APP and Alzheimer disease: In APP/PS1 transgenic mice (a transgenic mouse model of AD), obvious BACE1 expression is detected in the GCL of the retina at 3 months, spreading to the IPL and OPL at 6 and 8 months, respectively; meanwhile, only weak BACE1 expression is observed in wild-type mice at 6 and 8 months [59].