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Summary: Human stem-cell-derived organoids represent a promising substrate for transplantation-based neural repair. Here, we describe a protocol for transplanting forebrain organoids into an injured adult rat visual cortex. This protocol includes surgical details for craniectomy, aspiration injury, organoid transplantation, and cranioplasty. This platform represents a valuable tool for investigating the efficacy of organoids as structured grafts for neural repair.For complete details on the use and execution of this protocol, please refer to Jgamadze et al.1 : Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Neural transplantation represents a promising approach to repairing damaged brain circuitry. Cellular grafts have been shown to promote functional recovery through “bystander effects” and other indirect mechanisms. However, extensive brain lesions may require direct neuronal replacement to achieve meaningful restoration of function. While fetal cortical grafts have been shown to integrate with the host brain and appear to develop appropriate functional attributes, the significant ethical concerns and limited availability of this tissue severely hamper clinical translation. Induced pluripotent stem cell-derived cells and tissues represent a more readily scalable alternative. Significant progress has recently been made in developing protocols for generating a wide range of neural cell types in vitro. Here, we discuss recent progress in neural transplantation approaches for two conditions with distinct design needs: Parkinson’s disease and cortical injury. We discuss the current status and future application of injections of dopaminergic cells for the treatment of Parkinson’s disease as well as the use of structured grafts such as brain organoids for cortical repair.

Summary: Reestablishing cerebral connectivity is a critical part of restoring neuronal network integrity and brain function after trauma, stroke, and neurodegenerative diseases. Creating transplantable axon tracts in the laboratory is an unexplored strategy for overcoming the common barriers limiting axon regeneration in vivo, including growth-inhibiting factors and the limited outgrowth capacity of mature neurons in the brain. We describe the generation, phenotype, and connectivity of constrained three-dimensional human axon tracts derived from brain organoids. These centimeter-long constructs are encased in an agarose shell that permits physical manipulation and are composed of discrete cellular regions spanned by axon tracts, mirroring the separation of cerebral gray and white matter. Features of cerebral cortex also are emulated, as evidenced by the presence of neurons with different cortical layer phenotypes. This engineered neural tissue represents a first step toward potentially reconstructing brain circuits by physically replacing neuronal populations and long-range axon tracts in the brain. : Biological Sciences; Neuroscience; Tissue Engineering Subject Areas: Biological Sciences, Neuroscience, Tissue Engineering

OBJECTIVES/GOALS: Our goal is to develop a silk fibroin scaffold-based neural tissue construct and characterize it in a rat model of cortical injury. We aim to optimize the construct for transplantation, test pharmacologic interventions that may enhance its survival, and evaluate its integration with the host brain. METHODS/STUDY POPULATION: To optimize cell density and health, silk fibroin scaffolds varying in porosity and stiffness were seeded with E18 GFP+ rat cortical neurons and imaged at DIV 5. Different seeding methods and loads were similarly tested. Constructs, loaded with an inhibitor of apoptosis (ROCK inhibitor Y-27632) or necroptosis (necrostatin-1) in a fibrin hydrogel, were transplanted into aspiration lesions created in the primary motor cortex of Sprague-Dawley rats, and graft survival was compared to negative control at 2 weeks. Lastly, constructs were transplanted and evaluated via immunohistochemistry at 1, 2, and 4-month time points for survival, differentiation, inflammation, and anatomic integration. RESULTS/ANTICIPATED RESULTS: Scaffolds with smaller pore sizes retained more cells after seeding. Softer scaffolds, which enhance hemostasis at transplantation, did not compromise cell health on live/dead assay. We anticipate that seeding concentrated cell suspensions onto multiple surfaces of the construct will produce the most evenly seeded and cell-dense constructs. Based on a prior pilot study, we anticipate that necrostatin-1 will significantly improve intermediate-term construct survival. We have observed up to 15% cell survival at 1 month with retained neuronal identity and abundant axonal projections into the brain despite evidence of persistent inflammation; we anticipate similar outcomes at later time points. DISCUSSION/SIGNIFICANCE OF IMPACT: Our construct, due to its exceptional longevity in vitro, manipulability, and modularity, is an attractive platform for neural tissue engineering. In the present work, we optimize and validate this technology for transplantation with the goal of addressing the morbidity burden of cortical injury.

