Fibronectin Increases Survival of Rat Hepatic Stellate Cells - A Novel Profibrogenic Mechanism of Fibronectin

The aims of this study were to determine whether fibronectin increases survival of hepatic stellate cells (HSCs) in starving conditions, and to identify the signal transduction pathways involved in this effect. Methods: Primary culture of rat HSCs were plated on fibronectin-uncoated or coated culture wells, and grown in the presence of 0.2% or 20% fetal calf serum. Cell apoptosis was measured by an ELISA procedure. Signal transduction pathways were analyzed by inhibiting major intracellular transduction pathways with appropriated inhibitors and by detecting phosphorylated proteins. Results: Fibronectin increased survival of serum deprived HSCs. This effect was abrogated by the presence of the RGD peptide, by silencing FAK expression, and by inhibiting PI3K with LY294002 or wortmannin. Growth of HSCs on fibronectin induced integrin α5β1 expression, tyr 397 , ser 473 , and ser 136 phosphorylation of FAK, Akt, and Bad, respectively, and the binding of phosphorylated Bad to 14-3-3 proteins. Likewise, fibronectin increased Bcl2/Bax ratio and reduced release of mitochondrial cytochrome c into the cytoplasm, formation of apoptosome, and caspase 9 and 3 activity. These effects were avoided by treatment of cells with PI3K inhibitors. Conclusion: Fibronectin increases survival of HSCs via a pathway involving integrin α5β1 receptors, FAK, PI3K, Akt and proteins of Bcl2 family.