Evaluation of bumetanide as a potential therapeutic agent for Alzheimer's disease

Therapeutics discovery and development for Alzheimer's disease (AD) has been an area of intense research to alleviate memory loss and the underlying pathogenic processes. Recent drug discovery approaches have utilized in silico computational strategies for drug candidate selection which has opened the door to repurposing drugs for AD. Computational analysis of gene expression signatures of patients stratified by the APOE4 risk allele of AD led to the discovery of the FDA-approved drug bumetanide as a top candidate agent that reverses APOE4 transcriptomic brain signatures and improves memory deficits in APOE4 animal models of AD. Bumetanide is a loop diuretic which inhibits the kidney Na+-K+-2Cl- cotransporter isoform, NKCC2, for the treatment of hypertension and edema in cardiovascular, liver, and renal disease. Electronic health record data revealed that patients exposed to bumetanide have lower incidences of AD by 35%-70%. In the brain, bumetanide has been proposed to antagonize the NKCC1 isoform which mediates cellular uptake of chloride ions. Blocking neuronal NKCC1 leads to a decrease in intracellular chloride and thus promotes GABAergic receptor mediated hyperpolarization, which may ameliorate disease conditions associated with GABAergic-mediated depolarization. NKCC1 is expressed in neurons and in all brain cells including glia (oligodendrocytes, microglia, and astrocytes) and the vasculature. In consideration of bumetanide as a repurposed drug for AD, this review evaluates its pharmaceutical properties with respect to its estimated brain levels across doses that can improve neurologic disease deficits of animal models to distinguish between NKCC1 and non-NKCC1 mechanisms. The available data indicate that bumetanide efficacy may occur at brain drug levels that are below those required for inhibition of the NKCC1 transporter which implicates non-NKCC1 brain mechansims for improvement of brain dysfunctions and memory deficits. Alternatively, peripheral bumetanide mechanisms may involve cells outside the central nervous system (e.g., in epithelia and the immune system). Clinical bumetanide doses for improved neurological deficits are reviewed. Regardless of mechanism, the efficacy of bumetanide to improve memory deficits in the APOE4 model of AD and its potential to reduce the incidence of AD provide support for clinical investigation of bumetanide as a repurposed AD therapeutic agent.

Assaying Chemical Long-Term Potentiation in Human iPSC-Derived Neuronal Networks

Impairment of long-term potentiation (LTP) is a common feature of many preclinical models of neurological disorders. Modeling LTP on human induced pluripotent stem cells (hiPSC) enables the investigation of this critical plasticity process in disease-specific genetic backgrounds. Here, we describe a method to chemically induce LTP across entire networks of hiPSC-derived neurons on multi-electrode arrays (MEAs) and investigate effects on neuronal network activity and associated molecular changes.

Development of a platform to investigate long-term potentiation in human iPSC-derived neuronal networks

Impairment of long-term potentiation (LTP) is a common feature of many pre-clinical models of neurological disorders; however, studies in humans are limited by the inaccessibility of the brain. Human induced pluripotent stem cells (hiPSCs) provide a unique opportunity to study LTP in disease-specific genetic backgrounds. Here we describe a multi-electrode array (MEA)-based assay to investigate chemically induced LTP (cLTP) across entire networks of hiPSC-derived midbrain dopaminergic (DA) and cortical neuronal populations that lasts for days, allowing studies of the late phases of LTP and enabling detection of associated molecular changes. We show that cLTP on midbrain DA neuronal networks is largely independent of the N-methyl-D-aspartate receptor (NMDAR) and partially dependent on brain-derived neurotrophic factor (BDNF). Finally, we describe activity-regulated gene expression induced by cLTP. This cLTP-MEA assay platform will enable phenotype discovery and higher-throughput analyses of synaptic plasticity on hiPSC-derived neurons.

Ultra-Sharp Nanowire Arrays Natively Permeate, Record, and Stimulate Intracellular Activity in Neuronal and Cardiac Networks

We report innovative scalable, vertical, ultra-sharp nanowire arrays that are individually addressable to enable long-term, native recordings of intracellular potentials. Stable amplitudes of intracellular potentials from 3D tissue-like networks of neurons and cardiomyocytes are obtained. Individual electrical addressability is necessary for high-fidelity intracellular electrophysiological recordings. This study paves the way toward predictive, high-throughput, and low-cost electrophysiological drug screening platforms.

iMyoblasts for ex vivo and in vivo investigations of human myogenesis and disease modeling

Skeletal muscle myoblasts (iMyoblasts) were generated from human induced pluripotent stem cells (iPSCs) using an efficient and reliable transgene-free induction and stem cell selection protocol. Immunofluorescence, flow cytometry, qPCR, digital RNA expression profiling, and scRNA-Seq studies identify iMyoblasts as a PAX3+/MYOD1+ skeletal myogenic lineage with a fetal-like transcriptome signature, distinct from adult muscle biopsy myoblasts (bMyoblasts) and iPSC-induced muscle progenitors. iMyoblasts can be stably propagated for >12 passages or 30 population doublings while retaining their dual commitment for myotube differentiation and regeneration of reserve cells. iMyoblasts also efficiently xenoengrafted into irradiated and injured mouse muscle where they undergo differentiation and fetal-adult MYH isoform switching, demonstrating their regulatory plasticity for adult muscle maturation in response to signals in the host muscle. Xenograft muscle retains PAX3+ muscle progenitors and can regenerate human muscle in response to secondary injury. As models of disease, iMyoblasts from individuals with Facioscapulohumeral Muscular Dystrophy revealed a previously unknown epigenetic regulatory mechanism controlling developmental expression of the pathological DUX4 gene. iMyoblasts from Limb-Girdle Muscular Dystrophy R7 and R9 and Walker Warburg Syndrome patients modeled their molecular disease pathologies and were responsive to small molecule and gene editing therapeutics. These findings establish the utility of iMyoblasts for ex vivo and in vivo investigations of human myogenesis and disease pathogenesis and for the development of muscle stem cell therapeutics.

