Amyloid Precursor Protein Levels Research Articles

Genotype Load Modulates Amyloid Burden and Anxiety-Like Patterns in Male 3xTg-AD Survivors despite Similar Neuro-Immunoendocrine, Synaptic and Cognitive Impairments.

The wide heterogeneity and complexity of Alzheimer’s disease (AD) patients’ clinical profiles and increased mortality highlight the relevance of personalized-based interventions and the need for end-of-life/survival predictors. At the translational level, studying genetic and age interactions in a context of different levels of expression of AD-genetic-load can help to understand this heterogeneity better. In the present report, a singular cohort of long-lived (19-month-old survivors) heterozygous and homozygous male 3xTg-AD mice were studied to determine whether their AD-genotype load can modulate the brain and peripheral pathological burden, behavioral phenotypes, and neuro-immunoendocrine status, compared to age-matched non-transgenic controls. The results indicated increased amyloid precursor protein (APP) levels in a genetic-load-dependent manner but convergent synaptophysin and choline acetyltransferase brain levels. Cognitive impairment and HPA-axis hyperactivation were salient traits in both 3xTg-AD survivor groups. In contrast, genetic load elicited different anxiety-like profiles, with hypoactive homozygous, while heterozygous resembled controls in some traits and risk assessment. Complex neuro-immunoendocrine crosstalk was also observed. Bodyweight loss and splenic, renal, and hepatic histopathological injury scores provided evidence of the systemic features of AD, despite similar peripheral organs’ oxidative stress. The present study provides an interesting translational scenario to study further genetic-load and age-dependent vulnerability/compensatory mechanisms in Alzheimer’s disease.

HnRNP F and hnRNP H1 regulate mRNA stability of amyloid precursor protein.

Amyloid precursor protein (APP) is a transmembrane protein that plays a crucial role in the production of amyloid-β peptides. Any disruption in APP protein production, its mRNA decay rate or processing may result in abnormal production of amyloid-β peptides and subsequent development of protein aggregation diseases. Therefore, the equilibrium is crucial for neuronal function. An association study of heterogeneous nuclear ribonucleoprotein (hnRNP)-F and hnRNP H1 with APP was carried out in Neuro-2a (N2a) cells. In the present study, we found that hnRNP F and hnRNP H1 were significantly upregulated in the hippocampus of APP/PS1 mice. The changes in APP expression were positively associated with hnRNP F and hnRNP H1 when hnRNP F and hnRNP H1 were depleted or increased in N2a cells. Importantly, cross-linked RNA immunoprecipitation demonstrated binding affinities of hnRNP F and hnRNP H1 for App mRNA. Mechanistically, mRNA stability assay revealed that overexpression of hnRNP F or hnRNP H1 increases the APP level by stabilizing App mRNA half-life, implying that levels of hnRNP F and hnRNP H1 can change the production of APP. Further understanding of the regulatory mechanism of APP expression in association with hnRNP F and hnRNP H1 would provide insights into the mechanism underlying the maintenance of brain health and cognition. This study provides a theoretical basis for the development of hnRNP-stabilizing compounds to regulate APP.

Effect of Global Brain Ischemia on Amyloid Precursor Protein Metabolism and Expression of Amyloid-Degrading Enzymes in Rat Cortex: Role in Pathogenesis of Alzheimer's Disease.

The incidence of Alzheimer's disease (AD) increases significantly following chronic stress and brain ischemia which, over the years, cause accumulation of toxic amyloid species and brain damage. The effects of global 15-min ischemia and 120-min reperfusion on the levels of expression of the amyloid precursor protein (APP) and its processing were investigated in the brain cortex (Cx) of male Wistar rats. Additionally, the levels of expression of the amyloid-degrading enzymes neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), and insulin-degrading enzyme (IDE), as well as of some markers of oxidative damage were assessed. It was shown that the APP mRNA and protein levels in the rat Cx were significantly increased after the ischemic insult. Protein levels of the soluble APP fragments, especially of sAPPβ produced by β-secretase, (BACE-1) and the levels of BACE-1 mRNA and protein expression itself were also increased after ischemia. The protein levels of APP and BACE-1 in the Cx returned to the control values after 120-min reperfusion. The levels of NEP and ECE-1 mRNA also decreased after ischemia, which correlated with the decreased protein levels of these enzymes. However, we have not observed any changes in the protein levels of insulin-degrading enzyme. Contents of the markers of oxidative damage (di-tyrosine and lysine conjugates with lipid peroxidation products) were also increased after ischemia. The obtained data suggest that ischemia shifts APP processing towards the amyloidogenic β-secretase pathway and accumulation of the neurotoxic Aβ peptide as well as triggers oxidative stress in the cells. These results are discussed in the context of the role of stress and ischemia in initiation and progression of AD.

