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Embryonic Medaka Model of Microglia in the Developing CNS Allowing In Vivo Analysis of Their Spatiotemporal Recruitment in Response to Irradiation.

Yasuda T, Oda S, Hibi Y, Satoh S, Nagata K, Hirakawa K, Kutsuna N, Sagara H, Mitani H - PLoS ONE (2015)

Bottom Line: This strongly suggests that ApoE has a significant function in the late phase of phagocytosis by microglia in the medaka brain.In addition, the distribution of microglia in p53-deficient embryos at the late phase of phagocytosis was almost the same as in wild-type embryos, despite the low numbers of irradiation-induced apoptotic neurons, suggesting that constant numbers of activated microglia were recruited at the late phase of phagocytosis irrespective of the extent of neuronal injury.This medaka model of microglia demonstrated specific recruitment after irradiation in the developing CNS and could provide a useful potential therapeutic strategy to counteract the detrimental effects of RT.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, Tokyo University, Bioscience Bldg., Kashiwa, Chiba, Japan.

ABSTRACT
Radiation therapy (RT) is pivotal in the treatment of many central nervous system (CNS) pathologies; however, exposure to RT in children is associated with a higher risk of secondary CNS tumors. Although recent research interest has focused on the reparative and therapeutic role of microglia, their recruitment following RT has not been elucidated, especially in the developing CNS. Here, we investigated the spatiotemporal dynamics of microglia during tissue repair in the irradiated embryonic medaka brain by whole-mount in situ hybridization using a probe for Apolipoprotein E (ApoE), a marker for activated microglia in teleosts. Three-dimensional imaging of the distribution of ApoE-expressing microglia in the irradiated embryonic brain clearly showed that ApoE-expressing microglia were abundant only in the late phase of phagocytosis during tissue repair induced by irradiation, while few microglia expressed ApoE in the initial phase of phagocytosis. This strongly suggests that ApoE has a significant function in the late phase of phagocytosis by microglia in the medaka brain. In addition, the distribution of microglia in p53-deficient embryos at the late phase of phagocytosis was almost the same as in wild-type embryos, despite the low numbers of irradiation-induced apoptotic neurons, suggesting that constant numbers of activated microglia were recruited at the late phase of phagocytosis irrespective of the extent of neuronal injury. This medaka model of microglia demonstrated specific recruitment after irradiation in the developing CNS and could provide a useful potential therapeutic strategy to counteract the detrimental effects of RT.

No MeSH data available.


Related in: MedlinePlus

Distribution of ApoE-expressing microglia during phagocytosis shown by WISH.Activated microglia were identified as ApoE-expressing cells by WISH in nonirradiated control embryos (A), irradiated embryos at 24 h after irradiation (E), and at 42 h after irradiation (J). Frontal plastic sections including the eyes and the OT at the ‘a’ and ‘b’ levels of the brain in A, E, and J are shown in B, F, and K, and C, G, and L, respectively. A few ApoE-expressing cells were present in the retina of wt nonirradiated embryos (arrowhead in C), in the TE (arrowheads in B), and the OT (arrowhead in C). At 24 h after irradiation, hypertrophic and rounded ApoE-expressing microglia (H) appeared in the TE (arrowhead in F), retina (arrowhead in F, G), and OT (arrowhead in G). Unstained round areas were present in the TE, retina, and marginal regions of the OT (open arrowheads in F and G). At 42 h after irradiation, the number of ApoE-expressing microglia had increased markedly (arrowheads in K and L) and they showed a branched morphology (M). The numbers of unstained areas in the TE and OT (open arrowheads in K and L) decreased and they were small, not hypertrophied. Three-dimensional images were constructed from serial sections of WISH-stained nonirradiated (D), embryos at 24 h (I) and at 42 h after irradiation (N). ApoE-expressing microglia are in red and the unstained round areas appear white. MES, mesencephalon; OT, optic tectum; TE, telencephalon. Scale bars = 50 μm.
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pone.0127325.g004: Distribution of ApoE-expressing microglia during phagocytosis shown by WISH.Activated microglia were identified as ApoE-expressing cells by WISH in nonirradiated control embryos (A), irradiated embryos at 24 h after irradiation (E), and at 42 h after irradiation (J). Frontal plastic sections including the eyes and the OT at the ‘a’ and ‘b’ levels of the brain in A, E, and J are shown in B, F, and K, and C, G, and L, respectively. A few ApoE-expressing cells were present in the retina of wt nonirradiated embryos (arrowhead in C), in the TE (arrowheads in B), and the OT (arrowhead in C). At 24 h after irradiation, hypertrophic and rounded ApoE-expressing microglia (H) appeared in the TE (arrowhead in F), retina (arrowhead in F, G), and OT (arrowhead in G). Unstained round areas were present in the TE, retina, and marginal regions of the OT (open arrowheads in F and G). At 42 h after irradiation, the number of ApoE-expressing microglia had increased markedly (arrowheads in K and L) and they showed a branched morphology (M). The numbers of unstained areas in the TE and OT (open arrowheads in K and L) decreased and they were small, not hypertrophied. Three-dimensional images were constructed from serial sections of WISH-stained nonirradiated (D), embryos at 24 h (I) and at 42 h after irradiation (N). ApoE-expressing microglia are in red and the unstained round areas appear white. MES, mesencephalon; OT, optic tectum; TE, telencephalon. Scale bars = 50 μm.

