Susanne Pfeiler

Acute hypoxia triggers multiple physiological and immune responses, yet the immediate systemic effects on circulating complement proteins remain insufficiently characterized. The complement cascade plays a central role in inflammation, host defense, and ischemia-related tissue injury, but its regulation during transient oxygen deprivation and reoxygenation in humans is poorly understood. Sixteen healthy volunteers were exposed to stepwise normobaric hypoxia simulating altitudes of 0, 2, 4, and 6 km (pO₂ = 9.64 kPa) followed by reoxygenation under normoxic conditions. Blood samples were collected at baseline, peak hypoxia (6 km), and after reoxygenation. Quantitative plasma proteomics was performed using targeted multiple-reaction-monitoring mass spectrometry to quantify key complement components (C1 complex, C3–C9, factor B) in 16 participants with complete datasets. Hematological parameters were analyzed in parallel. Hypoxia transiently increased leukocyte and platelet count, whereas hematocrit and mean corpuscular volume slightly decreased. While only slightly increasing during hypoxia, most complement peptides - including C1S, C1R, C3, C5, C7, C9, and CFAB - showed a coordinated reduction in relative abundance upon reoxygenation compared to both baseline and hypoxia (median fold-change ≈ 0.6–0.8; p < 0.05). Correlation analysis revealed coherent clustering among complement components but only weak associations with hematological indices. Acute hypoxia elicits rapid and reversible changes in the circulating complement peptide pool in healthy humans. Targeted plasma proteomics demonstrates clear oxygen-phase–dependent dynamics, with a coordinated decrease after reoxygenation. This pattern is consistent with reduced circulating availability of complement components, activation-associated consumption, and/or redistribution within the intravascular compartment. Future validation of these findings in certain patient cohorts may define translational relevance and functional consequences. Graphical abstract Sixteen healthy volunteers were exposed to stepwise normobaric hypoxia simulating altitudes of 0 km, 2 km, 4 km, and 6 km. Hypoxia increased plasma concentrations of several proteins of the complement system as analyzed by quantitative mass spectrometry. Upon reoxygenation, most complement peptides decreased to or below baseline.

BACKGROUND: Red blood cells (RBCs) contribute to hemostasis and thrombosis by interacting with platelets via the FasL–FasR pathway to induce procoagulant activity and thrombin formation. Here, we identified a novel mechanism of platelet–RBC interaction via the CD36–TSP-1 (thrombospondin-1) signaling pathway that plays a prominent role in arterial thrombosis and abdominal aortic aneurysm (AAA) formation and progression. AAA is a life-threatening atherosclerotic-related disease, characterized by the progressive dilation of the abdominal aorta, due to chronic inflammation and extracellular matrix remodeling/degradation within the vessel wall. The objective of the present study was to elucidate a new mechanism of platelet–RBC interaction via the TSP1–CD36 axis and its significance for arterial thrombosis and the pathology of AAA. METHODS: TSP-1-deficient and CD36 cell-type-specific (RBCs and platelets) knock-out mice were analyzed in experimental mouse models of arterial thrombosis and AAA. Blood samples from patients with AAA from peripheral sites (laminar flow) and from inside the aneurysm segment (turbulent flow) were analyzed by flow cytometry and compared with age-matched controls. RESULTS: After platelet activation, platelet-released TSP-1 binds to CD36 at the RBC and platelet membrane to enhance procoagulant activity of both cells, leading to platelet aggregation and thrombosis. Patients with AAA exhibit enhanced procoagulant activity, elevated TSP-1 and CD36 plasma levels, as well as increased exposure of TSP-1 and CD36 at the RBC and platelet surface. In addition, biomechanically stress in the aneurysmal segment reinforces CD36 externalization on RBCs and platelets as well as the formation of platelet–RBC aggregates. In line, genetic deletion of either CD36 (RBC restricted) or TSP-1 protected mice against experimentally induced AAA formation. CONCLUSIONS: Our findings imply that CD36 on RBCs and platelets, as well as platelet-released TSP-1, contribute to procoagulant activity, playing a crucial role in arterial thrombosis and AAA progression.

