CRTAC1 (cartilage acidic protein 1) is a glycosylated calcium-binding extracellular matrix protein with diverse roles across multiple disease contexts. Primary Function: CRTAC1 functions as an extracellular protein involved in calcium signaling and cell-matrix interactions 1. Mechanism: The protein enhances intracellular calcium release through ryanodine receptor (RyR)-mediated pathways, promoting NFAT transcriptional activation and downstream signaling cascades 1. In degenerative ligament disease, CRTAC1-expressing chondrocyte-like cells are regulated by ATF3 transcription factor and interact with immune cells, contributing to tissue calcification 2. Disease Relevance: CRTAC1 serves as a key biomarker across multiple diseases. In osteoarthritis, elevated plasma CRTAC1 is one of the strongest predictors of future OA risk (hazard ratio 1.65), with levels deviating from normal over a decade before disease onset 3. In non-small cell lung cancer, CRTAC1 overexpression enhances cisplatin chemosensitivity by promoting Akt1 degradation and apoptosis 1. Conversely, CRTAC1 downregulation in urothelial carcinoma correlates with aggressive tumors and poor prognosis 4. Clinical Significance: CRTAC1 is identified as a prognostic marker in atherosclerotic plaque progression 5, pulmonary hypertension-related right ventricular dysfunction 6, and lung fibrosis, where it indicates alveolar epithelial cell health status 7. These associations suggest CRTAC1 has potential as a multimodal biomarker for early disease detection and risk stratification across diverse pathologies.