Human Pluripotent Stem Cell-Derived Organoids as Models of Liver Disease

Human liver organoids: From generation to applications

In the last decade, research into human hepatology has been revolutionized by the development of mini human livers in a dish. These liver organoids are formed by self-organizing stem cells and resemble their native counterparts in cellular content, multicellular architecture, and functional features. Liver organoids can be derived from the liver tissue or pluripotent stem cells generated from a skin biopsy, blood cells, or renal epithelial cells present in urine. With the development of liver organoids, a large part of previous hurdles in modeling the human liver is likely to be solved, enabling possibilities to better model liver disease, improve (personalized) drug testing, and advance bioengineering options. In this review, we address strategies to generate and use organoids in human liver disease modeling, followed by a discussion of their potential application in drug development and therapeutics, as well as their strengths and limitations.

Establishment of human induced pluripotent stem cell-derived hepatobiliary organoid with bile duct for pharmaceutical research use

In vitro models of the human liver are promising alternatives to animal tests for drug development. Currently, primary human hepatocytes (PHHs) are preferred for pharmacokinetic and cytotoxicity tests. However, they are unable to recapitulate the flow of bile in hepatobiliary clearance owing to the lack of bile ducts, leading to the limitation of bile analysis. To address the issue, a liver organoid culture system that has a functional bile duct network is desired. In this study, we aimed to generate human iPSC-derived hepatobiliary organoids (hHBOs) consisting of hepatocytes and bile ducts. The two-step differentiation process under 2D and semi-3D culture conditions promoted the maturation of hHBOs on culture plates, in which hepatocyte clusters were covered with monolayered biliary tubes. We demonstrated that the hHBOs reproduced the flow of bile containing a fluorescent bile acid analog or medicinal drugs from hepatocytes into bile ducts via bile canaliculi. Furthermore, the hHBOs exhibited pathophysiological responses to troglitazone, such as cholestasis and cytotoxicity. Because the hHBOs can recapitulate the function of bile ducts in hepatobiliary clearance, they are suitable as a liver disease model and would be a novel in vitro platform system for pharmaceutical research use.

Validating Well-Functioning Hepatic Organoids for Toxicity Evaluation

"Organoids", three-dimensional self-organized organ-like miniature tissues, are proposed as intermediary models that bridge the gap between animal and human studies in drug development. Despite recent advancements in organoid model development, studies on toxicity using these models are limited. Therefore, in this study, we aimed to analyze the functionality and gene expression of pre- and post-differentiated human hepatic organoids derived from induced pluripotent stem cells and utilize them for toxicity assessment. First, we confirmed the functional similarity of this hepatic organoid model to the human liver through various functional assessments, such as glycogen storage, albumin and bile acid secretion, and cytochrome P450 (CYP) activity. Subsequently, utilizing these functionally validated hepatic organoids, we conducted toxicity evaluations with three hepatotoxic substances (ketoconazole, troglitazone, and tolcapone), which are well known for causing drug-induced liver injury, and three non-hepatotoxic substances (sucrose, ascorbic acid, and biotin). The organoids effectively distinguished between the toxicity levels of substances with and without hepatic toxicity. We demonstrated the potential of hepatic organoids with validated functionalities and genetic characteristics as promising models for toxicity evaluation by analyzing toxicological changes occurring in hepatoxic drug-treated organoids.

Organoid-guided precision hepatology for metabolic liver disease

Metabolic dysfunction-associated steatotic liver disease affects millions of people worldwide. Progress towards a definitive cure has been incremental and treatment is currently limited to lifestyle modification. Hepatocyte-specific lipid accumulation is the main trigger of lipotoxic events, driving inflammation and fibrosis. The underlying pathology is extraordinarily heterogenous, and the manifestations of steatohepatitis are markedly influenced by metabolic communications across non-hepatic organs. Synthetic human tissue models have emerged as powerful platforms to better capture the mechanistic diversity in disease progression, while preserving person-specific genetic traits. In this review, we will outline current research efforts focused on integrating multiple synthetic tissue models of key metabolic organs, with an emphasis on organoid-based systems. By combining functional genomics and population-scale en masse profiling methodologies, human tissues derived from patients can provide insights into personalised genetic, transcriptional, biochemical, and metabolic states. These collective efforts will advance our understanding of steatohepatitis and guide the development of rational solutions for mechanism-directed diagnostic and therapeutic investigation.

3D Printing of a Vascularized Mini-Liver Based on the Size-Dependent Functional Enhancements of Cell Spheroids for Rescue of Liver Failure

The emerging stem cell-derived hepatocyte-like cells (HLCs) are the alternative cell sources of hepatocytes for treatment of highly lethal acute liver failure (ALF). However, the hostile local environment and the immature cell differentiation may compromise their therapeutic efficacy. To this end, human adipose-derived mesenchymal stromal/stem cells (hASCs) are engineered into different-sized multicellular spheroids and co-cultured with 3D coaxially and hexagonally patterned human umbilical vein endothelial cells (HUVECs) in a liver lobule-like manner to enhance their hepatic differentiation efficiency. It is found that small-sized hASC spheroids, with a diameter of ≈50 µm, show superior pro-angiogenic effects and hepatic differentiation compared to the other counterparts. The size-dependent functional enhancements are mediated by the Wnt signaling pathway. Meanwhile, co-culture of hASCs with HUVECs, at a HUVECs/hASCs seeding density ratio of 2:1, distinctly promotes hepatic differentiation and vascularization both in vitro and in vivo, especially when endothelial cells are patterned into hollow hexagons. After subcutaneous implantation, the mini-liver, consisting of HLC spheroids and 3D-printed interconnected vasculatures, can effectively improve liver regeneration in two ALF animal models through amelioration of local oxidative stress and inflammation, reduction of liver necrosis, as well as increase of cell proliferation, thereby showing great promise for clinical translation.

Molecular insights into experimental models and therapeutics for cholestasis

Cholestatic liver disease (CLD) is a range of conditions caused by the accumulation of bile acids (BAs) or disruptions in bile flow, which can harm the liver and bile ducts. To investigate its pathogenesis and treatment, it is essential to establish and assess experimental models of cholestasis, which have significant clinical value. However, owing to the complex pathogenesis of cholestasis, a single modelling method can merely reflect one or a few pathological mechanisms, and each method has its adaptability and limitations. We summarize the existing experimental models of cholestasis, including animal models, gene-knockout models, cell models, and organoid models. We also describe the main types of cholestatic disease simulated clinically. This review provides an overview of targeted therapy used for treating cholestasis based on the current research status of cholestasis models. In addition, we discuss the respective advantages and disadvantages of different models of cholestasis to help establish experimental models that resemble clinical disease conditions. In sum, this review not only outlines the current research with cholestasis models but also projects prospects for clinical treatment, thereby bridging basic research and practical therapeutic applications.

