Bridging COVID-19-mediated Myocardial Inflammation and the Epicardial Adipose Tissue in Heart Failure: ACE2 Regulation at Center Stage

• Author / Creator

  Viveiros, Anissa M

• ACE2 was discovered as the primary effector enzyme of the protective, counter-regulatory arm of the renin-angiotensin system (RAS). The canonical RAS, comprising the angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/AT 1 receptor (AT1R) axis, mediates proinflammatory, profibrotic, and hypertensive effects. Rather, ACE2 deactivates Ang II to Ang-(1-7), which acts on the Mas receptor (MasR) to exert protective, anti-inflammatory, and antifibrotic action. However, beyond this primary neurohumoral function, the understanding of the role of ACE2 has broadened to a regulator of multiple peptide cascades, as a chaperone for the transport of amino acids, and, more recently, as the host receptor hijacked for the cellular infection of SARS-CoV and SARS-CoV-2: the causative agents of SARS and COVID-19, respectively. Here, we aimed to understand the diverse roles of ACE2 as the receptor for SARS-CoV-2 and as a protective molecule in heart failure (HF). Further, we aimed to phenotype the epicardial adipose tissue (EAT) in HF and to tease apart the RAS's function and the role of ACE2 in this adipose tissue depot.
  Wild-type (WT) male and female C57BL/6J mice were divided into three age groups: young (3 months), adult (12 months), and aged (18 months). We assessed the heart, lungs, kidney, and small intestine using reverse transcription polymerase chain reaction (RT-PCR) for mRNA expression (Ace2 and transmembrane protease serine 2 (Tmprss2)), protein levels by immunoblot (ACE2 and TMPRSS2) and activity (ACE2) to determine if differences in viral entry factors could explain the increased older male susceptibility to COVID-19 that was recognized clinically. We further assessed ACE2 expression, protein levels and activity in young and aged male and female human donor hearts. Next, we utilized SARS-CoV-2 infected Syrian hamsters to assess lung pathology, myocardial inflammation and ACE2 levels using immunoblot, immunohistochemistry and histological staining. We mirrored this analysis in the hearts of autopsied patients who died of COVID-19. As ACE2 was found to be altered in physiology and disease, we assessed candidate modes of ACE2 regulation in myocardial samples from non-failing controls and patients with HF. We employed immunoblot, activity assays and RT-PCR to identify the levels and expression of ACE2, a disintegrin and metalloprotease 17 (ADAM17), and micro RNAs (miRNAs) anticipated to regulate ACE2. Finally, we characterized the EAT from non-failing controls and patients with HF using single nucleus RNA sequencing (snRNA Seq), histology, a multiplexed cytokine assay, and immunoblot.
  Taken together, we identified that increased tissue ACE2 may enhance older male susceptibility to severe COVID-19 and that myocardial ACE2 downregulation and myeloid dominant recruitment are common pathological features of COVID-19 in hamsters and humans. Further, post-transcriptional and post-translational regulation of ACE2 is likely etiology specific, whether in physiology or the pathophysiology of HF. Finally, we identify EAT dysregulation as a possible contributor to myocardial dysfunction in HF due to alterations in adipose tissue storage, EAT infiltration into the myocardium, aberrant adipogenesis, and, possibly, canonical RAS overactivation. The compilation of our efforts suggests that understanding the regulation of ACE2 is crucial to combating COVID-19 and HF, to ultimately finding novel therapeutic strategies to address these topical public health concerns.

• Subjects / Keywords

  • ACE2
  • Heart Failure
  • COVID-19
  • Epicardial Adipose Tissue

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-s6jf-bk91

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.