PO101 Using a novel zebrafish model for Marfan syndrome to search for novel treatment options

Background Aortic aneurysm and dissection are the primary causes of morbidity and mortality in Marfan syndrome (MFS), a connective tissue disorder caused by pathogenic variants in the fibrillin-1 gene. While timely surgical repair significantly increases life expectancy, lethal aortic dissection still occurs. This underscores the urgent need for versatile animal models to investigate disease mechanisms and identify new therapeutic targets. Purpose After systematically disrupting all fibrillin genes in zebrafish, we identified fibrillin-2b-deficient (fbn2b-/-) zebrafish as a suitable model for MFS. This zebrafish model provides a powerful platform for evaluating existing therapies and identifying novel drug candidates. Methods fbn2b-/- zebrafish were subjected to detailed cardiovascular phenotyping by fluorescent microscopy in embryonic stages, and cardiac ultrasound, histology, and synchrotron X-ray imaging in adults. We screened over 1500 FDA-approved compounds in fbn2b-/- zebrafish using a genetically encoded reporter for detecting cardiovascular stress. Positive hits were further assessed for phenotypic rescue. Additionally, we tested a β-adrenergic receptor blocker and an angiotensin receptor blocker, both commonly prescribed to patients with MFS. Results Approximately 60% of fbn2b-/- zebrafish embryos develop atrial endocardial detachment and pericardial edema by 2-3 dpf. The majority of these embryos progress to vascular embolism, loss of blood flow, and death at 7-9 dpf. The remaining fbn2b-/- zebrafish survive normally but develop dilation of the bulbus arteriosus during larval stages, which persists into adulthood. Adult fbn2b-/- zebrafish also show cardiac valve abnormalities. The high-throughput drug screen identified a number of promising candidate compounds, although a drug leading to robust phenotypic rescue is yet to be discovered. β-adrenergic and angiotensin receptor inhibition failed to reverse the mutant phenotype. Nevertheless, this outcome is consistent with clinical observations suggesting that these drugs do not directly target the underlying pathophysiological mechanisms driving the core cardiovascular manifestations of MFS. Interestingly, when assessing heart rate modulation in fbn2b-/- larvae, we observed an exaggerated negative chronotropic response to β-adrenergic receptor inhibition, indicating a potentially elevated baseline sympathetic tone. Conclusions The fbn2b-/- zebrafish model effectively recapitulates different aspects of the cardiovascular pathology observed in patients with MFS. This allows us to do in vivo compound screens to investigate underlying disease mechanisms and search for new therapeutic targets. While neither current clinical treatments nor compounds identified through the first round of unbiased high-throughput drug screening produced strong phenotypic rescue, these findings underscore the complexity of the disease and the pressing need for continued efforts to identify effective treatments.