BACKGROUND: Cardiogenic shock (CS) is a severe complication of acute myocardial infarction (AMI) leading to poor outcomes. Specific biomarkers, with subsequent validation of their prognostic relevance in CS, are urgently needed to improve therapies and outcomes. Accordingly, the present study investigated the plasma proteome using proximity extension assay technology to identify novel specific biomarkers with subsequent validation of their prognostic relevance in CS. METHODS: Using proximity extension assay (Olink Explore, 2942 proteins), the proteomic signature in the plasma of 9 AMI patients without shock and 8 AMI patients with CS (AMICS; exploration cohort) at admission was analyzed. Candidate biomarkers were measured in the plasma of 421 patients with AMICS from the CULPRIT-SHOCK cohort (Culprit Lesion Only PCI Versus Multivessel PCI in Cardiogenic Shock; REGISTRATION: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT01927549, validation cohort). Their prognostic relevance was assessed for 180-day survival as the primary end point. RESULTS: Proteome profiling was successful for 2925 proteins and identified VEGFR1 (vascular endothelial growth factor receptor 1, also known as Flt1) as elevated in AMICS compared with nonshock AMI in the exploration cohort ( P P P P <0.001). The levels of VEGFR1 in surviving (30 days; n=29) and nonsurviving (n=21) patients with AMICS were determined at different time points (days 0, 1, and 5) in a third cohort, showing continuously higher levels in nonsurvivors. CONCLUSIONS: Plasma proteomic screening identified VEGFR1 as an early biomarker in patients with AMICS that provided independent prognostic information in a large cohort of well-defined patients with AMICS.

Background/Objectives: Acute myocardial infarction (AMI), characterized by irreversible heart muscle damage and impaired cardiac function caused by myocardial ischemia, is a leading cause of global mortality. The damage associated with reperfusion, particularly mitochondrial dysfunction and reactive oxygen species (ROS) formation, has emerged as a crucial factor in the pathogenesis of cardiac diseases, leading to the recognition of mitochondrial proteins as potential markers for myocardial damage. This study aimed to identify differentially expressed proteins based on the type of cardiac injury, in particular those with and without reperfusion. Methods: Male C57Bl/6J mice were either left untreated, sham-operated, received non-reperfused AMI, or reperfused AMI. Twenty-four hours after the procedures, left ventricular (LV) function and morphological changes including infarct size were determined using echocardiography and triphenyl tetrazolium chloride (TTC) staining, respectively. In addition, plasma was isolated and subjected to untargeted mass spectrometry and, further on, the ELISA-based validation of candidate proteins. Results: We identified mitochondrial creatine kinase 2 (Ckmt2) as a differentially regulated protein in plasma of mice with reperfused but not non-reperfused AMI. Elevated levels of Ckmt2 were significantly associated with infarct size and impaired LV function following reperfused AMI, suggesting a specific involvement in reperfusion damage. Conclusions: Our study highlights the potential of plasma Ckmt2 as a biomarker for assessing reperfusion injury and its impact on cardiac function and morphology in the acute phase of MI.

Determination of infarct and scar size following myocardial infarction (MI) is commonly used to evaluate the efficacy of potential cardioprotective treatments in animal models. However, histological methods to determine morphological features in the infarcted heart have barely improved since implementation while still consuming large parts of the tissue and offering little options for parallel analyses. We aim to develop a new fluorescence technology for determining infarct area and area at risk that is comparable to 2,3,5-triphenyltetrazolium chloride (TTC) staining but allows for multiple analyses on the same heart tissue. For early and late time points following MI, we compared classical histochemical approaches with fluorescence staining methods. Reperfused MI was induced in male mice, the hearts were extracted 24 h, 7-, 21-, or 28-days later and fluorescently stained by combining Hoechst and phalloidin. This approach allowed for clear visualization of the infarct area, the area at ischemic risk and the remote area not affected by MI. The combined fluorescence staining correlated with the classic TTC/Evans Blue staining 24 h after MI (r = 0.8334). In later phases (>7 d) post-MI, wheat germ agglutinin (WGA) is equally accurate as classical Sirius Red (r = 0.9752), Masson’s (r = 0.9920) and Gomori’s Trichrome (r = 0.8082) staining for determination of scar size. Additionally, feasibility to co-localize fluorescence-stained immune cells in specific regions of the infarcted myocardium was demonstrated with this protocol. In conclusion, this new procedure for determination of post-MI infarct size is not inferior to classical TTC staining, yet provides substantial benefits, including the option for unbiased software-assisted analysis while sparing ample residual tissue for additional analyses. Overall, this enhances the data quality and reduces the required animal numbers consistent with the 3R concept of animal experimentation.

