Segregation of neuronal and neuroendocrine differentiation in the sympathoadrenal lineage

ALK upregulates POSTN and WNT signaling to drive neuroblastoma

Neuroblastoma is the most common extracranial solid tumor of childhood. While MYCN and mutant anaplastic lymphoma kinase (ALKF1174L) cooperate in tumorigenesis, how ALK contributes to tumor formation remains unclear. Here, we used a human stem cell-based model of neuroblastoma. Mis-expression of ALKF1174L and MYCN resulted in shorter latency compared to MYCN alone. MYCN tumors resembled adrenergic, while ALK/MYCN tumors resembled mesenchymal, neuroblastoma. Transcriptomic analysis revealed enrichment in focal adhesion signaling, particularly the extracellular matrix genes POSTN and FN1 in ALK/MYCN tumors. Patients with ALK-mutant tumors similarly demonstrated elevated levels of POSTN and FN1. Knockdown of POSTN, but not FN1, delayed adhesion and suppressed proliferation of ALK/MYCN tumors. Furthermore, loss of POSTN reduced ALK-dependent activation of WNT signaling. Reciprocally, inhibition of the WNT pathway reduced expression of POSTN and growth of ALK/MYCN tumor cells. Thus, ALK drives neuroblastoma in part through a feedforward loop between POSTN and WNT signaling.

Human iPSC modeling recapitulates in vivo sympathoadrenal development and reveals an aberrant developmental subpopulation in familial neuroblastoma

Studies defining normal and disrupted human neural crest cell development have been challenging given its early timing and intricacy of development. Consequently, insight into the early disruptive events causing a neural crest related disease such as pediatric cancer neuroblastoma is limited. To overcome this problem, we developed an in vitro differentiation model to recapitulate the normal in vivo developmental process of the sympathoadrenal lineage which gives rise to neuroblastoma. We used human in vitro pluripotent stem cells and single-cell RNA sequencing to recapitulate the molecular events during sympathoadrenal development. We provide a detailed map of dynamically regulated transcriptomes during sympathoblast formation and illustrate the power of this model to study early events of the development of human neuroblastoma, identifying a distinct subpopulation of cell marked by SOX2 expression in developing sympathoblast obtained from patient derived iPSC cells harboring a germline activating mutation in the anaplastic lymphoma kinase (ALK) gene.

BET and CDK Inhibition Reveal Differences in the Proliferation Control of Sympathetic Ganglion Neuroblasts and Adrenal Chromaffin Cells

Neuroblastoma arising from the adrenal differ from ganglionic neuroblastoma both genetically and clinically, with adrenal tumors being associated with a more severe prognosis. The different tumor properties may be linked to specific tumor founder cells in adrenal and sympathetic ganglia. To address this question, we first set up cultures of mouse sympathetic neuroblasts and adrenal chromaffin cells. These cultures were then treated with various proliferation inhibitors to identify lineage-specific responses. We show that neuroblast and chromaffin cell proliferation was affected by WNT, ALK, IGF1, and PRC2/EZH2 signaling inhibitors to a similar extent. However, differential effects were observed in response to bromodomain and extraterminal (BET) protein inhibitors (JQ1, GSK1324726A) and to the CDK-7 inhibitor THZ1, with BET inhibitors preferentially affecting chromaffin cells, and THZ1 preferentially affecting neuroblasts. The differential dependence of chromaffin cells and neuroblasts on BET and CDK signaling may indicate different mechanisms during tumor initiation in sympathetic ganglia and adrenal.

Cell Networks in Endocrine/Neuroendocrine Gland Function

Reproduction, growth, stress, and metabolism are determined by endocrine/neuroendocrine systems that regulate circulating hormone concentrations. All these systems generate rhythms and changes in hormone pulsatility observed in a variety of pathophysiological states. Thus, the output of endocrine/neuroendocrine systems must be regulated within a narrow window of effective hormone concentrations but must also maintain a capacity for plasticity to respond to changing physiological demands. Remarkably most endocrinologists still have a "textbook" view of endocrine gland organization which has emanated from 20^th century histological studies on thin 2D tissue sections. However, 21^st -century technological advances, including in-depth 3D imaging of specific cell types have vastly changed our knowledge. We now know that various levels of multicellular organization can be found across different glands, that organizational motifs can vary between species and can be modified to enhance or decrease hormonal release. This article focuses on how the organization of cells regulates hormone output using three endocrine/neuroendocrine glands that present different levels of organization and complexity: the adrenal medulla, with a single neuroendocrine cell type; the anterior pituitary, with multiple intermingled cell types; and the pancreas with multiple intermingled cell types organized into distinct functional units. We give an overview of recent methodologies that allow the study of the different components within endocrine systems, particularly their temporal and spatial relationships. We believe the emerging findings about network organization, and its impact on hormone secretion, are crucial to understanding how homeostatic regulation of endocrine axes is carried out within endocrine organs themselves. © 2022 American Physiological Society. Compr Physiol 12:3371-3415, 2022.

