YKL-40 is highly expressed in the epicardial adipose tissue of patients with atrial fibrillation and associated with atrial fibrosis

BACKGROUND: YKL-40 (CHI3L1) is a novel biomarker for inflammation, tissue remodeling, and fibrosis, as well as cardiovascular diseases. We investigated the association between YKL-40 expression in epicardial adipose tissue (EAT) and atrial fibrosis in patients with atrial fibrillation (AF). METHODS: Blood samples, subcutaneous adipose tissue (SAT), paracardial adipose tissue (PAT), EAT, and adjacent atrial myocardium were acquired from patients receiving coronary artery bypass grafts. The patients were divided into the AF group (n = 28) and the sinus rhythm (SR) group (n = 36). RESULTS: We did not detect a significant difference in the serum YKL-40 levels in the SR and AF groups (P = 0.145). Quantitative real-time PCR showed that YKL-40 (CHI3L1) mRNA levels in the EAT were significantly higher than in the SAT or PAT of AF patients, or the EAT of SR patients (All P < 0.001). We found similar results for YKL-40 protein levels by immunohistochemistry. Masson staining showed significantly more fibrosis in AF patients than in SR patients (P < 0.001). Western blotting indicated that AF patients had significantly higher expression of collagen I (P = 0.039). We found a linear relationship between YKL-40 mRNA expression and the collagen volume fraction of the atrial myocardium (y = 3.576x + 26.205, P < 0.001). Multivariate linear regression analysis revealed that body mass index is an independent risk factor for YKL-40 expression in EAT (β = 0.328, P = 0.011). CONCLUSIONS: YKL-40, which is highly expressed in the EAT of patients with AF, is affected by body mass index and associated with atrial fibrosis, which may contribute to the development of AF.