Signaling pathways in the treatment of Alzheimer's disease with acupuncture: a narrative review

BACKGROUND

To date, there is no effective treatment for Alzheimer's disease (AD), a progressive neurodegenerative disorder that is increasing in prevalence worldwide. The objective of this review was to summarize the core targets and signaling pathways involved in acupuncture treatment for AD.

METHODS

We reviewed numerous signaling pathways, including mammalian target of rapamycin (mTOR), phosphatidylinositol 3-kinase-protein kinase B (PI3 K/Akt), adenosine monophosphate-activated protein kinase (AMPK), mitogen-activated protein kinase (MAPK), nuclear factor (NF)-kB, p53, Wnt, nitric oxide (NO), Janus kinase / signal transducer and activator of transcription (JAK/ STAT), RhoA/ROCK (Rho-associated protein kinase) and Ca2+/ calmodulin-dependent protein kinase II (CaMKII) / cyclic adenosine monophosphate-response element-binding protein (CREB). The relevant data were obtained from PubMed, EMBASE, Web of Science, China National Knowledge Infrastructure (CNKI) and Wanfang databases.

RESULTS

In summary, the effects of acupuncture are mediated by multiple targets and pathways. Furthermore, acupuncture can improve pathological changes associated with AD (such as abnormal deposition of amyloid (A)β, tau hyperphosphorylation, synaptic dysfunction and neuronal apoptosis) through multiple signaling pathways.

CONCLUSION

Overall, our findings provide a basis for future research into the effects of acupuncture on AD.

A low-fouling electrochemical biosensor based on BSA hydrogel doped with carbon black for the detection of cortisol in human serum

Electrochemical biosensors with high sensitivity can detect low concentrations of biomarkers, but their practical detection applications in complex biological environments such as human serum and sweat are severely limited by the biofouling. Herein, a conductive hydrogel based on bovine serum albumin (BSA) and conductive carbon black (CCB) was prepared for the construction of an antifouling biosensor. The BSA hydrogel (BSAG) was doped with CCB, and the prepared composite hydrogel exhibited good conductivity originated from the CCB and antifouling capability owing to the BSA hydrogel. An antifouling biosensor for the sensitive detection of cortisol was fabricated by drop-coating the conductive hydrogel onto a poly(3,4-ethylenedioxythiophene) (PEDOT) modified electrode and further immobilizing the cortisol aptamer. The constructed biosensor showed a linear range of 100 pg mL-1 - 10 μg mL-1 and a limit of detection of 26.0 pg mL-1 for the detection of cortisol, and it was capable of assaying cortisol accurately in complex human serum. This strategy of preparing antifouling and conductive hydrogels provides an effective way to develop robust electrochemical biosensors for biomarker detection in complex biological media.

Interplay of G-proteins and Serotonin in the Neuroimmunoinflammatory Model of Chronic Stress and Depression: A Narrative Review

INTRODUCTION

This narrative review addresses the clinical challenges in stress-related disorders such as depression, focusing on the interplay between neuron-specific and pro-inflammatory mechanisms at the cellular, cerebral, and systemic levels.

OBJECTIVE

We aim to elucidate the molecular mechanisms linking chronic psychological stress with low-grade neuroinflammation in key brain regions, particularly focusing on the roles of G proteins and serotonin (5-HT) receptors.

METHODS

This comprehensive review of the literature employs systematic, narrative, and scoping review methodologies, combined with systemic approaches to general pathology. It synthesizes current research on shared signaling pathways involved in stress responses and neuroinflammation, including calcium-dependent mechanisms, mitogen-activated protein kinases, and key transcription factors like NF-κB and p53. The review also focuses on the role of G protein-coupled neurotransmitter receptors (GPCRs) in immune and pro-inflammatory responses, with a detailed analysis of how 13 of 14 types of human 5-HT receptors contribute to depression and neuroinflammation.

RESULTS

The review reveals a complex interaction between neurotransmitter signals and immunoinflammatory responses in stress-related pathologies. It highlights the role of GPCRs and canonical inflammatory mediators in influencing both pathological and physiological processes in nervous tissue.

CONCLUSION

The proposed Neuroimmunoinflammatory Stress Model (NIIS Model) suggests that proinflammatory signaling pathways, mediated by metabotropic and ionotropic neurotransmitter receptors, are crucial for maintaining neuronal homeostasis. Chronic mental stress can disrupt this balance, leading to increased pro-inflammatory states in the brain and contributing to neuropsychiatric and psychosomatic disorders, including depression. This model integrates traditional theories on depression pathogenesis, offering a comprehensive understanding of the multifaceted nature of the condition.