Cyclic Stretching Enhances Angiocrine Signals at Liver Bud Stage from Human Pluripotent Stem Cells in Two-Dimensional Culture

Angiocrine signals during the development and growth of organs, including the liver, intestine, lung, and bone, are essential components of intercellular communication. The signals elicited during the liver bud stage are critical for vascularization and enhanced during the intercellular communication between the cells negative for kinase insert domain receptor (KDR) (KDR- cells) and the cells positive for KDR (KDR+ cells), which constitute the liver bud. However, the use of a human pluripotent stem cell (hPSC)-derived system has not facilitated the generation of a perfusable vascularized liver organoid that allows elucidation of liver development and has great potential for liver transplantation. This is largely owing to the lack of fundamental understanding to induce angiocrine signals in KDR- and KDR+ cells during the liver bud stage. We hypothesized that mechanical stimuli of cyclic stretching/pushing by the fetal heart adjacent to the liver bud could be the main contributor to promoting angiocrine signals in KDR- and KDR+ cells during the liver bud stage. In this study, we show that an organ-on-a-chip platform allows the emulation of an in vivo-like mechanical environment for the liver bud stage in vitro and investigate the role of cyclic mechanical stretching (cMS) to angiocrine signals in KDR- and KDR+ cells derived from hPSCs. RNA sequencing revealed that the expression of genes associated with epithelial-to-mesenchymal transition, including angiocrine signals, such as hepatocyte growth factor (HGF) and matrix metallopeptidase 9 (MMP9), were increased by cMS in cocultured KDR- and KDR+ cells. The expression and secretions of HGF and MMP9 were increased by 1.98- and 1.69-fold and 3.23- and 3.72-fold with cMS in the cocultured KDR- and KDR+ cells but were not increased by cMS in the monocultured KDR- and KDR+ cells, respectively. Finally, cMS during the liver bud stage did not lead to the dedifferentiation of hepatocytes, as the cells with cMS showed hepatic maker expression (CYP3A4, CYP3A7, ALB, and AAT) and 1.71-fold higher CYP3A activity than the cells without cMS, during 12 day-hepatocyte maturation after halting cMS. Our findings provide new insights into the mechanical factors during the liver bud stage and directions for future improvements in the engineered liver tissue.

Wnt/β-catenin signaling pathway in liver biology and tumorigenesis

The Wnt/β-catenin pathway is an evolutionarily conserved signaling pathway that controls fundamental physiological and pathological processes by regulating cell proliferation and differentiation. The Wnt/β-catenin pathway enables liver homeostasis by inducing differentiation and contributes to liver-specific features such as metabolic zonation and regeneration. In contrast, abnormalities in the Wnt/β-catenin pathway promote the development and progression of hepatocellular carcinoma (HCC). Similarly, hepatoblastoma, the most common childhood liver cancer, is frequently associated with β-catenin mutations, which activate Wnt/β-catenin signaling. HCCs with activation of the Wnt/β-catenin pathway have unique gene expression patterns and pathological and clinical features. Accordingly, they are highly differentiated with retaining hepatocyte-like characteristics and tumorigenic. Activation of the Wnt/β-catenin pathway in HCC also alters the state of immune cells, causing "immune evasion" with inducing resistance to immune checkpoint inhibitors, which have recently become widely used to treat HCC. Activated Wnt/β-catenin signaling exhibits these phenomena in liver tumorigenesis through the expression of downstream target genes, and the molecular basis is still poorly understood. In this review, we describe the physiological roles of Wnt/b-catenin signaling and then discuss their characteristic changes by the abnormal activation of Wnt/b-catenin signaling. Clarification of the mechanism would contribute to the development of therapeutic agents in the future.

3D culture models to study pathophysiology of steatotic liver disease

Steatotic liver disease (SLD) refers to a spectrum of diseases caused by hepatic lipid accumulation. SLD has emerged as the leading cause of chronic liver disease worldwide. Despite this burden and many years, understanding the pathophysiology of this disease is challenging due to the inaccessibility to human liver specimens. Therefore, cell-based in vitro systems are widely used as models to investigate the pathophysiology of SLD. Culturing hepatic cells in monolayers causes the loss of their hepatocyte-specific phenotype and, consequently, tissue-specific function and architecture. Hence, three-dimensional (3D) culture models allow cells to mimic the in vivo microenvironment and spatial organization of the liver unit. The utilization of 3D in vitro models minimizes the drawbacks of two-dimensional (2D) cultures and aligns with the 3Rs principles to alleviate the number of in vivo experiments. This article provides an overview of liver 3D models highlighting advantages and limitations, and culminates by discussing their applications in pharmaceutical and biomedical research.

Bioengineered Organoids Offer New Possibilities for Liver Cancer Studies: A Review of Key Milestones and Challenges

Hepatic cancer is widely regarded as the leading cause of cancer-related mortality worldwide. Despite recent advances in treatment options, the prognosis of liver cancer remains poor. Therefore, there is an urgent need to develop more representative in vitro models of liver cancer for pathophysiology and drug screening studies. Fortunately, an exciting new development for generating liver models in recent years has been the advent of organoid technology. Organoid models hold huge potential as an in vitro research tool because they can recapitulate the spatial architecture of primary liver cancers and maintain the molecular and functional variations of the native tissue counterparts during long-term culture in vitro. This review provides a comprehensive overview and discussion of the establishment and application of liver organoid models in vitro. Bioengineering strategies used to construct organoid models are also discussed. In addition, the clinical potential and other relevant applications of liver organoid models in different functional states are explored. In the end, this review discusses current limitations and future prospects to encourage further development.

Comparative transcriptomic and phenotypic analysis of induced pluripotent stem cell hepatocyte-like cells and primary human hepatocytes

Primary human hepatocytes (PHHs) are used extensively for in vitro liver cultures to study hepatic functions. However, limited availability and invasive retrieval prevent their widespread use. Induced pluripotent stem cells exhibit significant potential since they can be obtained non-invasively and differentiated into hepatic lineages, such as hepatocyte-like cells (iHLCs). However, there are concerns about their fetal phenotypic characteristics and their hepatic functions compared to PHHs in culture. Therefore, we performed an RNA-sequencing (RNA-seq) analysis to understand pathways that are either up- or downregulated in each cell type. Analysis of the RNA-seq data showed an upregulation in the bile secretion pathway where genes such as AQP9 and UGT1A1 were higher expressed in PHHs compared to iHLCs by 455- and 15-fold, respectively. Upon immunostaining, bile canaliculi were shown to be present in PHHs. The TCA cycle in PHHs was upregulated compared to iHLCs. Cellular analysis showed a 2-2.5-fold increase in normalized urea production in PHHs compared to iHLCs. In addition, drug metabolism pathways, including cytochrome P450 (CYP450) and UDP-glucuronosyltransferase enzymes, were upregulated in PHHs compared to iHLCs. Of note, CYP2E1 gene expression was significantly higher (21,810-fold) in PHHs. Acetaminophen and ethanol were administered to PHH and iHLC cultures to investigate differences in biotransformation. CYP450 activity of baseline and toxicant-treated samples was significantly higher in PHHs compared to iHLCs. Our analysis revealed that iHLCs have substantial differences from PHHs in critical hepatic functions. These results have highlighted the differences in gene expression and hepatic functions between PHHs and iHLCs to motivate future investigation.

