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Protein post-translational modifications (PTM) play a crucial role in the modulation of synaptic function and their alterations are involved in the onset and progression of neurodegenerative disorders. S-palmitoylation is a PTM catalyzed by zinc finger DHHC domain containing (zDHHC) S-acyltransferases that affects both localization and activity of proteins regulating synaptic plasticity and amyloid-β (Aβ) metabolism. Here, we found significant increases of both zDHHC7 expression and protein S-palmitoylation in hippocampi of both 3×Tg-AD mice and post-mortem Alzheimer's disease (AD) patients. Chronic intranasal administration of the S-palmitoylation inhibitor 2-bromopalmitate counteracted synaptic plasticity and cognitive deficits, reduced the Aβ deposition in the hippocampus and extended the lifespan of both male and female 3×Tg-AD mice. Moreover, hippocampal silencing of zDHHC7 prevented the onset of cognitive deficits in the same experimental model. We also identified a FoxO1-mediated epigenetic mechanism inducing zDHHC7 expression, which was triggered by brain insulin resistance in 3×Tg-AD mice. Finally, in hippocampi of AD patients S-palmitoylation levels of Beta-Secretase 1 were associated with Aβ 1 to 42 load and they inversely correlated with Mini Mental State Examination scores. Our data reveal a key role of both zDHHC7 overexpression and protein hyperpalmitoylation in the onset and progression of AD-related alterations of synaptic plasticity and memory. [ABSTRACT FROM AUTHOR]

Background: Object recognition task (ORT) is a widely used behavioral paradigm to assess memory in rodent models, due to its easy technical execution, the lack of aversive stressful stimuli, and the possibility to repeat the test on the same animals. However, mouse exploration might be strongly influenced by a variety of variables.Objective: To study whether innate preferences influenced exploration in male and female wild type mice and the Alzheimer's disease (AD) model 3xTg.Methods: We first evaluated how object characteristics (material, size, and shape) influence exploration levels, latency, and exploration modality. Based on these findings, we evaluated whether these innate preferences biased the results of ORT performed in wild type mice and AD models.Results: Assessment of Exploration levels, i.e., the time spent in exploring a certain object in respect to the total exploration time, revealed an innate preference for objects made in shiny materials, such as metal and glass. A preference for bigger objects characterized by higher affordance was also evident, especially in male mice. When performing ORT, exploration was highly influenced by these innate preferences. Indeed, both wild type and AD mice spent more time in exploring the metal object, regardless of its novelty. Furthermore, the use of objects with higher affordance such as the cube was a confounding factor leading to "false" results that distorted ORT interpretation.Conclusion: When designing exploration-based behavioral experiments aimed at assessing memory in healthy and AD mice, object characteristics should be carefully evaluated to improve scientific outcomes and minimize possible biases. [ABSTRACT FROM AUTHOR]

