The role of TSC1 and TSC2 proteins in neuronal axons.

Tuberous Sclerosis Complex 1 and 2 proteins, TSC1 and TSC2 respectively, participate in a multiprotein complex with a crucial role for the proper development and function of the nervous system. This complex primarily acts as an inhibitor of the mechanistic target of rapamycin (mTOR) kinase, and mutations in either TSC1 or TSC2 cause a neurodevelopmental disorder called Tuberous Sclerosis Complex (TSC). Neurological manifestations of TSC include brain lesions, epilepsy, autism, and intellectual disability. On the cellular level, the TSC/mTOR signaling axis regulates multiple anabolic and catabolic processes, but it is not clear how these processes contribute to specific neurologic phenotypes. Hence, several studies have aimed to elucidate the role of this signaling pathway in neurons. Of particular interest are axons, as axonal defects are associated with severe neurocognitive impairments. Here, we review findings regarding the role of the TSC1/2 protein complex in axons. Specifically, we will discuss how TSC1/2 canonical and non-canonical functions contribute to the formation and integrity of axonal structure and function.

High-content screening identifies a small molecule that restores AP-4-dependent protein trafficking in neuronal models of AP-4-associated hereditary spastic paraplegia.

Unbiased phenotypic screens in patient-relevant disease models offer the potential to detect therapeutic targets for rare diseases. In this study, we developed a high-throughput screening assay to identify molecules that correct aberrant protein trafficking in adapter protein complex 4 (AP-4) deficiency, a rare but prototypical form of childhood-onset hereditary spastic paraplegia characterized by mislocalization of the autophagy protein ATG9A. Using high-content microscopy and an automated image analysis pipeline, we screened a diversity library of 28,864 small molecules and identified a lead compound, BCH-HSP-C01, that restored ATG9A pathology in multiple disease models, including patient-derived fibroblasts and induced pluripotent stem cell-derived neurons. We used multiparametric orthogonal strategies and integrated transcriptomic and proteomic approaches to delineate potential mechanisms of action of BCH-HSP-C01. Our results define molecular regulators of intracellular ATG9A trafficking and characterize a lead compound for the treatment of AP-4 deficiency, providing important proof-of-concept data for future studies.

High-Content Small Molecule Screen Identifies a Novel Compound That Restores AP-4-Dependent Protein Trafficking in Neuronal Models of AP-4-Associated Hereditary Spastic Paraplegia.

Unbiased phenotypic screens in patient-relevant disease models offer the potential to detect novel therapeutic targets for rare diseases. In this study, we developed a high-throughput screening assay to identify molecules that correct aberrant protein trafficking in adaptor protein complex 4 (AP-4) deficiency, a rare but prototypical form of childhood-onset hereditary spastic paraplegia, characterized by mislocalization of the autophagy protein ATG9A. Using high-content microscopy and an automated image analysis pipeline, we screened a diversity library of 28,864 small molecules and identified a lead compound, C-01, that restored ATG9A pathology in multiple disease models, including patient-derived fibroblasts and induced pluripotent stem cell-derived neurons. We used multiparametric orthogonal strategies and integrated transcriptomic and proteomic approaches to delineate putative molecular targets of C-01 and potential mechanisms of action. Our results define molecular regulators of intracellular ATG9A trafficking and characterize a lead compound for the treatment of AP-4 deficiency, providing important proof-of-concept data for future Investigational New Drug (IND)-enabling studies.

A Robust Pipeline for the Multi-Stage Accelerated Differentiation of Functional 3D Cortical Organoids from Human Pluripotent Stem Cells.

