Old Human Cells Rejuvenated With Stem Cells

Yamanaka protein factors are commonly used to transform adult cells into induced pluripotent stems cells, these iPS cells can become nearly any type of cell within the body regardless of the cell they originated from, and they have become important in regenerative medicine and drug discovery. 

Inducing old human cells in a lab dish to briefly express these proteins reversed many of the molecular hallmarks of aging, and rendered the treated cells to be nearly indistinguishable from their younger counterparts, according to this study published in Nature Communications. 

"When iPS cells are made from adult cells, they become both youthful and pluripotent," said Vittorio Sebastiano, PhD, assistant professor of obstetrics and gynecology and the Woods Family Faculty Scholar in Pediatric Translational Medicine. "We've wondered for some time if it might be possible to simply rewind the aging clock without inducing pluripotency. Now we've found that, by tightly controlling the duration of the exposure to these protein factors, we can promote rejuvenation in multiple human cell types."

"We are very excited about these findings," said study co-author Thomas Rando, MD, PhD, professor of neurology and neurological sciences and the director of Stanford's Glenn Center for the Biology of Aging. "My colleagues and I have been pursuing the rejuvenation of tissues since our studies in the early 2000s revealed that systemic factors can make old tissues younger. In 2012, Howard Chang and I proposed the concept of using reprogramming factors to rejuvenate cells and tissues, and it is gratifying to see evidence of success with this approach." Chang, MD, PhD, is a professor of dermatology and of genetics at Stanford.

The researchers made iPSs from adult cells by repeatedly exposing them over a period of 2 weeks to a panel of proteins important to early embryonic development, with daily introductions to short lived RNA messages that encode instructions for making the Yamanaka proteins. Over time the proteins reverse the cells along the developmental timeline until they resemble young embryonic-like pluripotent cells from which they originated. During the process the cells shed all memory of previous identity and revert to a younger state, which is accomplished by wiping their DNA clean of molecular tags that differentiate from other tags that accumulate as a cell ages. 

The team wondered if old human cells would respond to the process in a similar manner, and whether the response would be limited to just a few cell types or if it would be generalizable for many tissues. A way was devised to use genetic RNA messenger materials to temporarily express 6 reprogramming factors in human skin and blood vessels; these rapidly degrade in cells which allowed the researchers to tightly control the duration of the signals. Gene expression patterns of the treated cells and control cells both obtained from eldery adults were compared with those of untreated cells from younger donors. Treated cells from the elderly were found to exhibit signs of aging reversal after only 4 days of exposure to the reprogramming factors, while the untreated cells expressed higher levels of genes associated with aging pathways and the treated cells more closely resembled younger cells in patterns of gene expression. 

The patterns of aging associated methyl aging groups were examined as an indicator of chronological age to reveal that the treated cells appeared to be 1.5 to 3.5 years younger on average than the untreated cells from the elderly donors, with peaks of 3.5 years in skin cells and 7.5 year peaks in cells that line blood vessels. 

"We saw a dramatic rejuvenation across all hallmarks but one in all the cell types tested," Sebastiano said. "But our last and most important experiment was done on muscle stem cells. Although they are naturally endowed with the ability to self-renew, this capacity wanes with age. We wondered, can we also rejuvenate stem cells and have a long-term effect?"

When old mouse stems cells that were treated were transplanted back into the elderly mice the animals were observed to have regained the muscle strength of younger mice, according to the researchers. 

When cells were isolated from the cartilage of people with/without osteoarthritis temporary exposure to the reprogramming factors was observed to reduce the secretion of inflammatory molecules and to improve the cells’ ability to divide and function. 

"Although much more work needs to be done, we are hopeful that we may one day have the opportunity to reboot entire tissues," Sebastiano said. "But first we want to make sure that this is rigorously tested in the lab and found to be safe."