Role of the renin-angiotensin system in the development of severe COVID-19 in hypertensive patients.

A new form of severe acute respiratory syndrome (SARS) caused by SARS-coronavirus 2 (CoV-2), called COVID-19, has become a global threat in 2020. The mortality rate from COVID-19 is high in hypertensive patients, making this association especially dangerous. There appears to be a consensus, despite the lack of experimental data, that angiotensin II (ANG II) is linked to the pathogenesis of COVID-19. This process may occur due to acquired deficiency of angiotensin-converting enzyme 2 (ACE2), resulting in reduced degradation of ANG II. Furthermore, ANG II has a critical role in the genesis and worsening of hypertension. In this context, the idea that there is a surge in the level of ANG II with COVID-19 infection, causing multiple organ injuries in hypertensive patients becomes attractive. However, the role of other components of the renin angiotensin system (RAS) in this scenario requires elucidation. The identification of other RAS components in COVID-19 hypertension may provide both diagnostic and therapeutic benefits. Here, we summarize the pathophysiologic contributions of different components of RAS in hypertension and their possible correlation with poor outcome observed in hypertensive patients with COVID-19.

Angiotensin II type-1 receptor (AT1R) regulates expansion, differentiation, and functional capacity of antigen-specific CD8+ T cells.

Angiotensin II (Ang II) and its receptor AT1 (AT1R), an important effector axis of renin-angiotensin system (RAS), have been demonstrated to regulate T-cell responses. However, these studies characterized Ang II and AT1R effects using pharmacological tools, which do not target only Ang II/AT1R axis. The specific role of AT1R expressed by antigen-specific CD8+ T cells is unknown. Then we immunized transgenic mice expressing a T-cell receptor specific for SIINFEKL epitope (OT-I mice) with sporozoites of the rodent malaria parasite Plasmodium berghei expressing the cytotoxic epitope SIINFEKL. Early priming events after immunization were not affected but the expansion and contraction of AT1R-deficient (AT1R-/-) OT-I cells was decreased. Moreover, they seemed more activated, express higher levels of CTLA-4, PD-1, LAG-3, and have decreased functional capacity during the effector phase. Memory AT1R-/- OT-I cells exhibited higher IL-7Rα expression, activation, and exhaustion phenotypes but less cytotoxic capacity. Importantly, AT1R-/- OT-I cells show better control of blood parasitemia burden and ameliorate mice survival during lethal disease induced by blood-stage malaria. Our study reveals that AT1R in antigen-specific CD8+ T cells regulates expansion, differentiation, and function during effector and memory phases of the response against Plasmodium, which could apply to different infectious agents.

Interaction between bradykinin B2 and Ang-(1-7) Mas receptors regulates erythrocyte invasion by Plasmodium falciparum.

BACKGROUND: The molecular mechanisms involved in erythrocyte invasion by malaria parasite are well understood, but the contribution of host components is not. We recently reported that Ang-(1-7) impairs the erythrocytic cycle of P. falciparum through Mas receptor-mediated reduction of protein kinase A (PKA) activity. The effects of bradykinin (BK), a peptide of the kallikrein-kinin system (KKS), can be potentiated by Ang-(1-7), or angiotensin-converting enzyme (ACE) inhibitors, such as captopril. We investigated the coordinated action between renin-angiotensin system (RAS) and KKS peptides in the erythrocyte invasion by P. falciparum. METHODS: We used human erythrocytes infected with P. falciparum to assess the influence of RAS and KKS peptides in the invasion of new erythrocytes. RESULTS: The inhibitory effects of Ang-(1-7) were mimicked by captopril. 10(-8)M BK decreased new ring forms and this effect was sensitive to 10(-8)M HOE-140 and 10(-7)M A779, B2 and Mas receptor antagonists, respectively. However, DALBK, a B1 receptor blocker, had no effect. The inhibitory effect of Ang-(1-7) was reversed by HOE-140 and A779 at the same concentrations. Co-immunoprecipitation assay revealed an association between B2 and Mas receptors. BK also inhibited PKA activity, which was sensitive to both HOE-140 and A779. CONCLUSIONS: The results suggest that B2 and Mas receptors are mediators of Ang-(1-7) and BK inhibitory effects, through a cross-signaling pathway, possibly by the formation of a heterodimer. GENERAL SIGNIFICANCE: Our results describe new elements in host signaling that could be involved in parasite invasion during the erythrocyte cycle of P. falciparum.

