Engineering of human brain organoids with a functional vascular-like system

Single-cell RNA sequencing in the study of human retinal organoids

Single-cell RNA sequencing (scRNA-seq) has transformed the study of retinal development and diseases by enabling a detailed analysis of cellular diversity within retinal organoids (ROs). ROs generated from pluripotent stem cells mimic the essential characteristics of the human retina and provide a valuable in vitro model for investigating retinal development, cell interactions, and disease mechanisms. This review summarizes the application of scRNA-seq on RO research, emphasizing its capacity to identify distinct cell populations, uncover developmental trajectories, and reveal the molecular signatures of retinal diseases. scRNA-seq provides new insights into retinal neurogenesis, cellular diversity, and the pathophysiology of retinal degenerative diseases. This technology has enabled the identification of novel biomarkers and potential therapeutic targets. Integrating scRNA-seq with other technologies, such as spatial transcriptomics and CRISPR-based screening, can further deepen our understanding of retinal biology and improve treatment strategies.

Designer mammalian living materials through genetic engineering

Emerging genome editing and synthetic biology toolboxes can accurately program mammalian cells behavior from the inside-out. Such engineered living units can be perceived as key building blocks for bioengineering mammalian cell-dense materials, with promising features to be used as living therapeutics for tissue engineering or disease modeling applications. Aiming to reach full control over the code that governs cell behavior, inside-out engineering approaches have potential to fully unlock user-defined living materials encoded with tailored cellular functionalities and spatial arrangements. Dwelling on this, herein, we discuss the most recent advances and opportunities unlocked by genetic engineering strategies, and on their use for the assembly of next-generation cell-rich or cell-based materials, with an unprecedent control over cellular arrangements and customizable therapeutic capabilities. We envision that the continuous synergy between inside-out and outside-in cell engineering approaches will potentiate the future development of increasingly sophisticated cell assemblies that may operate with augmented biofunctionalities.

Advanced Animal Replacement Testing Strategies Using Stem Cell and Organoids

The increasing ethical concerns and regulatory restrictions surrounding animal testing have accelerated the development of advanced in vitro models that more accurately replicate human physiology. Among these, stem cell-based systems and organoids have emerged as revolutionary tools, providing ethical, scalable, and physiologically relevant alternatives. This review explores the key trends and driving factors behind the adoption of these models, such as technological advancements, the principles of the 3Rs (Replacement, Reduction, and Refinement), and growing regulatory support from agencies like the OECD and FDA. It also delves into the development and application of various model systems, including 3D reconstructed tissues, induced pluripotent stem cell-derived cells, and microphysiological systems, highlighting their potential to replace animal models in toxicity evaluation, disease modeling, and drug development. A critical aspect of implementing these models is ensuring robust quality control protocols to enhance reproducibility and standardization, which is necessary for gaining regulatory acceptance. Additionally, we discuss advanced strategies for assessing toxicity and efficacy, focusing on organ-specific evaluation methods and applications in diverse fields such as pharmaceuticals, cosmetics, and food safety. Despite existing challenges related to scalability, standardization, and regulatory alignment, these innovative models represent a transformative step towards reducing animal use and improving the relevance and reliability of preclinical testing outcomes.

Multiscale Organization of Neural Networks in a 3D Bioprinted Matrix

The efficient establishment of in vitro neural models that accurately mimic the structural and functional connectivity of neural networks is critical in neuroscience research. 3D bioprinting shows great potential for constructing sophisticated in vitro models with high freedom of design. However, mature neurons are delicate and susceptible to manipulation. Here, extrusion-based 3D bioprinting is employed to fabricate gelatin methacryloyl (GelMA)-based constructs containing embryonic day 18 (E18) rat cortical neurons, referred to as 3D neuMatrix. 3D neuMatrix displays favorable neuronal viability, with the progressive formation of a 3D brain-like neural network with local and long-range functional axon connections. Compared with 2D cultured neurons, 3D neuMatrix is more similar to the E18 cortex according to the bulk transcriptomic profile, with a recreation of cellular components in the cerebral cortex. The 3D neuMatrix is employed to establish a disease model of ischemic stroke, with a faithful recapitulation of the viability, function, and transcriptomic features of rats with middle cerebral artery occlusion/reperfusion (MCAO/R). These findings demonstrate the formation of multiscale neural circuits within 3D neuMatrix and its valuable potential in the study of neurodevelopment, disease modeling with drug screening, and in vitro intelligence.

Generation of Neural Organoids and Their Application in Disease Modeling and Regenerative Medicine

The complexity and precision of the human nervous system have posed significant challenges for researchers seeking suitable models to elucidate refractory neural disorders. Traditional approaches, including monolayer cell cultures and animal models, often fail to replicate the intricacies of human neural tissue. The advent of organoid technology derived from stem cells has addressed many of these limitations, providing highly representative platforms for studying the structure and function of the human embryonic brain and spinal cord. Researchers have induced neural organoids with regional characteristics by mimicking morphogen gradients in neural development. Recent advancements have demonstrated the utility of neural organoids in disease modeling, offering insights into the pathophysiology of various neural disorders, as well as in the field of neural regeneration. Developmental defects in neural organoids due to the lack of microglia or vascular systems are addressed. In addition to induction methods, microfluidics is used to simulate the dynamic physiological environment; bio-manufacturing technologies are employed to regulate physical signaling and shape the structure of complex organs. These technologies further expand the construction strategies and application scope of neural organoids. With the emergence of new material paradigms and advances in AI, new possibilities in the realm of neural organoids are witnessed.

The advancements of organoids push the boundaries of glioblastoma research

Glioblastoma (GBM) is a malignant tumor of the nervous system, which is difficult to treat due to its strong invasiveness, rapid progression, and poor prognosis. To understand the complex biological behavior of glioblasts and the interaction between tumors and hosts, a new in vitro platform based on human cells is required, which can summarize the complex cellular structure and cell diversity of the human brain, as well as the biological behavior of GBM. Organoids are 3D self-organizing tissues, partially similar to source tissues, which can simulate the structure and physiological functions of organs or tissues in vitro. In this review, we underline the widespread application of different types of GBOs models in GBM pathogenesis, including cells derived, tumor tissues derived, and other co-culture models, as well as their application and shortcomings in the treatment of GBM.

How neural stem cell therapy promotes brain repair after stroke

The human brain has a very limited capacity for self-repair, presenting significant challenges in recovery following injuries such as ischemic stroke. Stem cell-based therapies have emerged as promising strategies to enhance post-stroke recovery. Building on a large body of preclinical evidence, clinical trials are currently ongoing to prove the efficacy of stem cell therapy in stroke patients. However, the mechanisms through which stem cell grafts promote neural repair remain incompletely understood. Key questions include whether these effects are primarily driven by (1) the secretion of trophic factors that stimulate endogenous repair processes, (2) direct neural cell replacement, or (3) a combination of both mechanisms. This review explores the latest advancements in neural stem cell therapy for stroke, highlighting research insights in brain repair mechanisms. Deciphering the fundamental mechanisms underlying stem cell-mediated brain regeneration holds the potential to refine therapeutic strategies and advance treatments for a range of neurological disorders.

