Memantine prevents memory consolidation failure induced by soluble beta amyloid in rats

Acute Administration of HIV-1 Tat Protein Drives Glutamatergic Alterations in a Rodent Model of HIV-Associated Neurocognitive Disorders

HIV-1-associated neurocognitive disorders (HAND) are a major comorbidity of HIV-1 infection, marked by impairment of executive function varying in severity. HAND affects nearly half of people living with HIV (PLWH), with mild forms predominating since the use of anti-retroviral therapies (ART). The HIV-1 transactivator of transcription (Tat) protein is found in the cerebrospinal fluid of patients adherent to ART, and its administration or expression in animals causes cognitive symptoms. Studies of Tat interaction with the N-methyl-D-aspartate receptor (NMDAR) suggest that glutamate toxicity contributes to Tat-induced impairments. To identify changes in regional glutamatergic circuitry underlying cognitive impairment, we injected recombinant Tat86 or saline to medial prefrontal cortex (mPFC) of male Sprague-Dawley rats. Rats were assessed with behavioral tasks that involve intact functioning of mPFC including the novel object recognition (NOR), spatial object recognition (SOR), and temporal order (TO) tasks at 1 and 2 postoperative weeks. Following testing, mPFC tissue was collected and analyzed by RT-PCR. Results showed Tat86 in mPFC-induced impairment in SOR, and upregulation of Grin1 and Grin2a transcripts. To further understand the mechanism of Tat toxicity, we assessed the effects of full-length Tat101 on gene expression in mPFC by RNA sequencing. The results of RNAseq suggest that glutamatergic effects of Tat86 are maintained with Tat101, as Grin2a was upregulated in Tat101-injected tissue, among other differentially expressed genes. Spatial learning and memory impairment and Grin2a upregulation suggest that exposure to Tat protein drives adaptation in mPFC, altering the function of circuitry supporting spatial learning and memory.

Memantine: Updating a rare success story in pro-cognitive therapeutics

The great potential for NMDA receptor modulators as druggable targets in neurodegenerative disorders has been met with limited success. Considered one of the rare exceptions, memantine has consistently demonstrated restorative and prophylactic properties in many AD models. In clinical trials memantine slows the decline in cognitive performance associated with AD. Here, we provide an overview of the basic properties including pharmacological targets, toxicology and cellular effects of memantine. Evidence demonstrating reductions in molecular, physiological and behavioural indices of AD-like impairments associated with memantine treatment are also discussed. This represents both an extension and homage to Dr. Chris Parson's considerable contributions to our fundamental understanding of a success story in the AD treatment landscape.

Precision Medicine in Alzheimer's Disease: Investigating Comorbid Common Biological Substrates in the Rat Model of Amyloid Beta-Induced Toxicity

Alzheimer's disease (AD), one of the most widespread neurodegenerative disorder, is a fatal global burden for the elder population. Although many efforts have been made, the search of a curative therapy is still ongoing. Individuating phenotypic traits that might help in investigating treatment response is of growing interest in AD research. AD is a complex pathology characterized by many comorbidities, such as depression and increased susceptibility to pain perception, leading to postulate that these conditions may rely on common biological substrates yet to be determined. In order to investigate those biological determinants to be associable with phenotypic traits, we used the rat model of amyloid beta-induced toxicity. This established model of early phase of AD is obtained by the intracerebroventricular injection of soluble amyloid beta1-42 (Aβ) peptide 7 days before performing experiments. In this model, we have previously reported increased immobility in the forced swimming test, reduced cortical serotonin levels and subtle alterations in the cognitive domain a depressive-like phenotype associated with subtle alteration in memory processes. In light of evaluating pain perception in this animal model, we performed two different behavioral tests commonly used, such as the paw pressure test and the cold plate test, to analyze mechanical hyperalgesia and thermal allodynia, respectively. Behavioural outcomes confirmed the memory impairment in the social recognition test and, compared to sham, Aβ-injected rats showed an increased selective susceptibility to mechanical but not to thermal stimulus. Behavioural data were then corroborated by neurochemical and biochemical biomarker analyses either at central or peripheral level. Data showed that the peptide injection evoked a significant increase in hypothalamic glutamate, kynurenine and dopamine content, while serotonin levels were reduced. Plasma Cystatin-C, a cysteine protease, was increased while serotonin and melatonin levels were decreased in Aβ-injected rats. Urinary levels paralleled plasma quantifications, indicating that Aβ-induced deficits in pain perception, mood and cognitive domain may also depend on these biomarkers. In conclusion, in the present study, we demonstrated that this animal model can mimic several comorbid conditions typical of the early phase of AD. Therefore, in the perspective of generating novel therapeutic strategies relevant to precision medicine in AD, this animal model and the biomarkers evaluated herein may represent an advantageous approach.

JM-20 treatment prevents neuronal damage and memory impairment induced by aluminum chloride in rats

The number of people with dementia worldwide is estimated at 50 million by 2018 and continues to rise mainly due to increasing aging and population growth. Clinical impact of current interventions remains modest and all efforts aimed at the identification of new therapeutic approaches are therefore critical. Previously, we showed that JM-20, a dihydropyridine-benzodiazepine hybrid molecule, protected memory processes against scopolamine-induced cholinergic dysfunction. In order to gain further insight into the therapeutic potential of JM-20 on cognitive decline and Alzheimer's disease (AD) pathology, here we evaluated its neuroprotective effects after chronic aluminum chloride (AlCl3) administration to rats and assessed possible alterations in several types of episodic memory and associated pathological mechanisms. Oral administration of aluminum to rodents recapitulates several neuropathological alterations and cognitive impairment, being considered a convenient tool for testing the efficacy of new therapies for dementia. We used behavioral tasks to test spatial, emotional- associative and novel object recognition memory, as well as molecular, enzymatic and histological assays to evaluate selected biochemical parameters. Our study revealed that JM-20 prevented memory decline alongside the inhibition of AlCl3 -induced oxidative stress, increased AChE activity, TNF-α and pro-apoptotic proteins (like Bax, caspase-3, and 8) levels. JM-20 also protected against neuronal damage in the hippocampus and prefrontal cortex. Our findings expanded our understanding of the ability of JM-20 to preserve memory in rats under neurotoxic conditions and confirm its potential capacity to counteract cognitive impairment and etiological factors of AD by breaking the progression of key steps associated with neurodegeneration.