Background: Growing evidence points to altered metabolic signals as a risk factor for Alzheimer's disease (AD). The high fatty acid levels and brain insulin resistance (BIR) found in AD brains may impinge on protein S‐palmitoylation, which is a post‐translational modification critically involved in the regulation of neuronal protein localization and synaptic function. Our previous findings highlighted the critical role of aberrant palmitoylation in BIR‐dependent memory impairment (Spinelli et al., 2017). Method: We analyzed both the expression of palmitoyl‐transferase enzymes (zDHHCs) in mouse AD brains and S‐palmitoylation levels of key proteins in human AD brains. We also tested the effect of chronic intranasal injection of the palmitoylation inhibitor 2‐bromopalmitate (2BP) on a large cohort of male and female 3xTg‐AD mice, starting from 3 months of age, by performing cognitive (novel object recognition and object displacement tests), electrophysiological (LTP), immunohistochemical (Abeta deposition) and molecular analyses (Abeta measurement by ELISA). Finally, we investigated the effects of lentiviral particles‐mediated zDHHC7 or zDHHC21 silencing in the hippocampus of 3xTg‐AD. Result: We found increased levels of zDHHC7 and zDHHC21 in the hippocampus of 3xTg‐AD mice and aberrant palmitoylation of key enzymes triggering beta amyloid aggregation in human AD brains. 2BP delayed the onset of memory deficits in both male and female 3xTg‐AD mice. More importantly, 2BP significantly enhanced cognitive performances in 6‐, 9‐ and 12‐month‐old animals. Accordingly, electrophysiological analyses on hippocampal brain slices from 2BP‐treated 3xTg‐AD mice revealed greater long‐term potentiation at CA3‐CA1 synapses. In addition, both 2BP‐treated male and female mice showed lower Abeta deposition in hippocampus and a significant extension of lifespan. Finally, genetic inhibition of palmitoyl transferase zDHHC7 reverted the aberrant palmitoylation of proteins involved in synaptic plasticity and APP metabolism, and counteracted the onset of neurodegeneration and cognitive deficits in 3xTg‐AD mice. Conclusion: This is the first preclinical study on the effect of 2BP treatment on AD‐related cognitive decline. Our data indicate that aberrant palmitoylation plays a critical role in the onset and progression of AD and unveil the potential druggable role of zDHHC enzymes in dementia‐related neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Failure of anti-amyloid-β peptide (Aβ) therapies against Alzheimer’s disease (AD), a neurodegenerative disorder characterized by high amounts of the peptide in the brain, raised the question of the physiological role of Aβ released at low concentrations in the healthy brain. T o address this question, we studied the presynaptic and postsynaptic mechanisms underlying the neuromodulatory action of picomolar amounts of oligomeric Aβ42 (oAβ42) on synaptic glutamatergic function in male and female mice. We found that 200 pM oAβ42 induces an increase of frequency of miniature EPSCs and a decrease of paired pulse facilitation, associated with an increase in docked vesicle number, indicating that it augments neurotransmitter release at presynaptic level. oAβ42 also produced postsynaptic changes as shown by an increased length of postsynaptic density, accompanied by an increased expression of plasticity-related proteins such as cAMPresponsive element binding protein phosphorylated at Serl33, calcium-calmodulin-dependent kinase II phosphorylated at Thr286, and brain-derived neurotrophic factor, suggesting a role for Aβ in synaptic tagging. These changes resulted in the conversion of early into late long-term potentiation through the nitric oxide/cGMP/protein kinase G intracellular cascade consistent with a cGMP-dependent switch from short- to long-term memory observed in vivo after intrahippocampal administration of picomolar amounts of oAβ42. These effects were present upon extracellular but not intracellular application of the peptide and involved α7 nicotinic acetylcholine receptors. These observations clarified the physiological role of oAβ42 in synaptic function and memory formation providing solid fundamentals for investigating the pathological effects of high Aβ levels in the AD brains. [ABSTRACT FROM AUTHOR]

Background: The failure of cholinergic transmission and the increase of amyloid‐β peptide (Aβ) and tau protein are key players in Alzheimer's disease (AD). The interaction between α7 nicotinic acetylcholine receptors (α7‐nAChRs) and Aβ has been previously investigated, but few studies have focused on the crosstalk between α7‐nAChRs and tau. We previously reported that Aβ and tau might act independently or concomitantly to impair synaptic plasticity and memory, converging onto common targets such as amyloid precursor protein (APP). Here we investigated the role of α7‐nAChRs on tau‐mediated impairment of synaptic plasticity and memory, tau neuropathology, and their interplay with APP. Method: We used WT (C57Bl6/J) and α7 KO at different ages. 3XTg models of AD were used as positive controls. We performed electrophysiology to investigate synaptic transmission and plasticity at the CA3‐CA1 synapses from hippocampal slices, and behavioral studies (Novel Object Recognition and Location, Fear Conditioning) to evaluate memory. We used western blot for the expression of APP, tau (Ser199, Ser396, Thr205) and GSK‐3β (Ser9) phosphorylation. Formation of tau paired helical filaments (PHFs) and neurofibrillary tangles (NFTs) were evaluated by immunohistochemistry and Bielschowsky staining. Immunoreactivity for NeuN was measured to assess neuronal loss. Result: We found that α7 KO mice presented an AD phenotype characterized by the impairment of Long‐Term Potentiation and Paired Pulse Facilitation, and the reduction of different types of memory starting at 12 months of age. This age‐dependent phenotype was paralleled by an increase of APP expression, hyperphosphorylation of tau, and a decrease of GSK‐3β (Ser9) phosphorylation. α7 KO hippocampi presented a marked tau neuropathology with an increase of PHF‐1 immunoreactivity, the presence of PHFs and NFTs, and neuronal loss. Conclusion: In summary, the lack of α7‐nAChRs was sufficient to trigger an AD‐like phenotype characterized by a marked tau pathology. Our data also suggest that the concomitant increase of APP expression might contribute to tau neurotoxicity. [ABSTRACT FROM AUTHOR]

