Macrophage-derived human resistin promotes perivascular adipose tissue dysfunction in experimental inflammatory arthritis.

Cardiovascular disease (CVD) is the leading cause of death in rheumatoid arthritis (RA). Resistin is an adipokine that induces adipose tissue inflammation and activation of monocytes/macrophages via adenylate cyclase-associated protein-1 (CAP1). Resistin levels are increased in RA and might cause perivascular adipose tissue (PVAT) dysfunction, leading to vascular damage and CVD. This study aimed to investigate the role of resistin in promoting PVAT dysfunction by increasing local macrophage and inflammatory cytokines content in antigen-induced arthritis (AIA). Resistin pharmacological effects were assessed by using C57Bl/6J wild-type (WT) mice, humanized resistin mice expressing human resistin in monocytes-macrophages (hRTN+/-/-), and resistin knockout mice (RTN-/-) with AIA and respective controls. We investigated AIA disease activity and functional, cellular, and molecular parameters of the PVAT. Resistin did not contribute to AIA disease activity and its concentrations were augmented in the PVAT and plasma of WT AIA and hRTN+/-/- AIA animals. In vitro exposure of murine arteries to resistin impaired vascular function by decreasing the anti-contractile effect of PVAT. WT AIA mice and hRTN+/-/- AIA mice exhibited PVAT dysfunction and knockdown of resistin prevented it. Macrophage-derived cytokines, markers of types 1 and 2 macrophages, and CAP1 expression were increased in the PVAT of resistin humanized mice with AIA, but not in knockout mice for resistin. This study reveals that macrophage-derived resistin promotes PVAT inflammation and dysfunction regardless of AIA disease activity. Resistin might represent a translational target to reduce RA-driven vascular dysfunction and CVD.

Cytokine storm in individuals with severe COVID-19 decreases endothelial cell antioxidant defense via downregulation of the Nrf2 transcriptional factor.

The cytokine storm in SARS-CoV-2 infection contributes to the onset of inflammation and target-organ damage. The endothelium is a key player in COVID-19 pathophysiology and it is an important target for cytokines. Considering that cytokines trigger oxidative stress and negatively impact endothelial cell function, we sought to determine whether serum from individuals with severe COVID-19 decreases endothelial cells' main antioxidant defense, i.e., the antioxidant transcriptional factor Nrf2. Human umbilical vein endothelial cells (HUVECs) were incubated with serum from patients with severe COVID-19 at different time points and the effects on redox balance and Nrf2 activity were determined. Serum from individuals with COVID-19 increased oxidant species, as indicated by higher DHE (dihydroethydine) oxidation, increased protein carbonylation, and induced mitochondrial reactive oxygen species (ROS) generation and dysfunction. Serum from patients with COVID-19, but not serum from healthy individuals, induced cell death and diminished nitric oxide (NO) bioavailability. In parallel, Nrf2 nuclear accumulation and the expression of Nrf2-targeted genes were decreased in endothelial cells exposed to serum from individuals with COVID-19. In addition, these cells exhibited higher expression of Bach-1, a negative regulator of Nrf2 that competes for DNA binding. All events were prevented by tocilizumab, an IL-6 receptor blocker, indicating that IL-6 is key to the impairment of endothelial antioxidant defense. In conclusion, endothelial dysfunction related to SARS-CoV-2 infection is linked to decreased endothelial antioxidant defense via IL-6-dependent mechanisms. Pharmacological activation of Nrf2 may decrease endothelial cell damage in individuals with severe COVID-19.NEW & NOTEWORTHY We demonstrate that endothelial cell dysfunction in SARS-CoV-2-infected individuals is linked to decreased activity of the major antioxidant system regulator, the Nrf2 transcription factor. We provide evidence that this phenomenon relies on IL-6, an important cytokine involved in the pathophysiology of COVID-19. Our data support the view that Nrf2 activation is a potential therapeutical strategy to prevent oxidative stress and vascular inflammation in severe cases of COVID-19.

Inhibition of IL-6 signaling prevents serum-induced umbilical cord artery dysfunction from patients with severe COVID-19.

