An Alzheimer's disease risk variant in TTC3 modifies the actin cytoskeleton organization and the PI3K-Akt signaling pathway in iPSC-derived forebrain neurons

A missense variant in the tetratricopeptide repeat domain 3 (TTC3) gene (rs377155188, p.S1038C, NM_003316.4:c.3113C>G) was found to segregate with disease in a multigenerational family with late onset Alzheimers disease. This variant was introduced into induced pluripotent stem cells (iPSCs) derived from a cognitively intact individual using CRISPR genome editing and the resulting isogenic pair of iPSC lines were differentiated into cortical neurons. Transcriptome analysis showed an enrichment for genes involved in axon guidance, regulation of actin cytoskeleton, and GABAergic synapse. Functional analysis showed that the TTC3 p.S1038C iPSC-derived neuronal progenitor cells had altered 3D morphology and increased migration, while the corresponding neurons had longer neurites, increased branch points, and altered expression levels of synaptic proteins. Pharmacological treatment with small molecules that target the actin cytoskeleton could revert many of these cellular phenotypes, suggesting a central role for actin in mediating the cellular phenotypes associated with the TTC3 p.S1038C variant. HighlightsO_LIThe AD risk variant TTC3 p.S1038C reduces the expression levels of TTC3 C_LIO_LIThe variant modifies the expression of AD specific genes BACE1, INPP5F, and UNC5C C_LIO_LINeurons with the variant are enriched for genes in the PI3K-Akt pathway C_LIO_LIiPSC-derived neurons with the alteration have increased neurite length and branching C_LIO_LIThe variant interferes with actin cytoskeleton and is ameliorated by Cytochalasin D C_LI