Effect of menopausal hormonal therapy on cardiovascular risks in Korean postmenopausal women: A nationwide cohort study.

OBJECTIVE: To evaluate the association between menopausal hormonal therapy (MHT) and the risk of cardiovascular disease (CVD), according to various regimens, dosages, routes of administration and starting ages of MHT. DESIGN: A population-based cohort study using the Korean National Health Insurance Services database. SETTING: Nationwide health insurance database. POPULATION: Women who reported entering menopause at an age of ≥40 years with no history of CVD in the national health examination. METHODS: The study population comprised 1 120 705 subjects enrolled between 2002 and 2019, categorised according to MHT status (MHT group, n = 319 007; non-MHT group, n = 801 698). MAIN OUTCOME MEASURES: Incidence of CVD (a composite of myocardial infarction and stroke). RESULTS: The incidence of CVD was 59 266 (7.4%) in the non-MHT group and 17 674 (5.5%) in the MHT group. After adjusting for confounding factors, an increased risk of CVD was observed with the administration of tibolone (hazard ratio, HR 1.143, 95% CI 1.117-1.170), oral estrogen (HR 1.246, 95% CI 1.198-1.295) or transdermal estrogen (HR 1.289, 95% CI 1.066-1.558), compared with the non-MHT group; the risk was based on an increased risk of stroke. The risk trends were consistent regardless of the age of starting MHT or the physicians' specialty. Among tibolone users, a longer period from entering menopause to taking tibolone and the use of any dosage (1.25 or 2.5 mg) were linked with a higher risk of CVD, compared with non-MHT users. CONCLUSIONS: This nationwide cohort study demonstrated an increased risk of CVD, driven mainly by an increased risk of stroke, among tibolone and oral or transdermal estrogen users, compared with that of non-MHT users.

The increased risk of colorectal cancer in the women who underwent hysterectomy from the South Korean National Health Insurance Database.

BACKGROUND: Several population-based studies and observational studies have shown that oophorectomy is associated with an increased risk of colorectal cancer (CRC), and hormone replacement therapy has been associated with a reduction in the risk of colorectal cancer. This study was carried out to investigate whether hysterectomy, which may affect the levels of female hormones, is associated with a risk of cancer of the specific gastrointestinal tract. METHODS: This population-based retrospective cohort study was conducted using insurance data provided by the Health Insurance Review and Assessment Service (HIRA) from January 1, 2007, to December 31, 2020. The hysterectomy group included 40- to 59-year-old women who underwent hysterectomy with uterine leiomyoma or uterine endometriosis from January 1, 2011, to December 31, 2014. The control group included women aged 40 to 59 years who visited medical institutions for medical examination from January 1, 2011 to December 31, 2014. RESULTS: The hysterectomy and non-hysterectomhy groups comprised 66,204 and 89,768 subjects, respectively. The median ages in the non-hysterectomy group and hysterectomy group were 48 (range: 43-53) and 46 (range: 44-49) years, respectively. In the unadjusted results of the analysis, all colorectal cancer (CRC) increased in the hysterectomy alone group (HR 1.222, 95% confidence interval (CI) 1.016-1.47, p = 0.033), sigmoid colon cancer increased in the hysterectomy alone group (HR 1.71, 95% CI 1.073-2.724, p = 0.024), and rectal cancer increased in the hysterectomy with adnexal surgery group (HR 1.924, 95% CI 1.073-2.724, p = 0.002). The adjusted results showed that all CRC increased in the hysterectomy alone group (HR 1.406, 95% CI 1.057-1.871, p = 0.019), colon cancer increased in the hysterectomy alone group (HR 1.523, 95% CI 1.068-2.17, p = 0.02), and rectal cancer increased in the hysterectomy with adnexal surgery group (HR 1.933, 95% CI 1.131-3.302, p = 0.016). The all-cause mortality of GI cancer increased in the hysterectomy alone group (HR 3.495, 95% CI 1.347-9.07, p = 0.001). CONCLUSIONS: This study showed that the risk of all CRC increased in women who underwent hysterectomy compared with women who did not. In particular, the risk of rectal cancer was significantly higher in the women who underwent hysterectomy with adnexal surgery than in the controls. There was no association between hysterectomy and other GI cancers.

