Neural Crest Cell Implantation Restores Enteric Nervous System Function and Alters the Gastrointestinal Transcriptome in Human Tissue-Engineered Small Intestine

Brain organoid protocols and limitations

Stem cell-derived organoid technology is a powerful tool that revolutionizes the field of biomedical research and extends the scope of our understanding of human biology and diseases. Brain organoids especially open an opportunity for human brain research and modeling many human neurological diseases, which have lagged due to the inaccessibility of human brain samples and lack of similarity with other animal models. Brain organoids can be generated through various protocols and mimic whole brain or region-specific. To provide an overview of brain organoid technology, we summarize currently available protocols and list several factors to consider before choosing protocols. We also outline the limitations of current protocols and challenges that need to be solved in future investigation of brain development and pathobiology.

Updates and Challenges in ENS Cell Therapy for the Treatment of Neurointestinal Diseases

Neurointestinal diseases represent a significant challenge in clinical management with current palliative approaches failing to overcome disease and treatment-related morbidity. The recent progress with cell therapy to restore missing or defective components of the gut neuromusculature offers new hope for potential cures. This review discusses the progress that has been made in the sourcing of putative stem cells and the studies into their biology and therapeutic potential. We also explore some of the practical challenges that must be overcome before cell-based therapies can be applied in the clinical setting. Although a number of obstacles remain, the rapid advances made in the enteric neural stem cell field suggest that such therapies are on the near horizon.

Recent advances in the treatment of gastrointestinal motility disorders in children

INTRODUCTION

Pediatric gastrointestinal motility disorders represent some of the most challenging clinical conditions with largely undefined pathogenetic pathways and therefore limited therapeutic options. Herein, we provide an overview of the recent advances in treatment options for these disorders and their clinical impact.

AREAS COVERED

PubMed and Medline databases were searched for relevant articles related to the treatment of achalasia, esophageal atresia, gastroparesis, PIPO and constipation published between 2017 and 2022. In this article, we review and summarize recent advances in management of gastrointestinal motility disorders in children with a particular focus on emerging therapies as well as novel diagnostic modalities that help guide their application or develop new, more targeted treatments.

EXPERT OPINION

Gastrointestinal motility disorders represent one of the most challenging conundrums in pediatric age and despite significant advances in investigative tools, the palette of treatment options remain limited. Overall, while pharmacological options have failed to bring a curative solution, recent advances in minimal invasive therapeutic and diagnostic techniques have emerged as potential keys to symptom and quality of life improvement, such as ENDOFLIP, POEM, cine-MRI, fecal microbiota transplantation.

Clinical challenges of short bowel syndrome and the path forward for organoid-based regenerative medicine

Short bowel syndrome (SBS) is a rare condition, the main symptom of which is malabsorption following extensive resection of the small intestine. Treatment for SBS is mainly supportive, consisting of supplementation, prevention and treatment of complications, and promotion of intestinal adaptation. While development of parenteral nutrition and drugs promoting intestinal adaptation has improved clinical outcomes, the prognosis of patients with SBS remains poor. Intestinal transplantation is the only curative therapy but its outcome is unsatisfactory. In the absence of definitive therapy, novel treatment is urgently needed. With the advent of intestinal organoids, research on the intestine has developed remarkably in recent years. Concepts such as the "tissue-engineered small intestine" and "small intestinalized colon," which create a functional small intestine by combining organoids with other technologies, are potentially novel regenerative therapeutic approaches for SBS. Although they are still under development and there are substantial issues to be resolved, the problems that have prevented establishment of the complex function and structure of the small intestine are gradually being overcome. This review discusses the current treatments for SBS, the fundamentals of the intestine and organoids, the current status of these new technologies, and future perspectives.

Recent Advances in Cell-Based In Vitro Models to Recreate Human Intestinal Inflammation

Inflammatory bowel disease causes a major burden to patients and healthcare systems, raising the need to develop effective therapies. Technological advances in cell culture, allied with ethical issues, have propelled in vitro models as essential tools to study disease aetiology, its progression, and possible therapies. Several cell-based in vitro models of intestinal inflammation have been used, varying in their complexity and methodology to induce inflammation. Immortalized cell lines are extensively used due to their long-term survival, in contrast to primary cultures that are short-lived but patient-specific. Recently, organoids and organ-chips have demonstrated great potential by being physiologically more relevant. This review aims to shed light on the intricate nature of intestinal inflammation and cover recent works that report cell-based in vitro models of human intestinal inflammation, encompassing diverse approaches and outcomes.

Cutting-edge regenerative therapy for Hirschsprung disease and its allied disorders

Hirschsprung disease (HSCR) and its associated disorders (AD-HSCR) often result in severe hypoperistalsis caused by enteric neuropathy, mesenchymopathy, and myopathy. Notably, HSCR involving the small intestine, isolated hypoganglionosis, chronic idiopathic intestinal pseudo-obstruction, and megacystis-microcolon-intestinal hypoperistalsis syndrome carry a poor prognosis. Ultimately, small-bowel transplantation (SBTx) is necessary for refractory cases, but it is highly invasive and outcomes are less than optimal, despite advances in surgical techniques and management. Thus, regenerative therapy has come to light as a potential form of treatment involving regeneration of the enteric nervous system, mesenchyme, and smooth muscle in affected areas. We review the cutting-edge regenerative therapeutic approaches for managing HSCR and AD-HSCR, including the use of enteric nervous system progenitor cells, embryonic stem cells, induced pluripotent stem cells, and mesenchymal stem cells as cell sources, the recipient intestine's microenvironment, and transplantation methods. Perspectives on the future of these treatments are also discussed.

Modeling enteric glia development, physiology and disease using human pluripotent stem cells

Enteric glia play an integral role in many functions of the gastrointestinal (GI) system, but they have not been characterized comprehensively compared to other cells of the gut. Enteric glia are a specialized type of neuroglia in the enteric nervous system (ENS) that support neurons and interact with other cells of the gut such as immune and epithelial cells. The ENS is diffusely spread throughout the GI tract, making it extremely difficult to access and manipulate. As a result, it has remained extremely understudied. Nevertheless, much more is known about enteric neurons than enteric glia despite the glia being 6 times more abundant in humans [1]. In the past two decades, our understanding of enteric glia has greatly expanded and their many roles in the gut have been described and reviewed elsewhere [2-5]. While the field has made substantial progress, there are still a multitude of open questions about enteric glia biology and their role in disease. Many of these questions have remained intractable due to technical limitations of currently available experimental models of the ENS. In this review, we describe the benefits and limitations of the models commonly used to study enteric glia and discuss the ways in which a human pluripotent stem cell (hPSC) derived enteric glia model could help advance the field.