Defective autophagy and increased apoptosis contribute toward the pathogenesis of FKRP-associated muscular dystrophies

Fukutin-related protein (FKRP) is a glycosyltransferase involved in glycosylation of alpha-dystroglycan (α-DG). Mutations in FKRP are associated with muscular dystrophies (MD) ranging from limb-girdle LGMDR9 to Walker-Warburg Syndrome (WWS), a severe type of congenital MD. Although hypoglycosylation of α-DG is the main hallmark of this group of diseases, a full understanding of the underlying pathophysiology is still missing. Here, we investigated molecular mechanisms impaired by FKRP mutations in pluripotent stem (PS) cell–derived myotubes. FKRP-deficient myotubes show transcriptome alterations in genes involved in extracellular matrix receptor interactions, calcium signaling, PI3K-Akt pathway, and lysosomal function. Accordingly, using a panel of patient-specific LGMDR9 and WWS induced PS cell–derived myotubes, we found a significant reduction in the autophagy-lysosome pathway for both disease phenotypes. In addition, we show that WWS myotubes display decreased ERK1/2 activity and increased apoptosis, which were restored in gene edited myotubes. Our results suggest the autophagy-lysosome pathway and apoptosis may contribute to the FKRP-associated MD pathogenesis.

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The lysosome pathway is deregulated in FKRP-deficient myotubes

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Autophagy is decreased in patient-specific LGMDR9 and WWS iPS cell–derived myotubes

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FKRP WWS and LGMDR9 iPS cell–derived myotubes have increased apoptosis

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FKRP correction in WWS myotubes rescues changes in autophagy and apoptosis

Super-Selective Reconstruction of Causal and Direct Connectivity With Application to in vitro iPSC Neuronal Networks

Despite advancements in the development of cell-based in-vitro neuronal network models, the lack of appropriate computational tools limits their analyses. Methods aimed at deciphering the effective connections between neurons from extracellular spike recordings would increase utility of in vitro local neural circuits, especially for studies of human neural development and disease based on induced pluripotent stem cells (hiPSC). Current techniques allow statistical inference of functional couplings in the network but are fundamentally unable to correctly identify indirect and apparent connections between neurons, generating redundant maps with limited ability to model the causal dynamics of the network. In this paper, we describe a novel mathematically rigorous, model-free method to map effective-direct and causal-connectivity of neuronal networks from multi-electrode array data. The inference algorithm uses a combination of statistical and deterministic indicators which, first, enables identification of all existing functional links in the network and then reconstructs the directed and causal connection diagram via a super-selective rule enabling highly accurate classification of direct, indirect, and apparent links. Our method can be generally applied to the functional characterization of any in vitro neuronal networks. Here, we show that, given its accuracy, it can offer important insights into the functional development of in vitro hiPSC-derived neuronal cultures.

A universal gene correction approach for FKRP-associated dystroglycanopathies to enable autologous cell therapy

Mutations in the fukutin-related protein (FKRP) gene result in a broad spectrum of muscular dystrophy (MD) phenotypes, including the severe Walker-Warburg syndrome (WWS). Here, we develop a gene-editing approach that replaces the entire mutant open reading frame with the wild-type sequence to universally correct all FKRP mutations. We apply this approach to correct FKRP mutations in induced pluripotent stem (iPS) cells derived from patients displaying broad clinical severity. Our findings show rescue of functional α-dystroglycan (α-DG) glycosylation in gene-edited WWS iPS cell-derived myotubes. Transplantation of gene-corrected myogenic progenitors in the FKRPP448L-NSG mouse model gives rise to myofiber and satellite cell engraftment and, importantly, restoration of α-DG functional glycosylation in vivo. These findings suggest the potential feasibility of using CRISPR-Cas9 technology in combination with patient-specific iPS cells for the future development of autologous cell transplantation for FKRP-associated MDs.

NAD+ enhances ribitol and ribose rescue of α-dystroglycan functional glycosylation in human FKRP-mutant myotubes

Mutations in the fukutin-related protein (FKRP) cause Walker-Warburg syndrome (WWS), a severe form of congenital muscular dystrophy. Here, we established a WWS human induced pluripotent stem cell-derived myogenic model that recapitulates hallmarks of WWS pathology. We used this model to investigate the therapeutic effect of metabolites of the pentose phosphate pathway in human WWS. We show that functional recovery of WWS myotubes is promoted not only by ribitol but also by its precursor ribose. Moreover, we found that the combination of each of these metabolites with NAD+ results in a synergistic effect, as demonstrated by rescue of α-dystroglycan glycosylation and laminin binding capacity. Mechanistically, we found that FKRP residual enzymatic capacity, characteristic of many recessive FKRP mutations, is required for rescue as supported by functional and structural mutational analyses. These findings provide the rationale for testing ribose/ribitol in combination with NAD+ to treat WWS and other diseases associated with FKRP mutations.

Human Pluripotent Stem Cell-Derived Neural Cells and Brain Organoids Reveal SARS-CoV-2 Neurotropism Predominates in Choroid Plexus Epithelium

Neurological complications are common in patients with COVID-19. Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal pathogen of COVID-19, has been detected in some patient brains, its ability to infect brain cells and impact their function is not well understood. Here, we investigated the susceptibility of human induced pluripotent stem cell (hiPSC)-derived monolayer brain cells and region-specific brain organoids to SARS-CoV-2 infection. We found that neurons and astrocytes were sparsely infected, but choroid plexus epithelial cells underwent robust infection. We optimized a protocol to generate choroid plexus organoids from hiPSCs and showed that productive SARS-CoV-2 infection of these organoids is associated with increased cell death and transcriptional dysregulation indicative of an inflammatory response and cellular function deficits. Together, our findings provide evidence for selective SARS-CoV-2 neurotropism and support the use of hiPSC-derived brain organoids as a platform to investigate SARS-CoV-2 infection susceptibility of brain cells, mechanisms of virus-induced brain dysfunction, and treatment strategies.

