A novel technique for quantifying mouse heart valve leaflet stiffness with atomic force microscopy.

BACKGROUND AND AIM OF THE STUDY: The use of genetically altered small animal models is a powerful strategy for elucidating the mechanisms of heart valve disease. However, while the ability to manipulate genes in rodent models is well established, there remains a significant obstacle in determining the functional mechanical properties of the genetically mutated leaflets. Hence, a feasibility study was conducted using micromechanical analysis via atomic force microscopy (AFM) to determine the stiffness of mouse heart valve leaflets in the context of age and disease states. METHODS: A novel AFM imaging technique for the quantification of heart valve leaflet stiffness was performed on cryosectioned tissues. Heart valve leaflet samples were obtained from wild-type mice (2 and 17 months old) and genetically altered mice (10-month-old Notch1 heterozygous and 20-month-old ApoE homozygous). Histology was performed on adjacent sections to determine the extracellular matrix characteristics of the scanned areas. RESULTS: The 17-month-old wild-type, 10-month-old Notch1, and 20-month-old ApoE aortic valve leaflets were all significantly stiffer than leaflets from 2-month-old wild-type mice. Notch1 leaflets were significantly stiffer than all other leaflets examined, indicating that the Notch1 heterozygous mutation may alter leaflet stiffness, both earlier and to a greater degree than the homozygous ApoE mutation. However, these conclusions must be considered only preliminary due to the small sample size used in this proof-of-concept study. CONCLUSION: It is believed that this technique can provide a powerful end-point analysis for determining the mechanical properties of heart valve leaflets from genetically altered mice. Further, the technique is complementary to standard histological processing, and does not require excess tissue for mechanical testing. In this proof-of-concept study, AFM was shown to be a powerful tool for investigators of heart valve disease who develop genetically altered animals for their studies.