Inducing a visceral organ to protect a peripheral capillary bed: stabilizing hepatic HIF-1α prevents oxygen-induced retinopathy

Evidence for the Hepato-Retinal Axis: A Systematic Review

BACKGROUND AND OBJECTIVE

Liver health has been reported to be associated with retinal pathology in various ways. These include deposition of retino-toxins, neovascular drive, and disruption of the blood-retina barrier. Extrahepatic synthesis of implicated molecules and hemodynamic changes in liver dysfunction are also considered. The objective was to review the current evidence for and against a hepato-retinal axis that may guide further areas of preclinical and clinical investigation.

METHODS

This was a systematic review. PubMed and Cochrane were queried for English language studies examining the connection between hepatic dysfunction and retinal pathology.

RESULTS

Fourteen studies were included and examined out of 604 candidate publications. The studies selected include preclinical studies as well as clinical case series and studies.

CONCLUSIONS

Several liver pathologies may be linked to retinal pathology as mediated by hepatically synthesized molecules. The hepato-retinal axis may be present and further, targeted studies of the axis are warranted. [Ophthalmic Surg Lasers Imaging Retina 2024;55:587-596.].

The Role of HIF-1α in Retinopathy of Prematurity: A Review of Current Literature

Hypoxia-inducible factor (HIF) plays a crucial role in regulating oxygen sensing and adaptation at the cellular level, overseeing cellular oxygen homeostasis, erythrocyte production, angiogenesis, and mitochondrial metabolism. The hypoxia-sensitive HIF-1α subunit facilitates tissue adaptation to hypoxic conditions, including the stimulation of proangiogenic factors. Retinopathy of prematurity (ROP) is a proliferative vascular disease of the retina that poses a significant risk to prematurely born children. If untreated, ROP can lead to retinal detachment, severe visual impairment, and even blindness. The pathogenesis of ROP is not fully understood; however, reports suggest that premature birth leads to the exposure of immature ocular tissues to high levels of exogenous oxygen and hyperoxia, which increase the synthesis of reactive oxygen species and inhibit HIF expression. During the ischemic phase, HIF-1α expression is stimulated in the hypoxia-sensitive retina, causing an overproduction of proangiogenic factors and the development of pathological neovascularization. Given the significant role of HIF-1α in the development of ROP, considering it as a potential molecular target for therapeutic strategies appears justified. This review synthesizes information from the last six years (2018-2024) using databases such as PubMed, Google Scholar, and BASE, focusing on the role of HIF-1α in the pathogenesis of ROP and its potential as a target for new therapies.

Pathologic vs. protective roles of hypoxia-inducible factor 1 in RPE and photoreceptors in wet vs. dry age-related macular degeneration

It has previously been reported that antioxidant vitamins can help reduce the risk of vision loss associated with progression to advanced age-related macular degeneration (AMD), a leading cause of visual impairment among the elderly. Nonetheless, how oxidative stress contributes to the development of choroidal neovascularization (CNV) in some AMD patients and geographic atrophy (GA) in others is poorly understood. Here, we provide evidence demonstrating that oxidative stress cooperates with hypoxia to synergistically stimulate the accumulation of hypoxia-inducible factor (HIF)-1α in the retinal pigment epithelium (RPE), resulting in increased expression of the HIF-1-dependent angiogenic mediators that promote CNV. HIF-1 inhibition blocked the expression of these angiogenic mediators and prevented CNV development in an animal model of ocular oxidative stress, demonstrating the pathological role of HIF-1 in response to oxidative stress stimulation in neovascular AMD. While human-induced pluripotent stem cell (hiPSC)-derived RPE monolayers exposed to chemical oxidants resulted in disorganization and disruption of their normal architecture, RPE cells proved remarkably resistant to oxidative stress. Conversely, equivalent doses of chemical oxidants resulted in apoptosis of hiPSC-derived retinal photoreceptors. Pharmacologic inhibition of HIF-1 in the mouse retina enhanced-while HIF-1 augmentation reduced-photoreceptor apoptosis in two mouse models for oxidative stress, consistent with a protective role for HIF-1 in photoreceptors in patients with advanced dry AMD. Collectively, these results suggest that in patients with AMD, increased expression of HIF-1α in RPE exposed to oxidative stress promotes the development of CNV, but inadequate HIF-1α expression in photoreceptors contributes to the development of GA.

