Page 367 - 2014 Printable Abstract Book
P. 367
(PS7-25) Radiation-induced astrocyte activation results in downregulation of GLT-1 glutamate
transporter mRNA that is reversed by PPARδ ligands in vitro and in vivo. Mitra Kooshki; Caroline I.
Schnegg; Dana M. Greene-Schloesser; Michael E. Robbins; Linda J. Metheny-Barlow, Wake Forest School
of Medicine, Winston-Salem, NC
Partial or whole brain irradiation (WBI) is often required to treat metastatic brain cancer.
Unfortunately, radiation-induced brain injury, including progressive cognitive impairment, can
significantly affect the quality of life of patients receiving radiation therapy. Although the mechanisms
underlying radiation-induced brain injury are not fully understood, studies in rodents indicate that
neuroinflammatory responses may play a key role. Peroxisomal proliferator-activated receptor (PPAR) δ
has been shown to mitigate inflammatory responses in various cell types. We tested the hypothesis that
PPARδ agonists would modulate radiation-induced astrocyte inflammation. Incubating primary rat cortical
astrocytes with the PPARδ agonist, L-165041, inhibited the radiation-induced increase in the astrocyte
activation marker GFAP, as well as prevented upregulation of message levels for the inflammatory
cytokines IL-6 and MCP-1. A potential consequence of astrocyte activation and inflammatory cytokine
expression is dysregulation of the GLT-1 glutamate transporter, which functions to regulate glutamate
levels at excitatory synapses. We report that, concomitant with astrocyte activation, radiation decreased
GLT-1 mRNA expression; pretreatment with L-165041 prevented this decrease. L-165041 inhibition of all
of these radiation-induced changes occurred, in part, by preventing activation of the MEK1/2-ERK1/2
pathway. Consistent with this, we have reported that dietary administration of orally-bioavailable PPARδ
agonist GW0742 to mice receiving a single dose 10 Gy WBI prevented acute radiation-induced ERK1/2
activation and IL-1β mRNA upregulation. Here we show that, while WBI caused a 60% decrease of GLT-1
mRNA in the cortex at 1 week compared to sham controls, GW0742 administration completely prevented
loss of GLT-1. Together, these data suggest that radiation-induced inflammatory downregulation of GLT-
1 is a potential mechanism contributing to development of radiation-induced brain injury, including
cognitive impairment. Further, PPARδ agonists modulate radiation-induced cortical astrocyte activation,
proinflammatory response, and GLT-1 downregulation, and may have utility in the inhibition of radiation-
induced cognitive impairment. (Supported by NIH CA112593)
(PS7-26) No recruitment of peripheral monocytes to the brain after cranial irradiation. Wei Han; Takashi
Umekawa; Paoyan Lin; and Klas Blomgren, Karolinska Institutet, Stockholm, Sweden
Cranial irradiation (IR), a commonly used therapeutic modality in the treatment of pediatric brain
tumors, induces loss of neural stem and progenitor cells and is followed by progressive cognitive
deterioration. Earlier studies have suggested that neuroinflammation contributes to the development of
common adverse defects, including a shift from neurogenesis to gliogenesis. Given the difficulties in
distinguishing resident microglia from blood-borne, peripheral monocytes, the relative contribution of
these two evolutionarily different groups of macrophages and antigen-presenting cells is not known. To
address this, we utilized a unique reporter mouse (CCR2RFP/+CX3CR1GFP/+) to delineate the resident
(CX3CR1+; GFP-labeled [green]) versus peripheral (CCR2+; RFP-labeled [red]) innate immune response in
the brain following IR. Animals at postnatal day 10 were subjected to a single dose of 8 Gy to the brain
and were sacrificed after 6 hours, 1 day, 1 week and 1 month, respectively. Our results demonstrate that
6 hours after IR, resident GFP-labeled microglia in the subgranular zone of the hippocampus displayed an
amoeboid shape containing multiple chromatin fragments, indicating activation and phagocytosis of dead
365 | P a g e
transporter mRNA that is reversed by PPARδ ligands in vitro and in vivo. Mitra Kooshki; Caroline I.
