Post-transcriptional regulation of alpha-smooth muscle actin determines the contractile phenotype of Dupuytren's nodular cells

Abstract

The objective was to study Dupuytren's myofibroblast cells in constrained collagen matrices in order to more closely emulate their in vivo environment and, to correlate their contractility with -smooth muscle actin (-SMA) expression and determine if dermal fibroblasts regulate Dupuytren's myofibroblast phenotype. Isotonic and isometric force contraction by cells isolated from Dupuytren's nodules, palmar and non-palmar skin fibroblasts was measured in collagen matrices. The effect of co-culturing nodule cells with dermal fibroblasts on isometric contraction was examined. Isometric contraction was correlated with levels of -SMA mRNA by pcr and protein by Western blotting, and -SMA distribution assessed by immunofluorescence. Dupuytren's nodule cells exhibited similar levels of isotonic contraction to both palmar and non-palmar dermal fibroblasts. However, nodule cells generated high levels of isometric force (mean: 3.5 dynes/h), which continued to increase over 24 h to a maximum of 173 dynes. In contrast, dermal fibroblasts initially exhibited low levels of contraction (mean: 0.5 dynes/h) and reached tensional homeostasis on average after 15 h (range: 4–20 h), with a maximum force of 52 dynes. Although all three cell types had similar -SMA mRNA levels, increased levels of -SMA protein were observed in nodule cells compared to dermal fibroblasts. -SMA localised to stress fibres in 35% (range: 26–50%) of nodule cells compared to only 3% (range:0–6%) of dermal fibroblasts. Co-cultures of Dupuytren's cells and dermal fibroblasts showed no contractile differences. The contractile phenotype of Dupuytren's myofibroblasts is determined by increased -SMA protein distributed in stress fibres, not by cellular mRNA levels. Dupuytren's cell contractility is not influenced by dermal fibroblasts.