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Fractionated Radiation Exposure of Rat Spinal Cords Leads to Latent Neuro-Inflammation in Brain, Cognitive Deficits, and Alterations in Apurinic Endonuclease 1.

Suresh Kumar MA, Peluso M, Chaudhary P, Dhawan J, Beheshti A, Manickam K, Thapar U, Pena L, Natarajan M, Hlatky L, Demple B, Naidu M - PLoS ONE (2015)

Bottom Line: As radiation research on the central nervous system has predominantly focused on neurons, with few studies addressing the role of glial cells, we have focused our present research on identifying the latent effects of single/ fractionated -low dose of low/ high energy radiation on the role of base excision repair protein Apurinic Endonuclease-1, in the rat spinal cords oligodendrocyte progenitor cells' differentiation.Our studies show for the first time, that fractionation of protons cause latent damage to spinal cord architecture while fractionation of HZE (28Si) induce increase in APE1 with single dose, which then decreased with fractionation.The oligodendrocyte progenitor cells differentiation was skewed with increase in immature oligodendrocytes and astrocytes, which likely cause the observed decrease in white matter, increased neuro-inflammation, together leading to the observed significant cognitive defects.

View Article: PubMed Central - PubMed

Affiliation: Center for Radiological Research, Columbia University, New York, New York, United States of America.

ABSTRACT
Ionizing radiation causes degeneration of myelin, the insulating sheaths of neuronal axons, leading to neurological impairment. As radiation research on the central nervous system has predominantly focused on neurons, with few studies addressing the role of glial cells, we have focused our present research on identifying the latent effects of single/ fractionated -low dose of low/ high energy radiation on the role of base excision repair protein Apurinic Endonuclease-1, in the rat spinal cords oligodendrocyte progenitor cells' differentiation. Apurinic endonuclease-1 is predominantly upregulated in response to oxidative stress by low- energy radiation, and previous studies show significant induction of Apurinic Endonuclease-1 in neurons and astrocytes. Our studies show for the first time, that fractionation of protons cause latent damage to spinal cord architecture while fractionation of HZE (28Si) induce increase in APE1 with single dose, which then decreased with fractionation. The oligodendrocyte progenitor cells differentiation was skewed with increase in immature oligodendrocytes and astrocytes, which likely cause the observed decrease in white matter, increased neuro-inflammation, together leading to the observed significant cognitive defects.

No MeSH data available.


Related in: MedlinePlus

Cell markers staining of spinal cord cryosections from 28Si exposed rats.(A) Left image: Spinal cords from rats exposed to 0.5 Gy of 300 MeV/n 28Si,were isolated after 6 months post exposure. 8 μm thick cryosections from T7 (dorso cortico spinal (dcs) ventral column white matter section staining at 40X magnification is shown here) stained for APE1 and cell markers (A2B5, NG2), and imaged on Zeiss Axiovert Imaging system as described in Materials and Methods. Right image: Quantification of staining shown in left image. Total % of positive A2B5, NG2 and APE1 stains were measured and divided by the number of nuclei present in each field of view (n = 1 for one view). We averaged trend of staining per field of view and then averaged all the field of views. For those images we had n = 4 for all conditions except F1 where we had n = 3. The * represents p < 0.05 compared to the control. Other than that there was no significance between the conditions (although a trend is there). The scoring was obtained as an average of two independent investigators in a blinded fashion to ify any bias which arise from just one investigator’s analysis. (B) Duplicate ventral column white matter section from Fig 2 samples, fixed and stained for APE1 and GFAP, imaged on FM at 40X magnification is shown here. (C) APE1 endonuclease activity measured from T7 sections of 28Si exposed rats’ spinal cords, 6 months post exposure by specific endonuclease assay described in methods. Increase in progenitor cell, immature OL and astrocytes seen up to two fractions, where as APE1 decreased with fractionation.
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pone.0133016.g002: Cell markers staining of spinal cord cryosections from 28Si exposed rats.(A) Left image: Spinal cords from rats exposed to 0.5 Gy of 300 MeV/n 28Si,were isolated after 6 months post exposure. 8 μm thick cryosections from T7 (dorso cortico spinal (dcs) ventral column white matter section staining at 40X magnification is shown here) stained for APE1 and cell markers (A2B5, NG2), and imaged on Zeiss Axiovert Imaging system as described in Materials and Methods. Right image: Quantification of staining shown in left image. Total % of positive A2B5, NG2 and APE1 stains were measured and divided by the number of nuclei present in each field of view (n = 1 for one view). We averaged trend of staining per field of view and then averaged all the field of views. For those images we had n = 4 for all conditions except F1 where we had n = 3. The * represents p < 0.05 compared to the control. Other than that there was no significance between the conditions (although a trend is there). The scoring was obtained as an average of two independent investigators in a blinded fashion to ify any bias which arise from just one investigator’s analysis. (B) Duplicate ventral column white matter section from Fig 2 samples, fixed and stained for APE1 and GFAP, imaged on FM at 40X magnification is shown here. (C) APE1 endonuclease activity measured from T7 sections of 28Si exposed rats’ spinal cords, 6 months post exposure by specific endonuclease assay described in methods. Increase in progenitor cell, immature OL and astrocytes seen up to two fractions, where as APE1 decreased with fractionation.