Regenerative human liver organoids (HLOs) in a pillar/perfusion plate for hepatotoxicity assays

Human liver organoids (HLOs) differentiated from embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and adult stem cells (ASCs) can recapitulate structure and function of human fetal liver tissues, thus, considered as a promising tissue model for liver diseases and predictive compound screening. Nonetheless, there are still several technical challenges to adopt HLOs in the drug discovery process, which include relatively long-term cell differentiation with multiple culture media (3 - 4 weeks) leading to batch-to-batch variation, short-term hepatic function after maturation (3 - 5 days), low assay throughput due to Matrigel dissociation and HLO transfer to a microtiter well plate, and insufficient maturity as compared to primary hepatocytes. To address these issues, expandable HLOs (Exp-HLOs) derived from human iPSCs were generated by optimizing differentiation protocols, which were rapidly printed on a 144-pillar plate with sidewalls and slits (144PillarPlate) and dynamically cultured for up to 20 days into differentiated HLOs (Diff-HLOs) in a 144-perfusion plate with perfusion wells and reservoirs (144PerfusionPlate) for in situ organoid culture and analysis. Dynamically cultured Diff-HLOs were generated robustly and reproducibly in the pillar/perfusion plate with higher maturity as compared to those in statically cultured HLOs by differentiating Exp-HLOs for 10 days. In addition, Diff-HLOs in the pillar/perfusion plate were tested with acetaminophen and troglitazone for 3 days to assess drug-induced liver injury (DILI) and then incubated in an expansion medium for 10 days to evaluate the recovery of the liver from DILI. The assessment of liver regeneration post injury is critical to understand the mechanism of recovery and determine the threshold drug concentration beyond which there will be a sharp decrease in the liver's regenerative capacity. We envision that bioprinted Diff-HLOs in the pillar/perfusion plate could be used for high-throughput screening (HTS) of hepatotoxic compounds due to short-term differentiation of passage-able Exp-HLOs necessary, stable hepatic function after maturation, high reproducibility, and high throughput with capability of in situ organoid culture, testing, staining, imaging, and analysis.

Liver organoids and their application in liver cancer research

Liver cancer, a common and intractable liver-related disease, is a malignant tumor with a high morbidity, which needs a high treatment cost but still lacks perfect clinical treatment methods. Looking for an effective platform for liver cancer study and drug screening is urgent and important. Traditional analytical methods for liver disease studies mainly rely on the 2D cell culture and animal experiments, which both cannot fully recapitulate physiological and pathological processes of human liver. For example, cell culture can only show basic functions of cells in vitro, while animal models always hold the problem of species divergence. The organoids, a 3D invitro culture system emerged in recent years, is a cell-bound body with different cell types and has partial tissue functions. The organoid technology can reveal the growth state, structure, function and characteristics of the tissue or organ, and plays an important role in reconstructing invitro experimental models that can truly simulate the human liver. In this paper, we will give a brief introduction of liver organoids and review their applications in liver cancer research, especially in liver cancer pathogenesis, drug screening, precision medicine, regenerative medicine, and other fields. We have also discussed advantages and disadvantages of organoids, as well as future directions and perspectives towards liver organoids.

Models for calcific aortic valve disease in vivo and in vitro

Calcific Aortic Valve Disease (CAVD) is prevalent among the elderly as the most common valvular heart disease. Currently, no pharmaceutical interventions can effectively reverse or prevent CAVD, making valve replacement the primary therapeutic recourse. Extensive research spanning decades has contributed to the establishment of animal and in vitro cell models, which facilitates a deeper understanding of the pathophysiological progression and underlying mechanisms of CAVD. In this review, we provide a comprehensive summary and analysis of the strengths and limitations associated with commonly employed models for the study of valve calcification. We specifically emphasize the advancements in three-dimensional culture technologies, which replicate the structural complexity of the valve. Furthermore, we delve into prospective recommendations for advancing in vivo and in vitro model studies of CAVD.

The application of organoid models in research into metabolic diseases

Metabolic diseases have become a major threat to human health worldwide as a result of changing lifestyles. The exploration of the underlying molecular mechanisms of metabolic diseases and the development of improved therapeutic methods have been hindered by the lack of appropriate human experimental models. Organoids are three-dimensional in vitro models of self-renewing cells that spontaneously self-organize into structures similar to the corresponding in vivo tissues, recapitulating the original tissue function. Off-body organoid technology has been successfully applied to disease modelling, developmental biology, regenerative medicine, and tumour precision medicine. This new generation of biological models has received widespread attention. This article focuses on the construction process and research progress with regard to organoids related to metabolic diseases in recent years, and looks forward to their prospective applications.

Using Liver Organoids as Models to Study the Pathobiology of Rare Liver Diseases

Liver organoids take advantage of several important features of pluripotent stem cells that self-assemble in a three-dimensional culture matrix and reproduce many aspects of the complex organization found within their native tissue or organ counterparts. Compared to other 2D or 3D in vitro models, organoids are widely believed to be genetically stable or docile structures that can be programmed to virtually recapitulate certain biological, physiological, or pathophysiological features of original tissues or organs in vitro. Therefore, organoids can be exploited as effective substitutes or miniaturized models for the study of the developmental mechanisms of rare liver diseases, drug discovery, the accurate evaluation of personalized drug responses, and regenerative medicine applications. However, the bioengineering of organoids currently faces many groundbreaking challenges, including a need for a reasonable tissue size, structured organization, vascularization, functional maturity, and reproducibility. In this review, we outlined basic methodologies and supplements to establish organoids and summarized recent technological advances for experimental liver biology. Finally, we discussed the therapeutic applications and current limitations.

The Long Road to Develop Custom-built Livers: Current Status of 3D Liver Bioprinting

Although liver transplantation is the gold-standard therapy for end-stage liver disease, the shortage of suitable organs results in only 25% of waitlisted patients undergoing transplants. Three-dimensional (3D) bioprinting is an emerging technology and a potential solution for personalized medicine applications. This review highlights existing 3D bioprinting technologies of liver tissues, current anatomical and physiological limitations to 3D bioprinting of a whole liver, and recent progress bringing this innovation closer to clinical use. We reviewed updated literature across multiple facets in 3D bioprinting, comparing laser, inkjet, and extrusion-based printing modalities, scaffolded versus scaffold-free systems, development of an oxygenated bioreactor, and challenges in establishing long-term viability of hepatic parenchyma and incorporating structurally and functionally robust vasculature and biliary systems. Advancements in liver organoid models have also increased their complexity and utility for liver disease modeling, pharmacologic testing, and regenerative medicine. Recent developments in 3D bioprinting techniques have improved the speed, anatomical, and physiological accuracy, and viability of 3D-bioprinted liver tissues. Optimization focusing on 3D bioprinting of the vascular system and bile duct has improved both the structural and functional accuracy of these models, which will be critical in the successful expansion of 3D-bioprinted liver tissues toward transplantable organs. With further dedicated research, patients with end-stage liver disease may soon be recipients of customized 3D-bioprinted livers, reducing or eliminating the need for immunosuppressive regimens.

