Expression of the angiogenic mediator, angiopoietin-like 4, in the eyes of patients with proliferative sickle retinopathy

The recent success of therapies directly targeting the angiogenic mediator, vascular endothelial growth factor (VEGF), for the treatment of proliferative diabetic retinopathy has encouraged clinicians to extend the use of anti-VEGF therapies for the treatment of another ischemic retinal vascular disease, proliferative sickle cell retinopathy (PSR), the most common cause of irreversible blindness in patients with sickle cell disease. However, results from case reports evaluating anti-VEGF therapies for PSR have been mixed. This highlights the need to identify alternative therapeutic targets for the treatment of retinal neovascularization in sickle cell patients. In this regard, angiopoietin-like 4 (ANGPTL4) is a novel angiogenic factor regulated by the transcription factor, hypoxia-inducible factor 1, the master regulator of angiogenic mediators (including VEGF) in ischemic retinal disease. In an effort to identify alternative targets for the treatment of sickle cell retinopathy, we have explored the expression of ANGPTL4 in the eyes of patients with PSR. To this end, we examined expression and localization of ANGPTL4 by immunohistochemistry in autopsy eyes from patients with known PSR (n = 5 patients). Complementary studies were performed using enzyme-linked immunosorbent assays in aqueous (n = 8; 7 patients, 2 samples from one eye of same patient) and vitreous (n = 3 patients) samples from a second group of patients with active PSR. We detected expression of ANGPTL4 in neovascular tissue and in the ischemic inner retina in PSR, but not control, eyes. We further observed elevated expression of ANGPTL4 in the aqueous and vitreous of PSR patients compared to controls. These results suggest that ANGPTL4 could contribute to the development of retinal neovascularization in sickle cell patients and could therefore be a therapeutic target for the treatment of PSR.直接靶向血管生成介质血管内皮生长因子（vascular endothelial growth factor，VEGF）的疗法在增殖性糖尿病视网膜病变治疗中取得近期成功，促使临床医师将抗VEGF疗法的应用范围拓展至另一种缺血性视网膜血管疾病——增殖性镰状细胞视网膜病变（proliferative sickle cell retinopathy，PSR），而该病是镰状细胞病患者发生不可逆失明的最常见诱因。然而，针对PSR开展的抗VEGF疗法相关病例报告结果并不一致，这凸显出亟需明确镰状细胞病患者视网膜新生血管治疗的替代治疗靶点。在此背景下，血管生成素样4（angiopoietin-like 4，ANGPTL4）作为一种新型血管生成因子，其表达受转录因子缺氧诱导因子1（hypoxia-inducible factor 1）调控——后者是缺血性视网膜疾病中包括VEGF在内的各类血管生成介质的核心调控因子。为探寻镰状细胞视网膜病变的替代治疗靶点，本研究对PSR患者眼部组织中ANGPTL4的表达情况进行了探究。为此，我们通过免疫组织化学法，对5例确诊PSR患者的尸检眼部组织中ANGPTL4的表达与定位情况进行了检测；为补充验证，我们采用酶联免疫吸附测定法，对第二组活动性PSR患者的房水（共8份样本，涉及7例患者，其中1例患者的单眼采集了2份样本）与玻璃体（共3例患者的样本）样本进行了检测。本研究在PSR患者的新生血管组织及缺血性内层视网膜中检测到了ANGPTL4的表达，而对照组眼部组织中未检测到该因子；进一步研究发现，与对照组相比，PSR患者房水与玻璃体中ANGPTL4的表达水平显著升高。上述结果表明，ANGPTL4可能参与了镰状细胞病患者视网膜新生血管的形成过程，有望成为治疗PSR的潜在治疗靶点。