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Retinal organoids generated from human pluripotent stem cells exhibit considerable variability in temporal dynamics of differentiation. To assess the maturity of neural retina in vitro, we performed transcriptome analyses of developing organoids from human embryonic and induced pluripotent stem cell lines. We show that the developmental variability in organoids was reflected in gene expression profiles and could be evaluated by molecular staging with the human fetal and adult retinal transcriptome data. We also demonstrated that addition of 9-cis retinal, instead of widely-used all-trans retinoic acid, accelerated rod photoreceptor differentiation in organoid cultures, with higher rhodopsin expression and more mature mitochondrial morphology evident by day 120. Our studies thus provide an objective transcriptome-based modality for determining the differentiation state of retinal organoids, which should facilitate disease modeling and evaluation of therapies in vitro.

Ischemia/reperfusion (I/R) injury is a considerable insult to skeletal muscle, often resulting in prolonged functional deficits. The purpose of the current study was to evaluate the controlled release of the pro-regenerative growth factor, insulin-like growth factor-I (IGF-I), from a biodegradable polyethylene glycol (PEG)ylated fibrin gel matrix and the subsequent recovery of skeletal muscle from I/R. To accomplish this, the hind limbs of male Sprague–Dawley rats were subjected to 2-h tourniquet-induced I/R then treated with saline, bolus IGF-I (bIGF), PEGylated fibrin gel (PEG-Fib), or IGF-I conjugated PEGy-lated fibrin gel (PEG-Fib-IGF). Functional and histological evaluations were performed following 14 days of reperfusion, and muscles from 4-day reperfusion animals were analyzed by Western blotting and histological assessments. There was no difference in functional recovery between saline, bIGF, or PEG-Fib groups. However, PEG-Fib-IGF treatment resulted in significant improvement of muscle function and structure, as observed histologically. Activation of the PI3K/Akt pathway was significantly elevated in PEG-Fib-IGF muscles, compared to PEG-Fib treatment, at 4 days of reperfusion, suggesting involvement of the pathway PI3K/Akt as a mediator of the improved function. Surprisingly, myoblast activity was not evident as a result of PEG-Fib-IGF treatment. Taken together, these data give evidence for a protective role for the delivered IGF. These results indicate that PEG-Fib-IGF is a viable therapeutic technique in the treatment of skeletal muscle I/R injury.