3D culture models of Alzheimer's disease: a road map to a "cure-in-a-dish"

Mapping the scientific output of organoids for animal and human modeling infectious diseases: a bibliometric assessment

The escalation of antibiotic resistance, pandemics, and nosocomial infections underscores the importance of research in both animal and human infectious diseases. Recent advancements in three-dimensional tissue cultures, or "organoids", have revolutionized the development of in vitro models for infectious diseases. Our study conducts a bibliometric analysis on the use of organoids in modeling infectious diseases, offering an in-depth overview of this field's current landscape. We examined scientific contributions from 2009 onward that focused on organoids in host‒pathogen interactions using the Web of Science Core Collection and OpenAlex database. Our analysis included temporal trends, reference aging, author, and institutional productivity, collaborative networks, citation metrics, keyword cluster dynamics, and disruptiveness of organoid models. VOSviewer, CiteSpace, and Python facilitated this analytical assessment. The findings reveal significant growth and advancements in organoid-based infectious disease research. Analysis of keywords and impactful publications identified three distinct developmental phases in this area that were significantly influenced by outbreaks of Zika and SARS-CoV-2 viruses. The research also highlights the synergistic efforts between academia and publishers in tackling global pandemic challenges. Through mostly consolidating research efforts, organoids are proving to be a promising tool in infectious disease research for both human and animal infectious disease. Their integration into the field necessitates methodological refinements for better physiological emulation and the establishment of extensive organoid biobanks. These improvements are crucial for fully harnessing the potential of organoids in understanding infectious diseases and advancing the development of targeted treatments and vaccines.

Alzheimer's Disease: Cellular and Pharmacological Aspects

Alzheimer's disease was described more than 100 years ago and despite the fact that several molecules are being tested for its treatment, which are in phase III trials, the disease continues to progress. The main problem is that these molecules function properly in healthy neurons, while neuronal pathology includes plasma membrane disruption, malfunction of various organelles, and hyperphosphorylation of Tau and amyloid plaques. The main objective of this article is the discussion of a neuronal restoration therapy, where molecules designed for the treatment of Alzheimer's disease would probably be more effective, and the quality of life of people would be better.

Mechanisms linking cerebrovascular dysfunction and tauopathy: Adding a layer of epiregulatory complexity

Intracellular accumulation of hyperphosphorylated misfolded tau proteins are found in many neurodegenerative tauopathies, including Alzheimer's disease (AD). Tau pathology can impact cerebrovascular physiology and function through multiple mechanisms. In vitro and in vivo studies have shown that alterations in the blood-brain barrier (BBB) integrity and function can result in synaptic abnormalities and neuronal damage. In the present review, we will summarize how tau proteostasis dysregulation contributes to vascular dysfunction and, conversely, we will examine the factors and pathways leading to tau pathological alterations triggered by cerebrovascular dysfunction. Finally, we will highlight the role epigenetic and epitranscriptomic factors play in regulating the integrity of the cerebrovascular system and the progression of tauopathy including a few observartions on potential therapeutic interventions. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Microphysiological systems for human aging research

Recent advances in microphysiological systems (MPS), also known as organs-on-a-chip (OoC), enable the recapitulation of more complex organ and tissue functions on a smaller scale in vitro. MPS therefore provide the potential to better understand human diseases and physiology. To date, numerous MPS platforms have been developed for various tissues and organs, including the heart, liver, kidney, blood vessels, muscle, and adipose tissue. However, only a few studies have explored using MPS platforms to unravel the effects of aging on human physiology and the pathogenesis of age-related diseases. Age is one of the risk factors for many diseases, and enormous interest has been devoted to aging research. As such, a human MPS aging model could provide a more predictive tool to understand the molecular and cellular mechanisms underlying human aging and age-related diseases. These models can also be used to evaluate preclinical drugs for age-related diseases and translate them into clinical settings. Here, we provide a review on the application of MPS in aging research. First, we offer an overview of the molecular, cellular, and physiological changes with age in several tissues or organs. Next, we discuss previous aging models and the current state of MPS for studying human aging and age-related conditions. Lastly, we address the limitations of current MPS and present future directions on the potential of MPS platforms for human aging research.

Insights on the Use of Transgenic Mice Models in Alzheimer's Disease Research

Alzheimer's disease (AD), the leading cause of dementia, presents a significant global health challenge with no known cure to date. Central to our understanding of AD pathogenesis is the β-amyloid cascade hypothesis, which underlies drug research and discovery efforts. Despite extensive studies, no animal models of AD have completely validated this hypothesis. Effective AD models are essential for accurately replicating key pathological features of the disease, notably the formation of β-amyloid plaques and neurofibrillary tangles. These pathological markers are primarily driven by mutations in the amyloid precursor protein (APP) and presenilin 1 (PS1) genes in familial AD (FAD) and by tau protein mutations for the tangle pathology. Transgenic mice models have been instrumental in AD research, heavily relying on the overexpression of mutated APP genes to simulate disease conditions. However, these models do not entirely replicate the human condition of AD. This review aims to provide a comprehensive evaluation of the historical and ongoing research efforts in AD, particularly through the use of transgenic mice models. It is focused on the benefits gathered from these transgenic mice models in understanding β-amyloid toxicity and the broader biological underpinnings of AD. Additionally, the review critically assesses the application of these models in the preclinical testing of new therapeutic interventions, highlighting the gap between animal models and human clinical realities. This analysis underscores the need for refinement in AD research methodologies to bridge this gap and enhance the translational value of preclinical studies.

Novel Approaches to Studying SLC13A5 Disease

The role of the sodium citrate transporter (NaCT) SLC13A5 is multifaceted and context-dependent. While aberrant dysfunction leads to neonatal epilepsy, its therapeutic inhibition protects against metabolic disease. Notably, insights regarding the cellular and molecular mechanisms underlying these phenomena are limited due to the intricacy and complexity of the latent human physiology, which is poorly captured by existing animal models. This review explores innovative technologies aimed at bridging such a knowledge gap. First, I provide an overview of SLC13A5 variants in the context of human disease and the specific cell types where the expression of the transporter has been observed. Next, I discuss current technologies for generating patient-specific induced pluripotent stem cells (iPSCs) and their inherent advantages and limitations, followed by a summary of the methods for differentiating iPSCs into neurons, hepatocytes, and organoids. Finally, I explore the relevance of these cellular models as platforms for delving into the intricate molecular and cellular mechanisms underlying SLC13A5-related disorders.

Modeling the neuroimmune system in Alzheimer's and Parkinson's diseases

Parkinson's disease (PD) and Alzheimer's disease (AD) are neurodegenerative disorders caused by the interaction of genetic, environmental, and familial factors. These diseases have distinct pathologies and symptoms that are linked to specific cell populations in the brain. Notably, the immune system has been implicated in both diseases, with a particular focus on the dysfunction of microglia, the brain's resident immune cells, contributing to neuronal loss and exacerbating symptoms. Researchers use models of the neuroimmune system to gain a deeper understanding of the physiological and biological aspects of these neurodegenerative diseases and how they progress. Several in vitro and in vivo models, including 2D cultures and animal models, have been utilized. Recently, advancements have been made in optimizing these existing models and developing 3D models and organ-on-a-chip systems, holding tremendous promise in accurately mimicking the intricate intracellular environment. As a result, these models represent a crucial breakthrough in the transformation of current treatments for PD and AD by offering potential for conducting long-term disease-based modeling for therapeutic testing, reducing reliance on animal models, and significantly improving cell viability compared to conventional 2D models. The application of 3D and organ-on-a-chip models in neurodegenerative disease research marks a prosperous step forward, providing a more realistic representation of the complex interactions within the neuroimmune system. Ultimately, these refined models of the neuroimmune system aim to aid in the quest to combat and mitigate the impact of debilitating neuroimmune diseases on patients and their families.

