TRAF6 mediates high glucose-induced endothelial dysfunction
Introduction
Diabetes mellitus (DM) is characterized by chronic hyperglycemia, and impaired insulin secretion or action, or a combination of both, and is often associated with the development of vascular complications [1]. The prevalence of DM is about 2–5% in most western countries, and is rapidly increasing in Asian countries because of ongoing life style changes [2]. Effective strategies for DM treatment are urgently needed.
The simple endothelium that lines the internal surface of blood vessels is important for maintaining vascular tone and structure [3]. Substantial clinical and experimental evidence suggests that both DM and insulin resistance are responsible for endothelial changes that reduce the anti-atherogenic function of vascular endothelium [4], [5], [6], but the underlying mechanisms are not clear.
Previous studies have described TNF receptor associated factor (TRAF) mediated inflammatory responses [7], [8], [9]. TRAF6 acts downstream of cytokine and toll-like receptors (TLRs) to regulate the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) [10], which plays a key role in the progression of inflammation-related diseases [11], [12], [13]. However, the activity of TRAF6 in DM at the molecular has not been determined.
We investigated the role of TRAF6 in vitro in a high glucose-induced model of endothelial cell dysfunction and in vivo in a type I diabetes mouse model. We found that TRAF6 mediated high glucose-induced endothelial dysfunction via NF-κB- and activator protein (AP)-1-dependent signaling. Targeting TRAF6 in patients with DM and atherosclerosis might delay progression of vascular diseases.
Section snippets
Ethical approval of the study protocol
All research involving human participants was approved by the Institutional Review Board of Shanghai Jiaotong University School of Medicine, Shanghai, China. All participants gave written informed consent. The study protocol was approved by the Institutional Animal Care and Use Committee of Shanghai Jiao Tong University School of Medicine. The study was conducted following international guidelines for animal experimentation.
Cell culture
Human aortic endothelial cells (HAECs) were purchased from Lonza Co.
High glucose induces TRAF6 expression in HAECs
qPCR and western blotting revealed that high glucose significantly increased TRAF6 mRNA (Fig. 1A) and protein (Fig. 1B) expression in HAEC after 30 min of incubation, and that the levels remained elevated even after 8 h.
TRAF6 knockdown significantly reduces high glucose-induced endothelial cell dysfunction
Because high glucose elevated TRAF6 expression, we investigated the relationship of TRAF6 expression and endothelial cell dysfunction by gene knockdown in cell culture models (Fig. 2A). High glucose markedly reduced HAEC viability (Fig. 2B) and apoptosis (Fig. 2C), but those
Discussion
We demonstrated that culture in high glucose medium significantly increased TRAF6 mRNA and protein expression in HAEC in a time dependent manner. In the functional assay, we found that high glucose markedly reduced HAEC viability, apoptosis, and migration, and that these effects were significantly reversed by TRAF6 knockdown. Moreover, high glucose significantly increased adhesion of THP-1 monocytes by upregulating ICAM-1 and VCAM-1 expression, whereas TRAF6 knockdown attenuated that effect.
Conclusion
In conclusion, TRAF6 mediated high glucose-induced endothelial dysfunction via NF-κB and AP-1-dependent signaling. Treatments targeting TRAF6 might delay progression of vascular diseases in patients with DM and atherosclerosis.
Acknowledgement
None.
Disclosure of conflict
None.
Funding
This work was supported by the National Natural Science Foundation of China (Grant number 81300177, 81770282), Shanghai Municipal Education Commission-Gaofeng Clinical Medicine Grant Support (Grant number 20152232), National Natural Science Foundation of China (Grant number 81300177) and Shanghai Jiao Tong University (YG2013MS52), Project supported by Shanghai Jiao Tong University Affiliated Sixth People's Hospital (1715).
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These authors contributed equally to this work.