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Microglial displacement of inhibitory synapses provides neuroprotection in the adult brain.

Chen Z, Jalabi W, Hu W, Park HJ, Gale JT, Kidd GJ, Bernatowicz R, Gossman ZC, Chen JT, Dutta R, Trapp BD - Nat Commun (2014)

Bottom Line: Electrophysiological recordings further establish that the reduction in inhibitory GABAergic synapses increased synchronized firing of cortical neurons in γ-frequency band.Increased neuronal activity results in the calcium-mediated activation of CaM kinase IV, phosphorylation of CREB, increased expression of antiapoptotic and neurotrophic molecules and reduced apoptosis of cortical neurons following injury.These results indicate that activated microglia can protect the adult brain by migrating to inhibitory synapses and displacing them from cortical neurons.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA [2].

ABSTRACT
Microglia actively survey the brain microenvironment and play essential roles in sculpting synaptic connections during brain development. While microglial functions in the adult brain are less clear, activated microglia can closely appose neuronal cell bodies and displace axosomatic presynaptic terminals. Microglia-mediated stripping of presynaptic terminals is considered neuroprotective, but the cellular and molecular mechanisms are poorly defined. Using 3D electron microscopy, we demonstrate that activated microglia displace inhibitory presynaptic terminals from cortical neurons in adult mice. Electrophysiological recordings further establish that the reduction in inhibitory GABAergic synapses increased synchronized firing of cortical neurons in γ-frequency band. Increased neuronal activity results in the calcium-mediated activation of CaM kinase IV, phosphorylation of CREB, increased expression of antiapoptotic and neurotrophic molecules and reduced apoptosis of cortical neurons following injury. These results indicate that activated microglia can protect the adult brain by migrating to inhibitory synapses and displacing them from cortical neurons.

No MeSH data available.


Related in: MedlinePlus

Neuronal expression of prosurvival genes is elevated in LPS-treated animals.(a) Comparison of antiapoptotic (Bcl-2, Mcl-1 and pBAD) and neurotrophic (BDNF and FGF-2) molecules in cortices from PBS-injected mice at 1 DPI and LPS-injected mice at 1 or 14 DPI by western blot analysis. Full western blot images are shown in Supplementary Fig. 7. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. There is a significant increase in the expression of antiapoptotic and neurotrophic molecules in LPS-injected animals at 1 DPI. (c) Immunohistochemistry demonstrates the enrichment of Bcl-2 and BDNF in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. **P<0.01; one-way ANOVA. Scale bar, 40 μm.
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f5: Neuronal expression of prosurvival genes is elevated in LPS-treated animals.(a) Comparison of antiapoptotic (Bcl-2, Mcl-1 and pBAD) and neurotrophic (BDNF and FGF-2) molecules in cortices from PBS-injected mice at 1 DPI and LPS-injected mice at 1 or 14 DPI by western blot analysis. Full western blot images are shown in Supplementary Fig. 7. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. There is a significant increase in the expression of antiapoptotic and neurotrophic molecules in LPS-injected animals at 1 DPI. (c) Immunohistochemistry demonstrates the enrichment of Bcl-2 and BDNF in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. **P<0.01; one-way ANOVA. Scale bar, 40 μm.

Mentions: Phosphorylation of CREB is essential for neuronal survival during development or following injury through promoting the transcription of prosurvival molecules. Thus, we next quantified levels of proteins known to be regulated by activated pCREB and to confer neuroprotection. The expression of the antiapoptotic protein Bcl-2 was significantly increased (Fig. 5a,b). Myeloid cell leukaemia sequence (Mcl-1), a member of the Bcl-2 family that constitutes a negative regulator in the mitochondrial pathway leading to apoptosis, was also significantly increased (Fig. 5a,b). Levels of BAD (Bcl-associated death promoter), a Bcl-2/Bcl-XL-antagonist which is a proapoptotic member of the Bcl-2 family, were similar in control and LPS-treated animals. BAD phosphorylation at Ser112, however, was significantly increased in LPS-treated animals compared with saline-injected animals (Fig. 5a,b). Increase of BAD phosphorylation (and thus suppression of BAD activity) leads to the dissociation of BAD from Bcl-2 and thereby promotes cell survival29. The levels of brain-derived neurotrophic factor (BDNF), a neurotrophin known to be regulated by CREB3031, were significantly increased in LPS-treated mice at 1 DPI. Fibroblast growth factor 2 (FGF-2), which can induce phosphorylation of BAD at Ser112 through the ERK1/2 signalling pathway32, was also significantly increased at 1 DPI (Fig. 5a,b). Bcl-2 and BDNF were highly enriched in neurons as shown by immunohistochemistry (Fig. 5c). Gene profiling of microglia isolated from PBS- and LPS-treated mice did not detect increased expression of antiapoptotic or neuroprotective transcripts following LPS treatment (Supplementary Fig. 4). Collectively, our data support the induction of antiapoptotic and prosurvival proteins in cortical neurons in LPS-treated mice at the apex of microglial activation.