3D hepatic organoid production from human pluripotent stem cells

Hepatic organoids might provide a golden opportunity for realizing precision medicine in various hepatic diseases. Previously described hepatic organoid protocols from pluripotent stem cells rely on complicated multiple differentiation steps consisting of both 2D and 3D differentiation procedures. Therefore, the spontaneous formation of hepatic organoids from 2D monolayer culture is associated with a low-throughput production, which might hinder the standardization of hepatic organoid production and hamper the translation of this technology to the clinical or industrial setting. Here we describe the stepwise and fully 3D production of hepatic organoids from human pluripotent stem cells. We optimized every differentiation step by screening for optimal concentrations and timing of differentiation signals in each differentiation step. Hepatic organoids are stably expandable without losing their hepatic functionality. Moreover, upon treatment of drugs with known hepatotoxicity, we found hepatic organoids are more sensitive to drug-induced hepatotoxicity compared with 2D hepatocytes differentiated from PSCs, making them highly suitable for in vitro toxicity screening of drug candidates. The standardized fully 3D protocol described in the current study for producing functional hepatic organoids might serve as a novel platform for the industrial and clinical translation of hepatic organoid technology.

The Material World of 3D-Bioprinted and Microfluidic-Chip Models of Human Liver Fibrosis

Biomaterials are extensively used to mimic cell-matrix interactions, which are essential for cell growth, function, and differentiation. This is particularly relevant when developing in vitro disease models of organs rich in extracellular matrix, like the liver. Liver disease involves a chronic wound-healing response with formation of scar tissue known as fibrosis. At early stages, liver disease can be reverted, but as disease progresses, reversion is no longer possible, and there is no cure. Research for new therapies is hampered by the lack of adequate models that replicate the mechanical properties and biochemical stimuli present in the fibrotic liver. Fibrosis is associated with changes in the composition of the extracellular matrix that directly influence cell behavior. Biomaterials could play an essential role in better emulating the disease microenvironment. In this paper, the recent and cutting-edge biomaterials used for creating in vitro models of human liver fibrosis are revised, in combination with cells, bioprinting, and/or microfluidics. These technologies have been instrumental to replicate the intricate structure of the unhealthy tissue and promote medium perfusion that improves cell growth and function, respectively. A comprehensive analysis of the impact of material hints and cell-material interactions in a tridimensional context is provided.

Microphysiological Constructs and Systems: Biofabrication Tactics, Biomimetic Evaluation Approaches, and Biomedical Applications

In recent decades, microphysiological constructs and systems (MPCs and MPSs) have undergone significant development, ranging from self-organized organoids to high-throughput organ-on-a-chip platforms. Advances in biomaterials, bioinks, 3D bioprinting, micro/nanofabrication, and sensor technologies have contributed to diverse and innovative biofabrication tactics. MPCs and MPSs, particularly tissue chips relevant to absorption, distribution, metabolism, excretion, and toxicity, have demonstrated potential as precise, efficient, and economical alternatives to animal models for drug discovery and personalized medicine. However, current approaches mainly focus on the in vitro recapitulation of the human anatomical structure and physiological-biochemical indices at a single or a few simple levels. This review highlights the recent remarkable progress in MPC and MPS models and their applications. The challenges that must be addressed to assess the reliability, quantify the techniques, and utilize the fidelity of the models are also discussed.

Single-cell transcriptomics stratifies organoid models of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing cause of morbidity with limited treatment options. Thus, accurate in vitro systems to test new therapies are indispensable. While recently, human liver organoid models have emerged to assess steatotic liver disease, a systematic evaluation of their translational potential is still missing. Here, we evaluated human liver organoid models of MASLD, comparatively testing disease induction in three conditions: oleic acid, palmitic acid, and TGF-β1. Through single-cell analyses, we find that all three models induce inflammatory signatures, but only TGF-β1 promotes collagen production, fibrosis, and hepatic stellate cell expansion. In striking contrast, oleic acid ameliorates fibrotic signatures and reduces the hepatic stellate cell population. Linking data from each model to gene expression signatures associated with MASLD disease progression further demonstrates that palmitic acid and TGF-β1 more robustly model inflammation and fibrosis. Our findings highlight the importance of stratifying MASLD organoid models by signatures of clinical disease progression, provide a single-cell reference to benchmark future organoid injury models, and allow us to study evolving steatohepatitis, fibrosis, and HSC susceptibility to injury in a dynamic, multi-lineage human in vitro system.

Localized T3 production modifies the transcriptome and promotes the hepatocyte-like lineage in iPSC-derived hepatic organoids

Thyroid hormone (TH) levels are low during development, and the deiodinases control TH signaling through tissue-specific activation or inactivation of TH. Here, we studied human induced pluripotent stem cell-derived (iPSC-derived) hepatic organoids and identified a robust induction of DIO2 expression (the deiodinase that activates T4 to T3) that occurs in hepatoblasts. The surge in DIO2-T3 (the deiodinase that activates thyroxine [T4] to triiodothyronine [T3]) persists until the hepatoblasts differentiate into hepatocyte- or cholangiocyte-like cells, neither of which expresses DIO2. Preventing the induction of the DIO2-T3 signaling modified the expression of key transcription factors, decreased the number of hepatocyte-like cells by ~60%, and increased the number of cholangiocyte-like cells by ~55% without affecting the growth or the size of the mature liver organoid. Physiological levels of T3 could not fully restore the transition from hepatoblasts to mature cells. This indicates that the timed surge in DIO2-T3 signaling critically determines the fate of developing human hepatoblasts and the transcriptome of the maturing hepatocytes, with physiological and clinical implications for how the liver handles energy substrates.

Self-assembly of three-dimensional liver organoids: virtual reconstruction via endocytosed polymer dots for refactoring the fine structure

In vitro culture of organoids holds considerable promise for the treatment of diseases or the provision of artificial organs. Traditional 2D differentiation from mesenchymal stem cells (MSCs) faces challenges in replicating the development of embryonic organs at the cellular level; conversely, the cultivation of 3D organoids exhibits potential for application. It is crucial for clinicians and technology researchers to acquire insights into organoid tissue differentiation, autonomous morphogenesis, as well as 3D assembly processes in vitro. In this investigation, novel 3D organoids capable of engendering complex liver-like tissues in vitro were cultured, and a class of high-luminance semiconductor polymer dots (Pdots) was employed to monitor the self-assembly process of 3D liver organoid tissues and cellular interaction and migration dynamics. Three-dimensional liver-bud (3D-LB) organoid tissues were derived through the interplay of induced MSCs, Wharton's Jelly, and human umbilical vein endothelial cells (HUVECs), and their structural characteristics were determined during the liver-bud organoid development; ultimately, the co-cultured organoid spatial cellular clusters resembling a truffle were successfully replicated. Utilizing R8-Pdots with remarkable resolution and biocompatibility, the structural elements of functional and vascularized organs derived from liver organoid tissues were adeptly reconstituted, and this investigation shall contribute to a further understanding of human hepato-developmental physiology and liver-disease modeling.

Human chemically-derived hepatic progenitors (hCdHs) as a source of liver organoid generation: Application in regenerative medicine, disease modeling, and toxicology testing

BACKGROUND & AIMS

Several types of human stem cells from embryonic (ESCs) and induced pluripotent (iPSCs) to adult tissue-specific stem cells are commonly used to generate 3D liver organoids for modeling tissue physiology and disease. We have recently established a protocol for direct conversion of primary human hepatocytes (hPHs) from healthy donor livers into bipotent progenitor cells (hCdHs). Here we extended this culture system to generate hCdH-derived liver organoids for diverse biomedical applications.

