Organoids of liver diseases: From bench to bedside

Organoids: a novel modality in disease modeling

Limitations of monolayer culture conditions have motivated scientists to explore new models that can recapitulate the architecture and function of human organs more accurately. Recent advances in the improvement of protocols have resulted in establishing three-dimensional (3D) organ-like architectures called ‘organoids’ that can display the characteristics of their corresponding real organs, including morphological features, functional activities, and personalized responses to specific pathogens. We discuss different organoid-based 3D models herein, which are classified based on their original germinal layer. Studies of organoids simulating the complexity of real tissues could provide novel platforms and opportunities for generating practical knowledge along with preclinical studies, including drug screening, toxicology, and molecular pathophysiology of diseases. This paper also outlines the key challenges, advantages, and prospects of current organoid systems.

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.

Liver organoid as a 3D in vitro model for drug validation and toxicity assessment

The past decade has seen many advancements in the development of three-dimensional (3D) in vitro models in pharmaceutical sciences and industry. Specifically, organoids present a self-organising, self-renewing and more physiologically relevant model than conventional two-dimensional (2D) cell cultures. Liver organoids have been developed from a variety of cell sources, including stem cells, cell lines and primary cells. They have potential for modelling patient-specific disease and establishing personalised therapeutic approaches. Additionally, liver organoids have been used to test drug efficacy and toxicity. Herein we summarise cell sources for generating liver organoids, the advantages and limitations of each cell type, as well as the application of the organoids in modelling liver diseases. We focus on the use of liver organoids as tools for drug validation and toxicity assessment.

Adipose-Derived Stem Cells: Current Applications and Future Directions in the Regeneration of Multiple Tissues

Adipose-derived stem cells (ADSCs) can maintain self-renewal and enhanced multidifferentiation potential through the release of a variety of paracrine factors and extracellular vesicles, allowing them to repair damaged organs and tissues. Consequently, considerable attention has increasingly been paid to their application in tissue engineering and organ regeneration. Here, we provide a comprehensive overview of the current status of ADSC preparation, including harvesting, isolation, and identification. The advances in preclinical and clinical evidence-based ADSC therapy for bone, cartilage, myocardium, liver, and nervous system regeneration as well as skin wound healing are also summarized. Notably, the perspectives, potential challenges, and future directions for ADSC-related researches are discussed. We hope that this review can provide comprehensive and standardized guidelines for the safe and effective application of ADSCs to achieve predictable and desired therapeutic effects.

Organ-on-a-Chip: A Preclinical Microfluidic Platform for the Progress of Nanomedicine

Despite the progress achieved in nanomedicine during the last decade, the translation of new nanotechnology-based therapeutic systems into clinical applications has been slow, especially due to the lack of robust preclinical tissue culture platforms able to mimic the in vivo conditions found in the human body and to predict the performance and biotoxicity of the developed nanomaterials. Organ-on-a-chip (OoC) platforms are novel microfluidic tools that mimic complex human organ functions at the microscale level. These integrated microfluidic networks, with 3D tissue engineered models, have been shown high potential to reduce the discrepancies between the results derived from preclinical and clinical trials. However, there are many challenges that still need to be addressed, such as the integration of biosensor modules for long-time monitoring of different physicochemical and biochemical parameters. In this review, recent advances on OoC platforms, particularly on the preclinical validation of nanomaterials designed for cancer, as well as the current challenges and possible future directions for an end-use perspective are discussed.

Time-restricted feeding downregulates cholesterol biosynthesis program via RORγ-mediated chromatin modification in porcine liver organoids

BACKGROUND

Time-restricted feeding (TRF) is a dieting strategy based on nutrients availability and diurnal rhythm, shown to improve lipid metabolism efficiency. We have demonstrated previously that retinoic acid-related (RAR) orphan receptor (ROR) γ is the primary transcription factor controlling cholesterol (CHO) biosynthesis program of animals. However, the functional role of RORγ in liver physiology of pigs in response to TRF has not been determined, largely due to the lack of functional models and molecular tools. In the present study, we established porcine liver organoids and subjected them to restricted nutrients supply for 10-h during the light portion of the day.

RESULTS

Our results showed that TRF regimen did not alter hepatocyte physiology, including unchanged cell viability, caspase 3/7 enzyme activity and the gene signature of cell proliferation in porcine liver organoids, compared to the control group (P > 0.05). Furthermore, we found that TRF downregulated the hepatic CHO biosynthesis program at both mRNA and protein levels, along with the reduced cellular CHO content in porcine liver organoids (P < 0.05). Using unbiased bioinformatic analysis of a previous ChIP-seq data and ChIP-qPCR validation, we revealed RORγ as the predominant transcription factor that responded to TRF, amongst the 12 targeted nuclear receptors (NRs) (P < 0.05). This was likely through RORγ direct binding to the MVK gene (encoding mevalonate kinase). Finally, we showed that RORγ agonists and overexpression enhanced the enrichment of co-factor p300, histone marks H3K27ac and H3K4me1/2, as well as RNA polymerase II (Pol-II) at the locus of MVK, in TRF-porcine liver organoids, compared to TRF-vector control (P < 0.05).

CONCLUSIONS

Our findings demonstrate that TRF triggers the RORγ-mediated chromatin remodeling at the locus of CHO biosynthesis genes in porcine liver organoids and further improves lipid metabolism.

