Hyalocytes in proliferative vitreo-retinal diseases

Tissue engineering of the vitreous body: recent progress and future trends

PURPOSE OF REVIEW

In contrast to current clinically used tamponades including oils and gases, hydrogels offer a vitreous replacement that has the potential to present a niche for vitreous cells and elevate vitreous substitutes to the level of tissue engineering. This article, therefore, highlights and discusses recent hydrogel-based vitreous replacement strategies as well as the latest progress on vitreous cells, towards the development of a cellularized vitreous substitute.

RECENT FINDINGS

A variety of different crosslinked hydrogel systems have been recently investigated as preformed and in situ forming vitreous substitutes, based on biopolymers and/or synthetic polymers. In addition, a comprehensive understanding of the precise function and immunological significance of hyalocytes as vitreous macrophages has recently emerged using advanced imaging techniques and high-throughput transcriptional and protein analyses.

SUMMARY

Tissue engineering offers transformative potential for vitreous replacement by combining advanced hydrogel systems with hyalocytes as vitreous cells to further replicate the versatile characteristics and functions of the native vitreous.

Topographic relationship between glial cells and neovessels of the epiretinal membrane in proliferative diabetic retinopathy depends on the phase of angiogenesis

Objectives

To investigate the topographic relationship between glial tissue and active neovessels in epiretinal membranes (ERMs) in proliferative diabetic retinopathy (PDR).

Materials and methods

Phase-contrast and immunofluorescence microscopy were performed on 17 surgically removed ERMs from 17 eyes of 17 PDR patients. Clusters of active neovessels and the surrounding posterior hyaloid membrane were excised en bloc. ERMs were immunolabeled with anti-glial fibrillary acidic protein (GFAP) antibodies to identify glia, and with anti-collagen IV or anti-von Willebrand factor (VWF) antibodies to identify neovessels. All ERMs were analyzed as whole-mounted preparations, each including the area of leading neovessels.

Results

GFAP-immunopositive glial cells (GCs) were identified in 11 of 17 specimens (65%). These cells also co-expressed type IV collagen. Fibrils immunopositive for type IV collagen (GFAP-negative) were detected in all cases. The topography, structure, and GFAP immunoreactivity distinguished GCs from GFAP-negative hyalocytes. GCs had bipolar shape, small cell bodies, very long, sparsely branching, bidirectional processes, and showed a tendency to form clumps. The structure of GCs was more consistent with that of Müller cells. In all ERMs, the majority of GCs were localized around the epicenter of neovascular clusters (where neovessels branched from the maternal vessel), which also corresponded to the highest density of collagen fibrils. In four cases (23.5%), GCs were also identified in the area of the leading capillaries; however, no signs of direct interaction between GCs and developing neovessels was observed in these cases.

Conclusion

Our study found no evidence of direct interaction between GCs and leading neovessels in PDR, opposite to what was shown in embryonic retinal angiogenesis. The findings may suggest that the presence of GCs near the neovascular cluster epicenter and around leading capillaries reflects different phases of the proliferative process in PDR. In the first case, GFAP+ cells appear to be involved in the involution of neovessels, which occurs during vascular remodeling or regression. In the second case, when GCs were located around the leading neovessels, their proliferation was not directly related to blood vessel formation; in our opinion, these processes may represent independent events that might have common triggers.

Fibrotic Changes in Rhegmatogenous Retinal Detachment

Rhegmatogenous retinal detachment (RRD) is a sight-threatening condition involving retinal detachment and the accumulation of fluid in the subretinal space. Proliferative vitreoretinopathy (PVR) is a pathologic complication that develops after RRD surgery, and approximately 5-10% of RRD cases develop post-operative PVR. Prolonged inflammation in the wound healing process, epithelial-mesenchymal transition (EMT), retinal pigment epithelial (RPE) cell migration and proliferation, and epiretinal, intraretinal, and subretinal fibrosis are typical in the formation of PVR. RPE cells undergo EMT and become fibroblast-like cells that migrate to the retina and vitreous, promoting PVR formation. Fibroblasts transform into myofibroblasts, which promote fibrosis by overproducing the extracellular matrix (ECM). RPE cells, fibroblasts, glial cells, macrophages, T lymphocytes, and increased ECM production form contractile epiretinal membranes. Cytokine release, complement activation, RPE cells, glial cells, and endothelial cells are all involved in retinal immune responses. Normally, wounds heal within 4 to 6 weeks, including hemostasis, inflammation, proliferation, and remodeling phases. Properly initiated inflammation, complement activation, and the function of neutrophils and glial cells heal the wound in the first stage. In a retinal wound, glial cells proliferate and fill the injured area. Gliosis tries to protect the neurons and prevent damage, but it becomes harmful when it causes scarring. If healing is complicated, prolonged inflammation leads to pathological fibrosis. Currently, there is no preventive treatment for the formation of PVR, and it is worth studying in the future.

