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Astrocyte matricellular proteins that control excitatory synaptogenesis are regulated by inflammatory cytokines and correlate with paralysis severity during experimental autoimmune encephalomyelitis.

Blakely PK, Hussain S, Carlin LE, Irani DN - Front Neurosci (2015)

Bottom Line: Taken together, these data support a model whereby proinflammatory cytokines inhibit SPARCL1 and/or augment SPARC expression by astrocytes in spinal gray matter that, in turn, cause either transient or sustained synaptic retraction from lumbar spinal motor neurons thereby regulating hind limb paralysis during EAE.Ongoing studies seek ways to alter this SPARCL1:SPARC expression ratio in favor of synapse reformation/maintenance and thus help to modulate neurologic deficits during times of inflammation.This could identify new astrocyte-targeted therapies for diseases such as multiple sclerosis.

View Article: PubMed Central - PubMed

Affiliation: Holtom-Garrett Program in Neuroimmunology, Department of Neurology, University of Michigan Medical School Ann Arbor, MI, USA.

ABSTRACT
The matricellular proteins, secreted protein acidic and rich in cysteine (SPARC) and SPARC-like 1 (SPARCL1), are produced by astrocytes and control excitatory synaptogenesis in the central nervous system. While SPARCL1 directly promotes excitatory synapse formation in vitro and in the developing nervous system in vivo, SPARC specifically antagonizes the synaptogenic actions of SPARCL1. We hypothesized these proteins also help maintain existing excitatory synapses in adult hosts, and that local inflammation in the spinal cord alters their production in a way that dynamically modulates motor synapses and impacts the severity of paralysis during experimental autoimmune encephalomyelitis (EAE) in mice. Using a spontaneously remitting EAE model, paralysis severity correlated inversely with both expression of synaptic proteins and the number of synapses in direct contact with the perikarya of motor neurons in spinal gray matter. In both remitting and non-remitting EAE models, paralysis severity also correlated inversely with sparcl1:sparc transcript and SPARCL1:SPARC protein ratios directly in lumbar spinal cord tissue. In vitro, astrocyte production of both SPARCL1 and SPARC was regulated by T cell-derived cytokines, causing dynamic modulation of the SPARCL1:SPARC expression ratio. Taken together, these data support a model whereby proinflammatory cytokines inhibit SPARCL1 and/or augment SPARC expression by astrocytes in spinal gray matter that, in turn, cause either transient or sustained synaptic retraction from lumbar spinal motor neurons thereby regulating hind limb paralysis during EAE. Ongoing studies seek ways to alter this SPARCL1:SPARC expression ratio in favor of synapse reformation/maintenance and thus help to modulate neurologic deficits during times of inflammation. This could identify new astrocyte-targeted therapies for diseases such as multiple sclerosis.

No MeSH data available.


Related in: MedlinePlus

T cell-derived cytokines regulate astrocyte production of SPARCL1 in a complex manner in vitro. (A) Astrocytes spontaneously secrete measurable amounts of SPARCL1 into culture supernatants (n = 4 experimental replicates per time point). (B) Interferon-gamma (IFN-γ) modestly increases astrocyte SPARCL1 release (n = 3 experimental replicates per time point), p = 0.003 comparing changes over time. (C) Interleukin (IL)-17 has no significant effect on astrocyte SPARCL1 production (n = 3 experimental replicates per time point). (D) IL-10 potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0003 comparing changes over time, p = 0.002 comparing fold change differences. (E) Granulocyte macrophage colony stimulating factor (GM-CSF) potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0024 comparing changes over time. (F) Tumor necrosis factor (TNF)-α suppresses astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0384 comparing fold change differences.
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Figure 6: T cell-derived cytokines regulate astrocyte production of SPARCL1 in a complex manner in vitro. (A) Astrocytes spontaneously secrete measurable amounts of SPARCL1 into culture supernatants (n = 4 experimental replicates per time point). (B) Interferon-gamma (IFN-γ) modestly increases astrocyte SPARCL1 release (n = 3 experimental replicates per time point), p = 0.003 comparing changes over time. (C) Interleukin (IL)-17 has no significant effect on astrocyte SPARCL1 production (n = 3 experimental replicates per time point). (D) IL-10 potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0003 comparing changes over time, p = 0.002 comparing fold change differences. (E) Granulocyte macrophage colony stimulating factor (GM-CSF) potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0024 comparing changes over time. (F) Tumor necrosis factor (TNF)-α suppresses astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0384 comparing fold change differences.

