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News — Yale researchers are sifting through a mosaic of cells in a living animal — both normal cells and mutated cells — to better understand how cancer grabs a foothold. But they’re starting by studying tolerance.

Most biological organisms, including humans, accumulate cancer-causing mutations in their tissue. Many of these mutated cells, however, are tolerated by the body and therefore never develop into full-blown disease.

But why? What distinguishes the tolerated cells, or the body’s response to them, from cells that advance into cancers that grow?

Using mouse models, a team led by the Yale labs of Valentina Greco and Rachel Perry looked at two types of mutations in stem cells in the skin. They tracked the “competition” between normal stem cells and each of the mutated cells over time.

What the researchers discovered is that for tolerated mutations, the body’s first reaction is an immediate “redox” response, in which a cell experiences a rapid drop in its redox ratio — a chemical reaction that indicates more oxidation in the cells. It acts as a readout of changes in the way cells metabolize (or break down) glucose.

“We saw that metabolism responds very quickly to cancer mutations in the skin stem cell layer,” said Anupama Hemalatha, a former associate research scientist in Greco’s lab in the Yale School of Medicine’s Department of Genetics and first author of a . Hemalatha recently accepted a faculty position at the Friedrich Miescher Institute for Biomedical Research in Switzerland.

“Using our imaging technique, called multiphoton imaging, we capture these early changes in the mutated cell’s metabolism in the skin of a live mouse and track it through time,” Hemalatha added.

But the lowered redox itself was a big surprise, the researchers said.

There are two key pathways of glucose metabolism: glycolysis and oxidation. Glycolysis can be considered akin to chopping down a tree and cutting it into several large pieces, whereas oxidation equates to burning the tree in a bonfire, generating energy. Typically, while cancer cells are rabid users of glucose via the glycolytic pathway, they use less oxidation than healthy cells, because they prefer to divert glycolytic products toward building new cells. This is a phenomenon known as the Warburg effect.

“What we discovered was almost the opposite of the Warburg effect,” said Perry, who is an associate professor of endocrinology and of cellular and molecular physiology. “The mutation that persisted in the skin increased metabolism of glucose through both the glycolytic and oxidative pathways, whereas the mutation that was eliminated increased glucose oxidation despite reduced glycolysis.”

The researchers then continued tracking the progress of the two “tolerated” mutations, one that is typically removed from skin over time and another that remains in the skin but does not lead to disease.

The mutation that is normally eliminated from skin maintained its lower redox ratio, compared with neighboring healthy cells, they found. The mutation that remained in the skin saw its redox ratio increase, “flattening out” in comparison with neighboring, healthy cells said Greco, the Carolyn Walch Slayman Professor of Genetics and of cell biology and dermatology and a Howard Hughes Medical Institute Investigator.

As a final step in their investigation, the researchers treated the animals with mutated cells with the drug Metformin to inhibit the early redox and metabolic changes. The treatment caused a reversal of each mutation’s behavior in the tissue. Mutated cells that had been expanding halted their expansion; mutated cells that were being eliminated from the skin were no longer able to be eliminated efficiently.

“The implication is that the outcome of cell competition is dependent upon the early metabolic responses initiated by the cancer-causing mutations in the skin stem cells,” Hemalatha said. “If these metabolic changes didn’t happen, then many of the downstream changes would not happen.”

The researchers plan to expand their investigation into instances where cell mutations are not tolerated by neighboring cells to learn whether a similar redox response persists.

Co-authors of the study from Yale are Zongyu Li, David Gonzalez, Catherine Matte-Martone, Karen Tai, Elizabeth Lathrop, Smirthy Ganesan, and Lauren Gonzalez. Other authors are Daniel Gil and Melissa Skala from the University of Wisconsin-Madison.

Greco and Perry are also members of the Yale Cancer Center and Greco is a member of the Yale Stem Cell Center at Yale’s West Campus.

The research was supported by grants from the National Institutes of Health and the LEO Foundation, and a postdoctoral fellowship (for Hemalatha) from the New York Stem Cell Foundation.