A New Approach to Model Sporadic Alzheimer's Disease by Intracerebroventricular Streptozotocin Injection in APP/PS1 Mice.

Alzheimer's disease (AD) is the most common cause of dementia among elderly people. Majority of AD cases are sporadic (SAD) with unknown cause. Transgenic animal models closely reflect the familial (genetic) aspect of the disease but not the sporadic type. However, most new drug candidates which are tested positive in transgenic animal models failed in clinical studies so far. Herein, we aim to develop an AD animal model that combines most of the neuropathological features seen in sporadic AD in humans with amyloid plaques observed in transgenic mice. Four-month-old wild-type and APP/PS1 AD mice were given a single intracerebroventricular (ICV) injection of 3 mg/kg streptozotocin (STZ), a diabetogenic agent. Three weeks later, their cognitive behavior was assessed, and their brain tissues were collected for biochemical and histological analysis. STZ produced cognitive deficits in both non-transgenic mice and AD mice. Biochemical analysis showed a severe decline in synaptic proteins, increase in tau phosphorylation, oxidative stress, disturbed brain insulin signaling with extensive neuroinflammation, and cell death. Significant increase was also observed in the level of the soluble beta amyloid precursor protein (APP) fragments and robust accumulation of amyloid plaques in AD mice compared to the control. These results suggest that STZ ICV treatment causes disturbance in multiple metabolic and cell signaling pathways in the brain that facilitated amyloid plaque accumulation and tau phosphorylation. Therefore, this animal model can be used to evaluate new AD therapeutic agents for clinical translation.

The Absence of Myelin Basic Protein Reduces Non-Amyloidogenic Processing of Amyloid Precursor Protein.

The accumulation of amyloid β-protein (Aβ) in the brain is a pathological feature of Alzheimer's disease (AD). Aβ peptides originate from amyloid precursor protein (APP). APP can be proteolytically cleaved through amyloidogenic or non-amyloidogenic pathways. The molecular effects on APP metabolism/processing may be influenced by myelin and the breakdown of myelin basic protein (MBP) in AD patients and mouse models of AD pathology. We directly tested whether MBP can alter influence APP processing in MBP-/- mice, known as Shiverer (shi/shi) mice, in which no functional MBP is produced due to gene breakage from the middle of MBP exon ll. A significant reduction of the cerebral sAPPα level in Shiverer (shi/shi) mice was found, although the levels of both total APP and sAPPβ remain unchanged. The reduction of sAPPα was considered to be due to the changes in the expression levels of a disintegrin and metalloproteinase-9 (ADAM9) catalysis and non-amyloid genic processing of APP in the absence of MBP because it binds to ADAM9. MBP -/- mice exhibited increased Aβ oligomer production. These findings suggest that in the absence of MBP, there is a marked reduction of nonamyloidogenic APP processing to sAPPα, and targeting myelin of oligodendrocytes may be a novel therapy for the prevention and treatment of AD.

Normal levels of KIF5 but reduced KLC1 levels in both Alzheimer disease and Alzheimer disease in Down syndrome: evidence suggesting defects in anterograde transport

