MAST4 and Alzheimer disease: Subsequently, we showed that APP provides hormetic cytoprotection in the brain against 27-hydroxycholesterol (27OHC), a cholesterol derivative that binds APP and that is associated with neurodegeneration both in NPC and in AD [19], with a mechanism involving the modulation by APP of Rhotekin 2 (RTKN2), an NF-κB-dependent apoptotic regulator, and MAST4, a microtubule-associated kinase.