METRN (meteorin) is a secreted protein with dual roles in neural development and metabolic homeostasis. In the central nervous system, METRN promotes glial cell differentiation and axonal extension 1, functioning as a neurotrophic factor with angiogenic properties 2. Beyond its classical neurological functions, METRN acts as a circulating factor with broader physiological roles. As an adipokine, it promotes white adipose tissue browning and improves insulin sensitivity through AMPK and PPAR-δ signaling 3. METRN also functions as a cardiokine protecting against cardiac dysfunction 4. Pathologically, hepatocyte-derived METRN activates hepatic stellate cells via c-Kit-STAT3 signaling to promote MASH-associated liver fibrosis 5. In cancer, METRN overexpression correlates with poor prognosis in colorectal cancer 6 and associates with immune infiltration changes across multiple tumor types 1. In glioblastoma, radiation-induced exosomal circ-METRN enhances radioresistance through miR-4709-3p/GRB14/PDGFRα signaling 7. Clinically, reduced first-trimester serum METRN predicts preeclampsia risk 2, and circulating METRN levels serve as biomarkers for metabolic and cardiovascular diseases 4. These findings establish METRN as a multifunctional secreted factor with therapeutic potential across metabolic, cardiovascular, and oncological diseases.