Stem cells as a therapeutic avenue for active and long-term complications of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a devastating neonatal intestinal disease associated with significant morbidity and mortality. Although decades of research have been dedicated to understanding the pathogenesis of NEC and developing therapies, it remains the leading cause of death among neonatal gastrointestinal diseases. Mesenchymal stem cells (MSCs) have garnered significant interest recently as potential therapeutic agents for the treatment of NEC. They have been shown to rescue intestinal injury and reduce the incidence and severity of NEC in various preclinical animal studies. MSCs and MSC-derived organoids and tissue engineered small intestine (TESI) have shown potential for the treatment of long-term sequela of NEC such as short bowel syndrome, neurodevelopmental delay, and chronic lung disease. Although the advances made in the use of MSCs are promising, further research is needed prior to the widespread use of these cells for the treatment of NEC.

Regenerative medicine: current research and perspective in pediatric surgery

The field of regenerative medicine, encompassing several disciplines including stem cell biology and tissue engineering, continues to advance with the accumulating research on cell manipulation technologies, gene therapy and new materials. Recent progress in preclinical and clinical studies may transcend the boundaries of regenerative medicine from laboratory research towards clinical reality. However, for the ultimate goal to construct bioengineered transplantable organs, a number of issues still need to be addressed. In particular, engineering of elaborate tissues and organs requires a fine combination of different relevant aspects; not only the repopulation of multiple cell phenotypes in an appropriate distribution but also the adjustment of the host environmental factors such as vascularisation, innervation and immunomodulation. The aim of this review article is to provide an overview of the recent discoveries and development in stem cells and tissue engineering, which are inseparably interconnected. The current status of research on tissue stem cells and bioengineering, and the possibilities for application in specific organs relevant to paediatric surgery have been specifically focused and outlined.

An Engineered Living Intestinal Muscle Patch Produces Macroscopic Contractions that can Mix and Break Down Artificial Intestinal Contents

The intestinal muscle layers execute various gut wall movements to achieve controlled propulsion and mixing of intestinal content. Engineering intestinal muscle layers with complex contractile function is critical for developing bioartificial intestinal tissue to treat patients with short bowel syndrome. Here, the first demonstration of a living intestinal muscle patch capable of generating three distinct motility patterns and displaying multiple digesta manipulations is reported. Assessment of contractility, cellular morphology, and transcriptome profile reveals that successful generation of the contracting muscle patch relies on both biological factors in a serum-free medium and environmental cues from an elastic electrospun gelatin scaffold. By comparing gene-expression patterns among samples, it is shown that biological factors from the medium strongly affect ion-transport activities, while the scaffold unexpectedly regulates cell-cell communication. Analysis of ligandreceptor interactome identifies scaffold-driven changes in intercellular communication, and 78% of the upregulated ligand-receptor interactions are involved in the development and function of enteric neurons. The discoveries highlight the importance of combining biomolecular and biomaterial approaches for tissue engineering. The living intestinal muscle patch represents a pivotal advancement for building functional replacement intestinal tissue. It offers a more physiological model for studying GI motility and for preclinical drug discovery.

hPSC-derived lung organoids: Potential opportunities and challenges

Three-dimensional hPSC-derived lung organoids resemble the fetal lung stage, making them an excellent model for studying human lung development. However, current hPSC-derived lung organoids remain incomplete as they lack native lung components such as vasculature, neurons and immune cells. This highlights the need to generate more complex hPSC-derived lung organoids that can faithfully mimic native human lungs for studying human lung development, regeneration, disease modeling and drug screen. In this review, we will discuss the current studies related to the generation of hPSC-derived lung organoids, highlighting how hPSC-derived lung organoids can contribute to the understanding of human lung development. We further focus on potential approaches to generate more complex hPSC-derived lung organoids containing native cellular components. Finally, we discuss the present limitations and potential applications of hPSC-derived lung organoids in the future.

Tissue Engineering for Gastrointestinal and Genitourinary Tracts

The gastrointestinal and genitourinary tracts share several similarities. Primarily, these tissues are composed of hollow structures lined by an epithelium through which materials need to flow with the help of peristalsis brought by muscle contraction. In the case of the gastrointestinal tract, solid or liquid food must circulate to be digested and absorbed and the waste products eliminated. In the case of the urinary tract, the urine produced by the kidneys must flow to the bladder, where it is stored until its elimination from the body. Finally, in the case of the vagina, it must allow the evacuation of blood during menstruation, accommodate the male sexual organ during coitus, and is the natural way to birth a child. The present review describes the anatomy, pathologies, and treatments of such organs, emphasizing tissue engineering strategies.

Evaluation of Murine Host Sex as a Biological Variable in Transplanted Human Intestinal Organoid Development

BACKGROUND

Human intestinal organoids (HIOs), when transplanted into immunocompromised mice (tHIOs), demonstrate significant growth and maturation. While both male and female mice are reported to be viable hosts for these experiments, a direct comparison of sex-related differences in tHIO structure and development has not been performed.

AIMS

We sought to identify host sex-related differences in tHIO engraftment, morphology, and epithelial and mesenchymal development.

METHODS

HIOs were generated in vitro and transplanted beneath the kidney capsule of NSG male and female mice. tHIOs were harvested at 8-9 weeks. Anthropometric measurements were captured. tHIOs were divided in half and histology or RT-qPCR performed. Morphology was evaluated and epithelial architecture graded on a scale of 1 (absence of crypts/villi) to 4 (elongated crypt-villus axis). RT-qPCR and immunofluorescence microscopy were performed for epithelial and mesenchymal differentiation markers.

RESULTS

Host survival and tHIO engraftment were equivalent in male and female hosts. tHIO weight and length were also equivalent between groups. The number of lumens per tHIOs from male and female hosts was similar, but the mean lumen circumference was larger for tHIOs from male hosts. tHIOs from male hosts were more likely to demonstrate higher grades of epithelial development. However, both groups showed similar differentiation into secretory and absorptive epithelial lineages. Markers for intestinal identity, mesenchymal development, and brush border enzymes were also expressed similarly between groups.