BACKGROUND: Whether aortic valve stenosis (AS) can adversely affect systemic endothelial function independently of standard modifiable cardiovascular risk factors is unknown. METHODS: We therefore investigated endothelial and cardiac function in an experimental model of AS mice devoid of standard modifiable cardiovascular risk factors and human cohorts with AS scheduled for transcatheter aortic valve replacement. Endothelial function was determined by flow-mediated dilation using ultrasound. Extracellular hemoglobin (eHb) concentrations and nitric oxide (NO) consumption were determined in blood plasma of mice and humans by ELISA and chemiluminescence. This was complemented by measurements of aortic blood flow using 4-dimensional flow acquisition by magnetic resonance imaging and computational fluid dynamics simulations. The effects of plasma and red blood cell (RBC) suspensions on vascular function were determined in transfer experiments in a murine vasorelaxation bioassay system. RESULTS: In mice, the induction of AS caused systemic endothelial dysfunction. In the presence of normal systolic left ventricular function and mild hypertrophy, the increase in the transvalvular gradient was associated with elevated eryptosis, increased eHb, and increased plasma NO consumption; eHb sequestration by haptoglobin restored endothelial function. Because the aortic valve orifice area in patients with AS decreased, postvalvular mechanical stress in the central ascending aorta increased. This was associated with elevated eHb, circulating RBC-derived microvesicles, eryptotic cells, lower haptoglobin levels without clinically relevant anemia, and consecutive endothelial dysfunction. Transfer experiments demonstrated that reduction of eHb by treatment with haptoglobin or elimination of fluid dynamic stress by transcatheter aortic valve replacement restored endothelial function. In patients with AS and subclinical RBC fragmentation, the remaining circulating RBCs before and after transcatheter aortic valve replacement exhibited intact membrane function, deformability, and resistance to osmotic and hypoxic stress. CONCLUSIONS: AS increases postvalvular swirling blood flow in the central ascending aorta, triggering RBC fragmentation with the accumulation of hemoglobin in the plasma. This increases NO consumption in blood, thereby limiting vascular NO bioavailability. Thus, AS itself promotes systemic endothelial dysfunction independent of other established risk factors. Transcatheter aortic valve replacement is capable of limiting NO scavenging and rescuing endothelial function by realigning postvalvular blood flow to near physiological patterns. REGISTRATION: URL: https://www.clinicaltrials.gov ; Unique identifiers: NCT05603520 and NCT01805739.

Background: Determination of infarct area and scar size following myocardial infarction (MI) is commonly used to evaluate the efficacy of potential cardioprotective treatments in mice and other animal models. Methods: For both, early and late time points following MI, we compared classical histochemical approaches with fluorescence staining methods. Reperfused MI was induced in male C57BL/6J mice and hearts were extracted 24 hours, 7-, 21-, or 28-days following MI and stained with 2,3,5-Triphenyltetrazolium chloride (TTC) and Evans Blue, Hoechst, phalloidin, Sirius Red, Masson’s or Gomorís Trichrome or Wheat Germ Agglutinin (WGA). Results: Fluorescent staining combining Hoechst and phalloidin constitutes an alternative for TTC and Evans Blue, enabling a clear visualization of infarct area, area at risk, as well as remote area unaffected by MI. Infarct size early after reperfusion determined with TTC staining correlates strongly with that demarcated by phalloidin while combination of Hoechst and phalloidin staining can emulate classical TTC/Evans Blue staining 24 h post-MI. Moreover, WGA is equally accurate as the classical Sirius Red, Masson’s and Gomorís Trichrome stainings in identifying scar size in later phases (>7d) post-MI. Finally, we demonstrate feasibility of combining conventional fluorescence staining by localizing CD45 ⁺ leukocytes to specific regions of the infarcted myocardium. Conclusion: We established staining procedure is not inferior to classical TTC staining while providing substantial benefits including the option for unbiased software-assisted analysis while sparing ample residual tissue for additional analyses. Overall, this enhances the data quality and reduces the required animal numbers consistent with the 3R concept of animal experimentation. Graphical

