Activation of the Wnt pathway plays a pathogenic role in diabetic retinopathy in humans and animal models

Exploring the molecular mechanisms of MSC-derived exosomes in Alzheimer's disease: Autophagy, insulin and the PI3K/Akt/mTOR signaling pathway

Alzheimer's disease (AD) is a devastating neurological condition characterized by cognitive decline, motor coordination impairment, and amyloid plaque accumulation. The underlying molecular mechanisms involve oxidative stress, inflammation, and neuronal degeneration. This study aimed to investigate the therapeutic effects of mesenchymal stem cell-derived exosomes (MSC-exos) on AD and explore the molecular pathways involved, including the PI3K/Akt/mTOR axis, autophagy, and neuroinflammation. To assess the potential of MSC-exos for the treatment of AD, rats were treated with AlCl3 (17 mg/kg/once/day) for 8 weeks, followed by the administration of an autophagy activator (rapamycin), or MSC-exos with or without an autophagy inhibitor (3-methyladenin; 3-MA+ chloroquine) for 4 weeks. Memory impairment was tested, and brain tissues were collected for gene expression analyses, western blotting, histological studies, immunohistochemistry, and transmission electron microscopy. Remarkably, the administration of MSC-exos improved memory performance in AD rats and reduced the accumulation of amyloid-beta (Aβ) plaques and tau phosphorylation. Furthermore, MSC-exos promoted neurogenesis, enhanced synaptic function, and mitigated astrogliosis in AD brain tissues. These beneficial effects were associated with the modulation of autophagy and the PI3K/Akt/mTOR signalling pathway, as well as the inhibition of neuroinflammation. Additionally, MSC-exos were found to regulate specific microRNAs, including miRNA-21, miRNA-155, miRNA-17-5p, and miRNA-126-3p, further supporting their therapeutic potential. Histopathological and bioinformatic analyses confirmed these findings. This study provides compelling evidence that MSC-exos hold promise as a potential therapeutic approach for AD. By modulating the PI3K/Akt/mTOR axis, autophagy, and neuroinflammation, MSC-exos have the potential to improve memory, reduce Aβ accumulation, enhance neurogenesis, and mitigate astrogliosis. These findings shed light on the therapeutic potential of MSC-exos and highlight their role in combating AD.

Design principles and therapeutic applications of novel synthetic WNT signaling agonists

Wingless-related integration site or Wingless and Int-1 or Wingless-Int (WNT) signaling is crucial for embryonic development, and adult tissue homeostasis and regeneration, through its essential roles in cell fate, patterning, and stem cell regulation. The biophysical characteristics of WNT ligands have hindered efforts to interrogate ligand activity in vivo and prevented their development as therapeutics. Recent breakthroughs have enabled the generation of synthetic WNT signaling molecules that possess characteristics of natural ligands and potently activate the pathway, while also providing distinct advantages for therapeutic development and manufacturing. This review provides a detailed discussion of the protein engineering of these molecular platforms for WNT signaling agonism. We discuss the importance of WNT signaling in several organs and share insights from the initial application of these new classes of molecules in vitro and in vivo. These molecules offer a unique opportunity to enhance our understanding of how WNT signaling agonism promotes tissue repair, enabling targeted development of tailored therapeutics.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Neuroretinal Cell Culture Model as a Tool for the Development of New Therapeutic Approaches for Oxidative Stress-Induced Ocular Diseases, with a Focus on Glaucoma

Glaucoma is a heterogeneous group of optic neuropathies characterized by a progressive degeneration of the retinal ganglion cells (RGCs), leading to irreversible vision loss. Nowadays, the traditional therapeutic approach to glaucoma consists of lowering the intraocular pressure (IOP), which does not address the neurodegenerative features of the disease. Besides animal models of glaucoma, there is a considerable need for in vitro experimental models to propose new therapeutic strategies for this ocular disease. In this study, we elucidated the pathological mechanisms leading to neuroretinal R28 cell death after exposure to glutamate and hydrogen peroxide (H2O2) in order to develop new therapeutic approaches for oxidative stress-induced retinal diseases, including glaucoma. We were able to show that glutamate and H2O2 can induce a decrease in R28 cell viability in a concentration-dependent manner. A cell viability of about 42% was found after exposure to 3 mM of glutamate and about 56% after exposure to 100 µM of H2O2 (n = 4). Label-free quantitative mass spectrometry analysis revealed differential alterations of 193 and 311 proteins in R28 cells exposed to 3 mM of glutamate and 100 µM of H2O2, respectively (FDR < 1%; p < 0.05). Bioinformatics analysis indicated that the protein changes were associated with the dysregulation of signaling pathways, which was similar to those observed in glaucoma. Thus, the proteomic alteration induced by glutamate was associated with the inhibition of the PI3K/AKT signaling pathway. On the other hand, H2O2-induced toxicity in R28 cells was linked to the activation of apoptosis signaling and the inhibition of the mTOR and ERK/MAPK signaling pathways. Furthermore, the data show a similarity in the inhibition of the EIF2 and AMPK signaling pathways and the activation of the sumoylation and WNT/β-catenin signaling pathways in both groups. Our findings suggest that the exposure of R28 cells to glutamate and H2O2 could induce glaucoma-like neurodegenerative features and potentially provide a suitable tool for the development of new therapeutic strategies for retinal diseases.

Potential disease biomarkers for diabetic retinopathy identified through Mendelian randomization analysis

Background

Diabetic retinopathy (DR), a leading cause of vision loss, has limited options for effective prevention and treatment. This study aims to utilize genomics and proteomics data to identify potential drug targets for DR.

Methods

We utilized plasma protein quantitative trait loci data from the Atherosclerosis Risk in Communities Study and the Icelandic Decoding Genetics Study for discovery and replication, respectively. Genetic associations with DR, including its subtypes, were derived from the FinnGen study. Mendelian Randomization (MR) analysis estimated associations between protein levels and DR risk, complemented by colocalization analysis to examine shared causal variants.

Results

Our MR analysis identified significant associations of specific plasma proteins with DR and proliferative DR (PDR). Elevated genetically predicted levels of WARS (OR = 1.16; 95% CI = 0.095-0.208, FDR = 1.31×10-4) and SIRPG (OR = 1.15; 95% CI = 0.071-0.201, FDR = 1.46×10-2) were associated with higher DR risk, while increased levels of ALDOC (OR = 1.56; 95% CI = 0.246-0.637, FDR = 5.48×10-3) and SIRPG (OR = 1.15; 95% CI = 0.068-0.208, FDR = 4.73×10-2) were associated with higher PDR risk. These findings were corroborated by strong colocalization evidence.

Conclusions

Our study highlights WARS, SIRPG, and ALDOC as significant proteins associated with DR and PDR, providing a basis for further exploration in drug development. Additional studies are needed to validate these proteins as disease biomarkers across diverse populations.

Pharmacological Modulation of β-Catenin Preserves Endothelial Barrier Integrity and Mitigates Retinal Vascular Permeability and Inflammation

Compromised blood-retinal barrier (BRB) integrity is a significant factor in ocular diseases like uveitis and retinopathies, leading to pathological vascular permeability and retinal edema. Adherens and tight junction (AJ and TJ) dysregulation due to retinal inflammation plays a pivotal role in BRB disruption. We investigated the potential of ICG001, which inhibits β-catenin-mediated transcription, in stabilizing cell junctions and preventing BRB leakage. In vitro studies using human retinal endothelial cells (HRECs) showed that ICG001 treatment improved β-Catenin distribution within AJs post lipopolysaccharide (LPS) treatment and enhanced monolayer barrier resistance. The in vivo experiments involved a mouse model of LPS-induced ocular inflammation. LPS treatment resulted in increased albumin leakage from retinal vessels, elevated vascular endothelial growth factor (VEGF) and Plasmalemmal Vesicle-Associated Protein (PLVAP) expression, as well as microglia and macroglia activation. ICG001 treatment (i.p.) effectively mitigated albumin leakage, reduced VEGF and PLVAP expression, and reduced the number of activated microglia/macrophages. Furthermore, ICG001 treatment suppressed the surge in inflammatory cytokine synthesis induced by LPS. These findings highlight the potential of interventions targeting β-Catenin to enhance cell junction stability and improve compromised barrier integrity in various ocular inflammatory diseases, offering hope for better management and treatment options.