METHODS

To obtain hCdHs, hPHs were cultured in reprogramming medium containing A83-01 and CHIR99021 for 7 days. Liver organoids were established from hCdHs (hCdHOs) and human liver cells (hLOs) using the same donor livers for direct comparison, as well as from hiPSCs. Organoid properties were analyzed by standard in vitro assays. Molecular changes were determined by RT-qPCR and RNA-seq. Clinical relevance was evaluated by transplantation into FRG mice, modeling of alcohol-related liver disease (ARLD), and in vitro drug-toxicity tests.

RESULTS

hCdHs were clonally expanded as organoid cultures with low variability between starting hCdH lines. Similar to the hLOs, hCdHOs stably maintained stem cell phenotype based on accepted criteria. However, hCdHOs had an advantage over hLOs in terms of EpCAM expression, efficiency of organoid generation and capacity for directed hepatic differentiation as judged by molecular profiling, albumin secretion, glycogen accumulation, and CYP450 activities. Accordingly, FRG mice transplanted with hCdHOs survived longer than mice injected with hLOs. When exposed to ethanol, hCdHOs developed stronger ARLD phenotype than hLOs as evidenced by transcriptional profiling, lipid accumulation and mitochondrial dysfunction. In drug-induced injury assays in vitro, hCdHOs showed a similar or higher sensitivity response than hPHs.

CONCLUSION

hCdHOs provide a novel patient-specific stem cell-based platform for regenerative medicine, toxicology testing and modeling liver diseases.

Modeling Liver Development and Disease in a Dish

Historically, biological research has relied primarily on animal models. While this led to the understanding of numerous human biological processes, inherent species-specific differences make it difficult to answer certain liver-related developmental and disease-specific questions. The advent of 3D organoid models that are either derived from pluripotent stem cells or generated from healthy or diseased tissue-derived stem cells have made it possible to recapitulate the biological aspects of human organs. Organoid technology has been instrumental in understanding the disease mechanism and complements animal models. This review underscores the advances in organoid technology and specifically how liver organoids are used to better understand human-specific biological processes in development and disease. We also discuss advances made in the application of organoid models in drug screening and personalized medicine.

Liver organoid culture methods

Organoids, three-dimensional structures cultured in vitro, can recapitulate the microenvironment, complex architecture, and cellular functions of in vivo organs or tissues. In recent decades, liver organoids have been developed rapidly, and their applications in biomedicine, such as drug screening, disease modeling, and regenerative medicine, have been widely recognized. However, the lack of repeatability and consistency, including the lack of standardized culture conditions, has been a major obstacle to the development and clinical application of liver organoids. It is time-consuming for researchers to identify an appropriate medium component scheme, and the usage of some ingredients remains controversial. In this review, we summarized and compared different methods for liver organoid cultivation that have been published in recent years, focusing on controversial medium components and discussing their advantages and drawbacks. We aimed to provide an effective reference for the development and standardization of liver organoid cultivation.

Engineered human hepatocyte organoids enable CRISPR-based target discovery and drug screening for steatosis

The lack of registered drugs for nonalcoholic fatty liver disease (NAFLD) is partly due to the paucity of human-relevant models for target discovery and compound screening. Here we use human fetal hepatocyte organoids to model the first stage of NAFLD, steatosis, representing three different triggers: free fatty acid loading, interindividual genetic variability (PNPLA3 I148M) and monogenic lipid disorders (APOB and MTTP mutations). Screening of drug candidates revealed compounds effective at resolving steatosis. Mechanistic evaluation of effective drugs uncovered repression of de novo lipogenesis as the convergent molecular pathway. We present FatTracer, a CRISPR screening platform to identify steatosis modulators and putative targets using APOB-/- and MTTP-/- organoids. From a screen targeting 35 genes implicated in lipid metabolism and/or NAFLD risk, FADS2 (fatty acid desaturase 2) emerged as an important determinant of hepatic steatosis. Enhancement of FADS2 expression increases polyunsaturated fatty acid abundancy which, in turn, reduces de novo lipogenesis. These organoid models facilitate study of steatosis etiology and drug targets.

Found in translation-Fibrosis in metabolic dysfunction-associated steatohepatitis (MASH)

Metabolic dysfunction-associated steatohepatitis (MASH) is a severe form of liver disease that poses a global health threat because of its potential to progress to advanced fibrosis, leading to cirrhosis and liver cancer. Recent advances in single-cell methodologies, refined disease models, and genetic and epigenetic insights have provided a nuanced understanding of MASH fibrogenesis, with substantial cellular heterogeneity in MASH livers providing potentially targetable cell-cell interactions and behavior. Unlike fibrogenesis, mechanisms underlying fibrosis regression in MASH are still inadequately understood, although antifibrotic targets have been recently identified. A refined antifibrotic treatment framework could lead to noninvasive assessment and targeted therapies that preserve hepatocellular function and restore the liver's architectural integrity.

Fetal liver development and implications for liver disease pathogenesis

The metabolic, digestive and homeostatic roles of the liver are dependent on proper crosstalk and organization of hepatic cell lineages. These hepatic cell lineages are derived from their respective progenitors early in organogenesis in a spatiotemporally controlled manner, contributing to the liver's specialized and diverse microarchitecture. Advances in genomics, lineage tracing and microscopy have led to seminal discoveries in the past decade that have elucidated liver cell lineage hierarchies. In particular, single-cell genomics has enabled researchers to explore diversity within the liver, especially early in development when the application of bulk genomics was previously constrained due to the organ's small scale, resulting in low cell numbers. These discoveries have substantially advanced our understanding of cell differentiation trajectories, cell fate decisions, cell lineage plasticity and the signalling microenvironment underlying the formation of the liver. In addition, they have provided insights into the pathogenesis of liver disease and cancer, in which developmental processes participate in disease emergence and regeneration. Future work will focus on the translation of this knowledge to optimize in vitro models of liver development and fine-tune regenerative medicine strategies to treat liver disease. In this Review, we discuss the emergence of hepatic parenchymal and non-parenchymal cells, advances that have been made in in vitro modelling of liver development and draw parallels between developmental and pathological processes.

Liver Injury and Regeneration: Current Understanding, New Approaches, and Future Perspectives

The liver is a complex organ with the ability to regenerate itself in response to injury. However, several factors can contribute to liver damage beyond repair. Liver injury can be caused by viral infections, alcoholic liver disease, non-alcoholic steatohepatitis, and drug-induced liver injury. Understanding the cellular and molecular mechanisms involved in liver injury and regeneration is critical to developing effective therapies for liver diseases. Liver regeneration is a complex process that involves the interplay of various signaling pathways, cell types, and extracellular matrix components. The activation of quiescent hepatocytes that proliferate and restore the liver mass by upregulating genes involved in cell-cycle progression, DNA repair, and mitochondrial function; the proliferation and differentiation of progenitor cells, also known as oval cells, into hepatocytes that contribute to liver regeneration; and the recruitment of immune cells to release cytokines and angiogenic factors that promote or inhibit cell proliferation are some examples of the regenerative processes. Recent advances in the fields of gene editing, tissue engineering, stem cell differentiation, small interfering RNA-based therapies, and single-cell transcriptomics have paved a roadmap for future research into liver regeneration as well as for the identification of previously unknown cell types and gene expression patterns. In summary, liver injury and regeneration is a complex and dynamic process. A better understanding of the cellular and molecular mechanisms driving this phenomenon could lead to the development of new therapies for liver diseases and improve patient outcomes.

