Cortical cathepsin D activity and immunolocalization in Alzheimer disease, critical coronary artery disease, and aging

The activity and immunocytochemical localization of cathepsin D in the frontal cortex were investigated in patients with Alzheimer disease (AD) and two groups of nondemented subjects; individuals with critical coronary artery disease (cCAD; >75% stenosis) and nonheart disease controls (non-HD). The cathepsin D activity significantly increased with age in the non-HD population. No such age-related increase was observed in either AD or cCAD. Enzymatic activity was significantly increased in only the midaged, but not the older AD and cCAD subjects compared to controls. Immunocytochemical reactivity paralleled cathepsin D enzymatic activity. Frontal cortex neurons displayed an increased accumulation of cathepsin D immunoreactivity in aging (non-HD controls) with a further increase in cCAD, especially in the midaged group. Such immunoreactivity was markedly increased in AD. There was also an apparent age-related increase in the number of cathepsin D immunoreactive neurons in the non-HD population and a disease-related increase in only the mid-aged AD and cCAD subjects compared to controls. Senile plaques (SP) occured in all AD patients, many cCAD, and a few of the oldest non-HD subjects, and they were immunoreactive to cathepsin D in each group. The data suggest a possible relationship between activation of cathepsin D and SP formation in AD, cCAD, and aging.