Insights into the liver-eyes connections, from epidemiological, mechanical studies to clinical translation

Maintenance of internal homeostasis is a sophisticated process, during which almost all organs get involved. Liver plays a central role in metabolism and involves in endocrine, immunity, detoxification and storage, and therefore it communicates with distant organs through such mechanisms to regulate pathophysiological processes. Dysfunctional liver is often accompanied by pathological phenotypes of distant organs, including the eyes. Many reviews have focused on crosstalk between the liver and gut, the liver and brain, the liver and heart, the liver and kidney, but with no attention paid to the liver and eyes. In this review, we summarized intimate connections between the liver and the eyes from three aspects. Epidemiologically, we suggest liver-related, potential, protective and risk factors for typical eye disease as well as eye indicators connected with liver status. For molecular mechanism aspect, we elaborate their inter-organ crosstalk from metabolism (glucose, lipid, proteins, vitamin, and mineral), detoxification (ammonia and bilirubin), and immunity (complement and inflammation regulation) aspect. In clinical application part, we emphasize the latest advances in utilizing the liver-eye axis in disease diagnosis and therapy, involving artificial intelligence-deep learning-based novel diagnostic tools for detecting liver disease and adeno-associated viral vector-based gene therapy method for curing blinding eye disease. We aim to focus on and provide novel insights into liver and eyes communications and help resolve existed clinically significant issues.

Hyperoxia Induced Hypomyelination

We asked whether hyperoxia might induce hypomyelination of the corpus callosum, clinically described as periventricular leukomalacia (PVL) of the severely preterm infant. Mouse pups and their nursing dams were placed in 80% oxygen from P4-P8, then removed to room air until P11. Corpus callosal sections were probed myelin immunofluorescence, tested for myelin basic protein concentration by Western blot, and both glial fibrillary acidic protein levels and apoptosis quantified. Density of corpus callosal capillaries were measured after lectin staining and hypoxia measured by Hypoxyprobe. Numbers of oligodendrocytes were quantified by immunohistochemistry. We next used hypoxiamimesis as a surrogate to hypoxia by comparing cerebral hypoxia inducible factor (HIF) stabilization to hepatic HIF stabilization. Hyperoxia induced hypomyelination and a reduction of corpus callosal capillaries. Hyperoxia decreased numbers of oligodendrocytes with an increase in corpus callosal fibrosis and apoptosis. Cerebral hypoxiamimesis induced hypomyelination whereas hepatic hypoxiamimesis alone increased myelination, oligodendrocyte numbers, and corpus callosal capillary density. Hepatic HIF-1 dependence on myelination was confirmed using the cre/lox hepatic HIF-1 knockout. These findings suggest that hyperoxia can induce hypomyelination through vasoobliteration and subsequent ischemia, adding a potential oxygen induced mechanism to the diverse causes of periventricular leukomalacia of the severely preterm infant. Targeting hepatic HIF-1 alone led to increased myelination.

Neurovascular abnormalities in retinopathy of prematurity and emerging therapies

Blood vessels in the developing retina are formed in concert with neural growth, resulting in functional neurovascular network. Disruption of the neurovascular coordination contributes to the pathogenesis of retinopathy of prematurity (ROP), a potentially blinding retinal neovascular disease in preterm infants that currently lacks an approved drug therapy in the USA. Despite vasculopathy as predominant clinical manifestations, an increasing number of studies revealed complex neurovascular interplays among neurons, glial cells and blood vessels during ROP. Coordinated expression of glia-derived vascular endothelial growth factor (VEGF) in spatio-temporal gradients is pivotal to the formation of well-organized vascular plexuses in the healthy retina, whereas uncoordinated VEGF expression triggers pathological angiogenesis with disorganized vascular tufts in ROP. In contrast with VEGF driving both pathological and physiological angiogenesis, neuron-derived angiogenic factor secretogranin III (Scg3) stringently regulates ROP but not healthy retinal vessels in animal models. Anti-VEGF and anti-Scg3 therapies confer similar high efficacies to alleviate ROP in preclinical studies but are distinct in their disease selectivity and safety. This review discusses neurovascular communication among retinal blood vessels, neurons and glial cells during retinal development and ROP pathogenesis and summarizes the current and emerging therapies to address unmet clinical needs for the disease.