CONCLUSIONS

While male host sex was associated with larger tHIO lumen size and mucosal maturation, tHIOs from both groups had similar engraftment, growth, and epithelial and mesenchymal cytodifferentiation.

Recipient colon preoperative treatment with type I collagenase and fibronectin promotes the growth of transplanted enteric neural crest cells into Auerbach's plexus

PURPOSE

Cell-based therapy is a potential treatment option for neurointestinal diseases by serving as a source of neural progenitor cells to replace missing or abnormal enteric neurons. Using an ex vivo transplantation model, we recently demonstrated that treatment with collagenase and fibronectin promotes infiltration of transplanted enteric neural crest cells (ENCCs) toward the colon lumen. The aim of this study was to determine whether this new method also promotes colonization of transplanted ENCCs in vivo.

METHODS

Collagenase was applied locally on the anti-mesenteric area of the recipient colon using filter paper, followed by fibronectin. Neurospheres were generated from ENCCs isolated from fetal mouse intestines and transplanted into the collagenase and fibronectin-treated colon. Engraftment of neurospheres was confirmed by immunofluorescence.

RESULTS

Neurospheres transplanted onto PBS- or fibronectin-treated colons were not observed to infiltrate to the muscle layer. However, when used in combination with type I collagenase and fibronectin in the recipient colon, transplanted neurospheres reached Auerbach's plexus.

CONCLUSION

We demonstrated that transplanted neurospheres grow into Auerbach's plexus in the recipient colon pretreated with collagenase and fibronectin.

Investigation of murine host sex as a biological variable in epithelial barrier function and muscle contractility in human intestinal organoids

Intestinal failure (IF) occurs when intestinal surface area or function is not sufficient to support digestion and nutrient absorption. Human intestinal organoid (HIO)-derived tissue-engineered intestine is a potential cure for IF. Research to date has demonstrated successful HIO transplantation (tHIO) into mice with significant in vivo maturation. An area lacking in the literature is exploration of murine host sex as a biological variable (SABV) in tHIO function. In this study, we investigate murine host SABV in tHIO epithelial barrier function and muscle contractility. HIOs were generated in vitro and transplanted into nonobese diabetic, severe combined immunodeficiency gamma chain deficient male and female mice. tHIOs were harvested after 8-12 weeks in vivo. Reverse transcriptase polymerase chain reaction and immunohistochemistry were conducted to compare tight junctions and contractility-related markers in tHIOs. An Ussing chamber and contractility apparatus were used to evaluate tHIO epithelial barrier and muscle contractile function, respectively. The expression and morphology of tight junction and contractility-related markers from tHIOs in male and female murine hosts is not significantly different. Epithelial barrier function as measured by transepithelial resistance, short circuit current, and fluorescein isothiocyanate-dextran permeability is no different in tHIOs from male and female hosts, although these results may be limited by HIO epithelial immaturity and a short flux time. Muscle contractility as measured by total contractile activity, amplitude, frequency, and tension is not significantly different in tHIOs from male and female hosts. The data suggest that murine host sex may not be a significant biological variable influencing tHIO function, specifically epithelial barrier maintenance and muscle contractility, though limitations exist in our model.

Human Pluripotent Stem Cell-Based Models for Hirschsprung Disease: From 2-D Cell to 3-D Organoid Model

Hirschsprung disease (HSCR) is a complex congenital disorder caused by defects in the development of the enteric nervous system (ENS). It is attributed to failures of the enteric neural crest stem cells (ENCCs) to proliferate, differentiate and/or migrate, leading to the absence of enteric neurons in the distal colon, resulting in colonic motility dysfunction. Due to the oligogenic nature of the disease, some HSCR conditions could not be phenocopied in animal models. Building the patient-based disease model using human induced pluripotent stem cells (hPSC) has opened up a new opportunity to untangle the unknowns of the disease. The expanding armamentarium of hPSC-based therapies provides needed new tools for developing cell-replacement therapy for HSCR. Here we summarize the recent studies of hPSC-based models of ENS in 2-D and 3-D culture systems. These studies have highlighted how hPSC-based models complement the population-based genetic screens and bioinformatic approaches for the discovery of new HSCR susceptibility genes and provide a human model for the close-to-physiological functional studies. We will also discuss the potential applications of these hPSC-based models in translational medicines and their advantages and limitations. The use of these hPSC-based models for drug discovery or cell replacement therapy likely leads to new treatment strategies for HSCR in the future. Further improvements in incorporating hPSC-based models with the human-mouse chimera model and organ-on-a-chip system for establishing a better disease model of HSCR and for drug discovery will further propel us to success in the development of an efficacious treatment for HSCR.

Regional cytoarchitecture of the adult and developing mouse enteric nervous system

The organization and cellular composition of tissues are key determinants of their biological function. In the mammalian gastrointestinal (GI) tract, the enteric nervous system (ENS) intercalates between muscular and epithelial layers of the gut wall and can control GI function independent of central nervous system (CNS) input.1 As in the CNS, distinct regions of the GI tract are highly specialized and support diverse functions, yet the regional and spatial organization of the ENS remains poorly characterized.2 Cellular arrangements,3,4 circuit connectivity patterns,5,6 and diverse cell types7-9 are known to underpin ENS functional complexity and GI function, but enteric neurons are most typically described only as a uniform meshwork of interconnected ganglia. Here, we present a bird's eye view of the mouse ENS, describing its previously underappreciated cytoarchitecture and regional variation. We visually and computationally demonstrate that enteric neurons are organized in circumferential neuronal stripes. This organization emerges gradually during the perinatal period, with neuronal stripe formation in the small intestine (SI) preceding that in the colon. The width of neuronal stripes varies throughout the length of the GI tract, and distinct neuronal subtypes differentially populate specific regions of the GI tract, with stark contrasts between SI and colon as well as within subregions of each. This characterization provides a blueprint for future understanding of region-specific GI function and identifying ENS structural correlates of diverse GI disorders.

