Abstract 3674: Active Wnt Signaling in Cardiac Response to Injury
Objectives. After myocardial infarction (MI), injured myocardium is replaced by scar tissue leading to cardiac remodeling. Endogenous repair in vivo via activation of resident cardiac progenitor cells remains a big challenge as many pathways control their behaviour. One important pathway suggested is the Wnt signaling cascade, a regulatory signal of stem cell biology and behavior. Although extensively studied in heart development, the exact role of Wnt signaling after MI still needs to be unraveled. Contradictory results were found upon inhibition or stimulation of Wnt or its downstream targets with respect to the response on different hypertrophic stimuli and LAD ligation, suggesting that Wnt is involved in infarct healing. We set to evaluate the role of active Wnt signaling in the heart following MI.
Methods. After LAD ligation C57BL/6 Axin2+/LacZ reporter mice were sacrificed at day 0, 1, 3, 7, 14 and 21 post-MI. Hearts were snap-frozen for immunohistochemistry (IHC) or digested to obtain a single cell suspension for FACS analysis. Samples were stained with both Fluorescein di-β-D-Galactopyranoside (FDG) to detect β-galactosidase and antibodies against Sca, CD31, c-kit and CD45. For IHC, antibodies against β-galactosidase, tropomyosin, Sca, CD31 and CD45 were used. Data (mean±s.e.) were analyzed by Mann-Whitney U test, using a significance level of P<0.05.
Results. Wnt signaling increased markedly in the myocardium (border zone and remote area), starting at day 7 up to 21 days post-MI (P<0.01, n=5–10 per group). Using Sca and CD31 to identify progenitor and endothelial cells, a significant increase in both Sca+/CD31− (and c-kit) and Sca−/CD31+ cells co-expressing Wnt was observed at day 7 and 14. CD45+ cells expressing Wnt, showed a peak at 3 and 7 days post MI, returning to basal levels afterwards.
Conclusion. Wnt signaling increases significantly after MI, especially in Sca+/CD31− and Sca−/CD31+ cell populations, suggesting involvement of Wnt signaling in activation of resident Sca+ progenitor cells as well as endothelial cells. Furthermore, all cell populations studied displayed active Wnt signaling, suggesting a broader role of Wnt in cardiac responses to injury than restricted to progenitor cell populations.