|
Granulin
promotes proliferation and aggregation of differentiating neural
progenitors
Tom Nabhani, Ichiro Nakano, Rebecca Erickson, Robert Prins, Harley Kornblum, Linda
M. Liau
University of California at Los Angeles, Los Angeles, CA
Objective.
Granulin is a growth factor that is over expressed in high-grade
gliomas.
We have shown that granulin is
a potent mitogen for astrocytes and glioblastoma cells; however, the
cellular substrate for granulin is unknown.
The objective of our work was
to examine the role of granulin in neural progenitor
proliferation.
Our first hypothesis was that
granulin is an autocrine-paracrine growth factor that is released from
neural progenitors.
Our second hypothesis was that
granulin promotes proliferation of differentiating neural progenitors.
Methods. To test
our first hypothesis, we cultured dissociated neural progenitors on
poly-l-lysine coated glass cover slips and incubated them with
antibodies to granulin and nestin.
These cells were then labeled
with fluorescent secondary antibodies and examined using video
microscopy.
To address our second
hypothesis, we subcultured dissociated neurospheres in a
differentiation medium containing neurobasal medium and retinoic acid
(DM).
The first group was a control
group cultured in DM alone.
The second group was cultured
in a DM with granulin (GRN) at a concentration of 100 μg/ml.
The third group was cultured in
DM and 1:100 dilution of granulin antibody (GRNAB).
These cells were maintained in
these conditions, with the cells being fed appropriate concentrations
of either granulin peptide or granulin antibody each day. After five
days, the diameter and number of cell aggregates were recorded.
Results. After
immunolabeling, we found a population of cells that were strongly
positive for both granulin and nestin, indicating co-expression of
these molecules in neural progenitors.
The results of our cell
proliferation studies were as follows (mean number of cell aggregates
per well) control (33); GRN (44.3), GRNAB (55.7); cell diameter
measurements (mean μm ± standard deviation μm) control (56.4 ± 23.3), GRN
(88.9 ± 40.4), GRNAB (58.4 ± 21.8).
Conclusion. We
have identified a sub-population of nestin-positive, granulin-positive
neural progenitors.
Application of granulin to
differentiating neural progenitors results in cellular proliferation
and aggregation of proliferating progenitors.
Blockade of granulin activity
prevents formation of cellular aggregates and attenuates
proliferation.
These data suggest that
granulin plays an important role in controlling neural progenitor
proliferation.
Studies are currently underway
to validate these findings and to further examine the role of granulin
in neural progenitor proliferation and differentiation
Copyright © 2005 American
Association for Cancer Research. All rights reserved.
|