Charged dendrimers reduce glioblastoma viability by modulating lysosomal activity and HMGB1-RAGE interaction

Dendrimers and dendrimer-based self-assembly systems have emerged as promising nanocarriers for a variety of applications, including anti-cancer therapies, modulation of the tumor microenvironment, and imaging. Here, we explored the therapeutic potential of two charged dendrimers, dendritic polyglycerol sulfate (dPGS) and dendritic polyglycerol amine (dPGA), in the context of glioblastoma multiforme (GBM). Docosahexaenoic acid (DHA) has shown potential in GBM. We therefore examined dPGS and dPGA effects alone and in combination with DHA. Using 2D cell models and 3D tumoroids, we showed that DHA with dPGA reduced tumor integrity and cell viability. dPGS reduced oxidative stress, whereas dPGA reduced lysosomal acidification, contributing to cellular dysfunction. Both dendrimers influence the interaction between high mobility group box 1 (HMGB1) and the receptor for advanced glycation end products (RAGE). The surfaces of the HMGB1-RAGE complex provide binding sites for interactions of charged molecules like dPGS and dPGA, suggesting the contribution of these interactions to cytotoxicity. In summary, our findings show that combining DHA with charged dendrimers (dPGS and dPGA) enhances GBM cytotoxicity through several mechanisms, involving lysosomal alkalinization, lipid peroxidation and modulation of the HMGB1-RAGE complex.

Alzheimer's disease patient brain extracts induce multiple pathologies in novel vascularized neuroimmune organoids for disease modeling and drug discovery

Alzheimer's Disease (AD) is the most common cause of dementia, afflicting 55 million individuals worldwide, with limited treatment available. Current AD models mainly focus on familial AD (fAD), which is due to genetic mutations. However, models for studying sporadic AD (sAD), which represents over 95% of AD cases without specific genetic mutations, are severely limited. Moreover, the fundamental species differences between humans and animals might significantly contribute to clinical failures for AD therapeutics that have shown success in animal models, highlighting the urgency to develop more translational human models for studying AD, particularly sAD. In this study, we developed a complex human pluripotent stem cell (hPSC)-based vascularized neuroimmune organoid model, which contains multiple cell types affected in human AD brains, including human neurons, microglia, astrocytes, and blood vessels. Importantly, we demonstrated that brain extracts from individuals with sAD can effectively induce multiple AD pathologies in organoids four weeks post-exposure, including amyloid beta (Aβ) plaque-like aggregates, tau tangle-like aggregates, neuroinflammation, elevated microglial synaptic pruning, synapse/neuronal loss, and impaired neural network activity. Proteomics analysis also revealed disrupted AD-related pathways in our vascularized AD neuroimmune organoids. Furthermore, after treatment with Lecanemab, an FDA-approved antibody drug targeting Aβ, AD brain extracts exposed organoids showed a significant reduction of amyloid burden, along with an elevated vascular inflammation response. Thus, the vascularized neuroimmune organoid model provides a unique opportunity to study AD, particularly sAD, under a pathophysiological relevant three-dimensional (3D) human cell environment. It also holds great promise to facilitate AD drug development, particularly for immunotherapies.

Microplastics Accumulation Induces Kynurenine-Derived Neurotoxicity in Cerebral Organoids and Mouse Brain

Microplastics (MP) are pervasive environmental pollutants with potential adverse effects on human health, particularly concerning neurotoxicity. This study investigates the accumulation and neurotoxic effects of MP in cerebral organoids and mouse brains. Utilizing in vitro cerebral organoids and in vivo mouse models, we examined the penetration of MP, revealing that smaller MP (50 nm) infiltrated deeper into the organoids compared to larger ones (100 nm). Exposure to 50 nm MP resulted in a significant reduction in organoid viability. Furthermore, total RNA sequencing indicated substantial alterations in neurotoxicity-related gene expression. In vivo, MP-treated mice exhibited notable DNA fragmentation in the hippocampus and cortex, alongside elevated levels of inflammatory markers and neurotoxic metabolites, such as kynurenine (KYN) and 3-hydroxykynurenine (3-HK). Our findings suggest that MP may promote neurotoxicity through the kynurenine pathway, leading to heightened levels of neurotoxic compounds like quinolinic acid. This research highlights the potential for MP to induce neuroinflammatory responses and disrupt normal brain function, underscoring the need for further investigation into the long-term effects of MP exposure on neurological health.

Emerging brain organoids: 3D models to decipher, identify and revolutionize brain

Brain organoids are an emerging in vitro 3D brain model that is integrated from pluripotent stem cells. This model mimics the human brain's developmental process and disease-related phenotypes to a certain extent while advancing the development of human brain-based biological intelligence. However, many limitations of brain organoid culture (e.g., lacking a functional vascular system, etc.) prevent in vitro-cultured organoids from truly replicating the human brain in terms of cell type and structure. To improve brain organoids' scalability, efficiency, and stability, this paper discusses important contributions of material biology and microprocessing technology in solving the related limitations of brain organoids and applying the latest imaging technology to make real-time imaging of brain organoids possible. In addition, the related applications of brain organoids, especially the development of organoid intelligence combined with artificial intelligence, are analyzed, which will help accelerate the rational design and guidance of brain organoids.

Vascular network-inspired diffusible scaffolds for engineering functional midbrain organoids

Organoids, 3D organ-like tissue cultures derived from stem cells, show promising potential for developmental biology, drug discovery, and regenerative medicine. However, the function and phenotype of current organoids, especially neural organoids, are still limited by insufficient diffusion of oxygen, nutrients, metabolites, signaling molecules, and drugs. Herein, we present vascular network-inspired diffusible (VID) scaffolds to mimic physiological diffusion physics for generating functional organoids and phenotyping their drug response. Specifically, the VID scaffolds, 3D-printed meshed tubular channel networks, successfully engineer human midbrain organoids almost without necrosis and hypoxia in commonly used well plates. Compared with conventional organoids, these engineered organoids develop more physiologically relevant features and functions, including midbrain-specific identity, oxygen metabolism, neuronal maturation, and network activity. Moreover, these engineered organoids also better recapitulate pharmacological responses, such as neural activity changes to fentanyl exposure, compared with conventional organoids with significant diffusion limits. This platform may provide insights for organoid development and therapeutic innovation.