Human Pluripotent Stem Cell-Derived Neural Cells and Brain Organoids Reveal SARS-CoV-2 Neurotropism

Neurological complications are common in patients with COVID-19. While SARS-CoV-2, the causal pathogen of COVID-19, has been detected in some patient brains, its ability to infect brain cells and impact their function are not well understood, and experimental models using human brain cells are urgently needed. Here we investigated the susceptibility of human induced pluripotent stem cell (hiPSC)-derived monolayer brain cells and region-specific brain organoids to SARS-CoV-2 infection. We found modest numbers of infected neurons and astrocytes, but greater infection of choroid plexus epithelial cells. We optimized a protocol to generate choroid plexus organoids from hiPSCs, which revealed productive SARS-CoV-2 infection that leads to increased cell death and transcriptional dysregulation indicative of an inflammatory response and cellular function deficits. Together, our results provide evidence for SARS-CoV-2 neurotropism and support use of hiPSC-derived brain organoids as a platform to investigate the cellular susceptibility, disease mechanisms, and treatment strategies for SARS-CoV-2 infection.

A Physiological Instability Displayed in Hippocampal Neurons Derived From Lithium-Nonresponsive Bipolar Disorder Patients

BACKGROUND

We recently reported a hyperexcitability phenotype displayed in dentate gyrus granule neurons derived from patients with bipolar disorder (BD) as well as a hyperexcitability that appeared only in CA3 pyramidal hippocampal neurons that were derived from patients with BD who responded to lithium treatment (lithium responders) and not in CA3 pyramidal hippocampal neurons that were derived from patients with BD who did not respond to lithium (nonresponders).

METHODS

Here we used our measurements of currents in neurons derived from 4 control subjects, 3 patients with BD who were lithium responders, and 3 patients with BD who were nonresponders. We changed the conductances of simulated dentate gyrus and CA3 hippocampal neurons according to our measurements to derive a numerical simulation for BD neurons.

RESULTS

The computationally simulated BD dentate gyrus neurons had a hyperexcitability phenotype similar to the experimental results. Only the simulated BD CA3 neurons derived from lithium responder patients were hyperexcitable. Interestingly, our computational model captured a physiological instability intrinsic to hippocampal neurons that were derived from nonresponder patients that we also observed when re-examining our experimental results. This instability was caused by a drastic reduction in the sodium current, accompanied by an increase in the amplitude of several potassium currents. These baseline alterations caused nonresponder BD hippocampal neurons to drastically shift their excitability with small changes to their sodium currents, alternating between hyperexcitable and hypoexcitable states.

CONCLUSIONS

Our computational model of BD hippocampal neurons that was based on our measurements reproduced the experimental phenotypes of hyperexcitability and physiological instability. We hypothesize that the physiological instability phenotype strongly contributes to affective lability in patients with BD.

Cholesterol Metabolism Is a Druggable Axis that Independently Regulates Tau and Amyloid-β in iPSC-Derived Alzheimer's Disease Neurons

Genetic, epidemiologic, and biochemical evidence suggests that predisposition to Alzheimer's disease (AD) may arise from altered cholesterol metabolism, although the molecular pathways that may link cholesterol to AD phenotypes are only partially understood. Here, we perform a phenotypic screen for pTau accumulation in AD-patient iPSC-derived neurons and identify cholesteryl esters (CE), the storage product of excess cholesterol, as upstream regulators of Tau early during AD development. Using isogenic induced pluripotent stem cell (iPSC) lines carrying mutations in the cholesterol-binding domain of APP or APP null alleles, we found that while CE also regulate Aβ secretion, the effects of CE on Tau and Aβ are mediated by independent pathways. Efficacy and toxicity screening in iPSC-derived astrocytes and neurons showed that allosteric activation of CYP46A1 lowers CE specifically in neurons and is well tolerated by astrocytes. These data reveal that CE independently regulate Tau and Aβ and identify a druggable CYP46A1-CE-Tau axis in AD.

High-content screen for modifiers of Niemann-Pick type C disease in patient cells

Niemann-Pick type C (NPC) disease is a rare lysosomal storage disease caused primarily by mutations in NPC1. NPC1 encodes the lysosomal cholesterol transport protein NPC1. The most common NPC1 mutation is a missense mutation (NPC1I1061T) that causes misfolding and rapid degradation of mutant protein in the endoplasmic reticulum. Cholesterol accumulates in enlarged lysosomes as a result of decreased levels of lysosomal NPC1I1061T protein in patient cells. There is currently no cure or FDA-approved treatment for patients. We sought to identify novel compounds that decrease lysosomal cholesterol storage in NPC1I1061T/I1061T patient fibroblasts using a high-content screen with the cholesterol dye, filipin and the lysosomal marker, LAMP1. A total of 3532 compounds were screened, including 2013 FDA-approved drugs, 327 kinase inhibitors and 760 serum metabolites. Twenty-three hits were identified that decreased both filipin and LAMP1 signals. The majority of hits (16/21) were histone deacetylase (HDAC) inhibitors, a previously described class of modifiers of NPC cholesterol storage. Of the remaining hits, the antimicrobial compound, alexidine dihydrochloride had the most potent lysosomal cholesterol-reducing activity. Subsequent analyses showed that alexidine specifically increased levels of NPC1 transcript and mature protein in both control and NPC patient cells. Although unsuitable for systemic therapy, alexidine represents a unique tool compound for further NPC studies and as a potent inducer of NPC1. Together, these findings confirm the utility of high-content image-based compound screens of NPC1 patient cells and support extending the approach into larger compound collections.

