Similarly, comparing the mean levels of collagen II (106 ± 3 ng/μg and 160 ± 8.07 ng/μg) in NP and AF tissues of APOE-knockout rabbits with the mean levels (148 ± 6.02 ng/μg and 250 ± 2.34 ng/μg) in NP and AF tissues of wild-type rabbits, the levels of collagen II in NP and AF tissues of APOE-knockout rabbits were reduced by 28.3% and 36% respectively (p < 0.0001) (Fig 5B). Here, APOE is linked to atrial fibrillation.