Mentions: To clarify the critical roles of microglia in the clearance of damaged neurons in the developing brain, the expression of ApoE mRNA, as a putative marker for activated microglia [11, 28], was examined by WISH. Upregulation of ApoE expression was observed at 24 and 42 h after irradiation (Fig 4E and 4J); by contrast, no ApoE expression outside the retina was observed 12 h after irradiation (S3 Fig). In the brains of nonirradiated wt embryos, only a few ApoE-expressing microglia were present in the retina, telencephalon (TE), and OT (closed arrowheads in Fig 4B and 4C) without irradiation (Fig 4A and 4D; S1 Movie).


Embryonic Medaka Model of Microglia in the Developing CNS Allowing In Vivo Analysis of Their Spatiotemporal Recruitment in Response to Irradiation.

Yasuda T, Oda S, Hibi Y, Satoh S, Nagata K, Hirakawa K, Kutsuna N, Sagara H, Mitani H - PLoS ONE (2015)

Distribution of ApoE-expressing microglia during phagocytosis shown by WISH.Activated microglia were identified as ApoE-expressing cells by WISH in nonirradiated control embryos (A), irradiated embryos at 24 h after irradiation (E), and at 42 h after irradiation (J). Frontal plastic sections including the eyes and the OT at the ‘a’ and ‘b’ levels of the brain in A, E, and J are shown in B, F, and K, and C, G, and L, respectively. A few ApoE-expressing cells were present in the retina of wt nonirradiated embryos (arrowhead in C), in the TE (arrowheads in B), and the OT (arrowhead in C). At 24 h after irradiation, hypertrophic and rounded ApoE-expressing microglia (H) appeared in the TE (arrowhead in F), retina (arrowhead in F, G), and OT (arrowhead in G). Unstained round areas were present in the TE, retina, and marginal regions of the OT (open arrowheads in F and G). At 42 h after irradiation, the number of ApoE-expressing microglia had increased markedly (arrowheads in K and L) and they showed a branched morphology (M). The numbers of unstained areas in the TE and OT (open arrowheads in K and L) decreased and they were small, not hypertrophied. Three-dimensional images were constructed from serial sections of WISH-stained nonirradiated (D), embryos at 24 h (I) and at 42 h after irradiation (N). ApoE-expressing microglia are in red and the unstained round areas appear white. MES, mesencephalon; OT, optic tectum; TE, telencephalon. Scale bars = 50 μm.
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pone.0127325.g004: Distribution of ApoE-expressing microglia during phagocytosis shown by WISH.Activated microglia were identified as ApoE-expressing cells by WISH in nonirradiated control embryos (A), irradiated embryos at 24 h after irradiation (E), and at 42 h after irradiation (J). Frontal plastic sections including the eyes and the OT at the ‘a’ and ‘b’ levels of the brain in A, E, and J are shown in B, F, and K, and C, G, and L, respectively. A few ApoE-expressing cells were present in the retina of wt nonirradiated embryos (arrowhead in C), in the TE (arrowheads in B), and the OT (arrowhead in C). At 24 h after irradiation, hypertrophic and rounded ApoE-expressing microglia (H) appeared in the TE (arrowhead in F), retina (arrowhead in F, G), and OT (arrowhead in G). Unstained round areas were present in the TE, retina, and marginal regions of the OT (open arrowheads in F and G). At 42 h after irradiation, the number of ApoE-expressing microglia had increased markedly (arrowheads in K and L) and they showed a branched morphology (M). The numbers of unstained areas in the TE and OT (open arrowheads in K and L) decreased and they were small, not hypertrophied. Three-dimensional images were constructed from serial sections of WISH-stained nonirradiated (D), embryos at 24 h (I) and at 42 h after irradiation (N). ApoE-expressing microglia are in red and the unstained round areas appear white. MES, mesencephalon; OT, optic tectum; TE, telencephalon. Scale bars = 50 μm.
