Neovascularization is attenuated with aldosterone synthase inhibition in rats with retinopathy

Glaucoma and the ocular renin-angiotensin-aldosterone system: Update on molecular signalling and treatment perspectives

Glaucoma, a leading cause of blindness worldwide, encompasses a group of pathological conditions affecting the optic nerve and is characterized by progressive retinal ganglion cell loss, cupping of the optic nerve head, and distinct visual field defects. While elevated intraocular pressure (IOP) is the main risk factor for glaucoma, many patients do not have elevated IOP. Consequently, other risk factors, such as ocular blood flow abnormalities and immunological factors, have been implicated in its pathophysiology. Traditional therapeutic strategies primarily aim to reduce IOP, but there is growing interest in developing novel treatment approaches to improve disease management and reduce the high rates of severe visual impairment. In this context, targeting the ocular renin-angiotensin-aldosterone system (RAAS) has been found as a potential curative strategy. The RAAS contributes to glaucoma development through key effectors such as prorenin, angiotensin II, and aldosterone. Recent evidence has highlighted the potential of using RAAS modulators to combat glaucoma, yielding encouraging results. Our study aims to explore the molecular pathways linking the ocular RAAS and glaucoma, summarizing recent advances that elucidate the role of the RAAS in triggering oxidative stress, inflammation, and remodelling in the pathogenesis of glaucoma. Additionally, we will present emerging therapeutic approaches that utilize RAAS modulators and antioxidants to slow the progression of glaucoma.

RAAS in diabetic retinopathy: mechanisms and therapies

Diabetic retinopathy (DR) is a complication of diabetes with a complex pathophysiology and multiple factors involved. Recently, it has been found that the upregulation of the renin-angiotensin-aldosterone system (RAAS) leads to overexpression of angiotensin II (Ang II), which induces oxidative stress, inflammation, and angiogenesis in the retina. Therefore, RAAS may be a promising therapeutic target in DR. Notably, RAAS inhibitors are often used in the treatment of hypertension. Still, the potential role and mechanism of DR must be further studied. In this review, we discuss and summarize the pathology and potential therapeutic goals of RAAS in DR.

Transcription Factor EGR1 Facilitates Neovascularization in Mice with Retinopathy of Prematurity by Regulating the miR-182-5p/EFNA5 Axis

Neovascularization is the hallmark of retinopathy of prematurity (ROP). Early growth response 1 (EGR1) has been reported as an angiogenic factor. This study was conducted to probe the regulatory mechanism of EGR1 in neovascularization in ROP model mice. The ROP mouse model was established, followed by determination of EGR1 expression and assessment of neovascularization [vascular endothelial growth factor-A (VEGF-A) and pigment epithelium-derived factor (PEDF)]. Retinal vascular endothelial cells were cultured and treated with hypoxia, followed by the tube formation assay. The state of oxygen induction was assessed by real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot assay to determine hypoxia-inducible factor 1-alpha (HIF-1A). The levels of microRNA (miRNA)-182-5p and ephrin-A5 (EFNA5) in tissues and cells were determined by RT-qPCR. Chromatin immunoprecipitation and dual-luciferase assay were used to validate gene interaction. EGR1 and EFNA5 were upregulated in the retina of ROP mice while miR-182-5p was downregulated. EGR1 knockdown decreased VEGF-A and HIF-1A expression and increased PEDF expression in the retina of ROP mice. In vitro, EGR1 knockdown also reduced neovascularization. EGR1 binding to the miR-182-5p promoter inhibited miR-182-5p transcription and further promoted EFNA5 transcription. miR-182-5p downregulation or EFNA5 overexpression averted the inhibition of neovascularization caused by EGR1 downregulation. Overall, EGR1 bound to the miR-182-5p promoter to inhibit miR-182-5p transcription and further promoted EFNA5 transcription, thus promoting retinal neovascularization in ROP mice.

ADAMTS5 promotes neovascularization via autophagic degradation of PEDF in proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) adversely affects visual function. Extracellular matrix proteins (ECM) contribute significantly to the development of PDR. A Disintegrin and Metalloproteinase with Thrombospondin motifs 5 (ADAMTS5) is a member of ECM proteins. ADAMTS5 participates in angiogenesis and inflammation in diverse diseases. However, the role of ADAMTS5 in PDR remains elusive. Multiplex beam array technology was used to analyze vitreous humor of PDR patients and normal people. ELISA and Western blot were used to detect the expression of ADAMTS5, PEDF and autophagy related factors. Immunofluorescence assay was used to mark the expression and localization of ADAMTS5 and PEDF. The neovascularization was detected by tube formation test. Our results revealed that ADAMTS5 expression was increased in the vitreous humor of PDR patients and oxygen-induced retinopathy (OIR) mice retinas. Inhibiting ADAMTS5 alleviated pathological angiogenesis and upregulated PEDF expression in the OIR mice. In addition, ADAMTS5 inhibited PEDF secretion in ARPE-19 cells in vitro studies, thereby inhibiting the migration of HMEC-1. Mechanically, ADAMTS5 promoted the autophagic degradation of PEDF. Collectively, inhibition of ADAMTS5 during OIR suppresses pathological angiogenesis. Our study provides a new approach for resolving pathological angiogenesis in PDR.

Adverse effects of an aldosterone synthase (CYP11B2) inhibitor, fadrozole (FAD286), on inflamed rat colon

Recently, we described local aldosterone production in the murine large intestine. Upregulated local aldosterone synthesis in different tissues has been linked with inflammatory conditions, which have been attenuated by the aldosterone synthase (CYP11B2) inhibitor, fadrozole (FAD286). Therefore, we investigated the effect of inhibition of intestinal aldosterone synthesis on the development of intestinal inflammation. Sprague-Dawley rats were administered 5% (v/w) dextran sodium sulphate (DSS) for 7 days with or without daily FAD286 (30 mg/kg/d) subcutaneous injections on 3 days before, during and one day after DSS. Tissue aldosterone concentrations were evaluated by ELISA, CYP11B2 by Western blot and RT-qPCR. FAD286 halved adrenal aldosterone production but, intriguingly, increased the colonic aldosterone concentration. The lack of inhibitory effect of FAD286 in the colon might have been affected by the smaller size of colonic vs. adrenal CYP11B2, as seen in Western blot. When combined with DSS, FAD286 aggravated the macroscopic and histological signs of intestinal inflammation, lowered the animals' body weight gain and increased the incidence of gastrointestinal bleeding and the permeability to iohexol in comparison to DSS-animals. To conclude, FAD286 exerted harmful effects during intestinal inflammation. Local intestinal aldosterone did not seem to play any role in the inflammatory pathogenesis occurring in the intestine.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Finerenone, a Non-Steroidal Mineralocorticoid Receptor Antagonist, Reduces Vascular Injury and Increases Regulatory T-Cells: Studies in Rodents with Diabetic and Neovascular Retinopathy

Vision loss in diabetic retinopathy features damage to the blood-retinal barrier and neovascularization, with hypertension and the renin-angiotensin system (RAS) having causal roles. We evaluated if finerenone, a non-steroidal mineralocorticoid receptor (MR) antagonist, reduced vascular pathology and inflammation in diabetic and neovascular retinopathy. Diabetic and hypertensive transgenic (mRen-2)27 rats overexpressing the RAS received the MR antagonist finerenone (10 mg/kg/day, oral gavage) or the angiotensin-converting enzyme inhibitor perindopril (10 mg/kg/day, drinking water) for 12 weeks. As retinal neovascularization does not develop in diabetic rodents, finerenone (5 mg/kg/day, i.p.) was evaluated in murine oxygen-induced retinopathy (OIR). Retinal vasculopathy was assessed by measuring gliosis, vascular leakage, neovascularization, and VEGF. Inflammation was investigated by quantitating retinal microglia/macrophages, pro-inflammatory mediators, and anti-inflammatory regulatory T-cells (Tregs). In diabetes, both treatments reduced systolic blood pressure, gliosis, vascular leakage, and microglial/macrophage density, but only finerenone lowered VEGF, ICAM-1, and IL-1ß. In OIR, finerenone reduced neovascularization, vascular leakage, and microglial density, and increased Tregs in the blood, spleen, and retina. Our findings, in the context of the FIDELIO-DKD and FIGARO-DKD trials reporting the benefits of finerenone on renal and cardiovascular outcomes in diabetic kidney disease, indicate the potential of finerenone as an effective oral treatment for diabetic retinopathy.

