Megan F. Jones

Transplantation of Photoreceptors Derived From Human Müller Glia Restore Rod Function in the P23H Rat

Müller glia possess stem cell characteristics that have been recognized to be responsible for the regeneration of injured retina in fish and amphibians. Although these cells are present in the adult human eye, they are not known to regenerate human retina in vivo. Human Müller glia with stem cell characteristics (hMSCs) can acquire phenotypic and genotypic characteristics of rod photoreceptors in vitro, suggesting that they may have potential for use in transplantation strategies to treat human photoreceptor degenerations. Much work has been undertaken in rodents using various sources of allogeneic stem cells to restore photoreceptor function, but the effect of human Müller glia‐derived photoreceptors in the restoration of rod photoreceptor function has not been investigated. This study aimed to differentiate hMSCs into photoreceptor cells by stimulation with growth and differentiation factors in vitro to upregulate gene and protein expression of CRX, NR2E3, and rhodopsin and various phototransduction markers associated with rod photoreceptor development and function and to examine the effect of subretinal transplantation of these cells into the P23H rat, a model of primary photoreceptor degeneration. Following transplantation, hMSC‐derived photoreceptor cells migrated and integrated into the outer nuclear layer of the degenerated retinas and led to significant improvement in rod photoreceptor function as shown by an increase in a‐wave amplitude and slope using scotopic flash electroretinography. These observations suggest that hMSCs can be regarded as a cell source for development of cell‐replacement therapies to treat human photoreceptor degenerations and may also offer potential for the development of autologous transplantation.

Differences between the neurogenic and proliferative abilities of Müller glia with stem cell characteristics and the ciliary epithelium from the adult human eye

Much controversy has arisen on the nature and sources of stem cells in the adult human retina. Whilst ciliary epithelium has been thought to constitute a source of neural stem cells, a population of Müller glia in the neural retina has also been shown to exhibit neurogenic characteristics. This study aimed to compare the neurogenic and proliferative abilities between these two major cell populations. It also examined whether differences exist between the pigmented and non-pigmented ciliary epithelium (CE) from the adult human eye. On this basis, Müller glia with stem cell characteristics and pigmented and non-pigmented CE were isolated from human neural retina and ciliary epithelium respectively. Expression of glial, epithelial and neural progenitor markers was examined in these cells following culture under adherent and non-adherent conditions and treatments to induce neural differentiation. Unlike pigmented CE which did not proliferate, non-pigmented CE cells exhibited limited proliferation in vitro, unless epidermal growth factor (EGF) was present in the culture medium to prolong their survival. In contrast, Müller glial stem cells (MSC) cultured as adherent monolayers reached confluence within a few weeks and continued to proliferative indefinitely in the absence of EGF. Both MSC and non-pigmented CE expressed markers of neural progenitors, including SOX2, PAX6, CHX10 and NOTCH. Nestin, a neural stem cell marker, was only expressed by MSC. Non-pigmented CE displayed epithelial morphology, limited photoreceptor gene expression and stained strongly for pigmented epithelial markers upon culture with neural differentiation factors. In contrast, MSC adopted neural morphology and expressed markers of retinal ganglion cells and photoreceptors when cultured under similar conditions. This study provides the first demonstration that pigmented CE possess different proliferative abilities from non-pigmented CE. It also showed that although non-pigmented CE express genes of retinal progenitors, they do not differentiate into neurons in vitro, as that seen with Müller glia that proliferate indefinitely in vitro and that acquire markers of retinal neurons in culture under neural differentiation protocols. From these observations it is possible to suggest that Müller glia that express markers of neural progenitors and become spontaneously immortalized in vitro constitute a potential source of retinal neurons for transplantation studies and fulfil the characteristics of true stem cells due to their proliferative and neurogenic ability.

Gene expression and protein distribution of ADAMTSL-4 in human iris, choroid and retina

Background Mutations in ADAMTSL4 have recently been shown to be the major cause of autosomal recessive isolated ectopia lentis (IEL). However, the function and ocular localisation of the protein is yet to be fully established. We therefore aimed to confirm the expression of this gene and protein in normal ocular tissue. Methods Donor ocular tissue was obtained within 48 h post-mortem and iris, choroid and retina were isolated for analysis. Expression of mRNA coding for ADAMTSL4 was examined in four eyes using reverse transcription PCR. Protein coding for this molecule was also investigated in two eyes by western blot analysis. Furthermore, the in situ localisation of ADAMTSL4 was investigated in cryostat sections of whole eyes following immunostaining for this protein and confocal analysis of the stained tissue. Results mRNA and protein coding for ADAMTSL4 were both demonstrated to be expressed in iris and choroidal tissue but were absent from the neural retina. Confocal studies revealed ADAMTS-Like 4 to be present in the ciliary body and ciliary processes and also in the retinal pigment epithelium. Conclusions We have confirmed the gene and protein expression of ADAMTSL4 in human ocular tissue. The pattern of expression may suggest further functions of this gene beyond those suggested by its causative role in IEL.

Optimized feline vitrectomy technique for therapeutic stem cell delivery to the inner retina

Objective To describe an optimized surgical technique for feline vitrectomy which reduces bleeding and aids posterior gel clearance in order to facilitate stem cell delivery to the inner retina using cellular scaffolds. Procedures Three-port pars plana vitrectomies were performed in six-specific pathogen-free domestic cats using an optimized surgical technique to improve access and minimize severe intraoperative bleeding. Results The surgical procedure was successfully completed in all six animals. Lens sparing vitrectomy resulted in peripheral lens touch in one of three animals but without cataract formation. Transient bleeding from sclerotomies, which was readily controlled, was seen in two of the six animals. No cases of vitreous hemorrhage, severe postoperative inflammation, retinal detachment, or endophthalmitis were observed during postoperative follow-up. Conclusions Three-port pars plana vitrectomy can be performed successfully in the cat in a safe and controlled manner when the appropriate precautions are taken to minimize the risk of developing intraoperative hemorrhage. This technique may facilitate the use of feline models of inner retinal degeneration for the development of stem cell transplantation techniques using cellular scaffolds.

Biomaterials for repair and regeneration of the neural retina

Although major advances have been made in the treatment and prevention of retinal degenerative disorders, degeneration of the neural retina remains a significant cause of blindness. In cases of advanced disease or unresponsiveness to treatment, the only hope for restoration of vision is either neural cell replacement or induction of endogenous regeneration by resident stem cells. Various stem cell sources have been experimentally investigated for retinal transplantation with variable success, and refinement of protocols for cell delivery will undoubtedly benefit from the use of biomaterials. These could be used for the design of cellular scaffolds to facilitate cell engraftment, as well as for drug and growth factor delivery to promote immune protection and survival of transplanted cells. New scientific developments have yielded a wide range of biomaterials with high biodegradability and tissue compatibility, and the retina is an amenable tissue that could benefit from advances in this technology. However, much research is still needed before this approach can be safely translated into the clinic. This chapter addresses various aspects of retinal development and degeneration, sources of stem cells to repair the damaged retina, and recent advances in the development of biomaterials for use in retinal regeneration therapies.