Fig. 5.

Exogenous periostin is sufficient to induce a contractile phenotype. (A) The effect of periostin (PN) deletion on the ability of dermal fibroblasts to exert contractile force in a fixed, tethered floating collagen gel lattice was investigated using a culture force monitor. Forces generated by fibroblasts were measured over 24 hours; a representative trace is shown (n=3). (B) Cells contracted collagen gels over an additional 24 hours at 37°C, 5% CO₂. (C) Gel contraction was quantified by loss of gel weight, compared with gels lacking cells. Postn^−/− (KO) fibroblasts were unable to significantly contract collagen gels. Note that Postn^+/+ (WT) fibroblasts were able to contract collagen gels. Addition of 5 μg/ml rhPN to the collagen gels rescued the contractile ability of Postn^−/− fibroblasts (n=3). Data is expressed as a fraction of the initial gel weight; error bars represent s.d. (*P<0.05; two-way ANOVA). (D) Gels were treated with 10 μM PP2 (or DMSO vehicle) or 10 μg/ml β1-integrin blocking antibody (mouse IgG for controls). Data are expressed as a fraction of the initial gel weight; error bars represent s.d. (*P<0.05; one-way ANOVA, n=3). A Dunnett's multiple comparison test was used where Postn^−/−, rhPN and DMSO were used as the reference group. Extracellular periostin influences contractility through a β1-integrin- and FAK-dependent mechanism in vitro. (E) Fluorescent labeling of fibroblast populated collagen gels for α-SMA (green) and nuclei (blue). α-SMA-positive cells were counted in high magnification fields of view. Percentage of α-SMA-positive cells was significantly reduced in Postn^−/− fibroblast populated gels (P<0.01; n=3). Addition of 5 μg/ml rhPN to the collagen gels restored the percentage of α-SMA-positive cells. Data are expressed as mean; error bars represent s.d. (^#P<0.01; one-way ANOVA).