Accordingly, the degeneration score of the NP matrix staining was significantly higher in sham-injected degenerated IVDs (P ​< ​0.05) compared to healthy sham-injected IVDs, but not in BMP4-treated degenerated IVDs (Fig. 5B), while degenerative grading on EP morphology (P ​< ​0.05), AF morphology (P ​< ​0.01), and bone modeling at the external AF/bone interface (P ​< ​0.05) was significantly higher with BMP-4 treatment when compared to sham-injected healthy IVDs, but not sham-injected degenerated IVDs (Fig. 5C–E). This evidence concerns the gene BMP4 and atrial fibrillation.