Depression-like behaviors induced by defective PTPRT activity through dysregulated synaptic functions and neurogenesis.

PTPRT has been known to regulate synaptic formation and dendritic arborization of hippocampal neurons. PTPRT-/- null and PTPRT-D401A mutant mice displayed enhanced depression-like behaviors compared with wild-type mice. Transient knockdown of PTPRT in the dentate gyrus enhanced the depression-like behaviors of wild-type mice, whereas rescued expression of PTPRT ameliorated the behaviors of PTPRT-null mice. Chronic stress exposure reduced expression of PTPRT in the hippocampus of mice. In PTPRT-deficient mice the expression of GluR2 (also known as GRIA2) was attenuated as a consequence of dysregulated tyrosine phosphorylation, and the long-term potentiation at perforant-dentate gyrus synapses was augmented. The inhibitory synaptic transmission of the dentate gyrus and hippocampal GABA concentration were reduced in PTPRT-deficient mice. In addition, the hippocampal expression of GABA transporter GAT3 (also known as SLC6A11) was decreased, and its tyrosine phosphorylation was increased in PTPRT-deficient mice. PTPRT-deficient mice displayed reduced numbers and neurite length of newborn granule cells in the dentate gyrus and had attenuated neurogenic ability of embryonic hippocampal neural stem cells. In conclusion, our findings show that the physiological roles of PTPRT in hippocampal neurogenesis, as well as synaptic functions, are involved in the pathogenesis of depressive disorder.

Chemotherapeutics and CAR-T Cell-Based Immunotherapeutics Screening on a 3D Bioprinted Vascularized Breast Tumor Model.

Despite substantial advancements in development of cancer treatments, lack of standardized and physiologically-relevant in vitro testing platforms limit the early screening of anticancer agents. A major barrier is the complex interplay between the tumor microenvironment and immune response. To tackle this, a dynamic-flow based 3D bioprinted multi-scale vascularized breast tumor model, responding to chemo and immunotherapeutics is developed. Heterotypic tumors are precisely bioprinted at pre-defined distances from a perfused vasculature, exhibit tumor angiogenesis and cancer cell invasion into the perfused vasculature. Bioprinted tumors treated with varying dosages of doxorubicin for 72 h portray a dose-dependent drug response behavior. More importantly, a cell based immune therapy approach is explored by perfusing HER2-targeting chimeric antigen receptor (CAR) modified CD8+ T cells for 24 or 72 h. Extensive CAR-T cell recruitment to the endothelium, substantial T cell activation and infiltration to the tumor site, resulted in up to ≈70% reduction in tumor volumes. The presented platform paves the way for a robust, precisely fabricated, and physiologically-relevant tumor model for future translation of anti-cancer therapies to personalized medicine.

Tunable near-infrared Gires-Tournois resonators based on vanadium dioxide on gold film.

Vanadium dioxide (VO2) has been proposed as a phase-change material in tunable photonic and optoelectronic devices. In such devices, a thin layer of VO2 is typically deposited on metallic or insulating surfaces. In this Letter, we report the reflectance spectra of a subwavelength structure consisting of a thin layer of VO2 deposited on a gold film in the near-infrared spectral range, particularly near the wavelength of 1550 nm, which is significant for telecommunication applications. Our results indicate that in the insulating phase of VO2, the air/VO2/Au structure can be considered as a Gires-Tournois resonant cavity whose maximum absorption wavelength can be tuned by adjusting the thickness of the VO2 layer. In contrast, in the metallic phase of VO2, the reflectance of the structure increases by an amount of the order of a few tens of units. The proposed structure can prospectively lead to new design concepts in tunable photonic and optoelectronic devices.

Kv4.1, a Key Ion Channel For Low Frequency Firing of Dentate Granule Cells, Is Crucial for Pattern Separation.