Hippocampal Degeneration and Behavioral Impairment During Alzheimer-Like Pathogenesis Involves Glutamate Excitotoxicity

The hallmarks of Alzheimer's disease (AD) pathology include senile plaques accumulation and neurofibrillary tangles, which is thought to underlie synaptic failure. Recent evidence however supports that synaptic failure in AD may instead be instigated by enhanced N-methyl-D-aspartate (NMDA) activity, via a reciprocal relationship between soluble amyloid-β (Aβ) accumulation and increased glutamate agonist. While previous studies have shown Aβ-mediated alterations to the glutamatergic system during AD, the underlying etiology of excitotoxic glutamate-induced changes has not been explored. Here, we investigated the acute effects of stereotaxic dentate gyrus (DG) glutamate injection on behavior and molecular expression of specific proteins and neurochemicals modulating hippocampal functions. Dependence of glutamate-mediated effects on NMDA receptor (NMDAR) hyperactivation was tested using NMDARs antagonist memantine. DG of Wistar rats (12-weeks-old) were bilaterally microinjected with glutamate (500 mM) with or without daily intraperitoneal (i.p.) memantine injection (20 mg/kg) for 14 days, while controls received either intrahippocampal/i.p. PBS or i.p. memantine. Behavioral characterization in open field and Y-maze revealed that glutamate evoked anxiogenic responses and perturbed spatial memory were inhibited by memantine. In glutamate-treated rats, increased NO expression was accompanied by marked reduction in profiles of glutathione-s-transferase and glutathione peroxidase. Similarly, glutamate-mediated increase in acetylcholinesterase expression corroborated downregulation of synaptophysin and PSD-95, coupled with initiation of reactive astrogliosis (GFAP). While neurofilament immunolocalization/immunoexpression was unperturbed, we found glutamate-mediated reduction in neurogenic markers Ki67 and PCNA immunoexpression, with a decrease in NR2B protein expression, whereas mGluR1 remains unchanged. In addition, increased expression of apoptotic regulatory proteins p53 and Bax was seen in glutamate infused rats, corroborating chromatolytic degeneration of granule neurons in the DG. Interestingly, memantine abrogated most of the degenerative changes associated with glutamate excitotoxicity in this study. Taken together, our findings causally link acute glutamate dyshomeostasis in the DG with development of AD-related behavioral impairment and molecular neurodegeneration.

Investigation of Low Dose Cabazitaxel Potential as Microtubule Stabilizer in Experimental Model of Alzheimer's Disease: Restoring Neuronal Cytoskeleton

BACKGROUND

Neuronal Microtubule (MT) tau protein, providing cytoskeleton to neuronal cells, plays a vital role, including maintenance of cell shape, intracellular transport, and cell division. Tau hyperphosphorylation mediated MT destabilization results in axonopathy, additionally neurotransmitter deficit and ultimately causing Alzheimer's disease. Pre-clinically, streptozotocin (3mg/kg, 10μl/ unilateral, ICV) stereotaxically mimics the behavioral and neurochemical alterations similar to Alzheimer's tau pathology resulting in MT assembly defects further lead to neuropathological cascades.

OBJECTIVE

Clinically approved medications such as Donepezil (DNP), rivastigmine, and Memantine (MEM) are responsible for symptomatic care only, but there is no specific pharmacological intervention that directly interacts with the neuronal microtubule destabilization.

METHODS

The current study focused on the involvement of anti-cancer agent microtubule stabilizer cabazitaxel at a low dose (0.5 and 2 mg/kg) alone and in combination with standard drugs DNP (5 mg/kg), MEM (10 mg/kg) and microtubule stabilizer Epothilone D (EpoD) (3 mg/kg) in the prevention of intracerebroventricular streptozotocin (ICV-STZ) intoxicated microtubule-associated tau protein hyperphosphorylation.

RESULTS

Chronic treatment of CBZ at a low dose alone and in combination with standard drugs showing no side effect and significantly improve the cognitive impairment, neurochemical alterations along with reducing the level of hyperphosphorylated tau by preventing the breakdown of the neuronal cytoskeleton, respectively.

CONCLUSION

The above findings suggested that CBZ at low dose show neuroprotective effects against ICV-STZ induced microtubule-associated tau protein hyperphosphorylation in rats and may be an effective agent for the preventive treatment of AD.

Celecoxib Exerts Neuroprotective Effects in β-Amyloid-Treated SH-SY5Y Cells Through the Regulation of Heme Oxygenase-1: Novel Insights for an Old Drug

The formation and aggregation of amyloid-β-peptide (Aβ) into soluble and insoluble species represent the pathological hallmarks of Alzheimer’s disease (AD). Over the last few years, however, soluble Aβ (sAβ) prevailed over fibrillar Aβ (fAβ) as determinant of neurotoxicity. One of the main therapeutic strategies for challenging neurodegeneration is to fight against neuroinflammation and prevent free radical-induced damage: in this light, the heme oxygenase/biliverdin reductase (HO/BVR) system is considered a promising drug target. The aim of this work was to investigate whether or not celecoxib (CXB), a selective inhibitor of the pro-inflammatory cyclooxygenase-2, modulates the HO/BVR system and prevents lipid peroxidation in SH-SY5Y neuroblastoma cells. Both sAβ (6.25–50 nM) and fAβ (1.25–50 nM) dose-dependently over-expressed inducible HO (HO-1) after 24 h of incubation, reaching statistical significance at 25 and 6.25 nM, respectively. Interestingly, CXB (1–10 μM, for 1 h) further enhanced Aβ-induced HO-1 expression through the nuclear translocation of the transcriptional factor Nrf2. Furthermore, 10 μM CXB counteracted the Aβ-induced ROS production with a mechanism fully dependent on HO-1 up-regulation; nevertheless, 10 μM CXB significantly counteracted only 25 nM sAβ-induced lipid peroxidation damage in SH-SY5Y neurons by modulating HO-1. Both carbon monoxide (CORM-2, 50 nM) and bilirubin (50 nM) significantly prevented ROS production in Aβ-treated neurons and favored both the slowdown of the growth rate of Aβ oligomers and the decrease in oligomer/fibril final size. In conclusion, these results suggest a novel mechanism through which CXB is neuroprotective in subjects with early AD or mild cognitive impairment.

