Valvular interstitial cells (VICs) constitute the most prominent cell type in aortic valve cusps. VICs are a heterogeneous group of cells of multiple origins with mostly fibroblast properties. Like fibroblasts in general, VICs can acquire an activated state (myofibroblasts) upon exposure to several stimuli including mediators of inflammation, growth factors, mechanical stress or changes of ECM composition. An increase of activated VICs in adult valves is considered as indicator of pathological developments. Cultivation of VICs using standard 2D cell culture procedures also induces VIC activation resulting in contraction and spontaneous nodule formation. Our previous work has shown that this phenotype switch can be reversed by exposure to polyunsaturated fatty acids (PUFAs). In order to investigate underlying cellular mechanisms of the PUFA effects, VICs from porcine aortic valves were isolated and subcultured on collagen-coated surfaces. Spontaneous nodule formation after transfer to uncoated polystyrene was completely blocked by docosahexaenoic acid (DHA) and arachidoic acid (ARA) whereas eicosapentaenoic acid and a commercial extract from fish oil (Omacor) were less active. Oleic acid and palmitic acid were without effect. Treatment with ARA or DHA reduced the expression of myofibroblast marker proteins, α-smooth muscle actin (SMA) and myosin II, of a key enzyme of collagen synthesis (prolyl 4-hydroxylase), and of the phosphorylated (inactive) form of the F-actin severing protein, cofilin. In contrast, the abundance of fibroblast marker S100A4 was increased after treatment with PUFAs. The steady state level of active RhoA was reduced in the presence of DHA and ARA, and inhibition of RhoA or ROCK elicited the same effects as PUFAs. Finally, exposure to ARA and DHA reduced the G/F-actin ratio, and stabilization of F-actin with jasplakinolide blocked the effect of PUFAs on the expression of myofibroblast markers and on nodule formation. After culturing VICs with PUFAs for 14 days and subsequently in the absence of PUFAs for 4 days, cells regained the myofibroblast phenotype, showing the PUFA-induced phenotype switch was fully reversible. In conclusion, the results suggest that the differentiation of VICs to myofibroblasts can be truly reversed by certain PUFAs via the RhoA – ROCK – G-actin pathway, whereas an alternative mechanism, the preferential outgrowth of a undifferentiated subpopulation of VICs, seems to be unlikely since the PUFA effect was fully reversible.


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  • Accepted: 28 May 2012
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