SARS-CoV-2 Exacerbates COVID-19 Pathology Through Activation of the Complement and Kinin Systems.

Infection with SARS-CoV-2 triggers the simultaneous activation of innate inflammatory pathways including the complement system and the kallikrein-kinin system (KKS) generating in the process potent vasoactive peptides that contribute to severe acute respiratory syndrome (SARS) and multi-organ failure. The genome of SARS-CoV-2 encodes four major structural proteins - the spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and the envelope (E) protein. However, the role of these proteins in either binding to or activation of the complement system and/or the KKS is still incompletely understood. In these studies, we used: solid phase ELISA, hemolytic assay and surface plasmon resonance (SPR) techniques to examine if recombinant proteins corresponding to S1, N, M and E: (a) bind to C1q, gC1qR, FXII and high molecular weight kininogen (HK), and (b) activate complement and/or the KKS. Our data show that the viral proteins: (a) bind C1q and activate the classical pathway of complement, (b) bind FXII and HK, and activate the KKS in normal human plasma to generate bradykinin and (c) bind to gC1qR, the receptor for the globular heads of C1q (gC1q) which in turn could serve as a platform for the activation of both the complement system and KKS. Collectively, our data indicate that the SARS-CoV-2 viral particle can independently activate major innate inflammatory pathways for maximal damage and efficiency. Therefore, if efficient therapeutic modalities for the treatment of COVID-19 are to be designed, a strategy that includes blockade of the four major structural proteins may provide the best option.

SARS-CoV-2 Structural Proteins Exposure Alter Thrombotic and Inflammatory Responses in Human Endothelial Cells.

Introduction: We have experienced a pandemic induced by the interaction of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) structural proteins with innate structures. These interactions are especially prevalent for patients with underlying pathologies, such as cardiovascular diseases. However, there has been limited work to uncover the range of responses induced by SARS-CoV-2 structural proteins. Thus, our objective was to investigate how endothelial cell pro-thrombotic and pro-inflammatory responses are altered after exposure to SARS-CoV-2 spike, nucleocapsid, and membrane-envelope proteins. We hypothesized that after a short duration exposure, endothelial cells would have a heightened thrombotic and inflammatory potential. With longer exposures, this may lead to altered disease progression and the observed increased mortality and morbidity rates in patients with underlying vascular pathologies. Methods: To test this hypothesis, human endothelial cells were exposed to SARS-CoV-2 structural proteins. After the exposure, the expression of thrombomodulin, PECAM-1, connexin-43, and gC1qR were assessed. In parallel, standard cell culture readouts were assessed to determine if these incubations altered cell growth and metabolism. Results and Conclusions: We observed significant increases in thrombotic and inflammatory marker expression, with no change to the cell culture parameters (with the exception of a reduction in cell density in response to one SARS-CoV-2 structural protein). Importantly, these observations were dependent on the viral structural protein the cells were exposed to, suggesting that the interactions of SARS-CoV-2 with innate cells is complex and must be uncovered. Combined, this suggests that SARS-CoV-2 structural proteins can regulate inflammatory and thrombotic responses that underlie common pathologies observed during COVID-19.

Sir Peter J. Lachmann and Prof. Robert B. Sim: Gone but Will Never Be Forgotten!

