PKA-CREB Signaling Suppresses Tau Transcription

Recent advances on the molecular mechanisms of exercise-induced improvements of cognitive dysfunction

Physical exercise is of great significance for maintaining human health. Exercise can provide varying degrees of benefits to cognitive function at all stages of life cycle. Currently, with the aging of the world's population and increase of life expectancy, cognitive dysfunction has gradually become a disease of high incidence, which is accompanied by neurodegenerative diseases in elderly individuals. Patients often exhibit memory loss, aphasia and weakening of orientation once diagnosed, and are unable to have a normal life. Cognitive dysfunction largely affects the physical and mental health, reduces the quality of life, and causes a great economic burden to the society. At present, most of the interventions are aimed to maintain the current cognitive level and delay deterioration of cognition. In contrast, exercise as a nonpharmacological therapy has great advantages in its nontoxicity, low cost and universal application. The molecular mechanisms underlying the effect of exercise on cognition are complex, and studies have been extensively centered on neural plasticity, the direct target of exercise in the brain. In addition, mitochondrial stability and energy metabolism are essential for brain status. Meanwhile, the organ-brain axis responds to exercise and induces release of cytokines related to cognition. In this review, we summarize the latest evidence on the molecular mechanisms underlying the effects of exercise on cognition, and point out directions for future research.

Neuroprotective Action of Coumarin Derivatives through Activation of TRKB-CREB-BDNF Pathway and Reduction of Caspase Activity in Neuronal Cells Expressing Pro-Aggregated Tau Protein

Hyperphosphorylation and aggregation of the microtubule binding protein tau is a neuropathological hallmark of Alzheimer’s disease/tauopathies. Tau neurotoxicity provokes alterations in brain-derived neurotrophic factor (BDNF)/tropomycin receptor kinase B (TRKB)/cAMP-response-element binding protein (CREB) signaling to contribute to neurodegeneration. Compounds activating TRKB may therefore provide beneficial effects in tauopathies. LM-031, a coumarin derivative, has demonstrated the potential to improve BDNF signaling in neuronal cells expressing pro-aggregated ΔK280 tau mutant. In this study, we investigated if LM-031 analogous compounds provide neuroprotection effects through interaction with TRKB in SH-SY5Y cells expressing ΔK280 tau_RD-DsRed folding reporter. All four LMDS compounds reduced tau aggregation and reactive oxygen species. Among them, LMDS-1 and -2 reduced caspase-1, caspase-6 and caspase-3 activities and promoted neurite outgrowth, and the effect was significantly reversed by knockdown of TRKB. Treatment of ERK inhibitor U0126 or PI3K inhibitor wortmannin decreased p-CREB, BDNF and BCL2 in these cells, implying that the neuroprotective effects of LMDS-1/2 are via activating TRKB downstream ERK, PI3K-AKT and CREB signaling. Furthermore, LMDS-1/2 demonstrated their ability to quench the intrinsic fluorescence of tryptophan residues within the extracellular domain of TRKB, thereby consolidating their interaction with TRKB. Our results suggest that LMDS-1/2 exert neuroprotection through activating TRKB signaling, and shed light on their potential application in therapeutics of Alzheimer’s disease/tauopathies.

Repeated exposure to sevoflurane in neonatal rats impairs cognition in adulthood via the PKA-CREB-BDNF signaling pathway

