S100B dysregulation during brain development affects synaptic SHANK protein networks via alteration of zinc homeostasis
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ABSTRACT:
SUBMITTER: Daini E
PROVIDER: S-EPMC8571423 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Neuronal metal ions such as zinc are essential for brain function. In particular synaptic processes are tightly related to metal and protein homeostasis, for example through extracellular metal-binding proteins. One such protein is neuronal S100B, a calcium and zinc binding damage-associated molecular pattern (DAMP), whose chronic upregulation is associated with aging, Alzheimer's disease (AD), motor neuron disease and traumatic brain injury (TBI). Despite gained insights on the structure of S100B, it remains unclear how its calcium and zinc binding properties regulate its function on cellular level. Here we report a novel role of S100B in trace metal homeostasis, in particular the regulation of zinc levels in the brain. Our results show that S100B at increased extracellular levels is not toxic, persists at high levels, and is taken up into neurons, as shown by cell culture and biochemical analysis. Combining protein bioimaging and zinc quantitation, along with a zinc-binding impaired S100B variant, we conclude that S100B effectively scavenges zinc ions through specific binding, resulting in a redistribution of the intracellular zinc pool. Our results indicate that scavenging of zinc by increased levels of S100B affects calcium levels in vitro. Thereby S100B is able to mediate the cross talk between calcium and zinc homeostasis. Further, we investigated a possible new neuro-protective role of S100B in excitotoxicity via its effects on calcium and zinc homeostasis. Exposure of cells to zinc-S100B but not the zinc-binding impaired S100B results in an inhibition of excitotoxicity. We conclude that in addition to its known functions, S100B acts as sensor and regulator of elevated zinc levels in the brain and this metal-buffering activity is tied to a neuroprotective role.
| S-EPMC5776125 | biostudies-literature
Project description:The RNA-binding protein fused-in-sarcoma (FUS) has been associated with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), two neurodegenerative disorders that share similar clinical and pathological features. Both missense mutations and overexpression of wild-type FUS protein can be pathogenic in human patients. To study the molecular and cellular basis by which FUS mutations and overexpression cause disease, we generated novel transgenic mice globally expressing low levels of human wild-type protein (FUS(WT)) and a pathological mutation (FUS(R521G)). FUS(WT) and FUS(R521G) mice that develop severe motor deficits also show neuroinflammation, denervated neuromuscular junctions, and premature death, phenocopying the human diseases. A portion of FUS(R521G) mice escape early lethality; these escapers have modest motor impairments and altered sociability, which correspond with a reduction of dendritic arbors and mature spines. Remarkably, only FUS(R521G) mice show dendritic defects; FUS(WT) mice do not. Activation of metabotropic glutamate receptors 1/5 in neocortical slices and isolated synaptoneurosomes increases endogenous mouse FUS and FUS(WT) protein levels but decreases the FUS(R521G) protein, providing a potential biochemical basis for the dendritic spine differences between FUS(WT) and FUS(R521G) mice.
| S-EPMC4226112 | biostudies-literature
Project description:The communication of neurons is primarily maintained by synapses, which play a crucial role in the functioning of the nervous system. Therefore, synaptic failure may critically impair information processing in the brain and may underlie many neurodegenerative diseases. A number of studies have suggested that synaptic failure may preferentially target neurons with high connectivity (i.e., network hubs). As a result, the activity of these highly connected neurons can be significantly affected. It has been speculated that anesthetics regulate conscious state by affecting synaptic transmission at these network hubs and subsequently reducing overall coherence in the network activity. In addition, hubs in cortical networks are shown to be more vulnerable to amyloid deposition because of their higher activity within the network, causing decrease in coherence patterns and eventually Alzheimer's disease (AD). Here, we investigate how synaptic failure can affect spatio-temporal dynamics of scale free networks, having a power law scaling of number of connections per neuron - a relatively few neurons (hubs) with a lot of emanating or incoming connections and many cells with low connectivity. We studied two types of synaptic failure: activity-independent and targeted, activity-dependent synaptic failure. We defined scale-free network structures based on the dominating direction of the connections at the hub neurons: incoming and outgoing. We found that the two structures have significantly different dynamical properties. We show that synaptic failure may not only lead to the loss of coherence but unintuitively also can facilitate its emergence. We show that this is because activity-dependent synaptic failure homogenizes the activity levels in the network creating a dynamical substrate for the observed coherence increase. Obtained results may lead to better understanding of changes in large-scale pattern formation during progression of neuro-degenerative diseases targeting synaptic transmission.