Three-dimensional human bile duct formation from chemically induced human liver progenitor cells

Background: The intrahepatic bile ducts (BDs) play an important role in the modification and transport of bile, and the integration between the BD and hepatocytes is the basis of the liver function. However, the lack of a source of cholangiocytes limits in vitro research. The aim of the present study was to establish three-dimensional BDs combined with human mature hepatocytes (hMHs) in vitro using chemically induced human liver progenitor cells (hCLiPs) derived from hMHs. Methods: In this study, we formed functional BDs from hCLiPs using hepatocyte growth factor and extracellular matrix. BDs expressed the typical biliary markers CK-7, GGT1, CFTR and EpCAM and were able to transport the bile-like substance rhodamine 123 into the lumen. The established three-dimensional BDs were cocultured with hMHs. These cells were able to bind to the BDs, and the bile acid analog CLF was transported from the culture medium through the hMHs and accumulated in the lumen of the BDs. The BDs generated from the hCLiPs showed a BD function and a physiological system (e.g., the transport of bile within the liver) when they were connected to the hMHs. Conclusion: We present a novel in vitro three-dimensional BD combined with hMHs for study, drug screening and the therapeutic modulation of the cholangiocyte function.

Three-Dimensional Cell Cultures: The Bridge between In Vitro and In Vivo Models

Although historically, the traditional bidimensional in vitro cell system has been widely used in research, providing much fundamental information regarding cellular functions and signaling pathways as well as nuclear activities, the simplicity of this system does not fully reflect the heterogeneity and complexity of the in vivo systems. From this arises the need to use animals for experimental research and in vivo testing. Nevertheless, animal use in experimentation presents various aspects of complexity, such as ethical issues, which led Russell and Burch in 1959 to formulate the 3R (Replacement, Reduction, and Refinement) principle, underlying the urgent need to introduce non-animal-based methods in research. Considering this, three-dimensional (3D) models emerged in the scientific community as a bridge between in vitro and in vivo models, allowing for the achievement of cell differentiation and complexity while avoiding the use of animals in experimental research. The purpose of this review is to provide a general overview of the most common methods to establish 3D cell culture and to discuss their promising applications. Three-dimensional cell cultures have been employed as models to study both organ physiology and diseases; moreover, they represent a valuable tool for studying many aspects of cancer. Finally, the possibility of using 3D models for drug screening and regenerative medicine paves the way for the development of new therapeutic opportunities for many diseases.

NAFLD-Related HCC: Focus on the Latest Relevant Preclinical Models

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and one of the deadliest cancers worldwide. Despite extensive research, the biological mechanisms underlying HCC's development and progression remain only partially understood. Chronic overeating and/or sedentary-lifestyle-associated obesity, which promote Non-Alcoholic Fatty Liver Disease (NAFLD), have recently emerged as worrying risk factors for HCC. NAFLD is characterized by excessive hepatocellular lipid accumulation (steatosis) and affects one quarter of the world's population. Steatosis progresses in the more severe inflammatory form, Non-Alcoholic Steatohepatitis (NASH), potentially leading to HCC. The incidence of NASH is expected to increase by up to 56% over the next 10 years. Better diagnoses and the establishment of effective treatments for NAFLD and HCC will require improvements in our understanding of the fundamental mechanisms of the disease's development. This review describes the pathogenesis of NAFLD and the mechanisms underlying the transition from NAFL/NASH to HCC. We also discuss a selection of appropriate preclinical models of NAFLD for research, from cellular models such as liver-on-a-chip models to in vivo models, focusing particularly on mouse models of dietary NAFLD-HCC.

Pluripotent Stem Cell-Derived Hepatocyte-like Cells: Induction Methods and Applications

The development of regenerative medicine provides new options for the treatment of end-stage liver diseases. Stem cells, such as bone marrow mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells (iPSCs), are effective tools for tissue repair in regenerative medicine. iPSCs are an appropriate source of hepatocytes for the treatment of liver disease due to their unlimited multiplication capacity, their coverage of the entire range of genetics required to simulate human disease, and their evasion of ethical implications. iPSCs have the ability to gradually produce hepatocyte-like cells (HLCs) with homologous phenotypes and physiological functions. However, how to induce iPSCs to differentiate into HLCs efficiently and accurately is still a hot topic. This review describes the existing approaches for inducing the differentiation of iPSCs into HLCs, as well as some challenges faced, and summarizes various parameters for determining the quality and functionality of HLCs. Furthermore, the application of iPSCs for in vitro hepatoprotective drug screening and modeling of liver disease is discussed. In conclusion, iPSCs will be a dependable source of cells for stem-cell therapy to treat end-stage liver disease and are anticipated to facilitate individualized treatment for liver disease in the future.

NAFLD and AATD Are Two Diseases with Unbalanced Lipid Metabolism: Similarities and Differences

Non-alcoholic fatty liver disease (NAFLD) is a type of steatosis commonly associated with obesity, dyslipidemia, hypertension, and diabetes. Other diseases such as inherited alpha-1 antitrypsin deficiency (AATD) have also been related to the development of liver steatosis. The primary reasons leading to hepatic lipid deposits can be genetic and epigenetic, and the outcomes range from benign steatosis to liver failure, as well as to extrahepatic diseases. Progressive hepatocellular damage and dysregulated systemic immune responses can affect extrahepatic organs, specifically the heart and lungs. In this review, we discuss the similarities and differences between the molecular pathways of NAFLD and AATD, and the putative value of hepatic organoids as novel models to investigate the physio pathological mechanisms of liver steatosis.

3D bioprinted liver tissue and disease models: Current advances and future perspectives

Three-dimensional (3D) bioprinting is a promising technology for fabricating complex tissue constructs with biomimetic biological functions and stable mechanical properties. In this review, the characteristics of different bioprinting technologies and materials are compared, and development in strategies for bioprinting normal and diseased hepatic tissue are summarized. In particular, features of bioprinting and other bio-fabrication strategies, such as organoids and spheroids are compared to demonstrate the strengths and weaknesses of 3D printing technology. Directions and suggestions, such as vascularization and primary human hepatocyte culture, are provided for the future development of 3D bioprinting.

Organoids: The current status and biomedical applications

Organoids are three-dimensional (3D) miniaturized versions of organs or tissues that are derived from cells with stem potential and can self-organize and differentiate into 3D cell masses, recapitulating the morphology and functions of their in vivo counterparts. Organoid culture is an emerging 3D culture technology, and organoids derived from various organs and tissues, such as the brain, lung, heart, liver, and kidney, have been generated. Compared with traditional bidimensional culture, organoid culture systems have the unique advantage of conserving parental gene expression and mutation characteristics, as well as long-term maintenance of the function and biological characteristics of the parental cells in vitro. All these features of organoids open up new opportunities for drug discovery, large-scale drug screening, and precision medicine. Another major application of organoids is disease modeling, and especially various hereditary diseases that are difficult to model in vitro have been modeled with organoids by combining genome editing technologies. Herein, we introduce the development and current advances in the organoid technology field. We focus on the applications of organoids in basic biology and clinical research, and also highlight their limitations and future perspectives. We hope that this review can provide a valuable reference for the developments and applications of organoids.

