Pathomechanisms Underlying Hypoxemia in Two COVID-19-Associated Acute Respiratory Distress Syndrome Phenotypes: Insights From Thrombosis and Hemostasis

BACKGROUND

The pathomechanisms of hypoxemia and treatment strategies for type H and type L acute respiratory distress syndrome (ARDS) in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced coronavirus disease 2019 (COVID-19) have not been elucidated.

MAIN TEXT

SARS-CoV-2 mainly targets the lungs and blood, leading to ARDS, and systemic thrombosis or bleeding. Angiotensin II-induced coagulopathy, SARS-CoV-2-induced hyperfibrin(ogen)olysis, and pulmonary and/or disseminated intravascular coagulation due to immunothrombosis contribute to COVID-19-associated coagulopathy. Type H ARDS is associated with hypoxemia due to diffuse alveolar damage-induced high right-to-left shunts. Immunothrombosis occurs at the site of infection due to innate immune inflammatory and coagulofibrinolytic responses to SARS-CoV-2, resulting in microvascular occlusion with hypoperfusion of the lungs. Lung immunothrombosis in type L ARDS results from neutrophil extracellular traps containing platelets and fibrin in the lung microvasculature, leading to hypoxemia due to impaired blood flow and a high ventilation/perfusion (VA/Q) ratio. COVID-19-associated ARDS is more vascular centric than the other types of ARDS. D-dimer levels have been monitored for the progression of microvascular thrombosis in COVID-19 patients. Early anticoagulation therapy in critical patients with high D-dimer levels may improve prognosis, including the prevention and/or alleviation of ARDS.

CONCLUSIONS

Right-to-left shunts and high VA/Q ratios caused by lung microvascular thrombosis contribute to hypoxemia in type H and L ARDS, respectively. D-dimer monitoring-based anticoagulation therapy may prevent the progression to and/or worsening of ARDS in COVID-19 patients.

Angiotensin (ang) 1-7 inhibits ang II-induced atrial fibrosis through regulating the interaction of proto-oncogene tyrosine-protein kinase Src (c-Src) and Src homology region 2 domain-containing phosphatase-1 (SHP-1))

To verify whether Ang-(1-7) produces an antagonistic effect on Ang II-mediated atrial remodeling. Ang II–induced HL-1 cell model and a rat model of Ang II–induced atrial remodeling were constructed and intervened with Ang II Ang-(1-7), AngII +Ang-(1-7), Ang II+ c-Src specific inhibitor (SU6656), and Ang II + Ang-(1-7) + SSG (SHP-1/2 specific inhibitor, stibogluconate), respectively. The systolic blood pressure of the rat caudal artery was detected. And trial fibrosis was detected by Picrosirius red staining and Masson’s trichrome staining. Expressions of transforming growth factor-β (TGF-β), tissue inhibitor of metalloproteinases 1 (TIMP1), Matrix metalloproteinase 2 (MMP-2), connective tissue growth factor (CTGF), galectin-3, α-smooth muscle actin (α-SMA), and collagen I/III were subjected to qPCR and western blot. Furthermore, SHP-1 binding to c-Src was verified by co-immunoprecipitation (Co-IP). Results showed that the expressions of TGF-β, TIMP1, MMP-2, CTGF, α-SMA, galectin-3, and collagen I were increased markedly in the Ang II intervention group, and the expressions of p-ERK1/2, p-Akt, and p-p38MAPK were also increased dramatically. Ang-(1-7) or SU6656 addition could inhibit the action of Ang II factor, thereby minimizing the expressions of the previously described genes and proteins. Simultaneously, SSG supplement reversed the antagonistic effect of Ang-(1-7) on Ang II, and the latter elevated the blood pressure and induced atrial fibrosis in rats. Ang-(1-7) could reverse the changes related to Ang II–induced atrial fibrosis in rats. In conclusion, Ang-(1-7) antagonized Ang II–induced atrial remodeling by regulating SHP-1 and c-Src, thereby affecting the MAPKs/Akt signaling pathway.

RhACE2 - playing an important role in inhibiting apoptosis induced by Ang II in HUVECs

BACKGROUND

Henoch-Schonlein purpura (HSP) is a common hemorrhagic disease, which manifests the inflammation in the body's most microvasculars. Angiotensin II (Ang II) can induce the damage and apoptosis of vascular endothelial cells while angiotensin converting enzyme 2 (ACE2) can antagonist the action of Ang II. However, the effect of ACE2 on Ang II-induced endothelial damage remains unknown.

