PRNP and prion disease: Although certain aspects of the roles that these S9B peptidases play in PrP physiology and pathophysiology will require further clarification, our results suggest possibilities for therapeutic intervention against prion diseases and axes of investigation, given the published biologies of DPP4 and FAP in neuropeptide processing (58, , –61), cellular senescence (72, –74), and tissue remodeling (75, 76).