BACE2 variant identified from HSCR patient causes AD-like phenotypes in hPSC-derived brain organoids

Quintessential Synergy: Concurrent Transient Administration of Integrated Stress Response Inhibitors and BACE1 and/or BACE2 Activators as the Optimal Therapeutic Strategy for Alzheimer's Disease

The present study analyzes two potential therapeutic approaches for Alzheimer's disease (AD). One is the suppression of the neuronal integrated stress response (ISR). Another is the targeted degradation of intraneuronal amyloid-beta (iAβ) via the activation of BACE1 (Beta-site Aβ-protein-precursor Cleaving Enzyme) and/or BACE2. Both approaches are rational. Both are promising. Both have substantial intrinsic limitations. However, when combined in a carefully orchestrated manner into a composite therapy they display a prototypical synergy and constitute the apparently optimal, potentially most effective therapeutic strategy for AD.

It's good to know what to BACE the specificity of your inhibitors on

Production, aggregation, and clearance of the amyloid β peptide (Aβ) are important processes governing the initial pathogenesis of Alzheimer's disease (AD). Inhibition of β-site amyloid precursor protein (APP) cleaving enzyme (BACE1) (one of two key proteases responsible for Aβ production) as an AD-therapeutic approach so far has failed to yield a successful drug. BACE1 and its homologue BACE2 are frequently inhibited by the same inhibitors. Several genetic and cerebral organoid modeling studies suggest that BACE2 has dose-dependent AD-suppressing activity, which makes its unwanted inhibition potentially counterproductive for AD treatment. The in vivo effects of an unwanted cross inhibition of BACE2 have so far been impossible to monitor because of the lack of an easily accessible pharmacodynamic marker specific for BACE2 cleavage. In this issue of the JCI, work led by Stefan F. Lichtenthaler identifies soluble VEGFR3 (sVEGFR3) as a pharmacodynamic plasma marker for BACE2 activity not shared with BACE1.

The Alzheimer's disease-linked protease BACE2 cleaves VEGFR3 and modulates its signaling

The β-secretase β-site APP cleaving enzyme (BACE1) is a central drug target for Alzheimer's disease. Clinically tested, BACE1-directed inhibitors also block the homologous protease BACE2. Yet little is known about physiological BACE2 substrates and functions in vivo. Here, we identify BACE2 as the protease shedding the lymphangiogenic vascular endothelial growth factor receptor 3 (VEGFR3). Inactivation of BACE2, but not BACE1, inhibited shedding of VEGFR3 from primary human lymphatic endothelial cells (LECs) and reduced release of the shed, soluble VEGFR3 (sVEGFR3) ectodomain into the blood of mice, nonhuman primates, and humans. Functionally, BACE2 inactivation increased full-length VEGFR3 and enhanced VEGFR3 signaling in LECs and also in vivo in zebrafish, where enhanced migration of LECs was observed. Thus, this study identifies BACE2 as a modulator of lymphangiogenic VEGFR3 signaling and demonstrates the utility of sVEGFR3 as a pharmacodynamic plasma marker for BACE2 activity in vivo, a prerequisite for developing BACE1-selective inhibitors for safer prevention of Alzheimer's disease.

ACH2.0/E, the Consolidated Theory of Conventional and Unconventional Alzheimer's Disease: Origins, Progression, and Therapeutic Strategies