At that time, Peter's lab was also working on the identification of the various degradation fragments of C3, including a fragment that he later called C3g, and therefore, he wanted to see whether these degradation fragments share any functional or structural similarity. In addition to the ongoing COVID-19 pandemic, which has brought an unexpected global gloom, the beginning of this year was also particularly cruel to the complement field, as two of our greatest and dearest members - Sir Peter Lachmann and Prof. Bob Sim - passed away too soon. [Extracted from the article] Copyright of Viruses (1999-4915) is the property of MDPI Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Inflammatory, Thrombotic, and Diabetic Responses in Human Arterial Fibroblasts and Endothelial Cells are Regulated by SARS-CoV-2 Structural Proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for many pathological processes, such as altered vascular disease development, dysfunctional thrombosis, and a heightened inflammatory state. Although many clinical reports support these observations, there has been limited experimental work to determine the underlying mechanisms and cellular processes induced by exposure to SARS-CoV-2 structural proteins. Importantly, these structural proteins are conserved amongst all current known SARS-CoVs. Our objective was to investigate the effects of the Spike (S), Nucleocapsid (N), and Membrane-Envelope (M) SARS-CoV-2 structural proteins on inflammation, thrombosis, and diabetic disease markers of human aortic adventitial fibroblasts and human umbilical vein endothelial cells. We hypothesized that short-term exposure to SARS-CoV-2 structural proteins would result in increased expression of inflammatory, thrombotic, and diabetic proteins in both cell types, which would support a mechanism for altered vascular disease progression. To test this, the cells were incubated independently with the three SARS-CoV-2 proteins for one hour, after which we analyzed the expression of gC1qR, ICAM-1, tissue factor, RAGE, GLUT-4, thrombomodulin, PECAM-1, and Connexin-43 (in their respective cell types), using an ELISA approach. All cells were monitored for maintenance of typical culture parameters using a live/dead cell cytotoxicity assay and the MTT assay (for metabolic activity). We observed that each of these markers were significantly up-regulated after exposure to SARS-CoV-2 structural proteins as compared to fibroblasts or endothelial cells that were not exposed to these proteins. Interestingly, the extent of the expression of these markers was sometimes significantly different for each of the SARS-CoV-2 structural proteins. This suggests that each of the SARS-CoV-2 proteins interacts with these cells through different mechanisms, however, more work will need to be undertaken to determine the mechanisms by which these proteins interact with cells. Thus, these results indicate that the cellular response of vascular cells towards SARS-CoV-2 structural proteins promotes inflammatory, thrombotic, and vascular dysfunction. However, these interactions are regulated by complex and possibly different cellular receptors/signal transduction pathways that should be explored further.

SARS-CoV-2 proteins regulate inflammatory, thrombotic and diabetic responses in human arterial fibroblasts.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for many pathological processes, including altered vascular disease development, dysfunctional thrombosis and a heightened inflammatory response. However, there is limited work to determine the underlying cellular responses induced by exposure to SARS-CoV-2 structural proteins. Thus, our objective was to investigate how human arterial adventitial fibroblasts inflammation, thrombosis and diabetic disease markers are altered in response to Spike, Nucleocapsid and Membrane-Envelope proteins. We hypothesized that after a short-term exposure to SARS-CoV-2 proteins, adventitial fibroblasts would have a higher expression of inflammatory, thrombotic and diabetic proteins, which would support a mechanism for altered vascular disease progression. After incubation, the expression of gC1qR, ICAM-1, tissue factor, RAGE and GLUT-4 was significantly up-regulated. In general, the extent of expression was different for each SARS-CoV-2 protein, suggesting that SARS-CoV-2 proteins interact with cells through different mechanisms. Thus, SARS-CoV-2 protein interaction with vascular cells may regulate vascular disease responses.

Complement and coagulation: key triggers of COVID-19-induced multiorgan pathology.

In a stunningly short period of time, the unexpected coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has turned the unprepared world topsy-turvy. Although the rapidity with which the virus struck was indeed overwhelming, scientists throughout the world have been up to the task of deciphering the mechanisms by which SARS-CoV-2 induces the multisystem and multiorgan inflammatory responses that, collectively, contribute to the high mortality rate in affected individuals. In this issue of the JCI, Skendros and Mitsios et al. is one such team who report that the complement system plays a substantial role in creating the hyperinflammation and thrombotic microangiopathy that appear to contribute to the severity of COVID-19. In support of the hypothesis that the complement system along with neutrophils and platelets contributes to COVID-19, the authors present empirical evidence showing that treatment with the complement inhibitor compstatin Cp40 inhibited the expression of tissue factor in neutrophils. These results confirm that the complement axis plays a critical role and suggest that targeted therapy using complement inhibitors is a potential therapeutic option to treat COVID-19-induced inflammation.