Synaptic memory requires CaMKII

LUZP1 Regulates Dendritic Spine Maturation and Synaptic Plasticity in the Hippocampal Dentate Gyrus of Mice

Leucine zipper protein 1 (LUZP1) functions in the maintenance and dynamics of the cytoskeleton by interacting with actin and microtubules. Deficiency or mutation of LUZP1 is associated with brain developmental disorders; however, its precise role in brain function remains unclear. We showed that LUZP1 localizes to actin and is highly expressed in CaMKIIα-expressing neurons within the mouse hippocampal dentate gyrus. Depletion of LUZP1 impedes dendritic spine maturation, which is characterized by excess immature filopodia and loss of mature mushroom spines both in vitro and in vivo. LUZP1 knockdown reduces spontaneous electrical activity and synaptic plasticity in hippocampal neurons. Conditional deletion of LUZP1 in CaMKIIα-expressing neurons causes impaired learning and memory behavior in mice of both sexes. Mechanistically, LUZP1 control dendritic maturation by directly interacting with filamin A and modulating the Rac1-PAK1 signaling pathway. These findings shed light on the role of LUZP1 in regulating synaptic plasticity and brain function.

Protein kinases in neurodegenerative diseases: current understandings and implications for drug discovery

Neurodegenerative diseases (e.g., Alzheimer's, Parkinson's, Huntington's disease, and Amyotrophic Lateral Sclerosis) are major health threats for the aging population and their prevalences continue to rise with the increasing of life expectancy. Although progress has been made, there is still a lack of effective cures to date, and an in-depth understanding of the molecular and cellular mechanisms of these neurodegenerative diseases is imperative for drug development. Protein phosphorylation, regulated by protein kinases and protein phosphatases, participates in most cellular events, whereas aberrant phosphorylation manifests as a main cause of diseases. As evidenced by pharmacological and pathological studies, protein kinases are proven to be promising therapeutic targets for various diseases, such as cancers, central nervous system disorders, and cardiovascular diseases. The mechanisms of protein phosphatases in pathophysiology have been extensively reviewed, but a systematic summary of the role of protein kinases in the nervous system is lacking. Here, we focus on the involvement of protein kinases in neurodegenerative diseases, by summarizing the current knowledge on the major kinases and related regulatory signal transduction pathways implicated in diseases. We further discuss the role and complexity of kinase-kinase networks in the pathogenesis of neurodegenerative diseases, illustrate the advances of clinical applications of protein kinase inhibitors or novel kinase-targeted therapeutic strategies (such as antisense oligonucleotides and gene therapy) for effective prevention and early intervention.

Long-term variable photoperiod exposure impairs hippocampal synapse involving of the glutamate system and leads to memory deficits in male Wistar rats

Excessive artificial light at night can induce the human circadian misalignment, potentially impairing memory consolidation and the rhythms of hippocampal clock genes. To investigate the impact of circadian misalignment on hippocampal function, we measured various field excitatory postsynaptic potentials (fEPSP) and golgi staining in the CA1 and dentate gyrus (DG) regions in Wistar rats. Our findings revealed that circadian misalignment resulted in a leftward shift in the input-output (I-O) curve within the CA1 region, decreased long-term potentiation (LTP), multi-time interval paired-pulse ratio (PPR), as well as dendritic spines and complexity across both CA1 and DG regions. Additionally, magnetic resonance spectroscopy (MRS) showed that circadian misalignment downregulated glutamate-related neurotransmitters (Glu + Gln) in the hippocampus, contributing to impaired synaptic function. Furthermore, disruptions to glutamate receptor subunits due to circadian misalignment led to reduced expression of AMPA receptor and NMDA receptor subunits in the hippocampus. In summary, our results suggest that memory impairments resulting from circadian misalignment are associated with diminished functionality within the glutamatergic system; this includes reductions in both Glx levels and availability of glutamate receptor subunits-key factors contributing to compromised synaptic function within the hippocampus.

Evidence for cPLA2 activation in Alzheimer's Disease Synaptic Pathology

Background

Synapses are essential for learning and memory, and their loss predicts cognitive decline in Alzheimer's disease (AD). Synaptic loss is associated with excitotoxicity, neuroinflammation, amyloid-β, and tau pathology, but the molecular mechanisms remain unclear. There is an urgent need to identify new targets to modify the disease and slow synaptic loss and cognitive decline. This study examines if calcium-dependent phospholipase A2 (cPLA2) is implicated in AD synaptic loss. cPLA2 catalyzes membrane phospholipids to release arachidonic acid, which can be metabolized into inflammatory eicosanoids.

Methods

cPLA2 levels were examined in synaptosomes isolated from the postmortem frontal cortex of individuals with no cognitive impairment (NCI), mild cognitive impairment (MCI), and AD dementia from the Religious Orders Study (ROS). Eicosanoids in synaptosomes were analyzed using lipidomics. Immunofluorescent staining investigated cPLA2 interactions with synaptic markers. Human iPSCs-derived neurons were used to study cPLA2 overactivation after exposure to amyloid-β 42 oligomers (Aβ42O), its relationships with synaptic markers, and the effects of cPLA2 inhibitors.

Results

We observed elevated cPLA2 (cPLA2α and cPLA2β) in AD synaptosomes and positive correlations with postsynaptic density protein 95 (PSD-95) and cognitive dysfunction. Eicosanoids were increased in AD synaptosomes and correlated with cPLA2, indicating cPLA2 activity at synapses/synaptosomes. Phosphorylated cPLA2α (p-cPLA2α) colocalized with PSD-95 in synaptosomes, and with postsynaptic Ca 2+ /calmodulin-dependent protein kinase IIα (CaMKIIα) and dendritic microtubule-associated protein 2 (MAP2) in NCI and AD brains, where their levels were reduced in AD. P-cPLA2α colocalizes with MAP2 at the neuronal soma associated with neuritic plaques and neurodegeneration in AD. Aβ42O activates cPLA2α in human iPSCs-derived neurons, leading to p-cPLA2α relocation from the cytosol to synaptic and dendritic sites to colocalize with CaMKIIα and MAP2, resulting in their reduction. P-cPLA2α also colocalized with PSD-95 in Aβ42O-exposed neurons, accompanied with increased PSD-95 intensity at soma membrane. These processes were reversed by the cPLA2 inhibitor ASB14780.

Conclusions

cPLA2 overactivation at synapses, dendrites, and excitatory neuronal somas is associated with synaptic loss, neuritic plaques and neurodegeneration, potentially contributing to cognitive decline in AD. Future research needs to explore the role of cPLA2 as a disease-modifying target for AD.

Neurological Adverse Events Associated with the Use of Janus Kinase Inhibitors: A Pharmacovigilance Study Based on Vigibase

Background: Janus kinase (JAK) inhibitors are a new class of targeted therapies that block cytokines and the signal transduction and activators of transcription (STAT) pathway. However, post-marketing surveillance studies have led to revised recommendations, highlighting potential serious heart-related events and cancer risk of JAK inhibitors. Here, we aimed to determine the neurological adverse events (AEs) of JAK inhibitors (tofacitinib, ruxolitinib, and baricitinib) based on a global real-world database. Methods: We analyzed individual case safety reports from the Uppsala Monitoring Center from January 1968 to 4 April 2022. A disproportionality analysis was performed using the proportional reporting ratio (PRR), reporting odds ratio (ROR), and information component (IC) to detect signals. Signals were classified according to the hierarchy of the Medical Dictionary for Regulatory Activities (MedDRA). Additionally, a stratified disproportionality analysis by age group and sex was performed for major AEs. Results: A total of 30,051,159 reports for all drugs were analyzed in this study. Among 105,798 reports of tofacitinib, 14.1% (14,863 reports) were neurological AEs. For ruxolitinib and baricitinib, 14.5% (6317 reports) and 10.2% (1216 reports) were neurological AEs, respectively. Various neurological AE signals were detected for tofacitinib and ruxolitinib, with memory impairment exhibiting the highest number of reports and a positive signal in the stratified disproportionality analysis by age group. Baricitinib did not reach the signal detection threshold. Conclusions: This study suggests the potential for neurological AEs, including memory impairment, associated with tofacitinib and ruxolitinib use based on a real-world database.

Developmental outcome in infancy after epilepsy surgery and its associated factors: A systematic review and meta-analysis

OBJECTIVE

To investigate the impact of epilepsy surgery on the developmental outcome in infancy with pharmacoresistant epilepsy and its associated factors.

METHOD

This systematic review and meta-analysis was conducted in adherence with PRISMA 2020. Literature searching was done using PubMed, CENTRAL, and Scopus database. The risk of bias within included studies was evaluated using ROBINS-I. The developmental outcome was explored by comparing the developmental quotient (DQ) between before and after the epilepsy surgery. The subgroup analysis was planned for sex, etiology, affected side, affected lobe, surgical method and intention, and seizure-free state after the surgery. Age at onset of epilepsy, age at surgery, duration of disease, and follow-up time were explored as well in meta-regression.

