Abstract 18802: Transcriptome Profiles of Chronically Closed or Cycling Aortic Valve Leaflets are Highly Similar Compared to Chronically Open Valves: Distention Drives Leaflet Homeostasis
Introduction: Throughout the valve cycle mechanical forces of multiple types and intensities are exerted on the leaflets, sinus and annulus. The mechanisms through which these forces regulate the homeostatic maintenance of valve leaflet architecture are still poorly understood. Ventricular mechanical support with a continuous flow device results in chronic closure of the outflow valve. Whether chronic valve closure affects valve leaflet homeostasis is a significant but unsettled clinical concern.
Hypothesis: We asked if chronic closure of the aortic valve (AV) impairs leaflet homeostasis by comparing the transcriptome profiles of AV cultured under different mechanical force conditions: Normally cycling (Flow); Not cycling but open (Static); or Not cycling but closed (Static-Closed, SC).
Methods: Ex vivo culture of native rat aortic valves, (8 valves per bioreactor, 4 valves per condition) was conducted in a flow bioreactor for seven days at 37C in endothelial cell culture media under conditions approximating the normal stroke volume of the rat heart. In each of 4 independent experiments, flow-induced valve cycling (Flow) was compared with either Static or SC condition in paired groups. After culture, leaflets were dissected from 3 valves/condition and pooled, mRNA was extracted and expression was evaluated using whole genome microarrays.
Results: Statistical-based unsupervised hierarchical clustering analysis of the leaflet transcriptome profiles revealed only two distinct patterns of leaflet gene expression between the three groups of AV. Flow and SC groups had nearly identical profiles whereas the Static valve group was distinctly different (p<0.05).
Conclusions: These results reveal that the stretching of valve leaflets by a filling volume inducing full coaptation is apparently sufficient to largely preserve their architecture and phenotypic gene expression in the seven day culture period tested. In contrast, the absence of valve closure produces a markedly different pattern of gene expression. Therefore, the absence of flow through the closed AV valve does not appear to be inherently destructive compared with conditions in which the valve remains open.
Author Disclosures: K. Maeda: None. X. Ma: None. F. Hanley: None. R. Riemer: None.
- © 2015 by American Heart Association, Inc.