Single Particle Imaging of Polarized Hepatoma Organoids upon Hepatitis C Virus Infection Reveals an Ordered and Sequential Entry Process

Exploring in vitro modeling in hepatocarcinogenesis research: morphological and molecular features and similarities to the corresponding human disease

The hepatocellular carcinoma (HCC) features a remarkable epidemiological burden, ranking as the third most lethal cancer worldwide. As the HCC-related molecular and cellular complexity unfolds as the disease progresses, the use of a myriad of in vitro models available is mandatory in translational preclinical research setups. In this review paper, we will compile cutting-edge information on the in vitro bioassays for HCC research, (A) emphasizing their morphological and molecular parallels with human HCC; (B) delineating the advantages and limitations of their application; and (C) offering perspectives on their prospective applications. While bidimensional (2D) (co) culture setups provide a rapid low-cost strategy for metabolism and drug screening investigations, tridimensional (3D) (co) culture bioassays - including patient-derived protocols as organoids and precision cut slices - surpass some of the 2D strategies limitations, mimicking the complex microarchitecture and cellular and non-cellular microenvironment observed in human HCC. 3D models have become invaluable tools to unveil HCC pathophysiology and targeted therapy. In both setups, the recapitulation of HCC in different etiologies/backgrounds (i.e., viral, fibrosis, and fatty liver) may be considered as a fundamental guide for obtaining translational findings. Therefore, a "multimodel" approach - encompassing the advantages of different in vitro bioassays - is encouraged to circumvent "model-biased" outcomes in preclinical HCC research.

Liver organoids: updates on generation strategies and biomedical applications

The liver is the most important metabolic organ in the body. While mouse models and cell lines have further deepened our understanding of liver biology and related diseases, they are flawed in replicating key aspects of human liver tissue, particularly its complex structure and metabolic functions. The organoid model represents a major breakthrough in cell biology that revolutionized biomedical research. Organoids are in vitro three-dimensional (3D) physiological structures that recapitulate the morphological and functional characteristics of tissues in vivo, and have significant advantages over traditional cell culture methods. In this review, we discuss the generation strategies and current advances in the field focusing on their application in regenerative medicine, drug discovery and modeling diseases.

The application of organoids in cancers associated with pathogenic infections

Cancers associated with pathogen infections are gradually becoming important threats to human health globally, and it is of great significance to study the mechanisms of pathogen carcinogenesis. Current mechanistic studies rely on animal and two-dimensional (2D) cell culture models, but traditional methods have been proven insufficient for the rapid modeling of diseases caused by new pathogens. Therefore, research focus has shifted to organoid models, which can replicate the structural and genetic characteristics of the target tissues or organs in vitro, providing new platforms for the study of pathogen-induced oncogenic mechanisms. This review summarizes the application of organoid technology in the studies of four pathogen-associated cancers: gastric cancer linked to Helicobacter pylori, liver cancer associated with hepatitis B virus or hepatitis C virus, colorectal cancer caused by Escherichia coli, and cervical cancer related to human papillomavirus. This review also proposes several limitations of organoid technology to optimize organoid models and advance the treatment of cancer associated with pathogen infections in the future.

Research progress and application of liver organoids for disease modeling and regenerative therapy

The liver is a major metabolic organ of the human body and has a high incidence of diseases. In recent years, the annual incidence of liver disease has increased, seriously endangering human life and health. The study of the occurrence and development mechanism of liver diseases, discovery of new therapeutic targets, and establishment of new methods of medical treatment are major issues related to the national economy and people's livelihood. The development of stable and effective research models is expected to provide new insights into the pathogenesis of liver diseases and the search for more effective treatment options. Organoid technology is a new in vitro culture system, and organoids constructed by human cells can simulate the morphological structure, gene expression, and glucose and lipid metabolism of organs in vivo, providing a new model for related research on liver diseases. This paper reviews the latest research progress on liver organoids from the establishment of cell sources and application of liver organoids and discusses their application potential in the field of liver disease research.

Recent Advances in Graphene Oxide-Based on Organoid Culture as Disease Model and Cell Behavior - A Systematic Literature Review

Due to their ability to replicate the in vivo microenvironment through cell interaction and induce cells to stimulate cell function, three-dimensional cell culture models can overcome the limitations of two-dimensional models. Organoids are 3D models that demonstrate the ability to replicate the natural structure of an organ. In most organoid tissue cultures, matrigel made of a mouse tumor extracellular matrix protein mixture is an essential ingredient. However, its tumor-derived origin, batch-to-batch variation, high cost, and safety concerns have limited the usefulness of organoid drug development and regenerative medicine. Its clinical application has also been hindered by the fact that organoid generation is dependent on the use of poorly defined matrices. Therefore, matrix optimization is a crucial step in developing organoid culture that introduces alternatives as different materials. Recently, a variety of substitute materials has reportedly replaced matrigel. The purpose of this study is to review the significance of the latest advances in materials for cell culture applications and how they enhance build network systems by generating proper cell behavior. Excellence in cell behavior is evaluated from their cell characteristics, cell proliferation, cell differentiation, and even gene expression. As a result, graphene oxide as a matrix optimization demonstrated high potency in developing organoid models. Graphene oxide can promote good cell behavior and is well known for having good biocompatibility. Hence, advances in matrix optimization of graphene oxide provide opportunities for the future development of advanced organoid models.

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.

Organoid co-culture models of the tumor microenvironment promote precision medicine

In recent years, the three-dimensional (3D) culture system has emerged as a promising preclinical model for tumor research owing to its ability to replicate the tissue structure and molecular characteristics of solid tumors in vivo. This system offers several advantages, including high throughput, efficiency, and retention of tumor heterogeneity. Traditional Matrigel-submerged organoid cultures primarily support the long-term proliferation of epithelial cells. One solution for the exploration of the tumor microenvironment is a reconstitution approach involving the introduction of exogenous cell types, either in dual, triple or even multiple combinations. Another solution is a holistic approach including patient-derived tumor fragments, air-liquid interface, suspension 3D culture, and microfluidic tumor-on-chip models. Organoid co-culture models have also gained popularity for studying the tumor microenvironment, evaluating tumor immunotherapy, identifying predictive biomarkers, screening for effective drugs, and modeling infections. By leveraging these 3D culture systems, it is hoped to advance the clinical application of therapeutic approaches and improve patient outcomes.

