The structure and function of Alzheimer’s gamma secretase enzyme complex

Insulin resistance as the molecular link between diabetes and Alzheimer's disease

Diabetes mellitus (DM) and Alzheimer's disease (AD) are two major health concerns that have seen a rising prevalence worldwide. Recent studies have indicated a possible link between DM and an increased risk of developing AD. Insulin, while primarily known for its role in regulating blood sugar, also plays a vital role in protecting brain functions. Insulin resistance (IR), especially prevalent in type 2 diabetes, is believed to play a significant role in AD's development. When insulin signalling becomes dysfunctional, it can negatively affect various brain functions, making individuals more susceptible to AD's defining features, such as the buildup of beta-amyloid plaques and tau protein tangles. Emerging research suggests that addressing insulin-related issues might help reduce or even reverse the brain changes linked to AD. This review aims to explore the rela-tionship between DM and AD, with a focus on the role of IR. It also explores the molecular mechanisms by which IR might lead to brain changes and assesses current treatments that target IR. Understanding IR's role in the connection between DM and AD offers new possibilities for treatments and highlights the importance of continued research in this interdisciplinary field.

Signaling pathways in colorectal cancer implications for the target therapies

Colorectal carcinoma (CRC) stands as a pressing global health issue, marked by the unbridled proliferation of immature cells influenced by multifaceted internal and external factors. Numerous studies have explored the intricate mechanisms of tumorigenesis in CRC, with a primary emphasis on signaling pathways, particularly those associated with growth factors and chemokines. However, the sheer diversity of molecular targets introduces complexity into the selection of targeted therapies, posing a significant challenge in achieving treatment precision. The quest for an effective CRC treatment is further complicated by the absence of pathological insights into the mutations or alterations occurring in tumor cells. This study reveals the transfer of signaling from the cell membrane to the nucleus, unveiling recent advancements in this crucial cellular process. By shedding light on this novel dimension, the research enhances our understanding of the molecular intricacies underlying CRC, providing a potential avenue for breakthroughs in targeted therapeutic strategies. In addition, the study comprehensively outlines the potential immune responses incited by the aberrant activation of signaling pathways, with a specific focus on immune cells, cytokines, and their collective impact on the dynamic landscape of drug development. This research not only contributes significantly to advancing CRC treatment and molecular medicine but also lays the groundwork for future breakthroughs and clinical trials, fostering optimism for improved outcomes and refined approaches in combating colorectal carcinoma.

Amyloid Precursor Protein and Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders associated with age or inherited mutations. It is characterized by severe dementia in the late stages that affect memory, cognitive functions, and daily life overall. AD progression is linked to the accumulation of cytotoxic amyloid beta (Aβ) and hyperphosphorylated tau protein combined with other pathological features such as synaptic loss, defective energy metabolism, imbalances in protein, and metal homeostasis. Several treatment options for AD are under investigation, including antibody-based therapy and stem cell transplantation. Amyloid precursor protein (APP) is a membrane protein considered to play a main role in AD pathology. It is known that APP in physiological conditions follows a non-amyloidogenic pathway; however, it can proceed to an amyloidogenic scenario, which leads to the generation of extracellular deleterious Aβ plaques. Not all steps of APP biogenesis are clear so far, and these questions should be addressed in future studies. AD is a complex chronic disease with many factors that contribute to disease progression.

Molecular crosstalk between COVID-19 and Alzheimer's disease using microarray and RNA-seq datasets: A system biology approach

Objective

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). The clinical and epidemiological analysis reported the association between SARS-CoV-2 and neurological diseases. Among neurological diseases, Alzheimer's disease (AD) has developed as a crucial comorbidity of SARS-CoV-2. This study aimed to understand the common transcriptional signatures between SARS-CoV-2 and AD.

Materials and methods

System biology approaches were used to compare the datasets of AD and COVID-19 to identify the genetic association. For this, we have integrated three human whole transcriptomic datasets for COVID-19 and five microarray datasets for AD. We have identified differentially expressed genes for all the datasets and constructed a protein-protein interaction (PPI) network. Hub genes were identified from the PPI network, and hub genes-associated regulatory molecules (transcription factors and miRNAs) were identified for further validation.

Results

A total of 9,500 differentially expressed genes (DEGs) were identified for AD and 7,000 DEGs for COVID-19. Gene ontology analysis resulted in 37 molecular functions, 79 cellular components, and 129 biological processes were found to be commonly enriched in AD and COVID-19. We identified 26 hub genes which includes AKT1, ALB, BDNF, CD4, CDH1, DLG4, EGF, EGFR, FN1, GAPDH, INS, ITGB1, ACTB, SRC, TP53, CDC42, RUNX2, HSPA8, PSMD2, GFAP, VAMP2, MAPK8, CAV1, GNB1, RBX1, and ITGA2B. Specific miRNA targets associated with Alzheimer's disease and COVID-19 were identified through miRNA target prediction. In addition, we found hub genes-transcription factor and hub genes-drugs interaction. We also performed pathway analysis for the hub genes and found that several cell signaling pathways are enriched, such as PI3K-AKT, Neurotrophin, Rap1, Ras, and JAK-STAT.

Conclusion

Our results suggest that the identified hub genes could be diagnostic biomarkers and potential therapeutic drug targets for COVID-19 patients with AD comorbidity.

Natural Product-based Nanomedicine: Recent Advances and Issues for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) affects the elderly and is characterized by progressive neurodegeneration caused by different pathologies. The most significant challenges in treating AD include the inability of medications to reach the brain because of its poor solubility, low bioavailability, and the presence of the blood-brain barrier (BBB). Additionally, current evidence suggests the disruption of BBB plays an important role in the pathogenesis of AD. One of the critical challenges in treating AD is the ineffective treatments and their severe adverse effects. Nanotechnology offers an alternative approach to facilitate the treatment of AD by overcoming the challenges in drug transport across the BBB. Various nanoparticles (NP) loaded with natural products were reported to aid in drug delivery for the treatment of AD. The nano-sized entities of NP are great platforms for incorporating active materials from natural products into formulations that can be delivered effectively to the intended action site without compromising the material's bioactivity. The review highlights the applications of medicinal plants, their derived components, and various nanomedicinebased approaches for the treatment of AD. The combination of medicinal plants and nanotechnology may lead to new theragnostic solutions for the treatment of AD in the future.

