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Janice L Walker, Liping Zhang, Tung Chan, A Sue Menko; Myofibroblast emergence is induced in a PI3K isoform-specific Akt-independent manner in a mock cataract surgery model of PCO. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
This study examined whether a Phosphatidylinositol 3-kinase (PI3K) signal transduction pathway was key to induction of myofibroblast emergence in a mock cataract surgery model for the lens fibrotic disease Posterior Capsule Opacification (PCO). PI3K is a lipid kinase, composed of a regulatory subunit and a catalytic subunit. Class I PI3K p110 catalytic subunits, α, β, δ and γ, were investigated for their potential to regulate the intracellular signaling pathway that promotes fibrosis. The α, β, and δ isoforms are activated downstream of many inductive pathways including receptor tyrosine kinases. The γ isoform is an effector of G-protein coupled receptor signaling. There are many distinct downstream effectors PI3K signaling that include the classical Akt/PKB-dependent as well as Akt/PKB-independent PI3K signaling pathways. We examined Akt as a possible transducer of the PI3K pro-fibrotic signal.
An ex vivo mock cataract surgery lens epithelial explant model was used that recapitulates the major features of PCO. These studies focused on the cells that migrate off the edges of the explant onto the Extra Capsular Zone of the tissue culture substrate, a rigid pro-fibrotic microenvironment in which myofibroblast emergence is rapidly induced. Inhibitors included a pan-PI3K inhibitor, specific inhibitors of the class I PI3K isoforms p110α, p110β, p110δ/γ, and distinct inhibitors of Akt. Myofibroblast emergence was determined by Western Blot (WB) and immunofluorescence (IF) for aSMA. Effects on expression of Fibronectin EDA (FN EDA), the FN isoform associated with induction and progression of fibrosis was examined by IF.
Myofibroblast emergence was regulated in a PI3K isoform-specific manner. Inhibitors to PI3K p110a and p110β effectively blocked emergence of aSMA+ myofibroblasts and prevented organization of a FN EDA matrix. In contrast, inhibition of PI3K p110 γ/δ had no effect. Isoform specific inhibitors of PI3K all suppressed Akt activation yet two functionally distinct inhibitors for Akt did not prevent myofibroblast emergence or production of FN EDA. These results suggest that PI3K transduces a fibrosis promoting signal in a PI3K isoform-specific manner that is independent of Akt.
These studies reveal class I PI3K isoforms, p110α and p110β, as potential pharmaceutical targets for the prevention and treatment of the fibrotic disease PCO.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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