Recent advances in blood-brain barrier-on-a-chip models

The blood-brain barrier is a physiological barrier between the vascular system and the nervous system. Under healthy conditions, it restricts the passage of most biomolecules into the brain, making drug development exceedingly challenging. Conventional cell-based in vitro models provide valuable insights into certain features of the BBB. Nevertheless, these models often lack the three-dimensional structure and dynamic interactions of the surrounding microenvironment, which greatly influence cell functionality. Consequently, considerable efforts have been made to enhance in vitro models for drug development and disease research. Recently, microfluidic organ-on-a-chip systems have emerged as promising candidates to better mimic the dynamic nature of the BBB. This review provides a comprehensive overview of recent BBB-on-chip devices. The typical building blocks, chip designs, the perfusion infrastructure, and readouts used to characterize and evaluate BBB formation are presented, analyzed, and discussed in detail. STATEMENT OF SIGNIFICANCE: The blood-brain barrier (BBB) is a highly selective barrier that controls what can enter the brain. While it protects the brain from harmful substances, it also hinders the delivery of treatments for neurological diseases such as Alzheimer's and Parkinson's. Due to its complexity, studying the BBB in living organisms remains difficult. However, recent advances in "organ-on-a-chip" technology have allowed scientists to create small, engineered models that replicate the BBB. These models provide a powerful platform to study diseases and test potential drugs with greater accuracy than traditional methods. Organ-on-a-chip devices are designed to mimic the behavior of organs or tissues in the human body, offering a more realistic and controlled environment for research. This review highlights recent breakthroughs in BBB-on-a-chip technology, showing how these models enhance current research and have the potential to transform the way we study brain diseases and develop new drugs. By integrating biology and engineering, BBB-on-a-chip technology has the potential to transform neuroscience research, improve drug development, and enhance our understanding of brain disorders.

Getting Blood out of a Stone: Vascularization via Spheroids and Organoids in 3D Bioprinting

Current developments in bioequivalent technology have led to the creation of excellent models that mimic the structure and function of human organs. These models are based on the original tissues and organs of the human body, but they lack the complex interaction with the extensive network of vasculature, and this is a major challenge for these models. A functional vasculature is essential for oxygen, nutrient, and waste exchange. It is also responsible for inductive biochemical exchange, and provides a structural pattern for organ growth. In vitro systems, containing no perfusable vessels, suffer from the quick formation of a necrotic core of organoids, and further development does not occur due to increased metabolic demands. Another key limitation of 3D-based techniques is the absence of accurate architectural structures and large-scale tissue sizes. Recently, new 3D bioprinting methods have been developed for organoids and spheroids as living building blocks. These methods aim to address some of the challenges associated with 3D technologies. In this review, we discuss recent strategies for vascularization via organoids and spheroids, which are used as structural units in bioprinting to recreate natural organs and tissues with ever-increasing accuracy in structure and function.

Modelling human brain development and disease with organoids

Organoids are systems derived from pluripotent stem cells at the interface between traditional monolayer cultures and in vivo animal models. The structural and functional characteristics of organoids enable the modelling of early stages of brain development in a physiologically relevant 3D environment. Moreover, organoids constitute a tool with which to analyse how individual genetic variation contributes to the susceptibility and progression of neurodevelopmental disorders. This Roadmap article describes the features of brain organoids, focusing on the neocortex, and their advantages and limitations - in comparison with other model systems - for the study of brain development, evolution and disease. We highlight avenues for enhancing the physiological relevance of brain organoids by integrating bioengineering techniques and unbiased high-throughput analyses, and discuss future applications. As organoids advance in mimicking human brain functions, we address the ethical and societal implications of this technology.

Bioengineering innovations for neural organoids with enhanced fidelity and function

Neural organoids have been utilized to recapitulate different aspects of the developing nervous system. While hailed as promising experimental tools for studying human neural development and neuropathology, current neural organoids do not fully recapitulate the anatomy or microcircuitry-level functionality of the developing brain, spinal cord, or peripheral nervous system. In this review, we discuss emerging bioengineering approaches that control morphogen signals and biophysical microenvironments, which have improved the efficiency, fidelity, and utility of neural organoids. Furthermore, advancements in bioengineered tools have facilitated more sophisticated analyses of neural organoid functions and applications, including improved neural-bioelectronic interfaces and organoid-based information processing. Emerging bioethical issues associated with advanced neural organoids are also discussed. Future opportunities of neural organoid research lie in enhancing their fidelity, maturity, and complexity and expanding their applications in a scalable manner.

Evolution of Preclinical Models for Glioblastoma Modelling and Drug Screening

PURPOSE OF REVIEW

Isocitrate dehydrogenase wild-type glioblastoma is an extremely aggressive and fatal primary brain tumour, characterised by extensive heterogeneity and diffuse infiltration of brain parenchyma. Despite multimodal treatment and diverse research efforts to develop novel therapies, there has been limited success in improving patient outcomes. Constructing physiologically relevant preclinical models is essential to optimising drug screening processes and identifying more effective treatments.

RECENT FINDINGS

Traditional in-vitro models have provided critical insights into glioblastoma pathophysiology; however, they are limited in their ability to recapitulate the complex tumour microenvironment and its interactions with surrounding cells. In-vivo models offer a more physiologically relevant context, but often do not fully represent human pathology, are expensive, and time-consuming. These limitations have contributed to the low translational success of therapies from trials to clinic. Organoid and glioblastoma-on-a-chip technology represent significant advances in glioblastoma modelling and enable the replication of key features of the human tumour microenvironment, including its structural, mechanical, and biochemical properties. Organoids provide a 3D system that captures cellular heterogeneity and tumour architecture, while microfluidic chips offer dynamic systems capable of mimicking vascularisation and nutrient exchange. Together, these technologies hold tremendous potential for high throughput drug screening and personalised, precision medicine. This review explores the evolution of preclinical models in glioblastoma modelling and drug screening, emphasising the transition from traditional systems to more advanced organoid and microfluidic platforms. Furthermore, it aims to evaluate the advantages and limitations of both traditional and next-generation models, investigating their combined potential to address current challenges by integrating complementary aspects of specific models and techniques.

Towards advanced regenerative therapeutics to tackle cardio-cerebrovascular diseases

The development of vascularized organoids as novel modelling tools of the human cardio-cerebrovascular system for preclinical research has become an essential platform for studying human vascularized tissues/organs for development of personalized therapeutics during recent decades. Organ-on-chip technology is promising for investigating physiological in vitro responses in drug screening development and advanced disease models. Vascularized tissue/organ-on-a-chip benefits every step of drug discovery pipeline as a screening tool with close human genome relevance to investigate human systems biology. Simultaneously, cardio-cerebrovascular-on-chip-integrated microfluidic system serves as an alternative to preclinical animal research for studying (patho-)physiological processes of human blood vessels during embryonic development and cardio-cerebrovascular disease. Integrated with next-generation techniques, such as three-dimensional bioprinting of both cells and matrix, may enable vascularized organoid-on-chip-based novel drug development as personalized therapeutics.