Background: Dopamine D3 receptors (D3‐Rs) are involved in several functions such as reward and social behavior and they have been proposed as a therapeutical target for addiction, schizophrenia, and Parkinson's disease. However, the role of D3‐Rs in cognition has been poorly investigated, with few studies demonstrating that the activation of D3‐Rs impairs attention and working memory. Results obtained in our laboratory suggested that D3 inhibition exerts a pro‐cognitive effect on long term potentiation (LTP) and recognition memory on healthy wild‐type (WT) mice. Based on these findings, here, we aimed to investigate whether the positive effect shown by D3 inhibition at the synapse could be exploited to counteract the synaptic plasticity and memory impairment found in aged and AD mice. Method: We used D3 knock out (D3‐KO), WT at 18‐22 months of age as a physiological model of aging, the 3XTg transgenic mouse model of AD and a7 KO mice, recently found to present an AD‐like phenotype. The pharmacological inhibition of D3‐Rs was obtained with the selective antagonist NGB‐2904. To test whether the pharmacological inhibition of D3‐Rs or their genetic deletion could rescue LTP and memory impairment, we performed electrophysiological recordings at CA3‐CA1 synapses in hippocampal slices and behavioral experiments of novel object recognition, novel object location and Morris Water Maze. Result: We found that D3‐Rs antagonism rescued the impairment of LTP, and different forms of memory in aged WT mice. Consistently, aged D3 KO mice showed no alteration of LTP and memory, suggesting that the genetic deletion of D3 receptors prevented the synaptic plasticity and memory decline that occurs with aging. The pharmacological inhibition of D3‐Rs was also able to rescue the memory impairment in both 3XTg and a7 KO mice. Conclusion: In conclusion, our findings suggest that the pro‐cognitive effect exerted by D3‐Rs inhibition or genetic deletion could represent a viable therapeutic strategy to treat the cognitive dysfunction occurring during aging and AD. [ABSTRACT FROM AUTHOR]

High levels of amyloid-β peptide (Aβ) have been related to Alzheimer's disease pathogenesis. However, in the healthy brain, low physiologically relevant concentrations of Aβ are necessary for long-term potentiation (LTP) and memory. Because cGMP plays a key role in these processes, here we investigated whether the cyclic nucleotide cGMP influences Aβ levels and function during LTP and memory. We demonstrate that the increase of cGMP levels by the phosphodiesterase-5 inhibitors sildenafil and vardenafil induces a parallel release of Aβ due to a change in the approximation of amyloid precursor protein (APP) and the β-site APP cleaving enzyme 1. Moreover, electrophysiological and behavioral studies performed on animals of both sexes showed that blocking Aβ function, by using anti-murine Aβ antibodies or APP knock-out mice, prevents the cGMP-dependent enhancement of LTP and memory. Our data suggest that cGMP positively regulates Aβ levels in the healthy brain which, in turn, boosts synaptic plasticity and memory. [ABSTRACT FROM AUTHOR]

Rhodiola Rosea (R. Rosea) is a plant used in traditional popular medicine to enhance cognition and physical performance. R. Rosea medicinal properties have been related to its capability to act as an adaptogen, i.e., a substance able to increase the organism's resistance to a variety of chemical, biological, and physical stressors in a non-specific way. These adaptogen properties have been mainly attributed to the glycoside salidroside, one of the bioactive compounds present in the standardized extracts of R. Rosea. Here, we aimed to investigate whether a single dose of salidroside is able to affect memory and emotional behavior in wild type adult mice. We performed fear conditioning to assess cued and contextual memory, elevated plus maze and open field to evaluate anxiety, and tail suspension test to evaluate depression. Our results showed that a single i.p. administration of salidroside was able to enhance fear memory and exerted an anxiolytic and antidepressant effect. These data confirmed the adaptogenic effect of R. Rosea bioactive compounds in animal models and suggest that salidroside might represent an interesting pharmacological tool to ameliorate cognition and counteract mood disorders. [ABSTRACT FROM AUTHOR]