Wg/Wnt1 and Erasp link ER stress to proapoptotic signaling in an autosomal dominant retinitis pigmentosa model

The endoplasmic reticulum (ER) is a subcellular organelle essential for cellular homeostasis. Perturbation of ER functions due to various conditions can induce apoptosis. Chronic ER stress has been implicated in a wide range of diseases, including autosomal dominant retinitis pigmentosa (ADRP), which is characterized by age-dependent retinal degeneration caused by mutant rhodopsin alleles. However, the signaling pathways that mediate apoptosis in response to ER stress remain poorly understood. In this study, we performed an unbiased in vivo RNAi screen with a Drosophila ADRP model and found that Wg/Wnt1 mediated apoptosis. Subsequent transcriptome analysis revealed that ER stress-associated serine protease (Erasp), which has been predicted to show serine-type endopeptidase activity, was a downstream target of Wg/Wnt1 during ER stress. Furthermore, knocking down Erasp via RNAi suppressed apoptosis induced by mutant rhodopsin-1 (Rh-1P37H) toxicity, alleviating retinal degeneration in the Drosophila ADRP model. In contrast, overexpression of Erasp resulted in enhanced caspase activity in Drosophila S2 cells treated with apoptotic inducers and the stabilization of the initiator caspase Dronc (Death regulator Nedd2-like caspase) by stimulating DIAP1 (Drosophila inhibitor of apoptosis protein 1) degradation. These findings helped identify a novel cell death signaling pathway involved in retinal degeneration in an autosomal dominant retinitis pigmentosa model.

Sustained therapeutic effect of an anti-inflammatory peptide encapsulated in nanoparticles on ocular vascular leakage in diabetic retinopathy

Pigment epithelium-derived factor (PEDF), an endogenous Wnt signaling inhibitor in the serine proteinase inhibitors (SERPIN) super family, is present in multiple organs, including the vitreous. Significantly low levels of PEDF in the vitreous are found to associate with pathological retinal vascular leakage and inflammation in diabetic retinopathy (DR). Intravitreal delivery of PEDF represents a promising therapeutic approach for DR. However, PEDF has a short half-life after intravitreal injection, which represents a major hurdle for the long-term treatment. Here we report the prolonged therapeutic effects of a 34-mer peptide of the PEDF N-terminus, encapsulated in poly (lactic-co-glycolic acid) (PLGA) nanoparticles (PEDF34-NP), on DR. PEDF34-NP inhibited hypoxia-induced expression of vascular endothelial growth factor and reduced levels of intercellular adhesion molecule 1 (ICAM-1) in cultured retinal cells. In addition, PEDF34-NP significantly ameliorated ischemia-induced retinal neovascularization in the oxygen-induced retinopathy rat model, and significantly reduced retinal vascular leakage and inflammation in streptozotocin-induced diabetic rats up to 4 weeks after intravitreal injection, as compared to PLGA-NP control. Intravitreal injection of PEDF34-NP did not display any detectable toxicities to retinal structure and function. Our findings suggest that PEDF34-NP can confer sustained therapeutic effects on retinal inflammation and vascular leakage, having considerable potential to provide long-term treatment options for DR.

Selective Activation of the Wnt-Signaling Pathway as a Novel Therapy for the Treatment of Diabetic Retinopathy and Other Retinal Vascular Diseases

Retinal ischemia, often associated with various disorders such as diabetic retinopathy (DR), retinal vein occlusion, glaucoma, optic neuropathies, stroke, and other retinopathies, is a major cause of visual impairment and blindness worldwide. As proper blood supply to the retina is critical to maintain its high metabolic demand, any impediment to blood flow can lead to a decrease in oxygen supply, resulting in retinal ischemia. In the pathogenesis of DR, including diabetic macular edema (DME), elevated blood glucose leads to blood-retina barrier (BRB) disruptions, vascular leakage, and capillary occlusion and dropouts, causing insufficient delivery of oxygen to the retina, and ultimately resulting in visual impairment. Other potential causes of DR include neuronal dysfunction in the absence of vascular defect, genetic, and environmental factors. The exact disease progression remains unclear and varies from patient to patient. Vascular leakage leading to edema clearly links to visual impairment and remains an important target for therapy. Despite recent advances in the treatment of DME and DR with anti-VEGFs, effective therapies with new mechanisms of action to address current treatment limitations regarding vessel regeneration and reperfusion of ischemic retinal areas are still needed. The Wnt signaling pathway plays a critical role in proper vascular development and maintenance in the retina, and thus provides a novel therapeutic approach for the treatment of diabetic and other retinopathies. In this review, we summarize the potential of this pathway to address treatment gaps with current therapies, its promise as a novel and potentially disease modifying therapy for patients with DR and opportunities in other retinal vascular diseases.

Possible Role of Wnt Signaling Pathway in Diabetic Retinopathy

The core of impaired vision in working people suffering from insulin-dependent and noninsulin- dependent diabetes mellitus is diabetic retinopathy (DR). The Wnt Protein Ligands family influences various processes; this ensures the cells are able to interact and co-ordinate various mobile functions, including cell growth, division, survival, apoptosis, migration, and cell destiny. The extracellular Wnt signal activates other signals. It is seen that Wnt pathways play an important role in inflammation, oxidative stress, and angiogenesis. It has been illustrated that the canonically preserved Wnt signaling system has a vital role in the homeostasis of adulthood. Developmental disorders in each of these stages will lead to serious eye problems and eventually blindness. There is, therefore, a need to specifically organize and regulate the growth of ocular tissues. In tissue specification and polarities, axonal exhaust, and maintenance of cells, especially in the central nervous system, Wnt/frizzled pathways play an important role. Thus, Wnt route antagonists may act as have been possible therapeutic options in DR by inhibiting aberrant Wnt signals. Elaborative and continued research in this area will help in the advancement of current knowledge in the field of DR, and eventually, this can lead to the development of new therapeutic approaches.

Arterial Stiffness and the Canonical WNT/β-catenin Pathway

PURPOSE OF REVIEW

Arterial stiffness (AS) was mainly associated with cardiovascular morbidity and mortality in a hypertensive patient. Some risk factors contribute to the development of AS, such as aging, high blood pressure, vascular calcification, inflammation, and diabetes mellitus. The WNT/β-catenin pathway is implicated in numerous signaling and regulating pathways, including embryogenesis, cell proliferation, migration and polarity, apoptosis, and organogenesis. The activation of the WNT/β-catenin pathway is associated with the development of these risk factors.

RECENT FINDINGS

Aortic pulse wave velocity (PWV) is measured to determine AS, and in peripheral artery disease patients, PWV is higher than controls. An augmentation in PWV by 1 m/s has been shown to increase the risk of cardiovascular events by 14%. AS measured by PWV is characterized by the deregulation of the WNT/β-catenin pathway by the inactivation of its two inhibitors, i.e., DKK1 and sclerostin. Thus, this review focuses on the role of the WNT/β-catenin pathway which contributes to the development of arterial stiffness.

Effect of bone marrow mesenchymal stem cells-derived exosomes on diabetes-induced retinal injury: Implication of Wnt/ b-catenin signaling pathway

BACKGROUND

Diabetic retinopathy (DR) is a serious microvascular complication of diabetes mellitus. Mesenchymal stem cells are currently studied as therapeutic strategy for management of DR. Exosomes, considered as a promising cell-free therapy option, display biological functions similar to those of their parent cells. In retinal development, Wnt/b-catenin signaling provides key cues for functional progression. The present study aimed to evaluate the potential efficacy of bone marrow-derived mesenchymal stem cell-derived exosomes (BM-MSCs-Ex) in diabetes-induced retinal injury via modulation of the Wnt/ b-catenin signaling pathway.

METHODS

Eighty-one rats were allocated into 6 groups (control, DR, DR + DKK1, DR + exosomes, DR + Wnt3a and DR + exosomes+Wnt3a). Evaluation of each group was via histopathological examination, assessment of gene and/or protein expression concerned with oxidative stress (SOD1, SOD2, Nox2, Nox4, iNOS), inflammation (TNF-α, ICAM-1, NF-κB) and angiogenesis (VEGF, VE-cadherin).

RESULTS

Results demonstrated that exosomes blocked the wnt/b-catenin pathway in diabetic retina concomitant with significant reduction of features of DR as shown by downregulation of retinal oxidants, upregulation of antioxidant enzymes, suppression of retinal inflammatory and angiogenic markers. These results were further confirmed by histopathological results, fundus examination and optical coherence tomography. Additionally, exosomes ameliorative effects abrogated wnt3a-triggered retinal injury in DR.

CONCLUSION

Collectively, these data demonstrated that exosomes ameliorated diabetes-induced retinal injury via suppressing Wnt/ b-catenin signaling with subsequent reduction of oxidative stress, inflammation and angiogenesis.