JAK-STAT signaling in inflammation and stress-related diseases: implications for therapeutic interventions

The Janus kinase-signal transducer and transcription activator pathway (JAK-STAT) serves as a cornerstone in cellular signaling, regulating physiological and pathological processes such as inflammation and stress. Dysregulation in this pathway can lead to severe immunodeficiencies and malignancies, and its role extends to neurotransduction and pro-inflammatory signaling mechanisms. Although JAK inhibitors (Jakinibs) have successfully treated immunological and inflammatory disorders, their application has generally been limited to diseases with similar pathogenic features. Despite the modest expression of JAK-STAT in the CNS, it is crucial for functions in the cortex, hippocampus, and cerebellum, making it relevant in conditions like Parkinson's disease and other neuroinflammatory disorders. Furthermore, the influence of the pathway on serotonin receptors and phospholipase C has implications for stress and mood disorders. This review expands the understanding of JAK-STAT, moving beyond traditional immunological contexts to explore its role in stress-related disorders and CNS function. Recent findings, such as the effectiveness of Jakinibs in chronic conditions such as rheumatoid arthritis, expand their therapeutic applicability. Advances in isoform-specific inhibitors, including filgotinib and upadacitinib, promise greater specificity with fewer off-target effects. Combination therapies, involving Jakinibs and monoclonal antibodies, aiming to enhance therapeutic specificity and efficacy also give great hope. Overall, this review bridges the gap between basic science and clinical application, elucidating the complex influence of the JAK-STAT pathway on human health and guiding future interventions.

Microbiota dysbiosis caused by dietetic patterns as a promoter of Alzheimer's disease through metabolic syndrome mechanisms

Microbiota dysbiosis and metabolic syndrome, consequences of a non-adequate diet, generate a feedback pathogenic state implicated in Alzheimer's disease development. The lower production of short chain fatty acids (SCFAs) under dysbiosis status leads to lipid homeostasis deregulation and decreases Angptl4 release and AMPK activation in the adipose tissue, promoting higher lipid storage (adipocyte hypertrophy) and cholesterol levels. Also, low SCFA generation reduces GPR41 and GPR43 receptor activation at the adipose tissue (increasing leptin release and leptin receptor resistance) and intestinal levels, reducing the release of GLP-1 and YPP. Therefore, lower satiety sensation and energy expenditure occur, promoting a weight gaining environment mediated by higher food intake and lipid storage, developing dyslipemia. In this context, higher glucose levels, together with higher free fatty acids in the bloodstream, promote glycolipotoxicity, provoking a reduction in insulin released, insulin receptor resistance, advanced glycation products (AGEs) and type 2 diabetes. Intestinal dysbiosis and low SCFAs reduce bacterial biodiversity, increasing lipopolysaccharide (LPS)-producing bacteria and intestinal barrier permeability. Higher amounts of LPS pass to the bloodstream (endotoxemia), causing a low-grade chronic inflammatory state characterized by higher levels of leptin, IL-1β, IL-6 and TNF-α, together with a reduced release of adiponectin and IL-10. At the brain and neuronal levels, the generated insulin resistance, low-grade chronic inflammation, leptin resistance, AGE production and LPS increase directly impact the secretase enzymes and tau hyperphosphorylation, creating an enabling environment for β-amyloid senile plaque and tau tangled formations and, as a consequence, Alzheimer's initiation, development and maintenance.

G-protein coupled estrogen receptor (GPER1) activation promotes synaptic insertion of AMPA receptors and induction of chemical LTP at hippocampal temporoammonic-CA1 synapses

It is well documented that 17β estradiol (E2) regulates excitatory synaptic transmission at hippocampal Shaffer-collateral (SC)-CA1 synapses, via activation of the classical estrogen receptors (ERα and ERβ). Hippocampal CA1 pyramidal neurons are also innervated by the temporoammonic (TA) pathway, and excitatory TA-CA1 synapses are reported to be regulated by E2. Recent studies suggest a role for the novel G-protein coupled estrogen receptor (GPER1) at SC-CA1 synapses, however, the role of GPER1 in mediating the effects of E2 at juvenile TA-CA1 synapses is unclear. Here we demonstrate that the GPER1 agonist, G1 induces a persistent, concentration-dependent (1-10 nM) increase in excitatory synaptic transmission at TA-CA1 synapses and this effect is blocked by selective GPER1 antagonists. The ability of GPER1 to induce this novel form of chemical long-term potentiation (cLTP) was prevented following blockade of N-methyl-D-aspartate (NMDA) receptors, and it was not accompanied by any change in paired pulse facilitation ratio (PPR). GPER1-induced cLTP involved activation of ERK but was independent of phosphoinositide 3-kinase (PI3K) signalling. Prior treatment with philanthotoxin prevented the effects of G1, indicating that synaptic insertion of GluA2-lacking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors underlies GPER1-induced cLTP. Furthermore, activity-dependent LTP occluded G1-induced cLTP and vice versa, indicating that these processes have overlapping expression mechanisms. Activity-dependent LTP was blocked by the GPER1 antagonist, G15, suggesting that GPER1 plays a role in NMDA-dependent LTP at juvenile TA-CA1 synapses. These findings add a new dimension to our understanding of GPER1 in modulating neuronal plasticity with relevance to age-related neurodegenerative conditions.