Regenerative medicine technologies applied to transplant medicine.an update

Regenerative medicine (RM) is changing how we think and practice transplant medicine. In regenerative medicine, the aim is to develop and employ methods to regenerate, restore or replace damaged/diseased tissues or organs. Regenerative medicine investigates using tools such as novel technologies or techniques, extracellular vesicles, cell-based therapies, and tissue-engineered constructs to design effective patient-specific treatments. This review illustrates current advancements in regenerative medicine that may pertain to transplant medicine. We highlight progress made and various tools designed and employed specifically for each tissue or organ, such as the kidney, heart, liver, lung, vasculature, gastrointestinal tract, and pancreas. By combing both fields of transplant and regenerative medicine, we can harbor a successful collaboration that would be beneficial and efficacious for the repair and design of de novo engineered whole organs for transplantations.

Opportunities for novel diagnostic and cell-based therapies for Hirschsprung disease

Despite significant progress in our understanding of the etiology and pathophysiology of Hirschsprung disease (HSCR), early and accurate diagnosis and operative management can be challenging. Moreover, long-term morbidity following surgery, including fecal incontinence, constipation, and Hirschsprung-associated enterocolitis (HAEC), remains problematic. Recent advances applying state-of-the art imaging for visualization of the enteric nervous system and utilizing neuronal stem cells to replace the missing enteric neurons and glial cells offer the possibility of a promising new future for patients with HSCR. In this review, we summarize recent research advances that may one day offer novel approaches for the diagnosis and management of this disease.

Regenerative medicine: postnatal approaches

Paper 2 of the paediatric regenerative medicine Series focuses on recent advances in postnatal approaches. New gene, cell, and niche-based technologies and their combinations allow structural and functional reconstitution and simulation of complex postnatal cell, tissue, and organ hierarchies. Organoid and tissue engineering advances provide human disease models and novel treatments for both rare paediatric diseases and common diseases affecting all ages, such as COVID-19. Preclinical studies for gastrointestinal disorders are directed towards oesophageal replacement, short bowel syndrome, enteric neuropathy, biliary atresia, and chronic end-stage liver failure. For respiratory diseases, beside the first human tracheal replacement, more complex tissue engineering represents a promising solution to generate transplantable lungs. Genitourinary tissue replacement and expansion usually involve application of biocompatible scaffolds seeded with patient-derived cells. Gene and cell therapy approaches seem appropriate for rare paediatric diseases of the musculoskeletal system such as spinal muscular dystrophy, whereas congenital diseases of complex organs, such as the heart, continue to challenge new frontiers of regenerative medicine.

Building gut from scratch - progress and update of intestinal tissue engineering

Short bowel syndrome (SBS), a condition defined by insufficient absorptive intestinal epithelium, is a rare disease, with an estimated prevalence up to 0.4 in 10,000 people. However, it has substantial morbidity and mortality for affected patients. The mainstay of treatment in SBS is supportive, in the form of intravenous parenteral nutrition, with the aim of achieving intestinal autonomy. The lack of a definitive curative therapy has led to attempts to harness innate developmental and regenerative mechanisms to engineer neo-intestine as an alternative approach to addressing this unmet clinical need. Exciting advances have been made in the field of intestinal tissue engineering (ITE) over the past decade, making a review in this field timely. In this Review, we discuss the latest advances in the components required to engineer intestinal grafts and summarize the progress of ITE. We also explore some key factors to consider and challenges to overcome when transitioning tissue-engineered intestine towards clinical translation, and provide the future outlook of ITE in therapeutic applications and beyond.

Schwann Cells in Digestive System Disorders

Proper functioning of the digestive system is ensured by coordinated action of the central and peripheral nervous systems (PNS). Peripheral innervation of the digestive system can be viewed as intrinsic and extrinsic. The intrinsic portion is mainly composed of the neurons and glia of the enteric nervous system (ENS), while the extrinsic part is formed by sympathetic, parasympathetic, and sensory branches of the PNS. Glial cells are a crucial component of digestive tract innervation, and a great deal of research evidence highlights the important status of ENS glia in health and disease. In this review, we shift the focus a bit and discuss the functions of Schwann cells (SCs), the glial cells of the extrinsic innervation of the digestive system. For more context, we also provide information on the basic findings regarding the function of innervation in disorders of the digestive organs. We find diverse SC roles described particularly in the mouth, the pancreas, and the intestine. We note that most of the scientific evidence concerns the involvement of SCs in cancer progression and pain, but some research identifies stem cell functions and potential for regenerative medicine.

Transplanted neural crest cells migrate toward Auerbach's plexus layer instead of the colon surface in recipient colon pretreated with collagenase and fibronectin

The enteric nervous system (ENS) regulates gastrointestinal motility, secretion, and absorption. Developmental ENS dysplasia causes intestinal ganglion dysfunction, including Hirschsprung's disease. Given their potential ability to replenish insufficient neurons, transplantation of enteric neural cells provides the prospect of a cure. In this study, we used an ex vivo mouse colon transplant model to demonstrate that treatment with collagenase and fibronectin altered the migration of transplanted cells from the direction of the colon surface toward the lumen. Collagenase-treated colons exhibited enhanced expression of type III and VI collagens, which inhibited fibronectin-induced enteric neural crest cell (ENCC) migration. Invasion of neurospheres into colon was dependent on preoperative treatment of recipient colon with collagenase and fibronectin, which enhanced neurosphere motility towards the direction of colon lumen. Infiltration of transplanted ENCCs into the colon increased proportionally to the degree of dedifferentiation of surrounding smooth muscle cells, which was induced in a neurosphere-dependent manner in collagenase-treated colon. Furthermore, induction of GDNF expression, a Ret ligand that promotes enteric neural cell migration, was observed in treated colons. Our results suggest that the environment provided by the extracellular matrix of the colon surface affects the direction of transplanted ENCC migration. Moreover, these findings demonstrating that ENCCs can be accepted by the recipient colon will help to refine current strategies for cell therapy.

