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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

MMP9 KO mice show changes in microglial morphology. (A) The area occupied by microglial processes was measured using Image J software. (B) Quantitative analysis of microglial process area was not significantly different between CTL ND (black bars, 0.837 ± 0.008) and MMP9 KO ND (white bars, 0.812 ± 0.004; unpaired student’s t-test). (C) Process circularity index [1−(LA−SA)/(LA+SA)] was significantly decreased in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05) (D) The area of microglial soma was measured using Image J software. (E) Quantitative analysis of the soma area showed significantly larger microglial soma in MMP9 KO ND (unpaired student’s t-test, *p < 0.05) with no significant changes in overall soma circularity (F) Scale bar = 20 μm. All values reported are the mean ± SEM.
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Figure 9: MMP9 KO mice show changes in microglial morphology. (A) The area occupied by microglial processes was measured using Image J software. (B) Quantitative analysis of microglial process area was not significantly different between CTL ND (black bars, 0.837 ± 0.008) and MMP9 KO ND (white bars, 0.812 ± 0.004; unpaired student’s t-test). (C) Process circularity index [1−(LA−SA)/(LA+SA)] was significantly decreased in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05) (D) The area of microglial soma was measured using Image J software. (E) Quantitative analysis of the soma area showed significantly larger microglial soma in MMP9 KO ND (unpaired student’s t-test, *p < 0.05) with no significant changes in overall soma circularity (F) Scale bar = 20 μm. All values reported are the mean ± SEM.

Mentions: Microglia secrete proteases (Webster and Crowe, 2006; Konnecke and Bechmann, 2013), including MMP9, that contribute to localized proteolytic activity during physiological and pathological events. Furthermore, microglial interactions with synapses have recently been shown to promote healthy brain homeostasis, including the regulation of cell death, synapse elimination, neurogenesis, and neuronal surveillance (Paolicelli et al., 2011; Tremblay et al., 2011; Wake et al., 2013). Thus MMP9 depletion may alter microglia morphology and function and influence dendritic spine pruning (Szklarczyk et al., 2002). To determine the effects of MMP9 deficiency on microglia, we first investigated changes in microglial morphology as these can indicate changes in microglial function. Whereas pathological microglial activation is characterized by the thickening, polarization and retraction of branches, as well as an increase in soma size, a resting/ quiescent state is characterized by a ramified, circular arbor and small soma (Hanisch and Kettenmann, 2007; Kettenmann et al., 2011). CTL and MMP9 KO tissue from the binocular visual cortex was processed for the anti-microglial marker, Iba-1, visualized with immunofluorescence and analyzed using confocal microscopy. Confocal z-stack images allowed us to fully assess the extent of microglial process arbor (Figure 9A) and soma (Figure 9D). While we noted no significant difference in the area occupied by the microglial process arbor in CTL and MMP9 KO microglia (Figure 9B), we found a small but significant decrease in the process circularity index (Figure 9C, p < 0.05, Student’s t-test) signifying arbor elongation in MMP9 KO microglia. MMP9 KO microglia also had a small but significant increase in soma size (Figure 9E, p < 0.05, Student’s t-test) but not soma circularity (Figure 9F). These results suggest that MMP9 deficiency has a limited effect on microglial morphology but the morphological changes observed suggest a more activated state.


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)

MMP9 KO mice show changes in microglial morphology. (A) The area occupied by microglial processes was measured using Image J software. (B) Quantitative analysis of microglial process area was not significantly different between CTL ND (black bars, 0.837 ± 0.008) and MMP9 KO ND (white bars, 0.812 ± 0.004; unpaired student’s t-test). (C) Process circularity index [1−(LA−SA)/(LA+SA)] was significantly decreased in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05) (D) The area of microglial soma was measured using Image J software. (E) Quantitative analysis of the soma area showed significantly larger microglial soma in MMP9 KO ND (unpaired student’s t-test, *p < 0.05) with no significant changes in overall soma circularity (F) Scale bar = 20 μm. All values reported are the mean ± SEM.
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Figure 9: MMP9 KO mice show changes in microglial morphology. (A) The area occupied by microglial processes was measured using Image J software. (B) Quantitative analysis of microglial process area was not significantly different between CTL ND (black bars, 0.837 ± 0.008) and MMP9 KO ND (white bars, 0.812 ± 0.004; unpaired student’s t-test). (C) Process circularity index [1−(LA−SA)/(LA+SA)] was significantly decreased in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05) (D) The area of microglial soma was measured using Image J software. (E) Quantitative analysis of the soma area showed significantly larger microglial soma in MMP9 KO ND (unpaired student’s t-test, *p < 0.05) with no significant changes in overall soma circularity (F) Scale bar = 20 μm. All values reported are the mean ± SEM.
Mentions: Microglia secrete proteases (Webster and Crowe, 2006; Konnecke and Bechmann, 2013), including MMP9, that contribute to localized proteolytic activity during physiological and pathological events. Furthermore, microglial interactions with synapses have recently been shown to promote healthy brain homeostasis, including the regulation of cell death, synapse elimination, neurogenesis, and neuronal surveillance (Paolicelli et al., 2011; Tremblay et al., 2011; Wake et al., 2013). Thus MMP9 depletion may alter microglia morphology and function and influence dendritic spine pruning (Szklarczyk et al., 2002). To determine the effects of MMP9 deficiency on microglia, we first investigated changes in microglial morphology as these can indicate changes in microglial function. Whereas pathological microglial activation is characterized by the thickening, polarization and retraction of branches, as well as an increase in soma size, a resting/ quiescent state is characterized by a ramified, circular arbor and small soma (Hanisch and Kettenmann, 2007; Kettenmann et al., 2011). CTL and MMP9 KO tissue from the binocular visual cortex was processed for the anti-microglial marker, Iba-1, visualized with immunofluorescence and analyzed using confocal microscopy. Confocal z-stack images allowed us to fully assess the extent of microglial process arbor (Figure 9A) and soma (Figure 9D). While we noted no significant difference in the area occupied by the microglial process arbor in CTL and MMP9 KO microglia (Figure 9B), we found a small but significant decrease in the process circularity index (Figure 9C, p < 0.05, Student’s t-test) signifying arbor elongation in MMP9 KO microglia. MMP9 KO microglia also had a small but significant increase in soma size (Figure 9E, p < 0.05, Student’s t-test) but not soma circularity (Figure 9F). These results suggest that MMP9 deficiency has a limited effect on microglial morphology but the morphological changes observed suggest a more activated state.

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