Wire injury induced moderate aortic valve stenosis in mice is accompanied by a chronic systemic inflammatory reaction

Abstract Background Patients with aortic valve stenosis (AS) have elevated serum levels of inflammation markers, and blood cytokine levels correlate with ventricular recovery after transcatheter aortic valve replacement. While presence of inflammatory processes in stenotic aortic valves is acknowledged, no systematic characterization of the systemic immune reaction upon AS has been performed, yet. Purpose Hypothesis of this study was that AS induces a systemic inflammatory reaction linked with local processes in the heart. Methods AS was induced by wire injury (WI) or sham surgery was performed in 3-4 months old male C57Bl/6J mice. AS severity, left ventricular (LV) function and hypertrophy indices were assessed with echocardiography (echo). After four weeks, explanted organs were weighted, and flow cytometry identified total leukocyte numbers in blood, heart, and peripheral immune organs (spleen, liver, lymph nodes) and uptake of Cy5-labelled perfluorocarbon nanoemulsions by whole blood leukocytes. Costimulatory molecules (flow cytometry, RT-qPCR) and cytokines (RT-qPCR, Multiplex Immunoassay) were analysed in heart, peripheral immune organs and blood. Results R-values were positive for spleen weight correlation with AS severity, cardiac function and mass suggesting cardiac hypertrophy to preserve heart function. Myocardial myeloid and T cell r-values were positive or negative, respectively, for correlation with spleen and liver weight, hinting at T cell recruitment from peripheral stores. Immune cell numbers in peripheral lymph nodes and spleen showed negative r-values for correlation with heart hypertrophy indices; number of liver myeloid cells correlated negatively with LV wall thickness (monocytes=-0.8571, p=0.0238) suggesting immune cell recruitment to hypertrophic hearts. Cytokine mRNA levels trended mainly towards increase in heart and regional lymph nodes and reduction in spleen and liver after WI. Correlation with echo was more homogeneous after WI, with r-values mainly positive, except of T cell activation markers, for aortic valves, but negative for myocardium, hinting at mechanisms preserving heart function. Correlating unchanged cytokine protein levels in myocardium and plasma with echo, r-values were mostly positive for myocardium, and were more positive than in sham for plasma. Echo and costimulatory molecule correlation showed a more homogeneous pattern in WI, with mostly positive r-values in myocardium and periphery, while most r-values were negative in sham. Together with reduced PFC-uptake by lymphatic cells, this hints at systemic immune cell activation in AS. Conclusion The results suggest that number and activation state of leukocytes in peripheral organs are directly linked to cardiac processes in AS. Considering the pathological value of inflammation, it is crucial to in future studies find out if modulation of the systemic inflammatory reaction relieves severity of AS and prevents development of heart failure.