The dentate gyrus (DG) in the hippocampus may play key roles in remembering distinct episodes through pattern separation, which may be subserved by the sparse firing properties of granule cells (GCs) in the DG. Low intrinsic excitability is characteristic of mature GCs, but ion channel mechanisms are not fully understood. Here, we investigated ionic channel mechanisms for firing frequency regulation in hippocampal GCs using male and female mice, and identified Kv4.1 as a key player. Immunofluorescence analysis showed that Kv4.1 was preferentially expressed in the DG, and its expression level determined by Western blot analysis was higher at 8-week than 3-week-old mice, suggesting a developmental regulation of Kv4.1 expression. With respect to firing frequency, GCs are categorized into two distinctive groups: low-frequency (LF) and high-frequency (HF) firing GCs. Input resistance (Rin) of most LF-GCs is lower than 200 MΩ, suggesting that LF-GCs are fully mature GCs. Kv4.1 channel inhibition by intracellular perfusion of Kv4.1 antibody increased firing rates and gain of the input-output relationship selectively in LF-GCs with no significant effect on resting membrane potential and Rin, but had no effect in HF-GCs. Importantly, mature GCs from mice depleted of Kv4.1 transcripts in the DG showed increased firing frequency, and these mice showed an impairment in contextual discrimination task. Our findings suggest that Kv4.1 expression occurring at late stage of GC maturation is essential for low excitability of DG networks and thereby contributes to pattern separation.SIGNIFICANCE STATEMENT The sparse activity of dentate granule cells (GCs), which is essential for pattern separation, is supported by high inhibitory inputs and low intrinsic excitability of GCs. Low excitability of GCs is thought to be attributable to a high K+ conductance at resting membrane potentials, but this study identifies Kv4.1, a depolarization-activated K+ channel, as a key ion channel that regulates firing of GCs without affecting resting membrane potentials. Kv4.1 expression is developmentally regulated and Kv4.1 currents are detected only in mature GCs that show low-frequency firing, but not in less mature high-frequency firing GCs. Furthermore, mice depleted of Kv4.1 transcripts in the dentate gyrus show impaired pattern separation, suggesting that Kv4.1 is crucial for sparse coding and pattern separation.

Incidence and risk of venous thromboembolism according to primary treatment type in women with endometrial cancer: a population-based study.

BACKGROUND: Current prophylaxes and treatments for venous thromboembolism (VTE) in women with gynecologic cancer are mainly guided by studies on solid cancers because studies in gynecologic cancer did not provide sufficient data. Large-scale studies evaluating the incidence and risk of VTE according to therapeutic modality may guide prophylaxis and treatment of VTE in gynecologic cancer. This study was performed to determine the incidence and risk of VTE according to primary treatment type in Korean women with endometrial cancer. METHODS: We selected 26,256 women newly diagnosed with endometrial cancer between 2009 and 2018 from the Korean Health Insurance Review and Assessment Service database. During the total follow-up period and first six months after primary treatments initiation, the incidence and risk of VTE were evaluated according to primary treatment type, that is, no treatment, surgery, radiotherapy, chemotherapy, or hormone therapy. RESULTS: VTE occurred in 136 per 10,000 women during the total follow-up period and in 54 per 10,000 women during the first six months with the highest frequency in women that underwent chemotherapy. During the first year, the monthly incidence of VTE decreased with time among women that underwent no treatment, surgery, or hormone therapy and remained unchanged in those that received radiotherapy or chemotherapy. Compared with women that received no treatment, VTE risk, especially of PE significantly increased in women that underwent chemotherapy (VTE: hazard ratio (HR), 2.334; 95% CI, 1.38-3.949; P = 0.002) (PE: HR, 2.742; 95% CI, 1.424-5.278; P = 0.003) or hormone therapy (VTE: HR, 2.073; 95% CI, 1.356-3.17; P = 0.001) (PE: HR, 2.086; 95% CI, 1.19-3.657; P = 0.01) during the total follow-up period and women that underwent only chemotherapy during the first six months (VTE: HR, 2.532; 95% CI, 1.291-4.966; P = 0.007) (PE: HR, 3.366; 95% CI, 1.496-7.576; P = 0.003). CONCLUSIONS: In this cohort study, the incidence and risk of VTE were highest in women with endometrial cancer that underwent chemotherapy as a primary treatment. Notably, the incidence of VTE decreased over time in women that received no treatment, surgery, or hormone therapy. This study can help guide therapies for prophylaxis and treatment of VTE in women with endometrial cancer.

Histone demethylase PHF2 activates CREB and promotes memory consolidation.

