Biology prof finds methods of identifying usable stem cells

As a potential method for producing cells to repair failing systems in human bodies, many scientists are looking to stem cells cells that have the power to differentiate or transform into many different cell types. Scientists already know how to extract stem cells from adult human fat and hope they will someday be able to take a persons own cells and develop the tissues they need.

But there is a major constraint to this plan out of all the cells drawn from adult fat, only a small percentage can successfully turn into the desired cell type. Some could even turn into harmful cell types. To tackle this challenge, Eric Darling, assistant professor of biology, and his lab are working to produce two methods to sort the useable cells from the chaos.

Youre reliant on these cells, said Hetal Desai GS, lead researcher on one of the projects. If youre trying to grow a bone, youre reliant on how well the cells going to respond to (the chemical stimulus), how well theyre going to accomplish turning into (something like) bone. So if you have a bunch of cells that are essentially going to just hang out and not do anything, thats bad. If you can weed those out and keep the ones that are optimal thats where these techniques really have a lot of power. Desais research, published Sept. 5, focused on developing a probe that would light up when stem cells were transforming into the correct cell type. The labs other recent project in the area took a different tack measuring the physical properties of cells to see their potential to turn into bone, cartilage or fat.

Glowing beacons When a stem cell is differentiating, it sends messenger RNA signals that produce specific proteins and help it transform. Darlings team created a probe that binds to specific RNA and lights up showing when specific cells are beginning to differentiate specifically into bone.

We were basically able to quantify, in living cells and in real time, how many of these cells are expressing the genes at different stages of turning into bone, Desai said. She started work on the project while she was on rotation in Darlings lab and stayed on to make it a main research focus.

The probe, which was developed in 1996 and can be designed to respond to any specific gene, was dispatched into two groups of stem cells derived from fat one which had been treated by a chemical to induce differentiation into bone and one that had not. Looking at the cells, an observer could immediately tell by the glow which cells were responding positively to the chemical signals. Over the course of three weeks, the group watched the waves of fluorescence mark the different stages in the cells transformations.

Desai said the hardest part of the study was designing the probe. We needed it to be a fly on the wall of the process, she said. We didnt want it to interfere with the cell, but we wanted to make sure we had a really clear signal that we could assess really easily. The team designed the probe to only interface with the specific RNA that indicated differentiation, and they ran several experiments to ensure the probe was not blocking the cells from using the RNA normally.

Eventually, the researchers hope the probe can be used to pick out cells responding well to the chemical signals in a clinical setting, providing a mechanism for sorting between cells. Richard Freiman, associate professor of biology at Brown who was not involved in the study, called this the most exciting aspect of the research.

In thinking about therapy, measuring changes on those cells before you actually put them back into a patient is absolutely essential, he said. Its rare to be able to do that with living cells if one can, its very powerful.

A predictive approach In addition to developing the molecular probe, Darlings lab tackled the sorting from a predictive angle in a study published this May. The idea came to Darling during his post-doctorate at Duke University, when he used an atomic force microscope to examine the physical properties of cells. Darling said he found that stem cells had a wide variation and wondered whether that variation could predict the cells ability to turn into different kinds of tissue.

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Biology prof finds methods of identifying usable stem cells