ACAN and Alzheimer disease: Studies show that at pH ≤ 6.8, the expression of aggrecan and collagen II in BMSCs and AD-MSCs decreases, and cell viability and proliferation are impaired (Wuertz et al., 2008; Liang et al., 2012; Li et al., 2012), but changes in collagen I expression are inconsistent (Wuertz et al., 2008; Liang et al., 2012).