Article

Uncarboxylated osteocalcin ameliorates hepatic glucose and lipid metabolism in KKAy mice via activating insulin signaling pathway

Authors: Xiao-lin Zhang1,2, Ya-nan Wang2, Lu-yao Ma1, Zhong-sheng Liu1, Fei Ye2, Jian-hong Yang1
1 Medical School, University of Chinese Academy of Sciences, Beijing 101400, China
2 Beijing Key Laboratory of New Drug Mechanisms and Pharmacological Evaluation Study, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100050, China
Correspondence to: Fei Ye: yefei@imm.ac.cn, Jian-hong Yang: yangjh@ucas.edu.cn,
DOI: 10.1038/s41401-019-0311-z
Received: 8 March 2019
Accepted: 19 September 2019
Advance online: 28 October 2019

Abstract

Osteocalcin, expressed in osteoblasts of the bone marrow, undergoes post-translational carboxylation and deposits in mineralized bone matrix. A portion of osteocalcin remains uncarboxylated (uncarboxylated osteocalcin, GluOC) that is released into blood where it functions as a hormone to regulate insulin secretion and insulin sensitivity. As insulin resistance is closely associated with metabolic syndrome, this study is aimed to elucidate how GluOC regulates glucose and lipid metabolism in KKAy mice, an animal model displaying obese, hyperglycemia, hyperinsulinemia, insulin resistance, and hepatic steatosis. GluOC (3, 30 ng/g per day, ig) was orally administered to female KKAy mice for 4 weeks. Whole-body insulin sensitivity, glucose metabolism, hepatic steatosis, dyslipidemia were examined using routine laboratory assays. We found that GluOC administration significantly enhanced insulin sensitivity in KKAy mice by activating hepatic IRβ/PI3K/Akt pathway and elevated the whole-body insulin sensitivity with decreased FPI and HOMA-IR index. Furthermore, GluOC administration alleviated hyperglycemia through suppressing gluconeogenesis and promoting glycogen synthesis in KKAy mice and in cultured hepatocytes in vitro. Moreover, GluOC administration dose-dependently ameliorated dyslipidemia and attenuated hepatic steatosis in KKAy mice by inhibiting hepatic de novo lipogenesis and promoting fatty-acid β-oxidation. These results demonstrate that GluOC effectively enhances hepatic insulin sensitivity, improves hyperglycemia and ameliorates hepatic steatosis in KKAy mice, suggesting that GluOC could be a promising drug candidate for treating metabolic syndrome.
Keywords: metabolic syndrome; uncarboxylated osteocalcin (GluOC); insulin resistance; hyperglycemia; dyslipidemia; non-alcoholic fatty-liver disease (NAFLD); obese; KKAy mouse

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