STAT3 in medulloblastoma: a key transcriptional regulator and potential therapeutic target

Medulloblastoma is the most common malignant brain tumor of childhood accounting for about 60% of all pediatric embryonal tumors. Despite improvements in the overall survival rate, this tumor still lacks an efficient, reliable, and less toxic therapeutic approach. Characterization of the molecular mechanisms involved in medulloblastoma initiation and progression is a crucial step for the development of effective therapies. Signal transducer and activator of transcription 3 is a convergence point for several signaling cascades that are implicated in medulloblastoma tumorigenesis. Accumulated evidence has revealed the pivotal role of signal transducer and activator of transcription 3 in medulloblastoma pathogenesis such as proliferation, survival, angiogenesis, and immunosuppression as well as maintenance, drug resistance, and recurrence. In this review, we focus on the role of signal transducer and activator of transcription 3 in medulloblastoma tumorigenesis and discuss the recent advances of signal transducer and activator of transcription 3 inhibition as a promising developed strategy for medulloblastoma therapy.

Food for Thought: Leptin and Hippocampal Synaptic Function

It is well documented that the endocrine hormone, leptin controls energy homeostasis by providing key signals to specific hypothalamic nuclei. However, our knowledge of leptin’s central actions has advanced considerably over the last 20 years, with the hippocampus now established as an important brain target for this hormone. Leptin receptors are highly localised to hippocampal synapses, and increasing evidence reveals that activation of synaptically located leptin receptors markedly impacts cognitive processes, and specifically hippocampal-dependent learning and memory. Here, we review the recent actions of leptin at hippocampal synapses and explore the consequences for brain health and disease.

Aerobic Exercise Improves Type 2 Diabetes Mellitus-Related Cognitive Impairment by Inhibiting JAK2/STAT3 and Enhancing AMPK/SIRT1 Pathways in Mice

Type 2 diabetes mellitus (T2DM) is a prevalent risk factor for cognitive impairment. Aerobic exercise can improve T2DM-related cognitive impairment; however, the possible mechanisms remain elusive. Thus, we assessed db/m mice and leptin receptor-deficient (db/db) mice that did or did not perform aerobic exercise (8 m/min, 60 min/day, and 5 days/week for 12 weeks). In this study, cognitive function was significantly impaired in the T2DM mice; aerobic exercise improved cognitive impairment through activating the AMPK/SIRT1 signalling pathway and inhibiting the JAK2/STAT3 signalling pathway in T2DM mice. However, after the application of RO8191 (JAK2 activator) or Compound C (AMPK inhibitor), the positive improvement of the exercise was evidently suppressed. Taken together, our data indicated that long-term aerobic exercise improves type 2 diabetes mellitus-related cognitive impairment by inhibiting JAK2/STAT3 and enhancing AMPK/SIRT1 pathways in mice.

Role of JAK-STAT and PPAR-Gamma Signalling Modulators in the Prevention of Autism and Neurological Dysfunctions

The Janus-kinase (JAK) and signal transducer activator of transcription (STAT) signalling pathways regulate gene expression and control various factors involved in normal physiological functions such as cell proliferation, neuronal development, and cell survival. JAK activation phosphorylates STAT3 in astrocytes and microglia, and this phosphorylation has been linked to mitochondrial damage, apoptosis, neuroinflammation, reactive astrogliosis, and genetic mutations. As a regulator, peroxisome proliferator-activated receptor gamma (PPAR-gamma), in relation to JAK-STAT signalling, prevents this phosphorylation and aids in the treatment of the above-mentioned neurocomplications. Changes in cellular signalling may also contribute to the onset and progression of autism. Thus, PPAR-gamma agonist upregulation may be associated with JAK-STAT signal transduction downregulation. It may also be responsible for attenuating neuropathological changes by stimulating SOCS3 or involving RXR or SMRT, thereby reducing transcription of the various cytokine proteins and genes involved in neuronal damage. Along with JAK-STAT inhibitors, PPAR-gamma agonists could be used as target therapeutic interventions for autism. This research-based review explores the potential involvement and mutual regulation of JAK-STAT and PPAR-gamma signalling in controlling multiple pathological factors associated with autism.

