Management of retinopathy of prematurity

The Role of Insulin-like Growth Factor-1 and Its Receptor in the Eye: A Review and Implications for IGF-1R Inhibition

PURPOSE

FDA approval of teprotumumab for thyroid eye disease in January 2020 reinforced interest in the pharmacologic potential of insulin-like growth factor-1 (IGF-1) and its receptor, IGF-1R. Despite recent approval and adaptation for ophthalmic use, IGF-1R inhibitors are not a new therapeutic class. In 1986, Yamashita described aIR3, a monoclonal antibody to IGF-1R (anti-IGF-1R), that inhibited the effect of IGF-1 on growth hormone release. Given the widespread presence of IGF-1R, interrupting this receptor can lead to systemic physiologic effects, some adverse. We aim to review what is known about IGF-1/IGF-1R in the eye and consider the possible local side effects, unintended consequences, and potential uses of this medication class.

METHODS

A PubMed database search utilizing the keywords "insulin-like growth factor-1, eye, inhibitor, antibody, side effect" was performed to identify publications discussing IGF-1 in the human eye from January 2011 to August 2021. Criteria for acceptance included studies discussing human subjects or human tissue specifically related to the eye.

RESULTS

Out of a total of 230 articles, 47 were organized in 3 subject groups for discussion: thyroid-associated orbitopathy, cornea and the ocular surface, and the retina and neovascularization. Review of the literature demonstrated that IGF-1 affects growth and development of the eye, epithelial proliferation, retinal angiogenesis, inflammation, and is associated with thyroid-associated orbitopathy.

CONCLUSIONS

IGF-1R exists throughout in the human body, including the cornea, retina, and orbit. Research regarding ocular effects of IGF-1/IGF-1R outside thyroid eye disease is limited. Carefully designed studies and clinical assessments of patients undergoing treatment with anti-IGF-1R may identify ocular side effects and foster consideration of the role of anti-IGF-1R in ocular therapeutics. Given the increasing use of anti-IGF-1R antibodies, understanding their ocular effects, side effects, and potential systemic implications for use in disease is critical.

Neurodevelopmental outcomes following bevacizumab treatment for retinopathy of prematurity: a systematic review and meta-analysis

OBJECTIVE

To systematically review the studies exploring the association between bevacizumab and neurodevelopmental outcomes.

METHODS

Embase, Medline, CINAHL, and Cochrane Library databases were searched for studies examining neurodevelopmental outcomes of preterm infants treated with bevacizumab compared to laser ablation or cryotherapy for severe retinopathy of prematurity (ROP).

RESULTS

Thirteen studies (clinical trial = 1; cohort studies = 12) were included. Random-effects model meta-analysis showed significant increased odds of cognitive impairment associated with bevacizumab treatment on both unadjusted (unadjusted odds ratio (OR) 1.61; 95% confidence interval (CI) 1.12, 2.30) and adjusted analyses (adjusted OR 1.90; 95% CI 1.22, 2.97). Infants treated with bevacizumab for severe ROP had significantly lower Bayley-III cognitive (mean difference (MD) -1.66; 95% CI -3.21, -0.12), and language composite scores (MD -5.50; 95% CI -8.24, -2.76) compared to infants treated with laser ablation or cryotherapy.

CONCLUSION

Bevacizumab treatment for severe ROP is associated with increased risk of cognitive impairment and lower cognitive and language scores in preterm infants.

Vision-related quality of life in children with treated retinopathy of prematurity

Purpose:

To evaluate vision-related quality of life in children treated for retinopathy of prematurity.

Methods:

Cross sectional observational study of 54 treated ROP babies 2–7 years of age. The study excluded babies with chronic pediatric conditions and babies of parents suffering from mental illness. Detailed examination including visual acuity was done for all. Two versions of CVFQ questionnaire for children under 3 and above 3 years of age were posed to parents in this study. CVFQ contains six subscales: General health, vision health, competence, personality, family impact, and treatment difficulty. The scores ranged from 0 (worst score) to 1 (best score).

