Abstract 192: Neurotrophin 3 Mediates the Fibrogenic Response to Pro-inflammatory Stimulation in Human Aortic Valve Interstitial Cells

Abstract

Background: Calcific aortic valve disease is characterized by inflammation, fibrosis and calci[[Unable to Display Character: fi]]cation. Aortic valve interstitial cell (AVIC) proliferation and over-production of extracellular matrix (ECM) proteins result in valvular fibrosis and thickening, and an inflammatory milieu in valvular tissue is believed to promote aortic valve fibrosis and calcification. However, the factors that mediate AVIC fibrogenic response remain to be identified. Recently, we observed that AVICs of aortic valves affected by calcific disease express higher levels of neurotrophin 3 (NT3). It is unknown whether NT3 induces the fibrogenic response in AVICs and whether this growth factor plays a role in valvular fibrogenic response to pro-inflammatory stimulation. Hypotheses: NT3 is a pro-fibrogenic factor in the aortic valve and mediates the fibrogenic response to pro-inflammatory stimulation in human AVICs. Methods and Results: Stimulation of human AVICs with lipopolysaccharide (LPS, 0.20 μg/ml) induced proliferation and up-regulated production of MMP-9 and collagen III. TLR4-dependent NT3 over-production was observed in cells exposed to LPS and was attenuated by inhibition of the NF-κB, ERK1/2 or p38 MAPK pathway. Neutralization of NT3 or blocking the Trk receptors (neurotrophin receptors) with K252a suppressed LPS-induced fibrogenic response and reduced collagen deposition. Treatment of human AVICs with recombinant NT3 (0.10 μg/ml) also induced proliferation accompanied by up-regulated production of MMP-9 and collagen III. NT3-induced fibrogenic response was preceded by Akt phosphorylation and cyclin D1 up-regulation mediated by the Trk receptors. Inhibition of the Trk receptors, Akt or cyclin abrogated NT3-induced fibrogenic response. Conclusions: This study provides the first evidence that NT3 is capable of inducing human AVIC proliferation and ECM protein production via the Trk-Akt-cyclin D1 axis and plays an important role in mediating the TLR4-evoked fibrogenic response in human AVICs. Thus, NT3 is a pro-fibrogenic mediator in aortic valves. Up-regulation of AVIC production of NT3 by pro-inflammatory stimuli may have a mechanistic role in aortic valve fibrosis associated with calcific aortic valve disease.