The present invention provides methods for reducing the level of amyloid beta protein in a cell or tissue, the methods generally involving contacting the cell or tissue with an agent that reduces cystatin C levels and/or activity. The present invention provides methods for treating Alzheimer's disease (AD), and methods for treating cerebral angiopathy, in an individual, the methods generally involving administering to an individual having AD a therapeutically effective amount of an agent that reduces cystatin C levels and/or activity. The present invention further provides methods for identifying an agent that reduces cystatin C levels and/or activity.
