Glucocorticoids regulate glutamate and GABA synapse-specific retrograde transmission via divergent nongenomic signaling pathways.
Di S1, Maxson MM, Franco A, Tasker JG.
Glucocorticoids exert an opposing rapid regulation of glutamate and GABA synaptic inputs to hypothalamic magnocellular neurons via the activation of postsynaptic membrane-associated receptors and the release of retrograde messengers. Glucocorticoids suppress synaptic glutamate release via the retrograde release of endocannabinoids and facilitate synaptic GABA release via an unknown retrograde messenger. Here, we show that the glucocorticoid facilitation of GABA inputs is due to the retrograde release of neuronal nitric oxide and that glucocorticoid-induced endocannabinoid synthesis and nitric oxide synthesis are mediated by divergent G-protein signaling mechanisms. While the glucocorticoid-induced, endocannabinoid-mediated suppression of glutamate release is dependent on activation of the G(alpha)s G-protein subunit and cAMP-cAMP-dependent protein kinase activation, the nitric oxide facilitation of GABA release is mediated by G(beta)gamma signaling that leads to activation of neuronal nitric oxide synthase. Our findings indicate, therefore, that glucocorticoids exert opposing rapid actions on glutamate and GABA release by activating divergent G-protein signaling pathways that trigger the synthesis of, and glutamate and GABA synapse-specific retrograde actions of, endocannabinoids and nitric oxide, respectively. The simultaneous rapid stimulation of nitric oxide and endocannabinoid synthesis by glucocorticoids has important implications for the impact of stress on the brain as well as on neural-immune interactions in the hypothalamus.
CNS-targeted glucocorticoid reduces pathology in mouse model of amyotrophic lateral sclerosis.
Evans MC, Gaillard PJ, de Boer M, Appeldoorn C, Dorland R, Sibson NR, Turner MR, Anthony DC1, Stolp HB.
Hallmarks of CNS inflammation, including microglial and astrocyte activation, are prominent features in post-mortem tissue from amyotrophic lateral sclerosis (ALS) patients and in mice overexpressing mutant superoxide dismutase-1 (SOD1G93A). Administration of non-targeted glucocorticoids does not significantly alter disease progression, but this may reflect poor CNS delivery. Here, we sought to discover whether CNS-targeted, liposomal encapsulated glucocorticoid would inhibit the CNS inflammatory response and reduce motor neuron loss. SOD1G93A mice were treated with saline, free methylprednisolone (MP, 10 mg/kg/week) or glutathione PEGylated liposomal MP (2B3-201, 10 mg/kg/week) and compared to saline treated wild-type animals. Animals were treated weekly with intravenous injections for 9 weeks from 60 days of age. Weights and motor performance were monitored during this period. At the end of the experimental period (116 days) mice were imaged using T2-weighted MRI for brainstem pathology; brain and spinal cord tissue were then collected for histological analysis.
All SOD1G93A groups showed a significant decrease in motor performance, compared to baseline, from ~100 days. SOD1G93A animals showed a significant increase in signal intensity on T2 weighted MR images, which may reflect the combination of neuronal vacuolation and glial activation in these motor nuclei. Treatment with 2B3-201, but not free MP, significantly reduced T2 hyperintensity observed in SOD1G93A mice. Compared to saline-treated and free-MP-treated SOD1G93A mice, those animals given 2B3-201 displayed significantly improved histopathological outcomes in brainstem motor nuclei, which included reduced gliosis and neuronal loss.
In contrast to previous reports that employed free steroid preparations, CNS-targeted anti-inflammatory agent 2B3-201 (liposomal methylprednisolone) has therapeutic potential, reducing brainstem pathology in the SOD1G93A mouse model of ALS. 2B3-201 reduced neuronal loss and vacuolation in brainstem nuclei, and reduced activation preferentially in astrocytes compared with microglia. These data also suggest that other previously ineffective therapies could be of therapeutic value if delivered specifically to the CNS.
Neuroscience. 1993 Jul;55(2):445-9.
Steroid hormones protect spinal cord neurons from glutamate toxicity.
Ogata T1, Nakamura Y, Tsuji K, Shibata T, Kataoka K.
