An Ultrasensitive Calcium Reporter System via CRISPR-Cas9-Mediated Genome Editing in Human Pluripotent Stem Cells.

Genetically encoded calcium indicator (GCaMP) proteins have been reported for imaging cardiac cell activity based on intracellular calcium transients. To bring human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) to the clinic, it is critical to evaluate the functionality of CMs. Here, we show that GCaMP6s-expressing hPSCs can be generated and used for CM characterization. By leveraging CRISPR-Cas9 genome editing tools, we generated a knockin cell line that constitutively expresses GCaMP6s, an ultrasensitive calcium sensor protein. We further showed that this clone maintained pluripotency and cardiac differentiation potential. These knockin hPSC-derived CMs exhibited sensitive fluorescence fluctuation with spontaneous contraction. We then compared the fluorescence signal with mechanical contraction signal. The knockin hPSC-derived CMs also showed sensitive response to isoprenaline treatment in a concentration-dependent manner. Therefore, the GCaMP6s knockin hPSC line provides a non-invasive, sensitive, and economic approach to characterize the functionality of hPSC-derived CMs.