Novel Amylin Analogues Reduce Amyloid-β Cross-Seeding Aggregation and Neurotoxicity

BACKGROUND

Type 2 diabetes related human islet amyloid polypeptide (hIAPP) plays a dual role in Alzheimer's disease (AD). hIAPP has neuroprotective effects in AD mouse models whereas, high hIAPP concentrations can promote co-aggregation with amyloid-β (Aβ) to promote neurodegeneration. In fact, both low and high plasma hIAPP concentration has been associated with AD. Therefore, non-aggregating hIAPP analogues have garnered interest as a treatment for AD. The aromatic amino acids F23 and I26 in hIAPP have been identified as the key residues involved in self-aggregation and Aβ cross-seeding.

OBJECTIVE

Three novel IAPP analogues with single and double alanine mutations (A1 = F23, A2 = I26, and A3 = F23 + I26) were assessed for their ability to aggregate, modulate Aβ oligomer formation, and alter neurotoxicity.

METHODS

A range of biophysical methods including Thioflavin-T, gel electrophoresis, photo-crosslinking, circular dichroism combined with cell viability assays were utilized to assess protein aggregation and toxicity.

RESULTS

All IAPP analogues showed significantly less self-aggregation than hIAPP. Co-aggregated Aβ 42-A2 and A3 also showed reduced aggregation compared to Aβ 42-hIAPP mixtures. Self- and co-oligomerized A1, A2, and A3 exhibited random coil conformations with reduced beta sheet content compared to hIAPP and Aβ 42-hIAPP aggregates. A1 was toxic at high concentrations compared to A2 and A3. However, co-aggregated Aβ 42-A1, A2, or A3 showed reduced neurotoxicity compared to Aβ 42, hIAPP, and Aβ 42-hIAPP aggregates.

CONCLUSION

These findings confirm that hIAPP analogues with non-aromatic residues at positions 23 and 26 have reduced self-aggregation and the ability to neutralize Aβ 42 toxicity. This warrants further characterization of their protective effects in pre-clinical AD models.

Mechanistic Insights into the Polymorphic Associations and Cross-Seeding of Aβ and hIAPP in the Presence of Histidine Tautomerism: An All-Atom Molecular Dynamic Study

Hundreds of millions of people around the world have been affected by Type 2 diabetes (T2D) which is a metabolic disorder. Clinical research has revealed T2D as a possible risk factor for Alzheimer’s disease (AD) development (and vice versa). Amyloid-β (Aβ) and human islet amyloid polypeptide are the main pathological species in AD and T2D, respectively. However, the mechanisms by which these two amyloidogenic peptides co-aggregate are largely uninvestigated. Herein, for the first time, we present the cross-seeding between Amylin1-37 and Aβ40 considering the particular effect of the histidine tautomerism at atomic resolution applying the all-atom molecular dynamics (MD) simulations for heterodimeric complexes. The results via random seed MD simulations indicated that the Aβ40(δδδ) isomer in cross-talking with Islet(ε) and Islet(δ) isomers could retain or increase the β-sheet content in its structure that may make it more prone to further aggregation and exhibit higher toxicity. The other tautomeric isomers which initially did not have a β-sheet structure in their monomeric forms did not show any generated β-sheet, except for one seed of the Islet(ε) and Aβ40(εεε) heterodimers complex that displayed a small amount of formed β-sheet. This computational research may provide a different point of view to examine all possible parameters that may contribute to the development of AD and T2D and provide a better understanding of the pathological link between these two severe diseases.

Herbal Mixture of Carthamus tinctorius L. Seed and Taraxacum coreanum Attenuates Amyloid Beta-Induced Cognitive Dysfunction In Vivo

Deposition of amyloid-beta (Aβ) in the aging brain has been often observed and is thought to be a pathological feature of Alzheimer’s disease. The use of natural products for disease prevention and treatment is gaining attention worldwide. Carthamus tinctorius L. seed and Taraxacum coreanum have been used as traditional medicines in Asian countries, where they have been reported to exert anti-inflammatory and anti-oxidative effects. It has been demonstrated that the combination of C. tinctorius L. seed and T. coreanum has an effect on cognitive enhancement, indicating a ratio of 5:5 synergistically enhancing learning and memory abilities in comparison with a single treatment. Here, we aimed to investigate the protective effect of C. tinctorius L. seed and T. coreanum mixture (CT) at different concentrations on cognition in Aβ_25-35-infused mice. CT-administered mice showed significant cognitive improvement in the T-maze, novel object recognition, and Morris water maze tests. Moreover, amyloidogenesis-related proteins, such as β-secretase and γ-secretase, were detected and their protein levels decreased after treatment with CT. Our study shows that CT attenuates cognitive dysfunction by improving learning and memory capability and regulating Aβ-related proteins in Aβ_25-35-injected mice. These findings suggest that CT might be a candidate for functional food on cognitive improvement.

Modulatory Effects of Autophagy on APP Processing as a Potential Treatment Target for Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the formation of intracellular aggregate composed of heavily phosphorylated tau protein and extracellular deposit of amyloid-β (Aβ) plaques derived from proteolysis cleavage of amyloid precursor protein (APP). Autophagy refers to the lysosomal-mediated degradation of cytoplasmic constituents, which plays a critical role in maintaining cellular homeostasis. Importantly, recent studies reported that dysregulation of autophagy is associated in the pathogenesis of AD, and therefore, autophagy modulation has gained attention as a promising approach to treat AD pathogenesis. In AD, both the maturation of autolysosomes and its retrograde transports have been obstructed, which causes the accumulation of autophagic vacuoles and eventually leads to degenerating and dystrophic neurites function. However, the mechanism of autophagy modulation in APP processing and its pathogenesis have not yet been fully elucidated in AD. In the early stage of AD, APP processing and Aβ accumulation-mediated autophagy facilitate the removal of toxic protein aggregates via mTOR-dependent and -independent pathways. In addition, a number of autophagy-related genes (Atg) and APP are thought to influence the development of AD, providing a bidirectional link between autophagy and AD pathology. In this review, we summarized the current observations related to autophagy regulation and APP processing in AD, focusing on their modulation associated with the AD progression. Moreover, we emphasizes the application of small molecules and natural compounds to modulate autophagy for the removal and clearance of APP and Aβ deposits in the pathological condition of AD.

