As seen in Fig. 7A and D, the GAG content was reduced in sham-injected and BMP-4-injected degenerated IVDs compared to healthy sham-injected IVDs in both NP and AF (P ​< ​0.05), and no difference was observed between healthy and healthy sham-injected IVDs. This evidence concerns the gene BMP4 and atrial fibrillation.