An innovative viewpoint on the existing and prospectiveness of SR-B1

Scavenger Receptor Class B Type 1 (SR-B1), a receptor protein expressed on the cell membrane, plays a crucial role in the metabolism and transport of cholesterol and other lipids, contributing significantly to the homeostasis of lipid levels within the body. Bibliometric analysis involves the application of mathematical and statistical methods to quantitatively analyze different types of documents. It involves the analysis of structural and temporal trends in scholarly articles, coupled with the identification of subject emphasis and variations. Through a bibliometric analysis, this study examines the historical background, current research trends, and future directions in the exploration of SR-B1. By offering insights into the research status and development of SR-B1, this paper aims to assist researchers in identifying novel pathways and areas of investigation in this field of study. Following the screening process, it can be concluded that research on SR-B1 has consistently remained a topic of significant interest over the past 17 years. Interestingly, SR-B1 has recently garnered attention in areas beyond its traditional research focus, including the field of cancer. The primary objective of this review is to provide a concise and accessible overview of the development process of SR-B1 that can help readers who are not well-versed in SR-B1 research quickly grasp its key aspects. Furthermore, this review aims to offer insights and suggestions to researchers regarding potential future research directions and areas of emphasis relating to SR-B1.

Roles of epidermal growth factor receptor, claudin-1 and occludin in multi-step entry of hepatitis C virus into polarized hepatoma spheroids

The multi-step process of hepatitis C virus (HCV) entry is facilitated by various host factors, including epidermal growth factor receptor (EGFR) and the tight junction proteins claudin-1 (CLDN1) and occludin (OCLN), which are thought to function at later stages of the HCV entry process. Using single particle imaging of HCV infection of polarized hepatoma spheroids, we observed that EGFR performs multiple functions in HCV entry, both phosphorylation-dependent and -independent. We previously observed, and in this study confirmed, that EGFR is not required for HCV migration to the tight junction. EGFR is required for the recruitment of clathrin to HCV in a phosphorylation-independent manner. EGFR phosphorylation is required for virion internalization at a stage following the recruitment of clathrin. HCV entry activates the RAF-MEK-ERK signaling pathway downstream of EGFR phosphorylation. This signaling pathway regulates the sorting and maturation of internalized HCV into APPL1- and EEA1-associated early endosomes, which form the site of virion uncoating. The tight junction proteins, CLDN1 and OCLN, function at two distinct stages of HCV entry. Despite its appreciated function as a "late receptor" in HCV entry, CLDN1 is required for efficient HCV virion accumulation at the tight junction. Huh-7.5 cells lacking CLDN1 accumulate HCV virions primarily at the initial basolateral surface. OCLN is required for the late stages of virion internalization. This study produced further insight into the unusually complex HCV endocytic process.

The matrix metalloproteinase ADAM10 supports hepatitis C virus entry and cell-to-cell spread via its sheddase activity

Hepatitis C virus (HCV) exploits the four entry factors CD81, scavenger receptor class B type I (SR-BI, also known as SCARB1), occludin, and claudin-1 as well as the co-factor epidermal growth factor receptor (EGFR) to infect human hepatocytes. Here, we report that the disintegrin and matrix metalloproteinase 10 (ADAM10) associates with CD81, SR-BI, and EGFR and acts as HCV host factor. Pharmacological inhibition, siRNA-mediated silencing and genetic ablation of ADAM10 reduced HCV infection. ADAM10 was dispensable for HCV replication but supported HCV entry and cell-to-cell spread. Substrates of the ADAM10 sheddase including epidermal growth factor (EGF) and E-cadherin, which activate EGFR family members, rescued HCV infection of ADAM10 knockout cells. ADAM10 did not influence infection with other enveloped RNA viruses such as alphaviruses and a common cold coronavirus. Collectively, our study reveals a critical role for the sheddase ADAM10 as a HCV host factor, contributing to EGFR family member transactivation and as a consequence to HCV uptake.

Genetic and pharmacological perturbation of hepatitis-C virus entry

Hepatitis-C virus (HCV) chronically infects 58 million individuals worldwide with variable disease outcome. While a subfraction of individuals exposed to the virus clear the infection, the majority develop chronic infection if untreated. Another subfraction of chronically ill proceeds to severe liver disease. The underlying causes of this interindividual variability include genetic polymorphisms in interferon genes. Here, we review available data on the influence of genetic or pharmacological perturbation of HCV host dependency factors on the clinically observed interindividual differences in disease outcome. We focus on host factors mediating virus entry into human liver cells. We assess available data on genetic variants of the major entry factors scavenger receptor class-B type I, CD81, claudin-1, and occludin as well as pharmacological perturbation of these entry factors. We review cell culture experimental and clinical cohort study data and conclude that entry factor perturbation may contribute to disease outcome of hepatitis C.

Recent Updates on Viral Oncogenesis: Available Preventive and Therapeutic Entities

Human viral oncogenesis is a complex phenomenon and a major contributor to the global cancer burden. Several recent findings revealed cellular and molecular pathways that promote the development and initiation of malignancy when viruses cause an infection. Even, antiviral treatment has become an approach to eliminate the viral infections and prevent the activation of oncogenesis. Therefore, for a better understanding, the molecular pathogenesis of various oncogenic viruses like, hepatitis virus, human immunodeficiency viral (HIV), human papillomavirus (HPV), herpes simplex virus (HSV), and Epstein-Barr virus (EBV), could be explored, especially, to expand many potent antivirals that may escalate the apoptosis of infected malignant cells while sparing normal and healthy ones. Moreover, contemporary therapies, such as engineered antibodies antiviral agents targeting signaling pathways and cell biomarkers, could inhibit viral oncogenesis. This review elaborates the recent advancements in both natural and synthetic antivirals to control viral oncogenesis. The study also highlights the challenges and future perspectives of using antivirals in viral oncogenesis.

Organoids: approaches and utility in cancer research

ABSTRACT

Organoids are three-dimensional cellular structures with self-organizing and self-differentiation capacities. They faithfully recapitulate structures and functions of in vivo organs as represented by functionality and microstructural definitions. Heterogeneity in in vitro disease modeling is one of the main reasons for anti-cancer therapy failures. Establishing a powerful model to represent tumor heterogeneity is crucial for elucidating tumor biology and developing effective therapeutic strategies. Tumor organoids can retain the original tumor heterogeneity and are commonly used to mimic the cancer microenvironment when co-cultured with fibroblasts and immune cells; therefore, considerable effort has been made recently to promote the use of this new technology from basic research to clinical studies in tumors. In combination with gene editing technology and microfluidic chip systems, engineered tumor organoids show promising abilities to recapitulate tumorigenesis and metastasis. In many studies, the responses of tumor organoids to various drugs have shown a positive correlation with patient responses. Owing to these consistent responses and personalized characteristics with patient data, tumor organoids show excellent potential for preclinical research. Here, we summarize the properties of different tumor models and review their current state and progress in tumor organoids. We further discuss the substantial challenges and prospects in the rapidly developing tumor organoid field.