| S-EPMC6519395 | biostudies-literature
Project description:Hebbian changes of excitatory synapses are driven by and further enhance correlations between pre- and postsynaptic activities. Hence, Hebbian plasticity forms a positive feedback loop that can lead to instability in simulated neural networks. To keep activity at healthy, low levels, plasticity must therefore incorporate homeostatic control mechanisms. We find in numerical simulations of recurrent networks with a realistic triplet-based spike-timing-dependent plasticity rule (triplet STDP) that homeostasis has to detect rate changes on a timescale of seconds to minutes to keep the activity stable. We confirm this result in a generic mean-field formulation of network activity and homeostatic plasticity. Our results strongly suggest the existence of a homeostatic regulatory mechanism that reacts to firing rate changes on the order of seconds to minutes.
| S-EPMC3828150 | biostudies-other
Project description:Cognitive reserve (CR) explains differential susceptibility of cognitive performance to neuropathology. However, as brain pathologies progress, cognitive decline occurs even in individuals with initially high CR. The interplay between the structural brain health (= level of brain reserve) and CR-related brain networks therefore requires further research. Our sample included 142 individuals aged 60-70 years. National Adult Reading Test intelligence quotient (NART-IQ) was our CR proxy. On an in-scanner Letter Sternberg task, we used ordinal trend (OrT) analysis to extract a task-related brain activation pattern (OrT slope) for each participant that captures increased expression with task load (one, three, and six letters). We assessed whether OrT slope represents a neural mechanism underlying CR by associating it with task performance and NART-IQ. Additionally, we investigated how the following brain reserve measures affect the association between NART-IQ and OrT slope: mean cortical thickness, total gray matter volume, and brain volumes proximal to the areas contained in the OrT patterns. We found that higher OrT slope was associated with better task performance and higher NART-IQ. Further, the brain reserve measures were not directly associated with OrT slope, but they affected the relationship between NART-IQ and OrT slope: NART-IQ was associated with OrT slope only in individuals with high brain reserve. The degree of brain reserve has an impact on how (and perhaps whether) CR can be implemented in brain networks in older individuals.
| S-EPMC10960550 | biostudies-literature
Project description:The stability and dynamics of synapses rely on tight regulation of the synaptic proteome. Shank proteins, encoded by the three genes Shank1, Shank2 and Shank3 are scaffold molecules in the postsynaptic density of excitatory neurons that contribute to activity-dependent neuronal signalling. Mutations in the Shank genes are associated with neurological diseases. Using state-of-the-art technologies, we investigated the levels of expression of the Shank family messenger RNAs (mRNAs) within the synaptic neuropil of the rat hippocampus. We detected all three Shank transcripts in the neuropil of CA1 pyramidal neurons. We found Shank1 to be the most abundantly expressed among the three Shank mRNA homologues. We also examined the turnover of Shank mRNAs and predict the half-lives of Shank1, Shank2 and Shank3 mRNAs to be 18-28 h. Using 3'-end sequencing, we identified novel 3' ends for the Shank1 and Shank2 3' untranslated regions (3' UTRs) that may contribute to the diversity of alternative polyadenylation (APA) for the Shank transcripts. Our findings consolidate the view that the Shank molecules play a central role at the postsynaptic density. This study may shed light on synaptopathologies associated with disruption of local protein synthesis, perhaps linked to mutations in mRNA 3' UTRs or inappropriate 3' end processing.
| S-EPMC3843870 | biostudies-literature
Project description:Memory deficits in Alzheimer's disease (AD) manifest together with the loss of synapses caused by the disruption of the postsynaptic density (PSD), a network of scaffold proteins located in dendritic spines. However, the underlying molecular mechanisms remain elusive. Since it was shown that ProSAP2/Shank3 scaffold assembly within the PSD is Zn2+-dependent and that the amyloid beta protein (A?) is able to bind Zn2+, we hypothesize that sequestration of Zn2+ ions by A? contributes to ProSAP/Shank platform malformation.To test this hypothesis, we designed multiple in vitro and in vivo assays demonstrating ProSAP/Shank dysregulation in rat hippocampal cultures following A? oligomer accumulation. These changes were independent from alterations on ProSAP/Shank transcriptional level. However, application of soluble A? prevented association of Zn2+ ions with ProSAP2/Shank3 in a cell-based assay and decreased the concentration of Zn2+ clusters within dendrites. Zn2+ supplementation or saturation of A? with Zn2+ ions prior to cell treatment was able to counter the effects induced by A? on synapse density and ProSAP2/Shank3 levels at the PSD. Interestingly, intracellular Zn2+ levels in APP-PS1 mice and human AD hippocampus are reduced along with a reduction in synapse density and synaptic ProSAP2/Shank3 and Shank1 protein levels.We conclude that sequestration of Zn2+ ions by A? significantly contributes to changes in ProSAP2/Shank3 platforms. These changes in turn lead to less consolidated (mature) synapses reflected by a decrease in Shank1 protein levels at the PSD and decreased synapse density in hippocampal neurons.