BackgroundImpaired axonal transport may contribute to the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease (AD) and Down syndrome (DS). Axonal transport is a complex process in which specific motor proteins move cargoes to and from neuronal cell bodies and their processes. Inconsistent reports point to the changes in AD in the levels of the classical anterograde motor protein kinesin family member 5 (KIF5) and the primary neuronal KIF regulator kinesin light chain 1 (KLC1), raising the possibility that anterograde transport is compromised in AD.Methods and materialsTo address inconsistencies and determine if the shared pathologies in AD and elderly DS subjects with dementia (AD in DS; AD-DS) extend to the changes in KIF5 and KLC1, we measured the levels of all the three KIF5 family members and KLC1 in the AD and AD-DS frontal cortex and AD temporal cortex and cerebellum in samples taken with a short postmortem interval. To support future studies to explore the cell biological basis for any changes detected, we also examined the levels of these proteins in the brains of young and aged adult mice in the Dp (16)1Yey/+ (Dp16) mouse model of DS and J20 mouse model of AD.ResultsThere were no changes in comparison with controls in KIF5 family members in either the AD or AD-DS samples when normalized to either β-actin or glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Interestingly, however, samples from control brains as well as from AD and AD-DS demonstrated strong positive correlations between the levels of KIF5 family members, suggesting positive co-regulated expression. Importantly, while earlier reports pointed to a negative correlation between the levels of the amyloid precursor protein (APP) and KIF5A levels, we found the opposite to be true in AD-DS; this was especially striking given triplication of the APP gene, with increased APP protein levels. AD and control samples showed positive correlations between fl-hAPP and KIF5 members, but they were less consistent. In contrast to the findings for KIF5, the levels of KLC1 were downregulated in the frontal cortex of both AD and AD-DS brains; interestingly, this change was not seen in the AD temporal cortex or cerebellum. As postmortem interval has a negative effect on the levels of KLC1, but not KIF5 members, we analyzed a subset of samples with a very short postmortem interval (PMI) (≤ 6 h), a PMI that was not significantly correlated with the levels of KLC1 in either AD or AD-DS samples; we confirmed the presence of a statistically significant reduction of KLC1 in AD and AD-DS brains as compared with control brains. Studies comparing Dp16 to its euploid control recapitulated human studies in demonstrating no change in KIF5 levels and a positive correlation between the levels of KIF5 family members. J20 mice also showed normal KIF5 levels. However, unlike the AD and AD-DS frontal cortex, KLC1 levels were not reduced in the brains of Dp16 or J20 mice.ConclusionThese data point to significant reductions in KLC1 in AD and AD-DS. In so doing, they raise the possibility of compromised KLC1-mediated axonal transport in these conditions, a posit that can now be pursued in model systems in which KLC1 expression is reduced.

Tract-Specific Relationships Between Cerebrospinal Fluid Biomarkers and Periventricular White Matter in Posthemorrhagic Hydrocephalus of Prematurity.

Posthemorrhagic hydrocephalus (PHH) is associated with neurological morbidity and complex neurosurgical care. Improved tools are needed to optimize treatments and to investigate the developmental sequelae of PHH. To examine the relationship between diffusion magnetic resonance imaging (dMRI) and cerebrospinal fluid (CSF) biomarkers of PHH. A total of 14 preterm (PT) infants with PHH and 46 controls were included. PT CSF was collected at temporizing surgery in PHH infants (PHH PT CSF) or lumbar puncture in controls. Term-equivalent age (TEA) CSF was acquired via implanted device or at permanent CSF diversion surgery in PHH (PHH-TEA-CSF) or lumbar puncture in controls. TEA dMRI scans were used to measure fractional anisotropy (FA) and mean diffusivity (MD) in the genu of corpus callosum (gCC), posterior limb of internal capsule (PLIC), and optic radiations (OPRA). Associations between dMRI measures and CSF amyloid precursor protein (APP), neural cell adhesion-1 (NCAM-1), and L1 cell adhesion molecule (L1CAM) were assessed using Pearson correlations. APP, NCAM-1, and L1CAM were elevated over controls in PHH-PT-CSF and PHH-TEA-CSF. dMRI FA and MD differed between control and PHH infants across all tracts. PHH-PT-CSF APP levels correlated with gCC and OPRA FA and PLIC MD, while L1CAM correlated with gCC and OPRA FA. In PHH-TEA-CSF, only L1CAM correlated with OPRA MD. Tract-specific associations were observed between dMRI and CSF biomarkers at the initiation of PHH treatment. dMRI and CSF biomarker analyses provide innovative complementary methods for examining PHH-related white matter injury and associated developmental sequelae.