Activate or Inhibit? Implications of Autophagy Modulation as a Therapeutic Strategy for Alzheimer's Disease

Neurodegenerative diseases result in a range of conditions depending on the type of proteinopathy, genes affected or the location of the degeneration in the brain. Proteinopathies such as senile plaques and neurofibrillary tangles in the brain are prominent features of Alzheimer’s disease (AD). Autophagy is a highly regulated mechanism of eliminating dysfunctional organelles and proteins, and plays an important role in removing these pathogenic intracellular protein aggregates, not only in AD, but also in other neurodegenerative diseases. Activating autophagy is gaining interest as a potential therapeutic strategy for chronic diseases featuring protein aggregation and misfolding, including AD. Although autophagy activation is a promising intervention, over-activation of autophagy in neurodegenerative diseases that display impaired lysosomal clearance may accelerate pathology, suggesting that the success of any autophagy-based intervention is dependent on lysosomal clearance being functional. Additionally, the effects of autophagy activation may vary significantly depending on the physiological state of the cell, especially during proteotoxic stress and ageing. Growing evidence seems to favour a strategy of enhancing the efficacy of autophagy by preventing or reversing the impairments of the specific processes that are disrupted. Therefore, it is essential to understand the underlying causes of the autophagy defect in different neurodegenerative diseases to explore possible therapeutic approaches. This review will focus on the role of autophagy during stress and ageing, consequences that are linked to its activation and caveats in modulating this pathway as a treatment.

Amylin and beta amyloid proteins interact to form amorphous heterocomplexes with enhanced toxicity in neuronal cells

Human pancreatic islet amyloid polypeptide (hIAPP) and beta amyloid (Aβ) can accumulate in Type 2 diabetes (T2D) and Alzheimer's disease (AD) brains and evidence suggests that interaction between the two amyloidogenic proteins can lead to the formation of heterocomplex aggregates. However, the structure and consequences of the formation of these complexes remains to be determined. The main objective of this study was to characterise the different types and morphology of Aβ-hIAPP heterocomplexes and determine if formation of such complexes exacerbate neurotoxicity. We demonstrate that hIAPP promotes Aβ oligomerization and formation of small oligomer and large aggregate heterocomplexes. Co-oligomerized Aβ42-hIAPP mixtures displayed distinct amorphous structures and a 3-fold increase in neuronal cell death as compared to Aβ and hIAPP alone. However, in contrast to hIAPP, non-amyloidogenic rat amylin (rIAPP) reduced oligomer Aβ-mediated neuronal cell death. rIAPP exhibited reductions in Aβ induced neuronal cell death that was independent of its ability to interact with Aβ and form heterocomplexes; suggesting mediation by other pathways. Our findings reveal distinct effects of IAPP peptides in modulating Aβ aggregation and toxicity and provide new insight into the potential pathogenic effects of Aβ-IAPP hetero-oligomerization and development of IAPP based therapies for AD and T2D.

Synthesis, in vitro evaluation and molecular docking of a new class of indolylpropyl benzamidopiperazines as dual AChE and SERT ligands for Alzheimer's disease

During the last decade, the one drug-one target strategy has resulted to be inefficient in facing diseases with complex ethiology like Alzheimer's disease and many others. In this context, the multitarget paradigm has emerged as a promising strategy. Based on this consideration, we aim to develop novel molecules as promiscuous ligands acting in two or more targets at the same time. For such purpose, a new series of indolylpropyl-piperazinyl oxoethyl-benzamido piperazines were synthesized and evaluated as multitarget-directed drugs for the serotonin transporter (SERT) and acetylcholinesterase (AChE). The ability to decrease β-amyloid levels as well as cell toxicity of all compounds were also measured. In vitro results showed that at least four compounds displayed promising activity against SERT and AChE. Compounds 18 and 19 (IC₅₀ = 3.4 and 3.6 μM respectively) exhibited AChE inhibition profile in the same order of magnitude as donepezil (DPZ, IC₅₀ = 2.17 μM), also displaying nanomolar affinity in SERT. Moreover, compounds 17 and 24 displayed high SERT affinities (IC₅₀ = 9.2 and 1.9 nM respectively) similar to the antidepressant citalopram, and significant micromolar AChE activity at the same time. All the bioactive compounds showed a low toxicity profile in the range of concentrations studied. Molecular docking allowed us to rationalize the binding mode of the synthesized compounds in both targets. In addition, we also show that compounds 11 and 25 exhibit significant β-amyloid lowering activity in a cell-based assay, 11 (50% inhibition, 10 μM) and 25 (35% inhibition, 10 μM). These results suggest that indolylpropyl benzamidopiperazines based compounds constitute promising leads for a multitargeted approach for Alzheimer's disease.

CNS myelin protein 36K regulates oligodendrocyte differentiation through Notch

In contrast to humans and other mammals, zebrafish can successfully regenerate and remyelinate central nervous system (CNS) axons following injury. In addition to common myelin proteins found in mammalian myelin, 36K protein is a major component of teleost fish CNS myelin. Although 36K is one of the most abundant proteins in zebrafish brain, its function remains unknown. Here we investigate the function of 36K using translation-blocking Morpholinos. Morphant larvae showed fewer dorsally migrated oligodendrocyte precursor cells as well as upregulation of Notch ligand. A gamma secretase inhibitor, which prevents activation of Notch, could rescue oligodendrocyte precursor cell numbers in 36K morphants, suggesting that 36K regulates initial myelination through inhibition of Notch signaling. Since 36K like other short chain dehydrogenases might act on lipids, we performed thin layer chromatography and mass spectrometry of lipids and found changes in lipid composition in 36K morphant larvae. Altogether, we suggest that during early development 36K regulates membrane lipid composition, thereby altering the amount of transmembrane Notch ligands and the efficiency of intramembrane gamma secretase processing of Notch and thereby influencing oligodendrocyte precursor cell differentiation and further myelination. Further studies on the role of 36K short chain dehydrogenase in oligodendrocyte precursor cell differentiation during remyelination might open up new strategies for remyelination therapies in human patients.

Efficient production of a mature and functional gamma secretase protease

Baculoviral protein expression in insect cells has been previously used to generate large quantities of a protein of interest for subsequent use in biochemical and structural analyses. The MultiBac baculovirus protein expression system has enabled, the use of a single baculovirus to reconstitute a protein complex of interest, resulting in a larger protein yield. Using this system, we aimed to reconstruct the gamma (γ)-secretase complex, a multiprotein enzyme complex essential for the production of amyloid-β (Aβ) protein. A MultiBac vector containing all components of the γ-secretase complex was generated and expression was observed for all components. The complex was active in processing APP and Notch derived γ-secretase substrates and proteolysis could be inhibited with γ-secretase inhibitors, confirming specificity of the recombinant γ-secretase enzyme. Finally, affinity purification was used to purify an active recombinant γ-secretase complex. In this study we demonstrated that the MultiBac protein expression system can be used to generate an active γ-secretase complex and provides a new tool to study γ-secretase enzyme and its variants.