Results:

The study included 54 children with mean birth weight was 1194 grams, mean gestation age 30 weeks. The age, gender, birth weight, and gestational age didn’t affect the overall quality of life (P > 0.05). The severity of ROP (stage 4 and 5) had poorer CVFQ scores (personality and family impact subscales). Competence and personality scores were significantly lower in zone I disease. The quality of life especially general vision, competence, personality, and treatment difficulty subscales had significantly lower values in ROP with higher clock hour involvement (P < 0.05). With myopia after ROP treatment, only personality subscale was significantly affected (P 0.02). Mean CVFQ score including the family impact and treatment difficulty subscale score was also significantly lower in amblyopic and anisometropic children (P value < 0.05). Family impact subscale and overall quality of life was significantly lower in children with strabismus than children without strabismus (P 0.001).

Conclusion:

ROP has negative effect on the vision-related quality of life of children and their parents. The overall quality of life worsened with the increase in the severity of disease and the occurrence of ocular sequelae of ROP. The vision of the baby may not be the only cause of low scores in the quality of life questionnaire in ROP.

Turkish Neonatal and Turkish Ophthalmology Societies consensus guideline on the retinopathy of prematurity

Retinopathy of prematurity is a pathophysiological condition that occurs in relation to abnormal proliferation in the retinal vessels in premature babies. Its exact pathogenesis is not known. In Turkey, the increased chance of survival in premature babies with much younger gestational age and much lower birth weight in parallel with the developments in neonatal care causes retinopathy of prematurity, which has led to vision problems and blindness to emerge as a more frequent problem. Early diagnosis and timely and appropriate treatment of retinopathy of prematurity contributes to the developmental process and increases the quality of life by preventing vision loss. It should be kept in mind that retinopathy of prematurity may also lead to serious medicolegal problems.

Platelet mass index can be a reliable marker in predicting the prognosis of retinopathy of prematurity in very preterm infants

BACKGROUND

Retinopathy of prematurity (ROP) is a proliferative vitreoretinopathy resulting from vascular defect of the retina. The present study evaluates platelets, which are involved in VEGF storage, transport and release, and their functions with regard to the prognosis of the disease. The objective was to suggest a simple minimal invasive method that will facilitate the management of the disease and help clinicians in predicting the prognosis.

METHODS

In this single center, retrospective, case-control study, we included a control group consisting of very preterm newborns (n = 83) at risk of ROP and a laser photocoagulation group including infants (n = 63) who received laser therapy during their follow-up examinations. The employed assessments included platelet counts and platelet mass index (PMI) which provide guidance in understanding platelet activity. In doing so, consideration was given to the first and second phases of ROP. The accuracy of prognostication was assessed with receiver operating characteristic analyses.

RESULTS

The study groups did not differ statistically significantly by platelet count during the first and second phases of ROP (p > 0.05) nor were the PMI measurements statistically significantly different between the study groups during the first phase of the disease (p > 0.05). PMI values of the study groups, however, differed significantly in the second phase of ROP (p < 0.05).

CONCLUSION

The present study found a significant difference between the two groups in PMI measurements which reflect increased VEGF levels during the neovascularization phase, which underlies the disease. This conclusion demonstrated that monitoring the PMI values in newborns at risk of ROP can be considered to be a minimally invasive method that by changing the retinal examination procedure in use today which is rather troublesome for both the physician and the newborn, can provide facilities in monitoring the disease for both the physician and the newborn.

The efficacy of propranolol in very preterm infants at the risk of retinopathy of prematurity: Which newborn and when?

PURPOSE

Retinopathy of prematurity (ROP), a proliferative vitreoretinopathy resulting from the vascular disorder of the retina, is the most frequent cause of blindness in childhood. In our time, ROP in advanced stage, a serious problem in premature infants, has no other treatment more effective and with fewer side effects than laser photocoagulation (LPC) treatment, which narrows visual field. The search for methods with fewer side effects than LPC has increased in recent times for the treatment of ROP. We aimed to investigate the effects in question of propranolol on ROP in various stages (stages 1, 2, and 3 ROP).

