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Can we renew our brains?

Akiko Mori
Stanford University
August 2003

It has been commonly known that the process to make a brain is completed at young adulthood, and thereafter we lose brain cells gradually. But this is not the case. Researchers have found that humans continue to make new cells even in late adulthood. This occurs in two regions of the brain: the hippocampus, the center of memory, and the olfactory region, which works for smelling. Why only in these regions? I'm now trying to find the answer for this question by finding a specific signal in the hippocampus and olfactory region which allow cells to grow. I hope the knowledge gained from my work could be used to prevent and cure neurodegenerative diseases such as Alzheimer's.

Many people suffer from neurodegenerative diseases like Alzheimer's or Parkinson's. In the brain of such people, neurons (or nerve cells) die at a much higher speed than normal people. When this happens, these people suffer from memory loss in Alzheimer's disease or impairment of body movement in Parkinson's disease, respectively.

A major approach to fight against these diseases is trying to prevent neuron death by medication, because people have believed that a brain never regenerates. But recent findings that show new neurons born in an adult brain change the situation. It might be possible that we could induce regeneration of the brain.

Have you ever heard the word "stem cell"? A stem cell in the brain has the potential to become three types of cells: a neuron, a glia, or an oligodendrocyte. A neuron is a kind of cable that transmits signals. An oligodendrocyte covers this cable like insulation, and glia cells fill the space between cables. Among these cells, the neuron plays a central part for memory function. To take advantage of the potential of stem cells for medical applications, we should first stimulate stem cells to grow in the brain to increase the source of neurons, and then we need to instruct them to become neurons instead of the other two types.

I'm now studying how cells react to signals surrounding stem cells. Stem cells receive many signals from neighboring cells and extra-cellular matrix, a sponge-like structure where cells are embedded. Based on the complicated combination of the signals they receive, stem cells decide when they grow and which cell type they become. In my work, I treat purified stem cells from a rat brain with a couple of purified proteins in a plastic culture dish. This simplified system makes the result clearer than studying it in the rat brain itself. I dissect brain tissue and treat it with a solution to separate cells from each other. The various cell types are sorted so I can collect the stem cell population. When the isolated stem cells are placed on a plastic dish, they start to grow using nutrition in the culture medium. When I add a kind of protein factor into culture dish, stem cells start to grow faster, and then decide to become a neuron instead of a glia or oligodendrocyte. Then I will know whether the added factors induced stem cell growth, and then whether stem cells turned into neurons instead.

Accumulating this information will give us basic data to think about what are the key protein factors allowing stem cells to grow in the hippocampus and olfactory region, where neurons are born in adulthood. This will enable us to manipulate brain stem cells to reconstruct structures in other parts of the brain that are lost in neurodegenerative diseases. The day where we could renew our brain may possibly come true.