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Open Access Highly Accessed Original investigation

Osteocalcin attenuates high fat diet-induced impairment of endothelium-dependent relaxation through Akt/eNOS-dependent pathway

Jianxin Dou, Huating Li, Xiaojing Ma, Mingliang Zhang, Qichen Fang, Meiyun Nie, Yuqian Bao* and Weiping Jia

  • * Corresponding author: Yuqian Bao byq522@163.com

  • † Equal contributors

Author Affiliations

Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai Clinical Center for Diabetes, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Diabetes Institute, 600 Yishan Road, Shanghai 200233, China

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Cardiovascular Diabetology 2014, 13:74  doi:10.1186/1475-2840-13-74

Published: 7 April 2014

Abstract

Background

Recent studies have demonstrated a protective effect of osteocalcin (OCN) on glucose homeostasis and metabolic syndrome. However, its role in vascular function remains unknown. This study investigated the contribution of OCN to the pathogenesis of endothelial dysfunction in the thoracic aorta of apolipoprotein E-deficient (ApoE-KO) mice.

Methods

Eight-week-old ApoE–KO mice were given chow or high fat diet (HFD) for 12 weeks with or without daily intraperitoneal injection of OCN. Intraperitoneal glucose tolerance test (IPGTT), insulin tolerance test (ITT),measurement of serum lipid profiles and blood pressure were carried out. Endothelium-dependent relaxation (EDR) was measured by wire myography. Human umbilical vein endothelial cells (HUVECs) were used to study the role of OCN on eNOS levels in vitro. PI3K inhibitor (LY294002) and Akt inhibitor V were used ex-vivo to determine whether PI3K/Akt/eNOS contributes to the beneficial effect of OCN for the vascular or not.

Results

Daily injections of OCN can significantly improve lipid metabolism, glucose tolerance and insulin sensitivity in ApoE-KO mice. In ApoE-KO mice fed with HFD, the OCN-treated mice displayed an improved acetylcholine-stimulated EDR compared to the vehicle-treated group. In addition, compared to vehicle-treated HUVECs, OCN-treated HUVECs displayed increased activation of the Akt-eNOS signaling pathway, as evidenced by significantly higher levels of phosphorylated Akt and eNOS. Furthermore, a similar beneficial effect of OCN on thoracic aorta was observed using ex vivo organ culture of isolated mouse aortic segment. However, this effect was attenuated upon co-incubation with PI3K inhibitor or Akt inhibitor V.

Conclusions

Our study demonstrates that OCN has an endothelial-protective effect in atherosclerosis through mediating the PI3K/Akt/eNOS signaling pathway.

Keywords:
ApoE knockout mice; Osteocalcin; Endothelium-dependent relaxation; PI3K/Akt/eNOS signaling pathway; Metabolic syndrome; Atherosclerosis