Analysis of the interplay between MeCP2 and histone H1 during in vitro differentiation of human ReNCell neural progenitor cells

An immortalized neural cell line derived from the human ventral mesencephalon, called ReNCell, and its MeCP2 knock out were used. With it, we characterized the chromatin compositional transitions undergone during differentiation, with special emphasis on linker histones. While the WT cells displayed the development of dendrites and axons the KO cells did not, despite undergoing differentiation as monitored by NeuN. ReNCell expressed minimal amounts of histone H1.0 and their linker histone complement consisted mainly of histone H1.2, H1.4 and H1.5. The overall level of histone H1 exhibited a trend to increase during the differentiation of MeCP2 KO cells. The phosphorylation levels of histone H1 proteins decreased dramatically during ReNCell's cell differentiation independently of the presence of MeCP2. Immunofluorescence analysis showed that MeCP2 exhibits an extensive co-localization with linker histones. Interestingly, the average size of the nucleus decreased during differentiation but in the MeCP2 KO cells, the smaller size of the nuclei at the start of differentiation increased by almost 40% after differentiation by 8 days (8 DIV). In summary, our data provide a compelling perspective on the dynamic changes of H1 histones during neural differentiation, coupled with the intricate interplay between H1 variants and MeCP2.Abbreviations: ACN, acetonitrile; A230, absorbance at 230 nm; bFGF, basic fibroblast growth factor; CM, chicken erythrocyte histone marker; CNS, central nervous system; CRISPR, clustered regulated interspaced short palindromic repeatsDAPI, 4,'6-diaminidino-2-phenylindole; DIV, days in vitro (days after differentiation is induced); DMEM, Dulbecco's modified Eagle medium; EGF, epidermal growth factor; ESC, embryonic stem cell; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GFAP, glial fibrillary acidic proteinHPLC, high-performance liquid chromatography; IF, immunofluorescence; iPSCs, induced pluripotent stem cells; MAP2, microtubule-associated protein 2; MBD, methyl-binding domain; MeCP2, methyl-CpG binding protein 2; MS, mass spectrometry; NCP, nucleosome core particle; NeuN, neuron nuclear antigen; NPC, neural progenitor cellPAGE, polyacrylamide gel electrophoresis; PBS, phosphate buffered saline; PFA, paraformaldehyde; PTM, posttranslational modification; RP-HPLC, reversed phase HPLC; ReNCells, ReNCells VM; RPLP0, ribosomal protein lateral stalk subunit P0; RT-qPCR, reverse transcription quantitative polymerase-chain reaction; RTT, Rett Syndrome; SDS, sodium dodecyl sulphate; TAD, topologically associating domain; Triple KO, triple knockout.

Altered ubiquitin signaling induces Alzheimer's disease-like hallmarks in a three-dimensional human neural cell culture model

Alzheimer's disease (AD) is characterized by toxic protein accumulation in the brain. Ubiquitination is essential for protein clearance in cells, making altered ubiquitin signaling crucial in AD development. A defective variant, ubiquitin B + 1 (UBB+1), created by a non-hereditary RNA frameshift mutation, is found in all AD patient brains post-mortem. We now detect UBB+1 in human brains during early AD stages. Our study employs a 3D neural culture platform derived from human neural progenitors, demonstrating that UBB+1 alone induces extracellular amyloid-β (Aβ) deposits and insoluble hyperphosphorylated tau aggregates. UBB+1 competes with ubiquitin for binding to the deubiquitinating enzyme UCHL1, leading to elevated levels of amyloid precursor protein (APP), secreted Aβ peptides, and Aβ build-up. Crucially, silencing UBB+1 expression impedes the emergence of AD hallmarks in this model system. Our findings highlight the significance of ubiquitin signalling as a variable contributing to AD pathology and present a nonclinical platform for testing potential therapeutics.

Infiltrating CD8+ T cells exacerbate Alzheimer's disease pathology in a 3D human neuroimmune axis model

Brain infiltration of peripheral immune cells and their interactions with brain-resident cells may contribute to Alzheimer's disease (AD) pathology. To examine these interactions, in the present study we developed a three-dimensional human neuroimmune axis model comprising stem cell-derived neurons, astrocytes and microglia, together with peripheral immune cells. We observed an increase in the number of T cells (but not B cells) and monocytes selectively infiltrating into AD relative to control cultures. Infiltration of CD8+ T cells into AD cultures led to increased microglial activation, neuroinflammation and neurodegeneration. Using single-cell RNA-sequencing, we identified that infiltration of T cells into AD cultures led to induction of interferon-γ and neuroinflammatory pathways in glial cells. We found key roles for the C-X-C motif chemokine ligand 10 (CXCL10) and its receptor, CXCR3, in regulating T cell infiltration and neuronal damage in AD cultures. This human neuroimmune axis model is a useful tool to study the effects of peripheral immune cells in brain disease.

Rational Design and Acoustic Assembly of Human Cerebral Cortex-Like Microtissues from hiPSC-Derived Neural Progenitors and Neurons

Development of biologically relevant and clinically relevant human cerebral cortex models is demanded by mechanistic studies of human cerebral cortex-associated neurological diseases and discovery of preclinical neurological drug candidates. Here, rational design of human-sourced brain-like cortical tissue models is demonstrated by reverse engineering and bionic design. To implement this design, the acoustic assembly technique is employed to assemble hiPSC-derived neural progenitors and neurons separately in a label-free and contact-free manner followed by subsequent neural differentiation and culture. The generated microtissues encapsulate the neuronal microanatomy of human cerebral-cortex tissue that contains six-layered neuronal architecture, a 400-µm interlayer distance, synaptic connections between interlayers, and neuroelectrophysiological transmission. Furthermore, these microtissues are infected with herpes simplex virus type I (HSV-1) virus, and the HSV-induced pathogenesis associated with Alzheimer's disease is determined, including neuron loss and the expression of Aβ. Overall, a high-fidelity human-relevant in vitro histotypic model is provided for the cerebral cortex, which will facilitate wide applications in probing the mechanisms of neurodegenerative diseases and screening the candidates for neuroprotective agents.

Revolutionizing Disease Modeling: The Emergence of Organoids in Cellular Systems

Cellular models have created opportunities to explore the characteristics of human diseases through well-established protocols, while avoiding the ethical restrictions associated with post-mortem studies and the costs associated with researching animal models. The capability of cell reprogramming, such as induced pluripotent stem cells (iPSCs) technology, solved the complications associated with human embryonic stem cells (hESC) usage. Moreover, iPSCs made significant contributions for human medicine, such as in diagnosis, therapeutic and regenerative medicine. The two-dimensional (2D) models allowed for monolayer cellular culture in vitro; however, they were surpassed by the three-dimensional (3D) cell culture system. The 3D cell culture provides higher cell-cell contact and a multi-layered cell culture, which more closely respects cellular morphology and polarity. It is more tightly able to resemble conditions in vivo and a closer approach to the architecture of human tissues, such as human organoids. Organoids are 3D cellular structures that mimic the architecture and function of native tissues. They are generated in vitro from stem cells or differentiated cells, such as epithelial or neural cells, and are used to study organ development, disease modeling, and drug discovery. Organoids have become a powerful tool for understanding the cellular and molecular mechanisms underlying human physiology, providing new insights into the pathogenesis of cancer, metabolic diseases, and brain disorders. Although organoid technology is up-and-coming, it also has some limitations that require improvements.

