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M. J. Seiler, P. B. Yang, R. B. Aramant, F. Yan, M. J. Mahoney, L. M. Kitzes, H. S. Keirstead; Visual Restoration in a Rat Degeneration Model by Retinal Progenitor Sheet Transplants Is Corroborated by Laminar Organization and Evidence for Synaptic Connectivity With Cellular and Synaptic Markers. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5251.
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© ARVO (1962-2015); The Authors (2016-present)
To corroborate the functional restoration in a retinal degeneration model by study of organization and synaptic connectivity of retinal progenitor sheet transplants in degenerated host retinas.
Donor fetal retinal progenitor sheets of transgenic rats expressing human placental alkaline phosphatase (hPAP) were transplanted to transgenic S334ter line 3 rats (24-40 d), with or without BDNF and/or GDNF microspheres. Visual responses in the superior colliculus (SC; -5.0 to -0.1 log cd/m2) were recorded 55 - 270 d after surgery in rats with retinal and control cortex transplants and sham surgeries. Retinal cryostat sections were stained with antibodies against hPAP (donor marker), synaptic markers (synapsin, bassoon, synaptophysin, PSD 95), the metabotropic receptor mGluR6, and retinal cell markers (PKC, recoverin, CaMKII, rhodopsin, red-green and blue opsin, CRALBP).
About 45% of transplants with visual responses contained large areas with correct lamination (rod outer segments in contact with host RPE); the other 55% were disorganized in rosettes. Visual responses were found only in the SC of retina transplanted rats in an area corresponding to the transplant placement in the retina. Retinal degenerate controls had no responses. SC response thresholds of transplanted rats varied between -3.6 and - 0.1 log cd/m2. Laminated transplants showed significantly better visual thresholds (-2.15 ± 0.1 log cd/m2) and larger reponsive areas (30.5± 2.3% of the SC surface) than rosetted transplants (- 1.6 ± 0.15 log cd/m2 and 20.7± 2.4%, respectively). Growth factors improved visual thresholds, response levels and size of responsive areas. No histological difference was seen compared to untreated transplants. hPAP-labeling revealed extensive outgrowth of transplant processes into the host inner plexiform layer. No rods were found in the host retina, and only scattered remnants of cones. Transplants showed varying degrees of connectivity, with crossing of PKC-immunoreactive fibers and absence of glial limiting membranes between transplant and host. Transplant processes were closely associated with synaptic markers (both inside and outside the processes), indicating that transplant processes formed synapses with unlabeled host cells.
A key importance for the degree of restored host visual function is the laminar transplant organization and its synaptic connectivity with the host retina.
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