Two Phase 3 Studies on Ophthalmological Effects of Roxadustat versus Darbepoetin

Introduction

Roxadustat is an orally administered hypoxia-inducible factor (HIF) prolyl hydroxylase inhibitor that represents a novel therapeutic option for patients with anemia of chronic kidney disease (CKD).

Methods

Conducted in Japan, CL-0307 (NCT02952092) and CL-310 (NCT02988973) were phase 3, darbepoetin alfa (DA)-controlled studies conducted in dialysis-dependent (DD) and non–DD (NDD) patients with CKD, respectively, where patients were randomized to receive roxadustat or DA. Ophthalmic imaging and assessments of visual acuity were performed up to week 24 or at study discontinuation. Ophthalmic imaging was centrally evaluated by independent readers masked to the study treatment.

Results

In CL-0307, 302 patients (roxadustat, n = 150; DA, n = 152) received ≥1 dose of the study drug and were included in this analysis. In CL-0310, 262 patients (roxadustat, n = 131; DA, n = 131) received ≥1 dose of the study drug and were included in this analysis. Proportions of DD patients with new or worsening retinal hemorrhages (RHs) in the roxadustat group and DA group were 32.4% (46 of 142) and 36.6% (53 of 145), respectively. Proportions of NDD patients with CKD with new or worsening RH in the roxadustat and DA groups were 31.4% (38 of 121) and 39.8% (51 of 128), respectively. Similar trends were apparent in subgroup analyses: patients with/without RH at baseline and with/without diabetes mellitus at baseline. In both studies, there were no differences in retinal thickness, visual acuity, presence of hard exudates or cotton wool spots, or presence of intra- and subretinal fluid between groups, at any given time point.

Conclusion

In these studies, roxadustat, compared with DA, was not associated with an increased risk of adverse ophthalmologic events in these cohorts.

Adenosine A2A receptor antagonism protects against hyperoxia-induced retinal vascular loss via cellular proliferation

Retinopathy of prematurity (ROP) remains one of the major causes of blindness in children worldwide. While current ROP treatments are mostly disruptive to reduce proliferative neovascularization by targeting the hypoxic phase, protection against early hyperoxia-induced retinal vascular loss represents an effective therapeutic window, but no such therapeutic strategy is available. Built upon our recent demonstration that the protection against oxygen-induced retinopathy by adenosine A_2A receptor (A_2A R) antagonists is most effective when administered at the hyperoxia (not hypoxic) phase, we here uncovered the cellular mechanism underlying the A_2A R-mediated protection against early hyperoxia-induced retinal vascular loss by reversing the inhibition of cellular proliferation via possibly multiple signaling pathways. Specifically, we revealed two distinct stages of the hyperoxia phase with greater cellular proliferation and apoptosis activities and upregulation of adenosine signaling at postnatal 9 day (P9) but reduced cellular activities and adenosine-A_2A R signaling at P12. Importantly, the A_2A R-mediated protection at P9 was associated with the reversal of hyperoxia-induced inhibition of progenitor cells at the peripheral retina at P9 and of retinal endothelial proliferation at P9 and P12. The critical role of cellular proliferation in the hyperoxia-induced retinal vascular loss was validated by the increased avascular areas by siRNA knockdown of the multiple signaling molecules involved in modulation of cellular proliferation, including activin receptor-like kinase 1, DNA-binding protein inhibitor 1, and vascular endothelial growth factor-A.

