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Tools and approaches for analyzing the role of mitochondria in health, development and disease using human cerebral organoids.
Mitochondria are cellular organelles involved in generating energy to power various processes in the cell. Although the pivotal role of mitochondria in neurogenesis was demonstrated (first in animal models), very little is known about their role in human embryonic neurodevelopment and its pathology. In this respect human-induced pluripotent stem cells (hiPSC)-derived cerebral organoids provide a tractable, alternative model system of the early neural development and disease that is responsive to pharmacological and genetic manipulations, not possible to apply in humans. Although the involvement of mitochondria in the pathogenesis and progression of neurodegenerative diseases and brain dysfunction has been demonstrated, the precise role they play in cell life and death remains unknown, compromising the development of new mitochondria-targeted approaches to treat human diseases. The cerebral organoid model of neurogenesis and disease in vitro provides an unprecedented opportunity to answer some of the most fundamental questions about mitochondrial function in early human neurodevelopment and neural pathology. Largely an unexplored territory due to the lack of tools and approaches, this review focuses on recent technological advancements in fluorescent and molecular tools, imaging systems, and computational approaches for quantitative and qualitative analyses of mitochondrial structure and function in three-dimensional cellular assemblies-cerebral organoids. Future developments in this direction will further facilitate our understanding of the important role or mitochondrial dynamics and energy requirements during early embryonic development. This in turn will provide a further understanding of how dysfunctional mitochondria contribute to disease processes.
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Vascular Organoids Derived from Capillary malformation-induced Pluripotent Stem Cells Exhibit Disease-Relevant Phenotypes.
Capillary malformation (CM) is a congenital vascular anomaly that affects the skin, mucosa, eye, and brain. A major obstacle to mechanistic and drug screening studies for CM has been the lack of preclinical models. In this study, we established vascular organoids (VOs) generated through the self-assembly of vascular lineages of endothelial cells and smooth muscle cells differentiated from CM-induced pluripotent stem cells (iPSC). Within these VOs induced endothelial cells and smooth muscle cells organized into juxtapositions to form vascular branches. CM patient iPSC-derived VOs showed a higher density of endothelial and smooth muscle cell populations and greater vascular branch lengths as compared with VOs derived from iPSCs generated from healthy skin biopsies. Overall, this study represents the first disease-relevant VO model of CM, providing a valuable platform for future mechanistic studies and drug screening.
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iPSC models of mitochondrial diseases.
Mitochondrial diseases are historically difficult to study. They cause multi-systemic defects with prevalent impairment of hard-to-access tissues such as the brain and the heart. Furthermore, they suffer from a paucity of conventional model systems, especially because of the challenges associated with mitochondrial DNA (mtDNA) engineering. Consequently, most mitochondrial diseases are currently untreatable. Human induced pluripotent stem cells (iPSCs) represent a promising approach for developing human model systems and assessing therapeutic avenues in a patient- and tissue-specific context. iPSCs are being increasingly used to investigate mitochondrial diseases, either for dissecting mutation-specific defects within two-dimensional (2D) or three-dimensional (3D) progenies or for unveiling the impact of potential treatment options. Here, we review how iPSC-derived 2D cells and 3D organoid models have been applied to the study of mitochondrial diseases caused by either nuclear or mtDNA defects. We anticipate that the field of iPSC-driven modeling of mitochondrial diseases will continue to grow, likely leading to the development of innovative platforms for treatment discovery and toxicity that could benefit the patient community suffering from these debilitating disorders with highly unmet medical needs.
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Consequences of congenital Zika virus infection.
The 2015 Zika virus (ZIKV) epidemic in the Americas led to the discovery that ZIKV causes congenital abnormalities including microcephaly, intrauterine growth restriction, and eye disease that can result in blindness. Studies in animal models and human organoid cultures, together with human epidemiological studies, have shown that ZIKV crosses the placenta and subsequently replicates within fetal tissues including the developing brain. Preferential infection of neural cell precursors causes damage to the developing fetal brain. However, a majority of congenitally infected humans do not develop microcephaly or other overt congenital abnormalities, so longitudinal epidemiological studies are necessary to more completely define the long-term consequences of in utero ZIKV infection.
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Synchronization of the segmentation clock using synthetic cell-cell signaling.
During vertebrate development, the segmentation clock drives oscillatory gene expression in the presomitic mesoderm (PSM), leading to the periodic formation of somites. Oscillatory gene expression is synchronized at the cell population level; inhibition of Delta-Notch signaling results in the loss of synchrony and the fusion of somites. However, it remains unclear how cell-cell signaling couples oscillatory gene expression and controls synchronization. Here, we report that synthetic cell-cell signaling using designed ligand-receptor pairs can induce synchronized oscillations in PSM organoids. Optogenetic assays uncovered that the intracellular domains of synthetic ligands play key roles in dynamic cell-cell communication. Oscillatory coupling using synthetic cell-cell signaling recovered the synchronized oscillation in PSM cells deficient for Delta-Notch signaling; nonoscillatory coupling did not induce recovery. This study reveals the mechanism by which ligand-receptor molecules coordinate the synchronization of the segmentation clock and provides a way to program temporal gene expression in organoids and artificial tissues.
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Internet-Connected Cortical Organoids for Project-Based Stem Cell and Neuroscience Education.
The introduction of Internet-connected technologies to the classroom has the potential to revolutionize STEM education by allowing students to perform experiments in complex models that are unattainable in traditional teaching laboratories. By connecting laboratory equipment to the cloud, we introduce students to experimentation in pluripotent stem cell (PSC)-derived cortical organoids in two different settings: using microscopy to monitor organoid growth in an introductory tissue culture course and using high-density (HD) multielectrode arrays (MEAs) to perform neuronal stimulation and recording in an advanced neuroscience mathematics course. We demonstrate that this approach develops interest in stem cell and neuroscience in the students of both courses. All together, we propose cloud technologies as an effective and scalable approach for complex project-based university training.