OBJECTIVE

To evaluate the effect of recombinant human angiotensin converting enzyme 2 (rhACE2) on the Ang II-induced damage of human umbilical vein endothelial cells (HUVECs) and the release of inflammatory mediator in vitro.

METHODS

Cultured HUVECs were randomly divided into 6 groups: the control group, rhACE2 group, Ang II group, and Ang II+ rhACE2 groups (3 subgroups). The cell vitality, cell cycle, apoptosis rate of the HUVECs and the levels of reactive oxygen species (ROS), interleukin 8 (IL-8), tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1) and lactate dehydrogenase (LDH) were measured, respectively.

RESULTS

Compared with the control group, the cell viability and the rate of S phase cells in Ang II group significantly decreased (P < .05) while the apoptosis percentage and the levels of ROS, IL-8, TNF-α, TGF-β1, and LDH in Ang II group significantly increased (P < .05). There were no significant differences between the control group and rhACE2 group. Compared with the Ang II group, the cell viability and the rate of S phase cells in Ang II+rhACE2 groups were higher (P < .05) and the apoptosis percentage, the level of ROS, IL-8, TNF-α, TGF-β1, LDH in Ang II+rhACE2 groups were lower (P < .05).

CONCLUSIONS

Ang II can induce the apoptosis of HUVECs and the release of inflammatory mediator, while rhACE2 can inhibit the detrimental effects of Ang II. The results of this study suggest that rhACE2 has a protective effect on HSP, which is probably a new way for the prevention and treatment of HSP.

1-Sarcosine-angiotensin II infusion effects on food intake, weight loss, energy expenditure, and skeletal muscle UCP3 gene expression in a rat model

BACKGROUND

There are a myriad of proteins responsible for modulation of expenditure of energy. Angiotensin II (Ang II) is a vital component of renin-angiotensin system that affects blood pressure and also linked to both cachexia and obesity via fat and muscle metabolism. Previous research suggests that the direct action of Ang II is on the brain, via angiotensin II type 1 receptor protein, affecting food intake and energy expenditure. The objective of the study is to investigate the effect of 1-sarcosine (SAR)-Ang II infusion on energy expenditure and metabolism in a rat model of congestive heart failure cachexia.

METHODS

Adult female rats of the Sprague Dawley strain (n = 33) were used (11 pair-fed control, 12 ad libitum and 10, 1-sarcosine-angiotensin II-infused rats). Body weight, faecal excretion, feed intake (in grams), water intake (in milliliters) and urine excreted were recorded daily. The measurements were recorded in three different periods (4 days prior to surgery, "pre-infusion"; day of surgery and 5 days postsurgery, "infusion period"; days 7 to 14, "recovery" period). Different analytical methods were used to measure energy expenditure per period, uncoupling protein 3 mRNA expression, crude protein and adipose tissue body composition.

RESULTS

During the infusion period, the SAR-Ang II group experienced rapid weight loss (p < 0.05) in comparison to the ad libitum and pair-fed groups. The SAR-Ang II group displayed lower (p < 0.05) body fat content (in percent) than the controls. There was also increased (p < 0.05) uncoupling protein 3 (UCP3) mRNA expression in the SAR-Ang II group and pair-fed group when compared to the controls.

CONCLUSION

In summary, the results suggest that SAR-Ang II infusion impairs appetite and decreases body weight by wasting predominantly adipose tissue, which may be due to elevated energy expenditure via mitochondrial uncoupling (UCP3 protein activity).

