Stable mutated tau441 transfected SH-SY5Y cells as screening tool for Alzheimer's disease drug candidates

Populations of Tau Conformers Drive Prion-like Strain Effects in Alzheimer's Disease and Related Dementias

Recent findings of diverse populations of prion-like conformers of misfolded tau protein expand the prion concept to Alzheimer's disease (AD) and monogenic frontotemporal lobar degeneration (FTLD)-MAPT P301L, and suggest that distinct strains of misfolded proteins drive the phenotypes and progression rates in many neurodegenerative diseases. Notable progress in the previous decades has generated many lines of proof arguing that yeast, fungal, and mammalian prions determine heritable as well as infectious traits. The extraordinary phenotypic diversity of human prion diseases arises from structurally distinct prion strains that target, at different progression speeds, variable brain structures and cells. Although human prion research presents beneficial lessons and methods to study the mechanism of strain diversity of protein-only pathogens, the fundamental molecular mechanism by which tau conformers are formed and replicate in diverse tauopathies is still poorly understood. In this review, we summarize up to date advances in identification of diverse tau conformers through biophysical and cellular experimental paradigms, and the impact of heterogeneity of pathological tau strains on personalized structure- and strain-specific therapeutic approaches in major tauopathies.

Prion-like strain effects in tauopathies

Tau is a microtubule-associated protein that plays crucial roles in physiology and pathophysiology. In the realm of dementia, tau protein misfolding is associated with a wide spectrum of clinicopathologically diverse neurodegenerative diseases, collectively known as tauopathies. As proposed by the tau strain hypothesis, the intrinsic heterogeneity of tauopathies may be explained by the existence of structurally distinct tau conformers, “strains”. Tau strains can differ in their associated clinical features, neuropathological profiles, and biochemical signatures. Although prior research into infectious prion proteins offers valuable lessons for studying how a protein-only pathogen can encompass strain diversity, the underlying mechanism by which tau subtypes are generated remains poorly understood. Here we summarize recent advances in understanding different tau conformers through in vivo and in vitro experimental paradigms, and the implications of heterogeneity of pathological tau species for drug development.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

Streptocyclinones A and B ameliorate Alzheimer's disease pathological processes in vitro

Alzheimer's disease (AD) is a pathology characterized by the abnormal accumulation of amyloid-beta (Aβ) and hyperphosphorylated tau. Oxidative stress and neuroinflammation are also strongly related to this disease. The ability of two new glycosylated angucyclinones, streptocyclinones A and B (1 and 2), isolated from Streptomyces sp to improve AD hallmarks was evaluated. Compounds were able to protect SH-SY5Y neuroblastoma cells from H₂O₂-induced oxidative injury by activating the nuclear factor E2-related factor (Nrf2). Their capacity to modulate neuroinflammation was tested in lipopolysaccharide-activated BV2 microglial cells. Compounds reduced the release of pro-inflammatory factors, inhibited the activation of NFκB and mitogen activated kinases (MAPK), and induced the translocation of Nrf2 to the nucleus of microglial cells. A trans-well co-culture was established to determine the effect of microglia treated with streptocyclinones on the survival of SH-SY5Y cells. The cell viability of neuroblastoma cells increased when the compounds were added to BV2 cells. SH-SY5Y-TMHT441 cells were used to determine the effect of compounds on tau phosphorylation. Both compounds reduced tau hyperphophorylation by targeting MAPK kinases. Moreover, streptocyclinone B (2) was able to inhibit the activity of β-secretase 1 and decrease the release of reactive oxygen species in BV2 cells stimulated with Aβ. With the same co-culture trans-well system, the treatment of Aβ-stimulated microglia with compound 2 augmented the viability of SH-SY5Y-TMHT441 cells. The results presented in this work provide evidences of the multitarget activities displayed by these new Streptomyces compounds, making them good candidates for further studies in the treatment of AD.

Tau downregulates BDNF expression in animal and cellular models of Alzheimer's disease

In Alzheimer's disease, soluble tau accumulates and deposits as neurofibrillary tangles (NFTs). However, a precise toxic mechanism of tau is not well understood. We hypothesized that overexpression of wild-type tau downregulates brain-derived neurotrophic factor (BDNF), a neurotrophic peptide essential for learning and memory. Two transgenic mouse models of human tau expression and human tau (hTau40)-transfected human neuroblastoma (SH-SY5Y) cells were used to examine the effect of excess or pathologically modified wild-type human tau on BDNF expression. Both transgenic mouse models, with or without NFTs, as well as hTau40-SH-SY5Y cells significantly downregulated BDNF messenger RNA compared with controls. Similarly, transgenic mice overexpressing amyloid-β (Aβ) significantly downregulated BDNF expression. However, when crossed with tau knockout mice, the resulting animals exhibited BDNF levels that were not statistically different from wild-type mice. These results demonstrate that excess or pathologically modified wild-type human tau downregulates BDNF and that neither a mutation in tau nor the presence of NFTs is required for toxicity. Moreover, our findings suggest that tau at least partially mediates Aβ-induced BDNF downregulation. Therefore, Alzheimer's disease treatments targeting Aβ alone may not be effective without considering the impact of tau pathology on neurotrophic pathways.