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Patient-derived organoids and orthotopic xenografts of primary and recurrent gliomas represent relevant patient avatars for precision oncology.
Patient-based cancer models are essential tools for studying tumor biology and for the assessment of drug responses in a translational context. We report the establishment a large cohort of unique organoids and patient-derived orthotopic xenografts (PDOX) of various glioma subtypes, including gliomas with mutations in IDH1, and paired longitudinal PDOX from primary and recurrent tumors of the same patient. We show that glioma PDOXs enable long-term propagation of patient tumors and represent clinically relevant patient avatars that retain histopathological, genetic, epigenetic, and transcriptomic features of parental tumors. We find no evidence of mouse-specific clonal evolution in glioma PDOXs. Our cohort captures individual molecular genotypes for precision medicine including mutations in IDH1, ATRX, TP53, MDM2/4, amplification of EGFR, PDGFRA, MET, CDK4/6, MDM2/4, and deletion of CDKN2A/B, PTCH, and PTEN. Matched longitudinal PDOX recapitulate the limited genetic evolution of gliomas observed in patients following treatment. At the histological level, we observe increased vascularization in the rat host as compared to mice. PDOX-derived standardized glioma organoids are amenable to high-throughput drug screens that can be validated in mice. We show clinically relevant responses to temozolomide (TMZ) and to targeted treatments, such as EGFR and CDK4/6 inhibitors in (epi)genetically defined subgroups, according to MGMT promoter and EGFR/CDK status, respectively. Dianhydrogalactitol (VAL-083), a promising bifunctional alkylating agent in the current clinical trial, displayed high therapeutic efficacy, and was able to overcome TMZ resistance in glioblastoma. Our work underscores the clinical relevance of glioma organoids and PDOX models for translational research and personalized treatment studies and represents a unique publicly available resource for precision oncology.
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PCDH12 loss results in premature neuronal differentiation and impeded migration in a cortical organoid model.
Protocadherins (PCDHs) are cell adhesion molecules that regulate many essential neurodevelopmental processes related to neuronal maturation, dendritic arbor formation, axon pathfinding, and synaptic plasticity. Biallelic loss-of-function variants in PCDH12 are associated with several neurodevelopmental disorders (NDDs). Despite the highly deleterious outcome resulting from loss of PCDH12, little is known about its role during brain development and disease. Here, we show that PCDH12 loss severely impairs cerebral organoid development, with reduced proliferative areas and disrupted laminar organization. 2D models further show that neural progenitor cells lacking PCDH12 prematurely exit the cell cycle and differentiate earlier when compared with wild type. Furthermore, we show that PCDH12 regulates neuronal migration and suggest that this could be through a mechanism requiring ADAM10-mediated ectodomain shedding and/or membrane recruitment of cytoskeleton regulators. Our results demonstrate a critical involvement of PCDH12 in cortical organoid development, suggesting a potential cause for the pathogenic mechanisms underlying PCDH12-related NDDs.
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Organoids in domestic animals: with which stem cells?
Organoids are three-dimensional structures that are derived from the self-organization of stem cells as they differentiate in vitro. The plasticity of stem cells is one of the major criteria for generating organoids most similar to the tissue structures they intend to mimic. Stem cells are cells with unique properties of self-renewal and differentiation. Depending on their origin, a distinction is made between pluripotent (embryonic) stem cells (PSCs), adult (or tissue) stem cells (ASCs), and those obtained by somatic reprogramming, so-called induced pluripotent stem cells (iPSCs). While most data since the 1980s have been acquired in the mouse model, and then from the late 1990s in humans, the process of somatic reprogammation has revolutionized the field of stem cell research. For domestic animals, numerous attempts have been made to obtain PSCs and iPSCs, an approach that makes it possible to omit the use of embryos to derive the cells. Even if the plasticity of the cells obtained is not always optimal, the recent progress in obtaining reprogrammed cells is encouraging. Along with PSCs and iPSCs, many organoid derivations in animal species are currently obtained from ASCs. In this study, we present state-of-the-art stem cell research according to their origins in the various animal models developed.
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Transsynaptic tracing techniques to interrogate neuronal connectivity of glioblastomas.
Glioblastomas (GBMs) functionally integrate into diverse neuronal circuits within the central nervous system, which can promote tumor progression and affect neurons via neuron-to-glioma synapses. It remains challenging to identify and manipulate tumor-innervating neurons, which may remain localized or widely distributed throughout the brain. Building on GBM organoids (GBOs) derived from patient-resected surgical tissue, we present here detailed procedures for assessing interactions between tumors and neurons. We first discuss retrograde trans-monosynaptic tracing approaches to study the neuron-tumor connectome by using a rabies viral system in ex vivo human tissue and in xenogenic animal models. As a complementary approach, we then describe the use of anterograde transsynaptic tracing using herpes simplex virus in vivo and ex vivo to assess brain region-specific connectivity in GBMs. In addition, to facilitate the adaptability of these tracing methodologies in diverse systems, we provide procedures for the viral transduction into GBOs, the generation of assembloids comprising GBOs and human induced pluripotent stem cell-derived cortical organoids and the establishment of air-liquid interface cultures from surgical human brain tissue. Together, these techniques permit the flexible characterization and manipulation of tumor-neural circuits and can be easily adapted to other cancers with nervous system involvement. After the generation of GBOs and/or cortical organoids, transsynaptic tracing requires 12-35 d to complete ex vivo or in vivo. The procedure is suitable for users with expertise in human cell and organoid culture, viral production and transduction, rodent surgery and microscopy.