Acute and Chronic Mu Opioids Differentially RegulateThrombospondins 1 and 2 Isoforms in Astrocytes

摘要

Chronic opioids induce synaptic plasticity, a major neuronal adaptation. Astrocyte activation in synaptogenesis may play a critical role in opioid tolerance, withdrawal, and dependence. Thrombospondins 1 and 2 (TSP1/2) are astrocyte-secreted matricellular glycoproteins that promote neurite outgrowth as well as dendritic spine and synapse formation, all of which are inhibited by chronic μ opioids. In prior studies, we discovered that the mechanism of TSP1 regulation by μ opioids in astrocytes involves crosstalk between three different classes of receptors, μ opioid receptor, EGFR and TGFβR. Moreover, TGFβ1 stimulated TSP1 expression via EGFR and ERK/MAPK activation, indicating that EGFR is a signaling hub for opioid and TGFβ1 actions. Using various selective antagonists, and inhibitors, here we compared the mechanisms of chronic opioid regulation of TSP1/2 isoform expression in vivo and in immortalized rat cortical astrocytes. TSP1/2 release from astrocytes was also monitored. Acute and chronic μ opioids, morphine, and the prototypic μ ligand, DAMGO,modulated TSP2 protein levels. TSP2 but not TSP1 protein content wasup-regulated by acute (3 h) morphine or DAMGO by an ERK/MAPK dependentmechanism. Paradoxically, TSP2 protein levels were altered neitherby TGFβ1 nor by astrocytic neurotrophic factors, EGF, CNTF,and BMP4. TSP1/2 immunofluorescence was increased in astrocytes subjectedto scratch-wounding, suggesting TSPs may be useful markers for the“reactive” state of these cells and potentially fordifferent types of injury. Previously, we determined that chronicmorphine attenuated both neurite outgrowth and synapse formation incocultures of primary astrocytes and neurons under similar temporalconditions that μ opioids reduced TSP1 protein levels in astrocytes.Here we found that, after the same 8 day treatment, morphine or DAMGOdiminished TSP2 protein levels in astrocytes. Therefore, μ opioidsmay deter synaptogenesis via both TSP1/2 isoforms, but by distinctmechanisms.