Suspension culture promotes serosal mesothelial development in human intestinal organoids

Pluripotent-stem-cell-derived human intestinal organoids (HIOs) model some aspects of intestinal development and disease, but current culture methods do not fully recapitulate the diverse cell types and complex organization of the human intestine and are reliant on 3D extracellular matrix or hydrogel systems, which limit experimental control and translational potential for regenerative medicine. We describe suspension culture as a simple, low-maintenance method for culturing HIOs and for promoting in vitro differentiation of an organized serosal mesothelial layer that is similar to primary human intestinal serosal mesothelium based on single-cell RNA sequencing and histological analysis. Functionally, HIO serosal mesothelium has the capacity to differentiate into smooth-muscle-like cells and exhibits fibrinolytic activity. An inhibitor screen identifies Hedgehog and WNT signaling as regulators of human serosal mesothelial differentiation. Collectively, suspension HIOs represent a three-dimensional model to study the human serosal mesothelium.

The gut brain in a dish: Murine primary enteric nervous system cell cultures

BACKGROUND

The enteric nervous system (ENS) is an extensive neural network embedded in the wall of the gastrointestinal tract that regulates digestive function and gastrointestinal homeostasis. The ENS consists of two main cell types; enteric neurons and enteric glial cells. In vitro techniques allow simplified investigation of ENS function, and different culture methods have been developed over the years helping to understand the role of ENS cells in health and disease.

PURPOSE

This review focuses on summarizing and comparing available culture protocols for the generation of primary ENS cells from adult mice, including dissection of intestinal segments, enzymatic digestions, surface coatings, and culture media. In addition, the potential of human ENS cultures is also discussed.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

TALPID3/KIAA0586 Regulates Multiple Aspects of Neuromuscular Patterning During Gastrointestinal Development in Animal Models and Human

TALPID3/KIAA0586 is an evolutionary conserved protein, which plays an essential role in protein trafficking. Its role during gastrointestinal (GI) and enteric nervous system (ENS) development has not been studied previously. Here, we analyzed chicken, mouse and human embryonic GI tissues with TALPID3 mutations. The GI tract of TALPID3 chicken embryos was shortened and malformed. Histologically, the gut smooth muscle was mispatterned and enteric neural crest cells were scattered throughout the gut wall. Analysis of the Hedgehog pathway and gut extracellular matrix provided causative reasons for these defects. Interestingly, chicken intra-species grafting experiments and a conditional knockout mouse model showed that ENS formation did not require TALPID3, but was dependent on correct environmental cues. Surprisingly, the lack of TALPID3 in enteric neural crest cells (ENCC) affected smooth muscle and epithelial development in a non-cell-autonomous manner. Analysis of human gut fetal tissues with a KIAA0586 mutation showed strikingly similar findings compared to the animal models demonstrating conservation of TALPID3 and its necessary role in human GI tract development and patterning.

Shaping axial identity during human pluripotent stem cell differentiation to neural crest cells

The neural crest (NC) is a multipotent cell population which can give rise to a vast array of derivatives including neurons and glia of the peripheral nervous system, cartilage, cardiac smooth muscle, melanocytes and sympathoadrenal cells. An attractive strategy to model human NC development and associated birth defects as well as produce clinically relevant cell populations for regenerative medicine applications involves the in vitro generation of NC from human pluripotent stem cells (hPSCs). However, in vivo, the potential of NC cells to generate distinct cell types is determined by their position along the anteroposterior (A–P) axis and, therefore the axial identity of hPSC-derived NC cells is an important aspect to consider. Recent advances in understanding the developmental origins of NC and the signalling pathways involved in its specification have aided the in vitro generation of human NC cells which are representative of various A–P positions. Here, we explore recent advances in methodologies of in vitro NC specification and axis patterning using hPSCs.

Regenerative medicine for childhood gastrointestinal diseases

Several paediatric gastrointestinal diseases result in life-shortening organ failure. For many of these conditions, current therapeutic options are suboptimal and may not offer a cure. Regenerative medicine is an inter-disciplinary field involving biologists, engineers, and clinicians that aims to produce cell and tissue-based therapies to overcome organ failure. Exciting advances in stem cell biology, materials science, and bioengineering bring engineered gastrointestinal cell and tissue therapies to the verge of clinical trial. In this review, we summarise the requirements for bioengineered therapies, the possible sources of the various cellular and non-cellular components, and the progress towards clinical translation of oesophageal and intestinal tissue engineering to date.

Enteric glia in homeostasis and disease: From fundamental biology to human pathology

Glia, the non-neuronal cells of the nervous system, were long considered secondary cells only necessary for supporting the functions of their more important neuronal neighbors. Work by many groups over the past two decades has completely overturned this notion, revealing the myriad and vital functions of glia in nervous system development, plasticity, and health. The largest population of glia outside the brain is in the enteric nervous system, a division of the autonomic nervous system that constitutes a key node of the gut-brain axis. Here, we review the latest in the understanding of these enteric glia in mammals with a focus on their putative roles in human health and disease.

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.

Charting human development using a multi-endodermal organ atlas and organoid models

Organs are composed of diverse cell types that traverse transient states during organogenesis. To interrogate this diversity during human development, we generate a single-cell transcriptome atlas from multiple developing endodermal organs of the respiratory and gastrointestinal tract. We illuminate cell states, transcription factors, and organ-specific epithelial stem cell and mesenchyme interactions across lineages. We implement the atlas as a high-dimensional search space to benchmark human pluripotent stem cell (hPSC)-derived intestinal organoids (HIOs) under multiple culture conditions. We show that HIOs recapitulate reference cell states and use HIOs to reconstruct the molecular dynamics of intestinal epithelium and mesenchyme emergence. We show that the mesenchyme-derived niche cue NRG1 enhances intestinal stem cell maturation in vitro and that the homeobox transcription factor CDX2 is required for regionalization of intestinal epithelium and mesenchyme in humans. This work combines cell atlases and organoid technologies to understand how human organ development is orchestrated.