Adrenal medulla development and medullary-cortical interactions

The mammalian adrenal gland is composed of two distinct tissue types in a bidirectional connection, the catecholamine-producing medulla derived from the neural crest and the mesoderm-derived cortex producing steroids. The medulla mainly consists of chromaffin cells derived from multipotent nerve-associated descendants of Schwann cell precursors. Already during adrenal organogenesis, close interactions between cortex and medulla are necessary for proper differentiation and morphogenesis of the gland. Moreover, communication between the cortex and the medulla ensures a regular function of the adult adrenal. In tumor development, interfaces between the two parts are also common. Here, we summarize the development of the mammalian adrenal medulla and the current understanding of the cortical-medullary interactions under development and in health and disease.

Single-cell transcriptomic analyses provide insights into the developmental origins of neuroblastoma

Neuroblastoma is a pediatric tumor of the developing sympathetic nervous system. However, the cellular origin of neuroblastoma has yet to be defined. Here we studied the single-cell transcriptomes of neuroblastomas and normal human developing adrenal glands at various stages of embryonic and fetal development. We defined normal differentiation trajectories from Schwann cell precursors over intermediate states to neuroblasts or chromaffin cells and showed that neuroblastomas transcriptionally resemble normal fetal adrenal neuroblasts. Importantly, neuroblastomas with varying clinical phenotypes matched different temporal states along normal neuroblast differentiation trajectories, with the degree of differentiation corresponding to clinical prognosis. Our work highlights the roles of oncogenic MYCN and loss of TFAP2B in blocking differentiation and may provide the basis for designing therapeutic interventions to overcome differentiation blocks.

WNT Signaling in Neuroblastoma

The term WNT (wingless-type MMTV integration site family) signaling comprises a complex molecular pathway consisting of ligands, receptors, coreceptors, signal transducers and transcriptional modulators with crucial functions during embryonic development, including all aspects of proliferation, morphogenesis and differentiation. Its involvement in cancer biology is well documented. Even though WNT signaling has been divided into mainly three distinct branches in the past, increasing evidence shows that some molecular hubs can act in various branches by exchanging interaction partners. Here we discuss developmental and clinical aspects of WNT signaling in neuroblastoma (NB), an embryonic tumor with an extremely broad clinical spectrum, ranging from spontaneous differentiation to fatal outcome. We discuss implications of WNT molecules in NB onset, progression, and relapse due to chemoresistance. In the light of the still too high number of NB deaths, new pathways must be considered.

RNA-seq of Isolated Chromaffin Cells Highlights the Role of Sex-Linked and Imprinted Genes in Adrenal Medulla Development

Adrenal chromaffin cells and sympathetic neurons synthesize and release catecholamines, and both cell types are derived from neural crest precursors. However, they have different developmental histories, with sympathetic neurons derived directly from neural crest precursors while adrenal chromaffin cells arise from neural crest-derived cells that express Schwann cell markers. We have sought to identify the genes, including imprinted genes, which regulate the development of the two cell types in mice. We developed a method of separating the two cell types as early as E12.5, using differences in expression of enhanced yellow fluorescent protein driven from the tyrosine hydroxylase gene, and then used RNA sequencing to confirm the characteristic molecular signatures of the two cell types. We identified genes differentially expressed by adrenal chromaffin cells and sympathetic neurons. Deletion of a gene highly expressed by adrenal chromaffin cells, NIK-related kinase, a gene on the X-chromosome, results in reduced expression of adrenaline-synthesizing enzyme, phenyl-N-methyl transferase, by adrenal chromaffin cells and changes in cell cycle dynamics. Finally, many imprinted genes are up-regulated in chromaffin cells and may play key roles in their development.

