Phosphorylation in two discrete tau domains regulates a stepwise process leading to postsynaptic dysfunction.

KEY POINTS: Tau mislocalization to dendritic spines and associated postsynaptic deficits are mediated through different and non-overlapping phosphorylation sites. Tau mislocalization to dendritic spines depends upon the phosphorylation of either Ser396 or Ser404 in the C-terminus. Postsynaptic dysfunction instead depends upon the phosphorylation of at least one of five residues in the proline-rich region of tau. The blockade of both glycogen synthetase kinase 3ß and cyclin-dependent kinase 5 is required to prevent P301L-induced tau mislocalization to dendritic spines, supporting redundant pathways that control tau mislocalization to spines. ABSTRACT: Tau protein consists of an N-terminal projection domain, a microtubule-binding domain and a C-terminal domain. In neurodegenerative diseases, including Alzheimer's disease and frontotemporal dementia, the hyperphosphorylation of tau changes its shape, binding partners and resulting function. An early consequence of tau phosphorylation by proline-directed kinases is postsynaptic dysfunction associated with the mislocalization of tau to dendritic spines. The specific phosphorylation sites leading to these abnormalities have not been elucidated. Here, using imaging and electrophysiological techniques to study cultured rat hippocampal neurons, we show that postsynaptic dysfunction results from a sequential process involving differential phosphorylation in the N-terminal and C-terminal domains. First, tau mislocalizes to dendritic spines, in a manner that depends upon the phosphorylation of either Ser396 or Ser404 in the C-terminal domain. The blockade of both glycogen synthetase kinase 3ß and cyclin-dependent kinase 5 prevents tau mislocalization to dendritic spines. Second, a reduction of functional AMPA receptors depends upon the phosphorylation of at least one of five residues (Ser202, Thr205, Thr212, Thr217 and Thr231) in the proline-rich region of the N-terminal domain. This is the first report of differential phosphorylation in distinct tau domains governing separate, but linked, steps leading to synaptic dysfunction.

A53T Mutant Alpha-Synuclein Induces Tau-Dependent Postsynaptic Impairment Independently of Neurodegenerative Changes.

Abnormalities in α-synuclein are implicated in the pathogenesis of Parkinson's disease (PD). Because α-synuclein is highly concentrated within presynaptic terminals, presynaptic dysfunction has been proposed as a potential pathogenic mechanism. Here, we report novel, tau-dependent, postsynaptic deficits caused by A53T mutant α-synuclein, which is linked to familial PD. We analyzed synaptic activity in hippocampal slices and cultured hippocampal neurons from transgenic mice of either sex expressing human WT, A53T, and A30P α-synuclein. Increased α-synuclein expression leads to decreased spontaneous synaptic vesicle release regardless of genotype. However, only those neurons expressing A53T α-synuclein exhibit postsynaptic dysfunction, including decreased miniature postsynaptic current amplitude and decreased AMPA to NMDA receptor current ratio. We also found that long-term potentiation and spatial learning were impaired by A53T α-synuclein expression. Mechanistically, postsynaptic dysfunction requires glycogen synthase kinase 3ß-mediated tau phosphorylation, tau mislocalization to dendritic spines, and calcineurin-dependent AMPA receptor internalization. Previous studies reveal that human A53T α-synuclein has a high aggregation potential, which may explain the mutation's unique capacity to induce postsynaptic deficits. However, patients with sporadic PD with severe tau pathology are also more likely to have early onset cognitive decline. Our results here show a novel, functional role for tau: mediating the effects of α-synuclein on postsynaptic signaling. Therefore, the unraveled tau-mediated signaling cascade may contribute to the pathogenesis of dementia in A53T α-synuclein-linked familial PD cases, as well as some subgroups of PD cases with extensive tau pathology.SIGNIFICANCE STATEMENT Here, we report mutation-specific postsynaptic deficits that are caused by A53T mutant α-synuclein, which is linked to familial Parkinson's disease (PD). The overexpression of WT, A53T, or A30P human α-synuclein leads to decreased spontaneous synaptic vesicle release. However, only those neurons expressing A53T α-synuclein exhibit tau phosphorylation-dependent postsynaptic dysfunction, which is characterized by decreased miniature postsynaptic current amplitude and decreased AMPA to NMDA receptor current ratio. The mutation-specific postsynaptic effects caused by human A53T α-synuclein will help us better understand the neurobiological basis of this specific form of familial PD. The differential effects of exogenous human WT, A53T, A30P, and E46K α-synuclein on glutamatergic synaptic responses will help to explain the clinical heterogeneity of sporadic and familial PD.