Mentions: To clarify the critical roles of microglia in the clearance of damaged neurons in the developing brain, the expression of ApoE mRNA, as a putative marker for activated microglia [11, 28], was examined by WISH. Upregulation of ApoE expression was observed at 24 and 42 h after irradiation (Fig 4E and 4J); by contrast, no ApoE expression outside the retina was observed 12 h after irradiation (S3 Fig). In the brains of nonirradiated wt embryos, only a few ApoE-expressing microglia were present in the retina, telencephalon (TE), and OT (closed arrowheads in Fig 4B and 4C) without irradiation (Fig 4A and 4D; S1 Movie).

Bottom Line: This strongly suggests that ApoE has a significant function in the late phase of phagocytosis by microglia in the medaka brain.In addition, the distribution of microglia in p53-deficient embryos at the late phase of phagocytosis was almost the same as in wild-type embryos, despite the low numbers of irradiation-induced apoptotic neurons, suggesting that constant numbers of activated microglia were recruited at the late phase of phagocytosis irrespective of the extent of neuronal injury.This medaka model of microglia demonstrated specific recruitment after irradiation in the developing CNS and could provide a useful potential therapeutic strategy to counteract the detrimental effects of RT.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, Tokyo University, Bioscience Bldg., Kashiwa, Chiba, Japan.

ABSTRACT
Radiation therapy (RT) is pivotal in the treatment of many central nervous system (CNS) pathologies; however, exposure to RT in children is associated with a higher risk of secondary CNS tumors. Although recent research interest has focused on the reparative and therapeutic role of microglia, their recruitment following RT has not been elucidated, especially in the developing CNS. Here, we investigated the spatiotemporal dynamics of microglia during tissue repair in the irradiated embryonic medaka brain by whole-mount in situ hybridization using a probe for Apolipoprotein E (ApoE), a marker for activated microglia in teleosts. Three-dimensional imaging of the distribution of ApoE-expressing microglia in the irradiated embryonic brain clearly showed that ApoE-expressing microglia were abundant only in the late phase of phagocytosis during tissue repair induced by irradiation, while few microglia expressed ApoE in the initial phase of phagocytosis. This strongly suggests that ApoE has a significant function in the late phase of phagocytosis by microglia in the medaka brain. In addition, the distribution of microglia in p53-deficient embryos at the late phase of phagocytosis was almost the same as in wild-type embryos, despite the low numbers of irradiation-induced apoptotic neurons, suggesting that constant numbers of activated microglia were recruited at the late phase of phagocytosis irrespective of the extent of neuronal injury. This medaka model of microglia demonstrated specific recruitment after irradiation in the developing CNS and could provide a useful potential therapeutic strategy to counteract the detrimental effects of RT.

No MeSH data available.


Related in: MedlinePlus