Consideration of possible effects of vitamin D on established cancer, with reference to malignant melanoma

Epidemiological studies indicate that Vitamin D has a beneficial, inhibitory effect on cancer development and subsequent progression, including melanoma (MM), and favourable MM outcome has been reported as directly related to vitamin D3 status, assessed by serum 25-hydroxyvitamin D3 (25[OH]D3 ) levels taken at diagnosis. It has been recommended that MM patients with deficient levels of 25(OH)D3 be given vitamin D3 . We examine possible beneficial or detrimental effects of treating established cancer with vitamin D3 . We consider the likely biological determinants of cancer outcome, the reported effects of vitamin D3 on these in both cancerous and non-cancerous settings, and how the effect of vitamin D3 might change depending on the integrity of tumour vitamin D receptor (VDR) signalling. We would argue that the effect of defective tumour VDR signalling could result in loss of suppression of growth, reduction of anti-tumour immunity, with potential antagonism of the elimination phase and enhancement of the escape phase of tumour immunoediting, possibly increased angiogenesis but continued suppression of inflammation. In animal models, having defective VDR signalling, vitamin D3 administration decreased survival and increased metastases. Comparable studies in man are lacking but in advanced disease, a likely marker of defective VDR signalling, studies have shown modest or no improvement in outcome with some evidence of worsening. Work is needed in assessing the integrity of tumour VDR signalling and the safety of vitamin D3 supplementation when defective.

The Contribution of Wnt Signaling to Vascular Complications in Type 2 Diabetes Mellitus

Vascular complications are the leading cause of morbidity and mortality among patients with type 2 diabetes mellitus (T2DM). These vascular abnormalities result in a chronic hyperglycemic state, which influences many signaling molecular pathways that initially lead to increased oxidative stress, increased inflammation, and endothelial dysfunction, leading to both microvascular and macrovascular complications. Endothelial dysfunction represents the initial stage in both types of vascular complications; it represents "mandatory damage" in the development of microvascular complications and only "introductory damage" in the development of macrovascular complications. Increasing scientific evidence has revealed an important role of the Wnt pathway in the pathophysiology of the vascular wall. It is well known that the Wnt pathway is altered in patients with T2DM. This review aims to be an update of the current literature related to the Wnt pathway molecules that are altered in patients with T2DM, which may also be the cause of damage to the vasculature. Both microvascular complications (retinopathy, nephropathy, and neuropathy) and macrovascular complications (coronary artery disease, cerebrovascular disease, and peripheral arterial disease) are analyzed. This review aims to concisely concentrate all the evidence to facilitate the view on the vascular involvement of the Wnt pathway and its components by highlighting the importance of exploring possible therapeutic strategy for patients with T2DM who develop vascular pathologies.

Wnt/frizzled Signaling in Endothelium: A Major Player in Blood-Retinal- and Blood-Brain-Barrier Integrity

The Wnt/frizzled signaling pathway is one of the major regulators of endothelial biology, controlling key cellular activities. Many secreted Wnt ligands have been identified and can initiate diverse signaling via binding to a complex set of Frizzled (Fzd) transmembrane receptors and coreceptors. Roughly, Wnt signaling is subdivided into two pathways: the canonical Wnt/β-catenin signaling pathway whose main downstream effector is the transcriptional coactivator β-catenin, and the noncanonical Wnt signaling pathway, which is subdivided into the Wnt/Ca2+ pathway and the planar cell polarity pathway. Here, we will focus on its cross talk with other angiogenic pathways and on its role in blood-retinal- and blood-brain-barrier formation and its maintenance in a differentiated state. We will unravel how retinal vascular pathologies and neurovascular degenerative diseases result from disruption of the Wnt pathway related to vascular instability, and highlight current research into therapeutic options.

LMBR1L regulates proliferation and migration of endothelial cells through Norrin/β-catenin signaling

Precise Norrin/β-catenin signaling is critical for proper angiogenesis. Dysregulation of the signaling leads various diseases, of which retinal exudative vitreoretinopathy is the most prevalent. Here, we used global knockout mouse model to show that endothelial cells-derived limb region 1 like (LMBR1L), a transmembrane protein of unknown function in angiogenesis, is essential for retinal vascular development. In vitro experiments revealed that LMBR1L depletion resulted in aberrant activation of Norrin/β-catenin signaling pathway via decreased ubiquitination of FZD4, increased Norrin co-receptor LRP5 and p-GSK3β-Ser9 expression level, which caused accumulation of β-catenin. Moreover, inhibition of LMBR1L in human retinal microvascular endothelial cells (HRECs) caused increased proliferation ability and defective cell migration, which might due to upregulated expression levels of the AJ components. Treatment of p-GSK3β-Ser9 inhibitor AR-A014418 restored the phenotypes in LMBR1L-null HRECs, which further demonstrated the important regulatory role of LMBR1L in Norrin/β-catenin signaling pathway. Taken together, our data unravels an essential role of LMBR1L in angiogenesis.

Canonical Wnt Signaling in the Pathology of Iron Overload-Induced Oxidative Stress and Age-Related Diseases

Iron accumulates in the vital organs with aging. This is associated with oxidative stress, inflammation, and mitochondrial dysfunction leading to age-related disorders. Abnormal iron levels are linked to neurodegenerative diseases, liver injury, cancer, and ocular diseases. Canonical Wnt signaling is an evolutionarily conserved signaling pathway that regulates many cellular functions including cell proliferation, apoptosis, cell migration, and stem cell renewal. Recent evidences indicate that iron regulates Wnt signaling, and iron chelators like deferoxamine and deferasirox can inhibit Wnt signaling and cell growth. Canonical Wnt signaling is implicated in the pathogenesis of many diseases, and there are significant efforts ongoing to develop innovative therapies targeting the aberrant Wnt signaling. This review examines how intracellular iron accumulation regulates Wnt signaling in various tissues and their potential contribution in the progression of age-related diseases.

Misregulation of Wnt Signaling Pathways at the Plasma Membrane in Brain and Metabolic Diseases

Wnt signaling pathways constitute a group of signal transduction pathways that direct many physiological processes, such as development, growth, and differentiation. Dysregulation of these pathways is thus associated with many pathological processes, including neurodegenerative diseases, metabolic disorders, and cancer. At the same time, alterations are observed in plasma membrane compositions, lipid organizations, and ordered membrane domains in brain and metabolic diseases that are associated with Wnt signaling pathway activation. Here, we discuss the relationships between plasma membrane components-specifically ligands, (co) receptors, and extracellular or membrane-associated modulators-to activate Wnt pathways in several brain and metabolic diseases. Thus, the Wnt-receptor complex can be targeted based on the composition and organization of the plasma membrane, in order to develop effective targeted therapy drugs.

Cellular targets in diabetic retinopathy therapy

Despite the existence of treatment for diabetes, inadequate metabolic control triggers the appearance of chronic complications such as diabetic retinopathy. Diabetic retinopathy is considered a multifactorial disease of complex etiology in which oxidative stress and low chronic inflammation play essential roles. Chronic exposure to hyperglycemia triggers a loss of redox balance that is critical for the appearance of neuronal and vascular damage during the development and progression of the disease. Current therapies for the treatment of diabetic retinopathy are used in advanced stages of the disease and are unable to reverse the retinal damage induced by hyperglycemia. The lack of effective therapies without side effects means there is an urgent need to identify an early action capable of preventing the development of the disease and its pathophysiological consequences in order to avoid loss of vision associated with diabetic retinopathy. Therefore, in this review we propose different therapeutic targets related to the modulation of the redox and inflammatory status that, potentially, can prevent the development and progression of the disease.

Autophagy positively regulates Wnt signaling in mice with diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes. Aberrant Wnt signaling activation plays a pathological role in DR. However, the underlying mechanisms of aberrant Wnt signaling in DR remain unknown. Autophagy has been reported to be involved in the pathophysiology of DR. The present study aimed therefore to investigate the regulatory effects of autophagy on Wnt signaling in DR. Wnt signaling was activated in the retina of db/db mice combined with an increase in the expression of the autophagic proteins microtubule-associated protein 1A/1B-light chain 3 and beclin-1 and a decrease in the expression of the autophagic protein P62. Inhibition of autophagy by 3-methyladenin decreased Wnt signaling in diabetic retinas, indicating a potential association between Wnt signaling and autophagy. Rapamycin, an autophagy inducer, upregulated Wnt signaling in the retina of normal C57BL/6J mice. In cultured Müller cells, rapamycin induced autophagy and activated Wnt signaling, while chloroquine, an autophagy inhibitor, inhibited autophagy and downregulated Wnt signaling, suggesting that autophagy could regulate Wnt signaling in mice retina and retinal cells. In summary, this study demonstrated that autophagy may positively regulate Wnt signaling in diabetic retinas, indicating a potential mechanism of Wnt signaling upregulation in DR and a possible novel therapeutic target of DR.