Tau acts as a mediator for Alzheimer's disease-related synaptic deficits.

The two histopathological hallmarks of Alzheimer's disease (AD) are amyloid plaques containing multiple forms of amyloid beta (Aß) and neurofibrillary tangles containing phosphorylated tau proteins. As mild cognitive impairment frequently occurs long before the clinical diagnosis of AD, the scientific community has been increasingly interested in the roles of Aß and tau in earlier cellular changes that lead to functional deficits. Therefore, great progress has recently been made in understanding how Aß or tau causes synaptic dysfunction. However, the interaction between the Aß and tau-initiated intracellular cascades that lead to synaptic dysfunction remains elusive. The cornerstone of the two-decade-old hypothetical amyloid cascade model is that amyloid pathologies precede tau pathologies. Although the premise of Aß-tau pathway remains valid, the model keeps evolving as new signaling events are discovered that lead to functional deficits and neurodegeneration. Recent progress has been made in understanding Aß-PrP(C) -Fyn-mediated neurotoxicity and synaptic deficits. Although still elusive, many novel upstream and downstream signaling molecules have been found to modulate tau mislocalization and tau hyperphosphorylation. Here we will discuss the mechanistic interactions between Aß-PrP(C) -mediated neurotoxicity and tau-mediated synaptic deficits in an updated amyloid cascade model with calcium and tau as the central mediators.

Tau phosphorylation and tau mislocalization mediate soluble Aß oligomer-induced AMPA glutamate receptor signaling deficits.

In our previous studies, phosphorylation-dependent tau mislocalization to dendritic spines resulted in early cognitive and synaptic deficits. It is well known that amyloid beta (Aß) oligomers cause synaptic dysfunction by inducing calcineurin-dependent AMPA receptor (AMPAR) internalization. However, it is unknown whether Aß-induced synaptic deficits depend upon tau phosphorylation. It is also unknown whether changes in tau can cause calcineurin-dependent loss of AMPARs in synapses. Here, we show that tau mislocalizes to dendritic spines in cultured hippocampal neurons from APPSwe Alzheimer's disease (AD)-transgenic mice and in cultured rat hippocampal neurons treated with soluble Aß oligomers. Interestingly, Aß treatment also impairs synaptic function by decreasing the amplitude of miniature excitatory postsynaptic currents (mEPSCs). The above tau mislocalization and Aß-induced synaptic impairment are both diminished by the expression of AP tau, indicating that these events require tau phosphorylation. The phosphatase activity of calcineurin is important for AMPAR internalization via dephosphorylation of GluA1 residue S845. The effects of Aß oligomers on mEPSCs are blocked by the calcineurin inhibitor FK506. Aß-induced loss of AMPARs is diminished in neurons from knock-in mice expressing S845A mutant GluA1 AMPA glutamate receptor subunits. This finding suggests that changes in phosphorylation state at S845 are involved in this pathogenic cascade. Furthermore, FK506 rescues deficits in surface AMPAR clustering on dendritic spines in neurons cultured from transgenic mice expressing P301L tau proteins. Together, our results support the role of tau and calcineurin as two intermediate signaling molecules between Aß initiation and eventual synaptic dysfunction early in AD pathogenesis.

Differential modulation of drug-induced structural and functional plasticity of dendritic spines.

