Apelin is required for non-neovascular remodeling in the retina

Targeting circRNA-MAP4K2 for the treatment of diabetes-induced retinal vascular dysfunction

Diabetic retinopathy (DR) is an important ocular vascular disease in working-age adults. However, the molecular mechanism underlying retinal vascular dysfunction is still not fully understood in DR. Circular RNAs have been recognized as the crucial regulators in many biological processes and human diseases. Herein, we determined the role of circular RNA-MAP4K2 (cMAP4K2) in diabetes-induced retinal vascular dysfunction. The results showed that high glucose treatment led to increased levels of cMAP4K2 expression in vitro and in vivo. Silencing of cMAP4K2 could reduce endothelial cell viability, proliferation, migration, and tube formation in vitro and alleviate retinal vascular dysfunction in vivo as shown by decreased vascular leakage and inflammation. By contrast, cMAP4K2 overexpression had an opposite effect on retinal vascular dysfunction. Mechanistically, cMAP4K2 acted as miR-377 sponge to affect the biological activity of miR-377, which led to increased expression of vascular endothelial growth factor A (VEGFA). Clinically, cMAP4K2 expression was significantly up-regulated in the clinical sample of DR patients. Collectively, cMAP4K2 is shown as a potential target for the diagnosis and treatment of diabetic retinopathy.

Apelin-driven endothelial cell migration sustains intestinal progenitor cells and tumor growth

Stem and progenitor cells residing in the intestinal crypts drive the majority of colorectal cancers (CRCs), yet vascular contribution to this niche remains largely unexplored. VEGFA is a key driver of physiological and tumor angiogenesis. Accordingly, current anti-angiogenic cancer therapies target the VEGFA pathway. Here we report that in CRC expansion of the stem/progenitor pool in intestinal crypts requires VEGFA-independent growth and remodeling of blood vessels. Epithelial transformation induced expression of the endothelial peptide apelin, directs migration of distant venous endothelial cells towards progenitor niche vessels ensuring optimal perfusion. In the absence of apelin, loss of injury-inducible PROX1+ epithelial progenitors inhibited both incipient and advanced intestinal tumor growth. Our results establish fundamental principles for the reciprocal communication between vasculature and the intestinal progenitor niche and provide a mechanism for resistance to VEGFA-targeting drugs in CRCs.

Clinical significance of apelin in the treatment of type 2 diabetic peripheral neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is one of the most common chronic complications of diabetes. As apelin is an adipocytokine closely associated with diabetes, this study explored the clinical significance of serum apelin levels in patients with type 2 DPN before and after treatment.

METHODS

In total, 44 patients with T2DM without DPN (non-DPN group), 41 patients with DPN who received antihyperglycemic treatment (DPN-A group), 44 patients with DPN who received antihyperglycemic treatment combined with nutritional neurotherapy (DPN-B group), and 40 healthy control individuals (NC group) were selected continuously enrolled in the present study. Enzyme-linked immunosorbent assays (ELISA) were performed to determine serum levels of apelin and tumor necrosis factor-α (TNF-α). Related apelin, fasting blood glucose (FBG), glycosylated hemoglobin A1c, TNF-α, body mass index, fasting C peptide, and nerve conduction velocity (NCV) were recorded in each group before and after treatment.

RESULTS

Serum levels of apelin and TNF-α were higher in patients with diabetes than those in the NC group, as well as in the DPN group as compared to the non-DPN group; furthermore, some NCV values were significantly reduced in the DPN group. After treatment, the serum levels of apelin, TNF-α, and FBG reduced in patients with diabetes; moreover, apelin levels were found significantly lower in the DPN-B group as compared to the DPN-A group, while some NCV values significantly increased in the DPN-B group. Apelin was negatively correlated with part of NCV values and positively correlated with TNF-α and FBG (P < .01).

CONCLUSION

Our results show that the increase in serum apelin levels is an important clinical reference index for DPN, while a decrease indicates that the DPN treatment is effective.

