Angiotensin‐converting enzyme‐1, ACE‐1, and ACE‐2 are dysregulated in Alzheimer’s disease and related to ACE1 genotype

Abstract

AbstractBackgroundThe renin‐angiotensin system (RAS) is dysregulated in Alzheimer’s disease (AD): angiotensin‐converting enzyme (ACE‐1) activity, a rate‐limiting enzyme in the disease‐associated classical RAS (cRAS) pathway, is elevated, whereas ACE‐2 activity, a central mediator of the counter‐regulatory protective pathway (rRAS) (that generates Ang‐(1‐7) from Ang‐II) is defective. Previous meta‐analyses, more recently confirmed in GWAS studies, indicate that ACE1 variants, including an insertion (I)/deletion (D) (indel) polymorphism at intron 16, are risk variants in AD. In this study, we have determined if ACE‐1 and ACE‐2 are dysregulated in AD in relation to ACE1 variant (rs4343) (a proxy marker for the more commonly studied indel polymorphism).MethodWe studied brain tissue from the frontal and parietal cortex from 147 dementia cases (AD (n = 94) and vascular dementia n = 20 and mixed AD/VaD (n = 33)) and 104 age‐matched controls from the South West Dementia Brain Bank, University of Bristol. ACE‐1 and ACE‐2 protein levels were measured by ELISA, and enzyme activities were measured using fluorogenic peptide substrate assays. ACE1 (rs4343) polymorphism was genotyped by PCR.ResultACE‐1 protein level was increased (p<0.0001) and ACE‐2 protein level reduced (p = 0.0103) in AD cases compared to controls in the parietal cortex. In contrast, no significant changes in protein level were observed in the frontal cortex. ACE‐1 enzyme activity was elevated (p<0.0001) as was ACE‐2 enzyme activity in both frontal and parietal cortices (p<0.0001 and p = 0.001 respectively) in AD. Individuals with I/I compared with D/D and I/D genotypes in AD had unchanged ACE‐1 level (p = 0.079), lower ACE‐1 enzyme activity (p = 0.029), higher ACE‐2 level (p = 0.011) and unaltered ACE‐2 enzyme activity (p = 0.085) in the frontal cortex.ConclusionThese data confirm our previous findings showing that RAS is dysregulated in AD. Interestingly, we report regional differences in RAS signalling in AD and a reciprocal relationship between ACE‐2 protein level (reduced) and enzyme activity (increased) in AD that warrants further investigation. RAS appears to be most dysregulated in individuals with an I/I genotype in AD.