GB Virus B and Hepatitis C Virus, Distantly Related Hepaciviruses, Share an Entry Factor, Claudin-1

Due to increased and broadened screening efforts, the last decade has seen a rapid expansion in the number of viral species classified into the Hepacivirus genus. Conserved genetic features of hepaciviruses suggest that they have undergone specific adaptation and have evolved to hijack similar host proteins for efficient propagation in the liver. Here, we developed pseudotyped viruses to elucidate the entry factors of GB virus B (GBV-B), the first hepacivirus described in an animal after hepatitis C virus (HCV). GBV-B-pseudotyped viral particles (GBVBpp) were shown to be uniquely sensitive to the sera of tamarins infected with GBV-B, validating their usefulness as a surrogate for GBV-B entry studies. We screened GBVBpp infection of human hepatoma cell lines that were CRISPR/Cas9 engineered to ablate the expression of individual HCV receptors/entry factors and found that claudin-1 is essential for GBV-B infection, indicating the GBV-B and HCV share an entry factor. Our data suggest that claudin-1 facilitates HCV and GBV-B entry through distinct mechanisms since the former requires the first extracellular loop and the latter is reliant on a C-terminal region containing the second extracellular loop. The observation that claudin-1 is an entry factor shared between these two hepaciviruses suggests that the tight junction protein is of fundamental mechanistic importance during cell entry. IMPORTANCE Hepatitis C virus (HCV) is a major public health burden; approximately 58 million individuals have chronic HCV infection and are at risk of developing cirrhosis and liver cancer. To achieve the World Health Organization's target of eliminating hepatitis by 2030, new therapeutics and vaccines are needed. Understanding how HCV enters cells can inform the design of new vaccines and treatments targeting the first stage of infection. However, the HCV cell entry mechanism is complex and has been sparsely described. Studying the entry of related hepaciviruses will increase the knowledge of the molecular mechanisms of the first stages of HCV infection, such as membrane fusion, and inform structure-guided HCV vaccine design; in this work, we have identified a protein, claudin-1, that facilitates the entry of an HCV-related hepacivirus but with a mechanism not described for HCV. Similar work on other hepaciviruses may unveil a commonality of entry factors and, possibly, new mechanisms.

Hepatitis C Virus Disrupts Annexin 5-Mediated Occludin Integrity through Downregulation of Protein Kinase Cα (PKCα) and PKCη Expression, Thereby Promoting Viral Propagation

Annexins (ANXs) comprise a family of calcium- and phospholipid-binding proteins and are implicated in the hepatitis C virus (HCV) life cycle. Here, we demonstrate a novel role of ANX5 in the HCV life cycle. Comparative analysis by quantitative PCR in human hepatoma cells revealed that ANX2, ANX4, and ANX5 were highly expressed among the ANX family proteins. Knockdown of ANX5 mRNA resulted in marked enhancement of HCV RNA replication but had no effect on either HCV translation or assembly. Using the HCV pseudoparticle (HCVpp) system, we observed enhancement of HCVpp infectivity in ANX5 knockdown Huh-7OK1 cells, suggesting that ANX5 is involved in suppression of HCV entry. Additionally, we observed that subcellular localizations of tight-junction proteins, such as claudin 1 (CLDN1) and occludin (OCLN), were disrupted in the ANX5 knockdown cells. It was reported that HCV infection was facilitated by disruption of OCLN distribution and that proper distribution of OCLN was regulated by its phosphorylation. Knockdown of ANX5 resulted in a decrease of OCLN phosphorylation, thereby disrupting OCLN distribution and HCV infection. Further analysis revealed that protein kinase C (PKC) isoforms, including PKCα and PKCη, play important roles in the regulation of ANX5-mediated phosphorylation and distribution of OCLN and in the restriction of HCV infection. HCV infection reduced OCLN phosphorylation through the downregulation of PKCα and PKCη expression. Taken together, these results suggest that ANX5, PKCα, and PKCη contribute to restriction of HCV infection by regulating OCLN integrity. We propose a model that HCV disrupts ANX5-mediated OCLN integrity through downregulation of PKCα and PKCη expression, thereby promoting HCV propagation. IMPORTANCE Host cells have evolved host defense machinery to restrict viral infection. However, viruses have evolved counteracting strategies to achieve their infection. In the present study, we obtained results suggesting that ANX5 and PKC isoforms, including PKCα and PKCη, contribute to suppression of HCV infection by regulating the integrity of OCLN. The disruption of OCLN integrity increased HCV infection. We also found that HCV disrupts ANX5-mediated OCLN integrity through downregulation of PKCα and PKCη expression, thereby promoting viral infection. We propose that HCV disrupts ANX5-mediated OCLN integrity to establish a persistent infection. The disruption of tight-junction assembly may play important roles in the progression of HCV-related liver diseases.

Proteomic profiling of single extracellular vesicles reveals colocalization of SARS-CoV-2 with a CD81/integrin-rich EV subpopulation in sputum from COVID-19 severe patients

Background

The global outbreak of COVID-19, and the limited availability of clinical treatments, forced researchers around the world to search for the pathogenesis and potential treatments. Understanding the pathogenesis of SARS-CoV-2 is crucial to respond better to the current coronavirus disease 2019 (COVID-19) pandemic.

Methods

We collected sputum samples from 20 COVID-19 patients and healthy controls. Transmission electron microscopy was used to observe the morphology of SARS-CoV-2. Extracellular vesicles (EVs) were isolated from sputum and the supernatant of VeroE6 cells, and were characterized by transmission electron microscopy, nanoparticle tracking analysis and Western-Blotting. Furthermore, a proximity barcoding assay was used to investigate immune-related proteins in single EV, and the relationship between EVs and SARS-CoV-2.

Result

Transmission electron microscopy images of SARS-COV-2 virus reveal EV-like vesicles around the virion, and western blot analysis of EVs extracted from the supernatant of SARS-COV-2-infected VeroE6 cells showed that they expressed SARS-COV-2 protein. These EVs have the infectivity of SARS-COV-2, and the addition can cause the infection and damage of normal VeroE6 cells. In addition, EVs derived from the sputum of patients infected with SARS-COV-2 expressed high levels of IL6 and TGF-β, which correlated strongly with expression of the SARS-CoV-2 N protein. Among 40 EV subpopulations identified, 18 differed significantly between patients and controls. The EV subpopulation regulated by CD81 was the most likely to correlate with changes in the pulmonary microenvironment after SARS-CoV-2 infection. Single extracellular vesicles in the sputum of COVID-19 patients harbor infection-mediated alterations in host and virus-derived proteins.

Conclusions

These results demonstrate that EVs derived from the sputum of patients participate in virus infection and immune responses. This study provides evidence of an association between EVs and SARS-CoV-2, providing insight into the possible pathogenesis of SARS-CoV-2 infection and the possibility of developing nanoparticle-based antiviral drugs.

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.

