N-CAM exhibits a regulatory function in pathological angiogenesis in oxygen induced retinopathy

Retinopathy of prematurity: A review of pathophysiology and signaling pathways

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina and a leading cause of visual impairment and childhood blindness worldwide. The disease is characterized by an early stage of retinal microvascular degeneration, followed by neovascularization that can lead to subsequent retinal detachment and permanent visual loss. Several factors play a key role during the different pathological stages of the disease. Oxidative and nitrosative stress and inflammatory processes are important contributors to the early stage of ROP. Nitric oxide synthase and arginase play important roles in ischemia/reperfusion-induced neurovascular degeneration. Destructive neovascularization is driven by mediators of the hypoxia-inducible factor pathway, such as vascular endothelial growth factor and metabolic factors (succinate). The extracellular matrix is involved in hypoxia-induced retinal neovascularization. Vasorepulsive molecules (semaphorin 3A) intervene preventing the revascularization of the avascular zone. This review focuses on current concepts about signaling pathways and their mediators, involved in the pathogenesis of ROP, highlighting new potentially preventive and therapeutic modalities. A better understanding of the intricate molecular mechanisms underlying the pathogenesis of ROP should allow the development of more effective and targeted therapeutic agents to reduce aberrant vasoproliferation and facilitate physiological retinal vascular development.

Alterations in the polysialylated neural cell adhesion molecule and retinal ganglion cell density in mice with diabetic retinopathy

AIM

To investigate the impact of polysialylated neural cell adhesion molecule (PSA-NCAM) on the survival of retinal ganglion cells (RGCs) in the experimentally induced diabetes in mice.

METHODS

Diabetes was induced in 2.5 months old Swiss Webster mice by intraperitoneal injection of streptozotocin (STZ, 90 mg/kg) once daily for two consecutive days. Examination of the proteins of interest in the retinas from diabetic mice at 2mo after diabetes induction was performed using immunohistochemistry and Western blot analysis. RGCs were counted in the wholemounted retinas, and Brn3a marker was used.

RESULTS

Examination of retinas from diabetic mice at 2mo after diabetes induction revealed a considerable reduction in RGC density. Our experiments also demonstrated a redistribution of PSA-NCAM in the retina of diabetic animals. PSA-NCAM immunoreactivity was diminished in the inner part of the retina where RGCs were located. In contrast, an enhanced PSA-NCAM immunoreactivity was detected in the outer layers of the retina. PSA-NCAM signal was co-localized with glial fibrillary acidic protein immunoreactivity in the Müller cell branches. Previous studies have shown that matrix metalloproteinase-9 (MMP-9) is responsible for the reduction in PSA-NCAM levels in neuronal cells. The reduced levels of PSA-NCAM in inner layers (nerve fiber layer, ganglion cell layer) were accompanied by the increased expression of MMP-9. In contrast, in the outer retinal layers, the expression of MMP-9 was much less pronounced.

CONCLUSION

MMP-9 induces PSA-NCAM shedding in the inner part of the retina and the decreased level of PSA-NCAM in the inner part of the retina might be, at least in part, responsible for the loss of RGCs in diabetic mice.

Molecular Mechanisms Mediating Diabetic Retinal Neurodegeneration: Potential Research Avenues and Therapeutic Targets

Diabetic retinopathy (DR) is a devastating complication of diabetes with a prevalence rate of 35%, and no effective treatment options. Since the most visible clinical features of DR are microvascular irregularities, therapeutic interventions often attempt to reduce microvascular injury, but only after permanent retinal damage has ensued. However, recent data suggests that diabetes initially affects retinal neurons, leading to neurodegeneration as an early occurrence in DR, before onset of the more noticeable vascular abnormalities. In this review, we delineate the sequence of initiating events leading to retinal degeneration in DR, considering neuronal dysfunction as a primary event. Key molecular mechanisms and potential biomarkers associated with retinal neuronal degeneration in diabetes are discussed. In addition to glial reactivity and inflammation in the diabetic retina, the contribution of neurotrophic factors, cell adhesion molecules, apoptosis markers, and G protein signaling to neurodegenerative pathways warrants further investigation. These studies could complement recent developments in innovative treatment strategies for diabetic retinopathy, such as targeting retinal neuroprotection, promoting neuronal regeneration, and attempts to re-program other retinal cell types into functional neurons. Indeed, several ongoing clinical trials are currently attempting treatment of retinal neurodegeneration by means of such novel therapeutic avenues. The aim of this article is to highlight the crucial role of neurodegeneration in early retinopathy progression, and to review the molecular basis of neuronal dysfunction as a first step toward developing early therapeutic interventions that can prevent permanent retinal damage in diabetes. ClinicalTrials.gov: NCT02471651, NCT01492400.

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.

Novel Identity and Functional Markers for Human Corneal Endothelial Cells

Purpose

Human corneal endothelial cell (HCEC) density decreases with age, surgical complications, or disease, leading to vision impairment. Such endothelial dysfunction is an indication for corneal transplantation, although there is a worldwide shortage of transplant-grade tissue. To overcome the current poor donor availability, here we isolate, expand, and characterize HCECs in vitro as a step toward cell therapy.

Methods

Human corneal endothelial cells were isolated from cadaveric corneas and expanded in vitro. Cell identity was evaluated based on morphology and immunocytochemistry, and gene expression analysis and flow cytometry were used to identify novel HCEC-specific markers. The functional ability of HCEC to form barriers was assessed by transendothelial electrical resistance (TEER) assays.