Neurovascular Unit: A New Target for Treating Early Stages of Diabetic Retinopathy

The concept of diabetic retinopathy as a microvascular disease has evolved and is now considered a more complex diabetic complication in which neurovascular unit impairment plays an essential role and, therefore, can be considered as a main therapeutic target in the early stages of the disease. However, neurodegeneration is not always the apparent primary event in the natural story of diabetic retinopathy, and a phenotyping characterization is recommendable to identify those patients in whom neuroprotective treatment might be of benefit. In recent years, a myriad of treatments based on neuroprotection have been tested in experimental models, but more interestingly, there are drugs with a dual activity (neuroprotective and vasculotropic). In this review, the recent evidence concerning the therapeutic approaches targeting neurovascular unit impairment will be presented, along with a critical review of the scientific gaps and problems which remain to be overcome before our knowledge can be transferred to clinical practice.

Melatonin exerts protective effects on diabetic retinopathy via inhibition of Wnt/β-catenin pathway as revealed by quantitative proteomics

Diabetic retinopathy (DR), the most common ocular complication resulting from diabetes in working-age adults, causes vision impairment and even blindness because of microvascular damage to the retina. Melatonin is an endogenous neurohormone possessing various biological properties, including the regulation of oxidative stress, inflammation, autophagy, and angiogenesis functions. To evaluate the effects of melatonin on DR, we first investigated the role of melatonin in retinal angiogenesis and inner blood-retina barrier (iBRB) under high glucose conditions in vitro and in vivo. Melatonin administration ameliorated high glucose-induced iBRB disruption, cell proliferation, cell migration, invasion and tube formation, and decreased the expression levels of VEGF, MMP-2, and MMP-9. Furthermore, melatonin treatment increased the level of autophagy but decreased the expression levels of inflammation-related factors under high glucose conditions. To further explore the underlying mechanism, we evaluated human retinal microvascular endothelial cells (HRMECs) via tandem mass tags (TMT)-labeled quantitative proteomics under high-glucose conditions with or without melatonin. Bioinformatics analysis results revealed that the main enrichment pathway of differentially expressed proteins (DEPs) was the Wnt pathway. We found that melatonin inhibited the activation of Wnt/β-catenin pathway following DR. These abovementioned protective effects of melatonin under hyperglycemia were blocked by lithium chloride (LiCl; activator of the Wnt/β-catenin signaling pathway). In summary, melatonin exerts protective effects on experimental DR via inhibiting Wnt/β-catenin pathway by, at least partially, alleviating autophagic dysfunction and inflammatory activation.

Antiangiogenic therapy in diabetic nephropathy: A double‑edged sword (Review)

Diabetes and the associated complications are becoming a serious global threat and an increasing burden to human health and the healthcare systems. Diabetic nephropathy (DN) is the primary cause of end-stage kidney disease. Abnormal angiogenesis is well established to be implicated in the morphology and pathophysiology of DN. Factors that promote or inhibit angiogenesis serve an important role in DN. In the present review, the current issues associated with the vascular disease in DN are highlighted, and the challenges in the development of treatments are discussed.

Fenofibrate prevents iron induced activation of canonical Wnt/β-catenin and oxidative stress signaling in the retina

Accumulating evidence strongly implicates iron in the pathogenesis of aging and disease. Iron levels have been found to increase with age in both the human and mouse retinas. We and others have shown that retinal diseases such as age-related macular degeneration and diabetic retinopathy are associated with disrupted iron homeostasis, resulting in retinal iron accumulation. In addition, hereditary disorders due to mutation in one of the iron regulatory genes lead to age dependent retinal iron overload and degeneration. However, our knowledge on whether iron toxicity contributes to the retinopathy is limited. Recently, we reported that iron accumulation is associated with the upregulation of retinal and renal renin-angiotensin system (RAS). Evidences indicate that multiple genes/components of the RAS are targets of Wnt/β-catenin signaling. Interestingly, aberrant activation of Wnt/β-catenin signaling is observed in several degenerative diseases. In the present study, we explored whether iron accumulation regulates canonical Wnt signaling in the retina. We found that in vitro and in vivo iron treatment resulted in the upregulation of Wnt/β-catenin signaling and its downstream target genes including renin-angiotensin system in the retina. We confirmed further that iron activates canonical Wnt signaling in the retina using TOPFlash T-cell factor/lymphoid enhancer factor promoter assay and Axin2-LacZ reporter mouse. The presence of an iron chelator or an antioxidant reversed the iron-mediated upregulation of Wnt/β-catenin signaling in retinal pigment epithelial (RPE) cells. In addition, treatment of RPE cells with peroxisome proliferator-activated receptor (PPAR) α-agonist fenofibrate prevented iron-induced activation of oxidative stress and Wnt/β-catenin signaling by chelating the iron. The role of fenofibrate, an FDA-approved drug for hyperlipidemia, as an iron chelator has potentially significant therapeutic impact on iron associated degenerative diseases.

Association Between Pathophysiological Mechanisms of Diabetic Retinopathy and Parkinson's Disease

Diabetic retinopathy, the most common complication of diabetes, is a neurodegenerative disease in the eye. And Parkinson's disease, affecting the health of 1-2% of people over 60 years old throughout the world, is the second largest neurodegenerative disease in the brain. As the understanding of diabetic retinopathy and Parkinson's disease deepens, the two diseases are found to show correlation in incidence, similarity in clinical presentation, and close association in pathophysiological mechanisms. To reveal the association between pathophysiological mechanisms of the two disease, in this review, the shared pathophysiological factors of diabetic retinopathy and Parkinson's disease are summarized and classified into dopaminergic system, circadian rhythm, neurotrophic factors, α-synuclein, and Wnt signaling pathways. Furthermore, similar and different mechanisms so far as the shared pathophysiological factors of the two disorders are discussed systematically. Finally, a brief summary and new perspectives are presented to provide new directions for further efforts on the association, exploration, and clinical prevention and treatment of diabetic retinopathy and Parkinson's disease.

[Effect of acute insulin therapy on the concentration of vascular endothelial growth factor A (VEGF-A) in the intraocular fluid in an experiment]

PURPOSE

To study the effect of insulin therapy on the concentration of vascular endothelial growth factor A (VEGF-A) in the intraocular fluid of rats with alloxan model of diabetes mellitus.

MATERIAL AND METHODS

The experiment was conducted on 80 mongrel rats. In 65 rats, the alloxan model of diabetes mellitus was simulated by a single intraperitoneal injection of 100 mg/kg alloxan hydrate saluted in 0.4 ml of citrate buffer. 72 hours after intraperitoneal administration of alloxan monohydrate, these animals were divided into 2 groups. The main group (group 1) consisted of animals with alloxan model of diabetes mellitus, who started daily single intraperitoneal administration of prolonged-acting insulin at a therapeutic dose of 0.9 U/kg Body weight. The comparison group (group 2) consisted of animals with alloxan model of diabetes mellitus who did not receive specific therapy. 15 healthy rats constituted the control group (group 3). Experimental animals were removed from the study on day 31 of insulin therapy. The concentration of VEGF-A was determined in 80-90 μl of intraocular fluid collected from both eyes of each animal.

RESULTS

In the main group, the median of VEGF-A concentration [25th; 75th percentiles] in the intraocular fluid was 140 [136; 210] pg/ml, which is 1.94 times higher than in the comparison group (72 [58; 86] pg/ml) and 1.84 times higher than in the control group (76 [62.5; 88] pg/ml). The concentration of VEGF-A in the intraocular fluid in the main group was statistically significantly higher, as compared with the comparison group (p_m-u<0.0004), and compared with the control group (p_m-u=0.0045). The comparison group had no statistically significant differences when compared with the control group (p_m-u=0.9979).

CONCLUSION

Insulin therapy for 31 days increases the concentration of VEGF-A in the intraocular fluid of rats with alloxan model of diabetes mellitus.

