Body-to-brain insulin and Notch signaling regulates memory through neuronal CREB activity

While memory regulation is predominantly understood as autonomous to neurons, factors outside the brain can also affect neuronal function. In Caenorhabditis elegans, the insulin/IGF-1-like signaling (IIS) pathway regulates longevity, metabolism and memory: long-lived daf-2 insulin/IGF-1 receptor mutants more than double memory duration after a single training session, and it was assumed that memory regulation was strictly neuronal. However, here we show that degradation of DAF-2 in the hypodermis also greatly extends memory, via expression of the diffusible Notch ligand, OSM-11, which in turn activates Notch signaling in neurons. Single-nucleus RNA sequencing of neurons revealed increased expression of CREB and other memory genes. Furthermore, in aged animals, activation of the hypodermal IIS-Notch pathway as well as OSM-11 overexpression rescue both memory and learning via CREB activity. Thus, insulin signaling in the liver-like hypodermis non-autonomously regulates neuronal function, providing a systemic connection between metabolism and memory through IIS-Notch-CREB signaling from the body to the brain.