METHODS

This study is designed as a randomized, placebo-controlled, single-centered, double-blind clinical trial with parallel groups. A total of 126 very preterm infants, followed up in our unit from April 2011 to January 2013, were randomly selected and included in our study. They were separated into the groups of 0, 1, and 2 depending on their stage of ROP. In addition, all the patients were divided into control group (CG) and propranolol treatment group (PTG). While the cases in the CG were administered physiological saline solution, the cases in the PTG were administered propranolol (2 mg/kg/day) in the neovascularization phase (second phase) of the ROP.

RESULTS

Propranolol given to the group of stage 0-1 ROP was observed to have had no effect on the level of statistical significance between the CG and PTG in terms of increase in ROP stages (p > 0.05). However, propranolol was found to be more useful in patients with stage 2 ROP (p < 0.05).

CONCLUSION

When given in the neovascularization phase of the ROP, propranolol was found to be effective in the stage 2 (advanced stage) ROP patients but in stage 0-1 (early-stage) ROP patients, its efficacy was not sufficient.

The progress of prophylactic treatment in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a retinal vascular disorder frequently found in premature infants. Different therapeutic strategies have been developed to treat ROP. However, there are still many children with ROP suffering by severe limitations in vision or even blindness. Recently, ROP has been suggested to be caused by abnormal development of the retinal vasculature, but not simply resulted by retinal neovascularization which takes about 4 to 6wk after birth in premature infants. Thus, instead of focusing on how to reduce retinal neovascularization, understanding the pathological changes and mechanisms that occur prior to retinal neovascularization is meaningful, which may lead to identify novel target(s) for the development of novel strategy to promote the healthy growth of retinal blood vessels rather than passively waiting for the appearance of retinal neovascularization and removing it by force. In this review, we discussed recent studies about, 1) the pathogenesis prior to retinal neovascularization in oxygen-induced retinopathy (OIR; a ROP in animal model) and in premature infants with ROP; 2) the preclinical and clinical research on preventive treatment of early OIR and ROP. We will not only highlight the importance of the mechanisms and signalling pathways in regulating early stage of ROP but also will provide guidance for actively exploring novel mechanisms and discovering novel treatments for early phase OIR and ROP prior to retinal neovascularization in the future.

The annexin A2 system and angiogenesis

The formation of new blood vessels from pre-existing vasculature, the process known as angiogenesis, is highly regulated by pro- and anti-angiogenic signaling molecules including growth factors and proteases. As an endothelial cell-surface co-receptor for plasminogen and tissue plasminogen activator, the annexin A2 (ANXA2) complex accelerates plasmin generation and facilitates fibrinolysis. Plasmin can subsequently activate a downstream proteolytic cascade involving multiple matrix metalloproteinases. Thus, in addition to maintaining blood vessel patency, the ANXA2 complex can also promote angiogenesis via its pro-fibrinolytic activity. The generation of ANXA2-deficient mice allowed us to first observe the pro-angiogenic role of ANXA2 in vivo. Further investigations have provided additional details regarding the mechanism for ANXA2 regulation of retinal and corneal angiogenesis. Other studies have reported that ANXA2 supports angiogenesis in specific tumor-related settings. Here, we summarize results from in vivo studies that illustrate the pro-angiogenic role of ANXA2, and discuss the critical questions that may lead to an advanced understanding of the molecular mechanisms for ANXA2-mediated angiogenesis. Finally, highlights from studies on ANXA2-interacting agents offer potential therapeutic opportunities for the application of ANXA2-centered pharmaceuticals in angiogenesis-related disorders.

Early Erythropoietin Administration does not Increase the Risk of Retinopathy in Preterm Infants

BACKGROUND

Erythropoietin (EPO) administration prevents anemia of prematurity and may be associated with a significant increase in the risk of retinopathy of prematurity (ROP) in preterm infants. Nonetheless, early EPO treatment may prevent damage following retinal neovascularization. The aim of this meta-analysis was to elucidate whether EPO administration increases the risk of ROP.