The role of human lipoproteins for hepatitis C virus persistence

Hepatitis C virus (HCV) is a hepatotropic virus that establishes a chronic infection in most individuals. Effective treatments are available; however, many patients are not aware of their infection. Consequently, they do not receive treatment and HCV transmission remains high, particularly among groups at high risk of exposure such as people who inject intravenous drugs. A prophylactic vaccine may reduce HCV transmission, but is currently not available. HCV has evolved immune evasion strategies, which facilitate persistence and complicate development of a protective vaccine. The peculiar association of HCV particles with human lipoproteins is thought to facilitate evasion from humoral immune response and viral homing to liver cells. A better understanding of these aspects provides the basis for development of protective vaccination strategies. Here, we review key information about the composition of HCV particles, the mechanisms mediating lipoprotein incorporation, and the functional consequences of this interaction.

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.

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.

Liver Organoid Potential Application for Hepatitis E Virus Infection

Despite the advances in hepatitis E virus (HEV) cell infection models' development, HEV infection efficacy in these cell models is still low, which hampers the further study of molecular mechanism of HEV infection and replication and even the interaction between HEV and host. Along with the advances in the technology for liver organoids generation, major efforts will be made to develop liver organoids for HEV infection. Here, we summarize the entire new and impressive cell culture system of liver organoids and discuss their potential application in HEV infection and pathogenesis. Liver organoids can be generated from tissue-resident cells isolated from biopsies of adult tissues or from iPSCs/ESCs differentiation, which can expand the large-scale experiments such as antiviral drug screening. Different types of liver cells working together can recapitulate the liver organ maintaining the physiological and biochemical microenvironments to support cell morphogenesis, migration, and response to viral infections. Efforts to optimize the protocols for liver organoids generation will speed up the research for HEV infection and pathogenesis and even the antiviral drug identification and evaluation.

Tight Junctions, the Key Factor in Virus-Related Disease

Tight junctions (TJs) are highly specialized membrane structural domains that hold cells together and form a continuous intercellular barrier in epithelial cells. TJs regulate paracellular permeability and participate in various cellular signaling pathways. As physical barriers, TJs can block viral entry into host cells; however, viruses use a variety of strategies to circumvent this barrier to facilitate their infection. This paper summarizes how viruses evade various barriers during infection by regulating the expression of TJs to facilitate their own entry into the organism causing infection, which will help to develop drugs targeting TJs to contain virus-related disease.

Occludin stalls HCV particle dynamics apart from hepatocyte tight junctions, promoting virion internalization

BACKGROUND AND AIMS

Numerous HCV entry factors have been identified, and yet information regarding their spatiotemporal dynamics is still limited. Specifically, one of the main entry factors of HCV is occludin (OCLN), a protein clustered at tight junctions (TJs), away from the HCV landing site. Thus, whether HCV particles slide toward TJs or, conversely, OCLN is recruited away from TJs remain debated.

APPROACH AND RESULTS

Here, we generated CRISPR/CRISPR-associated protein 9 edited Huh7.5.1 cells expressing endogenous levels of enhanced green fluorescent protein/OCLN and showed that incoming HCV particles recruit OCLN outside TJs, independently of claudin 1 (CLDN1) expression, another important HCV entry factor located at TJs. Using ex vivo organotypic culture of hepatic slices obtained from human liver explants, a physiologically relevant model that preserves the overall tissue architecture, we confirmed that HCV associates with OCLN away from TJs. Furthermore, we showed, by live cell imaging, that increased OCLN recruitment beneath HCV particles correlated with lower HCV motility. To decipher the mechanism underlying virus slow-down upon OCLN recruitment, we performed CRISPR knockout (KO) of CLDN1, an HCV entry factor proposed to act upstream of OCLN. Although CLDN1 KO potently inhibits HCV infection, OCLN kept accumulating underneath the particle, indicating that OCLN recruitment is CLDN1 independent. Moreover, inhibition of the phosphorylation of Ezrin, a protein involved in HCV entry that links receptors to the actin cytoskeleton, increased OCLN accumulation and correlated with more efficient HCV internalization.

CONCLUSIONS

Together, our data provide robust evidence that HCV particles interact with OCLN away from TJs and shed mechanistic insights regarding the manipulation of transmembrane receptor localization by extracellular virus particles.

A Clathrin light chain A reporter mouse for in vivo imaging of endocytosis

Clathrin-mediated endocytosis (CME) is one of the best studied cellular uptake pathways and its contributions to nutrient uptake, receptor signaling, and maintenance of the lipid membrane homeostasis have been already elucidated. Today, we still have a lack of understanding how the different components of this pathway cooperate dynamically in vivo. Therefore, we generated a reporter mouse model for CME by fusing eGFP endogenously in frame to clathrin light chain a (Clta) to track endocytosis in living mice. The fusion protein is expressed in all tissues, but in a cell specific manner, and can be visualized using fluorescence microscopy. Recruitment to nanobeads recorded by TIRF microscopy validated the functionality of the Clta-eGFP reporter. With this reporter model we were able to track the dynamics of Alexa594-BSA uptake in kidneys of anesthetized mice using intravital 2-photon microscopy. This reporter mouse model is not only a suitable and powerful tool to track CME in vivo in genetic or disease mouse models it can also help to shed light into the differential roles of the two clathrin light chain isoforms in health and disease.

Streptococcal autolysin promotes dysfunction of swine tracheal epithelium by interacting with vimentin

Streptococcus suis serotype 2 (SS2) is a major zoonotic pathogen resulting in manifestations as pneumonia and septic shock. The upper respiratory tract is typically thought to be the main colonization and entry site of SS2 in pigs, but the mechanism through which it penetrates the respiratory barrier is still unclear. In this study, a mutant with low invasive potential to swine tracheal epithelial cells (STECs) was screened from the TnYLB-1 transposon insertion mutant library of SS2, and the interrupted gene was identified as autolysin (atl). Compared to wild-type (WT) SS2, Δatl mutant exhibited lower ability to penetrate the tracheal epithelial barrier in a mouse model. Purified Atl also enhanced SS2 translocation across STEC monolayers in Transwell inserts. Furthermore, Atl redistributed the tight junctions (TJs) in STECs through myosin light chain kinase (MLCK) signaling, which led to increased barrier permeability. Using mass spectrometry, co-immunoprecipitation (co-IP), pull-down, bacterial two-hybrid and saturation binding experiments, we showed that Atl binds directly to vimentin. CRISPR/Cas9-targeted deletion of vimentin in STECs (VIM KO STECs) abrogated the capacity of SS2 to translocate across the monolayers, SS2-induced phosphorylation of myosin II regulatory light chain (MLC) and MLCK transcription, indicating that vimentin is indispensable for MLCK activation. Consistently, vimentin null mice were protected from SS2 infection and exhibited reduced tracheal and lung injury. Thus, MLCK-mediated epithelial barrier opening caused by the Atl-vimentin interaction is found to be likely the key mechanism by which SS2 penetrates the tracheal epithelium.