RESULT

Ten articles were included in this review yielded 361 participants. The overall meta-analysis did not show a significant change of DQ after the surgery (MD -2.38; 95%CI -5.53 - 0.78). The comparison of delta DQ between seizure-free and not seizure-free population was not significantly different (seizure-free group; MD -4.33; 95%CI -20.37 - 11.70 vs. non-seizure-free group; MD -4.34; 95%CI -16.22 - 7.54). No independent significant moderator was identified.

CONCLUSION

Epilepsy surgery may offer some benefits in infants with PRE despite most participants having stable developmental progress. Seizure-free state following epilepsy surgery is crucial for infants' development; however, not all epileptogenic lesions are located in the favourable and resectable area. Hence, seizure control with palliative surgery shall be offered.

Cellular Cholesterol Loss Impairs Synaptic Vesicle Mobility via the CAMK2/Synapsin-1 Signaling Pathway

BACKGROUND

Neuronal cholesterol deficiency may contribute to the synaptopathy observed in Alzheimer's disease (AD). However, the underlying mechanisms remain poorly understood. Intact synaptic vesicle (SV) mobility is crucial for normal synaptic function, whereas disrupted SV mobility can trigger the synaptopathy associated with AD. In this study, we investigated whether cellular cholesterol deficiency affects SV mobility, with the aim of identifying the mechanism that links cellular cholesterol loss to synaptopathy in AD.

METHODS

Lentiviruses carrying 3β-hydroxysteroid-Δ24 reductase-complementary DNA (DHCR24-cDNA), DHCR24-short hairpin RNA (DHCR24- shRNA) or empty lentiviral vectors were transfected into SHSY-5Y cells in order to construct DHCR24 knock-down and knock-in models, along with corresponding controls. Filipin III cholesterol staining was employed to visualize membrane and intracellular cholesterol in the different cell models, and fluorescence intensity was assessed using confocal microscopy. Additionally, we performed immunoblotting to quantify the expression of DHCR24, total calmodulin-dependent protein kinase 2 (CAMK-2), p-CAMK2 (T286), caveolin-1, total synapsin-1, phosphorylated synapsin-1 (p-synapsin-1; S605), and synaptophysin in each experimental group.

RESULTS

In DHCR24-silenced cells, the loss of cellular cholesterol caused by knock-down of DCHR24 resulted in a significant decrease in the levels of phosphorylated CAMK2 (p-CAMK2) and phosphorylated synapsin-1 (p-synapsin-1) compared to control cells. The reduction in p-CAMK2 and p-synapsin-1 could disrupt SV mobility, thereby reducing replenishment of the readily releasable pool (RRP) from the reserve pool (RP). Furthermore, cells with DHCR24 knock-down showed downregulation of caveolin-1, a crucial lipid raft marker, compared to control cells. Conversely, elevated cellular cholesterol levels caused by knock-in of DHCR24 reversed the effects of cholesterol deficiency, suggesting that CAMK2-mediated synapsin-1 phosphorylation may be regulated in a lipid raft-associated manner. Additionally, we found that cellular cholesterol loss could significantly downregulate the expression of synaptophysin protein, which is vital for SV biogenesis and synaptic plasticity.

CONCLUSION

These results suggest that depletion of cellular cholesterol following knock-down of DHCR24 can decrease synaptophysin protein expression and impair SV mobility by regulating the CAMK2-meditated synapsin-1 phosphorylation pathway, potentially via a lipid raft-associated mechanism. Our study indicates a critical role for cellular cholesterol deficiency in AD-related synaptopathy, thus highlighting the potential for targeting cellular cholesterol metabolism in therapeutic strategies.

Research advances on CaMKs-mediated neurodevelopmental injury

Calcium/calmodulin-dependent protein kinases (CaMKs) are important proteins in the calcium signaling cascade response pathway, which can broadly regulate biological functions in vivo. Multifunctional CaMKs play key roles in neural development, including neuronal circuit building, synaptic plasticity establishment, and neurotrophic factor secretion. Currently, four familial proteins, calcium/calmodulin-dependent protein kinase I (CaMKI), calcium/calmodulin-dependent protein kinase II (CaMKII), eukaryotic elongation factor 2 kinase (eEF2K, popularly known as CaMKIII) and calcium/calmodulin-dependent protein kinase IV (CaMKIV), are thought to have been the most extensively studied during neurodevelopment. Although their spatial structures are extremely similar, as well as the initial starting point of activation, both require the activation of calcium and calmodulin (CaM) complexes to be involved in the process, and the phosphorylation sites and modes of each member are different. Furthermore, due to the high structural similarity of CaMKs, their members may play synergistic roles in the regulation of neural development, but different CaMKs also have their own means of regulating neural development. In this review, we first describe the visualized protein structural forms of CaMKI, CaMKII, eEF2K and CaMKIV, and then describe the functions of each kinase in neurodevelopment. After that, we focus on four main mechanisms of neurodevelopmental damage caused by CaMKs: CaMKI/ERK/CREB pathway inhibition leading to dendritic spine structural damage; Ca2+/CaM/CaMKII through induction of mitochondrial kinetic disorders leading to neurodevelopmental damage; CaMKIII/eEF2 hyperphosphorylation affects the establishment of synaptic plasticity; and CaMKIV/JNK/NF-κB through induction of an inflammatory response leading to neurodevelopmental damage. In conclusion, we briefly discuss the pathophysiological significance of aberrant CaMK family expression in neurodevelopmental disorders, as well as the protective effects of conventional CaMKII and CaMKIII antagonists against neurodevelopmental injury.

LTP expression mediated by autonomous activity of GluN2B-bound CaMKII

Learning and memory are thought to require the induction and maintenance of long-term potentiation (LTP) of synaptic strength. LTP induction requires the Ca2+/calmodulin-dependent protein kinase II (CaMKII) but for structural rather than enzymatic functions. We show that the relevant structural function is regulated by CaMKII binding to the NMDA-type glutamate receptor subunit GluN2B. This binding directly generates Ca2+-independent autonomous CaMKII activity, and we show that this enzymatic activity is dispensable for LTP induction (within 5 min) but required for a subsequent LTP phase (within 15 min). This requirement for CaMKII activity provides an objective temporal definition for the intermediary phase of LTP expression. Later LTP maintenance may still require structural functions of GluN2B-bound CaMKII but not the resulting enzymatic CaMKII activity or their co-condensation. Thus, autonomous CaMKII activity mediates post-induction LTP but (1) via GluN2B binding, not T286 autophosphorylation, and (2) during the intermediary expression phase rather than for long-term maintenance.

Neuroplasticity in the transition from acute to chronic pain

Acute pain is a transient sensation that typically serves as part of the body's defense mechanism. However, in certain patients, acute pain can evolve into chronic pain, which persists for months or even longer. Neuroplasticity refers to the capacity for variation and adaptive alterations in the morphology and functionality of neurons and synapses, and it plays a significant role in the transmission and modulation of pain. In this paper, we explore the molecular mechanisms and signaling pathways underlying neuroplasticity during the transition of pain. We also examine the effects of neurotransmitters, inflammatory mediators, and central sensitization on neuroplasticity, as well as the potential of neuroplasticity as a therapeutic strategy for preventing chronic pain. The aims of this article is to clarify the role of neuroplasticity in the transformation from acute pain to chronic pain, with the hope of providing a novel theoretical basis for unraveling the pathogenesis of chronic pain and offering more effective strategies and approaches for its diagnosis and treatment.

Effects of Kv1.3 knockout on pyramidal neuron excitability and synaptic plasticity in piriform cortex of mice

Kv1.3 belongs to the voltage-gated potassium (Kv) channel family, which is widely expressed in the central nervous system and associated with a variety of neuropsychiatric disorders. Kv1.3 is highly expressed in the olfactory bulb and piriform cortex and involved in the process of odor perception and nutrient metabolism in animals. Previous studies have explored the function of Kv1.3 in olfactory bulb, while the role of Kv1.3 in piriform cortex was less known. In this study, we investigated the neuronal changes of piriform cortex and feeding behavior after smell stimulation, thus revealing a link between the olfactory sensation and body weight in Kv1.3 KO mice. Coronal slices including the anterior piriform cortex were prepared, whole-cell recording and Ca2+ imaging of pyramidal neurons were conducted. We showed that the firing frequency evoked by depolarization pulses and Ca2+ influx evoked by high K+ solution were significantly increased in pyramidal neurons of Kv1.3 knockout (KO) mice compared to WT mice. Western blotting and immunofluorescence analyses revealed that the downstream signaling molecules CaMKII and PKCα were activated in piriform cortex of Kv1.3 KO mice. Pyramidal neurons in Kv1.3 KO mice exhibited significantly reduced paired-pulse ratio and increased presynaptic Cav2.1 expression, proving that the presynaptic vesicle release might be elevated by Ca2+ influx. Using Golgi staining, we found significantly increased dendritic spine density of pyramidal neurons in Kv1.3 KO mice, supporting the stronger postsynaptic responses in these neurons. In olfactory recognition and feeding behavior tests, we showed that Kv1.3 conditional knockout or cannula injection of 5-(4-phenoxybutoxy) psoralen, a Kv1.3 channel blocker, in piriform cortex both elevated the olfactory recognition index and altered the feeding behavior in mice. In summary, Kv1.3 is a key molecule in regulating neuronal activity of the piriform cortex, which may lay a foundation for the treatment of diseases related to piriform cortex and olfactory detection.