Microvascularization in 3D Human Engineered Tissue and Organoids

The microvasculature, a complex network of small blood vessels, connects systemic circulation with local tissues, facilitating the nutrient and oxygen exchange that is critical for homeostasis and organ function. Engineering these structures is paramount for advancing tissue regeneration, disease modeling, and drug testing. However, replicating the intricate architecture of native vascular systems-characterized by diverse vessel diameters, cellular constituents, and dynamic perfusion capabilities-presents significant challenges. This complexity is compounded by the need to precisely integrate biomechanical, biochemical, and cellular cues. Recent breakthroughs in microfabrication, organoids, bioprinting, organ-on-a-chip platforms, and in vivo vascularization techniques have propelled the field toward faithfully replicating vascular complexity. These innovations not only enhance our understanding of vascular biology but also enable the generation of functional, perfusable tissue constructs. Here, we explore state-of-the-art technologies and strategies in microvascular engineering, emphasizing key advancements and addressing the remaining challenges to developing fully functional vascularized tissues.

The potential of brain organoids in addressing the heterogeneity of synucleinopathies

Synucleinopathies are a group of diseases characterized by neuronal and glial accumulation of α-synuclein (aSyn) linked with different clinical presentations, including Parkinson's disease (PD), Parkinson's disease with dementia (PDD), Dementia with Lewy Bodies (DLB) and Multiple system atrophy (MSA). Interestingly, the structure of the aSyn aggregates can vary across different synucleinopathies. Currently, it is unclear how the aSyn protein can aggregate into diverse structures and affect distinct cell types and various brain regions, leading to different clinical symptoms. Recent advances in induced pluripotent stem cells (iPSCs)-based brain organoids (BOs) technology provide an unprecedented opportunity to define the etiology of synucleinopathies in human brain cells within their three-dimensional (3D) context. In this review, we will summarize current advances in investigating the mechanisms of synucleinopathies using BOs and discuss the scope of this platform to define mechanisms underlining the selective vulnerability of cell types and brain regions in synucleinopathies.

Organoid Vascularization: Strategies and Applications

Organoids provide 3D structures that replicate native tissues in biomedical research. The development of vascular networks within organoids enables oxygen and nutrient delivery while facilitating metabolic waste removal, which supports organoid growth and maturation. Recent studies demonstrate that vascularized organoid models offer insights into tissue interactions and promote tissue regeneration. However, the current limitations in establishing functional vascular networks affect organoid growth, viability, and clinical translation potential. This review examines the development of vascularized organoids, including the mechanisms of angiogenesis and vasculogenesis, construction strategies, and biomedical applications. The approaches are categorized into in vivo and in vitro methods, with analysis of their specific advantages and limitations. The review also discusses emerging techniques such as bioprinting and gene editing for improving vascularization and functional integration in organoid-based therapies. Current developments in organoid vascularization indicate potential applications in modeling human diseases and developing therapeutic strategies, contributing to advances in translational research.

Three-Dimensional Bioprinting of Astrocytes and Endothelial Cells to Direct Retinal Axon Growth and Vascularization

Retinal organoids (ROs) are currently used to study retinal development and diseases but cannot model glaucoma because they fail to form a nerve fiber layer (NFL) and optic nerve (ON). Utilizing three-dimensional bioprinting, ON head astrocytes (ONHAs) and vascular endothelial cells, both of which contribute to NFL development in vivo but are absent in ROs, were positioned at the center of scaffolds seeded with retinal ganglion cells (RGCs). In experiments using ONHAs isolated from developing retinas, polarization of RGC neurite growth increased by 43% while ONHA from adult retinas or astrocytes from the developing peripheral retina or developing cortex did not increase polarization above controls. Furthermore, RGC-seeded scaffolds increased both the number and rate of ONHAs migrating out from the printed center compared to scaffolds lacking RGCs, mimicking the migration pattern observed during retinal development. Finally, in scaffolds containing both ONHAs and endothelial cells, the endothelial cells preferentially migrate on and only form vascular tube structures on scaffolds also containing RGCs. These results suggest that recreating the developmental organization of the retina can recapitulate the mechanism of NFL development and retinal vascularization in vitro. This step is not only necessary for the development of retinal models of glaucoma but has the potential for translation to other parts of the central nervous system.

Exploring human brain development and disease using assembloids

How the human brain develops and what goes awry in neurological disorders represent two long-lasting questions in neuroscience. Owing to the limited access to primary human brain tissue, insights into these questions have been largely gained through animal models. However, there are fundamental differences between developing mouse and human brain, and neural organoids derived from human pluripotent stem cells (hPSCs) have recently emerged as a robust experimental system that mimics self-organizing and multicellular features of early human brain development. Controlled integration of multiple organoids into assembloids has begun to unravel principles of cell-cell interactions. Moreover, patient-derived or genetically engineered hPSCs provide opportunities to investigate phenotypic correlates of neurodevelopmental disorders and to develop therapeutic hypotheses. Here, we outline the advances in technologies that facilitate studies by using assembloids and summarize their applications in brain development and disease modeling. Lastly, we discuss the major roadblocks of the current system and potential solutions.

GRAMD1B is a regulator of lipid homeostasis, autophagic flux and phosphorylated tau

Lipid dyshomeostasis and tau pathology are present in frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). However, the relationship between lipid dyshomeostasis and tau pathology remains unclear. We report that GRAM Domain Containing 1B (GRAMD1B), a nonvesicular cholesterol transporter, is increased in excitatory neurons of human neural organoids (HNOs) with the MAPT R406W mutation. Human FTLD, AD cases, and PS19 tau mice also have increased GRAMD1B expression. We show that overexpression of GRAMD1B increases levels of free cholesterol, lipid droplets, and impairs autophagy flux. Modulating GRAMD1B in iPSC-derived neurons also alters key autophagy-related components such as PI3K, phospho-AKT, and p62, as well as phosphorylated tau, and CDK5R1. Blocking GRAMD1B function decreases free cholesterol and lipid droplets. Knocking down GRAMD1B additionally reduces phosphorylated tau, and CDK5R1 expression. Our findings elucidate the role of GRAMD1B in the nervous system and highlight its relevance to FTLD and AD.

Towards a Better Understanding of the Human Health Risk of Per- and Polyfluoroalkyl Substances Using Organoid Models

The ubiquitous presence of per- and polyfluoroalkyl substances (PFAS) in the environment has garnered global public concern. Epidemiological studies have proved that exposure to PFAS is associated with human health risks. Although evidence demonstrated the toxic mechanisms of PFAS based on animal models and traditional cell cultures, their limitations in inter-species differences and lack of human-relevant microenvironments hinder the understanding of health risks from PFAS exposure. There is an increasing necessity to explore alternative methodologies that can effectively evaluate human health risks. Human organoids derived from stem cells accurately mimic the sophisticated and multicellular structures of native human organs, providing promising models for toxicology research. Advanced organoids combined with innovative technologies are expected to improve understanding of the breadth and depth of PFAS toxicity.