Streptococcus suis serotype 2 (SS2), an emerging zoonotic agent, can breach the respiratory barrier and cause invasive disease in pigs. Here, we identified the novel role of autolysin Atl in penetration of the respiratory barrier by SS2 and its systemic dissemination and identified its binding partner, vimentin, a type III intermediate filament protein. Atl contributed to the MLCK-triggered redistribution of tight junctions to open the tracheal epithelial barrier. Knockout of vimentin abolished the ability of SS2 to penetrate the monolayer barrier and the activation of MLCK. Furthermore, vimentin null mice were protected from infection by intranasally administered SS2. This study is the first to demonstrate that the interaction between the GBS Bsp-like domain of Atl and vimentin promotes MLCK-mediated dysfunction of the epithelial barrier, which may provide theoretical information for prophylactic and/or therapeutic treatments against diseases caused by similar respiratory pathogens.

An entropic safety catch controls hepatitis C virus entry and antibody resistance

E1 and E2 (E1E2), the fusion proteins of Hepatitis C Virus (HCV), are unlike that of any other virus yet described, and the detailed molecular mechanisms of HCV entry/fusion remain unknown. Hypervariable region-1 (HVR-1) of E2 is a putative intrinsically disordered protein tail. Here, we demonstrate that HVR-1 has an autoinhibitory function that suppresses the activity of E1E2 on free virions; this is dependent on its conformational entropy. Thus, HVR-1 is akin to a safety catch that prevents premature triggering of E1E2 activity. Crucially, this mechanism is turned off by host receptor interactions at the cell surface to allow entry. Mutations that reduce conformational entropy in HVR-1, or genetic deletion of HVR-1, turn off the safety catch to generate hyper-reactive HCV that exhibits enhanced virus entry but is thermally unstable and acutely sensitive to neutralising antibodies. Therefore, the HVR-1 safety catch controls the efficiency of virus entry and maintains resistance to neutralising antibodies. This discovery provides an explanation for the ability of HCV to persist in the face of continual immune assault and represents a novel regulatory mechanism that is likely to be found in other viral fusion machinery.

3D Human Organoids: The Next "Viral" Model for the Molecular Basis of Infectious Diseases

The COVID-19 pandemic has driven the scientific community to adopt an efficient and reliable model that could keep up with the infectious disease arms race. Coinciding with the pandemic, three dimensional (3D) human organoids technology has also gained traction in the field of infectious disease. An in vitro construct that can closely resemble the in vivo organ, organoid technology could bridge the gap between the traditional two-dimensional (2D) cell culture and animal models. By harnessing the multi-lineage characteristic of the organoid that allows for the recapitulation of the organotypic structure and functions, 3D human organoids have emerged as an essential tool in the field of infectious disease research. In this review, we will be providing a comparison between conventional systems and organoid models. We will also be highlighting how organoids played a role in modelling common infectious diseases and molecular mechanisms behind the pathogenesis of causative agents. Additionally, we present the limitations associated with the current organoid models and innovative strategies that could resolve these shortcomings.

Micronutrient Improvement of Epithelial Barrier Function in Various Disease States: A Case for Adjuvant Therapy

The published literature makes a very strong case that a wide range of disease morbidity associates with and may in part be due to epithelial barrier leak. An equally large body of published literature substantiates that a diverse group of micronutrients can reduce barrier leak across a wide array of epithelial tissue types, stemming from both cell culture as well as animal and human tissue models. Conversely, micronutrient deficiencies can exacerbate both barrier leak and morbidity. Focusing on zinc, Vitamin A and Vitamin D, this review shows that at concentrations above RDA levels but well below toxicity limits, these micronutrients can induce cell- and tissue-specific molecular-level changes in tight junctional complexes (and by other mechanisms) that reduce barrier leak. An opportunity now exists in critical care—but also medical prophylactic and therapeutic care in general—to consider implementation of select micronutrients at elevated dosages as adjuvant therapeutics in a variety of disease management. This consideration is particularly pointed amidst the COVID-19 pandemic.

Impact of HCV Infection on Hepatocyte Polarity and Plasticity

The hepatitis C virus (HCV) is an oncogenic virus that alters the cell polarization machinery in order to enter the hepatocyte and replicate. While these alterations are relatively well defined, their consequences in the evolution of the disease remain poorly documented. Since 2012, HCV infection can be effectively cured with the advent of direct acting antivirals (DAA). Nevertheless, patients cured of their HCV infection still have a high risk of developing hepatocellular carcinoma (HCC). Importantly, it has been shown that some of the deregulations induced by HCV are maintained despite a sustained virologic response (SVR), including the down-regulation of some hepatocyte functions such as bile acid metabolism, exemplifying cell dedifferentiation, and the up-regulation of the epithelial–mesenchymal transition (EMT). EMT is a process by which epithelial cells lose their differentiation and their specific polarity to acquire mesenchymal cell properties, including migration and extracellular matrix remodeling capabilities. Of note, epithelial cell polarity acts as a gatekeeper against EMT. Thus, it remains important to elucidate the mechanisms by which HCV alters polarity and promotes EMT that could participate in viral-induced hepatic carcinogenesis. In this review, we define the main steps involved in the polarization process of epithelial cells and recall the essential cellular actors involved. We also highlight the particularities of hepatocyte polarity, responsible for their unique morphology. We then focus on the alterations by HCV of epithelial cell polarity and the consequences of the transformation of hepatocytes involved in the carcinogenesis process.

Applications of Brain Organoids for Infectious Diseases

Brain organoids are self-organized three-dimensional aggregates generated from pluripotent stem cells. They exhibit complex cell diversities and organized architectures that resemble human brain development ranging from neural tube formation, neuroepithelium differentiation, neurogenesis and gliogenesis, to neural circuit formation. Rapid advancements in brain organoid culture technologies have allowed researchers to generate more accurate models of human brain development and neurological diseases. These models also allow for direct investigation of pathological processes associated with infectious diseases affecting the nervous system. In this review, we first briefly summarize recent advancements in brain organoid methodologies and neurodevelopmental processes that can be effectively modeled by brain organoids. We then focus on applications of brain organoids to investigate the pathogenesis of neurotropic viral infection. Finally, we discuss limitations of the current brain organoid methodologies as well as applications of other organ specific organoids in the infectious disease research.