Background: Growing evidence points to altered metabolic signals as a risk factor for Alzheimer's disease (AD). The high fatty acid levels and brain insulin resistance (BIR) found in AD brains may impinge on protein palmitoylation (P‐S‐palm), a post‐translational modification critically involved in the regulation of neuronal protein localization and synaptic function. Our previous findings highlighted the critical role of aberrant palmitoylation in BIR‐dependent memory impairment (Spinelli et al., 2017). Method: We tested the effect of chronic intranasal injection of the palmitoylation inhibitor 2‐bromopalmitate (2BP) on a large cohort of male and female 3xTg‐AD mice, starting from 3 months of age, by performing cognitive (novel object recognition and object displacement tests), electrophysiological (LTP), immunohistochemical (Abeta deposition) and molecular analyses (Abeta measurement by ELISA). We also analyzed the palmitoyl‐proteome (by acyl biotin exchange assay and mass‐spectrometry) in the hippocampus of 9‐month‐old wild type, 3xTg‐AD and 2BP‐treated 3xTg‐AD mice. Result: 2BP delayed the onset of memory deficits in both male and female 3xTg‐AD mice. More importantly, 2BP significantly enhanced cognitive performances in 6‐, 9‐ and 12‐month‐old animals. Accordingly, electrophysiological analyses on hippocampal brain slices from 2BP‐treated 3xTg‐AD mice revealed greater long‐term potentiation at CA3‐CA1 synapses. In addition, 2BP mice showed lower Abeta deposition in hippocampus. Finally, palmitoyl‐proteome analysis revealed a large number of proteins involved in APP and tau metabolism, synaptic plasticity and brain metabolism aberrantly palmitoylated in the AD mouse model and reverted by 2BP. Conclusion: Our data indicate that aberrant palmitoylation plays a critical role in the onset and progression of AD and reveal novel targets of protein palmitoylation potentially involved in the development of neurodegeneration and dementia. This is also the first preclinical study on the effect of 2BP on AD‐related cognitive decline. [ABSTRACT FROM AUTHOR]

An erratum in the article "Role of Amyloid-β and Tau Proteins in Alzheimer's Disease: Confuting the Amyloid Cascade" which appeared in a 2018 issue is presented.

The "Amyloid Cascade Hypothesis" has dominated the Alzheimer's disease (AD) field in the last 25 years. It posits that the increase of amyloid-β (Aβ) is the key event in AD that triggers tau pathology followed by neuronal death and eventually, the disease. However, therapeutic approaches aimed at decreasing Aβ levels have so far failed, and tau-based clinical trials have not yet produced positive findings. This begs the question of whether the hypothesis is correct. Here we have examined literature on the role of Aβ and tau in synaptic dysfunction, memory loss, and seeding and spreading of AD, highlighting important parallelisms between the two proteins in all of these phenomena. We discuss novel findings showing binding of both Aβ and tau oligomers to amyloid-β protein precursor (AβPP), and the requirement for the presence of this protein for both Aβ and tau to enter neurons and induce abnormal synaptic function and memory. Most importantly, we propose a novel view of AD pathogenesis in which extracellular oligomers of Aβ and tau act in parallel and upstream of AβPP. Such a view will call for a reconsideration of therapeutic approaches directed against Aβ and tau, paving the way to an increased interest toward AβPP, both for understanding the pathogenesis of the disease and elaborating new therapeutic strategies. [ABSTRACT FROM AUTHOR]

Studies in vitro have demonstrated that β3-adrenergic receptors (β3-ARs) regulate protein metabolism in skeletal muscle by promoting protein synthesis and inhibiting protein degradation. In this study, we evaluated whether activation of β3-ARs by the selective agonist CL316,243 modifies the functional and structural properties of skeletal muscles of healthy mice. Daily injections of CL316,243 for 15 days resulted in a significant improvement in muscle force production, assessed by grip strength and weight tests, and an increased myofiber cross-sectional area, indicative of muscle hypertrophy. In addition, atomic force microscopy revealed a significant effect of CL316,243 on the transversal stiffness of isolated muscle fibers. Interestingly, the expression level of mammalian target of rapamycin (mTOR) downstream targets and neuronal nitric oxide synthase (NOS) was also found to be enhanced in tibialis anterior and soleus muscles of CL316,243 treated mice, in accordance with previous data linking β3-ARs to mTOR and NOS signaling pathways. In conclusion, our data suggest that CL316,243 systemic administration might be a novel therapeutic strategy worthy of further investigations in conditions of muscle wasting and weakness associated with aging and muscular diseases. [ABSTRACT FROM AUTHOR]

Transforming Growth Factor β1 (TGF-β1) is a well-known neuroprotective and neurotrophic factor demonstrated to play a role in synaptic transmission. However, its involvement in physiological mechanisms underlying synaptic plasticity and memory at hippocampal level has not been thoroughly investigated. Here, we examine the role of TGF-β1 in hippocampal long-term potentiation (LTP) and memory in adult wild type mice. Our data provide evidence that administration of exogenous TGF-β1 is able to convert early-phase-LTP into late-phase-LTP. Furthermore, we show that the block of the endogenous TGF-β1 signaling pathway by the specific TGF-β1 inhibitor SB431542, impairs LTP and object recognition memory. The latter impairment was rescued by administration of exogenous TGF-β1, suggesting that endogenously produced TGF-β1 plays a role in physiological mechanisms underlying LTP and memory. Finally, TGF-β1 functional effect correlates with an increased expression of the phosphorylated transcription factor cAMP-Responsive Element Binding protein. [ABSTRACT FROM AUTHOR]