Rank Order of Small Molecule Induced Hypoxiamimesis to Prevent Retinopathy of Prematurity

Here we rank order small molecule inhibitors of hypoxia inducible factor (HIF) prolyl hydroxylases (PHDs) using severity of oxygen induced retinopathy (OIR) as an outcome measure. Dose response analyses in cell cultures of hepatoma (Hep3B), retinal Müller cells (MIO-M1) and primary retinal endothelial cells were conducted to evaluate potency by comparing dose to HIF-1,2 protein levels by western blotting. In vivo dose response was determined using the luciferase-transgene HIF reporter (luc-ODD). Each compound was placed in rank order by their ability to reduce neovascularization and capillary drop out in the OIR mouse model. An Epas1 KO confined to retinal Müller cells was used to determine whether successful protection by HIF stabilization requires HIF-2. Two candidate small molecules can prevent OIR by stabilizing HIF-1 to prevent oxygen induced growth attenuation and vascular obliteration. Müller cell HIF-2, the mediator of pathologic retinal angiogenesis, is not required for protection. The lack of dependence on Müller cell HIF-2 predicts that inhibition of HIF PHD will not drive pathological angiogenesis.

Serine and 1-carbon metabolism are required for HIF-mediated protection against retinopathy of prematurity

We determined which metabolic pathways are activated by hypoxia-inducible factor 1-mediated (HIF-1-mediated) protection against oxygen-induced retinopathy (OIR) in newborn mice, the experimental correlate to retinopathy of prematurity, a leading cause of infant blindness. HIF-1 coordinates the change from oxidative to glycolytic metabolism and mediates flux through serine and 1-carbon metabolism (1CM) in hypoxic and cancer cells. We used untargeted metabolite profiling in vivo to demonstrate that hypoxia mimesis activates serine/1CM. Both [13C6] glucose labeling of metabolites in ex vivo retinal explants as well as in vivo [13C3] serine labeling of metabolites followed in liver lysates strongly suggest that retinal serine is primarily derived from hepatic glycolytic carbon and not from retinal glycolytic carbon in newborn pups. In HIF-1α2lox/2lox albumin-Cre-knockout mice, reduced or near-0 levels of serine/glycine further demonstrate the hepatic origin of retinal serine. Furthermore, inhibition of 1CM by methotrexate blocked HIF-mediated protection against OIR. This demonstrated that 1CM participates in protection induced by HIF-1 stabilization. The urea cycle also dominated pathway enrichment analyses of plasma samples. The dependence of retinal serine on hepatic HIF-1 and the upregulation of the urea cycle emphasize the importance of the liver to remote protection of the retina.

An iTRAQ-Based Quantitative Proteomic Analysis of Plasma Proteins in Preterm Newborns With Retinopathy of Prematurity

Purpose

Retinopathy of prematurity (ROP) is a vision-threatening complication of a premature birth, in which the etiology still remains unclear. Importantly, the molecular processes that govern these effects can be investigated in a perturbed plasma proteome composition. Thus, plasma proteomics may add new insights into a better understanding of the pathogenesis of this disease.

Methods

The cord and peripheral blood of neonates (≤30 weeks gestational age) was drawn at birth and at the 36th postmenstrual week (PMA), respectively. Blood samples were retrospectively subdivided into ROP(+) and ROP(-) groups, according to the development of ROP.

Results

The quantitative analysis of plasma proteome at both time points revealed 30 protein abundance changes between ROP(+) and ROP(-) groups. After standardization to gestational age, children who developed ROP were characterized by an increased C3 complement component and fibrinogen level at both analyzed time points.

Conclusions

Higher levels of the complement C3 component and fibrinogen, present in the cord blood and persistent to 36 PMA, may indicate a chronic low-grade systemic inflammation and hypercoagulable state that may play a role in the development of ROP.

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.