The effects of steroid hormones on glutamate neurotoxicity were examined in cultured spinal cord neurons. The extent of neuronal damage, produced by glutamate exposure for 15 min, was estimated based on the activity of lactate dehydrogenase released from degenerated neurons to the media during 24 h of post-exposure incubation. This damage was dependent on the glutamate concentrations used. The addition of dexamethasone, a synthetic steroid, in post-exposure media remarkably reduced the extent of damage in a dose-dependent manner. The half effective concentration for the steroid was approximately 0.7 microM, which was in the range of pharmacological concentration. Dexamethasone was effective even when it was added 2 h after glutamate exposure. Some endogenous steroid hormones--aldosterone, progesterone and testosterone--also showed similar neuroprotective effects. However, cholesterol, a precursor of these steroid hormones, had no effect on glutamate neurotoxicity. This direct protective effect on neurons against glutamate neurotoxicity may explain, at least partly, the mechanisms of beneficial effects of steroid hormones on in vivo spinal cord injury.
Autoimmunity in Amyotrophic Lateral Sclerosis: Past and Present
Mario Rafael Pagani,1 Laura Elisabeth Gonzalez,2 and Osvaldo Daniel Uchitel2,3
Copyright © 2011 Mario Rafael Pagani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting particularly motor neurons for which no cure or effective treatment is available. Although the cause of ALS remains unknown, accumulative evidence suggests an autoimmune mechanism of pathogenesis. In this paper, we will summarize the current research related to autoimmunity in the sporadic form of ALS and discuss the potential underlying pathogenic mechanisms and perspectives. Presented data supports the view that humoral immune responses against motor nerve terminals can initiate a series of physiological changes leading to alteration of calcium homeostasis. In turn, loss of calcium homeostasis may induce neuronal death through apoptotic signaling pathways. Additional approaches identifying specific molecular features of this hypothesis are required, which will hopefully allow us to develop techniques of early diagnosis and effective therapies.
The commonality of protein interaction networks determined in neurodegenerative disorders (NDDs)
From the 81 new common proteins, we found BCAP31 (B-cell receptor-associated protein 31), DNCL1 (dynein, cytoplasmic, light polypeptide 1), HSPCA (heat shock 90 kDa protein 1, alpha), NR3C1 [nuclear receptor subfamily 3, group C, member 1 (glucocorticoid receptor)] and PIN1 [protein (peptidyl-prolyl cis/trans isomerase) NIMA-interacting 1] are the most common in the six NDDs. BCAP31 is one of several candidate proteins that might contribute to the regulation of neuronal apoptosis. It is also a member of a novel class of sorting proteins regulating cellular anterograde transport (Zen et al., 2004). PIN1 is already known to be associated with AD and to function in neuronal dedifferentiation and apoptosis (Butterfield et al., 2006). DNCL1, a cytoplasmic dynein, physically interacts with neuronal nitric oxide synthase and inhibits its activity. In axons, retrograde transport is mediated mainly by cytoplasmic dynein, and dysfunction of motors results in NDDs (Hirokawa and Takemura, 2004). HSPCA is a molecular chaperone that plays an important role in conformational protein regulation and cell signaling (Barral et al., 2004). NR3C1 is an intracellular receptor for glucocorticoids. Marchetti et al. suggested that crosstalk between glucocorticoid and nitric oxide is a pivotal factor to organize neuroprotection in PD (Marchetti et al., 2005). It is already known that inflammation and oxidative stress have been closely associated with the pathogenesis of NDDs.
Glucocorticoid receptors and actions in the spinal cord of the Wobbler mouse, a model for neurodegenerative diseases.
González Deniselle MC1, González S, Piroli G, Ferrini M, Lima AE, De Nicola AF.
