Migratory capacity of the cell line RN33B and the host glial cell response after subretinal transplantation to normal adult rats

Photoreceptor Differentiation following Transplantation of Allogeneic Retinal Progenitor Cells to the Dystrophic Rhodopsin Pro347Leu Transgenic Pig

Purpose. Transplantation of stem, progenitor, or precursor cells has resulted in photoreceptor replacement and evidence of functional efficacy in rodent models of retinal degeneration. Ongoing work has been directed toward the replication of these results in a large animal model, namely, the pig. Methods. Retinal progenitor cells were derived from the neural retina of GFP-transgenic pigs and transplanted to the subretinal space of rhodopsin Pro347Leu-transgenic allorecipients, in the early stage of the degeneration and the absence of immune suppression. Results. Results confirm the survival of allogeneic porcine RPCs without immune suppression in the setting of photoreceptor dystrophy. The expression of multiple photoreceptor markers by grafted cells included the rod outer segment-specific marker ROM-1. Further evidence of photoreceptor differentiation included the presence of numerous photoreceptor rosettes within GFP-positive grafts, indicative of the development of cellular polarity and self-assembly into rudiments of outer retinal tissue. Conclusion. Together, these data support the tolerance of RPCs as allografts and demonstrate the high level of rod photoreceptor development that can be obtained from cultured RPCs following transplantation. Strategies for further progress in this area, together with possible functional implications, are discussed.

N-CAM exhibits a regulatory function in pathological angiogenesis in oxygen induced retinopathy

BACKGROUND

Diabetic retinopathy and retinopathy of prematurity are diseases caused by pathological angiogenesis in the retina as a consequence of local hypoxia. The underlying mechanism for epiretinal neovascularization (tuft formation), which contributes to blindness, has yet to be identified. Neural cell adhesion molecule (N-CAM) is expressed by Müller cells and astrocytes, which are in close contact with the retinal vasculature, during normal developmental angiogenesis.

METHODOLOGY/PRINCIPAL FINDINGS

Notably, during oxygen induced retinopathy (OIR) N-CAM accumulated on astrocytes surrounding the epiretinal tufts. Here, we show that N-CAM ablation results in reduced vascular tuft formation due to reduced endothelial cell proliferation despite an elevation in VEGFA mRNA expression, whereas retinal developmental angiogenesis was unaffected.

CONCLUSION/SIGNIFICANCE

We conclude that N-CAM exhibits a regulatory function in pathological angiogenesis in OIR. This is a novel finding that can be of clinical relevance in diseases associated with proliferative vasculopathy.

Embryonic stem cells and retinal repair

In this review we examine the potential of embryonic stem cells (ESCs) for use in the treatment of retinal diseases involving photoreceptors and retinal pigment epithelium (RPE). We outline the ontogenesis of target retinal cell types (RPE, rods and cones) and discuss how an understanding of developmental processes can inform our manipulation of ESCs in vitro. Due to their potential for cellular therapy, special emphasis is placed upon the derivation and culture of human embryonic stem cells (HESCs) and their differentiation towards a retinal phenotype. In terms of achieving this goal, we suggest that much of the success to date reflects permissive in vitro environments provided by established protocols for HESC derivation, propagation and neural differentiation. In addition, we summarise key factors that may be important for enhancing efficiency of retinal cell-type derivation from HESCs. The retina is an amenable component of the central nervous system (CNS) and as such, diseases of this structure provide a realistic target for the application of HESC-derived cellular therapy to the CNS. In order to further this goal, the second component of our review focuses on the cellular and molecular cues within retinal environments that may influence the survival and behaviour of transplanted cells. Our analysis considers both the potential barriers to transplant integration in the retina itself together with the remodelling in host visual centres that is known to accompany retinal dystrophy.

Survival, migration and differentiation of retinal progenitor cells transplanted on micro-machined poly(methyl methacrylate) scaffolds to the subretinal space

Stem and progenitor cells can be combined with polymer substrates to generate tissue equivalents in culture. The replacement of retinal tissue lost to disease or trauma using retinal progenitor cells (RPCs) delivered on polymer scaffolds and transplanted into the sub-retinal space of the damaged retina is a promising therapeutic strategy. Micromachining-based, ultra-thin PMMA poly(methyl methacrylate) scaffolds may provide a suitable cytoarchitectural environment for tissue engineering and transplantation to the diseased eye. Here, adhesion of RPCs to polymer, as well as migration and differentiation in the host retina were compared for PMMA scaffolds (6 microm thickness) with either smooth or porous (11 microm diameter) surface topography. RPCs were cultured under identical conditions on smooth or porous laminin-coated polymer scaffolds and transplanted into the subretinal space of C57BL/6 mice. RPCs could be cultured on both scaffolds with similar results, although transplantation with non-porous scaffolds showed limited RPC retention. Porous scaffolds demonstrated enhanced RPC adherence during transplantation and allowed for greater process outgrowth and cell migration into the host retinal layers. Integrated cells expressed the mature neuronal marker neurofilament-200 (nf-200), the glial marker glial fibrillary acidic protein (GFAP) and the retinal-specific marker recoverin. No host foreign body response was seen. In conclusion, ultra-thin film PMMA scaffolds micromachined to contain through pores retain adherent RPCs to a considerably greater extent than unmachined versions during the transplantation process and can serve as a biocompatible substrate for cell delivery in vivo.

Retinal neurospheres prepared as tissue for transplantation

The present work was conducted to study the cellular composition and developmental capacity of retinal neurospheres. Furthermore, the ability of grafted neurospheres to integrate into adult retinal tissue was studied in an in vitro model. Retinal progenitor cells isolated from rat embryos were expanded into neurospheres in vitro in the presence of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and leukemia inhibitory factor (LIF). Neurospheres labeled with a lipophilic dye were placed onto explants, and tissue interactions were analyzed after 2-6 days of culture. Immunocytochemical analysis of neurospheres revealed the presence of neuronal and glial cells. Proliferating neuronal and glial cells were observed after 2 weeks, whereas the neuronal cell proliferation declined considerably after 4 weeks. Few apoptotic cells were observed in the neurospheres. Neurospheres cultured on explanted adult retina engrafted with the surrounding tissue, but progenitor cell migration into the explants was low. However, the grafted neurospheres appeared to limit the experimentally induced photoreceptor apoptosis in the surrounding explant tissue.

Morphological changes in the Royal College of Surgeons rat retina during photoreceptor degeneration and after cell-based therapy

There are concomitant morphological and functional changes in the inner retina during the course of photoreceptor degeneration in a range of animal models of retina degeneration and in humans with eye disease. One concern that has been raised is that the changes occurring in the inner retina might compromise attempts to rescue or restore visual input by various interventional approaches. It is known that cell-based therapy can preserve significant visual capability for many months. In this study, we examine the overall changes in the Royal College of Surgeons (RCS) rat during degeneration and the effects of cell transplantation by means of immunohistochemistry and confocal microscopy. The degenerative changes are complex, and they progress with age. They involve the neurons with which both rods and cones interconnect--retinal second- and third-order neurons underwent dramatic modification, including sprouting, retraction as photoreceptor loss progressed--as well as Müller glia and secondary vascular changes, which were associated at later times with neuronal migration. The pathological vascular changes led to major disruption of inner retina. After introducing a retinal pigment epithelial cell line to the subretinal space early in the progress of photoreceptor degeneration, most inner retinal changes were held in abeyance for up to at least 10 months of age. Given the concern that has been raised regarding whether inner retinal changes might compromise any graft-related benefit, this is an encouraging finding.