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Proteolytic regulation of synaptic plasticity in the mouse primary visual cortex: analysis of matrix metalloproteinase 9 deficient mice.

Kelly EA, Russo AS, Jackson CD, Lamantia CE, Majewska AK - Front Cell Neurosci (2015)

Bottom Line: Loss of MMP9 also attenuated functional ODP following monocular deprivation (MD) and reduced excitatory synapse density and spine density in sensory cortex.We also analyzed the effects of MMP9 loss on microglia, as these cells are involved in extracellular remodeling and have been recently shown to be important for synaptic plasticity.Ultrastructural analysis, however, showed that the extracellular space surrounding microglia was increased, with concomitant increases in microglial inclusions, suggesting possible changes in microglial function in the absence of MMP9.

View Article: PubMed Central - PubMed

Affiliation: Center for Visual Science, School of Medicine and Dentistry, Department of Neurobiology and Anatomy, University of Rochester Rochester, NY, USA.

ABSTRACT
The extracellular matrix (ECM) is known to play important roles in regulating neuronal recovery from injury. The ECM can also impact physiological synaptic plasticity, although this process is less well understood. To understand the impact of the ECM on synaptic function and remodeling in vivo, we examined ECM composition and proteolysis in a well-established model of experience-dependent plasticity in the visual cortex. We describe a rapid change in ECM protein composition during Ocular Dominance Plasticity (ODP) in adolescent mice, and a loss of ECM remodeling in mice that lack the extracellular protease, matrix metalloproteinase-9 (MMP9). Loss of MMP9 also attenuated functional ODP following monocular deprivation (MD) and reduced excitatory synapse density and spine density in sensory cortex. While we observed no change in the morphology of existing dendritic spines, spine dynamics were altered, and MMP9 knock-out (KO) mice showed increased turnover of dendritic spines over a period of 2 days. We also analyzed the effects of MMP9 loss on microglia, as these cells are involved in extracellular remodeling and have been recently shown to be important for synaptic plasticity. MMP9 KO mice exhibited very limited changes in microglial morphology. Ultrastructural analysis, however, showed that the extracellular space surrounding microglia was increased, with concomitant increases in microglial inclusions, suggesting possible changes in microglial function in the absence of MMP9. Taken together, our results show that MMP9 contributes to ECM degradation, synaptic dynamics and sensory-evoked plasticity in the mouse visual cortex.

No MeSH data available.


Related in: MedlinePlus

Dendritic spine density and morphology are differentially affected in MMP9 KO mice. Representative confocal images of CTL (A,B) and MMP9 KO (C,D) cortical dendrites of layer 5 pyramidal neurons. (E) Quantitative analysis of spine density showed significantly more spines in CTL ND (black bar, 1.697 ± 0.176) compared to MMP9 KO mice (white bar; 1.116 ± 0.065; Student’s t-test with Mann Whitney test, *p < 0.05). (F) Example of spine measurements. Spine neck length (black bar) and spine head and neck width (gray bars) measurements were made using Image J software. (G) Correlation analysis depicting no differences between head and neck comparisons across genotypes (Linear regression analysis; CTL ND r2 = 0.002, MMP9 ND r2 = 0.006). (H) Head diameter, spine length, and relative neck diameter were comparable between the two genotypes (Two-way ANOVA with bonferroni multiple comparisons). Scale bar = 200 μm. All values reported are the mean ± SEM.
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Figure 7: Dendritic spine density and morphology are differentially affected in MMP9 KO mice. Representative confocal images of CTL (A,B) and MMP9 KO (C,D) cortical dendrites of layer 5 pyramidal neurons. (E) Quantitative analysis of spine density showed significantly more spines in CTL ND (black bar, 1.697 ± 0.176) compared to MMP9 KO mice (white bar; 1.116 ± 0.065; Student’s t-test with Mann Whitney test, *p < 0.05). (F) Example of spine measurements. Spine neck length (black bar) and spine head and neck width (gray bars) measurements were made using Image J software. (G) Correlation analysis depicting no differences between head and neck comparisons across genotypes (Linear regression analysis; CTL ND r2 = 0.002, MMP9 ND r2 = 0.006). (H) Head diameter, spine length, and relative neck diameter were comparable between the two genotypes (Two-way ANOVA with bonferroni multiple comparisons). Scale bar = 200 μm. All values reported are the mean ± SEM.