Neurons derived from patients with bipolar disorder divide into intrinsically different sub-populations of neurons, predicting the patients' responsiveness to lithium

Bipolar disorder (BD) is a progressive psychiatric disorder with more than 3% prevalence worldwide. Affected individuals experience recurrent episodes of depression and mania, disrupting normal life and increasing the risk of suicide greatly. The complexity and genetic heterogeneity of psychiatric disorders have challenged the development of animal and cellular models. We recently reported that hippocampal dentate gyrus (DG) neurons differentiated from induced pluripotent stem cell (iPSC)-derived fibroblasts of BD patients are electrophysiologically hyperexcitable. Here we used iPSCs derived from Epstein-Barr virus-immortalized B-lymphocytes to verify that the hyperexcitability of DG-like neurons is reproduced in this different cohort of patients and cells. Lymphocytes are readily available for research with a large number of banked lines with associated patient clinical description. We used whole-cell patch-clamp recordings of over 460 neurons to characterize neurons derived from control individuals and BD patients. Extensive functional analysis showed that intrinsic cell parameters are very different between the two groups of BD neurons, those derived from lithium (Li)-responsive (LR) patients and those derived from Li-non-responsive (NR) patients, which led us to partition our BD neurons into two sub-populations of cells and suggested two different subdisorders. Training a Naïve Bayes classifier with the electrophysiological features of patients whose responses to Li are known allows for accurate classification with more than 92% success rate for a new patient whose response to Li is unknown. Despite their very different functional profiles, both populations of neurons share a large, fast after-hyperpolarization (AHP). We therefore suggest that the large, fast AHP is a key feature of BD and a main contributor to the fast, sustained spiking abilities of BD neurons. Confirming our previous report with fibroblast-derived DG neurons, chronic Li treatment reduced the hyperexcitability in the lymphoblast-derived LR group but not in the NR group, strengthening the validity and utility of this new human cellular model of BD.

High-throughput screen for compounds that modulate neurite growth of human induced pluripotent stem cell-derived neurons

Development of technology platforms to perform compound screens of human induced pluripotent stem cell (hiPSC)-derived neurons with relatively high throughput is essential to realize their potential for drug discovery. Here, we demonstrate the feasibility of high-throughput screening of hiPSC-derived neurons using a high-content, image-based approach focused on neurite growth, a process that is fundamental to formation of neural networks and nerve regeneration. From a collection of 4421 bioactive small molecules, we identified 108 hit compounds, including 37 approved drugs, that target molecules or pathways known to regulate neurite growth, as well as those not previously associated with this process. These data provide evidence that many pathways and targets known to play roles in neurite growth have similar activities in hiPSC-derived neurons that can be identified in an unbiased phenotypic screen. The data also suggest that hiPSC-derived neurons provide a useful system to study the mechanisms of action and off-target activities of the approved drugs identified as hits, leading to a better understanding of their clinical efficacy and toxicity, especially in the context of specific human genetic backgrounds. Finally, the hit set we report constitutes a sublibrary of approved drugs and tool compounds that modulate neurites. This sublibrary will be invaluable for phenotypic analyses and interrogation of hiPSC-based disease models as probes for defining phenotypic differences and cellular vulnerabilities in patient versus control cells, as well as for investigations of the molecular mechanisms underlying human neurite growth in development and maintenance of neuronal networks, and nerve regeneration.

Summary: High-throughput, small molecule screening of hiPSC-derived neurons using a high-content, image-based approach focused on neurite growth identified hit compounds, including approved drugs, which target molecules or pathways known to regulate neurite growth.

Polyglutamine-Expanded Huntingtin Exacerbates Age-Related Disruption of Nuclear Integrity and Nucleocytoplasmic Transport

Onset of neurodegenerative disorders, including Huntington's disease, is strongly influenced by aging. Hallmarks of aged cells include compromised nuclear envelope integrity, impaired nucleocytoplasmic transport, and accumulation of DNA double-strand breaks. We show that mutant huntingtin markedly accelerates all of these cellular phenotypes in a dose- and age-dependent manner in cortex and striatum of mice. Huntingtin-linked polyglutamine initially accumulates in nuclei, leading to disruption of nuclear envelope architecture, partial sequestration of factors essential for nucleocytoplasmic transport (Gle1 and RanGAP1), and intranuclear accumulation of mRNA. In aged mice, accumulation of RanGAP1 together with polyglutamine is shifted to perinuclear and cytoplasmic areas. Consistent with findings in mice, marked alterations in nuclear envelope morphology, abnormal localization of RanGAP1, and nuclear accumulation of mRNA were found in cortex of Huntington's disease patients. Overall, our findings identify polyglutamine-dependent inhibition of nucleocytoplasmic transport and alteration of nuclear integrity as a central component of Huntington's disease.

Adeno-Associated Virus-Mediated Mini-Agrin Delivery Is Unable to Rescue Disease Phenotype in a Mouse Model of Limb Girdle Muscular Dystrophy Type 2I

Agrin is a basement membrane-specific proteoglycan that can regulate orientation of cytoskeleton proteins and improve function of dystrophic skeletal muscle. In skeletal muscle, agrin binds with high affinity to laminin(s) and α-dystroglycan (α-DG), an integral part of the dystrophin-glycoprotein complex. Miniaturized forms of agrin (mAgrin) have been shown to ameliorate disease pathology in a laminin-α2 knockout mouse model of muscular dystrophy, acting as a link between α-DG and laminin(s). Here, we test whether mAgrin might also improve pathologies associated with FKRP-related dystroglycanopathies, another form of muscular dystrophy characterized by weak interactions between muscle and basement membranes. We demonstrate in vitro that mAgrin enhances laminin binding to primary myoblasts and fibroblasts from an FKRP mutant mouse model and that this enhancement is abrogated when mAgrin is in molar excess relative to laminin. However, in vivo delivery of mAgrin via adeno-associated virus (AAV) into FKRP mutant mice was unable to improve dystrophic phenotypes, both histologically and functionally. These results likely reflect insufficient binding of mAgrin to hypoglycosylated α-DG on muscle fibers and possibly abrogation of binding from molar excess of overexpressed AAV-delivered mAgrin. Further exploration of mAgrin modification is necessary to strengthen its binding to other membrane components, including hypoglycosylated α-DG, for potential therapeutic applications.

