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S. L. Russell, I. M. Wormstone, A. R. Prescott, J. D. Rhodes; Cell Signalling Pathways Critical to Myotonic Dystrophy Lens Cell Survival. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4359.
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© ARVO (1962-2015); The Authors (2016-present)
Cataract is a key feature of Myotonic Dystrophy type 1 (DM). It has previously been shown that there is a greatly reduced cell density in the epithelia of DM lenses (Abe et al., British Journal of Ophthalmology, 1999). We have recently shown that DM lens cells have reduced cell growth and an impaired ability to withstand stress (Rhodes et al., Human Molecular Genetics, 2006). We have therefore investigated growth and survival pathways in DM lens cells.
Two cell lines were derived by SV40 transformation of lens capsulorhexis specimens, one from a normal donor lens and one from a DM cataract obtained immediately following cataract surgery. Cell growth was measured from total protein (BCA assay) and cell death was determined from LDH release. Levels of pAkt and pERK were detected by Western blotting. Conditioned medium (CM) was harvested from both cell types. CM was applied to the untransformed human lens cell line FHL-124 and the effects on cell signalling were determined.
It was found that DM lens cells have higher constitutive levels of pAkt and pERK than the control cells. The PI3-Kinase inhibitor, LY294002 (25 µM), caused greater cell death and reduced pAkt levels to a greater extent in the DM cells than the controls. Interestingly, treatment with LY294002 caused a stimulation of pERK that was greater in the DM cells. Inhibiting MEK with PD98059 (5 µM) reduced pERK by a similar amount in both cell lines, but caused a greater level of cell death in the control cell line. When applied to FHL-124 cells, DM CM increased cell growth to a greater extent than control CM. DM CM also activated pAkt more than control CM and this was inhibited by the FGF receptor inhibitor SU5402 (10 µM). ELISA analysis of bFGF showed that the concentration was 3 fold higher in DM CM compared to control CM.
Greatly increased cell death following inhibition of pAkt shows that this pathway is fundamental to DM lens cell survival. In contrast, in control cells there is a greater emphasis on cell growth via the MAP Kinase pathway, which appears less important in DM cells. Increased autocrine signalling and pAkt, possibly through FGF receptors, is therefore likely to be of major importance for DM cell survival.
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