Reduction of pTau and APP levels in mammalian brain after low-dose radiation

Brain radiation can occur from treatment of brain tumors or accidental exposures. Brain radiation has been rarely considered, though, as a possible tool to alter protein levels involved in neurodegenerative disorders. We analyzed possible molecular and neuropathology changes of phosphorylated-Tau (pTau), all-Tau forms, β-tubulin, amyloid precursor protein (APP), glial fibrillary acidic protein (GFAP), ionized calcium binding adaptor molecule 1 (IBA-1), myelin basic protein (MBP), and GAP43 in Frontal Cortex (FC), Hippocampus (H) and Cerebellum (CRB) of swine brains following total-body low-dose radiation (1.79 Gy). Our data show that radiated-animals had lower levels of pTau in FC and H, APP in H and CRB, GAP43 in CRB, and higher level of GFAP in H versus sham-animals. These molecular changes were not accompanied by obvious neurohistological changes, except for astrogliosis in the H. These findings are novel, and might open new perspectives on brain radiation as a potential tool to interfere with the accumulation of specific proteins linked to the pathogenesis of various neurodegenerative disorders.

Insulin-like growth factor-1 improves postoperative cognitive dysfunction following splenectomy in aged rats.

Postoperative cognitive dysfunction (POCD) is a serious complication following anesthesia and operations in aged patients undergoing surgical intervention. It is characterized by temporary or permanent cognitive decline, memory impairment and deterioration in language comprehension and social adaption ability. Therefore, the development of POCD prevention and treatment tools has become an area of interest. The current study assessed the therapeutic effects of insulin-like growth factor-1 (IGF-1) on POCD in aged rats and explored the underlying mechanisms. Model rats underwent splenectomy under 1.5-2% isoflurane and mechanical ventilation. IGF-1 (50 µg/kg) was diluted in normal saline and administered by abdominal hypodermic injection daily from the operation to day 7 post-operation. Following splenectomy, the animals showed marked cognitive impairment as determined by the Morris water maze test. Hippocampal protein levels of amyloid precursor protein (APP), β-site APP-cleaving enzyme-1 (BACE-1), amyloid-β (Aβ), capase3, Bax and Bcl-2 were assessed by immunoblotting. Neuronal apoptosis in the hippocampus was analyzed using a TUNEL assay. The results demonstrated that the levels of APP, BACE-1, Aβ, caspase3 and Bax were increased following splenectomy, while the levels of Bcl2 were reduced at days 1, 3 and 7 post-operation in aged rats. However, IGF-1 downregulated APP, BACE-1, Aβ, capase3 and Bax, and upregulated Bcl2 at these time points following splenectomy. TUNEL staining revealed that administration of IGF-1 significantly reduced neuronal apoptosis in the hippocampal CA1 region following splenectomy. These results indicated that IGF-1 decreased Aβ-protein production and inhibited neuronal apoptosis in the hippocampus following splenectomy, subsequently alleviating POCD.

Relationships between the Bone Expression of Alzheimer's Disease-Related Genes, Bone Remodelling Genes and Cortical Bone Structure in Neck of Femur Fracture.

Neck of femur (NOF) fracture is a prevalent fracture type amongst the ageing and osteoporotic populations, commonly requiring total hip replacement (THR) surgery. Increased fracture risk has also been associated with Alzheimer's disease (AD) in the aged. Here, we sought to identify possible relationships between the pathologies of osteoporosis and dementia by analysing bone expression of neurotropic or dementia-related genes in patients undergoing THR surgery for NOF fracture. Femoral bone samples from 66 NOF patients were examined for expression of the neurotropic genes amyloid precursor protein (APP), APP-like protein-2 (APLP2), Beta-Secretase Cleaving Enzyme-1 (BACE1) and nerve growth factor (NGF). Relationships were examined between the expression of these and of bone regulatory genes, systemic factors and bone structural parameters ascertained from plain radiographs. We found strong relative levels of expression and positive correlations between APP, APLP2, BACE1 and NGF levels in NOF bone. Significant correlations were found between APP, APLP2, BACE1 mRNA levels and bone remodelling genes TRAP, RANKL, and the RANKL:OPG mRNA ratio, indicative of potential functional relationships at the time of fracture. Analysis of the whole cohort, as well as non-dementia (n = 53) and dementia (n = 13) subgroups, revealed structural relationships between APP and APLP2 mRNA expression and lateral femoral cortical thickness. These findings suggest that osteoporosis and AD may share common molecular pathways of disease progression, perhaps explaining the common risk factors associated with these diseases. The observation of a potential pathologic role for AD-related genes in bone may also provide alternative treatment strategies for osteoporosis and fracture prevention.