Circular RNA-ZNF532 regulates diabetes-induced retinal pericyte degeneration and vascular dysfunction

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults. Vascular pericyte degeneration is the predominant clinical manifestation of DR, yet the mechanism governing pericyte degeneration is poorly understood. Circular RNAs (circRNAs) play important roles in multiple biological processes and disease progression. Here, we investigated the role of circRNA in pericyte biology and diabetes-induced retinal vascular dysfunction. cZNF532 expression was upregulated in pericytes under diabetic stress, in the retinal vessels of a diabetic murine model, and in the vitreous humor of diabetic patients. cZNF532 silencing reduced the viability, proliferation, and differentiation of pericytes and suppressed the recruitment of pericytes toward endothelial cells in vitro. cZNF532 regulated pericyte biology by acting as a miR-29a-3p sponge and inducing increased expression of NG2, LOXL2, and CDK2. Knockdown of cZNF532 or overexpression of miR-29a-3p aggravated streptozotocin-induced retinal pericyte degeneration and vascular dysfunction. By contrast, overexpression of cZNF532 or inhibition of miR-29a-3p ameliorated human diabetic vitreous-induced retinal pericyte degeneration and vascular dysfunction. Collectively, these data identify a circRNA-mediated mechanism that coordinates pericyte biology and vascular homeostasis in DR. Induction of cZNF532 or antagonism of miR-29a-3p is an exploitable therapeutic approach for the treatment of DR.

The Role of Apelin/APJ in a Mouse Model of Oxygen-induced Retinopathy

Purpose

The aim of this study was to investigate apelin and its potential neovascularization role in retinopathy of prematurity (ROP) along with the inhibitory effects of its antagonist.

Methods

We used an oxygen-induced retinopathy (OIR) mouse model to explore the progress of ROP. Apelin and angiotensin receptor-like 1 APJ expressions were examined in the retina using immunohistochemistry, quantitative polymerase chain reaction, and Western blot analysis. Additionally, the retina was examined by whole-mount staining to evaluate the retinal vessel area, vessel density, capillary width, and the number and length of tip cells. The expression of the phosphorylated mTOR (p-mTOR), p-PI3K/Akt, and p-Erk signaling pathway was also evaluated using Western blot analysis.

Results

Apelin promoted the development of superficial and deep retinal blood vessels, especially for tip cells during the physical development of retinal vessels. Additionally, apelin stimulated the density of the peripheral retinal zone vessels in OIR mice. The apelin and APJ expression levels significantly increased for the OIR model during their hypoxic phase. Next, we found that apelin mRNA levels in the OIR mice peaked at six hours after return to ambient conditions at P12, whereas the APJ mRNA levels peaked later at P17. Furthermore, the expression of p-mTOR, p-Akt, and p-Erk were all up-regulated in OIR mice whereas F13A suppressed them instead.

Conclusions

Our results suggest that apelin/APJ signaling pathway is a key factor for hypoxia-induced pathologic angiogenesis, which is a very promising new target for the treatment of ROP.

Emergence of Neuronal Diversity during Vertebrate Brain Development

Neurogenesis comprises many highly regulated processes including proliferation, differentiation, and maturation. However, the transcriptional landscapes underlying brain development are poorly characterized. We describe a developmental single-cell catalog of ∼220,000 zebrafish brain cells encompassing 12 stages from embryo to larva. We characterize known and novel gene markers for ∼800 clusters and provide an overview of the diversification of neurons and progenitors across these time points. We also introduce an optimized GESTALT lineage recorder that enables higher expression and recovery of Cas9-edited barcodes to query lineage segregation. Cell type characterization indicates that most embryonic neural progenitor states are transitory and transcriptionally distinct from neural progenitors of post-embryonic stages. Reconstruction of cell specification trajectories reveals that late-stage retinal neural progenitors transcriptionally overlap cell states observed in the embryo. The zebrafish brain development atlas provides a resource to define and manipulate specific subsets of neurons and to uncover the molecular mechanisms underlying vertebrate neurogenesis.

Pharmacological Advances in the Treatment of Age-related Macular Degeneration

Age-related macular degeneration is an acquired degenerative disease that is responsible for severe loss of vision in elderly people. There are two types: dry age-related macular degeneration and wet age-related macular degeneration. Its treatment has been improved and tries to be tailored in the future. The aim of this review is to summarize the pharmacological advances in the treatment of age-related macular degeneration. Regarding dry AMD, there is no effective treatment to reduce its progression. However, some molecules such as lampalizumab and eculizumab were under investigation, although they have shown low efficacy. Herein, in an attempt to prevent dry AMD progression, the most important studies suggested increasing the antioxidants intake and quitting the smoke habit. On the other hand, wet AMD has more developed treatment. Nowadays, the gold standard treatment is anti-VEGF injections. However, more effective molecules are currently under investigation. There are different molecules under research for dry AMD and wet AMD. This fact could help us treat our patients with more effective and lasting drugs but more clinical trials and safety studies are required in order to achieve an optimal treatment.

Retinal endothelial cell phenotypic modifications during experimental autoimmune uveitis: a transcriptomic approach

BACKGROUND

Blood-retinal barrier cells are known to exhibit a massive phenotypic change during experimental autoimmune uveitis (EAU) development. In an attempt to investigate the mechanisms of blood-retinal barrier (BRB) breakdown at a global level, we studied the gene regulation of total retinal cells and retinal endothelial cells during non-infectious uveitis.