The Values and Perspectives of Organoids in the Field of Metabolic Syndrome

Metabolic syndrome (MetS) has become a global health problem, and the prevalence of obesity at all stages of life makes MetS research increasingly important and urgent. However, as a comprehensive and complex disease, MetS has lacked more appropriate research models. The advent of organoids provides an opportunity to address this issue. However, it should be noted that organoids are still in their infancy. The main drawbacks are a lack of maturity, complexity, and the inability to standardize large-scale production. Could organoids therefore be a better choice for studying MetS than other models? How can these limitations be overcome? Here, we summarize the available data to present current progress on pancreatic and hepatobiliary organoids and to answer these open questions. Organoids are of human origin and contain a variety of human cell types necessary to mimic the disease characteristics of MetS in their development. Taken together with the discovery of hepatobiliary progenitors in situ, the dedifferentiation of beta cells in diabetes, and studies on hepatic macrophages, we suggest that promoting endogenous regeneration has the potential to prevent the development of end-stage liver and pancreatic lesions caused by MetS and outline the direction of future research in this field.

Cellular therapies in liver and pancreatic diseases

Over the past two decades, developments in regenerative medicine in gastroenterology have been greatly enhanced by the application of stem cells, which can self-replicate and differentiate into any somatic cell. The discovery of induced pluripotent stem cells has opened remarkable perspectives on tissue regeneration, including their use as a bridge to transplantation or as supportive therapy in patients with organ failure. The improvements in DNA manipulation and gene editing strategies have also allowed to clarify the physiopathology and to correct the phenotype of several monogenic diseases, both in vivo and in vitro. Further progress has been made with the development of three-dimensional cultures, known as organoids, which have demonstrated morphological and functional complexity comparable to that of a miniature organ. Hence, owing to its protean applications and potential benefits, cell and organoid transplantation has become a hot topic for the management of gastrointestinal diseases. In this review, we describe current knowledge on cell therapies in hepatology and pancreatology, providing insight into their future applications in regenerative medicine.

PDGF Receptors and Signaling Are Required for 3D-Structure Formation and Differentiation of Human iPSC-Derived Hepatic Spheroids

Human iPSC-derived liver organoids (LO) or hepatic spheroids (HS) have attracted widespread interest, and the numerous studies on them have recently provided various production protocols. However, the mechanism by which the 3D structures of LO and HS are formed from the 2D-cultured cells and the mechanism of the LO and HS maturation remain largely unknown. In this study, we demonstrate that PDGFRA is specifically induced in the cells that are suitable for HS formation and that PDGF receptors and signaling are required for HS formation and maturation. Additionally, in vivo, we show that the localization of PDGFRα is in complete agreement with mouse E9.5 hepatoblasts, which begin to form the 3D-structural liver bud from the single layer. Our results present that PDGFRA play important roles for 3D structure formation and maturation of hepatocytes in vitro and in vivo and provide a clue to elucidate the hepatocyte differentiation mechanism.

Liver organoids: established tools for disease modeling and drug development

In the past decade, liver organoids have evolved rapidly as valuable research tools, providing novel insights into almost all types of liver diseases, including monogenic liver diseases, alcohol-associated liver disease, metabolic-associated fatty liver disease, various types of (viral) hepatitis, and liver cancers. Liver organoids in part mimic the microphysiology of the human liver and fill a gap in high-fidelity liver disease models to a certain extent. They hold great promise to elucidate the pathogenic mechanism of a diversity of liver diseases and play a crucial role in drug development. Moreover, it is challenging but opportunistic to apply liver organoids for tailored therapies of various liver diseases. The establishment, applications, and challenges of different types of liver organoids, for example, derived from embryonic, adult, or induced pluripotent stem cells, to model different liver diseases, are presented in this review.

Liver three-dimensional cellular models for high-throughput chemical testing

Drug-induced hepatotoxicity is a leading cause of drug withdrawal from the market. High-throughput screening utilizing in vitro liver models is critical for early-stage liver toxicity testing. Traditionally, monolayer human hepatocytes or immortalized liver cell lines (e.g., HepG2, HepaRG) have been used to test compound liver toxicity. However, monolayer-cultured liver cells sometimes lack the metabolic competence to mimic the in vivo condition and are therefore largely appropriate for short-term toxicological testing. They may not, however, be adequate for identifying chronic and recurring liver damage caused by drugs. Recently, several three-dimensional (3D) liver models have been developed. These 3D liver models better recapitulate normal liver function and metabolic capacity. This review describes the current development of 3D liver models that can be used to test drugs/chemicals for their pharmacologic and toxicologic effects, as well as the advantages and limitations of using these 3D liver models for high-throughput screening.

Revolutionizing Disease Modeling: The Emergence of Organoids in Cellular Systems

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

Exploring the reprogramming potential of B cells and comprehending its clinical and therapeutic perspective

Initiating from multipotent progenitors, the lineages extrapolated from hematopoietic stem cells are determined by transcription factors specific to each of them. The commitment factors assist in the differentiation of progenitor cells into terminally differentiated cells. B lymphocytes constitute a population of cells that expresses clonally diverse cell surface immunoglobulin (Ig) receptors specific to antigenic epitopes. B cells are a significant facet of the adaptive immune system. The secreted antibodies corresponding to the B cell recognize the antigens via the B cell receptor (BCR). Following antigen recognition, the B cell is activated and thereafter undergoes clonal expansion and proliferation to become memory B cells. The essence of 'cellular reprogramming' has aided in reliably altering the cells to desired tissue type. The potential of reprogramming has been harnessed to decipher and find solutions for various genetically inherited diseases and degenerative disorders. B lymphocytes can be reprogrammed to their initial naive state from where they get differentiated into any lineage or cell type similar to a pluripotent stem cell which can be accomplished by the deletion of master regulators of the B cell lineage. B cells can be reprogrammed into pluripotent stem cells and also can undergo transdifferentiation at the midway of cell differentiation to other cell types. Mandated expression of C/EBP in specialized B cells corresponds to their fast and effective reprogramming into macrophages, reversing the cell fate of these lymphocytes and allowing them to differentiate freshly into other types of cells. The co-expression of C/EBPα and OKSM (Oct4, Sox2, Klf4, c-Myc) amplified the reprogramming efficiency of B lymphocytes. Various human somatic cells including the immune cells are compliant to reprogramming which paves a path for opportunities like autologous tissue grafts, blood transfusion, and cancer immunotherapy. The ability to reprogram B cells offers an unprecedented opportunity for developing a therapeutic approach for several human diseases. Here, we will focus on all the proteins and transcription factors responsible for the developmental commitment of B lymphocytes and how it is harnessed in various applications.

