Horvat, M.; Caboor, L.; De Rycke, K.; Mennens, L.; Daniels, E.; Wyseur, J.; Verhelst, E.; Roos, I.; Rodriguez-Rovira, I.; Egea, G.; De Backer, J.; Sips, P.

Background: Marfan syndrome (MFS) is a life threatening heritable connective tissue disorder caused by pathogenic variants in fibrillin-1, characterized by progressive cardiovascular disease. Current medical therapies slow disease progression but do not prevent major complications, underscoring the need for new treatment strategies and unbiased discovery approaches. Methods: We used a zebrafish model of MFS lacking fibrillin 3 (fbn3-/-), which recapitulates key cardiovascular phenotypes including cardiac stress, valvular defects, arrhythmia, and aortic dilation. To enable sensitive, quantitative assessment of cardiac stress, we generated a novel transgenic zebrafish reporter expressing secreted nanoluciferase under control of the stress responsive nppb promoter. This reporter was combined with morphological phenotyping and bulbus arteriosus (BA) imaging. We evaluated standard MFS therapies, targeted modulators of TGF {beta} signaling, and performed an unbiased high throughput drug screen of over 1 500 clinically approved compounds across multiple developmental treatment windows. Results: fbn3-/- larvae exhibited markedly elevated nppb activity that correlated with phenotypic severity and peaked during stages of highest mortality. The nanoluciferase reporter provided a ~1 000 fold dynamic range, substantially outperforming Firefly luciferase based assays. Pharmacological inhibition of TGF-{beta} signaling produced transient or deleterious effects, while {beta}-blockers, losartan, and allopurinol failed to consistently improve cardiac stress, pericardial edema, or BA dilation. The unbiased high-throughput drug screen identified a small number of primary and secondary hits; however, none demonstrated reproducible phenotypic rescue upon rigorous multi dose, multi time window validation. Conclusions: This study establishes a sensitive zebrafish based platform for early, quantitative assessment of cardiovascular stress in MFS. Our findings highlight the limited efficacy of current therapies, the context dependent nature of TGF {beta} modulation, and the biological complexity underlying MFS pathogenesis. Although no definitive therapeutic candidates were identified, this work lays a robust foundation for expanded unbiased discovery efforts aimed at identifying disease modifying interventions for MFS.