Fibroblast growth factor-2 promotes in vitro heart valve interstitial cell repair through the Akt1 pathway

Fibroblast growth factor-2 promotes in vitro heart valve interstitial cell repair. Fibroblast growth factor-2 acts through betaglycan which is known to bind both transforming growth factor-β and fibroblast growth factor-2 at different locations on the molecule. When fibroblast growth factor-2 binds to betaglycan, transforming growth factor-β binding to betaglycan is reduced, allowing for more transforming growth factor-β to be available to activate pSmad2/3 which then promotes repair. This study investigates another pathway through which fibroblast growth factor-2 regulates valve interstitial cell repair.

We used an in vitro model of cell culture disruption. Confluent valve interstitial cell monolayers were disrupted, creating an experimental wound in the confluent monolayer, and incubated in treatments of exogenous fibroblast growth factor-2, anti-fibroblast growth factor receptor antibody, active Akt1, and Akt inhibitor. Valve interstitial cell monolayers were immunohistochemically stained and quantified for nuclear pSmad2/3 at the wound edge. The extent of closure was measured up to 96 h after disruption.

Anti-fibroblast growth factor receptor antibody significantly increased both nuclear pSmad2/3 staining at the wound edge and wound closure compared to nontreated control. This increase was less than that seen when valve interstitial cells were treated with fibroblast growth factor-2 and combined treatments of fibroblast growth factor-2 and anti-fibroblast growth factor receptor antibody did not further increase nuclear pSmad2/3 staining compared to fibroblast growth factor-2 alone. This suggested that the regulation of wound closure by fibroblast growth factor-2 also involved pathways other than transforming growth factor-β/Smad signaling. Treatment with Akt1 significantly increased wound closure, while Akt inhibitor reduced closure as compared to nontreated valve interstitial cells. Fibroblast growth factor-2 and fibroblast growth factor-2 neutralizing antibody up-regulated and down-regulated phosphorylated Akt1 expression in valve interstitial cells, respectively.

Fibroblast growth factor-2 promotes valve interstitial cell repair in two ways: the fibroblast growth factor-2/fibroblast growth factor-2 receptor interaction through the activation of Akt1 independent of the transforming growth factor-β/Smad2/3 signaling pathway and the previously described transforming growth factor-β/Smad signaling.