Abstract 010: A Separable Upstream Promoter of the Slc8a1 (NCX1) Gene Efficiently Marks Cardiac Cell Populations Derived from Human Pluripotent Stem Cells
The sarcolemmal Na+/Ca2+ exchanger SLC8A1(NCX) regulates intracellular Ca+ in cardiomyocytes from early developmental stages. The upstream-most SLC8A1(NCX1) promoter is well conserved amongst the homoeothermic animals and contains putative binding sites for transcription factors of the NKX, GATA, STAT and CDX families. We hypothesized that functional cardiac cells with mature cardiac structural markers will express the sarcolemmal Na+/Ca2+ calcium antiporting channel, important for proper functional contractivity of in vitro differentiated human pluripotent stem cells. Pseudotyped lentiviral particles delivering NCX1cp-EGFP reporter cassette were used to confirm the efficiency and specificity of the reporter in rodent foetal cardiac cell isolates, and to establish stable human pluripotent stem cell lines. Cells were differentiated using a 2D induction protocol, and gene expression analysis and protein quantification carried at day 16. Initial NCX1cp-EGFP expression was observed from day 10-11 of cardiac differentiation. Beating foci were visualized 1-2 day after initial NCXCP-EGFP expression, reporter expression was confined to the grouped and individual beating cells, and highly correlated with the efficiency of spontaneously contractile cell production. At later stages, NCX1cp-EGFP expression correlated with clusters of formed spontaneously contractile units harbouring essentially all cardiomyocytes present in cultures, as evidenced by colocalization of high levels of cardiac troponin T (cTnT) and α-actinin proteins. The EGFP+ sorted fraction of differentiated cultures was found to be highly enriched in both early (ISL1, TBX5) and late (cTnT, MYH6) cardiomyocyte markers when compared to the EGFP- fraction. We conclude that a ~3 kb genomic fragment of the distal cardiac-specific promoter of the SLC8A1(NCX1) containing the upstream-most exon of the gene is sufficient to drive the expression of a lentiviral reporter in both rodent heart-derived primary and human (embryonic and induced) pluripotent stem cell-derived cardiac cells. Isolation of a homogenous and functional cardiomyogenic population represents one of the key objectives for cardiac tissue engineering, and in particular in vitro drug screening applications.
- © 2013 by American Heart Association, Inc.