Agnieszka Staniszewski

Picomolar amyloid-beta positively modulates synaptic plasticity and memory in hippocampus.

Amyloid-β (Aβ) peptides are produced in high amounts during Alzheimers disease, causing synaptic and memory dysfunction. However, they are also released in lower amounts in normal brains throughout life during synaptic activity. Here we show that low picomolar concentrations of a preparation containing both Aβ42 monomers and oligomers cause a marked increase of hippocampal long-term potentiation, whereas high nanomolar concentrations lead to the well established reduction of potentiation. Picomolar levels of Aβ42 also produce a pronounced enhancement of both reference and contextual fear memory. The mechanism of action of picomolar Aβ42 on both synaptic plasticity and memory involves α7-containing nicotinic acetylcholine receptors. These findings strongly support a model for Aβ effects in which low concentrations play a novel positive, modulatory role on neurotransmission and memory, whereas high concentrations play the well known detrimental effect culminating in dementia.

Ubiquitin Hydrolase Uch-L1 Rescues β-Amyloid-Induced Decreases in Synaptic Function and Contextual Memory

The neuronal ubiquitin/proteasomal pathway has been implicated in the pathogenesis of Alzheimers disease (AD). We now show that a component of the pathway, ubiquitin C-terminal hydrolase L1 (Uch-L1), is required for normal synaptic and cognitive function. Transduction of Uch-L1 protein fused to the transduction domain of HIV-transactivator protein (TAT) restores normal enzymatic activity and synaptic function both in hippocampal slices treated with oligomeric Abeta and in the APP/PS1 mouse model of AD. Moreover, intraperitoneal injections with the fusion protein improve the retention of contextual learning in APP/PS1 mice over time. The beneficial effect of the Uch-L1 fusion protein is associated with restoration of normal levels of the PKA-regulatory subunit IIalpha, PKA activity, and CREB phosphorylation.

Phosphodiesterase 5 Inhibition Improves Synaptic Function, Memory, and Amyloid-β Load in an Alzheimer's Disease Mouse Model

Memory loss, synaptic dysfunction, and accumulation of amyloid β-peptides (Aβ) are major hallmarks of Alzheimers disease (AD). Downregulation of the nitric oxide/cGMP/cGMP-dependent protein kinase/c-AMP responsive element-binding protein (CREB) cascade has been linked to the synaptic deficits after Aβ elevation. Here, we report that the phosphodiesterase 5 inhibitor (PDE5) sildenafil (Viagra), a molecule that enhances phosphorylation of CREB, a molecule involved in memory, through elevation of cGMP levels, is beneficial against the AD phenotype in a mouse model of amyloid deposition. We demonstrate that the inhibitor produces an immediate and long-lasting amelioration of synaptic function, CREB phosphorylation, and memory. This effect is also associated with a long-lasting reduction of Aβ levels. Given that side effects of PDE5 inhibitors are widely known and do not preclude their administration to a senile population, these drugs have potential for the treatment of AD and other diseases associated with elevated Aβ levels.

Retromer deficiency observed in Alzheimer's disease causes hippocampal dysfunction, neurodegeneration, and Aβ accumulation

Although deficiencies in the retromer sorting pathway have been linked to late-onset Alzheimers disease, whether these deficiencies underlie the disease remains unknown. Here we characterized two genetically modified animal models to test separate but related questions about the effects that retromer deficiency has on the brain. First, testing for cognitive defects, we investigated retromer-deficient mice and found that they develop hippocampal-dependent memory and synaptic dysfunction, which was associated with elevations in endogenous Aβ peptide. Second, testing for neurodegeneration and amyloid deposits, we investigated retromer-deficient flies expressing human wild-type amyloid precursor protein (APP) and human β-site APP-cleaving enzyme (BACE) and found that they develop neuronal loss and human Aβ aggregates. By recapitulating features of the disease, these animal models suggest that retromer deficiency observed in late-onset Alzheimers disease can contribute to disease pathogenesis.

Dysregulation of histone acetylation in the APP/PS1 mouse model of Alzheimer's disease.

Epigenetic mechanisms such as post-translational histone modifications are increasingly recognized for their contribution to gene activation and silencing in the brain. Histone acetylation in particular has been shown to be important both in hippocampal long-term potentiation (LTP) and memory formation in mice. The involvement of the epigenetic modulation of memory formation has also been proposed in neuropathological models, although up to now no clear-cut connection has been demonstrated between histone modifications and the etiology of Alzheimers disease (AD). Thus, we have undertaken preclinical studies in the APP/PS1 mouse model of AD to determine whether there are differences in histone acetylation levels during associative memory formation. After fear conditioning training, levels of hippocampal acetylated histone 4 (H4) in APP/PS1 mice were about 50% lower than in wild-type littermates. Interestingly, acute treatment with a histone deacetylase inhibitor, Trichostatin A (TSA), prior to training rescued both acetylated H4 levels and contextual freezing performance to wild-type values. Moreover, TSA rescued CA3-CA1 LTP in slices from APP/PS1 mice. Based on this evidence, we propose the hypothesis that epigenetic mechanisms are involved in the altered synaptic function and memory associated with AD. In this respect, histone deacetylase inhibitors represent a new therapeutic target to effectively counteract disease progression.

Endogenous amyloid-β is necessary for hippocampal synaptic plasticity and memory

The goal of this study was to investigate the role of endogenous amyloid‐β peptide (Aβ) in healthy brain.

