Researchers in Japan have developed a new, noninvasive way to monitor the tricky art of stem cell production.
The current era of ethical stem cell research was ushered in by the 2012 Nobel prize-winning discovery that ordinary cells could be coaxed to revert to their earliest pluripotent stage ushered in. Suddenly, scientists could have an ethical, near-inexhaustible supply of pluripotent stem cells — the most versatile of stem cells — that can become any type of cell much like how embryonic stem cells function.
These reprogrammed cells called induced pluripotent stem cells (or iPS cells) hold great promise for regenerative medicine, where they can be used to develop tissue or organ replacement-based treatments for life-threatening diseases.
One key challenge is that it is a lengthy and delicate process to artificially induce ordinary cells to reset back to pluripotency. Obtaining iPS cells therefore is a matter of chance. However, knowing all they can about the complex chemical changes happening inside during reprogramming can help scientists increase the chances of successfully obtaining viable iPS cells for clinical applications. Current methods that track reprogramming status, however, use destructive and costly techniques.
A study led by Dr Tomonobu Watanabe, professor at Hiroshima University’s Research Institute for Radiation Biology and Medicine, showed that Raman spectroscopy could be a low-cost, simpler, and non-intrusive technique to monitor the cell’s internal environment as it transitions.
Dr Watanabe explained: “The quality evaluation and sorting of existing cells have been carried out by investigating the presence or absence of expression of surface marker genes. However, since this method requires a fluorescent antibody, it is expensive and causes a problem of bringing the antibody into the cells.”
He added that the “solution of these problems can accelerate the spread of safe and low-cost regenerative medicine using artificial tissues. Through our method, we provide a technique for evaluating and sorting the quality of iPS cells inexpensively and safely, based on scattering spectroscopy.”
Raman spectroscopy is an alternative to invasive approaches that require dyes or labels to extract biochemical information. It instead makes use of vibration signatures produced when light beams interact with chemical bonds in the cell. Since each chemical has its own distinct vibration frequency, scientists can use it to identify the cell’s molecular makeup.
The team used this spectroscopic technique to get the “chemical fingerprints” of mouse embryonic stem cells, the neuronal cells they specialised into, and the iPS cells formed from those neuronal cells. These data were then used to train an AI model to can track the reprogramming is progressing, and verify iPS cell quality by checking for a “fingerprint” match with the embryonic stem cell.
To measure the progress, they assigned the “chemical fingerprint” of neuronal cells as the transformation starting point and the embryonic stem cell’s patterns as the desired end goal. Along the axis, they used “fingerprint” samples collected on days 5, 10, and 20 of the neuronal cells’ reprogramming as reference points on how the process is advancing.
“The Raman scattering spectrum contains comprehensive information on molecular vibrations, and the amount of information may be sufficient to define cells. If so, unlike gene profiling, it allows for a more expressive definition of cell function,” Dr Watanabe said.
“We aim to study stem cells from a different perspective than traditional life sciences.”
Source: Hiroshima University
Journal information: Germond, A., et al. (2020) Following Embryonic Stem Cells, Their Differentiated Progeny, and Cell-State Changes During iPS Reprogramming by Raman Spectroscopy. Analytical Chemistry doi.org/10.1021/acs.analchem.0c01800.