Norrin restores blood-retinal barrier properties after vascular endothelial growth factor-induced permeability

Vascular endothelial growth factor (VEGF) contributes to blood-retinal barrier (BRB) dysfunction in several blinding eye diseases, including diabetic retinopathy. Signaling via the secreted protein norrin through the frizzled class receptor 4 (FZD4)/LDL receptor-related protein 5-6 (LRP5-6)/tetraspanin 12 (TSPAN12) receptor complex is required for developmental vascularization and BRB formation. Here, we tested the hypothesis that norrin restores BRB properties after VEGF-induced vascular permeability in diabetic rats or in animals intravitreally injected with cytokines. Intravitreal co-injection of norrin with VEGF completely ablated VEGF-induced BRB permeability to Evans Blue-albumin. Likewise, 5-month diabetic rats exhibited increased permeability of FITC-albumin, and a single norrin injection restored BRB properties. These results were corroborated in vitro, where co-stimulation of norrin with VEGF or stimulation of norrin after VEGF exposure restored barrier properties, indicated by electrical resistance or 70-kDa RITC-dextran permeability in primary endothelial cell culture. Interestingly, VEGF promoted norrin signaling by increasing the FZD4 co-receptor TSPAN12 at cell membranes in an MAPK/ERK kinase (MEK)/ERK-dependent manner. Norrin signaling through β-catenin was required for BRB restoration, but glycogen synthase kinase 3 α/β (GSK-3α/β) inhibition did not restore BRB properties. Moreover, levels of the tight junction protein claudin-5 were increased with norrin and VEGF or with VEGF alone, but both norrin and VEGF were required for enriched claudin-5 localization at the tight junction. These results suggest that VEGF simultaneously induces vascular permeability and promotes responsiveness to norrin. Norrin, in turn, restores tight junction complex organization and BRB properties in a β-catenin-dependent manner.

The Presence of Wnt Signaling Mutations in Patients With Diabetic Retinopathy

Purpose:

The relationship between poor hemoglobin A1c (HbA1c) control and risk of proliferative diabetic retinopathy (PDR) is well known. Nevertheless, some patients have discordant disease (controlled HbA1c and severe PDR or vice versa). One potential explanation for this discrepancy is the presence of underlying genetic mutations in the Wingless-related integration site (Wnt) signaling pathway. However, minimal clinical data exist on the presence of Wnt signaling mutations in patients with diabetes mellitus (DM) and the correlation with diabetic retinopathy.

Methods:

Retrospective, nonconsecutive case review of patients with type 1 or 2 DM who underwent genetic testing for at least 1 recognized Wnt signaling pathway mutation from 2011 to 2016. The clinical course and retinal images were reviewed for patients with identifiable mutations.

Results:

Thirty-six patients, ages 13 to 79 years, consented for genetic analysis. Three patients (8.3%) exhibited at least 1 recognized genetic mutation in the Wnt signaling pathway. Case 1 was a 65-year-old female with type 1 diabetes for > 20 years, HbA1c <7.0%, and no findings of diabetic retinopathy (Tetraspanin 12). Case 2 was a 13-year-old male with type 1 diabetes for 8 years, moderate HbA1c control (7.6-8.3%), and absence of diabetic retinopathy (Norrin). Case 3 was a 48-year-old male with severe PDR requiring multiple laser and antivascular endothelial growth factor (anti-VEGF) treatments despite well-controlled HbA1c (6.0%) (Frizzled-4).

Conclusion:

Wnt signaling pathway mutations exist in patients with DM. Further studies investigating the prevalence and clinical significance of these mutations in a larger diabetic population are warranted. Identification of these patients with genetic testing may enable earlier medical intervention.

Role of the Wnt signalling pathway in the development of endothelial disorders in response to hyperglycaemia

INTRODUCTION

Diabetes mellitus (DM) is the most common metabolic disease. A WHO report from 2016 indicates that 422 million people worldwide suffer from DM or hyperglycaemia because of impaired glucose metabolism. Chronic hyperglycaemia leads to micro- and macrovessel damage, which may result in life-threatening complications. The Wnt pathway regulates cell proliferation and survival by modulating the expression of genes that control cell differentiation. Three linked Wnt pathways have been discovered thus far: a β-catenin-dependent pathway and two pathways independent of β-catenin - the planar cell polarity pathway and calcium-dependent pathway. The Wnt pathway regulates genes associated with inflammation, cell cycle, angiogenesis, fibrinolysis and other molecular processes.

AREAS COVERED

This review presents the current state of knowledge regarding the contribution of the Wnt pathway to endothelial ageing under hyperglycaemic conditions and provides new insights into the molecular basis of diabetic endothelial dysfunction.

CONCLUSION

The β-catenin-dependent pathway is a potential target in the prophylaxis and treatment of early-stage diabetes-related vascular complications. However, the underlying molecular mechanisms remain largely undetermined and require further investigation.

Therapies targeting Frizzled-7/β-catenin pathway prevent the development of pathological angiogenesis in an ischemic retinopathy model

Retinopathies remain major causes of visual impairment in diabetic patients and premature infants. Introduction of anti-angiogenic drugs targeting vascular endothelial growth factor (VEGF) has transformed therapy for these proliferative retinopathies. However, limitations associated with anti-VEGF medications require to unravel new pathways of vessel growth to identify potential drug targets. Here, we investigated the role of Wnt/Frizzled-7 (Fzd7) pathway in a mouse model of oxygen-induced retinopathy (OIR). Using transgenic mice, which enabled endothelium-specific and time-specific Fzd7 deletion, we demonstrated that Fzd7 controls both vaso-obliteration and neovascular phases (NV). Deletion of Fzd7 at P12, after the ischemic phase of OIR, prevented formation of aberrant neovessels into the vitreous by suppressing proliferation of endothelial cells (EC) in tufts. Next we validated in vitro two Frd7 blocking strategies: a monoclonal antibody (mAbFzd7) against Fzd7 and a soluble Fzd7 receptor (CRD). In vivo a single intravitreal microinjection of mAbFzd7 or CRD significantly attenuated retinal neovascularization (NV) in mice with OIR. Molecular analysis revealed that Fzd7 may act through the activation of Wnt/β-catenin and Jagged1 expression to control EC proliferation in extra-retinal neovessels. We identified Fzd7/β-catenin signaling as new regulator of pathological retinal NV. Fzd7 appears to be a potent pharmacological target to prevent or treat aberrant angiogenesis of ischemic retinopathies.

A Protective Effect of PPARα in Endothelial Progenitor Cells Through Regulating Metabolism

Deficiency of endothelial progenitor cells, including endothelial colony-forming cells (ECFCs) and circulating angiogenic cells (CACs), plays an important role in retinal vascular degeneration in diabetic retinopathy (DR). Fenofibrate, an agonist of peroxisome proliferator-activated receptor α (PPARα), has shown therapeutic effects on DR in both patients and diabetic animal models. However, the function of PPARα in ECFC/CACs has not been defined. In this study, we determined the regulation of ECFC/CAC by PPARα. As shown by flow cytometry and Seahorse analysis, ECFC/CAC numbers and mitochondrial function were decreased in the bone marrow, circulation, and retina of db/db mice, correlating with PPARα downregulation. Activation of PPARα by fenofibrate normalized ECFC/CAC numbers and mitochondrial function in diabetes. In contrast, PPARα knockout exacerbated ECFC/CAC number decreases and mitochondrial dysfunction in diabetic mice. Primary ECFCs from PPARα -/- mice displayed impaired proliferation, migration, and tube formation. Furthermore, PPARα -/- ECFCs showed reduced mitochondrial oxidation and glycolysis compared with wild type, correlating with decreases of Akt phosphorylation and expression of its downstream genes regulating ECFC fate and metabolism. These findings suggest that PPARα is an endogenous regulator of ECFC/CAC metabolism and cell fate. Diabetes-induced downregulation of PPARα contributes to ECFC/CAC deficiency and retinal vascular degeneration in DR.

Protein Kinase CK2-A Putative Target for the Therapy of Diabetes Mellitus?

Since diabetes is a global epidemic, the development of novel therapeutic strategies for the treatment of this disease is of major clinical interest. Diabetes is differentiated in two types: type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). T1DM arises from an autoimmune destruction of insulin-producing β-cells whereas T2DM is characterized by an insulin resistance, an impaired insulin reaction of the target cells, and/or dysregulated insulin secretion. In the past, a growing number of studies have reported on the important role of the protein kinase CK2 in the regulation of the survival and endocrine function of pancreatic β-cells. In fact, inhibition of CK2 is capable of reducing cytokine-induced loss of β-cells and increases insulin expression as well as secretion by various pathways that are regulated by reversible phosphorylation of proteins. Moreover, CK2 inhibition modulates pathways that are involved in the development of diabetes and prevents signal transduction, leading to late complications such as diabetic retinopathy. Hence, targeting CK2 may represent a novel therapeutic strategy for the treatment of diabetes.

