Aberrant calcium signaling in astrocytes inhibits neuronal excitability in a human Down syndrome stem cell model

Abstract

1Down syndrome (DS) is a devastating genetic disorder causing severe cognitive impairment. 2The staggering array of effects associated with an extra copy of human chromosome 21 3 (HSA21) complicates mechanistic understanding of DS pathophysiology. We developed an in 4 vitro system to examine the interplay of neurons and astrocytes in a fully recapitulated HSA21 5 trisomy model differentiated from DS patient-derived induced pluripotent stem cells (iPSCs). By 6 combining calcium imaging with genetic approaches, we utilized this system to investigate the 7 functional defects of DS astroglia and their effects on neuronal excitability. We found that, 8 compared with control isogenic astroglia, DS astroglia exhibited more-frequent spontaneous 9 calcium fluctuations, which reduced the excitability of co-cultured neurons. DS astrocytes 10 exerted this effect on both DS and healthy neurons. Neuronal activity could be rescued by 11 abolishing astrocytic spontaneous calcium activity either chemically by blocking adenosine-12 mediated astrocyte-neuron signaling or genetically by knockdown of inositol triphosphate (IP 3 ) 13 receptors or S100β, a calcium binding protein coded on HSA21. Our results suggest a novel 14 mechanism by which DS alters the function of astrocytes, which subsequently disturbs neuronal 15 excitability. Furthermore, our study establishes an all-optical neurophysiological platform for 16 studying human neuron-astrocyte interactions associated with neurological disorders.