Organoid Models for Infectious Disease

Infectious diseases affect individual health and have widespread societal impacts. New ex vivo models are critical to understand pathogenesis, host response, and features necessary to develop preventive and therapeutic treatments. Pluripotent and tissue stem cell-derived organoids provide new tools for the study of human infections. Organoid models recapitulate many characteristics of in vivo disease and are providing new insights into human respiratory, gastrointestinal, and neuronal host-microbe interactions. Increasing culture complexity by adding the stroma, interorgan communication, and the microbiome will improve the use of organoids as models for infection. Organoid cultures provide a platform with the capability to improve human health related to infectious diseases. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Stem cell therapy in liver regeneration: Focus on mesenchymal stem cells and induced pluripotent stem cells

The liver has the ability to repair itself after injury; however, a variety of pathological changes in the liver can affect its ability to regenerate, and this could lead to liver failure. Mesenchymal stem cells (MSCs) are considered a good source of cells for regenerative medicine, as they regulate liver regeneration through different mechanisms, and their efficacy has been demonstrated by many animal experiments and clinical studies. Induced pluripotent stem cells, another good source of MSCs, have also made great progress in the establishment of organoids, such as liver disease models, and in drug screening. Owing to the recent developments in MSCs and induced pluripotent stem cells, combined with emerging technologies including graphene, nano-biomaterials, and gene editing, precision medicine and individualized clinical treatment may be realized in the near future.

Organoid engineering with microfluidics and biomaterials for liver, lung disease, and cancer modeling

As life expectancy improves and the number of people suffering from various diseases increases, the need for developing effective personalized disease models is rapidly rising. The development of organoid technology has led to better recapitulation of the in vivo environment of organs, and can overcome the constraints of existing disease models. However, for more precise disease modeling, engineering approaches such as microfluidics and biomaterials, that aid in mimicking human physiology, need to be integrated with the organoid models. In this review, we introduce key elements for disease modeling and recent engineering advances using both liver and lung organoids. Due to the importance of personalized medicine, we also emphasize patient-derived cancer organoid models and their engineering approaches. These organoid-based disease models combined with microfluidics, biomaterials, and co-culture systems will provide a powerful research platform for understanding disease mechanisms and developing precision medicine; enabling preclinical drug screening and drug development. STATEMENT OF SIGNIFICANCE: The development of organoid technology has led to better recapitulation of the in vivo environment of organs, and can overcome the constraints of existing disease models. However, for more precise disease modeling, engineering approaches such as microfluidics and biomaterials, that aid in mimicking human physiology, need to be integrated with the organoid models. In this review, we introduce liver, lung, and cancer organoids integrated with various engineering approaches as a novel platform for personalized disease modeling. These engineered organoid-based disease models will provide a powerful research platform for understanding disease mechanisms and developing precision medicine.

Contribution of Extracellular Matrix Component Landscapes in the Adult Subventricular Zone to the Positioning of Neural Stem/Progenitor Cells

Neurogenesis persists in restricted regions of the adult brain, including the subventricular zone (SVZ). Adult neural stem cells (NSCs) in the SVZ proliferate and give rise to new neurons and glial cells depending on intrinsic and environmental cues. Among the multiple factors that contribute to the chemical, physical, and mechanical components of the neurogenic niche, we focused on the composition of the extracellular matrix (ECM) of vasculature and fractones in the SVZ. The SVZ consists of ECM-rich blood vessels and fractones during development and adulthood, and adult neural stem/progenitor cells (NS/PCs) preferentially attach to the laminin-rich basal lamina. To examine the ECM preference of adult NS/PCs, we designed a competition assay using cell micropatterning. Although both laminin and collagen type IV, which are the main components of basal lamina, act as physical scaffolds, adult NS/PCs preferred to adhere to laminin over collagen type IV. Interestingly, the ECM preference of adult NS/PCs could be manipulated by chemokines such as stromal-derived factor 1 (SDF1) and α6 integrin. As SDF1 re-routes NSCs and their progenitors toward the injury site after brain damage, these results suggest that the alteration in ECM preferences may provide a molecular basis for context-dependent NS/PC positioning.

Liver Organoids: Updates on Disease Modeling and Biomedical Applications

Liver organoids are stem cell-derived 3D structures that are generated by liver differentiation signals in the presence of a supporting extracellular matrix. Liver organoids overcome low complexity grade of bidimensional culture and high costs of in vivo models thus representing a turning point for studying liver disease modeling. Liver organoids can be established from different sources as induced pluripotent stem cells (iPSCs), embryonic stem cells (ESCs), hepatoblasts and tissue-derived cells. This novel in vitro system represents an innovative tool to deeper understand the physiology and pathological mechanisms affecting the liver. In this review, we discuss the current advances in the field focusing on their application in modeling diseases, regenerative medicine and drug discovery.

Organoids in modelling infectious diseases

Approaches based on animal and two-dimensional (2D) cell culture models cannot ensure reliable results in modeling novel pathogens or in drug testing in the short term; therefore, there is rising interest in platforms such as organoids. To develop a toolbox that can be used successfully to overcome current issues in modeling various infections, it is essential to provide a framework of recent achievements in applying organoids. Organoids have been used to study viruses, bacteria, and protists that cause, for example, respiratory, gastrointestinal, and liver diseases. Their future as models of infection will be associated with improvements in system complexity, including abilities to model tissue structure, a dynamic microenvironment, and coinfection. Teaser. Organoids are a flexible tool for modelling viral, bacterial and protist infections. They can provide fast and reliable information on the biology of pathogens and in drug screening, and thus have become essential in combatting emerging infectious diseases.

Cellular factors involved in the hepatitis C virus life cycle

The hepatitis C virus (HCV), an obligatory intracellular pathogen, highly depends on its host cells to propagate successfully. The HCV life cycle can be simply divided into several stages including viral entry, protein translation, RNA replication, viral assembly and release. Hundreds of cellular factors involved in the HCV life cycle have been identified over more than thirty years of research. Characterization of these cellular factors has provided extensive insight into HCV replication strategies. Some of these cellular factors are targets for anti-HCV therapies. In this review, we summarize the well-characterized and recently identified cellular factors functioning at each stage of the HCV life cycle.

Modeling Hepatotropic Viral Infections: Cells vs. Animals

The lack of an appropriate platform for a better understanding of the molecular basis of hepatitis viruses and the absence of reliable models to identify novel therapeutic agents for a targeted treatment are the two major obstacles for launching efficient clinical protocols in different types of viral hepatitis. Viruses are obligate intracellular parasites, and the development of model systems for efficient viral replication is necessary for basic and applied studies. Viral hepatitis is a major health issue and a leading cause of morbidity and mortality. Despite the extensive efforts that have been made on fundamental and translational research, traditional models are not effective in representing this viral infection in a laboratory. In this review, we discuss in vitro cell-based models and in vivo animal models, with their strengths and weaknesses. In addition, the most important findings that have been retrieved from each model are described.

