title: Mechanisms of protection against diabetes-induced impairment of endothelium-dependent vasorelaxation by Tanshinone IIA.
abstract: BACKGROUND
  Impairment of endothelium-dependent vasorelaxation has been suggested to play a principle role of endothelial dysfunction in the development of cardiovascular complications of diabetes. Recent studies have demonstrated a protective effect of Tanshinone IIA (Tan) on endothelial nitric oxide synthase (eNOS)-NO pathway. However, its role in endothelium-dependent vasorelaxation in diabetes and precise mechanisms remain elusive.
  
  
  METHODS
  Sprague-Dawley rats were injected intraperitoneally with streptozotocin (STZ) to induce diabetes and then administered orally with Tan for 2 weeks. For the in vitro study, human umbilical vein endothelial cells (HUVECs) were co-incubated with Tan and high glucose for 48 h.
  
  
  RESULTS
  eNOS expression and NO generation were significantly decreased in diabetic rats. These decreases were accompanied by an impairment of endothelium-dependent relaxation. Administration of Tan ameliorated the aberrant changes in eNOS expression, NO generation and endothelium-dependent relaxation in diabetic rats. Expectedly, Tan also inhibited high glucose-induced decrease of eNOS expression and NO generation in a concentration-dependent manner in HUVECs. Mechanistically, high glucose attenuated eNOS transcriptional activity through inhibiting the binding activity and nuclear translocation of Sp1 and AP-1. However, Tan did not prevent these effects. At post-transcriptional level, Tan increased eNOS expression and activity through multiple mechanisms including regulation of mRNA and protein half-life, degradation, coupling and serine 1177 phosphorylation. Rather than affecting protein phosphatase 2A (PP2A) expression and activity, Tan markedly inhibited the translocation of PP2A-A from cytosol to membrane and subsequently impaired PP2A-A/eNOS interaction, leading to prevent eNOS dephosphorylation. All these alterations underlie the protective role of Tan on eNOS expression following high glucose stimulation.
  
  
  CONCLUSIONS
  Our data demonstrate that high glucose decreases eNOS expression initiating at a transcriptional level, whereas Tan prevents such effect through multiple ways of post-transcriptional mechanism.
  
  
  CONCLUSIONS
  Our work provided novel mechanisms for Tan in regulating vasorelaxation and may help to better understand the cardiovascular protective action of Tan.
authors.affiliation: Department of Cardiology, PLA General Hospital, Beijing, China.
authors.forename: Yan-Hua
authors.initials: YH
authors.lastname: Li
authors.affiliation: Department of Cardiology, PLA General Hospital, Beijing, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Xu
authors.affiliation: Scientific Research Department, Medical Administrative Division, PLA General Hospital, Beijing, China.
authors.forename: Wen-Huan
authors.initials: WH
authors.lastname: Xu
authors.affiliation: Department of Cardiology, PLA General Hospital, Beijing, China.
authors.forename: Xin-Hong
authors.initials: XH
authors.lastname: Guo
authors.affiliation: Department of Respiration, PLA General Hospital, Beijing, China. Electronic address: zhangshumed@126.com.
authors.forename: Shu
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Cardiology, PLA General Hospital, Beijing, China. Electronic address: chenydmed@126.com.
authors.forename: Yun-Dai
authors.initials: YD
authors.lastname: Chen
mesh_terms: D045784:Abietanes / Q000494:pharmacology*; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000502:physiology*; D061307:Human Umbilical Vein Endothelial Cells / Q000502:physiology; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000096:biosynthesis; D052250:Nitric Oxide Synthase Type III / Q000502:physiology; D054648:Protein Phosphatase 2 / Q000502:physiology; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013311:Streptozocin; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D045784:Abietanes; C021751:tanshinone; D009569:Nitric Oxide; D013311:Streptozocin; D052250:Nitric Oxide Synthase Type III; D054648:Protein Phosphatase 2
keywords: Diabetes; High glucose; Human umbilical vein endothelial cell; NO synthase; Phosphorylation; Tanshinone IIA