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Lowdose Radiation Program Workshop V
Abstract
_____________________________________________________________________
Title: Radiation-Induced Modulation of Mitochondrial Protein
Import Capacity in Normal Human Fibroblasts
Authors: Badri N. Pandey1,2,
Donna Gordon3, Debkumar Pain3 and Edouard Azzam1
Institutions: 1Department
of Radiology, New Jersey Medical School, Newark, NJ 07103,
USA, 2Radiation Biology and Health Sciences Division
Bhabha Atomic Research Centre, Mumbai - 400 085, India, 3Department
of Pharmacology and Physiology, New Jersey Medical School,
Newark, NJ 07103, USA
To investigate the mitochondrial response
in cells exposed to low and high dose γ- radiation
from a 137Cs source, we examined the efficiency of protein
import into mitochondria isolated from control and irradiated
AG1522 normal human diploid fibroblasts. Experimental conditions
were optimized for the import of frataxin into the mitochondrial
matrix. Mitochondrial membrane potential (MMP) and an ATP-regenerating
system were found to be required for efficient import. Compared
to controls, a significant decrease in import capacity was
observed in mitochondria isolated from density-inhibited
cell cultures exposed to a toxic dose of 4 Gy (3.3 Gy/min)
and subsequently incubated at 37 °C for 1 h. Incubation
for a longer period (12 h) attenuated inhibition of protein
import, suggesting either repair or elimination of damaged
mitochondria. Compared to quiescent density-inhibited cells,
a more prominent decrease in protein import capacity occurred
in mitochondria from cells exposed to 4 Gy and harvested
at different incubation periods following subculture to lower
density. These changes in import efficiency appeared to be
linked with different stages of the cell cycle and correlated
with MMP modulation as quantified with JC-1 fluorescent probe.
In contrast to high-dose exposed cells, an increased protein
import was observed with mitochondria isolated from cells
exposed to low dose/low dose-rate γ-rays (10 cGy, 0.2
cGy/h). This increased import efficiency was associated with
an increase in MMP and correlated with the expression of
induced adaptive responses. Collectively, these data indicate
that the dose response to γ-rays is not linear, and
distinct biochemical events may underlie the cellular response
to high and low dose low linear energy transfer exposure.
We suggest that modulation of mitochondrial import capacity
is a novel physiological endpoint to study the role of endogenous
oxidative metabolism in the cellular response to ionizing
radiation.
Supported by Research Grant FG02-02ER63447 from
the U.S. Department of Energy (EA) and American Heart Association
0355710T (DP)
