Replenishable prevascularized cell encapsulation devices increase graft survival and function in the subcutaneous space.

Beta cell replacement therapy (BCRT) for patients with type 1 diabetes (T1D) improves blood glucose regulation by replenishing the endogenous beta cells destroyed by autoimmune attack. Several limitations, including immune isolation, prevent this therapy from reaching its full potential. Cell encapsulation devices used for BCRT provide a protective physical barrier for insulin-producing beta cells, thereby protecting transplanted cells from immune attack. However, poor device engraftment posttransplantation leads to nutrient deprivation and hypoxia, causing metabolic strain on transplanted beta cells. Prevascularization of encapsulation devices at the transplantation site can help establish a host vascular network around the implant, increasing solute transport to the encapsulated cells. Here, we present a replenishable prevascularized implantation methodology (RPVIM) that allows for the vascular integration of replenishable encapsulation devices in the subcutaneous space. Empty encapsulation devices were vascularized for 14 days, after which insulin-producing cells were inserted without disrupting the surrounding vasculature. The RPVIM devices were compared with nonprevascularized devices (Standard Implantation Methodology [SIM]) and previously established prevascularized devices (Standard Prevascularization Implantation Methodology [SPVIM]). Results show that over 75% of RPVIM devices containing stem cell-derived insulin-producing beta cell clusters showed a signal after 28 days of implantation in subcutaneous space. Notably, not only was the percent of RPVIM devices showing signal significantly greater than SIM and SPVIM devices, but the intraperitoneal glucose tolerance tests and histological analyses showed that encapsulated stem-cell derived insulin-producing beta cell clusters retained their function in the RPVIM devices, which is crucial for the successful management of T1D.

Single-cell chromatin accessibility of developing murine pancreas identifies cell state-specific gene regulatory programs.

Numerous studies have characterized the existence of cell subtypes, along with their corresponding transcriptional profiles, within the developing mouse pancreas. The upstream mechanisms that initiate and maintain gene expression programs across cell states, however, remain largely unknown. Here, we generate single-nucleus ATAC-Sequencing data of developing murine pancreas and perform an integrated, multi-omic analysis of both chromatin accessibility and RNA expression to describe the chromatin landscape of the developing pancreas at both E14.5 and E17.5 at single-cell resolution. We identify candidate transcription factors regulating cell fate and construct gene regulatory networks of active transcription factor binding to regulatory regions of downstream target genes. This work serves as a valuable resource for the field of pancreatic biology in general and contributes to our understanding of lineage plasticity among endocrine cell types. In addition, these data identify which epigenetic states should be represented in the differentiation of stem cells to the pancreatic beta cell fate to best recapitulate in vitro the gene regulatory networks that are critical for progression along the beta cell lineage in vivo.

Rab11 is essential to pancreas morphogenesis, lumen formation and endocrine mass.

The molecular links between tissue-level morphogenesis and the differentiation of cell lineages in the pancreas remain elusive despite a decade of studies. We previously showed that in pancreas both processes depend on proper lumenogenesis. The Rab GTPase Rab11 is essential for epithelial lumen formation in vitro, however few studies have addressed its functions in vivo and none have tested its requirement in pancreas. Here, we show that Rab11 is critical for proper pancreas development. Co-deletion of the Rab11 isoforms Rab11A and Rab11B in the developing pancreatic epithelium (Rab11pancDKO) results in ∼50% neonatal lethality and surviving adult Rab11pancDKO mice exhibit defective endocrine function. Loss of both Rab11A and Rab11B in the embryonic pancreas results in morphogenetic defects of the epithelium, including defective lumen formation and lumen interconnection. In contrast to wildtype cells, Rab11pancDKO cells initiate the formation of multiple ectopic lumens, resulting in a failure to coordinate a single apical membrane initiation site (AMIS) between groups of cells. This results in an inability to form ducts with continuous lumens. Here, we show that these defects are due to failures in vesicle trafficking, as apical and junctional components remain trapped within Rab11pancDKO cells. Together, these observations suggest that Rab11 directly regulates epithelial lumen formation and morphogenesis. Our report links intracellular trafficking to organ morphogenesis in vivo and presents a novel framework for decoding pancreatic development.

Loss of Fgf9 in mice leads to pancreatic hypoplasia and asplenia.