Long-term memory formation is attributed to experience-dependent gene expression. Dynamic changes in histone methylation are essential for the epigenetic regulation of memory consolidation-related genes. Here, we demonstrate that the plant homeodomain finger protein 2 (PHF2) histone demethylase is upregulated in the mouse hippocampus during the experience phase and plays an essential role in memory formation. PHF2 promotes the expression of memory-related genes by epigenetically reinforcing the TrkB-CREB signaling pathway. In behavioral tests, memory formation is enhanced by transgenic overexpression of PHF2 in mice, but is impaired by silencing PHF2 in the hippocampus. Electrophysiological studies reveal that PHF2 elevates field excitatory postsynaptic potential (fEPSP) and NMDA receptor-mediated evoked excitatory postsynaptic current (EPSC) in CA1 pyramidal neurons, suggesting that PHF2 promotes long-term potentiation. This study provides insight into the epigenetic regulation of learning and memory formation, which advances our knowledge to improve memory in patients with degenerative brain diseases.

Dual regulatory effects of PI(4,5)P2 on TREK-2 K+ channel through antagonizing interaction between the alkaline residues (K330 and R355-357) in the cytosolic C-terminal helix.

TWIK-related two-pore domain K+ channel-2 (TREK-2) has voltageindependent activity and shows additional activation by acidic intracellular pH (pHi) via neutralizing the E332 in the cytoplasmic C terminal (Ct). We reported opposite regulations of TREK-2 by phosphatidylinositol 4,5-bisphosphate (PIP2) via the alkaline K330 and triple Arg residues (R355-357); inhibition and activation, respectively. The G334 between them appeared critical because its mutation (G334A) endowed hTREK-2 with tonic activity, similar to the mutation of the inhibitory K330 (K330A). To further elucidate the role of putative bent conformation at G334, we compared the dual mutation forms, K330A/G334A and G334A/R355-7A, showing higher and lower basal activity, respectively. The results suggested that the tonic activity of G334A owes to a dominant influence from R355-7. Since there are additional triple Arg residues (R377-9) distal to R355-7, we also examined the triple mutant (G334A/R355-7A/R377-9A) that showed tonic inhibition same with G334A/R355-7A. Despite the state of tonic inhibition, the activation by acidic pHi was preserved in both G334A/R355-7A and G334A/R355-7A/R377-9A, similar to the R355-7A. Also, the inhibitory effect of ATP could be commonly demonstrated under the activation by acidic pHi in R355-7A, G334A/R355-7A, and G334A/R355-7A/R377-9A. These results suggest that the putative bent conformation at G334 is important to set the tug-of-war between K330 and R355-7 in the PIP2-dependent regulation of TREK-2.

Lrfn2-Mutant Mice Display Suppressed Synaptic Plasticity and Inhibitory Synapse Development and Abnormal Social Communication and Startle Response.

SALM1 (SALM (synaptic adhesion-like molecule), also known as LRFN2 (leucine rich repeat and fibronectin type III domain containing), is a postsynaptic density (PSD)-95-interacting synaptic adhesion molecule implicated in the regulation of NMDA receptor (NMDAR) clustering largely based on in vitro data, although its in vivo functions remain unclear. Here, we found that mice lacking SALM1/LRFN2 (Lrfn2-/- mice) show a normal density of excitatory synapses but altered excitatory synaptic function, including enhanced NMDAR-dependent synaptic transmission but suppressed NMDAR-dependent synaptic plasticity in the hippocampal CA1 region. Unexpectedly, SALM1 expression was detected in both glutamatergic and GABAergic neurons and Lrfn2-/- CA1 pyramidal neurons showed decreases in the density of inhibitory synapses and the frequency of spontaneous inhibitory synaptic transmission. Behaviorally, ultrasonic vocalization was suppressed in Lrfn2-/- pups separated from their mothers and acoustic startle was enhanced, but locomotion, anxiety-like behavior, social interaction, repetitive behaviors, and learning and memory were largely normal in adult male Lrfn2-/- mice. These results suggest that SALM1/LRFN2 regulates excitatory synapse function, inhibitory synapse development, and social communication and startle behaviors in mice.SIGNIFICANCE STATEMENT Synaptic adhesion molecules regulate synapse development and function, which govern neural circuit and brain functions. The SALM/LRFN (synaptic adhesion-like molecule/leucine rich repeat and fibronectin type III domain containing) family of synaptic adhesion proteins consists of five known members for which the in vivo functions are largely unknown. Here, we characterized mice lacking SALM1/LRFN2 (SALM1 KO) known to associate with NMDA receptors (NMDARs) and found that these mice showed altered NMDAR-dependent synaptic transmission and plasticity, as expected, but unexpectedly also exhibited suppressed inhibitory synapse development and synaptic transmission. Behaviorally, SALM1 KO pups showed suppressed ultrasonic vocalization upon separation from their mothers and SALM1 KO adults showed enhanced responses to loud acoustic stimuli. These results suggest that SALM1/LRFN2 regulates excitatory synapse function, inhibitory synapse development, social communication, and acoustic startle behavior.