Sevoflurane (Sev) anesthesia is widely used in pediatrics due to its low blood-gas partition coefficient and lack of pungency. However, Sev treatment may lead to cognitive dysfunction in later life. The current study administered Sev to neonatal rats to investigate the effects of Sev treatment on cognitive performance in adulthood. In total, 6-day-old rats received 3% Sev for 2 h daily for 3 consecutive days. The cognitive function of rats in adulthood was evaluated in 56-day-old rats by Morris water maze test. The hippocampal neuron morphology was observed by Nissl staining. Hippocampal brain-derived neurotrophic factor (BDNF) levels were measured by ELISA. The protein expression of protein kinase A (PKA), cAMP response element binding protein (CREB), phosphorylated-CREB (p-CREB) and BDNF in hippocampus were assessed by western blotting. The water maze results demonstrated that neonatal treatment with Sev resulted in a significant impairment of cognition in 56-day-old adult rats. Behavioral analysis revealed that Sev treatment increased latency to first pass the platform and decreased residence in target quadrants and across platform frequency compared with the control group in Morris water maze tests. Furthermore, compared with the control group, neonatal exposure to Sev reduced the number of neurons and the concentration of BDNF in the hippocampus, a brain region important for learning and memory. Additionally, Sev significantly decreased the expression of PKA, p-CREB, BDNF and the p-CREB/CREB ratio. Treatment with bucladesine, a selective PKA agonist, partially reversed the deleterious effects of Sev. In summary, the results indicated that PKA-CREB-BDNF signaling served an important role in the cognitive decline caused by neonatal exposure to Sev.

Magnolol upregulates CHRM1 to attenuate Amyloid-β-triggered neuronal injury through regulating the cAMP/PKA/CREB pathway

Alzheimer's disease (AD) is a common neurodegenerative disease characterized by neuronal degeneration and hyperphosphorylated Tau. Magnolol is an active component isolated from Magnolia officinalis with potential neuroprotection activity. However, the function and mechanism of magnolol in AD progression is largely uncertain. In present study, the biomarkers related to AD and magnolol were predicted by bioinformatics analyses. The key biomarker levels were predicted by GSE5281 and GSE36980 using AlzData. Cell viability was detected by CCK-8 assay. mRNA and protein levels were examined by qRT-PCR and western blotting assays. Cell apoptosis was investigated by caspase-3 activity and flow cytometry analyses. The cAMP/PKA/CREB signaling was evaluated by ELISA and western blotting analyses. The results showed that CHRM1 was a key biomarker for magnolol against AD progression. Magnolol attenuated Aβ-induced viability inhibition, Tau hyperphosphorylation and apoptosis in SH-SY5Y cells by upregulating CHRM1. In addition, the cAMP signaling might be a potential pathway of CHRM1 in AD. Magnolol contributed to activation of the cAMP/PKA/CREB pathway through enhancing CHRM1 level. Inactivation of the cAMP/PKA/CREB signaling reversed the suppressive effect of magnolol on Tau hyperphosphorylation and apoptosis in Aβ-treated SH-SY5Y cells. As a conclusion, magnolol mitigated Aβ-induced Tau hyperphosphorylation and neuron apoptosis by upregulating CHRM1 and activating the cAMP/PKA/CREB pathway.

SIRT1 Regulates Tau Expression and Tau Synaptic Pathology

BACKGROUND

Amyloid plaques and neurofibrillary tangles are two pathological hallmarks of Alzheimer's disease (AD). However, synaptic deficits occur much earlier and correlate stronger with cognitive decline than amyloid plaques and neurofibrillary tangles. Mislocalization of tau is an early hallmark of neurodegeneration and precedes aggregations. Sirtuin type 1 (SIRT1) is a deacetylase which acts on proteins including transcriptional factors and associates closely with AD.

OBJECTIVE

The present study investigated the association between SIRT1 and tau expression/tau localization in cells and in mice brains.

METHODS

Western blot was performed to detected tau, SIRT1, C/EBPα, and GAPDH protein levels. Immunological fluorescence assay was used to assess tau localization in primary cortical neuronal cells. Golgi staining was performed to evaluated dendritic spine morphology in mice brains.

RESULTS

In the present study, we found that SIRT1 negatively regulates expression of tau at the transcriptional level through transcriptional factor C/EBPα. Inhibition of the activity of SIRT1 limits the distribution of tau to the neurites. In the meantime, the alteration of dendritic spine morphology is also observed in the brains of SIRT1+/- mice.

