Human Tau Mutations in Cerebral Organoids Induce a Progressive Dyshomeostasis of Cholesterol

Mutations in the MAPT gene that encodes tau lead to frontotemporal dementia (FTD) with pathology evident in both cerebral neurons and glia. Human cerebral organoids (hCOs) from individuals harboring pathogenic tau mutations can reveal the earliest downstream effects on molecular pathways within a developmental context generating interacting neurons and glia. We found that in hCOs carrying the V337M and R406W tau mutations, the cholesterol biosynthesis pathway in astrocytes was the top upregulated gene set compared to isogenic controls by scRNAseq. The 15 upregulated genes included HMGCR, ACAT2, STARD4, LDLR, and SREBF2. This result was confirmed in a homozygous R406W mutant cell line, by immunostaining and sterol measurements. Cholesterol abundance in the brain is tightly regulated by efflux and cholesterol biosynthetic enzyme levels in astrocytes, and dysregulation can cause aberrant phosphorylation of tau. Our findings suggest that cholesterol dyshomeostasis is an early event in the etiology of neurodegeneration caused by tau mutations. Overall design: Droplet-based single-cell RNA sequencing was performed on cerebral organoids carrying MAPT V337M and R406W mutations, their isogenic controls and organoids carrying homozygous R406W mutation. Organoids were sampled at ages 1-8 months.