Background:
Fibrosis contributes to many heart valve diseases such as calcific aortic valve disease, rheumatic heart disease, and secondary mitral regurgitation. Heart valve leaflets are populated by quiescent, fibroblast-like valve interstitial cells (VICs). During fibrosis, VICs differentiate into activated, myofibroblast-like cells that adversely remodel the extracellular matrix. Activated VICs overexpress α-smooth muscle actin (ACTA2/αSMA) and smooth muscle 22-α (TAGLN/SM22α) and display increased contractility. Tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) have been reported to either promote or inhibit fibrosis, depending on tissue type. Understanding how TNF-α and IL-1β affect VIC activation in the mitral valve of the heart could enable development of pharmaceutical treatments for heart valve diseases, which are currently managed surgically.
Methods:
To avoid artifactual activation on tissue culture plastic, VICs were encapsulated in biomimetic scaffolds consisting of polyethylene glycol (4% w/v) functionalized with protease-degradable (GGGPQGIWGQGK) and integrin-binding (RGDS) peptides. These 3D cultures were treated with 10 ng/ml TNF-α, 10 ng/ml IL-1β, or vehicle for 2 days in low-serum (1%) media. RNA and protein were measured via qRT-PCR, western blotting, and immunostaining. To measure contractility, VICs were encapsulated in collagen I (2.5 mg/ml) gels and allowed to contract freely for 2 days.
Results:
TNF-α and IL-1β significantly decreased RNA expression of ACTA2 (TNF-α: -91±6%, IL-1β: -99±1% change vs. vehicle) and TAGLN (TNF-α: -77±9%, IL-1β: -93±1% change). TNF-α and IL-1β also significantly decreased αSMA protein expression (TNF-α: -76±11%, IL-1β: -91±5% change) and the percentage of αSMA-positive cells (vehicle: 21±3%, TNF-α: 13±2%, IL-1β: 13±5% positive). Finally, TNF-α and IL-1β attenuated VIC-mediated collagen gel contraction (vehicle: 81±7%, TNF-α: 71±3%, IL-1β: 61±4% contraction).
Conclusions:
TNF-α and IL-1β decrease VIC activation in a 3D culture model of the mitral valve. These results reveal novel pathway targets for reducing fibrosis during mitral valve disease. Future work will use this model to study the downstream signaling events that drive VIC de-activation.
Dynamic Heterogeneity of the Heart Valve Interstitial Cell Population in Mitral Valve Health and Disease