Vascular and Neuronal Protection in the Developing Retina: Potential Therapeutic Targets for Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a common retinal disease in preterm babies. To prolong the lives of preterm babies, high oxygen is provided to mimic the oxygen level in the intrauterine environment for postnatal organ development. However, hyperoxia-hypoxia induced pathological events occur when babies return to room air, leading to ROP with neuronal degeneration and vascular abnormality that affects retinal functions. With advances in neonatal intensive care, it is no longer uncommon for increased survival of very-low-birth-weight preterm infants, which, therefore, increased the incidence of ROP. ROP is now a major cause of preventable childhood blindness worldwide. Current proven treatment for ROP is limited to invasive retinal ablation, inherently destructive to the retina. The lack of pharmacological treatment for ROP creates a great need for effective and safe therapies in these developing infants. Therefore, it is essential to identify potential therapeutic agents that may have positive ROP outcomes, especially in preserving retinal functions. This review gives an overview of various agents in their efficacy in reducing retinal damages in cell culture tests, animal experiments and clinical studies. New perspectives along the neuroprotective pathways in the developing retina are also reviewed.

Canonical Wnt Signaling Promotes Neovascularization Through Determination of Endothelial Progenitor Cell Fate via Metabolic Profile Regulation

Endothelial progenitor cells (EPCs) contribute to blood vessel formation. Canonical Wnt signaling plays an important role in physiological and pathological angiogenesis and EPC fate regulation. However, the mechanism for Wnt signaling to regulate EPC fate in neovascularization (NV) has not been clearly defined. Here, we showed that very low-density lipoprotein receptor knockout (Vldlr ^-/- ) mice, a model of ocular NV induced by Wnt signaling overactivation, have increased EPC numbers in the bone marrow, blood, and retina, as well as an elevated mitochondrial membrane potential indicating higher mitochondrial function of EPCs in the circulation. Isolated EPCs from Vldlr ^-/- mice showed overactivated Wnt signaling, correlating with increased mitochondrial function, mass, and DNA copy numbers, compared with WT EPCs. Our results also demonstrated that Wnt signaling upregulated mitochondrial biogenesis and function, while inhibiting glycolysis in EPCs, which further decreased EPC stemness and promoted EPCs to a more active state toward differentiation, which may contribute to pathologic vascular formation. Fenofibric acid, an active metabolite of fenofibrate, inhibited Wnt signaling and mitochondrial function in EPCs and decreased EPC numbers in Vldlr ^-/- mice. It also decreased mitochondrial biogenesis and reactive oxygen species production in Vldlr ^-/- EPCs, which may be responsible for its therapeutic effect on diabetic retinopathy. These findings demonstrated that Wnt signaling regulates EPC fate through metabolism, suggesting potential application of the EPC metabolic profile as predictor and therapeutic target for neovascular diseases. Stem Cells 2019;37:1331-1343.

Oxidative stress upregulates Wnt signaling in human retinal microvascular endothelial cells through activation of disheveled

Abnormal retinal neovascularization associated with various retinopathies can result in irreversible vision loss. Although the mechanisms involved in this occurrence is unclear, increasing evidence suggests that aberrant Wnt signaling participates in the pathogenesis of abnormal neovascularization. Because Wnt signaling upregulation can be induced by oxidative stress through the activation of disheveled (DVL), a key molecule in the Wnt signaling pathway, we investigated whether oxidative stress can activate Wnt signaling and induce angiogenic phenotypes in human retinal microvascular endothelial cells (HRMECs). We found that increased Wnt signaling activity, as well as enhanced angiogenic phenotypes, such as tube formation and cell migration, were detected in the hydrogen peroxide-treated HRMECs. Moreover, these effects were effectively suppressed by a small-molecule Wnt inhibitor targeting the PDZ domain of DVL. Therefore, we propose that targeting abnormal Wnt signaling at the DVL level with a small-molecule inhibitor may represent a novel approach in retinal neovascularization treatment and prevention.

The identification of differentially expressed genes between extremes of placental efficiency in maternal line gilts on day 95 of gestation

Background

Placental efficiency (PE) describes the relationship between placental and fetal weights (fetal wt/placental wt). Within litters, PE can vary drastically, resulting in similarly sized pigs associated with differently sized placentas, up to a 25% weight difference. However, the mechanisms enabling the smaller placenta to grow a comparable littermate are unknown. To elucidate potential mechanisms, morphological measurements and gene expression profiles in placental and associated endometrial tissues of high PE and low PE feto-placental units were compared. Tissue samples were obtained from eight maternal line gilts during gestational day 95 ovario-hysterectomies. RNA was extracted from tissues of feto-placental units with the highest and lowest PE in each litter and sequenced.

Results

Morphological measurements, except placental weight, were not different (P > 0.05) between high and low PE. No DEG were identified in the endometrium and 214 DEG were identified in the placenta (FDR < 0.1), of which 48% were upregulated and 52% were downregulated. Gene ontology (GO) analysis revealed that a large percentage of DEG were involved in catalytic activity, binding, transporter activity, metabolism, biological regulation, and localization. Four GO terms were enriched in the upregulated genes and no terms were enriched in the downregulated genes (FDR < 0.05). Eight statistically significant correlations (P < 0.05) were identified between the morphological measurements and DEG.

Conclusion

Morphological measures between high and low PE verified comparisons were of similarly sized pigs grown on different sized placentas, and indicated that any negative effects of a reduced placental size on fetal growth were not evident by day 95. The identification of DEG in the placenta, but absence of DEG in the endometrium confirmed that the placenta responds to the fetus. The GO analyses provided evidence that extremes of PE are differentially regulated, affecting components of placental transport capacity like nutrient transport and blood flow. However, alternative GO terms were identified, indicating the complexity of the relationship between placental and fetal weights. These findings support the use of PE as a marker of placental function and provide novel insight into the genetic control of PE, but further research is required to make PE production applicable.

Therapeutic regulation of VE-cadherin with a novel oligonucleotide drug for diabetic eye complications using retinopathy mouse models

AIMS/HYPOTHESIS

A major feature of diabetic retinopathy is breakdown of the blood-retinal barrier, resulting in macular oedema. We have developed a novel oligonucleotide-based drug, CD5-2, that specifically increases expression of the key junctional protein involved in barrier integrity in endothelial cells, vascular-endothelial-specific cadherin (VE-cadherin). CD5-2 prevents the mRNA silencing by the pro-angiogenic microRNA, miR-27a. CD5-2 was evaluated in animal models of ocular neovascularisation and vascular leak to determine its potential efficacy for diabetic retinopathy.

METHODS

CD5-2 was tested in three mouse models of retinal dysfunction: conditional Müller cell depletion, streptozotocin-induced diabetes and oxygen-induced retinopathy. Vascular permeability in the Müller cell-knockout model was assessed by fluorescein angiography. The Evans Blue leakage method was used to determine vascular permeability in streptozotocin- and oxygen-induced retinopathy models. The effects of CD5-2 on retinal neovascularisation, inter-endothelial junctions and pericyte coverage in streptozotocin- and oxygen-induced retinopathy models were determined by staining for isolectin-B4, VE-cadherin and neural/glial antigen 2 (NG2). Blockmir CD5-2 localisation in diseased retina was determined using fluorescent in situ hybridisation. The effects of CD5-2 on VE-cadherin expression and in diabetic retinopathy-associated pathways, such as the transforming growth factor beta (TGF-β) and wingless/integrated (WNT) pathway, were confirmed using western blot of lysates from HUVECs, a mouse brain endothelial cell line and a VE-cadherin null mouse endothelial cell line.

RESULTS

CD5-2 penetrated the vasculature of the eye in the oxygen-induced retinopathy model. Treatment of diseased mice with CD5-2 resulted in reduced vascular leak in all three animal models, enhanced expression of VE-cadherin in the microvessels of the eye and improved pericyte coverage of the retinal vasculature in streptozotocin-induced diabetic models and oxygen-induced retinopathy models. Further, CD5-2 reduced the activation of retinal microglial cells in the streptozotocin-induced diabetic model. The positive effects of CD5-2 seen in vivo were further confirmed in vitro by increased protein expression of VE-cadherin, SMAD2/3 activity, and platelet-derived growth factor B (PDGF-B).

CONCLUSIONS/INTERPRETATION

CD5-2 has therapeutic potential for individuals with vascular-leak-associated retinal diseases based on its ease of delivery and its ability to reverse vascular dysfunction and inflammatory aspects in three animal models of retinopathy.