CONCLUSION

SIRT1 may be a potential drug target for early intervention in AD.

Involvement of 5-HT-BDNF signaling axis in mediating synergistic antidepressant-like effects after combined administration of two oligosaccharide esters

Potential mechanisms of depression involving herbal medicines and their specific compounds include elevated 5-HT level and downstream BDNF pathway. To identify potentially new combined therapeutic strategies, 3,6'-disinapoylsucrose (DISS) and tenuifoliside A (TFSA) have been observed to show antidepressant-like effects and its related 5-HT-BDNF pathway. We have tried to investigate whether combined administration of DISS and TFSA exerted more effective in the treatment of depression, as assessed through tail suspension test (TST) and forced swimming test (FST). In addition, we also analyzed the expression of three important proteins, cyclic adenosine monophosphate (cAMP) response element binding (CREB), brain-derived neurotrophic factor (BDNF), and cAMP-regulated transcriptional coactivators (CRTC1), which have been shown to be involved in the regulation of the neurotrophic factors in the hippocampus. The DISS and TFSA separately, both at a dose of 5 mg/kg each, displayed small effect in the immobility time. However, combined treatment of these two in multiple doses exhibited better effect. Moreover, combined treatment of DISS and TFSA also demonstrated enhanced levels of 5-hydroxytryptamine (5-HT), and stronger increase in the phosphorylation levels of CREB, BDNF, and CRTC1 proteins in the hippocampus. Overall, our results indicated that coadministration of these two oligosaccharide esters at low dose may induce more pronounced antidepressant activity, in comparison with individual treatment even at high dosage. Thus, the antidepressant properties of both these compounds can be attributed to their ability to influence 5-HT and BDNF pathway, and thereby suggesting that this combination strategy can definitely act as alternative therapy for depression disorder with very limited side effects.

SHP2 mutations induce precocious gliogenesis of Noonan syndrome-derived iPSCs during neural development in vitro

Background

Noonan syndrome (NS) is a developmental disorder caused by mutations of Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2). Although NS patients have diverse neurological manifestations, the mechanisms underlying the involvement of SHP2 mutations in neurological dysfunction remain elusive.

Methods

Induced pluripotent stem cells generated from dermal fibroblasts of three NS-patients (NS-iPSCs) differentiated to the neural cells by using two different culture systems, 2D- and 3D-cultured systems in vitro.

Results

Here we represent that SHP2 mutations cause aberrant neural development. The NS-iPSCs exhibited impaired development of EBs in which BMP and TGF-β signalings were activated. Defective early neuroectodermal development of NS-iPSCs recovered by inhibition of both signalings and further differentiated into NPCs. Intriguingly, neural cells developed from NS-NPCs exhibited abundancy of the glial cells, neurites of neuronal cells, and low electrophysiological property. Those aberrant phenotypes were also detected in NS-cerebral organoids. SHP2 inhibition in the NS-NPCs and NS-cerebral organoids ameliorated those anomalies such as biased glial differentiation and low neural activity.

Conclusion

Our findings demonstrate that SHP2 mutations contribute to precocious gliogenesis in NS-iPSCs during neural development in vitro.

SIRT1 regulates O-GlcNAcylation of tau through OGT

Tau is modified with O-GlcNAcylation extensively in human brain. The O-GlcNAcylation levels of tau are decreased in Alzheimer's disease (AD) brain. Sirtuin type 1 (SIRT1) is an enzyme that deacetylates proteins including transcriptional factors and associates with neurodegenerative diseases, such as AD. Aberrant SIRT1 expression levels in AD brain is in parallel with the accumulation of tau. cAMP response element binding protein (CREB), a cellular transcription factor, plays a critical role in learning and memory. In this present study, we found SIRT1 deacetylates CREB and inhibits phosphorylation of CREB at Ser133. The inactivated CREB suppresses OGT expression and therefore decreases the O-GlcNAcylation of tau and thus increases the phosphorylation of tau at specific sites. These findings suggest that SIRT1 may be a potential therapeutic target for treating tauopathies.