Galangin Rescues Alzheimer's Amyloid-β Induced Mitophagy and Brain Organoid Growth Impairment

Dysfunctional mitochondria and mitophagy are hallmarks of Alzheimer's disease (AD). It is widely accepted that restoration of mitophagy helps to maintain cellular homeostasis and ameliorates the pathogenesis of AD. It is imperative to create appropriate preclinical models to study the role of mitophagy in AD and to assess potential mitophagy-targeting therapies. Here, by using a novel 3D human brain organoid culturing system, we found that amyloid-β (Aβ_1-42,10 μM) decreased the growth level of organoids, indicating that the neurogenesis of organoids may be impaired. Moreover, Aβ treatment inhibited neural progenitor cell (NPC) growth and induced mitochondrial dysfunction. Further analysis revealed that mitophagy levels were reduced in the brain organoids and NPCs. Notably, galangin (10 μM) treatment restored mitophagy and organoid growth, which was inhibited by Aβ. The effect of galangin was blocked by the mitophagy inhibitor, suggesting that galangin possibly acted as a mitophagy enhancer to ameliorate Aβ-induced pathology. Together, these results supported the important role of mitophagy in AD pathogenesis and suggested that galangin may be used as a novel mitophagy enhancer to treat AD.

In Vitro 3D Modeling of Neurodegenerative Diseases

The study of neurodegenerative diseases (such as Alzheimer's disease, Parkinson's disease, Huntington's disease, or amyotrophic lateral sclerosis) is very complex due to the difficulty in investigating the cellular dynamics within nervous tissue. Despite numerous advances in the in vivo study of these diseases, the use of in vitro analyses is proving to be a valuable tool to better understand the mechanisms implicated in these diseases. Although neural cells remain difficult to obtain from patient tissues, access to induced multipotent stem cell production now makes it possible to generate virtually all neural cells involved in these diseases (from neurons to glial cells). Many original 3D culture model approaches are currently being developed (using these different cell types together) to closely mimic degenerative nervous tissue environments. The aim of these approaches is to allow an interaction between glial cells and neurons, which reproduces pathophysiological reality by co-culturing them in structures that recapitulate embryonic development or facilitate axonal migration, local molecule exchange, and myelination (to name a few). This review details the advantages and disadvantages of techniques using scaffolds, spheroids, organoids, 3D bioprinting, microfluidic systems, and organ-on-a-chip strategies to model neurodegenerative diseases.

Hyperglycemic Neurovasculature-On-A-Chip to Study the Effect of SIRT1-Targeted Therapy for the Type 3 Diabetes "Alzheimer's Disease"

Diabetes mellitus (DM) is closely related to Alzheimer's disease (AD), but individual cellular changes and the possibilities of recovery through molecular level regulation have not been investigated. Here, a neurovasculature-on-a-chip (NV chip) model is presented in which the perfusable brain microvasculature is surrounded by the neurons. Under hyperglycemic conditions, the brain microvasculature shows disruption of barrier function and reduced expression of junctional markers. The neurons show Tau pathology and amyloid-beta (Aß) accumulation. Endothelial cells and neurons in the NV chip show sirtuin 1 (SIRT1) downregulation under hyperglycemic conditions, suggesting SIRT1 as a key regulator of hyperglycemia-induced AD. The recovery of glucose levels rescue SIRT1 expression, suggesting that this type of intervention may rescue the progression of hyperglycemia-mediated AD. Furthermore, the short hairpin RNA (shRNA)-, clustered regularly interspaced short palindromic repeats (CRISPR)-, and pharmaceutics-mediated regulation of SIRT1 regulate the pathophysiology of the brain endothelium and neurons at the functional and molecular levels.

Brain organoid-on-a-chip: A next-generation human brain avatar for recapitulating human brain physiology and pathology

Neurodegenerative diseases and neurodevelopmental disorders have become increasingly prevalent; however, the development of new pharmaceuticals to treat these diseases has lagged. Animal models have been extensively utilized to identify underlying mechanisms and to validate drug efficacies, but they possess inherent limitations including genetic heterogeneity with humans. To overcome these limitations, human cell-based in vitro brain models including brain-on-a-chip and brain organoids have been developed. Each technique has distinct advantages and disadvantages in terms of the mimicry of structure and microenvironment, but each technique could not fully mimic the structure and functional aspects of the brain tissue. Recently, a brain organoid-on-a-chip (BOoC) platform has emerged, which merges brain-on-a-chip and brain organoids. BOoC can potentially reflect the detailed structure of the brain tissue, vascular structure, and circulation of fluid. Hence, we summarize recent advances in BOoC as a human brain avatar and discuss future perspectives. BOoC platform can pave the way for mechanistic studies and the development of pharmaceuticals to treat brain diseases in future.

Alzheimer's Disease: Treatment Strategies and Their Limitations

Alzheimer's disease (AD) is the most frequent case of neurodegenerative disease and is becoming a major public health problem all over the world. Many therapeutic strategies have been explored for several decades; however, there is still no curative treatment, and the priority remains prevention. In this review, we present an update on the clinical and physiological phase of the AD spectrum, modifiable and non-modifiable risk factors for AD treatment with a focus on prevention strategies, then research models used in AD, followed by a discussion of treatment limitations. The prevention methods can significantly slow AD evolution and are currently the best strategy possible before the advanced stages of the disease. Indeed, current drug treatments have only symptomatic effects, and disease-modifying treatments are not yet available. Drug delivery to the central nervous system remains a complex process and represents a challenge for developing therapeutic and preventive strategies. Studies are underway to test new techniques to facilitate the bioavailability of molecules to the brain. After a deep study of the literature, we find the use of soft nanoparticles, in particular nanoliposomes and exosomes, as an innovative approach for preventive and therapeutic strategies in reducing the risk of AD and solving problems of brain bioavailability. Studies show the promising role of nanoliposomes and exosomes as smart drug delivery systems able to penetrate the blood-brain barrier and target brain tissues. Finally, the different drug administration techniques for neurological disorders are discussed. One of the promising therapeutic methods is the intranasal administration strategy which should be used for preclinical and clinical studies of neurodegenerative diseases.

A next-generation iPSC-derived forebrain organoid model of tauopathy with tau fibrils by AAV-mediated gene transfer

It is known that the human cellular models of Alzheimer's disease (AD) and tauopathy can only recapitulate the very early stage of the disease. To overcome these limitations, we developed a technology to make forebrain organoids (FBOs) from feeder-free induced pluripotent stem cells (iPSC)s by regulating a FGF2 concentration and applied this method to generate FBOs from patients with familial AD (fAD FBOs). The obtained fAD FBOs recapitulated the amyloid-β pathology and increased tau phosphorylation but not tau aggregates. To fully induce the tau pathology, FBOs were injected with adeno-associated virus (AAV)-expressing P301L mutant tau. In these Tau-P301L FBOs, tau fibrils were observed in the neuronal cell body and neurites with immunoelectron microscopy, in addition to the sarkosyl-insoluble and thioflavin S-positive phospho-tau aggregates. Collectively, this model can be used as a platform for investigating pathogenetic mechanisms and evaluation of target molecules for drug discovery for tauopathy.

Poo-arporn R. An in vitro workflow of neuron-laden agarose-laminin hydrogel for studying small molecule-induced amyloidogenic condition

In vitro studies have been popularly used to determine the cellular and molecular mechanisms for many decades. However, the traditional two-dimension (2D) cell culture which grows cells on a flat surface does not fully recapitulate the pathological phenotypes. Alternatively, the three-dimension (3D) cell culture provides cell-cell and cell-ECM interaction that better mimics tissue-like structure. Thus, it has gained increasing attention recently. Yet, the expenses, time-consuming, and complications of cellular and biomolecular analysis are still major limitations of 3D culture. Herein, we describe a cost-effective and simplified workflow of the 3D neuronal cell-laden agarose-laminin preparation and the isolation of cells, RNAs, and proteins from the scaffold. To study the effects of the amyloidogenic condition in neurons, we utilized a neuron-like cell line, SH-SY5Y, and induced the amyloidogenic condition by using an amyloid forty-two inducer (Aftin-4). The effectiveness of RNAs, proteins and cells isolation from 3D scaffold enables us to investigate the cellular and molecular mechanisms underlying amyloidogenic cascade in neuronal cells. The results show that SH-SY5Y cultured in agarose-laminin scaffold differentiated to a mature TUJ1-expressing neuron cell on day 7. Furthermore, the gene expression profile from the Aftin-4-induced amyloidogenic condition revealed the expression of relevant gene-encoding proteins in the amyloidogenic pathway, including APP, BACE1, PS1, and PS2. This platform could induce the amyloid-beta 42 secretion and entrap secreted proteins in the scaffold. The induction of amyloidogenic conditions in a 3D culture facilitates the interaction between secreted amyloid-beta and neurons, which makes it resembles the pathological environment in Alzheimer’s brain. Together, this workflow is applicable for studying the cellular and molecular analysis of amyloid-induced neuronal toxicity, such as those occurred in Alzheimer’s disease progression. Importantly, our method is cost-effective, reproducible, and easy to manipulate.