We have previously demonstrated that activation of serotonin 5-HT 7 receptors (5-HT 7 R) reverses metabotropic glutamate receptor-mediated long term depression (mGluR-LTD) in the hippocampus of wild-type (WT) and Fmr1 Knockout (KO) mice, a model of Fragile X Syndrome (FXS) in which mGluR-LTD is abnormally enhanced. Here, we have investigated intracellular mechanisms underlying the effect of 5-HT 7 R activation using patch clamp on hippocampal slices. Furthermore, we have tested whether in vivo administration of LP-211, a selective 5-HT 7 R agonist, can rescue learning and behavior in Fmr1 KO mice. In the presence of an adenylate cyclase blocker, mGluR-LTD was slightly enhanced in WT and therefore the difference between mGluR-LTD in WT and Fmr1 KO slices was no longer present. Conversely, activation of adenylate cyclase by either forskolin or Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) completely reversed mGluR-LTD in WT and Fmr1 KO. 5-HT 7 R activation reversed mGluR-LTD in WT and corrected exaggerated mGluR-LTD in Fmr1 KO; this effect was abolished by blockade of either adenylate cyclase or protein kinase A (PKA). Exposure of hippocampal slices to LP-211 caused an increased phosphorylation of extracellular signal regulated kinase (ERK), an intracellular effector involved in mGluR-LTD, in WT mice. Conversely, this effect was barely detectable in Fmr1 KO mice, suggesting that 5-HT 7 R-mediated reversal of mGluR-LTD does not require ERK stimulation. Finally, an acute in vivo administration of LP-211 improved novel object recognition (NOR) performance in WT and Fmr1 KO mice and reduced stereotyped behavior in Fmr1 KO mice. Our results indicate that mGluR-LTD in WT and Fmr1 KO slices is bidirectionally modulated in conditions of either reduced or enhanced cAMP formation. Activation of 5-HT 7 receptors reverses mGluR-LTD by activation of the cAMP/PKA intracellular pathway. Importantly, a systemic administration of a 5-HT 7 R agonist to Fmr1 KO mice corrected learning deficits and repetitive behavior. We suggest that selective 5-HT 7 R agonists might become novel pharmacological tools for FXS therapy.

The concurrent application of subtoxic doses of soluble oligomeric forms of human amyloid-beta (oAβ) and Tau (oTau) proteins impairs memory and its electrophysiological surrogate long-term potentiation (LTP), effects that may be mediated by intra-neuronal oligomers uptake. Intrigued by these findings, we investigated whether oAβ and oTau share a common mechanism when they impair memory and LTP in mice. We found that as already shown for oAβ, also oTau can bind to amyloid precursor protein (APP). Moreover, efficient intra-neuronal uptake of oAβ and oTau requires expression of APP. Finally, the toxic effect of both extracellular oAβ and oTau on memory and LTP is dependent upon APP since APP-KO mice were resistant to oAβ- and oTau-induced defects in spatial/associative memory and LTP. Thus, APP might serve as a common therapeutic target against Alzheimer's Disease (AD) and a host of other neurodegenerative diseases characterized by abnormal levels of Aβ and/or Tau.

Introduction: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes, leading to dementia. Histopathological hallmarks are represented by aggregates of beta-amyloid peptide (Aβ) in senile plaques and deposition of hyperphosphorylated tau protein in neurofibrillary tangles in the brain. Rare forms of early onset familial Alzheimer's disease are due to gene mutations. This has prompted researchers to develop genetically modified animals that could recapitulate the main features of the disease. The use of these models is complemented by non-genetically modified animals., Areas Covered: This review summarizes the characteristics of the most used transgenic (Tg) and non-Tg models of AD. The authors have focused on models mainly used in their laboratories including amyloid precursor protein (APP) Tg2576, APP/presenilin 1, 3xAD, single h-Tau, non-Tg mice treated with acute injections of Aβ or tau, and models of physiological aging., Expert Opinion: Animal models of disease might be very useful for studying the pathophysiology of the disease and for testing new therapeutics in preclinical studies but they do not reproduce the entire clinical features of human AD. When selecting a model, researchers should consider the various factors that might influence the phenotype. They should also consider the timing of testing/treating animals since the age at which each model develops certain aspects of the AD pathology varies.