Alzheimer's Disease in the Down Syndrome: An Overview of Genetics and Molecular Aspects.

The overexpression of the amyloid precursor protein (APP) gene, encoded on chromosome 21, has been associated in Down syndrome (DS) with the development of early-onset Alzheimer's disease (EOAD). The increase in APP levels leads to an overproduction of amyloid-β (Aβ) peptide that accumulates in the brain. In response to this deposition, microglial cells are active and generate cascade events that include release cytokines and chemokine. The prolonged activation microglial cells induce neuronal loss, production of reactive oxygen species, neuron death, neuroinflammation, and consequently the development of Alzheimer's disease (AD). The intrinsically deficient immune systems in people with DS result in abnormalities in cytokine levels, which possibly contribute to the development of neurodegenerative disorders such as AD. Knowledge about the biomarkers involved in the process of neurodegeneration and neuroinflamation is important for understanding the mechanisms involved in the incidence and the precocity of AD in individuals with DS.

Caterpillar Medicinal Mushroom, Cordyceps militaris (Ascomycota), Attenuates Aβ1-42-Induced Amyloidogenesis and Inflammatory Response by Suppressing Amyloid Precursor Protein Progression and p38 MAPK/JNK Activation.

The deposition of amyloid beta (Aβ) is a neuropathological feature of Alzheimer's disease (AD). Cordyceps militaris is an edible medicinal fungus in Asian countries with antioxidative, antiaging, antitumor, and immunomodulatory effects. In this study, we investigated the neuroprotective mechanisms of C. militaris in the brain of Aβ1-42-injected AD mice. An intracerebroventricular injection of Aβ1-42 (total 3 µg/mouse) resulted in neurological damage, including amyloidogenesis and neuroinflammation; however, C. militaris attenuated Aβ1-42-induced amyloidogenesis and inflammatory responses. Oral administration of C. militaris at concentrations of 100 and 200 mg/kg suppressed acetylcholinesterase activity. In addition, C. militaris treatment downregulated amyloid precursor protein levels, with a decrease in β-secretase activity. Moreover, C. militaris significantly enhanced the expression of brain-derived neurotrophic factor. Furthermore, C. militaris-administered groups had inactivated inflammatory responses by downregulation of inducible nitric oxide synthase and cyclooxygenase-2 protein expression. The injection of Aβ1-42 resulted in the activation of p38 MAPK and c-Jun N-terminal kinase, which was rescued by C. militaris. These results suggest that C. militaris has a protective effect against Aβ1-42-induced neurological damage.

Peroxisomal Dysfunction Contributes to White Matter Injury Following Subarachnoid Hemorrhage in Rats via Thioredoxin-Interacting Protein-Dependent Manner.

Background and PurposeWhite matter injury (WMI) exists in the early stage of subarachnoid hemorrhage (SAH) and has not been well addressed so far.MethodsWe utilized short hairpin RNA (shRNA) and clustered regularly interspaced short palindromic repeats (CRISPR) to verify the role of peroxisomes in WMI following SAH. We evaluated short- and long-term neurobehavior after SAH. Western blotting, immunofluorescence, and Golgi staining techniques were performed to assess the changes in protein levels.ResultsCatalase (CAT) CRISPR treatment significantly attenuated neurological deficits and reduced long-term spatial learning and memory impairments after SAH by increasing the level of myelin basic protein (MBP) while decreasing the levels of amyloid precursor protein (APP), interleukin 6 (IL-6), and tumor necrosis factor (TNF)-α. The use of thioredoxin-interacting protein (TXNIP) shRNA significantly offset the effects of CAT shRNA, and the use of glycerone phosphate acyl transferase (GNPAT) shRNA significantly reversed the effects of CAT CRISPR by decreasing the levels of plasmalogens and reactive oxidative species (ROS).ConclusionPeroxisomal dysfunction induced by SAH reversely exacerbated cerebral WMI following SAH, which was at least partly mediated by TXNIP and GNPAT pathways.