METHODS

Retinal endothelial cells were isolated by flow cytometry either in Tie2-GFP mice (CD31+ CD45- GFP+ cells), or in wild type C57BL/6 mice (CD31+ CD45- endoglin+ cells). EAU was induced in C57BL/6 mice by adoptive transfer of IRBP1-20-specific T cells. Total retinal cells and retinal endothelial cells from naïve and EAU mice were sorted and their gene expression compared by RNA-Seq. Protein expression of selected genes was validated by immunofluorescence on retinal wholemounts and cryosections and by flow cytometry.

RESULTS

Retinal endothelial cell sorting in wild type C57BL/6 mice was validated by comparative transcriptome analysis with retinal endothelial cells sorted from Tie2-GFP mice, which express GFP under the control of the endothelial-specific receptor tyrosine kinase promoter Tie2. RNA-Seq analysis of total retinal cells mainly brought to light upregulation of genes involved in antigen presentation and T cell activation during EAU. Specific transcriptome analysis of retinal endothelial cells allowed us to identify 82 genes modulated in retinal endothelial cells during EAU development. Protein expression of 5 of those genes (serpina3n, lcn2, ackr1, lrg1 and lamc3) was validated at the level of inner BRB cells.

CONCLUSION

Those data not only confirm the involvement of known pathogenic molecules but further provide a list of new candidate genes and pathways possibly implicated in inner BRB breakdown during non-infectious posterior uveitis.

An improved method for establishment of murine retinal detachment model and its 3D vascular evaluation

Retinal detachment (RD) results in disruption of retinal physiology and visual function. Although surgical intervention has been well-developed to restore the retinal anatomic structure, post-op progression of visual function decline is prominent in a large proportion of patients. Therefore, the establishment of a disease model that accurately mimics RD pathogenesis is crucial to mechanistic study and drug screening. General protocols to induce RD in mice are frequently associated with complications leading to model instability and reduced reproducibility. In this study, we established a stable and reproducible mice RD model with a detached area of over 90% and rare complications. Briefly, the modified method was realized by vitreous humor extraction to reduce intraocular pressure, followed by directly-visible hyaluronic acid injection into subretinal space. The detachment of retina was confirmed by fundus photography, and progressive thinning of the outer nuclear layer (ONL) was determined by HE staining. Apoptotic signals were prominent in the ONL. Consistently, visual function was significantly compromised as determined by ERG. Moreover, retinal vasculature appeared to remodel and acquired winding, twisted and dilated structures illustrated by 3D reconstruction. In addition, activation of Müller cells and microglia, and infiltration of blood-derived macrophages were detected locally. Collectively, we have established a modified protocol to model RD with increased stability, reproducibility and fewer complications, and 3D high-resolution imaging and reconstruction of vasculature could provide new tools to evaluate this model.

What is normal? Apelin and VEGFA, drivers of tumor vessel abnormality

In this issue of EMBO Molecular Medicine, Uribesalgo and coworkers show that high Apelin expression correlates with poor survival in advanced breast (MMTV‐NeuT) and lung (KRAS^G12D) murine tumor models as well as in breast and lung cancer in humans. Combining Apelin inhibition (genetically or using an inactive Apelin agonist) with anti‐angiogenic therapy using different small molecular weight kinase inhibitors (sunitinib, axitinib) led to marked delay in breast cancer growth in mice. The vasculature in Apelin‐targeted cancer showed normalized features including improved perfusion and reduced leakage. These important data provide a strong incentive to target Apelin in human cancer treatment.

Single Cell RNA Sequencing Identifies HSPG2 and APLNR as Markers of Endothelial Cell Injury in Systemic Sclerosis Skin

Objective: The mechanisms that lead to endothelial cell (EC) injury and propagate the vasculopathy in Systemic Sclerosis (SSc) are not well understood. Using single cell RNA sequencing (scRNA-seq), our goal was to identify EC markers and signature pathways associated with vascular injury in SSc skin.

Methods: We implemented single cell sorting and subsequent RNA sequencing of cells isolated from SSc and healthy control skin. We used t-distributed stochastic neighbor embedding (t-SNE) to identify the various cell types. We performed pathway analysis using Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA). Finally, we independently verified distinct markers using immunohistochemistry on skin biopsies and qPCR in primary ECs from SSc and healthy skin.

