Limits...
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

Ultrastructural analysis of microglia suggest mild activation in the absence of MMP9. (A,B) Iba-1 immunoperoxidase EM in non-deprived control mice (CTL ND) and non-deprived MMP9 KO mice (MMP9 KO ND). (C) Quantitative analysis of microglial process area showed no significant differences, while surrounding extracellular space was significantly increased in MMP9 KO ND compared to CTL ND (One-Way ANOVA, *p < 0.05). (D) Average number of inclusions per area of Iba-1 labeling in 50 microglia per animals demonstrating a significant increase in inclusions in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05). (E) Average number of synaptic contacts per area of Iba-1 labeling in 50 microglia per animals showing no significant differences between CTL ND and MMP9 KO ND mice. (F) Iba-1 immunoperoxidase EM showing close apposition of a microglial process to excitatory synaptic sites (sc). (G) Quantification of neighboring contacts to Iba-1 immunoreactive microglial processes. We found no significant differences between microglial contacts which showed similar interactions with spines and terminals in both CTL and MMP9 KO mice (One-Way ANOVA, **p < 0.001). All values reported are the mean ± SEM. t, axon terminal; s, dendritic spine; i, inclusion; cm, cellular membrane; sc, synaptic contact; *, extracellular space. Scale bar = 500 nm.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4585116&req=5

Figure 10: Ultrastructural analysis of microglia suggest mild activation in the absence of MMP9. (A,B) Iba-1 immunoperoxidase EM in non-deprived control mice (CTL ND) and non-deprived MMP9 KO mice (MMP9 KO ND). (C) Quantitative analysis of microglial process area showed no significant differences, while surrounding extracellular space was significantly increased in MMP9 KO ND compared to CTL ND (One-Way ANOVA, *p < 0.05). (D) Average number of inclusions per area of Iba-1 labeling in 50 microglia per animals demonstrating a significant increase in inclusions in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05). (E) Average number of synaptic contacts per area of Iba-1 labeling in 50 microglia per animals showing no significant differences between CTL ND and MMP9 KO ND mice. (F) Iba-1 immunoperoxidase EM showing close apposition of a microglial process to excitatory synaptic sites (sc). (G) Quantification of neighboring contacts to Iba-1 immunoreactive microglial processes. We found no significant differences between microglial contacts which showed similar interactions with spines and terminals in both CTL and MMP9 KO mice (One-Way ANOVA, **p < 0.001). All values reported are the mean ± SEM. t, axon terminal; s, dendritic spine; i, inclusion; cm, cellular membrane; sc, synaptic contact; *, extracellular space. Scale bar = 500 nm.

Mentions: To further investigate the potential activation of microglia, we preformed pre-embedding immuno-peroxidase electron microscopy on samples taken from the primary visual cortex at P28 in both control C57BL/6 and experimental MMP9 KO mice. Sections were processed for Iba-1 immunoreactivity, resulting in clear demarcation of microglial processes, internal content and neighboring elements in both control (CTL ND, Figure 10A) and MMP9 KO mice (MMP9 KO ND, Figure 10B). We observed no difference in microglial process size in MMP9 KO mice, but found significantly larger pockets of extracellular space surrounding microglia (Figure 10C). Furthermore, we found significantly more inclusions (intracellular vacuoles often containing engulfed cellular content) in the MMP9 KO (Figure 10D). To determine whether this increase in inclusions was due to changes in microglial behavior towards synapses (Paolicelli et al., 2011), we quantified microglial contacts with stereotypic excitatory synapses. We measured the degree of microglial contact with excitatory pre- and postsynaptic terminals (characterized by synaptic vesicle accumulation in the presynaptic terminal abutting a postsynaptic terminal containing a visible PSD) often surrounding the synaptic cleft. We found no differences in microglial contacts with the synaptic cleft (Figure 10E) suggesting that increased phagocytosis in MMP9 KO microglia may not be specific to synapses. We also found a similar profile of structures that contacted microglial processes in CTL or MMP9 KO microglia (aside from a significant increase in the number of pockets of extracellular space surrounding MMP9 KO microglia), further suggesting a lack of microglial targeting to specific elements in MMP9 KO mice as compared to CTL (Figures 10F,G).


