Myeloid-Specific Blockade of Notch Signaling Attenuates Choroidal Neovascularization through Compromised Macrophage Infiltration and Polarization in Mice

Angiogenic and Fibrogenic Dual-effect of Gremlin1 on Proliferative Diabetic Retinopathy

Ocular angiogenic diseases, such as proliferative diabetic retinopathy (PDR), are often characterized by pathological new vessels and fibrosis formation. Anti-vascular endothelial growth factor (VEGF) therapy, despite of its efficiency to inhibit new vessels, has limitations, including drug resistance and retinal fibrosis. Here, we identified that Gremlin1, a novel angiogenesis and fibrosis inducer, was secreted from Müller glial cells, and its expression increased in the vitreous fluid from patients with PDR. Mechanistically, Gremlin1 triggered angiogenesis by promoting endothelial-mesenchymal transition via the EGFR/RhoA/ROCK pathway. In addition, Gremlin1 activated microglia to present profibrotic and fibrogenic properties. Further, anti-Gremlin1 antibody inhibited ocular angiogenesis and microglia fibrosis in mouse models. Collectively, Gremlin1 could be a potential therapeutic target in the treatment of ocular angiogenic diseases.

Antibody blockade of Jagged1 attenuates choroidal neovascularization

Antibody-based blocking of vascular endothelial growth factor (VEGF) reduces choroidal neovascularization (CNV) and retinal edema, rescuing vision in patients with neovascular age-related macular degeneration (nAMD). However, poor response and resistance to anti-VEGF treatment occurs. We report that targeting the Notch ligand Jagged1 by a monoclonal antibody reduces neovascular lesion size, number of activated phagocytes and inflammatory markers and vascular leakage in an experimental CNV mouse model. Additionally, we demonstrate that Jagged1 is expressed in mouse and human eyes, and that Jagged1 expression is independent of VEGF signaling in human endothelial cells. When anti-Jagged1 was combined with anti-VEGF in mice, the decrease in lesion size exceeded that of either antibody alone. The therapeutic effect was solely dependent on blocking, as engineering antibodies to abolish effector functions did not impair the therapeutic effect. Targeting of Jagged1 alone or in combination with anti-VEGF may thus be an attractive strategy to attenuate CNV-bearing diseases.

Microglia-Derived Spp1 Promotes Pathological Retinal Neovascularization via Activating Endothelial Kit/Akt/mTOR Signaling

Pathological retinal neovascularization (RNV) is the main character of ischemic ocular diseases, which causes severe visual impairments. Though retinal microglia are well acknowledged to play important roles in both physiological and pathological angiogenesis, the molecular mechanisms by which microglia communicates with endothelial cells (EC) remain unknown. In this study, using single-cell RNA sequencing, we revealed that the pro-inflammatory secreted protein Spp1 was the most upregulated gene in microglia in the mouse model of oxygen-induced retinopathy (OIR). Bioinformatic analysis showed that the expression of Spp1 in microglia was respectively regulated via nuclear factor-kappa B (NF-κB) and hypoxia-inducible factor 1α (HIF-1α) pathways, which was further confirmed through in vitro assays using BV2 microglia cell line. To mimic microglia-EC communication, the bEnd.3 endothelial cell line was cultured with conditional medium (CM) from BV2. We found that adding recombinant Spp1 to bEnd.3 as well as treating with hypoxic BV2 CM significantly enhanced EC proliferation and migration, while Spp1 neutralizing blocked those CM-induced effects. Moreover, RNA sequencing of BV2 CM-treated bEnd.3 revealed a significant downregulation of Kit, one of the type III tyrosine kinase receptors that plays a critical role in cell growth and activation. We further revealed that Spp1 increased phosphorylation and expression level of Akt/mTOR signaling cascade, which might account for its pro-angiogenic effects. Finally, we showed that intravitreal injection of Spp1 neutralizing antibody attenuated pathological RNV and improved visual function. Taken together, our work suggests that Spp1 mediates microglia-EC communication in RNV via activating endothelial Kit/Akt/mTOR signaling and is a potential target to treat ischemic ocular diseases.