The centrality of amyloid-beta (Aβ) is an indisputable tenet of Alzheimer's disease (AD). It was initially indicated by the detection (1991) of a mutation within Aβ protein precursor (AβPP) segregating with the disease, which served as a basis for the long-standing Amyloid Cascade Hypothesis (ACH) theory of AD. In the intervening three decades, this notion was affirmed and substantiated by the discovery of numerous AD-causing and AD-protective mutations with all, without an exception, affecting the structure, production, and intraneuronal degradation of Aβ. The ACH postulated that the disease is caused and driven by extracellular Aβ. When it became clear that this is not the case, and the ACH was largely discredited, a new theory of AD, dubbed ACH2.0 to re-emphasize the centrality of Aβ, was formulated. In the ACH2.0, AD is caused by physiologically accumulated intraneuronal Aβ (iAβ) derived from AβPP. Upon reaching the critical threshold, it triggers activation of the autonomous AβPP-independent iAβ generation pathway; its output is retained intraneuronally and drives the AD pathology. The bridge between iAβ derived from AβPP and that generated independently of AβPP is the neuronal integrated stress response (ISR) elicited by the former. The ISR severely suppresses cellular protein synthesis; concurrently, it activates the production of a small subset of proteins, which apparently includes components necessary for operation of the AβPP-independent iAβ generation pathway that are absent under regular circumstances. The above sequence of events defines "conventional" AD, which is both caused and driven by differentially derived iAβ. Since the ISR can be elicited by a multitude of stressors, the logic of the ACH2.0 mandates that another class of AD, referred to as "unconventional", has to occur. Unconventional AD is defined as a disease where a stressor distinct from AβPP-derived iAβ elicits the neuronal ISR. Thus, the essence of both, conventional and unconventional, forms of AD is one and the same, namely autonomous, self-sustainable, AβPP-independent production of iAβ. What distinguishes them is the manner of activation of this pathway, i.e., the mode of causation of the disease. In unconventional AD, processes occurring at locations as distant from and seemingly as unrelated to the brain as, say, the knee can potentially trigger the disease. The present study asserts that these processes include traumatic brain injury (TBI), chronic traumatic encephalopathy, viral and bacterial infections, and a wide array of inflammatory conditions. It considers the pathways which are common to all these occurrences and culminate in the elicitation of the neuronal ISR, analyzes the dynamics of conventional versus unconventional AD, shows how the former can morph into the latter, explains how a single TBI can hasten the occurrence of AD and why it takes multiple TBIs to trigger the disease, and proposes the appropriate therapeutic strategies. It posits that yet another class of unconventional AD may occur where the autonomous AβPP-independent iAβ production pathway is initiated by an ISR-unrelated activator, and consolidates the above notions in a theory of AD, designated ACH2.0/E (for expanded ACH2.0), which incorporates the ACH2.0 as its special case and retains the centrality of iAβ produced independently of AβPP as the driving agent of the disease.

Tyrosine phosphorylation-mediated YAP1-TFAP2A interactions coordinate transcription and trastuzumab resistance in HER2+ breast cancer

Trastuzumab resistance in HER2+ breast cancer (BC) is the major reason leading to poor prognosis of BC patients. Oncogenic gene overexpression or aberrant activation of tyrosine kinase SRC is identified to be the key modulator of trastuzumab response. However, the detailed regulatory mechanisms underlying SRC activation-associated trastuzumab resistance remain poorly understood. In the present study, we discover that SRC-mediated YAP1 tyrosine phosphorylation facilitates its interaction with transcription factor AP-2 alpha (activating enhancer binding protein 2 alpha, TFAP2A), which in turn promotes YAP1/TEAD-TFAP2A (YTT) complex-associated transcriptional outputs, thereby conferring trastuzumab resistance in HER2+ BC. Inhibition of SRC kinase activity or disruption of YTT complex sensitizes cells to trastuzumab treatment in vitro and in vivo. Additionally, we also identify YTT complex co-occupies the regulatory regions of a series of genes related to trastuzumab resistance and directly regulates their transcriptions, including EGFR, HER2, H19 and CTGF. Moreover, YTT-mediated transcriptional regulation is coordinated by SRC kinase activity. Taken together, our study reveals that SRC-mediated YTT complex formation and transcriptions are responsible for multiple mechanisms associated with trastuzumab resistance. Therefore, targeting HER2 signaling in combination with the inhibition of YTT-associated transcriptional outputs could serve as the treatment strategy to overcome trastuzumab resistance caused by SRC activation.

