Tifft, C. | Search bioRxiv

bioRxiv2024

Cellular Modeling of CLN6 with IPSC-derived Neurons and Glia

Neuronal ceroid lipofuscinosis (NCL), type 6 (CLN6) is a neurodegenerative disorder associated with progressive neurodegeneration leading to dementia, seizures, and retinopathy. CLN6 encodes a resident-ER protein involved in trafficking lysosomal proteins to the Golgi. CLN6p deficiency results in lysosomal dysfunction and deposition of storage material comprised of Nile Red+ lipids/proteolipids that include subunit C of the mitochondrial ATP synthase (SUBC). White matter involvement has been recently noted in several CLN6 animal models and several CLN6 subjects had neuroimaging was consistent with leukodystrophy. CLN6 patient-derived induced pluripotent stem cells (IPSCs) were generated from several of these subjects. IPSCs were differentiated into oligodendroglia or neurons using well-established small-molecule protocols. A doxycycline-inducible transgenic system expressing neurogenin-2 (the I3N-system) was also used to generate clonal IPSC-lines (I3N-IPSCs) that could be rapidly differentiated into neurons (I3N-neurons). All CLN6 IPSC-derived neural cell lines developed significant storage material, CLN6-I3N-neuron lines revealed significant Nile Red+ and SUBC+ storage within three and seven days of neuronal induction, respectively. CLN6-I3N-neurons had decreased tripeptidyl peptidase-1 activity, increased Golgi area, along with increased LAMP1+ in cell bodies and neurites. SUBC+ signal co-localized with LAMP1+ signal. Bulk-transcriptomic evaluation of control- and CLN6-I3N-neurons identified >1300 differentially-expressed genes (DEGs) with Gene Ontogeny (GO) Enrichment and Canonical Pathway Analyses having significant changes in lysosomal, axonal, synaptic, and neuronal-apoptotic gene pathways. These findings indicate that CLN6-IPSCs and CLN6-I3N-IPSCs are appropriate cellular models for this disorder. These I3N-neuron models may be particularly valuable for developing therapeutic interventions with high-throughput drug screening assays and/or gene therapy.

neuroscience↗

bioRxiv2022

De Novo Variants in MRTFB have gain of function activity in Drosophila and are associated with a novel neurodevelopmental phenotype with dysmorphic features.

Myocardin-Related Transcription Factor B (MRTFB) is an important transcriptional regulator which promotes the activity of an estimated 300 genes during different stages of development. Here we report two pediatric probands with de novo variants in MRTFB (R104G and A91P) and mild dysmorphic features, intellectual disability, global developmental delays, speech apraxia, and impulse control issues. As the MRTFB protein is highly conserved between vertebrate and invertebrate model organisms, we generated a humanized Drosophila model expressing the human MRTFB protein in the same spatial and temporal pattern as the fly gene. Expression of the human MRTFBR104G variant using a mrtf-T2A-GAL4 line proved to be embryonic lethal. Additional phenotypes were also identified by expressing the MRTFBR104G and MRTFBA91P variant in a subset of Drosophila tissues. Notably, expression within wing tissues resulted in an expansion of intervein tissue, wing vein thickening, shortening or loss of wing veins, and blistering. The MRTFBR104G and MRTFBA91P variants also display a decreased level of actin binding within critical RPEL domains, resulting in increased transcriptional activity and changes in the organization of the Actin cytoskeleton. These changes were not observed in flies expressing two additional candidate variants, MRTFBN95Sand MRTFBR109Q, highlighting that the location of the mutation within the 2nd RPEL domain is critical to the pathogenicity of the variant. These changes suggest that the MRTFBR104G and MRTFBA91P alleles we have identified affect the regulation of the protein and that these variants in MRTFB underly a novel neurodevelopmental disorder.

genetics↗