Coordinated differentiation of human intestinal organoids with functional enteric neurons and vasculature

Human intestinal organoids (HIOs) derived from human pluripotent stem cells co-differentiate both epithelial and mesenchymal lineages in vitro but lack important cell types such as neurons, endothelial cells, and smooth muscle, which limits translational potential. Here, we demonstrate that the intestinal stem cell niche factor, EPIREGULIN (EREG), enhances HIO differentiation with epithelium, mesenchyme, enteric neuroglial populations, endothelial cells, and organized smooth muscle in a single differentiation, without the need for co-culture. When transplanted into a murine host, HIOs mature and demonstrate enteric nervous system function, undergoing peristaltic-like contractions indicative of a functional neuromuscular unit. HIOs also form functional vasculature, demonstrated in vitro using microfluidic devices and in vivo following transplantation, where HIO endothelial cells anastomose with host vasculature. These complex HIOs represent a transformative tool for translational research in the human gut and can be used to interrogate complex diseases as well as for testing therapeutic interventions with high fidelity to human pathophysiology.

The promise of cerebral organoids for neonatology

PURPOSE OF REVIEW

Applying discoveries from basic research to patients in the neonatal intensive care unit (NICU) is challenging given the difficulty of modeling this population in animal models, lack of translational relevance from animal models to humans, and scarcity of primary human tissue. Human cell-derived cerebral organoid models are an appealing way to address some of these gaps. In this review, we will touch on previous work to model neonatal conditions in cerebral organoids, some limitations of this approach, and recent strategies that have attempted to address these limitations.

RECENT FINDINGS

While modeling of neurodevelopmental disorders has been an application of cerebral organoids since their initial description, recent studies have dramatically expanded the types of brain regions and disease models available. Additionally, work to increase the complexity of organoid models by including immune and vascular cells, as well as modeling human heterogeneity with mixed donor organoids will provide new opportunities to model neonatal pathologies.

SUMMARY

Organoids are an attractive model to study human neurodevelopmental pathologies relevant to patients in the neonatal ICU. New technologies will broaden the applicability of these models to neonatal research and their usefulness as a drug screening platform.

Expanding the neuroimmune research toolkit with in vivo brain organoid technologies

Human pluripotent stem cell-derived microglia-like cells (MLCs) and brain organoid systems have revolutionized the study of neuroimmune interactions, providing new opportunities to model human-specific brain development and disease. Over the past decade, advances in protocol design have improved the fidelity, reproducibility and scalability of MLC and brain organoid generation. Co-culturing of MLCs and brain organoids have enabled direct investigations of human microglial interactions in vitro, although opportunities remain to improve microglial maturation and long-term survival. To address these limitations, innovative xenotransplantation approaches have introduced MLCs, organoids or neuroimmune organoids into the rodent brain, providing a vascularized environment that supports prolonged development and potential behavioral readouts. These expanding in vitro and in vivo toolkits offer complementary strategies to study neuroimmune interactions in health and disease. In this Perspective, we discuss the strengths, limitations and synergies of these models, highlighting important considerations for their future applications.

Modeling forebrain regional development and connectivity by human brain organoids

The forebrain is one of the most important brain structures for modern human existence, which houses the uniquely sophisticated social and cognitive functions that distinguish our species. Therefore, modeling the forebrain development by using human cells is especially critical for our understanding of the intricacies of human development and devising treatments for related diseases. Recent advancements in brain organoid fields have offered unprecedented tools to investigate forebrain development from studies on specific regions to exploring tract formation and connectivity between different regions of the forebrain. In this review, we discuss the developmental biology of the forebrain and diverse methods for modeling its development by using organoids.

Meta-analysis of the make-up and properties of in vitro models of the healthy and diseased blood-brain barrier

In vitro models of the human blood-brain barrier (BBB) are increasingly used to develop therapeutics that can cross the BBB for treating diseases of the central nervous system. Here we report a meta-analysis of the make-up and properties of transwell and microfluidic models of the healthy BBB and of BBBs in glioblastoma, Alzheimer's disease, Parkinson's disease and inflammatory diseases. We found that the type of model, the culture method (static or dynamic), the cell types and cell ratios, and the biomaterials employed as extracellular matrix are all crucial to recapitulate the low permeability and high expression of tight-junction proteins of the BBB, and to obtain high trans-endothelial electrical resistance. Specifically, for models of the healthy BBB, the inclusion of endothelial cells and pericytes as well as physiological shear stresses (~10-20 dyne cm-2) are necessary, and when astrocytes are added, astrocytes or pericytes should outnumber endothelial cells. We expect this meta-analysis to facilitate the design of increasingly physiological models of the BBB.

Engineering organoids as cerebral disease models

Cerebral organoids pioneered in replicating complex brain tissue architectures in vitro, offering a vast potential for human disease modeling. They enable the in vitro study of human physiological and pathophysiological mechanisms of various neurological diseases and disorders. The trajectory of technological advancements in brain organoid generation and engineering over the past decade indicates that the technology might, in the future, mature into indispensable solutions at the horizon of personalized and regenerative medicine. In this review, we highlight recent advances in the engineering of brain organoids as disease models and discuss some of the challenges and opportunities for future research in this rapidly evolving field.

Dietary Flavonoid Chrysin Functions as a Dual Modulator to Attenuate Amyloid-β and Tau Pathology in the Models of Alzheimer's Disease

Growing evidence indicates that healthy diets are associated with a slower progression of Alzheimer's disease (AD). Flavonoids are among the most abundant natural products in diets beneficial to AD, such as the Mediterranean diet. However, the effect and mechanism of these dietary flavonoids on AD remains incompletely understood. Here, we found that a representative dietary natural flavonoid, chrysin (Chr), significantly ameliorated cognitive impairment and AD pathology in APP/PS1 mice. Furthermore, mechanistic studies showed that Chr significantly reduced the levels of amyloid-β (Aβ) and phosphorylated tau (p-tau), along with dual inhibitory activity against β-site amyloid precursor protein cleaving enzyme 1 (BACE1) and glycogen synthase kinase 3β (GSK3β). Moreover, the effect of Chr was further confirmed by EW233, a structural analog of Chr that exhibited an improved pharmacokinetic profile. To further verify the role of Chr and EW233, we utilized our previously established chimeric human cerebral organoid (chCO) model for AD, in which astrogenesis was promoted to mimic the neuron-astrocyte ratio in human brain tissue, and similar dual inhibition of Aβ and p-tau was also observed. Altogether, our study not only reveals the molecular mechanisms through which dietary flavonoids, such as Chr, mitigate AD pathology, but also suggests that identifying a specific constituent that mimics some of the benefits of these healthy diets could serve as a promising approach to discover new treatments for AD.

