Abstract 19693: Modeling Adaptive Growth -- Biomimetic Culture of Neonatal Aortic Root Explants

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Background: Heart valve disease afflicts individuals of all ages, but current treatments, involving replacement with non-viable prosthetics, are particularly suboptimal for young patients. To design “growing” valve replacements, postnatal growth mechanisms must be elucidated; models of adaptive growth are lacking, thereby hindering these investigations. We hypothesized that physiologic mechanical loading with growth factor stimulation would enable the adaptive growth of aortic root explants in vitro. To this end, we designed a biomimetic perfusion bioreactor that permits the concomitant delivery of these factors. Methods and Results: We constructed a chamber for culturing neonatal rat hearts under pulsatile flow conditions. Parameters were adjusted to mimic native physiology using ultrasound assessment of cusp motion and invasive measurement of left ventricular and aortic pressures. Culture medium was designed by quantification of key growth factor (IGF-1, TGF-β 2 , VEGF, EGF, BMP-2 and FGF-2) concentrations within age-matched serum via ELISA. Explants were cultured for five days. Controls were explanted from age- and size-matched pups. Dynamically-cultured samples exhibited similar proliferation rates at early time points when compared to those of valve cusps in vivo as assessed by EdU incorporation (10.5% vs. 14.9%, p=0.35). After five days of dynamic culture, native proliferation rates were achieved only with concomitant growth factor administration (13.3% control; 13.1% dynamic+GF; 3.1% dynamic alone). There was no evidence of proliferation in statically-cultured controls. Conclusions: We describe a novel biomimetic culture system that permits the modeling of adaptive growth in aortic root explants. Our results demonstrate recapitulation of in vivo cell proliferation rates in dynamically-cultured hearts and suggest a role for mechanical and humoral stimulation in mediating aortic valve growth. This system enables the elucidation and manipulation of the mechanisms driving postnatal heart valve growth, thereby informing the design of the ideal pediatric valve graft with adaptive growth potential.