Mechanism of Ang II involvement in activation of NF-κB through phosphorylation of p65 during aging

Angiotensin II (Ang II), a major effector of the renin-angiotensin system, is now recognized as a pro-inflammatory mediator. This Ang II signaling, which causes transcription of pro-inflammatory genes, is regulated through nuclear factor-κB (NF-κB). At present, the molecular mechanisms underlying the effect of aging on Ang II signaling and NF-κB activation are not fully understood. The purpose of this study was to document altered molecular events involved in age-related changes in Ang II signaling and NF-κB activation. Experimentations were carried out using kidney tissues from Fischer 344 rats at 6, 12, 18, and 24 months of age, and the rat endothelial cell line, YPEN-1 for the detailed molecular work. Results show that increases in Ang II and Ang II type 1 receptor during aging were accompanied by the generation of reactive species. Increased Ang II activated NF-κB by phosphorylating IκBα and p65. Increased phosphorylation of p65 at Ser 536 was mediated by the enhanced phosphorylation of IκB kinase αβ, while phosphorylation site Ser 276 of p65 was mediated by upregulated mitogen-activated and stress-activated protein kinase-1. These altered molecular events in aged animals were partly verified by experiments using YPEN-1 cells. Collectively, our findings provide molecular insights into the pro-inflammatory actions of Ang II, actions that influence the phosphorylation of p65-mediated NF-κB activation during aging. Our study demonstrates the age-related pleiotropic nature of the physiologically important Ang II can change into a deleterious culprit that contributes to an increased incidence of many chronic diseases such as atherosclerosis, diabetes, and dementia.

The role of TASK1 in aldosterone production and its expression in normal adrenal and aldosterone-producing adenomas

OBJECTIVES

Aldosterone production in the adrenal glomerulosa is mainly regulated by angiotensin II and K+. Adrenal glomerulosa cells are uniquely sensitive to extracellular K+. Genetic deletion of subunits of K+-selective leak-channels (KCNK), TASK1 and/or TASK3, in mice generates animals with hyperaldosteronism and histological changes in the adrenal cortex. Herein, we studied the expression of TASK1 in human adrenocortical cells, as well as its role in aldosterone production in H295R cells.

DESIGN

TASK1 expression was investigated by comparative microarray analysis of aldosterone-producing adenomas (APA) and normal adrenals (NAs). The effects of TASK1 knockdown by siRNA transfection were investigated in H295R cells. Fluo-4 fluorescent measurements of intracellular Ca2+ and pharmacological inhibition of Ca2+ -dependent calmodulin kinases (CaMK) were performed to better define the effects of TASK1 on Ca2+ signalling pathways.

RESULTS

Microarray analysis of APA and NA showed similar expression of TASK1 between these two groups. However, in APA, NA and H295R cells the expression of TASK1 was predominant when compared with other KCNK family members. Knockdown of TASK1 (with siRNA) induced the expression of steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2), and also stimulated pregnenolone and aldosterone production. Cells transfected with siTASK1 had increased intracellular Ca2+, leading to activation of CaMK and increased expression of CYP11B2.

CONCLUSIONS

Our study reveals the predominant expression of TASK1 over other KCNK family genes in the human adrenal cortex. Herein, we also described the role of TASK1 in the regulation of human aldosterone production through regulation of intracellular Ca2+ and CaMK signalling pathways.

Angiotensin-II-induced apoptosis requires regulation of nucleolin and Bcl-xL by SHP-2 in primary lung endothelial cells

Angiotensin II (Ang II) is a key proapoptotic factor in fibrotic tissue diseases. However, the mechanism of Ang-II-induced cell death in endothelial cells has not been previously elucidated. Using the neutral comet assay and specific receptor antagonists and agonists, we found that Ang-II-mediated apoptosis in primary pulmonary endothelial cells required the AT2 receptor. Ang II caused cytochrome c release from the mitochondria concurrent with caspase-3 activation and DNA fragmentation, and apoptosis was suppressed by an inhibitor of Bax-protein channel formation, implicating mitochondrial-mediated apoptosis. There was no evidence that the extrinsic apoptotic pathway was involved, because caspase-9, but not caspase-8, was activated by Ang-II treatment. Apoptosis required phosphoprotein phosphatase activation, and inhibition of the SHP-2 phosphatase (encoded by Ptpn11) blocked cell death. Reduced levels of anti-apoptotic Bcl-2-family members can initiate intrinsic apoptosis, and we found that Ang-II treatment lowered cytosolic Bcl-x(L) protein levels. Because the protein nucleolin has been demonstrated to bind Bcl-x(L) mRNA and prevent its degradation, we investigated the role of nucleolin in Ang-II-induced loss of Bcl-x(L). RNA-immunoprecipitation experiments revealed that Ang II reduced the binding of nucleolin to Bcl-x(L) mRNA in an AU-rich region implicated in instability of Bcl-x(L) mRNA. Inhibition of SHP-2 prevented Ang-II-induced degradation of Bcl-x(L) mRNA. Taken together, our findings suggest that nucleolin is a primary target of Ang-II signaling, and that Ang-II-activated SHP-2 inhibits nucleolin binding to Bcl-x(L) mRNA, thus affecting the equilibrium between pro- and anti-apoptotic members of the Bcl-2 family.

