Therapeutic effect against retinal neovascularization in a mouse model of oxygen-induced retinopathy: bone marrow-derived mesenchymal stem cells versus Conbercept

Microglia in retinal angiogenesis and diabetic retinopathy

Diabetic retinopathy has a high probability of causing visual impairment or blindness throughout the disease progression and is characterized by the growth of new blood vessels in the retina at an advanced, proliferative stage. Microglia are a resident immune population in the central nervous system, known to play a crucial role in regulating retinal angiogenesis in both physiological and pathological conditions, including diabetic retinopathy. Physiologically, they are located close to blood vessels and are essential for forming new blood vessels (neovascularization). In diabetic retinopathy, microglia become widely activated, showing a distinct polarization phenotype that leads to their accumulation around neovascular tufts. These activated microglia induce pathogenic angiogenesis through the secretion of various angiogenic factors and by regulating the status of endothelial cells. Interestingly, some subtypes of microglia simultaneously promote the regression of neovascularization tufts and normal angiogenesis in neovascularization lesions. Modulating the state of microglial activation to ameliorate neovascularization thus appears as a promising potential therapeutic approach for managing diabetic retinopathy.

Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms

Diabetic retinopathy (DR) represents a severe complication of diabetes mellitus, characterized by irreversible visual impairment resulting from microvascular abnormalities. Since the global prevalence of diabetes continues to escalate, DR has emerged as a prominent area of research interest. The development and progression of DR encompass a complex interplay of pathological and physiological mechanisms, such as high glucose-induced oxidative stress, immune responses, vascular endothelial dysfunction, as well as damage to retinal neurons. Recent years have unveiled the involvement of genomic and epigenetic factors in the formation of DR mechanisms. At present, extensive research explores the potential of biomarkers such as cytokines, molecular and cell therapies, antioxidant interventions, and gene therapy for DR treatment. Notably, certain drugs, such as anti-VEGF agents, antioxidants, inhibitors of inflammatory responses, and protein kinase C (PKC)-β inhibitors, have demonstrated promising outcomes in clinical trials. Within this context, this review article aims to introduce the recent molecular research on DR and highlight the current progress in the field, with a particular focus on the emerging and experimental treatment strategies targeting the immune and redox signaling pathways.

Oncostatin M Reduces Pathological Neovascularization in the Retina Through Müller Cell Activation

Purpose

Continuous vision loss due to vasoproliferative eye disease still represents an unsolved issue despite anti-vascular endothelial growth factor (VEGF) therapy. The impact of signal transducer and activator of transcription 3 (STAT3) signaling on retinal angiogenesis and its potential use as a therapeutic target remain controversial. In vitro, oncostatin M (OSM), as a strong STAT3 activator, possesses robust proangiogenic activity. This study investigated to what extent the proangiogenic effects of OSM translate to the in vivo setting of vasoproliferative eye disease.

Methods

The in vitro effect of OSM on endothelial cells was investigated in the spheroid sprouting assay and through RNA sequencing. The mouse model for oxygen-induced retinopathy (OIR) was used to evaluate the impact of OSM in vivo. Signaling patterns were measured by western blot and retinal cryosections. Primary Müller cell cultures were used to evaluate the effect of OSM on the Müller cell secretome. Murine retinal vascular endothelial cells were isolated from OIR retinas using fluorescence-activated cell sorting (FACS) and were used for RNA sequencing.

Results

Although OSM induced pro-angiogenic responses in vitro, in the OIR model intravitreal injection of OSM reduced retinal neovascularization by 65.2% and vaso-obliteration by 45.5% in Müller cells. Injecting OSM into the vitreous activated the STAT3 signaling pathway in multiple retinal cell types, including Müller cells. In vitro, OSM treatment increased CXCL10 secretion. RNA sequencing of sorted vascular endothelial cells at OIR P17 following OSM treatment indicated downregulation of angiogenesis- and mitosis-associated genes.

