RELATIVE INCREASE IN ALZHEIMERS-DISEASE OF SOLUBLE FORMS OF CEREBRAL A-BETA AMYLOID PROTEIN-PRECURSOR CONTAINING THE KUNITZ PROTEASE INHIBITORY DOMAIN

Although a number of studies have examined amyloid precursor protein ( APP) mRNA levels in Alzheimer's disease (AD), no clear consensus has e merged as to whether the levels of transcripts for isoforms containing a Kunitz protease inhibitory (KPI)-encoded region are increased or de creased in AD, Here we compare AD and control brain for the relative a mounts of APP protein containing KPI to APP protein lacking this domai n. APP protein was purified from the soluble subcellular fraction and Triton X-100 membrane pellet extract of one hemisphere of AD (n = 10), normal (n = 7), and neurological control (n = 5) brains, The amount o f KPI-containing APP in the purified protein samples was determined us ing two independent assay methods, The first assay exploited the inhib itory action of KPI-containing APP on trypsin. The second assay employ ed reflectance analysis of Western blots, The proportion of KPI-contai ning forms of APP in the soluble subcellular fraction of AD brains is significantly elevated (p < 0.01) compared with controls, Species cont aining a HPI domain comprise 32-41 and 76-77% of purified soluble APP from control and AD brains, respectively, For purified membrane-associ ated APP, 72-77 and 65-82% of control and AD samples, respectively, co ntain a KPI domain. Since KPI-containing species of APP may be more am yloidogenic (Ho, L., Fukuchi, K., and Yonkin, S. G. (1996) J. Biol. Ch em. 271, 30929-30934), our findings support an imbalance of isoforms a s one possible mechanism for amyloid deposition in sporadic AD.