Therapeutic impact of rHuEPO on abnormal platelet APP, BACE 1, presenilin 1, ADAM 10 and Aβ expressions in chronic kidney disease patients with cognitive dysfunction like Alzheimer's disease: A pilot study

BACKGROUND

Cognitive dysfunction is reported to be a major cause of morbidity in chronic kidney disease (CKD). The senile plaques (SPs) in the brain are one of the most pathophysiological characteristics of cognitive dysfunction and its major constituent amyloid β (Aβ) released from amyloid precursor protein (APP) by β (BACE1) and γ (presenilin 1) secretases . Platelets contain more than 95% of the circulating APP and implicate as a candidate biomarker for cognitive decline. Recombinant human erythropoietin (rHuEPO) is a standard therapy for anemia in CKD and also acts as a neuroprotective agent. The aim of the study is to determine the impact of rHuEPO therapy on platelet APP processing in CKD with Cognitive Dysfunction.

METHODS

A total of 60 subjects comprising of 30 CKD without cognitive dysfunction and 30 CKD with cognitive dysfunction based on neuropsychological assessment. APP, BACE1, Presenilin 1, ADAM 10 (α secretase) and Aβ expressions in platelets were determined by western blotting and lipid peroxidation (LPO) in platelet rich plasma (PRP) was done by spectrophotometrically. The parameters were statistically compared with Alzheimer's disease (AD), Normocytic normochromic anemic and healthy subjects.

RESULTS

Significantly (p < 0.05) decreased APP, ADAM 10 while increased BACE1, Presenilin 1, Aβ and LPO were observed in CKD with cognitive dysfunction like AD subjects compared to other groups. The parameters were reassessed in CKD with cognitive dysfunction subjects after rHuEPO (100 IU/ kg, weekly twice, 6 months) therapy. All the parameters were retrieved significantly (p < 0.05) along with improved neuropsychological tests scoring after rHuEPO therapy.

CONCLUSIONS

This study demonstrated that rHuEPO is an effective neuroprotective agent in the context of CKD associated cognitive dysfunction and proved its clinical usefulness.

Memorcise and Alzheimer's disease

Alzheimer's disease (AD) is a debilitating disease influencing a multitude of outcomes, including memory function. Recent work suggests that memory may be influenced by exercise ('memorcise'), even among those with AD. The present narrative review details (1) the underlying mechanisms of AD; (2) whether exercise has a protective effect in preventing AD; (3) the mechanisms through which exercise may help to prevent AD; (4) the mechanisms through which exercise may help attenuate the progression of AD severity among those with existing AD; (5) the effects and mechanisms through which exercise is associated with memory among those with existing AD; and (6) exercise recommendations for those with existing AD. Such an understanding will aid clinicians in their ability to use exercise as a potential behavioral strategy to help prevent and treat AD.

The Link between Type 2 Diabetes and Neurodegeneration: Roles for Amyloid-β, Amylin, and Tau Proteins

A wealth of evidence indicates a strong link between type 2 diabetes (T2D) and neurodegenerative diseases such as Alzheimer's disease (AD). Although the precise mechanism remains unclear, T2D can exacerbate neurodegenerative processes. Brain atrophy, reduced cerebral glucose metabolism, and central nervous system insulin resistance are features of both AD and T2D. The T2D phenotype (glucose dyshomeostasis, insulin resistance, impaired insulin signaling) also promotes AD pathology, namely accumulation of amyloid-β (Aβ) and hyperphosphorylated tau and can induce other aspects of neuronal degeneration including inflammatory and oxidative processes. Aβ and hyperphosphorylated tau may also have roles in pancreatic β-cell dysfunction and in reducing insulin sensitivity and glucose uptake by peripheral tissues such as liver, skeletal muscle, and adipose tissue. This suggests a role for these AD-related proteins in promoting T2D. The accumulation of the islet amyloid polypeptide (IAPP, or amylin) within islet β-cells is a major pathological feature of the pancreas in patients with chronic T2D. Co-secreted with insulin, amylin accumulates over time and contributes to β-cell toxicity, ultimately leading to reduced insulin secretion and onset of overt (insulin dependent) diabetes. Recent evidence also suggests that this protein accumulates in the brain of AD patients and may interact with Aβ to exacerbate the neurodegenerative process. In this review, we highlight evidence indicating T2D in promoting Aβ and tau mediated neurodegeneration and the potential contributions of Aβ and tau in promoting a diabetic phenotype that could further exacerbate neurodegeneration. We also discuss underlying mechanisms by which amylin can contribute to the neurodegenerative processes.

Diabetes and Alzheimer's Disease: Can Tea Phytochemicals Play a Role in Prevention?

Dementia and diabetes mellitus are prevalent disorders in the elderly population. While recognized as two distinct diseases, diabetes has more recently recognized as a significant contributor to risk for developing dementia, and some studies make reference to type 3 diabetes, a condition resulting from insulin resistance in the brain. Alzheimer's disease, the most common form of dementia, and diabetes, interestingly, share underlying pathological processes, commonality in risk factors, and, importantly, pathways for intervention. Tea has been suggested to possess potent antioxidant properties. It is rich in phytochemicals including, flavonoids, tannins, caffeine, polyphenols, boheic acid, theophylline, theobromine, anthocyanins, gallic acid, and finally epigallocatechin-3-gallate, which is considered to be the most potent active ingredient. Flavonoid phytochemicals, known as catechins, within tea offer potential benefits for reducing the risk of diabetes and Alzheimer's disease by targeting common risk factors, including obesity, hyperlipidemia, hypertension, cardiovascular disease, and stroke. Studies also show that catechins may prevent the formation of amyloid-β plaques and enhance cognitive functions, and thus may be useful in treating patients who have Alzheimer's disease or dementia. Furthermore, other phytochemicals found within tea offer important antioxidant properties along with innate properties capable of modulating intracellular neuronal signal transduction pathways and mitochondrial function.

Noncoding RNAs in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the main cause of dementia among the elderly worldwide. Despite intense efforts to develop drugs for preventing and treating AD, no effective therapies are available as yet, posing a growing burden at the personal, medical, and socioeconomic levels. AD is characterized by the production and aggregation of amyloid β (Aβ) peptides derived from amyloid precursor protein (APP), the presence of hyperphosphorylated microtubule-associated protein Tau (MAPT), and chronic inflammation leading to neuronal loss. Aβ accumulation and hyperphosphorylated Tau are responsible for the main histopathological features of AD, Aβ plaques, and neurofibrillary tangles (NFTs), respectively. However, the full spectrum of molecular factors that contribute to AD pathogenesis is not known. Noncoding (nc)RNAs, including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), regulate gene expression at the transcriptional and posttranscriptional levels in various diseases, serving as biomarkers and potential therapeutic targets. There is rising recognition that ncRNAs have been implicated in both the onset and pathogenesis of AD. Here, we review the ncRNAs implicated posttranscriptionally in the main AD pathways and discuss the growing interest in targeting regulatory ncRNAs therapeutically to combat AD pathology. WIREs RNA 2018, 9:e1463. doi: 10.1002/wrna.1463 This article is categorized under: RNA in Disease and Development > RNA in Disease.