Conclusions

In vivo, OSM reveals a beneficial angiomodulatory effect by activating Müller cells and changing their secretome. The data highlight contradictions between cytokine-induced effects in vitro and in vivo depending on the cell types mediating the effect.

Effects of fresh bone marrow mononuclear cell therapy in rat model of retinopathy of prematurity

Introduction

Retinopathy of prematurity (ROP) is a vasoproliferative disease that alters retinal vascular patterns in preterm neonates with immature retinal vasculature. This study was conducted to investigate the effects of cell therapy by bone marrow mononuclear cells (BMMNC) on neurological and vascular damages in a rat model of ROP.

Methods

Ten newborn Wistar rats were divided randomly into the control and the oxygen-induced retinopathy (OIR) groups. Animals in the OIR group were incubated in an oxygen chamber to induce retinopathy. One eye of animals in the OIR group received BMMNC suspension (treated eyes), and the contralateral eye received the same volume of saline injection. Then, all animals underwent funduscopy, angiography, electroretinography, histopathology and immunohistochemical assessments.

Results

Compared to the saline injection group, eyes treated with BMMNC had less vascular tortuosity while veins and arteries had relatively the same caliber, as revealed by fundus examinations. Eyes in the treatment group showed significantly elevated photopic and scotopic B waves amplitude. Neovascularization in the inner retinal layer and apoptosis of neural retina cells in the treatment group was significantly lower compared to untreated eyes. Also, BMMNC transplantation decreased glial cell activation and VEGF expression in ischemic retina.

Conclusions

Our results indicate that intravitreal injection of BMMNC reduces neural and vascular damages and results in recovered retinal function in rat model of ROP. Ease of extraction without in vitro processing, besides the therapeutic effects of BMMNCs, make this source of cells as a new choice of therapy for ROP or other retinal ischemic diseases.

Macrophage/microglia polarization for the treatment of diabetic retinopathy

Macrophages/microglia are immune system defense and homeostatic cells that develop from bone marrow progenitor cells. According to the different phenotypes and immune responses of macrophages (Th1 and Th2), the two primary categories of polarized macrophages/microglia are those conventionally activated (M1) and alternatively activated (M2). Macrophage/microglial polarization is a key regulating factor in the development of inflammatory disorders, cancers, metabolic disturbances, and neural degeneration. Macrophage/microglial polarization is involved in inflammation, oxidative stress, pathological angiogenesis, and tissue healing processes in ocular diseases, particularly in diabetic retinopathy (DR). The functional phenotypes of macrophages/microglia affect disease progression and prognosis, and thus regulate the polarization or functional phenotype of microglia at different DR stages, which may offer new concepts for individualized therapy of DR. This review summarizes the involvement of macrophage/microglia polarization in physiological situations and in the pathological process of DR, and discusses the promising role of polarization in personalized treatment of DR.

Retinal Ischaemia in Diabetic Retinopathy: Understanding and Overcoming a Therapeutic Challenge

BACKGROUND

Retinal ischaemia is present to a greater or lesser extent in all eyes with diabetic retinopathy (DR). Nonetheless, our understanding of its pathogenic mechanisms, risk factors, as well as other characteristics of retinal ischaemia in DR is very limited. To date, there is no treatment to revascularise ischaemic retina.

METHODS

Review of the literature highlighting the current knowledge on the topic of retinal ischaemia in DR, important observations made, and underlying gaps for which research is needed.

RESULTS

A very scarce number of clinical studies, mostly cross-sectional, have evaluated specifically retinal ischaemia in DR. Interindividual variability on its natural course and consequences, including the development of its major complications, namely diabetic macular ischaemia and proliferative diabetic retinopathy, have not been investigated. The in situ, surrounding, and distance effect of retinal ischaemia on retinal function and structure and its change over time remains also to be elucidated. Treatments to prevent the development of retinal ischaemia and, importantly, to achieve retinal reperfusion once capillary drop out has ensued, are very much needed and remain to be developed.

CONCLUSION

Research into retinal ischaemia in diabetes should be a priority to save sight.