RO4929097, a Selective γ-Secretase Inhibitor, Inhibits Subretinal Fibrosis Via Suppressing Notch and ERK1/2 Signaling in Laser-Induced Mouse Model

Purpose

This study aimed to explore whether RO4929097 (RO), a specific γ-secretase inhibitor, could inhibit the subretinal fibrosis in laser-induced mouse model and the relevant molecular mechanisms.

Methods

Male C57BL/6J mice were used to produce choroidal neovascularization (CNV) and subretinal fibrosis by laser photocoagulation, and RO was administered intravitreally 1 day after laser induction. The sizes of CNV and subretinal fibrosis were measured and quantified in both 2D and 3D constructions. The ARPE-19 cell line and primary human RPE (phRPE) cells were treated with TGFβ1, in combination with or without RO, to examine Notch related molecules, epithelial mesenchymal transition (EMT), cell viability, migration, and contractile function, as well as the crosstalk between Notch and other EMT relevant signaling pathways.

Results

Intravitreal injection of RO reduced the sizes of both CNV and subretinal fibrosis in laser-induced young and old mice at day 7 and day 14 after laser induction. Moreover, EMT and Notch activation in RPE-choroid complexes from laser-induced mice were significantly attenuated by RO. In vitro, TGFβ1 activated Notch signaling and induced EMT in ARPE-19 cells, accompanied by enhanced EMT-related function, which were inhibited by RO. The inhibition of RO on EMT was further confirmed in TGFβ1-treated phRPE cells. Blockage of Notch signaling by RO could inhibit ERK1/2 signaling; whereas ERK1/2 inhibition had no effect on Notch. The action of RO was independent of Smad2/3 or p38, and co-inhibition of Notch and Smad2/3 showed synergistic effect on EMT inhibition.

Conclusions

RO exerts its antifibrotic effect by directly inhibiting Notch signaling and indirectly suppressing ERK1/2 signaling. Targeting Notch signaling might provide a therapeutic strategy in prevention and treatment of subretinal fibrosis in neovascular age-related macular degeneration (nAMD).

Receptor-selective interleukin-4 mutein attenuates laser-induced choroidal neovascularization through the regulation of macrophage polarization in mice

Macrophage polarization has been recognized as an important inflammatory regulator in choroidal neovascularization (CNV). However, the mechanisms regulating macrophage activation and polarization, as well as their effects on angiogenesis and CNV, have not yet been elucidated. IL-4 is implicated in macrophage activation and exerts different functions in various diseases through several receptors. In the current study, the effect of IL-4 muteins on CNV was investigated in vivo. CNV was induced by laser coagulation in wild type mice. IL-4 muteins were recombined into adenoviruses and injected into mice via the tail vein. To evaluate CNV, fluorescein fundus angiography and optical coherence tomography were performed on day 7 after coagulation. Quantitative PCR, western blotting and immunofluorescence staining were used to assess the levels of inflammatory markers. AdIL-4/Q116E, an adenovirus-expressed recombinant IL-4 mutein, selectively activated macrophages, alleviated laser-induced CNV in mice with reduced expression of M2 macrophages and increased the expression of M1 macrophages. Furthermore, the expression of monocyte to macrophage differentiation-associated and delta-like 4 (Dll4) in CNV lesions was upregulated. Employing AdIL-4/Q116E, a IL-4RI-selective mutein, may serve as a new strategy for CNV therapy. Moreover, the results indicated that Dll4 signaling served an important role in the regulation of macrophage polarization.