MicroRNA-200a-3p Is a Positive Regulator in Cardiac Hypertrophy Through Directly Targeting WDR1 as Well as Modulating PTEN/PI3K/AKT/CREB/WDR1 Signaling

Cardiac hypertrophy is an adaptive expansion of the myocardium due to the overloaded stress of heart. Recently, emerging studies have drawn a conclusion that microRNAs (miRNAs) are involved in myocardial hypertrophy and even heart failure. To figure out the role of microRNA-200a-3p (miR-200a-3p) in cardiac hypertrophy, the in vitro cardiac hypertrophy model was established in H9c2 cells using angiotensin II (Ang-II) as previously described. First of all, we observed a significant increase of miR-200a-3p expression in Ang-II-induced hypertrophic H9c2 cells. Moreover, inhibition of miR-200a-3p dramatically reversed the Ang-II-upregulated expression of hypertrophic markers (atrial natriuretic peptide, brain natriuretic peptide, and β-MHC) and the expanded cell surface area in H9c2 cells. In addition, our results indicated that miR-200a-3p directly targeted both WDR1 and phosphatase and tensin homolog (PTEN). In this regard, miR-200a-3p further activated PI3K/AKT/CREB pathway so as to intensify its negative regulation on WDR1. At length, WDR1 silence, PTEN inhibitor, and PI3K activator recovered the repressive effect of miR-200a-3p suppression on the development of cardiac hypertrophy. Jointly, our study suggested that miR-200a-3p facilitated cardiac hypertrophy by not only directly targeting WDR1 but also through modulating PTEN/PI3K/AKT/CREB/WDR1 signaling, therefore proving novel downstream molecular pathway of miR-200a-3p in cardiac hypertrophy.

Effects of progesterone on glucose uptake in neurons of Alzheimer's disease animals and cell models

AIMS

Alzheimer's disease (AD) is closely related to abnormal glucose metabolism in the central nervous system. Progesterone has been shown to have obvious neuroprotective effects in the pathogenesis of AD, but the specific mechanism has not been fully elucidated. Therefore, the purpose of this study was to investigate the effect of progesterone on the glucose metabolism of neurons in amyloid precursor protein (APP)/presenilin 1 (PS1) mice and Aβ-induced AD cell model.

MATERIALS AND METHODS

APP/PS1 mice were treated with 40 mg/kg progesterone for 40 days and primary cultured cortical neurons were treated with 1 μM progesterone for 48 h.Then behavior tests,2-NBDG glucose uptake tests and the protein levels of glucose transporter 3 (GLUT3), GLUT4, cAMP-response element binding protein (CREB) and proliferator-activated receptor γ (PPARγ) were examined.

KEY FINDINGS

Progesterone increased the expression levels of GLUT3 and GLUT4 in the cortex of APP/PS1 mice, accompanied by an improvement in learning and memory. Progesterone increased the levels of CREB and PPARγ in the cerebral cortex of APP/PS1 mice. In vitro, progesterone increased glucose uptake in primary cultured cortical neurons, this effect was blocked by the progesterone receptor membrane component 1 (PGRMC1)-specific blocker AG205 but not by the progesterone receptor (PR)-specific blocker RU486. Meanwhile, progesterone increased the expression of GLUT3, GLUT4, CREB and PPARγ, and AG205 blocked this effect.

SIGNIFICANCE

These results confirm that progesterone significantly improves the glucose metabolism of neurons.One of the mechanisms of this effect is that progesterone upregulates protein expression of GLUT3 and GLUT4 through pathways PGRMC1/CREB/GLUT3 and PGRMC1/PPARγ/GLUT4.