METHODS

We searched MEDLINE, PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials with no language restrictions. Randomized controlled trials that reported the association between EPO treatment in preterm infants and ROP were eligible. All of the included studies were stratified into two groups according to the age of initiation of EPO treatment: before 8 days of age (early EPO), and 8-28 days of age (late EPO).

RESULTS

Thirteen studies were identified that included a total of 1999 preterm infants. EPO administration did not increase the risk of ROP of any stage or Stage ≥3 (any relative risk: 0.99, 95% confidence interval: 0.84-1.16, p = 0.89; Stage ≥3 relative risk: 1.34, 95% confidence interval: 0.90-1.99, p = 0.15). This trend remained unchanged in both the early and late EPO groups. There did not seem to be any evidence of publication bias for outcomes as the funnel plots were symmetrical.

CONCLUSION

EPO administration did not significantly increase the risk of ROP of any stage reported or Stage ≥3. Further clinical trials investigating the impact of EPO on ROP in premature infants should include all confounding factors to clarify this important issue.

Eye pathologies in neonates

In the United Kingdom, newborn assessment incorporates a screening eye examination for any structural abnormalities, observation of neonate's visual behaviour and direct ophthalmoscopy examination looking for red reflex. Early identification and immediate management of eye related pathologies should commence soon after birth as early diagnosis and prompt intervention may have significant impact on the prognosis for many potentially blinding but treatable disorders such as congenital cataracts and retinoblastoma. If left undetected and untreated, such problems may potentially lead to irreversible damage to the vision which persists into adulthood resulting in lack of self-confidence together with difficulties in educational attainment and job opportunities.

Pharmacologic interventions for the prevention and treatment of retinopathy of prematurity

Retinopathy of prematurity (ROP), a significant morbidity in prematurely born infants, is the most common cause of visual impairment and blindness in children and persists till adulthood. Strict control of oxygen therapy and prevention of intermittent hypoxia are the keys in the prevention of ROP, but pharmacologic interventions have decreased risk of ROP. Various drug classes such as methylxanthines (caffeine), VEGF inhibitors, antioxidants, and others have decreased ROP occurrence. The timing of pharmacologic intervention remains unsettled, but early prevention rather than controlling disease progression may be preferred. These drugs act through different mechanisms, and synergistic approaches should be considered to maximize efficacy and safety.

Retinopathy of Prematurity: Therapeutic Strategies Based on Pathophysiology

Retinopathy of prematurity (ROP) continues to be a major preventable cause of blindness and visual handicaps globally. With improved perinatal care, improved survival of moderately preterm infants, and limited resources for oxygen delivery and monitoring, more mature preterm infants are developing severe ROP in developing countries. The pathophysiology of ROP is characterized by two phases. Phase I ROP is due to vaso-obliteration beginning immediately after birth secondary to a marked decrease in vascular endothelial growth factor (VEGF) and insulin-like growth factor-1 (IGF-1). Phase II begins around 33 weeks' postmenstrual age (PMA). During this phase, VEGF levels increase, especially if there is retinal hypoxia with increasing retinal metabolism and demand for oxygen leading to abnormal vasoproliferation. Since the original description of ROP in 1942 by Terry et al. [Am J Ophthalmol 1942;25:203-204], four epidemics of ROP have been observed. Prevention or early treatment of ROP involves careful titration of oxygen saturation by pulse oximeter (SpO2). Optimal SpO2 target remains elusive. Most of the large trials have focused on either a low SpO2 (85-89%) or a high SpO2 (91-95%) from the first day of birth to 36 weeks' PMA. Although the incidence of severe ROP and bronchopulmonary dysplasia decreased significantly, predischarge mortality was higher in these studies. Use of graded SpO2 during the 2 different phases of ROP (early, low SpO2 during phase I vs. late, high SpO2 during phase II) may be the best approach to prevent this disabling condition. Further trials should focus on this strategy. Other biological agents that are currently being studied include IGF-1 with IGF-binding protein-3 (rhIGF-1 + rhIGFBP-3) and propranolol. For advanced stages of ROP, laser ablation of avascular retina, early treatment of ROP (ETROP) protocol, intravitreal injection of anti-VEGF antibodies (e.g. bevacizumab) and vitrectomy are used to protect central vision and prevent retinal detachment. Long-term complications such as refractory errors, recurrence of ROP and risk of retinal detachment require continued follow-up with an ophthalmologist through adolescence and beyond. Optimal nutrition including adequate intake of omega-3 polyunsaturated fatty acids and decreasing infection/inflammation to promote normal vascularization are important strategies. Screening guidelines for ROP based on local incidence of ROP in different regions of the world are very important. Oxygen therapy is clearly a modifiable risk factor to decrease ROP that needs further study. Understanding the two phases of ROP will help to identify appropriate therapeutic strategies and improve visual outcomes in many preterm infants globally.