Microglial displacement of inhibitory synapses provides neuroprotection in the adult brain.

Chen Z, Jalabi W, Hu W, Park HJ, Gale JT, Kidd GJ, Bernatowicz R, Gossman ZC, Chen JT, Dutta R, Trapp BD - Nat Commun (2014)

Neuronal expression of prosurvival genes is elevated in LPS-treated animals.(a) Comparison of antiapoptotic (Bcl-2, Mcl-1 and pBAD) and neurotrophic (BDNF and FGF-2) molecules in cortices from PBS-injected mice at 1 DPI and LPS-injected mice at 1 or 14 DPI by western blot analysis. Full western blot images are shown in Supplementary Fig. 7. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. There is a significant increase in the expression of antiapoptotic and neurotrophic molecules in LPS-injected animals at 1 DPI. (c) Immunohistochemistry demonstrates the enrichment of Bcl-2 and BDNF in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. **P<0.01; one-way ANOVA. Scale bar, 40 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4109015&req=5

f5: Neuronal expression of prosurvival genes is elevated in LPS-treated animals.(a) Comparison of antiapoptotic (Bcl-2, Mcl-1 and pBAD) and neurotrophic (BDNF and FGF-2) molecules in cortices from PBS-injected mice at 1 DPI and LPS-injected mice at 1 or 14 DPI by western blot analysis. Full western blot images are shown in Supplementary Fig. 7. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. There is a significant increase in the expression of antiapoptotic and neurotrophic molecules in LPS-injected animals at 1 DPI. (c) Immunohistochemistry demonstrates the enrichment of Bcl-2 and BDNF in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. **P<0.01; one-way ANOVA. Scale bar, 40 μm.
Mentions: Phosphorylation of CREB is essential for neuronal survival during development or following injury through promoting the transcription of prosurvival molecules. Thus, we next quantified levels of proteins known to be regulated by activated pCREB and to confer neuroprotection. The expression of the antiapoptotic protein Bcl-2 was significantly increased (Fig. 5a,b). Myeloid cell leukaemia sequence (Mcl-1), a member of the Bcl-2 family that constitutes a negative regulator in the mitochondrial pathway leading to apoptosis, was also significantly increased (Fig. 5a,b). Levels of BAD (Bcl-associated death promoter), a Bcl-2/Bcl-XL-antagonist which is a proapoptotic member of the Bcl-2 family, were similar in control and LPS-treated animals. BAD phosphorylation at Ser112, however, was significantly increased in LPS-treated animals compared with saline-injected animals (Fig. 5a,b). Increase of BAD phosphorylation (and thus suppression of BAD activity) leads to the dissociation of BAD from Bcl-2 and thereby promotes cell survival29. The levels of brain-derived neurotrophic factor (BDNF), a neurotrophin known to be regulated by CREB3031, were significantly increased in LPS-treated mice at 1 DPI. Fibroblast growth factor 2 (FGF-2), which can induce phosphorylation of BAD at Ser112 through the ERK1/2 signalling pathway32, was also significantly increased at 1 DPI (Fig. 5a,b). Bcl-2 and BDNF were highly enriched in neurons as shown by immunohistochemistry (Fig. 5c). Gene profiling of microglia isolated from PBS- and LPS-treated mice did not detect increased expression of antiapoptotic or neuroprotective transcripts following LPS treatment (Supplementary Fig. 4). Collectively, our data support the induction of antiapoptotic and prosurvival proteins in cortical neurons in LPS-treated mice at the apex of microglial activation.

Bottom Line: Electrophysiological recordings further establish that the reduction in inhibitory GABAergic synapses increased synchronized firing of cortical neurons in γ-frequency band.Increased neuronal activity results in the calcium-mediated activation of CaM kinase IV, phosphorylation of CREB, increased expression of antiapoptotic and neurotrophic molecules and reduced apoptosis of cortical neurons following injury.These results indicate that activated microglia can protect the adult brain by migrating to inhibitory synapses and displacing them from cortical neurons.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA [2].

ABSTRACT
Microglia actively survey the brain microenvironment and play essential roles in sculpting synaptic connections during brain development. While microglial functions in the adult brain are less clear, activated microglia can closely appose neuronal cell bodies and displace axosomatic presynaptic terminals. Microglia-mediated stripping of presynaptic terminals is considered neuroprotective, but the cellular and molecular mechanisms are poorly defined. Using 3D electron microscopy, we demonstrate that activated microglia displace inhibitory presynaptic terminals from cortical neurons in adult mice. Electrophysiological recordings further establish that the reduction in inhibitory GABAergic synapses increased synchronized firing of cortical neurons in γ-frequency band. Increased neuronal activity results in the calcium-mediated activation of CaM kinase IV, phosphorylation of CREB, increased expression of antiapoptotic and neurotrophic molecules and reduced apoptosis of cortical neurons following injury. These results indicate that activated microglia can protect the adult brain by migrating to inhibitory synapses and displacing them from cortical neurons.

No MeSH data available.


Related in: MedlinePlus