Quercetin ameliorates diabetic encephalopathy through SIRT1/ER stress pathway in db/db mice

Studies have shown that diabetes is an important risk factor for cognitive dysfunction, also called diabetic encephalopathy (DE). Quercetin has been reported to be effective in improving cognitive dysfunction in DE. But its detailed mechanism is still ambiguous. In this study, we used db/db mice to investigate whether quercetin could activate SIRT1 and inhibit ER pathways to improve DE. Behavioral tests (Morris water maze and new objects) showed that quercetin (70 mg/kg) can effectively improve the learning and memory ability in db/db mice. OGTT and ITT tests indicated that quercetin could alleviate impaired glucose tolerance and insulin resistance in db/db mice. Western blot analysis and Nissl staining showed that quercetin can improve the expression of nerve and synapse-associated proteins (PSD93, PSD95, NGF and BDNF) and inhibit neurodegeneration. Meanwhile, quercetin up-regulates SIRT1 protein expression and inhibits the expression of ER signaling pathway-related proteins (PERK, IRE-1α, ATF6, eIF2α, BIP and PDI). In addition, oxidative stress levels were significantly reduced after quercetin treatment. In conclusion, current experimental results indicated that SIRT1/ER stress is a promising mechanism involved in quercetin-treated diabetic encephalopathy.

Quercetin protects against diabetic encephalopathy via SIRT1/NLRP3 pathway in db/db mice

Epidemiological studies have found that diabetes and cognitive dysfunction are closely related. Quercetin has been certified with the effect on improving diabetes mellitus (DM) and cognitive impairment. However, the effect and related mechanism of quercetin on diabetic encephalopathy (DE) are still ambiguous. In this study, we used the db/db mice (diabetic model) to discover whether quercetin could improve DE through the Sirtuin1/NLRP3 (NOD‐, LRR‐ and pyrin domain‐containing 3) pathway. Behavioural results (Morris water maze and new object recognition tests) showed that quercetin (70 mg/kg) improved the learning and memory. Furthermore, quercetin alleviated insulin resistance and the level of fasting blood glucose. Besides, Western blot analysis also showed that quercetin increased the protein expressions of nerve‐ and synapse‐related protein, including postsynapticdensity 93 (PSD93), postsynapticdensity 95 (PSD95), brain‐derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the brain of db/db mice. Quercetin also increased the protein expression of SIRT1 and decreased the expression of NLRP3 inflammation‐related proteins, including NLRP3, the adaptor protein ASC and cleaved Caspase‐1, the pro‐inflammatory cytokines IL‐1β and IL‐18. In conclusion, the present results indicate that the SIRT1/NLRP3 pathway may be a crucial mechanism for the neuroprotective effect of quercetin against DE.

Chronic Fluoxetine Treatment Induces Maturation-Compatible Changes in the Dendritic Arbor and in Synaptic Responses in the Auditory Cortex

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) used to treat mood and anxiety disorders. Chronic treatment with this antidepressant drug is thought to favor functional recovery by promoting structural and molecular changes in several forebrain areas. At the synaptic level, chronic fluoxetine induces an increased size and density of dendritic spines and an increased ratio of GluN2A over GluN2B N-methyl-D-aspartate (NMDA) receptor subunits. The “maturation”-promoting molecular changes observed after chronic fluoxetine should also induce structural remodeling of the neuronal dendritic arbor and changes in the synaptic responses. We treated adult rats with fluoxetine (0.7 mg/kg i.p. for 28 days) and performed a morphometric analysis using Golgi stain in limbic and nonlimbic cortical areas. Then, we focused especially on the auditory cortex, where we evaluated the dendritic morphology of pyramidal neurons using a 3-dimensional reconstruction of neurons expressing mRFP after in utero electroporation. With both methodologies, a shortening and decreased complexity of the dendritic arbors was observed, which is compatible with an increased GluN2A over GluN2B ratio. Recordings of extracellular excitatory postsynaptic potentials in the auditory cortex revealed an increased synaptic response after fluoxetine and were consistent with an enrichment of GluN2A-containing NMDA receptors. Our results confirm that fluoxetine favors maturation and refinement of extensive cortical networks, including the auditory cortex. The fluoxetine-induced receptor switch may decrease GluN2B-dependent toxicity and thus could be applied in the future to treat neurodegenerative brain disorders characterized by glutamate toxicity and/or by an aberrant network connectivity.

Monoaminergic System Modulation in Depression and Alzheimer's Disease: A New Standpoint?

The prevalence of depression has dramatically increased, and it has been estimated that over 300 million people suffer from depression all over the world. Depression is highly comorbid with many central and peripheral disorders. In this regard, depressive states have been associated with the development of neurological disorders such as Alzheimer's disease (AD). Accordingly, depression is a risk factor for AD and depressive symptomatology is common in pre-clinical AD, representing an early manifestation of this disease. Neuropsychiatric symptoms may represent prodromal symptoms of dementia deriving from neurobiological changes in specific cerebral regions; thus, the search for common biological substrates is becoming an imperative and intriguing field of research. Soluble forms of beta amyloid peptide (Aβ) have been implicated both in the development of early memory deficits and neuropsychiatric symptoms. Indeed, soluble Aβ species have been shown to induce a depressive-like phenotype in AD animal models. Alterations in monoamine content are a common feature of these neuropathologies. Interestingly, serotonergic system modulation has been implicated in alteration of Aβ production. In addition, noradrenaline is considered crucially involved in compensatory mechanisms, leading to increased Aβ degradation via several mechanisms, including microglia modulation. In further agreement, antidepressant drugs have also been shown to potentially modulate cognitive symptoms in AD and depression. Thus, the present review summarizes the main knowledge about biological and pathological substrates, such as monoamine and related molecules, commonly involved in AD and depression pathology, thus shading light on new therapeutic approaches.

A long-term treatment with taurine prevents cardiac dysfunction in mdx mice

Taurine is an amino acid abundantly present in heart and skeletal muscle. Duchenne muscular dystrophy (DMD) is a genetic disorder in which the absence of dystrophin leads to skeletal muscle wasting and heart failure. An altered taurine metabolism has been described in dystrophic animals and short-term taurine administration exerts promising amelioration of early muscular alterations in the mdx mouse model of DMD. To reinforce the therapeutic and nutraceutical taurine potential in DMD, we evaluated the effects of a long-term treatment on cardiac and skeletal muscle function of mdx mice in a later disease stage. Taurine was administered in drinking water (1 g/kg/day) to wt and mdx mice for 6 months, starting at 6 months of age. Ultrasonography evaluation of heart and hind limb was performed, in parallel with in vivo and ex vivo functional tests and biochemical, histological and gene expression analyses. 12-month-old mdx mice showed a significant worsening of left ventricular function parameters (shortening fraction, ejection fraction, stroke volume), which were significantly counteracted by the taurine treatment. In parallel, histologic signs of damage were reduced by taurine along with the expression of proinflammatory myocardial IL-6. Interestingly, no effects were observed on hind limb volume and percentage of vascularization or on in vivo and ex vivo muscle functional parameters, suggesting a tissue-specific action of taurine in relation to the disease phase. A trend toward increase in taurine was found in heart and quadriceps from treated animals, paralleled by a slight decrease in mdx mice plasma. Our study provides evidences that taurine can prevent late heart dysfunction in mdx mice, further corroborating the interest on this amino acid toward clinical trials.

