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Linda Musil, Bruce Boswell; TGFB Induces Fiber Differentiation as well as Myofibroblast Transformation of Embryonic Chick Lens Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5888.
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Epithelial-to-mesenchymal transition (EMT) and fiber differentiation are abnormally upregulated in posterior capsule opacification (PCO) and anterior subcapsular cataract (ASC), disorders causally linked to enhanced TGFB signaling. Although it is well established that TGFB induces EMT in lens cells in vitro and in vivo, its role in the fiber-like changes associated with PCO and ASC are unknown. We tested the response to TGFB of serum-free primary cultures of embryonic chick lens epithelial cells (termed DCDMLs).
Expression of established markers of fiber differentiation and of EMT in lens cells was assessed by Western blotting, metabolic labeling, or immunocytochemistry.
Culturing DCDMLs in the presence of 4 ng/ml TGFB for > 4 d led to a large increase in the number of cells that express hallmarks of EMT including (1) decreased cell-cell interface staining and/or expression of vinculin, Cx43, and Z0-1, (2) increased expression of integrin alpha 5 in focal adhesions, and (3) expression of the myofibroblast marker alpha-smooth muscle actin (aSMA) in stress fibers. TGFB also induced in DCDMLs a striking increase in the number and size of lentoids that expressed fiber proteins such as delta-crystallin, CP49, MP28, and filensin. Lentoids were negative for EMT markers, and aSMA stress fiber-positive cells never expressed fiber markers. Inhibitors of FGF- or BMP- induced fiber differentiation had no effect on fiber upregulation by TGFB, and visa versa. Blocking p38 kinase activity prevented TGFB from promoting EMT in DCDMLs, but not fiber differentiation. The clinically used mTOR inhibitor rapamycin had the converse effect.
Unlike rat central epithelial explants, and similar to lens cells in vivo, DCDMLs do not respond to TGFB with massive cell loss and apoptosis. Instead, they undergo EMT or fiber-like changes (but not both in the same cell) via distinct signaling pathways. As the first culture system in which TGFB upregulates both myofibroblast and fiber differentiation, DCDMLs provide an unprecedented opportunity to identify the molecular mechanisms that govern these two cell fates, and are a novel system to screen for potential anti-PCO/ASC therapeutics.
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