Dexmedetomidine protects rats from postoperative cognitive dysfunction via regulating the GABABR‐mediated cAMP‐PKA‐CREB signaling pathway

This work attempts to discuss whether dexmedetomidine (Dex) can protect rats from postoperative cognitive dysfunction (POCD) through regulating the γ‐aminobutyric acid‐_B receptor (GABA_BR)‐mediated cyclic adenosine monophosphate (cAMP) – protein kinase A (PKA) – cAMP‐response element binding (cAMP‐PKA‐CREB) signaling pathway. Sprague‐Dawley rats were divided into a non‐surgical group (Control), a surgical group (Model), a surgical group treated with Dex (Model + Dex), a surgical group treated with GABA_BR antagonist (Model + CGP 35348) and a surgical group treated with Dex and GABA_BR agonist (Model + Dex + Baclofen). Cognitive and memory functions were evaluated by Y‐maze test and open‐field test. The neuronal morphology of the hippocampus was observed by hematoxylin and eosin staining and neuronal apoptosis was by terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick‐end labeling method. Inflammatory factors and cAMP levels were detected by enzyme‐linked immunosorbent assay while expressions of GABA_BR and PKA‐CREB pathway‐related molecules by Western blot. Compared with control rats, the model rats exhibited reduced alternation rates with a prolonged time spent in the central zone; meanwhile, levels of tumor necrosis factor‐α and interleukin‐1β and the apoptotic index, as well as GABA_BR1 and GABA_BR2 expressions were increased in the model rats, but the cAMP‐PKA‐CREB pathway was inhibited (all P < 0.05). When treated with either Dex or CGP 35348, the surgical rats displayed an opposite tendency concerning the above factors as compared to the model rats (all P < 0.05). Furthermore, Baclofen, the agonist of GABA_BR, could reverse the protective effect of Dex against POCD in rats. Dex protects rats from POCD possibly via suppressing GABA_BR to up‐regulate the cAMP‐PKA‐CREB signaling pathway, thereby alleviating the hippocampal inflammation caused by surgical trauma.     

Resveratrol prevents CA1 neurons against ischemic injury by parallel modulation of both GSK‐3β and CREB through PI3‐K/Akt pathways

Accumulating evidence indicates that resveratrol potently protects against cerebral ischemia damage due to its oxygen free radicals scavenging and antioxidant properties. However, cellular mechanisms that may underlie the neuroprotective effects of resveratrol in brain ischemia are not fully understood yet. This study aimed to investigate the potential association between the neuroprotective effect of resveratrol and the apoptosis/survival signaling pathways, in particular the glycogen synthase kinase 3 (GSK‐3β) and cAMP response element‐binding protein (CREB) through phosphatidylinositol 3‐kinase (PI3‐K)‐dependent pathway. An experimental model of global cerebral ischemia was induced in rats by the four‐vessel occlusion method for 10 min and followed by different periods of reperfusion. Nissl staining indicated extensive neuronal death at 7 days after ischemia/reperfusion. Administration of resveratrol by i.p. injections (30 mg/kg) for 7 days before ischemia significantly attenuated neuronal death. Both GSK‐3β and CREB appear to play a critical role in resveratrol neuroprotection through the PI3‐K/Akt pathway, as resveratrol pretreatment increased the phosphorylation of Akt, GSK‐3β and CREB in 1 h in the CA1 hippocampus after ischemia/reperfusion. Furthermore, administration of LY294002, an inhibitor of PI3‐K, compromised the neuroprotective effect of resveratrol and decreased the level of p‐Akt, p‐GSK‐3β and p‐CREB after ischemic injury. Taken together, the results suggest that resveratrol protects against delayed neuronal death in the hippocampal CA1 by maintaining the pro‐survival states of Akt, GSK‐3β and CREB pathways. These data suggest that the neuroprotective effect of resveratrol may be mediated through activation of the PI3‐K/Akt signaling pathway, subsequently downregulating expression of GSK‐3β and CREB, thereby leading to prevention of neuronal death after brain ischemia in rats.     

