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Linda Musil; PCO and the TGFβ paradox. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3789.
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© ARVO (1962-2015); The Authors (2016-present)
In cancer, is it well know that TGFβ can act as a tumor suppressor as well as an enhancer of tumor growth (the so-called “TGFβ paradox”). In intact rodent lens in vivo and in our primary lens cell cultures, TGFβ can induce lens cells to undergo two very different, PCO-causing cell fates: differentiation into myofibroblasts, or into immature lens fiber cells. Because TGFβ signaling is linked to PCO, we are investigating how TGFβ can promote lens cells to adopt two such disparate phenotypes.
Serum-free, primary cultures of embryonic chick lens epithelial cells grown on laminin (DCDMLs) were treated with 4 ng/ml TGFβ for 6 days. The effect of manipulating signaling pathways on differentiation of DCDMLs was assessed using established markers of lens fiber cells (δ-crystallin, CP115, CP49; AQP0) or EMT (procollagen I, fibronectin; α-SMA in stress fibers). The activity of MTOR complex 2 (MTORC2) was assessed by monitoring the phosphorylation of its direct downstream target AKT on serine 473.
We have shown that in DCDMLs, inhibitors of p38 are among the conditions that prevent TGFβ from inducing EMT and myofibroblast differentiation without blocking lens fiber formation. Rapamycin has the opposite effect. Downregulation of TGFβ-induced fiber differentiation by rapamycin is associated with inhibition of MTORC2 in a process in which AKT does not appear to play a key role. A 6 day treatment with rapamycin also increased the proportion of cells in DCDMLs that have myofibroblast properties compared to cells cultured with TGFβ alone. We demonstrate that rapamycin’s ability to block fiber differentation is not a downstream consequence of upregulation of EMT, nor is enhancement of EMT dependent on decreased fiber formation. Inhibitors of p38 or MTOR do not affect cell viability or stimulate cell proliferation in the presence of TGFβ.
Inhibition of MTOR favors TGFβ-mediated fibrosis by both preventing lens fiber formation (likely by blocking MTORC2) and by upregulating myofibroblast differentiation (likely by inhibiting MTORC1). An individual lens epithelial cell does not appear to be preprogramed to respond to TGFβ by either differentiating into a lens fiber cell or into a myofibroblast, but instead has the capacity to undergo either cell fate depending on extrinsic factors. By understanding and manipulating these factors, lens cells could remain epithelial after cataract surgery, thereby preventing the development of PCO.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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