Phospholipase D2 Ablation Ameliorates Alzheimer's Disease-Linked Synaptic Dysfunction and Cognitive Deficits

Growing evidence implicates aberrant lipid signaling in Alzheimers disease (AD). While phospholipases A2 and C have been recently shown to mediate key actions of amyloid β-peptide (Aβ) through a dysregulation of arachidonic acid and phosphatidylinositol-4,5-bisphosphate metabolism, respectively, the role of phospholipase D (PLD) has so far remained elusive. PLD produces phosphatidic acid (PA), a bioactive lipid involved in multiple aspects of cell physiology, including signaling and membrane trafficking processes. Here we show that oligomeric Aβ enhances PLD activity in cultured neurons and that this stimulatory effect does not occur upon ablation of PLD2 via gene targeting. Aβ fails to suppress long-term potentiation in PLD2-deficient hippocampal slices, suggesting that PLD2 is required for the synaptotoxic action of this peptide. In vivo PLD activity, as assessed by detection of phosphatidylethanol levels using mass spectrometry (MS) following ethanol injection, is also increased in the brain of a transgenic mouse model of AD (SwAPP). Furthermore, Pld2 ablation rescues memory deficits and confers synaptic protection in SwAPP mice despite a significant Aβ load. MS-based lipid analysis of Pld2 mutant brains in the presence or absence of the SwAPP transgene unmasks striking crosstalks between different PA species. This lipid analysis shows an exquisite acyl chain specificity and plasticity in the perturbation of PA metabolism. Collectively, our results point to specific molecular species of PA as key modulators of AD pathogenesis and identify PLD2 as a novel potential target for therapeutics.

Extracellular Tau Oligomers Produce An Immediate Impairment of LTP and Memory

Non-fibrillar soluble oligomeric forms of amyloid-β peptide (oAβ) and tau proteins are likely to play a major role in Alzheimer’s disease (AD). The prevailing hypothesis on the disease etiopathogenesis is that oAβ initiates tau pathology that slowly spreads throughout the medial temporal cortex and neocortices independently of Aβ, eventually leading to memory loss. Here we show that a brief exposure to extracellular recombinant human tau oligomers (oTau), but not monomers, produces an impairment of long-term potentiation (LTP) and memory, independent of the presence of high oAβ levels. The impairment is immediate as it raises as soon as 20 min after exposure to the oligomers. These effects are reproduced either by oTau extracted from AD human specimens, or naturally produced in mice overexpressing human tau. Finally, we found that oTau could also act in combination with oAβ to produce these effects, as sub-toxic doses of the two peptides combined lead to LTP and memory impairment. These findings provide a novel view of the effects of tau and Aβ on memory loss, offering new therapeutic opportunities in the therapy of AD and other neurodegenerative diseases associated with Aβ and tau pathology.

Synthesis of Quinoline Derivatives: Discovery of a Potent and Selective Phosphodiesterase 5 Inhibitor for the Treatment of Alzheimer's disease

Phosphodiesterase type 5 (PDE5) mediates the degradation of cGMP in a variety of tissues including brain. Recent studies have demonstrated the importance of the nitric oxide/cGMP/cAMP-responsive element-binding protein (CREB) pathway to the process of learning and memory. Thus, PDE5 inhibitors (PDE5Is) are thought to be promising new therapeutic agents for the treatment of Alzheimers disease (AD), a neurodegenerative disorder characterized by memory loss. To explore this possibility, a series of quinoline derivatives were synthesized and evaluated. We found that compound 7a selectively inhibits PDE5 with an IC(50) of 0.27 nM and readily crosses the blood brain barrier. In an in vivo mouse model of AD, compound 7a rescues synaptic and memory defects. Quinoline-based, CNS-permeant PDE5Is have potential for AD therapeutic development.

Development of Novel In Vivo Chemical Probes to Address CNS Protein Kinase Involvement in Synaptic Dysfunction.

Serine-threonine protein kinases are critical to CNS function, yet there is a dearth of highly selective, CNS-active kinase inhibitors for in vivo investigations. Further, prevailing assumptions raise concerns about whether single kinase inhibitors can show in vivo efficacy for CNS pathologies, and debates over viable approaches to the development of safe and efficacious kinase inhibitors are unsettled. It is critical, therefore, that these scientific challenges be addressed in order to test hypotheses about protein kinases in neuropathology progression and the potential for in vivo modulation of their catalytic activity. Identification of molecular targets whose in vivo modulation can attenuate synaptic dysfunction would provide a foundation for future disease-modifying therapeutic development as well as insight into cellular mechanisms. Clinical and preclinical studies suggest a critical link between synaptic dysfunction in neurodegenerative disorders and the activation of p38αMAPK mediated signaling cascades. Activation in both neurons and glia also offers the unusual potential to generate enhanced responses through targeting a single kinase in two distinct cell types involved in pathology progression. However, target validation has been limited by lack of highly selective inhibitors amenable to in vivo use in the CNS. Therefore, we employed high-resolution co-crystallography and pharmacoinformatics to design and develop a novel synthetic, active site targeted, CNS-active, p38αMAPK inhibitor (MW108). Selectivity was demonstrated by large-scale kinome screens, functional GPCR agonist and antagonist analyses of off-target potential, and evaluation of cellular target engagement. In vitro and in vivo assays demonstrated that MW108 ameliorates beta-amyloid induced synaptic and cognitive dysfunction. A serendipitous discovery during co-crystallographic analyses revised prevailing models about active site targeting of inhibitors, providing insights that will facilitate future kinase inhibitor design. Overall, our studies deliver highly selective in vivo probes appropriate for CNS investigations and demonstrate that modulation of p38αMAPK activity can attenuate synaptic dysfunction.