Injury‐induced release of basic fibroblast growth factor from bovine aortic endothelium

Abstract

Although the basic fibroblast growth factor (bFGF) gene lacks a traditional consensus signal peptide domain indicative for secretion, many cell types have receptors for bFGF. Since endothelium is a rich source of cell-associated bFGF, we asked under what conditions could bFGF be released or secreted from confluent cultures of bovine aortic endothelial (BAE) cells. The level of bFGF in BAE cell lysates was compared with the level of heparin-releasable bFGF in intact BAE cell monolayers, intact cells with exposed extracellular matrix (nonlytic matrices), and extracellular matrices prepared by cell lysis (lytic matrices). Less than 10% of total cell-associated bFGF was released from intact cell monolayers and nonlytic matrices. In contrast, the levels of bFGF released from lytic matrices depended upon the conditions used to prepare the matrices. Cell lysis at neutral pH generated matrices that released the highest bFGF levels (approximately 50% of total cell-associated bFGF). These matrices were heavily contaminated by histones, indicating the cellular release and adsorption of intracellular proteins to the matrix. Matrices prepared by BAE cell exposure to basic pH (100 mM NH4OH) contained low bFGF content and minor histone contamination. These latter matrices were chosen to study bFGF sequestration, under physiological conditions, into the extracellular matrix of confluent BAE cell cultures. Incubation with endotoxin, an agent acutely toxic to BAE cells, resulted in cellular release and adsorption of endogenous bFGF to cells and matrices, accompanied by histone deposition in the matrices. These results suggested that one mechanism for bFGF release from BAE cell monolayers was passive release induced by severe cell injury and/or cell lysis with secondary adsorption to the matrix.

Diabetes Autoantibodies Mediate Neural- and Endothelial Cell- Inhibitory Effects Via 5-Hydroxytryptamine- 2 Receptor Coupled to Phospholipase C/Inositol Triphosphate/Ca2+ Pathway

“…One possibility is endothelial injury which releases sequestered auto-antigens, e.g. basic fibroblast growth factor (bFGF) [29], whose increased concentration in plasma correlated with the spontaneous appearance of agonist FGF-like autoantibodies in various pathologies including cancer subsets [11,30] and obese type 2 diabetes [31]. Vascular injury also causes platelets to release serotonin together with polyphosphates, the latter of which, like heparin, is a highly anionic substance capable of binding and protecting (locallyreleased) bFGF from inactivation [32].…”

Basic Fibroblast Growth Factor Modulates the Aminophospholipid Translocase Activity Present in the Plasma Membrane of Bovine Aortic Endothelial Cells

“…Basic FGF does not possess the leader sequence required for secretion by classic secretory pathways (Abraham et al, 1986) and normally this growth factor is not secreted by the endothelial cells (Vlodavski et al, 1987a, b ;Maier et al, 1990). Sometimes referred to as a wound hormone (D'Amore et al, 1994), basic FGF shows an autocrine activity following local release as a result of injury (Sato and Rifkin, 1988;Gajdusek and Carbon, 1989;McNeil et al, 1989), cell necrosis (D'Amore et al, 1994) or mobilization from the extracellular matrix where it has been shown to be sequestered (Vlodavsky et al, 1987a). Such adverse conditions are not expected to prevail when working with cells at confluence and in conditions which fully preserve their integrity.…”

Fibroblast growth factor/fibroblast growth factor receptor system in angiogenesis

“…Endothelial cell damage results in increased FGF2 production and release [217]; exudated fibrin(ogen) can bind FGF2 and enhances its biological activity (see above); hypoxia upregulates the production of angiogenic growth factor, including VEGF [218] and FGF2 [204]. Furthermore, hypoxia increases endothelial cell responsiveness to FGF2 by promoting HSPG synthesis [219] and upregulates FGF2 production also in vascular pericytes [220].…”