Mentions: To further explore the differences in synaptic behavior caused by loss of MMP9, we crossed MMP9 KO mice with GFP-M transgenic mice (Feng et al., 2000) in which GFP is expressed in L5 pyramidal neurons (Figures 7A–D). Because GFP expression is low in visual cortex during adolescence we assayed dendritic spine morphology in S1, a brain area in which dendritic spine development mirrors that in primary visual cortex (Elston and Fujita, 2014). Confocal microscopy revealed GFP-labeled dendritic branches in both GFP-M (CTL ND, Figure 7A) and MMP9 KO-GFP (MMP9 KO, Figure 7C) adolescent (P28) S1, with clearly discernable dendritic spines on the apical dendritic branches (in L2/3) in both genotypes (Figures 7B,D). As the formation and elimination of synapses is believed to be one of the mechanisms underlying adaptive remodeling of neural circuits (Trachtenberg et al., 2002; Majewska et al., 2006) and previous reports implicate a role for MMP9 on dendritic spine development (Szklarczyk et al., 2002; Tian et al., 2007; Stawarski et al., 2014), we wanted to know how the density, structure and dynamics of dendritic spines were affected by MMP9 loss. We first wanted to determine whether dendritic spines in S1 were regulated similarly to those in V1. Therefore, we first compared changes in synaptic density between GFP-M and MMP9 KO-GFP mice in S1 to see if initial development of networks was compromised. We found a significant reduction in spine density in MMP9 KO mice (Figure 7E, p < 0.05), consistent with the decrease in asymmetric synapse density observed in V1 (Figure 6C). This suggests that MMP9 may have similar roles in synaptic development across sensory cortical areas. Since spine density changes are often associated with alterations in spine morphology (Wallace and Bear, 2004), we measured the dimensions of each spine, including spine head and relative neck diameter (Figure 7F, gray bars) and dendritic spine length (Figure 7F, black bar measuring from dendritic shaft to tip of protrusion). Changes in spine shape can predict spine developmental profiles; where thinner spine heads and longer necks suggest an immature phenotype while a wider head and short neck might suggest maturity (reviewed in Sala and Segal, 2014). Interestingly, while we noted a significant reduction in dendritic spine density in MMP9 KO mice, we found no differences in the distribution of spine “types”, as spine head and neck comparisons did not differ across genotypes and these comparisons correspond to relative distributions of mushroom, thin and stubby spines (Figure 7G). Similarly, spine morphology was unchanged when compared to GFP control mice (Figure 7H) suggesting no clear changes in the morphological classes of spines present in GFP CTL and MMP9 KO GFP mice, supporting the data obtained in visual cortex showing no difference in PSD size between the two genotypes.


Proteolytic regulation of synaptic plasticity in the mouse primary visual cortex: analysis of matrix metalloproteinase 9 deficient mice.

Kelly EA, Russo AS, Jackson CD, Lamantia CE, Majewska AK - Front Cell Neurosci (2015)