Leptin regulation of synaptic function at hippocampal TA-CA1 and SC-CA1 synapses

Increasing evidence indicates that the metabolic hormone, leptin markedly influences the functioning of the hippocampus. In particular, exposure to leptin results in persistent changes in synaptic efficacy at both temporoammonic (TA) and Schaffer Collateral (SC) inputs to hippocampal CA1 neurons. The ability of leptin to regulate TA-CA1 and SC-CA1 synapses has important functional implications, as both synaptic connections play important roles in hippocampal-dependent learning and memory. Here we review the modulatory actions of the hormone leptin at these hippocampal CA1 synapses and explore the impact on learning and memory processes.

Shenqi Yizhi Granule attenuates Aβ1-42 induced cognitive dysfunction via inhibiting JAK2/STAT3 activated astrocyte reactivity

Shenqi Yizhi Granule (SYG), a modern preparation herbs based on the theory of traditional Chinese medicine, has been proved to be effective against Alzheimer's disease in clinical trials, APP/PS1 mice and 5XFAD transgenic mice. But the underlying mechanism remains ambiguous. Increasing evidence supports the crucial role of astrocyte reactivity in the pathogenesis of Alzheimer's disease (AD). In the present study, we attempt to explore the underlying mechanisms of SYG from astrocyte reactivity in Aβ_1-42-induced rat model of Alzheimer's disease. After SYG treatment, the impairment of learning and memory induced by Aβ_1-42 was significantly improved and the hippocampal neuron damages were alleviated. Additionally, the activity of glutamine synthetase and the concentration of glutamate, which might be involved in the cognitive dysfunctions, were outstandingly reduced. Meanwhile, the astrocyte reactivity was also remarkably inhibited. The expressions of JAK2 and STAT3, key proteins in the JAK2/STAT3 signaling pathway that is tightly associated with reactive astrocytes, were clearly attenuated, too. Collectively, our data demonstrate that SYG might exert protective effects on cognitive impairment induced by amyloid-β oligomers via inhibition of astrocyte reactivity regulated by the JAK2/STAT3 signaling pathway. It may be a potential therapeutic for cognitive dysfunctions in many neurological and psychiatric disorders such as Alzheimer's disease.

Regulation of hippocampal synaptic function by the metabolic hormone leptin: Implications for health and disease

Significant advances have been made in our understanding of the hormone, leptin and its CNS actions in recent years. It is now evident that leptin has a multitude of brain functions, that extend beyond its established role in the hypothalamic control of energy balance. Additional brain regions including the hippocampus are important targets for leptin, with a high density of leptin receptors (LepRs) expressed in specific hippocampal regions and localised to CA1 synapses. Extensive evidence indicates that leptin has pro-cognitive actions, as it rapidly modifies synaptic efficacy at excitatory Schaffer collateral (SC)-CA1 and temporoammonic (TA)-CA1 synapses and enhances performance in hippocampal-dependent memory tasks. There is a functional decline in hippocampal responsiveness to leptin with age, with significant reductions in the modulatory effects of leptin at SC-CA1 and TA-CA1 synapses in aged, compared to adult hippocampus. As leptin has pro-cognitive effects, this decline in leptin sensitivity is likely to have negative consequences for cognitive function during the aging process. Here we review how evaluation of the hippocampal actions of leptin has improved our knowledge of the regulatory brain functions of leptin in health and provided significant insight into the impact of leptin in age-related neurodegenerative disorders linked to cognitive decline.

Ablation of STAT3 in Purkinje cells reorganizes cerebellar synaptic plasticity in long-term fear memory network

Emotional memory processing engages a large neuronal network of brain regions including the cerebellum. However, the molecular and cellular mechanisms of the cerebellar cortex modulating the fear memory network are unclear. Here, we illustrate that synaptic signaling in cerebellar Purkinje cells (PCs) via STAT3 regulates long-term fear memory. Transcriptome analyses revealed that PC-specific STAT3 knockout (STAT3^PKO) results in transcriptional changes that lead to an increase in the expression of glutamate receptors. The amplitude of AMPA receptor-mediated excitatory postsynaptic currents at parallel fiber (PF) to PC synapses was larger in STAT3^PKO mice than in wild-type (WT) littermates. Fear conditioning induced long-term depression of PF–PC synapses in STAT3^PKO mice while the same manipulation induced long-term potentiation in WT littermates. STAT3^PKO mice showed an aberrantly enhanced long-term fear memory. Neuronal activity in fear-related regions increased in fear-conditioned STAT3^PKO mice. Our data suggest that STAT3-dependent molecular regulation in PCs is indispensable for proper expression of fear memory.

