Compromised lipid metabolism, mitochondria respiration and neuroprotective effects in iPSC-derived astrocytes from a Smith-Lemli-Opitz syndrome patient
Smith-Lemli-Opitz syndrome (SLOS) is a rare, autosomal recessive disorder characterized by congenital malformations, intellectual disability, and behavioral abnormalities. SLOS results from mutations in the DHCR7 gene, leading to impaired cholesterol biosynthesis due to dysregulation of 7-dehydrocholesterol reductase. Cholesterol plays crucial roles in neurophysiology, including synaptic formation and neurotransmitter receptor regulation, which likely contribute to neurological manifestations in SLOS patients. While astrocytes are the main cholesterol producing cells in the brain, their specific role in SLOS pathogenesis remains unclear. In this study, we utilized induced pluripotent stem cell (iPSC)-derived astrocytes from a SLOS patient with DHCR7 c.C278T mutation and the isogenic control. We found decreased lipid droplet formation in SLOS iPSC astrocytes compared to controls, accompanied with diminished efflux of cholesterol and apolipoprotein E. Lipidomics revealed reduced cholesterol and cholesterol esters, as well as altered profiles of other lipids in SLOS iPSC astrocytes. While RNA-sequencing identified various genes and pathways affected by the disease status, those related to mitochondria functions were top-ranked. Mitochondrial electron transport chain oxidative phosphorylation gene expression decreased in SLOS iPSC astrocytes, alongside impaired mitochondrial respiration. Furthermore, SLOS iPSC astrocytes less effectively mediated neuroprotection on iPSC neurons than control astrocytes in serum-starvation conditions. SLOS iPSC astrocytes also poorly contributed to synaptic networks when co-cultured with iPSC neurons. Overall, our findings provide mechanistic insights into how DHCR7 disruption impacts astrocyte function, contributing to SLOS neuropathology by dysregulating lipid metabolism, mitochondrial respiration, and impaired neuroprotection. Overall design: We performed bulk RNA sequencing of induced pluripotent stem cell (iPSC)-derived astrocytes from a SLOS patient with DHCR7 c.C278T mutation and the isogenic control to investigate genes and pathways affected by the disease status.