Jiao-Tai-Wan Improves Cognitive Dysfunctions through Cholinergic Pathway in Scopolamine-Treated Mice

Cognitive dysfunction is characterized as the gradual loss of learning ability and cognitive function, as well as memory impairment. Jiao-tai-wan (JTW), a Chinese medicine prescription including Coptis chinensis and cinnamon, is mainly used for the treatment of insomnia, while the effect of JTW in improving cognitive function has not been reported. In this study, we employed a scopolamine- (SCOP-) treated learning and memory deficit model to explore whether JTW could alleviate cognitive dysfunction. In behavioral experiments, Morris water maze, Y-maze, fearing condition test, and novel object discrimination test were conducted. Results showed that oral administration of JTW (2.1 g/kg, 4.2 g/kg, and 8.4 g/kg) can effectively promote the ability of spatial recognition, learning and memory, and the memory ability of fresh things of SCOP-treated mice. In addition, the activity of acetylcholinesterase (AChE) was effectively decreased; the activity of choline acetyltransferase (ChAT) and concentration of acetylcholine (Ach) were improved after JTW treatment in both hippocampus and cortex of SCOP-treated mice. JTW effectively ameliorated oxidative stress because of decreased the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) and increased the activities of superoxide dismutase (SOD) and catalase (CAT) in hippocampus and cortex. Furthermore, JTW promotes the expressions of neurotrophic factors including postsynaptic density protein 95 (PSD95) and synaptophysin (SYN) and brain-derived neurotrophic factor (BDNF) in both hippocampus and cortex. Nissl's staining shows that the neuroprotective effect of JTW was very effective. To sum up, JTW might be a promising candidate for the treatment of cognitive dysfunction.

Effect of a long-term treatment with metformin in dystrophic mdx mice: A reconsideration of its potential clinical interest in Duchenne muscular dystrophy

The pharmacological stimulation of AMP-activated protein kinase (AMPK) via metabolic enhancers has been proposed as potential therapeutic strategy for Duchenne muscular dystrophy (DMD). Metformin, a widely-prescribed anti-hyperglycemic drug which activates AMPK via mitochondrial respiratory chain, has been recently tested in DMD patients in synergy with nitric oxide (NO)-precursors, with encouraging results. However, preclinical data supporting the use of metformin in DMD are still poor, and its actions on skeletal muscle appear controversial. Therefore, we investigated the effects of a long-term treatment with metformin (200 mg/kg/day in drinking water, for 20 weeks) in the exercised mdx mouse model, characterized by a severe mechanical-metabolic maladaptation. Metformin significantly ameliorated histopathology in mdx gastrocnemius muscle, in parallel reducing TGF-β1 with a recovery score (r.s) of 106%; this was accompanied by a decreased plasma matrix-metalloproteinase-9 (r.s. 43%). In addition, metformin significantly increased mdx diaphragm twitch and tetanic tension ex vivo (r.s. 44% and 36%, respectively), in spite of minor effects on in vivo weakness. However, no clear protective actions on dystrophic muscle metabolism were observed, as shown by the poor metformin effect on AMPK activation measured by western blot, on the expression of mechanical-metabolic response genes analyzed by qPCR, and by the lack of fast-to-slow fiber-type-shift assessed by SDH staining in tibialis anterior muscle. Similar results were obtained in the milder phenotype of sedentary mdx mice. The lack of metabolic effects could be, at least partly, due to metformin inability to increase low mdx muscle levels of l-arginine, l-citrulline and taurine, found by HPLC. Our findings encourage to explore alternative, metabolism-independent mechanisms of action to differently repurpose metformin in DMD, supporting its therapeutic combination with NO-sources.

Asiaticoside Attenuates Cell Growth Inhibition and Apoptosis Induced by Aβ1-42 via Inhibiting the TLR4/NF-κB Signaling Pathway in Human Brain Microvascular Endothelial Cells

Alzheimer's disease (AD) is a very common progressive neurodegenerative disorder with the highest incidence in the world. Dysfunction of the blood-brain barrier (BBB) may be responsible for the pathogenesis and pathology of AD for abnormally transporting amyloid-β (Aβ, the main component of the senile plaques) from the sera into the central nervous system. Aβ peptides induce apoptosis in human brain microvascular endothelial cells (hBMECs), the main component of BBB. Apoptosis in neuronal cells plays a critical role in the pathogenesis of AD. Asiaticoside, a natural glycoside extracted from Centella asiatica (L.) Urban, has an anti-apoptotic effect on hBMECs but the molecule mechanism remains unclear. Therefore, we investigate the protective effect of asiaticoside on Aβ_1-42-induced cytotoxicity and apoptosis as well as associated mechanism in hBMECs with commonly used in vitro methods for clinical development of asiaticoside as a novel anti-AD agent. In the present study, we investigated the effects of asiaticoside on cytotoxicity by Cell Counting Kit-8 assay, mitochondrial membrane potential by JC-1 fluorescence analysis, anti-apoptosis by Hoechst 33258 staining and Annexin V-FITC (fluorescein isothiocyanate) and propidium iodide (PI) analyses, the expressions of TNF-α and IL-6 by enzyme-linked immunosorbent assay (ELISA) and TLR4, MyD88, TRAF6, p-NF-κB p65, and total NF-κB p65 by Western blotting, and nuclear translocation of NF-κB p65 by immunofluorescence analysis in hBMECs. The results showed that pretreatment of asiaticoside (25, 50, and 100 μM) for 12 h significantly attenuated cell growth inhibition and apoptosis, and restored declined mitochondrial membrane potential induced by Aβ_1-42 (50 μM) in hBMECs. Asiaticoside also significantly downregulated the elevated expressions of TNF-α, IL-6, TLR4, MyD88, TRAF6, and p-NF-κB p65, as well as inhibited NF-κB p65 translocation from cytoplasm to nucleus induced by Aβ_1-42 in hBMECs in a concentration-dependent manner. The possible underlying molecular mechanism of asiaticoside may be through inhibiting the TLR4/NF-κB signaling pathway. Therefore, asiaticoside may be developed as a novel agent for the prevention and/or treatment of AD clinically.

