Synaptic repair and vision restoration in advanced degenerating eyes by transplantation of retinal progenitor cells.

Stem cell transplantation shows enormous potential for treatment of incurable retinal degeneration (RD). To determine if and how grafts connect with the neural circuits of the advanced degenerative retina (ADR) and improve vision, we perform calcium imaging of GCaMP5-positive grafts in retinal slices. The organoid-derived C-Kit+/SSEA1- (C-Kit+) retinal progenitor cells (RPCs) become synaptically organized and build spontaneously active synaptic networks in three major layers of ADR. Light stimulation of the host photoreceptors elicits distinct neuronal responses throughout the graft RPCs. The graft RPCs and their differentiated offspring cells in inner nuclear layer synchronize their activities with the host cells and exhibit presynaptic calcium flux patterns that resemble intact retinal neurons. Once graft-to-host network is established, progressive vision loss is stabilized while control eyes continually lose vision. Therefore, transplantation of organoid-derived C-Kit+ RPCs can form functional synaptic networks within ADR and it holds promising avenue for advanced RD treatment.

Functional assessment of cryopreserved clinical grade hESC-RPE cells as a qualified cell source for stem cell therapy of retinal degenerative diseases.

The biosafety and efficiency of transplanting retinal pigment epithelial (RPE) cells derived from both human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have been evaluated in phase I and phase II clinical trials. For further large-scale application, cryopreserved RPE cells must be used; thus, it is highly important to investigate the influence of cryopreservation and thawing on the biological characteristics of hESC-RPE cells and their post-transplantation vision-restoring function. Here, via immunofluorescence, qPCR, transmission electron microscopy, transepithelial electrical resistance, and enzyme-linked immunosorbent assays (ELISAs), we showed that cryopreserved hESC-RPE cells retained the specific gene expression profile, morphology, ultrastructure, and maturity-related functions of induced RPE cells. Additionally, cryopreserved hESC-RPE cells exhibited a polarized monolayer, tight junction, and gap junction structure and an in vitro nanoparticle phagocytosis capability similar to those of induced hESC-RPE cells. However, the level of pigment epithelium-derived factor (PEDF) secretion was significantly decreased in cryopreserved hESC-RPE cells. Royal College of Surgeons rats with cryopreserved hESC-RPE cells engrafted into the subretinal space exhibited a significant decrease in the b-wave amplitude compared with rats engrafted with induced hESC-RPE cells at 4 weeks post transplantation. However, the difference disappeared at 8 weeks and 12 weeks post operation. No significant difference in the outer nuclear layer (ONL) thickness was observed between the two groups. Our data showed that even after cryopreservation and thawing, cryopreserved hESC-RPE cells are still qualified as a donor cell source for cell-based therapy of retinal degenerative diseases.

Microglia Mediate Synaptic Material Clearance at the Early Stage of Rats With Retinitis Pigmentosa.

Resident microglia are the main immune cells in the retina and play a key role in the pathogenesis of retinitis pigmentosa (RP). Many previous studies on the roles of microglia mainly focused on the neurotoxicity or neuroprotection of photoreceptors, while their contributions to synaptic remodeling of neuronal circuits in the retina of early RP remained unclarified. In the present study, we used Royal College of Surgeons (RCS) rats, a classic RP model characterized by progressive microglia activation and synapse loss, to investigate the constitutive effects of microglia on the synaptic lesions and ectopic neuritogenesis. Rod degeneration resulted in synapse disruption and loss in the outer plexiform layer (OPL) at the early stage of RP. Coincidentally, the resident microglia in the OPL increased phagocytosis and mainly engaged in phagocytic engulfment of postsynaptic mGluR6 of rod bipolar cells (RBCs). Complement pathway might be involved in clearance of postsynaptic elements of RBCs by microglia. We pharmacologically deleted microglia using a CSF1 receptor (CSF1R) inhibitor to confirm this finding, and found that it caused the accumulation of postsynaptic mGluR6 levels and increased the number and length of ectopic dendrites in the RBCs. Interestingly, the numbers of presynaptic sites expressing CtBP2 and colocalized puncta in the OPL of RCS rats were not affected by microglia elimination. However, sustained microglial depletion led to progressive functional deterioration in the retinal responses to light in RCS rats. Based on our results, microglia mediated the remodeling of RBCs by phagocytosing postsynaptic materials and inhibiting ectopic neuritogenesis, contributing to delay the deterioration of vision at the early stage of RP.

