Proliferative Cells Isolated from the Adult Human Peripheral Retina only Transiently Upregulate Key Retinal Markers upon Induced Differentiation

Adult stem cells in the eye: Identification, characterisation, and therapeutic application in ocular regeneration - A review

Adult stem cells, present in various parts of the human body, are undifferentiated cells that can proliferate and differentiate to replace dying cells within tissues. Stem cells have specifically been identified in the cornea, trabecular meshwork, crystalline lens, iris, ciliary body, retina, choroid, sclera, conjunctiva, eyelid, lacrimal gland, and orbital fat. The identification of ocular stem cells broadens the potential therapeutic strategies for untreatable eye diseases. Currently, stem cell transplantation for corneal and conjunctival diseases remains the most common stem cell-based therapy in ocular clinical management. Lens epithelial stem cells have been applied in the treatment of paediatric cataracts. Several early-phase clinical trials for corneal and retinal regeneration using ocular stem cells are also underway. Extensive preclinical studies using ocular stem cells have been conducted, showing encouraging outcomes. Ocular stem cells currently demonstrate great promise in potential treatments of eye diseases. In this review, we focus on the identification, characterisation, and therapeutic application of adult stem cells in the eye.

Retinal Stem Cell 'Retirement Plans': Growth, Regulation and Species Adaptations in the Retinal Ciliary Marginal Zone

The vertebrate retina develops from a specified group of precursor cells that adopt distinct identities and generate lineages of either the neural retina, retinal pigmented epithelium, or ciliary body. In some species, including teleost fish and amphibians, proliferative cells with stem-cell-like properties capable of continuously supplying new retinal cells post-embryonically have been characterized and extensively studied. This region, termed the ciliary or circumferential marginal zone (CMZ), possibly represents a conserved retinal stem cell niche. In this review, we highlight the research characterizing similar CMZ-like regions, or stem-like cells located at the peripheral margin, across multiple different species. We discuss the proliferative parameters, multipotency and growth mechanisms of these cells to understand how they behave in vivo and how different molecular factors and signalling networks converge at the CMZ niche to regulate their activity. The evidence suggests that the mature retina may have a conserved propensity for homeostatic growth and plasticity and that dysfunction in the regulation of CMZ activity may partially account for dystrophic eye growth diseases such as myopia and hyperopia. A better understanding of the properties of CMZ cells will enable important insight into how an endogenous generative tissue compartment can adapt to altered retinal physiology and potentially even restore vision loss caused by retinal degenerative conditions.

Autologous neurosensory retinal transplantation for large refractory idiopathic macular hole

PURPOSE

To investigate the structural and functional reconstruction of the macula after autologous neurosensory retinal-free flap transplantation (ANRFFT) in eyes with large refractory idiopathic macular holes (IMHs).

METHODS

Patients with refractory IMHs after multiple surgeries who underwent ANRFFT were retrospectively reviewed. The main outcomes were anatomic closure of MH, change in external limiting membrane (ELM) defect on optical coherence tomography (OCT) and best-corrected visual acuity (BCVA).

RESULTS

A total of 7 patients (4 female and 3 male; mean age 60.6 ± 8.6 years) were included in the study. Mean preoperative largest basal diameter was 1146.7 ± 413.7 µm (range, 653-1768 µm), and mean narrowest inner-opening diameter was 788.9 ± 148.8 µm (range, 644-1100 µm). Mean BCVA (logarithm of the minimum angle of resolution [logMAR]) significantly improved from 1.53 ± 0.16 (range, 1.3-1.7) to 0.89 ± 0.23 (range, 0.6-1.3) at the final follow-up (P < 0.001). OCT revealed complete closure of MH in all eyes. Mean preoperative ELM defect significantly decreased from 1450.3 ± 306.5 µm (range, 1044-1908 mm) to 533.1 ± 399.2 µm (range, 0-1156 µm, P = 0.001). Postoperative complications included retinal detachment (n = 1), cystoid macular edema like changes in the graft (n = 1) and reactive pigment epithelial hyperplasia (n = 1).

CONCLUSION

Although some postoperative complications did occur, ANRFFT seems to be an effective treatment for large refractory IMHs, and can promote recovery of the outer retinal structure resulting in functional improvement.