Accelerated neuronal aging in vitro ∼melting watch ∼

In developed countries, the aging of the population and the associated increase in age-related diseases are causing major unresolved medical, social, and environmental matters. Therefore, research on aging has become one of the most important and urgent issues in life sciences. If the molecular mechanisms of the onset and progression of neurodegenerative diseases are elucidated, we can expect to develop disease-modifying methods to prevent neurodegeneration itself. Since the discovery of induced pluripotent stem cells (iPSCs), there has been an explosion of disease models using disease-specific iPSCs derived from patient-derived somatic cells. By inducing the differentiation of iPSCs into neurons, disease models that reflect the patient-derived pathology can be reproduced in culture dishes, and are playing an active role in elucidating new pathological mechanisms and as a platform for new drug discovery. At the same time, however, we are faced with a new problem: how to recapitulate aging in culture dishes. It has been pointed out that cells differentiated from pluripotent stem cells are juvenile, retain embryonic traits, and may not be fully mature. Therefore, attempts are being made to induce cell maturation, senescence, and stress signals through culture conditions. It has also been reported that direct conversion of fibroblasts into neurons can reproduce human neurons with an aged phenotype. Here, we outline some state-of-the-art insights into models of neuronal aging in vitro. New frontiers in which stem cells and methods for inducing differentiation of tissue regeneration can be applied to aging research are just now approaching, and we need to keep a close eye on them. These models are forefront and intended to advance our knowledge of the molecular mechanisms of aging and contribute to the development of novel therapies for human neurodegenerative diseases associated with aging.

Role of Specialized Pro-resolving Mediators in Reducing Neuroinflammation in Neurodegenerative Disorders

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are neurodegenerative disorders that affect millions of individuals worldwide. As incidence of these conditions increases with age, there will undoubtedly be an increased prevalence of cases in the near future. Neuroinflammation is a hallmark in the development and progression of neurodegenerative diseases and prevention or resolution of chronic neuroinflammation may represent a novel approach to treatment. The present review highlights the potential of the anti-inflammatory and pro-resolving effects of polyunsaturated fatty acid (PUFA)-derived mediators (Specialized Pro-resolving Mediators—SPM) in neurodegenerative disorders. PUFA-derived SPM are biosynthesized in response to chemicals produced from acute inflammatory responses. Preclinical studies from both AD and PD models suggest a dysregulation of SPM and their receptors in neurological disorders. Decreased SPM may be due to inadequate substrate, an imbalance between SPM and pro-inflammatory mediators or a disruption in SPM synthesis. SPMs hold great promise for neuroprotection in AD by altering expression of pro-inflammatory genes, modulating macrophage function, serving as a biomarker for AD status, and promoting resolution of neuroinflammation. In PD, data suggest SPM are able to cross the blood-brain barrier, inhibit microglial activation and decrease induced markers of inflammation, possibly as a result of their ability to downregulate NFκB signaling pathways. Several in vivo and in vitro studies suggest a benefit from administration of SPMs in both neurodegenerative disorders. However, extrapolation of these outcomes to humans is difficult as no models are able to replicate all features of AD or PD. Minimal data evaluating these PUFA-derived metabolites in humans with neurodegenerative disorders are available and a gap in knowledge exists regarding behavior of SPM and their receptors in patients with these conditions. There is also large gap in our knowledge regarding which lipid mediator would be most effective in which model of AD or PD and how dietary intake or supplementation can impact SPM levels. Future direction should include focused, translational efforts to investigate SPM as an add-on (in addition to standard treatment) or as standalone agents in patients with neurodegenerative disorders.

Roles and Mechanisms of the Protein Quality Control System in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the deposition of senile plaques (SPs) and the formation of neurofibrillary tangles (NTFs), as well as neuronal dysfunctions in the brain, but in fact, patients have shown a sustained disease progression for at least 10 to 15 years before these pathologic biomarkers can be detected. Consequently, as the most common chronic neurological disease in the elderly, the challenge of AD treatment is that it is short of effective biomarkers for early diagnosis. The protein quality control system is a collection of cellular pathways that can recognize damaged proteins and thereby modulate their turnover. Abundant evidence indicates that the accumulation of abnormal proteins in AD is closely related to the dysfunction of the protein quality control system. In particular, it is the synthesis, degradation, and removal of essential biological components that have already changed in the early stage of AD, which further encourages us to pay more attention to the protein quality control system. The review mainly focuses on the endoplasmic reticulum system (ERS), autophagy-lysosome system (ALS) and the ubiquitin-proteasome system (UPS), and deeply discusses the relationship between the protein quality control system and the abnormal proteins of AD, which can not only help us to understand how and why the complex regulatory system becomes malfunctional during AD progression, but also provide more novel therapeutic strategies to prevent the development of AD.

Chondrocyte Spheroids Laden in GelMA/HAMA Hybrid Hydrogel for Tissue-Engineered Cartilage with Enhanced Proliferation, Better Phenotype Maintenance, and Natural Morphological Structure

Three-dimensional cell-laden tissue engineering has become an extensive research direction. This study aimed to evaluate whether chondrocyte spheroids (chondro-spheroids) prepared using the hanging-drop method could develop better cell proliferation and morphology maintenance characteristics, and be optimized as a micro unit for cartilage tissue engineering. Chondro-spheroids were loaded into a cross-linkable hybrid hydrogel of gelatin methacrylate (GelMA) and hyaluronic acid methacrylate (HAMA) in vivo and in vitro. Cell proliferation, aggregation, cell morphology maintenance as well as cartilage-related gene expression and matrix secretion in vitro and in vivo were evaluated. The results indicated that compared with chondrocyte-laden hydrogel, chondro-spheroid-laden hydrogel enhanced proliferation, had better phenotype maintenance, and a more natural morphological structure, which made it appropriate for use as a micro unit in cartilage tissue engineering.

Can platelet activation result in increased plasma Aβ levels and contribute to the pathogenesis of Alzheimer's disease?

One of the central lesions in the brain of subjects with Alzheimer's disease (AD) is represented by aggregates of β-amyloid (Aβ), a peptide of 40-42 amino acids derived from the amyloid precursor protein (APP). The reasons why Aβ accumulates in the brain of individuals with sporadic forms of AD are unknown. Platelets are the primary source of circulating APP and, upon activation, can secrete significant amounts of Aβ into the blood which can be actively transported to the brain across the blood-brain barrier and promote amyloid deposition. Increased platelet activity can stimulate platelet adhesion to endothelial cells, trigger the recruitment of leukocytes into the vascular wall and cause perivascular inflammation, which can spread inflammation in the brain. Neuroinflammation is fueled by activated microglial cells and reactive astrocytes that release neurotoxic cytokines and chemokines. Platelet activation is also associated with the progression of carotid artery disease resulting in an increased risk of cerebral hypoperfusion which may also contribute to the AD neurodegenerative process. Platelet activation may thus be a pathophysiological mechanism of AD and for the strong link between AD and cerebrovascular diseases. Interfering with platelet activation may represent a promising potential adjunct therapeutic approach for AD.