Changes in intrinsic excitability of ganglion cells in degenerated retinas of RCS rats.

AIM: To evaluate the intrinsic excitability of retinal ganglion cells (RGCs) in degenerated retinas. METHODS: The intrinsic excitability of various morphologically defined RGC types using a combination of patch-clamp recording and the Lucifer yellow tracer in retinal whole-mount preparations harvested from Royal College of Surgeons (RCS) rats, a common retinitis pigmentosa (RP) model, in a relatively late stage of retinal degeneration (P90) were investigated. Several parameters of RGC morphologies and action potentials (APs) were measured and compared to those of non-dystrophic control rats, including dendritic stratification, dendritic field diameter, peak amplitude, half width, resting membrane potential, AP threshold, depolarization to threshold, and firing rates. RESULTS: Compared with non-dystrophic control RGCs, more depolarizations were required to reach the AP threshold in RCS RGCs with low spontaneous spike rates and in RCS OFF cells (especially A2o cells), and RCS RGCs maintained their dendritic morphologies, resting membrane potentials and capabilities to generate APs. CONCLUSION: RGCs are relatively well preserved morphologically and functionally, and some cells are more susceptible to decreased excitability during retinal degeneration. These findings provide valuable considerations for optimizing RP therapeutic strategies.

Proteomic profiling of early degenerative retina of RCS rats.

AIM: To identify the underlying cellular and molecular changes in retinitis pigmentosa (RP). METHODS: Label-free quantification-based proteomics analysis, with its advantages of being more economic and consisting of simpler procedures, has been used with increasing frequency in modern biological research. Dystrophic RCS rats, the first laboratory animal model for the study of RP, possess a similar pathological course as human beings with the diseases. Thus, we employed a comparative proteomics analysis approach for in-depth proteome profiling of retinas from dystrophic RCS rats and non-dystrophic congenic controls through Linear Trap Quadrupole - orbitrap MS/MS, to identify the significant differentially expressed proteins (DEPs). Bioinformatics analyses, including Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation and upstream regulatory analysis, were then performed on these retina proteins. Finally, a Western blotting experiment was carried out to verify the difference in the abundance of transcript factor E2F1. RESULTS: In this study, we identified a total of 2375 protein groups from the retinal protein samples of RCS rats and non-dystrophic congenic controls. Four hundred thirty-four significantly DEPs were selected by Student's t-test. Based on the results of the bioinformatics analysis, we identified mitochondrial dysfunction and transcription factor E2F1 as the key initiation factors in early retinal degenerative process. CONCLUSION: We showed that the mitochondrial dysfunction and the transcription factor E2F1 substantially contribute to the disease etiology of RP. The results provide a new potential therapeutic approach for this retinal degenerative disease.

Effect of optogenetic stimulus on the proliferation and cell cycle progression of neural stem cells.

Modulation of stem cell proliferation is a crucial aspect of neural developmental biology and regenerative medicine. To investigate the effect of optical stimulation on neural stem cell proliferation, cells transduced with channelrhodopsin-2 (ChR2) were used to analyze changes in cell proliferation and cell cycle distribution after light stimulation. Blue light significantly inhibited cell proliferation and affected the cell cycle, which increased the percentage of cells in G1 phase and reduced the percentage in S phase. It is likely that the influence of blue light on cell proliferation and the cell cycle was mediated by membrane depolarization, which induced accumulation of p21 and p27 proteins. Our data provide additional specific evidence that membrane depolarization may inhibit neural stem cell proliferation.

Transplanted olfactory ensheathing cells reduce retinal degeneration in Royal College of Surgeons rats.

