Expression Pattern of HIF-1α and VEGF Supports Circumferential Application of Scatter Laser for Proliferative Sickle Retinopathy

Abstract

PurposeRetinal vascular occlusions in sickle cell anemia patients cause tissue ischemia and the release of angiogenic mediators that promote the development of retinal neovascularization, initiating proliferative sickle retinopathy (PSR). Laser photocoagulation (LPC) has emerged as the most common treatment for PSR. Nonetheless, only two randomized controlled clinical trials have evaluated the use of LPC for PSR, and both failed to definitively demonstrate efficacy of this approach. This may be due to a lack of knowledge regarding the appropriate location for placement of laser coagulations in PSR eyes. To help address this question, we examined the expression of hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) in PSR eyes.MethodsThe expression pattern of HIF-1α and VEGF in PSR (n = 5) and control (n = 3) eyes was examined by immunohistochemistry in different retinal regions defined by the presence or absence of retinal vessels.ResultsHypoxia-inducible factor 1α and VEGF were expressed in the inner retina of 5/5 untreated PSR eyes adjacent to retinal neovascularization; expression of HIF-1α was not detected (and VEGF only lightly detected) in normal retinal and choroidal vasculature of 3/3 control eyes. Hypoxia-inducible factor 1α and VEGF were strongly expressed in retinal cells within avascular (nonperfused) retina, anterior to the boundary between perfused and nonperfused retina, as well as in posterior ischemic retina in the presence or absence of neovascular sea fans.ConclusionsIf the goal of LPC in PSR is to quench the expression of HIF-1–driven angiogenic mediators, our results support broad application of peripheral laser for its treatment.

Sickle cell retinopathy. A focused review

“…The reason why there was no clear benefit of laser compared with observation in PSR may thus have been related to a lack of consensus regarding how to apply the laser treatment. Recently, the study of autopsy eyes with SCD suggested that hypoxia-inducible factor 1 (HIF-1α) and vascular endothelial growth factor (VEGF) are being produced not only in the endothelial cells lining the neovascularizations and in the inner retina of the peripheral non-perfused retina distantly from the neovascularizations but also to some extent in a 2-mm wide transitional zone posterior to the non-perfused periphery [67]. This may support broad application of peripheral laser, such as circumferential scatter covering the entire area from the Ora Serrata anteriorly up to 1-2 mm posteriorly to the neovascularization for the treatment of PSR [67].…”

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

“…To evaluate the expression of the HIF-regulated angiogenic mediator, ANGPTL4, in the eyes of patients with known PSR, we examined 5 paraffin-embedded autopsy eyes from 5 non-diabetic patients sickle cell disease with untreated PSR (i.e., no prior history of scatter laser photocoagulation or intravitreal anti-VEGF therapy), and no history of another ischemic retinal disease. We focused on areas of the peripheral retina anterior to the margin between perfused and non-perfused retina, as we have recently reported that VEGF and the α-subunit of HIF-1, the transcription factor that regulates its expression, are expressed in the peripheral ischemic retina in this region in PSR eyes[ 17 ]. We have also previously demonstrated that ANGPTL4 expression is regulated by HIF-1 in diabetic eye disease[ 13 – 15 ] as well as in the intraocular tumor, uveal melanoma[ 18 ], similar to VEGF.…”

“…We have previously reported that HIF-1α and VEGF are also expressed in the peripheral ischemic retina in regions without active NV in PSR eyes[ 17 ]. We therefore examined expression of ANGPTL4 in the ischemic peripheral retina of autopsy eyes from patients with sickle cell retinopathy in regions without active NV.…”

“…Immunohistochemical detection of ANGPTL4 (1:400 dilution; Abcam, Cambridge, MA) and CD34 (1:500 dilution; Covance, Princeton, NJ) was performed in paraffin-embedded tissue sections using premixed biotinylated anti-rabbit, anti-mouse and anti-goat immunoglobulins in phosphate buffered saline (PBS) from an ABC system (Dako, Santa Clara, CA) performed according to the manufacturer’s protocols as previously described[ 16 , 17 ]. All immunohistochemical reagents, including antibodies, were identical for all specimens.…”

Hypoxia, angiogenesis, and metabolism in the hereditary kidney cancers

“…For instance, brain, spinal cord, and eye/retina hemangioblastoma formation is commonplace in VHL disease (94,95), owing in part to disruption of the VEGF-A (96, 97) and Notch pathways (98), among others. Dysfunction in HIF signaling is also likely involved in the aberrant vessel remodeling found in nonkidney tissues, as recent studies have implicated this pathway, and downstream mediators such as ANGPT-like 4 (ANGPTL4), in angiogenesis-related conditions including pterygia (99), uveal melanoma (100), and proliferative retinopathies (101)(102)(103). Increased insight into how angiogenesis defects lead to clinical manifestations of ocular VHL disease, such as retinal capillary hemangioblastoma (RCH) formation, will advance future therapies as well as enhance the diagnostic strategies of ophthalmological examination of VHL patients (104)(105)(106).…”