Engineered Human Induced Pluripotent Cells Enable Genetic Code Expansion in Brain Organoids

Human induced pluripotent stem cell (hiPSC) technology has revolutionized studies on human biology. A wide range of cell types and tissue models can be derived from hiPSCs to study complex human diseases. Here, we use PiggyBac-mediated transgenesis to engineer hiPSCs with an expanded genetic code. We demonstrate that genomic integration of expression cassettes for a pyrrolysyl-tRNA synthetase (PylRS), pyrrolysyl-tRNA (PylT) and the target protein of interest enables site-specific incorporation of a non-canonical amino acid (ncAA) in response to an amber stop codon. Neural stem cells, neurons and brain organoids derived from the engineered hiPSCs continue to express the amber suppression machinery and produce ncAA-bearing reporter. The incorporated ncAA can serve as a minimal bioorthogonal handle for further modifications by labeling with fluorescent dyes. Site-directed ncAA mutagenesis will open a wide range of applications to probe and manipulate proteins in brain organoids and other hiPSC-derived cell types and complex tissue models.

Deconstructing Alzheimer's Disease: How to Bridge the Gap between Experimental Models and the Human Pathology?

Discovered more than a century ago, Alzheimer's disease (AD) is not only still present in our societies but has also become the most common dementia, with 50 million people worldwide affected by the disease. This number is expected to double in the next generation, and no cure is currently available to slow down or stop the disease progression. Recently, some advances were made due to the approval of the aducanumab treatment by the American Food and Drug Administration. The etiology of this human-specific disease remains poorly understood, and the mechanisms of its development have not been completely clarified. Several hypotheses concerning the molecular mechanisms of AD have been proposed, but the existing studies focus primarily on the two main markers of the disease: the amyloid β peptides, whose aggregation in the brain generates amyloid plaques, and the abnormally phosphorylated tau proteins, which are responsible for neurofibrillary tangles. These protein aggregates induce neuroinflammation and neurodegeneration, which, in turn, lead to cognitive and behavioral deficits. The challenge is, therefore, to create models that best reproduce this pathology. This review aims at gathering the different existing AD models developed in vitro, in cellulo, and in vivo. Many models have already been set up, but it is necessary to identify the most relevant ones for our investigations. The purpose of the review is to help researchers to identify the most pertinent disease models, from the most often used to the most recently generated and from simple to complex, explaining their specificities and giving concrete examples.

Optimization of cerebral organoids: a more qualified model for Alzheimer's disease research

Alzheimer's disease (AD) is a neurodegenerative disease that currently cannot be cured by any drug or intervention, due to its complicated pathogenesis. Current animal and cellular models of AD are unable to meet research needs for AD. However, recent three-dimensional (3D) cerebral organoid models derived from human stem cells have provided a new tool to study molecular mechanisms and pharmaceutical developments of AD. In this review, we discuss the advantages and key limitations of the AD cerebral organoid system in comparison to the commonly used AD models, and propose possible solutions, in order to improve their application in AD research. Ethical concerns associated with human cerebral organoids are also discussed. We also summarize future directions of studies that will improve the cerebral organoid system to better model the pathological events observed in AD brains.

3D Models as an Adjunct for Models in Studying Alzheimer’s Disease

Alzheimer’s disease (AD) is one of the most common causes of dementia. Disease progression is marked by cognitive decline and memory impairment due to neurodegenerative processes in the brain stemming from amyloid-β (Aβ) deposition and formation of neurofibrillary tangles. Pathogenesis in AD is dependent on two main neurological processes: formation of intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein and deposition of extracellular senile Aβ peptides. Given the nature of the disease, the pathology and progression of AD in vivo in humans have been difficult to study in vivo. To this degree, models can help to study the disease pathogenesis, biochemistry, immunological functions, genetics, and potential pharmacotherapy. While animal and two-dimensional (2D) cell culture models have facilitated significant progress in studying the disease, more recent application of novel three-dimensional (3D) culture models has exhibited several advantages. Herein, we describe a brief background of AD, and how current animal, 2D, and 3D models facilitate the study of this disease and associated therapeutics.

Overwhelming Evidence for a Major Role for Herpes Simplex Virus Type 1 (HSV1) in Alzheimer's Disease (AD); Underwhelming Evidence against

This review describes investigations of specific topics that lie within the general subject of HSV1's role in AD/dementia, published in the last couple of years. They include studies on the following: relationship of HSV1 to AD using neural stem cells; the apparent protective effects of treatment of HSV1 infection or of VZV infection with antivirals prior to the onset of dementia; the putative involvement of VZV in AD/dementia; the possible role of human herpes virus 6 (HHV6) in AD; the seemingly reduced risk of dementia after vaccination with diverse types of vaccine, and the association shown in some vaccine studies with reduced frequency of HSV1 reactivation; anti-HSV serum antibodies supporting the linkage of HSV1 in brain with AD in APOE-ε4 carriers, and the association between APOE and cognition, and association of APOE and infection with AD/dementia. The conclusions are that there is now overwhelming evidence for HSV1's role-probably causal-in AD, when it is present in brain of APOE-ε4 carriers, and that further investigations should be made on possible prevention of the disease by vaccination, or by prolonged antiviral treatment of HSV1 infection in APOE-ε4 carriers, before disease onset.

CK1δ-Derived Peptides as Novel Tools Inhibiting the Interactions between CK1δ and APP695 to Modulate the Pathogenic Metabolism of APP

Alzheimer’s disease (AD) is the major cause of dementia, and affected individuals suffer from severe cognitive, mental, and functional impairment. Histologically, AD brains are basically characterized by the presence of amyloid plaques and neurofibrillary tangles. Previous reports demonstrated that protein kinase CK1δ influences the metabolism of amyloid precursor protein (APP) by inducing the generation of amyloid-β (Aβ), finally contributing to the formation of amyloid plaques and neuronal cell death. We therefore considered CK1δ as a promising therapeutic target and suggested an innovative strategy for the treatment of AD based on peptide therapeutics specifically modulating the interaction between CK1δ and APP. Initially, CK1δ-derived peptides manipulating the interactions between CK1δ and APP695 were identified by interaction and phosphorylation analysis in vitro. Selected peptides subsequently proved their potential to penetrate cells without inducing cytotoxic effects. Finally, for at least two of the tested CK1δ-derived peptides, a reduction in Aβ levels and amyloid plaque formation could be successfully demonstrated in a complex cell culture model for AD. Consequently, the presented results provide new insights into the interactions of CK1δ and APP695 while also serving as a promising starting point for further development of novel and highly innovative pharmacological tools for the treatment of AD.

Analyzing Olfactory Neuron Precursors Non-Invasively Isolated through NADH FLIM as a Potential Tool to Study Oxidative Stress in Alzheimer's Disease

Among all the proposed pathogenic mechanisms to understand the etiology of Alzheimer’s disease (AD), increased oxidative stress seems to be a robust and early disease feature where many of those hypotheses converge. However, despite the significant lines of evidence accumulated, an effective diagnosis and treatment of AD are not yet available. This limitation might be partially explained by the use of cellular and animal models that recapitulate partial aspects of the disease and do not account for the particular biology of patients. As such, cultures of patient-derived cells of peripheral origin may provide a convenient solution for this problem. Peripheral cells of neuronal lineage such as olfactory neuronal precursors (ONPs) can be easily cultured through non-invasive isolation, reproducing AD-related oxidative stress. Interestingly, the autofluorescence of key metabolic cofactors such as reduced nicotinamide adenine dinucleotide (NADH) can be highly correlated with the oxidative state and antioxidant capacity of cells in a non-destructive and label-free manner. In particular, imaging NADH through fluorescence lifetime imaging microscopy (FLIM) has greatly improved the sensitivity in detecting oxidative shifts with minimal intervention to cell physiology. Here, we discuss the translational potential of analyzing patient-derived ONPs non-invasively isolated through NADH FLIM to reveal AD-related oxidative stress. We believe this approach may potentially accelerate the discovery of effective antioxidant therapies and contribute to early diagnosis and personalized monitoring of this devastating disease.