ABSTRACT IMPACT: This study will provide the essential characterization of intrinsic neural activity in human brain organoids, both at the single cell and network levels, to harness for translational purposes. OBJECTIVES/GOALS: Brain organoids are 3D, stem cell-derived neural tissues that recapitulate neurodevelopment. However, to levy their full translational potential, a deeper understanding of their intrinsic neural activity is essential. Here, we present our preliminary analysis of maturing neural activity in human forebrain organoids. METHODS/STUDY POPULATION: Forebrain organoids were generated from human iPSC lines derived from healthy volunteers. Linear microelectrode probes were employed to record spontaneous electrical activity from day 77, 100, and 130 organoids. Single unit recordings were collected during hour-long recordings, involving baseline recordings followed by glutamatergic blockade. Subsequently, tetrodotoxin, was used to abolish action potential firing. Single units were identified via spike sorting, and the spatiotemporal evolution of baseline neural properties and network dynamics was characterized. RESULTS/ANTICIPATED RESULTS: Nine organoids were recorded successfully (n=3 per timepoint). A significant difference in number of units was seen across age groups (F (2,6) = 6.4178, p = 0.0323). Post hoc comparisons by the Tukey HSD test showed significantly more units in day 130 (51.67 ±14.15) than day 77 (16.33 ±14.98) organoids. Mean firing rates were significantly different in organoids based on age, with drug condition also trending toward significance (F (6,12) = 9.97; p = 0.0028 and p = 0.08 respectively). Post hoc comparisons showed a higher baseline firing rate in day 130 (0.99Hz ±0.30) organoids than their day 77 counterparts at baseline (0.31Hz ±0.066) and glutamate blockade (0.31Hz ±0.045). Preliminary network analysis showed no modularity or small-world features; however, these features are expected to emerge as organoids mature. DISCUSSION/SIGNIFICANCE OF FINDINGS: Initial analysis of brain organoid activity demonstrates changes in single unit properties as they mature. Additional work in this area, as well as further network analyses, will confer better sense of how to rationally utilize brain organoids for translational purposes.

Neuronal degeneration and the deterioration of neuronal communication lie at the origin of many neuronal disorders, and there have been major efforts to develop cell replacement therapies for treating such diseases. One challenge, however, is that differentiated cells are challenging to transplant due to their sensitivity both to being uprooted from their cell culture growth support and to shear forces inherent in the implantation process. Here, we describe an approach to address these problems. We demonstrate that rat hippocampal neurons can be grown on colloidal particles or beads, matured and even transfected in vitro, and subsequently transplanted while adhered to the beads into the young adult rat hippocampus. The transplanted cells have a 76% cell survival rate one week post-surgery. At this time, most transplanted neurons have left their beads and elaborated long processes, similar to the host neurons. Additionally, the transplanted cells distribute uniformly across the host hippocampus. Expression of a fluorescent protein and the light-gated glutamate receptor in the transplanted neurons enabled them to be driven to fire by remote optical control. At 1-2 weeks after transplantation, calcium imaging of host brain slice shows that optical excitation of the transplanted neurons elicits activity in nearby host neurons, indicating the formation of functional transplant-host synaptic connections. After 6 months, the transplanted cell survival and overall cell distribution remained unchanged, suggesting that cells are functionally integrated. This approach, which could be extended to other cell classes such as neural stem cells and other regions of the brain, offers promising prospects for neuronal circuit repair via transplantation of in vitro differentiated, genetically engineered neurons.

Height is a highly heritable, classic polygenic trait with approximately 700 common associated variants identified through genome-wide association studies so far. Here, we report 83 height-associated coding variants with lower minor-allele frequencies (in the range of 0.1-4.8%) and effects of up to 2 centimetres per allele (such as those in IHH, STC2, AR and CRISPLD2), greater than ten times the average effect of common variants. In functional follow-up studies, rare height-increasing alleles of STC2 (giving an increase of 1-2 centimetres per allele) compromised proteolytic inhibition of PAPP-A and increased cleavage of IGFBP-4 in vitro, resulting in higher bioavailability of insulin-like growth factors. These 83 height-associated variants overlap genes that are mutated in monogenic growth disorders and highlight new biological candidates (such as ADAMTS3, IL11RA and NOX4) and pathways (such as proteoglycan and glycosaminoglycan synthesis) involved in growth. Our results demonstrate that sufficiently large sample sizes can uncover rare and low-frequency variants of moderate-to-large effect associated with polygenic human phenotypes, and that these variants implicate relevant genes and pathways.