MMP9 and Alzheimer disease: NGF dysmetabolism is also found in the brain of people with prodromal AD, also referred to as mild cognitive impairment (MCI), and with clinical AD as represented by increased levels of proNGF, neuroserpin, as well as MMP-3 and MMP-9 activity (Peng et al., 2004; Bruno et al., 2009a,b; Mufson et al., 2012; Pentz et al., 2020).