Objective Inflammation is a critical process during the progressive development and complication of abdominal aortic aneurysm. The co-stimulatory dyad CD40-CD40L is a major driver of inflammation and modulates immune responses. This study evaluates the potential of a small molecule inhibitor, which blocks the interaction between CD40 and tumor necrosis factor (TNF) receptor-associated factor (TRAF)-6, referred to as TRAF-STOP, in the early and later phase during AAA progression. Methods and results AAAs were induced in C57BL/6J mice by infrarenal aortic porcine pancreatic elastase infusion for 7, 14 or 28 days. Inhibition of CD40 signaling by TRAF-STOP resulted in less severe AAA formation and reduced the incidence of AAA development. TRAF-STOP treatment attenuated aortic structural remodeling, characterized by a reduced elastic fiber degradation, lowered expression of matrix metalloproteinase (MMP)-2 and MMP9, as well as preserved collagen type IV content in aneurysmal tissue. Furthermore, this is accompanied by the reduction of key pro-inflammatory genes such as TNFα. Conclusion Pharmacological inhibition of CD40-TRAF6 signaling protects from adverse aortic structural remodeling during the early phase of AAA progression representing a translational strategy to limit progression of human AAA disease.

Background Abdominal aortic aneurysm (AAA) is a life-threatening cardiovascular disease, and the pathogenesis is still poorly understood. Recent evidence suggests that AAA displays characteristics of an autoimmune disease and it gained increasing prominence that specific antigen-driven T cells in the aortic tissue may contribute to the initial immune response. Single-cell RNA T- and B cell receptor (TCR and BCR) sequencing is a powerful tool to investigate TCR and BCR clonality and thus to further test this hypothesis. However, difficulties such as very limited numbers of isolated cells must be considered during implementation and data analysis making biological interpretation of the data challenging. Here, we perform a representative analysis of scRNA TCR and BCR sequencing data of experimental murine AAA and show a reliable and streamlined bioinformatic processing pipeline highlighting opportunities and limitations of this approach. Methods We performed single-cell RNA TCR and BCR sequencing of isolated lymphocytes from the infrarenal aortic segment of male C57BL/6J mice 3, 7, 14, and 28 days after AAA induction via elastase perfusion of the aorta. Sham operated mice at day 3 and 28 as well as non-operated mice served as controls. Results Comparison of complementarity-determining region (CDR3) length distribution of 179 B cells and 796 T cells revealed no differences between AAA and control nor between the disease stages. We found no clonal expansion of B cells in AAA. For T cells, we identified multiple clones in 11 of 16 AAA samples and in 1 of 8 control samples. Comparison of the immune receptor repertoires indicated that only few clones were shared between the individual AAA samples. The most frequently used V-genes in the TCR beta chain in AAA were TRBV3, TRBV19, and TRBV12-2+TRBV13-2. Conclusion In summary, we found no clonal expansion of TCRs or BCRs in elastase-induced AAA in mice. Our findings imply that a more precise characterization of TCR and BCR distribution requires a more extensive amount of T and B cells to prevent undersampling and to enable detection of potential rare clones. Using this current scSeq-based approach we did not identify clonal enrichment of T or B cells in experimental AAA.

Multiple receptors on platelets drive Alzheimer’s disease–associated amyloid deposits in brain vessels.