Identifying Hyperreflective Foci in Diabetic Retinopathy via VEGF-Induced Local Self-Renewal of CX3CR1+ Vitreous Resident Macrophages

Liquid Biopsy for Proliferative Diabetic Retinopathy: Single-Cell Transcriptomics of Human Vitreous Reveals Inflammatory T-Cell Signature

Purpose

Current therapies for proliferative diabetic retinopathy (PDR) do not specifically target VEGF-independent, cell-type-specific processes that lead to vision loss, such as inflammatory pathways. This study aimed to identify targetable cell types and corresponding signaling pathways by elucidating the single-cell landscape of the vitreous of patients with PDR.

Design

Case series.

Subjects

Vitreous and peripheral blood obtained from 5 adult patients (6 eyes) undergoing pars plana vitrectomy for vision-threatening PDR.

Methods

Single-cell RNA sequencing (scRNA-seq) was performed on vitreous cells obtained from diluted cassette washings during vitrectomy from 6 eyes and peripheral blood mononuclear cells (PBMCs, n = 5). Droplet-based scRNA-seq was performed using the Chromium 10x platform to obtain single-cell transcriptomes. Differences in tissue compartments were analyzed with gene ontology enrichment of differentially expressed genes and an unbiased ligand-receptor interaction analysis.

Main Outcome Measures

Single-cell transcriptomic profiles of vitreous and peripheral blood.

Results

Transcriptomes from 13 675 surgically harvested vitreous cells and 22 636 PBMCs were included. Clustering revealed 4 cell states consistently across all eyes with representative transcripts for T cells (CD2, CD3D, CD3E, and GZMA), B cells (CD79A, IGHM, MS4A1 (CD20), and HLA-DRA), myeloid cells (LYZ, CST3, AIF1, and IFI30), and neutrophils (BASP1, CXCR2, S100A8, and S100A9). Most vitreous cells were T cells (91.6%), unlike the peripheral blood (46.2%), whereas neutrophils in the vitreous were essentially absent. The full repertoire of adaptive T cells including CD4+, CD8+ and T regulatory cells (Treg) and innate immune system effectors (i.e., natural killer T cells) was present in the vitreous. Pathway analysis also demonstrated activation of CD4+ and CD8+ memory T cells and ligand-receptor interactions unique to the vitreous.

Conclusions

In the first single-cell transcriptomic characterization of human vitreous in a disease state, we show PDR vitreous is primarily composed of T cells, a critical component of adaptive immunity, with activity and proportions distinct from T cells within the peripheral blood, and neutrophils are essentially absent. These results demonstrate the feasibility of liquid vitreous biopsies via collection of otherwise discarded, diluted cassette washings during vitrectomy to gain mechanistic and therapeutic insights into human vitreoretinal disease.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Heterotypic macrophages/microglia differentially contribute to retinal ischaemia and neovascularisation

AIMS/HYPOTHESIS

Diabetic retinopathy is characterised by neuroinflammation that drives neuronal and vascular degenerative pathology, which in many individuals can lead to retinal ischaemia and neovascularisation. Infiltrating macrophages and activated retina-resident microglia have been implicated in the progression of diabetic retinopathy, although the distinct roles of these immune cells remain ill-defined. Our aim was to clarify the distinct roles of macrophages/microglia in the pathogenesis of proliferative ischaemic retinopathies.

METHODS

Murine oxygen-induced retinopathy is commonly used as a model of ischaemia-induced proliferative diabetic retinopathy (PDR). We evaluated the phenotype macrophages/microglia by immunostaining, quantitative real-time RT-PCR (qRT-PCR), flow cytometry and scRNA-seq analysis. In clinical imaging studies of diabetic retinopathy, we used optical coherence tomography (OCT) and OCT angiography.

RESULTS

Immunostaining, qRT-PCR and flow cytometry showed expression levels of M1-like macrophages/microglia markers (CD80, CD68 and nitric oxide synthase 2) and M2-like macrophages/microglia markers (CD206, CD163 and macrophage scavenger receptor 1) were upregulated in areas of retinal ischaemia and around neo-vessels, respectively. scRNA-seq analysis of the ischaemic retina revealed distinct ischaemia-related clusters of macrophages/microglia that express M1 markers as well as C-C chemokine receptor 2. Inhibition of Rho-kinase (ROCK) suppressed CCL2 expression and reduced CCR2-positive M1-like macrophages/microglia in areas of ischaemia. Furthermore, the area of retinal ischaemia was reduced by suppressing blood macrophage infiltration not only by ROCK inhibitor and monocyte chemoattractant protein-1 antibody but also by GdCl3. Clinical imaging studies of diabetic retinopathy using OCT indicated potential involvement of macrophages/microglia represented by hyperreflective foci in areas of reduced perfusion.

CONCLUSIONS/INTERPRETATION

These results collectively indicated that heterotypic macrophages/microglia differentially contribute to retinal ischaemia and neovascularisation in retinal vascular diseases including diabetic retinopathy. This adds important new information that could provide a basis for a more targeted, cell-specific therapeutic approach to prevent progression to sight-threatening PDR.