Vitamin D deficiency exacerbates Alzheimer-like pathologies by reducing antioxidant capacity

Vitamin D (VD) deficiency is prevalent among aging people and Alzheimer's disease (AD) patients. However, the roles of VD deficiency in the pathology of AD remain largely unexplored. In this study, APP/PS1 mice were fed a VD-deficient diet for 13 weeks to evaluate the effects of VD deficiency on the learning and memory functions and the neuropathological characteristics of the mice. Our study revealed that VD deficiency accelerated cognitive impairment in the APP/PS1 mice. Mechanistic studies revealed that VD deficiency promoted glial activation and increased inflammatory factor secretion. Furthermore, VD deficiency increased the production and deposition of Aβ by elevating the expression levels of amyloid precursor protein (APP) and β-site APP cleavage enzyme 1 (BACE1). In addition, VD deficiency increased the phosphorylation of Tau at Thr181, Thr205 and Ser396 by increasing the activities of cyclin-dependent kinase 5 (CDK5) and glycogen synthase kinase 3α/β (GSK3α/β) and promoted synaptic dystrophy and neuronal loss. All these effects of VD deficiency may be ascribed to enhanced oxidative stress via the downregulation of superoxide dismutase 1 (SOD1), glutathione peroxidase 4 (GPx4) and cystine/glutamate exchanger (xCT). Taken together, our data suggest that VD deficiency exacerbates Alzheimer-like pathologies via promoting inflammatory stress, increasing Aβ production and elevating Tau phosphorylation by decreasing antioxidant capacity in the brains of APP/PS1 mice. Hence, rescuing the VD status of AD patients should be taken into consideration during the treatment of AD.

Targeting increased levels of APP in Down syndrome: Posiphen-mediated reductions in APP and its products reverse endosomal phenotypes in the Ts65Dn mouse model.

ObjectiveRecent clinical trials targeting amyloid beta (Aβ) and tau in Alzheimer's disease (AD) have yet to demonstrate efficacy. Reviewing the hypotheses for AD pathogenesis and defining possible links between them may enhance insights into both upstream initiating events and downstream mechanisms, thereby promoting discovery of novel treatments. Evidence that in Down syndrome (DS), a population markedly predisposed to develop early onset AD, increased APP gene dose is necessary for both AD neuropathology and dementia points to normalization of the levels of the amyloid precursor protein (APP) and its products as a route to further define AD pathogenesis and discovering novel treatments.BackgroundAD and DS share several characteristic manifestations. DS is caused by trisomy of whole or part of chromosome 21; this chromosome contains about 233 protein‐coding genes, including APP. Recent evidence points to a defining role for increased expression of the gene for APP and for its 99 amino acid C‐terminal fragment (C99, also known as β‐CTF) in dysregulating the endosomal/lysosomal system. The latter is critical for normal cellular function and in neurons for transmitting neurotrophic signals.New/updated hypothesisWe hypothesize that the increase in APP gene dose in DS initiates a process in which increased levels of full‐length APP (fl‐APP) and its products, including β‐CTF and possibly Aβ peptides (Aβ42 and Aβ40), drive AD pathogenesis through an endosome‐dependent mechanism(s), which compromises transport of neurotrophic signals. To test this hypothesis, we carried out studies in the Ts65Dn mouse model of DS and examined the effects of Posiphen, an orally available small molecule shown in prior studies to reduce fl‐APP. In vitro, Posiphen lowered fl‐APP and its C‐terminal fragments, reversed Rab5 hyperactivation and early endosome enlargement, and restored retrograde transport of neurotrophin signaling. In vivo, Posiphen treatment (50 mg/kg/d, 26 days, intraperitoneal [i.p.]) of Ts65Dn mice was well tolerated and demonstrated no adverse effects in behavior. Treatment resulted in normalization of the levels of fl‐APP, C‐terminal fragments and small reductions in Aβ species, restoration to normal levels of Rab5 activity, reduced phosphorylated tau (p‐tau), and reversed deficits in TrkB (tropomyosin receptor kinase B) activation and in the Akt (protein kinase B [PKB]), ERK (extracellular signal‐regulated kinase), and CREB (cAMP response element–binding protein) signaling pathways. Remarkably, Posiphen treatment also restored the level of choline acetyltransferase protein to 2N levels. These findings support the APP gene dose hypothesis, point to the need for additional studies to explore the mechanisms by which increased APP gene expression acts to increase the risk for AD in DS, and to possible utility of treatments to normalize the levels of APP and its products for preventing AD in those with DS.Major challenges for the hypothesisImportant unanswered questions are: (1) When should one intervene in those with DS; (2) would an APP‐based strategy have untoward consequences on possible adaptive changes induced by chronically increased APP gene dose; (3) do other genes present on chromosome 21, or on other chromosomes whose expression is dysregulated in DS, contribute to AD pathogenesis; and (4) can one model strategies that combine the use of an APP‐based treatment with those directed at other AD phenotypes including p‐tau and inflammation.Linkage to other major theoriesThe APP gene dose hypothesis interfaces with the amyloid cascade hypothesis of AD as well as with the genetic and cell biological observations that support it. Moreover, upregulation of fl‐APP protein and products may drive downstream events that dysregulate tau homeostasis and inflammatory responses that contribute to propagation of AD pathogenesis.