Neuroprotective Effects of Human Adipose-Derived Mesenchymal Stem Cells in Oxygen-Induced Retinopathy

This study was designed to provide evidence of the neuroprotective of human adipose-derived mesenchymal stem cells (hADSCs) in oxygen-induced retinopathy (OIR). In vivo, hADSCs were intravitreally injected into OIR mice. Various assessments, including HE (histological evaluation), TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) staining, electroretinogram (ERG) analysis, and retinal flat-mount examination, were performed separately at postnatal days 15 (P15) and 17 (P17) to evaluate neurological damage and functional changes. Western blot analysis of ciliary neurotrophic factor (CNTF), glial cell line-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF) was conducted at P17 to elucidate the neuroprotective mechanism. The P17 OIR group exhibited a significant increase in vascular endothelial cell nuclei and neovascularization that breached the ILM (inner limiting membrane) to the P17 control group. In addition, the retinal nonperfusion areas in the P17 OIR group and the number of apoptotic retinal cells in the P15 OIR group were significantly higher than in the corresponding hADSCs treatment group and control group. There was no significant thickness change in the inner nuclear layer (INL) but the outer nuclear layer (ONL) in the P17 OIR treatment group compared with the P17 OIR group. The cell density in the INL and ONL at P17 in the hADSCs treatment group was not significantly different from the OIR group. The amplitude of a-wave and b-wave in scotopic ERG analysis for the P17 OIR group was significantly lower than in the P17 hADSCs treatment group and the P17 control group. Furthermore, the latency of the a-wave and b-wave in the P17 OIR group was significantly longer than in the P17 hADSCs treatment group and the P17 control group. In addition, the expression levels of CNTF and BDNF in the P17 OIR group were statistically higher than those in the P17 control group, whereas the expression of GDNF was statistically lower in the P17 OIR group, compared with the P17 control group. The expression of CNTF and GDNF in the P17 hADSCs treatment group was statistically higher than in the P17 OIR group. However, the expression of BDNF in the P17 hADSCs treatment group was statistically lower than in the P17 OIR group. This study provides evidence for the neuroprotective effects of hADSCs in OIR.

Advances in cell therapies using stem cells/progenitors as a novel approach for neurovascular repair of the diabetic retina

BACKGROUND

Diabetic retinopathy, a major complication of diabetes mellitus, is a leading cause of sigh-loss in working age adults. Progressive loss of integrity of the retinal neurovascular unit is a central element in the disease pathogenesis. Retinal ischemia and inflammatory processes drive interrelated pathologies such as blood retinal barrier disruption, fluid accumulation, gliosis, neuronal loss and/or aberrant neovascularisation. Current treatment options are somewhat limited to late-stages of the disease where there is already significant damage to the retinal architecture arising from degenerative, edematous and proliferative pathology. New preventive and interventional treatments to target early vasodegenerative and neurodegenerative stages of the disease are needed to ensure avoidance of sight-loss.

MAIN BODY

Historically, diabetic retinopathy has been considered a primarily microvascular disease of the retina and clinically it is classified based on the presence and severity of vascular lesions. It is now known that neurodegeneration plays a significant role during the pathogenesis. Loss of neurons has been documented at early stages in pre-clinical models as well as in individuals with diabetes and, in some, even prior to the onset of clinically overt diabetic retinopathy. Recent studies suggest that some patients have a primarily neurodegenerative phenotype. Retinal pigment epithelial cells and the choroid are also affected during the disease pathogenesis and these tissues may also need to be addressed by new regenerative treatments. Most stem cell research for diabetic retinopathy to date has focused on addressing vasculopathy. Pre-clinical and clinical studies aiming to restore damaged vasculature using vasoactive progenitors including mesenchymal stromal/stem cells, adipose stem cells, CD34+ cells, endothelial colony forming cells and induced pluripotent stem cell derived endothelial cells are discussed in this review. Stem cells that could replace dying neurons such as retinal progenitor cells, pluripotent stem cell derived photoreceptors and ganglion cells as well as Müller stem cells are also discussed. Finally, challenges of stem cell therapies relevant to diabetic retinopathy are considered.