Coronavirus disease 2019 (COVID-19) infection has a negative impact on the cytokine profile of pregnant women. Increased levels of proinflammatory cytokines seem to be correlated with the severity of the disease, in addition to predisposing to miscarriage or premature birth. Proinflammatory cytokines increase the generation of reactive oxygen species (ROS). It is unclear how interleukin-6 (IL-6) found in the circulation of patients with severe COVID-19 might affect gestational health, particularly concerning umbilical cord function. This study tested the hypothesis that IL-6 present in the circulation of women with severe COVID-19 causes umbilical cord artery dysfunction by increasing ROS generation and activating redox-sensitive proteins. Umbilical cord arteries were incubated with serum from healthy women and women with severe COVID-19. Vascular function was assessed using concentration-effect curves to serotonin in the presence or absence of pharmacological agents, such as tocilizumab (antibody against the IL-6 receptor), tiron (ROS scavenger), ML171 (Nox1 inhibitor), and Y27632 (Rho kinase inhibitor). ROS generation was assessed by the dihydroethidine probe and Rho kinase activity by an enzymatic assay. Umbilical arteries exposed to serum from women with severe COVID-19 were hyperreactive to serotonin. This effect was abolished in the presence of tocilizumab, tiron, ML171, and Y27632. In addition, serum from women with severe COVID-19 increased Nox1-dependent ROS generation and Rho kinase activity. Increased Rho kinase activity was abolished by tocilizumab and tiron. Serum cytokines in women with severe COVID-19 promote umbilical artery dysfunction. IL-6 is key to Nox-linked vascular oxidative stress and activation of the Rho kinase pathway.

Mitochondrial DNA and TLR9 activation contribute to SARS-CoV-2-induced endothelial cell damage.

BACKGROUND AND PURPOSE: Mitochondria play a central role in the host response to viral infection and immunity, being key to antiviral signaling and exacerbating inflammatory processes. Mitochondria and Toll-like receptor (TLR) have been suggested as potential targets in SARS-CoV-2 infection. However, the involvement of TLR9 in SARS-Cov-2-induced endothelial dysfunction and potential contribution to cardiovascular complications in COVID-19 have not been demonstrated. This study determined whether infection of endothelial cells by SARS-CoV-2 affects mitochondrial function and induces mitochondrial DNA (mtDNA) release. We also questioned whether TLR9 signaling mediates the inflammatory responses induced by SARS-CoV-2 in endothelial cells. EXPERIMENTAL APPROACH: Human umbilical vein endothelial cells (HUVECs) were infected by SARS-CoV-2 and immunofluorescence was used to confirm the infection. Mitochondrial function was analyzed by specific probes and mtDNA levels by real-time polymerase chain reaction (RT-PCR). Inflammatory markers were measured by ELISA, protein expression by western blot, intracellular calcium (Ca2+) by FLUOR-4, and vascular reactivity with a myography. KEY RESULTS: SARS-CoV-2 infected HUVECs, which express ACE2 and TMPRSS2 proteins, and promoted mitochondrial dysfunction, i.e. it increased mitochondria-derived superoxide anion, mitochondrial membrane potential, and mtDNA release, leading to activation of TLR9 and NF-kB, and release of cytokines. SARS-CoV-2 also decreased nitric oxide synthase (eNOS) expression and inhibited Ca2+ responses in endothelial cells. TLR9 blockade reduced SARS-CoV-2-induced IL-6 release and prevented decreased eNOS expression. mtDNA increased vascular reactivity to endothelin-1 (ET-1) in arteries from wild type, but not TLR9 knockout mice. These events were recapitulated in serum samples from COVID-19 patients, that exhibited increased levels of mtDNA compared to sex- and age-matched healthy subjects and patients with comorbidities. CONCLUSION AND APPLICATIONS: SARS-CoV-2 infection impairs mitochondrial function and activates TLR9 signaling in endothelial cells. TLR9 triggers inflammatory responses that lead to endothelial cell dysfunction, potentially contributing to the severity of symptoms in COVID-19. Targeting mitochondrial metabolic pathways may help to define novel therapeutic strategies for COVID-19.