VHL and atrial fibrillation: Histological analysis of NP and AF showed no significant difference between Vhl cKO and Cre-negative mice after 4 months [Fig. 4a, panels (a)–(d), 4b] At 8 and 12 months, the NP and AF of Vhl cKO mice showed more Safranin O-positive staining with the appearance of some chondrocyte-like cells, indicating the presence of degenerative changes.