— Clumps of misfolded proteins cause traffic jams in brain cells. Those jams
may have deadly consequences in neurodegenerative diseases.
Clusters of prions
block passage of crucial cargo along intracellular roadways in brain cells,
cell biologist Tai Chaiamarit of the Scripps Research Institute in La Jolla,
Calif., reported December 10 at the joint annual meeting of the American
Society for Cell Biology and the European Molecular Biology Organization.
Prions, misshaped versions of a normal
brain protein, clump together in large aggregates that are hallmarks of
degenerative brain diseases, such as mad cow disease in cattle, chronic wasting
disease in deer and Creutzfeldt-Jakob disease in people. It’s unclear why those
clumpy proteins are so deadly to nerve cells called neurons, but the new study
may provide clues about what goes wrong in these diseases.
Axons, the long stringlike projections
of nerve cells that carry electrical signals to other nerves, are the sites of
prion traffic jams, Chaiamarit and colleagues found. As more prions clump
together, they cause swollen bulges that make the axon look like a snake that
has just swallowed a big meal.
Through a microscope, Chaiamarit and colleagues
saw mitochondria being transported toward the cell’s furthest reaches derailed
at the bulges.
Mitochondria, cells’ energy-generating
organelles, are carried outbound from the main body of the cell by a motor
protein called kinesin-1. The protein motors along molecular rails called
microtubules. A different motor protein, dynein, transports mitochondria back
toward the cell body along those same rails.
Prion clumps disrupt outbound traffic,
causing kinesin-1 and mitochondria to jump the microtubule tracks in the
swollen sections, the researchers discovered. Microtubules may be bent or
broken in those spots. Mitochondria movement back toward the cell body wasn’t impaired,
perhaps because dynein is better at avoiding obstacles than kinesin-1,
Brain cells are alive when the traffic
jams start, but the researchers think the jams contribute to cell death later.
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