Abstract: Mononuclear phagocytes (MP) comprise a family of cells that include microglial cells (MC), monocytes, and macrophages. The subretinal space, located between the RPE and the photoreceptor outer segments, is physiologically devoid of MPs and a zone of immune privilege mediated, among others, by immunosuppressive RPE signals. Age-related macular degeneration (AMD) is a highly heritable major cause of blindness, characterized by a breakdown of the subretinal immunosuppressive environment and an accumulation of pathogenic inflammatory MPs. Studies in mice and humans suggest that the AMD-associated APOE2 isoform promotes the breakdown of subretinal immunosuppression and increased MP survival. Of all genetic factors, variants of complement factor H (CFH) are associated with greatest linkage to AMD. Using loss of function genetics and orthologous models of AMD, we provide mechanistic evidence that CFH inhibits the elimination of subretinal MPs. Importantly, the AMD-associated CFH402H isoform markedly increased this inhibitory effect on microglial cells, indicating a causal link to disease etiology. Pharmacological acceleration of resolution of subretinal inflammation might be a powerful tool for controlling inflammation and neurodegeneration in late AMD.
Abstract: Pathological retinal neovascularization is the hallmark of primary blinding diseases across all age groups, yet surprisingly little is known about the causative factors. These diseases include diabetic retinopathy and retinopathy of prematurity where progressive decay of retinal vasculature yields zones of neural ischemia. These avascular zones and the hypoxic neurons and glia that reside in them are the source of pro-angiogenic factors that mediate destructive pre-retinal angiogenesis. Central neurons such as retinal ganglion cells (RGCs), which are directly apposed to degenerating vasculature in ischemic retinopathies, require stable metabolic supply for proper function. However, we unexpectedly found that RGCs are resilient to hypoxia/ischemia and a generally compromised metabolic supply and instead of degenerating, trigger protective mechanisms of cellular senescence. Paradoxically, while potentially favoring neuronal survival, the senescent state of RGCs is incompatible with vascular repair as they adopt a senescence-associated secretory phenotype (SASP) that provokes release of a secretome of inflammatory cytokines that drives paracrine senescence and further exacerbates pathological angiogenesis. The mechanisms that lead to retinal cellular senescence and dormancy as well as the therapeutic potential of targeting these pathways will be discussed.
Background: The goal of this study was to engineer an epithelialized and endothelialized pigmented choroidal substitute using the self-assembly approach of tissue engineering.
Methods: Cells from human choroids were isolated and cultured. Culture purity was assessed using immunostaining (CD31, HMB45, vimentin, keratins 8/18). To engineer the choroid, fibroblasts were cultured in the presence of serum and ascorbic acid to promote extracellular matrix (ECM) assembly. Endothelial cells, melanocytes or RPE cells were separately seeded on the stromal substitutes. Choroidal substitutes were further characterized by histology, mass spectrometry, immunostaining, and compared to native human choroids.
Results: The technique used to isolate choroidal cells yielded pure cultures of fibroblasts, melanocytes and vascular endothelial cells. The stromal substitutes engineered using the self-assembly approach were composed of collagen (types I, VI, XII and XIV), proteoglycans (decorin, lumican) and other ECM proteins. Protein expression was confirmed using immunostaining. Endothelial cells spontaneously assembled into capillary-like structures and vascular networks when cocultured with fibroblast-containing ECM sheets.
Conclusions: This study shows that the self-assembly approach of tissue engineering can be used to reconstruct a choroid using native cells. This model represents a unique tool to better understand the crosstalk between the different choroidal cell types and cell-ECM interactions.
Abstract: Genetic studies have revealed that variants in genes that encode regulators of the complement system are major risk factors for the development of age-related macular degeneration (AMD). The biochemical consequences of the common polymorphism in complement factor H (Tyr402His) include increased formation of the membrane attack complex (MAC), which is deposited at the level of the inner choroid and choriocapillaris. Whereas the MAC is normally protective against foreign pathogens, it can also damage resident bystander cells when it is insufficiently regulated. Indeed, human maculas with early AMD show loss of endothelial cells in the choriocapillaris, the principal site of MAC activation. Modeling of MAC injury of choroidal endothelial cells in vitro reveals that these cells are susceptible to cell lysis by the MAC, and that unlysed cells alter their gene expression profile to undergo a pro-angiogenic phenotype that includes increased expression of matrix metalloproteinase-9. Strategies for protecting choriocapillaris endothelial cells from MAC-mediated lysis and for replacing lysed endothelial cells will be discussed.