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.

Three-Dimensional Human Neural Stem Cell Models to Mimic Heparan Sulfate Proteoglycans and the Neural Niche

Heparan sulfate proteoglycans (HSPGs) are a diverse family of polysaccharides, consisting of a core protein with glycosaminoglycan (GAG) side chains attached. The heterogeneous GAG side-chain carbohydrates consist of repeating disaccharides, with each side chain possessing a specific sulfation pattern. It is the variable sulfation pattern that allows HSPGs to interact with numerous ligands including growth factors, cytokines, chemokines, morphogens, extracellular matrix (ECM) glycoproteins, collagens, enzymes, and lipases. HSPGs are classified according to their localization within an individual cell, and include the membrane bound syndecans (SDCs) and glypicans (GPCs), with perlecan, agrin, and type-XVIII collagen secreted into the ECM. The stem cell niche is defined as the environment that circumscribes stem cells when they are in their naïve state, and includes the ECM, which provides a complex contribution to various biological processes during development and throughout life. These contributions include facilitating cell adhesion, proliferation, migration, differentiation, specification, and cell survival. In contrast, HSPGs play an anticoagulant role in thrombosis through being present on the luminal surface of cells, while also playing roles in the stimulation and inhibition of angiogenesis, highlighting their varied and systemic roles in cellular control. To fully understand the complexities of cell-cell and cell-matrix interactions, three-dimensional (3D) models such as hydrogels offer researchers exciting opportunities, such as controllable 3D in vitro environments, that more readily mimic the in vivo/in situ microenvironment. This review examines our current knowledge of HSPGs in the stem cell niche, human stem cell models, and their role in the development of 3D models that mimic the in vivo neural ECM.

Nanogold induces anti-inflammation against oxidative stress induced in human neural stem cells exposed to amyloid-beta peptide

Alzheimer's disease (AD) is a neurodegenerative disorder with progressive memory loss resulting in dementia. Amyloid-beta (Aβ) peptides play a critical role in the pathogenesis of the disease by promoting inflammation and oxidative stress, leading to neurodegeneration in the brains of AD patients. Numerous in vitro 3D cell culture models are useful mimics for understanding cellular changes that occur during AD under in vivo conditions. The 3D Bioprinter developed at the CELLINK INKREDIBLE was used in this study to directly investigate the influence of 3D conditions on human neural stem cells (hNSCs) exposed to Aβ. The development of anti-AD drugs is usually difficult, mainly due to a lack of therapeutic efficacy and enhanced serious side effects. Gold nanoparticles (AuNPs) demonstrate benefits in the treatment of several diseases, including AD, and may provide a novel therapeutic approach for AD patients. However, the neuroprotective mechanisms by which AuNPs exert these beneficial effects in hNSCs treated with Aβ are still not well understood. Therefore, we tested the hypothesis that AuNPs protect against Aβ-induced inflammation and oxidative stress in hNSCs under 3D conditions. Here, we showed that AuNPs improved the viability of hNSCs exposed to Aβ, which was correlated with the reduction in the expression of inflammatory cytokines, such as TNF-α and IL-1β. In addition, AuNPs rescued the levels of the transcripts of inhibitory kappa B kinase (IKK) in Aβ-treated hNSCs. The Aβ-mediated increases in mRNA, protein, and nuclear translocation levels of NF-κB (p65), a key transcription factor involved in inflammatory responses, were all significantly abrogated following co-treatment of hNSCs with AuNPs. In addition, treatment with AuNPs significantly restored iNOS and COX-2 levels in Aβ-treated hNSCs. Importantly, hNSCs co-treated with AuNPs were significantly protected from Aβ-induced oxidative stress, as detected using the DCFH-DA and DHE staining assays. Furthermore, hNSCs co-treated with AuNPs were significantly protected from the Aβ-induced reduction in the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2 downstream antioxidant target genes (SOD-1, SOD-2, Gpx1, GSH, Catalase, and HO-1). Moreover, AuNPs reduced the aggregates and increased the proteasome activity and the expression of HSP27 and HSP70 genes in Aβ-treated hNSCs. Taken together, these findings provide the first evidence extending our understanding of the molecular mechanisms under 3D scaffold conditions by which AuNPs reverse the inflammation and oxidative stress-induced in hNSCs exposed to Aβ. These findings may facilitate the development of novel treatments for AD.

Mind the translational gap: using iPS cell models to bridge from genetic discoveries to perturbed pathways and therapeutic targets

Autism spectrum disorder (ASD) comprises a group of neurodevelopmental disorders characterized by impaired social interactions as well as the presentation of restrictive and repetitive behaviors. ASD is highly heritable but genetically heterogenous with both common and rare genetic variants collaborating to predispose individuals to the disorder. In this review, we synthesize recent efforts to develop human induced pluripotent stem cell (iPSC)-derived models of ASD-related phenotypes. We firstly address concerns regarding the relevance and validity of available neuronal iPSC-derived models. We then critically evaluate the robustness of various differentiation and cell culture protocols used for producing cell types of relevance to ASD. By exploring iPSC models of ASD reported thus far, we examine to what extent cellular and neuronal phenotypes with potential relevance to ASD can be linked to genetic variants found to underlie it. Lastly, we outline promising strategies by which iPSC technology can both enhance the power of genetic studies to identify ASD risk factors and nominate pathways that are disrupted across groups of ASD patients that might serve as common points for therapeutic intervention.

Translational Scoring of Candidate Treatments for Alzheimer's Disease: A Systematic Approach

BACKGROUND

There are many failures in treatment development for Alzheimer's disease (AD). Some of these failures are the result of development programs that lacked critical information about candidate drugs as these were advanced from one phase of development to the next. Translational scoring (TS) has been proposed as a means of increasing the rigor with which treatment development programs are executed. Previously, these approaches were not specific to AD or to the phase of drug development. Detailed information on the characteristics needed to advance a candidate agent from one phase to the next is the basis for success in subsequent phases.

SUMMARY

The TS approach is presented with a score range of 0-25 for agents entering phases 1, 2, and 3 of development and those that have completed phase 3 and are being considered for regulatory review. Each phase has 5 essential categories scored from 0-5 indicating the completeness of the data available when the agent is being considered for promotion to the next phase. Lower scores suggest that the development program should be reexamined for missing information while higher scores increase the confidence that the agent has the potential to succeed in the next phase. Scoring guidelines are provided and examples of scores for drugs in recent development programs are provided to illustrate the principles of TS. Key Messages: Successful development of drugs for AD treatment requires disciplined informed decision-making at each phase of development. TS is a methodology for more rigorous drug development to help ensure that inadequately characterized drugs are not advanced and that the development platform at each phase is optimal to support success at the next phase.

The complexity of Alzheimer's disease: an evolving puzzle

The history of Alzheimer's disease (AD) started in 1907, but we needed to wait until the end of the century to identify the components of pathological hallmarks and genetic subtypes and to formulate the first pathogenic hypothesis. Thanks to biomarkers and new technologies, the concept of AD then rapidly changed from a static view of an amnestic dementia of the presenium to a biological entity that could be clinically manifested as normal cognition or dementia of different types. What is clearly emerging from studies is that AD is heterogeneous in each aspect, such as amyloid composition, tau distribution, relation between amyloid and tau, clinical symptoms, and genetic background, and thus it is probably impossible to explain AD with a single pathological process. The scientific approach to AD suffers from chronological mismatches between clinical, pathological, and technological data, causing difficulty in conceiving diagnostic gold standards and in creating models for drug discovery and screening. A recent mathematical computer-based approach offers the opportunity to study AD in real life and to provide a new point of view and the final missing pieces of the AD puzzle.