Transcriptome Analysis of Choroid and Retina From Tree Shrew With Choroidal Neovascularization Reveals Key Signaling Moieties

Pathological neovascularization in choroid, a leading cause of blindness, is a characteristic of many fundus diseases, such as diabetic retinopathy and age-related macular degeneration. The present study aimed to elucidate the key signaling pathways in choroidal neovascularization (CNV) by analyzing the mRNA profiles of choroid and retina in tree shrews with CNV. We induced choroidal angiogenesis by laser photocoagulation in 15 tree shrews and obtained mRNA profiles of their choroids and retinas by high-throughput transcriptome sequencing. Hierarchical cluster analysis, weighted gene co-expression network analysis (WGCNA), protein-protein interaction (PPI) network analysis, hematoxylin and eosin (HE) staining, CD31 immunohistochemistry (IHC), and reverse transcription quantitative PCR (RT-qPCR) were performed. After laser photocoagulation, we obtained a total of 350 differentially expressed genes (DEGs) in the choroid, including 59 genes in Module-FASN (“ME-FASN”) module and 28 genes in Module-RPL (“ME-RPL”) module. A total of 69 DEGs in retina, including 20 genes in Module-SLC (“ME-SLC”) module. Bioinformatics analysis demonstrated that DEGs in choroid were mainly involved in membrane transport; DEGs in “ME-RPL” were prominent in pathways associated with IgA production, antigen presentation, and cell adhesion molecules (CAMs) signaling. DEGs in “ME-FASN” were involved in fatty acid metabolism and PPAR signaling pathway, while DEGs in “ME-SLC” were involved in GABAergic synapse, neuroactive life receptor interaction, cholinergic synapse, and retrograde endocannabinoid signaling pathway. PPI network analysis demonstrated that the ribosomal protein family genes (RPL31, RPL7, RPL26L1, and RPL19) are key factors of “ME-RPL,” acyl-CoA superfamily genes (ACACA, ACAT1, ACAA2, and ACACB) and FASN are key factors of “ME-FASN” and superfamily of solid carrier genes (SLC17A6, SLC32A1, SLC12A5, and SLC6A1) and complement genes (C4A, C3, and C2) are key factors of “ME-SLC.” In conclusion, the present study discovered the important signal transductions (fatty acid metabolic pathway and CAMs signaling) and genes (ribosomal protein family and the complement system) in tree shrew CNV. We consider that our findings hold implications in unraveling molecular mechanisms that underlie occurrence and development of CNV.

Innate Immunity in Age-Related Macular Degeneration

Multiple lines of investigation have demonstrated that inflammation plays significant roles in etiology of age-related macular degeneration (AMD). Although interventional trials in AMD therapy targeting inflammatory pathways have been conducted, they have not yet been successful and a detailed understanding as to why some have failed is still elusive. One limitation is the relative dearth of information on how immune cells interact with retinal cells to generate AMD phenotypes at each disease stage. Here, we summarize current research evidence and hypotheses regarding potential pathogenic roles of innate immune cells in the eye, which include resident retinal microglia, macrophages derived from infiltrating systemic monocytes, and macrophages resident in the choroid. We relate recent findings regarding the physiology, function, and cellular interactions involving innate immune cells in the retina and choroid to AMD-related processes, including: (1) drusen formation and regression, (2) the onset and spread of degeneration in late atrophic AMD, and (3) the initiation, growth, and exudation of neovascular vessels in late "wet" AMD. Understanding how innate immune cells contribute to specific AMD phenotypes can assist in generating a comprehensive view on the inflammatory etiology of AMD and aid in identifying anti-inflammatory therapeutic strategies and selecting appropriate clinical outcomes for the planned interventions.

Tumor-Associated Macrophages: Protumoral Macrophages in Inflammatory Tumor Microenvironment