Synaptic and memory dysfunction induced by tau oligomers is rescued by up-regulation of the nitric oxide cascade

BACKGROUND

Soluble aggregates of oligomeric forms of tau protein (oTau) have been associated with impairment of synaptic plasticity and memory in Alzheimer's disease. However, the molecular mechanisms underlying the synaptic and memory dysfunction induced by elevation of oTau are still unknown.

METHODS

This work used a combination of biochemical, electrophysiological and behavioral techniques. Biochemical methods included analysis of phosphorylation of the cAMP-responsive element binding (CREB) protein, a transcriptional factor involved in memory, histone acetylation, and expression immediate early genes c-Fos and Arc. Electrophysiological methods included assessment of long-term potentiation (LTP), a type of synaptic plasticity thought to underlie memory formation. Behavioral studies investigated both short-term spatial memory and associative memory. These phenomena were examined following oTau elevation.

RESULTS

Levels of phospho-CREB, histone 3 acetylation at lysine 27, and immediate early genes c-Fos and Arc, were found to be reduced after oTau elevation during memory formation. These findings led us to explore whether up-regulation of various components of the nitric oxide (NO) signaling pathway impinging onto CREB is capable of rescuing oTau-induced impairment of plasticity, memory, and CREB phosphorylation. The increase of NO levels protected against oTau-induced impairment of LTP through activation of soluble guanylyl cyclase. Similarly, the elevation of cGMP levels and stimulation of the cGMP-dependent protein kinases (PKG) re-established normal LTP after exposure to oTau. Pharmacological inhibition of cGMP degradation through inhibition of phosphodiesterase 5 (PDE5), rescued oTau-induced LTP reduction. These findings could be extrapolated to memory because PKG activation and PDE5 inhibition rescued oTau-induced memory impairment. Finally, PDE5 inhibition re-established normal elevation of CREB phosphorylation and cGMP levels after memory induction in the presence of oTau.

CONCLUSIONS

Up-regulation of CREB activation through agents acting on the NO cascade might be beneficial against tau-induced synaptic and memory dysfunctions.

Role of cellular prion protein in interneuronal amyloid transmission

Several studies have indicated that certain misfolded amyloids composed of tau, β-amyloid or α-synuclein can be transferred from cell to cell, suggesting the contribution of mechanisms reminiscent of those by which infective prions spread through the brain. This process of a 'prion-like' spreading between cells is also relevant as a novel putative therapeutic target that could block the spreading of proteinaceous aggregates throughout the brain which may underlie the progressive nature of neurodegenerative diseases. The relevance of β-amyloid oligomers and cellular prion protein (PrP^C) binding has been a focus of interest in Alzheimer's disease (AD). At the molecular level, β-amyloid/PrP^C interaction takes place in two differently charged clusters of PrP^C. In addition to β-amyloid, participation of PrP^C in α-synuclein binding and brain spreading also appears to be relevant in α-synucleopathies. This review summarizes current knowledge about PrP^C as a putative receptor for amyloid proteins and the physiological consequences of these interactions.

Perturbed Calcineurin-NFAT Signaling Is Associated with the Development of Alzheimer's Disease

Down syndrome (DS), the most common genetic disorder, is caused by trisomy 21. DS is accompanied by heart defects, hearing and vision problems, obesity, leukemia, and other conditions, including Alzheimer's disease (AD). In comparison, most cancers are rare in people with DS. Overexpression of dual specificity tyrosine-phosphorylation-regulated kinase 1A and a regulator of calcineurin 1 located on chromosome 21 leads to excessive suppression of the calcineurin-nuclear factor of activated T cells (NFAT) signaling pathway, resulting in reduced expression of a critical angiogenic factor. However, it is unclear whether the calcineurin-NFAT signaling pathway is involved in AD pathology in DS patients. Here, we investigated the association between the calcineurin-NFAT signaling pathway and AD using neuronal cells. Short-term pharmacological stimulation decreased gene expression of tau and neprilysin, and long-term inhibition of the signaling pathway decreased that of amyloid precursor protein. Moreover, a calcineurin inhibitor, cyclosporine A, also decreased neprilysin activity, leading to increases in amyloid-β peptide levels. Taken together, our results suggest that a dysregulation in calcineurin-NFAT signaling may contribute to the early onset of AD in people with DS.

