Resonance assignment of the Shank1 PDZ domain

Shank proteins are among the most abundant and well-studied postsynaptic scaffold proteins. Their PDZ domain has unique characteristics as one of its loop regions flanking the ligand-binding site is uniquely long and has also been implicated in the formation of PDZ dimers. Here we report the initial characterization of the Shank1 PDZ domain by solution NMR spectroscopy. The assigned chemical shifts are largely consistent with the common features of PDZ domains in general and the available Shank PDZ crystal structures in particular. Our analysis suggests that under the conditions investigated, the domain is monomeric and the unique loop harbors a short helical segment, observed in only one of the known X-ray structures so far. Our work stresses the importance of solution-state investigations to fully decipher the functional relevance of the structural and dynamical features unique to Shank PDZ domains.

Suv39h1 regulates memory stability by inhibiting the expression of Shank1 in hippocampal newborn neurons

Adult newborn neurons are involved in memory encoding and extinction, but the neural mechanism is unclear. We found the adult newborn neurons at 4 weeks are recruited by learning and subjected to epigenetic regulations, consequently reducing their ability to be re-recruited later. After removal of the epigenetic blockage, Suv39h1 KO mice showed an increased recruiting number of aged newborn neurons and enhanced flexibility in learning tasks. Besides NRXN1, we found SHANK1, the synaptic scaffold protein, is one of the major targets of Suv39h1, regulating memory stability. Expression of Shank1 is transiently engaged to enhance synaptogenesis during learning and is strongly suppressed by Suv39h1 from 5 hours after learning. Exogenously overexpression of Shank1 in dentate gyrus increased the density of mushroom spines and decreased the persistency of old memories. Our study indicated the activity-regulated epigenetic modification in newly matured newborn neurons in hippocampus insulates temporally distinct experiences and stabilizes old memories.

Protective effects of Bushen Tiansui decoction on hippocampal synapses in a rat model of Alzheimer's disease

Bushen Tiansui decoction is composed of six traditional Chinese medicines: Herba Epimedii, Radix Polygoni multiflori, Plastrum testudinis, Fossilia Ossis Mastodi, Radix Polygalae, and Rhizoma Acorus tatarinowii. Because Bushen Tiansui decoction is effective against amyloid beta (Aβ) toxicity, we hypothesized that it would reduce hippocampal synaptic damage and improve cognitive function in Alzheimer's disease. To test this hypothesis, we used a previously established animal model of Alzheimer's disease, that is, microinjection of aggregated Aβ25-35 into the bilateral brain ventricles of Sprague-Dawley rats. We found that long-term (28 days) oral administration of Bushen Tiansui decoction (0.563, 1.688, and 3.375 g/mL; 4 mL/day) prevented synaptic loss in the hippocampus and increased the expression levels of synaptic proteins, including postsynaptic density protein 95, the N-methyl-D-aspartate receptor 2B subunit, and Shank1. These results suggested that Bushen Tiansui decoction can protect synapses by maintaining the expression of these synaptic proteins. Bushen Tiansui decoction also ameliorated measures reflecting spatial learning and memory deficits that were observed in the Morris water maze (i.e., increased the number of platform crossings and the amount of time spent in the target quadrant and decreased escape latency) following intraventricular injections of aggregated Aβ25-35 compared with those measures in untreated Aβ25-35-injected rats. Overall, these results provided evidence that further studies on the prevention and treatment of dementia with this traditional Chinese medicine are warranted.

Selective Localization of Shanks to VGLUT1-Positive Excitatory Synapses in the Mouse Hippocampus

Members of the Shank family of multidomain proteins (Shank1, Shank2, and Shank3) are core components of the postsynaptic density (PSD) of excitatory synapses. At synaptic sites Shanks serve as scaffolding molecules that cluster neurotransmitter receptors as well as cell adhesion molecules attaching them to the actin cytoskeleton. In this study we investigated the synapse specific localization of Shank1-3 and focused on well-defined synaptic contacts within the hippocampal formation. We found that all three family members are present only at VGLUT1-positive synapses, which is particularly visible at mossy fiber contacts. No costaining was found at VGLUT2-positive contacts indicating that the molecular organization of VGLUT2-associated PSDs diverges from classical VGLUT1-positive excitatory contacts in the hippocampus. In light of SHANK mutations in neuropsychiatric disorders, this study indicates which glutamatergic networks within the hippocampus will be primarily affected by shankopathies.

