Organogenesis in vitro

Organoids as a novel tool in modelling infectious diseases

Infectious diseases worldwide affect human health and have important societal impacts. A better understanding of infectious diseases is urgently needed. In vitro and in vivo infection models have brought notable contributions to the current knowledge of these diseases. Organoids are multicellular culture systems resembling tissue architecture and function, recapitulating many characteristics of human disease and elucidating mechanisms of host-infectious agent interactions in the respiratory and gastrointestinal systems, the central nervous system and the skin. Here, we discuss the applicability of the organoid technology for modeling pathogenesis, host response and features, which can be explored for the development of preventive and therapeutic treatments.

Mapping and exploring the organoid state space using synthetic biology

The functional relevance of an organoid is dependent on the differentiation, morphology, cell arrangement and biophysical properties, which collectively define the state of an organoid. For an organoid culture, an individual organoid or the cells that compose it, these state variables can be characterised, most easily by transcriptomics and by high-content image analysis. Their states can be compared to their in vivo counterparts. Current evidence suggests that organoids explore a wider state space than organs in vivo due to the lack of niche signalling and the variability of boundary conditions in vitro. Using data-driven state inference and in silico modelling, phase diagrams can be constructed to systematically sort organoids along biochemical or biophysical axes. These phase diagrams allow us to identify control strategies to modulate organoid state. To do so, the biochemical and biophysical environment, as well as the cells that seed organoids, can be manipulated.

Multicellular Liver Organoids: Generation and Importance of Diverse Specialized Cellular Components

Over 40,000 patients in the United States are estimated to suffer from end-stage liver disease and acute hepatic failure, for which liver transplantation is the only available therapy. Human primary hepatocytes (HPH) have not been employed as a therapeutic tool due to the difficulty in growing and expanding them in vitro, their sensitivity to cold temperatures, and tendency to dedifferentiate following two-dimensional culture. The differentiation of human-induced pluripotent stem cells (hiPSCs) into liver organoids (LO) has emerged as a potential alternative to orthotropic liver transplantation (OLT). However, several factors limit the efficiency of liver differentiation from hiPSCs, including a low proportion of differentiated cells capable of reaching a mature phenotype, the poor reproducibility of existing differentiation protocols, and insufficient long-term viability in vitro and in vivo. This review will analyze various methodologies being developed to improve hepatic differentiation from hiPSCs into liver organoids, paying particular attention to the use of endothelial cells as supportive cells for their further maturation. Here, we demonstrate why differentiated liver organoids can be used as a research tool for drug testing and disease modeling, or employed as a bridge for liver transplantation following liver failure.

Monitoring Effects of Membrane Traffic Via Changes in Cell Polarity and Morphogenesis in Three-Dimensional Human Pluripotent Stem Cell Cysts

Membrane traffic at the Golgi and endosomes plays many critical roles in the polarization and the morphogenesis of epithelial tissues. Studies into the roles of traffic in morphogenesis in mammals are often complicated by early embryonic lethality of mutations in membrane traffic as well as the inherent difficulty in imaging developing embryos posed by their size and location. Increasingly, human pluripotent stem cell (hPSC)-derived embryo- and organ-like systems (e.g., embryoids, organoids) provide a useful platform to illuminate the requirements of traffic in human embryonic tissue morphogenesis because these in vitro models are highly amenable to fluorescence microscopy and provide the ability to examine the role of essential genes not possible with animal studies. Here, we present a method to generate hPSC-cysts, a 3-D hPSC-based model of human epiblast lumen formation. This system provides unique opportunities to examine the role of membrane traffic during epithelial morphogenesis. We also present methods to process hPSC-cysts for immunofluorescence and staining with commonly used fluorescence labels useful for detecting defects in polarization and morphogenesis caused by defects in membrane traffic.

Directed differentiation of human pluripotent stem cells into diverse organ-specific mesenchyme of the digestive and respiratory systems

Development of visceral organs such as the esophagus, lung, liver and stomach are coordinated by reciprocal signaling interactions between the endoderm and adjacent mesoderm cells in the fetal foregut. Although the recent successes in recapitulating developmental signaling in vitro has enabled the differentiation of human pluripotent stem cells (hPSCs) into various types of organ-specific endodermal epithelium, the generation of organ-specific mesenchyme has received much less attention. This is a major limitation in ongoing efforts to engineer complex human tissue. Here, we describe a protocol to differentiate hPSCs into different types of organ-specific mesoderm, leveraging signaling networks and molecular markers elucidated from single-cell transcriptomics of mouse foregut organogenesis. Building on established methods, hPSC-derived lateral plate mesoderm treated with either retinoic acid (RA) or RA together with a Hedgehog (HH) agonist generates posterior or anterior foregut splanchnic mesoderm, respectively, after 4-d cultures. These are directed into organ-specific mesenchyme lineages by the combinatorial activation or inhibition of WNT, BMP, RA or HH pathways from days 4 to 7 in cultures. By day 7, the cultures are enriched for different types of mesoderm with distinct molecular signatures: 60-90% pure liver septum transversum/mesothelium-like, 70-80% pure liver-like fibroblasts and populations of ~35% respiratory-like mesoderm, gastric-like mesoderm or esophageal-like mesoderm. This protocol can be performed by anyone with moderate experience differentiating hPSCs, provides a novel platform to study human mesoderm development and can be used to engineer more complex foregut tissue for disease modeling and regenerative medicine.