Disordered cellular development, abnormal neuroanatomical formations, and dysfunction of neuronal circuitry are among the pathological manifestations of cortical regions in the brain that are often implicated in complex neurodevelopmental disorders. With the advancement of stem cell methodologies such as cerebral organoid generation, it is possible to study these processes in vitro using 3D cellular platforms that mirror key developmental stages occurring throughout embryonic neurogenesis. Patterning-based stem cell models of directed neuronal development offer one approach to accomplish this, but these protocols often require protracted periods of cell culture to generate diverse cell types and current methods are plagued by a lack of specificity, reproducibility, and temporal control over cell derivation. Although ectopic expression of transcription factors offers another avenue to rapidly generate neurons, this process of direct lineage conversion bypasses critical junctures of neurodevelopment during which disease-relevant manifestations may occur. Here, we present a directed differentiation approach for generating human pluripotent stem cell (hPSC)-derived cortical organoids with accelerated lineage specification to generate functionally mature cortical neurons in a shorter timeline than previously established protocols. This novel protocol provides precise guidance for the specification of neuronal cell type identity as well as temporal control over the pace at which cortical lineage trajectories are established. Furthermore, we present assays that can be used as tools to interrogate stage-specific developmental signaling mechanisms. By recapitulating major components of embryonic neurogenesis, this protocol allows for improved in vitro modeling of cortical development while providing a platform that can be utilized to uncover disease-specific mechanisms of disordered development at various stages across the differentiation timeline. © 2023 Wiley Periodicals LLC. Basic Protocol 1: 3D hPSC neural induction Support Protocol 1: Neural rosette formation assay Support Protocol 2: Neurosphere generation Support Protocol 3: Enzymatic dissociation, NSC expansion, and cryopreservation Basic Protocol 2: 3D neural progenitor expansion Basic Protocol 3: 3D accelerated cortical lineage patterning and terminal differentiation.

Dynamic 3D Combinatorial Generation of hPSC-Derived Neuromesodermal Organoids With Diverse Regional and Cellular Identities.

Neuromesodermal progenitors represent a unique, bipotent population of progenitors residing in the tail bud of the developing embryo, which give rise to the caudal spinal cord cell types of neuroectodermal lineage as well as the adjacent paraxial somite cell types of mesodermal origin. With the advent of stem cell technologies, including induced pluripotent stem cells (iPSCs), the modeling of rare genetic disorders can be accomplished in vitro to interrogate cell-type specific pathological mechanisms in human patient conditions. Stem cell-derived models of neuromesodermal progenitors have been accomplished by several developmental biology groups; however, most employ a 2D monolayer format that does not fully reflect the complexity of cellular differentiation in the developing embryo. This article presents a dynamic 3D combinatorial method to generate robust populations of human pluripotent stem cell-derived neuromesodermal organoids with multi-cellular fates and regional identities. By utilizing a dynamic 3D suspension format for the differentiation process, the organoids differentiated by following this protocol display a hallmark of embryonic development that involves a morphological elongation known as axial extension. Furthermore, by employing a combinatorial screening assay, we dissect essential pathways for optimally directing the patterning of pluripotent stem cells into neuromesodermal organoids. This protocol highlights the influence of timing, duration, and concentration of WNT and fibroblast growth factor (FGF) signaling pathways on enhancing early neuromesodermal identity, and later, downstream cell fate specification through combined synergies of retinoid signaling and sonic hedgehog activation. Finally, through robust inhibition of the Notch signaling pathway, this protocol accelerates the acquisition of terminal cell identities. This enhanced organoid model can serve as a powerful tool for studying normal developmental processes as well as investigating complex neurodevelopmental disorders, such as neural tube defects. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Robust generation of 3D hPSC-derived spheroid populations in dynamic motion settings Support Protocol 1: Pluronic F-127 reagent preparation and coating to generate low-attachment suspension culture dishes Basic Protocol 2: Enhanced specification of hPSCs into NMP organoids Support Protocol 2: Combinatorial pathway assay for NMP organoid protocol optimization Basic Protocol 3: Differentiation of NMP organoids along diverse cellular trajectories and accelerated terminal fate specification into neurons, neural crest, and sclerotome derivatives.