We have studied glucocorticoid receptors (GR) and actions in the spinal cord of the Wobbler mouse, a model for amyotrophic lateral sclerosis and infantile spinal muscular atrophy. Basal and stress levels of circulating corticosterone (CORT) were increased in Wobbler mice. Single point binding assays showed that cytosolic type II GR in the spinal cord of Wobbler mice of both sexes were slightly reduced compared with normal littermates. Saturation analysis further demonstrated a non-significant reduction in Bmax with increased Kd. In the hippocampus, however, we found down-regulation of GR, a probable response to increased CORT levels. We also found that the basal activity of ornithine decarboxylase (ODC), a rate-limiting enzyme of polyamine biosynthesis, was higher in Wobbler mice than in control animals. Both groups showed a two-fold stimulation of ODC activity after treatment with dexamethasone (DEX). Additionally, Wobbler mice presented with an intense proliferation of astrocytes immunoreactive (ir) for glial fibrillary acidic protein (GFAP) in grey and white matter of the spinal cord. The enhanced GFAP-ir was attenuated after four days of treatment with a corticosterone (CORT) pellet implant, producing a pharmacological increase in peripheral circulating CORT. Taking into consideration the content of GR and the changes in ODC activity and GFAP-ir brought about by glucocorticoids, we suggest that Wobbler mice are hormone responsive. Further elucidation of glucocorticoid effects in this model may be relevant for understanding the possible use of hormones in human neurodegenerative diseases.
Inhibition of cyclooxygenase-2 protects motor neurons in an organotypic model of amyotrophic lateral sclerosis.
Drachman DB1, Rothstein JD.
The pathogenesis of motor neuron loss in amyotrophic lateral sclerosis (ALS) is thought to involve both glutamate-mediated excitotoxicity and oxidative damage due to the accumulation of free radicals and other toxic molecules. Cyclooxygenase-2 (COX-2) may play a key role in these processes by producing prostaglandins, which trigger astrocytic glutamate release, and by inducing free radical formation. We tested the effects of COX-2 inhibition in an organotypic spinal cord culture model of ALS. The COX-2 inhibitor (SC236) provided significant protection against loss of spinal motor neurons in this system, suggesting that it may be useful in the treatment of ALS.
Effect of antiinflammatory drugs on COX-1 and COX-2 activity in human articular chondrocytes.
Blanco FJ1, Guitian R, Moreno J, de Toro FJ, Galdo F.
To study the effect of steroidal and nonsteroidal antiinflammatory drugs (NSAID) on cyclooxygenase (COX-1 and COX-2) activity in human articular chondrocytes.
Chondrocytes were isolated from articular cartilage of donors with no articular disease. Unstimulated and interleukin 1 (IL-1) stimulated chondrocytes were used as models to study the effects of drugs on COX-1 and COX-2. Cells were incubated with vehicle or drugs; supernatants were removed and the level of prostaglandin E2 (PGE2) in each sample was determined by enzyme immunoassay. IC50 were calculated from the reduction in PGE2 content by different concentrations of the test substance by linear regression analysis.
COX- mRNA was detected in unstimulated cells, but stimulation with IL-1 for up 12 h did not modify the levels of COX-1 mRNA. In contrast, COX-2 mRNA was not detectable in unstimulated cells, but it was induced by IL-1. Dexamethasone inhibited COX-2 mRNA expression induced by IL-1. COX-2 protein levels correlated with mRNA expression. Dexamethasone was the strongest drug inhibitor of COX-2 (IC50 = 0.0073 microM). However, it did not inhibit COX-1 activity. Among all NSAID tested, meloxicam and aspirin were the least potent inhibitors of COX-1 (IC50 = 36.6 microM and 3.57 microM, respectively). Indomethacin and diclofenac were the most potent inhibitors of COX-1 (IC50 = 0.063 microM and 0.611 microM, respectively) and COX-2 isoforms (IC50 = 0.48 microM and IC50 = 0.63 microM, respectively). Meloxicam was a more potent inhibitor of COX-2 (IC50 = 4.7 microM) than aspirin (IC50 = 29.3 microM) and similar to piroxicam (IC50 = 4.4 microM). Among all drugs tested dexamethasone showed the greatest selectivity for COX-2 and meloxicam was the NSAID with the best COX-2/COX-1 ratio (r = 0.12). Aspirin and piroxicam were about 8 times more active against COX-1 than COX-2, indomethacin was 7 times more active, and diclofenac was an equipotent inhibitor of COX-1 and COX-2.
We found that COX-1 and COX-2 isoforms are expressed in human chondrocytes at rest and in IL-1 stimulated cells, respectively. Antiinflammatory drugs have different capacities to inhibit COX enzyme in human articular chondrocytes.
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