Synaptic rearrangement of NMDA receptors controls memory engram formation and malleability in the cortex

Initially hippocampal dependent, memory representations rely on a broadly distributed cortical network as they mature over time. How these cortical engrams acquire stability during systems-level memory consolidation without compromising their dynamic nature remains unclear. We identified a highly responsive "consolidation switch" in the synaptic composition of N-methyl-d-aspartate receptors (NMDARs), which dictates the progressive embedding and persistence of enduring memories in the rat cortex. Cortical GluN2B subunit-containing NMDARs were preferentially recruited upon encoding of associative olfactory memory to support neuronal allocation of memory engrams. As consolidation proceeds, a learning-induced redistribution of GluN2B subunit-containing NMDARs outward synapses increased synaptic GluN2A subunit contribution and enabled stabilization of remote memories. In contrast, synaptic reincorporation of GluN2B subunits occurred during subsequent forgetting. By manipulating the surface distribution of GluN2A and GluN2B subunit-containing NMDARs at cortical synapses, we uncovered that the rearrangement of GluN2B-containing NMDARs constitutes an essential tuning mechanism that determines the fate of cortical memory engrams and controls their malleability.

Nanocurcumin prevents memory impairment, hippocampal apoptosis, Akt and CaMKII-α signaling disruption in the central STZ model of Alzheimer's disease in rat

The central route of streptozotocin (STZ) administration has been introduced as a rat model of sporadic Alzheimer's disease (AD). Curcumin was suggested to possess possible neuroprotective effects, which may be profitable in AD. However, the low bioavailability of curcumin hinders its beneficial effects in clinical studies. Earlier studies suggested that a bovine serum albumin-based nanocurcumin, produces superior neuroprotective effects compared to natural curcumin. In the present study, the protective effect of nanocurcumin in rat model of central STZ induced memory impairment was assessed. In addition, due to the importance of the hippocampus in memory, the amounts of hippocampal active caspase-3, Akt, and CaMKII-α were evaluated. Adult male Wistar rats weighing 250-300 g were used. STZ (icv) was injected during days 1 and 3 (3 mg/kg in divided), and nanocurcumin or curcumin 50 mg/kg/oral gavage was administered daily during days 4-14. Morris water maze training was performed on days 15-17, and the retention memory test was achieved on the 18th day. Following memory assessment, the rats were sacrificed and the hippocampi were used to assess caspase-3 cleavage, Akt, and CaMKII-α signaling. The findings revealed that nanocurcumin ingestion (but not natural curcumin) in the dose of 50 mg/kg was capable to prevent the impairment of water maze learning and memory induced by central STZ. Molecular assessments indicated that STZ treatment increased the caspase-3 cleavage in the hippocampus while deactivating Akt and CaMKII-α. Nanocurcumin reduced caspase-3 cleavage to a non-significant level compared to control group and restored Akt and CaMKII-α within the hippocampus while natural curcumin exerted no significant effect. These findings might suggest that nanocurcumin can restore memory deficit, hippocampal apoptosis as well as Akt and CaMKII-α signaling disruption associated with brain insulin resistance.

Myosin Va-dependent Transport of NMDA Receptors in Hippocampal Neurons

N-methyl-D-aspartate receptor (NMDAR) trafficking is a key process in the regulation of synaptic efficacy and brain function. However, the molecular mechanism underlying the surface transport of NMDARs is largely unknown. Here we identified myosin Va (MyoVa) as the specific motor protein that traffics NMDARs in hippocampal neurons. We found that MyoVa associates with NMDARs through its cargo binding domain. This association was increased during NMDAR surface transport. Knockdown of MyoVa suppressed NMDAR transport. We further demonstrated that Ca2+/calmodulin-dependent protein kinase II (CaMKII) regulates NMDAR transport through its direct interaction with MyoVa. Furthermore, MyoVa employed Rab11 family-interacting protein 3 (Rab11/FIP3) as the adaptor proteins to couple themselves with NMDARs during their transport. Accordingly, the knockdown of FIP3 impairs hippocampal memory. Together, we conclude that in hippocampal neurons, MyoVa conducts active transport of NMDARs in a CaMKII-dependent manner.

CaMKIIα mediates spermidine-induced memory enhancement in rats: A potential involvement of PKA/CREB pathway

Memory consolidation is associated with the regulation of protein kinases, which impact synaptic functions and promote synaptogenesis. The administration of spermidine (SPD) has been shown to modulate major protein kinases associated with memory improvement, including the Ca2+-dependent protein kinase (PKC) and cAMP-dependent protein kinase (PKA), key players in the cAMP response element-binding protein (CREB) activation. Nevertheless, the initial mechanism underlying SPD-mediated memory consolidation remains unknown, as we hypothesize a potential involvement of the memory consolidation precursor, Ca2+/calmodulin-dependent protein kinase II-α (CaMKIIα), in this process. Based on this, our study aimed to investigate potential interactions among PKC, PKA, and CREB activation, mediated by CaMKIIα activation, in order to elucidate the SPD memory consolidation pathway. Our findings suggest that the post-training administration of the CaMKII inhibitor, KN-62 (0.25 nmol, intrahippocampal), prevented the memory enhancement induced by SPD (0.2 nmol, intrahippocampal) in the inhibitory avoidance task. Through western immunoblotting, we observed that phosphorylation of CaMKIIα in the hippocampus was facilitated 15 min after intrahippocampal SPD administration, resulting in the activation of PKA and CREB, 180 min after infusion, suggesting a possible sequential mechanism, since SPD with KN-62 infusion leads to a downregulation in CaMKIIα/PKA/CREB pathway. However, KN-62 does not alter the memory-facilitating effect of SPD on PKC, possibly demonstrating a parallel cascade in memory acquisition via PKA, without modulating CAMKIIα. These results suggest that memory enhancement induced by SPD administration involves crosstalk between CaMKIIα and PKA/CREB, with no PKC interaction.

Biophysical Modeling of Synaptic Plasticity

Dendritic spines are small, bulbous compartments that function as postsynaptic sites and undergo intense biochemical and biophysical activity. The role of the myriad signaling pathways that are implicated in synaptic plasticity is well studied. A recent abundance of quantitative experimental data has made the events associated with synaptic plasticity amenable to quantitative biophysical modeling. Spines are also fascinating biophysical computational units because spine geometry, signal transduction, and mechanics work in a complex feedback loop to tune synaptic plasticity. In this sense, ideas from modeling cell motility can inspire us to develop multiscale approaches for predictive modeling of synaptic plasticity. In this article, we review the key steps in postsynaptic plasticity with a specific focus on the impact of spine geometry on signaling, cytoskeleton rearrangement, and membrane mechanics. We summarize the main experimental observations and highlight how theory and computation can aid our understanding of these complex processes.

KIBRA anchoring the action of PKMζ maintains the persistence of memory

How can short-lived molecules selectively maintain the potentiation of activated synapses to sustain long-term memory? Here, we find kidney and brain expressed adaptor protein (KIBRA), a postsynaptic scaffolding protein genetically linked to human memory performance, complexes with protein kinase Mzeta (PKMζ), anchoring the kinase's potentiating action to maintain late-phase long-term potentiation (late-LTP) at activated synapses. Two structurally distinct antagonists of KIBRA-PKMζ dimerization disrupt established late-LTP and long-term spatial memory, yet neither measurably affects basal synaptic transmission. Neither antagonist affects PKMζ-independent LTP or memory that are maintained by compensating PKCs in ζ-knockout mice; thus, both agents require PKMζ for their effect. KIBRA-PKMζ complexes maintain 1-month-old memory despite PKMζ turnover. Therefore, it is not PKMζ alone, nor KIBRA alone, but the continual interaction between the two that maintains late-LTP and long-term memory.

CaMKII autophosphorylation is the only enzymatic event required for synaptic memory

Ca2+/calmodulin (CaM)-dependent kinase II (CaMKII) plays a critical role in long-term potentiation (LTP), a well-established model for learning and memory through the enhancement of synaptic transmission. Biochemical studies indicate that CaMKII catalyzes a phosphotransferase (kinase) reaction of both itself (autophosphorylation) and of multiple downstream target proteins. However, whether either type of phosphorylation plays any role in the synaptic enhancing action of CaMKII remains hotly contested. We have designed a series of experiments to define the minimal requirements for the synaptic enhancement by CaMKII. We find that autophosphorylation of T286 and further binding of CaMKII to the GluN2B subunit are required both for initiating LTP and for its maintenance (synaptic memory). Once bound to the NMDA receptor, the synaptic action of CaMKII occurs in the absence of target protein phosphorylation. Thus, autophosphorylation and binding to the GluN2B subunit are the only two requirements for CaMKII in synaptic memory.

