Biologists in Shanghai, China, have achieved direct conversion of normal and familial Alzheimer's Disease (FAD) human fibroblasts into functional neuronal cells through use of small molecules. In their published report, they aim to prove the resulting human chemical-induced neuronal cells (hciNs) are similar to human induced pluripotent stem cell (hiPSC)-derived neurons and other human induced neurons in morphology, gene expression profiles, and electrophysiological properties. In a previous paper, the biologists applied a chemical cocktail to convert mouse fibroblasts and human urinary cells into neural progenitor cells. Thus, for their current report, successfully converting fibroblasts sourced from FAD patients illustrates their steps toward potential treatments in regenerative medicine and provides novel strategies for modeling neurological disease.

After completing the induction of their neuronal cells, the next objective was to verify that the hciNs were able to function properly. Since patch-clamp analysis could only process a small amount of cells, the researchers decided to use calcium indicator Cal-520^® to observe the activity of large numbers of hciNs at once. The researchers observed very robust and spontaneous calcium responses, suggesting that the hciN neural network was active. They compared the percentage of active hciNs with a culture of iPSC-derived neurons under the same Cal-520^® treatment and concluded that they were not significantly different from one another.

Cal-520^® is often used as a sensitive fluorescent probe for visualizing neural activity, due to its affinity and fluorogenic response with and to calcium. Cal-520^® is also relatively easy to use and apply to larger amounts of cells, including thicker bolus loading. Therefore, Cal-520^® is a most fitting dye for this study and other similar neuroscience experiments.