Mentions: The effects of single/ fractionated doses of HZE on OPC cell differentiation, and APE1 were measured, revealing altered APE1 induction with most of it appearing outside the nucleus with single dose, which became increasingly nuclear with fractionation, and also showed initial increase in progenitor, immature OL (Fig 2A) and astrocytes (Fig 2B) staining which decreased after second fraction. Finally, when we assayed the T7 extracts for APE1 endonuclease activity, we saw a similar trend (Fig 2C) APE1 increases with single dose, but decreases with fractionation, although the total APE1 levels are too low to show statistically significant differences. Total protein extracts of the T7 sections were also measured for the same APE1, A2B5 and NG2 proteins by western blots (Fig 3), revealing a similar trend of increase in APE1 with single dose of Si that reduced when dose was fractionated. A2B5 and NG2 also showed similar trend to Fig 2B, thus corroborating the immunostaining data of sections.


Fractionated Radiation Exposure of Rat Spinal Cords Leads to Latent Neuro-Inflammation in Brain, Cognitive Deficits, and Alterations in Apurinic Endonuclease 1.

Suresh Kumar MA, Peluso M, Chaudhary P, Dhawan J, Beheshti A, Manickam K, Thapar U, Pena L, Natarajan M, Hlatky L, Demple B, Naidu M - PLoS ONE (2015)