High Density Individually Addressable Nanowire Arrays Record Intracellular Activity from Primary Rodent and Human Stem Cell Derived Neurons

We report a new hybrid integration scheme that offers for the first time a nanowire-on-lead approach, which enables independent electrical addressability, is scalable, and has superior spatial resolution in vertical nanowire arrays. The fabrication of these nanowire arrays is demonstrated to be scalable down to submicrometer site-to-site spacing and can be combined with standard integrated circuit fabrication technologies. We utilize these arrays to perform electrophysiological recordings from mouse and rat primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons, which revealed high signal-to-noise ratios and sensitivity to subthreshold postsynaptic potentials (PSPs). We measured electrical activity from rodent neurons from 8 days in vitro (DIV) to 14 DIV and from hiPSC-derived neurons at 6 weeks in vitro post culture with signal amplitudes up to 99 mV. Overall, our platform paves the way for longitudinal electrophysiological experiments on synaptic activity in human iPSC based disease models of neuronal networks, critical for understanding the mechanisms of neurological diseases and for developing drugs to treat them.

A scalable system for production of functional pancreatic progenitors from human embryonic stem cells

Development of a human embryonic stem cell (hESC)-based therapy for type 1 diabetes will require the translation of proof-of-principle concepts into a scalable, controlled, and regulated cell manufacturing process. We have previously demonstrated that hESC can be directed to differentiate into pancreatic progenitors that mature into functional glucose-responsive, insulin-secreting cells in vivo. In this study we describe hESC expansion and banking methods and a suspension-based differentiation system, which together underpin an integrated scalable manufacturing process for producing pancreatic progenitors. This system has been optimized for the CyT49 cell line. Accordingly, qualified large-scale single-cell master and working cGMP cell banks of CyT49 have been generated to provide a virtually unlimited starting resource for manufacturing. Upon thaw from these banks, we expanded CyT49 for two weeks in an adherent culture format that achieves 50–100 fold expansion per week. Undifferentiated CyT49 were then aggregated into clusters in dynamic rotational suspension culture, followed by differentiation en masse for two weeks with a four-stage protocol. Numerous scaled differentiation runs generated reproducible and defined population compositions highly enriched for pancreatic cell lineages, as shown by examining mRNA expression at each stage of differentiation and flow cytometry of the final population. Islet-like tissue containing glucose-responsive, insulin-secreting cells was generated upon implantation into mice. By four- to five-months post-engraftment, mature neo-pancreatic tissue was sufficient to protect against streptozotocin (STZ)-induced hyperglycemia. In summary, we have developed a tractable manufacturing process for the generation of functional pancreatic progenitors from hESC on a scale amenable to clinical entry.

Cell-surface markers for the isolation of pancreatic cell types derived from human embryonic stem cells

Using a flow cytometry-based screen of commercial antibodies, we have identified cell-surface markers for the separation of pancreatic cell types derived from human embryonic stem (hES) cells. We show enrichment of pancreatic endoderm cells using CD142 and of endocrine cells using CD200 and CD318. After transplantation into mice, enriched pancreatic endoderm cells give rise to all the pancreatic lineages, including functional insulin-producing cells, demonstrating that they are pancreatic progenitors. In contrast, implanted, enriched polyhormonal endocrine cells principally give rise to glucagon cells. These antibodies will aid investigations that use pancreatic cells generated from pluripotent stem cells to study diabetes and pancreas biology.

Pancreatic endoderm derived from human embryonic stem cells generates glucose-responsive insulin-secreting cells in vivo

Development of a cell therapy for diabetes would be greatly aided by a renewable supply of human beta-cells. Here we show that pancreatic endoderm derived from human embryonic stem (hES) cells efficiently generates glucose-responsive endocrine cells after implantation into mice. Upon glucose stimulation of the implanted mice, human insulin and C-peptide are detected in sera at levels similar to those of mice transplanted with approximately 3,000 human islets. Moreover, the insulin-expressing cells generated after engraftment exhibit many properties of functional beta-cells, including expression of critical beta-cell transcription factors, appropriate processing of proinsulin and the presence of mature endocrine secretory granules. Finally, in a test of therapeutic potential, we demonstrate that implantation of hES cell-derived pancreatic endoderm protects against streptozotocin-induced hyperglycemia. Together, these data provide definitive evidence that hES cells are competent to generate glucose-responsive, insulin-secreting cells.

Production of pancreatic hormone-expressing endocrine cells from human embryonic stem cells

Of paramount importance for the development of cell therapies to treat diabetes is the production of sufficient numbers of pancreatic endocrine cells that function similarly to primary islets. We have developed a differentiation process that converts human embryonic stem (hES) cells to endocrine cells capable of synthesizing the pancreatic hormones insulin, glucagon, somatostatin, pancreatic polypeptide and ghrelin. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm, gut-tube endoderm, pancreatic endoderm and endocrine precursor--en route to cells that express endocrine hormones. The hES cell-derived insulin-expressing cells have an insulin content approaching that of adult islets. Similar to fetal beta-cells, they release C-peptide in response to multiple secretory stimuli, but only minimally to glucose. Production of these hES cell-derived endocrine cells may represent a critical step in the development of a renewable source of cells for diabetes cell therapy.

Expression of Xenopus laevis Lhx2 during eye development and evidence for divergent expression among vertebrates

Members of the LIM homeodomain (LIM-HD) family of proteins are double zinc-finger containing transcription factors with important functions in pattern formation and cell lineage determination. The LIM-HD family member Lhx2 is required for normal eye, liver, and central nervous system formation. Lhx2(-/-) mice lack eyes, and experiments in Xenopus predict that Lhx2 forms a regulatory network with other eye field transcription factors to specify the eye field during eye formation. Here, we describe the structure and developmental expression pattern of the Xenopus laevis homologue, XLhx2. We show that XLhx2 shares significant amino acid sequence identity with other vertebrate Lhx2 proteins and Drosophila apterous (ap). The expression patterns of XLhx2 in the early neural plate and during eye development are consistent with a role in eye field specification and retinal differentiation. Despite highly similar expression patterns in the mouse and Xenopus central nervous system, divergent expression patterns were also observed. Phylogenetic analysis confirmed the identity of the isolated cDNA as a Xenopus ortholog of Lhx2. Therefore, in spite of structural similarities, the mouse and Xenopus Lhx2 expression patterns differ, suggesting potential functional differences in these species.

