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Maryada Sharma, Hetian Lei, Steven Pennock, Andrius Kazlauskas; Epithelial cells promote fibroblast-mediated contraction of collagen gels by secreting bFGF. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6258.
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Fibrotic diseases compromise the function of many organs (e.g. skin, liver, heart, lung, kidneys) and arise at least in part from a breakdown in the relationship between epithelial and mesenchymal cells. One such disease is proliferative vitreoretinopathy (PVR), a blinding condition that has the quintessential feature of fibrotic diseases of being difficult to manage. In many cases, the pathogenesis of PVR involves formation of a tractional, fibrotic membrane populated by retinal pigment epithelial (RPE) cells and fibroblasts. The overall goal of this study was to investigate the nature of the relationship between these two cell types, with a particular focus on contraction.
Collagen gel contraction assay, which is an in vitro model for PVR, was used to assess the contraction abilities of RPE cells and fibroblasts in absence or presence of desired treatments. Condition medium (CM) was generated from RPE cells grown at high cell density in DMEM without serum for 24-48 hr. A panel of 16 growth factors and cytokines that are implicated in PVR were quantified in CM by multiplex assay, and the best candidates were tested for their relative contribution to contraction by using neutralizing antibodies against them. The CM and potential candidate were tested for their ability to promote signalling events that are intrinsic to PVR.
We discovered that while the intrinsic ability of RPE cells to contract collagen type I gels was dramatically lower than fibroblasts, RPEs greatly enhanced contraction of fibroblast-loaded collagen gels by secreting soluble factors. bFGF (basic fibroblast growth factor) was an essential component of the contraction promoting activity that RPEs secreted. Conditioned medium from human mammary epithelial cells also induced maximal contraction of fibroblast-containing collagen gels, and this activity was dependent on bFGF. In contrast to the nearly complete contraction of collagen gels observed under these conditions, TGFβs (transforming growth factor βs) or PDGF (platelet-derived growth factor) induced only a submaximal response.
We conclude that epithelial cells promote maximal contraction of fibroblasts by secreting growth factors such as bFGF. These insights provide a conceptual foundation for the design of approaches to prevent and manage fibrotic diseases that are driven by a dysfunctional relationship between epithelial cells and fibroblasts.
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