Mentions: Hind limb paralysis in mice with EAE is driven by local CNS inflammation initiated by myelin-specific CD4+ T cells. In this setting, a wide range of cytokines and chemokines get induced in the spinal cord at peak disease (Table 1). We used primary glial cell cultures to investigate whether some of these mediators directly altered astrocyte production of SPARCL1 or SPARC, focusing on those factors made directly by encephalitogenic CD4+ T cells. Primary astrocytes released substantial amounts of SPARCL1 into culture supernatants without any direct provocation (Figure 6A). When cells were treated with varying concentrations of T cell-derived cytokines, a wide range of effects on SPARCL1 production was observed. IFN-γ, the prototype Th1 pro-inflammatory cytokine, modestly increased SPARCL1 levels in astrocyte culture supernatant (Figure 6B), while the canonical Th17 cytokine, IL-17, had no effects on SPARCL1 release (Figure 6C). The anti-inflammatory cytokine, IL-10, potently increased astrocyte SPARCL1 production (Figure 6D). Granulocyte-macrophage colony stimulating factor (GM-CSF) also potently increased SPARCL1 levels (Figure 6E), even though it also serves as an important effector in Th17-driven EAE by mobilizing myeloid cells to the CNS (Kroenke et al., 2008; Codarri et al., 2011). Finally, TNF-α suppressed SPARCL1 release (Figure 6F). We conclude that as a group, T cell-derived cytokines exert complex effects on astrocyte SPARCL1 release. Practical considerations prevented us from examining the extent to which the many candidate non-T cell-derived cytokines and chemokines influenced SPARCL1 production. Nonetheless, astrocytes express a wide range of cytokine and chemokine receptors meaning that other mediators could also contribute to the effects observed in vivo (Farina et al., 2007).


Astrocyte matricellular proteins that control excitatory synaptogenesis are regulated by inflammatory cytokines and correlate with paralysis severity during experimental autoimmune encephalomyelitis.

Blakely PK, Hussain S, Carlin LE, Irani DN - Front Neurosci (2015)

T cell-derived cytokines regulate astrocyte production of SPARCL1 in a complex manner in vitro. (A) Astrocytes spontaneously secrete measurable amounts of SPARCL1 into culture supernatants (n = 4 experimental replicates per time point). (B) Interferon-gamma (IFN-γ) modestly increases astrocyte SPARCL1 release (n = 3 experimental replicates per time point), p = 0.003 comparing changes over time. (C) Interleukin (IL)-17 has no significant effect on astrocyte SPARCL1 production (n = 3 experimental replicates per time point). (D) IL-10 potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0003 comparing changes over time, p = 0.002 comparing fold change differences. (E) Granulocyte macrophage colony stimulating factor (GM-CSF) potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0024 comparing changes over time. (F) Tumor necrosis factor (TNF)-α suppresses astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0384 comparing fold change differences.
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Figure 6: T cell-derived cytokines regulate astrocyte production of SPARCL1 in a complex manner in vitro. (A) Astrocytes spontaneously secrete measurable amounts of SPARCL1 into culture supernatants (n = 4 experimental replicates per time point). (B) Interferon-gamma (IFN-γ) modestly increases astrocyte SPARCL1 release (n = 3 experimental replicates per time point), p = 0.003 comparing changes over time. (C) Interleukin (IL)-17 has no significant effect on astrocyte SPARCL1 production (n = 3 experimental replicates per time point). (D) IL-10 potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0003 comparing changes over time, p = 0.002 comparing fold change differences. (E) Granulocyte macrophage colony stimulating factor (GM-CSF) potently induces astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0024 comparing changes over time. (F) Tumor necrosis factor (TNF)-α suppresses astrocyte SPARCL1 production (n = 3 experimental replicates per time point), p = 0.0384 comparing fold change differences.
Mentions: Hind limb paralysis in mice with EAE is driven by local CNS inflammation initiated by myelin-specific CD4+ T cells. In this setting, a wide range of cytokines and chemokines get induced in the spinal cord at peak disease (Table 1). We used primary glial cell cultures to investigate whether some of these mediators directly altered astrocyte production of SPARCL1 or SPARC, focusing on those factors made directly by encephalitogenic CD4+ T cells. Primary astrocytes released substantial amounts of SPARCL1 into culture supernatants without any direct provocation (Figure 6A). When cells were treated with varying concentrations of T cell-derived cytokines, a wide range of effects on SPARCL1 production was observed. IFN-γ, the prototype Th1 pro-inflammatory cytokine, modestly increased SPARCL1 levels in astrocyte culture supernatant (Figure 6B), while the canonical Th17 cytokine, IL-17, had no effects on SPARCL1 release (Figure 6C). The anti-inflammatory cytokine, IL-10, potently increased astrocyte SPARCL1 production (Figure 6D). Granulocyte-macrophage colony stimulating factor (GM-CSF) also potently increased SPARCL1 levels (Figure 6E), even though it also serves as an important effector in Th17-driven EAE by mobilizing myeloid cells to the CNS (Kroenke et al., 2008; Codarri et al., 2011). Finally, TNF-α suppressed SPARCL1 release (Figure 6F). We conclude that as a group, T cell-derived cytokines exert complex effects on astrocyte SPARCL1 release. Practical considerations prevented us from examining the extent to which the many candidate non-T cell-derived cytokines and chemokines influenced SPARCL1 production. Nonetheless, astrocytes express a wide range of cytokine and chemokine receptors meaning that other mediators could also contribute to the effects observed in vivo (Farina et al., 2007).

