Oxidative Stress and Inflammation in SARS-CoV-2- and Chlamydia pneumoniae-Associated Cardiovascular Diseases

Porcine reproductive and respiratory syndrome virus nsp5 inhibits the activation of the Nrf2/HO-1 pathway by targeting p62 to antagonize its antiviral activity

Porcine reproductive and respiratory syndrome virus (PRRSV) infections often trigger oxidative stress and cytokine storms, resulting in significant tissue damage that causes fatalities in piglets and reproductive issues in sows. However, it is still unknown how oxidative stress is regulated by viral and host factors in response to PRRSV infection. Here, we found that PRRSV induced cellular oxidative stress by triggering the production of reactive oxygen species and inhibiting the expression of antioxidant enzymes. Although Nrf2 is an important redox regulator that initiates the expression of downstream antioxidant genes, PRRSV can impair the Nrf2/HO-1 pathway. The overexpression of Nrf2 showed a significant anti-PRRSV effect, and inhibiting the expression of Nrf2 promoted the proliferation of PRRSV. Further analysis showed that Nrf2 positively regulated the production of type I interferons and interferon-stimulated genes, which may contribute to its anti-PRRSV effect. By screening the PRRSV-encoded protein, we found that the PRRSV nsp5 protein can degrade Nrf2 at the protein level. Mechanistically, nsp5 promotes Nrf2-Keap1 binding affinity by inhibiting p62-mediated Keap1 sequestration and increasing Keap1 expression. Subsequently, this increased Keap1-mediated degradation of Nrf2 ubiquitination through K48-linked polyubiquitin. Furthermore, we found that the residues Tyr146 and Arg147 of nsp5 are crucial for inhibiting the activation of the p62-mediated Nrf2 antioxidant pathway. Thus, our findings uncover a novel mechanism by which PRRSV disrupts the host antioxidant defense system and highlight the crucial role of the Nrf2/HO-1 antioxidant pathway in host defense against PRRSV.IMPORTANCEOxidative stress-induced redox imbalance is a crucial pathogenic mechanism in viral infections. Nrf2 and its antioxidant genes serve as the main defense pathways against oxidative stress. However, the role of Nrf2 in the context of porcine reproductive and respiratory syndrome virus (PRRSV) infection remains unclear. In this study, we demonstrated that PRRSV infection decreased the expression of antioxidant genes of the Nrf2 signaling pathway and overexpression of Nrf2 triggered a strong anti-PRRSV effect. PRRSV nsp5 enhanced Keap1-dependent degradation of Nrf2 ubiquitination, thereby weakening cellular resistance to oxidative stress and antagonizing the antiviral activity of Nrf2. Our study further revealed a new mechanism by which PRRSV evades host antiviral innate immunity by disturbing cellular redox homeostasis, providing a new target for developing anti-PRRSV drugs.

The pathogenesis of aging-induced left atrial appendage thrombus formation and cardioembolic stroke in mice is influenced by inflammation-derived matrix metalloproteinases

Elderly people without atrial fibrillation (AF) still have a high incidence of cardioembolic stroke, suggesting that thrombus formation within the left atrial appendage (LAA) may also occur in an AF-independent manner. In the present study, we explored the potential mechanisms for aging-induced LAA thrombus formation and stroke in mice. We monitored stroke events in 180 aging male mice (14-24 months) and assessed left atrium (LA) remodeling by echocardiography at different ages. Mice that had stroke were implanted with telemeters to confirm AF. Histological features of LA and LAA thrombi were examined, as well as collagen content, expression of matrix metalloproteinases (MMPs), and leukocyte density in the atria at different ages, in mice with or without stroke. Also, the effects of MMP inhibition on stroke incidence and atrial inflammation were tested. We detected 20 mice (11 %) with stroke, 60 % of which were within 18-19 months of age. Although we did not detect AF in mice with stroke, we detected the presence of LAA thrombi, suggesting that stroke originated from the hearts of these mice. Compared with 18-month-old mice without stroke, 18-month-old stroke mice had enlarged LA with a very thin endocardium, that was associated with less collagen and heightened MMP expression in the atria. During aging, we found that the expression of mRNAs for atrial MMP7, MMP8, and MMP9 peaked at 18 months, which closely correlated with reductions in collagen content and the time-window for cardioembolic stroke in these mice. Treatment of mice with an MMP inhibitor at 17-18 months of age reduced atrial inflammation and remodeling, and stroke incidence. Taken together, our study demonstrates that aging-induced LAA thrombus formation occurs through a mechanism involving upregulation of MMPs and breakdown of collagen, and that treatment with an MMP inhibitor may be effective as a treatment strategy for this heart condition.

SARS-CoV-2 virus NSP14 Impairs NRF2/HMOX1 activation by targeting Sirtuin 1

Most deaths from the COVID-19 pandemic are due to acute respiratory distress syndrome (ARDS)-related respiratory failure. Cytokine storms and oxidative stress are the major players in ARDS development during respiratory virus infections. However, it is still unknown how oxidative stress is regulated by viral and host factors in response to SARS-CoV-2 infection. Here, we found that activation of NRF2/HMOX1 significantly suppressed SARS-CoV-2 replication in multiple cell types by producing the metabolite biliverdin, whereas SARS-CoV-2 impaired the NRF2/HMOX1 axis through the action of the nonstructural viral protein NSP14. Mechanistically, NSP14 interacts with the catalytic domain of the NAD-dependent deacetylase Sirtuin 1 (SIRT1) and inhibits its ability to activate the NRF2/HMOX1 pathway. Furthermore, both genetic and pharmaceutical evidence corroborated the novel antiviral activity of SIRT1 against SARS-CoV-2. Therefore, our findings reveal a novel mechanism by which SARS-CoV-2 dysregulates the host antioxidant defense system and emphasize the vital role played by the SIRT1/NRF2 axis in host defense against SARS-CoV-2.

Modulating the Antioxidant Response for Better Oxidative Stress-Inducing Therapies: How to Take Advantage of Two Sides of the Same Medal?

Oxidative stress-inducing therapies are characterized as a specific treatment that involves the production of reactive oxygen and nitrogen species (RONS) by external or internal sources. To protect cells against oxidative stress, cells have evolved a strong antioxidant defense system to either prevent RONS formation or scavenge them. The maintenance of the redox balance ensures signal transduction, development, cell proliferation, regulation of the mechanisms of cell death, among others. Oxidative stress can beneficially be used to treat several diseases such as neurodegenerative disorders, heart disease, cancer, and other diseases by regulating the antioxidant system. Understanding the mechanisms of various endogenous antioxidant systems can increase the therapeutic efficacy of oxidative stress-based therapies, leading to clinical success in medical treatment. This review deals with the recent novel findings of various cellular endogenous antioxidant responses behind oxidative stress, highlighting their implication in various human diseases, such as ulcers, skin pathologies, oncology, and viral infections such as SARS-CoV-2.