Unsaturated mannuronate oligosaccharide ameliorates β‐amyloid pathology through autophagy in Alzheimer’s disease cell models

Unsaturated mannuronate oligosaccharide (MOS) is an enzymatic depolymerization product from alginate-derived polymannuronate (PM). In this study, we investigated for the first time the potential therapeutic effect of MOS on Alzheimer’s disease (AD) and its molecular mechanism in N2a-sw cells and 3×Tg-AD primary cortex neurons. Our results showed that MOS ranges from mannuronate dimer to mannuronate undecamer (M2-M11) with an unsaturated nonreducing terminal structure and with a double bond and 1,4-glycosidic linkages. It significantly inhibited the aggregation of amyloid-β (Aβ)1-42 oligomer, decreased expression of Aβ1-42 and reduced levels of amyloid precursor protein (APP) and BACE1. It promoted the autophagy, which involves the inactivation of mTOR signaling pathway and the facilitation of the fusion of autophagosomes and lysosomes. Finally, autophagy inhibitors blocked MOS’ anti-AD actions, confirming the involvement of autophagy. In conclusion, MOS from seaweed alginate might be a promising nutraceutical or natural medicine for AD therapy.

Effects of U1 Small Nuclear Ribonucleoprotein Inhibition on the Expression of Genes Involved in Alzheimer's Disease.

Deposition and dysfunction of U1 small nuclear ribonucleoprotein (snRNP) have been revealed in Alzheimer’s disease (AD), but whether U1 is involved in the amyloid precursor protein (APP) and Tau pathways remains unclear. Here, we investigate this by inhibiting the U1 components in cultured cells and examining the expression changes of AD-related genes to these two canonic pathways. We find that knockdown of U1-70K and U1C increases the protein expressions of APP and GSK-3β while reduces that of Nicastrin in a dose-dependent manner. Knockdown of U1A shows no effects on the expression of these proteins. The real-time PCR results show that the mRNA expression levels of APP, Nicastrin and GSK-3β are unchanged, decreased, and increased, respectively. In addition, U1-70K knockdown suppresses Tau phosphorylation and causes altered splicing of Tau exon 10. This study suggests that the effect of U1 snRNP knockdown is component-specific and more likely involved in APP deregulation in AD.

Penetrating Ballistic-Like Brain Injury Leads to MicroRNA Dysregulation, BACE1 Upregulation, and Amyloid Precursor Protein Loss in Lesioned Rat Brain Tissues.

Severe traumatic brain injury (TBI) is a risk factor for neurodegenerative diseases. Yet, the molecular events involving dysregulated miRNAs that may be associated with protein degradation in the brain remains elusive. Quantitation of more than 800 miRNAs was conducted using rat ipsilateral coronal brain tissues collected 1, 3, or 7 days after penetrating ballistic-like brain injury (PBBI). As a control for each time-point, Sham-operated animals received craniotomy alone. Microarray and systems biology analysis indicated that the amplitude and complexity of miRNAs affected were greatest 7 day after PBBI. Arrays and Q-PCR inferred that dysregulation of miR-135a, miR-328, miR-29c, and miR-21 were associated with altered levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), PSEN1, PSEN2, and amyloid precursor protein (APP) genes. These events were followed by increased levels of mature BACE1 protein and concomitant loss of full length APP within 3–7 days, then elevation of amyloid beta (Aβ)-40 7 days after PBBI. This study indicates that miRNA arrays, coupled with systems biology, may be used to guide study design prior validation of miRNA dysregulation. Associative analysis of miRNAs, mRNAs, and proteins within a proposed pathway are poised for further validation as biomarkers and therapeutic targets relevant to TBI-induced APP loss and subsequent Aβ peptide generation during neurodegeneration.

