Extracellular ASC Specks as Drivers and Drug Targets in Calcific Aortic-Valve Stenosis.

• Applicants: Dr. Benedikt Bartsch; Professor Dr. Bernardo Franklin
• Subject Area: Cardiology, Angiology ; Cardiac and Vascular Surgery ; Clinical Immunology and Allergology
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574394705

Aortic stenosis (AS) is the most common form of heart valve disease globally. Despite significant advancements in valve replacement in recent years, symptomatic AS continues to be associated with high morbidity and mortality. Calcific aortic valve stenosis is marked by gradual fibro-calcific remodeling and thickening of the valve leaflets, ultimately resulting in impaired valve opening and obstructed blood flow. Mounting evidence shows that chronic, sterile inflammation is a key driver of harmful immune-cell infiltration and mineral deposition that stiffen the valve. Central to this response is the NLRP3 inflammasome. When triggered, NLRP3 assembles macromolecular signaling platforms by recruiting the adapter protein ASC, forming the so-called ASC specks. ASC specks serve as hubs for the activation of caspase-1, provoking the lytic death program known as pyroptosis. We have discovered that upon pyroptosis, ASC specks are released from dying cells and continue to sustain inflammation in the extracellular space. Extracellular ASC specks (eASC) are remarkably stable and persist in tissues, where they act as long-lived alarmins that perpetuate inflammation. We therefore propose that eASC fuel the calcific remodeling of the aortic valve and represent an as-yet unrecognized driver of AS. Our goal is to test this hypothesis rigorously and to determine whether eASC can be neutralized by single-domain antibodies (nanobodies) as a first step toward a disease-modifying therapy. To achieve this goal, we will follow a translational path that links patient samples, cultured human valve cells and a well-validated mouse model of calcific AS. First, newly optimized assays will be used to quantify eASC in the blood of patients spanning the full spectrum of AS severity and to map their exact distribution within explanted valve tissue. Next, primary human valvular endothelial and interstitial cells will be exposed to pro-inflammatory and pro-calcific cues in vitro so that we can define how inflammasome activation generates ASC specks and how the specks themselves reinforce fibrotic and osteogenic responses; loss- and gain-of-function experiments will establish causality. In parallel, we will visualize the appearance and spread of eASC in vivo by subjecting ASC–mCherry reporter mice to AS induced by valvular wire injury. Finally, we will treat injured mice with nanobodies that dismantle ASC polymers without disturbing normal intracellular defenses, and we will evaluate valve architecture and trans-valvular flow. By tracing eASC from the molecular level to whole-animal physiology and back to human disease, this program will provide the first evidence of their role in AS. This project will not only uncover a new pathogenic mechanism but also lay the groundwork for a drug capable of delaying, or even preventing, the need for valve replacement in an aging population.

• DFG Programme: Research Grants