Identification of the Wnt signaling activator leucine-rich repeat in Flightless interaction protein 2 by a genome-wide functional analysis

The Wnt signaling pathway acts ubiquitously in metazoans to control various aspects of embryonic development. Wnt ligands bind their receptors Frizzled and low-density lipoprotein receptor-related protein 5/6 and function through Disheveled (Dvl), Axin, adenomatous polyposis coli, glycogen synthase kinase 3beta, and casein kinase (CK) 1 to stabilize beta-catenin and induce lymphocyte enhancer-binding factor (LEF)/T cell factor (TCF)-dependent transcriptional activities. To identify previously unrecognized Wnt signaling modulators, a genome-wide functional screen was performed using large-scale arrayed cDNA collections. From this screen, both known components and previously uncharacterized regulators of this pathway were identified, including beta-catenin, Dvl1, Dvl3, Fbxw-1, Cul1, CK1epsilon, CK1delta, and gamma-catenin. In particular, a previously unrecognized activator, LRRFIP2 (leucine-rich repeat in Flightless interaction protein 2), was found that interacts with Dvl to increase the cellular levels of beta-catenin and activate beta-catenin/LEF/TCF-dependent transcriptional activity. The function of LRRFIP2 is blocked when a dominant negative Dvl (Xdd1) is coexpressed. Expression of LRRFIP2 in Xenopus embryos induced double axis formation and Wnt target gene expression; a dominant negative form of LRRFIP2 suppresses ectopic Wnt signaling in Xenopus embryos and partially inhibits endogenous dorsal axis formation. These data suggest that LRRFIP2 plays an important role in transducing Wnt signals.

Default repression and Notch signaling: Hairless acts as an adaptor to recruit the corepressors Groucho and dCtBP to Suppressor of Hairless

The DNA-binding transcription factor Suppressor of Hairless [Su(H)] functions as an activator during Notch (N) pathway signaling, but can act as a repressor in the absence of signaling. Hairless (H), a novel Drosophila protein, binds to Su(H) and has been proposed to antagonize N signaling by inhibiting DNA binding by Su(H). Here we show that, in vitro, H directly binds two corepressor proteins, Groucho (Gro) and dCtBP. Reduction of gro or dCtBP function enhances H mutant phenotypes and suppresses N phenotypes in the adult mechanosensory bristle. This activity of gro is surprising, because it is directed oppositely to its traditionally defined role as a neurogenic gene. We find that Su(H)-H complexes can bind to DNA with high efficiency in vitro. Furthermore, a H-VP16 fusion protein causes dominant-negative phenotypes in vivo, a result consistent with the proposal that H functions in transcriptional repression. Taken together, our findings indicate that "default repression" of N pathway target genes by an unusual adaptor/corepressor complex is essential for proper cell fate specification during Drosophila peripheral nervous system development.

Rhomboid and Star facilitate presentation and processing of the Drosophila TGF-alpha homolog Spitz

Activation of the Drosophila epidermal growth factor receptor (DER) by the transmembrane ligand, Spitz (Spi), requires two additional transmembrane proteins, Rhomboid and Star. Genetic evidence suggests that Rhomboid and Star facilitate DER signaling by processing membrane-bound Spi (mSpi) to an active, soluble form. To test this model, we use an assay based on Xenopus animal cap explants in which Spi activation of DER is Rhomboid and Star dependent. We show that Spi is on the cell surface but is kept in an inactive state by its cytoplasmic and transmembrane domains; Rhomboid and Star relieve this inhibition, allowing Spi to signal. We show further that Spi is likely to be cleaved within its transmembrane domain. However, a mutant form of mSpi that is not cleaved still signals to DER in a Rhomboid and Star-dependent manner. These results suggest strongly that Rhomboid and Star act primarily to present an active form of Spi to DER, leading secondarily to the processing of Spi into a secreted form.

Rhomboid and Star facilitate presentation and processing of the Drosophila TGF-α homolog Spitz

Activation of the Drosophila epidermal growth factor receptor (DER) by the transmembrane ligand, Spitz (Spi), requires two additional transmembrane proteins, Rhomboid and Star. Genetic evidence suggests that Rhomboid and Star facilitate DER signaling by processing membrane-bound Spi (mSpi) to an active, soluble form. To test this model, we use an assay based on Xenopus animal cap explants in which Spi activation of DER is Rhomboid and Star dependent. We show that Spi is on the cell surface but is kept in an inactive state by its cytoplasmic and transmembrane domains; Rhomboid and Star relieve this inhibition, allowing Spi to signal. We show further that Spi is likely to be cleaved within its transmembrane domain. However, a mutant form of mSpi that is not cleaved still signals to DER in a Rhomboid and Star-dependent manner. These results suggest strongly that Rhomboid and Star act primarily to present an active form of Spi to DER, leading secondarily to the processing of Spi into a secreted form.

Expression of Pax-3 in the lateral neural plate is dependent on a Wnt-mediated signal from posterior nonaxial mesoderm

During early patterning of the vertebrate neuraxis, the expression of the paired-domain transcription factor Pax-3 is induced in the lateral portions of the posterior neural plate via posteriorizing signals emanating from the late organizer and posterior nonaxial mesoderm. Using a dominant-negative approach, we show in explant assays that Pax-3 inductive activities from the organizer do not depend on FGF, retinoic acid, or XWnt-8, either alone or in combination, suggesting that the organizer may produce an unknown posteriorizing factor. However, Pax-3 inductive signals from posterior nonaxial mesoderm are Wnt-dependent. We show that Pax-3 expression in the lateral neural plate expands in XWnt-8-injected embryos and is blocked by dominant-negative XWnt-8. Similarly, we show that the homeodomain transcription factor Msx-1, which like Pax-3 is an early marker of the lateral neural plate, is induced by posterior nonaxial mesoderm and blocked by dominant-negative XWnt-8. Finally, we show that Rohon-Beard primary neurons, a cell type that develops within the lateral neural plate, are also blocked in vivo by dominant-negative Xwnt-8. Together these data support a model in which patterning of the lateral neural plate by Wnt-mediated signals is an early event that establishes a posteriolateral domain, marked by Pax-3 and Msx-1 expression, from which Rohon-Beard cells and neural crest will subsequently arise.

