Apolipoprotein D Upregulation in Alzheimer's Disease but Not Frontotemporal Dementia

Frontotemporal dementia (FTD) and Alzheimer's disease (AD) are the two common forms of dementia. FTD syndromes are characterized by lobar atrophy (frontotemporal lobar degeneration or FTLD) and the presence of either cellular TDP43 (FTLD-TDP), tau (FTLD-tau), or FUS aggregates, while extracellular β-amyloid plaques and hyperphosphorylated tau tangles develop in AD. Oxidative stress can induce these pathological modifications in disease models, and is thought to play a role in these syndromes. Apolipoprotein D (apoD) is a glial-expressed lipocalin known to protect against oxidative stress, with increased levels in AD, supporting a protective role. The expression of apoD has not been studied in FTLD. This study assesses apoD expression in FTLD-TDP and FTLD-tau in comparison to AD and controls. It also analyzes the effect of apoD on TARDBP (TDP43 gene) and β-amyloid precursor protein (APP). The expression of apoD was analyzed by Western blotting in FTLD-TDP, FTLD-tau, AD, and control post-mortem brain tissue. An apoD-overexpressing cell model was used to study the impact of increased apoD on APP and TARDBP expression. We confirm that apoD expression was increased in AD but surprisingly it was not affected in either of the two main pathological forms of FTLD. Under oxidative stress conditions, apoD had no effect on TDP43 expression but it did decrease APP expression. This suggests that apoD does not act as a neuroprotective factor in FTLD in the same way as in AD. This could contribute to the more rapid degeneration observed in FTLD.