Emerging Insights into Brain Inflammation: Stem-Cell-Based Approaches for Regenerative Medicine

Neuroinflammation is a complex immune response triggered by brain injury or pathological stimuli, and is highly exacerbated in neurodegenerative diseases. It plays a dual role in the central nervous system, promoting repair in acute stages while aggravating disease progression by contributing to neuronal loss, synaptic dysfunction, and glial dysregulation in chronic phases. Inflammatory responses are mainly orchestrated by microglia and infiltrated monocytes, which, when dysregulated, not only harm existing neurons, but also impair the survival and differentiation of neural stem and progenitor cells in the affected brain regions. Modulating neuroinflammation is crucial for harnessing its protective functions while minimizing its detrimental effects. Current therapeutic strategies focus on fine-tuning inflammatory responses through pharmacological agents, bioactive molecules, and stem cell-based therapies. These approaches aim to restore immune homeostasis, support neuroprotection, and promote regeneration in various neurological disorders. However, animal models sometimes fail to reproduce human-specific inflammatory responses in the brain. In this context, stem-cell-derived models provide a powerful tool to study neuroinflammatory mechanisms in a patient-specific and physiologically relevant context. These models facilitate high-throughput screening, personalized medicine, and the development of targeted therapies while addressing the limitations of traditional animal models, paving the way for more targeted and effective treatments.

Advances in humanoid organoid-based research on inter-organ communications during cardiac organogenesis and cardiovascular diseases

The intimate correlation between cardiovascular diseases and other organ pathologies, such as metabolic and kidney diseases, underscores the intricate interactions among these organs. Understanding inter-organ communications is crucial for developing more precise drugs and effective treatments for systemic diseases. While animal models have traditionally been pivotal in studying these interactions, human-induced pluripotent stem cells (hiPSCs) offer distinct advantages when constructing in vitro models. Beyond the conventional two-dimensional co-culture model, hiPSC-derived humanoid organoids have emerged as a substantial advancement, capable of replicating essential structural and functional attributes of internal organs in vitro. This breakthrough has spurred the development of multilineage organoids, assembloids, and organoids-on-a-chip technologies, which allow for enhanced physiological relevance. These technologies have shown great potential for mimicking coordinated organogenesis, exploring disease pathogenesis, and facilitating drug discovery. As the central organ of the cardiovascular system, the heart serves as the focal point of an extensively studied network of interactions. This review focuses on the advancements and challenges of hiPSC-derived humanoid organoids in studying interactions between the heart and other organs, presenting a comprehensive exploration of this cutting-edge approach in systemic disease research.

Dissecting endothelial cell heterogeneity with new tools

The formation of a blood vessel network is crucial for organ development and regeneration. Over the past three decades, the central molecular mechanisms governing blood vessel growth have been extensively studied. Recent evidence indicates that vascular endothelial cells-the specialized cells lining the inner surface of blood vessels-exhibit significant heterogeneity to meet the specific needs of different organs. This review focuses on the current understanding of endothelial cell heterogeneity, which includes both intra-organ and inter-organ heterogeneity. Intra-organ heterogeneity encompasses arterio-venous and tip-stalk endothelial cell specialization, while inter-organ heterogeneity refers to organ-specific transcriptomic profiles and functions. Advances in single-cell RNA sequencing (scRNA-seq) have enabled the identification of new endothelial subpopulations and the comparison of gene expression patterns across different subsets of endothelial cells. Integrating scRNA-seq with other high-throughput sequencing technologies promises to deepen our understanding of endothelial cell heterogeneity at the epigenetic level and in a spatially resolved context. To further explore human endothelial cell heterogeneity, vascular organoids offer powerful tools for studying gene function in three-dimensional culture systems and for investigating endothelial-tissue interactions using human cells. Developing organ-specific vascular organoids presents unique opportunities to unravel inter-organ endothelial cell heterogeneity and its implications for human disease. Emerging technologies, such as scRNA-seq and vascular organoids, are poised to transform our understanding of endothelial cell heterogeneity and pave the way for innovative therapeutic strategies to address human vascular diseases.

Protocol for generating liver metastasis microtissues to decipher cellular interactions between metastatic intestinal cancer and liver tissue

Cell competition is a quality control mechanism that promotes elimination of suboptimal cells relative to fitter neighbors. Cancer cells exploit these mechanisms for expansion, but the underlying molecular pathways remain elusive. Here, we present a protocol for generating matrix-free microtissues recapitulating cellular interactions between intestinal cancer and hepatocyte-like cells using microscopy or transcriptomics/proteomics. We describe steps for generating and differentiating liver progenitor organoids and microtissue formation. We then detail procedures for immunofluorescence staining, mounting microtissues, and sorting cells. For complete details on the use and execution of this protocol, please refer to Krotenberg Garcia et al.1.

Evolution of organoid genetics

Organoids have revolutionized in vitro research by offering three-dimensional, multicellular systems that recapitulate the structure, function, and genetics of human tissues. Initially developed from both pluripotent stem cells (PSCs) and adult stem cells (AdSCs), organoids have expanded to model nearly every major human organ, significantly advancing developmental biology, disease modeling, and therapeutic screening. This review highlights the progression of organoid technologies, emphasizing the integration of genetic tools, including CRISPR-Cas9, prime editing, and lineage tracing. These advancements have facilitated precise modeling of human-specific pathologies and drug responses, often surpassing traditional 2D cultures and animal models in accuracy. Emerging technologies, such as organoid fusion, xenografting, and optogenetics, are expected to further enhance our understanding of cellular interactions and microenvironmental dynamics. As organoid complexity and genetic engineering methods continue to evolve, they will become increasingly indispensable for personalized medicine and translational research, bridging gaps between in vitro and in vivo systems.

Novel co-culture model of T cells and midbrain organoids for investigating neurodegeneration in Parkinson's disease

Recent studies demonstrate that brain infiltration of peripheral immune cells and their interaction with brain-resident cells contribute to Parkinson's disease (PD). However, mechanisms of T cell-brain cell communication are not fully elucidated and models allowing investigation of interaction between T cells and brain-resident cells are required. In this study, we developed a three-dimensional (3D) model composed of stem cell-derived human midbrain organoids (hMO) and peripheral blood T cells. We demonstrated that organoids consist of multiple midbrain-specific cell types, allowing to study T cell motility and interactions with midbrain tissue in a spatially organized microenvironment. We optimized co-culture conditions and demonstrated that T cells infiltrate hMO tissue, leading to neural cell loss. Our work establishes a novel 3D cell co-culture model as a promising tool to investigate the effect of the adaptive immune system on the midbrain and can be used in future studies to address these processes in the context of PD.

