Harnessing the Potential of Human Pluripotent Stem Cells and Gene Editing for the Treatment of Retinal Degeneration

PURPOSE OF REVIEW: A major cause of visual disorders is dysfunction and/or loss of the light-sensitive cells of the retina, the photoreceptors. To develop better treatments for patients, we need to understand how inherited retinal disease mutations result in the dysfunction of photoreceptors. New advances in the field of stem cell and gene editing research offer novel ways to model retinal dystrophies in vitro and present opportunities to translate basic biological insights into therapies. This brief review will discuss some of the issues that should be taken into account when carrying out disease modelling and gene editing of retinal cells. We will discuss (i) the use of human induced pluripotent stem cells (iPSCs) for disease modelling and cell therapy; (ii) the importance of using isogenic iPSC lines as controls; (iii) CRISPR/Cas9 gene editing of iPSCs; and (iv) in vivo gene editing using AAV vectors. RECENT FINDINGS: Ground-breaking advances in differentiation of iPSCs into retinal organoids and methods to derive mature light sensitive photoreceptors from iPSCs. Furthermore, single AAV systems for in vivo gene editing have been developed which makes retinal in vivo gene editing therapy a real prospect. SUMMARY: Genome editing is becoming a valuable tool for disease modelling and in vivo gene editing in the retina

Assessment of AAV vector tropisms for mouse and human pluripotent stem cell-derived RPE and photoreceptor cells

Adeno-associated viral vectors are showing great promise as gene therapy vectors for a wide range of retinal disorders. To date, evaluation of therapeutic approaches has depended almost exclusively on the use of animal models. With recent advances in human stem cell technology, stem-cell derived retina now offers the possibility to assess efficacy in human organoids in vitro. Here we test 6 AAV serotypes (AAV2/2, AAV2/9, AAV2/8, AAV2/8T(Y733F), AAV2/5 and ShH10) to determine their efficiency in transducing mouse and human pluripotent stem cell (PSC)-derived RPE and photoreceptor cells in vitro. All the serotypes tested were capable of transducing RPE and photoreceptor cells in vitro. AAV ShH10 and AAV2/5 are the most efficient vectors at transducing both mouse and human RPE, while AAV2/8 and ShH10 achieved similarly robust transduction of human ESC-derived cone photoreceptors. Furthermore, we show that hESC-derived photoreceptors can be used to establish promoter specificity in human cells in vitro. The results of this study will aid capsid selection and vector design for pre-clinical evaluation of gene therapy approaches, such as gene editing, that require the use of human cells and tissues

Harnessing the Potential of Human Pluripotent Stem Cells and Gene Editing for the Treatment of Retinal Degeneration

PURPOSE OF REVIEW: A major cause of visual disorders is dysfunction and/or loss of the light-sensitive cells of the retina, the photoreceptors. To develop better treatments for patients, we need to understand how inherited retinal disease mutations result in the dysfunction of photoreceptors. New advances in the field of stem cell and gene editing research offer novel ways to model retinal dystrophies in vitro and present opportunities to translate basic biological insights into therapies. This brief review will discuss some of the issues that should be taken into account when carrying out disease modelling and gene editing of retinal cells. We will discuss (i) the use of human induced pluripotent stem cells (iPSCs) for disease modelling and cell therapy; (ii) the importance of using isogenic iPSC lines as controls; (iii) CRISPR/Cas9 gene editing of iPSCs; and (iv) in vivo gene editing using AAV vectors.RECENT FINDINGS: Ground-breaking advances in differentiation of iPSCs into retinal organoids and methods to derive mature light sensitive photoreceptors from iPSCs. Furthermore, single AAV systems for in vivo gene editing have been developed which makes retinal in vivo gene editing therapy a real prospect.SUMMARY: Genome editing is becoming a valuable tool for disease modelling and in vivo gene editing in the retina.</p

Identification of Factors in Regulating a Protein Ubiquitination by Immunoprecipitation: a Case Study of TRF2 on Human REST4 Ubiquitination.

Ubiquitination is the first step of the ubiquitin-proteasome pathway that regulates cells for their homeostatic functions and is an enzymatic, protein post-translational modification process in which ubiquitin is transferred to a target protein substrate by a set of three ubiquitin enzymes (Weissman et al., 2011; Bhattacharyya et al., 2014; Ristic et al., 2014). Given the importance of this process, it is plausible that ubiquitination is under strict control by many factors and that the regulatory machineries are protein-specific. An assay for the detection of a specific protein ubiquitination will enable us to examine whether a factor has a function to regulate the ubiquitination of this protein. Here we describe a protocol that detects the ubiquitination status of the human REST4 protein in cultured cells, a neural alternative splicing isoform of REST (RE-1 silencing transcription factor), that antagonizes the repressive function of REST on neural differentiation and neuron formation. Using this protocol, we show that the telomere binding protein TRF2 stabilizes the expression of the human REST4 by inhibiting its ubiquitination. This indicates that TRF2 plays a positive role in neural differentiation (Ovando-Roche et al., 2014). This protocol is also useful for the detection of ubiquitination of other proteins of interest

Specific Localization of the Drosophila Telomere Transposon Proteins and RNAs, Give Insight in Their Behavior, Control and Telomere Biology in This Organism

Drosophila telomeres constitute a remarkable exception to the telomerase mechanism. Although maintaining the same cytological and functional properties as telomerase maintain telomeres, Drosophila telomeres embed the telomere retrotransposons whose specific and highly regulated terminal transposition maintains the appropriate telomere length in this organism. Nevertheless, our current understanding of how the mechanism of the retrotransposon telomere works and which features are shared with the telomerase system is very limited. We report for the first time a detailed study of the localization of the main components that constitute the telomeres in Drosophila, HeT-A and TART RNAs and proteins. Our results in wild type and mutant strains reveal localizations of HeT-A Gag and TART Pol that give insight in the behavior of the telomere retrotransposons and their control. We find that TART Pol and HeT-A Gag only co-localize at the telomeres during the interphase of cells undergoing mitotic cycles. In addition, unexpected protein and RNA localizations with a well-defined pattern in cells such as the ovarian border cells and nurse cells, suggest possible strategies for the telomere transposons to reach the oocyte, and/or additional functions that might be important for the correct development of the organism. Finally, we have been able to visualize the telomere RNAs at different ovarian stages of development in wild type and mutant lines, demonstrating their presence in spite of being tightly regulated by the piRNA mechanism.This work was supported by a grant from the Spanish Ministry of Science and Innovation BFU2009-08318/BMC to EC. A National Institutes of Health grant R01GM067758 to ERG. EL-P acknowledges the following short term Fellowships: Ruth Lee Kennedy (Fulbright), EMBO short term, Journal Cell Science traveling Fellowship, and the Spanish Society of Genetics traveling fellowship.Peer reviewe