Bottom Line: Taken together, these data support a model whereby proinflammatory cytokines inhibit SPARCL1 and/or augment SPARC expression by astrocytes in spinal gray matter that, in turn, cause either transient or sustained synaptic retraction from lumbar spinal motor neurons thereby regulating hind limb paralysis during EAE.Ongoing studies seek ways to alter this SPARCL1:SPARC expression ratio in favor of synapse reformation/maintenance and thus help to modulate neurologic deficits during times of inflammation.This could identify new astrocyte-targeted therapies for diseases such as multiple sclerosis.

View Article: PubMed Central - PubMed

Affiliation: Holtom-Garrett Program in Neuroimmunology, Department of Neurology, University of Michigan Medical School Ann Arbor, MI, USA.

ABSTRACT
The matricellular proteins, secreted protein acidic and rich in cysteine (SPARC) and SPARC-like 1 (SPARCL1), are produced by astrocytes and control excitatory synaptogenesis in the central nervous system. While SPARCL1 directly promotes excitatory synapse formation in vitro and in the developing nervous system in vivo, SPARC specifically antagonizes the synaptogenic actions of SPARCL1. We hypothesized these proteins also help maintain existing excitatory synapses in adult hosts, and that local inflammation in the spinal cord alters their production in a way that dynamically modulates motor synapses and impacts the severity of paralysis during experimental autoimmune encephalomyelitis (EAE) in mice. Using a spontaneously remitting EAE model, paralysis severity correlated inversely with both expression of synaptic proteins and the number of synapses in direct contact with the perikarya of motor neurons in spinal gray matter. In both remitting and non-remitting EAE models, paralysis severity also correlated inversely with sparcl1:sparc transcript and SPARCL1:SPARC protein ratios directly in lumbar spinal cord tissue. In vitro, astrocyte production of both SPARCL1 and SPARC was regulated by T cell-derived cytokines, causing dynamic modulation of the SPARCL1:SPARC expression ratio. Taken together, these data support a model whereby proinflammatory cytokines inhibit SPARCL1 and/or augment SPARC expression by astrocytes in spinal gray matter that, in turn, cause either transient or sustained synaptic retraction from lumbar spinal motor neurons thereby regulating hind limb paralysis during EAE. Ongoing studies seek ways to alter this SPARCL1:SPARC expression ratio in favor of synapse reformation/maintenance and thus help to modulate neurologic deficits during times of inflammation. This could identify new astrocyte-targeted therapies for diseases such as multiple sclerosis.

No MeSH data available.


Related in: MedlinePlus