Microglia: The breakthrough to treat neovascularization and repair blood-retinal barrier in retinopathy

Microglia are the primary resident retinal macrophages that monitor neuronal activity in real-time and facilitate angiogenesis during retinal development. In certain retinal diseases, the activated microglia promote retinal angiogenesis in hypoxia stress through neurovascular coupling and guide neovascularization to avascular areas (e.g., the outer nuclear layer and macula lutea). Furthermore, continuously activated microglia secrete inflammatory factors and expedite the loss of the blood-retinal barrier which causes irreversible damage to the secondary death of neurons. In this review, we support microglia can be a potential cellular therapeutic target in retinopathy. We briefly describe the relevance of microglia to the retinal vasculature and blood-retinal barrier. Then we discuss the signaling pathway related to how microglia move to their destinations and regulate vascular regeneration. We summarize the properties of microglia in different retinal disease models and propose that reducing the number of pro-inflammatory microglial death and conversing microglial phenotypes from pro-inflammatory to anti-inflammatory are feasible for treating retinal neovascularization and the damaged blood-retinal barrier (BRB). Finally, we suppose that the unique properties of microglia may aid in the vascularization of retinal organoids.

The role of aldosterone in the pathogenesis of diabetic retinopathy

Aldosterone, as a mineralocorticoid of adrenal origin, has effects that are not limited to the urinary tract. As an important regulator in Vasoactive hormone pathways, aldosterone may play an effect in the pathogenesis of diabetic retinopathy (DR) through the regulation of oxidative stress, vascular regulation, and inflammatory mechanisms. This implies that mineralocorticoids, including aldosterone, have great potential and value for the diagnosis and treatment of DR. Because early studies did not focus on the intrinsic association between mineralocorticoids and DR, targeted research is still in its infancy and there are still many obstacles to its application in the clinical setting. Recent studies have improved the understanding of the effects of aldosterone on DR, and we review them with the aim of exploring possible mechanisms for the treatment and prevention of DR.

Aldosterone as a Possible Contributor to Eye Diseases

Aldosterone, an effector molecule of the renin-angiotensin-aldosterone system (RAAS), has been receiving more attention in the field of ophthalmology because of its possible role in the pathogenesis of various eye diseases or abnormalities; it may even become a target for their treatment. Primary aldosteronism, a typical model of a systemic aldosterone excess, may cause vision loss due to various ocular diseases, such as retinal vein occlusion, central serous chorioretinopathy, and, possibly glaucoma. RAAS components are present in various parts and types of cells present in the eye. Investigations of the local RAAS in various animal models of diabetic macular edema, retinal vein occlusion, retinopathy of prematurity, central serous chorioretinopathy, and glaucoma have found evidence that aldosterone or mineralocorticoid receptors may exacerbate the pathology of these disorders. Further studies are needed to elucidate whether the modulation of aldosterone or mineralocorticoid receptors is an effective treatment for preventing vision loss in patients with eye diseases.

Nonsteroidal Mineralocorticoid Receptor Antagonism by Finerenone-Translational Aspects and Clinical Perspectives across Multiple Organ Systems

Perception of the role of the aldosterone/mineralocorticoid receptor (MR) ensemble has been extended from a previously renal epithelial-centered focus on sodium and volume homeostasis to an understanding of their role as systemic modulators of reactive oxygen species, inflammation, and fibrosis. Steroidal MR antagonists (MRAs) are included in treatment paradigms for resistant hypertension and heart failure with reduced ejection fraction, while more recently, the nonsteroidal MRA finerenone was shown to reduce renal and cardiovascular outcomes in two large phase III trials (FIDELIO-DKD and FIGARO-DKD) in patients with chronic kidney disease and type 2 diabetes, respectively. Here, we provide an overview of the pathophysiologic role of MR overactivation and preclinical evidence with the nonsteroidal MRA finerenone in a range of different disease models with respect to major components of the aggregate mode of action, including interfering with reactive oxygen species generation, inflammation, fibrosis, and hypertrophy. We describe a time-dependent effect of these mechanistic components and the potential modification of major clinical parameters, as well as the impact on clinical renal and cardiovascular outcomes as observed in FIDELIO-DKD and FIGARO-DKD. Finally, we provide an outlook on potential future clinical indications and ongoing clinical studies with finerenone, including a combination study with a sodium-glucose cotransporter-2 inhibitor.

The Mineralocorticoid receptor signal could be a new molecular target for the treatment of diabetic retinal complication

BACKGROUND

Activation of the mineralocorticoid receptor (MR) is involved in the pathophysiology of diabetic vascular complications. In recent years, it has been indicated that the MR expressed in retinal Müller cells plays an important role in regulating the potassium and water balance in the retina. Therefore, it has also been speculated that abnormal MR signaling contributes to edematous diseases of the retina.

RESEARCH DESIGN AND METHODS

We examined the effect of high-glucose conditions on MR protein and mRNA levels in human retinal Müller cells and changes in cell size in vitro. We also investigated MR transcriptional activity and signaling in high-glucose conditions.

RESULTS

The MR protein increased by 2.2-fold with high-glucose treatment. Additionally, high-glucose treatment induced Müller cell swelling. Aldosterone-induced MR transcriptional activity was enhanced in high-glucose conditions, resulting in the upregulation of αENaC, AQP4 and Kir4.1 mRNA. Treatment with an MR antagonist led to the suppression of aldosterone-induced cell swelling, MR transcriptional activity and upregulation of the target genes in high-glucose conditions.

CONCLUSIONS

High glucose induces Müller cell swelling through activation of MR signaling, which could be associated with aggravation of macular edema. Thus, Müller cell swelling and diabetic macular edema may represent a target for treatment with MR antagonists.

Chinmedomics Strategy for Elucidating the Pharmacological Effects and Discovering Bioactive Compounds From Keluoxin Against Diabetic Retinopathy

Keluoxin (KLX) is an active agent in the treatment of diabetic retinopathy (DR). However, its mechanism, targets, and effective constituents against DR are still unclear, which seriously restricts its clinical application. Chinmedomics has the promise of explaining the pharmacological effects of herbal medicines and investigating the effective mechanisms. The research results from electroretinography and electron microscope showed that KLX could reduce retinal dysfunction and pathological changes by the DR mouse model. Based on effectiveness, we discovered 64 blood biomarkers of DR by nontargeted metabolomics analysis, 51 of which returned to average levels after KLX treatment including leukotriene D4 and A4, l-tryptophan, 6-hydroxymelatonin, l-phenylalanine, l-tyrosine, and gamma-linolenic acid (GLA). The metabolic pathways involved were phenylalanine metabolism, steroid hormone biosynthesis, sphingolipid metabolism, etc. Adenosine monophosphate-activated protein kinase (AMPK), extracellular signal-regulated protein kinase1/2 (ERK1/2), phosphatidylinositol-3-kinase (PI3K), and protein 70 S6 kinase (p70 S6K) might be potential targets of KLX against DR. This was related to the mammalian target of rapamycin (mTOR) signaling and AMPK signaling pathways. We applied the chinmedomics strategy, integrating serum pharm-chemistry of traditional Chinese medicine (TCM) with metabolomics, to discover astragaloside IV (AS-IV), emodin, rhein, chrysophanol, and other compounds, which were the core effective constituents of KLX when against DR. Our study was the first to apply the chinmedomics strategy to discover the effective constituents of KLX in the treatment of DR, which fills the gap of unclear effective constituents of KLX. In the next step, the research of effective constituents can be used to optimize prescription preparation, improve the quality standard, and develop an innovative drug.

The Retinal Renin-Angiotensin-Aldosterone System: Implications for Glaucoma

Aldosterone is one of the main effectors of the renin-angiotensin-aldosterone system (RAAS) along with having roles in hypertension, and cardiovascular and renal diseases. Recent evidence has also shown the presence of an active local RAAS within the human eye. It has been shown that at 12 h after a retinal ischemia-reperfusion injury, there is an upregulation of the protein levels of angiotensin II type 1 receptor (AT1-R) in the retina. Furthermore, at 12 h after reperfusion, there is an increase in reactive oxygen species (ROS) production in the retina that is mediated via an NADPH oxidase pathway. This ischemia-reperfusion injury-induced increase of retinal ROS levels and NADPH oxidase expression can be prevented by the administration of an AT1-R antagonist. This suggests that one of the main retinal ischemic injury pathways is via the local RAAS. It has also been reported that progressive retinal ganglion cell loss and glaucomatous optic nerve degeneration without elevated intraocular pressure occur after administration of local or systemic aldosterone. Elucidation of glaucoma pathogenesis, especially normal-tension glaucoma (NTG) subtype by our current animal model can be used for identifying potential therapeutic targets. Based on these results, we are further evaluating NTG prevalence among primary aldosteronism patients.