Monomeric pilose antler peptide improves depression-like behavior in mice by inhibiting FGFR3 protein expression

ETHNOPHARMACOLOGICAL RELEVANCE

It has been found that pilose antler peptide has an antidepressant effect on depression. However, the exact molecular mechanism of its antidepressant effect is still unclear.

AIM OF THE STUDY

The study sought to determine the impact of monomeric pilose antler peptide (PAP; sequence LVLVEAELRE) on depression as well as investigate potential molecular mechanisms.

MATERIALS AND METHODS

Chronic unexpected mild stress (CUMS) was used to establish the model, and the effect of PAP on CUMS mice was detected by the behavioral test. The influence of PAP on neuronal cells and dendritic spine density was observed by immunofluorescence and Golgi staining. FGFR3 and the CaMKII-associated pathway were identified using quantitative real-time polymerase chain reaction, and Western blot analysis was utilized to measure their proteins and gene expression levels. Molecular docking and microscale thermophoresis were applied to detect the binding of PAP and FGFR3. Finally, the effect of FGFR3's overexpression on PAP treatment of depression was detected.

RESULTS

PAP alleviated the changes in depressive behavior induced by CUMS, promoted the growth of nerve cells, and the density of dendritic spines was increased to its original state. PAP therapy successfully downregulated the expression of FGFR3 and ERK1/2 while upregulating the expression of CREB, BDNF, and CaMKII.

CONCLUSION

Based on the current research, PAP has a therapeutic effect on depression brought on by CUMS by inhibiting FGFR3 expression and enhancing synaptic plasticity.

Anoxia-induced hippocampal LTP is regeneratively produced by glutamate and nitric oxide from the neuro-glial-endothelial axis

Transient anoxia causes amnesia and neuronal death. This is attributed to enhanced glutamate release and modeled as anoxia-induced long-term potentiation (aLTP). aLTP is mediated by glutamate receptors and nitric oxide (·NO) and occludes stimulation-induced LTP. We identified a signaling cascade downstream of ·NO leading to glutamate release and a glutamate-·NO loop regeneratively boosting aLTP. aLTP in entothelial ·NO synthase (eNOS)-knockout mice and blocking neuronal NOS (nNOS) activity suggested that both nNOS and eNOS contribute to aLTP. Immunostaining result showed that eNOS is predominantly expressed in vascular endothelia. Transient anoxia induced a long-lasting Ca2+ elevation in astrocytes that mirrored aLTP. Blocking astrocyte metabolism or depletion of the NMDA receptor ligand D-serine abolished eNOS-dependent aLTP, suggesting that astrocytic Ca2+ elevation stimulates D-serine release from endfeet to endothelia, thereby releasing ·NO synthesized by eNOS. Thus, the neuro-glial-endothelial axis is involved in long-term enhancement of glutamate release after transient anoxia.

Rapid sequential clustering of NMDARs, CaMKII, and AMPARs upon activation of NMDARs at developing synapses

Rapid, synapse-specific neurotransmission requires the precise alignment of presynaptic neurotransmitter release and postsynaptic receptors. How postsynaptic glutamate receptor accumulation is induced during maturation is not well understood. We find that in cultures of dissociated hippocampal neurons at 11 days in vitro (DIV) numerous synaptic contacts already exhibit pronounced accumulations of the pre- and postsynaptic markers synaptotagmin, synaptophysin, synapsin, bassoon, VGluT1, PSD-95, and Shank. The presence of an initial set of AMPARs and NMDARs is indicated by miniature excitatory postsynaptic currents (mEPSCs). However, AMPAR and NMDAR immunostainings reveal rather smooth distributions throughout dendrites and synaptic enrichment is not obvious. We found that brief periods of Ca2+ influx through NMDARs induced a surprisingly rapid accumulation of NMDARs within 1 min, followed by accumulation of CaMKII and then AMPARs within 2-5 min. Postsynaptic clustering of NMDARs and AMPARs was paralleled by an increase in their mEPSC amplitudes. A peptide that blocked the interaction of NMDAR subunits with PSD-95 prevented the NMDAR clustering. NMDAR clustering persisted for 3 days indicating that brief periods of elevated glutamate fosters permanent accumulation of NMDARs at postsynaptic sites in maturing synapses. These data support the model that strong glutamatergic stimulation of immature glutamatergic synapses results in a fast and substantial increase in postsynaptic NMDAR content that required NMDAR binding to PSD-95 or its homologues and is followed by recruitment of CaMKII and subsequently AMPARs.

Rem2 interacts with CaMKII at synapses and restricts long-term potentiation in hippocampus

Synaptic plasticity, the process whereby neuronal connections are either strengthened or weakened in response to stereotyped forms of stimulation, is widely believed to represent the molecular mechanism that underlies learning and memory. The holoenzyme CaMKII plays a well-established and critical role in the induction of a variety of forms of synaptic plasticity such as long-term potentiation (LTP), long-term depression (LTD) and depotentiation. Previously, we identified the GTPase Rem2 as a potent, endogenous inhibitor of CaMKII. Here, we report that knock out of Rem2 enhances LTP at the Schaffer collateral to CA1 synapse in hippocampus, consistent with an inhibitory action of Rem2 on CaMKII in vivo. Further, re-expression of WT Rem2 rescues the enhanced LTP observed in slices obtained from Rem2 conditional knock out (cKO) mice, while expression of a mutant Rem2 construct that is unable to inhibit CaMKII in vitro fails to rescue increased LTP. In addition, we demonstrate that CaMKII and Rem2 interact in dendritic spines using a 2pFLIM-FRET approach. Taken together, our data lead us to propose that Rem2 serves as a brake on runaway synaptic potentiation via inhibition of CaMKII activity. Further, the enhanced LTP phenotype we observe in Rem2 cKO slices reveals a previously unknown role for Rem2 in the negative regulation of CaMKII function.

Advancements in the study of synaptic plasticity and mitochondrial autophagy relationship

Synapses serve as the points of communication between neurons, consisting primarily of three components: the presynaptic membrane, synaptic cleft, and postsynaptic membrane. They transmit signals through the release and reception of neurotransmitters. Synaptic plasticity, the ability of synapses to undergo structural and functional changes, is influenced by proteins such as growth-associated proteins, synaptic vesicle proteins, postsynaptic density proteins, and neurotrophic growth factors. Furthermore, maintaining synaptic plasticity consumes more than half of the brain's energy, with a significant portion of this energy originating from ATP generated through mitochondrial energy metabolism. Consequently, the quantity, distribution, transport, and function of mitochondria impact the stability of brain energy metabolism, thereby participating in the regulation of fundamental processes in synaptic plasticity, including neuronal differentiation, neurite outgrowth, synapse formation, and neurotransmitter release. This article provides a comprehensive overview of the proteins associated with presynaptic plasticity, postsynaptic plasticity, and common factors between the two, as well as the relationship between mitochondrial energy metabolism and synaptic plasticity.

Unraveling the complex relationship between prenatal alcohol exposure, hippocampal LTP, and learning and memory

Prenatal alcohol exposure (PAE) has been extensively studied for its profound impact on neurodevelopment, synaptic plasticity, and cognitive outcomes. While PAE, particularly at moderate levels, has long-lasting cognitive implications for the exposed individuals, there remains a substantial gap in our understanding of the precise mechanisms underlying these deficits. This review provides a framework for comprehending the neurobiological basis of learning and memory processes that are negatively impacted by PAE. Sex differences, diverse PAE protocols, and the timing of exposure are explored as potential variables influencing the diverse outcomes of PAE on long-term potentiation (LTP). Additionally, potential interventions, both pharmacological and non-pharmacological, are reviewed, offering promising avenues for mitigating the detrimental effects of PAE on cognitive processes. While significant progress has been made, further research is required to enhance our understanding of how prenatal alcohol exposure affects neural plasticity and cognitive functions and to develop effective therapeutic interventions for those impacted. Ultimately, this work aims to advance the comprehension of the consequences of PAE on the brain and cognitive functions.

