While it has been demonstrated that gene mutations are associated with an increasing number of neurodegenerative syndromes, environmental neurotoxicants remain a key factor in the etiology of many such diseases. For example, exposure to pesticides such as maneb and paraquat increase the risk of developing Parkinson's disease. Unfortunately, there is no optimal in vitro model system to assess the neurotoxic potential of compounds. As result, exposure to poorly characterized compounds represents a significant contributor to the development of environmentally-induced diseases. There is a compelling unmet need for in vitro models and endpoint assays that are cost-effective, accurate, predictive, and sensitive that would also be amenable to high throughput screening. In particular, there is a need to develop homogeneous in vitro screens that can be used in quantitative high-throughput screening to query large libraries of chemical compounds such as the 'Tox21 10K' chemical library. We will take advantage of our core strengths in site-specific nuclease genome engineering and Footprint-Free' Gene Editing to produce reporter cell lines in which we will insert reporter genes into the endogenous toxicant-responsive genes SERPINE1 and DDIT3 by homologous recombination (i.e., create knockin mutations) in order to create a cost- effective, rapid system for neurotoxicity testing. Briefly, we engineer a SERPINE1 exon 2-specific site-specific nuclease in-house to drive the targeted insertion of firefly luciferase T2A-renilla luciferase (lux) reporter immediately downstream of the SERPINE1 initiator ATG so that the lux gene will be placed under the control of SERPINE1 promoter within the native genomic context; similarly we will knock in a TEM1-beta lactamase reporter behind the ATG of DDIT3. The targeting vectors will contain a piggyBac selection module containing the puromycin resistance and thymidine kinase genes, to allow selection for candidate targeted clones via puromycin resistance and to select for complete removal of the expression module upon transient expression of excision-only piggyBac transposase via ganciclovir resistance. As a result, the endogenous SERPINE1 and DDIT3 loci will contain their respective reporters without any other foreign DNA sequences will be created. To validate the function of the reporter cells, we will compare the induction properties of the targeted lux and BLA reporters with that of their corresponding untargeted (wild type) alleles using reporter (luciferase or beta-lactamase) and qRT-PCR assays, respectively. Success will be achieved if the magnitude of induction for the reporters falls within 20% of the induction observed for each reporter's corresponding endogenous gene for each test compound assayed. Validation of the cell lines will provide an initial tool for screening high-throughput screening for neurotoxicants and will represent the development of a powerful platform technology for the creation of cell lines for neurotoxicology screening. In the long term, Phase II studies would be aimed at creating a bank of reporter cell lines that sample the responses of multiple loci in a variety of lines that we will be able to markt as catalog items; we would also be able to market custom creation of knock-in, toxicant-responsive reporter lines and the use of either catalog or custom cell lines in fee-for-service toxicity testing as a service to academic and industry investigators, and open new opportunities for examining the impact of agents on specific pathways in a wide variety of cellular contexts.
The in vitro tools currently used for testing the toxicity of potential neurotoxicants are not optimal and frequently result in incorrect information about a compound or screen. Given that neurotoxicity can lead to Parkinson-like degenerative diseases; new strategies that are cost-effective; accurate; predictive; and sensitive would be a great value for preventing disease caused by man-made or natural compound exposure.
| Singh, Amar M; Adjan Steffey, Valeriya V; Yeshi, Tseten et al. (2015) Gene Editing in Human Pluripotent Stem Cells: Choosing the Correct Path. J Stem Cell Regen Biol 1: |
