Human cardiosphere-derived stromal cells exposed to SARS-CoV-2 evolve into hyper-inflammatory/pro-fibrotic phenotype and produce infective viral particles depending on the levels of ACE2 receptor expression

Abstract

Aims

Patients with severe respiratory syndrome caused by SARS-CoV-2 undergo cardiac complications due to hyper-inflammatory conditions. Although the presence of the virus has been detected in the myocardium of infected patients, and infection of induced pluripotent cells-derived cardiomyocytes has been demonstrated, the reported expression of ACE2 in cardiac stromal cells suggests that SARS-CoV-2 may determine cardiac injury by sustaining productive infection and increasing inflammation.

Methods and Results

We analyzed expression of ACE2 receptor in primary human cardiac stromal cells derived from cardiospheres, using proteomics and transcriptomics before exposing them to SARS-CoV-2 in vitro. Using conventional and high sensitivity PCR methods, we measured virus release in the cellular supernatants and monitored the intracellular viral bioprocessing. We performed high-resolution imaging to show the sites of intracellular viral production and demonstrated the presence of viral particles in the cells with electron microscopy. We finally used RT-qPCR assays to detect genes linked to innate immunity and fibrotic pathways coherently regulated in cells after exposure to the virus.

Conclusions

Our findings indicate that cardiac stromal cells are susceptible to SARS-CoV-2 infection and produce variable viral yields depending on the extent of cellular ACE2 receptor expression. Interestingly, these cells also evolved toward hyper-inflammatory/pro-fibrotic phenotypes independently of ACE2 levels. Thus, SARS-CoV-2 infection of myocardial stromal cells could be involved in cardiac injury, and explain the high number of complications observed in severe cases of COVID-19.

Translational Perspective

In the present investigation, we provide evidence that human cardiac stromal cells, a major component of the non-contractile cellular fraction in the heart can be infected by SARS-CoV-2 in vitro, in direct relationship to the extent of ACE2 receptor expression. Our work also suggests that these cells, when exposed to the virus, can evolve toward inflammatory and fibrotic phenotypes independently of ACE2. In addition to describing a novel cellular target of SARS-CoV-2 in the human heart, our study generates new hypothesis on potential mechanisms underlying cardiac complications observed in COVID-19 patients.