Narrative engineering of the liver

Liver organoids are primary or pluripotent stem cell-derived three-dimensional structures that recapitulate regenerative or ontogenetic processes in vitro towards biomedical applications including disease modelling and diagnostics, drug safety and efficacy prediction, and therapeutic use. The cellular composition and structural organization of liver organoids may vary depending on the goal at hand, and the key challenge in general is to direct their development in a rational and controlled fashion for gaining targeted maturity, reproducibility, and scalability. Such endeavor begins with a detailed understanding of the biological processes in space and time behind hepatogenesis, followed by precise translation of these narrative processes through a bioengineering approach. Here, we discuss advancements in liver organoid technology through the lens of 'narrative engineering' in an attempt to synergize evolving understanding around molecular and cellular landscape governing hepatogenesis with engineering-inspired approaches for organoidgenesis.

Regeneration of spermatogenesis by mouse germ cell transplantation into allogeneic and xenogeneic testis primordia or organoids

Gametogenesis requires close interactions between germ cells and somatic cells. Derivation of sperm from spermatogonial stem cells (SSCs) is hampered by the inefficiency of spermatogonial transplantation technique in many animal species because it requires a large number of SSCs and depletion of endogenous spermatogenesis. Here we used mouse testis primordia and organoids to induce spermatogenesis from SSCs. We microinjected mouse SSCs into embryonic gonads or reaggregated neonatal testis organoids, which were transplanted under the tunica albuginea of mature testes. As few as 1 × 10⁴ donor cells colonized both types of transplants and produced sperm. Moreover, rat embryonic gonads supported xenogeneic spermatogenesis from mouse SSCs when transplanted in testes of immunodeficient mice. Offspring with normal genomic imprinting patterns were born after microinsemination. These results demonstrate remarkable flexibility of the germ cell-somatic cell interaction and raise new strategies of SSC manipulation for animal transgenesis and analysis of male infertility.

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SSCs can be injected into embryonic gonads or reaggregated neonatal testes

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Spermatogenesis occurs in the gonads or reaggregated testes after transplantation

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Offspring are born from SSC-derived sperm using microinsemination

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Offspring show normal DNA methylation in imprinted genes

Engineering a functional thyroid as a potential therapeutic substitute for hypothyroidism treatment: A systematic review

BACKGROUND

Hypothyroidism is a common hormone deficiency disorder. Although hormone supplemental therapy can be easily performed by daily levothyroxine administration, a proportion of patients suffer from persisting complaints due to unbalanced hormone levels, leaving room for new therapeutic strategies, such as tissue engineering and regenerative medicine.

METHODS

Electronic searches of databases for studies of thyroid regeneration or thyroid organoids were performed. A systematic review including both in vitro and in vivo models of thyroid regenerative medicine was conducted.

RESULTS

Sixty-six independent studies published between 1959 and May 1st, 2022 were included in the current systematic review. Among these 66 studies, the most commonly involved species was human (19 studies), followed by mouse (18 studies), swine (14 studies), rat (13 studies), calf/bovine (4 studies), sheep/lamb (4 studies) and chick (1 study). In addition, in these experiments, the most frequently utilized tissue source was adult thyroid tissue (46 studies), followed by embryonic stem cells (ESCs)/pluripotent stem cells (iPSCs) (10 studies), rat thyroid cell lines (7 studies), embryonic thyroid tissue (2 studies) and newborn or fetal thyroid tissue (2 studies). Sixty-three studies reported relevant thyroid follicular regeneration experiments in vitro, while 21 studies showed an in vivo experiment section that included transplanting engineered thyroid tissue into recipients. Together, 12 studies were carried out using 2D structures, while 50 studies constructed 3D structures.

CONCLUSIONS

Each aspect of thyroid regenerative medicine was comprehensively described in this review. The recovery of optimal hormonal equilibrium by the transplantation of an engineered functional thyroid holds great therapeutic promise.