Innate Immune Activation and Mitochondrial ROS Invoke Persistent Cardiac Conduction System Dysfunction after COVID-19 (preprint)

BackgroundCardiac risk rises during acute SARS-CoV-2 infection and in long COVID syndrome in humans, but the mechanisms behind COVID-19-linked arrhythmias are unknown. This study explores the acute and long term effects of SARS-CoV-2 on the cardiac conduction system (CCS) in a hamster model of COVID-19. MethodsRadiotelemetry in conscious animals was used to non-invasively record electrocardiograms and subpleural pressures after intranasal SARS-CoV-2 infection. Cardiac cytokines, interferon-stimulated gene expression, and macrophage infiltration of the CCS, were assessed at 4 days and 4 weeks post-infection. A double-stranded RNA mimetic, polyinosinic:polycytidylic acid (PIC), was used in vivo and in vitro to activate viral pattern recognition receptors in the absence of SARS-CoV-2 infection. ResultsCOVID-19 induced pronounced tachypnea and severe cardiac conduction system (CCS) dysfunction, spanning from bradycardia to persistent atrioventricular block, although no viral protein expression was detected in the heart. Arrhythmias developed rapidly, partially reversed, and then redeveloped after the pulmonary infection was resolved, indicating persistent CCS injury. Increased cardiac cytokines, interferon-stimulated gene expression, and macrophage remodeling in the CCS accompanied the electrophysiological abnormalities. Interestingly, the arrhythmia phenotype was reproduced by cardiac injection of PIC in the absence of virus, indicating that innate immune activation was sufficient to drive the response. PIC also strongly induced cytokine secretion and robust interferon signaling in hearts, human iPSC-derived cardiomyocytes (hiPSC-CMs), and engineered heart tissues, accompanied by alterations in electrical and Ca2+ handling properties. Importantly, the pulmonary and cardiac effects of COVID-19 were blunted by in vivo inhibition of JAK/STAT signaling or by a mitochondrially-targeted antioxidant. ConclusionsThe findings indicate that long term dysfunction and immune cell remodeling of the CCS is induced by COVID-19, arising indirectly from oxidative stress and excessive activation of cardiac innate immune responses during infection, with implications for long COVID Syndrome.

Mesenchymal Stromal Cell Delivery via an Ex Vivo Bioreactor Preclinical Test System Attenuates Clot Formation for Intravascular Application (preprint)

While mesenchymal stromal cells (MSCs) are an appealing therapeutic option for a range of clinical applications, their potential to induce clotting when used systemically remains a safety concern, particularly in hypercoagulable conditions, such as in patients with severe COVID-19, trauma, or cancers. Here, we tested a novel ex vivo approach aimed at improving the safety of MSC systemic administration by use of a bioreactor. In this device, MSCs are seeded on the outside of a hollow-fiber filter, sequestering them behind a hemocompatible membrane, while still maintaining cross talk with blood cells and circulating signaling molecules. The potential for these bioreactor MSCs to induce clots in coagulable plasma was compared against “free” MSCs, as a model of systemic administration, which were directly injected into the circuit. Our results showed that physical isolation of the MSCs via a bioreactor extends the time necessary for clot formation to occur when compared to “free” MSCs. Measurement of cell surface data indicates the presence of known clot inducing factors, namely tissue factor and phosphatidylserine. Results also showed that recovering cells and flushing the bioreactor prior to use further prolonged clot formation time. Further, application of this technology in two in vivo models did not require additional heparin to maintain target ACT levels relative to the acellular device. Taken together, the use of hollow fiber filters to house MSCs, if adopted clinically, could offer a novel method to control systemic MSC exposure and prolong clot formation time.