Basic Science and Pathogenesis

Dementia with Lewy bodies (DLB) is the second most common form of degenerative dementia in older people. The clinical feature of DLB includes cognitive impairment, visual hallucinations, parkinsonism, and fluctuating attention. Three genes, SNCA (-synuclein), APOE (apolipoprotein E), and GBA (glucosylceramidase), have been convincingly demonstrated to be associated with DLB. Our previous studies reported that a variant in MFSD3 (rs143475431, c.888T>A:p.C296*) is associated with DLB in the Japanese population through whole-genome sequencing and association studies. However, the precise mechanisms that this variant contributes to DLB development remains unclear. We introduced the MFSD3 p.C296* variant into a human neural stem cell line using the CRISPR/Cas9 system. Subsequently, the mutant cells were analyzed for cell proliferation rate using CyQUANT Cell Proliferation Assay Kit. The mutant cells were further induced to differentiate into neurons and astrocytes to assess their differentiation ability. Additionally, we generated the homologous Mfsd3 knockout (KO) mice using the CRISPR/Cas9 system. The neurogenesis was evaluated by the number of doublecortin positive cells in the hippocampus. The behavior of Mfsd3 KO and wild-type mice was analyzed using IntelliCage. We revealed that the MFSD3 p.C296* variant was associated with decreased cell proliferation and reduced neurogenesis in the human neural stem cell line analyses. This decline in neurogenesis was also observed in the hippocampal dentate gyrus of Mfsd3 KO mice, and the Mfsd3 KO mice had smaller hippocampi compared to the wild-type mice. Furthermore, Mfsd3 KO mice exhibited a reduced level of curiosity about the new environment. Our results demonstrate that loss of function of MFSD3 affects neurons and the brain, as indicated by our studies using human neural stem cell lines and Mfsd3 KO mice. Further functional verification will contribute to elucidating the mechanism of DLB pathogenesis.