The contribution of transgenic and nontransgenic animal models in Alzheimer's disease drug research and development

Over the last few years, several papers have become available in the literature on both the main hallmarks of Alzheimer's disease (AD) and the several intracellular pathways whose alteration is responsible for its onset and progression. The use of transgenic and nontransgenic animal models has played a key role in achieving such a remarkable amount of preclinical data, allowing researchers to dissect the cellular changes occurring in the AD brain. In addition, the huge amount of preclinical evidence arising from these animal models was necessary for the further clinical development of pharmacological agents capable of interfering with most of the impaired neural pathways in AD patients. In this respect, a significant role is played by the dysfunction of excitatory and inhibitory neurotransmission responsible for the cognitive and behavioral symptoms described in AD patients. The aim of this review is to summarize the main animal models that contributed toward unraveling the pathological changes in neurotransmitter synthesis, release, and receptor binding in AD preclinical studies. The review also provides an updated description of the current pharmacological agents - still under clinical development - acting on the neurotransmitter systems.

Celecoxib Prevents Cognitive Impairment and Neuroinflammation in Soluble Amyloid β-treated Rats

Recent findings suggest that soluble forms of amyloid-β (sAβ) peptide contribute to synaptic and cognitive dysfunctions in early stages of Alzheimer's disease (AD). On the other hand, neuroinflammation and cyclooxygenase-2 (COX-2) enzyme have gained increased interest as key factors involved early in AD, although the signaling pathways and pathophysiologic mechanisms underlying a link between sAβ-induced neurotoxicity and inflammation are still unclear. Here, we investigated the effects of selective COX-2 enzyme inhibition on neuropathological alterations induced by sAβ administration in rats. To this purpose, animals received an intracerebroventricular (icv) injection of predominantly monomeric forms of sAβ and, 7 days after, behavioral as well as biochemical parameters and neurotransmitter alterations were evaluated. During this period, rats also received a sub-chronic treatment with celecoxib. Biochemical results demonstrated that icv sAβ injection significantly increased both COX-2 and pro-inflammatory cytokines expression in the hippocampus (Hipp) of treated rats. In addition, the number of hypertrophic microglial cells and astrocytes were upregulated in sAβ-treated group. Interestingly, rats treated with sAβ showed long-term memory deficits, as confirmed by a significant reduction of discrimination index in the novel object recognition test, along with reduced brain-derived neurotrophic factor expression and increased noradrenaline levels in the Hipp. Systemic administration of celecoxib prevented behavioral dysfunctions, as well as biochemical and neurotransmitter alterations. In conclusion, our results suggest that sAβ neurotoxicity might be associated to COX-2-mediated inflammatory pathways and that early treatment with selective COX-2 inhibitor might provide potential remedies to counterbalance the sAβ-induced effects.

N-3 PUFA diet enrichment prevents amyloid beta-induced depressive-like phenotype

Among neuropsychiatric diseases, depression is one of the most prevalent. Many pathologies have been indicated as comorbid with depression and in particular, neurodegenerative disorders such as Alzheimer's diseases (AD). In this regard, several evidences endorse a strong relationship between depression and AD, so much that this mental illness has been proposed either as a risk factor for AD or as a prodromic AD phase. Furthermore, amyloid beta (Aβ) peptide, the main constituent of amyloid plaques commonly considered the principal hallmark of AD brains, has been shown to be increased, in its soluble form, in depressed patients. Accordingly, we have previously found that Aβ, intracerebroventricularly (i.c.v.) injected, is able to evoke a depressive-like profile in rats accompanied by low cortical serotonin and reduced neurotrophin content. Taking into account the great increase in AD and depression prevalence, many environmental factors have been under study, particularly dietary factors, and the role of polyunsaturated fatty acids (PUFA) is becoming central in this field of research. Thus, aim of the present study was to evaluate the neurobehavioral effects of lifelong exposure to either n-3 PUFA rich or n-3 PUFA poor diet after Aβ central administration. Results showed that n-3 PUFA enriched diet prevented the Aβ- induced depressive-like behaviors, as reveled by the reduction in the immobility time in the FST test. Furthermore, n-3 PUFA rich diet exposure reverted also serotonin and neurotrophin level reduction in prefrontal cortex of Aβ treated rats. Taken together, our data support the concept that supplementation of diet with n-3 PUFA represents a valid approach to reduce the risk of developing depressive symptoms, as well as reducing the risk of Aβ-related pathologies, such as AD.

Antidepressant drugs for beta amyloid-induced depression: A new standpoint?

Mounting evidence suggests that depression represents a risk factor and an early manifestation of Alzheimer's disease (AD). Neuropsychiatric symptoms may derive from neurobiological changes in specific brain areas and may be considered prodromal of dementia. We have previously reported the depressive-like profile in rats receiving a single intracerebroventricular injection of soluble amyloid beta protein (ßA). Here, we verified the effect of different classes of antidepressants on the ßA-induced depressive behavior and on cortical monoamine levels. To these purposes, the forced swimming test was performed and cortical levels of serotonin (5-HT) and noradrenaline (NA) were quantified by high performance liquid chromatography (HPLC). We found that acute fluoxetine (20mg/kg, s.c.), reboxetine (10mg/kg, s.c.), and ketamine (15mg/kg, i.p.) significantly reduced the immobility in ßA-treated rats compared to controls. Fluoxetine and reboxetine reversed 5-HT reduction, while βA-induced NA increase was further enhanced by all treatments. Treatments with fluoxetine, reboxetine and ketamine were able to revert soluble ßA-induced decrease of cortical BDNF levels, while only fluoxetine and ketamine, but not reboxetine, had the same effects on cortical NGF expression. Moreover, plasma soluble ßA-levels were lowered by fluoxetine, but not reboxetine and ketamine, treatments. Our data suggest that different classes of antidepressants yield a short-acting effect on rat soluble ßA-induced depressive profile. Thus, we hypothesize a novel common mechanism of action of these drugs also based upon a "ßA lowering" effect. Although further investigations are still needed, our study might open a new scenario for unravelling the molecular antidepressant mechanisms of these drugs.

Mitochondrial involvement in memory impairment induced by scopolamine in rats

OBJECTIVE

Scopolamine (SCO) administration to rats induces molecular features of AD and other dementias, including impaired cognition, increased oxidative stress, and imbalanced cholinergic transmission. Although mitochondrial dysfunction is involved in different types of dementias, its role in cognitive impairment induced by SCO has not been well elucidated. The aim of this work was to evaluate the in vivo effect of SCO on different brain mitochondrial parameters in rats to explore its neurotoxic mechanisms of action.

