Protease digestion indicates that endogenous presenilin 1 is present in at least two physical forms

Presenilins function in ER calcium leak and Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide and is at present, incurable. The accumulation of toxic amyloid-beta (Aβ) peptide aggregates in AD brain is thought to trigger the extensive synaptic loss and neurodegeneration linked to cognitive decline, an idea that underlies the 'amyloid hypothesis' of AD etiology in both the familal (FAD) and sporadic forms of the disease. Genetic mutations causing FAD also result in the dysregulation of neuronal calcium (Ca(2+)) handling and may contribute to AD pathogenesis, an idea termed the 'calcium hypothesis' of AD. Mutations in presenilin proteins account for the majority of FAD cases. Presenilins function as catalytic subunits of γ-secretase involved in the generation of Aβ peptide. Recently, we discovered that presenilns function as low-conductance, passive ER Ca(2+) leak channels, independent of γ-secretase activity. We further discovered that many FAD mutations in presenilins results in the loss of ER Ca(2+) leak function activity and Ca(2+) overload in the ER. These results provided potential explanation for abnormal Ca(2+) signaling observed in FAD cells with mutations in presenilns. The implications of these findings for understanding AD pathogenesis are discussed in this article.

Characterization of an atypical gamma-secretase complex from hematopoietic origin

Gamma-secretase is a widely expressed multisubunit enzyme complex which is involved in the pathogenesis of Alzheimer disease and hematopoietic malignancies through its aberrant processing of the amyloid precursor protein (APP) and Notch1, respectively. While gamma-secretase has been extensively studied, there is a dearth of information surrounding the activity, composition, and function of gamma-secretase expressed in distinct cellular populations. Here we show that endogenous gamma-secretase complexes of hematopoietic origin are distinct from epithelial derived gamma-secretase complexes. Hematopoietic gamma-secretase has reduced activity for APP and Notch1 processing compared to epithelial gamma-secretase. Characterization of the active complexes with small molecule affinity probes reveals that hematopoietic gamma-secretase has an atypical subunit composition with significantly altered subunit stoichiometry. Furthermore, we demonstrate that these discrete complexes exhibit cell-line specific substrate selectivity suggesting a possible mechanism of substrate regulation. These data underscore the need for studying endogenous gamma-secretase to fully understand of the biology of gamma-secretase and its complexity as a molecular target for the development of disease therapeutics.