Expression pattern of delta-like 1 homolog in developing sympathetic neurons and chromaffin cells

Delta-like 1 homolog (DLK1) is a member of the epidermal growth factor (EGF)-like family and an atypical notch ligand that is widely expressed during early mammalian development with putative functions in the regulation of cell differentiation and proliferation. During later stages of development, DLK1 is downregulated and becomes increasingly restricted to specific cell types, including several types of endocrine cells. DLK1 has been linked to various tumors and associated with tumor stem cell features. Sympathoadrenal precursors are neural crest derived cells that give rise to either sympathetic neurons of the autonomic nervous system or the endocrine chromaffin cells located in the adrenal medulla or extraadrenal positions. As these cells are the putative cellular origin of neuroblastoma, one of the most common malignant tumors in early childhood, their molecular characterization is of high clinical importance. In this study we have examined the precise spatiotemporal expression of DLK1 in developing sympathoadrenal cells. We show that DLK1 mRNA is highly expressed in early sympathetic neuron progenitors and that its expression depends on the presence of Phox2B. DLK1 expression becomes quickly restricted to a small subpopulation of cells in sympathetic ganglia, while virtually all chromaffin cells in the adrenal medulla and the Organ of Zuckerkandl still express high levels of DLK1 at late gestational stages.

Striking parallels between carotid body glomus cell and adrenal chromaffin cell development

Carotid body glomus cells mediate essential reflex responses to arterial blood hypoxia. They are dopaminergic and secrete growth factors that support dopaminergic neurons, making the carotid body a potential source of patient-specific cells for Parkinson's disease therapy. Like adrenal chromaffin cells, which are also hypoxia-sensitive, glomus cells are neural crest-derived and require the transcription factors Ascl1 and Phox2b; otherwise, their development is little understood at the molecular level. Here, analysis in chicken and mouse reveals further striking molecular parallels, though also some differences, between glomus and adrenal chromaffin cell development. Moreover, histology has long suggested that glomus cell precursors are ‘émigrés’ from neighbouring ganglia/nerves, while multipotent nerve-associated glial cells are now known to make a significant contribution to the adrenal chromaffin cell population in the mouse. We present conditional genetic lineage-tracing data from mice supporting the hypothesis that progenitors expressing the glial marker proteolipid protein 1, presumably located in adjacent ganglia/nerves, also contribute to glomus cells. Finally, we resolve a paradox for the ‘émigré’ hypothesis in the chicken - where the nearest ganglion to the carotid body is the nodose, in which the satellite glia are neural crest-derived, but the neurons are almost entirely placode-derived - by fate-mapping putative nodose neuronal 'émigrés' to the neural crest.

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Glomus cell precursors express the neuron-specific marker Elavl3/4 (HuC/D).

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Developing glomus cells express multiple ‘sympathoadrenal' genes.

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Glomus cell development requires Hand2 and Sox4/11, but not Ret or Tfap2b.

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Multipotent progenitors with a glial phenotype contribute to glomus cells.

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Fate-mapping resolves a paradox for the ganglionic 'émigré' hypothesis in birds.

WNT signaling, the development of the sympathoadrenal-paraganglionic system and neuroblastoma

Neuroblastoma (NB) is a tumor of the sympathoadrenal system arising in children under 15 years of age. In Germany, NB accounts for 7% of childhood cancer cases, but 11% of cancer deaths. It originates from highly migratory progenitor cells that leave the dorsal neural tube and contribute neurons and glial cells to sympathetic ganglia, and chromaffin and supportive cells to the adrenal medulla and paraganglia. Clinically, histologically and molecularly, NBs present as extremely heterogeneous, ranging from very good to very poor prognosis. The etiology of NB still remains unclear and needs to be elucidated, however, aberrant auto- and paracrine embryonic cell communications seem to be likely candidates to initiate or facilitate the emergence, progression and regression of NB. The wingless-type MMTV integration site (WNT) family of proteins represents an evolutionary highly conserved signaling system that orchestrates embryogenesis. At least 19 ligands in the human, numerous receptors and co-receptors are known, which control not only proliferation, but also cell polarity, migration and differentiation. Here we seek to interconnect aspects of WNT signaling with sympathoadrenal and paraganglionic development to define new WNT signaling cues in the etiology and progression of NB.