Comparative Hippocampal Proteome and Phosphoproteome in a Niemann-Pick, Type C1 Mouse Model Reveal Insights into Disease Mechanisms

Niemann-Pick disease, type C (NPC) is a neurodegenerative, lysosomal storage disorder in individuals carrying two mutated copies of either the NPC1 or NPC2 gene. Consequently, impaired cholesterol recycling and an array of downstream events occur. Interestingly, in NPC, the hippocampus displays lysosomal lipid storage but does not succumb to progressive neurodegeneration as significantly as other brain regions. Since defining the neurodegeneration mechanisms in this disease is still an active area of research, we use mass spectrometry to analyze the overall proteome and phosphorylation pattern changes in the hippocampal region of a murine model of NPC. Using 3 week old mice representing an early disease time point, we observed changes in the expression of 47 proteins, many of which are consistent with the previous literature. New to this study, changes in members of the SNARE complex, including STX7, VTI1B, and VAMP7, were identified. Furthermore, we identified that phosphorylation of T286 on CaMKIIα and S1303 on NR2B increased in mutant animals, even at the late stage of the disease. These phosphosites are crucial to learning and memory and can trigger neuronal death by altering protein-protein interactions.

Mitochondrial protein prohibitin promotes learning memory recovery in mice following intracerebral hemorrhage via CAMKII/CRMP signaling pathway

Prohibitin (PHB) is a mitochondrial inner membrane protein with neuroprotective, antioxidant, and apoptosis-reducing effects. This study aimed to explore the role of PHB in pathological symptoms, behavioral deficits, and cognitive impairment in a collagenase-IV-induced intracerebral hemorrhage (ICH) murine model. In this study, mice that received collagenase IV injection were pretreated with PHB or saline 21 days prior to modeling. The role of PHB in memory and learning ability was monitored using the Morris water maze, Y-maze, and rotarod, social, startle, and nest-building tests. The effect of PHB on depression-like symptoms was examined using the forced swimming, tail suspension, and sucrose preference tests. Subsequently, mouse samples were analyzed using immunohistochemistry, western blotting, Perls staining, Nissl staining, and gene sequencing. Results showed that collagenase IV significantly induced behavioral deficits, brain edema, cognitive impairment, and depressive symptoms. PHB overexpression effectively alleviated memory, learning, and motor deficits in mice with ICH. PHB markedly inhibited the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling-positive cells and protein levels of ionized calcium-binding adapter molecule 1, glial fibrillary acidic protein, and interleukin-1β in the perihematomal region of ICH mice. PHB overexpression also remarkably promoted production of neurologin1 (NLGL1), and upregulated levels of Ca2+-calmodulin-dependent kinase II (CaMKII) and collapsin response mediator protein-1 (CRMP1) proteins. In conclusion, PHB overexpression can effectively alleviate the neurological deficits and neurodegeneration around the hematoma region. This may play a protective role by upregulating the expression of NLGL1 and promoting expression of CaMKII and CRMP1.

Cationic peptides erase memories by removing synaptic AMPA receptors through endophilin-mediated endocytosis

Administration of the Zeta Inhibitory Peptide (ZIP) interferes with memory maintenance and long-term potentiation (LTP). However, mice lacking its putative target, the protein kinase PKMζ, exhibit normal learning and memory as well as LTP, making ZIP's mechanism unclear. Here, we show that ZIP disrupts LTP by removing surface AMPA receptors through its cationic charge alone. This effect was fully blocked by drugs that block macropinocytosis and is dependent on endophilin A2 (endoA2)-mediated endocytosis. ZIP and other cationic peptides selectively removed newly inserted AMPAR nanoclusters, providing a mechanism by which these peptides erase memories without effects on basal synaptic function. Lastly, cationic peptides can be administered locally and/or systemically and can be combined with local microinjection of macropinocytosis inhibitors to modulate memories on local and brain-wide scales. Our findings have critical implications for an entire field of memory mechanisms and highlight a previously unappreciated mechanism by which memories can be lost.

Controlling the interaction between CaMKII and Calmodulin with a photocrosslinking unnatural amino acid

Using unnatural amino acid mutagenesis, we made a mutant of CaMKII that forms a covalent linkage to Calmodulin upon illumination by UV light. Like wild-type CaMKII, the L308BzF mutant stoichiometrically binds to Calmodulin, in a calcium-dependent manner. Using this construct, we demonstrate that Calmodulin binding to CaMKII, even under these stochiometric conditions, does not perturb the CaMKII oligomeric state. Furthermore, we were able to achieve activation of CaMKII L308BzF by UV-induced binding of Calmodulin, which, once established, is further insensitive to calcium depletion. In addition to the canonical auto-inhibitory role of the regulatory segment, inter-subunit crosslinking in the absence of CaM indicates that kinase domains and regulatory segments are substantially mobile in basal conditions. Characterization of CaMKIIL308BzF in vitro, and its expression in mammalian cells, suggests it could be a promising candidate for control of CaMKII activity in mammalian cells with light.

Excitation-transcription coupling, neuronal gene expression and synaptic plasticity

Excitation-transcription coupling (E-TC) links synaptic and cellular activity to nuclear gene transcription. It is generally accepted that E-TC makes a crucial contribution to learning and memory through its role in underpinning long-lasting synaptic enhancement in late-phase long-term potentiation and has more recently been linked to late-phase long-term depression: both processes require de novo gene transcription, mRNA translation and protein synthesis. E-TC begins with the activation of glutamate-gated N-methyl-D-aspartate-type receptors and voltage-gated L-type Ca2+ channels at the membrane and culminates in the activation of transcription factors in the nucleus. These receptors and ion channels mediate E-TC through mechanisms that include long-range signalling from the synapse to the nucleus and local interactions within dendritic spines, among other possibilities. Growing experimental evidence links these E-TC mechanisms to late-phase long-term potentiation and learning and memory. These advances in our understanding of the molecular mechanisms of E-TC mean that future efforts can focus on understanding its mesoscale functions and how it regulates neuronal network activity and behaviour in physiological and pathological conditions.

Sevoflurane anaesthesia induces cognitive impairment in young mice through sequential tau phosphorylation

BACKGROUND

The volatile anaesthetic sevoflurane induces time (single or multiple exposures)-dependent effects on tau phosphorylation and cognitive function in young mice. The underlying mechanism for this remains largely undetermined.

METHODS

Mice received 3% sevoflurane for 0.5 h or 2 h daily for 3 days on postnatal day (P) 6, 9, and 12. Another group of mice received 3% sevoflurane for 0.5 h or 1.5 h (3 × 0.5) on P6. We investigated effects of sevoflurane anaesthesia on tau phosphorylation on P6 or P12 mice, on cognitive function from P31 to P37, and on protein interactions, using in vivo studies, in vitro phosphorylation assays, and nanobeam single-molecule level interactions in vitro.

RESULTS

An initial sevoflurane exposure induced CaMKIIα phosphorylation (132 [11]% vs 100 [6]%, P<0.01), leading to tau phosphorylation at serine 262 (164 [7]% vs 100 [26]%, P<0.01) and tau detachment from microtubules. Subsequent exposures to the sevoflurane induced GSK3β activation, which phosphorylated detached or free tau (tau phosphorylated at serine 262) at serine 202 and threonine 205, resulting in cognitive impairment in young mice. In vitro phosphorylation assays also demonstrated sequential tau phosphorylation. Nanobeam analysis of molecular interactions showed different interactions between tau or free tau and CaMKIIα or GSK3β, and between tau and tubulin at a single-molecule level.

CONCLUSIONS

Multiple exposures to sevoflurane can induce sequential tau phosphorylation, leading to cognitive impairment in young mice, highlighting the need to investigate the underlying mechanisms of anaesthesia-induced tau phosphorylation in developing brain.

Synaptic memory and CaMKII

Ca2+/calmodulin-dependent protein kinase II (CaMKII) and long-term potentiation (LTP) were discovered within a decade of each other and have been inextricably intertwined ever since. However, like many marriages, it has had its up and downs. Based on the unique biochemical properties of CaMKII, it was proposed as a memory molecule before any physiological linkage was made to LTP. However, as reviewed here, the convincing linkage of CaMKII to synaptic physiology and behavior took many decades. New technologies were critical in this journey, including in vitro brain slices, mouse genetics, single-cell molecular genetics, pharmacological reagents, protein structure, and two-photon microscopy, as were new investigators attracted by the exciting challenge. This review tracks this journey and assesses the state of this marriage 40 years on. The collective literature impels us to propose a relatively simple model for synaptic memory involving the following steps that drive the process: 1) Ca2+ entry through N-methyl-d-aspartate (NMDA) receptors activates CaMKII. 2) CaMKII undergoes autophosphorylation resulting in constitutive, Ca2+-independent activity and exposure of a binding site for the NMDA receptor subunit GluN2B. 3) Active CaMKII translocates to the postsynaptic density (PSD) and binds to the cytoplasmic C-tail of GluN2B. 4) The CaMKII-GluN2B complex initiates a structural rearrangement of the PSD that may involve liquid-liquid phase separation. 5) This rearrangement involves the PSD-95 scaffolding protein, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), and their transmembrane AMPAR-regulatory protein (TARP) auxiliary subunits, resulting in an accumulation of AMPARs in the PSD that underlies synaptic potentiation. 6) The stability of the modified PSD is maintained by the stability of the CaMKII-GluN2B complex. 7) By a process of subunit exchange or interholoenzyme phosphorylation CaMKII maintains synaptic potentiation in the face of CaMKII protein turnover. There are many other important proteins that participate in enlargement of the synaptic spine or modulation of the steps that drive and maintain the potentiation. In this review we critically discuss the data underlying each of the steps. As will become clear, some of these steps are more firmly grounded than others, and we provide suggestions as to how the evidence supporting these steps can be strengthened or, based on the new data, be replaced. Although the journey has been a long one, the prospect of having a detailed cellular and molecular understanding of learning and memory is at hand.