Regulated expression of VP16CREB in neuroblastoma cells: analysis of differentiation and apoptosis

Highly malignant neuroblastoma tumors generally have defects in differentiation and apoptotic pathways. For a better understanding of these events, we use a murine neuroblastoma cell line (NBP2) that terminally differentiates into mature neurons in response to elevated levels of cAMP. Because one of the main downstream effectors of the cAMP signaling pathway is cAMP-response element binding (CREB), we reasoned that it might affect the expression of genes associated with differentiation and apoptotic events in NBP2 cells. To investigate this, we established tetracycline-regulated expression (TetOff) of VP16CREB, which constitutively transactivates promoters containing the CRE sequence motif. Using this system, we found that inducible expression of VP16CREB in NBP2 cells results in 1) morphological differentiation that is characterized by the formation of neurites and growth cones, 2) reversible cell differentiation unlike cAMP-induced terminal differentiation, 3) cell cycle arrest at G1, 4) no apoptosis in the presence of partial inhibition of proteasome unlike an increase in cAMP levels, and 5) changes in the expression of many genes, including down-regulation of N-myc, cyclin B1, Dickkopf-1, and Mad-2 and up-regulation of tyrosine hydroxylase, c-fos, N10, and ICER genes. Although VP16CREB expression and activation of the cAMP pathway impart many similar effects in NBP2 cells, they also bear some distinct genetic and morphological differences. Our data suggest that increased levels of cAMP function through not only CREB but also other signaling pathways that account for the additional cAMP-induced effects, including irreversible differentiation and onset of apoptosis during partial inhibition of proteasome in NBP2 cells.     

Nonredundant function of two highly homologous octopamine receptors in food‐deprivation‐mediated signaling in Caenorhabditis elegans

It is common for neurotransmitters to possess multiple receptors that couple to the same intracellular signaling molecules. This study analyzes two highly homologous G‐protein‐coupled octopamine receptors using the model animal Caenorhabditis elegans. In C. elegans, the amine neurotransmitter octopamine induces activation of cAMP response element‐binding protein (CREB) in the cholinergic SIA neurons in the absence of food through activation of the Gq‐coupled octopamine receptor SER‐3 in these neurons. We also analyzed another Gq‐coupled octopamine receptor, SER‐6, that is highly homologous to SER‐3. As seen in ser‐3 deletion mutants, octopamine‐ and food‐deprivation‐mediated CREB activation was decreased in ser‐6 deletion mutants compared with wild‐type animals, suggesting that both SER‐3 and SER‐6 are required for signal transduction. Cell‐specific expression of SER‐6 in the SIA neurons was sufficient to restore CREB activation in the ser‐6 mutants, indicating that SER‐6, like SER‐3, functions in these neurons. Taken together, these results demonstrate that two similar G‐protein‐coupled receptors, SER‐3 and SER‐6, function in the same cells in a nonredundant manner. © 2014 Wiley Periodicals, Inc.     

Corticotropin‐releasing factor‐2 activation prevents gentamicin‐induced oxidative stress in cells derived from the inner ear

Generation of reactive oxygen species (ROS) is a common denominator in many conditions leading to cell death in the cochlea, yet little is known of the cochlea's endogenous mechanisms involved in preventing oxidative stress and its consequences in the cochlea. We have recently described a corticotropin‐releasing factor (CRF) signaling system in the inner ear involved in susceptibility to noise‐induced hearing loss. We use biochemical and proteomics assays to define further the role of CRF signaling in the response of cochlear cells to aminoglycoside exposure. We demonstrate that activity via the CRF₂ class of receptors protects against aminoglycoside‐induced ROS production and activation of cell death pathways. This study suggests for the first time a role for CRF signaling in protecting the cochlea against oxidative stress, and our proteomics data suggest novel mechanisms beyond induction of free radical scavengers that are involved in its protective mechanisms. © 2010 Wiley‐Liss, Inc.     