Autologous neurosensory retinal transplantation for recurrent macular hole retinal detachment in highly myopic eyes

PURPOSE

To investigate the morphological and functional reconstruction of the macular fovea after autologous neurosensory retinal transplantation for recurrent macular hole retinal detachment (MHRD) in highly myopic eyes.

METHODS

Ten consecutive cases of recurrent MHRD with high myopia were retrospectively reviewed. All eyes underwent pars plana vitrectomy combined with autologous neurosensory retinal transplantation and were followed up for at least 3 months after silicone oil extraction. The main outcomes were whether or not the retina was reattached and the macular hole (MH) was closed, morphological changes in the retinal graft, best-corrected visual acuity (BCVA), the sensitivity threshold and blood flow signal in the macula.

RESULTS

At the one month postoperative visit, there was an obvious boundary between the graft and the surrounding retinal tissue, and some retinal structural layers could be seen in the graft on optical coherence tomography scans. At the final follow-up, eight eyes (80%) showed retinal reattachment and closure of the MH. Optical coherence tomography revealed blurring of the boundary between the graft and surrounding retinal tissue and that the retinal structure in the graft was disordered. The MH was not closed in two eyes (20%), in one case because of partial displacement of the graft and in the other because of incomplete coverage of the MH as a result of a smaller graft. The post-BCVA was significantly better than the pre-BCVA (1.32 ± 0.33 versus 2.01 ± 0.29 logMAR; p = 0.000, paired t-test).

CONCLUSION

Autologous neurosensory retinal transplantation can be an effective treatment for recurrent MHRD in highly myopic eyes. 'Fusion' between the neurosensory retinal graft and the original retinal tissue may be the mechanism involved in the closure of the MH and reconstruction of the macular fovea.

Changes in vitreal protein profile and retina mRNAs in Reeler mice: NGF, IL33 and Müller cell activation

A possible link between Nerve Growth Factor (NGF) and Reelin might take place during impaired retinal development occurring in the Reelin deficient mouse model (Reeler). To better characterize NGF and retina impairments at the Reeler retina, vitreous and retina were investigated by means of protein expression and glial cell activation. Reeler (n = 9; RELN^-/-) and WT (n = 9; wild-type RELN^+/+, B6C3Fe) mice were analyzed at 14, 21 and 28 postnatal days (p). Retinas and vitreous were subjected to confocal analysis and protein array, followed by conventional analysis. A significant increase of NGF, IL33 and TIMP1, a trend to a decrease of IL12 and IL6, as well as a significant decrease of NT3 were detected in Reeler vitreous, particularly at p28 (p<0.05). MIP3β mRNA was decreased while IL33mRNA was significantly upregulated in Reeler retina. Increased number of GFAP⁺ and Nestin⁺ cells as well as upregulation of Glutamine Synthetase and Nestin mRNAs were observed in Reeler retinas (p<0.05). These findings extend our previous studies on Reeler retina showing a selective Müller cell activation. NGF and IL33 release into vitreous would suggest a local activation of Müller cells, in addition to retinal ganglion and accessory cells. Overall, the data from this experimental study would strength the potential neuroprotective role played by activated Muller cells through NGF release.

Adult Stem Cells, Tools for Repairing the Retina

Purpose

Retinal degenerative diseases lead to the death of retinal neurons causing visual impairment and blindness. In lower order vertebrates, the retina and its surrounding tissue contain stem cell niches capable of regenerating damaged tissue. Here we examine these niches and review their capacity to be used as retinal stem/progenitor cells (RSC/RPCs) for retinal repair.

Recent Findings

Exogenous factors can control the in vitro activation of RSCs/PCs found in several niches within the adult eye including cells in the ciliary margin, the retinal pigment epithelium, iris pigment epithelium as well as the inducement of Müller and amacrine cells within the neural retina itself. Recently, factors have been identified for the activation of adult mammalian Müller cells to a RPC state in vivo.

Summary

Whereas cell transplantation still holds potential for retinal repair, activation of the dormant native regeneration process may lead to a more successful process including greater integration efficiency and proper synaptic targeting.