Acute Type A Aortic Dissection in a 37-Week Pregnant Patient: An Unusual Clinical Presentation.

BACKGROUND: Aortic dissection in pregnancy is relatively rare, but it is often fatal. The estimated incidence of aortic dissection in the general population is 2.9 per 100,000 person-years. Early recognition and treatment of aortic dissections are crucial for survival. Whereas the majority of patients who present with aortic dissection are older than 50 years of age and have a history of hypertension, younger patients with connective tissue disease, bicuspid aortic valves, or a family history of aortic dissection are also at increased risk for developing this condition. CASE REPORT: We report the successful diagnosis and surgical repair of an acute type A aortic dissection in a 35-year-old woman who presented to the emergency department (ED) at 37 weeks of gestation. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Emergency physicians should be alert to the possibility of aortic dissection in any pregnant woman who presents to the ED with unexplained chest, abdominal, or back pain, even those without risk factors for aortic dissection.

High efficiency near diffraction-limited mid-infrared flat lenses based on metasurface reflectarrays.

We report the first demonstration of a mid-IR reflection-based flat lens with high efficiency and near diffraction-limited focusing. Focusing efficiency as high as 80%, in good agreement with simulations (83%), has been achieved at 45° incidence angle at λ = 4.6 µm. The off-axis geometry considerably simplifies the optical arrangement compared to the common geometry of normal incidence in reflection mode which requires beam splitters. Simulations show that the effects of incidence angle are small compared to parabolic mirrors with the same NA. The use of single-step photolithography allows large scale fabrication. Such a device is important in the development of compact telescopes, microscopes, and spectroscopic designs.

Kv1.2 mediates heterosynaptic modulation of direct cortical synaptic inputs in CA3 pyramidal cells.

KEY POINTS: We investigated the cellular mechanisms underlying mossy fibre-induced heterosynaptic long-term potentiation of perforant path (PP) inputs to CA3 pyramidal cells. Here we show that this heterosynaptic potentiation is mediated by downregulation of Kv1.2 channels. The downregulation of Kv1.2 preferentially enhanced PP-evoked EPSPs which occur at distal apical dendrites. Such enhancement of PP-EPSPs required activation of dendritic Na(+) channels, and its threshold was lowered by downregulation of Kv1.2. Our results may provide new insights into the long-standing question of how mossy fibre inputs constrain the CA3 network to sparsely represent direct cortical inputs. ABSTRACT: A short high frequency stimulation of mossy fibres (MFs) induces long-term potentiation (LTP) of direct cortical or perforant path (PP) synaptic inputs in hippocampal CA3 pyramidal cells (CA3-PCs). However, the cellular mechanism underlying this heterosynaptic modulation remains elusive. Previously, we reported that repetitive somatic firing at 10 Hz downregulates Kv1.2 in the CA3-PCs. Here, we show that MF inputs induce similar somatic firing and downregulation of Kv1.2 in the CA3-PCs. The effect of Kv1.2 downregulation was specific to PP synaptic inputs that arrive at distal apical dendrites. We found that the somatodendritic expression of Kv1.2 is polarized to distal apical dendrites. Compartmental simulations based on this finding suggested that passive normalization of synaptic inputs and polarized distributions of dendritic ionic channels may facilitate the activation of dendritic Na(+) channels preferentially at distal apical dendrites. Indeed, partial block of dendritic Na(+) channels using 10 nm tetrodotoxin brought back the enhanced PP-evoked excitatory postsynaptic potentials (PP-EPSPs) to the baseline level. These results indicate that activity-dependent downregulation of Kv1.2 in CA3-PCs mediates MF-induced heterosynaptic LTP of PP-EPSPs by facilitating activation of Na(+) channels at distal apical dendrites.