Generation of multi-cellular human liver organoids from pluripotent stem cells

A growing number of in vitro hepatic models exist to study human genetics, liver biology, disease modeling and drug development and range from 2D hepatocytes to 3D multi-cellular tissues that are derived from human stem cells. However, stem cell-based models generally suffer from batch-, clone- and donor-dependent variability, hindering broader usage in diverse biomedical applications. To circumvent this challenge, we herein describe a reproducible protocol to generate human liver organoids in 20-25 days derived from pluripotent stem cells (PSCs). These organoids are intra-luminally polarized to form canalicular structures and are comprised of mainly hepatic epithelial cells, co-differentiated with stellate-like and hepatic macrophage-like cells that enables hepatic inflammatory disease modeling in vitro. These multi-lineage liver organoids express hepatocyte genes, secrete albumin and have vital metabolic functions. This protocol utilizes PSC derived 3D human liver organoids as a renewable, reproducible and personalized cell source, thus facilitating disease modeling and mechanistic studies with a future goal of developing novel therapeutics against currently intractable diseases.

Organoids and Microphysiological Systems: New Tools for Ophthalmic Drug Discovery

Organoids are adept at preserving the inherent complexity of a given cellular environment and when integrated with engineered micro-physiological systems (MPS) present distinct advantages for simulating a precisely controlled geometrical, physical, and biochemical micro-environment. This then allows for real-time monitoring of cell-cell interactions. As a result, the two aforementioned technologies hold significant promise and potential in studying ocular physiology and diseases by replicating specific eye tissue microstructures in vitro. This miniaturized review begins with defining the science behind organoids/MPS and subsequently introducing methods for generating organoids and engineering MPS. Furthermore, we will discuss the current state of organoids and MPS models in retina, cornea surrogates, and other ocular tissue, in regards to physiological/disease conditions. Finally, future prospective on organoid/MPS will be covered here. Organoids and MPS technologies closely recapture the in vivo microenvironment and thusly will continue to provide new understandings in organ functions and novel approaches to drug development.

Advanced Biomaterials and Processing Methods for Liver Regeneration: State-of-the-Art and Future Trends

Liver diseases contribute markedly to the global burden of mortality and disease. The limited organ disposal for orthotopic liver transplantation results in a continuing need for alternative strategies. Over the past years, important progress has been made in the field of tissue engineering (TE). Many of the early trials to improve the development of an engineered tissue construct are based on seeding cells onto biomaterial scaffolds. Nowadays, several TE approaches have been developed and are applied to one vital organ: the liver. Essential elements must be considered in liver TE-cells and culturing systems, bioactive agents or growth factors (GF), and biomaterials and processing methods. The potential of hepatocytes, mesenchymal stem cells, and others as cell sources is demonstrated. They need engineered biomaterial-based scaffolds with perfect biocompatibility and bioactivity to support cell proliferation and hepatic differentiation as well as allowing extracellular matrix deposition and vascularization. Moreover, they require a microenvironment provided using conventional or advanced processing technologies in order to supply oxygen, nutrients, and GF. Herein the biomaterials and the conventional and advanced processing technologies, including cell-sheets process, 3D bioprinting, and microfluidic systems, as well as the future trends in these major fields are discussed.

Pluripotent-Stem-Cell-Derived Hepatic Cells: Hepatocytes and Organoids for Liver Therapy and Regeneration

The liver is a very complex organ that ensures numerous functions; it is thus susceptible to multiple types of damage and dysfunction. Since 1983, orthotopic liver transplantation (OLT) has been considered the only medical solution available to patients when most of their liver function is lost. Unfortunately, the number of patients waiting for OLT is worryingly increasing, and extracorporeal liver support devices are not yet able to counteract the problem. In this review, the current and expected methodologies in liver regeneration are briefly analyzed. In particular, human pluripotent stem cells (hPSCs) as a source of hepatic cells for liver therapy and regeneration are discussed. Principles of hPSC differentiation into hepatocytes are explored, along with the current limitations that have led to the development of 3D culture systems and organoid production. Expected applications of these organoids are discussed with particular attention paid to bio artificial liver (BAL) devices and liver bio-fabrication.

Potential Clinical Applications of Stem Cells in Regenerative Medicine

The field of regenerative medicine is looking for a pluripotent/multipotent stem cell able to differentiate across germ layers and be safely employed in therapy. Unfortunately, with the exception of hematopoietic stem/progenitor cells (HSPCs) for hematological applications, the current clinical results with stem cells are somewhat disappointing. The potential clinical applications of the more primitive embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have so far been discouraging, as both have exhibited several problems, including genomic instability, a risk of teratoma formation, and the possibility of rejection. Therefore, the only safe stem cells that have so far been employed in regenerative medicine are monopotent stem cells, such as the abovementioned HSPCs or mesenchymal stem cells (MSCs) isolated from postnatal tissues. However, their monopotency, and therefore limited differentiation potential, is a barrier to their broader application in the clinic. Interestingly, results have accumulated indicating that adult tissues contain rare, early-development stem cells known as very small embryonic-like stem cells (VSELs), which can differentiate into cells from more than one germ layer. This chapter addresses different sources of stem cells for potential clinical application and their advantages and problems to be solved.