Reserve Stem Cells Come to the Rescue

Johns Hopkins University, May 6, 2007

Our sense of smell is continually attacked by harsh chemicals that we unintentionally inhale, risking damage or death to our olfactory cells. Without these nerve cells, the only cells in the body to run directly to the brain with information of the outside world, we would lose our sense of smell.

But we may be able to repair the most severe damage to the nerves responsible for our sense of smell with the assistance of a backup supply of stem cell that were discovered by Johns Hopkins researchers. When adjacent cells die, the reserve cells move to correct the deficiency. But usually, they remain dormant. Next weeks online edition of Nature Neuroscience will repot on the new discovery.

“These stem cells act like the Army Reserves of our nose,” explains lead author Randall Reed, Ph.D., a professor of neuroscience at Johns Hopkins, “supporting a class of active-duty stem cells that help repair normal wear and tear. They don’t come in until things are really bad.”

Mouse olfactory nerves were exposed to a cloud of toxic methyl-bromide gas in order to determine how the olfactory system repairs severely damaged nerve cells. Adjacent non-nerve cells within the nasal passage were also killed alongside the olfactory nerve cells when subjected to a methyl bromide environment. Reed’s team checked to see if any of the nasal cells grew back three weeks following the chemical exposure.

HBCs, a population of cells that were not known beforehand for repair abilities, were the origin of both the new non-nerve and nerve cells.

“We were stunned because HBCs normally don’t grow much or do anything,” says Reed. “And the most surprising thing is that HBCs can grow into both nerves and non-nerve cells; they do so by generating the other active type of nasal stem cell.”

Where only the olfactory nerve cells are killed under less damaging circumstances, the team went back to study the nerve repair in this specific situation. The team’s observation resulted in the finding that the HBCs permitted the previously known stem cells to do all the repair work, as opposed to repair the damaged cells themselves.

“The ability to smell is crucial for eating, mating and survival, and it’s important that the olfactory system be fully operational all the time,” explains Reed. “The HBCs act as a fail-safe to ensure continued function of the sense of smell.”

Reed is interested in discovering similar repair mechanisms working in other types of nerves in the body. His discovery of one neural tissue harboring two distinct types of stem cells is a first.

The National Institutes of Health and the Howard Hughes Medical Institute funded the research.