Anti-VEGF therapy prevents M\xfcller intracellular edema by decreasing VEGF-A in diabetic retinopathy

Tianqin Wang,Mengmeng Jiang,Jingfa Zhang,Guo-Tong Xu,Hai Xie,Lixia Lu,Chaoyang Zhang,Lin Liu,Haibin Tian

doi:10.1186/s40662-021-00237-3

Abstract

BackgroundAlthough vascular endothelial growth factor A (VEGF-A) is known to play a key role in causing retinal edema, whether and how VEGF-A induces intracellular edema in the retina still remains unclear.MethodsSprague-Dawley rats were rendered diabetic with intraperitoneal injection of streptozotocin. Intravitreal injection of ranibizumab was performed 8 weeks after diabetes onset. rMC-1 cells (rat Müller cell line) were treated with glyoxal for 24 h with or without ranibizumab. The expression levels of inwardly rectifying K+ channel 4.1 (Kir4.1), aquaporin 4 (AQP4), Dystrophin 71 (Dp71), VEGF-A, glutamine synthetase (GS) and sodium-potassium-ATPase (Na+-K+-ATPase) were examined using Western blot. VEGF-A in the supernatant of the cell culture was detected with ELISA. The intracellular potassium and sodium levels were detected with specific indicators.ResultsCompared with normal control, protein expressions of Kir4.1 and AQP4 were down-regulated significantly in diabetic rat retinas, which were prevented by ranibizumab. The above changes were recapitulated in vitro. Similarly, the intracellular potassium level in glyoxal-treated rMC-1 cells was increased, while the intracellular sodium level and Na+-K+-ATPase protein level remained unchanged, compared with control. However, ranibizumab treatment decreased intracellular sodium, but not potassium.ConclusionRanibizumab protected Müller cells from diabetic intracellular edema through the up-regulation of Kir4.1 and AQP4 by directly binding VEGF-A. It also caused a reduction in intracellular osmotic pressure.

Highlights

Vascular endothelial growth factor A (VEGF-A) is known to play a key role in causing retinal edema, whether and how vascular endothelial growth factor A (VEGF-A) induces intracellular edema in the retina still remains unclear
Müller intracellular edema was increased in diabetic rat retina, which was alleviated by ranibizumab In order to evaluate Müller intracellular edema in vivo, we adopted the published method by using semithin sections of the retina.[21]
We found that increased VEGF-A, and decreased Kir4.1, aquaporin 4 (AQP4) and Dystrophin 71 (Dp71) in diabetic retinas contributed to the intracellular edema seen in Müller cells

Summary

Introduction

Vascular endothelial growth factor A (VEGF-A) is known to play a key role in causing retinal edema, whether and how VEGF-A induces intracellular edema in the retina still remains unclear. The breakdown of the inner BRB plays the most important role, caused by junctional complex alternation,[4] enhanced transcellular permeability,[5] loss of endothelial cells,[6] loss of pericytes[7] and vessel abnormality.[8, 9] Dysfunction of Müller glia and RPE contribute to the fluid accumulation in the neural retina and subretinal space leading to intracellular and extracellular edema.[10] In our previous study, a strong correlation was found between central subfield thickness (CSFT) and the thickness of inner nuclear layer (INLT) in more severe DME (CSFT > 275 μm), suggesting that intracellular edema, Müller glial edema, contributes to DME formation.[11] Müller cells, as specific macroglia in the retina, regulate the homeostasis of ion and water mainly through inward rectifying potassium channel 4.1 (Kir4.1) and aquaporin 4 (AQP4).[12,13,14] Müller cells are the main source of vascular endothelial growth factor (VEGF) apart from vascular endothelial cells.[15]

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