Mechanisms of Angiotensin I Converting Enzyme in Alzheimer's disease

Angiotensin converting enzyme (ACE1) and the renin-angiotensin system (RAS) function in the vascular system to regulate blood pressure (BP), although they are also expressed in neurons of the brain and may have a role in Alzheimer’s disease (AD). We discovered a rare protein-altering variant in ACE1, R1279Q, that is associated with AD in families. To investigate the pathogenic mechanism of ACE1 R1279Q, we made knockin (KI) mice that express the cognate murine ACE1 variant. ACE1 KI mice have increased brain ACE1 and have age-related neurodegeneration, neuroinflammation, memory deficits, and abnormal EEG in the hippocampus (HIP), while other brain regions like cerebellum are resistant, demonstrating selective neurodegeneration. These effects are accelerated by A pathology and occur in the absence of BP changes. Importantly, ACE1 KI-mediated HIP neurodegeneration is prevented by treatment with ACE1 inhibitor (ACEi) and angiotensin II (AngII) receptor type 1 (AT1R) blocker (ARB) drugs. Apoptosis and AT1R signaling via phosphorylated ERK are increased in ACE1 KI brains. ACE1 is also increased in sporadic AD brain, suggesting that elevated RAS activity is a common feature of AD. We hypothesize that ACE1 R1279Q causes over-activation of AT1R signaling via elevated AngII, which leads to neurodegeneration of vulnerable neurons in susceptible brain regions such as HIP. A and other “second hits” may potentiate the age-induced increase in ACE1/RAS signaling to accelerate selective neurodegeneration. However, the mechanisms and cell types responsible for ACE1-associated neurodegeneration are unclear. In this R01, we will test hypotheses about the roles of microglia, microvessel pericytes, and neurons in ACE1-mediated neurodegeneration. In addition to hypothesis testing, we will take innovative discovery-based approaches. We will confirm in human AD brain molecular changes identified in mouse. In Aim 1, we will determine the single cell transcriptomes and phosphoproteomes of microglial cells of ACE1 KI mice with or without A pathology. In addition, we will analyze ACE1 KI mice in which the AT1R gene is conditionally knocked out (cKO) in microglia. In Aim 2, we will investigate the single cell transcriptomes and phosphoproteomes of microvessel pericytes of ACE1 KI mice with or without A pathology. We will also determine if the ACE1 mutation impairs cerebral blood flow and causes blood-brain barrier leakage in ACE1 KI mice. Additionally, we will analyze ACE1 KI mice crossed with pericyte-specific AT1R cKO mice. In Aim 3, we will determine the single cell transcriptomes and phosphoproteomes of neurons of ACE1 KI mice with or without A pathology and with or without treatment with the ARB losartan. In addition, we will analyze ACE1 KI mice crossed with neuron-specific AT1R cKO mice. In Aim 4, we will validate molecules and pathways identified in ACE1 KI mice in human AD brain. We expect this R01 will provide mechanistic insights into ACE1/RAS-mediated neurodegeneration and its relationship with A pathology, knowledge that will be highly valuable for the development of AD therapeutics.