After a patient has undergone a stroke, his brain creates new nerve cells – the mechanism behind this process has remained undeciphered until now. Recently, a team from a university in Sweden has discovered the events that lead to the production of new neurones following a stroke. The study was published in the journal Science.
A stroke occurs when the brain is deprived of oxygen. This happens when the blood flow that is supposed to drain its cells is blocked by a blood clot in one of its blood vessels. As a result, nerve cells die because of the chronic lack of oxygen.
However, in the aftermath of a stroke, new nerve cells are formed. But, how does this happen?
Astrocytes converting into mature nerve cells
The researchers experimented on laboratory mice. The animals were made to have strokes. Later, it was observed that certain cells began manufacturing nerve cells in the region of the brain where the damage was done. The scientists wanted to prove that the origin of the new nerve cells are, in fact, support cells known as astrocytes. They used genetic mapping methods to show that the astrocytes transformed from being immature nerve cells to later develop into mature nerve cells.
“This is the first time that astrocytes have been shown to have the capacity to start a process that leads to the generation of new nerve cells after a stroke,” says Zaal Kokaia, Professor of Experimental Medical Research at Lund University.
Signalling mechanism unveiled
The results of the study also revealed the signalling mechanism that triggers the transformation of the astrocytes into nerve cells. It was shown that this process was inhibited in a healthy brain, with the signalling mechanism activated. However, after a stroke, the mechanism is suppressed and the astrocytes are then allowed to generate new nerve cells.
“Interestingly, even when we blocked the signalling mechanism in mice not subjected to a stroke, the astrocytes formed new nerve cells,” says Zaal Kokaia. “This indicates that it is not only a stroke that can activate the latent process in astrocytes. Therefore, the mechanism is a potentially useful target for the production of new nerve cells, when replacing dead cells following other brain diseases or damage.”
However, it is still a mystery as to the exact role of the newly-generated nerve cells: are they functional, and what is their part in post-stroke recovery?
“One of the major tasks now is to explore whether astrocytes are also converted to neurons in the human brain following damage or disease. Interestingly, it is known that in the healthy human brain, new nerve cells are formed in the striatum. The new data raise the possibility that some of these nerve cells derive from local astrocytes. If the new mechanism also operates in the human brain and can be potentiated, this could become of clinical importance not only for stroke patients, but also for replacing neurons which have died, thus restoring function in patients with other disorders such as Parkinson’s disease and Huntington’s disease,” says Olle Lindvall, Senior Professor of Neurology.