Salutary effect of fenofibrate on type 1 diabetic retinopathy via inhibiting oxidative stress-mediated Wnt/β-catenin pathway activation

Fenofibrate has been shown to have therapeutic effects on diabetic retinopathy (DR). Our previous studies demonstrated that the oxidative stress-activated Wnt/β-catenin pathway plays a pathogenic role in diabetic complications. In the present study, we evaluate the effect and mechanism of fenofibrate on regulating the oxidative stress-activated Wnt/β-catenin pathway by using the genetic type 1 diabetes model of C57BL/6J-Ins2^Akita mice and high glucose (HG)-treated ARPE-19. Our results demonstrated that retinal phosphorylation of LRP6 and nuclear β-catenin were increased in C57BL/6J-Ins2^Akita mice suggesting activation of Wnt/β-catenin signaling. Meanwhile, C57BL/6J-Ins2^Akita showed upregulation of oxidant enzyme Nox4 and Nox2 and downregulation of antioxidant enzyme SOD1 and SOD2. All these alterations were reversed in C57BL/6J-Ins2^Akita mice with fenofibrate treatment. Moreover, fenofibrate significantly ameliorated diabetes-induced retinal vascular leakage in C57BL/6J-Ins2^Akita mice. In cultured ARPE-19, fenofibrate decreased HG-induced Nox2 and Nox4 upregulation, attenuated SOD1 and SOD2 downregulation and inhibited LRP6 phosphorylation. Moreover, activation of Wnt/β-catenin by Wnt3a conditional medium (WCM) reduced SOD1 and SOD2 and did not affect Nox2 and Nox4. Fenofibrate suppressed WCM-induced LRP6 phosphorylation and reversed SOD downregulation. Importantly, Nox4 overexpression directly phosphorylated LPR6 in ARPE19; conversely, Nox4 knockdown suppressed HG-induced LPR6 phosphorylation. Taken together, Nox-mediated oxidative stress contributes to Wnt/β-catenin activation in DR. Fenofibrate ameliorated DR through coordinate attenuation of oxidative stress and blockade of Wnt/β-catenin signaling.

Wnt Signaling in vascular eye diseases

The Wnt signaling pathway plays a pivotal role in vascular morphogenesis in various organs including the eye. Wnt ligands and receptors are key regulators of ocular angiogenesis both during the eye development and in vascular eye diseases. Wnt signaling participates in regulating multiple vascular beds in the eye including regression of the hyaloid vessels, and development of structured layers of vasculature in the retina. Loss-of-function mutations in Wnt signaling components cause rare genetic eye diseases in humans such as Norrie disease, and familial exudative vitreoretinopathy (FEVR) with defective ocular vasculature. On the other hand, experimental studies in more prevalent vascular eye diseases, such as wet age-related macular degeneration (AMD), diabetic retinopathy (DR), retinopathy of prematurity (ROP), and corneal neovascularization, suggest that aberrantly increased Wnt signaling is one of the causations for pathological ocular neovascularization, indicating the potential of modulating Wnt signaling to ameliorate pathological angiogenesis in eye diseases. This review recapitulates the key roles of the Wnt signaling pathway during ocular vascular development and in vascular eye diseases, and pharmaceutical approaches targeting the Wnt signaling as potential treatment options.

Antagonising Wnt/β-catenin signalling ameliorates lens-capsulotomy-induced retinal degeneration in a mouse model of diabetes

AIMS/HYPOTHESIS

Cataract surgery in diabetic individuals worsens pre-existing retinopathy and triggers the development of diabetic ocular complications, although the underlying cellular and molecular pathophysiology remains elusive. We hypothesise that lens surgery may exaggerate pre-existing retinal inflammation in diabetes, which may accelerate neurovascular degeneration in diabetic eyes.

METHODS

Male heterozygous Ins2^Akita mice (3 months of age) and C57BL/6 J age-matched siblings received either lens capsulotomy (to mimic human cataract surgery) or corneal incision (sham surgery) in the right eye. At different days post surgery, inflammation in anterior/posterior ocular tissues was assessed by immunohistochemistry and proinflammatory gene expression in the retina by quantitative PCR (qPCR). Degenerative changes in the retina were evaluated by electroretinography, in vivo examination of retinal thickness (using spectral domain optical coherence tomography [SD-OCT]) and morphometric analysis of retinal neurons. The therapeutic benefit of neutralising Wnt/β-catenin signalling following lens capsulotomy was evaluated by intravitreal administration of monoclonal antibody against the co-receptor low-density lipoprotein receptor-related protein 6 (LRP6) (Mab2F1; 5 μg/μl in each eye).

RESULTS

Lens capsulotomy triggered the early onset of retinal neurodegeneration in Ins2^Akita mice, evidenced by abnormal scotopic a- and b-wave responses, reduced retinal thickness and degeneration of outer/inner retinal neurons. Diabetic Ins2^Akita mice also had a higher number of infiltrating ionised calcium-binding adapter molecule 1 (IBA1)/CD68⁺ cells in the anterior/posterior ocular tissues and increased retinal expression of inflammatory mediators (chemokine [C-C motif] ligand 2 [CCL2] and IL-1β). The expression of β-catenin was significantly increased in the inner nuclear layer, ganglion cells and infiltrating immune cells in Ins2^Akita mice receiving capsulotomy. Neutralisation of Wnt/β-catenin signalling by Mab2F1 ameliorated ocular inflammation and prevented capsulotomy-induced retinal degeneration in the Ins2^Akita mouse model of diabetes.

CONCLUSIONS/INTERPRETATION

Targeting the canonical Wnt/β-catenin signalling pathway may provide a novel approach for the postoperative management of diabetic individuals needing cataract surgery.

Extract of the Blood Circulation-Promoting Recipe-84 Can Protect Rat Retinas by Inhibiting the β-Catenin Signaling Pathway

Extract of the Blood Circulation-Promoting Recipe (EBR-84) from the Chinese Herbal medicine “Blood Circulation Promoting Recipe” could retard retinopathy development. This study investigated whether EBR-84 protects retinas by inhibiting the β-catenin pathway using a rat model of retinopathy and a retinal ganglion cell 5 (RGC-5) cell death model. RGC death was induced by either N-methyl-d-aspartic acid (NMDA) or TWS119 (an activator of the β-catenin pathway). After the corresponding treatment with EBR-84, RGC death and the protein expression levels of β-catenin, cyclooxygenase-2 (COX-2), and vascular endothelial growth factor (VEGF) in rat retinas were examined. β-Catenin accumulated in the retinal ganglion cell layer (GCL) of NMDA-treated rats. EBR-84 (3.9, 7.8, and 15.6 g/kg) significantly attenuated the NMDA-induced RGC loss accompanying the reduction of β-catenin expression. Moreover, the expression levels of COX-2 and VEGF were decreased by EBR-84 in a dose-dependent manner. For the TWS119-treated rats, EBR-84 also ameliorated RGC loss and lowered the expression levels of β-catenin, COX-2, and VEGF. In vitro, EBR-84 increased the viability of NMDA-treated RGC-5 while decreased β-catenin expression. In conclusion, EBR-84 retarded ratretinopathy, and the β-catenin signaling pathway played an important role during this protective process.

Lycopene treatment inhibits activation of Jak1/Stat3 and Wnt/β-catenin signaling and attenuates hyperproliferation in gastric epithelial cells

Helicobacter pylori (H pylori) colonizes the human stomach and increases the risk of gastric diseases including gastric cancer. H pylori increases reactive oxygen species (ROS), which activate Janus-activator kinase 1 (Jak1)/signal transducers and activators of transcription 3 (Stat3) in gastric epithelial cells. ROS mediate hyperproliferation, a hallmark of carcinogenesis, by activating Wnt/β-catenin signaling in various cells. Lycopene is a potent antioxidant exhibiting anticancer effects. We hypothesized that lycopene may inhibit H pylori-induced hyperproliferation by suppressing ROS-mediated activation of Jak1/Stat3 and Wnt/β-catenin signaling, and β-catenin target gene expression in gastric epithelial cells. We determined cell viability, ROS levels, and the protein levels of phospho- and total Jak1/Stat3, Wnt/β-catenin signaling molecules, Wnt-1, lipoprotein-related protein 5, and β-catenin target oncogenes (c-Myc and cyclin E) in H pylori-infected gastric epithelial AGS cells. The Jak1/Stat3 inhibitor AG490 served as the control treatment. The significance of the differences among groups was calculated using the 1-way analysis of variance followed by Newman-Keuls post hoc tests. The results show that lycopene reduced ROS levels and inhibited Jak1/Stat3 activation, alteration of Wnt/β-catenin multiprotein complex molecules, expression of c-Myc and cyclin E, and cell proliferation in H pylori-infected AGS cells. AG490 similarly inhibited H pylori-induced cell proliferation, alteration of Wnt/β-catenin multiprotein complex molecules, and oncogene expression. H pylori increased the levels of Wnt-1 and its receptor lipoprotein-related protein 5; this increase was inhibited by either lycopene or AG490 in AGS cells. In conclusion, lycopene inhibits ROS-mediated activation of Jak1/Stat3 and Wnt/β-catenin signaling and, thus, oncogene expression in relation to hyperproliferation in H pylori-infected gastric epithelial cells. Lycopene might be a potential and promising nutrient for preventing H pylori-associated gastric diseases including gastric cancer.