Age-Related Neurodegenerative Diseases: A Stem Cell's Perspective

Neurodegenerative diseases encompass a number of very heterogeneous disorders, primarily characterized by neuronal loss and a concomitant decline in neurological function. Examples of this type of clinical condition are Alzheimer's Disease, Parkinson's Disease, Huntington's Disease and Amyotrophic Lateral Sclerosis. Age has been identified as a major risk in the etiology of these disorders, which explains their increased incidence in developed countries. Unfortunately, despite continued and intensive efforts, no cure has yet been found for any of these diseases; reliable markers that allow for an early diagnosis of the disease and the identification of key molecular events leading to disease onset and progression are lacking. Altered adult neurogenesis appears to precede the appearance of severe symptoms. Given the scarcity of human samples and the considerable differences with model species, increasingly complex human stem-cell-based models are being developed. These are shedding light on the molecular alterations that contribute to disease development, facilitating the identification of new clinical targets and providing a screening platform for the testing of candidate drugs. Moreover, the secretome and other promising features of these cell types are being explored, to use them as replacement cells of high plasticity or as co-adjuvant therapy in combinatorial treatments.

Application progress of bio-manufacturing technology in kidney organoids

Kidney transplantation remains a pivotal treatment modality for kidney disease, yet its progress is significantly hindered by the scarcity of donor kidneys and ethical dilemmas surrounding their procurement. As organoid technology evolves and matures, the creation of bionic human kidney organoids offers profound potential for advancing kidney disease research, drug nephrotoxicity screening, and regenerative medicine. Nevertheless, current kidney organoid models grapple with limitations such as constrained cellular differentiation, underdeveloped functional structures, and a crucial absence of vascularization. This deficiency in vascularization, in particular, stunts organoid development, restricts their size, diminishes filtration capabilities, and may trigger immune inflammatory reactions through the resulting ischemic microenvironment. Hence, the achievement of vascularization within kidney organoids and the successful establishment of functional microvascular networks constitutes a paramount goal for their future progression. In this review, we provide an overview of recent advancements in biotechnology domains, encompassing organ-on-a-chip technology, biomimetic matrices, and bioprinting, with the aim of catalyzing technological breakthroughs that can enhance the vascularization of kidney organoids and broaden their applicability. These technologies hold the key to unlocking the full potential of kidney organoids as a transformative therapeutic option for kidney disease.

Retina-on-chip: engineering functional in vitro models of the human retina using organ-on-chip technology

The retina is a complex and highly metabolic tissue in the back of the eye essential for human vision. Retinal diseases can lead to loss of vision in early and late stages of life, significantly affecting patients' quality of life. Due to its accessibility for surgical interventions and its isolated nature, the retina is an attractive target for novel genetic therapies and stem cell-based regenerative medicine. Understanding disease mechanisms and evaluating new treatments require relevant and robust experimental models. Retina-on-chip models are microfluidic organ-on-chip systems based on human tissue that capture multi-cellular interactions and tissue-level functions in vitro. Various retina-on-chip models have been described in literature. Some of them capture basic retinal barrier functions while others replicate key events underlying vision. In addition, some of these cellular systems have also been used in studies to explore their added value in retinal disease modeling. Most existing retina-on-chip models capture limited aspects of the phenotypic complexity of human diseases. This limitation arises primarily from the challenges related to controlled recapitulation of retinal function, including the relevant multi-cellular interactions and functional read-outs. In this review, we provide an update on recent advancements in the field of retina-on-chip, and we discuss the biotechnical strategies to further enhance the physiological relevance of the models. We emphasize that developers and researchers should prioritize the incorporation of the full spectrum of retinal complexity to effectuate a direct impact of retina-on-chip models in disease modeling and development of therapeutic strategies.

Understanding monocyte-driven neuroinflammation in Alzheimer's disease using human brain organoid microphysiological systems

Increasing evidence suggests that Alzheimer's disease (AD) pathogenesis strongly correlates with neuroinflammation. Peripheral monocytes are crucial components of the human immune system that may play a role in neuroinflammation, but their contribution to AD pathogenesis is largely understudied partially due to the lack of appropriate human models. Here, we present human cortical organoid microphysiological systems (hCO-MPSs) for modeling dynamic AD neuroinflammation mediated by monocytes. By incorporating 3D printed devices into an existing cortical organoid protocol, 96 hCO-MPSs can be established with significantly reduced necrosis and hypoxia as well as enhanced viability within a commonly used 96 well plate, and each hCO-MPS consists of a doughnut-shaped hCO and a 3D printed device per well. Using this approach, monocytes from AD patients exhibit higher infiltration, decreased amyloid-beta (Aβ) clearance, and stronger inflammatory responses compared to monocytes from age-matched control donors. Moreover, pro-inflammatory effects such as elevated astrocyte activation and neuronal apoptosis were observed to be induced by AD monocytes. Furthermore, the significant increase in the expression of IL1B and CCL3, both at the transcriptional and protein levels, indicated the pivotal role of these cytokine and chemokine in monocyte-mediated AD neuroinflammation. Our findings provide insight for understanding monocytes' role in AD pathogenesis, and the user-friendly MPS models we present are compatible with existing laboratory settings, highlighting their potential for modeling neuroinflammation and developing new therapeutics for various neuroinflammatory diseases.

Purified adipose tissue-derived extracellular vesicles facilitate adipose organoid vascularization through coordinating adipogenesis and angiogenesis

One of the major challenges in the way of better fabricating vascularized adipose organoids is the destructive effect of adipogenic differentiation on preformed vasculature, which probably stems from the discrepancy between thein vivophysiological microenvironment and thein vitroculture conditions. As an intrinsic component of adipose tissue (AT), adipose tissue-derived extracellular vesicles (AT-EVs) have demonstrated both adipogenic and angiogenic ability in recent studies. However, whether AT-EVs could be employed to coordinate the angiogenesis and adipogenesis in the vascularization of adipose organoids remains largely unexplored. Herein, we present an efficient method for isolating higher-purity AT-EV preparations from lipoaspirates, and verify the superiority of AT-EV preparations' angiogenic and adipogenic capabilities over those from unpurified lipoaspirates. Next, in the spheroid culture model, it was discovered that the addition of AT-EVs could effectively improve the aggregation through enhancing intercellular adhesion of monoculture spheroids composed of human umbilical vascular endothelial cells (HUVECs), and helped produce vascularized adipose organoids with proper lipolysis and glucose uptake ability in the coculture spheroids comprised of adipose-derived stem cells (ADSCs) and HUVECs. Subsequently, it was observed that AT-EVs could exert a retaining effect on the vasculature of prevascularized coculture spheroids cultured in an adipogenic environment, compared to the reduced vascular networks where AT-EVs were absent. Altogether, these results indicate that AT-EVs, by means of releasing bioactive molecules that emulate thein vivomicroenvironment, can modify non-replicativein vitromicroenvironments, coordinatein vitroadipogenesis and angiogenesis, and facilitate the fabrication of vascularized adipose organoids.

A multiphysics hybrid continuum - agent-based model of in vitro vascularized organoids

BACKGROUND

Organoids are 3D in vitro models that fulfill a hierarchical function, representing a small version of living tissues and, therefore, a good approximation of cellular mechanisms. However, one of the main disadvantages of these models is the appearance of a necrotic core due to poor vascularization. The aim of this work is the development of a numerical framework that incorporates the mechanical stimulation as a key factor in organoid vascularization. Parameters, such as fluid velocity and nutrient consumption, are analyzed along the organoid evolution.

