PHLPP1 and atrial fibrillation: Little positive staining was observed in grade 1 and 2 IVDs, with greater staining in moderate (grade 3) IDD and strong staining in severe (grades 4 and 5) IDD (Fig. 2b), indicating a strong and positive correlation of Phlpp1 expression with IDD within the NP (R2 = 0.849; p < 0.001) and AF (R2 = 0.694; p < 0.001).