Retinopathy of prematurity: New developments bring concern and hope

Blindness from retinopathy of prematurity (ROP) in Australian and New Zealand is an uncommon event although 3% of <31 weeks gestation infants receive treatment for the disease. New world-wide estimates of the incidence of blindness from ROP are much higher than previously at 20 000 children annually. The impact of severe ROP can be reduced through good evidence-based care of very preterm infants and careful organisation of eye examinations and follow-up services. Recent oxygen saturation targeting trial results might mean the adoption of higher targets than formerly in very preterm infants and will require vigilance to ensure all eligible infants are examined appropriately. A true screening examination for acute ROP might involve non-opthalmologists obtaining photographic retinal images and remote reading of these. Although treatment with laser gives good outcomes, there is interest in intravitreal anti-vascular endothelial factor agents, but issues concerning the systemic safety and retinal results of such treatment are unresolved.

Outcomes after Intravitreal Bevacizumab versus Laser Photocoagulation for Retinopathy of Prematurity: A 5-Year Retrospective Analysis

PURPOSE

To determine the relative effectiveness, major complications, and refractive errors associated with intravitreal bevacizumab (IVB) versus panretinal photocoagulation (PRP) to treat type 1 retinopathy of prematurity (ROP).

DESIGN

Retrospective case series.

PARTICIPANTS

Consecutive infants with type 1 ROP who received either IVB or PRP and had at least 6 months of follow-up.

METHODS

The data from infants treated with either IVB or PRP for type 1 ROP between 2008 and 2012 were recorded from 2 medical centers in Atlanta, Georgia.

MAIN OUTCOME MEASURES

Recurrence rate, complication rate, and refractive error.

RESULTS

A total of 54 eyes (28 patients) with type 1 ROP were evaluated: 22 eyes (11 patients) received IVB, and 32 eyes (17 patients) received PRP. Among the 22 eyes treated with IVB, 16 eyes had zone I ROP and 6 eyes had posterior zone II ROP. The number of zone I and II ROP eyes treated with PRP were 5 and 27, respectively. Mean gestational age, birth weight, postmenstrual age at initial treatment, and follow-up period for the infants receiving IVB were 24.2 weeks, 668.1 g, 35.1 weeks, and 21.7 weeks, respectively, and for the infants receiving PRP, these were 24.8 weeks, 701.4 g, 36.1 weeks, and 34.5 weeks, respectively. Retinopathy of prematurity recurred in 3 (14%) of 22 IVB-treated eyes and in 1 (3%) of 32 PRP-treated eyes. Neither retinal detachment nor macular ectopia developed in any of the IVB-treated eyes. In PRP-treated eyes, retinal detachment developed in only 1 eye and macular ectopia developed in 5 eyes. Mean spherical equivalent and postgestational age at the last refraction for IVB-treated eyes were -2.4 diopters (D) and 22.4 months, respectively, and for PRP-treated eyes, these were -5.3 D and 37.1 months, respectively. Mean spherical equivalent for zone I ROP eyes treated with IVB and PRP were -3.7 D and -10.1 D, respectively, and for zone II ROP eyes, these were 0.6 D and -4.7 D, respectively.