Cell markers staining of spinal cord cryosections from 28Si exposed rats.(A) Left image: Spinal cords from rats exposed to 0.5 Gy of 300 MeV/n 28Si,were isolated after 6 months post exposure. 8 μm thick cryosections from T7 (dorso cortico spinal (dcs) ventral column white matter section staining at 40X magnification is shown here) stained for APE1 and cell markers (A2B5, NG2), and imaged on Zeiss Axiovert Imaging system as described in Materials and Methods. Right image: Quantification of staining shown in left image. Total % of positive A2B5, NG2 and APE1 stains were measured and divided by the number of nuclei present in each field of view (n = 1 for one view). We averaged trend of staining per field of view and then averaged all the field of views. For those images we had n = 4 for all conditions except F1 where we had n = 3. The * represents p < 0.05 compared to the control. Other than that there was no significance between the conditions (although a trend is there). The scoring was obtained as an average of two independent investigators in a blinded fashion to ify any bias which arise from just one investigator’s analysis. (B) Duplicate ventral column white matter section from Fig 2 samples, fixed and stained for APE1 and GFAP, imaged on FM at 40X magnification is shown here. (C) APE1 endonuclease activity measured from T7 sections of 28Si exposed rats’ spinal cords, 6 months post exposure by specific endonuclease assay described in methods. Increase in progenitor cell, immature OL and astrocytes seen up to two fractions, where as APE1 decreased with fractionation.
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pone.0133016.g002: Cell markers staining of spinal cord cryosections from 28Si exposed rats.(A) Left image: Spinal cords from rats exposed to 0.5 Gy of 300 MeV/n 28Si,were isolated after 6 months post exposure. 8 μm thick cryosections from T7 (dorso cortico spinal (dcs) ventral column white matter section staining at 40X magnification is shown here) stained for APE1 and cell markers (A2B5, NG2), and imaged on Zeiss Axiovert Imaging system as described in Materials and Methods. Right image: Quantification of staining shown in left image. Total % of positive A2B5, NG2 and APE1 stains were measured and divided by the number of nuclei present in each field of view (n = 1 for one view). We averaged trend of staining per field of view and then averaged all the field of views. For those images we had n = 4 for all conditions except F1 where we had n = 3. The * represents p < 0.05 compared to the control. Other than that there was no significance between the conditions (although a trend is there). The scoring was obtained as an average of two independent investigators in a blinded fashion to ify any bias which arise from just one investigator’s analysis. (B) Duplicate ventral column white matter section from Fig 2 samples, fixed and stained for APE1 and GFAP, imaged on FM at 40X magnification is shown here. (C) APE1 endonuclease activity measured from T7 sections of 28Si exposed rats’ spinal cords, 6 months post exposure by specific endonuclease assay described in methods. Increase in progenitor cell, immature OL and astrocytes seen up to two fractions, where as APE1 decreased with fractionation.
Mentions: The effects of single/ fractionated doses of HZE on OPC cell differentiation, and APE1 were measured, revealing altered APE1 induction with most of it appearing outside the nucleus with single dose, which became increasingly nuclear with fractionation, and also showed initial increase in progenitor, immature OL (Fig 2A) and astrocytes (Fig 2B) staining which decreased after second fraction. Finally, when we assayed the T7 extracts for APE1 endonuclease activity, we saw a similar trend (Fig 2C) APE1 increases with single dose, but decreases with fractionation, although the total APE1 levels are too low to show statistically significant differences. Total protein extracts of the T7 sections were also measured for the same APE1, A2B5 and NG2 proteins by western blots (Fig 3), revealing a similar trend of increase in APE1 with single dose of Si that reduced when dose was fractionated. A2B5 and NG2 also showed similar trend to Fig 2B, thus corroborating the immunostaining data of sections.

Bottom Line: As radiation research on the central nervous system has predominantly focused on neurons, with few studies addressing the role of glial cells, we have focused our present research on identifying the latent effects of single/ fractionated -low dose of low/ high energy radiation on the role of base excision repair protein Apurinic Endonuclease-1, in the rat spinal cords oligodendrocyte progenitor cells' differentiation.Our studies show for the first time, that fractionation of protons cause latent damage to spinal cord architecture while fractionation of HZE (28Si) induce increase in APE1 with single dose, which then decreased with fractionation.The oligodendrocyte progenitor cells differentiation was skewed with increase in immature oligodendrocytes and astrocytes, which likely cause the observed decrease in white matter, increased neuro-inflammation, together leading to the observed significant cognitive defects.

View Article: PubMed Central - PubMed

Affiliation: Center for Radiological Research, Columbia University, New York, New York, United States of America.

ABSTRACT
Ionizing radiation causes degeneration of myelin, the insulating sheaths of neuronal axons, leading to neurological impairment. As radiation research on the central nervous system has predominantly focused on neurons, with few studies addressing the role of glial cells, we have focused our present research on identifying the latent effects of single/ fractionated -low dose of low/ high energy radiation on the role of base excision repair protein Apurinic Endonuclease-1, in the rat spinal cords oligodendrocyte progenitor cells' differentiation. Apurinic endonuclease-1 is predominantly upregulated in response to oxidative stress by low- energy radiation, and previous studies show significant induction of Apurinic Endonuclease-1 in neurons and astrocytes. Our studies show for the first time, that fractionation of protons cause latent damage to spinal cord architecture while fractionation of HZE (28Si) induce increase in APE1 with single dose, which then decreased with fractionation. The oligodendrocyte progenitor cells differentiation was skewed with increase in immature oligodendrocytes and astrocytes, which likely cause the observed decrease in white matter, increased neuro-inflammation, together leading to the observed significant cognitive defects.

No MeSH data available.


Related in: MedlinePlus