Results

Cultured HCECs demonstrated canonical morphology for up to four passages and later underwent endothelial-to-mesenchymal transition (EnMT). Quality of donor tissue influenced cell measures in culture including proliferation rate. Cultured HCECs expressed identity markers, and microarray analysis revealed novel endothelial-specific markers that were validated by flow cytometry. Finally, canonical HCECs expressed higher levels of CD56, which correlated with higher TEER than fibroblastic HCECs.

Conclusions

In vitro expansion of HCECs from cadaveric donor corneas yields functional cells identifiable by morphology and a panel of novel markers. Markers described correlated with function in culture, suggesting a basis for cell therapy for corneal endothelial dysfunction.

Exenatide Alters Gene Expression of Neural Cell Adhesion Molecule (NCAM), Intercellular Cell Adhesion Molecule (ICAM), and Vascular Cell Adhesion Molecule (VCAM) in the Hippocampus of Type 2 Diabetic Model Mice

Background

Glucagon-like peptide-1 (GLP-1), a potent and selective agonist for the GLP-1 receptor, ameliorates the symptoms of diabetes through stimulation of insulin secretion. Exenatide is a potent and selective agonist for the GLP-1 receptor. Cell adhesion molecules are members of the immunoglobulin superfamily and are involved in synaptic rearrangements in the mature brain.

Material/Methods

The present study demonstrated the effects of exenatide treatment (0.1 μg/kg, subcutaneously, twice daily for 2 weeks) on the gene expression levels of cell adhesion molecules, neural cell adhesion molecule (NCAM), intercellular cell adhesion molecule (ICAM), and vascular cell adhesion molecule (VCAM) in the brain tissue of diabetic BALB/c male mice by real-time quantitative polymerase chain reaction (PCR). Diabetes was induced by streptozotocin/nicotinamide (STZ-NA) injection to male mice.

Results

The results of this study revealed that hippocampal gene expression of NCAM, ICAM, and VCAM were found to be up-regulated in STZ-NA-induced diabetic mice compared to those of controls. A significant decrease in the gene expression levels of NCAM, ICAM, and VCAM were determined after 2 weeks of exenatide administration.

Conclusions

Cell adhesion molecules may be involved in the molecular mechanism of diabetes. Exenatide has a strong beneficial action in managing diabetes induced by STZ/NA by altering gene expression of NCAM, ICAM, and VCAM.

Gpr116 Receptor Regulates Distinctive Functions in Pneumocytes and Vascular Endothelium

Despite its known expression in both the vascular endothelium and the lung epithelium, until recently the physiological role of the adhesion receptor Gpr116/ADGRF5 has remained elusive. We generated a new mouse model of constitutive Gpr116 inactivation, with a large genetic deletion encompassing exon 4 to exon 21 of the Gpr116 gene. This model allowed us to confirm recent results defining Gpr116 as necessary regulator of surfactant homeostasis. The loss of Gpr116 provokes an early accumulation of surfactant in the lungs, followed by a massive infiltration of macrophages, and eventually progresses into an emphysema-like pathology. Further analysis of this knockout model revealed cerebral vascular leakage, beginning at around 1.5 months of age. Additionally, endothelial-specific deletion of Gpr116 resulted in a significant increase of the brain vascular leakage. Mice devoid of Gpr116 developed an anatomically normal and largely functional vascular network, surprisingly exhibited an attenuated pathological retinal vascular response in a model of oxygen-induced retinopathy. These data suggest that Gpr116 modulates endothelial properties, a previously unappreciated function despite the pan-vascular expression of this receptor. Our results support the key pulmonary function of Gpr116 and describe a new role in the central nervous system vasculature.

Do endothelial cells dream of eclectic shape?

Endothelial cells (ECs) exhibit dramatic plasticity of form at the single- and collective-cell level during new vessel growth, adult vascular homeostasis, and pathology. Understanding how, when, and why individual ECs coordinate decisions to change shape, in relation to the myriad of dynamic environmental signals, is key to understanding normal and pathological blood vessel behavior. However, this is a complex spatial and temporal problem. In this review we show that the multidisciplinary field of Adaptive Systems offers a refreshing perspective, common biological language, and straightforward toolkit that cell biologists can use to untangle the complexity of dynamic, morphogenetic systems.

Endothelial tip cells in ocular angiogenesis: potential target for anti-angiogenesis therapy

Endothelial tip cells are leading cells at the tips of vascular sprouts coordinating multiple processes during angiogenesis. In the developing retina, tip cells play a tightly controlled, timely role in angiogenesis. In contrast, excessive numbers of tip cells are a characteristic of the chaotic pathological blood vessels in proliferative retinopathies. Tip cells control adjacent endothelial cells in a hierarchical manner to form the stalk of the sprouting vessel, using, among others, the VEGF-DLL-Notch signaling pathway, and recruit pericytes. Tip cells are guided toward avascular areas by signals from the local extracellular matrix that are released by cells from the neuroretina such as astrocytes. Recently, tip cells were identified in endothelial cell cultures, enabling identification of novel molecular markers and mechanisms involved in tip cell biology. These mechanisms are relevant for understanding proliferative retinopathies. Agents that primarily target tip cells can block pathological angiogenesis in the retina efficiently and safely without adverse effects. A striking example is platelet-derived growth factor, which was recently shown to be an efficacious additional target in the treatment of retinal neovascularization. Here we discuss these and other tip cell-based strategies with respect to their potential to treat patients with ocular diseases dominated by neovascularization.