Mineralocorticoid pathway in retinal health and diseases

In the retina, the mineralocorticoid receptor (MR) is expressed in retinal and choroidal vessels and in cells from neural and glial origins. Like in the brain, the major ligand of the MR is cortisol and the MR/glucocorticoid receptor (GR) balance regulates the activation of the MR pathway. Experimental MR pathway activation using either pharmacological agents or transgenic manipulation favors retinal and choroidal pathology. In various models of retinal diseases, such as glaucomatous neuropathy, retinopathy of prematurity, ischemic retinopathies, diabetic retinopathy and choroidal neovascularization, MR antagonism exerts beneficial effects, demonstrating its potential in the treatment of major blinding retinal diseases. But specific formulations are required to optimize the bioavailability of MR antagonists in various compartments of the eye and molecular biomarkers of MR pathway activation remain to be identify in humans to select patients amenable to clinical trials.

Characterization of a murine model of endothelial dysfunction induced by chronic intraperitoneal administration of angiotensin II

Endothelial dysfunction (ED) is a key factor for the development of cardiovascular diseases. Due to its chronic, life-threatening nature, ED only can be studied experimentally in animal models. Therefore, this work was aimed to characterize a murine model of ED induced by a daily intraperitoneal administration of angiotensin II (AGII) for 10 weeks. Oxidative stress, inflammation, vascular remodeling, hypertension, and damage to various target organs were evaluated in treated animals. The results indicated that a chronic intraperitoneal administration of AGII increases the production of systemic soluble VCAM, ROS and ICAM-1 expression, and the production of TNFα, IL1β, IL17A, IL4, TGFβ, and IL10 in the kidney, as well as blood pressure levels; it also promotes vascular remodeling and induces non-alcoholic fatty liver disease, glomerulosclerosis, and proliferative retinopathy. Therefore, the model herein proposed can be a representative model for ED; additionally, it is easy to implement, safe, rapid, and inexpensive.

Prostaglandin E2 promotes pathological retinal neovascularisation via EP4R-EGFR-Gab1-AKT signaling pathway

Proliferative retinopathies, such as proliferative diabetic retinopathy (PDR) and retinopathy of prematurity (ROP) are major causes of visual impairment and blindness in industrialized countries. Prostaglandin E2 (PGE2) is implicated in cellular proliferation and migration via E-prostanoid receptor (EP4R). The aim of this study was to investigate the role of PGE2/EP4R signaling in the promotion of retinal neovascularisation. In a streptozotocin (STZ)-induced diabetic model and an oxygen-induced retinopathy (OIR) model, rats received an intravitreal injection of PGE2, cay10598 (an EP4R agonist) or AH23848 (an EP4R antagonist). Optical coherence tomography, retinal histology and biochemical markers were assessed. Treatment with PGE2 or cay10598 accelerated pathological retinal angiogenesis in STZ and OIR-induced rat retina, which was ameliorated in rats pretreated with AH23848. Serum VEGF-A was upregulated in the PGE2-treated diabetic rats vs non-treated diabetic rats and significantly downregulated in AH23848-treated diabetic rats. PGE2 or cay10598 treatment also significantly accelerated endothelial tip-cell formation in new-born rat retina. In addition, AH23848 treatment attenuated PGE2-or cay10598-induced proliferation and migration by repressing the EGF receptor (EGFR)/Growth factor receptor bound protein 2-associated binder protein 1 (Gab1)/Akt/NF-κB/VEGF-A signaling network in human retinal microvascular endothelial cells (hRMECs). PGE2/EP4R signaling network is thus a potential therapeutic target for pathological intraocular angiogenesis.

In vivo imaging of the hyaloid vascular regression and retinal and choroidal vascular development in rat eyes using optical coherence tomography angiography

This study investigates the hyaloid vascular regression and its relationship to the retinal and choroidal vascular developments using optical coherence tomography angiography (OCTA). Normal and oxygen-induced retinopathy (OIR) rat eyes at postnatal day 15, 18, 21, and 24 were longitudinally imaged using OCTA. At each day, two consecutive imaging for visualizing the hyaloid vasculature and the retinal and choroidal vasculatures were conducted. The hyaloid vessel volume and the retinal and choroidal vessel densities were measured. The hyaloid vessel volumes gradually decreased during the regression, although the OIR eyes exhibited large vessel volumes at all time points. A spatial relationship between persistent hyaloid vasculature and retardation of underlying retinal vascular development was observed in the OIR eyes. Furthermore, anti-vascular endothelial growth factor (VEGF) was administered intravitreally to additional OIR eyes to observe its effect on the vascular regression and development. The VEGF injection to OIR eyes showed reduced persistent hyaloid vessels in the injected eyes as well as in the non-injected fellow eyes. This study presents longitudinal imaging of intraocular vasculatures in the developing eye and shows the utility of OCTA that can be widely used in studies of vascular development and regression and preclinical evaluation of new anti-angiogenic drugs.

Deletion of the myeloid endothelin-B receptor confers long-term protection from angiotensin II-mediated kidney, eye and vessel injury

The endothelin system may be an important player in hypertensive end-organ injury as endothelin-1 increases blood pressure and is pro-inflammatory. The immune system is emerging as an important regulator of blood pressure and we have shown that the early hypertensive response to angiotensin-II infusion was amplified in mice deficient of myeloid endothelin-B (ET_B) receptors (LysM-CreEdnrblox/lox). Hypothesizing that these mice would display enhanced organ injury, we gave angiotensin-II to LysM-CreEdnrblox/lox and littermate controls (Ednrblox/lox) for six weeks. Unexpectedly, LysM-CreEdnrblox/lox mice were significantly protected from organ injury, with less proteinuria, glomerulosclerosis and inflammation of the kidney compared to controls. In the eye, LysM-CreEdnrblox/lox mice had fewer retinal hemorrhages, less microglial activation and less vessel rarefaction. Cardiac remodeling and dysfunction were similar in both groups at week six but LysM-CreEdnrblox/lox mice had better endothelial function. Although blood pressure was initially higher in LysM-CreEdnrblox/lox mice, this was not sustained. A natriuretic switch at about two weeks, due to enhanced ET_B signaling in the kidney, induced a hypertensive reversal. By week six, blood pressure was lower in LysM-CreEdnrblox/lox mice than in controls. At six weeks, macrophages from LysM-CreEdnrblox/lox mice were more anti-inflammatory and had greater phagocytic ability compared to the macrophages of Ednrblox/lox mice. Thus, myeloid cell ET_B receptor signaling drives this injury both through amplifying hypertension and by inflammatory polarization of macrophages.

Aldosterone Synthase in Peripheral Sensory Neurons Contributes to Mechanical Hypersensitivity during Local Inflammation in Rats

Background

Recent emerging evidence suggests that extra-adrenal synthesis of aldosterone occurs (e.g., within the failing heart and in certain brain areas). In this study, the authors investigated evidence for a local endogenous aldosterone production through its key processing enzyme aldosterone synthase within peripheral nociceptive neurons.

Methods

In male Wistar rats (n = 5 to 8 per group) with Freund’s complete adjuvant hind paw inflammation, the authors examined aldosterone, aldosterone synthase, and mineralocorticoid receptor expression in peripheral sensory neurons using quantitative reverse transcriptase–polymerase chain reaction, Western blot, immunohistochemistry, and immunoprecipitation. Moreover, the authors explored the nociceptive behavioral changes after selective mineralocorticoid receptor antagonist, canrenoate-K, or specific aldosterone synthase inhibitor application.

Results

In rats with Freund’s complete adjuvant–induced hind paw inflammation subcutaneous and intrathecal application of mineralocorticoid receptor antagonist, canrenoate-K, rapidly and dose-dependently attenuated nociceptive behavior (94 and 48% reduction in mean paw pressure thresholds, respectively), suggesting a tonic activation of neuronal mineralocorticoid receptors by an endogenous ligand. Indeed, aldosterone immunoreactivity was abundant in peptidergic nociceptive neurons of dorsal root ganglia and colocalized predominantly with its processing enzyme aldosterone synthase and mineralocorticoid receptors. Moreover, aldosterone and its synthesizing enzyme were significantly upregulated in peripheral sensory neurons under inflammatory conditions. The membrane mineralocorticoid receptor consistently coimmunoprecipitated with endogenous aldosterone, confirming a functional link between mineralocorticoid receptors and its endogenous ligand. Importantly, inhibition of endogenous aldosterone production in peripheral sensory neurons by a specific aldosterone synthase inhibitor attenuated nociceptive behavior after hind paw inflammation (a 32% reduction in paw pressure thresholds; inflammation, 47 ± 2 [mean ± SD] vs. inflammation + aldosterone synthase inhibitor, 62 ± 2).

