Amyloid-β25-35 Induces Apolipoprotein D Synthesis and Growth Arrest in HT22 Hippocampal Cells

Apolipoprotein D (ApoD) is a secreted glycoprotein that is markedly induced in several pathological and stressful conditions in the nervous system. In the central nervous system, ApoD expression is upregulated during aging, after traumatic brain injury, and in several human neuropathologies such as Alzheimer's disease (AD), where it is found associated with amyloid-beta (A beta) plaques. Recent studies have indicated that ApoD has an important function as a neuroprotective and antioxidant protein. The aim of this work is to study the effect of the peptide fragment A beta(25-35), which is believed to play a major role in the neurodegenerative process of AD, in ApoD expression in a mouse hippocampal cell line. In addition, we studied whether direct addition of exogenous human recombinant ApoD protein has neuroprotective effect against A beta(25-35) treatment on neuronal cells. Our results demonstrate that A beta(25-35) induces ApoD expression in hippocampal cells in response to stress-induced growth arrest. This observed relationship between A beta and ApoD expression could explain the elevated levels of ApoD found in AD brain, where it may be a neuroprotective molecule in the course of AD, probably related to its lipid transport function or a direct antioxidant property. However, the addition of exogenous human recombinant ApoD does not exert any protective effect, most likely due to its major structural modifications.