Advances in development and application of human organoids

Innumerable studies associated with cellular differentiation, tissue response and disease modeling have been conducted in two-dimensional (2D) culture systems or animal models. This has been invaluable in deciphering the normal and disease states in cell biology; the key shortcomings of it being suitability for translational or clinical correlations. The past decade has seen several major advances in organoid culture technologies and this has enhanced our understanding of mimicking organ reconstruction. The term organoid has generally been used to describe cellular aggregates derived from primary tissues or stem cells that can self-organize into organotypic structures. Organoids mimic the cellular microenvironment of tissues better than 2D cell culture systems and represent the tissue physiology. Human organoids of brain, thyroid, gastrointestinal, lung, cardiac, liver, pancreatic and kidney have been established from various diseases, healthy tissues and from pluripotent stem cells (PSCs). Advances in patient-derived organoid culture further provides a unique perspective from which treatment modalities can be personalized. In this review article, we have discussed the current strategies for establishing various types of organoids of ectodermal, endodermal and mesodermal origin. We have also discussed their applications in modeling human health and diseases (such as cancer, genetic, neurodegenerative and infectious diseases), applications in regenerative medicine and evolutionary studies.

Optimized cell systems for the investigation of hepatitis C virus E1E2 glycoproteins

Great strides have been made in understanding and treating hepatitis C virus (HCV) thanks to the development of various experimental systems including cell-culture-proficient HCV, the HCV pseudoparticle system and soluble envelope glycoproteins. The HCV pseudoparticle (HCVpp) system is a platform used extensively in studies of cell entry, screening of novel entry inhibitors, assessing the phenotypes of clinically observed E1 and E2 glycoproteins and, most pertinently, in characterizing neutralizing antibody breadth induced upon vaccination and natural infection in patients. Nonetheless, some patient-derived clones produce pseudoparticles that are either non-infectious or exhibit infectivity too low for meaningful phenotyping. The mechanisms governing whether any particular clone produces infectious pseudoparticles are poorly understood. Here we show that endogenous expression of CD81, an HCV receptor and a cognate-binding partner of E2, in producer HEK 293T cells is detrimental to the infectivity of recovered HCVpp for most strains. Many HCVpp clones exhibited increased infectivity or had their infectivity rescued when they were produced in 293T cells CRISPR/Cas9 engineered to ablate CD81 expression (293T^CD81KO). Clones made in 293T^CD81KO cells were antigenically very similar to their matched counterparts made parental cells and appear to honour the accepted HCV entry pathway. Deletion of CD81 did not appreciably increase the recovered titres of soluble E2 (sE2). However, we did, unexpectedly, find that monomeric sE2 made in 293T cells and Freestyle 293-F (293-F) cells exhibit important differences. We found that 293-F-produced sE2 harbours mostly complex-type glycans whilst 293T-produced sE2 displays a heterogeneous mixture of both complex-type glycans and high-mannose or hybrid-type glycans. Moreover, sE2 produced in 293T cells is antigenically superior; exhibiting increased binding to conformational antibodies and the large extracellular loop of CD81. In summary, this work describes an optimal cell line for the production of HCVpp and reveals that sE2 made in 293T and 293-F cells are not antigenic equals. Our findings have implications for functional studies of E1E2 and the production of candidate immunogens.

Kinase Inhibitors as Underexplored Antiviral Agents

Viral infections are a major health problem; therefore, there is an urgent need for novel therapeutic strategies. Antivirals used to target proteins encoded by the viral genome usually enhance drug resistance generated by the virus. A potential solution may be drugs acting at host-based targets since viruses are dependent on numerous cellular proteins and phosphorylation events that are crucial during their life cycle. Repurposing existing kinase inhibitors as antiviral agents would help in the cost and effectiveness of the process, but this strategy usually does not provide much improvement, and specific medicinal chemistry programs are needed in the field. Anyway, extensive use of FDA-approved kinase inhibitors has been quite useful in deciphering the role of host kinases in viral infection. The present perspective aims to review the state of the art of kinase inhibitors that target viral infections in different development stages.

Bioengineered Liver Cell Models of Hepatotropic Infections

Hepatitis viruses and liver-stage malaria are within the liver infections causing higher morbidity and mortality rates worldwide. The highly restricted tropism of the major human hepatotropic pathogens-namely, the human hepatitis B and C viruses and the Plasmodium falciparum and Plasmodium vivax parasites-has hampered the development of disease models. These models are crucial for uncovering the molecular mechanisms underlying the biology of infection and governing host-pathogen interaction, as well as for fostering drug development. Bioengineered cell models better recapitulate the human liver microenvironment and extend hepatocyte viability and phenotype in vitro, when compared with conventional two-dimensional cell models. In this article, we review the bioengineering tools employed in the development of hepatic cell models for studying infection, with an emphasis on 3D cell culture strategies, and discuss how those tools contributed to the level of recapitulation attained in the different model layouts. Examples of host-pathogen interactions uncovered by engineered liver models and their usefulness in drug development are also presented. Finally, we address the current bottlenecks, trends, and prospect toward cell models' reliability, robustness, and reproducibility.

Hepatitis C Virus Uses Host Lipids to Its Own Advantage

Lipids and lipoproteins constitute indispensable components for living not only for humans. In the case of hepatitis C virus (HCV), the option of using the products of our lipid metabolism is “to be, or not to be”. On the other hand, HCV infection, which is the main cause of chronic hepatitis, cirrhosis and hepatocellular carcinoma, exerts a profound influence on lipid and lipoprotein metabolism of the host. The consequences of this alternation are frequently observed as hypolipidemia and hepatic steatosis in chronic hepatitis C (CHC) patients. The clinical relevance of these changes reflects the fact that lipids and lipoprotein play a crucial role in all steps of the life cycle of HCV. The virus circulates in the bloodstream as a highly lipidated lipo-viral particle (LVP) that defines HCV hepatotropism. Thus, strict relationships between lipids/lipoproteins and HCV are indispensable for the mechanism of viral entry into hepatocytes, viral replication, viral particles assembly and secretion. The purpose of this review is to summarize the tricks thanks to which HCV utilizes host lipid metabolism to its own advantage.

Microfilaments and microtubules alternately coordinate the multi-step endosomal trafficking of Classical Swine Fever Virus

