BACE1 and Alzheimer disease: Male transgenic mice show reduced brain plague formation, improved cognitive functions, increased NEP activity, and reduced expression of BACE1.Findings suggest that in males an increase in endogenous T due to removal of the CYP19 enzyme protects against AD.This protection might be due to increase T downregulation of BACE1 activity leading to decreased β-amyloid production and upregulation of NEP to enhance β-amyloid degradation.