Group V Secretory Phospholipase A2 Is Involved in Tubular Integrity and Sodium Handling in the Kidney.

Group V (GV) phospholipase A2 (PLA2) is a member of the family of secreted PLA2 (sPLA2) enzymes. This enzyme has been identified in several organs, including the kidney. However, the physiologic role of GV sPLA2 in the maintenance of renal function remains unclear. We used mice lacking the gene encoding GV sPLA2 (Pla2g5-/-) and wild-type breeding pairs in the experiments. Mice were individually housed in metabolic cages and 48-h urine was collected for biochemical assays. Kidney samples were evaluated for glomerular morphology, renal fibrosis, and expression/activity of the (Na+ + K+)-ATPase α1 subunit. We observed that plasma creatinine levels were increased in Pla2g5-/- mice following by a decrease in creatinine clearance. The levels of urinary protein were higher in Pla2g5-/- mice than in the control group. Markers of tubular integrity and function such as γ-glutamyl transpeptidase, lactate dehydrogenase, and sodium excretion fraction (FENa+) were also increased in Pla2g5-/- mice. The increased FENa+ observed in Pla2g5-/- mice was correlated to alterations in cortical (Na+ + K+) ATPase activity/ expression. In addition, the kidney from Pla2g5-/- mice showed accumulation of matrix in corticomedullary glomeruli and tubulointerstitial fibrosis. These data suggest GV sPLA2 is involved in the maintenance of tubular cell function and integrity, promoting sodium retention through increased cortical (Na+ + K+)-ATPase expression and activity.

5-Lypoxygenase products are involved in renal tubulointerstitial injury induced by albumin overload in proximal tubules in mice.

The role of albumin overload in proximal tubules (PT) in the development of tubulointerstitial injury and, consequently, in the progression of renal disease has become more relevant in recent years. Despite the importance of leukotrienes (LTs) in renal disease, little is known about their role in tubulointerstitial injury. The aim of the present work was to investigate the possible role of LTs on tubulointerstitial injury induced by albumin overload. An animal model of tubulointerstitial injury challenged by bovine serum albumin was developed in SV129 mice (wild-type) and 5-lipoxygenase-deficient mice (5-LO(-/-)). The changes in glomerular morphology and nestin expression observed in wild-type mice subjected to kidney insult were also observed in 5-LO(-/-) mice. The levels of urinary protein observed in the 5-LO(-/-) mice subjected or not to kidney insult were lower than those observed in respective wild-type mice. Furthermore, the increase in lactate dehydrogenase activity, a marker of tubule damage, observed in wild-type mice subjected to kidney insult did not occur in 5-LO(-/-) mice. LTB4 and LTD4, 5-LO products, decreased the uptake of albumin in LLC-PK1 cells, a well-characterized porcine PT cell line. This effect correlated with activation of protein kinase C and inhibition of protein kinase B. The level of proinflammatory cytokines, tumor necrosis factor-α and interleukin (IL)-6, increased in mice subjected to kidney insult but this effect was not modified in 5-LO(-/-) mice. However, 5-LO(-/-) mice subjected to kidney insult presented lower macrophage infiltration and higher levels of IL-10 than wild-type mice. Our results reveal that LTs have an important role in tubulointerstitial disease induced by albumin overload.

Inhibitory effects of Trypanosoma cruzi sialoglycoproteins on CD4+ T cells are associated with increased susceptibility to infection.

