Actin as a Potential Target to Spur Regeneration of Axons in the Adult Nervous System

Adult neurons retain the developmental infrastructure to be able to regrow damaged axons, in principle, but this capability is repressed after early development ends. Researchers here explore the details of the controlling mechanism. The goal at the end of the day is to produce the means to unlock regrowth in adult nerve tissue, particularly the spinal column. A great deal of research and development in regenerative medicine is of this nature, a search for ways to reenable the processes of regulated growth that took place during early development.

It is commonly accepted that neurons of the central nervous system shut down their ability to grow when they no longer need it; this occurs normally after they have found their target cells and established synapses. However, recent findings show that old nerve cells have the potential to regrow and to repair damage similar to young neurons. "Actually, this is quite surprising. It is by no means a matter of course that young and adult nerve cells share the same mechanisms. Neurons show vigorous growth during embryonic development. Mature nerve cells, on the other hand, usually do not grow and fail to regenerate. Our study now reveals that although the ability to grow is inhibited in adult cells, the neurons keep the disposition for growth and regeneration."

Neurons only show their growth talent during embryonic development. At this stage, they form long projections called axons in order to connect and thus transmit signals. However, the ability to grow and thus regrow after injury dwindles when the nervous system reaches the adult stage. Only neurons of the periphery, e. g. those in the arms and legs, retain a pronounced potential for mending damaged connections. However, if axons in the spinal cord are severed, they do not regrow. Consequently, the pathway for nerve impulses remains disturbed.

In recent years scientists identified various factors that influence the growth of neurons. Certain proteins - those of the cofilin/ADF family - proved to play a pivotal role. During embryonic development, these molecules control the formation of cell protuberances that ultimately evolve into axons. The scientists found that the growth and regrowth of neurons is fueled by the turnover of actin filaments. These string shaped molecules belong to the molecular scaffold that gives the cell its form and stability. The proteins of the cofilin/ADF family partially dissolve this corset. It is only through this breakup that the structure of the cell can change - and thus the neuron can grow and regenerate. "In our recent study, we found that it is precisely these proteins that drive growth and regeneration, also in adult neurons. An approach for future regenerative interventions could be to target actin."



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