Background and aim of the study: Myxomatous mitral valves (MVs) contain elevated proportions of myofibroblasts, a valve interstitial cell (VIC) subpopulation that may be important in disease pathogenesis. A novel technique was recently developed for the isolation of VIC myofibroblasts using time-dependent adhesion to fibronectin (FN). Cells that adhere rapidly to FN ('FAST') demonstrate myofibroblast cell phenotype markers, in contrast to cells that fail to adhere after a longer time ('SLOW'). The study aim was to characterize the functionality of these subpopulations using three-dimensional (3D) collagen constructs.

Methods: The VICs were harvested from porcine mitral valve posterior leaflets. FAST and SLOW subpopulations, as well as unseparated VIC populations grown on FN and tissue culture plastic (TCP) (UNSEP FN, UNSEP TCP), were seeded within 3D collagen gels and cultured for three weeks. Collagen gel contraction was assessed throughout the culture duration; the mechanical properties of the resultant collagen constructs were assessed using uniaxial tensile testing.

Results: FAST cells demonstrated a greater contraction of collagen gels compared to SLOW cells, particularly after 10 days (p < 0.05). Interestingly, the collagen gel contraction by both FN-separated VIC subpopulations (FAST and SLOW) was greater than for gels seeded with UNSEP TCP VICs (p < 0.05). Further, the contraction of UNSEP FN gels was greater than UNSEP TCP throughout the culture duration (p < OR = 0.002), suggesting that the subculture of VICs on FN potentiated these phenotypic changes. Finally, the collagen constructs seeded with FAST cells were stiffer than those seeded with SLOW, followed by UNSEP TCP (p < 0.001). The same pattern was found for failure stress (p = 0.006).

Conclusion: Time-dependent adhesion to FN produced a VIC subpopulation (FAST), the function of which in 3D culture was consistent with that of myofibroblasts; FN exposure alone also caused VICs to function similarly to myofibroblasts. This novel isolation method may prove valuable in future studies of myofibroblasts in valve disease.