Cytoskeleton, as a ubiquitous structure in the cells, plays an important role in the process of virus entry, replication, and survival. However, the action mechanism of cytoskeleton in the invasion of Pestivirus into host cells remains unclear. In this study, we systematically dissected the key roles of the main cytoskeleton components, microfilaments and microtubules in the endocytosis of porcine Pestivirus, Classical swine fever virus (CSFV). We observed the dynamic changes of actin filaments in CSFV entry. Confocal microscopy showed that CSFV invasion induced the dissolution and aggregation of stress fibers, resulting in the formation of lamellipodia and filopodia. Chemical inhibitors and RNA interference were used to find that the dynamic changes of actin were caused by EGFR-PI3K/MAPK-RhoA/Rac1/Cdc42-cofilin signaling pathway, which regulates the microfilaments to help CSFV entry. Furthermore, co-localization of the microfilaments with clathrin and Rab5 (early endosome), as well as microtubules with Rab7 (late endosome) and Lamp1 (lysosome) revealed that microfilaments were activated and rearranged to help CSFV trafficking to early endosome after endocytosis. Subsequently, recruitment of microtubules by CSFV also assisted membrane fusion of the virions from late endosome to lysosome with the help of a molecular motor, dynein. Unexpectedly, vimentin, which is an intermediate filament, had no effect on CSFV entry. Taken together, our findings comprehensively revealed the molecular mechanisms of cytoskeletal components that regulated CSFV endocytosis and facilitated further understanding of Pestivirus entry, which would be conducive to explore antiviral molecules to control classical swine fever.IMPORTANCEEndocytosis, an essential biological process mediating cellular internalization events, is often exploited by pathogens for their entry into target cells. Previously, we have reported different mechanisms of CSFV endocytosis into the porcine epithelial cells (PK-15) and macrophages (3D4/21); however, the details of microfilaments/microtubules mediated virus migration within the host cells remained to be elucidated. In this study, we found that CSFV infection induced rearrangement of actin filaments regulated by cofilin through EGFR-PI3K/MAPK-RhoA/Rac1/Cdc42 pathway. Furthermore, we found that CSFV particles were trafficked along actin filaments in early and late endosomes, and through microtubules in lysosomes after entry. Here, we provide for the first time a comprehensive description of the cytoskeleton that facilitates entry and intracellular transport of highly pathogenic swine virus. Results from this study will greatly contribute to the understanding of virus-induced early and complex changes in host cells that are important in CSFV pathogenesis.

3D culture models to study SARS-CoV-2 infectivity and antiviral candidates: From spheroids to bioprinting

The pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is receiving worldwide attention, due to the severity of the disease (COVID-19) that resulted in more than a million global deaths so far. The urgent need for vaccines and antiviral drugs is mobilizing the scientific community to develop strategies for studying the mechanisms of SARS-CoV-2 infection, replication kinetics, pathogenesis, host-virus interaction, and infection inhibition. In this work, we review the strategies of tissue engineering in the fabrication of three-dimensional (3D) models used in virology studies, which presented many advantages over conventional cell cultures, such as complex cytoarchitecture and a more physiological microenvironment. Scaffold-free (spheroids and organoids) and scaffold-based (3D scaffolding and 3D bioprinting) approach allow the biofabrication of more realistic models relevant to the pandemic, to be used as in vitro platforms for the development of new vaccines and therapies against COVID-19.

Investigating virus-host cell interactions: Comparative binding forces between hepatitis C virus-like particles and host cell receptors in 2D and 3D cell culture models

Cell cultures have been successfully used to study hepatitis C virus (HCV) for many years. However, most work has been done using traditional, 2-dimensional (2D) cell cultures (cells grown as a monolayer in growth flasks or dishes). Studies have shown that when cells are grown suspended in an extra-cellular-matrix-like material, they develop into spherical, 'organoid' arrangements of cells (3D growth) that display distinct differences in morphological and functional characteristics compared to 2D cell cultures. In liver organoids, one key difference is the development of clearly differentiated apical and basolateral surfaces separated and maintained by cellular tight junctions. This phenomenon, termed polarity, is vital to normal barrier function of hepatocytes in vivo. It has also been shown that viruses, and virus-like particles, interact very differently with cells derived from 2D as compared to 3D cell cultures, bringing into question the usefulness of 2D cell cultures to study virus-host cell interactions. Here, we investigate differences in cellular architecture as a function of cell culture system, using confocal scanning laser microscopy, and determine differences in binding interactions between HCV virus-like particles (VLPs) and their cognate receptors in the different cell culture systems using atomic force microscopy (AFM). We generated organoid cultures that were polarized, as determined by localization of key apical and basolateral markers. We found that, while uptake of HCV VLPs by both 2D and 3D Huh7 cells was observed by flow cytometry, binding interactions between HCV VLPs and cells were measurable by AFM only on polarized cells. The work presented here adds to the growing body of research suggesting that polarized cell systems are more suitable for the study of HCV infection and dynamics than non-polarized systems.

Three-Dimensional Cell Culture Systems for Studying Hepatitis C Virus

Hepatocytes, the major target of hepatitis C virus (HCV), are highly polarized. HCV infection requires extensive trafficking to distinct subcellular domains in the polarized hepatocyte. Polarized cells and three-dimensional organoids are commonly used to study liver functions and differentiation. Researchers have begun adapting these cell culture models that morphologically and physiologically resemble hepatocytes in vivo to study HCV infection. This review summarizes the use of three-dimensional cell culture systems in studies of HCV infection.

Novel approaches to liver disease diagnosis and modeling

Lack of a prompt and accurate diagnosis remains on top of the list of challenges faced by patients with rare liver diseases. Although rare liver diseases affect a significant percentage of the population as a group, when taken singularly they represent unique diseases and the approaches used for diagnosis of common liver diseases are insufficient. However, the development of new methods for the acquisition of molecular and clinical data (i.e., genomic, proteomics, metabolomics) and computational tools for their analysis and integration, together with advances in modeling diseases using stem cell-based technology [i.e., induced pluripotent stem cells (iPSCs) and tissue organoids] represent a promising and powerful tool to improve the clinical management of these patients. This is the goal of precision medicine, a novel approach of modern medicine that aims at delivering a specific treatment based on disease-specific biological insights and individual profile. This review will discuss the application and advances of these technologies and how they represent a new opportunity in hepatology.

Gaining New Biological and Therapeutic Applications into the Liver with 3D In Vitro Liver Models

BACKGROUND

Three-dimensional (3D) cell cultures with architectural and biomechanical properties similar to those of natural tissue have been the focus for generating liver tissue. Microarchitectural organization is believed to be crucial to hepatic function, and 3D cell culture technologies have enabled the construction of tissue-like microenvironments, thereby leading to remarkable progress in vitro models of human tissue and organs. Recently, to recapitulate the 3D architecture of tissues, spheroids and organoids have become widely accepted as new practical tools for 3D organ modeling. Moreover, the combination of bioengineering approach offers the promise to more accurately model the tissue microenvironment of human organs. Indeed, the employment of sophisticated bioengineered liver models show long-term viability and functional enhancements in biochemical parameters and disease-orient outcome.

RESULTS

Various 3D in vitro liver models have been proposed as a new generation of liver medicine. Likewise, new biomedical engineering approaches and platforms are available to more accurately replicate the in vivo 3D microarchitectures and functions of living organs. This review aims to highlight the recent 3D in vitro liver model systems, including micropatterning, spheroids, and organoids that are either scaffold-based or scaffold-free systems. Finally, we discuss a number of challenges that will need to be addressed moving forward in the field of liver tissue engineering for biomedical applications.

CONCLUSION

The ongoing development of biomedical engineering holds great promise for generating a 3D biomimetic liver model that recapitulates the physiological and pathological properties of the liver and has biomedical applications.