Human placenta mesenchymal stem cells suppress airway inflammation in asthmatic rats by modulating Notch signaling

Neurogenic locus notch homolog protein (Notch) signaling mediates intracellular communication and may regulate cell fate decisions, including cell proliferation, differentiation, and apoptosis. Mesenchymal stem cells (MSCs) possess immunomodulatory properties and the potential for use in stem cell replacement treatments. The aim of the present study was to evaluate the therapeutic effects of human placenta‑deviated MSCs (hPMSCs) in asthma and to investigate the mechanisms of Notch signaling mediated by transplanted MSCs. A Sprague‑Dawley rat ovalbumin (OVA)‑sensitized acute asthma model was established and challenged. MSCs derived from human placenta (hPMSCs) were transplanted into the asthmatic rats. Transplantation resulted in reduced Notch‑1, Notch‑2 and jagged‑1, and increased Notch‑3, Notch‑4 and delta‑like ligand (delta)‑4 expression in lung, blood, and lymph samples. Notch‑1, Notch‑2, and jagged‑1 expression in OVA‑treated rats was significantly decreased compared with controls and hPMSC‑treated rats; however, Notch‑3, Notch‑4 and delta‑4 expression was significantly increased. Serum interferon‑γ significantly increased after hPMSCs transplantation, whereas interleukin‑4 and immunoglobulin E decreased. In OVA‑treated rats, Notch‑1, Notch‑2 and jagged‑1 levels were increased in the lymph compared with the blood, although Notch‑4 and delta‑4 levels were decreased. Peribronchial infiltration of cells and goblet cell hyperplasia were markedly decreased in the OVA + hPMSCs group compared with those in the OVA‑treated and control groups. Alterations in Notch signaling pathway expression were accompanied by decreased inflammatory cell infiltration, goblet cell hyperplasia and mucus production in lung tissues. The results of the present study are consistent with hPMSC suppression of asthma symptoms and inflammation by regulating the Notch signaling pathway in the rat asthma model.

Structural Characterization of the Amyloid Precursor Protein Transmembrane Domain and Its γ-Cleavage Site

Alzheimer's disease is the most common form of dementia that affects about 50 million of sufferers worldwide. A major role for the initiation and progression of Alzheimer's disease has been associated with the amyloid β-peptide (Aβ), which is a protease cleavage product of the amyloid precursor protein. The amyloid precursor protein is an integral membrane protein with a single transmembrane domain. Here, we assessed the structural integrity of the transmembrane domain within oriented phosphatidylcholine lipid bilayers and determined the tilt angle distribution and dynamics of various subdomains using solid-state NMR and attenuated total reflectance Fourier transform infrared spectroscopies. Although the overall secondary structure of the transmembrane domain is α-helical, pronounced conformational and topological heterogeneities were observed for the γ- and, to a lesser extent, the ζ-cleavage site, with pronounced implications for the production of Aβ and related peptides, the development of the disease, and pharmaceutical innovation.

A blood-based biomarker panel indicates IL-10 and IL-12/23p40 are jointly associated as predictors of β-amyloid load in an AD cohort

Alzheimer’s Disease (AD) is the most common form of dementia, characterised by extracellular amyloid deposition as plaques and intracellular neurofibrillary tangles of tau protein. As no current clinical test can diagnose individuals at risk of developing AD, the aim of this project is to evaluate a blood-based biomarker panel to identify individuals who carry this risk. We analysed the levels of 22 biomarkers in clinically classified healthy controls (HC), mild cognitive impairment (MCI) and Alzheimer’s participants from the well characterised Australian Imaging, Biomarker and Lifestyle (AIBL) study of aging. High levels of IL-10 and IL-12/23p40 were significantly associated with amyloid deposition in HC, suggesting that these two biomarkers might be used to detect at risk individuals. Additionally, other biomarkers (Eotaxin-3, Leptin, PYY) exhibited altered levels in AD participants possessing the APOE ε4 allele. This suggests that the physiology of some potential biomarkers may be altered in AD due to the APOE ε4 allele, a major risk factor for AD. Taken together, these data highlight several potential biomarkers that can be used in a blood-based panel to allow earlier identification of individuals at risk of developing AD and/or early stage AD for which current therapies may be more beneficial.

Natural products against Alzheimer's disease: Pharmaco-therapeutics and biotechnological interventions

Alzheimer's disease (AD) is a severe, chronic and progressive neurodegenerative disease associated with memory and cognition impairment ultimately leading to death. It is the commonest reason of dementia in elderly populations mostly affecting beyond the age of 65. The pathogenesis is indicated by accumulation of the amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFT) in brain tissues and hyperphosphorylation of tau protein in neurons. The main cause is considered to be the formation of reactive oxygen species (ROS) due to oxidative stress. The current treatment provides only symptomatic relief by offering temporary palliative therapy which declines the rate of cognitive impairment associated with AD. Inhibition of the enzyme acetylcholinesterase (AChE) is considered as one of the major therapeutic strategies offering only symptomatic relief and moderate disease-modifying effect. Other non-cholinergic therapeutic approaches include antioxidant and vitamin therapy, stem cell therapy, hormonal therapy, use of antihypertensive or lipid-lowering medications and selective phosphodiesterase (PDE) inhibitors, inhibition of β-secretase and γ-secretase and Aβ aggregation, inhibition of tau hyperphosphorylation and intracellular NFT, use of nonsteroidal anti-inflammatory drugs (NSAIDs), transition metal chelators, insulin resistance drugs, etanercept, brain-derived neurotrophic factor (BDNF) etc. Medicinal plants have been reported for possible anti-AD activity in a number of preclinical and clinical trials. Ethnobotany, being popular in China and in the Far East and possibly less emphasized in Europe, plays a substantial role in the discovery of anti-AD agents from botanicals. Chinese Material Medica (CMM) involving Chinese medicinal plants has been used traditionally in China in the treatment of AD. Ayurveda has already provided numerous lead compounds in drug discovery and many of these are also undergoing clinical investigations. A number of medicinal plants either in their crude forms or as isolated compounds have exhibited to reduce the pathological features associated with AD. In this present review, an attempt has been made to elucidate the molecular mode of action of various plant extracts, phytochemicals and traditional herbal formulations investigated against AD as reported in various preclinical and clinical tests. Herbal synergism often found in polyherbal formulations were found effective to combat disease heterogeneity as found in complex pathogenesis of AD. Finally a note has been added to describe biotechnological improvement, genetic and genomic resources and mathematical and statistical techniques for empirical model building associated with anti-AD plant secondary metabolites and their source botanicals.