Changes in Hippocampal Plasticity in Depression and Therapeutic Approaches Influencing These Changes

Depression is a common neurological disease that seriously affects human health. There are many hypotheses about the pathogenesis of depression, and the most widely recognized and applied is the monoamine hypothesis. However, no hypothesis can fully explain the pathogenesis of depression. At present, the brain-derived neurotrophic factor (BDNF) and neurogenesis hypotheses have highlighted the important role of plasticity in depression. The plasticity of neurons and glial cells plays a vital role in the transmission and integration of signals in the central nervous system. Plasticity is the adaptive change in the nervous system in response to changes in external signals. The hippocampus is an important anatomical area associated with depression. Studies have shown that some antidepressants can treat depression by changing the plasticity of the hippocampus. Furthermore, caloric restriction has also been shown to affect antidepressant and hippocampal plasticity changes. In this review, we summarize the latest research, focusing on changes in the plasticity of hippocampal neurons and glial cells in depression and the role of BDNF in the changes in hippocampal plasticity in depression, as well as caloric restriction and mitochondrial plasticity. This review may contribute to the development of antidepressant drugs and elucidating the mechanism of depression.

Identification of Crucial Genes and Diagnostic Value Analysis in Major Depressive Disorder Using Bioinformatics Analysis

AIM AND OBJECTIVE

Despite the prevalence and burden of major depressive disorder (MDD), our current understanding of the pathophysiology is still incomplete. Therefore, this paper aims to explore genes and evaluate their diagnostic ability in the pathogenesis of MDD.

METHODS

Firstly, the expression profiles of mRNA and microRNA were downloaded from the gene expression database and analyzed by the GEO2R online tool to identify differentially expressed genes (DEGs) and differentially expressed microRNAs (DEMs). Then, the DAVID tool was used for functional enrichment analysis. Secondly, the comprehensive protein- protein interaction (PPI) network was analyzed using Cytoscape, and the network MCODE was applied to explore hub genes. Thirdly, the receiver operating characteristic (ROC) curve of the core gene was drawn to evaluate clinical diagnostic ability. Finally, mirecords was used to predict the target genes of DEMs.

RESULTS

A total of 154 genes were identified as DEGs, and 14 microRNAs were identified as DEMs. Pathway enrichment analysis showed that DEGs were mainly involved in hematopoietic cell lineage, PI3K-Akt signaling pathway, cytokinecytokine receptor interaction, chemokine signaling pathway, and JAK-STAT signaling pathway. Three important modules are identified and selected by the MCODE clustering algorithm. The top 12 hub genes including CXCL16, CXCL1, GNB5, GNB4, OPRL1, SSTR2, IL7R, MYB, CSF1R, GSTM1, GSTM2, and GSTP1 were identified as important genes for subsequent analysis. Among these important hub genes, GSTM2, GNB4, GSTP1 and CXCL1 have good diagnostic ability. Finally, by combining these four genes, the diagnostic ability of MDD can be improved to 0.905, which is of great significance for the clinical diagnosis of MDD.

CONCLUSION

Our results indicate that GSTM2, GNB4, GSTP1 and CXCL1 have potential diagnostic markers and are of great significance in clinical research and diagnostic application of MDD. This result needs a large sample study to further confirm the pathogenesis of MDD.

Identification of the significant pathways of Banxia Houpu decoction in the treatment of depression based on network pharmacology

Banxia Houpu decoction (BXHPD) has been used to treat depression in clinical practice for centuries. However, the pharmacological mechanisms of BXHPD still remain unclear. Network Pharmacology (NP) approach was used to explore the potential molecular mechanisms of BXHPD in treating depression. Potential active compounds of BXHPD were obtained from the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform Database. STRING database was used to build a interaction network between the active compounds and target genes associated with depression. The topological features of nodes were visualized and calculated. Significant pathways and biological functions were identified using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. A total of 44 active compounds were obtained from BXHPD, and 121 potential target genes were considered to be therapeutically relevant. Pathway analysis indicated that MAPK signaling pathway, ErbB signaling pathway, HIF-1 signaling pathway and PI3K-Akt pathway were significant pathways in depression. They were mainly involved in promoting nerve growth and nutrition and alleviating neuroinflammatory conditions. The result provided some potential ways for modern medicine in the treatment of depression.