Vitreoschisis-induced vitreous cortex remnants in proliferative vitreoretinopathy: A comprehensive review from basic research to clinical practice

Proliferative vitreoretinopathy (PVR) significantly impacts the prognosis of rhegmatogenous retinal detachment (RRD), one of the most critical and increasing causes of vision loss in the Western world. Despite advancements in surgical instruments and techniques, the failure rate due to PVR remains substantial, necessitating additional surgeries and often leading to unsatisfactory visual outcomes. This comprehensive review explores the role of vitreoschisis-induced vitreous cortex remnants (VCR) as a critical, previously under-recognised factor contributing to PVR. Vitreoschisis, a phenomenon where the inner lamellae of the posterior vitreous cortex detach while the outermost layers remain attached to the retina, creates VCR that may contain hyalocytes and serve as scaffolds for fibrocellular proliferation. These remnants are difficult to visualise without triamcinolone acetonide (TA) staining, leading to their frequent lack of recognition in clinical practice. Moreover, removing VCR can be challenging and time-consuming, often requiring meticulous surgical techniques to avoid retinal damage and ensure complete elimination. This review consolidates insights from basic research and clinical practice, emphasising the importance of complete vitreous removal and effective VCR detection and removal to mitigate PVR risks. It highlights the histopathological and clinical evidence supporting the hypothesis that VCR, containing hyalocytes, play a pivotal role in preretinal membrane formation. The review also discusses epidemiological data, surgical management strategies and potential future directions, including improved visualisation techniques and the development of new surgical tools and methods. This review aims to improve surgical outcomes and reduce the frequency and burden of RRD-related complications by addressing VCR as a critical factor in PVR.

The multifaceted role of vitreous hyalocytes: Orchestrating inflammation, angiomodulation and erythrophagocytosis in proliferative diabetic retinopathy

BACKGROUND

Despite great advances in proliferative diabetic retinopathy (PDR) therapy over the last decades, one third of treated patients continue to lose vision. While resident vitreous macrophages called hyalocytes have been implicated in the pathophysiology of vitreoretinal proliferative disease previously, little is known about their exact role in PDR. In this study, we address molecular and cellular alterations in the vitreous of PDR patients as a means towards assessing the potential contribution of hyalocytes to disease pathogenesis.

RESULTS

A total of 55 patients were included in this study encompassing RNA-Sequencing analysis of hyalocytes isolated from the vitreous of PDR and control patients, multiplex immunoassay and ELISA analyses of vitreous samples from PDR and control patients, as well as isolation and immunohistochemical staining of cultured porcine hyalocytes. Transcriptional analysis revealed an enhanced inflammatory response of hyalocytes contributing to the cytokine pool within the vitreous of PDR patients by expressing interleukin-6, among others. Further, increased angiopoietin-2 expression indicated that hyalocytes from PDR patients undergo a proangiogenic shift and may thus mediate the formation of retinal neovascularizations, the hallmark of PDR. Finally, RNA-Sequencing revealed an upregulation of factors known from hemoglobin catabolism in hyalocytes from PDR patients. By immunohistochemistry, cultured porcine hyalocytes exposed to red blood cells were shown to engulf and phagocytose these, which reveals hyalocytes' potential to dispose of erythrocytes. Thus, our data suggest a potential role for vitreous macrophages in erythrophagocytosis and, thereby, clearance of vitreous hemorrhage, a severe complication of PDR.

CONCLUSION

Our results strongly indicate a critical role for vitreous hyalocytes in key pathophysiological processes of proliferative diabetic retinopathy: inflammation, angiomodulation and erythrophagocytosis. Immunomodulation of hyalocytes may thus prove an essential novel therapeutic approach in diabetic vitreoretinal disease.

