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Segregating glutamate receptor trafficking function from the changes in synaptic spine morphology, this study finds that actin depolymerizing factor (ADF)- and cofilin-mediated actin dynamics control AMPAR trafficking during chemically induced long-term potentiation independent of actin's structural role. Dendritic spines undergo actin-based growth and shrinkage during synaptic plasticity, in which the actin depolymerizing factor (ADF)/cofilin family of actin-associated proteins are important. Elevated ADF/cofilin activities often lead to reduced spine size and immature spine morphology but can also enhance synaptic potentiation in some cases. Thus, ADF/cofilin may have distinct effects on postsynaptic structure and function. We found that ADF/cofilin-mediated actin dynamics regulated AMPA receptor (AMPAR) trafficking during synaptic potentiation, which was distinct from actin's structural role in spine morphology. Specifically, elevated ADF/cofilin activity markedly enhanced surface addition of AMPARs after chemically induced long-term potentiation (LTP), whereas inhibition of ADF/cofilin abolished AMPAR addition. We found that chemically induced LTP elicited a temporal sequence of ADF/cofilin dephosphorylation and phosphorylation that underlies AMPAR trafficking and spine enlargement. These findings suggest that temporally regulated ADF/cofilin activities function in postsynaptic modifications of receptor number and spine size during synaptic plasticity.

Background GABA A receptors are ligand-gated Cl - channels, and the intracellular Cl - concentration governs whether GABA function is excitatory or inhibitory. During early brain development, GABA undergoes functional switch from excitation to inhibition: GABA depolarizes immature neurons but hyperpolarizes mature neurons due to a developmental decrease of intracellular Cl - concentration. This GABA functional switch is mainly mediated by the up-regulation of KCC2, a potassium-chloride cotransporter that pumps Cl - outside neurons. However, the upstream factor that regulates KCC2 expression is unclear. Results We report here that KCC2 is unexpectedly regulated by neuroligin-2 (NL2), a cell adhesion molecule specifically localized at GABAergic synapses. The expression of NL2 precedes that of KCC2 in early postnatal development. Upon knockdown of NL2, the expression level of KCC2 is significantly decreased, and GABA functional switch is significantly delayed during early development. Overexpression of shRNA-proof NL2 rescues both KCC2 reduction and delayed GABA functional switch induced by NL2 shRNAs. Moreover, NL2 appears to be required to maintain GABA inhibitory function even in mature neurons, because knockdown NL2 reverses GABA action to excitatory. Gramicidin-perforated patch clamp recordings confirm that NL2 directly regulates the GABA equilibrium potential. We further demonstrate that knockdown of NL2 decreases dendritic spines through down-regulating KCC2. Conclusions Our data suggest that in addition to its conventional role as a cell adhesion molecule to regulate GABAergic synaptogenesis, NL2 also regulates KCC2 to modulate GABA functional switch and even glutamatergic synapses. Therefore, NL2 may serve as a master regulator in balancing excitation and inhibition in the brain.

Human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can provide sources for midbrain dopaminergic (mDA) neural progenitors (NPCs) for cell therapy to treat Parkinson’s disease (PD) patients. However, the well-known line-to-cell line variability in the differentiation capacity of individual cell lines needs to be improved for the success of this therapy. To address this issue, we sought to identify mDA NPC specific cell surface markers for fluorescence activated cell sorting (FACS). Through RNA isolation after sorting for NPCs based on staining for cell-specific transcription factors followed by microarray, we identified two positive cell surface markers (CORIN and CD166) and one negative cell surface marker (CXCR4) for mDA NPC sorting. These three markers can enrich floor plate NPCs to 90% purity, and the sorted NPCs more efficiently differentiate to mature dopaminergic neurons compared to unsorted or CORIN + alone mDA NPCs. This surface marker identification strategy can be used broadly to facilitate isolation of cell subtypes of interest from heterogeneous cultures.

