PRG4 and atrial fibrillation: Interestingly, our study demonstrated that exposure of AF cells to CTS at low (0.1 Hz) and high (2.0 Hz) frequencies induced a significant increase in the gene expression of Prg4. Lubricin, the protein encoded by Prg4, is a large mucinous glycoprotein that serves as the primary boundary lubricant for articular cartilage75 and its expression has been found to be protective against the development of osteoarthritis.76