Generation of Healthy Mice from Gene-Corrected Disease-Specific Induced Pluripotent Stem Cells

Using the murine model of tyrosinemia type 1 (fumarylacetoacetate hydrolase [FAH] deficiency; FAH−/− mice) as a paradigm for orphan disorders, such as hereditary metabolic liver diseases, we evaluated fibroblast-derived FAH−/−-induced pluripotent stem cells (iPS cells) as targets for gene correction in combination with the tetraploid embryo complementation method. First, after characterizing the FAH−/− iPS cell lines, we aggregated FAH−/−-iPS cells with tetraploid embryos and obtained entirely FAH−/−-iPS cell–derived mice that were viable and exhibited the phenotype of the founding FAH−/− mice. Then, we transduced FAH cDNA into the FAH−/−-iPS cells using a third-generation lentiviral vector to generate gene-corrected iPS cells. We could not detect any chromosomal alterations in these cells by high-resolution array CGH analysis, and after their aggregation with tetraploid embryos, we obtained fully iPS cell–derived healthy mice with an astonishing high efficiency for full-term development of up to 63.3%. The gene correction was validated functionally by the long-term survival and expansion of FAH-positive cells of these mice after withdrawal of the rescuing drug NTBC (2-(2-nitro-4-fluoromethylbenzoyl)-1,3-cyclohexanedione). Furthermore, our results demonstrate that both a liver-specific promoter (transthyretin, TTR)-driven FAH transgene and a strong viral promoter (from spleen focus-forming virus, SFFV)-driven FAH transgene rescued the FAH-deficiency phenotypes in the mice derived from the respective gene-corrected iPS cells. In conclusion, our data demonstrate that a lentiviral gene repair strategy does not abrogate the full pluripotent potential of fibroblast-derived iPS cells, and genetic manipulation of iPS cells in combination with tetraploid embryo aggregation provides a practical and rapid approach to evaluate the efficacy of gene correction of human diseases in mouse models

Hepatic Differentiation of Murine Disease-Specific Induced Pluripotent Stem Cells Allows Disease Modelling In Vitro

Direct reprogramming of somatic cells into pluripotent cells by retrovirus-mediated expression of OCT4, SOX2, KLF4, and C-MYC is a promising approach to derive disease-specific induced pluripotent stem cells (iPSCs). In this study, we focused on three murine models for metabolic liver disorders: the copper storage disorder Wilson's disease (toxic-milk mice), tyrosinemia type 1 (fumarylacetoacetate-hydrolase deficiency, FAH−/− mice), and alpha1-antitrypsin deficiency (PiZ mice). Colonies of iPSCs emerged 2-3 weeks after transduction of fibroblasts, prepared from each mouse strain, and were maintained as individual iPSC lines. RT-PCR and immunofluorescence analyses demonstrated the expression of endogenous pluripotency markers. Hepatic precursor cells could be derived from these disease-specific iPSCs applying an in vitro differentiation protocol and could be visualized after transduction of a lentiviral albumin-GFP reporter construct. Functional characterization of these cells allowed the recapitulation of the disease phenotype for further studies of underlying molecular mechanisms of the respective disease

Synthetic Notch-Receptor-Mediated Transmission of a Transient Signal into Permanent Information via CRISPR/Cas9-Based Genome Editing

Synthetic receptor biology and genome editing are emerging techniques, both of which are currently beginning to be used in preclinical and clinical applications. We were interested in whether a combination of these techniques approaches would allow for the generation of a novel type of reporter cell that would recognize transient cellular events through specifically designed synthetic receptors and would permanently store information about these events via associated gene editing. Reporting cells could be used in the future to detect alterations in the cellular microenvironment, including degenerative processes or malignant transformation into cancer cells. Here, we explored synthetic Notch (synNotch) receptors expressed in human embryonic kidney cells to investigate the efficacy of antigen recognition events in a time- and dose-dependent manner. First, we evaluated the most suitable conditions for synNotch expression based on dsRed-Express fluorophore expression. Then, we used a synNotch receptor coupled to transcriptional activators to induce the expression of a Cas9 nuclease targeted to a specific genomic DNA site. Our data demonstrate that recognition of various specific antigens via synNotch receptors robustly induced Cas9 expression and resulted in an indel formation frequency of 34.5%–45.5% at the targeted CXCR4 locus. These results provide proof of concept that reporter cells can be designed to recognize a given event and to store transient information permanently in their genomes