Generating Enteric Nervous System Progenitors from Human Pluripotent Stem Cells

The intrinsic innervation of the gastrointestinal (GI) tract is comprised of enteric neurons and glia, which are buried within the wall of the bowel and organized into two concentric plexuses that run along the length of the gut forming the enteric nervous system (ENS). The ENS regulates vital GI functions including gut motility, blood flow, fluid secretion, and absorption and thus maintains gut homeostasis. During vertebrate development it originates predominantly from the vagal neural crest (NC), a multipotent cell population that emerges from the caudal hindbrain region, migrates to and within the gut to ultimately generate neurons and glia in response to gut-derived signals. Loss of GI innervation due to congenital or acquired defects in ENS development causes enteric neuropathies which lack curative treatment. Human pluripotent stem cells (hPSCs) offer a promising in vitro source of enteric neurons for modeling human ENS development and pathology and potential use in cell therapy applications. Here we describe in detail a differentiation strategy for the derivation of enteric neural progenitors and neurons from hPSCs through a vagal NC intermediate. Using a combination of instructive signals and retinoic acid in a dose/time dependent manner, vagal NC cells commit into the ENS lineage and develop into enteric neurons and glia upon culture in neurotrophic media. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Generation of vagal neural crest/early ENS progenitors from hPSCs Basic Protocol 2: Differentiation of hPSC-derived vagal NC/early ENS progenitors to enteric neurons and glia.

NH2-terminal deletion of specific phosphorylation sites on PHOX2B disrupts the formation of enteric neurons in vivo

Mutations in the paired-like homeobox 2 b (PHOX2B) gene are associated with congenital central hypoventilation syndrome (CCHS), which is a rare condition in which both autonomic dysregulation with hypoventilation and an enteric neuropathy may occur. The majority of patients with CCHS have a polyalanine repeat mutation (PARM) in PHOX2B, but a minority of patients have nonpolyalanine repeat mutations (NPARMs), some of which have been localized to exon 1. A PHOX2B-Y14X nonsense mutation previously generated in a human pluripotent stem cell (hPSC) line results in an NH₂-terminus truncated product missing the first 17 or 20 amino acids, possibly due to translational reinitiation at an alternate ATG start site. This NH₂-terminal truncation in the PHOX2B protein results in the loss of two key phosphorylation residues. Though the deletion does not affect the potential for PHOX2B^Y14X/Y14X mutant hPSC to differentiate into enteric neural crest cells (ENCCs) in culture, it impedes in vivo development of neurons in an in vivo model of human aganglionic small intestine.NEW & NOTEWORTHY A mutation that affects only 17-20 NH₂-terminal amino acids in the paired-like homeobox 2 b (PHOX2B) gene hinders the subsequent in vivo establishment of intestinal neuronal cells, but not the in vitro differentiation of these cells.

Bioengineering of the digestive tract: approaching the clinic

The field of regenerative medicine is developing technologies that, in the near future, will offer alternative approaches to either cure diseases affecting the gastrointestinal tract or slow their progression by leveraging the intrinsic ability of our tissues and organs to repair after damage. This article will succinctly illustrate the three technologies that are closer to clinical translation-namely, human intestinal organoids, sphincter bioengineering and decellularization, whereby the cellular compartment of a given segment of the digestive tract is removed to obtain a scaffold consisting of the extracellular matrix. The latter will be used as a template for the regeneration of a functional organ, whereby the newly generated cellular compartment will be obtained from the patient's own cells. Although clinical application of this technology is approaching, product development challenges are being tackled to warrant safety and efficacy.

Organoid Technology: Current Standing and Future Perspectives

Organoids are powerful systems to facilitate the study of individuals' disorders and personalized treatments. Likewise, emerging this technology has improved the chance of translatability of drugs for pre-clinical therapies and mimicking the complexity of organs, while it proposes numerous approaches for human disease modeling, tissue engineering, drug development, diagnosis, and regenerative medicine. In this review, we outline the past/present organoid technology and summarize its faithful applications, then, we discuss the challenges and limitations encountered by 3D organoids. In the end, we offer the human organoids as basic mechanistic infrastructure for "human modelling" systems to prescribe personalized medicines. © AlphaMed Press 2021 SIGNIFICANCE STATEMENT: This concise review concerns about organoids, available methods for in vitro organoid formation and different types of human organoid models. We, then, summarize biological approaches to improve 3D organoids complexity and therapeutic potentials of organoids. Despite the existing incomprehensive review articles in literature that examine partial aspects of the organoid technology, the present review article comprehensively and critically presents this technology from different aspects. It effectively provides a systematic overview on the past and current applications of organoids and discusses the future perspectives and suggestions to improve this technology and its applications.

Neural crest-like stem cells for tissue regeneration

Neural crest stem cells (NCSCs) are a transient population of cells that arise during early vertebrate development and harbor stem cell properties, such as self‐renewal and multipotency. These cells form at the interface of non‐neuronal ectoderm and neural tube and undergo extensive migration whereupon they contribute to a diverse array of cell and tissue derivatives, ranging from craniofacial tissues to cells of the peripheral nervous system. Neural crest‐like stem cells (NCLSCs) can be derived from pluripotent stem cells, placental tissues, adult tissues, and somatic cell reprogramming. NCLSCs have a differentiation capability similar to NCSCs, and possess great potential for regenerative medicine applications. In this review, we present recent developments on the various approaches to derive NCLSCs and the therapeutic application of these cells for tissue regeneration.

Premigratory neural crest stem cells generate enteric neurons populating the mouse colon and regulating peristalsis in tissue-engineered intestine

Hirschsprung's disease (HSCR) is a common congenital defect. It occurs when bowel colonization by neural crest‐derived enteric nervous system (ENS) precursors is incomplete during the first trimester of pregnancy. Several sources of candidate cells have been previously studied for their capacity to regenerate the ENS, including enteric neural crest stem cells (En‐NCSCs) derived from native intestine or those simulated from human pluripotent stem cells (hPSCs). However, it is not yet known whether the native NCSCs other than En‐NCSCs would have the potential of regenerating functional enteric neurons and producing neuron dependent motility under the intestinal environment. The present study was designed to determine whether premigratory NCSCs (pNCSCs), as a type of the nonenteric NCSCs, could form enteric neurons and mediate the motility. pNCSCs were firstly transplanted into the colon of adult mice, and were found to survive, migrate, differentiate into enteric neurons, and successfully integrate into the adult mouse colon. When the mixture of pNCSCs and human intestinal organoids was implanted into the subrenal capsule of nude mice and grown into the mature tissue‐engineered intestine (TEI), the pNCSCs‐derived neurons mediated neuron‐dependent peristalsis of TEI. These results show that the pNCSCs that were previously assumed to not be induced by intestinal environment or cues can innervate the intestine and establish neuron‐dependent motility. Future cell candidates for ENS regeneration may include nonenteric NCSCs.