Pancreatic development requires spatially and temporally controlled expression of growth factors derived from mesenchyme. Here, we report that in mice the secreted factor Fgf9 is expressed principally by mesenchyme and then mesothelium during early development, then subsequently by both mesothelium and rare epithelial cells by E12.5 and onwards. Global knockout of the Fgf9 gene resulted in the reduction of pancreas and stomach size, as well as complete asplenia. The number of early Pdx1+ pancreatic progenitors was reduced at E10.5, as was proliferation of mesenchyme at E11.5. Although loss of Fgf9 did not interfere with differentiation of later epithelial lineages, single-cell RNA-Sequencing identified transcriptional programs perturbed upon loss of Fgf9 during pancreatic development, including loss of the transcription factor Barx1. Lastly, we identified conserved expression patterns of FGF9 and receptors in human fetal pancreas, suggesting that FGF9 expressed by pancreatic mesenchyme may similarly affect the development of the human pancreas.

Doxycycline Significantly Enhances Induction of Induced Pluripotent Stem Cells to Endoderm by Enhancing Survival Through Protein Kinase B Phosphorylation.

BACKGROUND AND AIMS: Induced pluripotent stem cells (iPSCs) provide an important tool for the generation of patient-derived cells, including hepatocyte-like cells, by developmental cues through an endoderm intermediate. However, most iPSC lines fail to differentiate into endoderm, with induction resulting in apoptosis. APPROACH AND RESULTS: To address this issue, we built upon published methods to develop an improved protocol. We discovered that doxycycline dramatically enhances the efficiency of iPSCs to endoderm differentiation by inhibiting apoptosis and promoting proliferation through the protein kinase B pathway. We tested this protocol in >70 iPSC lines, 90% of which consistently formed complete sheets of endoderm. Endoderm generated by our method achieves similar transcriptomic profiles, expression of endoderm protein markers, and the ability to be further differentiated to downstream lineages. CONCLUSIONS: Furthermore, this method achieves a 4-fold increase in endoderm cell number and will accelerate studies of human diseases in vitro and facilitate the expansion of iPSC-derived cells for transplantation studies.

Human pluripotent stem cell-derived insulin-producing cells: A regenerative medicine perspective.

Tremendous progress has been made over the last two decades in the field of pancreatic beta cell replacement therapy as a curative measure for diabetes. Transplantation studies have demonstrated therapeutic efficacy, and cGMP-grade cell products are currently being deployed for the first time in human clinical trials. In this perspective, we discuss current challenges surrounding the generation, delivery, and engraftment of stem cell-derived islet-like cells, along with strategies to induce durable tolerance to grafted cells, with an eye toward a functional cellular-based therapy enabling insulin independence for patients with diabetes.

Single-cell transcriptional profiling of human thymic stroma uncovers novel cellular heterogeneity in the thymic medulla.

The thymus' key function in the immune system is to provide the necessary environment for the development of diverse and self-tolerant T lymphocytes. While recent evidence suggests that the thymic stroma is comprised of more functionally distinct subpopulations than previously appreciated, the extent of this cellular heterogeneity in the human thymus is not well understood. Here we use single-cell RNA sequencing to comprehensively profile the human thymic stroma across multiple stages of life. Mesenchyme, pericytes and endothelial cells are identified as potential key regulators of thymic epithelial cell differentiation and thymocyte migration. In-depth analyses of epithelial cells reveal the presence of ionocytes as a medullary population, while the expression of tissue-specific antigens is mapped to different subsets of epithelial cells. This work thus provides important insight on how the diversity of thymic cells is established, and how this heterogeneity contributes to the induction of immune tolerance in humans.

A Hierarchy of Proliferative and Migratory Keratinocytes Maintains the Tympanic Membrane.

The tympanic membrane (TM) is critical for hearing and requires continuous clearing of cellular debris, but little is known about homeostatic mechanisms in the TM epidermis. Using single-cell RNA sequencing, lineage tracing, whole-organ explant, and live-cell imaging, we show that homeostatic TM epidermis is distinct from other epidermal sites and has discrete proliferative zones with a three-dimensional hierarchy of multiple keratinocyte populations. TM stem cells reside in a discrete location of the superior TM and generate long-lived clones and committed progenitors (CPs). CP clones exhibit lateral migration, and their proliferative capacity is supported by Pdgfra+ fibroblasts, generating migratory but non-proliferative progeny. Single-cell sequencing of the human TM revealed similar cell types and transcriptional programming. Thus, during homeostasis, TM keratinocytes transit through a proliferative CP state and exhibit directional lateral migration. This work forms a foundation for understanding TM disorders and modeling keratinocyte biology.

A single-cell atlas and lineage analysis of the adult Drosophila ovary.