Abstract: Ocular vessel networks develop in a highly stereotyped fashion. Abnormal ocular angiogenesis is associated with major diseases including age-related macular degeneration and diabetic retinopathy. Better understanding of mechanisms driving angiogenesis is expected to uncover novel targets to prevent vision loss. Capillary growth is driven by endothelial tip cells, which are selected by dynamic interplay between VEGF, Notch and BMP signaling, with VEGF acting as a positive regulator, and Notch and the BMP receptor Alk1 acting as negative regulators of tip cell formation. The concerted interplay between these molecules ensures that appropriate tip cell numbers leading new vessel branches are formed. In addition, guidance receptors including Neuropilins and Roundabout receptors contribute to vascular patterning by regulating VEGF and BMP signaling. Possibilities to target these pathways during pathological ocular neovascularization will be discussed.
Abstract: The inverted retina is a basic characteristic of the vertebrate eye. This implies that vertebrates must have a common ancestor with an inverted retina. Of the two groups of chordates, cephalochordates have an inverted retina and urochordates a direct retina. Surprisingly, recent genetics studies favor urochordates as the closest ancestor to vertebrates. The evolution of increasingly complex organs such as the eye implies not only tissular but also structural modifications at the organ level. How these configurational modifications give rise to a functional eye at any step is still subject to debate and speculation. Here we propose an orderly sequence of phylogenetic events that closely follows the sequence of developmental eye formation in extant vertebrates. The progressive structural complexity has been clearly recorded during vertebrate development at the period of organogenesis. Matching the chain of increasing eye complexity in Mollusca that leads to the bicameral eye of the octopus and the developmental sequence in vertebrates, we delineate the parallel evolution of the two-chambered eye of vertebrates starting with an early ectodermal eye. This sequence allows for some interesting predictions regarding the eyes of not preserved intermediary species. The clue to understanding the inverted retina of vertebrates and the similarity between the sequence followed by Mollusca and chordates is the notion that the eye in both cases is an ectodermal structure, in contrast to an exclusively (de novo) neuroectodermal origin in the eye of vertebrates. This analysis places cephalochordates as the closest branch to vertebrates contrary to urochordates, claimed as a closer branch by some researchers that base their proposals in a genetic analysis.
Abstract: Pediatric neuro-ophthalmology is a subspecialty within neuro-ophthalmology. Pediatric neuro-ophthalmic diseases must be considered separate from their adult counterparts, due to the distinctive nature of the examination, clinical presentations, and management choices. This manuscript will highlight four common pediatric neuro-ophthalmic disorders by describing common clinical presentations, recommended management, and highlighting recent developments. Diseases discussed include pediatric idiopathic intracranial hypertension (IIH), pseudopapilledema, optic neuritis (ON) and optic pathway gliomas (OPG). The demographics, diagnosis and management of common pediatric neuro-ophthalmic disease require a working knowledge of the current research presented herein. Special attention should be placed on the differences between pediatric and adult entities such that children can be appropriately diagnosed and treated.
Background: Disruption of the microstructure in corneal stroma can lead to the loss of transparency. The lack of a characterization method for the microstructure prevents such scaffolds to be implemented in tissue transplantation. The non-invasive, three-dimensional (3D) rendering multiphoton microscopy (MPM) poses the potential to solve this problem.
Methods: MPM images and data analyses were performed with three kinds of samples with known and different quality. Isosurfaces (ISOs) were constructed for the evaluation of void volume and collagen distribution.
Results: The differences in the microstructures of these samples were revealed with clear indications and links to their behaviours in rehydration and possible transparency. According to this analysis, the scaffold with the highest void space ratio amongst the three presented the highest successful rates to be thoroughly rehydrated.
Conclusions: Such a method can be developed for assessing the quality of tissue engineered corneas, or donated corneas, and be useful as a powerful research tool in cornea related research.
Abstract: Corneal blindness represents one of the world’s three major causes of blindness, and the fundamental problem of corneal transplantation is a severe shortage of donor tissues worldwide, resulting in approximately 1.5 million new cases of blindness annually. To address the growing need for corneal transplants two main approaches are being pursued: allogenic and bioengineering cornea. Bioengineering corneas are constructed by naturally generating an extracellular matrix (ECM) component as the scaffold structure with or without corneal cells. It is well established that the scaffold structure directs the fate of cells, therefore, the fabrication of the correct scaffold structure components could produce an ideal corneal substitute, able to mimic the native corneal function. Another key factor in the construction of tissue engineering cornea is seed cells. However, unlike the epithelium and stroma cells, human cornea endothelium cells (HCECs) are notorious for having a limited proliferative capacity in vivo because of the mitotic block at the G1 phase of the cell cycle due to “contact-inhibition”. This review will focus on the main concepts of recent progress towards the scaffold and seed cells, especially endothelial cells for bioengineering cornea, along with future perspectives.