Brain Aggregates: An Effective In Vitro Cell Culture System Modeling Neurodegenerative Diseases

Drug discovery for neurodegenerative diseases is particularly challenging because of the discrepancies in drug effects between in vitro and in vivo studies. These discrepancies occur in part because current cell culture systems used for drug screening have many limitations. First, few cell culture systems accurately model human aging or neurodegenerative diseases. Second, drug efficacy may differ between dividing and stationary cells, the latter resembling nondividing neurons in the CNS. Brain aggregates (BrnAggs) derived from embryonic day 15 gestation mouse embryos may represent neuropathogenic processes in prion disease and reflect in vivo drug efficacy. Here, we report a new method for the production of BrnAggs suitable for drug screening and suggest that BrnAggs can model additional neurological diseases such as tauopathies. We also report a functional assay with BrnAggs by measuring electrophysiological activities. Our data suggest that BrnAggs could serve as an effective in vitro cell culture system for drug discovery for neurodegenerative diseases.

The Streptomyces metabolite anhydroexfoliamycin ameliorates hallmarks of Alzheimer's disease in vitro and in vivo

Anhydroexfoliamycin (1) and undecylprodigiosin (2) have been previously described as neuroprotective molecules against oxidative stress in neurons. Since oxidative stress is strongly correlated with neurodegenerative diseases, we have evaluated their effects over the principal hallmarks of Alzheimer's disease (AD). Both compounds were tested in vitro in two different neuroblastoma cellular models, one for amyloid precursor protein metabolism studies (BE(2)-M17) and another one specific for taupathology in AD (SH-SY5Y-TMHT441). Amyloid-beta (Aβ) levels, β-secretase (BACE1) activity, tau phosphorylation, extracellular signal-regulated kinase (ERK) and glycogen synthase kinase-3beta (GSK3β) expression were analyzed and while undecylprodigiosin (2) produced poor results, anhydroexfoliamycin (1) strongly inhibited GSK3β, reducing tau phosphorylation in vitro (0.1 μM). A competitive assay of anhydroexfoliamycin (1) and the specific c-Jun N-terminal kinase (JNK) inhibitor, SP600125, showed that the reduction of the phosphorylated tau levels is mediated by the JNK pathway in SH-SY5Y-TMHT441 cells. Thus, this compound was tested in vivo by intraperitoneal administration in 3xTg-AD mice, confirming the positive results registered in the in vitro assays. This work presents anhydroexfoliamycin (1) as a promising candidate for further studies in drug development against neurodegenerative diseases.

Isolation and characterization of antibody fragments selective for toxic oligomeric tau

Oligomeric tau species are important in the onset and progression of Alzheimer's disease (AD), as they are neurotoxic and can propagate tau-tangle pathology. Therefore, reagents that selectively recognize different key morphologies of tau are needed to help define the role of tau in AD and related diseases. We utilized a biopanning protocol that combines the binding diversity of phage-displayed antibody libraries with the powerful imaging capability of atomic force microscopy to isolate single-chain antibody fragments (scFvs) that selectively bind toxic oligomeric tau. We isolated 3 different antibody fragments that bind oligomeric but not monomeric or fibrillar tau. The scFvs differentiate brain tissue homogenates of both 3×TG and tau-AD mice from wild-type mice, detecting oligomeric tau at much earlier ages than when neurofibrillary tangles are typically detected. The scFvs also distinguish human postmortem AD brain tissue from cognitively normal postmortem human brain tissue, demonstrating the potential of this approach for developing biomarkers for early detection and progression of AD.

Familial Alzheimer’s disease modelling using induced pluripotent stem cell technology

Alzheimer’s disease (AD) is a progressive neurodegenerative disease in which patients exhibit gradual loss of memory that impairs their ability to learn or carry out daily tasks. Diagnosis of AD is difficult, particularly in early stages of the disease, and largely consists of cognitive assessments, with only one in four patients being correctly diagnosed. Development of novel therapeutics for the treatment of AD has proved to be a lengthy, costly and relatively unproductive process with attrition rates of > 90%. As a result, there are no cures for AD and few treatment options available for patients. Therefore, there is a pressing need for drug discovery platforms that can accurately and reproducibly mimic the AD phenotype and be amenable to high content screening applications. Here, we discuss the use of induced pluripotent stem cells (iPSCs), which can be derived from adult cells, as a method of recapitulation of AD phenotype in vitro. We assess their potential use in high content screening assays and the barriers that exist to realising their full potential in predictive efficacy, toxicology and disease modelling. At present, a number of limitations need to be addressed before the use of iPSC technology can be fully realised in AD therapeutic applications. However, whilst the use of AD-derived iPSCs in drug discovery remains a fledgling field, it is one with immense potential that is likely to reach fruition within the next few years.

