Are factors originating from serum, plasma, or cultured cells involved in the growth‐promoting effect of the extracellular matrix produced by cultured bovine corneal endothelial cells?

Abstract

The possibilities that the growth‐promoting effect of the extracellular matrix (ECM) produced by cultured bovine corneal endothelial (BCE) cells could be due to: (1) adsorbed cellular factors released during the cell lysis process leading to the denudation of the ECM; (2) adsorbed serum or plasma factors: or (3) adsorbed exogenous growth factors have been examined. Exposure of confluent BCE cultures to 2 M urea in medium supplemented with 0.5% calf serum denudes the ECM without cell lysis. The ECM prepared by this procedure supports cell growth just as well as ECM prepared by denudation involving cell lysis. Thus, it is unlikely that the growth‐promoting properties of ECM are due to adsorbed cellular factors. When the ECM produced by BCE cells grown in defined medium supplemented with high‐density lipoprotein, transferrin, and insulin was compared to the ECMs produced by cells grown in the presence of serum‐ or plasma‐supplemented medium, all were found to be equally potent in stimulating cell growth. It is therefore unlikely that the growth‐promoting ability of the ECM is due to adsorbed plasma or serum components. When fibroblast growth factor (FGF)‐coated and ECM‐coated plastic dishes were submitted to a heat treatment (70°C, 30 min) which results in the inactivation of FGF, the growth‐supporting ability of FGF‐coated dishes was lost, while the comparable ability of ECM‐coated dishes was not affected significantly. This observation tends to demonstrate that the active factor present in the ECM is not FGF. Nor is it platelet derived growth factor (PDGF), since treatment known to destroy the activity of PDGF, such as exposure to dithiothreitol (0.1 M, 30 min, 22°C) or to β‐mercaptoethanol (10%) in the presence or absence of 6 M urea for 30 min at 227°C, does not affect the growth‐promoting activity of ECM. It is therefore unlikely that the growth‐promoting effect of ECM is due to cellular growth‐promoting agents or to plasma or serum factors adsorbed onto the ECM.