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Human neural organoids (NOs) provide a powerful platform for investigating synaptic development and dysfunction during early neurodevelopment. However, methodologies for isolating functional synaptic structures from these models remain limited. Here, we present a differential centrifugation protocol enabling the enrichment of growth cone particles (GCPs) and immature synaptosomes from air‐liquid interface cerebral organoids (ALI‐COs) at distinct developmental stages (Day 90 and 150). Notably, the method avoids density gradients, requires minimal starting material while maintaining reproducibility across human and murine tissues. Quantitative proteomic profiling revealed significant enrichment of growth cone markers (e.g., GAP43) and classical synaptosomal proteins (e.g., PCLO, BSN, SYN1). Transmission electron microscopy (TEM) confirmed the presence of membrane‐enclosed GCPs with fibrous content and mitochondria in Day 90 isolates, and immature synaptosomes containing synaptic vesicles on day 150. Functional viability of both types of synaptic structures was demonstrated through KCl‐induced depolarization, which triggered phosphorylation changes in growth cone proteins (GAP43, MARCKS, MARCKSL1), cytoskeletal regulators (DCLK1, SHTN1, MARK4, MAP1B) and protein kinases (CAMK2G, PRKCE) in Day 90 GCPs, as well as classical synaptic vesicle cycle proteins (SYN1, DNM1, RPH3A) at Day 150. Overall, this study establishes a centrifugation‐based protocol for isolating growth cones and immature synapses from human organoids, capturing key stages of synaptic development and enabling scalable, patient‐compatible models to study synaptic function and dysfunction in neurodevelopmental and neurodegenerative disorders. Synapses are implicated in several neurological disorders and psychiatric diseases. The emergence and wide use of neural organoids provide a new opportunity to study human synapses in healthy and disease settings. Therefore, we developed a simple method for the enrichment of synaptosomes and growth cone particles from forebrain organoids. The method is based on differential centrifugation, works with small tissue amounts, and is highly reproducible. We validated the functionality of the isolated structures using KCl stimulation and phosphoproteomics. The method enables detailed mapping of protein composition and function during growth cone pathfinding, synaptogenesis, and establishment of neural circuits in organoids.

Background and Objectives: Recent studies have identified variants in the kinesin family member 5A (KIF5A) gene that predispose to amyotrophic lateral sclerosis (ALS). These ALS-linked KIF5A variants lead to the exclusion of exon 27, resulting in the production of a mutated protein with an altered C-terminal region (KIF5A ΔExon27). Through whole genome sequencing, we identified a novel KIF5A intronic variant, rs1057522322 (c.2993-6C > A; chr12:57582596C > A, GRCh38.p14), in a family segregating ALS. Our goal is to investigate the effect of this variant on exon 27 splicing and to assess its functional consequences on KIF5A-mediated cargo transport. Methods: Induced pluripotent stem cells (iPSCs) were generated from siblings with and without the c.2993-6C > A variant. RT-PCR was performed on RNA extracted from iPSC-derived neurons to assess exon 27 splicing. Functional studies were conducted on iPSC-derived motor neurons (MNs). Results: RT-PCR confirmed that the c.2993-6C > A variant induced exon 27 skipping in KIF5A. Immunofluorescent staining showed that KIF5A ΔExon27 abolished the axonal interaction with splicing factor proline- and glutamine-rich, a cargo specifically transported by KIF5A. Under stress conditions, MNs carrying the c.2993-6C > A variant exhibited TDP-43 proteinopathy. Discussion: KIF5A intronic variant c.2993-6C > A could be a risk factor for ALS. KIF5A ΔExon27 impairs KIF5A-mediated cargo transport and contributes to ALS pathogenesis in a TDP-43–dependent manner.

West Nile virus (WNV), an arbovirus of emerging global interest, can cause neuroinvasive disease in humans. Currently, no protective vaccine or specific treatment is available for human WNV encephalitis. The virus induces neuronal cell death, while astrocytes and microglia cells are suspected to contribute to WNV pathology. Hence, understanding their role is crucial for future treatment approaches. In this study, we establish a WNV encephalitis model using human cerebral organoids, generated with male iPSCs. Infection results in heterogeneous kinetics with an early strong replication potentially leading to viral clearance, while a late peak was associated with more long-term infection. Viral foci are seen in cortical-like areas, rich in neurons and astrocytes, however void of microglia. Pro-inflammatory cytokines (IL-6, TNF-α, IL-18), chemokines (CXCL10, CCL17, CX3CL1, CCL2) and biomarkers (IL-1RA, sTREM-1, sRAGE, BDNF) are increasingly released. Conclusively, human cerebral organoids make suitable WNV encephalitis models with valuable properties to study acute and long-term infection. West Nile virus (WNV) can cause neuroinvasive disease. Here the authors develop a human cerebral organoid model for WNV infection and find heterogeneous viral kinetics with viral foci in neuron- and astrocyte-rich areas devoid of microglia, as well as increased release of cytokines and other biomarkers.