METHODS

The mathematical model created for this purpose combines continuum and discrete approaches. In the continuum part, the fluid flow and the diffusion of oxygen and nutrients are modeled using a finite element method approach. Meanwhile, the growth of the organoid, blood vessel evolution, as well as their interaction with the surrounding environment, are modeled using agent-based methods.

RESULTS

Continuum model outcomes include the distribution of shear stress, pressure and fluid velocity around the organoid surface, in addition to the concentration of oxygen and nutrients in its interior. The agent models account for cell proliferation, differentiation, organoid growth and blood vessel morphology, for the different case studies considered.

CONCLUSIONS

Two main conclusions are achieved in this work: (i) the results of the study quantitatively predict in vitro data, with an enhanced blood vessel invasion under high fluid flow and (ii) the diffusion and consumption model parameters of the organoid cells determine the thickness of the proliferative, quiescent, hypoxic and necrotic layers.

Vascularization of human islets by adaptable endothelium for durable and functional subcutaneous engraftment

Tissue-specific endothelial cells (ECs) are critical for the homeostasis of pancreatic islets and most other tissues. In vitro recapitulation of islet biology and therapeutic islet transplantation both require adequate vascularization, which remains a challenge. Using human reprogrammed vascular ECs (R-VECs), human islets were functionally vascularized in vitro, demonstrating responsive, dynamic glucose-stimulated insulin secretion and Ca2+ influx. Subcutaneous transplantation of islets with R-VECs reversed hyperglycemia in diabetic mice, with high levels of human insulin detected within recipient serum and relapses of hyperglycemia following graft removal. Examination of retrieved grafts demonstrated that engrafted human islets were mainly vascularized by the cotransplanted R-VECs, which had anastomosed with the host microcirculation. Notably, single-cell RNA-sequencing revealed that R-VECs, when cocultured with islets, acquired islet EC-specific characteristics. Together, R-VECs establish an adaptable vascular niche that supports islet homeostasis both in vitro and in vivo.

Emerging approaches to enhance human brain organoid physiology

Brain organoids are important 3D models for studying human brain development, disease, and evolution. To overcome some of the existing limitations that affect organoid quality, reproducibility, characteristics, and in vivo resemblance, current efforts are directed to improve their physiological relevance by exploring different, yet interconnected, routes. In this review, these approaches and their latest developments are discussed, including stem cell optimization, refining morphogen administration strategies, altering the extracellular matrix (ECM) niche, and manipulating tissue architecture to mimic in vivo brain morphogenesis. Additionally, strategies to increase cell diversity and enhance organoid maturation, such as establishing co-cultures, assembloids, and organoid in vivo xenotransplantation, are reviewed. We explore how these various factors can be tuned and intermingled and speculate on future avenues towards even more physiologically-advanced brain organoids.

Engineering the 3D structure of organoids

Organoids form through the sel f-organizing capabilities of stem cells to produce a variety of differentiated cell and tissue types. Most organoid models, however, are limited in terms of the structure and function of the tissues that form, in part because it is difficult to regulate the cell type, arrangement, and cell-cell/cell-matrix interactions within these systems. In this article, we will discuss the engineering approaches to generate more complex organoids with improved function and translational relevance, as well as their advantages and disadvantages. Additionally, we will explore how biofabrication strategies can manipulate the cell composition, 3D organization, and scale-up of organoids, thus improving their utility for disease modeling, drug screening, and regenerative medicine applications.

Two- and Three-Dimensional In Vitro Models of Parkinson's and Alzheimer's Diseases: State-of-the-Art and Applications

In vitro models play a pivotal role in advancing our understanding of neurodegenerative diseases (NDs) such as Parkinson's and Alzheimer's disease (PD and AD). Traditionally, 2D cell cultures have been instrumental in elucidating the cellular mechanisms underlying these diseases. Cultured cells derived from patients or animal models provide valuable insights into the pathological processes at the cellular level. However, they often lack the native tissue environment complexity, limiting their ability to fully recapitulate their features. In contrast, 3D models offer a more physiologically relevant platform by mimicking the 3D brain tissue architecture. These models can incorporate multiple cell types, including neurons, astrocytes, and microglia, creating a microenvironment that closely resembles the brain's complexity. Bioengineering approaches allow researchers to better replicate cell-cell interactions, neuronal connectivity, and disease-related phenotypes. Both 2D and 3D models have their advantages and limitations. While 2D cultures provide simplicity and scalability for high-throughput screening and basic processes, 3D models offer enhanced physiological relevance and better replicate disease phenotypes. Integrating findings from both model systems can provide a better understanding of NDs, ultimately aiding in the development of novel therapeutic strategies. Here, we review existing 2D and 3D in vitro models for the study of PD and AD.

Establishment of nasal and olfactory epithelium organoids for unveiling mechanism of tissue regeneration and pathogenesis of nasal diseases

Organoid is an ideal in vitro model with cellular heterogeneity and genetic stability when passaging. Currently, organoids are exploited as new tools in a variety of preclinical researches and applications for disease modeling, drug screening, host-microbial interactions, and regenerative therapy. Advances have been made in the establishment of nasal and olfactory epithelium organoids that are used to investigate the pathogenesis of smell-related diseases and cellular/molecular mechanism underlying the regeneration of olfactory epithelium. A set of critical genes are identified to function in cell proliferation and neuronal differentiation in olfactory epithelium organoids. Besides, nasal epithelium organoids derived from chronic rhinosinusitis patients have been established to reveal the pathogenesis of this disease, potentially applied in drug responses in individual patient. The present article reviews recent research progresses of nasal and olfactory epithelium organoids in fundamental and preclinical researches, and proposes current advances and potential future direction in the field of organoid research and application.

Generation of self-organized neuromusculoskeletal tri-tissue organoids from human pluripotent stem cells

The human body function requires crosstalk between different tissues. An essential crosstalk is in the neuromusculoskeletal (NMS) axis involving neural, muscular, and skeletal tissues, which is challenging to model using human cells. Here, we describe the generation of three-dimensional, NMS tri-tissue organoids (hNMSOs) from human pluripotent stem cells through a co-development strategy. Staining, single-nucleus RNA sequencing, and spatial transcriptome profiling revealed the co-emergence and self-organization of neural, muscular, and skeletal lineages within individual organoids, and the neural domains of hNMSOs obtained a ventral-specific identity and produced motor neurons innervating skeletal muscles. The neural, muscular, and skeletal regions of hNMSOs exhibited maturation and established functional connections during development. Notably, structural, functional, and transcriptomic analyses revealed that skeletal support in hNMSOs benefited human muscular development. Modeling with hNMSOs also unveiled the neuromuscular alterations following pathological skeletal degeneration. Together, our study provides an accessible experimental model for future studies of human NMS crosstalk and abnormality.