Short-Term Culture of Human Hyalocytes Retains Their Initial Phenotype and Displays Their Contraction Abilities

BACKGROUND

Hyalocytes are the main vitreal cell types with critical functions in health and vitreoretinal diseases. Our aim was to develop cultures of human hyalocytes and verify the retention of their initial cellular features after 3 and 6 days of culturing (3 d and 6 d) by analyzing and comparing a few morphological and functional parameters.

METHODS

Vitreous samples (n = 22) were collected and vitreous cells and bead-enriched hyalocytes were developed and compared (3 d vs. 6 d cultures). Vitreous and conditioned media were tested for collagen, vascular endothelial growth factor (VEGF), transforming growth factor β1 (TGFβ1), nerve growth factor (NGF), matrix metalloproteinases (MMPs)/tissue inhibitors of metalloproteinases (TIMPs) and alpha-smooth muscle actin (αSMA) expression (ELISA, array/IP/WB, RT-PCR). Cells were observed at light and fluorescent microscopy (phenotypical properties) and tested for their 3D collagen gel contraction abilities.

RESULTS

An increased expression of collagens, vimentin, fibronectin, and the MMP9/TIMP1 ratio were observed in vitreous tissues. In 3 d cultures, collagens and MMP9 were upregulated while the related tissue-enzymes were deregulated. Vitreous samples also showed high levels of TGFβ1, VEGF, and NGF, and this protein signature was retained at 3 d while decreased at 6 d. The original phenotype (low αSMA) was retained at 3 d from seeding while an increased αSMA expression was observed at 6 d; NGF/trkANGFR was expressed in cultured hyalocytes and partially drives the collagen retraction.

CONCLUSIONS

The vitreous print comparison between untouched and cultured hyalocytes allowed us, on one side, to select 3 d cultures and, on the other, to highlight the neuroprotective/contractile NGF in vitro hyalocytes effects. The possibility of scoring reactive hyalocytes would represent an interesting aspect of screening the vitreoretinal interface severity.

Hyalocytes-guardians of the vitreoretinal interface

Originally discovered in the nineteenth century, hyalocytes are the resident macrophage cell population in the vitreous body. Despite this, a comprehensive understanding of their precise function and immunological significance has only recently emerged. In this article, we summarize recent in-depth investigations deciphering the critical role of hyalocytes in various aspects of vitreous physiology, such as the molecular biology and functions of hyalocytes during development, adult homeostasis, and disease. Hyalocytes are involved in fetal vitreous development, hyaloid vasculature regression, surveillance and metabolism of the vitreoretinal interface, synthesis and breakdown of vitreous components, and maintenance of vitreous transparency. While sharing certain resemblances with other myeloid cell populations such as retinal microglia, hyalocytes possess a distinct molecular signature and exhibit a gene expression profile tailored to the specific needs of their host tissue. In addition to inflammatory eye diseases such as uveitis, hyalocytes play important roles in conditions characterized by anomalous posterior vitreous detachment (PVD) and vitreoschisis. These can be hypercellular tractional vitreo-retinopathies, such as macular pucker, proliferative vitreo-retinopathy (PVR), and proliferative diabetic vitreo-retinopathy (PDVR), as well as paucicellular disorders such as vitreo-macular traction syndrome and macular holes. Notably, hyalocytes assume a significant role in the early pathophysiology of these disorders by promoting cell migration and proliferation, as well as subsequent membrane contraction, and vitreoretinal traction. Thus, early intervention targeting hyalocytes could potentially mitigate disease progression and prevent the development of proliferative vitreoretinal disorders altogether, by eliminating the involvement of vitreous and hyalocytes.

Redefining the ontogeny of hyalocytes as yolk sac-derived tissue-resident macrophages of the vitreous body

BACKGROUND

The eye is a highly specialized sensory organ which encompasses the retina as a part of the central nervous system, but also non-neural compartments such as the transparent vitreous body ensuring stability of the eye globe and a clear optical axis. Hyalocytes are the tissue-resident macrophages of the vitreous body and are considered to play pivotal roles in health and diseases of the vitreoretinal interface, such as proliferative vitreoretinopathy or diabetic retinopathy. However, in contrast to other ocular macrophages, their embryonic origin as well as the extent to which these myeloid cells might be replenished by circulating monocytes remains elusive.