The CaMKII Inhibitory Peptide AIP Alleviates Renal Fibrosis Through the TGF-β/Smad and RAF/ERK Pathways

Renal fibrosis is characterized by the excessive deposition of extracellular matrix that destroys and replaces the functional renal parenchyma, ultimately leading to organ failure. It is a common pathway by which chronic kidney disease can develop into end-stage renal disease, which has high global morbidity and mortality, and there are currently no good therapeutic agents available. Calcium/calmodulin-dependent protein kinase II (CaMKII) has been indicated to be closely related to the occurrence of renal fibrosis, and its specific inhibitory peptide, autocamtide-2-related inhibitory peptide (AIP), was shown to directly bind the active site of CaMKII. In this study, we examined the effect of AIP on the progression of renal fibrosis and its possible mechanism. The results showed that AIP could inhibit the expression of the fibrosis markers fibronectin, collagen I, matrix metalloproteinase 2, and α-smooth muscle actin in vivo and in vitro. Further analysis revealed that AIP could inhibit the expression of various epithelial-to-mesenchymal transformation-related markers, such as vimentin and Snail 1, in vivo and in vitro. Mechanistically, AIP could significantly inhibit the activation of CaMKII, Smad 2, Raf, and extracellular regulated protein kinases (ERK) in vitro and in vivo and reduce the expression of transforming growth factor-β (TGF-β) in vivo. These results suggested that AIP could alleviate renal fibrosis by inhibiting CaMKII and blocking activation of the TGF-β/Smad2 and RAF/ERK pathways. Our study provides a possible drug candidate and demonstrates that CaMKII is a potential pharmacological target for the treatment of renal fibrosis. SIGNIFICANCE STATEMENT: We have demonstrated that AIP significantly attenuated transforming growth factor-β-1-induced fibrogenesis and ameliorated unilateral ureteral obstruction-induced renal fibrosis through the CaMKII/TGF-β/Smad and CaMKII/RAF/ERK signaling pathways in vitro and in vivo. Our study provides a possible drug candidate and demonstrates that CaMKII can be a potential pharmacological target for the treatment of renal fibrosis.

CaMKII autophosphorylation but not downstream kinase activity is required for synaptic memory

CaMKII plays a critical role in long-term potentiation (LTP), a well-established model for learning and memory through the enhancement of synaptic transmission. Biochemical studies indicate that CaMKII catalyzes a phosphotransferase (kinase) reaction of both itself (autophosphorylation) and of multiple downstream target proteins. However, whether either type of phosphorylation plays any role in the synaptic enhancing action of CaMKII remains hotly contested. We have designed a series of experiments to define the minimal requirements for the synaptic enhancement by CaMKII. We find that autophosphorylation of T286 and further binding of CaMKII to the GluN2B subunit are required both for initiating LTP and for its maintenance (synaptic memory). Once bound to the NMDA receptor, the synaptic action of CaMKII occurs in the absence of kinase activity. Thus, autophosphorylation, together with binding to the GluN2B subunit, are the only two requirements for CaMKII in synaptic memory.

CaMKII autophosphorylation can occur between holoenzymes without subunit exchange

The dodecameric protein kinase CaMKII is expressed throughout the body. The alpha isoform is responsible for synaptic plasticity and participates in memory through its phosphorylation of synaptic proteins. Its elaborate subunit organization and propensity for autophosphorylation allow it to preserve neuronal plasticity across space and time. The prevailing hypothesis for the spread of CaMKII activity, involving shuffling of subunits between activated and naive holoenzymes, is broadly termed subunit exchange. In contrast to the expectations of previous work, we found little evidence for subunit exchange upon activation, and no effect of restraining subunits to their parent holoenzymes. Rather, mass photometry, crosslinking mass spectrometry, single molecule TIRF microscopy and biochemical assays identify inter-holoenzyme phosphorylation (IHP) as the mechanism for spreading phosphorylation. The transient, activity-dependent formation of groups of holoenzymes is well suited to the speed of neuronal activity. Our results place fundamental limits on the activation mechanism of this kinase.

Mechanisms of mGluR-dependent plasticity in hippocampal area CA2

Pyramidal cells in hippocampal area CA2 have synaptic properties that are distinct from the other CA subregions. Notably, this includes a lack of typical long-term potentiation of stratum radiatum synapses. CA2 neurons express high levels of several known and potential regulators of metabotropic glutamate receptor (mGluR)-dependent signaling including Striatal-Enriched Tyrosine Phosphatase (STEP) and several Regulator of G-protein Signaling (RGS) proteins, yet the functions of these proteins in regulating mGluR-dependent synaptic plasticity in CA2 are completely unknown. Thus, the aim of this study was to examine mGluR-dependent synaptic depression and to determine whether STEP and the RGS proteins RGS4 and RGS14 are involved. Using whole cell voltage-clamp recordings from mouse pyramidal cells, we found that mGluR agonist-induced long-term depression (mGluR-LTD) is more pronounced in CA2 compared with that observed in CA1. This mGluR-LTD in CA2 was found to be protein synthesis and STEP dependent, suggesting that CA2 mGluR-LTD shares mechanistic processes with those seen in CA1, but in addition, RGS14, but not RGS4, was essential for mGluR-LTD in CA2. In addition, we found that exogenous application of STEP could rescue mGluR-LTD in RGS14 KO slices. Supporting a role for CA2 synaptic plasticity in social cognition, we found that RGS14 KO mice had impaired social recognition memory as assessed in a social discrimination task. These results highlight possible roles for mGluRs, RGS14, and STEP in CA2-dependent behaviors, perhaps by biasing the dominant form of synaptic plasticity away from LTP and toward LTD in CA2.

Mitogen- and stress-activated protein kinase (MSK1/2) regulated gene expression in normal and disease states

The mitogen- and stress-activated protein kinases (MSK) are epigenetic modifiers that regulate gene expression in normal and disease cell states. MSK1 and 2 are involved in a chain of signal transduction events bringing signals from the external environment of a cell to specific sites in the genome. MSK1/2 phosphorylate histone H3 at multiple sites, resulting in chromatin remodeling at regulatory elements of target genes and the induction of gene expression. Several transcription factors (RELA of NF-κB and CREB) are also phosphorylated by MSK1/2 and contribute to induction of gene expression. In response to signal transduction pathways, MSK1/2 can stimulate genes involved in cell proliferation, inflammation, innate immunity, neuronal function, and neoplastic transformation. Abrogation of the MSK-involved signaling pathway is among the mechanisms by which pathogenic bacteria subdue the host's innate immunity. Depending on the signal transduction pathways in play and the MSK-targeted genes, MSK may promote or hinder metastasis. Thus, depending on the type of cancer and genes involved, MSK overexpression may be a good or poor prognostic factor. In this review, we focus on mechanisms by which MSK1/2 regulate gene expression, and recent studies on their roles in normal and diseased cells.

A synaptic amplifier of hunger for regaining body weight in the hypothalamus

Restricting caloric intake effectively reduces body weight, but most dieters fail long-term adherence to caloric deficit and eventually regain lost weight. Hypothalamic circuits that control hunger drive critically determine body weight; yet, how weight loss sculpts these circuits to motivate food consumption until lost weight is regained remains unclear. Here, we probe the contribution of synaptic plasticity in discrete excitatory afferents on hunger-promoting AgRP neurons. We reveal a crucial role for activity-dependent, remarkably long-lasting amplification of synaptic activity originating from paraventricular hypothalamus thyrotropin-releasing (PVHTRH) neurons in long-term body weight control. Silencing PVHTRH neurons inhibits the potentiation of excitatory input to AgRP neurons and diminishes concomitant regain of lost weight. Brief stimulation of the pathway is sufficient to enduringly potentiate this glutamatergic hunger synapse and triggers an NMDAR-dependent gaining of body weight that enduringly persists. Identification of this activity-dependent synaptic amplifier provides a previously unrecognized target to combat regain of lost weight.

