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Preventing Neurodegenerative Memory Loss in Hopfield Neuronal Networks Using Cerebral Organoids or External Microelectronics.
Developing technologies have made significant progress towards linking the brain with brain-machine interfaces (BMIs) which have the potential to aid damaged brains to perform their original motor and cognitive functions. We consider the viability of such devices for mitigating the deleterious effects of memory loss that is induced by neurodegenerative diseases and/or traumatic brain injury (TBI). Our computational study considers the widely used Hopfield network, an autoassociative memory model in which neurons converge to a stable state pattern after receiving an input resembling the given memory. In this study, we connect an auxiliary network of neurons, which models the BMI device, to the original Hopfield network and train it to converge to its own auxiliary memory patterns. Injuries to the original Hopfield memory network, induced through neurodegeneration, for instance, can then be analyzed with the goal of evaluating the ability of the BMI to aid in memory retrieval tasks. Dense connectivity between the auxiliary and Hopfield networks is shown to promote robustness of memory retrieval tasks for both optimal and nonoptimal memory sets. Our computations estimate damage levels and parameter ranges for which full or partial memory recovery is achievable, providing a starting point for novel therapeutic strategies.
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The molecular footprint of valproic acid in human hippocampal organoid.
Autism spectrum disorder (ASD) is a multifaceted neurodevelopmental condition characterized by neuroinflammation, and disruption in neuronal development. Valproic acid (VPA) is a known environmental risk factor for ASD. Induced pluripotent stem cells (IPSCs IMR90-4)-derived human hippocampal organoids (hHOs) at 60 days of development were used to investigate VPA-induced changes in mRNA and microRNA (miRNA) profiles. The molecular effects of VPA on hHOs were deciphered by meaningfully integrating the ability of miRNA to regulate expression of their predicted mRNA targets crucial to altering neuroinflammatory pathways. Molecular footprint can be defined as the VPA-induced changes to the miRNA profile resulting in coordinated post-transcriptional (mRNA) regulation of neuronal and inflammatory pathways associated with ASD. Based on the results, the molecular footprint of VPA in hHOs was generated for the first time. These findings highlight the contribution of miRNA-mediated regulatory mRNA networks to VPA-induced neuroinflammation-associated with ASD in hHOs.
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Studying Human Neurological Disorders Using Induced Pluripotent Stem Cells: From 2D Monolayer to 3D Organoid and Blood Brain Barrier Models.
Neurological disorders have emerged as a predominant healthcare concern in recent years due to their severe consequences on quality of life and prevalence throughout the world. Understanding the underlying mechanisms of these diseases and the interactions between different brain cell types is essential for the development of new therapeutics. Induced pluripotent stem cells (iPSCs) are invaluable tools for neurological disease modeling, as they have unlimited self-renewal and differentiation capacity. Mounting evidence shows: (i) various brain cells can be generated from iPSCs in two-dimensional (2D) monolayer cultures; and (ii) further advances in 3D culture systems have led to the differentiation of iPSCs into organoids with multiple brain cell types and specific brain regions. These 3D organoids have gained widespread attention as in vitro tools to recapitulate complex features of the brain, and (iii) complex interactions between iPSC-derived brain cell types can recapitulate physiological and pathological conditions of blood-brain barrier (BBB). As iPSCs can be generated from diverse patient populations, researchers have effectively applied 2D, 3D, and BBB models to recapitulate genetically complex neurological disorders and reveal novel insights into molecular and genetic mechanisms of neurological disorders. In this review, we describe recent progress in the generation of 2D, 3D, and BBB models from iPSCs and further discuss their limitations, advantages, and future ventures. This review also covers the current status of applications of 2D, 3D, and BBB models in drug screening, precision medicine, and modeling a wide range of neurological diseases (e.g., neurodegenerative diseases, neurodevelopmental disorders, brain injury, and neuropsychiatric disorders). © 2019 American Physiological Society. Compr Physiol 9:565-611, 2019.
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Midbrain organoids as next-generation models for Parkinson's disease: From pathogenesis to therapeutic discovery.