Leptin stimulates synaptogenesis in hippocampal neurons via KLF4 and SOCS3 inhibition of STAT3 signaling

Normal development of neuronal connections in the hippocampus requires neurotrophic signals, including the cytokine leptin. During neonatal development, leptin induces formation and maturation of dendritic spines, the main sites of glutamatergic synapses in the hippocampal neurons. However, the molecular mechanisms for leptin-induced synaptogenesis are not entirely understood. In this study, we reveal two novel targets of leptin in developing hippocampal neurons and address their role in synaptogenesis. First target is Kruppel-Like Factor 4 (KLF4), which we identified using a genome-wide target analysis strategy. We show that leptin upregulates KLF4 in hippocampal neurons and that leptin signaling is important for KLF4 expression in vivo. Furthermore, KLF4 is required for leptin-induced synaptogenesis, as shKLF4 blocks and upregulation of KLF4 phenocopies it. We go on to show that KLF4 requires its signal transducer and activator of transcription 3 (STAT3) binding site and thus potentially blocks STAT3 activity to induce synaptogenesis. Second, we show that leptin increases the expression of suppressor of cytokine signaling 3 (SOCS3), another well-known inhibitor of STAT3, in developing hippocampal neurons. SOCS3 is also required for leptin-induced synaptogenesis and sufficient to stimulate it alone. Finally, we show that constitutively active STAT3 blocks the effects of leptin on spine formation, while the targeted knockdown of STAT3 is sufficient to induce it. Overall, our data demonstrate that leptin increases the expression of both KLF4 and SOCS3, inhibiting the activity of STAT3 in the hippocampal neurons and resulting in the enhancement of glutamatergic synaptogenesis during neonatal development.

Activation of oestrogen receptor α induces a novel form of LTP at hippocampal temporoammonic-CA1 synapses

BACKGROUND AND PURPOSE

17β estradiol (E2) rapidly regulates excitatory synaptic transmission at the classical Schaffer collateral (SC) input to hippocampal CA1 neurons. However, the impact of E2 on excitatory synaptic transmission at the distinct temporoammonic (TA) input to CA1 neurons and the oestrogen receptors involved is less clear.

EXPERIMENTAL APPROACH

Extracellular recordings were used to monitor excitatory synaptic transmission in hippocampal slices from juvenile male (P11-24) Sprague Dawley rats. Immunocytochemistry combined with confocal microscopy was used to monitor the surface expression of the AMPA receptor (AMPAR) subunit, GluA1 in hippocampal neurons cultured from neonatal (P0-3) rats.

KEY RESULTS

Here, we show that E2 induces a novel form of LTP at TA-CA1 synapses, an effect mirrored by the ERα agonist, PPT, and blocked by an ERα antagonist. ERα-induced LTP is NMDA receptor (NMDAR)-dependent and involves a postsynaptic expression mechanism that requires PI 3-kinase signalling and synaptic insertion of GluA2-lacking AMPARs. ERα-induced LTP has overlapping expression mechanisms with classical Hebbian LTP, as HFS-induced LTP occluded PPT-induced LTP and vice versa. In addition, activity-dependent LTP was blocked by the ERα antagonist, suggesting that ERα activation is involved in NMDA-LTP at TA-CA1 synapses.

CONCLUSION AND IMPLICATIONS

ERα induces a novel form of LTP at juvenile male hippocampal TA-CA1 synapses. As TA-CA1 synapses are implicated in episodic memory processes and are an early target for neurodegeneration, these findings have important implications for the role of oestrogens in CNS health and neurodegenerative disease.

Ciliary neurotrophic factor signaling in the rat orbitofrontal cortex ameliorates stress-induced deficits in reversal learning

Deficits in cognitive flexibility, i.e. the ability to modify behavior in response to changes in the environment, are present in several psychiatric disorders and are often refractory to treatment. However, improving treatment response has been hindered by a lack of understanding of the neurobiology of cognitive flexibility. Using a rat model of chronic stress (chronic intermittent cold stress, CIC) that produces selective deficits in reversal learning, a form of cognitive flexibility dependent on orbitofrontal cortex (OFC) function, we have previously shown that JAK2 signaling is required for optimal reversal learning. In this study we explore the molecular basis of those effects. We show that, within the OFC, CIC stress reduces the levels of phosphorylated JAK2 and of ciliary neurotrophic factor (CNTF), a promoter of neuronal survival and an activator of JAK2 signaling, and that neutralizing endogenous CNTF with an intra-OFC microinjection of a specific antibody is sufficient to produce reversal-learning deficits similar to stress. Intra-OFC delivery of recombinant CNTF to CIC-stressed rats, at a dose that induces JAK2 and Akt but not STAT3 or ERK, ameliorates reversal-learning deficits, and Akt blockade prevents the positive effects of CNTF. Further analysis revealed that CNTF may exert its beneficial effects by inhibiting GSK3β, a substrate of Akt and a regulator of protein degradation. We also revealed a novel mechanism of CNTF action through modulation of p38/Mnk1/eIF4E signaling. This cascade controls translation of select mRNAs, including those encoding several plasticity-related proteins. Thus, we suggest that CNTF-driven JAK2 signaling corrects stress-induced reversal learning deficits by modulating the steady-state levels of plasticity-related proteins in the OFC.