COVID-19-induced neurological symptoms: focus on the role of metal ions

Neurological symptoms are prevalent in both the acute and post-acute phases of coronavirus disease 2019 (COVID-19), and they are becoming a major concern for the prognosis of COVID-19 patients. Accumulation evidence has suggested that metal ion disorders occur in the central nervous system (CNS) of COVID-19 patients. Metal ions participate in the development, metabolism, redox and neurotransmitter transmission in the CNS and are tightly regulated by metal ion channels. COVID-19 infection causes neurological metal disorders and metal ion channels abnormal switching, subsequently resulting in neuroinflammation, oxidative stress, excitotoxicity, neuronal cell death, and eventually eliciting a series of COVID-19-induced neurological symptoms. Therefore, metal homeostasis-related signaling pathways are emerging as promising therapeutic targets for mitigating COVID-19-induced neurological symptoms. This review provides a summary for the latest advances in research related to the physiological and pathophysiological functions of metal ions and metal ion channels, as well as their role in COVID-19-induced neurological symptoms. In addition, currently available modulators of metal ions and their channels are also discussed. Collectively, the current work offers a few recommendations according to published reports and in-depth reflections to ameliorate COVID-19-induced neurological symptoms. Further studies need to focus on the crosstalk and interactions between different metal ions and their channels. Simultaneous pharmacological intervention of two or more metal signaling pathway disorders may provide clinical advantages in treating COVID-19-induced neurological symptoms.

Differential roles of CaMKII isoforms in phase separation with NMDA receptors and in synaptic plasticity

Calcium calmodulin-dependent kinase II (CaMKII) is critical for synaptic transmission and plasticity. Two major isoforms of CaMKII, CaMKIIα and CaMKIIβ, play distinct roles in synaptic transmission and long-term potentiation (LTP) with unknown mechanisms. Here, we show that the length of the unstructured linker between the kinase domain and the oligomerizing hub determines the ability of CaMKII to rescue the basal synaptic transmission and LTP defects caused by removal of both CaMKIIα and CaMKIIβ (double knockout [DKO]). Remarkably, although CaMKIIβ binds to GluN2B with a comparable affinity as CaMKIIα does, only CaMKIIα with the short linker forms robust dense clusters with GluN2B via phase separation. Lengthening the linker of CaMKIIα with unstructured "Gly-Gly-Ser" repeats impairs its phase separation with GluN2B, and the mutant enzyme cannot rescue the basal synaptic transmission and LTP defects of DKO mice. Our results suggest that the phase separation capacity of CaMKII with GluN2B is critical for its cellular functions in the brain.

Voltage-Gated T-Type Calcium Channel Modulation by Kinases and Phosphatases: The Old Ones, the New Ones, and the Missing Ones

Calcium (Ca2+) can regulate a wide variety of cellular fates, such as proliferation, apoptosis, and autophagy. More importantly, changes in the intracellular Ca2+ level can modulate signaling pathways that control a broad range of physiological as well as pathological cellular events, including those important to cellular excitability, cell cycle, gene-transcription, contraction, cancer progression, etc. Not only intracellular Ca2+ level but the distribution of Ca2+ in the intracellular compartments is also a highly regulated process. For this Ca2+ homeostasis, numerous Ca2+ chelating, storage, and transport mechanisms are required. There are also specialized proteins that are responsible for buffering and transport of Ca2+. T-type Ca2+ channels (TTCCs) are one of those specialized proteins which play a key role in the signal transduction of many excitable and non-excitable cell types. TTCCs are low-voltage activated channels that belong to the family of voltage-gated Ca2+ channels. Over decades, multiple kinases and phosphatases have been shown to modulate the activity of TTCCs, thus playing an indirect role in maintaining cellular physiology. In this review, we provide information on the kinase and phosphatase modulation of TTCC isoforms Cav3.1, Cav3.2, and Cav3.3, which are mostly described for roles unrelated to cellular excitability. We also describe possible potential modulations that are yet to be explored. For example, both mitogen-activated protein kinase and citron kinase show affinity for different TTCC isoforms; however, the effect of such interaction on TTCC current/kinetics has not been studied yet.

Crosstalk between biochemical signalling network architecture and trafficking governs AMPAR dynamics in synaptic plasticity

Synaptic plasticity involves modification of both biochemical and structural components of neurons. Many studies have revealed that the change in the number density of the glutamatergic receptor AMPAR at the synapse is proportional to synaptic weight update; an increase in AMPAR corresponds to strengthening of synapses while a decrease in AMPAR density weakens synaptic connections. The dynamics of AMPAR are thought to be regulated by upstream signalling, primarily the calcium-CaMKII pathway, trafficking to and from the synapse, and influx from extrasynaptic sources. Previous work in the field of deterministic modelling of CaMKII dynamics has assumed bistable kinetics, while experiments and rule-based modelling have revealed that CaMKII dynamics can be either monostable or ultrasensitive. This raises the following question: how does the choice of model assumptions involving CaMKII dynamics influence AMPAR dynamics at the synapse? To answer this question, we have developed a set of models using compartmental ordinary differential equations to systematically investigate contributions of different signalling and trafficking variations, along with their coupled effects, on AMPAR dynamics at the synaptic site. We find that the properties of the model including network architecture describing different stability features of CaMKII and parameters that capture the endocytosis and exocytosis of AMPAR significantly affect the integration of fast upstream species by slower downstream species. Furthermore, we predict that the model outcome, as determined by bound AMPAR at the synaptic site, depends on (1) the choice of signalling model (bistable CaMKII or monostable CaMKII dynamics), (2) trafficking versus influx contributions and (3) frequency of stimulus. KEY POINTS: The density of AMPA receptors (AMPARs) at the postsynaptic density of the synapse provides a readout of synaptic plasticity, which involves crosstalk between complex biochemical signalling networks including CaMKII dynamics and trafficking pathways including exocytosis and endocytosis. Here we build a model that integrates CaMKII dynamics and AMPAR trafficking to explore this crosstalk. We compare different models of CaMKII that result in monostable or bistable kinetics and their impact on AMPAR dynamics. Our results show that AMPAR density depends on the coupling between aspects of biochemical signalling and trafficking. Specifically, assumptions regarding CaMKII dynamics and its stability features can alter AMPAR density at the synapse. Our model also predicts that the kinetics of trafficking versus influx of AMPAR from the extrasynaptic space can further impact AMPAR density. Thus, the contributions of both signalling and trafficking should be considered in computational models.

Exploring molecular signatures related to the mechanism of aging in different brain regions by integrated bioinformatics

The mechanism of brain aging is not fully understood. Few studies have attempted to identify molecular changes using bioinformatics at the subregional level in the aging brain. This study aimed to identify the molecular signatures and key genes involved in aging, depending on the brain region. Differentially expressed genes (DEGs) associated with aging of the cerebral cortex (CX), hippocampus (HC), and cerebellum (CB) were identified based on five datasets from the Gene Expression Omnibus (GEO). The molecular signatures of aging were explored using functional and pathway analyses. Hub genes of each brain region were determined by protein-protein interaction network analysis, and commonly expressed DEGs (co-DEGs) were also found. Gene-microRNAs (miRNAs) and gene-disease interactions were constructed using online databases. The expression levels and regional specificity of the hub genes and co-DEGs were validated using animal experiments. In total, 32, 293, and 141 DEGs were identified in aging CX, HC, and CB, respectively. Enrichment analysis indicated molecular changes related to leukocyte invasion, abnormal neurotransmission, and impaired neurogenesis due to inflammation as the major signatures of the CX, HC, and CB. Itgax is a hub gene of cortical aging. Zfp51 and Zfp62 were identified as hub genes involved in hippocampal aging. Itgax and Cxcl10 were identified as hub genes involved in cerebellar aging. S100a8 was the only co-DEG in all three regions. In addition, a series of molecular changes associated with inflammation was observed in all three brain regions. Several miRNAs interact with hub genes and S100a8. The change in gene levels was further validated in an animal experiment. Only the upregulation of Zfp51 and Zfp62 was restricted to the HC. The molecular signatures of aging exhibit regional differences in the brain and seem to be closely related to neuroinflammation. Itgax, Zfp51, Zfp62, Cxcl10, and S100a8 may be key genes and potential targets for the prevention of brain aging.

Unraveling the mysteries of dendritic spine dynamics: Five key principles shaping memory and cognition

Recent research extends our understanding of brain processes beyond just action potentials and chemical transmissions within neural circuits, emphasizing the mechanical forces generated by excitatory synapses on dendritic spines to modulate presynaptic function. From in vivo and in vitro studies, we outline five central principles of synaptic mechanics in brain function: P1: Stability - Underpinning the integral relationship between the structure and function of the spine synapses. P2: Extrinsic dynamics - Highlighting synapse-selective structural plasticity which plays a crucial role in Hebbian associative learning, distinct from pathway-selective long-term potentiation (LTP) and depression (LTD). P3: Neuromodulation - Analyzing the role of G-protein-coupled receptors, particularly dopamine receptors, in time-sensitive modulation of associative learning frameworks such as Pavlovian classical conditioning and Thorndike's reinforcement learning (RL). P4: Instability - Addressing the intrinsic dynamics crucial to memory management during continual learning, spotlighting their role in "spine dysgenesis" associated with mental disorders. P5: Mechanics - Exploring how synaptic mechanics influence both sides of synapses to establish structural traces of short- and long-term memory, thereby aiding the integration of mental functions. We also delve into the historical background and foresee impending challenges.

