Abstract 20783: B-Raf Regulates Vascular Growth Signaling in the Neonatal Mouse Heart
Introduction: The early postnatal mouse heart is still growing by proliferation and differentiation of cardiomyocytes (CMC) to just after the first week of life. Vascular growth in this time period is also crucial as the left ventricular myocardium must prepare for a near doubling of work load at birth, which includes having an adequate vascular tree to supply the muscle itself. CMC-specific loss of B-Raf leads to lesser CMC volume fraction, at 3 and 8 days postnatal reflective of blunted CMC proliferation.
Hypothesis: We hypothesize CMC-specific loss of B-Raf reduces vascular growth signals.
Methods: CMC-specific knockout (KO) of B-Raf was generated using CRE/lox (floxed B-Raf x αMHC CRE) resulting in a truncated, unstable B-Raf and a null phenotype. KO mice (α-MHC-CRE / B-Raf lox/lox) were compared to CRE negative / B-Raf lox/lox mice (wild type; WT). Hearts from postnatal day (PND) 1, 3, 8, and 14 pups were harvested for molecular analysis (n=8/age group). Expression levels of vascular factors were determined by qPCR and normalized against β-actin levels. Only statistically significant data (p<0.05) are reported.
Results: In PND1 KO hearts there is a reduction in HIF-1a and VEGF-R2 gene expression compared to WT. There is no difference in VEGF and Angiopoietin-2 levels. HIF-1a, VEGF and VEGF-R2 levels were elevated in PND3 and 8 hearts (KO and WT). Angiopoietin-2 gene expression was reduced by 50% in both ages compared to PND1. In PND14 WT, all gene expression dramatically dropped several-fold while levels remained significantly higher in KO hearts.
Conclusions: Early reduction in HIF-1a and VEGF-R1 gene expression in PND1 KO hearts corroborates our histological finding that vascular volume fraction in those hearts are reduced. The increase in vascular signaling during PND3 and PND8 would support still proliferating and differentiating CMCs as the mouse heart matures. While we did not expect to see a strong vascular growth signal in the PND14 heart, it was even more surprising to see that loss of B-Raf maintained high levels of these genes. CMC-specific B-Raf loss suggests it is necessary for normal vascular growth factor signaling/interaction with endothelial cells in the heart.
Author Disclosures: N.N. Chattergoon: None. K.P. Rees: None. P.J. Stork: None.
- © 2016 by American Heart Association, Inc.