Kappa opioids promote the proliferation of astrocytes via Gβγ and β‐arrestin 2‐dependent MAPK‐mediated pathways

Bancroft

2017

Journal of Neurotrauma

Opioids are frequently used for the treatment of pain following spinal cord injury (SCI). Unfortunately, we have shown that morphine administered in the acute phase of SCI results in significant, adverse secondary consequences including compromised locomotor and sensory recovery. Similarly, we showed that selective activation of the j-opioid receptor (KOR), even at a dose 32-fold lower than morphine, is sufficient to attenuate recovery of locomotor function. In the current study, we tested whether activation of the KOR is necessary to produce morphine's adverse effects using norBinaltorphimine (norBNI), a selective KOR antagonist. Rats received a moderate spinal contusion (T12) and 24 h later, baseline locomotor function and nociceptive reactivity were assessed. Rats were then administered norBNI (0, 0.02, 0.08, or 0.32 lmol) followed by morphine (0 or 0.32 lmol). Nociception was reassessed 30 min after drug treatment, and recovery was evaluated for 21 days. The effects of norBNI on morphine-induced attenuation of recovery were dose dependent. At higher doses, norBNI blocked the adverse effects of morphine on locomotor recovery, but analgesia was also significantly decreased. Conversely, at low doses, analgesia was maintained, but the adverse effects on recovery persisted. A moderate dose of norBNI, however, adequately protected against morphine's adverse effects without eliminating its analgesic efficacy. This suggests that activation of the KOR system plays a significant role in the morphineinduced attenuation of recovery. Our research suggests that morphine, and other opioid analgesics, may be contraindicated for the SCI population. Blocking KOR activity may be a viable strategy for improving the safety of clinical opioid use.

Section: Resultsmentioning

confidence: 99%

Nor-Binaltorphimine Blocks the Adverse Effects of Morphine after Spinal Cord Injury

Bancroft

2017

Journal of Neurotrauma

Journal of Biological Chemistry

“…For ERK1/2 assay, growth medium was replaced with DMEM without serum 24 h prior to ligand treatment. Of the total number of cells in primary cultures, 90% were glial fibrillary acidic proteinpositive and Ͻ1% were TuJ1 (neuronal marker)-positive (58).…”

Section: Methodsmentioning

confidence: 99%

“…Measurement of ERK Activity-Upon treatment with opioids, ERK phosphorylation was measured by immunoblotting as described previously (58). Blots were incubated with a phospho-ERK Ab (1:2000) overnight at 4°C, followed by incubation with HRP-conjugated IgG (1:2000, Sigma) for 1 h at room temperature.…”

Section: Methodsmentioning

confidence: 99%

“…Using an astrocytoma model system, C6 glioma cells, and immortalized type 1 astrocytes, we implicated phosphatidylinositol turnover, discrete PKC isoforms, different secondary messengers, and transactivation of EGFR as well as FGF receptor in and opioid receptor (MOR and KOR) activation of ERK (53)(54)(55)(56)(57). Recently, we found that KOR agonists stimulate proliferation of immortalized and primary astrocytes via both rapid pertussis toxin-sensitive G␤␥-and sustained ␤arrestin2-dependent ERK pathways (58). Acute morphine and DAMGO activate ERK via G protein, calmodulin (CaM), and ␤arrestin2-dependent mechanisms.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Morphine Modulation of Thrombospondin Levels in Astrocytes and Its Implications for Neurite Outgrowth and Synapse Formation

