Cholesterol, Alzheimer's disease, prion disorders: a ménage à trois?

Aberrant folded proteins are hallmarks of amyloidogenic diseases. Examples are Alzheimer's disease (AD) and prion-related disorders (PrD). These disorders, although clinically different, have the same underlying pathogenetic mechanism: an altered protein conformer with high beta-sheet structure content: the amyloid beta peptide (Abeta) in the case of AD, and the aberrant prion protein, PrPsc, in PrD. Although the molecular processes that cause these proteins to adopt non-native structures in vivo and become cytotoxic are still largely unknown, there is good reason to expect prion research to profit from advances in the understanding of AD, and vice versa. Growing evidence indicates that the various pathways of lipid/lipoprotein metabolism play a key role in AD and PrD pathophysiology. These findings clearly highlight the possible involvement of cholesterol in misfolded protein generation. In this review, we focus on recent studies which provide evidence that membrane domains, called lipid rafts, directly promote protein misfolding, and that this process takes place only if changes occur in the fine regulation of intracellular cholesterol. In addition, we discuss the implications of these results to introduce the concept that pharmacological interventions restoring cholesterol homeostasis could have potential preventive/therapeutic value against the progression of misfolding disorders. The aim of the review is to provide researchers with a general understanding of cholesterol's involvement in protein folding/misfolding processes which maybe relevant for knowledge advancement regarding amyloidogenic proteins, and possible ways to prevent their pathological activity.