Conclusions

Local production of aldosterone by its processing enzyme aldosterone synthase within peripheral sensory neurons contributes to ongoing mechanical hypersensitivity during local inflammation via intrinsic activation of neuronal mineralocorticoid receptors.

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MiR-203a-3p inhibits retinal angiogenesis and alleviates proliferative diabetic retinopathy in oxygen-induced retinopathy (OIR) rat model via targeting VEGFA and HIF-1α

Proliferative diabetic retinopathy (PDR) is a common complication of diabetes mellitus, characterized by abnormal retinal angiogenesis. MicroRNA-203-3p (miR-203-3p) was found to be down-regulated in a murine model of proliferative retinopathy. This study was performed to explore the role of miR-203a-3p in retinal angiogenesis of PDR. Firstly, a rat OIR model, which was used to mimic PDR, was established and the OIR rats were treated with scrambled control or miR-203a-3p agomir by intravitreal injection. The results showed that the level of miR-203a-3p was decreased in OIR rats, and forced over-expression of miR-203a-3p inhibited OIR-induced retinal angiogenesis as evidenced by reduced blood vessel profiles and CD31 expression. OIR-induced up-regulation of VEGFA, HIF-α, PCNA, and MMPs in the retina was also counteracted by miR-203a-3p. Additionally, high glucose (HG)-induced proliferation, migration and tube formation of human retinal microvascular endothelial cells (HRMECs) were also dampened by the up-regulation of miR-203a-3p. Dual-luciferase reporter assay showed that miR-203a-3p could specifically bind to the 3'UTR of VEGFA and HIF-1α. Over-expression of VEGFA or HIF-1α restored the tube formation activity of HRMECs suppressed by miR-203a-3p. In conclusion, our findings demonstrate that up-regulation of miR-203a-3p might inhibit pathological retinal angiogenesis of PDR by targeting VEGFA and HIF-1α.

Angiotensin II and aldosterone activate retinal microglia

Microglial cells are important contributors to the neuroinflammation and blood vessel damage that occurs in ischemic retinopathies. We hypothesized that key effectors of the renin-angiotensin aldosterone system, angiotensin II (Ang II) and aldosterone, increase the density of microglia in the retina and stimulate their production of reactive oxygen species (ROS) as well as pro-angiogenic and pro-inflammatory factors. Two animal models were studied that featured up-regulation of Ang II or aldosterone and included transgenic Ren-2 rats which overexpress renin and Ang II in tissues including the retina, and Sprague Dawley rats with ischemic retinopathy and infused with aldosterone. Complementary studies were performed in primary cultures of retinal microglia from neonatal Sprague Dawley rats exposed to hypoxia (0.5% O₂) and inhibitors of the angiotensin type 1 receptor (valsartan), the mineralocorticoid receptor (spironolactone) or aldosterone synthase (FAD286). In both in vivo models, the density of ionized calcium-binding adaptor protein-1 labelled microglia/macrophages was increased in retina compared to genetic or vehicle controls. In primary cultures of retinal microglia, hypoxia increased ROS (superoxide) levels as well as the expression of the NADPH oxidase (NOX) isoforms, NOX1, NOX2 and NOX4. The elevated levels of ROS as well as NOX2 and NOX4 were reduced by all of the treatments, and valsartan and FAD286 also reduced NOX1 mRNA levels. A protein cytokine array of retinal microglia revealed that valsartan, spironolactone and FAD286 reduced the hypoxia-induced increase in the potent pro-angiogenic and pro-inflammatory agent, vascular endothelial growth factor as well as the inflammatory factors, CCL5 and interferon γ. Valsartan also reduced the hypoxia-induced increase in IL-6 and TIMP-1 as well as the chemoattractants, CXCL2, CXCL3, CXCL5 and CXCL10. Spironolactone and FAD286 reduced the levels of CXCL2 and CXCL10, respectively. In conclusion, our findings that both Ang II and aldosterone influence the activation of retinal microglia implicates the renin-angiotensin aldosterone system in the pathogenesis of ischemic retinopathies.

Long noncoding RNA MALAT1 participates in the pathological angiogenesis of diabetic retinopathy in an oxygen-induced retinopathy mouse model by sponging miR-203a-3p

Diabetic retinopathy (DR) is a devastating complication of diabetes. The aim of the present study is to investigate the exact role and mechanism of long noncoding RNA MALAT1 (MALAT1) in the progress of DR. An oxygen-induced retinopathy (OIR) mouse model and high glucose (HG) stimulated human retinal microvascular endothelial cells (HRMECs) were employed to mimic the pathological statues of DR. Quantitative real-time PCR (qRT-PCR) and Western blot results showed that MALAT1, VEGFA, and HIF-1α levels were increased in DR retinal tissues and HG-stimulated HRMECs, whereas the expression of miR-203a-3p was decreased. Knockdown of MALAT1 or upregulation of miR-203a-3p both suppressed HG-induced proliferation, migration, and tube formation of HRMECs. A dual-luciferase reporter assay showed that miR-203a-3p could bind to the predicted seed regions of MALAT1 as evidenced by the reduced luciferase activity. Furthermore, enforced downregulation of miR-203a-3p abolished the suppressive effect of MALAT1 silencing on HRMEC cell migration and tube formation. In conclusion, these data demonstrated that MALAT1 may affect angiogenesis by sponging miR-203a-3p in DR, suggesting that MALAT1 may act as a novel therapeutic target for the treatment of DR.

Aldosterone as a mediator of severity in retinal vascular disease: Evidence and potential mechanisms

Diabetic retinopathy (DR) and retinal vein occlusion (RVO) are the two most common retinal vascular diseases and are major causes of vision loss and blindness worldwide. Recent and ongoing development of medical therapies including anti-vascular endothelial growth factor and corticosteroid drugs for treatment of these diseases have greatly improved the care of afflicted patients. However, severe manifestations of retinal vascular disease result in persistent macular edema, progressive retinal ischemia and incomplete visual recovery. Additionally, choroidal vascular diseases including neovascular age-related macular degeneration (NVAMD) and central serous chorioretinopathy (CSCR) cause vision loss for which current treatments are incompletely effective in some cases and highly burdensome in others. In recent years, aldosterone has gained attention as a contributor to the various deleterious effects of retinal and choroidal vascular diseases via a variety of mechanisms in several retinal cell types. The following is a review of the role of aldosterone in retinal and choroidal vascular diseases as well as our current understanding of the mechanisms by which aldosterone mediates these effects.

Vascular mineralocorticoid receptor activation and disease

Mineralocorticoid receptor activation in endothelial and smooth muscle cells can promote vascular disease by increasing oxidative stress, promoting inflammation, accelerating vascular stiffness, remodeling, and calcification, altering vessel responsiveness to various vasoactive factors, thus altering vascular tone and blood pressure, and by altering angiogenesis. Here, we review the recent evidence highlighting the impact of vascular mineralocorticoid receptor activation in pathological situations, including kidney injury, vascular injury associated with metabolic diseases, atherosclerosis, cerebral vascular injury during hypertension, vascular stiffening and aging, pulmonary hypertension, vascular calcification, cardiac remodeling, wound healing, inflammation, thrombosis, and disorders related to angiogenic defects in the eye. The possible mechanisms implicating mineralocorticoid receptor activation in various vascular disorders are discussed. Altogether, recent evidence points towards pharmacological mineralocorticoid receptor inhibition as a strategy to treat diseases in which overactivation of the mineralocorticoid receptor in endothelial and/or smooth muscle cells may play a pivotal role.

Angiotensin II and aldosterone in retinal vasculopathy and inflammation

Angiotensin II and aldosterone are the main effectors of the renin-angiotensin aldosterone system (RAAS) and have a central role in hypertension as well as cardiovascular and renal disease. The localization of RAAS components within the retina has led to studies investigating the roles of angiotensin II, aldosterone and the counter regulatory arm of the pathway in vision-threatening retinopathies. This review will provide a brief overview of RAAS components as well as the vascular pathology that develops in the retinal diseases, retinopathy of prematurity, diabetic retinopathy and neovascular age-related macular degeneration. The review will discuss pre-clinical and clinical evidence that modulation of the RAAS alters the development of vasculopathy and inflammation in the aforementioned retinopathies, as well as the emerging role of aldosterone and the mineralocorticoid receptor in central serous chorioretinopathy.

