IT HAS only recently been accepted that adult human brains can generate new cells. Now it appears that, in at least one degenerative disease, the brain can greatly increase production in an attempt to repair damage.
The brains of people with Huntington鈥檚 disease churn out new brain cells at a far higher rate than normal, according to neuroscientist Richard Faull of the University of Auckland in New Zealand. 鈥淏ut it鈥檚 too little, too late,鈥� he told the conference.
However, the discovery raises the possibility of developing drugs to encourage cells to regenerate faster and sooner. 鈥淭he damaged brain is obviously trying to mend itself, but the disease is so devastating it doesn鈥檛 succeed,鈥� says Piers Emson, who works on neurodegenerative diseases at Britain鈥檚 Babraham Institute in Cambridge. 鈥淏ut if you could manipulate the system, you鈥檇 potentially be in the business of treating conditions like Huntington鈥檚, Parkinson鈥檚 or epilepsy.鈥�
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The nerve cells of the adult human brain were long thought to be too specialised to regenerate. That dogma was overturned just five years ago, with the discovery that new nerve cells are generated in some parts of adult brains. But Faull鈥檚 team is the first to show that the brain may ratchet up the production rate in response to damage.
In Huntington鈥檚, a defective protein kills brain cells in the striatum. This causes patients to lose control of their movement, and leads to severe cognitive and behavioural deterioration. So the team looked at the part of a layer of cells called the subependyma that is just above the striatum in the brains of 18 people who had just died, nine of them from Huntington鈥檚 disease.
The researchers studied the subependyma layer because it spawns new cells in the brains of developing fetuses and, to a far lesser extent, in adults. Special staining techniques revealed that the cells were indeed dividing. Although most of the new cells were developing into glial cells, which support nerve cells, about 5 per cent were developing into neurons.
Far more new cells were found in the nine people with Huntington鈥檚. 鈥淚n milder cases, we saw moderate numbers of new cells. In the most severe cases, we saw massive numbers. It鈥檚 that clear,鈥� says Faull.
Neurosurgeons can now access the brain relatively easily and safely. So it might even be possible to collect growing brain cells from people with, say, a spinal injury, generate large numbers in the lab and then use them to treat that person鈥檚 injury. Using a patient鈥檚 own cells would prevent problems with immune rejection.
Winning by a nose in the race for stem cells
THE nose could be a convenient source of adult stem cells.
Stem cells that can develop into a variety of different tissue types have great potential for treating diseases. But although adult stem cells are found in many tissue, the most promising ones seem to be those in bone marrow, and extracting them is a serious procedure.
However, Wayne Murrell and Alan Mackay-Simm of Griffith University in Brisbane suspected that stem cells should also exist in the nose, because nasal nerve cells regenerate throughout life. The team has already tried to exploit this by attempting to repair spinal cords using nasal nerve cells called olfactory ensheathing cells (麻豆传媒, 13 July 2002, p 18). The results of that study have yet to be announced.
In the meantime, Murrell told the meeting, the team has identified cells in human noses that can be grown in large numbers in the lab and that turn into heart, muscle and liver cells when transplanted into chick embryos. The cells also form nerve and muscle cells in the lab. Stem cells from the noses of rats seem to have even wider potential.
Other stem cell experts are cautious about the announcement, because it is difficult to prove a cell is a true stem cell that can spawn fully functional tissue. 鈥淯ntil we have peer review of the fine detail of the experiments, we don鈥檛 know whether they have definitively proved they have a stem cell,鈥� says Peter Mountford of Stem Cell Sciences in Melbourne.
If the results do stand up to scrutiny, it would be a boon for those working on adult human stem cells, because the nasal cells can be collected in minutes using a probe inserted into the nostrils, after first numbing the nose. Extracting bone marrow, by contrast, involves inserting a needle into the hip bone under general or local anaesthetic. It can take several days to recover.