Results: By combining the t-SNE analysis with the expression of known EC markers, we positively identified ECs among the sorted cells. Subsequently, we examined the differential expression profile between the ECs from healthy and SSc skin. Using GSEA and IPA analysis, we demonstrated that the SSc endothelial cell expression profile is enriched in processes associated with extracellular matrix generation, negative regulation of angiogenesis and epithelial-to-mesenchymal transition. Two of the top differentially expressed genes, HSPG2 and APLNR, were independently verified using immunohistochemistry staining and real-time qPCR analysis.

Conclusion: ScRNA-seq, differential gene expression and pathway analysis revealed that ECs from SSc patients show a discrete pattern of gene expression associated with vascular injury and activation, extracellular matrix generation and negative regulation of angiogenesis. HSPG2 and APLNR were identified as two of the top markers of EC injury in SSc.

Molecular Beacon Gold Nanosensors for Leucine-Rich Alpha-2-Glycoprotein-1 Detection in Pathological Angiogenesis

Leucine-rich alpha-2-glycoprotein-1 (Lrg1) is an emerging biomarker for angiogenesis. Its expression in ocular tissues is up-regulated in both human patients with proliferative diabetic retinopathy and rodent models of pathological angiogenesis. However, there is no existing sensor that allows visualization and monitoring of Lrg1 expression noninvasively and in real time. Herein, we report a nucleic acid-gold nanorod-based nanosensor for the noninvasive monitoring of cellular Lrg1 expression in angiogenesis. Specifically, this platform is constructed by covalently conjugating molecular beacons onto gold nanorods, which prequench the fluorophores on the molecular beacons. Upon intracellular entry and endosomal escape, the complexes interact with cellular Lrg1 mRNA through hybridization of the loop area of the molecular beacons. This complexation distances the fluorophores from nanorod and restores the prequenched fluorescence. The reliability of this platform is confirmed by examining the increased Lrg1 expression in migrating keratinocytes and the Lrg1 gene changes in different postnatal stages of mouse retinal vasculature growth in the mouse retina model.

Nanosurfaces modulate the mechanism of peri-implant endosseous healing by regulating neovascular morphogenesis

Nanosurfaces have improved clinical osseointegration by increasing bone/implant contact. Neovascularization is considered an essential prerequisite to osteogenesis, but no previous reports to our knowledge have examined the effect of surface topography on the spatio-temporal pattern of neovascularization during peri-implant healing. We have developed a cranial window model to study peri-implant healing intravitally over clinically relevant time scales as a function of implant topography. Quantitative intravital confocal imaging reveals that changing the topography (but not chemical composition) of an implant profoundly affects the pattern of peri-implant neovascularization. New vessels develop proximal to the implant and the vascular network matures sooner in the presence of an implant nanosurface. Accelerated angiogenesis can lead to earlier osseointegration through the delivery of osteogenic precursors to, and direct formation of bone on, the implant surface. This study highlights a critical aspect of peri-implant healing, but also informs the biological rationale for the surface design of putative endosseous implant materials.

Retinal vasculature development in health and disease

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

An apelin receptor antagonist prevents pathological retinal angiogenesis with ischemic retinopathy in mice

Pathological retinal angiogenesis is caused by the progression of ischemic retinal diseases and can result in retinal detachment and irreversible blindness. This neovascularization is initiated from the retinal veins and their associated capillaries and involves the overgrowth of vascular endothelial cells. Since expression of the apelin receptor (APJ) is restricted to the veins and proliferative endothelial cells during physiological retinal angiogenesis, in the present study, we investigated the effect of APJ inhibition on pathological retinal angiogenesis in a mouse model of oxygen-induced retinopathy (OIR). In vitro experiments revealed that ML221, an APJ antagonist, suppressed cultured-endothelial cell proliferation in a dose-dependent manner. Intraperitoneal administration of ML221 inhibited pathological angiogenesis but enhanced the recovery of normal vessels into the ischemic regions in the retina of the OIR model mice. ML221 did not affect the expression levels of vascular endothelial growth factor (VEGF) and its receptor (VEGFR2) in the retina. APJ was highly expressed in the endothelial cells within abnormal vessels but was only detected in small amounts in morphologically normal vessels. These results suggest that APJ inhibitors selectively prevent pathological retinal angiogenesis and that the drugs targeting APJ may be new a candidate for treating ischemic retinopathy.

Do endothelial cells dream of eclectic shape?

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

Expression of neonatal Fc receptor in the eye

PURPOSE

The neonatal Fc receptor (FcRn) plays a critical role in the homeostasis and degradation of immunoglobulin G (IgG). It mediates the transport of IgG across epithelial cell barriers and recycles IgG in endothelial cells back into the bloodstream. These functions critically depend on the binding of FcRn to the Fc domain of IgG. The half-life and distribution of intravitreally injected anti-VEGF molecules containing IgG-Fc domains might therefore be affected by FcRn expressed in the eye. In order to establish whether FcRn-Fc(IgG) interactions may occur in the eye, we studied the mRNA and protein distribution of FcRn in postmortem ocular tissue.

