Elevated plasma cholestrol does not affect brain Aβ in mice lacking the low-density lipoprotein receptor

Epidemiological studies support an association between vascular risk factors, including hypercholesterolernia, and Alzheimer's disease (AD). Recently, there has been much interest in the possibility that hypercholesterolernia might directly promote P-amyloid (A beta) production. Indeed, in vitro studies have shown that increasing cellular cholesterol levels enhances AP production. However, studies in AD transgenic mouse models have not consistently found that elevated plasma cholesterol leads to increased AP production or deposition in vivo. In this study, we determined whether elevated peripheral cholesterol influences AP production in mice with a null mutation of the low-density lipoprotein receptor (LDLR). We show that dramatically elevated plasma cholesterol levels, whether induced by high cholesterol, high fat, or high fat/high cholesterol diets, did not affect either levels of brain AP40, A beta 42, or APP, or the A beta 42/40 or APP-CTF/APP ratios, nor substantially alter brain cholesterol levels. ApoE protein levels in brain were, however, elevated, in LDLR-/mice by post-transcriptional mechanisms. Collectively, these studies argue that plasma cholesterol levels do not normally regulate production of brain A beta.