CONCLUSION

Stem cell therapies hold great potential to replace dying cells during early and even late stages of diabetic retinopathy. However, due to the presence of different phenotypes, selecting the most suitable stem cell product for individual patients will be crucial for successful treatment.

Photo-mediated ultrasound therapy for the treatment of retinal neovascularization in rabbit eyes

Objectives

Retinal neovascularization (RNV) is the growth of abnormal microvessels on the retinal surface and into the vitreous, which can lead to severe vision loss. By combining relatively low‐intensity ultrasound and nanosecond‐pulse‐duration laser, we developed a novel treatment method, namely photo‐mediated ultrasound therapy (PUT), which holds a potential to remove RNV with minimal or no damage to the adjacent tissues.

Methods

RNV was created in both albino and pigmented rabbits (n = 10) through a single intravitreal injection with DL‐α‐aminoadipic acid. RNV was treated with PUT 8 weeks postinjection. After PUT treatment, animals were evaluated longitudinally for up to 6 weeks. Treatment outcomes were evaluated through fundus photography, red‐free fundus photography, fluorescein angiography (FA), and histopathology.

Results

In both albino and pigmented rabbits, there were no leakage in the treatment area immediately after PUT treatment as demonstrated by FA, indicating the cessation of blood perfusion of the RNV in the treated area. The fluorescence leakage did not recover in albino rabbits during the 6‐week posttreatment monitoring period, and only 9.9 ± 9.8% of the neovascularization remained at the end of 6 weeks. In the pigmented rabbits, the fluorescence leakage partially returned, but the level of leakage decreased over time during the 6‐week posttreatment monitoring period, and only 10.8 ± 9.8% of the neovascularization remained at the end of 6 weeks. Histology demonstrated removal of vasculature without damage to the surrounding neurosensory retina.

Conclusions

These results demonstrate that PUT could precisely remove RNV without damage to the surrounding neurosensory retina in both rabbit strains.

Inhibitory effect of maspinon neovascularization in diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a serious and potentially blinding complication of diabetes mellitus. Retinal neovascularization is one of the main pathological features of proliferative DR, and inhibiting retinal neovascularization is a research focus.

AIM

The aim was to evaluate the effect of intravitreal injection of recombinant human maspin on neovascularization in DR.

METHODS

An oxygen-induced retinopathy (OIR) mouse model was used to simulate neovascularization in DR. New born C57BL/6J mice were randomly divided to a normal control group, a maspin injection OIR group, and an OIR group. The mice in the maspin injection OIR group were injected with recombinant human maspin in the bilateral vitreous cavity on postnatal day P12, and those in the OIR group were injected with sterile phosphate buffered saline. The protein expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1-alpha (HIF-1α) in the retina was measured by western blotting, and the mRNA expression of VEGF and HIF-1α was measured by real-time polymerase chain reaction. The vascular cell nuclei that broke through the inner limiting membrane (ILM) were counted in haematoxylin-eosin stained retinal sections.

RESULTS

It was found that the number of vascular cell nuclei breaking through the ILM was 31.8 ± 8.75 in the OIR group, which was significantly more than that in the normal control group (P < 0.001). The number of vascular cell nuclei breaking through the ILM was 6.19 ± 2.91 in the maspin injection OIR group, which was significantly less than that in OIR group (P < 0.01). The relative protein and mRNA expression of VEGF and HIF-1α was significantly lower in the retinas in the maspin injection OIR group than in those in the OIR group (P < 0.01).

CONCLUSION

Maspin inhibited neovascularization in DR by modulating the HIF-1α/VEGF pathway, which provides a potential and effective strategy for the treatment of DR.

