Cambridge scientists have grown beating heart cells in the lab and shown how they are vulnerable to SARS-CoV-2 infection. In a study published in Communications Biology, they used this system to show that an experimental peptide drug called DX600 can prevent the virus entering the heart cells.
The heart is one the major organs damaged by infection with SARS-CoV-2, particularly the heart cells, or “cardiomyocytes,” which contract and circulate blood. It is also thought that damage to heart cells may contribute to the symptoms of long COVID.
Patients with underlying heart problems are more than four times as likely to die from COVID-19, the disease caused by SARS-CoV-2 infection. The case fatality rate in patients with COVID-19 rises from 2.3% to 10.5% in these individuals.
To gain entry into our cells, SARS-CoV-2 hijacks a protein on the surface of the cells, a receptor known as ACE2. Spike proteins on the surface of SARS-CoV-2 – which give it its characteristic “corona”-like appearance – bind to ACE2.
Both the spike protein and ACE2 are then cleaved, allowing genetic material from the virus to enter the host cell. The virus manipulates the host cell’s machinery to allow itself to replicate and spread.
A team of scientists at the University of Cambridge has used human embryonic stem cells to grow clusters of heart cells in the lab and shown that these cells mimic the behavior of the cells in the body, beating as if to pump blood. Crucially, these model heart cells also contained the key components necessary for SARS-CoV-2 infection – in particular, the ACE2 receptor.
Working in special biosafety laboratories and using a safer, modified synthetic (“pseudotyped’) virus decorated with the SARS-CoV-2 spike protein, the team mimicked how the virus infects the heart cells. They then used this model to screen for potential drugs to block infection.
Dr. Sanjay Sinha from the Wellcome-MRC Cambridge Stem Cell Institute said: “Using stem cells, we’ve managed to create a model which, in many ways, behaves just like a heart does, beating in rhythm. This has allowed us to look at how the coronavirus infects cells and, importantly, helps us screen possible drugs that might prevent damage to the heart.”
The team showed that some drugs that targeted the proteins involved in SARS-CoV-2 viral entry signiﬁcantly reduced levels of infection. These included an ACE2 antibody that has been shown previously to neutralize pseudotyped SARS-CoV-2 virus, and DX600, an experimental drug.
DX600 is an ACE2 peptide antagonist – that is, a molecule that specifically targets ACE2 and inhibits the activity of peptides that play a role in allowing the virus to break into the cell.
DX600 was around seven times more effective at preventing infection compared to the antibody, though the researchers say this may be because it was used in higher concentrations. The drug did not affect the number of heart cells, implying that it would be unlikely to be toxic.
Professor Anthony Davenport from the Department of Medicine and a fellow at St Catharine’s College, Cambridge said: “The spike protein is like a key that fits into the ‘lock’ on the surface of the cells – the ACE2 receptor – allowing it entry. DX600 acts like gum, jamming the lock’s mechanism, making it much more difficult for the key to turn and unlock the cell door.
“We need to do further research on this drug, but it could provide us with a new treatment to help reduce harm to the heart in patients recently infected with the virus, particularly those who already have underlying heart conditions or who have not been vaccinated. We believe it may also help reduce the symptoms of long COVID.”
A variety of investigations support the contention that a local tissue angiotensin (ANG) system is critical in the pathogenesis of pulmonary fibrosis in both animal models [1, 2] and in idiopathic pulmonary fibrosis (IPF) [3, 4], the most frequent and insidious interstitial lung disease (ILD) encountered by pulmonary physicians.
Several lines of evidence point to a critical role for ANGII in the signalling of cellular and molecular events believed to be critical in the pathogenesis of lung fibrosis, including alveolar epithelial cell (AEC) apoptosis , fibroblast proliferation and migration [6, 7] and collagen synthesis .
