Details of the immune response and impact of the microbiome in murine calcific aortic valve stenosis

Abstract

Calcific aortic valve stenosis (AVS) is the most common heart valve disorder in Western countries. It results from complex cellular processes involving valvular interstitial, endothelial and immune cells, which lead to progressive fibro-calcific remodelling of the valve leaflets. With the years, remodelling culminates in impaired leaflet motion with hemodynamic consequences. Key pathophysiological mechanisms driving AVS are still poorly understood. At present, surgical intervention remains the only treatment option. Therefore, it is fundamental to unfold the mechanisms of disease initiation and progression to identify novel therapeutic venues. Here, we aimed at elucidating the details of the immune response and the impact of the gut microbiome in AVS onset and progression.<br /> Using a murine model of wire-induced AVS, we confirmed that immune cells infiltrate the aortic valve. Despite T and B cells being present in the pool of infiltrating cells, they did not play a key role in disease. In contrast, aortic valve-resident macrophages (AV-Mac) emerged as central players mitigating disease. Ablation of AV- Mac was associated with neutrophil-triggered coagulation and fibrin deposition that perpetuated the inflammatory response. Fibrin deposits turned into calcification foci, which further grew in a RANKL/Runx2-dependent manner.<br /> Furthermore, we sought to identify gut microbial candidates, or microbial-derived metabolites, that may influence disease. We provided evidence of direct impact of the gut microbiome on AVS. We showed that antibiotic conditioning of the gut microbiota dampened AVS development. Antibiotic treatment reduced the intestinal bacterial content without enrichment of any specific taxa. Pilot data suggested that microbiome- associated metabolites were most likely underlying the protective mechanisms. Further investigation is still required for molecular identification.<br /> In summary, here I report in vivo evidence of direct link between AV-Mac, their anti-thrombotic role and the fibrocalcific events during AVS, as well as preliminary evidence of the influence of the gut-microbiota in disease onset. Despite the need to continue gaining insights on the mechanisms behind both processes, these findings provide new cues for novel therapeutic approaches.