Investigating the Roles of Angiotensin-Converting Enzyme 2, Angiotensin 1–7, and Neprilysin in Heart Failure, COVID-19, and Multiorgan Injury
Creators: Gheblawi, Mahmoud
Publisher: name: University of Alberta Library
Year: 2024

<p>Cardiovascular disease (CVD) etiology is increasingly being understood as a disease with pathological inputs spanning multiple organs and with injury impacting biological functions beyond the cardiovasculature. New insights point to an interconnected gut-heart-brain axis regulating homeostasis. CVD, in the setting of diabetes and obesity continues to be a leading cause global of morbidity and mortality. An activated RAS in patients with obesity drives underlying multiorgan injury, including CVD, through chronic angiotensin II (Ang II) signaling. Two enzymes that regulate Ang II are the angiotensin-converting enzyme 2 (ACE2) and neprilysin (NEP).<br>
ACE2 exists as part of the counter-regulatory axis of the RAS by converting Ang II into the cardioprotective Ang 1–7. ACE2 also functions as the receptor for SARS-CoV-2 infection, which leads to multiorgan injury and imposes a significant clinical burden on patients with diabetes and obesity. Promotion of the ACE2/Ang 1–7 axis has been hypothesized as a therapy for obesity-associated CVD by acting across the gut-heart-brain axis.<br>
NEP is a proteolytic enzyme that cleaves multiple substrates of cardiovascular importance, such as Ang 1–7, and apelin, which plays a critical role in remedying myocardial infarction (MI) injury. NEP inhibition (NEPi) through angiotensin receptor neprilysin inhibitor (ARNi) treatment is a new approach to treating patients with heart failure. However, the underlying mechanism by which NEPi is beneficial for heart failure patients remains elusive.<br>
Just as ACE2 and NEP are interconnected through shared substrates and overlapping expression patterns this thesis is composed of 3 interconnected parts: 1) Examining whether ACE2 is lost with SARS-CoV-2 infection and the ramifications of ACE2 loss across the gut-heart-brain axis in the setting of obesity-related diabetes; 2) The efficacy of Ang 1–7 and ACE2 as therapeutics for treating advanced endothelial injury and obesity-related diabetes and CVD, respectively; 3) The role of NEP in MI injury. A brief objective and summary for each focus follows.</p>

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<li>ACE2, COVID-19, Diabetes &amp; Obesity:
Objective: Understanding whether SARS-CoV-2 infection leads to loss of ACE2, and whether loss of ACE2 drives the high prevalence of adverse outcomes in diabetic and obese COVID-19 patients.
Summary: By examining patient plasma and autopsy samples, we were able to determine that COVID-19 leads to loss of tissue ACE2 which is reflected in increased plasma ACE2 levels (Chapter 2). SARS-CoV-2 directly mediates this loss of ACE2 which confirmed in vitro (Chapter 3). Loss of ACE2, independent of SARS-CoV-2 cytopathicity, leads to dysfunction across the gut-heart-brain axis in mice with obesity and associated diabetes. ACE2 knockout leads to gut dysbiosis, impaired amino acid absorption, circulation of toxic metabolites of gut microbiota origin, and neurocognitive impairment (Chapter 4). ACE2 loss in the setting of diabetes and obesity furthers CVD, renal insufficiency, and insulin resistance. Acute, regional, small intestine ACE2 loss following SARS-CoV-2 infection of mice, is enough to phenocopy altered metabolomic signatures which are congruent with ACE2 knockout and COVID-19 patient metabolomes (Chapter 5). The immune response is impaired in the heart of diabetic obese mice, with viral infection leading to elevated Wnt signaling pathways. Understanding how and why this occurs is key to reducing adverse outcomes for patients with diabetes and obesity.</li>
<li>ACE2/Ang 1-7 as CVD Therapies:
Objective: Examining the efficacy of Ang 1–7 in rescuing an advanced model of CVD and whether Ace2 gene therapy can alleviate CVD arising from obesity-related diabetes.
Summary: Using the db/db eNOS-/- mouse model with advanced endothelial injury we determined that the ameliorating effects of Ang 1–7 acts primarily through endothelial nitric oxide synthase (eNOS) (Chapter 6). Ace2 gene therapy using an adeno-associated virus vector led to cardiac reverse remodeling, improved vascular function, and enhanced glucose tolerance (Chapter 7). Clinical ACE2 gene therapy has the potential to improve both cardiovascular and diabetic parameters in patients.</li>
<li>NEP in MI Injury:
Objective: Determining the mechanism through which NEPi is beneficial to heart failure patients by studying MI in NEP knockout (NEPKO) mice.
Summary: NEPKO mice have a distinct survival advantage against MI injury with improved cardiac efficiency, calcium handling, preserved β-adrenergic signaling, and increased infarct vascularity (Chapter 8). Lack of infarct rupture, improved angiogenesis, and preserved contractile function point to NEP involvement in the three main heart cell types, which future studies should focus on.</li>
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