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dose damage. 8 week-old Trp53 heterozygous female mice were given a single CT scan, PET injection or
sham-irradiated 24 hours prior to a single 4 Gy whole-body dose of γ-radiation. Cardiac inflammation and
fibrosis were characterized using Hematoxylin and Eosin (H&E), Masson's Trichrome and Picrosirius Red
staining. We found that cardiac fibrosis was increased after a large 4 Gy dose of γ-radiation, but also after
a low dose CT scan or PET injection. Cardiac inflammation only increased after a CT scan or PET injection
and was not significantly increased after a 4 Gy dose when compared to control. When given a CT scan or
PET injection 24 hours prior to a large 4 Gy dose both inflammation and fibrosis were near control levels,
suggesting that the low dose CT and PET exposures induced a protective adaptive response. We also
investigated the dose response of PET injections on the heart in wild type adult mice given a single PET
injection ranging from 20 µCi to 1000 µCi or sham irradiated. Increasing dose did not have an effect on
inflammation and fibrosis. In fact, a PET injection of 20, 500 and 1000 µCi lead to a decrease in
inflammation and fibrosis when compared to control. These findings suggest that low dose radiation alone
or a low dose followed by a high dose does not produce additive negative effects but induces an adaptive
response in the heart.
(PS1-14) Cytoplasmic irradiation induces autophagy in human small airway epithelial cells as a result of
mitochondrial dysfunction. Jinhua Wu; Bo Zhang; Mercey M. Davidson; and Tom K. Hei, Columbia
University, New York, NY
Although the odds that an alpha particle traverses the cytoplasm is three times higher than the
nucleus for a bronchial epithelial cell, the effect of high linear energy transfer (LET) radiation on organelles
in the cytoplasm, and subsequently, how it affects cellular behavior is poorly understood. Recent studies
from our laboratory have shown that mitochondrial fragmentation induced by targeted cytoplasmic
irradiation of human small airway epithelial cells (SAEC), is mediated by up-regulation of dynamin-
regulated protein 1 (DRP1), a mitochondrial fission protein. To further explore the role of mitochondria in
modulating the biological activities of high LET radiation, we focused on autophagy in SAEC. Autophagy
was observed as early as 30 minutes after cytoplasmic irradiation with 10 alpha particles and peaked at 4
hours based on LC3B punctae formation. Sequestration of free radicals by DMSO abolished the induction
of LC3B punctae formation, suggesting that activation of autophagy is free radical-dependent. Triggering
of autophagy by cytoplasmic irradiation led to an increase of γ-H2AX foci that was dramatically reduced
by choloroquine (CQ) or 3-methyladenine (3-MA), which are known inhibitors for autophagy. The DRP1
inhibitor mdivi-1 also significantly reduced autophagy, indicating that DRP1 played a key role in activation
of autophagy. DRP1 knockout HCT116 cells showed little or no autophagy after cytoplasmic irradiation,
further confirming its role in autophagy induction. An up-regulation of autophagy initiating protein beclin-
1 was also observed in SAEC in a DRP1-dependent manner. Finally, a sustained activation of ERK was
detected suggesting potential involvement of the non-canonical MEK/ERK pathway in regulating
autophagy in cytoplasmic irradiated cells. Our results demonstrated a role of mitochondrial fragmentation
in initiating autophagy by high LET radiation.
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sham-irradiated 24 hours prior to a single 4 Gy whole-body dose of γ-radiation. Cardiac inflammation and
fibrosis were characterized using Hematoxylin and Eosin (H&E), Masson's Trichrome and Picrosirius Red
staining. We found that cardiac fibrosis was increased after a large 4 Gy dose of γ-radiation, but also after
a low dose CT scan or PET injection. Cardiac inflammation only increased after a CT scan or PET injection
and was not significantly increased after a 4 Gy dose when compared to control. When given a CT scan or
PET injection 24 hours prior to a large 4 Gy dose both inflammation and fibrosis were near control levels,
suggesting that the low dose CT and PET exposures induced a protective adaptive response. We also
investigated the dose response of PET injections on the heart in wild type adult mice given a single PET
injection ranging from 20 µCi to 1000 µCi or sham irradiated. Increasing dose did not have an effect on
inflammation and fibrosis. In fact, a PET injection of 20, 500 and 1000 µCi lead to a decrease in
inflammation and fibrosis when compared to control. These findings suggest that low dose radiation alone
or a low dose followed by a high dose does not produce additive negative effects but induces an adaptive
response in the heart.
(PS1-14) Cytoplasmic irradiation induces autophagy in human small airway epithelial cells as a result of
mitochondrial dysfunction. Jinhua Wu; Bo Zhang; Mercey M. Davidson; and Tom K. Hei, Columbia
University, New York, NY
Although the odds that an alpha particle traverses the cytoplasm is three times higher than the
nucleus for a bronchial epithelial cell, the effect of high linear energy transfer (LET) radiation on organelles
in the cytoplasm, and subsequently, how it affects cellular behavior is poorly understood. Recent studies
from our laboratory have shown that mitochondrial fragmentation induced by targeted cytoplasmic
irradiation of human small airway epithelial cells (SAEC), is mediated by up-regulation of dynamin-
regulated protein 1 (DRP1), a mitochondrial fission protein. To further explore the role of mitochondria in
modulating the biological activities of high LET radiation, we focused on autophagy in SAEC. Autophagy
was observed as early as 30 minutes after cytoplasmic irradiation with 10 alpha particles and peaked at 4
hours based on LC3B punctae formation. Sequestration of free radicals by DMSO abolished the induction
of LC3B punctae formation, suggesting that activation of autophagy is free radical-dependent. Triggering
of autophagy by cytoplasmic irradiation led to an increase of γ-H2AX foci that was dramatically reduced
by choloroquine (CQ) or 3-methyladenine (3-MA), which are known inhibitors for autophagy. The DRP1
inhibitor mdivi-1 also significantly reduced autophagy, indicating that DRP1 played a key role in activation
of autophagy. DRP1 knockout HCT116 cells showed little or no autophagy after cytoplasmic irradiation,
further confirming its role in autophagy induction. An up-regulation of autophagy initiating protein beclin-
1 was also observed in SAEC in a DRP1-dependent manner. Finally, a sustained activation of ERK was
detected suggesting potential involvement of the non-canonical MEK/ERK pathway in regulating
autophagy in cytoplasmic irradiated cells. Our results demonstrated a role of mitochondrial fragmentation
in initiating autophagy by high LET radiation.
109 | P a g e