METHODS

Saline (Control) or SCO (1 mg/kg) was administered intraperitoneally 30 min prior to neurobehavioral and biochemical evaluations. Novel object recognition and Y-maze paradigms were used to evaluate the impact on memory, while redox profiles in different brain regions and the acetylcholinesterase (AChE) activity of the whole brain were assessed to elucidate the amnesic mechanism of SCO. Finally, the effects of SCO on brain mitochondria were evaluated both ex vivo and in vitro, the latter to determine whether SCO could directly interfere with mitochondrial function.

RESULTS

SCO administration induced memory deficit, increased oxidative stress, and increased AChE activities in the hippocampus and prefrontal cortex. Isolated brain mitochondria from rats administered with SCO were more vulnerable to mitochondrial swelling, membrane potential dissipation, H₂O₂ generation and calcium efflux, all likely resulting from oxidative damage. The in vitro mitochondrial assays suggest that SCO did not affect the organelle function directly.

CONCLUSION

In conclusion, the present results indicate that SCO induced cognitive dysfunction and oxidative stress may involve brain mitochondrial impairment, an important target for new neuroprotective compounds against AD and other dementias.

Fluoxetine Prevents Aβ1-42-Induced Toxicity via a Paracrine Signaling Mediated by Transforming-Growth-Factor-β1

Selective reuptake inhibitors (SSRIs), such as fluoxetine and sertraline, increase circulating Transforming-Growth-Factor-β1 (TGF-β1) levels in depressed patients, and are currently studied for their neuroprotective properties in Alzheimer’s disease. TGF-β1 is an anti-inflammatory cytokine that exerts neuroprotective effects against β-amyloid (Aβ)-induced neurodegeneration. In the present work, the SSRI, fluoxetine, was tested for the ability to protect cortical neurons against 1 μM oligomeric Aβ_1-42-induced toxicity. At therapeutic concentrations (100 nM–1 μM), fluoxetine significantly prevented Aβ-induced toxicity in mixed glia-neuronal cultures, but not in pure neuronal cultures. Though to a lesser extent, also sertraline was neuroprotective in mixed cultures, whereas serotonin (10 nM–10 μM) did not mimick fluoxetine effects. Glia-conditioned medium collected from astrocytes challenged with fluoxetine protected pure cortical neurons against Aβ toxicity. The effect was lost in the presence of a neutralizing antibody against TGF-β1 in the conditioned medium, or when the specific inhibitor of type-1 TGF-β1 receptor, SB431542, was added to pure neuronal cultures. Accordingly, a 24 h treatment of cortical astrocytes with fluoxetine promoted the release of active TGF-β1 in the culture media through the conversion of latent TGF-β1 to mature TGF-β1. Unlike fluoxetine, both serotonin and sertraline did not stimulate the astrocyte release of active TGF-β1. We conclude that fluoxetine is neuroprotective against Aβ toxicity via a paracrine signaling mediated by TGF-β1, which does not result from a simplistic SERT blockade.

Synthesis and Biological Evaluation of Novel Multi-target-Directed Benzazepines Against Excitotoxicity

Excitotoxicty, a key pathogenic event is characteristic of the onset and development of neurodegeneration. The glutamatergic neurotransmission mediated through different glutamate receptor subtypes plays a pivotal role in the onset of excitotoxicity. The role of NMDA receptor (NMDAR), a glutamate receptor subtype, has been well established in the excitotoxicity pathogenesis. NMDAR overactivation triggers excessive calcium influx resulting in excitotoxic neuronal cell death. In the present study, a series of benzazepine derivatives, with the core structure of 3-methyltetrahydro-3H-benzazepin-2-one, were synthesised in our laboratory and their NMDAR antagonist activity was determined against NMDA-induced excitotoxicity using SH-SY5Y cells. In order to assess the multi-target-directed potential of the synthesised compounds, Aβ_1-42 aggregation inhibitory activity of the most potent benzazepines was evaluated using thioflavin T (ThT) and Congo red (CR) binding assays as Aβ also imparts toxicity, at least in part, through NMDAR overactivation. Furthermore, neuroprotective, free radical scavenging, anti-oxidant and anti-apoptotic activities of the two potential test compounds (7 and 14) were evaluated using primary rat hippocampal neuronal culture against Aβ_1-42-induced toxicity. Finally, in vivo neuroprotective potential of 7 and 14 was assessed using intracerebroventricular (ICV) rat model of Aβ_1-42-induced toxicity. All of the synthesised benzazepines have shown significant neuroprotection against NMDA-induced excitotoxicity. The most potent compound (14) showed relatively higher affinity for the glycine binding site as compared with the glutamate binding site of NMDAR in the molecular docking studies. 7 and 14 have been shown experimentally to abrogate Aβ_1-42 aggregation efficiently. Additionally, 7 and 14 showed significant neuroprotective, free radical scavenging, anti-oxidant and anti-apoptotic properties in different in vitro and in vivo experimental models. Finally, 7 and 14 attenuated Aβ_1-42-induced tau phosphorylation by abrogating activation of tau kinases, i.e. MAPK and GSK-3β. Thus, the results revealed multi-target-directed potential of some of the synthesised novel benzazepines against excitotoxicity.

Chlorella sorokiniana Extract Improves Short-Term Memory in Rats

Increasing evidence shows that eukaryotic microalgae and, in particular, the green microalga Chlorella, can be used as natural sources to obtain a whole variety of compounds, such as omega (ω)-3 and ω-6 polyunsatured fatty acids (PUFAs). Although either beneficial or toxic effects of Chlorella sorokiniana have been mainly attributed to its specific ω-3 and ω-6 PUFAs content, the underlying molecular pathways remain to be elucidated yet. Here, we investigate the effects of an acute oral administration of a lipid extract of Chlorella sorokiniana, containing mainly ω-3 and ω-6 PUFAs, on cognitive, emotional and social behaviour in rats, analysing possible underlying neurochemical alterations. Our results showed improved short-term memory in Chlorella sorokiniana-treated rats compared to controls, without any differences in exploratory performance, locomotor activity, anxiety profile and depressive-like behaviour. On the other hand, while the social behaviour of Chlorella sorokiniana-treated animals was significantly decreased, no effects on aggressivity were observed. Neurochemical investigations showed region-specific effects, consisting in an elevation of noradrenaline (NA) and serotonin (5-HT) content in hippocampus, but not in the prefrontal cortex and striatum. In conclusion, our results point towards a beneficial effect of Chlorella sorokiniana extract on short-term memory, but also highlight the need of caution in the use of this natural supplement due to its possible masked toxic effects.