Mitogen‐ and stress‐activated protein kinase 1 modulates photic entrainment of the suprachiasmatic circadian clock

The master circadian clock in mammals, the suprachiasmatic nucleus (SCN), is under the entraining influence of the external light cycle. At a mechanistic level, intracellular signaling via the p42/44 mitogen‐activated protein kinase pathway appears to play a central role in light‐evoked clock entrainment; however, the precise downstream mechanisms by which this pathway influences clock timing are not known. Within this context, we have previously reported that light stimulates activation of the mitogen‐activated protein kinase effector mitogen‐stress‐activated kinase 1 (MSK1) in the SCN. In this study, we utilised MSK1^?/? mice to further investigate the potential role of MSK1 in circadian clock timing and entrainment. Locomotor activity analysis revealed that MSK1 null mice entrained to a 12 h light/dark cycle and exhibited circadian free‐running rhythms in constant darkness. Interestingly, the free‐running period in MSK1 null mice was significantly longer than in wild‐type control animals, and MSK1 null mice exhibited a significantly greater variance in activity onset. Further, MSK1 null mice exhibited a significant reduction in the phase‐delaying response to an early night light pulse (100 lux, 15 min), and, using an 8 h phase‐advancing ‘jet‐lag’ experimental paradigm, MSK1 knockout animals exhibited a significantly delayed rate of re‐entrainment. At the molecular level, early night light‐evoked cAMP response element‐binding protein (CREB) phosphorylation, histone phosphorylation and Period1 gene expression were markedly attenuated in MSK1^?/? animals relative to wild‐type mice. Together, these data provide key new insights into the molecular mechanisms by which MSK1 affects the SCN clock.     

CREB‐BDNF pathway influences alcohol cue‐elicited activation in drinkers

Alcohol use disorder (AUD) is suggested to have polygenic risk factors and also exhibits neurological complications, strongly encouraging a translational study to explore the associations between aggregates of genetic variants and brain function alterations related to alcohol use. In this study, we used a semiblind multivariate approach, parallel independent component analysis with multiple references (pICA‐MR) to investigate relationships of genome‐wide single nucleotide polymorphisms with alcohol cue‐elicited brain activations in 315 heavy drinkers, where pICA‐MR assesses multiple reference genes for their architecture and functional influences on neurobiological conditions. The genetic component derived from the cAMP‐response element‐binding protein and ‐brain derived neurotrophic factor (CREB‐BDNF) pathway reference was significantly associated (r = ?0.38, P = 3.98 × 10^?12) with an imaging component reflecting hyperactivation in precuneus, superior parietal lobule, and posterior cingulate for drinkers with more severe alcohol dependence symptoms. The highlighted brain regions participate in many cognitive processes and have been robustly implicated in craving‐related studies. The genetic factor highlighted the CREB and BDNF references, as well as other genes including GRM5, GRM7, GRID1, GRIN2A, PRKCA, and PRKCB. Ingenuity Pathway Analysis indicated that the genetic component was enriched in synaptic plasticity, GABA, and protein kinase A signaling. Collectively, our findings suggest that genetic variations in various neural plasticity and signaling pathways partially explain the variance of precuneus reactivity to alcohol cues which appears to be associated with AUD severity. Hum Brain Mapp 36:3007–3019, 2015. © 2015 Wiley Periodicals, Inc .     

Aerobic exercise reduces hippocampal ERK and p38 activation and improves memory of middle‐aged rats

Aging is often accompanied by cognitive decline, memory impairment, and an increased susceptibility to neurodegenerative disorders. Although the physiological processes of aging are not fully understood, these age‐related changes have been interpreted by means of various cellular and molecular theories. Among these theories, alterations in the intracellular signaling pathways associated with cell growth, proliferation, and survival have been highlighted. Based on these observations and on recent evidence showing the beneficial effects of exercise on cognitive function in the elderly, we investigated the cell signaling pathways in the hippocampal formation of middle‐aged rats (18 months old) submitted to treadmill exercise over 10 days. To do this, we evaluated the hippocampal activation of intracellular signaling proteins linked to cell growth, proliferation, and survival, such as Akt, mTOR, p70S6K, ERK, CREB, and p38. We also explored the cognitive performance (inhibitory avoidance) of middle‐aged rats. It was found that physical exercise reduces ERK and p38 activation in the hippocampal formation of aged rats, when compared to the control group. The hippocampal activation and expression of Akt, mTOR, p70S6K, and CREB were not statistically different between the groups. It was also observed that aged rats from the exercise group exhibited better cognitive performance in the inhibitory avoidance task (aversive memory) than aged rats from the control group. Our results indicate that physical exercise reduces intracellular signaling pathways linked to inflammation and cell death (i.e., ERK and p38) and improves memory in middle‐aged rats.     

