruvate carboxykinase 1 (PCK1) is a key day, n = 10), distilled water (0.02 ml/g BW/day, n =7) gluconeogenic enzyme in the liver [6]. It is the cytosolic and metformin (MET, Sigma, USA, the first-line medica- form of phosphoenolpyruvate carboxykinase (PCK or tion for treating T2D, 150 mg/kg BW/day, n =10)for8 PEPCK) and catalyzes the initial step in hepatic gluco- weeks. The oil tea contained 24.6% polyphenols and 0.3% neogenesis. The expression of PCK1 gene is regulated by [6]-gingerol, as described previously [1]. Up to five mice insulin, glucocorticoids, glucagon, cyclic adenosine per cage were maintained in a temperature-controlled monophosphate (cAMP) and diet, all of which have been (22 ± 2 °C) mouse facility on a reverse 12-h light/dark considered associated with diabetic conditions. It has cycle and provided water and chow-diet ad libitum. been reported that PCK1 is up-regulated in diabetic The full nutritional composition of oil tea has been rodent models [7], and overexpression in the transgenic described previously [1]. Body weight and food intake mice resulted in insulin resistance [8] and hyperglycemia were measured each week. [9]. Reciprocally, silencing of PCK1 has been demon- strated to improve glycemia control, insulin sensitivity FBG detection and OGTT test and dyslipidemia in db/db mice [10]. Furthermore, re- Fasting blood glucose (FBG) levels were examined every search has indicated that induced expression of PCK1 week after the db/db mice overnight fasting. The oral may be a useful indicator for effect assessment in dia- glucose tolerance test (OGTT) was performed at weeks betes therapy. Indeed, studies of the effect of Rosmarinic 4 and 8 after the mice were orally gavaged with oil tea acid, insulin, retinoic acid and phenobarbital showed or MET, combined with glucose solution (1 g/kg BW). decreased expression of PCK1 and improvement of Blood glucose levels were measured in tail blood hyperglycemia in diabetic rats [11–13]. Moreover, PCK1 samples collected at 0, 15, 30, 60, 90 and 120 min after has been demonstrated to be a candidate genetic marker glucose treatment. Blood glucose was measured using a for diabetes and obesity risk [14], and more recent glucometer (OMRON Healthcare Co., Ltd., China). research implicated this locus in type 2 diabetes (T2D) risk in Chinese [15], South Asian [16] and Finnish popu- Serum lipid measurement lations [17]. At the end of experiment, mice were killed by cervical In the present study, we investigated the molecular dislocation, and blood samples were collected for the mechanisms of antidiabetic effect of oil tea by examining measurement of biochemical profiles. Levels of serum the expression of PCK1, as well as other genes involved triglycerides (TG), total cholesterol (TC), low-density in glucose metabolism in db/db mice. We also assessed lipoprotein (LDL) and high-density lipoprotein (HDL) whether PCK1 is a genetic marker for T2D risk in the were measured using commercial kits (Shanghai minority population in Guangxi. Enzyme-linked Biotechnology Co., Ltd., China). Insulin was measured using a commercial Mouse Insulin ELISA Methods kit (ALPCO Diagnostics, USA). Preparation of oil tea The oil tea was prepared as previously described [1, 18]. RT2 profiler PCR array analysis In brief, the proportions of green tea, ginger, peanut, After mice were killed, the fresh livers were collected cooking oil and salt were 9:10:5:2:1. The manufacturing and snap frozen in liquid nitrogen, and then stored at − process was as follows: firstly, soaked green tea leaf was 80 °C until analysis. Total RNA was isolated from the stir-fried and beaten with ginger, peanut and cooking oil liver samples of db/db control group and oil tea group in a hot iron pot for 3 min, then hot water and salt using Qiagen RNeasy® Mini Kit (QIAGEN, Shanghai, Hu et al. Nutrition & Metabolism (2019) 16:12 Page 3 of 12 China) according to the manufacturer’s instructions. according to the manufacturer’s instructions. The quan- Single-strand cDNA was synthesized from 1 μg of total titative expressions of genes, again, were calculated from −ΔΔ RNA by reverse transcription reaction using Qiagen RT2 the CT value using the 2 CT method. Those genes First Strand Kit (QIAGEN, Shanghai, China). The cDNA with expressions less than 0.75-fold were selected fur- was mixed with Qiagen PCR RT2 SYBR Green Master ther for pathway and biological process analysis by using Mix (QIAGEN, Shanghai, China). WEB-based GEne SeT AnaLysis Toolkit (WebGestalt, To explore the underlying mechanisms of oil tea http://www.webgestalt.org/). Target genes were those ex- induced-effects, the expression of 84 genes involved in pression significantly differed between the oil tea group glucose metabolism including PCK1 were examined and db/db control group (p < 0.05) and were analyzed using a Qiagen mouse glucose metabolism RT2 profiler the correlation with FBG further. PCR array (PAMM-006Z, QIAGEN, Shanghai, China). Relative quantification of mRNA levels was determined Selection of the human subjects by real-time quantitative PCR using a Bio-Rad CFX96 Eighty-six T2D patients and 286 healthy subjects were Sequence Detector instrument. The quantitative expres- recruited from the nutrition survey conducted in the mi- sion of gene was calculated from the cycle threshold nority areas in Gongcheng Yao Autonomous County and (CT) value of each sample in the linear part of the curve Binyang County, Guangxi, China from 2014 to 2015.