Dendritic spine density and morphology are differentially affected in MMP9 KO mice. Representative confocal images of CTL (A,B) and MMP9 KO (C,D) cortical dendrites of layer 5 pyramidal neurons. (E) Quantitative analysis of spine density showed significantly more spines in CTL ND (black bar, 1.697 ± 0.176) compared to MMP9 KO mice (white bar; 1.116 ± 0.065; Student’s t-test with Mann Whitney test, *p < 0.05). (F) Example of spine measurements. Spine neck length (black bar) and spine head and neck width (gray bars) measurements were made using Image J software. (G) Correlation analysis depicting no differences between head and neck comparisons across genotypes (Linear regression analysis; CTL ND r2 = 0.002, MMP9 ND r2 = 0.006). (H) Head diameter, spine length, and relative neck diameter were comparable between the two genotypes (Two-way ANOVA with bonferroni multiple comparisons). Scale bar = 200 μm. All values reported are the mean ± SEM.
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Figure 7: Dendritic spine density and morphology are differentially affected in MMP9 KO mice. Representative confocal images of CTL (A,B) and MMP9 KO (C,D) cortical dendrites of layer 5 pyramidal neurons. (E) Quantitative analysis of spine density showed significantly more spines in CTL ND (black bar, 1.697 ± 0.176) compared to MMP9 KO mice (white bar; 1.116 ± 0.065; Student’s t-test with Mann Whitney test, *p < 0.05). (F) Example of spine measurements. Spine neck length (black bar) and spine head and neck width (gray bars) measurements were made using Image J software. (G) Correlation analysis depicting no differences between head and neck comparisons across genotypes (Linear regression analysis; CTL ND r2 = 0.002, MMP9 ND r2 = 0.006). (H) Head diameter, spine length, and relative neck diameter were comparable between the two genotypes (Two-way ANOVA with bonferroni multiple comparisons). Scale bar = 200 μm. All values reported are the mean ± SEM.
Mentions: To further explore the differences in synaptic behavior caused by loss of MMP9, we crossed MMP9 KO mice with GFP-M transgenic mice (Feng et al., 2000) in which GFP is expressed in L5 pyramidal neurons (Figures 7A–D). Because GFP expression is low in visual cortex during adolescence we assayed dendritic spine morphology in S1, a brain area in which dendritic spine development mirrors that in primary visual cortex (Elston and Fujita, 2014). Confocal microscopy revealed GFP-labeled dendritic branches in both GFP-M (CTL ND, Figure 7A) and MMP9 KO-GFP (MMP9 KO, Figure 7C) adolescent (P28) S1, with clearly discernable dendritic spines on the apical dendritic branches (in L2/3) in both genotypes (Figures 7B,D). As the formation and elimination of synapses is believed to be one of the mechanisms underlying adaptive remodeling of neural circuits (Trachtenberg et al., 2002; Majewska et al., 2006) and previous reports implicate a role for MMP9 on dendritic spine development (Szklarczyk et al., 2002; Tian et al., 2007; Stawarski et al., 2014), we wanted to know how the density, structure and dynamics of dendritic spines were affected by MMP9 loss. We first wanted to determine whether dendritic spines in S1 were regulated similarly to those in V1. Therefore, we first compared changes in synaptic density between GFP-M and MMP9 KO-GFP mice in S1 to see if initial development of networks was compromised. We found a significant reduction in spine density in MMP9 KO mice (Figure 7E, p < 0.05), consistent with the decrease in asymmetric synapse density observed in V1 (Figure 6C). This suggests that MMP9 may have similar roles in synaptic development across sensory cortical areas. Since spine density changes are often associated with alterations in spine morphology (Wallace and Bear, 2004), we measured the dimensions of each spine, including spine head and relative neck diameter (Figure 7F, gray bars) and dendritic spine length (Figure 7F, black bar measuring from dendritic shaft to tip of protrusion). Changes in spine shape can predict spine developmental profiles; where thinner spine heads and longer necks suggest an immature phenotype while a wider head and short neck might suggest maturity (reviewed in Sala and Segal, 2014). Interestingly, while we noted a significant reduction in dendritic spine density in MMP9 KO mice, we found no differences in the distribution of spine “types”, as spine head and neck comparisons did not differ across genotypes and these comparisons correspond to relative distributions of mushroom, thin and stubby spines (Figure 7G). Similarly, spine morphology was unchanged when compared to GFP control mice (Figure 7H) suggesting no clear changes in the morphological classes of spines present in GFP CTL and MMP9 KO GFP mice, supporting the data obtained in visual cortex showing no difference in PSD size between the two genotypes.

Bottom Line: Loss of MMP9 also attenuated functional ODP following monocular deprivation (MD) and reduced excitatory synapse density and spine density in sensory cortex.We also analyzed the effects of MMP9 loss on microglia, as these cells are involved in extracellular remodeling and have been recently shown to be important for synaptic plasticity.Ultrastructural analysis, however, showed that the extracellular space surrounding microglia was increased, with concomitant increases in microglial inclusions, suggesting possible changes in microglial function in the absence of MMP9.

View Article: PubMed Central - PubMed

Affiliation: Center for Visual Science, School of Medicine and Dentistry, Department of Neurobiology and Anatomy, University of Rochester Rochester, NY, USA.

ABSTRACT
The extracellular matrix (ECM) is known to play important roles in regulating neuronal recovery from injury. The ECM can also impact physiological synaptic plasticity, although this process is less well understood. To understand the impact of the ECM on synaptic function and remodeling in vivo, we examined ECM composition and proteolysis in a well-established model of experience-dependent plasticity in the visual cortex. We describe a rapid change in ECM protein composition during Ocular Dominance Plasticity (ODP) in adolescent mice, and a loss of ECM remodeling in mice that lack the extracellular protease, matrix metalloproteinase-9 (MMP9). Loss of MMP9 also attenuated functional ODP following monocular deprivation (MD) and reduced excitatory synapse density and spine density in sensory cortex. While we observed no change in the morphology of existing dendritic spines, spine dynamics were altered, and MMP9 knock-out (KO) mice showed increased turnover of dendritic spines over a period of 2 days. We also analyzed the effects of MMP9 loss on microglia, as these cells are involved in extracellular remodeling and have been recently shown to be important for synaptic plasticity. MMP9 KO mice exhibited very limited changes in microglial morphology. Ultrastructural analysis, however, showed that the extracellular space surrounding microglia was increased, with concomitant increases in microglial inclusions, suggesting possible changes in microglial function in the absence of MMP9. Taken together, our results show that MMP9 contributes to ECM degradation, synaptic dynamics and sensory-evoked plasticity in the mouse visual cortex.

No MeSH data available.


Related in: MedlinePlus