Schnegg; Dana M. Greene-Schloesser; Michael E. Robbins; Linda J. Metheny-Barlow, Wake Forest School
of Medicine, Winston-Salem, NC
Partial or whole brain irradiation (WBI) is often required to treat metastatic brain cancer.
Unfortunately, radiation-induced brain injury, including progressive cognitive impairment, can
significantly affect the quality of life of patients receiving radiation therapy. Although the mechanisms
underlying radiation-induced brain injury are not fully understood, studies in rodents indicate that
neuroinflammatory responses may play a key role. Peroxisomal proliferator-activated receptor (PPAR) δ
has been shown to mitigate inflammatory responses in various cell types. We tested the hypothesis that
PPARδ agonists would modulate radiation-induced astrocyte inflammation. Incubating primary rat cortical
astrocytes with the PPARδ agonist, L-165041, inhibited the radiation-induced increase in the astrocyte
activation marker GFAP, as well as prevented upregulation of message levels for the inflammatory
cytokines IL-6 and MCP-1. A potential consequence of astrocyte activation and inflammatory cytokine
expression is dysregulation of the GLT-1 glutamate transporter, which functions to regulate glutamate
levels at excitatory synapses. We report that, concomitant with astrocyte activation, radiation decreased
GLT-1 mRNA expression; pretreatment with L-165041 prevented this decrease. L-165041 inhibition of all
of these radiation-induced changes occurred, in part, by preventing activation of the MEK1/2-ERK1/2
pathway. Consistent with this, we have reported that dietary administration of orally-bioavailable PPARδ
agonist GW0742 to mice receiving a single dose 10 Gy WBI prevented acute radiation-induced ERK1/2
activation and IL-1β mRNA upregulation. Here we show that, while WBI caused a 60% decrease of GLT-1
mRNA in the cortex at 1 week compared to sham controls, GW0742 administration completely prevented
loss of GLT-1. Together, these data suggest that radiation-induced inflammatory downregulation of GLT-
1 is a potential mechanism contributing to development of radiation-induced brain injury, including
cognitive impairment. Further, PPARδ agonists modulate radiation-induced cortical astrocyte activation,
proinflammatory response, and GLT-1 downregulation, and may have utility in the inhibition of radiation-
induced cognitive impairment. (Supported by NIH CA112593)
(PS7-26) No recruitment of peripheral monocytes to the brain after cranial irradiation. Wei Han; Takashi
Umekawa; Paoyan Lin; and Klas Blomgren, Karolinska Institutet, Stockholm, Sweden
Cranial irradiation (IR), a commonly used therapeutic modality in the treatment of pediatric brain
tumors, induces loss of neural stem and progenitor cells and is followed by progressive cognitive
deterioration. Earlier studies have suggested that neuroinflammation contributes to the development of
common adverse defects, including a shift from neurogenesis to gliogenesis. Given the difficulties in
distinguishing resident microglia from blood-borne, peripheral monocytes, the relative contribution of
these two evolutionarily different groups of macrophages and antigen-presenting cells is not known. To
address this, we utilized a unique reporter mouse (CCR2RFP/+CX3CR1GFP/+) to delineate the resident
(CX3CR1+; GFP-labeled [green]) versus peripheral (CCR2+; RFP-labeled [red]) innate immune response in
the brain following IR. Animals at postnatal day 10 were subjected to a single dose of 8 Gy to the brain
and were sacrificed after 6 hours, 1 day, 1 week and 1 month, respectively. Our results demonstrate that
6 hours after IR, resident GFP-labeled microglia in the subgranular zone of the hippocampus displayed an
amoeboid shape containing multiple chromatin fragments, indicating activation and phagocytosis of dead
365 | P a g e