Origin and initiation mechanisms of neuroblastoma

Neuroblastoma is an embryonal malignancy that affects normal development of the adrenal medulla and paravertebral sympathetic ganglia in early childhood. Extensive studies have revealed the molecular characteristics of human neuroblastomas, including abnormalities at genome, epigenome and transcriptome levels. However, neuroblastoma initiation mechanisms and even its origin are long-standing mysteries. In this review article, we summarize the current knowledge about normal development of putative neuroblastoma sources, namely sympathoadrenal lineage of neural crest cells and Schwann cell precursors that were recently identified as the source of adrenal chromaffin cells. A plausible origin of enigmatic stage 4S neuroblastoma is also discussed. With regard to the initiation mechanisms, we review genetic abnormalities in neuroblastomas and their possible association to initiation mechanisms. We also summarize evidences of neuroblastoma initiation observed in genetically engineered animal models, in which epigenetic alterations were involved, including transcriptomic upregulation by N-Myc and downregulation by polycomb repressive complex 2. Finally, several in vitro experimental methods are proposed that hopefully will accelerate our comprehension of neuroblastoma initiation. Thus, this review summarizes the state-of-the-art knowledge about the mechanisms of neuroblastoma initiation, which is critical for developing new strategies to cure children with neuroblastoma.

MYCN induces neuroblastoma in primary neural crest cells

Neuroblastoma (NBL) is an embryonal cancer of the sympathetic nervous system (SNS), which causes 15% of pediatric cancer deaths. High-risk NBL is characterized by N-Myc amplification and segmental chromosomal gains and losses. Owing to limited disease models, the etiology of NBL is largely unknown, including both the cell of origin and the majority of oncogenic drivers. We have established a novel system for studying NBL based on the transformation of neural crest cells (NCCs), the progenitor cells of the SNS, isolated from mouse embryonic day 9.5 trunk neural tube explants. Based on pathology and gene expression analysis, we report the first successful transformation of wild-type NCCs into NBL by enforced expression of N-Myc, to generate phenotypically and molecularly accurate tumors that closely model human MYCN-amplified NBL. Using comparative genomic hybridization, we found that NCC-derived NBL tumors acquired copy number gains and losses that are syntenic to those observed in human MYCN-amplified NBL including 17q gain, 2p gain and loss of 1p36. When p53-compromised NCCs were transformed with N-Myc, we generated primitive neuroectodermal tumors with divergent differentiation including osteosarcoma. These subcutaneous tumors were metastatic to regional lymph nodes, liver and lung. Our novel experimental approach accurately models human NBL and establishes a new system with potential to study early stages of NBL oncogenesis, to functionally assess NBL oncogenic drivers and to characterize NBL metastasis.

Functional Coupling with Cardiac Muscle Promotes Maturation of hPSC-Derived Sympathetic Neurons

Neurons derived from human pluripotent stem cells (hPSCs) are powerful tools for studying human neural development and diseases. Robust functional coupling of hPSC-derived neurons with target tissues in vitro is essential for modeling intercellular physiology in a dish and to further translational studies, but it has proven difficult to achieve. Here, we derive sympathetic neurons from hPSCs and show that they can form physical and functional connections with cardiac muscle cells. Using multiple hPSC reporter lines, we recapitulated human autonomic neuron development in vitro and successfully isolated PHOX2B::eGFP+ neurons that exhibit sympathetic marker expression and electrophysiological properties and norepinephrine secretion. Upon pharmacologic and optogenetic manipulation, PHOX2B::eGFP+ neurons controlled beating rates of cardiomyocytes, and the physical interactions between these cells increased neuronal maturation. This study provides a foundation for human sympathetic neuron specification and for hPSC-based neuronal control of organs in a dish.

Sympatho-adrenal morphogenesis regulated by the dorsal aorta

The autonomic nervous system, composed of sympathetic- and para-sympathetic neurons, plays essential roles in a variety of physiological functions including homeostasis and responses to external stimuli. We here present an overview of recent findings concerning how the sympathetic nervous system is formed during the early development, paying particular attention to the morphogenesis of those tissues derived from migrating neural crest cells. Neural crest cells, originally multipotent, are progressively specified to sympathetic ganglia neurons and adrenomedullary cells during their migration through the body. Importantly, the dorsal aorta, the first-forming blood vessel, acts as a signaling center for their migration and differentiation. BMP signals emanating from the dorsal aorta are essential for establishing environmental cues that directly act on the migrating cells. The mechanisms underlying these early neuro-vascular interactions provide insights into understanding diseases caused by malfunctions and malformations of the autonomic nervous system.