Characterization of canonical Wnt signalling changes after induced disruption of Müller cell in murine retina

Müller cells are the primary glia in the retina, playing a critical role in retinal homeostasis and retinal pathology. This study evaluated the canonical Wnt signalling pathway and its downstream effects on retinal degeneration in a transgenic mouse model of inducible Müller cell disruption. Increased expression of the LacZ reporter gene in the retina suggested Wnt signalling had been activated after induced Müller cell disruption. Activation was validated by observing nuclear translocation of β-Catenin. The mRNA expression of 80 Wnt related genes were assessed using real-time PCR. The Wnt signalling inhibitors Dkk1, Dkk3 and sFRP3 were significantly downregulated. Furthermore, the ubiquitin-mediated β-Catenin proteolysis genes β-TrCP and SHFM3, were also significantly downregulated. The downstream target genes of the Wnt signalling, including Fra1, CyclinD2 and C-Myc were upregulated. The changes of these genes at the protein level were validated by Western blot. Their distributions in the retina were evaluated by immunofluorescent staining. Our findings indicate that Müller cells are involved in retinal Wnt signalling. Activation of Wnt signalling and its downstream target genes may play important roles in photoreceptor degeneration and neovascularization occurring in the retina after induced disruption of Müller cells.

Anti-angiogenic effect of a humanized antibody blocking the Wnt/β-catenin signaling pathway

PURPOSE

Our previous study demonstrated that Mab2F1, a murine monoclonal antibody blocking the Wnt/β-catenin signaling pathway, has beneficial effects on experimental diabetic retinopathy and choroidal neovascularization (NV). The aforementioned antibody has been humanized. This study evaluated effects of the humanized antibody, H1L1, on NV.

METHODS

H1L1 was evaluated in the alkali burn-induced corneal NV rat model. Rats with corneal NV were injected subconjunctivally with Mab2F1 or H1L1 using non-specific mouse or human IgG as controls. Corneal NV and opacity were evaluated using corneal NV area and inflammatory index. Expression of angiogenic and inflammatory factors and components of the Wnt/β-catenin pathway in both the corneas of the animal model and human corneal epithelial (HCE) cells exposed to Wnt3a conditioned medium (WCM) were determined by Western blotting and a luciferase-based promoter assay. Cytotoxicities of these antibodies were evaluated by MTT assay.

RESULTS

H1L1 reduced the area of corneal NV and opacity, similar to Mab2F1. Both Mab2F1 and H1L1 down-regulated the overexpression of angiogenic and inflammatory factors including VEGF, TNF-α and ICAM-1, and blocked the aberrant activation of the Wnt/β-catenin pathway as shown by down-regulation of phosphorylated LRP6, total LRP6 and non-phosphorylated β-catenin in the cornea of the NV model and cultured HCE cells exposed to WCM. Both antibodies also inhibited the transcriptional activity of β-catenin induced by WCM in HCE cells. No toxic effects of the antibodies were observed in cultured HCE cells.

CONCLUSIONS

H1L1 exhibits anti-angiogenic activities through blocking the Wnt/β-catenin pathway.

Clinical Decision-Making when Treating Diabetic Macular Edema Patients with Dexamethasone Intravitreal Implants

Diabetes mellitus (DM) is a metabolic disease frequently associated with comorbidities that include diabetic macular edema (DME). The current medical approach to treating DME involves intravitreal injections with either anti-vascular endothelial growth factors or steroids. However, the burden associated with intravitreal injections and DM-derived complications is high, underlining the need to find optimal treatment regimens. In this article we describe the considerations we apply when treating DME patients with dexamethasone intravitreal implants (Ozurdex®), particularly those that influence the clinical decision-making process during the follow-up period. These considerations are based both on the available medical literature and on our clinical experience following the use of these implants in this type of patient, the goal being to optimize the number of injections and the clinical outcome of this therapy. We also provide a general overview of the pathophysiology of DME, highlighting the inflammatory component as a rationale to use steroids in these patients.

The Role of Microglia in Diabetic Retinopathy: Inflammation, Microvasculature Defects and Neurodegeneration

Diabetic retinopathy is a common complication of diabetes mellitus, which appears in one third of all diabetic patients and is a prominent cause of vision loss. First discovered as a microvascular disease, intensive research in the field identified inflammation and neurodegeneration to be part of diabetic retinopathy. Microglia, the resident monocytes of the retina, are activated due to a complex interplay between the different cell types of the retina and diverse pathological pathways. The trigger for developing diabetic retinopathy is diabetes-induced hyperglycemia, accompanied by leukostasis and vascular leakages. Transcriptional changes in activated microglia, mediated via the nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and extracellular signal–regulated kinase (ERK) signaling pathways, results in release of various pro-inflammatory mediators, including cytokines, chemokines, caspases and glutamate. Activated microglia additionally increased proliferation and migration. Among other consequences, these changes in microglia severely affected retinal neurons, causing increased apoptosis and subsequent thinning of the nerve fiber layer, resulting in visual loss. New potential therapeutics need to interfere with these diabetic complications even before changes in the retina are diagnosed, to prevent neuronal apoptosis and blindness in patients.

The Involvement of β-Catenin/COX-2/VEGF Axis in NMDA-Caused Retinopathy

NMDA, a molecule that is capable of producing the loss of retinal ganglia cells (RGCs), has been widely studied; however, the detailed mechanism is not yet clarified. Previously, Wnt/β-catenin signaling has been suggested to be involved in the NMDA-induced retinopathy. In addition, previous investigations in our group demonstrated the presence of a Wnt/β-catenin/COX-2 axis in dorsal root ganglions (DRGs). Therefore, here in this paper, we tested whether there is an association of such axis with NMDA-induced RGC loss. Rat retinal damage models generated by intravitreal injection of NMDA were used to measure the expression levels of β-catenin, COX-2, and VEGF in retinas, and the neuron numbers of the retinal GCL of rats were counted. Then, pharmacological tools (MK801, a NMDA receptor inhibitor; Dickkopf homolog 1, a specific inhibitor of the Wnt pathway; NS-398, a COX-2 inhibitor; and bevacizumab, IVB, a VEGF inhibitor) were introduced to evaluate the detailed roles of Wnt/β-catenin, COX-2, and VEGF in retinopathy of rats. Results demonstrated that all three factors in sequence are positively regulated neuronal loss induced by NMDA. These observations indicated that the Wnt pathway/COX-2/VEGF axis plays a pathogenic role in retinopathy and represented novel therapeutic targets.

Antibody-Mediated Inhibition of Tspan12 Ameliorates Vasoproliferative Retinopathy Through Suppression of β-Catenin Signaling

Background:

Anti-angiogenic biologicals represent an important concept for the treatment of vasoproliferative diseases. However, the need for continued treatment, the presence of nonresponders, and the risk of long-term side effects limit the success of existing therapeutic agents. Although Tspan12 has been shown to regulate retinal vascular development, nothing is known about its involvement in neovascular disease and its potential as a novel therapeutic target for the treatment of vasoproliferative diseases.

Methods:

Rodent models of retinal neovascular disease, including the mouse model of oxygen-induced retinopathy and the very low density lipoprotein receptor knockout mouse model were analyzed for Tspan/β-catenin regulation. Screening of a phage display of a human combinatorial antibody (Ab) library was used for the development of a high-affinity Ab against Tspan12. Therapeutic effects of the newly developed Ab on vascular endothelial cells were tested in vitro and in vivo in the oxygen-induced retinopathy and very low density lipoprotein receptor knockout mouse model.

Results:

The newly developed anti-Tspan12 Ab exhibited potent inhibitory effects on endothelial cell migration and tube formation. Mechanistic studies confirmed that the Ab inhibited the interaction between Tspan12 and Frizzled-4 and effectively modulates β-catenin levels and target genes in vascular endothelial cells. Tspan12/β-catenin signaling was activated in response to acute and chronic stress in the oxygen-induced retinopathy and very low density lipoprotein receptor mouse model of proliferative retinopathy. Intravitreal application of the Ab showed significant therapeutic effects in both models without inducing negative side effects on retina function. Moreover, combined intravitreal injection of the Ab with a known vascular endothelial growth factor inhibitor, Aflibercept, resulted in significant enhancement of the therapeutic efficacy of each monotherapy. Combination therapy with the Tspan12 blocking antibody can be used to reduce anti-vascular endothelial growth factor doses, thus decreasing the risk of long-term off-target effects.

Conclusions:

Tspan12/β-catenin signaling is critical for the progression of vasoproliferative disease. The newly developed anti-Tspan12 antibody has therapeutic effects in vasoproliferative retinopathy and can enhance the potency of existing anti- vascular endothelial growth factor agents.