title: High glucose induces and activates Toll-like receptor 4 in endothelial cells of diabetic retinopathy.
abstract: BACKGROUND
  Hyperglycemia-induced inflammation causes the dysfunction of blood vessels, and Toll-like receptor 4 (TLR4) plays a key role in inflammation-induced angiogenesis. However, the impact of TLR4 on the pathogenesis of diabetic retinopathy (DR) is poorly understood. In this study, we examined the expression of TLR4 in retinal vascular endothelial cells of patients with DR and diabetic mice, and explored the role of TLR4 in mediating inflammatory responses by human microvascular endothelial cells (HMEC-1) under high-glucose condition.
  
  
  METHODS
  The expression of TLR4 in retinal vascular endothelial cells of patients with proliferative diabetic retinopathy and diabetic mice induced by streptozotocin was examined using immunofluorescence. HMEC-1 cells were cultured and the expression of TLR4, MyD88 and Interleukin-1β (IL-1β) was examined under high-glucose condition. Endothelial cells with TLR4 silencing and antagonist of TLR4 as well as endothelial cells from TLR4 deficient mice were used to study the effect of activated TLR4 on inflammation induced by high-glucose treatment.
  
  
  RESULTS
  We observed that TLR4 was detected in CD31-labled human retinal vascular endothelia and its expression was markedly increased in fibrovascular membranes from DR patients and in retinal vascular endothelial cells of diabetic mice. The expression of TLR4, MyD88 and IL-1β was enhanced by high glucose in cultured HMEC-1 and the expression of TLR4 and IL-1β was inhibited by TLR4 siRNA knock-down and TLR4 antagonist. The expression of IL-1β by endothelial cells from TLR4 deficient mice under high glucose condition was decreased.
  
  
  CONCLUSIONS
  Our results revealed that hyperglycemia induced overexpression and activation of TLR4 in endothelial cells. This effect may lead to inflammatory responses contribute to the pathogenesis of diabetic retinopathy.
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China ; Guangdong Province Hospital of Traditional Chinese Medicine, Guangzhou, 510120 China.
authors.forename: Lu
authors.initials: L
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China.
authors.forename: Jiazhu
authors.initials: J
authors.lastname: Fang
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China.
authors.forename: Xialin
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China.
authors.forename: Shao Bo
authors.initials: SB
authors.lastname: Su
keywords: Angiogenesis; Diabetic retinopathy; Endothelium; Inflammation; Toll-like receptor 4