Cryopreservation of Organoids

Organoids represent indispensable opportunities for biomedicine, including drug discovery, cancer biology, regenerative and personalised medicine or tissue and organ transplantation. However, the lack of optimised preservation strategies limits the wide use of organoids in research or clinical fields. In this review, we present a short outline of the recent developments in organoid research and current cryopreservation strategies for organoid systems. While both vitrification and slow controlled freezing have been utilized for the cryopreservation of organoid structures or their precursor components, the controlled-rate slow freezing under protection of Me2 SO remains the most common approach. The application of appropriate pre- or post-treatment strategies, like the addition of Rho-kinase or myosin inhibitors into cell culture or cryopreservation medium, can increase the recovery of complex organoid constructs post-thaw. However, the high complexity of the organoid structure and heterogeneity of cellular composition bring challenges associated with cryoprotectant distribution, distinct response of cells to the solution and freezing-induced injuries. The deficit of adequate quality control methods, which may ensure the assessment of organoid recovery in due term without prolonged re-cultivation process, represents another challenge limiting the reproducibility of current cryobanking technology. In this review, we attempt to assess the current demands and achievements in organoid cryopreservation and highlight the key questions to focus on during the development of organoid preservation technologies.

Human liver cancer organoids: Biological applications, current challenges, and prospects in hepatoma therapy

Liver cancer and disease are among the most socially challenging global health concerns. Although organ transplantation, surgical resection and anticancer drugs are the main methods for the treatment of liver cancer, there are still no proven cures owing to the lack of donor livers and tumor heterogeneity. Recently, advances in tumor organoid technology have attracted considerable attention as they can simulate the spatial constructs and pathophysiological characteristics of tumorigenesis and metastasis in a more realistic manner. Organoids may further contribute to the development of tailored therapies. Combining organoids with other emerging techniques, such as CRISPR-HOT, organ-on-a-chip, and 3D bioprinting, may further develop organoids and address their bottlenecks to create more practical models that generalize different tissue or organ interactions in tumor progression. In this review, we summarize the various methods in which liver organoids may be generated and describe their biological and clinical applications, present challenges, and prospects for their integration with emerging technologies. These rapidly developing liver organoids may become the focus of in vitro clinical model development and therapeutic research for liver diseases in the near future.

Induced Pluripotent Stem Cell-Derived Organoids: Their Implication in COVID-19 Modeling

The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a significant global health issue. This novel virus's high morbidity and mortality rates have prompted the scientific community to quickly find the best COVID-19 model to investigate all pathological processes underlining its activity and, more importantly, search for optimal drug therapy with minimal toxicity risk. The gold standard in disease modeling involves animal and monolayer culture models; however, these models do not fully reflect the response to human tissues affected by the virus. However, more physiological 3D in vitro culture models, such as spheroids and organoids derived from induced pluripotent stem cells (iPSCs), could serve as promising alternatives. Different iPSC-derived organoids, such as lung, cardiac, brain, intestinal, kidney, liver, nasal, retinal, skin, and pancreatic organoids, have already shown immense potential in COVID-19 modeling. In the present comprehensive review article, we summarize the current knowledge on COVID-19 modeling and drug screening using selected iPSC-derived 3D culture models, including lung, brain, intestinal, cardiac, blood vessels, liver, kidney, and inner ear organoids. Undoubtedly, according to reviewed studies, organoids are the state-of-the-art approach to COVID-19 modeling.

Generation of multilineage liver organoids with luminal vasculature and bile ducts from human pluripotent stem cells via modulation of Notch signaling

BACKGROUND

The generation of liver organoids recapitulating parenchymal and non-parenchymal cell interplay is essential for the precise in vitro modeling of liver diseases. Although different types of multilineage liver organoids (mLOs) have been generated from human pluripotent stem cells (hPSCs), the assembly and concurrent differentiation of multiple cell types in individual mLOs remain a major challenge. Particularly, most studies focused on the vascularization of mLOs in host tissue after transplantation in vivo. However, relatively little information is available on the in vitro formation of luminal vasculature in mLOs themselves.

METHODS

The mLOs with luminal blood vessels and bile ducts were generated by assembling hepatic endoderm, hepatic stellate cell-like cells (HscLCs), and endothelial cells derived entirely from hPSCs using 96-well ultra-low attachment plates. We analyzed the effect of HscLC incorporation and Notch signaling modulation on the formation of both bile ducts and vasculature in mLOs using immunofluorescence staining, qRT-PCR, ELISA, and live-perfusion imaging. The potential use of the mLOs in fibrosis modeling was evaluated by histological and gene expression analyses after treatment with pro-fibrotic cytokines.

RESULTS

We found that hPSC-derived HscLCs are crucial for generating functional microvasculature in mLOs. HscLC incorporation and subsequent vascularization substantially reduced apoptotic cell death and promoted the survival and growth of mLOs with microvessels. In particular, precise modulation of Notch signaling during a specific time window in organoid differentiation was critical for generating both bile ducts and vasculature. Live-cell imaging, a series of confocal scans, and electron microscopy demonstrated that blood vessels were well distributed inside mLOs and had perfusable lumens in vitro. In addition, exposure of mLOs to pro-fibrotic cytokines induced early fibrosis-associated events, including upregulation of genes associated with fibrotic induction and endothelial cell activation (i.e., collagen I, α-SMA, and ICAM) together with destruction of tissue architecture and organoid shrinkage.

CONCLUSION

Our results demonstrate that mLOs can reproduce parenchymal and non-parenchymal cell interactions and suggest that their application can advance the precise modeling of liver diseases in vitro.

3D multicellular systems in disease modelling: From organoids to organ-on-chip

Cell-cell interactions underlay organ formation and function during homeostasis. Changes in communication between cells and their surrounding microenvironment are a feature of numerous human diseases, including metabolic disease and neurological disorders. In the past decade, cross-disciplinary research has been conducted to engineer novel synthetic multicellular organ systems in 3D, including organoids, assembloids, and organ-on-chip models. These model systems, composed of distinct cell types, satisfy the need for a better understanding of complex biological interactions and mechanisms underpinning diseases. In this review, we discuss the emerging field of building 3D multicellular systems and their application for modelling the cellular interactions at play in diseases. We report recent experimental and computational approaches for capturing cell-cell interactions as well as progress in bioengineering approaches for recapitulating these complexities ex vivo. Finally, we explore the value of developing such multicellular systems for modelling metabolic, intestinal, and neurological disorders as major examples of multisystemic diseases, we discuss the advantages and disadvantages of the different approaches and provide some recommendations for further advancing the field.

Liver Organoids, Novel and Promising Modalities for Exploring and Repairing Liver Injury

The past decades have witnessed great advances in organoid technology. Liver is the biggest solid organ, performing multifaceted physiological functions. Nowadays, liver organoids have been applied in many fields including pharmaceutical research, precision medicine and disease models. Compared to traditional 2-dimensional cell line cultures and animal models, liver organoids showed the unique advantages. More importantly, liver organoids can well model the features of the liver and tend to be novel and promising modalities for exploring liver injury, thus finding potential treatment targets and repairing liver injury. In this review, we reviewed the history of the development of liver organoids and summarized the application of liver organoids and recent studies using organoids to explore and further repair the liver injury. These novel modalities could provide new insights about the process of liver injury.