| S-EPMC3189132 | biostudies-literature
Project description:Neuronal morphology and number of synapses is not static, but can change in response to a variety of factors, a process called synaptic plasticity. These structural and molecular changes are believed to represent the basis for learning and memory, thereby underling both the developmental and activity-dependent remodelling of excitatory synapses. Here, we report that Zn(2+) ions, which are highly enriched within the postsynaptic density (PSD), are able to influence the recruitment of ProSAP/Shank proteins to PSDs in a family member-specific manner during the course of synaptogenesis and synapse maturation. Through selectively overexpressing each family member at excitatory postsynapses and comparing this to shRNA-mediated knockdown, we could demonstrate that only the overexpression of zinc-sensitive ProSAP1/Shank2 or ProSAP2/Shank3 leads to increased synapse density, although all of them cause a decrease upon knockdown. Furthermore, depletion of synaptic Zn(2+) along with the knockdown of zinc-insensitive Shank1 causes the rapid disintegration of PSDs and the loss of several postsynaptic molecules including Homer1, PSD-95 and NMDA receptors. These findings lead to the model that the concerted action of ProSAP/Shank and Zn(2+) is essential for the structural integrity of PSDs and moreover that it is an important element of synapse formation, maturation and structural plasticity.
| S-EPMC3034012 | biostudies-literature
Project description:During development, pyramidal neurons undergo dynamic regulation of AMPA receptor (AMPAR) subunit composition and density to help drive synaptic plasticity and maturation. These normal developmental changes in AMPARs are particularly vulnerable to risk factors for Autism Spectrum Disorders (ASDs), which include loss or mutations of synaptic proteins and environmental insults, such as dietary zinc deficiency. Here, we show how Shank2 and Shank3 mediate a zinc-dependent regulation of AMPAR function and subunit switch from GluA2-lacking to GluA2-containing AMPARs. Over development, we found a concomitant increase in Shank2 and Shank3 with GluA2 at synapses, implicating these molecules as potential players in AMPAR maturation. Since Shank activation and function require zinc, we next studied whether neuronal activity regulated postsynaptic zinc at glutamatergic synapses. Zinc was found to increase transiently and reversibly with neuronal depolarization at synapses, which could affect Shank and AMPAR localization and activity. Elevated zinc induced multiple functional changes in AMPAR, indicative of a subunit switch. Specifically, zinc lengthened the decay time of AMPAR-mediated synaptic currents and reduced their inward rectification in young hippocampal neurons. Mechanistically, both Shank2 and Shank3 were necessary for the zinc-sensitive enhancement of AMPAR-mediated synaptic transmission and act in concert to promote removal of GluA1 while enhancing recruitment of GluA2 at pre-existing Shank puncta. These findings highlight a cooperative local dynamic regulation of AMPAR subunit switch controlled by zinc signaling through Shank2 and Shank3 to shape the biophysical properties of developing glutamatergic synapses. Given the zinc sensitivity of young neurons and its dependence on Shank2 and Shank3, genetic mutations and/or environmental insults during early development could impair synaptic maturation and circuit formation that underlie ASD etiology.
| S-EPMC6256285 | biostudies-literature
Project description:Synapses may undergo variable changes during plasticity because of the variability of spike patterns such as temporal stochasticity and spatial randomness. Here, we call the variability of synaptic weight changes during plasticity to be efficacy variability. In this paper, we investigate how four aspects of spike pattern statistics (i.e., synchronous firing, burstiness/regularity, heterogeneity of rates and heterogeneity of cross-correlations) influence the efficacy variability under pair-wise additive spike-timing dependent plasticity (STDP) and synaptic homeostasis (the mean strength of plastic synapses into a neuron is bounded), by implementing spike shuffling methods onto spike patterns self-organized by a network of excitatory and inhibitory leaky integrate-and-fire (LIF) neurons. With the increase of the decay time scale of the inhibitory synaptic currents, the LIF network undergoes a transition from asynchronous state to weak synchronous state and then to synchronous bursting state. We first shuffle these spike patterns using a variety of methods, each designed to evidently change a specific pattern statistics; and then investigate the change of efficacy variability of the synapses under STDP and synaptic homeostasis, when the neurons in the network fire according to the spike patterns before and after being treated by a shuffling method. In this way, we can understand how the change of pattern statistics may cause the change of efficacy variability. Our results are consistent with those of our previous study which implements spike-generating models on converging motifs. We also find that burstiness/regularity is important to determine the efficacy variability under asynchronous states, while heterogeneity of cross-correlations is the main factor to cause efficacy variability when the network moves into synchronous bursting states (the states observed in epilepsy).
| S-EPMC4977343 | biostudies-literature