Effects of curcumin on synapses in APPswe/PS1dE9 mice

Significant losses of synapses have been demonstrated in studies of Alzheimer's disease (AD), but structural and functional changes in synapses that depend on alterations of the postsynaptic density (PSD) area occur prior to synaptic loss and play a crucial role in the pathology of AD. Evidence suggests that curcumin can ameliorate the learning and memory deficits of AD. To investigate the effects of curcumin on synapses, APPswe/PS1dE9 double transgenic mice (an AD model) were used, and the ultra-structures of synapses and synapse-associated proteins were observed. Six months after administration, few abnormal synapses were observed upon electron microscopy in the hippocampal CA1 areas of the APPswe/PS1dE9 double transgenic mice. The treatment of the mice with curcumin resulted in improvements in the quantity and structure of the synapses. Immunohistochemistry and western blot analyses revealed that the expressions of PSD95 and Shank1 were reduced in the hippocampal CA1 areas of the APPswe/PS1dE9 double transgenic mice, but curcumin treatment increased the expressions of these proteins. Our findings suggest that curcumin improved the structure and function of the synapses by regulating the synapse-related proteins PSD95 and Shank1.

Shank3 is localized in axons and presynaptic specializations of developing hippocampal neurons and involved in the modulation of NMDA receptor levels at axon terminals

Autism-related Shank1, Shank2, and Shank3 are major postsynaptic scaffold proteins of excitatory glutamatergic synapses. A few studies, however, have already indicated that within a neuron, the presence of Shank family members is not limited to the postsynaptic density. By separating axons from dendrites of developing hippocampal neurons in microfluidic chambers, we show that RNA of all three Shank family members is present within axons. Immunostaining confirms these findings as all three Shanks are indeed found within separated axons and further co-localize with well-known proteins of the presynaptic specialization in axon terminals. Therefore, Shank proteins might not only serve as postsynaptic scaffold proteins, but also play a crucial role during axonal outgrowth and presynaptic development and function. This is supported by our findings that shRNA-mediated knockdown of Shank3 results in up-regulation of the NMDA receptor subunit GluN1 in axon terminals. Taken together, our findings will have major implications for the future analysis of neuronal Shank biology in both health and disease. Shank1, Shank2, and Shank3 are major postsynaptic scaffold proteins of excitatory glutamatergic synapses strongly related to several neuropsychiatric disorders. However, a few studies have already implicated a functional role of the Shanks beyond the postsynaptic density (PSD). We here show that all three Shanks are localized in both axons and pre-synaptic specializiations of developing hippocampal neurons in culture. We further provide evidence that Shank3 is involved in the modulation of NMDA receptor levels at axon terminals. Taken together, our study will open up novel avenues for the future analysis of neuronal Shank biology in both health and disease.

Translational neurobiology in Shank mutant mice--model systems for neuropsychiatric disorders

The Shank family comprises three core postsynaptic scaffold proteins of excitatory synapses in the mammalian brain: Shank1, Shank2 and Shank3. Since mutations in all three human SHANK genes are linked to neuropsychiatric disorders such as autism and schizophrenia, Shank mutant mice serve as corresponding in vivo model systems. Besides intriguing alterations in behavior, dysfunction of glutamatergic synapses has emerged as a pathological hallmark among several Shank mutant lines. However, there is very limited knowledge of the underlying pathomechanisms. Therefore, precise neurobiological evaluation of morphological, molecular and electrophysiological phenotypes in Shank mutants is crucially needed. In this brief review, I will focus on the Shank mutant mouse lines we have generated so far and discuss how they might help us to develop translational treatment studies in the future.