Method to Identify Liver-to-Brain Region-Specific Crosstalk Using TurboID

Endocrine crosstalk between the liver and the brain regulates systemic energy homeostasis. However, this communication has not been comprehensively evaluated because identification of liver-derived proteins, or hepatokines, is difficult to define using bulk serum proteomics alone. To overcome this problem, we applied hepatocyte-restricted endoplasmic-reticulum-targeted TurboID (ER-TurboID) in vivo and recovered biotinylated, liver-secretion-competent proteins directly from specific brain regions, including the hypothalamus and hindbrain (nucleus of the solitary tract (NTS) and area postrema (AP)). Compared with AAV8-Null transduced controls, TurboID-expressing animals showed 3-to 21-fold enrichment of liver-expressed and predicted liver-secreted proteins among brain regions, with 81 canonical liver-secretome proteins, including multiple carboxylesterase (CES) family members. These results establish a method to identify novel secreted factors from peripheral tissues that can potentially act on specific brain regions.