AAV Targeting of Glial Cell Types in the Central and Peripheral Nervous System and Relevance to Human Gene Therapy

Different glial cell types are found throughout the central (CNS) and peripheral nervous system (PNS), where they have important functions. These cell types are also involved in nervous system pathology, playing roles in neurodegenerative disease and following trauma in the brain and spinal cord (astrocytes, microglia, oligodendrocytes), nerve degeneration and development of pain in peripheral nerves (Schwann cells, satellite cells), retinal diseases (Müller glia) and gut dysbiosis (enteric glia). These cell type have all been proposed as potential targets for treating these conditions. One approach to target these cell types is the use of gene therapy to modify gene expression. Adeno-associated virus (AAV) vectors have been shown to be safe and effective in targeting cells in the nervous system and have been used in a number of clinical trials. To date, a number of studies have tested the use of different AAV serotypes and cell-specific promoters to increase glial cell tropism and expression. However, true glial-cell specific targeting for a particular glial cell type remains elusive. This review provides an overview of research into developing glial specific gene therapy and discusses some of the issues that still need to be addressed to make glial cell gene therapy a clinical reality.

Using multi-organ culture systems to study Parkinson's disease

In recent years, it has been revealed that Parkinson's disease pathology may begin to manifest in the gastrointestinal track at a much earlier time point than in the brain. This paradigm shift has been suggested following evidence in humans that has been reproduced in animal models. Since rodent models cannot recapitulate many of the human disease features, human induced pluripotent stem cells derived from Parkinson's patients have been used to generate brain organoids, greatly contributing to our understanding of the disease pathophysiology. To understand the multifaced aspects of Parkinson's disease, it may be desirable to expand the complexity of these models, to include different brain regions, vasculature, immune cells as well as additional diverse organ-specific organoids such as gut and intestine. Furthermore, the contribution of gut microbiota to disease progression cannot be underestimated. Recent biotechnological advances propose that such combinations may be feasible. Here we discuss how this need can be met and propose that additional brain diseases can benefit from this approach.

Neuron-Glia Interaction in the Developing and Adult Enteric Nervous System

The enteric nervous system (ENS) constitutes the largest part of the peripheral nervous system. In recent years, ENS development and its neurogenetic capacity in homeostasis and allostasishave gained increasing attention. Developmentally, the neural precursors of the ENS are mainly derived from vagal and sacral neural crest cell portions. Furthermore, Schwann cell precursors, as well as endodermal pancreatic progenitors, participate in ENS formation. Neural precursorsenherite three subpopulations: a bipotent neuron-glia, a neuronal-fated and a glial-fated subpopulation. Typically, enteric neural precursors migrate along the entire bowel to the anal end, chemoattracted by glial cell-derived neurotrophic factor (GDNF) and endothelin 3 (EDN3) molecules. During migration, a fraction undergoes differentiation into neurons and glial cells. Differentiation is regulated by bone morphogenetic proteins (BMP), Hedgehog and Notch signalling. The fully formed adult ENS may react to injury and damage with neurogenesis and gliogenesis. Nevertheless, the origin of differentiating cells is currently under debate. Putative candidates are an embryonic-like enteric neural progenitor population, Schwann cell precursors and transdifferentiating glial cells. These cells can be isolated and propagated in culture as adult ENS progenitors and may be used for cell transplantation therapies for treating enteric aganglionosis in Chagas and Hirschsprung's diseases.

Farm Animal-derived Models of the Intestinal Epithelium: Recent Advances and Future Applications of Intestinal Organoids

Farm animals play an important role in translational research as large animal models of the gastrointestinal (GI) tract. The mechanistic investigation of zoonotic diseases of the GI tract, in which animals can act as asymptomatic carriers, could provide important information for therapeutic approaches. In veterinary medicine, farm animals are no less relevant, as they can serve as models for the development of diagnostic and therapeutic approaches of GI diseases in the target species. However, farm animal-derived cell lines of the intestinal epithelium are rarely available from standardised cell banks and, in addition, are not usually specific for certain sections of the intestine. Immortalised porcine or bovine enterocytic cell lines are more widely available, compared to goat or sheep-derived cell lines; no continuous cell lines are available from the chicken. Other epithelial cell types with intestinal section-specific distribution and function, such as goblet cells, enteroendocrine cells, Paneth cells and intestinal stem cells, are not represented in those cell line-based models. Therefore, intestinal organoid models of farm animal species, which are already widely used for mice and humans, are gaining importance. Crypt-derived or pluripotent stem cell-derived intestinal organoid models offer the possibility to investigate the mechanisms of inter-cell or host-pathogen interactions and to answer species-specific questions. This review is intended to give an overview of cell culture models of the intestinal epithelium of farm animals, discussing species-specific differences, culture techniques and some possible applications for intestinal organoid models. It also highlights the need for species-specific pluripotent stem cell-derived or crypt-derived intestinal organoid models for promotion of the Three Rs principles (replacement, reduction and refinement).

Hirschsprung's Disease-Recent Understanding of Embryonic Aspects, Etiopathogenesis and Future Treatment Avenues

Hirschsprung's disease is a neurocristopathy, caused by defective migration, proliferation, differentiation and survival of neural crest cells, leading to gut aganglionosis. It usually manifests rapidly after birth, affecting 1 in 5000 live births around the globe. In recent decades, there has been a significant improvement in the understanding of its genetics and the association with other congenital anomalies, which share the pathomechanism of improper development of the neural crest. Apart from that, several cell populations which do not originate from the neural crest, but contribute to the development of Hirschsprung's disease, have also been described, namely mast cells and interstitial cells of Cajal. From the diagnostic perspective, researchers also focused on "Variants of Hirschsprung's disease", which can mimic the clinical signs of the disease, but are in fact different entities, with distinct prognosis and treatment approaches. The treatment of Hirschsprung's disease is usually surgical resection of the aganglionic part of the intestine, however, as many as 30-50% of patients experience persisting symptoms. Considering this fact, this review article also outlines future hopes and perspectives in Hirschsprung's disease management, which has the potential to benefit from the advancements in the fields of cell-based therapy and tissue engineering.

In Vivo Transplantation of Human Intestinal Organoids Enhances Select Tight Junction Gene Expression

BACKGROUND

Short bowel syndrome is a potentially fatal condition with inadequate management options. Tissue-engineered small intestine (TESI) is a promising solution, but confirmation of TESI function will be crucial before human application. We sought to define intestinal epithelial barrier function in human intestinal organoid (HIO)-derived TESI.