Expression of Pax-3 is initiated in the early neural plate by posteriorizing signals produced by the organizer and by posterior non-axial mesoderm

Pax-3 is a paired-type homeobox gene that is specifically expressed in the dorsal and posterior neural tube. We have investigated inductive interactions that initiate Pax-3 transcript expression in the early neural plate. We present several lines of evidence that support a model where Pax-3 expression is initiated by signals that posteriorize the neuraxis, and then secondarily restricted dorsally in response to dorsal-ventral patterning signals. First, in chick and Xenopus gastrulae the onset of Pax-3 expression occurs in regions fated to become posterior CNS. Second, Hensen's node and posterior non-axial mesoderm which underlies the neural plate induce Pax-3 expression when combined with presumptive anterior neural plate explants. In contrast, presumptive anterior neural plate explants are not competent to express Pax-3 in response to dorsalizing signals from epidermal-ectoderm. Third, in a heterospecies explant recombinant assay with Xenopus animal caps (ectoderm) as a responding tissue, late, but not early, Hensen's node induces Pax-3 expression. Chick posterior non-axial mesoderm also induces Pax-3, provided that the animal caps are neuralized by treatment with noggin. Finally we show that the putative posteriorizing factors, retinoic acid and bFGF, induce Pax-3 in neuralized animal caps. However, blocking experiments with a dominant-inhibitory FGF receptor and a dominant-inhibitory retinoic acid receptor suggest that Pax-3 inductive activities arising from Hensen's node and posterior non-axial mesoderm do not strictly depend on FGF or retinoic acid.

Regulation of vertebrate neural cell fate by transcription factors

Evidence that region- and cell-type-specific transcription factors regulate morphogenesis and differentiation of the vertebrate nervous system comes from numerous studies, including descriptions of discrete patterns of expression during neural development and analysis of mutant phenotypes. Recently published works provide insights into the roles of vertebrate transcription factors in regulating the generation of neural precursors, regionalization of the nervous system, and subsequent differentiation of specific cell types within these regions. For instance, misexpression studies in Xenopus embryos show that the newly isolated basic helix-loop-helix protein NeuroD is able to promote neurogenesis, whereas analysis of mouse embryos mutant for the homeobox gene En-1 demonstrates that this transcription factor is required for proper development of the midbrain-hindbrain region. A recent study in chick shows that the combinatorial expression of Islet-1, Lim-1, and two other LIM homeobox genes, Islet-2 and Lim-3, defines subclasses of motor neurons in the spinal cord, supporting a model where combinatorial repertoires of transcription factors may act to generate diverse cell types.

Hairless promotes stable commitment to the sensory organ precursor cell fate by negatively regulating the activity of the Notch signaling pathway

In Drosophila imaginal discs, the function of the Hairless (H) gene is required at multiple steps during the development of adult sensory organs. Here we report the results of a series of experiments designed to investigate the in vivo role of H in sensory organ precursor (SOP) cell specification. We show that the proneural cluster pattern of proneural gene expression and of transcriptional activation by proneural proteins is established normally in the absence of H activity. By contrast, single cells with the high levels of achaete, scabrous, and neuralized expression characteristic of SOPs almost always fail to appear in H mutant proneural clusters. These results indicate that H is required for a relatively late step in the development of the proneural cluster, namely, the stable commitment of a single cell to the SOP cell fate. We also show that expression of an activated form of the Notch receptor leads to bristle loss with the same cellular basis--failure of SOP determination--as loss of H function and that simultaneous overexpression of H suppresses this effect. Finally, we demonstrate by epistasis experiments that the failure of stable commitment to the SOP fate in H null mutants requires the activity of the genes of the Enhancer of split complex, including groucho. Our results indicate that H promotes SOP determination by antagonizing the activity of the Notch pathway in this cell, thereby protecting it from inhibitory signaling by its neighbors in the proneural cluster. We propose a simple threshold model in which the principal role of H in SOP specification is to translate a quantitative difference in the activity of the Notch pathway (in the SOP versus the non-SOP cells) into a stable binary cell fate decision.

Direct downstream targets of proneural activators in the imaginal disc include genes involved in lateral inhibitory signaling

In Drosophila imaginal discs, the spatially restricted activities of the achaete (ac) and scute (sc) proteins, which are transcriptional activators of the basic-helix-loop-helix class, define proneural clusters (PNCs) of potential sensory organ precursor (SOP) cells. Here, we report the identification of several genes that are direct downstream targets of ac-sc activation, as judged by the following criteria. The genes are expressed in the PNCs of the wing imaginal disc in an ac-sc-dependent manner; the proximal promoter regions of all of these genes contain one or two high-affinity ac-sc binding sites, which define the novel consensus GCAGGTG(T/G)NNNYY; where tested, these binding sites are required in vivo for PNC expression of promoter-reporter fusion genes. Interestingly, these ac-sc target genes, including Bearded, Enhancer of split m7, Enhancer of split m8, and scabrous, are all known or believed to function in the selection of a single SOP from each PNC, a process mediated by inhibitory cell-cell interactions. Thus, one of the earliest steps in adult peripheral neurogenesis is the direct activation by proneural proteins of genes involved in restricting the expression of the SOP cell fate.