Inhibition of Amino Acids Influx into Proximal Tubular Cells Improves Lysosome Function in Diabetes

Key Points

Collectrin serves as a chaperone for the trafficking of neutral amino acid (AA) transporters in the apical membranes of proximal tubular cells (PTCs). Cltrn knockout reduced AAs influx into PTCs, inactivated mTOR, activated transcription factor EB, improved lysosome function, and ameliorated vacuolar formation of PTCs in diabetic mice treated with streptozotocin and high-fat diet. The inhibition of neutral AA transporter, such as B0AT1 (SLC6A19), and transcription factor EB activator is a new therapeutic strategy against diabetic kidney disease.

Background

Inhibition of glucose influx into proximal tubular cells (PTCs) by sodium–glucose cotransporter 2 inhibitors revealed prominent therapeutic effects on diabetic kidney disease. Collectrin (CLTRN) serves as a chaperone for the trafficking of neutral amino acid (AA) transporters in the apical membranes of PTCs. We investigated the beneficial effects of reduced influx of AAs into PTCs in diabetes and obesity model of Cltrn−/y mice.

Methods

Cltrn+/y and Cltrn−/y mice at age 5 weeks were assigned to standard diet and streptozotocin and high-fat diet (STZ-HFD)–treated groups.

Results

At age 22–23 weeks, body weight and HbA1c levels significantly increased in STZ-HFD-Cltrn+/y compared with standard diet-Cltrn+/y; however, they were not altered in STZ-HFD-Cltrn−/y compared with STZ-HFD-Cltrn+/y. At age 20 weeks, urinary albumin creatinine ratio was significantly reduced in STZ-HFD-Cltrn−/y compared with STZ-HFD-Cltrn+/y. Under the treatments with STZ and HFD, the Cltrn gene deficiency caused significant increase in urinary concentration of AAs such as Gln, His, Gly, Thr, Tyr, Val, Trp, Phe, Ile, Leu, and Pro. In PTCs in STZ-HFD-Cltrn+/y, the enlarged lysosomes with diameter of 10 μ m or more were associated with reduced autolysosomes, and the formation of giant lysosomes was prominently suppressed in STZ-HFD-Cltrn−/y. Phospho-mTOR and inactive form of phospho-transcription factor EB were reduced in STZ-HFD-Cltrn−/y compared with STZ-HFD-Cltrn+/y.

Conclusions

The reduction of AAs influx into PTCs inactivated mTOR, activated transcription factor EB, improved lysosome function, and ameliorated vacuolar formation of PTCs in STZ-HFD-Cltrn−/y mice.

A Strategy for Allowing Earlier Diagnosis and Rigorous Evaluation of BACE1 Inhibitors in Preclinical Alzheimer's Disease

Given continued failure of BACE1 inhibitor programs at symptomatic and prodromal stages of Alzheimer's disease (AD), clinical trials need to target the earlier preclinical stage. However, trial design is complex in this population with negative diagnosis of classical hippocampal amnesia on standard memory tests. Besides recent advances in brain imaging, electroencephalogram, and fluid-based biomarkers, new cognitive markers should be established for earlier diagnosis that can optimize recruitment to BACE1 inhibitor trials in presymptomatic AD. Notably, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between asymptomatic individuals with high risks for developing AD and healthy controls. ALF is a form of declarative memory impairment characterized by increased forgetting rates over longer delays (days to months) despite normal storage within the standard delays of testing (20-60 min). Therefore, ALF may represent a harbinger of preclinical dementia and the impairment of systems memory consolidation, during which memory traces temporarily stored in the hippocampus become gradually integrated into cortical networks. This review provides an overview of the utility of ALF in a rational design of next-generation BACE1 inhibitor trials in preclinical AD. I explore potential mechanisms underlying ALF and relevant early-stage biomarkers useful for BACE1 inhibitor evaluation, including synaptic protein alterations, astrocytic dysregulation and neuron hyperactivity in the hippocampal-cortical network. Furthermore, given the physiological role of the isoform BACE2 as an AD-suppressor gene, I also discuss the possible association between the poor selectivity of BACE1 inhibitors and their side effects (e.g., cognitive worsening) in prior clinical trials.