Heterogeneity in oligodendroglia: Is it relevant to mouse models and human disease?

There are many lines of evidence indicating that oligodendrocyte progenitor cells and oligodendrocyte populations in the central nervous system (CNS) are heterogeneous based on their developmental origins as well as from morphological and molecular criteria. Whether these distinctions reflect functional heterogeneity is less clear and has been the subject of considerable debate. Recent findings, particularly from knockout mouse models, have provided new evidence for regional variations in myelination phenotypes, particularly between brain and spinal cord. These data raise the possibility that oligodendrocytes in these regions have different functional capacities and/or ability to compensate for loss of a specific gene. The goal of this review is to briefly revisit the evidence for oligodendrocyte heterogeneity and then to present data from transgenic and demyelinating mouse models suggesting functional heterogeneity in myelination, demyelination, and remyelination in the CNS and, finally, to discuss the implications of these findings for human diseases. © 2016 Wiley Periodicals, Inc.

The Effects of Latrepirdine on Amyloid-β Aggregation and Toxicity

Latrepirdine (Dimebon) has been demonstrated to be a neuroprotective and cognition improving agent in neurodegenerative diseases that feature protein aggregation and deposition, such as Alzheimer's disease (AD). The accumulation of amyloid-β (Aβ) protein aggregates is a key event in the neurodegenerative process in AD. This study explores if latrepirdine modulation of protein aggregation contributes to its neuroprotective mechanism of action. Assessment of neuronal cell death showed that there was a significant reduction in lactate dehydrogenase release at an equimolar ratio of Aβ:latrepirdine and with lower concentrations of latrepirdine. The ability of latrepirdine to alter the formation of Aβ42 aggregates was assessed by thioflavin-T fluorescence, western immunoblotting and atomic force microscopy (AFM). Despite showing a reduction in thioflavin-T fluorescence with latrepirdine treatment, indicating a decrease in aggregation, immunoblotting and AFM showed a modest increase in both the formation and size of Aβ aggregates. The discrepancies between thioflavin-T and the other assays are consistent with previous evidence that cyclic molecules can interfere with thioflavin-T binding of amyloid protein preparations. The ability of latrepirdine to modulate Aβ aggregation appears to be independent of its neuroprotective effects, and is unlikely to be a mechanism by which latrepirdine offers protection. This study investigates the effect of latrepirdine on Aβ aggregation, and presents evidence suggesting that caution should be applied in the use of thioflavin-T fluorescence based assays as a method for screening compounds for protein aggregation altering properties.

Blockade of Notch Signalling by γ-Secretase Inhibitor in Lung T Cells of Asthmatic Mice Affects T Cell Differentiation and Pulmonary Inflammation

Notch is a single-pass transmembrane receptor protein expressed by T cells, which contributes to the pathogenesis of asthma through regulation of the development and differentiation of T cells. γ-Secretase inhibitor (GSI) acts as an effective blocker of Notch signalling. The present study aimed to investigate the role of GSI MW167 in T cell differentiation and antigen-induced airway inflammation. An OVA-induced airway inflammation mouse model was established. Blockade of Notch signalling was achieved using MW167. The expression of IL-4, IL-5, IFN-γ, Notch1 signalling and pro-inflammatory transcription factors in activated lung T cells was evaluated. Finally, the therapeutic effect of MW167 was investigated by haematoxylin and eosin staining, real-time PCR and ELISA. The expression of IL-4 and IL-5 decreased and that of IFN-γ increased significantly, and the protein expression levels of pro-inflammatory transcription factors reduced in active lung T cells after administration of MW167, compared to the control group. MW167 treatment prevented OVA-induced airway inflammation and histological changes. The serum and bronchoalveolar lavage fluid (BALF) levels of IL-4 and IL-5 in MW167-treated mice decreased significantly, whereas those of IFN-γ increased, relative to the levels in OVA-challenged animals treated with PBS. Our findings indicate that Notch signalling plays an important role in the pathogenesis of asthma and that MW167 may be a potential therapeutic target for allergen-induced airway inflammation.

Examining the potential clinical value of curcumin in the prevention and diagnosis of Alzheimer’s disease

Curcumin derived from turmeric is well documented for its anti-carcinogenic, antioxidant and anti-inflammatory properties. Recent studies show that curcumin also possesses neuroprotective and cognitive-enhancing properties that may help delay or prevent neurodegenerative diseases, including Alzheimer’s disease (AD). Currently, clinical diagnosis of AD is onerous, and it is primarily based on the exclusion of other causes of dementia. In addition, phase III clinical trials of potential treatments have mostly failed, leaving disease-modifying interventions elusive. AD can be characterised neuropathologically by the deposition of extracellular β amyloid (Aβ) plaques and intracellular accumulation of tau-containing neurofibrillary tangles. Disruptions in Aβ metabolism/clearance contribute to AD pathogenesis. In vitro studies have shown that Aβ metabolism is altered by curcumin, and animal studies report that curcumin may influence brain function and the development of dementia, because of its antioxidant and anti-inflammatory properties, as well as its ability to influence Aβ metabolism. However, clinical studies of curcumin have revealed limited effects to date, most likely because of curcumin’s relatively low solubility and bioavailability, and because of selection of cohorts with diagnosed AD, in whom there is already major neuropathology. However, the fresh approach of targeting early AD pathology (by treating healthy, pre-clinical and mild cognitive impairment-stage cohorts) combined with new curcumin formulations that increase bioavailability is renewing optimism concerning curcumin-based therapy. The aim of this paper is to review the current evidence supporting an association between curcumin and modulation of AD pathology, including in vitro and in vivo studies. We also review the use of curcumin in emerging retinal imaging technology, as a fluorochrome for AD diagnostics.

