ACAN and atrial fibrillation: In fact, physiological HP only seems to increase the expression of collagen II and aggrecan in healthy NP cells and not in degenerated ones [44]; on the other hand, the application of 20% CTS at 1 Hz on degenerated AF cells not only fails to downregulate matrix proteases’ gene expression, but it also results in reduced aggrecan and collagen I gene expression [41].