Diminished CRE-Induced Plasticity is Linked to Memory Deficits in Familial Alzheimer's Disease Mice

The mechanism underlying impaired learning and memory in Alzheimer's disease is not fully elucidated. The phosphorylation of cyclic-AMP response element binding protein (pCREB) in the hippocampus is thought to be a critical initiating step in the formation of long-term memories. Here, we tested CRE-driven gene expression following learning in mice harboring the familial Alzheimer's disease-linked APPswe/PS1ΔE9 mutations using CRE-β galactosidase reporter. We show that young adult APPswe/PS1ΔE9 mice exhibit impaired recognition memory and reduced levels of pCREB, and its cofactors CREB binding protein (CBP) and p-300 following a learning task, compared to their wild type littermate counterparts. Impairments in learning-induced activation of CREB in these mice are manifested by reduced CRE-driven gene transcription. Importantly, expression of the CRE-driven immediate early gene, Egr-1 (Zif268) is decreased in the CA1 region of the hippocampus. These studies implicate defective CREB-dependent plasticity in the mechanism underlying learning and memory deficits in Alzheimer's disease.

Extrasynaptic NMDA receptor-induced tau overexpression mediates neuronal death through suppressing survival signaling ERK phosphorylation

Intracellular accumulation of the hyperphosphorylated tau is a pathological hallmark in the brain of Alzheimer disease. Activation of extrasynaptic NMDA receptors (E-NMDARs) induces excitatory toxicity that is involved in Alzheimer's neurodegeneration. However, the intrinsic link between E-NMDARs and the tau-induced neuronal damage remains elusive. In the present study, we showed in cultured primary cortical neurons that activation of E-NMDA receptors but not synaptic NMDA receptors dramatically increased tau mRNA and protein levels, with a simultaneous neuronal degeneration and decreased neuronal survival. Memantine, a selective antagonist of E-NMDARs, reversed E-NMDARs-induced tau overexpression. Activation of E-NMDARs in wild-type mouse brains resulted in neuron loss in hippocampus, whereas tau deletion in neuronal cultures and in the mouse brains rescued the E-NMDARs-induced neuronal death and degeneration. The E-NMDARs-induced tau overexpression was correlated with a reduced ERK phosphorylation, whereas the increased MEK activity, decreased binding and activity of ERK phosphatase to ERK, and increased ERK phosphorylation were observed in tau knockout mice. On the contrary, addition of tau proteins promoted ERK dephosphorylation in vitro. Taking together, these results indicate that tau overexpression mediates the excitatory toxicity induced by E-NMDAR activation through inhibiting ERK phosphorylation.

Reduced pCREB in Alzheimer's disease prefrontal cortex is reflected in peripheral blood mononuclear cells

Cyclic-AMP response element-binding protein (CREB) signaling has a critical role in the formation of memories. CREB signaling is dysfunctional in the brains of mouse models of Alzheimer's disease (AD), and evidence suggests that CREB signaling may be disrupted in human AD brains as well. Here, we show that both CREB and its activated form pCREB-Ser(133) (pCREB) are reduced in the prefrontal cortex of AD patients. Similarly, the transcription cofactors CREB-binding protein (CBP) and p300 are reduced in the prefrontal cortex of AD patients, indicating additional dysfunction of CREB signaling in AD. Importantly, we show that pCREB expression is reduced in peripheral blood mononuclear cells (PBMC) of AD subjects. In addition, pCREB levels in PBMC positively correlated with pCREB expression in the postmortem brain of persons with AD. These results suggest that pCREB expression in PBMC may be indicative of its expression in the brain, and thus offers the intriguing possibility of pCREB as a biomarker of cognitive function and disease progression in AD.