The impact of luteinizing hormone and testosterone on beta amyloid (Aβ) accumulation: Animal and human clinical studies

This article is part of a Special Issue "SBN 2014". Hormonal changes associated with ageing have been implicated in the pathogenesis of Alzheimer's disease (AD), the most common form of dementia. Reductions in serum testosterone and increases in luteinizing hormone (LH) are established AD risk factors for dementia in men and have important roles in modulating AD pathogenesis. One of the defining features of AD is the accumulation of amyloid-beta (Aβ) in the brain, which has a key role in the neurodegenerative cascade. Both testosterone and LH have been shown to modulate CNS Aβ accumulation in animal studies, and associations with cerebral amyloid load in human studies have supported this. The underlying mechanisms by which these hormones modulate Aβ accumulation and contribute to neurodegeneration are not completely understood, however they have been shown to regulate Aβ metabolism, enhance its clearance and alter the processing of its parent molecule, the amyloid precursor protein. This review will discuss underlying mechanisms by which testosterone and LH modulate Aβ and provide an update on therapeutic approaches targeting these hormones.

The keystone of Alzheimer pathogenesis might be sought in Aβ physiology

For several years Amyloid-beta peptide (Aβ) has been considered the main pathogenetic factor of Alzheimer's disease (AD). According to the so called Amyloid Cascade Hypothesis the increase of Aβ triggers a series of events leading to synaptic dysfunction and memory loss as well as to the structural brain damage in the later stage of the disease. However, several evidences suggest that this hypothesis is not sufficient to explain AD pathogenesis, especially considering that most of the clinical trials aimed to decrease Aβ levels have been unsuccessful. Moreover, Aβ is physiologically produced in the healthy brain during neuronal activity and it is needed for synaptic plasticity and memory. Here we propose a model interpreting AD pathogenesis as an alteration of the negative feedback loop between Aβ and its physiological receptors, focusing on alpha7 nicotinic acetylcholine receptors (α7-nAchRs). According to this vision, when Aβ cannot exert its physiological function a negative feedback mechanism would induce a compensatory increase of its production leading to an abnormal accumulation that reduces α7-nAchR function, leading to synaptic dysfunction and memory loss. In this perspective, the indiscriminate Aβ removal might worsen neuronal homeostasis, causing a further impoverishment of learning and memory. Even if further studies are needed to better understand and validate these mechanisms, we believe that to deepen the role of Aβ in physiological conditions might represent the keystone to elucidate important aspects of AD pathogenesis.

What can triumphs and tribulations from drug research in Alzheimer's disease tell us about the development of psychotropic drugs in general?

Drug development for psychiatric disorders has almost ground to a halt. Some newer drugs are better tolerated or safer than older ones, but none is more effective. Years of failure in preventing or delaying the onset of illness, ameliorating symptoms, lowering suicide rates, or improving quality of life has put the commercial investments that had previously funded drug development at risk. To promote the development of psychiatric drugs with greater efficacy, we need to improve the way we bring potentially beneficial drugs to market. We need to acknowledge, as has been done in other specialties, that people differ in their response to drugs. Psychiatric drug research needs to be grounded in a better understanding of molecular brain mechanisms, neural circuits, and their relations to clinical disease. With this understanding, drugs need to be more precisely directed at specific brain targets. In psychiatric drug development, government, industry, regulatory bodies, and academia should realign to ensure medical science is used in the best interests of patients.

Diet, nutrients and metabolism: cogs in the wheel driving Alzheimer's disease pathology?

Alzheimer's disease (AD), the most common form of dementia, is a chronic, progressive neurodegenerative disease that manifests clinically as a slow global decline in cognitive function, including deterioration of memory, reasoning, abstraction, language and emotional stability, culminating in a patient with end-stage disease, totally dependent on custodial care. With a global ageing population, it is predicted that there will be a marked increase in the number of people diagnosed with AD in the coming decades, making this a significant challenge to socio-economic policy and aged care. Global estimates put a direct cost for treating and caring for people with dementia at $US604 billion, an estimate that is expected to increase markedly. According to recent global statistics, there are 35.6 million dementia sufferers, the number of which is predicted to double every 20 years, unless strategies are implemented to reduce this burden. Currently, there is no cure for AD; while current therapies may temporarily ameliorate symptoms, death usually occurs approximately 8 years after diagnosis. A greater understanding of AD pathophysiology is paramount, and attention is now being directed to the discovery of biomarkers that may not only facilitate pre-symptomatic diagnosis, but also provide an insight into aberrant biochemical pathways that may reveal potential therapeutic targets, including nutritional ones. AD pathogenesis develops over many years before clinical symptoms appear, providing the opportunity to develop therapy that could slow or stop disease progression well before any clinical manifestation develops.

Lipids in Amyloid-β Processing, Aggregation, and Toxicity

Aggregation of amyloid-beta (Aβ) peptide is the major event underlying neuronal damage in Alzheimer's disease (AD). Specific lipids and their homeostasis play important roles in this and other neurodegenerative disorders. The complex interplay between the lipids and the generation, clearance or deposition of Aβ has been intensively investigated and is reviewed in this chapter. Membrane lipids can have an important influence on the biogenesis of Aβ from its precursor protein. In particular, increased cholesterol in the plasma membrane augments Aβ generation and shows a strong positive correlation with AD progression. Furthermore, apolipoprotein E, which transports cholesterol in the cerebrospinal fluid and is known to interact with Aβ or compete with it for the lipoprotein receptor binding, significantly influences Aβ clearance in an isoform-specific manner and is the major genetic risk factor for AD. Aβ is an amphiphilic peptide that interacts with various lipids, proteins and their assemblies, which can lead to variation in Aβ aggregation in vitro and in vivo. Upon interaction with the lipid raft components, such as cholesterol, gangliosides and phospholipids, Aβ can aggregate on the cell membrane and thereby disrupt it, perhaps by forming channel-like pores. This leads to perturbed cellular calcium homeostasis, suggesting that Aβ-lipid interactions at the cell membrane probably trigger the neurotoxic cascade in AD. Here, we overview the roles of specific lipids, lipid assemblies and apolipoprotein E in Aβ processing, clearance and aggregation, and discuss the contribution of these factors to the neurotoxicity in AD.

Emerging roles of the γ-secretase-notch axis in inflammation

γ-Secretase is a distinct proteolytic complex required for the activation of many transmembrane proteins. The cleavage of substrates by γ-secretase plays diverse biological roles in producing essential products for the organism. More than 90 transmembrane proteins have been reported to be substrates of γ-secretase. Two of the most widely known and studied of these substrates are the amyloid precursor protein (APP) and the Notch receptor, which are precursors for the generation of amyloid-β (Aβ) and the Notch intracellular domain (NICD), respectively. The wide spectrum of γ-secretase substrates has made analyses of the pathology of γ-secretase-related diseases and underlying mechanisms challenging. Inflammation is an important aspect of disease pathology that requires an in-depth analysis. γ-Secretase may contribute to disease development or progression by directly increasing and regulating production of pro-inflammatory cytokines. This review summarizes recent evidence for a role of γ-secretase in inflammatory diseases, and discusses the potential use of γ-secretase inhibitors as an effective future treatment option.