Tumor microenvironment consists of malignant and non-malignant cells. The interaction of these dynamic and different cells is responsible for tumor progression at different levels. The non-malignant cells in TME contain cells such as tumor-associated macrophages (TAMs), cancer associated fibroblasts, pericytes, adipocytes, T cells, B cells, myeloid-derived suppressor cells (MDSCs), tumor-associated neutrophils (TANs), dendritic cells (DCs) and Vascular endothelial cells. TAMs are abundant in most human and murine cancers and their presence are associated with poor prognosis. The major event in tumor microenvironment is macrophage polarization into tumor-suppressive M1 or tumor-promoting M2 types. Although much evidence suggests that TAMS are primarily M2-like macrophages, the mechanism responsible for polarization into M1 and M2 macrophages remain unclear. TAM contributes cancer cell motility, invasion, metastases and angiogenesis. The relationship between TAM and tumor cells lead to used them as a diagnostic marker, therapeutic target and prognosis of cancer. This review presents the origin, polarization, role of TAMs in inflammation, metastasis, immune evasion and angiogenesis as well as they can be used as therapeutic target in variety of cancer cells. It is obvious that additional substantial and preclinical research is needed to support the effectiveness and applicability of this new and promising strategy for cancer treatment.

Triptolide attenuates laser-induced choroidal neovascularization via M2 macrophage in a mouse model

PURPOSE

To investigate whether triptolide has inhibitory effects on the development of choroidal neovascularization (CNV), together with its underlying anti-angiogenic mechanisms.

METHODS

CNV was induced in C57BL/6 J mice using laser photocoagulation. Triptolide at concentrations of 0.035 and 0.07 mg/kg body weight (BW) or the same volume of phosphate-buffered saline (PBS) was intraperitoneally injected into mice 2 days before laser photocoagulation, which was continued daily till the end of the experiment. CNV areas were measured on day 7. The numbers of M1, M2, and F4/80⁺ macrophages were detected on day 1, 3, and 7 in each group. The levels of vascular endothelial growth factor (VEGF) and inflammatory molecules,including intercellular adhesion molecule (ICAM)-1,tumor necrosis factor (TNF)-α, and interleukin 6 (IL-6) were determined by enzyme-linked immunosorbent assay. Cell proliferation, migration, and tube-formation assays were performed in vitro.

RESULTS

Triptolide at doses of 0.035 mg/kg BW (66,562 ± 39,253 μm², n = 5, P＜0.05) and 0.07 mg/kg BW (37,271 ± 25,182 μm², n = 5, P＜0.001) significantly reduced CNV areas by 54.9 and 74.8 %, respectively, compared with PBS control (147,699 ± 112,900 μm², n = 5) in a dose-dependent manner. Protein levels of VEGF, ICAM-1, TNF-α, and IL-6 in the RPE-choroid-sclera complex were significantly downregulated by triptolide treatment on day 3, which was in accordance with the reduced number of infiltrated F4/80⁺ macrophages and the reduced ratio of M2/F4/80⁺ macrophages. However, no toxic effects of triptolide on the retina or other systemic organs were observed. In addition, triptolide treatment exerted inhibitory effects on cell proliferation, migration, and tube formation in vitro in a concentration-dependent manner.

CONCLUSIONS

Triptolide has therapeutic potential in CNV owing to its anti-angiogenic effect.

Notch Signaling in Macrophages in the Context of Cancer Immunity

Macrophages play both tumor-suppressing and tumor-promoting roles depending on the microenvironment. Tumor-associated macrophages (TAMs) are often associated with poor prognosis in most, but not all cancer. Understanding how macrophages become TAMs and how TAMs interact with tumor cells and shape the outcome of cancer is one of the key areas of interest in cancer therapy research. Notch signaling is involved in macrophage activation and its effector functions. Notch signaling has been indicated to play roles in the regulation of macrophage activation in pro-inflammatory and wound-healing processes. Recent evidence points to the involvement of canonical Notch signaling in the differentiation of TAMs in a breast cancer model. On the other hand, hyperactivation of Notch signaling specifically in macrophages in tumors mass has been shown to suppress tumor growth in an animal model of cancer. Investigations into how Notch signaling is regulated in TAMs and translates into pro- or anti-tumor functions are still largely in their infancy. Therefore, in this review, we summarize the current understanding of the conflicting roles of Notch signaling in regulating the effector function of macrophages and the involvement of Notch signaling in TAM differentiation and function. Furthermore, how Notch signaling in TAMs affects the tumor microenvironment is reviewed. Finally, the direct or indirect cross-talk among TAMs, tumor cells and other cells in the tumor microenvironment via Notch signaling is discussed along with the possibility of its clinical application. Investigations into Notch signaling in macrophages may lead to a more effective way for immune intervention in the treatment of cancer in the future.