Next Generation Therapeutic Strategy for Treatment and Prevention of Alzheimer's Disease and Aging-Associated Cognitive Decline: Transient, Once-in-a-Lifetime-Only Depletion of Intraneuronal Aβ (iAβ) by Its Targeted Degradation via Augmentation of Intra-iAβ-Cleaving Activities of BACE1 and/or BACE2

Although the long-standing Amyloid Cascade Hypothesis (ACH) has been largely discredited, its main attribute, the centrality of amyloid-beta (Aβ) in Alzheimer's disease (AD), remains the cornerstone of any potential interpretation of the disease: All known AD-causing mutations, without a single exception, affect, in one way or another, Aβ. The ACH2.0, a recently introduced theory of AD, preserves this attribute but otherwise differs fundamentally from the ACH. It posits that AD is a two-stage disorder where both stages are driven by intraneuronal (rather than extracellular) Aβ (iAβ) albeit of two distinctly different origins. The first asymptomatic stage is the decades-long accumulation of Aβ protein precursor (AβPP)-derived iAβ to the critical threshold. This triggers the activation of the self-sustaining AβPP-independent iAβ production pathway and the commencement of the second, symptomatic AD stage. Importantly, Aβ produced independently of AβPP is retained intraneuronally. It drives the AD pathology and perpetuates the operation of the pathway; continuous cycles of the iAβ-stimulated propagation of its own AβPP-independent production constitute an engine that drives AD, the AD Engine. It appears that the dynamics of AβPP-derived iAβ accumulation is the determining factor that either drives Aging-Associated Cognitive Decline (AACD) and triggers AD or confers the resistance to both. Within the ACH2.0 framework, the ACH-based drugs, designed to lower levels of extracellular Aβ, could be applicable in the prevention of AD and treatment of AACD because they reduce the rate of accumulation of AβPP-derived iAβ. The present study analyzes their utility and concludes that it is severely limited. Indeed, their short-term employment is ineffective, their long-term engagement is highly problematic, their implementation at the symptomatic stages of AD is futile, and their evaluation in conventional clinical trials for the prevention of AD is impractical at best, impossible at worst, and misleading in between. In contrast, the ACH2.0-guided Next Generation Therapeutic Strategy for the treatment and prevention of both AD and AACD, namely the depletion of iAβ via its transient, short-duration, targeted degradation by the novel ACH2.0-based drugs, has none of the shortcomings of the ACH-based drugs. It is potentially highly effective, easily evaluable in clinical trials, and opens up the possibility of once-in-a-lifetime-only therapeutic intervention for prevention and treatment of both conditions. It also identifies two plausible ACH2.0-based drugs: activators of physiologically occurring intra-iAβ-cleaving capabilities of BACE1 and/or BACE2.

Presenilin-1-Derived Circular RNAs: Neglected Epigenetic Regulators with Various Functions in Alzheimer's Disease