RESULTS

In this study, we combine transgenic reporter mice, embryonic and adult fate mapping approaches as well as parabiosis experiments with multicolor immunofluorescence labeling and confocal laser-scanning microscopy to comprehensively characterize the murine hyalocyte population throughout development and in adulthood. We found that murine hyalocytes express numerous well-known myeloid cell markers, but concomitantly display a distinct immunophenotype that sets them apart from retinal microglia. Embryonic pulse labeling revealed a yolk sac-derived origin of murine hyalocytes, whose precursors seed the developing eye prenatally. Finally, postnatal labeling and parabiosis established the longevity of hyalocytes which rely on Colony Stimulating Factor 1 Receptor (CSF1R) signaling for their maintenance, independent of blood-derived monocytes.

CONCLUSION

Our study identifies hyalocytes as long-living progeny of the yolk sac hematopoiesis and highlights their role as integral members of the innate immune system of the eye. As a consequence of their longevity, immunosenescence processes may culminate in hyalocyte dysfunction, thereby contributing to the development of vitreoretinal diseases. Therefore, myeloid cell-targeted therapies that convey their effects through the modification of hyalocyte properties may represent an interesting approach to alleviate the burden imposed by diseases of the vitreoretinal interface.

Visualizing features with wide-field volumetric OCT angiography

Optical coherence tomography (OCT) and its extension OCT angiography (OCTA) have become essential clinical imaging modalities due to their ability to provide depth-resolved angiographic and tissue structural information non-invasively and at high resolution. Within a field of view, the anatomic detail available is sufficient to identify several structural and vascular pathologies that are clinically relevant for multiple prevalent blinding diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and vein occlusions. The main limitation in contemporary OCT devices is that this field of view is limited due to a fundamental trade-off between system resolution/sensitivity, sampling density, and imaging window dimensions. Here, we describe a swept-source OCT device that can capture up to a 12 × 23-mm field of view in a single shot and show that it can identify conventional pathologic features such as non-perfusion areas outside of conventional fields of view. We also show that our approach maintains sensitivity sufficient to visualize novel features, including choriocapillaris morphology beneath the macula and macrophage-like cells at the inner limiting membrane, both of which may have implications for disease.

Prevalence of vitreoschisis-induced vitreous cortex remnants over the peripheral retinal surface in eyes undergoing vitrectomy for primary rhegmatogenous retinal detachment

PURPOSE

Unremoved vitreoschisis-induced vitreous cortex remnants over the peripheral retinal surface posterior to the vitreous base (pVCR) may increase the risk of surgical failure after primary rhegmatogenous retinal detachment (RRD) repair. The purpose of this study was to validate our previous findings on pVCR prevalence during vitrectomy for RRD and to examine their association with proliferative vitreoretinopathy (PVR) and surgical failure.

METHODS

Prospective observational multisurgeon study of 100 eyes of 100 consecutive patients who underwent vitrectomy for RRD by one of four vitreoretinal surgeons. Collected data included detected pVCR and known PVR risk factors. Pooled analysis with our previous retrospective study (251 eyes of 251 patients) was also performed.

RESULTS

Initial PVR (≥C) was present and removed in 6/100 (6%) patients, pVCR were detected in 36/100 (36%) patients, pVCR were removed in 30/36 (83%) patients with pVCR, and 4/36 (11%) patients with pVCR were high myopes (≤-6D). Six per cent (6/100) developed a retinal redetachment, of which 3/6 (50%) had initial PVR (≥C). Surgical failure rates in eyes with and without pVCR were 17% (6/36) and 0% (0/64), respectively. In eyes with pVCR and surgical failure, pVCR were not or not completely removed during the first surgery. Overall analysis showed that pVCR were statistically significantly associated with PVR.

CONCLUSIONS

This study confirms our previous findings: a pVCR prevalence of around 35% and an association between pVCR, PVR formation and surgical failure in patients undergoing vitrectomy for RRD. More research is needed to determine which patients would benefit most from pVCR removal.

