Zuzana Matusova

Gaucher disease is a rare lysosomal storage disorder caused by autosomal recessive mutations in the GBA1 gene, encoding the lysosomal enzyme glucocerebrosidase. Gaucher disease is classified in 3 different subtypes depending on the presence and severity of neurological involvement, with type 2 resulting in fatal early-onset neuropathology and patients exhibiting developmental delays, seizures and early death. Studies investigating disease mechanisms of neuronopathic Gaucher disease are mainly based on animal models and focus predominantly on late neuronal phenotypes. Here, we established healthy control and Gaucher disease patient-derived iPSC lines and engineered them to obtain isogenic control and disease lines. Using these lines, we generated cortical and subpallial brain organoids in which we identified early-onset lipid dysregulation in form of glucosylceramide accumulation, highly elevated glucosylsphingosine, and a later increase in ganglioside levels, recapitulating clinical findings. Furthermore, single-cell transcriptomic profiling uncovered novel phenotypes in both cortical and subpallial forebrain organoids. Subpallial alterations consisted of an early increase in migrating interneurons in subpallial organoids, which upregulated cholesterol metabolism. Cortical alterations showed early upregulation of mitochondrial genes and a downregulation of proliferation, with a subsequent switch from GABAergic to glutamatergic neuron fate with a striking increase in gene expression related to the synaptic assembly. Functional assays demonstrated a marked hyperexcitability of cortical organoids and reduced response to GABA-A receptor blockage in Gaucher disease. Additional 2D neuronal network models confirmed the organoid data and showed that both glutamatergic and GABAergic neurons contribute to the phenotype, with hyperexcitability of Gaucher glutamatergic neurons and incapacity of Gaucher GABAergic neurons to balance the excessive excitation. This alteration represents a clinically significant phenotype as many patients exhibit an excitation/inhibition imbalance leading to treatment-resistant seizures, hastening their decline. In conclusion, our defined human models of Gaucher disease identify novel and clear phenotypes that can be used for drug screening or aid in development of new therapeutic strategies to ameliorate Gaucher disease.

Single-cell RNA sequencing has advanced our understanding of glial diversity, yet tissue dissociation remains an important technical variable. We revealed that a widely used commercial dissociation protocol can underrepresent reactive astrocytes in an acute ischemic stroke model, with preliminary observations indicating a comparable trend in a chronic tauopathy model. Benchmarking against an optimized, low-shear workflow demonstrates that different tissue dissociation workflows can substantially alter the recovery and apparent transcriptomic profile of disease-associated astrocytes, selectively losing signatures of morphological remodeling. Our findings indicate that workflow-dependent recovery biases affecting reactive astrocytes may be more prevalent than recognized, underscoring the need for pathology-tailored, gentle isolation workflows to avoid distortions in downstream neuropathological interpretations and the prioritization of therapeutic targets.

Glial fibrillary acidic protein (GFAP) is a type‐3 intermediate filament protein mainly expressed in astrocytes in the central nervous system. Mutations in GFAP cause Alexander disease (AxD), a rare and fatal neurological disorder. How exactly mutant GFAP eventually leads to white and gray matter deterioration in AxD remains unknown. GFAP is known to be expressed also in neural precursor cells in the developing brain. Here, we used AxD patient‐derived induced pluripotent stem cells (iPSCs) to explore the impact of mutant GFAP during neurodifferentiation. Our results show that GFAP is already expressed in iPSCs. Moreover, we have found that mutations in GFAP can severely affect neural organoid development through altering lineage commitment in embryoid bodies. Together, these results support the notion that GFAP plays a role as an early modulator of neurodevelopment.

Alexander disease (AxD) is a rare and severe neurodegenerative disorder caused by mutations in glial fibrillary acidic protein (GFAP). While the exact disease mechanism remains unknown, previous studies suggest that mutant GFAP influences many cellular processes, including cytoskeleton stability, mechanosensing, metabolism, and proteasome function. While most studies have primarily focused on GFAP‐expressing astrocytes, GFAP is also expressed by radial glia and neural progenitor cells, prompting questions about the impact of GFAP mutations on central nervous system (CNS) development. In this study, we observed impaired differentiation of astrocytes and neurons in co‐cultures of astrocytes and neurons, as well as in neural organoids, both generated from AxD patient‐derived induced pluripotent stem (iPS) cells with a GFAP^R239C mutation. Leveraging single‐cell RNA sequencing (scRNA‐seq), we identified distinct cell populations and transcriptomic differences between the mutant GFAP cultures and a corrected isogenic control. These findings were supported by results obtained with immunocytochemistry and proteomics. In co‐cultures, the GFAP^R239C mutation resulted in an increased abundance of immature cells, while in unguided neural organoids and cortical organoids, we observed altered lineage commitment and reduced abundance of astrocytes. Gene expression analysis revealed increased stress susceptibility, cytoskeletal abnormalities, and altered extracellular matrix and cell–cell communication patterns in the AxD cultures, which also exhibited higher cell death after stress. Overall, our results point to altered cell differentiation in AxD patient‐derived iPS‐cell models, opening new avenues for AxD research.