Background— We previously identified the G-protein–coupled receptor Mas, encoded by the Mas proto-oncogene, as an endogenous receptor for the heptapeptide angiotensin-(1-7); however, the receptor is also suggested to be involved in actions of angiotensin II. We therefore tested whether this could be mediated indirectly through an interaction with the angiotensin II type 1 receptor, AT ₁ . Methods and Results— In transfected mammalian cells, Mas was not activated by angiotensin II; however, AT ₁ receptor–mediated, angiotensin II–induced production of inositol phosphates and mobilization of intracellular Ca ²⁺ was diminished by 50% after coexpression of Mas , despite a concomitant increase in angiotensin II binding capacity. Mas and the AT ₁ receptor formed a constitutive hetero-oligomeric complex that was unaffected by the presence of agonists or antagonists of the 2 receptors. In vivo, Mas acts as an antagonist of the AT ₁ receptor; mice lacking the Mas gene show enhanced angiotensin II–mediated vasoconstriction in mesenteric microvessels. Conclusions— These results demonstrate that Mas can hetero-oligomerize with the AT ₁ receptor and by so doing inhibit the actions of angiotensin II. This is a novel demonstration that a G-protein–coupled receptor acts as a physiological antagonist of a previously characterized receptor. Consequently, the AT ₁ -Mas complex could be of great importance as a target for pharmacological intervention in cardiovascular diseases.

Dialysis and kidney transplant patients are vulnerable populations for COVID-19 related disease and mortality. We conducted a prospective study exploring the eight week time course of specific cellular (interferon-γ release assay and flow cytometry) or/and humoral immune responses (ELISA) to SARS-CoV-2 boost vaccination in more than 3100 participants including medical personnel, dialysis patients and kidney transplant recipients using mRNA vaccines BNT162b2 or mRNA-1273. SARS-CoV-2-vaccination induced seroconversion efficacy in dialysis patients was similar to medical personnel (> 95%), but markedly impaired in kidney transplant recipients (42%). T-cellular immunity largely mimicked humoral results. Major risk factors of seroconversion failure were immunosuppressive drug number and type (belatacept, MMF-MPA, calcineurin-inhibitors) as well as vaccine type (BNT162b2 mRNA). Seroconversion rates induced by mRNA-1273 compared to BNT162b2 vaccine were 97% to 88% (p < 0.001) in dialysis and 49% to 26% in transplant patients, respectively. Specific IgG directed against the new binding domain of the spike protein (RDB) were significantly higher in dialysis patients vaccinated by mRNA-1273 (95%) compared to BNT162b2 (85%, p < 0.001). Vaccination appeared safe and highly effective demonstrating an almost complete lack of symptomatic COVID-19 disease after boost vaccination as well as ceased disease incidences during third pandemic wave in dialysis patients. Dialysis patients exhibit a remarkably high seroconversion rate of 95% after boost vaccination, while humoral response is impaired in the majority of transplant recipients. Immunosuppressive drug number and type as well as vaccine type (BNT162b2) are major determinants of seroconversion failure in both dialysis and transplant patients suggesting immune monitoring and adaption of vaccination protocols.

Acute kidney injury (AKI) is morphologically characterized by a synchronized plasma membrane rupture of cells in a specific section of a nephron, referred to as acute tubular necrosis (ATN). Whereas the involvement of necroptosis is well characterized, genetic evidence supporting the contribution of ferroptosis is lacking. Here, we demonstrate that the loss of ferroptosis suppressor protein 1 (Fsp1) or the targeted manipulation of the active center of the selenoprotein glutathione peroxidase 4 (Gpx4^cys/-) sensitize kidneys to tubular ferroptosis, resulting in a unique morphological pattern of tubular necrosis. Given the unmet medical need to clinically inhibit AKI, we generated a combined small molecule inhibitor (Nec-1f) that simultaneously targets receptor interacting protein kinase 1 (RIPK1) and ferroptosis in cell lines, in freshly isolated primary kidney tubules and in mouse models of cardiac transplantation and of AKI and improved survival in models of ischemia-reperfusion injury. Based on genetic and pharmacological evidence, we conclude that GPX4 dysfunction hypersensitizes mice to ATN during AKI. Additionally, we introduce Nec-1f, a solid inhibitor of RIPK1 and weak inhibitor of ferroptosis.