Drug-induced plasticity of excitatory synapses has been proposed to be the cellular mechanism underlying the aberrant learning associated with addiction. Exposure to various drugs of abuse causes both morphological plasticity of dendritic spines and functional plasticity of excitatory synaptic transmission. Chronic activation of µ-opioid receptors (MOR) in cultured hippocampal neurons causes two forms of synaptic plasticity: loss of dendritic spines and loss of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. With use of live imaging, patch-clamp electrophysiology, and immunocytochemistry, the present study reveals that these two forms of synaptic plasticity are mediated by separate, but interactive, intracellular signaling cascades. The inhibition of Ca(2+)/calmodulin-dependent protein kinase II with 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-l-tyrosyl]-4-phenylpiperazine (KN-62) blocks MOR-mediated structural plasticity of dendritic spines, but not MOR-mediated cellular redistribution of GluR1 and GluR2 AMPA receptor subunits. In contrast, the inhibition of calcineurin with tacrolimus (FK506) blocks both cellular processes. These findings support the idea that drug-induced structural and functional plasticity of dendritic spines is mediated by divergent, but interactive, signaling pathways.

Reducing anticoagulant medication adverse vents and avoidable patient harm.

BACKGROUND: The conventional standard of care for many patients at Saint Joseph HealthCare, a three-hospital system in Kentucky, includes the use of anticoagulant therapy. In view of the morbidity and mortality associated with anticoagulation-related complications, the prevention of bleeding and thrombotic adverse drug events was identified as a primary process improvement initiative. METHODS: Following establishment of an interdisciplinary team, formal evaluations of anticoagulant-use practices and associated patient outcomes occurred via several mechanisms. A variety of process improvement activities were conducted, including the creation of a pharmacist-managed hospital anticoagulant therapy service. A pharmacist consult service for the medical staff provided initiation, management, and monitoring of anticoagulation, including bridge therapy and reversal if necessary. RESULTS: The rate of thrombotic events decreased from 4.6% in 2004 to 3.9% in 2006 and further decreased to 0.0% for patients managed by collaborative physician and pharmacist practice. Hospitalwide bleeding and thrombotic reactions decreased from a monthly average of 11.52 events per 1,000 anticoagulant doses dispensed in 2004 to 0.07 in 2006. A cost-benefit evaluation indicated an annual savings of up to $9.8 million in avoidable costs. DISCUSSION: In this interdisciplinary project, anticoagulant safety was integrated throughout the institution, and a variety of medication safety systems were successfully employed.

Dendritic spine dysgenesis in Rett syndrome.

Spines are small cytoplasmic extensions of dendrites that form the postsynaptic compartment of the majority of excitatory synapses in the mammalian brain. Alterations in the numerical density, size, and shape of dendritic spines have been correlated with neuronal dysfunction in several neurological and neurodevelopmental disorders associated with intellectual disability, including Rett syndrome (RTT). RTT is a progressive neurodevelopmental disorder associated with intellectual disability that is caused by loss of function mutations in the transcriptional regulator methyl CpG-binding protein 2 (MECP2). Here, we review the evidence demonstrating that principal neurons in RTT individuals and Mecp2-based experimental models exhibit alterations in the number and morphology of dendritic spines. We also discuss the exciting possibility that signaling pathways downstream of brain-derived neurotrophic factor (BDNF), which is transcriptionally regulated by MeCP2, offer promising therapeutic options for modulating dendritic spine development and plasticity in RTT and other MECP2-associated neurodevelopmental disorders.

Determination of Trace Elements in Ruby Laser Crystals by Neutron Activation Analysis.

Methods are described by which concentration levels have been determined for up to ten different trace elements and upper limits established for over 40 additional elements at the parts per million level or below in ruby crystals using neutron activation analysis. This information is required to determine the effect of trace element levels on laser performance. With conventional analytical methods difficulties arise because of both the refractory and insulating properties of the material. Because the crystals cannot be readily dissolved, the activation analysis was carried out nondestructively, irradiating the samples with highly thermalized neutrons to minimize formation of 24Na and 27Mg from (n, α) and (n, p) reactions on the Al2O3 matrix, and using a 47-cm3 Ge(Li) detector.