Behind the Mechanics of Brain Injury: The Buckling of Microtubules in Axons

The mechanics of traumatic brain injury (TBI) are beginning to be unveiled.  A team at the University of Pennsylvania, led by Douglas Smith, has discovered exactly what happens when a brain experiences a sudden blow.  The team observed microtubules snapping inside the axons, the long fibers that extend from brain cells.

Microtubules are the “superhighways of protein transfer,” according to Douglas Smith ((Sanders, Laura. "Brain at the Breaking Point." ScienceNews 13 Mar 2010: n. pag. Web. 28 Feb 2010. <http://sciencenews.org/view/generic/id/56455/title/Brain_at_the_breaking_point>)). These cytoskeletal tracks are hollow crystalline cylinders composed of tubulin, lattices of protein. Microtubules form synaptic connections in the neurons.

Vital cellular materials and nutrients are transported along the microtubules to the terminal buttons of the axon.  Axons that make up neurons depend on this axoplamic transport for survival.

Researchers have tried to uncover what component of the axon rapid deforms as a result of injury. By using mimicked neuron cultures on silicone membranes, Smith and his colleagues examined the bending and collapsing of the microtubules by stretching the axons ((Tang-Schomer MD. "Mechanical breaking of microtubules in axons during dynamic stretch injury underlies delayed elasticity, microtubule disassembly, and axon degeneration..." PubMed (2009): n. pag. Web. 28 Feb 2010. <http://www.ncbi.nlm.nih.gov/pubmed/20019243?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=1>)). It was concluded that the specific points along the “cargo track” disintegrate and impede the reshaping of the axons.

Such splitting of microtubules can be fatal because the torn axons release their internal chemicals, which are possibly toxic once outside of the cell.  In addition, activities of the cells are discontinued, which disrupts the normal transport of the axoplasm and ultimately leads to the swelling of axons and degeneration of brain cells ((Tang-Schomer MD. "Mechanical breaking of microtubules in axons during dynamic stretch injury underlies delayed elasticity, microtubule disassembly, and axon degeneration..." PubMed (2009): n. pag. Web. 28 Feb 2010. <http://www.ncbi.nlm.nih.gov/pubmed/20019243?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=1>)).

Because these microtubules are the stiffest part of the axons and also grow stiffer as the human ages, they are the most susceptible to damage from a dynamic external force.  Any stress applied over short duration, such as those from car crashes, ruptures the microtubules, resulting in diffuse axonal injury.

More than 1.4 million people suffer from TBI in the United States ((Sanders, Laura. "Brain at the Breaking Point." ScienceNews 13 Mar 2010: n. pag. Web. 28 Feb 2010. <http://sciencenews.org/view/generic/id/56455/title/Brain_at_the_breaking_point>)). The results of this research will prove to be a huge stepping stone in discovering ways to treat traumatic brain injuries as researchers determine what they must focus on.  With increased understanding of how and why these injuries occur, scientists may find ways to minimize microtubule damage, aiding millions of patients around the globe.

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