Mouse models of congenital aortic valve malformations are useful for studying disease pathobiology, but most models have incomplete penetrance (e.g., ~2 to 77% prevalence of bicuspid aortic valves (BAVs) across multiple models). For longitudinal studies of pathologies associated with BAVs and other congenital valve malformations, which manifest over months in mice, it is operationally inefficient, economically burdensome, and ethically challenging to enroll large numbers of mice in studies without first identifying those with valvular abnormalities. To address this need, we established and validated a novel in vivo high frequency (30 MHz) ultrasound imaging protocol capable of detecting aortic valvular malformations in juvenile mice. Fifty natriuretic peptide receptor 2 heterozygous mice on a low density lipoprotein receptor deficient background (Npr2+/-;Ldlr-/-; 32 male, 18 female) were imaged at 4- and 8-weeks of age. Fourteen percent of the Npr2+/-;Ldlr-/- mice exhibited features associated with aortic valve malformations, including: i) abnormal trans-aortic flow patterns on color Doppler (recirculation and regurgitation); ii) peak systolic flow velocities distal to the aortic valves reaching or surpassing ~1250 mm/s by pulsed wave Doppler; and iii) putative fusion of cusps along commissures and abnormal movement elucidated by 2D imaging with ultra-high temporal resolution. Valves with these features were confirmed by ex vivo gross anatomy and histological visualization to have thickened cusps, partial fusions, or Sievers type 0 bicuspid valves. This ultrasound imaging protocol will enable efficient, cost-effective and humane implementation of studies of congenital aortic valvular abnormalities and associated pathologies in a wide range of mouse models.
Keywords: bicuspid aortic valve disease; congential valve disease; high frequency ultrasound; mouse model; natriuretic peptide receptor 2.