Lysophosphatidylcholine Offsets the Protective Effects of Bone Marrow Mesenchymal Stem Cells on Inflammatory Response and Oxidative Stress Injury of Retinal Endothelial Cells via TLR4/NF-κB Signaling

Diabetic retinopathy (DR), as a major cause of blindness worldwide, is one common complication of diabetes mellitus. Inflammatory response and oxidative stress injury of endothelial cells play significant roles in the pathogenesis of DR. The study is aimed at investigating the effects of lysophosphatidylcholine (LPC) on the dysfunction of high glucose- (HG-) treated human retinal microvascular endothelial cells (HRMECs) after being cocultured with bone marrow mesenchymal stem cells (BMSCs) and the underlying regulatory mechanism. Coculture of BMSCs and HRMECs was performed in transwell chambers. The activities of antioxidant-related enzymes and molecules of oxidative stress injury and the contents of inflammatory cytokines were measured by ELISA. Flow cytometry analyzed the apoptosis of treated HRMECs. HRMECs were further treated with 10-50 μg/ml LPC to investigate the effect of LPC on the dysfunction of HRMECs. Western blotting was conducted to evaluate levels of TLR4 and p-NF-κB proteins. We found that BMSCs alleviated HG-induced inflammatory response and oxidative stress injury of HRMECs. Importantly, LPC offsets the protective effects of BMSCs on inflammatory response and oxidative stress injury of HRMECs. Furthermore, LPC upregulated the protein levels of TLR4 and p-NF-κB, activating the TLR4/NF-κB signaling pathway. Overall, our study demonstrated that LPC offsets the protective effects of BMSCs on inflammatory response and oxidative stress injury of HRMECs via TLR4/NF-κB signaling.

Sodium Butyrate Inhibits Neovascularization Partially via TNXIP/VEGFR2 Pathway

Control of neovascularization with small molecules is a promising tactics. Here, we tested the roles of sodium butyrate (NaBu) on the neovascularization and primary explained its underlining molecular links. We used models including cell and ex vivo culture of choroid and mouse, as well as the biochemical and cellular techniques, to confirm our hypothesis. We found that treating HUVEC cells with NaBu (both 2.5 mM and 5 mM) significantly inhibited its ability in tube formation and proliferation. This inhibitory effect was also observed in choroid sprouting experiments, compared to the control. Interestingly, the choroid sprouting suppressed by NaBu can proliferate again after removing it, indicating that the cell cycle progression might be arrested. The laser-induced choroid neovascularization (CNV) was significantly alleviated by assessing the CNV size (decreased to 0.73 fold) in contrast with the vehicle control group after 2.5 mM NaBu injection for 7 days. Mechanistically, we found an enhanced TXNIP expression in response to NaBu treatment in all the three models. Overexpressing TXNIP in HUVEC cells blocked its tube formation and inhibited its proliferation; on the other hand, knocking down its expression with shRNA reversed those phenotypes in context of NaBu treatment. Further investigation showed the expression of VEGF receptor 2 (VEGFR2) in HUVEC cells was regulated by TXNIP undergoing NaBu treatment. We therefore argued that NaBu inhibited neovascularization partially through TXNIP-regulated VEGFR2 signal pathway.

The Potential of Mesenchymal Stromal Cell as Therapy in Neonatal Diseases

Mesenchymal stromal cells (MSCs) can be derived from various tissue sources, such as the bone marrow (BMSCs), adipose tissue (ADSCs), umbilical cord (UC-MSCs) and umbilical cord blood (UCB-MSCs). Clinical trials have been conducted to investigate the potential of MSCs in ameliorating neonatal diseases, including bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH) and necrotizing enterocolitis (NEC). In preclinical studies, MSC therapy has been tested for the treatment of various neonatal diseases affecting the heart, eye, gut, and brain as well as sepsis. Up to date, the number of clinical trials using MSCs to treat neonatal diseases is still limited. The data reported thus far positioned MSC therapy as safe with positive outcomes. However, most of these trials are still preliminary and generally smaller in scale. Larger trials with more appropriate controls and a longer follow-up period need to be conducted to prove the safety and efficacy of the therapy more conclusively. This review discusses the current application of MSCs in treating neonatal diseases, its mechanism of action and future direction of this novel therapy, including the potential of using MSC-derived extracellular vesicles instead of the cells to treat various clinical conditions in the newborn.