The presenilin-1 (PSEN1) gene is crucial in developing Alzheimer's disease (AD), a progressive neurodegenerative disorder and the most common cause of dementia. Circular RNAs (circRNAs) are non-coding RNA generated through back-splicing, resulting in a covalently closed circular molecule. This study aimed to investigate PSEN1-gene-derived circular RNAs (circPSEN1s) and their potential functions in AD. Our in silico analysis indicated that circPSEN1s (hsa_circ_0008521 and chr14:73614502-73614802) act as sponge molecules for eight specific microRNAs. Surprisingly, two of these miRNAs (has-mir-4668-5p and has-mir-5584-5p) exclusively interact with circPSEN1s rather than mRNA-PSEN1. Furthermore, the analysis of pathways revealed that these two miRNAs predominantly target mRNAs associated with the PI3K-Akt signaling pathway. With sponging these microRNAs, circPSEN1s were found to protect mRNAs commonly targeted by these miRNAs, including QSER1, BACE2, RNF157, PTMA, and GJD3. Furthermore, the miRNAs sequestered by circPSEN1s have a notable preference for targeting the TGF-β and Hippo signaling pathways. We also demonstrated that circPSEN1s potentially interact with FOXA1, ESR1, HNF1B, BRD4, GATA4, EP300, CBX3, PRDM9, and PPARG proteins. These proteins have a prominent preference for targeting the TGF-β and Notch signaling pathways, where EP300 and FOXA1 have the highest number of protein interactions. Molecular docking analysis also confirms the interaction of these hub proteins and Aβ42 with circPSEN1s. Interestingly, circPSEN1s-targeted molecules (miRNAs and proteins) impacted TGF-β, which served as a shared signaling pathway. Finally, the analysis of microarray data unveiled distinct expression patterns of genes influenced by circPSEN1s (WTIP, TGIF, SMAD4, PPP1CB, and BMPR1A) in the brains of AD patients. In summary, our findings suggested that the interaction of circPSEN1s with microRNAs and proteins could affect the fate of specific mRNAs, interrupt the function of unique proteins, and influence cell signaling pathways, generally TGF-β. Further research is necessary to validate these findings and gain a deeper understanding of the precise mechanisms and significance of circPSEN1s in the context of AD.

BACE2 deficiency impairs expression and function of endothelial nitric oxide synthase in brain endothelial cells

Beta-site amyloid precursor protein (APP)-cleaving enzyme 2 (BACE2) is highly expressed in cerebrovascular endothelium. Notably, BACE2 is one of the most downregulated genes in cerebrovascular endothelium derived from patients with Alzheimer's disease. The present study was designed to determine the role of BACE2 in control of expression and function of endothelial nitric oxide synthase (eNOS). Genetic downregulation of BACE2 with small interfering RNA (BACE2siRNA) in human brain microvascular endothelial cells (BMECs) significantly decreased expression of eNOS and elevated levels of eNOS phosphorylated at threonine residue Thr495, thus leading to reduced production of nitric oxide (NO). BACE2siRNA also suppressed expression of APP and decreased production and release of soluble APPα (sAPPα). In contrast, adenovirus-mediated overexpression of APP increased expression of eNOS. Consistent with these observations, nanomolar concentrations of sAPPα and APP 17mer peptide (derived from sAPPα) augmented eNOS expression. Further analysis established that γ-aminobutyric acid type B receptor subunit 1 and Krüppel-like factor 2 may function as downstream molecular targets significantly contributing to BACE2/APP/sAPPα-induced up-regulation of eNOS. In agreement with studies on cultured human endothelium, endothelium-dependent relaxations to acetylcholine and basal production of cyclic GMP were impaired in cerebral arteries of BACE2-deficient mice. We propose that in the brain blood vessels, BACE2 may function as a vascular protective protein.

Development of brain organoid technology derived from iPSC for the neurodegenerative disease modelling: a glance through

Neurodegenerative diseases are adult-onset neurological conditions that are notoriously difficult to model for drug discovery and development because most models are unable to accurately recapitulate pathology in disease-relevant cells, making it extremely difficult to explore the potential mechanisms underlying neurodegenerative diseases. Therefore, alternative models of human or animal cells have been developed to bridge the gap and allow the impact of new therapeutic strategies to be anticipated more accurately by trying to mimic neuronal and glial cell interactions and many more mechanisms. In tandem with the emergence of human-induced pluripotent stem cells which were first generated in 2007, the accessibility to human-induced pluripotent stem cells (hiPSC) derived from patients can be differentiated into disease-relevant neurons, providing an unrivaled platform for in vitro modeling, drug testing, and therapeutic strategy development. The recent development of three-dimensional (3D) brain organoids derived from iPSCs as the best alternative models for the study of the pathological features of neurodegenerative diseases. This review highlights the overview of current iPSC-based disease modeling and recent advances in the development of iPSC models that incorporate neurodegenerative diseases. In addition, a summary of the existing brain organoid-based disease modeling of Alzheimer's disease was presented. We have also discussed the current methodologies of regional specific brain organoids modeled, its potential applications, emphasizing brain organoids as a promising platform for the modeling of patient-specific diseases, the development of personalized therapies, and contributing to the design of ongoing or future clinical trials on organoid technologies.