Ketamine and Active Ketamine Metabolites Regulate STAT3 and the Type I Interferon Pathway in Human Microglia: Molecular Mechanisms Linked to the Antidepressant Effects of Ketamine

Inflammation is an important biological process which contributes to risk for depression, in part as a result of the production of proinflammatory cytokines and of alterations in glutamatergic neurotransmission. Ketamine has anti-inflammatory properties which might contribute to its antidepressant effects. This study was designed to clarify mechanisms of action for ketamine and its active metabolites, (2R,6R;2S,6S)-hydroxynorketamine (HNK), which also appear to play a major role in ketamine's rapid antidepressant effects. An HMC3 human microglial cell line was used as a model system to test a possible role for ketamine in immune response regulation that might contribute to its antidepressant effects. Our results highlight the fact that ketamine and its two active metabolites can regulate the type I interferon pathway mediated, at least partially, through signal transducer and activation of transcription 3 (STAT3) which plays a major role in the immune response. Specifically, STAT3 downstream genes that were modulated by either ketamine or its active metabolites were enriched in the "response to type I interferon" pathway. Our data also suggest that STAT3 might play a role in ketamine's antidepressant effects, mediated, at least in part, through eukaryotic elongation factor 2 (EEF2), resulting in the augmentation of brain-derived neurotropic factor (BDNF) expression and promoting the synthesis of synaptic proteins postsynaptic density protein 95 (PSD95) and synapsin I (SYN1).

Genetic and Real-World Clinical Data, Combined with Empirical Validation, Nominate Jak-Stat Signaling as a Target for Alzheimer's Disease Therapeutic Development

As genome-wide association studies (GWAS) have grown in size, the number of genetic variants that have been associated per disease has correspondingly increased. Despite this increase in the number of single-nucleotide polymorphisms (SNPs) identified per disease, their biological interpretation has in many cases remained elusive. To address this, we have combined GWAS results with orthogonal sources of evidence, namely the current knowledge of molecular pathways; real-world clinical data from six million patients; RNA expression across tissues from Alzheimer’s disease (AD) patients, and purpose-built rodent models for experimental validation. In more detail, first we show that when examined at a pathway level, analysis of all GWAS studies groups AD in a cluster with disorders of immunity and inflammation. Using clinical data, we show that the degree of comorbidity of these diseases with AD correlates with the strength of their genetic association with molecular participants in the Janus kinases/signal transducer and activator of transcription (JAK-STAT) pathway. Using four independent RNA expression datasets we then find evidence for the altered regulation of JAK-STAT pathway genes in AD. Finally, we use both in vitro and in vivo rodent models to demonstrate that Aβ induces gene expression of the key drivers of this pathway, providing experimental evidence to validate these data-driven observations. These results therefore nominate JAK-STAT anomalies as a prominent aetiopathological event in AD and hence a potential target for therapeutic development, and moreover demonstrate a de novo multi-modal approach to derive information from rapidly increasing genomic datasets.

Leptin Regulation of Synaptic Function at Hippocampal TA-CA1 and SC-CA1 Synapses: Implications for Health and Disease

Growing evidence indicates that the endocrine hormone leptin regulates hippocampal synaptic function in addition to its established role as a hypothalamic satiety signal. Indeed, numerous studies show that leptin facilitates the cellular events that underlie hippocampal learning and memory including activity-dependent synaptic plasticity and glutamate receptor trafficking, indicating that leptin may be a potential cognitive enhancer. Although there has been extensive investigation into the modulatory role of leptin at hippocampal Schaffer collateral (SC)-CA1 synapses, recent evidence indicates that leptin also potently regulates excitatory synaptic transmission at the anatomically distinct temporoammonic (TA) input to hippocampal CA1 neurons. The cellular mechanisms underlying activity-dependent synaptic plasticity at TA-CA1 synapses differ from those at SC-CA1 synapses and the TA input is implicated in spatial and episodic memory formation. Furthermore, the TA input is an early target for neurodegeneration in Alzheimer's disease (AD) and aberrant leptin function is linked to AD. Here, we review the evidence that leptin regulates hippocampal synaptic function at both SC- and TA-CA1 synapses and discuss the consequences for neurodegenerative disorders like AD.