Oxygen-Induced Retinopathy and Choroidopathy: In Vivo Longitudinal Observation of Vascular Changes Using OCTA

Purpose

The purpose of this study was to assess the retinal and choroidal vasculatures of an oxygen-induced retinopathy (OIR) rat model using optical coherence tomography angiography (OCTA) as well as to verify the performance of OCTA for visualizing in vivo vascular alterations, longitudinally and quantitatively.

Methods

To induce OIR, Sprague Dawley rat pups were incubated in an 80% oxygen chamber from postnatal day 1 (P1) to P11 and returned to room air. OCTA imaging was performed in six eyes at P15, P18, P21, and P24. All eyes were imaged with ex vivo retinal flat mount immunofluorescence microscopy for comparison with OCTA. The areas of the neovascular tufts, retinal vessel tortuosities and diameters, and vessel densities of different retinal and choroidal layers were quantified.

Results

The neovascular tufts were observed in two OIR eyes. The tuft areas decreased spontaneously from P18 to P24. The increase in arterial tortuosity and venous dilation were observed in the OIR eyes at P15 and P18. The retardation of vascular developments was observed in the deep vascular plexus and the choroidal layer in the OIR group while the superficial vascular plexus did not show developmental delay.

Conclusions

This study demonstrates an application of OCTA for quantitative and longitudinal studies on in vivo vascular alterations, including neovascular tufts, increase in arterial tortuosity, venous dilation, and developmental delay in the OIR rat model.

Aldosterone Exposure Causes Increased Retinal Edema and Severe Retinopathy Following Laser-Induced Retinal Vein Occlusion in Mice

Purpose

To determine the effects of aldosterone exposure on retinal edema and retinopathy in a mouse model of retinal vein occlusion (RVO).

Methods

RVO was induced immediately following intravenous injection of Rose bengal (66 mg/kg) using a 532-nm wavelength laser to place three to seven applications at 80 mW and 50-μm spot size directed at the superior retinal vein one disc diameter away from the nerve. Negative control consisted of placing an equal number of laser spots without targeting the vein. Male and female C57BL/6J mice aged 7 to 9 months with confirmed absence of Crb1rd8 were used. Aldosterone pellets releasing a daily dose of 0.83 μg/day were implanted subcutaneously 4 weeks prior to RVO. Retinal imaging by optical coherence tomography (OCT) was performed using a Micron IV rodent imaging system. Retinas were analyzed by immunohistochemistry using standard techniques. Retinal imaging and tissue analysis were performed 2, 4, and 7 days following RVO. Comparisons were made using Student's t-test, ANOVA, and Pearson's χ2.

Results

RVO caused retinal edema in the form of cystic spaces and retinal thickening detectable by both OCT and histology. RVO also caused Müller glia (MG) dysfunction manifest as upregulated glial fibrillary acidic protein (GFAP) and altered localization of aquaporin 4 (AQP4) and Kir4.1. Treatment with aldosterone caused a significant increase in retinal edema and more severe retinopathy manifest as retinal whitening and extensive intraretinal hemorrhage. MG dysfunction was more severe and persistent in aldosterone-treated mice. Finally, aldosterone greatly increased the number of infiltrating mononuclear phagocytes following RVO.

Conclusions

Systemic aldosterone exposure causes a more severe RVO phenotype manifest as increased severity and duration of retinal edema and more severe retinopathy. The effects of aldosterone may be mediated by MG dysfunction and increased infiltration of mononuclear phagocytes. This suggests that small increases in aldosterone levels may be a risk factor for severe RVO.

Retinal microglia - A key player in healthy and diseased retina

Microglia, the resident immune cells of the brain and retina, are constantly engaged in the surveillance of their surrounding neural tissue. During embryonic development they infiltrate the retinal tissues and participate in the phagocytosis of redundant neurons. The contribution of microglia in maintaining the purposeful and functional histo-architecture of the adult retina is indispensable. Within the retinal microenvironment, robust microglial activation is elicited by subtle changes caused by extrinsic and intrinsic factors. When there is a disturbance in the cell-cell communication between microglia and other retinal cells, for example in retinal injury, the activated microglia can manifest actions that can be detrimental. This is evidenced by activated microglia secreting inflammatory mediators that can further aggravate the retinal injury. Microglial activation as a harbinger of a variety of retinal diseases is well documented by many studies. In addition, a change in the microglial phenotype which may be associated with aging, may predispose the retina to age-related diseases. In light of the above, the focus of this review is to highlight the role played by microglia in the healthy and diseased retina, based on findings of our own work and from that of others.

AAV-mediated gene delivery of the calreticulin anti-angiogenic domain inhibits ocular neovascularization

Ocular neovascularization is a common pathological feature in diabetic retinopathy and neovascular age-related macular degeneration that can lead to severe vision loss. We evaluated the therapeutic efficacy of a novel endogenous inhibitor of angiogenesis, the calreticulin anti-angiogenic domain (CAD180), and its functional 112-residue fragment, CAD-like peptide 112 (CAD112), delivered using a self-complementary adeno-associated virus serotype 2 (scAAV2) in rodent models of oxygen-induced retinopathy and laser-induced choroidal neovascularization. The expression of CAD180 and CAD112 was elevated in human umbilical vein endothelial cells transduced with scAAV2-CAD180 or scAAV2-CAD112, respectively, and both inhibited angiogenic activity in vitro. Intravitreal gene delivery of scAAV2-CAD180 or scAAV2-CAD112 significantly inhibited ischemia-induced retinal neovascularization in rat eyes (CAD180: 52.7% reduction; CAD112: 49.2% reduction) compared to scAAV2-mCherry, as measured in retinal flatmounts stained with isolectin B4. Moreover, the retinal structure and function were unaffected by scAAV2-CAD180 or scAAV2-CAD112, as measured by optical coherence tomography and electroretinography. Moreover, subretinal delivery of scAAV2-CAD180 or scAAV2-CAD112 significantly attenuated laser-induced choroidal neovascularization in mouse eyes compared to scAAV2-mCherry, as measured by fundus fluorescein angiography (CAD180: 62.4% reduction; CAD112: 57.5% reduction) and choroidal flatmounts (CAD180: 40.21% reduction; CAD112: 43.03% reduction). Gene delivery using scAAV2-CAD180 or scAAV2-CAD112 has significant potential as a therapeutic option for the management of ocular neovascularization.

Endothelin-2 Injures the Blood-Retinal Barrier and Macroglial Müller Cells: Interactions with Angiotensin II, Aldosterone, and NADPH Oxidase

Although increasing evidence indicates that endothelin-2 (Edn2) has distinct roles in tissue pathology, including inflammation, glial cell dysfunction, and angiogenesis, its role in the retina and the factors that regulate its actions are not fully understood. We hypothesized that Edn2 damages the blood-retinal barrier (BRB) and that this is mediated by interactions with the renin-angiotensin-aldosterone system and reactive oxygen species derived from NADPH oxidase (Nox). C57BL/6J mice received an intravitreal injection of Edn2 or control vehicle to examine the blood pressure-independent effects of Edn2. Mice administered Edn2 were randomized to receive by intraperitoneal injection treatments that inhibited the Edn type a receptor, Edn type b receptor, angiotensin type 1 receptor, mineralocorticoid receptor, or Nox isoforms 1 to 4. One month later, mice administered Edn2 exhibited breakdown of the BRB with increased vascular leakage, vascular endothelial growth factor expression, and infiltrating macrophages (Ly6C⁺CD45^highCD11b⁺). Further, macroglial Müller cells, which influence the integrity of the BRB and prevent retinal edema, became gliotic and expressed increased levels of water (aquaporin-4) and ion (Kir4.1) channels. This Edn2-mediated retinopathy was reduced by all treatments. Complementary in vitro studies in cultured Müller cells supported these findings and demonstrated the importance of reactive oxygen species in mediating these events. In conclusion, Edn2 has detrimental effects on the BRB and Müller cells that involve interactions with the renin-angiotensin aldosterone system and Nox1/4.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: The role of the mineralocorticoid receptor in the vasculature

Since the mineralocorticoid receptor (MR) was cloned 30 years ago, it has become clear that MR is expressed in extra-renal tissues, including the cardiovascular system, where it is expressed in all cells of the vasculature. Understanding the role of MR in the vasculature has been of particular interest as clinical trials show that MR antagonism improves cardiovascular outcomes out of proportion to changes in blood pressure. The last 30 years of research have demonstrated that MR is a functional hormone-activated transcription factor in vascular smooth muscle cells and endothelial cells. This review summarizes advances in our understanding of the role of vascular MR in regulating blood pressure and vascular function, and its contribution to vascular disease. Specifically, vascular MR contributes directly to blood pressure control and to vascular dysfunction and remodeling in response to hypertension, obesity and vascular injury. The literature is summarized with respect to the role of vascular MR in conditions including: pulmonary hypertension; cerebral vascular remodeling and stroke; vascular inflammation, atherosclerosis and myocardial infarction; acute kidney injury; and vascular pathology in the eye. Considerations regarding the impact of age and sex on the function of vascular MR are also described. Further investigation of the precise molecular mechanisms by which MR contributes to these processes will aid in the identification of novel therapeutic targets to reduce cardiovascular disease (CVD)-related morbidity and mortality.