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)

Ultrastructural analysis of microglia suggest mild activation in the absence of MMP9. (A,B) Iba-1 immunoperoxidase EM in non-deprived control mice (CTL ND) and non-deprived MMP9 KO mice (MMP9 KO ND). (C) Quantitative analysis of microglial process area showed no significant differences, while surrounding extracellular space was significantly increased in MMP9 KO ND compared to CTL ND (One-Way ANOVA, *p < 0.05). (D) Average number of inclusions per area of Iba-1 labeling in 50 microglia per animals demonstrating a significant increase in inclusions in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05). (E) Average number of synaptic contacts per area of Iba-1 labeling in 50 microglia per animals showing no significant differences between CTL ND and MMP9 KO ND mice. (F) Iba-1 immunoperoxidase EM showing close apposition of a microglial process to excitatory synaptic sites (sc). (G) Quantification of neighboring contacts to Iba-1 immunoreactive microglial processes. We found no significant differences between microglial contacts which showed similar interactions with spines and terminals in both CTL and MMP9 KO mice (One-Way ANOVA, **p < 0.001). All values reported are the mean ± SEM. t, axon terminal; s, dendritic spine; i, inclusion; cm, cellular membrane; sc, synaptic contact; *, extracellular space. Scale bar = 500 nm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585116&req=5

Figure 10: Ultrastructural analysis of microglia suggest mild activation in the absence of MMP9. (A,B) Iba-1 immunoperoxidase EM in non-deprived control mice (CTL ND) and non-deprived MMP9 KO mice (MMP9 KO ND). (C) Quantitative analysis of microglial process area showed no significant differences, while surrounding extracellular space was significantly increased in MMP9 KO ND compared to CTL ND (One-Way ANOVA, *p < 0.05). (D) Average number of inclusions per area of Iba-1 labeling in 50 microglia per animals demonstrating a significant increase in inclusions in MMP9 KO ND mice (unpaired student’s t-test, *p < 0.05). (E) Average number of synaptic contacts per area of Iba-1 labeling in 50 microglia per animals showing no significant differences between CTL ND and MMP9 KO ND mice. (F) Iba-1 immunoperoxidase EM showing close apposition of a microglial process to excitatory synaptic sites (sc). (G) Quantification of neighboring contacts to Iba-1 immunoreactive microglial processes. We found no significant differences between microglial contacts which showed similar interactions with spines and terminals in both CTL and MMP9 KO mice (One-Way ANOVA, **p < 0.001). All values reported are the mean ± SEM. t, axon terminal; s, dendritic spine; i, inclusion; cm, cellular membrane; sc, synaptic contact; *, extracellular space. Scale bar = 500 nm.
Mentions: To further investigate the potential activation of microglia, we preformed pre-embedding immuno-peroxidase electron microscopy on samples taken from the primary visual cortex at P28 in both control C57BL/6 and experimental MMP9 KO mice. Sections were processed for Iba-1 immunoreactivity, resulting in clear demarcation of microglial processes, internal content and neighboring elements in both control (CTL ND, Figure 10A) and MMP9 KO mice (MMP9 KO ND, Figure 10B). We observed no difference in microglial process size in MMP9 KO mice, but found significantly larger pockets of extracellular space surrounding microglia (Figure 10C). Furthermore, we found significantly more inclusions (intracellular vacuoles often containing engulfed cellular content) in the MMP9 KO (Figure 10D). To determine whether this increase in inclusions was due to changes in microglial behavior towards synapses (Paolicelli et al., 2011), we quantified microglial contacts with stereotypic excitatory synapses. We measured the degree of microglial contact with excitatory pre- and postsynaptic terminals (characterized by synaptic vesicle accumulation in the presynaptic terminal abutting a postsynaptic terminal containing a visible PSD) often surrounding the synaptic cleft. We found no differences in microglial contacts with the synaptic cleft (Figure 10E) suggesting that increased phagocytosis in MMP9 KO microglia may not be specific to synapses. We also found a similar profile of structures that contacted microglial processes in CTL or MMP9 KO microglia (aside from a significant increase in the number of pockets of extracellular space surrounding MMP9 KO microglia), further suggesting a lack of microglial targeting to specific elements in MMP9 KO mice as compared to CTL (Figures 10F,G).

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