Ikeda

Miyatake

Koshikawa

et al. 2010

Self Cite

Opioid receptor signaling via EGF receptor (EGFR) transactivation and ERK/MAPK phosphorylation initiates diverse cellular responses that are cell type-dependent. In astrocytes, multiple opioid receptor-mediated mechanisms of ERK activation exist that are temporally distinctive and feature different outcomes. Upon discovering that chronic opiate treatment of rats down-regulates thrombospondin 1 (TSP1) expression in the nucleus accumbens and cortex, we investigated the mechanism of action of this modulation in astrocytes. TSP1 is synthesized in astrocytes and is released into the extracellular matrix where it is known to play a role in synapse formation and neurite outgrowth. Acute morphine (hours) reduced TSP1 levels in astrocytes. Chronic (days) opioids repressed TSP1 gene expression and reduced its protein levels by opioid receptor and ERK-dependent mechanisms in astrocytes. Morphine also depleted TSP1 levels stimulated by TGF␤1 and abolished ERK activation induced by this factor. Chronic morphine treatment of astrocyte-neuron co-cultures reduced neurite outgrowth and synapse formation. Therefore, inhibitory actions of morphine were detected after both acute and chronic treatments. An acute mechanism of morphine signaling to ERK that entails depletion of TSP1 levels was suggested by inhibition of morphine activation of ERK by a function-blocking TSP1 antibody. This raises the novel possibility that acute morphine uses TSP1 as a source of EGF-like ligands to activate EGFR. Chronic morphine inhibition of TSP1 is reminiscent of the negative effect of opioids on EGFR-induced astrocyte proliferation via a phospho-ERK feedback inhibition mechanism. Both of these variations of classical EGFR transactivation may enable opiates to diminish neurite outgrowth and synapse formation.Astrocytes are the source of a diverse group of molecules that are required for synapse formation, function, and maintenance in neurons (1-7). Thrombospondin (TSP) 3 is a member of the astrocyte-derived intercellular signaling components that have been implicated in synaptogenesis and other neuronal glial interactions of the developing brain (8 -17). In addition, synaptic plasticity and other neuroadaptations involving astrocyte neuron interactions are thought to play a role in reward learning and addiction (18). Some chronic morphine-responsive genes (Homer1, PSD-95, and synaptotagmin1) may subserve the long lived neuronal and behavioral plasticity observed in regions of the mesolimbic reward system, and they are involved in synaptogenesis (19 -26).TSPs are multidomain, multimeric glycoproteins that are secreted into the extracellular matrix of many cells and serve as bridging molecules in cell-cell interactions (27,28). First discovered in platelet ␣-granules and secreted upon platelet activation, the superfamily of TSPs modulate varied functions of cell signaling and cell adhesion in a broad array of cell types. The five TSP genes are expressed in the CNS and peripheral nervous system where they play important roles in neural development. T...

“…58,63 The diminution of the percentage of GFAP + immortalized astrocytes may explain the absence of an increase in their distribution upon scratch wounding in this population of astrocytes. Alternatively, the immortalized GFAP + astrocyte subtype may be reactive astrocytes that are not influenced further by injury.…”

Section: ■ Discussionmentioning

confidence: 99%

Acute and Chronic Mu Opioids Differentially Regulate Thrombospondins 1 and 2 Isoforms in Astrocytes

Phamduong

Rathore

Crews

et al. 2013

ACS Chem. Neurosci.

Self Cite

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 was up-regulated by acute (3 h) morphine or DAMGO by an ERK/MAPK dependent mechanism. Paradoxically, TSP2 protein levels were altered neither by TGFβ1 nor by astrocytic neurotrophic factors, EGF, CNTF, and BMP4. TSP1/2 immunofluorescence was increased in astrocytes subjected to scratch-wounding, suggesting TSPs may be useful markers for the "reactive" state of these cells and potentially for different types of injury. Previously, we determined that chronic morphine attenuated both neurite outgrowth and synapse formation in cocultures of primary astrocytes and neurons under similar temporal conditions that μ opioids reduced TSP1 protein levels in astrocytes. Here we found that, after the same 8 day treatment, morphine or DAMGO diminished TSP2 protein levels in astrocytes. Therefore, μ opioids may deter synaptogenesis via both TSP1/2 isoforms, but by distinct mechanisms. KEYWORDS: Opioids, morphine, opioid receptors, astrocytes, ERK/MAPK, growth factors A strocytes make integral contributions to neuronal signaling in the brain by releasing molecules that act at synapses during different stages of synaptogenesis. These phases include pre-and postsynaptic development, function, maintenance, and plasticity.1−7 One family of key astrocyte-secreting molecules includes thrombospondins (TSPs), oligomeric, multidomain glycoproteins that promote synapse formation in vivo and in vitro.8−14 Yet another molecule is TGFβ that induces excitatory synapses at least in part via a D-serine dependent mechanism. 15 Interestingly, TGFβ and TSPs maintain a reciprocal relationship in astrocytes. Early on, it was recognized that TSP1 activates TGFβ. 16 Alternatively, several independent research groups have reported that in astrocytes TGFβ increases TSP1 gene expression and/or protein levels as shown by immunoblotting, qRT-PCR, and in situ hybridization.17−20 Both of these processes appear to be initiated in the extrac...