Macrophage heterogeneity and renin-angiotensin system disorders

Macrophages are heterogeneous innate immune cells which are important in both the maintenance of tissue homeostasis and its disruption, by promoting tissue inflammation and fibrosis. The renin-angiotensin system is central to the pathophysiology of a large suite of diseases, which are driven in part by large amounts of tissue inflammation and fibrosis. Here, we review recent advances in understanding macrophage heterogeneity in origin and function, and how these may lead to new insights into the pathogenesis of these chronic diseases.

Corticosteroids and the retina: a role for the mineralocorticoid receptor

PURPOSE OF REVIEW

Long-lasting devices releasing steroids have been approved recently for macular edema of various origins. Identification of the retina as a novel mineralo-sensitive tissue also raises new therapeutic options.

RECENT FINDINGS

Recently, the over activation of the mineralocorticoid receptor (MR) pathway has been shown to cause fluid accumulation in the retina, choroidal vasodilation, and to promote retinal neovascularization in hypoxic conditions. These findings indicate that MR antagonists could have beneficial effects in the treatment of retinal diseases. Central serous chorioretinopathy is a retinal disease associated with choroidal vasodilation and subretinal fluid that affects mostly men with type A personality and occurrence has been associated with steroid intake. In several independent studies, MR antagonists have shown beneficial effects, significantly reducing subretinal fluid in eyes of chronic central serous chorioretinopathy patients.

SUMMARY

The role of MR in retinal disorder is emerging and the potential association with psychological traits is considered. The place of MR antagonists for retinal diseases treatment is discussed.

New agents modulating the renin-angiotensin-aldosterone system-Will there be a new therapeutic option?

The renin-angiotensin-aldosterone system (RAAS) is more complex than it was originally regarded. According to the current subject knowledge, there are two main axes of the RAAS: (1) angiotensin-converting enzyme (ACE)-angiotensin II-AT₁ receptor axis and (2) ACE2-angiotensin-(1-7)-Mas receptor axis. The activation of the first axis leads to deleterious effects, including vasoconstriction, endothelial dysfunction, thrombosis, inflammation, and fibrosis; therefore, blocking the components of this axis is a highly rational and commonly used therapeutic procedure. The ACE2-Ang-(1-7)-Mas receptor axis has a different role, since it often opposes the effects induced by the classical ACE-Ang II-AT₁ axis. Once the positive effects of the ACE2-Ang-(1-7)-Mas axis were discovered, the alternative ways of pharmacotherapy activating this axis of RAAS appeared. This article briefly describes new molecules affecting the RAAS, namely: recombinant human ACE2, ACE2 activators, angiotensin-(1-7) peptide and non-peptide analogs, aldosterone synthase inhibitors, and the third and fourth generation of mineralocorticoid receptor antagonists. The results of the experimental and clinical studies are encouraging, which leads us to believe that these new molecules can support the treatment of cardiovascular diseases as well as cardiometabolic disorders.

Promoting vascular repair in the retina: can stem/progenitor cells help?

Since its first epidemic in the 1940s, retinopathy of prematurity (ROP) has been a challenging illness in neonatology. Higher than physiological oxygen levels impede the development of the immature retinal neuropil and vasculature. Current treatment regimens include cryotherapy, laser photocoagulation, and anti-VEGF agents. Unfortunately, none of these approaches can rescue the normal retinal vasculature, and each has significant safety concerns. The limitations of these approaches have led to new efforts to understand the pathological characteristics in each phase of ROP and to find a safer and more effective therapeutic approach. In the era of stem cell biology and with the need for new treatments for ROP, this review discusses the possible future use of unique populations of proangiogenic cells for therapeutic revascularization of the preterm retina.

Adeno-Associated Virus Overexpression of Angiotensin-Converting Enzyme-2 Reverses Diabetic Retinopathy in Type 1 Diabetes in Mice

Angiotensin-converting enzyme (ACE)-2 is the primary enzyme of the vasoprotective axis of the renin angiotensin system that regulates the classic renin angiotensin system axis. We aimed to determine whether local retinal overexpression of adenoassociated virus (AAV)-ACE2 prevents or reverses diabetic retinopathy. Green fluorescent protein (GFP)-chimeric mice were generated to distinguish resident (retinal) from infiltrating bone marrow-derived inflammatory cells and were made diabetic using streptozotocin injections. Retinal digestion using trypsin was performed and acellular capillaries enumerated. Capillary occlusion by GFP(+) cells was used to measure leukostasis. Overexpression of ACE2 prevented (prevention cohort: untreated diabetic, 11.3 ± 1.4; ACE2 diabetic, 6.4 ± 0.9 per mm(2)) and partially reversed (reversal cohort: untreated diabetic, 15.7 ± 1.9; ACE2 diabetic, 6.5 ± 1.2 per mm(2)) the diabetes-associated increase of acellular capillaries and the increase of infiltrating inflammatory cells into the retina (F4/80(+)) (prevention cohort: untreated diabetic, 24.2 ± 6.7; ACE2 diabetic, 2.5 ± 1.6 per mm(2); reversal cohort: untreated diabetic, 56.8 ± 5.2; ACE2 diabetic, 5.6 ± 2.3 per mm(2)). In both study cohorts, intracapillary bone marrow-derived cells, indicative of leukostasis, were only observed in diabetic animals receiving control AAV injections. These results indicate that diabetic retinopathy, and possibly other diabetic microvascular complications, can be prevented and reversed by locally restoring the balance between the classic and vasoprotective renin angiotensin system.

Hypertensive retinopathy in a transgenic angiotensin-based model

Severe hypertension destroys eyesight. The RAS (renin-angiotensin system) may contribute to this. This study relied on an established angiotensin, AngII (angiotensin II)-elevated dTGR (double-transgenic rat) model and same-background SD (Sprague-Dawley) rat controls. In dTGRs, plasma levels of AngII were increased. We determined the general retinal phenotype and observed degeneration of ganglion cells that we defined as vascular degeneration. We also inspected relevant gene expression and lastly observed alterations in the outer blood-retinal barrier. We found that both scotopic a-wave and b-wave as well as oscillatory potential amplitude were significantly decreased in dTGRs, compared with SD rat controls. However, the b/a-wave ratio remained unchanged. Fluorescence angiography of the peripheral retina indicated that exudates, or fluorescein leakage, from peripheral vessels were increased in dTGRs compared with controls. Immunohistological analysis of blood vessels in retina whole-mount preparations showed structural alterations in the retina of dTGRs. We then determined the general retinal phenotype. We observed the degeneration of ganglion cells, defined vascular degenerations and finally found differential expression of RAS-related genes and angiogenic genes. We found the expression of both human angiotensinogen and human renin in the hypertensive retina. Although the renin gene expression was not altered, the AngII levels in the retina were increased 4-fold in the dTGR retina compared with that in SD rats, a finding with mechanistic implications. We suggest that alterations in the outer blood-retinal barrier could foster an area of visual-related research based on our findings. Finally, we introduce the dTGR model of retinal disease.

