Activity-dependent cholesterol biosynthesis in human-derived astrocytes regulates the functional maturation of human-derived cortical neurons

Astrocytes regulate the functional maturation of neurons by providing trophic support, regulating membrane properties and coordinating synapse formation. However, it is unclear to what degree astrocytes use activity-dependent mechanisms in these intercellular signalling processes. Using an induced pluripotent stem cell system and long-term optogenetic stimulation of human astrocytes, we reveal that activity-dependent astrocytic signals enhance the functional maturation of human cortical neurons, through increases in synaptic connectivity and excitability. Transcriptomic analyses determine that this involves the activity-dependent up-regulation of cholesterol synthesis – a process ascribed to astrocytes, which regulates neuronal maturation. Up-regulated astrocyte genes encode enzymes and transcription factors that control the levels of cholesterol synthesis. Biochemical assays confirm an activity-dependent upregulation of cholesterol synthesis in astrocytes, which is required for the maturational effects upon neurons. Thus, we reveal a novel mechanism that may dynamically match astrocyte function to neuronal needs, and identify targets for modulating cholesterol synthesis in the CNS. Overall design: 22 samples of human induced pluripotent stem cell (iPSC) derived astrocytes and neurons. Each sample corresponds to the co-culture of iPSC-astrocytes and iPSC-neurons from the same donor. A total of 3 different donors/lines were used. There were two main experimental conditions, iPSC-astrocytes were transduced with either YFP alone (the 'YFP control' condition) or with Channelrhodopsin-2, (ChR2-YFP condition), so that blue light could be used to selectively modulate astrocytes.