Astrocyte-Derived Thrombospondins Mediate the Development of Hippocampal Presynaptic PlasticityIn Vitro

Abstract

Astrocytes contribute to many neuronal functions, including synaptogenesis, but their role in the development of synaptic plasticity remains unclear. Presynaptic muting of hippocampal glutamatergic terminals defends against excitotoxicity. Here we studied the role of astrocytes in the development of presynaptic muting at glutamatergic synapses in rat hippocampal neurons. We found that astrocytes were critical for the development of depolarization-dependent and Gi/o-dependent presynaptic muting. The ability of cAMP analogues to modulate presynaptic function was also impaired by astrocyte deficiency. Although astrocyte deprivation resulted in postsynaptic glutamate receptor deficits, this effect appeared independent of astrocytes’ role in presynaptic muting. Muting was restored with chronic, but not acute, treatment with astrocyte-conditioned medium, indicating that a soluble factor is permissive for muting. Astrocyte-derived thrombospondins (TSPs) are likely responsible because TSP1 mimicked the effect of conditioned medium, and gabapentin, a high-affinity antagonist of TSP binding to the α2δ-1 calcium channel subunit, mimicked astrocyte deprivation. We found evidence that protein kinase A activity is abnormal in astrocyte-deprived neurons but restored by TSP1, so protein kinase A dysfunction may provide a mechanism by which muting is disrupted during astrocyte deficiency. In summary our results suggest an important role for astrocyte-derived TSPs, acting through α2δ-1, in maturation of a potentially important form of presynaptic plasticity.

Establishment of a Human Neuronal Network Assessment System by Using a Human Neuron/Astrocyte Co-Culture Derived from Fetal Neural Stem/Progenitor Cells

“…Thrombospondins are also astrocyte-secreted proteins that were reported to promote synaptic maturation of rat primary hippocampal neurons through an interaction with the α2δ-1 calcium channel subunit. 18 Beattie et al 19 showed that astrocyte-derived TNFα enhanced the synaptic strength of rat hippocampal neurons and slices by increasing trafficking of AMPA receptors to the cell surface. Taken together with these reports, we considered that accelerated electrophysiological maturation of HIP-009 neurons by the addition of ACM is caused by concentrated glia-derived neurotrophic factors contained in it.…”

Thrombospondin-1 prevents amyloid beta–mediated synaptic pathology in Alzheimer's disease

“…The density of the dendritic protrusions was measured from 3 to 5 dendrites of 8e10 neurons and calculated by quantifying the number of spines per unit length of dendrite and normalized per 50 mm of dendrite length. For dendritic spine density analysis, immunocytochemistry was performed as described previously (Crawford et al, 2012). After fixation, primary antibodies were microtubule-associated protein 2B (MAP2B; 1:200; BD Transduction Laboratories, San Jose, CA, USA), and vesicular glutamate transporter 1 (vGlut1; 1:100; Neuromab, Davis, CA, USA).…”

“…The TSP family consists of 2 subfamilies, A and B, according to their organization and domain structure: A includes the trimeric TSP-1 and TSP-2, whereas B includes the pentameric TSP-3, TSP-4, and TSP-5 (Lawler, 2002). Expression of all TSPs has been found in the brain, and studies using purified retinal ganglion cell cultures indicate that TSPs, especially TSP-1 and TSP-2, promote the formation of new excitatory (glutamatergic) synapses (Christopherson et al, 2005;Crawford et al, 2012). TSPs mediate these functions via interactions with their various neuronal receptors, including integrin, neuroligin, cluster of differentiation 47 (CD47) and/or integrin-associated protein, and alpha-2-delta-1 (a2d1) (Eroglu et al, 2009;Graf et al, 2004;Ohnishi et al, 2005).…”

Glial Contributions to Neural Function and Disease

“…This observation led to extensive searches for these factors, which are now known to contribute to structural assembly of synapses and modulation of pre-and postsynaptic function (15). For example, thrombospondins, which are large extracellular ma- trix molecules secreted by astrocytes, have a myriad of functions including the induction of glutamatergic synapse formation (16) and the inhibition of presynaptic release (17). Not only do astrocytes promote synapse assembly, but recent studies of astrocyte gene expression suggested that they also participate in the refinement of neural circuits during development and in adult animals by activity-dependent synapse elimination.…”