The Drosophila ovary is a widely used model for germ cell and somatic tissue biology. Here we use single-cell RNA-sequencing (scRNA-seq) to build a comprehensive cell atlas of the adult Drosophila ovary that contains transcriptional profiles for every major cell type in the ovary, including the germline stem cells and their niche cells, follicle stem cells, and previously undescribed subpopulations of escort cells. In addition, we identify Gal4 lines with specific expression patterns and perform lineage tracing of subpopulations of escort cells and follicle cells. We discover that a distinct subpopulation of escort cells is able to convert to follicle stem cells in response to starvation or upon genetic manipulation, including knockdown of escargot, or overactivation of mTor or Toll signalling.

Beta Living through Alpha Cells.

Recently in Nature, Furuyama et al. (2019) provide evidence for lineage plasticity in the human endocrine pancreas, demonstrating that α cells derived from adult human pancreatic islets can be reprogrammed to become glucose-responsive, insulin-secreting ß-like cells that are capable of reversing diabetes in mouse models.

Lineage dynamics of murine pancreatic development at single-cell resolution.

Organogenesis requires the complex interactions of multiple cell lineages that coordinate their expansion, differentiation, and maturation over time. Here, we profile the cell types within the epithelial and mesenchymal compartments of the murine pancreas across developmental time using a combination of single-cell RNA sequencing, immunofluorescence, in situ hybridization, and genetic lineage tracing. We identify previously underappreciated cellular heterogeneity of the developing mesenchyme and reconstruct potential lineage relationships among the pancreatic mesothelium and mesenchymal cell types. Within the epithelium, we find a previously undescribed endocrine progenitor population, as well as an analogous population in both human fetal tissue and human embryonic stem cells differentiating toward a pancreatic beta cell fate. Further, we identify candidate transcriptional regulators along the differentiation trajectory of this population toward the alpha or beta cell lineages. This work establishes a roadmap of pancreatic development and demonstrates the broad utility of this approach for understanding lineage dynamics in developing organs.

Expansion of hedgehog disrupts mesenchymal identity and induces emphysema phenotype.

GWAS have repeatedly mapped susceptibility loci for emphysema to genes that modify hedgehog signaling, but the functional relevance of hedgehog signaling to this morbid disease remains unclear. In the current study, we identified a broad population of mesenchymal cells in the adult murine lung receptive to hedgehog signaling, characterized by higher activation of hedgehog surrounding the proximal airway relative to the distal alveoli. Single-cell RNA-sequencing showed that the hedgehog-receptive mesenchyme is composed of mostly fibroblasts with distinct proximal and distal subsets with discrete identities. Ectopic hedgehog activation in the distal fibroblasts promoted expression of proximal fibroblast markers and loss of distal alveoli and airspace enlargement of over 20% compared with controls. We found that hedgehog suppressed mesenchymal-derived mitogens enriched in distal fibroblasts that regulate alveolar stem cell regeneration and airspace size. Finally, single-cell analysis of the human lung mesenchyme showed that segregated proximal-distal identity with preferential hedgehog activation in the proximal fibroblasts was conserved between mice and humans. In conclusion, we showed that differential hedgehog activation segregates mesenchymal identities of distinct fibroblast subsets and that disruption of fibroblast identity can alter the alveolar stem cell niche, leading to emphysematous changes in the murine lung.

Stem Cell Therapies for Treating Diabetes: Progress and Remaining Challenges.

Restoration of insulin independence and normoglycemia has been the overarching goal in diabetes research and therapy. While whole-organ and islet transplantation have become gold-standard procedures in achieving glucose control in diabetic patients, the profound lack of suitable donor tissues severely hampers the broad application of these therapies. Here, we describe current efforts aimed at generating a sustainable source of functional human stem cell-derived insulin-producing islet cells for cell transplantation and present state-of-the-art efforts to protect such cells via immune modulation and encapsulation strategies.

Defining epithelial cell dynamics and lineage relationships in the developing lacrimal gland.

The tear-producing lacrimal gland is a tubular organ that protects and lubricates the ocular surface. The lacrimal gland possesses many features that make it an excellent model in which to investigate tubulogenesis, but the cell types and lineage relationships that drive lacrimal gland formation are unclear. Using single-cell sequencing and other molecular tools, we reveal novel cell identities and epithelial lineage dynamics that underlie lacrimal gland development. We show that the lacrimal gland from its earliest developmental stages is composed of multiple subpopulations of immune, epithelial and mesenchymal cell lineages. The epithelial lineage exhibits the most substantial cellular changes, transitioning through a series of unique transcriptional states to become terminally differentiated acinar, ductal and myoepithelial cells. Furthermore, lineage tracing in postnatal and adult glands provides the first direct evidence of unipotent KRT5+ epithelial cells in the lacrimal gland. Finally, we show conservation of developmental markers between the developing mouse and human lacrimal gland, supporting the use of mice to understand human development. Together, our data reveal crucial features of lacrimal gland development that have broad implications for understanding epithelial organogenesis.

