GPC1 (glypican 1) is a heparan sulfate proteoglycan anchored to the plasma membrane via a glycosylphosphatidylinositol anchor 1. Its primary function involves regulating signaling pathways through heparan sulfate-dependent binding to growth factors and morphogens, particularly modulating fibroblast growth factor (FGF) signaling and Hedgehog pathways 1. GPC1 negatively regulates FGF2-mediated signaling by sequestering FGF2 in lipid rafts, preventing receptor binding and inhibiting proliferation in keratinocytes and other cell types 2. Clinically, GPC1 serves as a cancer biomarker, being specifically enriched on cancer-derived exosomes and circulating supermeres 34. GPC1-positive circulating exosomes detect pancreatic cancer with absolute specificity and sensitivity, correlating with tumor burden and patient survival, offering potential for non-invasive early cancer diagnosis 3. Additionally, GPC1 is implicated in biliary atresia susceptibility; deletions at chromosome 2.3 affecting GPC1 increase disease risk in genetically susceptible individuals, with zebrafish studies demonstrating that Gpc1 knockdown causes developmental biliary defects through dysregulated Hedgehog signaling 5. GPC1 expression significantly decreases with age in skin keratinocytes, suggesting importance in skin aging and maintaining epidermal function 2.