Chronic non-social stress affects depressive behaviors but not anxiety in mice.

The etiology of most psychiatric disorders is still incompletely understood. However, growing evidence suggests that stress is a potent environmental risk factor for depression and anxiety. In rodents, various stress paradigms have been developed, but psychosocial stress paradigms have received more attention than non-social stress paradigms because psychosocial stress is more prevalent in humans. Interestingly, some recent studies suggest that chronic psychosocial stress and social isolation affects mainly anxiety-related behaviors in mice. However, it is unclear whether chronic non-social stress induces both depression- and anxiety-related phenotypes or induces one specific phenotype in mice. In the present study, we examined the behavioral consequences of three chronic non-social stress paradigms: chronic predictable (restraint) stress (CPS), chronic unpredictable stress (CUS), and repeated corticosterone-HBC complex injection (RCI). Each of the three paradigms induced mild to severe depression/despair-like behaviors in mice and resulted in increased immobility in a tail suspension test. However, anxiety-related phenotypes, thigmotaxis and explorative behaviors, were not changed by the three paradigms. These results suggest that depression- and anxiety-related phenotypes can be dissociated in mouse stress models and that social and non-social stressors might affect brain circuits and behaviors differently.

Relationship between menopausal hormone therapy and colorectal cancer: a cohort study utilizing the health insurance database in South Korea (HISK)-II.

OBJECTIVE: Many studies have demonstrated that menopausal hormone therapy is associated with a reduced risk for colorectal cancer. This study investigated the relationship between specific hormone therapy regimens and colorectal cancer risk in postmenopausal women in South Korea using national insurance claims data. METHODS: This population-based, retrospective cohort study used insurance data provided by the Health Insurance Review and Assessment Service between 2007 and 2020. The hormone therapy group comprised women ≥40 years of age who underwent hormone therapy for the first time between 2011 and 2014. The control group included women ≥40 years of age who visited medical institutions for menopause-related issues during the same period but did not undergo hormone therapy. RESULTS: After 1:1 propensity score matching, 153,736 women were grouped into either the hormone therapy or nonhormone therapy groups. The incidence of colorectal cancer was 46 and 53 per 100,000 person-years in the nonhormone therapy and hormone therapy groups, respectively. Hormone therapy was associated with an increased risk for colorectal cancer (hazard ratio 1.124 [95% confidence interval 1.002-1.261]). Subgroup analysis, according to hormone therapy type, revealed no significant differences in the risk of colorectal cancer for estrogen plus progestogen or estrogen therapy alone; however, tibolone was associated with an increased risk of colorectal cancer compared to nonhormone therapy (hazard ratio, 1.178 [95% confidence interval, 1.021-1.359]). CONCLUSIONS: This study found an increased risk of colorectal cancer in women receiving hormone therapy, and tibolone was significantly associated with an increased risk of colorectal cancer. However, the magnitude of the increase was small and unlikely to be of clinical significance.

Signal transducer and activator of transcription 3 (Stat3) contributes to T-cell homeostasis by regulating pro-survival Bcl-2 family genes.

The naive T-cell pool in peripheral lymphoid tissues is fairly stable in terms of number, diversity and functional capabilities in spite of the absence of prominent stimuli. This stability is attributed to continuous tuning of the composition of the T-cell pool by various homeostatic signals. Despite extensive research into the link between signal transducer and activator of transcription 3 (Stat3) and T-cell survival, little is known about how Stat3 regulates homeostasis by maintaining the required naive T-cell population in peripheral lymphoid organs. We assessed whether the elimination of Stat3 in T cells limits T-cell survival. We demonstrated that the proportion and number of single-positive thymocytes as well as T cells in the spleen and lymph nodes were significantly decreased in the Stat3-deficient group as a result of the enhanced susceptibility of Stat3-deleted T lymphocytes to apoptosis. Importantly, expression of the anti-apoptotic Bcl-2 and Bcl-xL was markedly decreased in Stat3-deleted single-positive thymocytes and T lymphocytes, suggesting that Stat3 helps to maintain the T-cell pool in the resting condition by promoting the expression of Bcl-2 family genes. These findings suggest the importance of Stat3 in the integration of homeostatic cues for the maintenance and functional tuning of the T-cell pool.