Maternal Malnutrition in the Etiopathogenesis of Psychiatric Diseases: Role of Polyunsaturated Fatty Acids

Evidence from human studies indicates that maternal metabolic state and malnutrition dramatically influence the risk for developing psychiatric complications in later adulthood. In this regard, the central role of polyunsaturated fatty acids (PUFAs), and particularly n-3 PUFAs, is emerging considering that epidemiological evidences have established a negative correlation between n-3 PUFA consumption and development of mood disorders. These findings were supported by clinical studies indicating that low content of n-3 PUFAs in diet is linked to an increased susceptibility to psychiatric disorders. PUFAs regulate membrane fluidity and exert their central action by modulating synaptogenesis and neurotrophic factor expression, neurogenesis, and neurotransmission. Moreover, they are precursors of molecules implicated in modulating immune and inflammatory processes in the brain. Importantly, their tissue concentrations are closely related to diet intake, especially to maternal consumption during embryonal life, considering that their synthesis from essential precursors has been shown to be inefficient in mammals. The scope of this review is to highlight the possible mechanisms of PUFA functions in the brain during pre- and post-natal period and to evaluate their role in the pathogenesis of psychiatric diseases.

Chronic Psychosocial Stress Impairs Bone Homeostasis: A Study in the Social Isolation Reared Rat

Chronic psychosocial stress is a key player in the onset and aggravation of mental diseases, including psychosis. Although a strong association between this psychiatric condition and other medical co-morbidities has been recently demonstrated, few data on the link between psychosis and bone homeostasis are actually available. The aim of this study was to investigate whether chronic psychosocial stress induced by 4 or 7 weeks of social isolation in drug-naïve male Wistar rats could alter bone homeostasis in terms of bone thickness, mineral density and content, as well as markers of bone formation and resorption (sclerostin, cathepsin K, and CTX-I). We found that bone mineral density was increased in rats exposed to 7 weeks of social isolation, while no differences were detected in bone mineral content and area. Moreover, 7 weeks of social isolation lead to increase of femur thickness with respect to controls, suggesting the development of a hyperostosis condition. Isolated rats showed no changes in sclerostin levels, a marker of bone formation, compared to grouped animals. Conversely, bone resorption markers were significantly altered after 7 weeks of social isolation in terms of decrease in cathepsin K and increase of CTX-I. No alterations were found after 4 weeks of isolation rearing. Our observations suggest that chronic psychosocial stress might affect bone homeostasis, more likely independently from drug treatment. Thus, the social isolation model might help to identify possible new therapeutic targets to treat the burden of chronic psychosocial stress and to attempt alternative therapy choices.

Intrahippocampal administration of a domain antibody that binds aggregated amyloid-β reverses cognitive deficits produced by diet-induced obesity

BACKGROUND

The prevalence of high fat diets (HFD), diet-induced obesity (DIO) and Type 2 diabetes continues to increase, associated with cognitive impairment in both humans and rodent models. Mechanisms transducing these impairments remain largely unknown: one possibility is that a common mechanism may be involved in the cognitive impairment seen in obese and/or diabetic states and in dementia, specifically Alzheimer's disease (AD). DIO is well established as a risk factor for development of AD. Oligomeric amyloid-β (Aβ) is neurotoxic, and we showed that intrahippocampal oligomeric Aβ produces cognitive and metabolic dysfunction similar to that seen in DIO or diabetes. Moreover, animal models of DIO show elevated brain Aβ, a hallmark of AD, suggesting that this may be one source of cognitive impairment in both conditions.

METHODS

Intrahippocampal administration of a novel anti-Aβ domain antibody for aggregated Aβ, or a control domain antibody, to control or HFD-induced DIO rats. Spatial learning measured in a conditioned contextual fear (CCF) task after domain antibody treatment; postmortem, hippocampal NMDAR and AMPAR were measured.

RESULTS

DIO caused impairment in CCF, and this impairment was eliminated by intrahippocampal administration of the active domain antibody. Measurement of hippocampal proteins suggests that DIO causes dysregulation of hippocampal AMPA receptors, which is also reversed by acute domain antibody administration.

CONCLUSIONS

Our findings support the concept that oligomeric Aβ within the hippocampus of DIO animals may not only be a risk factor for development of AD but may also cause cognitive impairment before the development of dementia.

GENERAL SIGNIFICANCE AND INTEREST

Our work integrates the engineering of domain antibodies with conformational- and sequence-specificity for oligomeric amyloid beta with a clinically relevant model of diet-induced obesity in order to demonstrate not only the pervasive effects of obesity on several aspects of brain biochemistry and behavior, but also the bioengineering of a successful treatment against the long-term detrimental effects of a pre-diabetic state on the brain. We show for the first time that cognitive impairment linked to obesity and/or insulin resistance may be due to early accumulation of oligomeric beta-amyloid in the brain, and hence may represent a pre-Alzheimer's state.

Mechanism of soluble beta-amyloid 25-35 neurotoxicity in primary cultured rat cortical neurons

This study aimed to determine the effects of different concentrations of soluble beta-amyloid 25-35 (Aβ25-35) on cell viability, calcium overload, and PI3K-p85 expression in cultured cortical rat neurons. Primary cultured cerebral cortical neurons of newborn rats were divided randomly into six groups. Five groups were treated with soluble Aβ25-35 at concentrations of 10nmol/L, 100nmol/L, 1μmol/L, 10μmol/L, or 30μmol/L. Cell Counting Kit-8 staining was used to measure cell viability, laser-scanning confocal imaging was used to detect changes in intracellular free calcium concentration, and western blot assay was used to measure neuronal PI3K-p85 expression. Soluble Aβ25-35 was found to reduce cell viability and induce calcium overload in primary cultured rat cerebral cortical neurons, in a concentration-dependent manner. At certain concentrations, soluble Aβ25-35 also increased neuronal PI3K-p85 expression. These findings reveal that soluble Aβ25-35 reduces the viability of cultured cerebral cortical rat neurons. The neurotoxicity mechanism may involve calcium overload and disruption of insulin signal transduction pathways.

