Three-dimensional tissue structure affects sensitivity of fibroblasts to TGF-beta 1

Transforming growth factor-(TGF-) is known to induce -smooth muscle actin (-SMA) infibroblasts and is supposed to play a role in myofibroblastdifferentiation and tumor desmoplasia. Our objective was to elucidatethe impact of TGF-1 on -SMA expression in fibroblasts in athree-dimensional (3-D) vs. two-dimensional (2-D) environment. Inmonolayer culture, all fibroblast cultures responded in a similarfashion to TGF-1 with regard to -SMA expression. In fibroblastspheroids, -SMA expression was reduced and induction by TGF-1 washighly variable. This difference correlated with a differentialregulation in the TGF- receptor (TGFR) expression, in particularwith a reduction in TGF-RII in part of the fibroblast types. Ourdata indicate that 1) sensitivity to TGF-1-induced -SMA expression in a 3-D environment is fibroblast-type specific, 2) fibroblast type-independent regulatory mechanisms, suchas a general reduction/loss in TGF-RIII, contribute to an altered TGFR expression profile in spheroid compared with monolayer culture, and 3) fibroblast type-specific alterations in TGFR typesI and II determine the sensitivity to TGF-1-induced -SMAexpression in the 3-D setting. We suggest that fibroblasts that can beinduced by TGF-1 to produce -SMA in spheroid culture reflect a"premyofibroblastic" phenotype.