Tilianin improves cognition in a vascular dementia rodent model by targeting miR-193b-3p/CaM- and miR-152-3p/CaMKIIα-mediated inflammatory and apoptotic pathways

Introduction

Although vascular dementia (VaD) is the second most prevalent form of dementia, there is currently a lack of effective treatments. Tilianin, isolated from the traditional drug Dracocephalum moldavica L., may protect against ischemic injury by inhibiting oxidative stress and inflammation via the CaMKII-related pathways but with weak affinity with the CaMKII molecule. microRNAs (miRNAs), functioning in post-transcriptional regulation of gene expression, may play a role in the pathological process of VaD via cognitive impairment, neuroinflammatory response, and neuronal dysfunction. This study aimed to investigate the role of tilianin in VaD therapy and the underlying mechanism through which tilianin regulates CaMKII signaling pathways based on miRNA-associated transcriptional action.

Methods

Rats with 2-vessel occlusion (2VO), a standard model of VaD, were treated with tilianin, vehicle control, and target overexpression or downregulation. High-throughput sequencing, qRT-PCR, and western blot analyses were utilized to identify the downstream target genes and signaling pathways of tilianin involved in VaD.

Results

Our results showed that tilianin ameliorated cognitive deficits, neurodegeneration, and microglial and astrocytic activation in rats with 2VO. Subsequent high-throughput sequencing and qRT-PCR analyses revealed that tilianin increased the downregulated miR-193b-3p and miR-152-3p levels in the cortex and hippocampus of 2VO rats. Mechanistically, miR-193b-3p targeting CaM and miR-152-3p targeting CaMKIIα were identified to play a role in VaD-associated pathology, inhibiting the p38 MAPK/NF--κB p65 pathway and decreasing TNF-α and IL-6 levels. Further gain- and loss-of-function experiments for these key genes showed that tilianin-exerted cognitive improvement by activating the p38 MAPK/NF--κB p65 and Bcl-2/Bax/caspase-3/PARP pathways in the brain of 2VO rats was abolished by miR-193b-3p and miR-152-3p inhibition. Moreover, CaM and CaMKIIα overexpression eliminated the elevated effects of miR-193b-3p and miR-152-3p on tilianin's protection against ischemic injury through increased inflammatory reactions and apoptotic signaling.

Discussion

Together, these findings indicate that tilianin improves cognition by regulating the miR-193b-3p/CaM- and miR-152-3p/CaMKIIα-mediated inflammatory and apoptotic pathways, suggesting a potential small-molecule regulator of miRNA associated with inflammatory signaling for VaD treatment.

Hippocampus Insulin Receptors Regulate Episodic and Spatial Memory Through Excitatory/Inhibitory Balance

It is well known that the hippocampus is a vital brain region playing a key role in both episodic and spatial memory. Insulin receptors (InsRs) are densely distributed in the hippocampus and are important for its function. However, the effects of InsRs on the function of the specific hippocampal cell types remain elusive. In this study, hippocampal InsRs knockout mice had impaired episodic and spatial memory. GABAergic neurons and glutamatergic neurons in the hippocampus are involved in the balance between excitatory and inhibitory (E/I) states and participate in the processes of episodic and spatial memory. InsRs are located mainly at excitatory neurons in the hippocampus, whereas 8.5% of InsRs are glutamic acid decarboxylase 2 (GAD2)::Ai9-positive (GABAergic) neurons. Next, we constructed a transgenic mouse system in which InsR expression was deleted from GABAergic (glutamate decarboxylase 2::InsRfl/fl, GAD2Cre::InsRfl/fl) or glutamatergic neurons (vesicular glutamate transporter 2::InsRfl/fl,Vglut2Cre::InsRfl/fl). Our results showed that in comparison to the InsRfl/fl mice, both episodic and spatial memory were lower in GAD2Cre::InsRfl/fl and Vglut2Cre::InsRfl/fl. In addition, both GAD2Cre::InsRfl/fl and Vglut2Cre::InsRfl/fl were associated with more anxiety and lower glucose tolerance. These findings reveal that hippocampal InsRs might be crucial for episodic and spatial memory through E/I balance hippocampal regulation.

The role of calcium and CaMKII in sleep

Sleep is an evolutionarily conserved phenotype shared by most of the animals on the planet. Prolonged wakefulness will result in increased sleep need or sleep pressure. However, its mechanisms remain elusive. Recent findings indicate that Ca²⁺ signaling, known to control diverse physiological functions, also regulates sleep. This review intends to summarize research advances in Ca²⁺ and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) in sleep regulation. Significant changes in sleep phenotype have been observed through calcium-related channels, receptors, and pumps. Mathematical modeling for neuronal firing patterns during NREM sleep suggests that these molecules compose a Ca²⁺-dependent hyperpolarization mechanism. The intracellular Ca²⁺ may then trigger sleep induction and maintenance through the activation of CaMKII, one of the sleep-promoting kinases. CaMKII and its multisite phosphorylation status may provide a link between transient calcium dynamics typically observed in neurons and sleep-wake dynamics observed on the long-time scale.

Synaptic memory survives molecular turnover

Activation of Ca²⁺/calmodulin-dependent kinase II (CaMKII) plays a critical role in long-term potentiation (LTP), a long accepted cellular model for learning and memory. However, how LTP and memories survive the turnover of synaptic proteins, particularly CaMKII, remains a mystery. Here, we take advantage of the finding that constitutive Ca²⁺-independent CaMKII activity, acquired prior to slice preparation, provides a lasting memory trace at synapses. In slice culture, this persistent CaMKII activity, in the absence of Ca²⁺ stimulation, remains stable over a 2-wk period, well beyond the turnover of CaMKII protein. We propose that the nascent CaMKII protein present at 2 wk acquired its activity from preexisting active CaMKII molecules, which transferred their activity to newly synthesized CaMKII molecules and thus maintain the memory in the face of protein turnover.

Triphenyl phosphate disturbs placental tryptophan metabolism and induces neurobehavior abnormal in male offspring

Epidemiological studies have shown that prenatal triphenyl phosphate (TPhP) exposure is related to abnormal neurobehavior in children. However, the neurodevelopmental toxicity of TPhP in mammals is limited. To study the neurodevelopmental toxicity of TPhP in mammals and investigate the underlying mechanism, we used a mouse intrauterine TPhP exposure model. We measured the inflammatory factors (IL-6, TNFα) and NFκB levels, and tryptophan metabolism in placentae, detected the fetal brain transcriptome, hippocampal neuron development and neurobehavioral in the male offspring. The results showed that the protein level of IL-6, TNFα and NFκB in the placenta of the TPhP treatment group (1, 5 mg/kg) were significantly increased. Change of the protein level of these pro-inflammatory factors in maternal serum or fetal brain was not observed. Expression of genes along tryptophan-serotonin metabolism pathway were significantly decreased. While, the concentration of 5-HT levels in the placenta or fetal brain were significantly increased. Consistent with the increased 5-HT, the Nissl body was reduced in the hippocampus of treatment group. The expression of serotonergic neuron gene markers including Tph2, Htr1A, Htr2A, Pet1 and Lmx1b in the hippocampus of treatment group was significantly decreased. The neurobehavioral test showed that TPhP decreased center time that represent anxiety-like behavior, and reduced learning and memory in male offspring. Meanwhile, expression of genes along tryptophan-kynurenine metabolism pathway were significantly increased. The result of the transcriptome analysis of fetal brain showed that the differentially expressed genes are mainly involved in the transcription regulation of DNA as a template in the nucleus, and the enriched pathways are mainly signal pathways regulated by axon guidance and neurotrophic factors, dopaminergic and cholinergic synapses, suggest that not only serotonergic neuronal was affected. Overall, this study demonstrates that TPhP has the potential to induce placental inflammatory response in the placenta, disturb placental tryptophan metabolism, compromise the neuronal development and synaptic transmission, and cause abnormal neurobehavior in male offspring.

CaMKII: a central molecular organizer of synaptic plasticity, learning and memory

Calcium-calmodulin (CaM)-dependent protein kinase II (CaMKII) is the most abundant protein in excitatory synapses and is central to synaptic plasticity, learning and memory. It is activated by intracellular increases in calcium ion levels and triggers molecular processes necessary for synaptic plasticity. CaMKII phosphorylates numerous synaptic proteins, thereby regulating their structure and functions. This leads to molecular events crucial for synaptic plasticity, such as receptor trafficking, localization and activity; actin cytoskeletal dynamics; translation; and even transcription through synapse-nucleus shuttling. Several new tools affording increasingly greater spatiotemporal resolution have revealed the link between CaMKII activity and downstream signalling processes in dendritic spines during synaptic and behavioural plasticity. These technologies have provided insights into the function of CaMKII in learning and memory.