Parkinson's disease (PD) is characterized by selective degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) and pathological aggregation of α-synuclein. Traditional two-dimensional (2D) cell cultures and animal models have provided valuable insights but fail to recapitulate the cellular architecture and pathophysiology of the human midbrain. Three-dimensional (3D) midbrain organoids self-organize into neural structures that mimic key aspects of human midbrain development and disease pathology. This review examines midbrain organoid-based PD modeling through a concept-driven lens, addressing five questions: (i) Which aspects of PD can organoids model? (ii) How are technological advances reshaping the field? (iii) How do organoids complement existing model systems? (iv) What are the current limitations, and how can they be addressed? (v) What is the path toward clinical translation? Organoids reliably reproduce mitochondrial and lysosomal dysfunction and, in SNCA triplication models, α-synuclein accumulation, but seldom progressive neurodegeneration or mature Lewy pathology. By distinguishing established findings from emerging technologies and providing a realistic assessment of current limitations, this review offers a framework for prioritizing organoid applications in PD research and translation.
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A next-generation iPSC-derived forebrain organoid model of tauopathy with tau fibrils by AAV-mediated gene transfer.
It is known that the human cellular models of Alzheimer's disease (AD) and tauopathy can only recapitulate the very early stage of the disease. To overcome these limitations, we developed a technology to make forebrain organoids (FBOs) from feeder-free induced pluripotent stem cells (iPSC)s by regulating a FGF2 concentration and applied this method to generate FBOs from patients with familial AD (fAD FBOs). The obtained fAD FBOs recapitulated the amyloid-β pathology and increased tau phosphorylation but not tau aggregates. To fully induce the tau pathology, FBOs were injected with adeno-associated virus (AAV)-expressing P301L mutant tau. In these Tau-P301L FBOs, tau fibrils were observed in the neuronal cell body and neurites with immunoelectron microscopy, in addition to the sarkosyl-insoluble and thioflavin S-positive phospho-tau aggregates. Collectively, this model can be used as a platform for investigating pathogenetic mechanisms and evaluation of target molecules for drug discovery for tauopathy.
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Human Pituitary Organoids: Transcriptional Landscape Deciphered by scRNA-Seq and Stereo-Seq, with Insights into SOX3's Role in Pituitary Development.
The 3D human pituitary organoid represents a promising laboratory model for investigating human pituitary diseases. Nonetheless, this technology is still in its nascent stage, with uncertainties regarding the cellular composition, intercellular interactions, and spatial distribution of the human pituitary organoids. To address these gaps, the culture conditions are systematically adjusted and the efficiency of induced pluripotent stem cells' (iPSCs') differentiation into pituitary organoids is successfully improved, achieving results comparable to or exceeding those of previous studies. Additionally, single-cell RNA-sequencing (scRNA-seq) and stereomics sequencing (Stereo-seq) are performed on the pituitary organoids for the first time, and unveil the diverse cell clusters, intricate intercellular interactions, and spatial information within the organoids. Furthermore, the SOX3 gene interference impedes the iPSCs' differentiation into pituitary organoids, thereby highlighting the potential of pituitary organoids as an ideal experimental model. Altogether, the research provides an optimized protocol for the human pituitary organoid culture and a valuable transcriptomic dataset for future explorations, laying the foundation for subsequent research in the field of pituitary organoids or pituitary diseases.
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A human forebrain organoid model reveals the essential function of GTF2IRD1-TTR-ERK axis for the neurodevelopmental deficits of Williams syndrome.
Williams syndrome (WS; OMIM#194050) is a rare disorder, which is caused by the microdeletion of one copy of 25-27 genes, and WS patients display diverse neuronal deficits. Although remarkable progresses have been achieved, the mechanisms for these distinct deficits are still largely unknown. Here, we have shown that neural progenitor cells (NPCs) in WS forebrain organoids display abnormal proliferation and differentiation capabilities, and synapse formation. Genes with altered expression are related to neuronal development and neurogenesis. Single cell RNA-seq (scRNA-seq) data analysis revealed 13 clusters in healthy control and WS organoids. WS organoids show an aberrant generation of excitatory neurons. Mechanistically, the expression of transthyretin (TTR) are remarkably decreased in WS forebrain organoids. We have found that GTF2IRD1 encoded by one WS associated gene GTF2IRD1 binds to TTR promoter regions and regulates the expression of TTR. In addition, exogenous TTR can activate ERK signaling and rescue neurogenic deficits of WS forebrain organoids. Gtf2ird1-deficient mice display similar neurodevelopmental deficits as observed in WS organoids. Collectively, our study reveals critical function of GTF2IRD1 in regulating neurodevelopment of WS forebrain organoids and mice through regulating TTR-ERK pathway.
