To visualize protein aggregates (red) under the microscope, they have to be stained previously. The cellular nucleus was stained blue and the mRNA, the construction manual for proteins, was stained green. Credit: MPI of Biochemistry
January 12, 2016
In the
brains of patients with neurodegenerative diseases, medical researchers can
observe protein deposits, also called aggregates. For many years, these
aggregates have been suspected to contribute to the death of nerve cells, and
to diseases like Alzheimer's, Parkinson's, or Huntington's. Scientists from the
Max Planck Institute of Biochemistry in Martinsried, led by Mark Hipp and
Ulrich Hartl, have now shown that the location of protein aggregates strongly
influences the survival of cells. While aggregates within the nucleus barely
influence cellular function, deposits of identical proteins within the
cytoplasm interfere with important transport routes between the nucleus and the
cytoplasm. This results in a blockage of protein and RNA transport into and out
of the nucleus. In the long run this can lead to the death of the affected
cells, and progression of the disease. The results of these studies have now
been published in the journal Science.
Proteins
consist of long chains of amino acids and function in cells like small
machines. To be able to fulfill their function proteins have to assume a
predetermined three-dimensional structure. In healthy cells there is a large
variety of folding helpers and extensive quality control machinery. Misfolded
proteins are either repaired or rapidly degraded. If this occurs inadequately,
or not at all, proteins will clump together, form aggregates and harm the cell.
Protein
aggregates are associated with many neurodegenerative diseases
including ALS, Alzheimer's, Parkinson's and Huntington's Disease. How exactly
aggregates harm cells is however still unknown. In 2013 several groups in
Martinsried formed the ToPAG consortium to address this question, and can now
report their first success. Scientists in the lab of Prof. Hartl, a
world-renowned expert on protein
folding, have demonstrated that the location of the aggregates determines the
fate of the nerve cells.
Together
with Konstanze Winklhofer and Jörg Tatzelt from the Ruhr-University Bochum, the
researchers have expressed artificial aggregation prone proteins as well as
Huntington's disease-causing mutants of the protein huntingtin in cultured
cells. Both types of protein accumulate in large protein deposits. "It
came as a big surprise to us that the direction of the proteins to the
cytoplasm instead of the nucleus resulted in more soluble, but also more toxic
aggregates", says Mark Hipp, a group leader in the department of Ulrich
Hartl and leader of the study. The protein deposits in the cytoplasm blocked
the transport of RNA and correctly folded proteins between the nucleus and the
cytoplasm. It seems that the sticky surfaces of the aggregates can sequester important
proteins and thereby inactivate them. "We have detected multiple
components of the cellular transport machinery inside the aggregates. This
results in the depletion of these factors from the cell, and, like a machine
with missing parts, the cell is then unable to function properly",
explains Andreas Woerner the first author of the study. Once the blueprint for
all proteins, the RNA, is trapped within the nucleus, protein synthesis cannot
progress, and the cells deteriorate. It is not completely clear why the nuclear
aggregates are less harmful, but the researchers have evidence that the nuclear
protein NPM1 plays a central role in shielding these aggregates.
"The
results of this study bring us researchers and physicians one big step
further", summarizes Mark Hipp. "Only if we understand how aggregates
damage cells is it possible to
develop appropriate countermeasures in the future."
Read more
at: http://phys.org/news/2016-01-protein-aggregates-cytoplasm-important-routes.html#jCp
http://phys.org/news/2016-01-protein-aggregates-cytoplasm-important-routes.html |
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