CONCLUSIONS

Both IVB and PRP are effective treatment options for type 1 ROP with low complication rates. IVB was associated with less myopia than PRP, although longer follow-up was available for PRP.

Population-based trends in mortality and neonatal morbidities among singleton, very preterm, very low birth weight infants over 16 years

BACKGROUND

Improved survival of singleton very preterm, very low birth weight (VPTVLBW) infants has been associated with increasing rates of severe neonatal morbidities.

AIM

To assess changes in mortality and neonatal morbidities among singleton VPT-VLBW infants.

STUDY DESIGN

Population-based observational study of data collected by the Israel Neonatal Network.

SUBJECTS

10,705 singleton VPT-VLBW infants born at 24-32 gestational weeks in 1995-2010.

OUTCOME MEASURES

Mortality and major neonatal morbidities over 3 time periods: 1995-2000, 2001-2005, and 2006-2010. Major neurological morbidities comprised intraventricular hemorrhage grades 3-4, periventricular leukomalacia and retinopathy of prematurity grades 3-4.

RESULTS

The mortality rate decreased over time from 20.2% to 13.8% for all birth weight and gestational age groups. Compared to the 1995-2000 period, the adjusted odds ratios (aORs) (95% confidence intervals,) for mortality in 2001-2005 and 2006-2010 were 0.78 (0.67-0.90) and 0.72 (0.62-0.84), respectively. The combined outcomes of death or major neurological morbidities, aOR 0.74 (0.65-0.84) and death or major neurological morbidities and/or bronchopulmonary dysplasia aOR 0.85 (0.75-0.96) decreased significantly between the first and last periods. A significant improvement in mortality rates and survival without one or more major neonatal morbidity was observed for all birth weight and gestational age groups. Among 8,886 surviving infants the rates of major neurological morbidities decreased from 16.4% to 12.8%, aOR 0.80 (0.68-0.95).

CONCLUSION

The improving survival of singleton VTP-VLBW infants was not associated with a concomitant increase in the risk for major neonatal neurological morbidities among surviving infants. Bronchopulmonary dysplasia, however, remained a significant burden. This analysis emphasizes the need to direct efforts towards the prevention and treatment of adverse respiratory sequelae.

[Off-label use of intravitreal bevacizumab for severe retinopathy of prematurity]

OBJECTIVE

To examine the quality of evidence and the variability in the off-label use of intravitreal bevacizumab for retinopathy of prematurity (ROP).

METHODS

A wide review of the literature was performed using Pubmed, Medline, and Cochrane database, using the words vascular endothelial growth factor (VEGF), retinopathy of prematurity, treatment and bevacizumab.

RESULTS

Case reports, case series, reviews, one sistematic review and one randomized controlled trial were found on the use of intravitreal bevacizumab in severe ROP, as monotherapy or combined with láser and/or vitrectomy.

CONCLUSIONS

The results shown on the use of intravitreal bevacizumab in ROP stage 3+ in zone I or in aggressive posterior ROP are promising. However, uncertainty remains regarding its maximum tolerable dose in the neonatal group, its ocular and systemic safety profile, or its efficacy and bioactivity in a developing child. This report found no significant differences in the recurrence rates of ROP stage 3+ in zone II in patients treated with intravitreal bevacizumab monotherapy in comparison to láser, although the latter is the best option due to long-term safety and efficacy. The use of intravitreal bevacizumab is not indicated in stages 1 and 2 of ROP as the risk of severe visual loss is low and VEFG is necessary for normal retinal vessel development. On the other hand, the use of intravitreal bevacizumab would be contraindicated in stages 4 and 5 because the retinal detachment is accelerated.