[Biomechanics of diabetic vitreopapillary traction syndrome]

Diabetic vitreopapillary traction syndrome (VPT) is a variant of diabetic retinopathy (DR) that can lead to vision loss in advanced stages. This review reports on the biomechanics of the vitreous in the pathogenesis of proliferative DR, in particular diabetic VPT. The article analyzes and summarizes literature data, presents the views of different authors on this problem, and provides the results of Russian and foreign scientific research on this pathology. It is concluded that further research in this area can lead to a significant improvement in the results of therapy, timely diagnosis, and preservation of vision in patients with DR.

3-D OCT imaging of hyalocytes in partial posterior vitreous detachment and vaso-occlusive retinal disease

Purpose

To describe the spatial distribution and morphologic characteristics of macrophage-like cells called hyalocytes in the posterior vitreous cortex of a patient with unilateral partial posterior vitreous detachment (PVD) using coronal plane en face optical coherence tomography (OCT).

Observations

A 54-year-old male with sickle cell disease (HbSC genotype) presented with a partial PVD in one eye. Rendered volumes of a slab extending from 600 μm to 3 μm anterior to the inner limiting membrane (ILM) revealed hyperreflective foci in the detached posterior vitreous cortex suspended anterior to the macula, likely representing hyalocytes. In the fellow eye without PVD, hyperreflective foci were located 3 μm anterior to the ILM. The morphology of the cells in the eye with PVD varied between a ramified state with multiple elongated processes and a more activated state characterized by a plump cell body with fewer retracted processes. In the same anatomical location, the hyperreflective foci were 10-fold more numerous in the patient with vaso-occlusive disease than in an unaffected, age-matched control.

Conclusions and Importance

Direct, non-invasive, and label-free techniques of imaging cells at the vitreoretinal interface and within the vitreous body is an emerging field. The findings from this case report suggest that coronal plane en face OCT can be used to provide a detailed and quantitative characterization of cells at the human vitreo-retinal interface in vivo. Importantly, this case report demonstrates that 3D-OCT renderings can enhance visualization of these cells in relation to the ILM, which may provide clues concerning the identity and contribution of these cells to the pathogenesis of vitreo-retinal diseases.

Novel Surgical Treatment of an Intraretinal Juxtapapillary Hemangioblastoma Using Intraocular Diathermy Forceps: A Case Report

The surgical treatment of intraretinal juxtapapillary retinal hemangioblastomas (JRHs) was previously contraindicated because of the significant risk of collateral damage to the macula and optic nerve. This case report discusses the effectiveness and safety of a novel surgical technique using intraocular bipolar diathermy forceps to coagulate feeder and draining blood vessels of an intraretinal JRH. The patient suffered from bilateral retinal hemangioblastomas with loss of visual function in one eye and the development of an intraretinal JRH in the other eye. Despite intensive treatment with intravitreal bevacizumab and subconjunctival triamcinolone acetonide, growth of the intraretinal JRH continued, macular exudation worsened, and visual acuity decreased. Surgical treatment was undertaken in which, first, the feeder and draining vessels of the JRH were identified by comparing the retinal imaging of the JRH with the imaging before the emergence of the JRH 4 years earlier. Then, retinal incisions were made above the blood vessels and parallel to the nerve fibers during a pars plana vitrectomy. Lastly, these vessels were lifted above the retinal surface and coagulated using intraocular diathermy forceps. Postoperatively, macular edema reduced, and visual acuity increased and remained stable for about 6 months. Using intraocular diathermy forceps, this case report demonstrates effective and safe intraretinal JRH blood vessel coagulation above the retinal surface. This novel surgical approach was able to delay the deterioration of visual acuity due to tumor growth and exudation in this patient. This suggests that coagulation with intraocular diathermy forceps can be considered an additional surgical treatment option for JRHs, especially those with an intraretinal growth pattern.

Hyalocyte origin, structure, and imaging

Introduction

Hyalocytes have been recognized as resident tissue macrophages of the vitreous body since the mid-19th century. Despite this, knowledge about their origin, turnover, and dynamics is limited.

Areas covered

Historically, initial studies on the origin of hyalocytes used light and electron microscopy. Modern investigations across species including rodents and humans will be described. Novel imaging is now available to study human hyalocytes in vivo. The shared ontogeny with retinal microglia and their eventual interdependence as well as differences will be discussed.

Expert opinion

Owing to a common origin as myeloid cells, hyalocytes and retinal microglia have similarities, but hyalocytes appear to be distinct as resident macrophages of the vitreous body.