Combined GWAS and single cell transcriptomics uncover the underlying genes and cell types in disorders of gut-brain interaction

Disorders of gut-brain interaction (DGBIs), formerly known as functional gastrointestinal disorders, are extremely common and historically difficult to manage. This is largely because their cellular and molecular mechanisms have remained poorly understood and understudied. One approach to unravel the molecular underpinnings of complex disorders such as DGBIs is performing genome wide association studies (GWASs). However, due to the heterogenous and non-specific nature of GI symptoms, it has been difficult to accurately classify cases and controls. Thus, to perform reliable studies, we need to access large patient populations which has been difficult to date. Here, we leveraged the UK Biobank (UKBB) database, containing genetic and medical record data of over half a million individuals, to perform GWAS for five DGBI categories: functional chest pain, functional diarrhea, functional dyspepsia, functional dysphagia, and functional fecal incontinence. By applying strict inclusion and exclusion criteria, we resolved patient populations and identified genes significantly associated with each condition. Leveraging multiple human single-cell RNA-sequencing datasets, we found that the disease associated genes were highly expressed in enteric neurons, which innervate and control GI functions. Further expression and association testing-based analyses revealed specific enteric neuron subtypes consistently linked with each DGBI. Furthermore, protein-protein interaction analysis of each of the disease associated genes revealed protein networks specific to each DGBI, including hedgehog signaling for functional chest pain and neuronal function and neurotransmission for functional diarrhea and functional dyspepsia. Finally, through retrospective medical record analysis we found that drugs that inhibit these networks are associated with an increased disease risk, including serine/threonine kinase 32B drugs for functional chest pain, solute carrier organic anion transporter family member 4C1, mitogen-activated protein kinase 6, and dual serine/threonine and tyrosine protein kinase drugs for functional dyspepsia, and serotonin transporter drugs for functional diarrhea. This study presents a robust strategy for uncovering the tissues, cell types, and genes involved in DGBIs, presenting novel predictions of the mechanisms underlying these historically intractable and poorly understood diseases.

Accelerated long-term forgetting: A sensitive paradigm for detecting subtle cognitive impairment and evaluating BACE1 inhibitor efficacy in preclinical Alzheimer's disease

Given a long preclinical stage of Alzheimer's disease (AD) continuum before the onset of dementia, there is a growing demand for tools capable of detecting the earliest feature of subtle cognitive impairment and optimizing recruitment to clinical trials for potentially disease-modifying therapeutic interventions such as BACE1 inhibitors. Now that all BACE1 inhibitor programs in symptomatic and prodromal AD populations have ended in failure, trials need to shift to target the earlier preclinical stage. However, evaluating cognitive efficacy (if any) in asymptomatic AD individuals is a great challenge. In this context, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between presymptomatic individuals with high risks for developing AD and healthy controls. ALF is characterized by increased forgetting rates over extended delays (e.g., days, weeks, months) despite normal learning and short-term retention on standard memory assessments that typically use around 30-min delays. This review provides an overview of recent progress in animal model and clinical studies on this topic, focusing on the utility and underlying mechanism of ALF that may be applicable to earlier diagnosis and BACE1 inhibitor efficacy evaluation at a preclinical stage of AD.

Cartilage organoids for cartilage development and cartilage-associated disease modeling

Cartilage organoids have emerged as powerful modelling technology for recapitulation of joint embryonic events, and cartilage regeneration, as well as pathophysiology of cartilage-associated diseases. Recent breakthroughs have uncovered "mini-joint" models comprising of multicellular components and extracellular matrices of joint cartilage for development of novel disease-modifying strategies for personalized therapeutics of cartilage-associated diseases. Here, we hypothesized that LGR5-expressing embryonic joint chondroprogenitor cells are ideal stem cells for the generation of cartilage organoids as "mini-joints" ex vivo "in a dish" for embryonic joint development, cartilage repair, and cartilage-associated disease modelling as essential research models of drug screening for further personalized regenerative therapy. The pilot research data suggested that LGR5-GFP-expressing embryonic joint progenitor cells are promising for generation of cartilage organoids through gel embedding method, which may exert various preclinical and clinical applications for realization of personalized regenerative therapy in the future.

