Cortical interneuron development is affected in 4H leukodystrophy.

4H leukodystrophy is a rare genetic disorder classically characterized by hypomyelination, hypodontia and hypogonadotropic hypogonadism. With the discovery that 4H is caused by mutations that affect RNA polymerase III, mainly involved in the transcription of small non-coding RNAs, patients with atypical presentations with mainly a neuronal phenotype were also identified. Pathomechanisms of 4H brain abnormalities are still unknown and research is hampered by a lack of preclinical models. We aimed to identify cells and pathways that are affected by 4H mutations using induced pluripotent stem cell models. RNA sequencing analysis on induced pluripotent stem cell-derived cerebellar cells revealed several differentially expressed genes between 4H patients and control samples, including reduced ARX expression. As ARX is involved in early brain and interneuron development, we studied and confirmed interneuron changes in primary tissue of 4H patients. Subsequently, we studied interneuron changes in more depth and analysed induced pluripotent stem cell-derived cortical neuron cultures for changes in neuronal morphology, synaptic balance, network activity and myelination. We showed a decreased percentage of GABAergic synapses in 4H, which correlated to increased neuronal network activity. Treatment of cultures with GABA antagonists led to a significant increase in neuronal network activity in control cells but not in 4H cells, also pointing to lack of inhibitory activity in 4H. Myelination and oligodendrocyte maturation in cultures with 4H neurons was normal, and treatment with sonic hedgehog agonist SAG did not improve 4H related neuronal phenotypes. Quantitative PCR analysis revealed increased expression of parvalbumin interneuron marker ERBB4, suggesting that the development rather than generation of interneurons may be affected in 4H. Together, these results indicate that interneurons are involved, possibly parvalbumin interneurons, in disease mechanisms of 4H leukodystrophy.

Streamlined 3D Cerebellar Differentiation Protocol with Optional 2D Modification.

Reducing the complexity and cost of differentiation protocols is important for researchers. This interest fits with concerns about possible unintended effects that extrinsic patterning factors might introduce into human pluripotent stem cell (hPSC) models of brain development or pathophysiology, such as masking disease phenotype. Here, we present two cerebellar differentiation protocols for hPSCs, designed with simpler startup method, fewer patterning factors, and less material requirements than previous protocols. Recently, we developed culture procedures, which generate free-floating 3-dimensional (3D) products consistent with other brain "organoid" protocols, including morphologies relevant to modeling brain development such as sub/ventricular zone- and rhombic lip-like structures. The second uses an adherent, 2D monolayer procedure to complete differentiation, which is shown capable of generating functional cerebellar neurons, as products are positive for cerebellar-associated markers, and exhibit neuron-like calcium influxes. Together, these protocols offer scientists a choice of options suited to different research purposes, as well as a basic model for testing other types of streamlined neural differentiations.

Simplified 3D protocol capable of generating early cortical neuroepithelium.

Here, we report a 3D cerebellar differentiation protocol with quick startup method, defined medium and no special materials or handling requirements. Three fibroblast growth factors (FGF2, 4 and 8) were used for cerebellar patterning and smoothened agonist (SAG) for granule cell development. After 35 days, differentiation products exhibited similar structures and neuronal markers reported in prior 'organoid' and 'spheroid' protocols. This included cells positive for KIRREL2 (a marker of early cerebellar neuroepithelium) and ZIC1 (a marker for granule cells). Follow-up tests indicated that addition of FGFs, if helpful, was not required to generate observed structures and cell types. This suggests that intrinsic production of patterning factors by aggregates themselves may be adequate for region-specific 3D modeling. This protocol may be used as a quick, easy and cost-efficient method for 3D culture, whether to research development of the early cerebellar neuroepithelium, a base to generate mature cortical structures, or to optimize minimal-factor protocols for other brain regions.