Fasting-Mimicking Diet Promotes Ngn3-Driven ß-Cell Regeneration to Reverse Diabetes.

Stem-cell-based therapies can potentially reverse organ dysfunction and diseases, but the removal of impaired tissue and activation of a program leading to organ regeneration pose major challenges. In mice, a 4-day fasting mimicking diet (FMD) induces a stepwise expression of Sox17 and Pdx-1, followed by Ngn3-driven generation of insulin-producing ß cells, resembling that observed during pancreatic development. FMD cycles restore insulin secretion and glucose homeostasis in both type 2 and type 1 diabetes mouse models. In human type 1 diabetes pancreatic islets, fasting conditions reduce PKA and mTOR activity and induce Sox2 and Ngn3 expression and insulin production. The effects of the FMD are reversed by IGF-1 treatment and recapitulated by PKA and mTOR inhibition. These results indicate that a FMD promotes the reprogramming of pancreatic cells to restore insulin generation in islets from T1D patients and reverse both T1D and T2D phenotypes in mouse models. PAPERCLIP.

Brief report: VGLL4 is a novel regulator of survival in human embryonic stem cells.

Human embryonic stem cells (hESCs) are maintained in a self-renewing state by an interconnected network of mechanisms that sustain pluripotency, promote proliferation and survival, and prevent differentiation. We sought to find novel genes that could contribute to one or more of these processes using a gain-of-function screen of a large collection of human open reading frames. We identified Vestigial-like 4 (VGLL4), a cotranscriptional regulator with no previously described function in hESCs, as a positive regulator of survival in hESCs. Specifically, VGLL4 overexpression in hESCs significantly decreases cell death in response to dissociation stress. Additionally, VGLL4 overexpression enhances hESC colony formation from single cells. These effects may be attributable, in part, to a decreased activity of initiator and effector caspases observed in the context of VGLL4 overexpression. Additionally, we show an interaction between VGLL4 and the Rho/Rock pathway, previously implicated in hESC survival. This study introduces a novel gain-of-function approach for studying hESC maintenance and presents VGLL4 as a previously undescribed regulator of this process. Stem Cells 2013;31:2833-2841.

Self-renewal of embryonic-stem-cell-derived progenitors by organ-matched mesenchyme.

One goal of regenerative medicine, to use stem cells to replace cells lost by injury or disease, depends on producing an excess of the relevant cell for study or transplantation. To this end, the stepwise differentiation of stem cells into specialized derivatives has been successful for some cell types, but a major problem remains the inefficient conversion of cells from one stage of differentiation to the next. If specialized cells are to be produced in large numbers it will be necessary to expand progenitor cells, without differentiation, at some steps of the process. Using the pancreatic lineage as a model for embryonic-stem-cell differentiation, we demonstrate that this is a solvable problem. Co-culture with organ-matched mesenchyme permits proliferation and self-renewal of progenitors, without differentiation, and enables an expansion of more than a million-fold for human endodermal cells with full retention of their developmental potential. This effect is specific both to the mesenchymal cell and to the progenitor being amplified. Progenitors that have been serially expanded on mesenchyme give rise to glucose-sensing, insulin-secreting cells when transplanted in vivo. Theoretically, the identification of stage-specific renewal signals can be incorporated into any scheme for the efficient production of large numbers of differentiated cells from stem cells and may therefore have wide application in regenerative biology.

The contribution of niche-derived factors to the regulation of cancer cells.

In normal adult tissues, paracrine signals that derive from the stem cell niche, or microenvironment, play an important role in regulating the critical balance between activity and quiescence of stem cells. Similarly, evidence has emerged to support the hypothesis that signals derived from the microenvironment regulate cancer cells in an analogous manner. We recently reported that in basal cell carcinoma of the skin and in diverse other solid tumors, fibroblasts that comprise the tumor cell niche are, indeed, molecularly distinct from those that comprise the normal stroma. In particular, we found evidence suggesting that expression of secreted BMP antagonists by tumor-associated stromal cells may promote self-renewal of tumor stem cells in vivo. This chapter describes methods for identifying and evaluating the molecular signals that derive from fibroblasts in human tumors.