Dpbx, a new homeobox gene closely related to the human proto-oncogene pbx1 molecular structure and developmental expression

Recently, a new class of homeodomain containing proteins, pbx1, pbx2, and pbx3 has been described. pbx proteins are most closely related to two yeast regulatory proteins, a1 and alpha 2. Here, we identify and characterize the pbx homolog in Drosophila, designated Dpbx. Dpbx is 95% identical to the pbx proteins within the homeodomain and, more remarkably, is 85% to 88% identical within a 201 amino acid region adjacent to the homeodomain. Cytologically, the Dpbx gene is located on the X chromosome at 14A. mRNA expression is both maternal and zygotic and occurs throughout the life cycle. Prior to full germband retraction, Dpbx is rather ubiquitously present and variations are minor. The most notable feature of Dpbx expression is that after germband retraction, high levels of Dpbx are observed in the anterior portion of the ventral nerve cord.

The Drosophila gene Hairless encodes a novel basic protein that controls alternative cell fates in adult sensory organ development

The mechanosensory bristles of adult Drosophila are composed of four cells that, in most cases, are progeny of a single sensory organ precursor (SOP) cell. Two sister cells in this lineage, the trichogen and tormogen, produce the external shaft and socket of the bristle, respectively. Loss-of-function mutations of Hairless (H) confer two distinct mutant phenotypes on adult bristles. The bristle loss phenotype results from the failure to specify and/or execute the SOP cell fate; the double socket phenotype results from the transformation of the trichogen (shaft) cell into a second tormogen (socket) cell. We have found that the H gene encodes a novel basic protein with a predicted molecular mass of 109 kD. Basal levels of expression of a transgene (P[Hs-H]) in which the H protein-coding region is under the control of the Hsp70 promoter are sufficient to provide full rescue of H mutant phenotypes. Heat shock treatment of P[Hs-H] transgenic animals as late larvae and early pupae produces a tormogen-to-trichogen (double shaft) cell fate transformation, as well as bristle multiplication and loss phenotypes very similar to those caused by loss-of-function mutations in the neurogenic gene Notch. Our results indicate that the SOP cell fate requires H to antagonize the activity of the neurogenic group of genes and that the expression of distinct cell fates by the trichogen/tormogen sister cell pair depends on an asymmetry in their levels of H+ activity or in their thresholds for response to H.

Hairless is required for the development of adult sensory organ precursor cells in Drosophila

Reduction of the wild-type activity of the gene Hairless (H) results in two major phenotypic effects on the mechanosensory bristles of adult Drosophila. Bristles are either ‘lost’ (i.e. the shaft and socket fail to appear) or they exhibit a ‘double socket’ phenotype, in which the shaft is apparently transformed into a second socket. Analysis of the phenotypes conferred by a series of H mutant genotypes demonstrates (1) that different sensilla exhibit different patterns of response to decreasing levels of H+ function, and (2) that the ‘bristle loss’ phenotype results from greater loss of H+ function than the ‘double socket’ phenotype. The systematic study of H allelic combinations enabled us to identify genotypes that reliably produce specific mutant defects in particular positions on the bodies of adult flies. This permitted us to investigate the cellular development of sensilla in these same positions in larvae and pupae and thereby establish the developmental basis for the mutant phenotypes. We have found that H is required for at least two steps of adult sensillum development. In positions where ‘double socket’ microchaetes appear on the notum of H mutant flies, sensillum precursor cells are present in the developing pupa and divide normally, but their progeny adopt an aberrant spatial arrangement and fail to differentiate correctly. In regions of the notum exhibiting ‘bristle loss’ in adult H mutants, we were unable at the appropriate stages of development to detect sensillum-specific cell types, the precursor cell divisions that generate them, or the primary precursor cells themselves. Thus, the H ‘bristle loss’ phenotype appears to reflect a very early defect in sensillum development, namely the failure to specify and/or execute the sensory organ precursor cell fate. This finding indicates that H is one of a small number of identified genes for which the loss-of-function phenotype is the failure of sensillum precursor cell development.

Transcript and sequence analysis of a 5.1 kb contiguous fragment of Dictyostelium discoideum plasmid Ddp1 that contains the origin of replication and codes for several transcripts

The sequence of a 5.1 kb contiguous fragment of the Dictyostelium plasmid Ddp1 is presented. This fragment contains three long open reading frames which correspond to the developmentally regulated and cAMP-inducible transcript d-5, the growth phase specific transcript g-1 and the three overlapping transcripts g-2, g-3 and d-4. The transcripts that originate from Ddp1 resemble chromosomally-encoded ones: they are products of RNA polymerase II, are polyadenylated and accumulate at different time points during Dictyostelium development. The presented nucleotide sequence encompasses a 2,033 bp HindIII fragment that had previously been shown to carry all the information necessary for extrachromosomal replication. None of the identified genes is completely contained within this HindIII fragment.

Human muscle glycogen synthase cDNA sequence: a negatively charged protein with an asymmetric charge distribution

The cDNA for human muscle glycogen synthase encodes a protein of 737 amino acids. The primary structure of glycogen synthase is not related either to bacterial glycogen synthase or to any glycogen phosphorylase. All nine of the serines that are phosphorylated in the rabbit muscle enzyme in vivo are conserved in the human muscle sequence. The amino- and carboxyl-terminal fragments, which contain all the phosphorylation sites, are very negatively charged. Overall the unphosphorylated protein has a charge of -13, while the fully phosphorylated inactive protein has a net charge of -31. The importance of the asymmetrical charge distribution is discussed.

The watermelon mitochondrial URF-1 gene: evidence for a complex structure

We have cloned and sequenced a fragment of watermelon mitochondrial DNA (mtDNA) which contains a gene homologous to mitochondrial URF-1 (Unidentified Reading Frame-1) of vertebrates, Drosophila yakuba and Aspergillus nidulans. URF-1 is thought to encode a component of the respiratory chain NADH dehydrogenase. Two coding regions in the watermelon gene are separated by approximately 1,450 bp of untranslatable DNA. These two exons encode the central portions of URF-1, and are highly conserved. We postulate that three additional exons, selected by their map location and amino acid homology to other URF-1 sequences, encode the remainder of the polypeptide. This is the first description of a plant mitochondrial gene with multiple introns.