A potent Nrf2 activator, dh404, bolsters antioxidant capacity in glial cells and attenuates ischaemic retinopathy

An imbalance in oxidative stress and antioxidant defense mechanisms contributes to the development of ischaemic retinopathies such as diabetic retinopathy and retinopathy of prematurity (ROP). Currently, the therapeutic utility of targeting key transcription factors to restore this imbalance remains to be determined. We postulated that dh404, an activator of nuclear factor erythroid-2 related factor 2 (Nrf2), the master regulator of oxidative stress responses, would attenuate retinal vasculopathy by mechanisms involving protection against oxidative stress-mediated damage to glia. Oxygen-induced retinopathy (OIR) was induced in neonatal C57BL/6J mice by exposure to hyperoxia (phase I) followed by room air (phase II). dh404 (1 mg/kg/every second day) reduced the vaso-obliteration of phase I OIR and neovascularization, vascular leakage and inflammation of phase II OIR. In phase I, the astrocytic template and vascular endothelial growth factor (VEGF) expression necessary for physiological angiogenesis are compromised resulting in vaso-obliteration. These events were attenuated by dh404 and related to dh404's ability to reduce the hyperoxia-induced increase in reactive oxygen species (ROS) and markers of cell damage as well as boost the Nrf2-responsive antioxidants in cultured astrocytes. In phase II, neovascularization and vascular leakage occurs following gliosis of Müller cells and their subsequent increased production of angiogenic factors. dh404 reduced Müller cell gliosis and vascular leakage in OIR as well as the hypoxia-induced increase in ROS and angiogenic factors with a concomitant increase in Nrf2-responsive antioxidants in cultured Müller cells. In conclusion, agents such as dh404 that reduce oxidative stress and promote antioxidant capacity offer a novel approach to lessen the vascular and glial cell damage that occurs in ischaemic retinopathies.

Prorenin stimulates a pro-angiogenic and pro-inflammatory response in retinal endothelial cells and an M1 phenotype in retinal microglia

Angiogenesis and inflammation are causative factors in the development of neovascular retinopathies. These processes involve the retinal endothelium and the retinal immune cells, microglia. The renin-angiotensin system contributes to retinal injury via the actions of the type 1 angiotensin receptor (AT1R). However, it has been suggested that prorenin, the initiator of the renin-angiotensin system cascade, influences retinal injury independently from the AT1R. We evaluated whether prorenin induced a pro-angiogenic and pro-inflammatory response in retinal endothelial cells and a pro-inflammatory phenotype in retinal microglia. Primary cultures of retinal endothelial cells and microglia were studied. Rat recombinant prorenin (2 nmol/L) stimulated the proliferation and tubulogenesis of retinal endothelial cells; it increased the levels of pro-angiogenic factors, vascular endothelial growth factor, angiopoietin-1, and tyrosine kinase with immunoglobulin and epidermal growth factor homology domains, and pro-inflammatory factors, intercellular adhesion molecule-1 and monocyte chemoattractant protein-1, relative to the controls. The messenger RNA levels of the (pro)renin receptor were also increased. These effects occurred in the presence of the AT1R blocker candesartan (10 μmol/L) and the renin inhibitor aliskiren (10 μmol/L). Microglia, which express the (pro)renin receptor, elicited an activated phenotype when exposed to prorenin, which was characterized by increased levels of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, tumour necrosis factor-α, interleukin-6, and interleukin-1β and by decreased levels of interleukin-10 and arginase-1 relative to controls. Candesartan did not influence the effects of prorenin on retinal microglia. In conclusion, prorenin has distinct pro-angiogenic and pro-inflammatory effects on retinal cells that are independent of the AT1R, indicating the potential importance of prorenin in retinopathy.

Inhibition of NOX1/4 with GKT137831: a potential novel treatment to attenuate neuroglial cell inflammation in the retina

BACKGROUND

Inflammation and the excess production of reactive oxygen species (ROS) contribute significantly to the pathogenesis of ischemic retinopathies such as diabetic retinopathy and retinopathy of prematurity. We hypothesized that GKT137831, a dual inhibitor of NADPH oxidases (NOX) 1 and NOX4, reduces inflammation in the ischemic retina by dampening the pro-inflammatory phenotype of retinal immune cells as well as macroglial Müller cells and neurons.

METHODS

Ischemic retinopathy was induced in Sprague-Dawley rats by exposure to 80 % O2 cycled with 21 % O2 for 3 h per day from postnatal day (P) 0 to P11, followed by room air (P12 to P18). GKT137831 was administered P12 to P18 (60 mg/kg, subcutaneous) and comparisons were to room air controls. Retinal inflammation was examined by measuring leukocyte adherence to the retinal vasculature, ionized calcium-binding adaptor protein-1-positive microglia/macrophages, and the mRNA and protein levels of key inflammatory factors involved in retinal disease. Damage to Müller cells was evaluated by quantitating glial fibrillary acidic protein-positive cells and vascular leakage with an albumin ELISA. To verify the anti-inflammatory actions of GKT137831 on glia and neurons involved in ischemic retinopathy, primary cultures of rat retinal microglia, Müller cells, and ganglion cells were exposed to the in vitro counterpart of ischemia, hypoxia (0.5 %), and treated with GKT137831 for up to 72 h. ROS levels were evaluated with dihydroethidium and the protein and gene expression of inflammatory factors with quantitative PCR, ELISA, and a protein cytokine array.

RESULTS

In the ischemic retina, GKT137831 reduced the increased leukocyte adherence to the vasculature, the pro-inflammatory phenotype of microglia and macroglia, the increased gene and protein expression of vascular endothelial growth factor, monocyte chemoattractant protein-1, and leukocyte adhesion molecules as well as vascular leakage. In all cultured cell types, GKT137831 reduced the hypoxia-induced increase in ROS levels and protein expression of various inflammatory mediators.

CONCLUSIONS

NOX1/4 enzyme inhibition with GKT137831 has potent anti-inflammatory effects in the retina, indicating its potential as a treatment for a variety of vision-threatening retinopathies.

The microglia in healthy and diseased retina

The microglia are the immune cells of the central nervous system and, also the retina. They fulfil several tasks of surveillance in the healthy retina. In case of an injury or disease, microglia become activated and tries to repair the damage. However, in a lot of cases it does not work, and microglia deteriorate the situation by releasing toxic and pro-inflammatory compounds. Moreover, they further promote degenerative processes by attacking and phagocytosing damaged neurones and photoreceptors that otherwise would possibly have the chance to survive. Such deleterious action of the microglia has been observed in degeneration of retinal ganglion cells and photoreceptors, and it takes place in hereditary diseases, infections as well as in case of traumatic or light injuries. Therefore, a number of attempts has been undertaken so far to inhibit the microglia, with varying success. The task remains to study behaviour of the microglia and their interaction with other retinal cell populations in more detail with respect to released factors and expressed receptors including the time points of the corresponding events. The goal has to be to find a better balance between helpful and detrimental actions of the microglia.

Ebselen by modulating oxidative stress improves hypoxia-induced macroglial Müller cell and vascular injury in the retina

Oxidative stress is an important contributor to glial and vascular cell damage in ischemic retinopathies. We hypothesized that ebselen via its ability to reduce reactive oxygen species (ROS) and augment nuclear factor-like 2 (Nrf2) anti-oxidants would attenuate hypoxia-induced damage to macroglial Müller cells and also lessen retinal vasculopathy. Primary cultures of rat Müller cells were exposed to normoxia (21% O2), hypoxia (0.5% O2) and ebselen (2.5 μM) for up to 72 h. Oxygen-induced retinopathy (OIR) was induced in C57BL/6J mice while control mice were housed in room air. Mice received vehicle (saline, 5% dimethyl sulfoxide) or ebselen (10 mg/kg) each day between postnatal days 6-18. In cultured Müller cells, flow cytometry for dihydroethidium revealed that ebselen reduced the hypoxia-induced increase in ROS levels, whilst increasing the expression of Nrf2-regulated anti-oxidant genes, heme oxygenase 1, glutathione peroxidase-1, NAD(P)H dehydrogenase quinone oxidoreductase 1 and glutamate-cysteine ligase. Moreover, in Müller cells, ebselen reduced the hypoxia-induced increase in protein levels of pro-angiogenic and pro-inflammatory factors including vascular endothelial growth factor, interleukin-6, monocyte chemoattractant-protein 1 and intercellular adhesion molecule-1, and the mRNA levels of glial fibrillary acidic protein (GFAP), a marker of Müller cell injury. Ebselen improved OIR by attenuating capillary vaso-obliteration and neovascularization and a concomitant reduction in Müller cell gliosis and GFAP. We conclude that ebselen protects against hypoxia-induced injury of retinal Müller cells and the microvasculature, which is linked to its ability to reduce oxidative stress, vascular damaging factors and inflammation. Agents such as ebselen may be potential treatments for retinopathies that feature oxidative stress-mediated damage to glia and the microvasculature.