The Role of Leptin and Adiponectin in Obesity-Associated Cognitive Decline and Alzheimer's Disease

Cross-talk between adipose tissue and central nervous system (CNS) underlies the increased risk of obese people to develop brain diseases such as cognitive and mood disorders. Detailed mechanisms for how peripheral changes caused by adipose tissue accumulation in obesity impact the CNS to cause brain dysfunction are poorly understood. Adipokines are a large group of substances secreted by the white adipose tissue to regulate a wide range of homeostatic processes including, but not limited to, energy metabolism and immunity. Obesity is characterized by a generalized change in the levels of circulating adipokines due to abnormal accumulation and dysfunction of adipose tissue. Altered adipokine levels underlie complications of obesity as well as the increased risk for the development of obesity-related comorbidities such as type 2 diabetes, cardiovascular and neurodegenerative diseases. Here, we review the literature for the role of adipokines as key mediators of the communication between periphery and CNS in health and disease. We will focus on the actions of leptin and adiponectin, two of the most abundant and well studied adipokines, in the brain, with particular emphasis on how altered signaling of these adipokines in obesity may lead to cognitive dysfunction and augmented risk for Alzheimer's disease. A better understanding of adipokine biology in brain disorders may prove of major relevance to diagnostic, prevention and therapy.

Age-dependent regulation of excitatory synaptic transmission at hippocampal temporoammonic-CA1 synapses by leptin

The hippocampus is a key target for the hormone leptin and leptin regulation of excitatory synaptic transmission at Schaffer-collateral-CA1 synapses during aging are well documented. However, little is known about the age-dependent actions of leptin at the temporoammonic (TA) input to CA1 neurons. Here we show that leptin induces a novel form of N-methyl-D-aspartate receptor-dependent long-term depression (LTD) at adult (12-24 weeks old) TA-CA1 synapses. Leptin-induced LTD requires activation of canonical Janus tyrosine kinase 2- signal transducer and activator of transcription signaling and removal of GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors from synapses. Moreover, leptin-induced LTD is occluded by activity-dependent LTD at TA-CA1 synapses. By contrast, leptin has no effect on excitatory synaptic transmission at aged (12-14 months old) TA-CA1 synapses, and low-frequency stimulation also fails to induce LTD at this age. These findings demonstrate clear age-related alterations in the leptin sensitivity of TA-CA1 synapses and provide valuable information on how the leptin system alters with age. As leptin has been linked to Alzheimer's disease, these findings have important implications for understanding of age-related disorders such as Alzheimer's disease.

The trophic effect of nerve growth factor in primary cultures of rat hippocampal neurons is associated to an anti-inflammatory and immunosuppressive transcriptional program

Nerve growth factor, the prototype of a family of neurotrophins, elicits differentiation and survival of peripheral and central neuronal cells. Although its neural mechanisms have been studied extensively, relatively little is known about the transcriptional regulation governing its effects. We have previously observed that in primary cultures of rat hippocampal neurons treatment with nerve growth factor for 72 hr increases neurite outgrowth and cell survival. To obtain a comprehensive view of the underlying transcriptional program, we performed whole-genome expression analysis by microarray technology. We identified 541 differentially expressed genes and characterized dysregulated pathways related to innate immunity: the complement system and neuro-inflammatory signaling. The exploitation of such genes and pathways may help interfering with the intracellular mechanisms involved in neuronal survival and guide novel therapeutic strategies for neurodegenerative diseases.

Upregulation of Vesicular Glutamate Transporter 2 and STAT3 Activation in the Spinal Cord of Mice Receiving 3,3'-Iminodipropionitrile

Chronic administration of 3,3'-iminodipropionitrile (IDPN) causes axonal impairment. Although controversy still remains, it has been suggested that IDPN intoxication mimics the axonopathy of amyotrophic lateral sclerosis (ALS). Interestingly, recent studies including our own showed that signal transducer and activator of transcription 3 (STAT3) in spinal α-motoneurons was activated in both IDPN-treated mice and SOD1 ^G93A mice, a genetic model of familial ALS. Because activation of STAT3 occurs in response to various stimuli, such as axonal injury, ischemia, and excessive glutamate, here we focused on a potential link between phosphorylated STAT3 (pSTAT3, an active form) and vesicular glutamate transporter 2 (VGluT2, a regulator of glutamate storage and release) in IDPN-treated mice and SOD1 ^G93A mice. Impairment of axonal transport was confirmed by western blot analysis: the expression levels of phosphorylated neurofilament H were elevated in both models. As shown in SOD1 ^G93A mice, the expression frequencies of VGluT2 in synaptophysin-positive (SYP)⁺ presynaptic terminals around spinal α-motoneurons were significantly higher in IDPN-treated mice than in vehicle controls. The coverages of spinal α-motoneurons by VGluT2⁺ presynaptic terminals were more elevated around pSTAT3⁺ cells than around pSTAT3^- cells in IDPN-treated mice and SOD1 ^G93A mice. Considering that excessive glutamate is shown to be involved in axonal impairment and STAT3 activation, the present results suggest that IDPN-induced upregulation of VGluT2 may result in an increase in glutamate, which might cause axonopathy and induction of pSTAT3. The link between upregulation of VGluT2 and activation of STAT3 via glutamate may represent a common pathological feature of IDPN-treated mice and SOD1 ^G93A mice.