New microscopy technique assists with stem cell screening

Japanese researchers have found a new way to identify stem cells with the greatest potential for medical use.

Pluripotent stem cells (PSCs) can transform into any type of cell in the human body. This unique property gives them enormous potential for regenerative medicine, as stem cells might eventually be used to replace tissues that are lost as a result of degenerative disorders or from injuries.

Not all stem cells are created equal, though, and some are better than others at differentiating into the desired tissues. With this in mind, a research team led by the University of Tsukuba developed a new microscopy technique that can identify the PSCs most likely to undergo transformation. Their work has been published in the journal Scientific Reports.

“When stem cells are used for medical purposes, it’s incredibly important that the right type of PSCs are selected at the outset,” said Koji Hisatake, corresponding author on the study. “Cells that have low pluripotency are not especially effective after being transplanted in a patient. Even worse, in some cases there’s a risk that they can form tumours. Our goal was to improve on earlier microscopy techniques so that we can do a better job at isolating stem cells with high pluripotency, which are more likely to be safe and effective for therapeutic use.”

Traditionally, such stem cells have been identified by staining or labelling them with special fluorescent markers — rigorous and invasive processes that can damage or destroy the cells. Taking a different tack, the researchers developed a modified form of differential interference contrast (DIC) microscopy, a non-invasive approach that is commonly used to look at cells. Their new technique, coined phase distribution (PD) imaging, takes DIC one step further by offering higher resolution at the cellular level.

“The basic principle behind DIC is that cell structures can be visualised because they each scatter light a little bit differently,” lead investigator Ken Nishimura explained. “These differences are captured using crystal prisms that polarise light waves as they travel through the microscope.

“Our PD microscope works similarly, but is unique in that the prisms are actually movable. This lets us capture two separate images of the cell, at right angles from one another, and then merge the images together using a computer. The final picture has a much greater level of detail than what we’re able to get with a traditional DIC microscope. With PD, we can not only visualise but also quantifiably measure important structures inside the cell, most notably mitochondria.”

Mitochondria are the tiny, oxygen-devouring energy powerhouses of the cell, and while most cells are jam-packed with them, highly potent stem cells in fact have fewer and smaller mitochondria. The research team took advantage of this key difference and, with the help of their improved imaging system, they were able to quantify the level of mitochondria in each cell and use it as a reliable way to isolate PSCs with the greatest medical potential.

“PD imaging allows us to non-invasively identify stem cells that have been fully reprogrammed and likely have exceptional pluripotency,” Nishimura said. “The system is less costly and time-consuming than other screening methods, so we’re hopeful that this will eventually become an important tool in the screening arsenal, especially during the critical early stages of stem cell selection.”

Image credit: ©stock.adobe.com/au/catalin

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