BACE2: A Promising Neuroprotective Candidate for Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia that affects millions of predominantly elderly individuals worldwide. Despite intensive research over several decades, controversies still surround the etiology of AD and the disease remains incurable. Meanwhile, new molecular players of the central amyloid cascade hypothesis have emerged and among these is a protease known as β-site APP cleavage enzyme 2 (BACE2). Unlike BACE1, BACE2 cleaves the amyloid-β protein precursor within the Aβ domain that accordingly prevents the generation of Aβ42 peptides, the aggregation of which is commonly regarded as the toxic entity that drives neurodegeneration in AD. Given this non-amyloidogenic role of BACE2, it is attractive to position BACE2 as a therapeutic target for AD. Indeed, several groups including ours have demonstrated a neuroprotective role for BACE2 in AD. In this review, we discuss emerging evidence supporting the ability of BACE2 in mitigating AD-associated pathology in various experimental systems including human pluripotent stem cell-derived cerebral organoid disease models. Alongside this, we also provide an update on the identification of single nucleotide polymorphisms occurring in the BACE2 gene that are linked to increased risk and earlier disease onset in the general population. In particular, we highlight a recently identified point mutation on BACE2 that apparently leads to sporadic early-onset AD. We believe that a better understanding of the role of BACE2 in AD would provide new insights for the development of viable therapeutic strategies for individuals with dementia.

Human Brain Organoid: A Versatile Tool for Modeling Neurodegeneration Diseases and for Drug Screening

Clinical trials serve as the fundamental prerequisite for clinical therapy of human disease, which is primarily based on biomedical studies in animal models. Undoubtedly, animal models have made a significant contribution to gaining insight into the developmental and pathophysiological understanding of human diseases. However, none of the existing animal models could efficiently simulate the development of human organs and systems due to a lack of spatial information; the discrepancy in genetic, anatomic, and physiological basis between animals and humans limits detailed investigation. Therefore, the translational efficiency of the research outcomes in clinical applications was significantly weakened, especially for some complex, chronic, and intractable diseases. For example, the clinical trials for human fragile X syndrome (FXS) solely based on animal models have failed such as mGluR5 antagonists. To mimic the development of human organs more faithfully and efficiently translate in vitro biomedical studies to clinical trials, extensive attention to organoids derived from stem cells contributes to a deeper understanding of this research. The organoids are a miniaturized version of an organ generated in vitro, partially recapitulating key features of human organ development. As such, the organoids open a novel avenue for in vitro models of human disease, advantageous over the existing animal models. The invention of organoids has brought an innovative breakthrough in regeneration medicine. The organoid-derived human tissues or organs could potentially function as invaluable platforms for biomedical studies, pathological investigation of human diseases, and drug screening. Importantly, the study of regeneration medicine and the development of therapeutic strategies for human diseases could be conducted in a dish, facilitating in vitro analysis and experimentation. Thus far, the pilot breakthrough has been made in the generation of numerous types of organoids representing different human organs. Most of these human organoids have been employed for in vitro biomedical study and drug screening. However, the efficiency and quality of the organoids in recapitulating the development of human organs have been hindered by engineering and conceptual challenges. The efficiency and quality of the organoids are essential for downstream applications. In this article, we highlight the application in the modeling of human neurodegenerative diseases (NDDs) such as FXS, Alzheimer's disease (AD), Parkinson's disease (PD), and autistic spectrum disorders (ASD), and organoid-based drug screening. Additionally, challenges and weaknesses especially for limits of the brain organoid models in modeling late onset NDDs such as AD and PD., and future perspectives regarding human brain organoids are addressed.