Abstract
Purpose:
Relatively little is known about how changes in the extracellular matrix (ECM) affect growth factor signaling in the lens. This is a pathophysiologically important issue given that certain ECM components, including fibronectin and collagen I, are upregulated during disease states characterized by abnormal lens cell differentiation (e.g., PCO and ASC).
Methods:
Serum-free primary cultures of embryonic chick lens cells (referred to as DCDMLs) were plated on various ECM substrates and then cultured for up to 6 days with or without noggin, a potent antagonist of BMP signaling that acts by very tightly and specifically binding to BMPs 2, 4, and 7. Western blotting and metabolic labeling were used to quantitate expression of lens cell differentiation markers. Activation of ERK was assessed by Western blotting of whole cell lysates using anti-phospho-ERK (Thr202/Tyr204) antibodies.
Results:
In DCDML cultures plated on laminin, upregulation of expression of markers of lens fiber differentiation in response to FGF2 is dependent on signaling by endogenous BMP4 and/or BMP7 as indicated by its inhibition by noggin. High (> 5 ng/ml) concentrations of exogenously added BMP4 or 7 also induce fiber differentiation in a noggin-sensitive manner. Similar results were obtained with cells cultured on collagen IV, another major component of the normal lens capsule. When the experiment was repeated with cultures plated on fibronectin, FGF2 and > 5 ng/ml BMP4 upregulated lens fiber differentiation as in laminin-plated cells. Although noggin abolished BMP4-induced differentiation, it did not block differentiation in response to FGF. An uncoupling of FGF-induced differentiation from BMP signaling was also observed in cells cultured on collagen I. Because of the importance of MAPKs in lens cell fate, we examined if ECM influences activation of ERK. We found that noggin markedly reduced upregulation of ERK by FGF in cells cultured for 6 days on laminin, but not in cells plated on fibronectin.
Conclusions:
These and additional experiments indicate that the lens cell environment can influence growth factor signaling and its downstream effects on cell fate in unexpected ways, with implications for fibrotic conditions including PCO.
Keywords: 714 signal transduction •
500 differentiation •
652 posterior capsular opacification (PCO)