METHODS

We used qPCR to study mRNA expression of the transmembrane chain of FcRn (FCGRT) in retina, optic nerve, RPE/choroid plexus, ciliary body/iris plexus, lens, cornea, and conjunctiva isolated from mouse, rat, pig, and human postmortem eyes and used immunohistochemistry to determine the pattern of FcRn expression in FCGRT-transgenic mouse and human eyes.

RESULTS

In all four tested species, Fcgrt mRNA was expressed in the retina, RPE/choroid, and the ciliary body/iris, while immunohistochemistry documented FcRn protein expression in the ciliary body epithelium, macrophages, and endothelial cells in the retinal and choroidal vasculature.

CONCLUSIONS

Our results demonstrate that FcRn has the potential to interact with IgG-Fc domains in the ciliary epithelium and retinal and choroidal vasculature, which might affect the half-life and distribution of intravitreally injected Fc-carrying molecules.

ERK1/2 mediates lung adenocarcinoma cell proliferation and autophagy induced by apelin-13

The aim of this study was to investigate the role of apelin in the cell proliferation and autophagy of lung adenocarcinoma. The over-expression of APJ in lung adenocarcinoma was detected by immunohistochemistry, while plasma apelin level in lung cancer patients was measured by enzyme-linked immunosorbent assay. Our findings revealed that apelin-13 significantly increased the phosphorylation of ERK1/2, the expression of cyclin D1, microtubule-associated protein 1 light chain 3A/B (LC3A/B), and beclin1, and confirmed that apelin-13 promoted A549 cell proliferation and induced A549 cell autophagy via ERK1/2 signaling. Moreover, there are pores on the surface of human lung adenocarcinoma cell line A549 and apelin-13 causes cell surface smooth and glossy as observed under atomic force microscopy. These results suggested that ERK1/2 signaling pathway mediates apelin-13-induced lung adenocarcinoma cell proliferation and autophagy. Under our experimental condition, autophagy associated with 3-methyladenine was not involved in cell proliferation.

The apelin receptor APJ: journey from an orphan to a multifaceted regulator of homeostasis

The apelin receptor (APJ; gene symbol APLNR) is a member of the G protein-coupled receptor gene family. Neural gene expression patterns of APJ, and its cognate ligand apelin, in the brain implicate the apelinergic system in the regulation of a number of physiological processes. APJ and apelin are highly expressed in the hypothalamo-neurohypophysial system, which regulates fluid homeostasis, in the hypothalamic-pituitary-adrenal axis, which controls the neuroendocrine response to stress, and in the forebrain and lower brainstem regions, which are involved in cardiovascular function. Recently, apelin, synthesised and secreted by adipocytes, has been described as a beneficial adipokine related to obesity, and there is growing awareness of a potential role for apelin and APJ in glucose and energy metabolism. In this review we provide a comprehensive overview of the structure, expression pattern and regulation of apelin and its receptor, as well as the main second messengers and signalling proteins activated by apelin. We also highlight the physiological and pathological roles that support this system as a novel therapeutic target for pharmacological intervention in treating conditions related to altered water balance, stress-induced disorders such as anxiety and depression, and cardiovascular and metabolic disorders.

LRG1 promotes angiogenesis by modulating endothelial TGF-β signalling

Aberrant neovascularization contributes to diseases such as cancer, blindness and atherosclerosis, and is the consequence of inappropriate angiogenic signalling. Although many regulators of pathogenic angiogenesis have been identified, our understanding of this process is incomplete. Here we explore the transcriptome of retinal microvessels isolated from mouse models of retinal disease that exhibit vascular pathology, and uncover an upregulated gene, leucine-rich alpha-2-glycoprotein 1 (Lrg1), of previously unknown function. We show that in the presence of transforming growth factor-β1 (TGF-β1), LRG1 is mitogenic to endothelial cells and promotes angiogenesis. Mice lacking Lrg1 develop a mild retinal vascular phenotype but exhibit a significant reduction in pathological ocular angiogenesis. LRG1 binds directly to the TGF-β accessory receptor endoglin, which, in the presence of TGF-β1, results in promotion of the pro-angiogenic Smad1/5/8 signalling pathway. LRG1 antibody blockade inhibits this switch and attenuates angiogenesis. These studies reveal a new regulator of angiogenesis that mediates its effect by modulating TGF-β signalling.