MiR-149-5p inhibition reduces Alzheimer's disease β-amyloid generation in 293/APPsw cells by upregulating H4K16ac via KAT8.

Alzheimer's disease (AD), the leading cause of age-related dementia, is characterized by abnormal β-amyloid accumulation. During learning, memory formation and consolidation, increased levels of histone H3 and H4 acetylation are observed. The present study reported significantly decreased level of H4K16ac in the plasma of patients with AD compared with healthy subjects via western blotting and reverse transcription-quantitative (RT-q)PCR. Lysine acetyltransferase 8 (KAT8) expression, the major lysine acetyltransferase responsible for the acetylation of H4K16, was significantly decreased in patients with AD compared with healthy subjects as determined via western blotting and RT-qPCR. The results indicated that aberrant expression patterns of H4K16ac and KAT8 might be associated with AD progression. Moreover, western blot analysis demonstrated that KAT8-overexpression cells displayed increased levels of H4K16ac, accompanied by higher levels of neuroprotective soluble amyloid precursor protein (sAPP)α and β-secretase (BACE)2, and decreased levels of sAPPβ and BACE1 compared with negative control and vector cells. In neurodegenerative disorders, microRNAs (miRNAs/miRs) are deregulated; however, the effect of miRNA dysregulation on histone acetylation is not completely understood. To the best of our knowledge, the present study identified a novel inhibitory interaction between miR-149-5p and KAT8 3'-UTR that contributed to the pathological alterations in an AD cell model for the first time, using bioinformatics and a dual-luciferase reporter assay. The western blotting results indicated that, compared with the inhibitor control group, miR-149-5p inhibitor markedly increased H4K16ac levels, which were significantly suppressed by co-transfection with KAT8 short hairpin (sh)RNA. KAT8 shRNA and miR-149-5p inhibitor co-transfection abolished the beneficial effects of miR-149-5p inhibitor. The results indicated that miR-149-5p regulated KAT8 and H4K16ac expression in an AD cell model, which may be associated with the pathological process of AD; therefore, miRNA may serve as a potential drug target for AD.

Correction of microtubule defects within Aβ plaque-associated dystrophic axons results in lowered Aβ release and plaque deposition.

The hallmark pathologies of the Alzheimer's disease (AD) brain are amyloid beta (Aβ)-containing senile plaques and neurofibrillary tangles formed from the microtubule (MT)-binding tau protein. Tau becomes hyperphosphorylated and disengages from MTs in AD, with evidence of resulting MT structure/function defects. Brain-penetrant MT-stabilizing compounds can normalize MTs and axonal transport in mouse models with tau pathology, thereby reducing neuron loss and decreasing tau pathology. MT dysfunction is also observed in dystrophic axons adjacent to Aβ plaques, resulting in accumulation of amyloid precursor protein (APP) and BACE1 with the potential for enhanced localized Aβ generation. We have examined whether the brain-penetrant MT-stabilizing compound CNDR-51657 might decrease plaque-associated axonal dystrophy and Aβ release in 5XFAD mice that develop an abundance of Aβ plaques. Administration of CNDR-51657 to 1.5-month-old male and female 5XFAD mice for 4 or 7 weeks led to decreased soluble brain Aβ that coincided with reduced APP and BACE1 levels, resulting in decreased formation of insoluble Aβ deposits. These data suggest a vicious cycle whereby initial Aβ plaque formation causes MT disruption in nearby axons, resulting in the local accumulation of APP and BACE1 that facilitates additional Aβ generation and plaque deposition. The ability of a MT-stabilizing compound to attenuate this cycle, and also reduce deficits resulting from reduced tau binding to MTs, suggests that molecules of this type hold promise as potential AD therapeutics.