Myricetin: A Dietary Molecule with Diverse Biological Activities

Myricetin is a common plant-derived flavonoid and is well recognised for its nutraceuticals value. It is one of the key ingredients of various foods and beverages. The compound exhibits a wide range of activities that include strong anti-oxidant, anticancer, antidiabetic and anti-inflammatory activities. It displays several activities that are related to the central nervous system and numerous studies have suggested that the compound may be beneficial to protect against diseases such as Parkinson's and Alzheimer's. The use of myricetin as a preserving agent to extend the shelf life of foods containing oils and fats is attributed to the compound's ability to protect lipids against oxidation. A detailed search of existing literature revealed that there is currently no comprehensive review available on this important molecule. Hence, the present work includes the history, synthesis, pharmaceutical applications and toxicity studies of myricetin. This report also highlights structure-activity relationships and mechanisms of action for various biological activities.

Neuroprotective Potential of Novel Multi-Targeted Isoalloxazine Derivatives in Rodent Models of Alzheimer's Disease Through Activation of Canonical Wnt/β-Catenin Signalling Pathway

Previous reports suggest that Alzheimer's disease is protected by cholinesterase inhibitors. We synthesized some isoalloxazine derivatives and evaluated them using in vitro cholinesterase inhibition assay. Two of the compounds (7m and 7q) were figured out as potent cholinesterase inhibitors. They further showed anti-Aβ aggregatory activity in the in vitro assay. The current study deals with the evaluation of neuroprotective potentials of the potent compounds (7m and 7q) using different in vitro and in vivo experiments. The compounds were first assessed for their tendency to cross blood-brain barrier using in vitro permeation assay. They were evaluated using scopolamine-induced amnesic mice model. Additionally, ROS scavenging and anti-apoptotic properties of 7m and 7q were established against Aβ1-42-induced toxicity in rat hippocampal neuronal cells. 7m and 7q were also evaluated using Aβ1-42-induced Alzheimer's rat model. Lastly, their involvement in Wnt/β-catenin pathway was also demonstrated. The results indicated good CNS penetration for 7m and 7q. The neuroprotective effects of 7m and 7q were evidenced by improved cognitive ability in both scopolamine and Aβ1-42-induced Alzheimer's-like condition in rodents. The in vivo results also confirmed their anti-cholinesterase and anti-oxidant potential. Immunoblot results showed that treatment with 7m and 7q decreased Aβ1-42, p-tau, cleaved caspase-3, and cleaved PARP levels in Aβ1-42-induced Alzheimer's rat brain. Additionally, immunoblot results demonstrated that 7m and 7q activated the Wnt/β-catenin pathway as evidenced by increased p-GSK-3, β-catenin, and neuroD1 levels in Aβ1-42-induced Alzheimer's rat brain. These findings have shown that isoalloxazine derivatives (7m and 7q) could be the potential leads for developing effective drugs for the treatment of AD.

Soluble beta amyloid evokes alteration in brain norepinephrine levels: role of nitric oxide and interleukin-1

Strong evidence showed neurotoxic properties of beta amyloid (Aβ) and its pivotal role in the Alzheimer's disease (AD) pathogenesis. Beside, experimental data suggest that Aβ may have physiological roles considering that such soluble peptide is produced and secreted during normal cellular activity. There is now suggestive evidence that neurodegenerative conditions, like AD, involve nitric oxide (NO) in their pathogenesis. Nitric oxide also possess potent neuromodulatory actions in brain regions, such as prefrontal cortex (PFC), hippocampus (HIPP), and nucleus accumbens (NAC). In the present study, we evaluated the effect of acute Aβ injection on norepinephrine (NE) content before and after pharmacological manipulations of nitrergic system in above mentioned areas. Moreover, effects of the peptide on NOS activity were evaluated. Our data showed that 2 h after i.c.v. soluble Aβ administration, NE concentrations were significantly increased in the considered areas along with increased iNOS activity. Pre-treatment with NOS inhibitors, 7-Nitroindazole (7-NI), and N6-(1-iminoethyl)-L-lysine-dihydrochloride (L-NIL), reversed Aβ-induced changes. Ultimately, pharmacological block of interleukin1 (IL-1) receptors prevented NE increase in all brain regions. Taken together our findings suggest that NO and IL-1 are critically involved in regional noradrenergic alterations induced by soluble Aβ injection.

Effects of rivastigmine and memantine alone and in combination on learning and memory in rats with scopolamine-induced amnesia

Background

Cholinesterase inhibitors and glutamate blockers are commonly used for the treatment of cognitive impairment in Alzheimer’s disease. The aim was to evaluate the effects of rivastigmine and memantine alone or in combination in rats with scopolamine-impaired memory.

Method

5 groups of rats were used: control, scopolamine (model), model with rivastigmine, model with memantine, and model with both drugs. Active avoidance test was performed and the number of conditioned responses, unconditioned responses and intertrial crossing were recorded. Passive avoidance tests step-through with criteria latency of reaction 180 s in the light chamber and step-down with criteria latency of reaction 60 s on the platform were done.

Results

Control rats learned the task and kept it on memory tests. Scopolamine treated rats failed to perform it. The rivastigmine, memantine and its combination groups showed increased CRs during learning and memory retention tests. In both passive avoidance tests an increased latency of reaction was observed in the drug treated groups.

Conclusion

The combination of both drugs rivastigmine and memantine is more effective than the use of the single drug in cognitive impaired rats. Cholinesterase inhibitors and NMDA blockers may be combined in the treatment of different kind of dementias.

Synaptic dysfunction and septin protein family members in neurodegenerative diseases

Cognitive decline and disease progression in different neurodegenerative diseases typically involves synaptic dysfunction preceding the neuronal loss. The synaptic dysfunction is suggested to be caused by imbalanced synaptic plasticity i.e. enhanced induction of long-term depression and concomitantly decreased long-term potentiation accompanied with excess stimulation of extrasynaptic N-Methyl-D-aspartate (NMDA) receptors due to various disturbances in pre- and postsynaptic sites. Recent research has identified neurodegenerative disease-related changes in protein accumulation and aggregation, gene expression, and protein functions, which may contribute to imbalanced synaptic function. Nevertheless, a comprehensive understanding of the mechanisms regulating synaptic plasticity in health and disease is still lacking and therefore characterization of new candidates involved in these mechanisms is needed. Septins, a highly conserved group of guanosine-5'-triphosphate (GTP)-binding proteins, show high neuronal expression and are implicated in the regulation of synaptic vesicle trafficking and neurotransmitter release. In this review, we first summarize the evidence how synaptic dysfunction is related to the pathogenesis of Alzheimer's, Parkinson's and Huntington's disease and frontotemporal lobar degeneration. Then, we discuss different aspects of the potential involvement of the septin family members in the regulation of synaptic function in relation to the pathogenesis of neurodegenerative diseases.