PURPOSE OF THE STUDY: Retinitis pigmentosa (RP) is a group of genetic disorders and a slow loss of vision that is caused by a cascade of retinal degenerative events. We examined whether these retinal degenerative events were reduced after cultured mixtures of adult olfactory ensheathing cells (OECs) and olfactory nerve fibroblasts (ONFs) were transplanted into the subretinal space of 1-month-old RCS rat, a classic model of RP. MATERIALS AND METHODS: The changes in retinal photoreceptors and Müller cells of RCS rats after cell transplantation were observed by the expression of recoverin and glial fibrillary acidic protein (GFAP), counting peanut agglutinin (PNA)-positive cone outer segments and calculating the relative apoptotic area. The retinal function was also evaluated by Flash electroretinography (ERG). To further investigate the mechanisms, by which OECs/ONFs play important roles in the transplanted retinas, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF) secretion of the cultured cells were analyzed by ELISA. The ability of OECs/ONFs to ingest porcine retinal outer segments and the amount of phagocytosis were compared with retinal pigment epithelium (RPE) cells. RESULTS: Our research showed that the transplantation of OECs/ONFs mixtures restored recoverin expression, protected retinal outer segments, increased PNA-positive cone outer segments, reduced caspase-positive apoptotic figures, downregulated GFAP, and maintained the b-wave of the ERG. Cultured OECs/ONFs expressed and secreted NGF, BDNF, and bFGF which made contributions to assist survival of the photoreceptors. An in vitro phagocytosis assay showed that OECs, but not ONFs, phagocytosed porcine retinal outer segments, and the phagocytic ability of OECs was even superior to that of RPE cells. CONCLUSIONS: These findings demonstrate that transplantation of OECs/ONFs cleaned up the accumulated debris in subretinal space, and provided an intrinsic continuous supply of neurotrophic factors. It suggested that transplantation of OECs/ONFs might be a possible future route for protection of the retina and reducing retinal degeneration in RP.

[The modification of electrophysiology affected by ectopic synapse in ON-retinal bipolar cells of RCS rats].

OBJECTIVE: To study the influence of the ectopic synapse for electrophysiological characteristics modification in ON retinal bipolar cells (ON-RBCs) of RCS rat. METHODS: Immunofluorescence of the retinal frozen section was taken in P60 d, P90 d of RCS rat (RCS) and control rat (CTR) with the anti-mGluR6 and anti-Synaptophysin, Lucifer Yellow staining solo ON-RBCs was taken in all the group. The whole cell recording was performed in the retinal slice of P60 d, P90 d in RCS and CTR. The modification of the passive membrane properties and the outward currents properties in RCS-ON-RBCs, CTR-ON-RBCs and CTR-OFF-RBCs were observed. RESULTS: RCS-ON-RBCs stretched out the ectopic neurite in different direction and the activity of synapse could be detected around the ectopic neurite. From Pn60d, passive membrane properties of RCS-ON-RBCs kept immature, The RMP in RCS-ON-RBCs and CTR-ON-RBCs were (-61.8 ± 3.07), (-50.44 ± 1.36) mV and (-63.1 ± 2.59), (-48.37 ± 3.69) mV when P60 d and P90 d, there ware significantly higher than CTR group (t = 2.191, 2.435, 5.817, 6.912;P < 0.05). The IR in RCS-ON-RBCs and CTR-ON-RBCs were (323.3 ± 42.6), (337.6 ± 71.3) MΩ and (321.2 ± 58.6), (340.3 ± 62.8) MΩ when P60 d and P90 d, there ware significantly higher than CTR group (t = 3.561, 1.987, 5.211, 4.034; P < 0.05). Outward currents were recorded when giving hyper- and depolarized voltage steps. In retinal degeneration, the amplitude of outward currents in RCS-ON-RBCs is significantly different with CTR-ON-RBCs (t = 5.561, 6.341; P < 0.05) or CTR-OFF-RBCs (t = 5.357, 6.997; P < 0.05). CONCLUSION: The ectopic neurite from RCS-ON-RBCs has the possibility for translating the signal. In retinitis pigmentosa, the modification of electrophysiology characteristics in RCS-ON-RBCs was significantly different with CTR-ON-RBCs and CTR-OFF-RBCs. Influence with the ectopic neurite is the possible cause.