A high-throughput screening assay for determining cellular levels of total tau protein

The microtubule-associated protein (MAP) tau has been implicated in the pathology of numerous neurodegenerative diseases. In the past decade, the hyperphosphorylated and aggregated states of tau protein have been important targets in the drug discovery field for the potential treatment of Alzheimer's disease. Although several compounds have been reported to reduce the hyperphosphorylated state of tau or impact the stabilization of tau, their therapeutic activities are remain to be validated. Recently, reduction of total cellular tau protein has emerged as an alternate intervention point for drug development and a potential treatment of tauopathies. We have developed and optimized homogenous assays, using the AlphaLISA and HTRF assay technologies, for the quantification of total cellular tau protein levels in the SH-SY5Y neuroblastoma cell line. The signal-to-basal ratios were 375 and 5.3, and the Z' factors were 0.67 and 0.60 for the AlphaLISA and HTRF tau assays, respectively. The clear advantages of these homogeneous tau assays over conventional total tau assays, such as ELISA and Western blot, are the elimination of plate wash steps and miniaturization of the assay into 1536-well plate format for the ultra-high-throughput screening of large compound libraries.

Replication-defective HSV-1 effectively targets trigeminal ganglion and inhibits viral pathopoiesis by mediating interferon gamma expression in SH-SY5Y cells

It has been widely believed that recurrence of herpes simplex keratitis (HSK) is due to the reactivation of herpes simplex virus type 1 (HSV-1) from latent sites in trigeminal ganglion (TG). However, there are also not effective vectors which could target TG for therapy. Replication-defective HSV-1 vector (rdHSV-IFNγ) was established by calcium phosphate co-transfection of complementing cells. We firstly infected rdHSV-IFNγ to SH-SY5Y, and detected IFNγ expression by western blot, evaluated 50 % cellular cytotoxicity (CC(50)) by ELISA. Antiviral activity of rdHSV-IFNγ was examined by immunofluorescence and antiviral concentration of 50 % effectiveness (EC(50)) assay. The rdHSV-IFNγ vector was immunized to Wistar rats to observe targeting function to TG. Kaplan-Meier survival analysis was utilized to assess security of rdHSV-IFNγ. RT-PCR and immunohistochemistry assay were employed to detect rdHSV-IFNγ localization in TG. Western blot was employed to detect IFNγ expression. rdHSV-IFNγ was successfully established, and performed an effective antiviral activity and higher security in SH-SY5Y. There were no significant differences of survival and corneal infection rate of rdHSV-IFNγ immunized rats among groups (P > 0.05). RT-PCR and immunohistochemistry indicated that expression of glycoprotein D (gD) in TG could target TG and decreased following with times post immunization. Furthermore, IFNγ was expressed effectively in TG tissues. Our findings indicated that established rdHSV-IFNγ vector effectively transported therapeutic gene into TG tissues. The administration of replication-defective vector carrying therapeutic genes may become a promising tool in inhibition or reoccurrence of HSK in clinical.

Induced tauopathy in a novel 3D-culture model mediates neurodegenerative processes: a real-time study on biochips

Tauopathies including Alzheimer's disease represent one of the major health problems of aging population worldwide. Therefore, a better understanding of tau-dependent pathologies and consequently, tau-related intervention strategies is highly demanded. In recent years, several tau-focused therapies have been proposed with the aim to stop disease progression. However, to develop efficient active pharmaceutical ingredients for the broad treatment of Alzheimer's disease patients, further improvements are necessary for understanding the detailed neurodegenerative processes as well as the mechanism and side effects of potential active pharmaceutical ingredients (API) in the neuronal system. In this context, there is a lack of suitable complex in vitro cell culture models recapitulating major aspects of taupathological degenerative processes in sufficient time and reproducible manner.Herewith, we describe a novel 3D SH-SY5Y cell-based, tauopathy model that shows advanced characteristics of matured neurons in comparison to monolayer cultures without the need of artificial differentiation promoting agents. Moreover, the recombinant expression of a novel highly pathologic fourfold mutated human tau variant lead to a fast and emphasized degeneration of neuritic processes. The neurodegenerative effects could be analyzed in real time and with high sensitivity using our unique microcavity array-based impedance spectroscopy measurement system. We were able to quantify a time- and concentration-dependent relative impedance decrease when Alzheimer's disease-like tau pathology was induced in the neuronal 3D cell culture model. In combination with the collected optical information, the degenerative processes within each 3D-culture could be monitored and analyzed. More strikingly, tau-specific regenerative effects caused by tau-focused active pharmaceutical ingredients could be quantitatively monitored by impedance spectroscopy.Bringing together our novel complex 3D cell culture taupathology model and our microcavity array-based impedimetric measurement system, we provide a powerful tool for the label-free investigation of tau-related pathology processes as well as the high content analysis of potential active pharmaceutical ingredient candidates.