Lactate-activated macrophages induced aerobic glycolysis and epithelial-mesenchymal transition in breast cancer by regulation of CCL5-CCR5 axis: a positive metabolic feedback loop

Aberrant energy metabolism is critical for cancer progression. Tumor-associated macrophages (TAMs) can stimulate tumor angiogenesis and enhance cancer metastasis; however, the metabolic interaction between cancer cells and macrophages characterized by lactate shuttles remains unclear. Here, we showed that lactate activated human macrophages to a TAM-like phenotype and stimulated the secretion of CCL5 by activation of Notch signaling in macrophages. Reciprocally, CCL5 increased cell migration, induced cancer cell EMT, and promoted aerobic glycolysis in breast cancer cells, suggesting a positive metabolic feedback loop in the co-culture system. Inhibition of CCR5, the cognate receptor of CCL5, or neutralization of CCL5, broke the metabolic loop and decreased cancer cell migration and EMT. Inhibition of aerobic glycolysis significantly reduced breast cancer cell EMT, indicated that aerobic glycolysis was necessary for the invasive phenotype of cancer cells. We further showed that TGF-β signaling regulated the expression of CCR5 in the co-culture system, and CCL5 induced glycolysis by mediation of AMPK signaling. The expression of CCL5-CCR5 axis was highly associated with macrophage infiltration, TGF-β and p-AMPK in clinical samples. CCL5-CCR5 axis promoted breast cancer metastasis in vivo. Our findings suggested a pivotal role of CCL5-CCR5 axis in the metabolic communication between cancer cells and macrophages.

Microenvironmental regulation of tumour angiogenesis

Tumours display considerable variation in the patterning and properties of angiogenic blood vessels, as well as in their responses to anti-angiogenic therapy. Angiogenic programming of neoplastic tissue is a multidimensional process regulated by cancer cells in concert with a variety of tumour-associated stromal cells and their bioactive products, which encompass cytokines and growth factors, the extracellular matrix and secreted microvesicles. In this Review, we discuss the extrinsic regulation of angiogenesis by the tumour microenvironment, highlighting potential vulnerabilities that could be targeted to improve the applicability and reach of anti-angiogenic cancer therapies.

Induced neural stem cells modulate microglia activation states via CXCL12/CXCR4 signaling

We previously reported that induced neural stem cells (iNSCs) directly reprogrammed from mouse embryonic fibroblasts can expand and differentiate into neurons, astrocytes and oligodendrocytes. Whether iNSCs have immunoregulatory properties in addition to facilitating cell replacement remains uncertain. In this study, we aimed to characterize the immunomodulatory effects of iNSCs on the activation states of microglia and to elucidate the mechanisms underlying these effects. Using a mouse model of closed head injury (CHI), we observed that iNSC grafts decreased the levels of ED1⁺/Iba1⁺ and TNF-α⁺/Iba1⁺ microglia but increased the levels of IGF1⁺/Iba1⁺ microglia in the injured cortex. Subsequently, using a Transwell co-culture system, we discovered that iNSCs could modulate LPS-pretreated microglia phenotypes in vitro via CXCL12/CXCR4 signaling, which we demonstrated through the administration of the CXCR4 antagonist AMD3100 and CXCR4-specific siRNA treatment. An in vivo loss-of-function study also revealed that iNSC grafts regulated the behavior of resident microglia via CXCL12/CXCR4 signaling, influencing their activation state such that they promoted neurological functional recovery and neuron survival. Furthermore, the beneficial effects of iNSC transplantation were significantly diminished by CXCR4 knockdown. In short, iNSCs have the potential to influence microglia activation and the acquisition of neuroprotective phenotypes via CXCL12/CXCR4 signaling.