NMDA receptor–dependent signaling pathways that underlie amyloid β‐protein disruption of LTP in the hippocampus

Alzheimer's disease (AD), the most common neurodegenerative disease in the elderly population, is characterized by the hippocampal deposition of fibrils formed by amyloid β‐protein (Aβ), a 40‐ to 42‐amino‐acid peptide. The folding of Aβ into neurotoxic oligomeric, protofibrillar, and fibrillar assemblies is believed to mediate the key pathologic event in AD. The hippocampus is especially susceptible in AD and early degenerative symptoms include significant deficits in the performance of hippocampal‐dependent cognitive abilities such as spatial learning and memory. Transgenic mouse models of AD that express C‐terminal segments or mutant variants of amyloid precursor protein, the protein from which Aβ is derived, exhibit age‐dependent spatial memory impairment and attenuated long‐term potentiation (LTP) in the hippocampal CA1 and dentate gyrus (DG) regions. Recent experimental evidence suggests that Aβ disturbs N‐methyl‐D ‐aspartic acid (NMDA) receptor–dependent LTP induction in the CA1 and DG both in vivo and in vitro. Furthermore, these studies suggest that Aβ specifically interferes with several major signaling pathways downstream of the NMDA receptor, including the Ca²⁺‐dependent protein phosphatase calcineurin, Ca²⁺/calmodulin‐dependent protein kinase II (CaMKII), protein phosphatase 1, and cAMP response element–binding protein (CREB). The influence of Aβ on each of these downstream effectors of the NMDA receptor is reviewed in this article. Additionally, other mechanisms of LTP modulation, such as Aβ attenuation of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor currents, are briefly discussed. © 2009 Wiley‐Liss, Inc.     

Post‐cocaine changes in regulator of G‐protein signaling (RGS) proteins in the dorsal striatum: Relevance for cocaine‐seeking and protein kinase C‐mediated phosphorylation

Persistent cocaine‐induced neuroadaptations within the cortico‐striatal circuitry might be related to elevated risk of relapse observed in human addicts even after months or years of drug‐free abstinence. Identification of these neuroadaptations may lead development of novel, neurobiologically‐based treatments of relapse. In the current study, 12 adult male Sprague‐Dawley rats self‐administered cocaine (or received yoked‐saline) for two weeks followed by three weeks of home‐cage abstinence. At this point, we analyzed expression of proteins involved in regulation of Gαi‐ and Gαq‐protein signaling in the dorsal striatum (dSTR). Animals abstinent from chronic cocaine showed decreased expression of regulator of G‐protein signaling 2 (RGS2) and RGS4, as well as upregulation of RGS9. These data, together with the increased ratio of Gαq‐to‐Gαi proteins indicated, “sensitized” Gαq signaling in the dSTR of abstinent cocaine animals. To evaluate activation of Gαq signaling during relapse, another group of abstinent cocaine animals (and yoked saline controls, 22 rats together) was reintroduced to the cocaine context and PKC‐mediated phosphorylation in the dSTR was analyzed. Re‐exposure to the cocaine context triggered cocaine seeking and increase in phosphorylation of cellular PKC substrates, including phospho‐ERK and phospho‐CREB. In conclusion, this study demonstrates persistent dysregulation of RGS proteins in the dSTR of abstinent cocaine animals that may produce an imbalance in local Gαq‐to‐Gαi signaling. This imbalance might be related to augmented PKC‐mediated phosphorylation during relapse to cocaine‐seeking. Future studies will address whether selective targeting of RGS proteins in the dSTR can be utilized to suppress PKC‐mediated phosphorylation and relapse to cocaine‐seeking.