A delicate balance between excitation and inhibition is crucial for brain functions, and the disturbance of this balance is an emerging hypothesis underlying many neuropsychiatric disorders. Neuroligins are a family of cell adhesion molecules found at the postsynaptic sites of both excitatory glutamatergic and inhibitory GABAergic synapses. The trans-synaptic interactions between neuroligins and their presynaptic receptor neurexins regulate synapse formation and function. Accumulating genetic studies have implicated neuroligin mutations in neuropsychiatric disorders, such as autism spectrum disorders. However, the functional relevance of neuroligins and the molecular mechanisms of their contribution to disease onset are largely unknown. First, I investigated the functional defects of novel neuroligin-2 mutations linked to schizophrenia. Among neuroligins, neuroligin-2 is selectively localized at GABAergic synapses and is critical for regulating inhibitory synaptic transmission. Since GABAergic deficits have been implicated in schizophrenia by both human postmortem and genetic studies, we hypothesized that neuroligin-2 is a potential risk gene for schizophrenia. In a cohort of 584 schizophrenia patients, we identified novel neuroligin-2 missense point mutations. Among them, I identified R215H as a loss-of-function mutation applying a heterologous GABAergic synapse induction assay. The R215H mutant was defective in mediating cell adhesion and in promoting GABAergic synapse formation. Mechanistically, the R215H mutant showed significantly reduced cell surface expression possibly due to incomplete glycosylation. My work suggests that defect in GABAergic synapse formation may be a potential risk factor for schizophrenia. In the second part of my thesis, I reported a novel function of neuroligin-2 in regulating GABA functional switch from excitation to inhibition through KCC2. KCC2 is a neuron specific potassium-chloride co-transporter that exports chloride. The developmental up-regulation of KCC2 mediates GABA functional switch by decreasing intracellular chloride concentration. Surprisingly, KCC2 expression was significantly reduced after knockdown of neuroligin-2 by shRNA-mediated RNA interference. As functional consequences of decreased KCC2, knockdown of neuroligin-2 abolished GABA functional switch in developing neurons and reversed GABA action to excitatory in mature neurons. Overexpression of shRNA proof neuroligin-2, but not neuroligin-1, rescued both decreased KCC2 expression and delayed GABA functional switch induced by shRNAs. Using gramicidin-perforated patch clamp recordings, I further demonstrated that neuroligin-2 expression level directly regulates GABA equilibrium potential. It has been reported that knockdown of neuroligin-2 decreased the number of both GABAergic and glutamatergic synapses, but the mechanism was unknown. I showed that KCC2 overexpression rescued glutamatergic synapse loss induced by knockdown of neuroligin- 2, suggesting that neuroligin-2 regulates glutamatergic synapses through KCC2. In summary, my findings uncovered a new function of neuroligin-2 in regulating GABA functional switch and glutamatergic synapse formation. Therefore, in addition to its conventional role of cell adhesion at GABAergic synapses, neuroligin-2 may serve as a master regulator in balancing excitation and inhibition in the brain. Dysfunctions of neuroligin-2 may cause excitation/inhibition imbalance and contribute to the etiology of neuropsychiatric disorders, as indicated by the case of neuroligin-2 R215H mutant in schizophrenia.

Fragile X Syndrome (FXS) is the most common genetic form of intellectual disability caused by a CGG repeat expansion in the 5′-UTR of the Fragile X mental retardation gene FMR1, triggering epigenetic silencing and the subsequent absence of the protein, FMRP. Reactivation of FMR1 represents an attractive therapeutic strategy targeting the genetic root cause of FXS. However, largely missing in the FXS field is an understanding of how much FMR1 reactivation is required to rescue FMRP-dependent mutant phenotypes. Here, we utilize FXS patient derived excitatory neurons to model FXS in vitro and confirm that the absence of FMRP leads to neuronal hyperactivity. We further determined the levels of FMRP and the percentage of FMRP positive cells necessary to correct this phenotype utilizing a mixed and mosaic neuronal culture system and a combination of CRISPR, antisense and expression technologies to titrate FMRP in FXS and WT neurons. Our data demonstrate that restoration of greater than 5% of overall FMRP expression levels or greater than 20% FMRP expressing neurons in a mosaic pattern is sufficient to normalize a FMRP-dependent, hyperactive phenotype in FXS iPSC-derived neurons. Footnotes * Minor grammatical changes

The decomposed plastic products in the natural environment evolve into tiny plastic particles with characteristics such as small size, lightweight, and difficulty in removal, resulting in a significant pollution issue in aquatic environments. Significant progress has been made in microplastic separation technology benefiting from microfluidic chips in recent years. Based on the mechanisms of microfluidic control technology, this study investigates the enrichment and separation mechanisms of polystyrene particles in an unbuffered solution. The Faraday reaction caused by the bipolar electrodes changes the electric field gradient and improves the separation efficiency. We also propose  an evaluation scheme to measure the separation efficiency. Finite element simulations are conducted to parametrically analyze the influence of applied voltages, channel geometry, and size of electrodes on plastic particle separation. The numerical cases indicate that the electrode-installed microfluidic channels separate microplastic particles effectively and precisely. The electrodes play an important role in local electric field distribution and trigger violent chemical reactions. By optimizing the microchannel structure, applied voltages, and separation channel angle, an optimal solution for separating microplastic particles can be found. This study could supply some references to control microplastic pollution in the future.

