BDNF and Alzheimer disease: Yasutake et al., 2006, showed a decrease in BDNF levels in blood in the late stages of AD. Additionally, Aβ has been shown to directly inhibit BDNF proteolysis from pro-BDNF (Zheng et al., 2010) and reduce the retrograde axonal transport of the BDNF/TrkB system through a mechanism including ubiquitin carboxy-terminal hydrolase L1 (Poon et al., 2013).