Macrophage activation contributes to diabetic retinopathy

Diabetic retinopathy (DR) is recognized as a neurovascular complication of diabetes, and emerging evidence underscores the pivotal role of inflammation in its pathophysiology. Macrophage activation is increasingly acknowledged as a key contributor to the onset and progression of DR. Different populations of macrophages originating from distinct sources contribute to DR-associated inflammation. Retinal macrophages can be broadly categorized into two main groups based on their origin: intrinsic macrophages situated within the retina and vitreoretinal interface and macrophages derived from infiltrating monocytes. The former comprises microglia (MG), perivascular macrophages, and macrophage-like hyalocytes. Retinal MG, as the principal population of tissue-resident population of mononuclear phagocytes, exhibits high heterogeneity and plasticity while serving as a crucial connector between retinal capillaries and synapses. This makes MG actively involved in the pathological processes across various stages of DR. Activated hyalocytes also contribute to the pathological progression of advanced DR. Additionally, recruited monocytes, displaying rapid turnover in circulation, augment the population of retinal macrophages during DR pathogenesis, exerting pathogenic or protective effect based on different subtypes. In this review, we examine novel perspectives on macrophage biology based on recent studies elucidating the diversity of macrophage identity and function, as well as the mechanisms influencing macrophage behavior. These insights may pave the way for innovative therapeutic strategies in the management of DR.

Assessment of intraretinal hyperreflective foci using multimodal imaging in eyes with age-related macular degeneration

PURPOSE

This study aimed to investigate the correspondence between intraretinal hyperreflective foci (IHRF) identified on optical coherence tomography (OCT) B-scans with hyperpigmentation on colour fundus photography (CFP) or hyperreflectivity on infrared reflectance (IR) images in eyes with age-related macular degeneration (AMD).

METHODS

Flash CFP, IR images and OCT B-scans obtained at the same visit were evaluated. Individual IHRF identified on OCT B-scans were assessed for the qualitative presence or absence of a hypotransmission tail into the choroid. The corresponding IR image obtained at the time of OCT acquisition was analysed for the presence or absence of hyperreflectivity in this region. The IR images were manually registered to the CFP image, and CFP images were inspected for the presence or absence of hyperpigmentation at the location of IHRF.

RESULTS

From 122 eyes, a total of 494 IHRF were evaluated. For the primary analysis of qualitative presence or absence of hyperpigmentation on CFP and hyperreflectivity on IR at the locations corresponding to IHRF on OCT, 301 (61.0%) of the IHRFs demonstrated evidence of hyperpigmentation on CFP, while only 115 (23.3%) showed evidence of hyperreflectivity on IR. The qualitative determination of the presence or absence of an abnormality on CFP or IR were significantly different (p < 0.0001). 327 (66.2%) of the IHRF showed hypotransmission, and 80.4% of these IHRF showed hyperpigmentation on CFP, though only 23.9% (p < 0.0001) demonstrated hyperreflectivity on IR.

CONCLUSIONS

Less than two-thirds of IHRF evident on OCT manifest as hyperpigmentation on colour photos, though IHRF with posterior shadowing are more likely to be evident as pigment. IR imaging appears to be even more poorly sensitive for visualizing IHRF.

Association between macrophage-like cell density and ischemia metrics in diabetic eyes

We previously showed that macrophage-like cells (MLCs) are increased in eyes with advanced diabetic retinopathy (DR). Here, we hypothesized that MLC density was correlated with ischemia using optical coherence tomography angiography (OCTA) and ultra-widefield fluorescein angiography (UWF-FA). Treatment-naïve diabetic eyes were prospectively imaged with repeated OCTA (average 5.3 scans per eye) and UWF-FA imaging. OCTA images were registered and averaged to generate a superficial capillary plexus (SCP), deep capillary plexus (DCP), and MLC slab. We calculated geometric perfusion deficit (GPD), vessel length density, and vessel density for the SCP and DCP. MLC density was quantified by two masked graders and averaged. Ischemia on UWF-FA was measured to generate a non-perfusion area (NPA) and index (NPI). Since MLC density was non-parametrically distributed, MLC density was correlated with ischemia metrics using Spearman correlations. Forty-five treatment-naïve eyes of 45 patients (59 ± 12 years of age; 56% female) were imaged. We included 6 eyes with no DR, 7 eyes with mild non-proliferative DR (NPDR), 22 moderate NPDR, 4 severe NPDR, and 6 PDR eyes. MLC density between graders was highly correlated (r = 0.9592, p < 0.0001). MLC density was correlated with DCP GPD (r = 0.296, p = 0.049), but no other OCTA ischemia metrics. MLC density was also correlated with UWF-FA NPA (r = 0.330, p = 0.035) and NPI (r = 0.332, p = 0.034). MLC density was correlated with total ischemia on UWF-FA and local DCP GPD. Since both UWF-FA and DCP non-perfusion are associated with higher risk for DR progression, MLC density could be another potential biomarker for DR progression.