BACKGROUND: The Trypanosoma cruzi infection is associated with severe T cell unresponsiveness to antigens and mitogens characterized by decreased IL-2 synthesis. Trypanosoma cruzi mucin (Tc Muc) has been implicated in this phenomenom. These molecules contain a unique type of glycosylation consisting of several sialylated O-glycans linked to the protein backbone via N-acetylglucosamine residues. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we evaluated the ability of Tc Muc to modulate the activation of CD4(+) T cells. Our data show that cross-linking of CD3 on naïve CD4(+) T cells in the presence of Tc Muc resulted in the inhibition of both cytokine secretion and proliferation. We further show that the sialylated O-Linked Glycan residues from tc mucin potentiate the suppression of T cell response by inducing G1-phase cell cycle arrest associated with upregulation of mitogen inhibitor p27(kip1). These inhibitory effects cannot be reversed by the addition of exogenous IL-2, rendering CD4(+) T cells anergic when activated by TCR triggering. Additionally, in vivo administration of Tc Muc during T. cruzi infection enhanced parasitemia and aggravated heart damage. Analysis of recall responses during infection showed lower frequencies of IFN-γ producing CD4(+) T cells in the spleen of Tc Muc treated mice, compared to untreated controls. CONCLUSIONS/SIGNIFICANCE: Our results indicate that Tc Muc mediates inhibitory efects on CD4(+) T expansion and cytokine production, by blocking cell cycle progression in the G1 phase. We propose that the sialyl motif of Tc Muc is able to interact with sialic acid-binding Ig-like lectins (Siglecs) on CD4(+) T cells, which may allow the parasite to modulate the immune system.

Angiotensin II is a new component involved in splenic T lymphocyte responses during Plasmodium berghei ANKA infection.

The contribution of T cells in severe malaria pathogenesis has been described. Here, we provide evidence for the potential role of angiotensin II (Ang II) in modulating splenic T cell responses in a rodent model of cerebral malaria. T cell activation induced by infection, determined by 3 to 4-fold enhancement in CD69 expression, was reduced to control levels when mice were treated with 20 mg/kg losartan (IC50 = 0.966 mg/kg/d), an AT1 receptor antagonist, or captopril (IC50 = 1.940 mg/kg/d), an inhibitor of angiotensin-converting enzyme (ACE). Moreover, the production of interferon-γ and interleukin-17 by CD4+ T cells diminished 67% and 70%, respectively, by both treatments. Losartan reduced perforin expression in CD8+ T cells by 33% while captopril completely blocked it. The upregulation in chemokine receptor expression (CCR2 and CCR5) observed during infection was abolished and CD11a expression was partially reduced when mice were treated with drugs. T cells activated by Plasmodium berghei ANKA antigens showed 6-fold enhance in AT1 levels in comparison with naive cells. The upregulation of AT1 expression was reduced by losartan (80%) but not by captopril. Our results suggest that the AT1/Ang II axis has a role in the establishment of an efficient T cell response in the spleen and therefore could participate in a misbalanced parasite-induced T cell immune response during P. berghei ANKA infection.

AT1 receptor-mediated angiotensin II activation and chemotaxis of T lymphocytes.

Angiotensin II (Ang II), a central renin-angiotensin system (RAS) effector molecule, and its receptors, AT(1) and AT(2), have been shown to be involved in the inflammatory aspects of different diseases, however the cellular mechanisms underlying the regulation of immunity are not fully understood. In this work, using spleen-derived CD4(+) and CD8(+) T lymphocytes activated in vitro, we tested the influence of Ang II on different aspects of the T cell function, such as activation and adhesion/transmigration through endothelial basal membrane proteins. The addition of 10(-8)M Ang II did not change any of the parameters evaluated. However, 10(-6)M losartan, an AT(1) receptor antagonist: (i) reduced the percentage of CD25(+) and CD69(+) cells of both subsets; (ii) inhibited adhesion of these cells to fibronectin or laminin by 53% or 76%, respectively and (iii) significantly reduced transmigration through fibronectin or laminin by 57% or 43%, respectively. In addition, 10(-6)M captopril, an angiotensin-converting enzyme inhibitor had similar effects to Ang II, however its effects were reverted by exogenous Ang II (10(-8)M). None of these responses was modified by 10(-7)M PD123319, an AT(2) antagonist. These data reinforce the notion of endogenous production of Ang II by T cells, which is important for T cell activation, and adhesion/transmigration induced on interaction with basal membrane proteins, possibly involving AT(1) receptor activation. Moreover, AT(1) receptor expression is 10-fold higher in activated T lymphocytes compared with naive cells, but AT(2) receptor expression did not change after T cell receptor triggering.