Presenilin 1 Mutations Linked to Familial Alzheimer's Disease Increase the Intracellular Levels of Amyloid β‐Protein 1–42 and Its N‐Terminally Truncated Variant(s) Which Are Generated at Distinct Sites

Abstract

Mutations in the presenhlin genes PSi and P52 cause the most common form of early-onset familial Alzheimer's disease. The influence of PSi mutations on the generation of endogenous intracellular amyloid /9-protein (Ajl) species was assessed using a highly sensitive immunoblotting technique with inducible mouse neuroblastoma (Neuro 2a) cell lines expressing the human wild-type (wt) or mutated PSi (M146L or z~exon10). The induction of mutated PSi increased the intracellular levels of two distinct A/3 species ending at residue 42 that were likely to be A/31 -42 and its N-terminally truncated variant(s) A/9x-42. The induction of mutated PSi resulted in a higher level of intracellular Afi1 -42 than of intracellular A/3x-42, whereas extracellular levels ofA/31 -42 and A/3x-42 were increased proportionally. In addition, the intracellular generation of these A/142 species in wt and mutated PSi-induced cells was completely blocked by brefeldin A, whereas it exhibited differential sensitivities to monensin: the increased accumulation of intracellular A/lx-42 versus inhibition of intracellular A~91-42 generation. These data strongly suggest that A/lx-42 is generated in a proximal Golgi, whereas A/31 -42 is generated in a distal Golgi and/or a post-Golgi compartment. Thus, it appears that PSi mutations enhance the degree of 42-specific y-secretase cleavage that occurs in the normal /3-amyloid precursor protein processing pathway (a) in the endoplasmic reticulum or the early Golgi apparatus prior to /3-secretase cleavage or (b) in the distinct sites where A/3x-42 and A/31 -42 are generated. Key Words: Presenilin 1-Alzheimer's disease-Amyloid /9-protein. J. Neurochem. 71, 1535Neurochem. 71, -1543Neurochem. 71, (1998. Mutations in presenilin 1 (PS])and presenilin 2 (PS2) are the most common genetic factors underlying the development of early-onset familial Alzheimer's disease (FAD) Sherrington et al., 1995). These genes encode highly homologous transmembrane proteins localized to the endoplasmic reticulum (ER) and the early Golgi apparatus (for review, see Haass, 1997). Recent studies using a sandwich ELISA specific for amyloid /9-protein (A/3) species indicated that conditioned medium from the fibroblasts or plasma of affected members of pedigrees with PS] /PS2-linked mutations shows a highly significant increase in the extracellular ratio of A/342 to A/340 relative to that in unaffected family members (Scheuner et al., 1996;Citron et al., 1997). Similar results were also obtained by overexpressing a variety of mutated PS cDNA in culture cells and transgenic mice (Borchelt et al., 1996;Duff et al., 1996;Tomita et al., 1997). These results provide strong evidence for a direct link between increased levels of A,842 generation and PS mutations causing early-onset FAD, making it likely that the increased

Independent Inhibition of Alzheimer Disease β- and γ-Secretase Cleavage by Lowered Cholesterol Levels

“…The small decrease in A␤ 42 levels observed as a result of peripheral cholesterol depletion may be due to depletion of the fraction of A␤ 42 that is produced beyond the early secretory pathway (19,70,71). Although the peripheral cholesterol extraction protocol mainly affected the plasma membrane we cannot exclude that a limited depletion of cholesterol had occurred from the early secretory pathways.…”

A form of DISC1 enriched in nucleus: Altered subcellular distribution in orbitofrontal cortex in psychosis and substance/alcohol abuse

“…The solubilized proteins were subjected to immunoprecipitation as described in ref. 19 by using anti-DISC1-C2 antibody (12), and the precipitated proteins were subjected to SDS͞PAGE. The major band of DISC1 at 75-85 kDa was visualized by Coomassie staining.…”

Evaluating the role of Toll-like receptors in diseases of the central nervous system

“…Although the etiology of the disease is unknown, accumulation of β amyloid (Aβ), leads to the development of extracellular senile plaques and intracellular neurofibrillary tangles. Aβ is a 42 amino acid (Aβ 42 ) fragment derived from the amyloid precursor protein [24] [25] and it is the inflammatory response to this pathological agent that is central to the disease [26]. Microglia are found in an actived state around senile plaques in the brains of AD patients and are considered to be important in the pathogenesis of the disease.…”