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Ultrasound-enhanced exosome secretion and antibody-free SERS profiling for Alzheimer's disease via iPSC-derived cortical organoids.
Exosomes offer a promising vehicle for noninvasive diagnosis of neurodegenerative diseases by carrying multiple biomarkers across the blood-brain barrier. However, traditional exosome analysis often misses subtle genotype-specific variations because of weak signals from a few exosomes, reliance on markers, and limited understanding of disease signatures. Here, we present a sound way to understand Alzheimer's disease through label-free surface-enhanced Raman scattering (SERS) profiling of cortical organoid-derived exosomes. Initially, we enhanced exosomal SERS signal levels by optimizing ultrasound parameters to increase exosome secretion from cortical organoids. Using this strategy, we distinguished apolipoprotein E genotype-dependent differences in intact exosomal fingerprints. Transcriptome analysis confirmed that ultrasound stimulation increased exosome secretion and up-regulated exosome-related genes functionally linked to Alzheimer's pathology. Ultrasound-based stimulation and label-free exosome profiling reveal genotype-specific pathologies, providing a precision-diagnostic framework for Alzheimer's disease.
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Maturation and circuit integration of transplanted human cortical organoids.
Self-organizing neural organoids represent a promising in vitro platform with which to model human development and disease1-5. However, organoids lack the connectivity that exists in vivo, which limits maturation and makes integration with other circuits that control behaviour impossible. Here we show that human stem cell-derived cortical organoids transplanted into the somatosensory cortex of newborn athymic rats develop mature cell types that integrate into sensory and motivation-related circuits. MRI reveals post-transplantation organoid growth across multiple stem cell lines and animals, whereas single-nucleus profiling shows progression of corticogenesis and the emergence of activity-dependent transcriptional programs. Indeed, transplanted cortical neurons display more complex morphological, synaptic and intrinsic membrane properties than their in vitro counterparts, which enables the discovery of defects in neurons derived from individuals with Timothy syndrome. Anatomical and functional tracings show that transplanted organoids receive thalamocortical and corticocortical inputs, and in vivo recordings of neural activity demonstrate that these inputs can produce sensory responses in human cells. Finally, cortical organoids extend axons throughout the rat brain and their optogenetic activation can drive reward-seeking behaviour. Thus, transplanted human cortical neurons mature and engage host circuits that control behaviour. We anticipate that this approach will be useful for detecting circuit-level phenotypes in patient-derived cells that cannot otherwise be uncovered.
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Glioblastoma Cortical Organoids Recapitulate Cell-State Heterogeneity and Intercellular Transfer.
Glioblastoma (GBM) is characterized by heterogeneous malignant cells that are functionally integrated within the neuroglial microenvironment. In this study, we model this ecosystem by growing GBM into long-term cultured human cortical organoids that contain the major neuroglial cell types found in the cerebral cortex. Single-cell RNA sequencing analysis suggests that, compared with matched gliomasphere models, GBM cortical organoids more faithfully recapitulate the diversity and expression programs of malignant cell states found in patient tumors. Additionally, we observe widespread transfer of GBM transcripts and GFP to nonmalignant cells in the organoids. Mechanistically, this transfer involves extracellular vesicles and is biased toward defined GBM cell states and astroglia cell types. These results extend previous GBM organoid modeling efforts and suggest widespread intercellular transfer in the GBM neuroglial microenvironment. Significance: Models that recapitulate intercellular communications in GBM are limited. In this study, we leverage GBM cortical organoids to characterize widespread mRNA and GFP transfer from malignant to nonmalignant cells in the GBM neuroglial microenvironment. This transfer involves extracellular vesicles, may contribute to reprogramming the microenvironment, and may extend to other cancer types. See related commentary by Shakya et al., p. 261.