Aldosterone promotes cardiac endothelial cell proliferation in vivo

BACKGROUND

Experimentally, aldosterone in association with NaCl induces cardiac fibrosis, oxidative stress, and inflammation through mineralocorticoid receptor activation; however, the biological processes regulated by aldosterone alone in the heart remain to be identified.

METHODS AND RESULTS

Mice were treated for 7 days with aldosterone, and then cardiac transcriptome was analyzed. Aldosterone regulated 60 transcripts (51 upregulated and 9 downregulated) in the heart (fold change ≥1.5, false discovery rate <0.01). To identify the biological processes modulated by aldosterone, a gene ontology analysis was performed. The majority of aldosterone-regulated genes were involved in cell division. The cardiac Ki-67 index (an index of proliferation) of aldosterone-treated mice was higher than that of nontreated mice, confirming microarray predictions. Costaining of Ki-67 with vinculin, CD68, α-smooth muscle actin, CD31, or caveolin 1 revealed that the cycling cells were essentially endothelial cells. Aldosterone-induced mineralocorticoid receptor-dependent proliferation was confirmed ex vivo in human endothelial cells. Moreover, pharmacological-specific blockade of mineralocorticoid receptor by eplerenone inhibited endothelial cell proliferation in a preclinical model of heart failure (transverse aortic constriction).

CONCLUSIONS

Aldosterone modulates cardiac gene expression and induces the proliferation of cardiac endothelial cells in vivo.

Therapeutic efficacy of a novel non-peptide αvβ3 integrin antagonist for pathological retinal angiogenesis in mice

αvβ3 integrin has been reported as a promising therapeutic target for angiogenesis. In the present study, we tested the antiangiogenic activity of 3-[3-(6-guanidino-1-oxoisoindolin-2-yl) propanamido]-3-(pyridin-3-yl) propanoic acid dihydrochloride (GOPPP), a novel non-peptide αvβ3 antagonist. Both human umbilical vein endothelial cells (HUVECs) and a mouse model of oxygen-induced retinopathy (OIR) were investigated separately. HUVEC adhesion, proliferation, migration, ERK1/2 and Akt phosphorylation were assessed. C57BL/6 mice were used for the studies in the OIR model. After exposure to 75% oxygen from postnatal day (PD) 7 to PD12, the mice were returned to room air, and GOPPP was intravitreally administered on PD12. Retinal neovascularization was evaluated on PD17. Hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) protein levels and ERK1/2 phosphorylation were determined by Western blot analysis of retina proteins. GOPPP significantly inhibited the pro-angiogenic effects of vitronectin on HUVECs, including adhesion, proliferation, and migration, and inhibited ERK1/2 and Akt phosphorylation. Retinal neovascularization in the OIR model was significantly suppressed by intravitreal administration of 50 ng GOPPP. The pro-angiogenic factors HIF-1α and VEGF induced by hypoxia were significantly inhibited by GOPPP in OIR mice. GOPPP administration also inhibited ERK1/2 phosphorylation in the OIR model. These results indicate that GOPPP, a novel αvβ3 integrin antagonist, may have potential for the treatment of pathological retinal angiogenesis.

Aldosterone synthase inhibitors in cardiovascular and renal diseases

Aldosterone is involved in various cardiovascular pathologies, including hypertension, heart failure, atherosclerosis and fibrosis. Mineralocorticoid receptor (MR)-dependent and -independent, genomic and non-genomic processes mediate its complex effects. Spironolactone and eplerenone, both MR antagonists, are the only commercially available compounds targeting directly the actions of aldosterone. However, due to the poor selectivity (spironolactone), low potency (eplerenone) and the fact that only MR-dependent effects of aldosterone can be inhibited, these drugs have limited clinical use. An attractive approach to abolish potentially all of aldosterone-mediated pathologies is the inhibition of aldosterone synthase. This review summarizes current knowledge on the complex effects mediated by aldosterone, potential advantages and disadvantages of aldosterone inhibition and novel directions in the development of aldosterone synthase inhibitors.

Post-translational modifications of the mineralocorticoid receptor: How to dress the receptor according to the circumstances?

Aldosterone or glucocorticoid stimulation of the mineralocorticoid receptor (MR) is involved in numerous physiological responses, including ions and water homeostasis, blood pressure control and metabolism. The understanding of MR signaling regulation in the patho/physiological context took a new direction the last few years with a focus on the post-translational modifications of MR. Depending on its environment, cellular expression, activity or its binding partners, the MR is submitted to several post-translational modifications such as phosphorylation, ubiquitylation, sumoylation and acetylation that regulate its localization, activity and/or stability. A complex interplay between all these modifications allows a fine tuning of MR signaling depending on the physiological context. This review reports recent knowledge about post-translational modifications of MR and describes the enzymes and the molecular mechanisms involved.

Retinal vasculopathy is reduced by dietary salt restriction: involvement of Glia, ENaCα, and the renin-angiotensin-aldosterone system

OBJECTIVE

Neovascularization and vaso-obliteration are vision-threatening events that develop by interactions between retinal vascular and glial cells. A high-salt diet is causal in cardiovascular and renal disease, which is linked to modulation of the renin-angiotensin-aldosterone system. However, it is not known whether dietary salt influences retinal vasculopathy and if the renin-angiotensin-aldosterone system is involved. We examined whether a low-salt (LS) diet influenced vascular and glial cell injury and the renin-angiotensin-aldosterone system in ischemic retinopathy.

APPROACH AND RESULTS

Pregnant Sprague Dawley rats were fed LS (0.03% NaCl) or normal salt (0.3% NaCl) diets, and ischemic retinopathy was induced in the offspring. An LS diet reduced retinal neovascularization and vaso-obliteration, the mRNA and protein levels of the angiogenic factors, vascular endothelial growth factor, and erythropoietin. Microglia, which influence vascular remodeling in ischemic retinopathy, were reduced by LS as was tumor necrosis factor-α. Macroglial Müller cells maintain the integrity of the blood-retinal barrier, and in ischemic retinopathy, LS reduced their gliosis and also vascular leakage. In retina, LS reduced mineralocorticoid receptor, angiotensin type 1 receptor, and renin mRNA levels, whereas, as expected, plasma levels of aldosterone and renin were increased. The aldosterone/mineralocorticoid receptor-sensitive epithelial sodium channel alpha (ENaCα), which is expressed in Müller cells, was increased in ischemic retinopathy and reduced by LS. In cultured Müller cells, high salt increased ENaCα, which was prevented by mineralocorticoid receptor and angiotensin type 1 receptor blockade. Conversely, LS reduced ENaCα, angiotensin type 1 receptor, and mineralocorticoid receptor expression.

CONCLUSIONS

An LS diet reduced retinal vasculopathy, by modulating glial cell function and the retinal renin-angiotensin-aldosterone system.

NADPH oxidase, NOX1, mediates vascular injury in ischemic retinopathy

AIMS

Ischemic retinal diseases such as retinopathy of prematurity are major causes of blindness due to damage to the retinal microvasculature. Despite this clinical situation, retinopathy of prematurity is mechanistically poorly understood. Therefore, effective preventative therapies are not available. However, hypoxic-induced increases in reactive oxygen species (ROS) have been suggested to be involved with NADPH oxidases (NOX), the only known dedicated enzymatic source of ROS. Our major aim was to determine the contribution of NOX isoforms (1, 2, and 4) to a rodent model of retinopathy of prematurity.

RESULTS

Using a genetic approach, we determined that only mice with a deletion of NOX1, but not NOX2 or NOX4, were protected from retinal neovascularization and vaso-obliteration, adhesion of leukocytes, microglial accumulation, and the increased generation of proangiogenic and proinflammatory factors and ROS. We complemented these studies by showing that the specific NOX inhibitor, GKT137831, reduced vasculopathy and ROS levels in retina. The source of NOX isoforms was evaluated in retinal vascular cells and neuro-glial elements. Microglia, the immune cells of the retina, expressed NOX1, 2, and 4 and responded to hypoxia with increased ROS formation, which was reduced by GKT137831.

INNOVATION

Our studies are the first to identify the NOX1 isoform as having an important role in the pathogenesis of retinopathy of prematurity.

CONCLUSIONS

Our findings suggest that strategies targeting NOX1 have the potential to be effective treatments for a range of ischemic retinopathies.