Systemic administration of erythropoietin inhibits retinopathy in RCS rats

Objective

Royal College of Surgeons (RCS) rats develop vasculopathy as photoreceptors degenerate. The aim of this study was to examine the effect of erythropoietin (EPO) on retinopathy in RCS rats.

Methods

Fluorescein angiography was used to monitor retinal vascular changes over time. Changes in retinal glia and vasculature were studied by immunostaining. To study the effects of EPO on retinal pathology, EPO (5000 IU/kg) was injected intraperitoneally in 14 week old normal and RCS rats twice a week for 4 weeks. Changes in the retinal vasculature, glia and microglia, photoreceptor apoptosis, differential expression of p75 neurotrophin receptor (p75^NTR), pro-neurotrophin 3 (pro-NT3), tumour necrosis factor-α (TNFα), pigment epithelium derived factor (PEDF) and vascular endothelial growth factor-A (VEGF-A), the production of CD34⁺ cells and mobilization of CD34⁺/VEGF-R2⁺ cells as well as recruitment of CD34⁺ cells into the retina were examined after EPO treatment.

Results

RCS rats developed progressive capillary dropout and subretinal neovascularization which were accompanied by retinal gliosis. Systemic administration of EPO stabilized the retinal vasculature and inhibited the development of focal vascular lesions. Further studies showed that EPO modulated retinal gliosis, attenuated photoreceptor apoptosis and p75^NTR and pro-NT3 upregulation, promoted the infiltration of ramified microglia and stimulated VEGF-A expression but had little effect on TNFα and PEDF expression. EPO stimulated the production of red and white blood cells and CD34⁺ cells along with effective mobilization of CD34⁺/VEGF-R2⁺ cells. Immunofluorescence study demonstrated that EPO enhanced the recruitment of CD34⁺ cells into the retina.

Conclusions

Our results suggest that EPO has therapeutic potentials in treatment of neuronal and vascular pathology in retinal disease. The protective effects of EPO on photoreceptors and the retinal vasculature may involve multiple mechanisms including regulation of retinal glia and microglia, inhibition of p75^NTR-pro-NT3 signaling together with stimulation of production and mobilization of bone marrow derived cells.

TWEAK/Fn14 pathway is a novel mediator of retinal neovascularization

PURPOSE

Retinal neovascularization (NV) is a major cause of vision loss in ischemia-induced retinopathy. Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor inducible-14 (Fn14), have been implicated in angiogenesis, but their role in retinal diseases is unknown. The goal of this study was to investigate the role of TWEAK/Fn14 pathway in retinal NV.

METHODS

Studies were performed in a mouse model of oxygen-induced retinopathy (OIR) and in primary human retinal microvascular endothelial cells (HRMECs). Hyperoxia treatment was initiated on postnatal day (P)14. Immunohistochemistry and quantitative PCR (qPCR) were used to assess retinal vascular changes in relation to expression of Fn14 and TWEAK.

RESULTS

Fibroblast growth factor-inducible 14 mRNA was prominently increased from P13 to P17 in OIR retinas, whereas TWEAK level was slightly decreased. These alterations were normalized by hyperoxia treatment and were more striking in isolated retinal vessels. There was a discernible shift in the immunoreactivity of Fn14 and TWEAK from the neuronal layers in the healthy retina to the neovascular tufts in that of OIR. Blockade of TWEAK/Fn14 significantly prevented retinal NV while slightly accelerated revascularization. In contrast, activation of Fn14 positively regulated survival pathways in the B-cell lymphoma-2 (Bcl2) family and robustly enhanced HRMEC survival. Furthermore, gene analysis revealed the regulatory region of Fn14 gene contains several conserved hypoxia inducible factor (HIF)-1α binding sites. Overexpression of HIF-1α prominently induced Fn14 expression in HRMECs.

CONCLUSIONS

We found that the TNF-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor inducible-14 (Fn14) pathway is involved in the development of pathologic retinal neovascularization. Hypoxia inducible factor-1α is likely implicated in the upregulation of Fn14.