Complement system alteration in iPSC-derived astrocytes from individuals with Down syndrome

Down syndrome (DS), or trisomy 21 (T21), resulting from an extra copy of chromosome 21, occurs in 1 in 700–1,000 live births. Neuroinflammation is increasingly recognized as a critical contributor to DS neuropathology, although its underlying drivers remain unclear. In this study, we analyzed available single-nucleus RNA sequencing data from postmortem cortical brain samples of individuals with DS and controls aged 36 years or younger, identifying significant alterations in complement system gene sets. We validated these findings using astrocytes differentiated from urine-derived induced pluripotent stem cells (iPSCs) from individuals with DS (T21-iPSC), marking the first study to assess gene expression and protein levels of complement components in T21-iPSC-derived astrocytes. Our results revealed distinct phenotypic changes in T21-iPSC-derived astrocytes, including enlarged cell and nuclear sizes, and enhanced glutamate uptake. Elevated levels of C5aR1 and MASP1 transcripts, as well as increased C4 protein secretion in culture supernatants, suggest dysregulation of the complement system in DS. These findings underscore the role of complement pathway in DS neuropathogenesis and point to potential therapeutic targets to improve the quality of life for individuals with DS.