Diabetic nephropathy is the leading cause of end-stage renal disease in humans in the Western world. The recent development of Na⁺-glucose cotransporter 2 (SGLT2) inhibitors offers a new antidiabetic therapy via enhanced glucose excretion. Whether this strategy exerts beneficial effects on the development of type 2 diabetic nephropathy is still largely unclear. We investigated the effects of the specific SGLT2 inhibitor empagliflozin in BTBR.Cg-Lep/WiscJ (BTBR ob/ ob) mice, which spontaneously develop type 2 diabetic nephropathy. In the first experiment, BTBR ob/ ob mice received either a diet containing 300 ppm empagliflozin or equicaloric placebo chow for 12 wk. In the second experiment, BTBR ob/ ob mice received 1 μg·kg body wt⁻¹·day⁻¹ ANG II to induce arterial hypertension and were separated into the same two diet groups for 6 wk. In both experiments, empagliflozin treatment enhanced glucosuria, thereby lowering blood glucose. Independently of hypertension, empagliflozin reduced albuminuria in diabetic mice. However, empagliflozin treatment affected diabetes-related glomerular hypertrophy, markers of renal inflammation, and mesangial matrix expansion only in BTBR ob/ ob mice without hypertension. In summary, empagliflozin demonstrated significant antihyperglycemic effects, differentially ameliorating early features of diabetic nephropathy in BTBR ob/ ob mice with and without hypertension.

Objectives: Recently, recombinant angiotensin-converting enzyme 2 was shown to protect mice from acute lung injury, an effect attributed to reduced bioavailability of angiotensin II. Since angiotensin-converting enzyme 2 metabolizes angiotensin II to angiotensin-(1–7), we hypothesized that this effect is alternatively mediated by angiotensin-(1–7) and activation of its receptor(s). Design: To test this hypothesis, we investigated the effects of intravenously infused angiotensin-(1–7) in three experimental models of acute lung injury. Setting: Animal research laboratory. Subjects: Male Sprague-Dawley rats, Balb/c mice, and C57Bl6/J mice. Interventions: Angiotensin-(1–7) was administered with ventilator- or acid aspiration–induced lung injury in mice or 30 minutes after oleic acid infusion in rats. In vitro, the effect of angiotensin-(1–7) on transendothelial electrical resistance of human pulmonary microvascular endothelial cells was analyzed. Measurements and Main Results: Infusion of angiotensin-(1–7) starting 30 minutes after oleic acid administration protected rats from acute lung injury as evident by reduced lung edema, myeloperoxidase activity, histological lung injury score, and pulmonary vascular resistance while systemic arterial pressure was stabilized. Such effects were largely reproduced by the nonpeptidic angiotensin-(1–7) analog AVE0991. Infusion of angiotensin-(1–7) was equally protective in murine models of ventilator- or acid aspiration–induced lung injury. In the oleic acid model, the two distinct angiotensin-(1–7) receptor blockers A779 and D-Pro⁷-angiotensin-(1–7) reversed the normalizing effects of angiotensin-(1–7) on systemic and pulmonary hemodynamics, but only D-Pro⁷-angiotensin-(1–7) blocked the protection from lung edema and protein leak, whereas A779 restored the infiltration of neutrophils. Rats were also protected from acute lung injury by the AT₁ antagonist irbesartan; however, this effect was again blocked by A779 and D-Pro⁷-angiotensin-(1–7). In vitro, angiotensin-(1–7) protected pulmonary microvascular endothelial cells from thrombin-induced barrier failure, yet D-Pro⁷-angiotensin-(1–7) or NO synthase inhibition blocked this effect. Conclusions: Angiotensin-(1–7) or its analogs attenuate the key features of acute lung injury and may present a promising therapeutic strategy for the treatment of this disease.