The induction of apoptosis in cultured AECs in response to a variety of proapoptotic and profibrotic stimuli [9–12] has been shown to both activate and require the synthesis of angiotensinogen (AGT) and the processed peptide ANGII, the effector peptide of this system. ANGII is both motogenic  and mitogenic  for human lung fibroblasts, and increases collagen synthesis through a mechanism that is mediated by autocrine transactivation of transforming growth factor (TGF)-β1 in the fibroblast itself .
TGF-β1 transactivation in turn stimulates procollagen synthesis and the myofibroblast transition [13, 14], in addition to activating AGT expression in an apparent autocrine loop . Reductions in lung fibrogenesis by ANG receptor AT1 blockers in mice or rats [1, 15] or AT1 receptor deletion in mice  support the contention that the mechanisms just discussed are active in vivo as well as in the in vitro systems in which they were first identified.
Evidence from our laboratory supports an important role in lung fibrosis for the counterregulatory axis composed of angiotensin-converting enzyme (ACE)-2, its product ANG1-7 and the ANG1-7 receptor mas . In the bleomycin model of lung fibrosis in mice or rats, ACE-2 was shown to be protective through the use of small interfering RNA (siRNA) knockdown or competitive inhibition of ACE-2 with the peptide DX600, either of which exacerbated collagen deposition in response to bleomycin .
Other authors have shown a similar protective role for ACE-2 in lung fibrosis induced by monocrotaline . By contrast, administration of purified recombinant ACE-2 inhibited bleomycin-induced collagen deposition .
In a recent study of the regulation of apoptosis in cultured AECs, ACE-2 and its product ANG1-7 were found to protect against AEC death through the ability of ANG1-7 to reduce c-Jun N-terminal kinase (JNK) phosphorylation, an event required for the signalling of AEC apoptosis in response to ANGII and other proapoptotic inducers . The inhibitory effect of ANG1-7 on AEC death was mediated by the ANG1-7 receptor mas.
These results, together with those showing inhibition of collagen deposition discussed in the preceding paragraph, demonstrate the antiapoptotic and antifibrotic roles of the ACE-2/ANG1-7/mas axis in experimental pulmonary fibrosis.
An important finding in the study by Li et al.  was the demonstration that the protective enzyme ACE-2 was downregulated in both experimental and human lung fibrosis. In human lung tissue obtained by biopsy from patients with IPF, ACE-2 was reduced at the level of mRNA, immunoreactive protein and enzymatic activity, all of which were reduced to a similar severe degree.
Likewise, ACE-2 protein, enzymatic activity and mRNA were also reduced in bleomycin-induced mouse and rat models of IPF, but no reduction was seen in ACE-2 mRNA in cultured AECs exposed to bleomycin in vitro. For this reason, we sought to find a mechanism that could explain the loss of ACE-2 mRNA, protein and activity in fibrotic human lungs that were never exposed to bleomyin or other xenobiotic inducers of apoptosis.
For many years the alveolar epithelium of the fibrotic human lung has been described as the “hyperplastic” or “cuboidal” epithelium, based on the observation of predominantly type II pneumocytes that are proliferating in response to ongoing epithelial injury [17, 18]. In contrast, the alveolar epithelium of normal lung is essentially quiescent, with few or no proliferating cells and numerous type I cells, the terminally differentiated progeny of type II cells .
On this basis, it was hypothesised that the decrease in ACE-2 observed in fibrotic human lungs  might be a consequence of cell cycle progression by type II pneumocytes. We report here the finding that ACE-2 mRNA, immunoreactive protein and enzymatic activity are all highly expressed in AECs that are quiescent, but are downregulated in AECs that have entered the cell cycle. We also report evidence that the upregulation of ACE-2 that accompanies the progression of AECs to quiescence is transcriptionally regulated by a mechanism mediated by JNK.
reference link: https://erj.ersjournals.com/content/42/1/198
More information: Thomas L. Williams et al, Human embryonic stem cell-derived cardiomyocyte platform screens inhibitors of SARS-CoV-2 infection, Communications Biology (2021). DOI: 10.1038/s42003-021-02453-y