Proliferation of monocytes and macrophages in homeostasis, infection, injury, and disease

Monocytes (Mo) and macrophages (Mφ) play important roles in the function of tissues, organs, and systems of all animals during homeostasis, infection, injury, and disease. For decades, conventional wisdom has dictated that Mo and Mφ are end-stage cells that do not proliferate and that Mφ accumulation in tissues is the result of infiltration of Mo from the blood and subsequent differentiation to Mφ. However, reports from the early 1900s to the present describe evidence of Mo and Mφ proliferation in different tissues and contexts. The purpose of this review is to summarize both historical and current evidence for the contribution of Mφ proliferation to their accumulation in different tissues during homeostasis, infection, injury, and disease. Mφ proliferate in different organs and tissues, including skin, peritoneum, lung, heart, aorta, kidney, liver, pancreas, brain, spinal cord, eye, adipose tissue, and uterus, and in different species including mouse, rat, rabbit, and human. Mφ can proliferate at different stages of differentiation with infiltrating Mo-like cells proliferating in certain inflammatory contexts (e.g. skin wounding, kidney injury, bladder and liver infection) and mature resident Mφ proliferating in other inflammatory contexts (e.g. nematode infection, acetaminophen liver injury) and during homeostasis. The pathways involved in stimulating Mφ proliferation also may be context dependent, with different cytokines and transcription factors implicated in different studies. Although Mφ are known to proliferate in health, injury, and disease, much remains to be learned about the regulation of Mφ proliferation in different contexts and its impact on the homeostasis, injury, and repair of different organs and tissues.

Cholesterol crystal formation is a unifying pathogenic mechanism in the development of diabetic retinopathy

AIMS/HYPOTHESIS

Hyper-reflective crystalline deposits found in retinal lesions have been suggested to predict the progression of diabetic retinopathy, but the nature of these structures remains unknown.

METHODS

Scanning electron microscopy and immunohistochemistry were used to identify cholesterol crystals (CCs) in human donor, pig and mouse tissue. The effects of CCs were analysed in bovine retinal endothelial cells in vitro and in db/db mice in vivo using quantitative RT-PCR, bulk RNA sequencing, and cell death and permeability assays. Cholesterol homeostasis was determined using 2H2O and 2H7-cholesterol.

RESULTS

We identified hyper-reflective crystalline deposits in human diabetic retina as CCs. Similarly, CCs were found in the retina of a diabetic mouse model and a high-cholesterol diet-fed pig model. Cell culture studies demonstrated that treatment of retinal cells with CCs can recapitulate all major pathogenic mechanisms leading to diabetic retinopathy, including inflammation, cell death and breakdown of the blood-retinal barrier. Fibrates, statins and α-cyclodextrin effectively dissolved CCs present in in vitro models of diabetic retinopathy, and prevented CC-induced endothelial pathology. Treatment of a diabetic mouse model with α-cyclodextrin reduced cholesterol levels and CC formation in the retina, and prevented diabetic retinopathy.

CONCLUSIONS/INTERPRETATION

We established that cholesterol accumulation and CC formation are a unifying pathogenic mechanism in the development of diabetic retinopathy.

1,8-Cineole ameliorates diabetic retinopathy by inhibiting retinal pigment epithelium ferroptosis via PPAR-γ/TXNIP pathways

1,8-Cineole, the main component of volatile oil in aromatic plants, has diverse pharmacological properties, including antioxidant, anti-inflammatory, and anti-cancer properties. Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus (DM). Here, we investigated the protective effect of 1,8-cineole on DR and found that 1,8-cineole treatment could alter the expression of several genes in both high glucose (HG)-induced ARPE-19 cells and retinal tissues of DM mice, as well as inhibit ferroptosis. Subsequent investigations into the molecular mechanisms underlying this inhibition revealed that expression of thioredoxin-interacting protein (TXNIP) was significantly upregulated while that of peroxisome proliferator-activated receptor γ (PPAR-γ) was significantly downregulated in HG-induced ARPE-19 cells, and treatment with 1,8-cineole could effectively reverse these changes. Treatment with a PPAR-γ pharmacological agonist (rosiglitazone), alone or combined with 1,8-cineole, significantly inhibited the transcription of TXNIP and ferroptosis in HG-induced ARPE-19 cells. Conversely, pretreatment with GW9662, a PPAR-γ inhibitor, upregulated the transcription and expression of TXNIP in HG-induced ARPE-19 cells; 1,8-cineole failed to reverse this upregulated expression. To explore these relationships, we constructed a PPAR-γ adenovirus shRNA to elucidate the effect of 1,8-cineole on the negative regulation of TXNIP by PPAR-γ. Taken together, the present findings indicate that HG-induced ferroptosis in retinal tissue plays an essential role in the pathogenesis of DR, which can be ameliorated by 1,8-cineole.