Developmental upregulation of presynaptic NCKX underlies the decrease of mitochondria-dependent posttetanic potentiation at the rat calyx of Held synapse.

The sensitivity of posttetanic potentiation (PTP) to high-frequency stimulation (HFS) steeply decays during the first 2 postnatal weeks. We investigated the underlying mechanisms for the developmental change of PTP induced by HFS (100 Hz, 2 s) at postnatal days 4-6 and 9-11 at the rat calyx of Held synapse. Low-concentration tetraphenylphosphonium (2 µM), an inhibitor of mitochondrial Na(+)/Ca(2+) exchanger, suppressed the amount of posttetanic residual Ca(2+) and PTP to a larger extent at the immature calyx synapse, indicating a developmental reduction of mitochondrial contribution to PTP. The higher amount of mitochondrial Ca(2+) uptake during HFS and consequent posttetanic residual Ca(2+) at the immature calyx of Held was associated with higher peak of HFS-induced Ca(2+) transients, most likely because the mitochondrial Ca(2+) uptake during HFS was supralinearly dependent on the presynaptic resting Ca(2+) level. Probing into the contribution of Na(+)/Ca(2+) exchangers to Ca(2+) clearance, we found a specific upregulation of the K(+)-dependent Na(+)/Ca(2+) exchanger (NCKX) activity in the mature calyx of Held. We conclude that the upregulation of NCKX limits the Ca(2+) buildup and inhibits mitochondrial Ca(2+) uptake during HFS, which in turn results in the reduction of posttetanic residual Ca(2+) and PTP at the mature calyx of Held synapse.

Synaptic removal of diacylglycerol by DGKzeta and PSD-95 regulates dendritic spine maintenance.

Diacylglycerol (DAG) is an important lipid signalling molecule that exerts an effect on various effector proteins including protein kinase C. A main mechanism for DAG removal is to convert it to phosphatidic acid (PA) by DAG kinases (DGKs). However, it is not well understood how DGKs are targeted to specific subcellular sites and tightly regulates DAG levels. The neuronal synapse is a prominent site of DAG production. Here, we show that DGKzeta is targeted to excitatory synapses through its direct interaction with the postsynaptic PDZ scaffold PSD-95. Overexpression of DGKzeta in cultured neurons increases the number of dendritic spines, which receive the majority of excitatory synaptic inputs, in a manner requiring its catalytic activity and PSD-95 binding. Conversely, DGKzeta knockdown reduces spine density. Mice deficient in DGKzeta expression show reduced spine density and excitatory synaptic transmission. Time-lapse imaging indicates that DGKzeta is required for spine maintenance but not formation. We propose that PSD-95 targets DGKzeta to synaptic DAG-producing receptors to tightly couple synaptic DAG production to its conversion to PA for the maintenance of spine density.

Down-regulation of RalBP1 expression reduces seizure threshold and synaptic inhibition in mice.

Idiopathic epilepsy is characterized by seizures without a clear etiology and is believed to have a strong genetic component but exhibits a complex inheritance pattern. Genetic factors seem to confer a low seizure threshold to susceptible individuals and thereby enhance epileptogenesis. However, the identity of susceptibility genes and the mechanisms regulating seizure threshold are still poorly understood. Here, we describe that reduced expression of RalBP1, a downstream effector of the small GTPases RalA and RalB, lowers the seizure threshold in mice. The intraperitoneal injection of the chemoconvulsant pentylenetetrazol induced more severe seizures in RalBP1 hypomorphic mice than in their wild-type littermates. The reduction of RalBP1 in the brain has no effect on neuronal excitability, but does decrease the inhibitory synaptic transmission onto CA1 pyramidal neurons. This impaired synaptic inhibition was associated with the loss of GABAergic interneurons in the CA1 subfield of the hippocampus. The present study identifies RalBP1 as a gene regulating the seizure threshold in mice and provides direct evidence for the role of RalBP1 in synaptic inhibition in vivo.