The angiotensin type 2 receptor (AT2R) and the receptor MAS are receptors of the protective arm of the renin-angiotensin system. They mediate strikingly similar actions. Moreover, in various studies, AT2R antagonists blocked the effects of MAS agonists and vice versa. Such cross-inhibition may indicate heterodimerization of these receptors. Therefore, this study investigated the molecular and functional interplay between MAS and the AT2R. Molecular interactions were assessed by fluorescence resonance energy transfer and by cross correlation spectroscopy in human embryonic kidney-293 cells transfected with vectors encoding fluorophore-tagged MAS or AT2R. Functional interaction of AT2R and MAS was studied in astrocytes with CX3C chemokine receptor-1 messenger RNA expression as readout. Coexpression of fluorophore-tagged AT2R and MAS resulted in a fluorescence resonance energy transfer efficiency of 10.8 ± 0.8%, indicating that AT2R and MAS are capable to form heterodimers. Heterodimerization was verified by competition experiments using untagged AT2R and MAS. Specificity of dimerization of AT2R and MAS was supported by lack of dimerization with the transient receptor potential cation channel, subfamily C-member 6. Dimerization of the AT2R was abolished when it was mutated at cysteine residue 35. AT2R and MAS stimulation with the respective agonists, Compound 21 or angiotensin-(1-7), significantly induced CX3C chemokine receptor-1 messenger RNA expression. Effects of each agonist were blocked by an AT2R antagonist (PD123319) and also by a MAS antagonist (A-779). Knockout of a single of these receptors made astrocytes unresponsive for both agonists. Our results suggest that MAS and the AT2R form heterodimers and that-at least in astrocytes-both receptors functionally depend on each other.

The angiotensin type 2 receptor (AT2R) and the receptor Mas are components of the protective arms of the renin-angiotensin system (RAS), i.e. they both mediate tissue protective and regenerative actions. The spectrum of actions of these two receptors and their signalling mechanisms display striking similarities. Moreover, in some instances, antagonists for one receptor are able to inhibit the action of agonists for the respective other receptor. These observations suggest that there may be a functional or even physical interaction of both receptors. This article discusses potential mechanisms underlying the phenomenon of blockade of angiotensin-(1-7) [Ang-(1-7)] actions by AT2R antagonists and vice versa. Such mechanisms may comprise dimerization of the receptors or dimerization-independent mechanisms such as lack of specificity of the receptor ligands used in the experiments or involvement of the Ang-(1-7) metabolite alamandine and its receptor MrgD in the observed effects. We conclude that evidence for a functional interaction of both receptors is strong, but that such an interaction may be species- and/or tissue-specific and that elucidation of the precise nature of the interaction is only at the very beginning.

β-Glucan derived from cell walls of Candida albicans is a potent immune modulator. It has been shown to induce trained immunity in monocytes via epigenetic and metabolic reprogramming and to protect from lethal sepsis if applied prior to infection. Since β-glucan-trained monocytes have not been classified within the system of mononuclear phagocytes we analyzed these cells metabolically, phenotypically and functionally with a focus on monocyte-to-macrophage differentiation and compared them with naïve monocytes and other types of monocyte-derived cells such as classically (M1) or alternatively (M2) activated macrophages and monocyte-derived dendritic cells (moDCs). We show that β-glucan inhibits spontaneous apoptosis of monocytes independent from autocrine or paracrine M-CSF release and stimulates monocyte differentiation into macrophages. β-Glucan-differentiated macrophages exhibit increased cell size and granularity and enhanced metabolic activity when compared to naïve monocytes. Although β-glucan-primed cells expressed markers of alternative activation and secreted higher levels of IL-10 after lipopolysaccharide (LPS), their capability to release pro-inflammatory cytokines and to kill bacteria was unaffected. Our data demonstrate that β-glucan priming induces a population of immune competent long-lived monocyte-derived macrophages that may be involved in immunoregulatory processes.

Background & Aims Retention of bile acids in the blood is a hallmark of liver failure. Recent studies have shown that increased serum bile acid levels correlate with bacterial infection and increased mortality. However, the mechanisms by which circulating bile acids influence patient outcomes still are elusive. Methods Serum bile acid profiles in 33 critically ill patients with liver failure and their effects on Takeda G-protein–coupled receptor 5 (TGR5), an immunomodulatory receptor that is highly expressed in monocytes, were analyzed using tandem mass spectrometry, novel highly sensitive TGR5 bioluminescence resonance energy transfer using nanoluciferase (NanoBRET, Promega Corp, Madison, WI) technology, and in vitro assays with human monocytes. Results Twenty-two patients (67%) had serum bile acids that led to distinct TGR5 activation. These TGR5-activating serum bile acids severely compromised monocyte function. The release of proinflammatory cytokines (eg, tumor necrosis factor α or interleukin 6) in response to bacterial challenge was reduced significantly if monocytes were incubated with TGR5-activating serum bile acids from patients with liver failure. By contrast, serum bile acids from healthy volunteers did not influence cytokine release. Monocytes that did not express TGR5 were protected from the bile acid effects. TGR5-activating serum bile acids were a risk factor for a fatal outcome in patients with liver failure, independent of disease severity. Conclusions Depending on their composition and quantity, serum bile acids in liver failure activate TGR5. TGR5 activation leads to monocyte dysfunction and correlates with mortality, independent of disease activity. This indicates an active role of TGR5 in liver failure. Therefore, TGR5 and bile acid metabolism might be promising targets for the treatment of immune dysfunction in liver failure.

Extracorporeal albumin dialysis (ECAD) represents a supplemental therapy for patients with liver failure. Most experience was gained with the molecular adsorbent recirculating system (MARS). However, the ADVanced Organ Support (ADVOS) system was recently introduced. This study aims to compare effects of MARS and ADVOS on biochemical and clinical parameters in critically ill patients with liver failure using a retrospective analysis of ECAD at Jena University Hospital. Laboratory parameters, health scoring values, and need for transfusion were recorded before and after treatment. Generalized estimating equations were used to account for repeated measurements of multiple ECAD cycles per patient. Between 2012 and 2017, n = 75 MARS and n = 58 ADVOS cycles were evaluated. Although ADVOS runs significantly longer, both devices provided comparable reduction rates of bilirubin (MARS: −48 [−80.5 to −18.5] μmol/L vs ADVOS: −35 [−87.8 to −2.0] μmol/L, P = .194), a surrogate for detoxification capacity, while urea and lactate levels were more significantly lowered by the ADVOS system. In cycles with similar treatment times, both systems provided comparable reduction rates for bilirubin, renal replacement, coagulation, and metabolic parameters. Citrate was the preferred anticoagulant in case of bleeding. Neither bleeding tendency nor fibrinogen levels or platelets were altered by the type of anticoagulation. No adverse events were reported, but two sessions (one MARS and one ADVOS) were terminated early due to filter clotting. Experience is needed in the application of ADVOS and more prospective trials comparing the detoxification capacity of ECAD devices are needed to support and enlarge the findings of the current evaluation.