An in vitro bioengineered model of the human arterial neurovascular unit to study neurodegenerative diseases

INTRODUCTION

The neurovascular unit (NVU) - the interaction between the neurons and the cerebrovasculature - is increasingly important to interrogate through human-based experimental models. Although advanced models of cerebral capillaries have been developed in the last decade, there is currently no in vitro 3-dimensional (3D) perfusible model of the human cortical arterial NVU.

METHOD

We used a tissue-engineering technique to develop a scaffold-directed, perfusible, 3D human NVU that is cultured in native-like flow conditions that mimics the anatomy and physiology of cortical penetrating arteries.

RESULTS

This system, composed of primary human vascular cells (endothelial cells, smooth muscle cells and astrocytes) and induced pluripotent stem cell (iPSC) derived neurons, demonstrates a physiological multilayer organization of the involved cell types. It reproduces key characteristics of cortical neurons and astrocytes and enables formation of a selective and functional endothelial barrier. We provide proof-of-principle data showing that this in vitro human arterial NVU may be suitable to study neurovascular components of neurodegenerative diseases such as Alzheimer's disease (AD), as endogenously produced phosphorylated tau and beta-amyloid accumulate in the model over time. Finally, neuronal and glial fluid biomarkers relevant to neurodegenerative diseases are measurable in our arterial NVU model.

CONCLUSION

This model is a suitable research tool to investigate arterial NVU functions in healthy and disease states. Further, the design of the platform allows culture under native-like flow conditions for extended periods of time and yields sufficient tissue and media for downstream immunohistochemistry and biochemistry analyses.

Inhibition of Histone Methyltransferases EHMT1/2 Reverses Amyloid-β-Induced Loss of AMPAR Currents in Human Stem Cell-Derived Cortical Neurons

Emerging evidence suggests that epigenetic dysregulation of gene expression is one of the key molecular mechanisms of neurodegeneration and Alzheimer's disease (AD). However, little is known about the role of epigenetic dysregulation on synaptic dysfunction in humans, because of the difficulties of obtaining live human neurons. Here we generated mature human cortical neurons differentiated from human embryonic stem cells, and exposed them to amyloid-β (Aβ). We found that the histone methyltransferase, EHMT1, which catalyzes histone lysine 9 dimethylation (H3K9me2, a mark for gene repression), was significantly elevated in Aβ-treated human stem cell-derived neurons. Aβ treatment led to a significant reduction of AMPAR-mediated whole-cell current and excitatory postsynaptic current. Application of BIX01294, a selective inhibitor of EHMT1/2, restored AMPAR currents and glutamatergic synaptic transmission in Aβ-treated human cortical neurons. These results suggest that inhibition of the aberrant histone methylation is a novel approach to reverse Aβ-induced synaptic deficits in human neurons.

Microphysiological Systems for Neurodegenerative Diseases in Central Nervous System

Neurodegenerative diseases are among the most severe problems in aging societies. Various conventional experimental models, including 2D and animal models, have been used to investigate the pathogenesis of (and therapeutic mechanisms for) neurodegenerative diseases. However, the physiological gap between humans and the current models remains a hurdle to determining the complexity of an irreversible dysfunction in a neurodegenerative disease. Therefore, preclinical research requires advanced experimental models, i.e., those more physiologically relevant to the native nervous system, to bridge the gap between preclinical stages and patients. The neural microphysiological system (neural MPS) has emerged as an approach to summarizing the anatomical, biochemical, and pathological physiology of the nervous system for investigation of neurodegenerative diseases. This review introduces the components (such as cells and materials) and fabrication methods for designing a neural MPS. Moreover, the review discusses future perspectives for improving the physiological relevance to native neural systems.

A microfiber scaffold-based 3D in vitro human neuronal culture model of Alzheimer's disease

Increasing evidence indicates superiority of three-dimensional (3D) in vitro cell culture systems over conventional two-dimensional (2D) monolayer cultures in mimicking native in vivo microenvironments. Tissue-engineered 3D culture models combined with stem cell technologies have advanced Alzheimer's disease (AD) pathogenesis studies. However, existing 3D neuronal models of AD overexpress mutant genes or have heterogeneities in composition, biological properties and cell differentiation stages. Here, we encapsulate patient induced pluripotent stem cell (iPSC) derived neural progenitor cells (NPC) in poly(lactic-co-glycolic acid) (PLGA) microtopographic scaffolds fabricated via wet electrospinning to develop a novel 3D culture model of AD. First, we enhanced cellular infiltration and distribution inside the scaffold by optimizing various process parameters such as fiber diameter, pore size, porosity and hydrophilicity. Next, we compared key neural stem cell features including viability, proliferation and differentiation in 3D culture with 2D monolayer controls. The 3D microfibrous substrate reduces cell proliferation and significantly accelerates neuronal differentiation within seven days of culture. Furthermore, 3D culture spontaneously enhanced pathogenic amyloid-beta 42 (Aβ42) and phospho-tau levels in differentiated neurons carrying familial AD (FAD) mutations, compared with age-matched healthy controls. Overall, our tunable scaffold-based 3D neuronal culture platform serves as a suitable in vitro model that robustly recapitulates and accelerates the pathogenic characteristics of FAD-iPSC derived neurons.

Spheroids as a Type of Three-Dimensional Cell Cultures-Examples of Methods of Preparation and the Most Important Application

Cell cultures are very important for testing materials and drugs, and in the examination of cell biology and special cell mechanisms. The most popular models of cell culture are two-dimensional (2D) as monolayers, but this does not mimic the natural cell environment. Cells are mostly deprived of cell-cell and cell-extracellular matrix interactions. A much better in vitro model is three-dimensional (3D) culture. Because many cell lines have the ability to self-assemble, one 3D culturing method is to produce spheroids. There are several systems for culturing cells in spheroids, e.g., hanging drop, scaffolds and hydrogels, and these cultures have their applications in drug and nanoparticles testing, and disease modeling. In this paper we would like to present methods of preparation of spheroids in general and emphasize the most important applications.

Brain Organoids: Tiny Mirrors of Human Neurodevelopment and Neurological Disorders

Unravelling the complexity of the human brain is a challenging task. Nowadays, modern neurobiologists have developed 3D model systems called "brain organoids" to overcome the technical challenges in understanding human brain development and the limitations of animal models to study neurological diseases. Certainly like most model systems in neuroscience, brain organoids too have limitations, as these minuscule brains lack the complex neuronal circuitry required to begin the operational tasks of human brain. However, researchers are hopeful that future endeavors with these 3D brain tissues could provide mechanistic insights into the generation of circuit complexity as well as reproducible creation of different regions of the human brain. Herein, we have presented the contemporary state of brain organoids with special emphasis on their mode of generation and their utility in modelling neurological disorders, drug discovery, and clinical trials.