Molecular drug targets and therapies for Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is characterized by normal memory loss and cognitive impairment in humans. Many drug targets and disease-modulating therapies are available for treatment of AD, but none of these are effective enough in reducing problems associated with recognition and memory. Potential drug targets so far reported for AD are β-secretase, Γ-secretase, amyloid beta (Aβ) and Aβ fibrils, glycogen synthase kinase-3 (GSK-3), acyl-coenzyme A: cholesterol acyl-transferase (ACAT) and acetylcholinesterase (AChE). Herbal remedies (antioxidants) and natural metal-chelators have shown a very significant role in reducing the risk of AD, as well as lowering the effect of Aβ in AD patients. Researchers are working in the direction of antisense and stem cell-based therapies for a cure for AD, which mainly depends on the clearance of misfolded protein deposits — including Aβ, tau, and alpha-synuclein. Computational approaches for inhibitor designing, interaction analysis, principal descriptors and an absorption, distribution, metabolism, excretion and toxicity (ADMET) study could speed up the process of drug development with higher efficacy and less chance of failure. This paper reviews the known drugs, drug targets, and existing and future therapies for the treatment of AD.

Processing of the platelet amyloid precursor protein in the mild cognitive impairment (MCI)

It has been suggested that mild cognitive impairment (MCI) patients deteriorate faster than the healthy elderly population and have an increased risk of developing dementia. Certain blood molecular biomarkers have been identified as prognostic markers in Alzheimer's disease (AD). The present study was aimed to assess the status of the platelet amyloid precursor protein (APP) metabolism in MCI and AD subjects and establish to what extent any variation could have a prognostic value suggestive of predictive AD in MCI patients. Thirty-four subjects diagnosed with MCI and 45 subjects with AD were compared to 28 healthy elderly individuals for assessing for protein levels of APP, β-APP cleaving enzyme 1 (BACE1), presenilin 1 (PS1) and a disintegrin and metalloproteinase-10 (ADAM-10) by western blot, and for the enzyme activities of BACE1 and γ-secretase by using specific fluorogenic substrates, in samples of platelets. A similar pattern in the healthy elderly and MCI patients was found for BACE1 and PS1 levels. A reduction of APP levels in MCI and AD patients compared with healthy elderly individuals was found. Augmented levels of ADAM-10 in both MCI and AD were displayed in comparison with age-matched control subjects. The ratio ADAM-10/BACE1 was higher for the MCI group versus AD group. Whereas BACE1 and PS1 levels were only increased in AD regarding to controls, BACE1 and γ-secretase activities augmented significantly in both MCI and AD groups. Finally, differences and similarities between MCI and AD patients were observed in several markers of platelet APP processing. Larger sample sets from diverse populations need to be analyzed to define a signature for the presence of MCI or AD pathology and to early detect AD at the MCI stage.

Therapeutic targets of brain insulin resistance in sporadic Alzheimer's disease

Growing evidence supports roles for brain insulin and insulin-like growth factor (IGF) resistance and metabolic dysfunction in the pathogenesis of Alzheimer's disease (AD). Whether the underlying problem stems from a primary disorder of central nervous system (CNS) neurons and glia, or secondary effects of systemic diseases such as obesity, Type 2 diabetes, or metabolic syndrome, the end-results include impaired glucose utilization, mitochondrial dysfunction, increased oxidative stress, neuroinflammation, and the propagation of cascades that result in the accumulation of neurotoxic misfolded, aggregated, and ubiquitinated fibrillar proteins. This article reviews the roles of impaired insulin and IGF signaling to AD-associated neuronal loss, synaptic disconnection, tau hyperphosphorylation, amyloid-beta accumulation, and impaired energy metabolism, and discusses therapeutic strategies and lifestyle approaches that could be used to prevent, delay the onset, or reduce the severity of AD. Finally, it is critical to recognize that AD is heterogeneous and has a clinical course that fully develops over a period of several decades. Therefore, early and multi-modal preventive and treatment approaches should be regarded as essential.

The recent updates of therapeutic approaches against aβ for the treatment of Alzheimer's disease

One of the main neuropathological lesions observed in brain autopsy of Alzheimer's disease (AD) patients is the extracellular senile plaques mainly composed of amyloid-beta (Aβ) peptide. Recently, treatment strategies have focused on modifying the formation, clearance, and accumulation of this potentially neurotoxic peptide. β- and γ-secretase are responsible for the cleavage of amyloid precursor protein (APP) and the generation of Aβ peptide. Treatments targeting these two critical secretases may therefore reduce Aβ peptide levels and positive impact on AD. Vaccination is also an advanced approach against Aβ. This review focuses on recent advances of our understanding of this key peptide, with emphasis on Aβ peptide synthesis, accumulation and neurotoxicity, and current therapies including vaccination and two critical secretase inhibitors. MicroRNAs (miRNAs) are a class of conserved endogenous small noncoding RNAs, known to regulate the expression of complementary messenger RNAs, involved in AD development. We therefore address the relationship of miRNAs in the brain and Aβ generation, as a novel therapeutic approach to the treatment of AD while also providing new insights on the etiology of this neurological disorder.

Evidence from solid-state NMR for nonhelical conformations in the transmembrane domain of the amyloid precursor protein

The amyloid precursor protein (APP) is subject to proteolytic processing by γ-secretase within neuronal membranes, leading to Alzheimer's disease-associated β-amyloid peptide production by cleavage near the midpoint of the single transmembrane (TM) segment of APP. Conformational properties of the TM segment may affect its susceptibility to γ-secretase cleavage, but these properties have not been established definitively, especially in bilayer membranes with physiologically relevant lipid compositions. In this article, we report an investigation of the APP-TM conformation, using (13)C chemical shifts obtained with two-dimensional solid-state NMR spectroscopy as site-specific conformational probes. We find that the APP-TM conformation is not a simple α-helix, particularly at 37°C in multilamellar vesicles with compositions that mimic the composition of neuronal cell membranes. Instead, we observe a mixture of helical and nonhelical conformations at the N- and C-termini and in the vicinity of the γ-cleavage site. Conformational plasticity of the TM segment of APP may be an important factor in the γ-secretase cleavage mechanism.