MATERIALS AND METHODS

HIOs were generated in vitro from human embryonic stem cells. After 1 mo, HIOs were collected for analysis or transplanted into the kidney capsule of immunocompromised mice. Transplanted HIOs (tHIOs) were harvested for analysis at 4 or 8 wk. Reverse transcription quantitative polymerase chain reaction and immunofluorescent staining were performed for tight junction components: claudin 3 (CLDN3), claudin 15 (CLDN15), occludin (OCLN), and zonula occludens-1, or tight junction protein-1 (TJP1/ZO-1).

RESULTS

Four-week-old tHIOs demonstrated significantly (P < 0.05) higher levels of CLDN15 (6x), OCLN (4x), and TJP1/ZO-1 (3x) normalized to GAPDH than in vitro HIOs. Eight-week-old tHIOs demonstrated significantly (P < 0.05) higher expression levels of CLDN3 (26x), CLDN15 (29x), OCLN (4x), and TJP1/ZO-1 (5x) than in vitro HIOs. There was no significant difference in expression of these tight junction components between 4- and 8-week-old tHIOs. Immunofluorescent staining revealed the presence of claudin 3, claudin 15, occludin, and zonula occludens-1 in both in vitro HIOs and tHIOs; however, the morphology appeared more mature in tHIOs.

CONCLUSIONS

In vitro HIOs have lower levels of tight junction mRNA, and tight junction proteins appear morphologically immature. Transplantation facilitates maturation of the HIOs and enhances select tight junction gene expression.

Functional circuits and signal processing in the enteric nervous system

The enteric nervous system (ENS) is an extensive network comprising millions of neurons and glial cells contained within the wall of the gastrointestinal tract. The major functions of the ENS that have been most studied include the regulation of local gut motility, secretion, and blood flow. Other areas that have been gaining increased attention include its interaction with the immune system, with the gut microbiota and its involvement in the gut-brain axis, and neuro-epithelial interactions. Thus, the enteric circuitry plays a central role in intestinal homeostasis, and this becomes particularly evident when there are faults in its wiring such as in neurodevelopmental or neurodegenerative disorders. In this review, we first focus on the current knowledge on the cellular composition of enteric circuits. We then further discuss how enteric circuits detect and process external information, how these signals may be modulated by physiological and pathophysiological factors, and finally, how outputs are generated for integrated gut function.

Insights into Differentiation of Melanocytes from Human Stem Cells and Their Relevance for Melanoma Treatment

Simple Summary

The reactivation of embryonic developmental programs is crucial for melanoma cells to grow and to metastasize. In order to understand this process better, we first summarize the melanocytic differentiation process both in vivo and in vitro. Secondly, we compare and highlight important similarities between neural crest cell fate during differentiation and tumor cell characteristics during melanoma mestastasis. Finally, we suggest possible therapeutic targets, which could be used to inhibit phenotype switching by developmental cues and hence also suppress the metastatic melanoma spread.

Abstract

Malignant melanoma represents a highly aggressive form of skin cancer. The metastatic process itself is mostly governed by the so-called epithelial mesenchymal transition (EMT), which confers cancer cells migrative, invasive and resistance abilities. Since EMT represents a conserved developmental process, it is worthwhile further examining the nature of early developmental steps fundamental for melanocyte differentiation. This can be done either in vivo by analyzing the physiologic embryo development in different species or by in vitro studies of melanocytic differentiation originating from embryonic human stem cells. Most importantly, external cues drive progenitor cell differentiation, which can be divided in stages favoring neural crest specification or melanocytic differentiation and proliferation. In this review, we describe ectopic factors which drive human pluripotent stem cell differentiation to melanocytes in 2D, as well as in organoid models. Furthermore, we compare developmental mechanisms with processes described to occur during melanoma development. Finally, we suggest differentiation factors as potential co-treatment options for metastatic melanoma patients.

Advanced Modeling of Peripheral Neuro-Effector Communication and -Plasticity

The peripheral nervous system (PNS) plays crucial roles in physiology and disease. Neuro-effector communication and neuroplasticity of the PNS are poorly studied, since suitable models are lacking. The emergence of human pluripotent stem cells (hPSCs) has great promise to resolve this deficit. hPSC-derived PNS neurons, integrated into organ-on-a-chip systems or organoid cultures, allow co-cultures with cells of the local microenvironment to study neuro-effector interactions and to probe mechanisms underlying neuroplasticity.

Differentiation of Human Intestinal Organoids with Endogenous Vascular Endothelial Cells

Human pluripotent stem cell (hPSC)-derived intestinal organoids (HIOs) lack some cellular populations found in the native organ, including vasculature. Using single-cell RNA sequencing (scRNA-seq), we have identified a population of endothelial cells (ECs) present early in HIO differentiation that declines over time in culture. Here, we developed a method to expand and maintain this endogenous population of ECs within HIOs (vHIOs). Given that ECs possess organ-specific gene expression, morphology, and function, we used bulk RNA-seq and scRNA-seq to interrogate the developing human intestine, lung, and kidney in order to identify organ-enriched EC gene signatures. By comparing these gene signatures and validated markers to HIO ECs, we find that HIO ECs grown in vitro share the highest similarity with native intestinal ECs relative to kidney and lung. Together, these data demonstrate that HIOs can co-differentiate a native EC population that is properly patterned with an intestine-specific EC transcriptional signature in vitro.

The Intestinal Barrier in Parkinson's Disease: Current State of Knowledge

The intestinal barrier, which primarily consists of epithelial cells stitched together with connecting proteins called tight junctions, plays a critical role in health and disease. It is in close contact with the gut microbiota on its luminal side and with the enteric neurons on the tissue side. Both microbiota and the enteric nervous system are regulatory housekeepers of the intestinal barrier. Therefore, the recently observed enteric neuropathology along with gut dysbiosis in Parkinson's disease have prompted research on intestinal permeability in this neurodegenerative disorder. In this mini-review we attempt to concisely summarize the current knowledge on intestinal barrier in Parkinson's disease. We envision future direction research that should be pursued in order to demonstrate its possible role in disease development and progression.