A Three-Dimensional Alzheimer's Disease Cell Culture Model Using iPSC-Derived Neurons Carrying A246E Mutation in PSEN1

Alzheimer's disease (AD) is a chronic brain disorder characterized by progressive intellectual decline and memory and neuronal loss, caused mainly by extracellular deposition of amyloid-β (Aβ) and intracellular accumulation of hyperphosphorylated tau protein, primarily in areas implicated in memory and learning as prefrontal cortex and hippocampus. There are two forms of AD, a late-onset form that affects people over 65 years old, and the early-onset form, which is hereditable and affect people at early ages ~45 years. To date, there is no cure for the disease; consequently, it is essential to develop new tools for the study of processes implicated in the disease. Currently, in vitro AD three-dimensional (3D) models using induced pluripotent stem cells (iPSC)-derived neurons have broadened the horizon for in vitro disease modeling and gained interest for mechanistic studies and preclinical drug discovery due to their potential advantages in providing a better physiologically relevant information and more predictive data for in vivo tests. Therefore, this study aimed to establish a 3D cell culture model of AD in vitro using iPSCs carrying the A246E mutation. We generated human iPSCs from fibroblasts from a patient with AD harboring the A246E mutation in the PSEN1 gene. Cell reprogramming was performed using lentiviral vectors with Yamanaka's factors (OSKM: Oct4, Sox2, Klf4, and c-Myc). The resulting iPSCs expressed pluripotency genes (such as Nanog and Oct4), alkaline phosphatase activity, and pluripotency stem cell marker expression, such as OCT4, SOX2, TRA-1-60, and SSEA4. iPSCs exhibited the ability to differentiate into neuronal lineage in a 3D environment through dual SMAD inhibition as confirmed by Nestin, MAP2, and Tuj1 neural marker expression. These iPSC-derived neurons harbored Aβ oligomers confirmed by Western Blot (WB) and immunostaining. With human iPSC-derived neurons able to produce Aβ oligomers, we established a novel human hydrogel-based 3D cell culture model that recapitulates Aβ aggregation without the need for mutation induction or synthetic Aβ exposure. This model will allow the study of processes implicated in disease spread throughout the brain, the screening of molecules or compounds with therapeutic potential, and the development of personalized therapeutic strategies.

Compound-based Chinese medicine formula: From discovery to compatibility mechanism

ETHNOPHARMACOLOGICAL RELEVANCE

Chinese medicine formula (CMF) has a long history of clinical use in the treatment of various diseases under the guidance of traditional Chinese medicine (TCM) theory. The application of CMF can be divided into three levels, crude extracts, homologous compounds mixture, and specific compounds. However, the modern scientific connotation of the CMF theory has not been clarified.

AIM OF THE REVIEW

To critically evaluate the research strategy for the investigation of compound-based CMF (CCMF).

MATERIALS AND METHODS

The related information was collected from the scientific databases, including CNKI, Elsevier, ScienceDirect, PubMed, SpringerLink, Web of Science, and Wiley Online.

RESULTS

The research design including discovery, screening, optimization, pharmacodynamics models, and target research techniques including the targets for compatibility compounds were evaluated. Essentially it has been evaluated that the in vitro multicellular three-dimensional culture or organoid model has been proposed for the optimization model for compatibility research of CCMF. Based on these, the traditional compatibility theory of CMF, such as Monarch-Minister-Assistant-Guide (Jun-Chen-Zuo-Shi in Chinese), can probably be elucidated by the CCMF research.

CONCLUSIONS

CCMF has the clear advantage of providing the exact composition and controllable quality of modern medicines, in addition to having the characteristics of multi-ingredients and multi-targets synergistic effects of TCM. However, CCMF is still associated with challenges which need to be addressed for its future use.

Midbrain Organoids: A New Tool to Investigate Parkinson's Disease

The study of human 3D cell culture models not only bridges the gap between traditional 2D in vitro experiments and in vivo animal models, it also addresses processes that cannot be recapitulated by either of these traditional models. Therefore, it offers an opportunity to better understand complex biology including brain development. The brain organoid technology provides a physiologically relevant context, which holds great potential for its application in modeling neurological diseases. Here, we compare different methods to obtain highly specialized structures that resemble specific features of the human midbrain. Regionally patterned neural stem cells (NSCs) were utilized to derive such human midbrain-specific organoids (hMO). The resulting neural tissue exhibited abundant neurons with midbrain dopaminergic neuron identity, as well as astroglia and oligodendrocyte differentiation. Within the midbrain organoids, neurite myelination, and the formation of synaptic connections were observed. Regular neuronal fire patterning and neural network synchronicity were determined by multielectrode array recordings. In addition to electrophysiologically functional neurons producing and secreting dopamine, responsive neuronal subtypes, such as GABAergic and glutamatergic neurons were also detected. In order to model disorders like Parkinson's disease (PD) in vitro, midbrain organoids carrying a disease specific mutation were derived and compared to healthy control organoids to investigate relevant neurodegenerative pathophysiology. In this way midbrain-specific organoids constitute a powerful tool for human-specific in vitro modeling of neurological disorders with a great potential to be utilized in advanced therapy development.

Amyloid-β oligomers in cellular models of Alzheimer's disease

Amyloid-β (Aβ) dysmetabolism is tightly associated with pathological processes in Alzheimer's disease (AD). Currently, it is thought that, in addition to Aβ fibrils that give rise to plaque formation, Aβ aggregates into non-fibrillar soluble oligomers (AβOs). Soluble AβOs have been extensively studied for their synaptotoxic and neurotoxic properties. In this review, we discuss physicochemical properties of AβOs and their impact on different brain cell types in AD. Additionally, we summarize three decades of studies with AβOs, providing a compelling bulk of evidence regarding cell-specific mechanisms of toxicity. Cellular models may lead us to a deeper understanding of the detrimental effects of AβOs in neurons and glial cells, putatively shedding light on the development of innovative therapies for AD.

In vitro Models of Neurodegenerative Diseases

Neurodegenerative diseases are progressive degenerative conditions characterized by the functional deterioration and ultimate loss of neurons. These incurable and debilitating diseases affect millions of people worldwide, and therefore represent a major global health challenge with severe implications for individuals and society. Recently, several neuroprotective drugs have failed in human clinical trials despite promising pre-clinical data, suggesting that conventional cell cultures and animal models cannot precisely replicate human pathophysiology. To bridge the gap between animal and human studies, three-dimensional cell culture models have been developed from human or animal cells, allowing the effects of new therapies to be predicted more accurately by closely replicating some aspects of the brain environment, mimicking neuronal and glial cell interactions, and incorporating the effects of blood flow. In this review, we discuss the relative merits of different cerebral models, from traditional cell cultures to the latest high-throughput three-dimensional systems. We discuss their advantages and disadvantages as well as their potential to investigate the complex mechanisms of human neurodegenerative diseases. We focus on in vitro models of the most frequent age-related neurodegenerative disorders, such as Parkinson’s disease, Alzheimer’s disease and prion disease, and on multiple sclerosis, a chronic inflammatory neurodegenerative disease affecting young adults.

Alzheimer's disease, neural stem cells and neurogenesis: cellular phase at single-cell level

Alzheimer’s disease cannot be cured as of yet. Our current understanding on the causes of Alzheimer’s disease is limited. To develop treatments, experimental models that represent a particular cellular phase of the disease and more rigorous scrutiny of the cellular pathological mechanisms are crucial. In recent years, Alzheimer’s disease research underwent a paradigm shift. According to this tendency, Alzheimer’s disease is increasingly being conceived of a disease where not only neurons but also multiple cell types synchronously partake to manifest the pathology. Knowledge on every cell type adds an alternative approach and hope for the efforts towards the treatment. Neural stem cells and their neurogenic ability are making an appearance as a new aspect of the disease manifestation based on the recent findings that neurogenesis reduces dramatically in Alzheimer’s disease patients compared to healthy individuals. Therefore, understanding how neural stem cells can form new neurons in Alzheimer’s disease brains holds an immense potential for clinics. However, this provocative idea requires further evidence and tools for investigation. Recently, single cell sequencing appeared as a revolutionary tool to understand cellular programs in unprecedented resolution and it will undoubtedly facilitate comprehensive investigation of different cell types in Alzheimer’s disease. In this mini-review, we will touch upon recent studies that use single cell sequencing for investigating cellular response in Alzheimer’s disease and some consideration pertaining to the utilization of neural regeneration for Alzheimer’s disease research.