This study presents an experimental investigation into the dynamic response and blast resistance of aluminum foam-cored sandwich panels with varied face sheet thicknesses under impulsive loading conditions. The primary focus is on analyzing how the thickness of front and back face sheets affects the deformation behavior and energy absorption capabilities of the sandwich panels. By employing a 3D digital image correlation (3D-DIC) system coupled with post-test analyses, the dynamic responses and permanent deformations were quantitatively characterized. Failure modes of the core layers, front face sheets, and back face sheets were identified and discussed. The results demonstrated that sandwich panels with thick front face sheets exhibited superior blast resistance and energy absorption performance than their thin-front counterparts under high localized impulsive loading. The findings provide important comparative insights about face sheet thickness distribution effects, though further studies with broader thickness variations are needed to establish comprehensive design guidelines.

This study explored the applicability of TRMM, TRMM nonlinear downscaling, and ANUSPLIN (ANU) interpolation of three different types of precipitation data to define regional-scale rainfall-triggered landslide thresholds. The spatial resolution of TRMM precipitation data was downscaled from 0.25° to 500 m by the downscaling model considering the relationship between humidity, NDVI, and numerous topographic factors and precipitation. The rainfall threshold was calculated using the rainfall intensity–duration threshold model. The calculation showed that TRMM downscaled precipitation data have better detection capability for extreme precipitation events than the other two, the TRMM downscaling threshold was better than the ANU interpolation, and the cumulative effective rainfall of TRMM downscaling was preferred as the macroscopic critical rainfall-triggered landslide threshold for the early warning of the Wudu. The predictive performance of the rainfall threshold of 50% was better than the other two (10% and 90%). When the probability of landslide occurrence was 50%, the TRMM downscaled threshold curve was given by I50=21.03×D−1.004. The authors also analyzed the influence of factors such as topography landform and soil type on the rainfall threshold of landslides in the study area. The rainfall intensity of small undulating mountains was higher than that of medium and large undulating mountains, and the rainfall intensity of landslides peaks at high altitude mountains of 3500–5000 m.

For an active suspension system based on a reference model, tracking errors always exist due to nonlinearity and unmodeled dynamics. This results in the difficulty of effectively achieving the reference trajectory’s acceleration in practical situations, meaning that ride comfort cannot be effectively improved. To solve this problem, the paper explores a tracking controller with dual objectives. This includes a nonlinear PD controller for tracking the desired trajectory and a sliding mode controller concerning body velocity and acceleration. This approach ensures that the body displacement approximately tracks the desired trajectory while significantly improving ride comfort. Additionally, this control method has the advantages of structural simplicity and insensitivity to tracking errors, implying that control parameters can be easily tuned, and control inputs can be effectively reduced. The stability of the controlled system is demonstrated through the Lyapunov stability theory, and a range for the body displacement tracking error is derived. Finally, the controller’s performance is tested on an experimental platform and simulation model. The experimental results indicated a substantial reduction of 69.22% and 54.66% in the root mean square values of body acceleration under bump and random excitation, respectively.

Electroosmotic flow (EOF) is a universal phenomenon in most microfluidic systems when an external electric field exists along charged channel walls. The mechanism of ion transport and fluid flow in such systems has been extensively studied, largely based on simplified models without consideration of electrode reactions and water dissociation. To study the effects of these electrochemical reactions, we build an electrokinetic model with full consideration of these processes, namely electrochemistry (EC) model, and compare its performance with that of the traditional electrokinetic (EK) model. Our results show that electrode reactions alter the electric potential and reduce the current, causing a significant reduction in EOF velocity. These potential changes and EOF reduction are driven almost entirely by electrode reactions, because the difference between the results from the EC model and those from the EK model with potential adjustment induced by chemical reactions is slight. In addition, the participation of ions in electrode reactions leads to notable alterations in their concentration within the microchannel and significant pH change, which are ignored in the traditional EK model. It is found that at a typical applied electric field of 50 V/cm, the EOF velocity in the EC model is 63% of that in the EK model. This difference in velocity decreases to only 4.0% as the EK model considers electric potential shifts caused by electrode reactions. In the microchannel, the Cl− concentration drops by approximately 50% while the OH− increases, leading to a pH growth 3.5. The results presented in this work can improve the understanding of electrode effects on the physicochemical properties of EOF systems, providing essential guidance for manipulating fluid flow and amphoteric molecular transport in various microfluidic systems.