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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

Increased neuronal synchronization is associated with increased phosphorylation of CREB.(a) Comparison of total and phosphorylated forms of CREB, CaMKIV, ERK1/2 and Akt in cortices from PBS-injected mice at 1DPI (control) and LPS-injected mice at 1 or 14 DPI. GAPDH was used as protein loading controls. Full western blot images are shown in Supplementary Fig. 6. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. (c) Immunohistochemistry demonstrates the enrichment of pCREB, CaMKIV and ERK1/2 in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. *P<0.05, **P<0.01; one-way ANOVA. Scale bar, 40 μm.
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f4: Increased neuronal synchronization is associated with increased phosphorylation of CREB.(a) Comparison of total and phosphorylated forms of CREB, CaMKIV, ERK1/2 and Akt in cortices from PBS-injected mice at 1DPI (control) and LPS-injected mice at 1 or 14 DPI. GAPDH was used as protein loading controls. Full western blot images are shown in Supplementary Fig. 6. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. (c) Immunohistochemistry demonstrates the enrichment of pCREB, CaMKIV and ERK1/2 in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. *P<0.05, **P<0.01; one-way ANOVA. Scale bar, 40 μm.

Mentions: Increased neuronal synchronization is critical for synaptic NMDAR-mediated neuronal survival27. NMDAR activation results in increased cytosolic Ca2+ levels, which can subsequently activate Ca2+/calmodulin-dependent kinase IV (CaMKIV) and ERK1/2 (ref. 27). While levels of both CaMKIV and ERK1/2 were similar in control and LPS-treated animals, their activated (phosphorylated) forms were significantly increased in the cortex of LPS-treated mice compared with controls (Fig. 4a,b). It has been shown that both pCaMKIV and pERK1/2 can catalyse the activation of CREB27. While CREB levels were similar in the cortices of saline- and LPS-treated mice (Fig. 4a), phosphorylated CREB (pCREB) was significantly increased in the LPS-treated group (Fig. 4b). Activation of NMDARs can also mediate antiapoptotic effects through a mitogen-activated protein kinase-dependent phosphorylation of the threonine/serine kinase Akt at Ser473 (ref. 28). Akt levels were similar in cortices of LPS-treated and control mice. In contrast, the levels of pAkt at Ser473 were significantly increased 1 day after four LPS injections (Fig. 4a,b). Expression of these activated molecules is specifically found in neurons, as confirmed by pCREB, pCaMKIV and pERK1/2 immunohistochemistry at 1 DPI (Fig. 4c). Even though the subtle increase in intensity of these molecules can be appreciated in LPS-treated animals when compared with the controls, immunohistochemistry is not used to quantify the differences due to its intrinsic technical limitation but only to determine the cellular location of these molecules and to confirm that they are highly enriched in neurons.


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)

Increased neuronal synchronization is associated with increased phosphorylation of CREB.(a) Comparison of total and phosphorylated forms of CREB, CaMKIV, ERK1/2 and Akt in cortices from PBS-injected mice at 1DPI (control) and LPS-injected mice at 1 or 14 DPI. GAPDH was used as protein loading controls. Full western blot images are shown in Supplementary Fig. 6. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. (c) Immunohistochemistry demonstrates the enrichment of pCREB, CaMKIV and ERK1/2 in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. *P<0.05, **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

f4: Increased neuronal synchronization is associated with increased phosphorylation of CREB.(a) Comparison of total and phosphorylated forms of CREB, CaMKIV, ERK1/2 and Akt in cortices from PBS-injected mice at 1DPI (control) and LPS-injected mice at 1 or 14 DPI. GAPDH was used as protein loading controls. Full western blot images are shown in Supplementary Fig. 6. (b) Densitometry quantification of a with the relative intensity of the controls set as 100%. (c) Immunohistochemistry demonstrates the enrichment of pCREB, CaMKIV and ERK1/2 in cortical neurons of LPS-injected mice at 1 DPI. Data are presented as mean+s.e.m. *P<0.05, **P<0.01; one-way ANOVA. Scale bar, 40 μm.
Mentions: Increased neuronal synchronization is critical for synaptic NMDAR-mediated neuronal survival27. NMDAR activation results in increased cytosolic Ca2+ levels, which can subsequently activate Ca2+/calmodulin-dependent kinase IV (CaMKIV) and ERK1/2 (ref. 27). While levels of both CaMKIV and ERK1/2 were similar in control and LPS-treated animals, their activated (phosphorylated) forms were significantly increased in the cortex of LPS-treated mice compared with controls (Fig. 4a,b). It has been shown that both pCaMKIV and pERK1/2 can catalyse the activation of CREB27. While CREB levels were similar in the cortices of saline- and LPS-treated mice (Fig. 4a), phosphorylated CREB (pCREB) was significantly increased in the LPS-treated group (Fig. 4b). Activation of NMDARs can also mediate antiapoptotic effects through a mitogen-activated protein kinase-dependent phosphorylation of the threonine/serine kinase Akt at Ser473 (ref. 28). Akt levels were similar in cortices of LPS-treated and control mice. In contrast, the levels of pAkt at Ser473 were significantly increased 1 day after four LPS injections (Fig. 4a,b). Expression of these activated molecules is specifically found in neurons, as confirmed by pCREB, pCaMKIV and pERK1/2 immunohistochemistry at 1 DPI (Fig. 4c). Even though the subtle increase in intensity of these molecules can be appreciated in LPS-treated animals when compared with the controls, immunohistochemistry is not used to quantify the differences due to its intrinsic technical limitation but only to determine the cellular location of these molecules and to confirm that they are highly enriched in neurons.

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