Angiotensin II blocks nicotine-mediated neuroprotection against beta-amyloid (1-42) via activation of the tyrosine phosphatase SHP-1

We showed recently that nicotine activates the growth-promoting enzyme Janus kinase 2 (JAK2) in PC12 cells and that preincubation of these cells with the JAK2-specific inhibitor AG-490 blocked the nicotine-induced neuroprotection against beta-amyloid (1-42) [Abeta (1-42)]. These results provided direct evidence for linkage between JAK2 and the alpha7 nicotinic acetylcholine receptor-induced neuroprotection in PC12 cells. We also showed that preincubation with angiotensin II (Ang II), functioning via the angiotensin II type 2 (AT2) receptor, blocked both the nicotine-induced activation of JAK2 and its neuroprotection against Abeta (1-42). Recently growth-inhibitory effects of the AT2 receptor have been reported to be mediated by the activation of protein tyrosine phosphatases (PTPases) and that AT2 receptor stimulation is associated with a rapid activation of the PTPase SHP-1 (the cytoplasmic tyrosine phosphatase that contains Src homology 2 domains), a negative regulator of JAK2 signaling. Therefore, the potential biological significance of AT2 receptor-induced effects on both the nicotine-induced activation of JAK2 and its neuroprotection against Abeta (1-42) led us to investigate whether SHP-1 activation could be involved in this process. We found that Ang II induced the activation of SHP-1 and that an antisense against SHP-1 not only augmented the nicotine-induced tyrosine phosphorylation of JAK2 but also blocked the Ang II neutralization of the nicotine-induced neuroprotection. These results demonstrate that nicotine-induced tyrosine phosphorylation of JAK2 and neuroprotection against Abeta (1-42) in PC12 cells are blocked by Ang II via AT2 receptor-induced activation of SHP-1.

Urinary excretion of angiotensinogen reflects intrarenal angiotensinogen production

BACKGROUND

In rats maintained on a high salt diet (H/S) to suppress basal renal angiotensinogen levels, angiotensin II (Ang II) infusion for 13 days increased renal angiotensinogen mRNA and protein, thus providing a mechanism for further augmentation of intrarenal Ang II levels. The present study tested the hypothesis that enhanced intrarenal angiotensinogen formation during Ang II infusion is reflected by secretion into the tubular fluid leading to increased urinary excretion of angiotensinogen (UAGT).

METHODS

The effects of chronic Ang II infusion were examined on kidney and plasma Ang II levels and UAGT in male Sprague-Dawley rats maintained on an 8% salt diet for three weeks (N=10). Following one week on the H/S diet, Ang II (40 ng/min) was administered for two weeks via an osmotic minipump to one group (H/S + Ang II, N=5), while the remaining rats were sham-operated (H/S + Sham, N=5). Additionally, a control group was prepared with normal salt diet and sham-operation (N/S + Sham, N=5).

RESULTS

H/S alone did not alter systolic blood pressure (BP) (103 +/- 2 vs. 104 +/- 2 mm Hg), while Ang II infusion to H/S rats significantly increased systolic BP from 103 +/- 2 to 154 +/- 2 after two weeks. Intrarenal Ang II content in H/S + Ang II was significantly greater than H/S + Sham (435 +/- 153 vs. 65 +/- 14 fmol/g). Ang II infusion significantly increased UAGT (4.0 +/- 0.5 vs. 1.0 +/- 0.2 nmol Ang I/day by radioimmunoassay of generated Ang I; 57 +/- 15 vs. 14 +/- 2 densitometric units by Western blotting analysis) compared to Sham. UAGT by radioimmunoassay was highly correlated with kidney Ang II content (r=0.79); but not with plasma Ang II concentration (r=0.20).

CONCLUSIONS

These data demonstrate that chronic Ang II infusion increases urinary excretion rate of angiotensinogen, and suggest that UAGT provides a specific index of intrarenal angiotensinogen production in Ang II-dependent hypertension.