The age of wisdom. That’s what Google, and the American Association of Oral and Maxillofacial Surgeons, calls the period between the ages of 17 and 25, when wisdom teeth typically emerge. As I keenly recall my late teens and early 20s, I’m now not so sure that “wisdom teeth” is a particularly apt term. But I am sure that researchers have recently discovered a very smart way to use our third molars: as a source of stem cells that could one day help regrow and repair damaged tissue.
For more than a decade, researchers in the field of regenerative medicine have been looking for ways to regrow human tissues to replace tissue that’s diseased, or damaged from birth defect or injury. They’ve turned to stem cells for starting material.
Tissues of adults and children supply so-called “adult stem cells,” the least controversial type. But, unfortunately, adult stem cells that can be extracted from tissues like the skin or bone marrow are rather limited. They can usually regenerate only one or two types of cells out of the more than 200 types in the body.
In a breakthrough finding in 2006, researchers at Kyoto University in Japan reported that by activating four key genes in adult mouse cells, they could reprogram the cells to resemble the cells of the early embryo. The new cells are known as induced pluripotent stem (iPS) cells, and like the controversial embryonic stem cells, they can transform into any type of human cell. Since 2006, scientists have reprogrammed human cells called fibroblasts from the deep layers of the skin to create human iPS cells. These discoveries raise hopes of replacement tissues regrown from a patient’s own cells.
But making human iPS cells has not proved easy. Only a tiny percentage of the fibroblasts form iPS cells. Two of the genes that researchers use to reprogram fibroblasts may predispose the iPS cells to cancer. To develop a safe, easy way to tap source of cells, Hajime Ohgushi, MD, Ph.D. of the Health Research Institute in Hyogo, Japan, turned to extracted wisdom teeth.
Ohgushi’s team obtained mesenchymal stromal cells from wisdom teeth pulled from a ten-year-old, a 13-year-old, and a 16-year-old and grew them in the lab. The soft pulp inside teeth contains cells called mesenchymal stromal cells.
First, they showed that these cells could grown readily in the lab, and that these fast-growing cells could be quickly reprogrammed, and much more efficiently than skin cells could. They reprogrammed the cells by adding three of the four genes that reprogrammed fibroblasts—but not either of the two that are linked to cancer. Then they performed five biochemical tests, which together showed that the reprogrammed cells closely resembled human embryonic stem cells. More importantly, the reprogrammed cells could morph into a variety of human tissue types.
That was all good news. “Because human third molars are discarded as clinical waste,” Ohgushi and colleagues write, the stem cells inside them could be “frozen and stored for many years.” This makes them “a useful cell source for the generation of iPS cells,” the Japanese team concludes.
But the bad news was that the tooth-derived iPS cells, like other iPS cells, easily formed a tumor called a teratoma when implanted in immune-deficient mice. For that reason, Tom Diekwisch, DMD, Ph.D., professor of oral biology at the University of Illinois, Chicago, is cautious about saying when, or if, this advance will help patients. “Experimentally, the paper is wonderful,” and the iPS cells derived from wisdom teeth should be very helpful to researchers. But because of the cancer risk, “practically it’s still a little too early” for clinical use, Diekwisch says. Nevertheless, Diekwisch says, in generating iPS cells from wisdom teeth, “they have done the right thing.”
CONNECT THE DOTS
The California Institute for Regenerative Medicine offers this FAQ on stem cells, where they come from, and the advantages and disadvantages of each type. The American Association of Oral and Maxillofacial Surgeons offers this good background information on wisdom teeth.
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