Date of Award
Doctor of Philosophy (PhD)
Cardiac arrhythmias, particularly ventricular arrhythmias, can be life-threatening and caused by both congenital genetic mutations and acquired cardiac injury. My thesis work was originally focused on delineating the effects of genetic mutation-driven dysregulation of a protein called Hey2 in Brugada Syndrome, a complex disease characterized by a predisposition to dangerous arrhythmias originating in the right ventricular outflow tract. In response to the pandemic, my thesis work shifted toward understanding the mechanisms of cardiovascular injury in Coronavirus disease 2019 (COVID-19), which is associated with serious cardiovascular complications, including ventricular arrhythmias and sudden cardiac death as well as endothelial dysfunction and coagulopathies. While the main dissertation is focused on the COVID-19 work, the original Hey2 project is covered in a supplemental chapter. COVID-19 patients can present with serious and sometimes lethal cardiovascular manifestations of the disease. Patients with severe cases of COVID-19 often suffer ventricular arrhythmias and sudden cardiac death, leading to increased morbidity and mortality, especially for patients with predisposing cardiovascular diseases. There is also substantial clinical evidence of patients experiencing acute myocardial infarctions, which may be caused by either direct damage to the myocardium or from vascular dysfunction that leads to blood clots and ultimately occlusions. Currently, there is significant discussion in the field about whether this cardiac damage is being caused by direct viral infection of the heart or due to systemic inflammatory effects. Many groups have sought to determine whether it is likely that SARS-CoV-2 could directly infect the heart via the ACE2 receptor. SARS-CoV-2 utilizes the ACE2 receptor to bind to cellular membranes and enter susceptible cells. Many groups have performed single-cell RNA-sequencing studies have been performed on human hearts that indicate ACE2 RNA is expressed in multiple cell types in the heart, with pericytes having the highest expression. Pericytes are perivascular cells that are found in abundance in the microvasculature in all vascularized organs where they regulate numerous functions, including vessel growth, permeability, and contractility. Since pericytes play a critical role in supporting endothelial cells and maintaining vascular integrity, we and others hypothesized that pericytes may be a culprit for cardiovascular damage in COVID-19. In healthy vessels, intact endothelial junctions would prevent SARS-CoV-2 was reaching pericytes due to size exclusion. However, if vessels have compromised barriers due to diseases, such as diabetes, SARS-CoV-2 could cross the barrier and infect pericytes, which could then lead to endothelial cell activation and inflammation. This could in turn lead to the coagulopathies and infarcts that are being reported in COVID-19 patients. In my thesis work, I started by collaborating with Dr. Michael Diamond’s lab to combine the expertise and resources necessary to study the intrinsic cardiac effects of SARS-CoV-2 in COVID-19. Together, we adapted the Rentschler lab’s previously establish human organotypic cardiac slice culture methodology to evaluate cellular tropism of SARS-CoV-2 in explanted donor human hearts rejected from transplantation. We identified cardiac pericytes as a direct target of SARS-CoV-2 infection in organotypic cardiac slices and then collaborated with Dr. Kory Lavine’s lab to further evaluate viral entry and downstream effects of infection in primary cardiac pericytes. We found that primary cardiac pericytes were productively infected by SARS-CoV-2; however, we determined that other types of primary human pericytes from other organs, including the brain and placenta, were not infected likely due to significantly lower expression of the main viral entry receptor, ACE2, compared to cardiac pericytes. Furthermore, we determined that viral entry into cardiac pericytes is mediated by endosomal proteases rather than transmembrane serine proteases as seen in the lung epithelium. We demonstrate that cardiac pericyte infection leads to upregulation of Type I interferon signaling, inflammatory markers, and mediators of vasoreactivity, along with NF-ĸB cell death, with viability being partially improved by cytokine inhibition. Interestingly, we demonstrate that endothelial cell exposure to infected pericytes and their supernatant can lead to upregulation of Type I interferon signaling and neutrophil and T-cell chemokines combined with dysregulation of thrombosis mediators, further linking infected cardiac pericytes with endothelial dysfunction. And finally, we present evidence of cardiac pericyte infection in COVID-19 myocarditis patients. Together, the results in my thesis work demonstrate that human cardiac pericytes are susceptible to SARS-CoV-2 infection and suggest a role of pericyte infection in COVID-19.
Stacey L. Rentschler
Nathaniel Huebsch, Kristen Kroll, Jeanne Nerbonne, Jonathan Silva,
Available for download on Saturday, August 10, 2024