HIF-1α stabilization reduces retinal degeneration in a mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive and irreversible loss of vision due to rod and cone degeneration. Evidence suggests that an inappropriate oxygen level could contribute to its pathogenesis. Rod cell death could increase oxygen concentration, reduce hypoxia-inducible factor 1 (HIF-1α) and contribute to cone cell death. The purposes of this study were: 1) to analyze the temporal profile of HIF-1α, its downstream effectors VEGF, endothelin-1 (ET-1), iNOS, and glucose transporter 1 (GLUT1), and neuroinflammation in retinas of the murine model of rd10 ( retinal degeneration 10) mice with RP; 2) to study oxygen bioavailability in these retinas; and 3) to investigate how stabilizing HIF-1α proteins with dimethyloxaloglycine (DMOG), a prolyl hydroxylase inhibitor, affects retinal degeneration, neuroinflammation, and antioxidant response in rd10 mice. A generalized down-regulation of HIF-1α and its downstream targets was detected in parallel with reactive gliosis, suggesting high oxygen levels during retinal degeneration. At postnatal d 18, DMOG treatment reduced photoreceptor cell death and glial activation. In summary, retinas of rd10 mice seem to be exposed to a hyperoxic environment even at early stages of degeneration. HIF-1α stabilization could have a temporal neuroprotective effect on photoreceptor cell survival, glial activation, and antioxidant response at early stages of RP.-Olivares-González, L., Martínez-Fernández de la Cámara, C., Hervás, D., Millán, J. M., Rodrigo, R. HIF-1α stabilization reduces retinal degeneration in a mouse model of retinitis pigmentosa.

Retinal vasculature development in health and disease

Development of the retinal vasculature is based on highly coordinated signalling between different cell types of the retina, integrating internal metabolic requirements with external influences such as the supply of oxygen and nutrients. The developing mouse retinal vasculature is a useful model system to study these interactions because it is experimentally accessible for intra ocular injections and genetic manipulations, can be easily imaged and develops in a similar fashion to that of humans. Research using this model has provided insights about general principles of angiogenesis as well as pathologies that affect the developing retinal vasculature. In this review, we discuss recent advances in our understanding of the molecular and cellular mechanisms that govern the interactions between neurons, glial and vascular cells in the developing retina. This includes a review of mechanisms that shape the retinal vasculature, such as sprouting angiogenesis, vascular network remodelling and vessel maturation. We also explore how the disruption of these processes in mice can lead to pathology - such as oxygen induced retinopathy - and how this translates to human retinopathy of prematurity.

Comparative systems pharmacology of HIF stabilization in the prevention of retinopathy of prematurity

Retinopathy of prematurity (ROP) causes 100,000 new cases of childhood blindness each year. ROP is initiated by oxygen supplementation necessary to prevent neonatal death. We used organ systems pharmacology to define the transcriptomes of mice that were cured of oxygen-induced retinopathy (OIR, ROP model) by hypoxia-inducible factor (HIF) stabilization via HIF prolyl hydroxylase inhibition using the isoquinolone Roxadustat or the 2-oxoglutarate analog dimethyloxalylglycine (DMOG). Although both molecules conferred a protective phenotype, gene expression analysis by RNA sequencing found that Roxadustat can prevent OIR by two pathways: direct retinal HIF stabilization and induction of aerobic glycolysis or indirect hepatic HIF-1 stabilization and increased serum angiokines. As predicted by pathway analysis, Roxadustat rescued the hepatic HIF-1 knockout mouse from retinal oxygen toxicity, whereas DMOG could not. The simplicity of systemic treatment that targets both the liver and the eye provides a rationale for protecting the severely premature infant from oxygen toxicity.

Systems Pharmacology Links GPCRs with Retinal Degenerative Disorders

In most biological systems, second messengers and their key regulatory and effector proteins form links between multiple cellular signaling pathways. Such signaling nodes can integrate the deleterious effects of genetic aberrations, environmental stressors, or both in complex diseases, leading to cell death by various mechanisms. Here we present a systems (network) pharmacology approach that, together with transcriptomics analyses, was used to identify different G protein-coupled receptors that experimentally protected against cellular stress and death caused by linked signaling mechanisms. We describe the application of this concept to degenerative and diabetic retinopathies in appropriate mouse models as an example. Systems pharmacology also provides an attractive framework for devising strategies to combat complex diseases by using (repurposing) US Food and Drug Administration-approved pharmacological agents.