MSc Candidate Dalhousie University Halifax, Nova Scotia, Canada
Background: Recent evidence suggests that most stem cell antigen-1 expressing cells (Sca-1+ cells) are the tissue-resident endothelial stem/progenitor cells and may contribute to angiogenesis during cardiac remodelling. Importantly, adequate angiogenic response has been shown to be critical for right ventricular (RV) adaptation and survival in pulmonary hypertension (PH). Therefore, in this study, we examined the relevance of Sca-1+ cells in RV remodelling using the rat chronic hypoxia model.
METHODS AND RESULTS:
Methods: Heart samples from male and female Sprague Dawley and Fischer CDF rats were collected and digested to obtain single cell suspension. Cells were stained with antibodies against Sca-1 and CD31 (endothelial cell marker) and analysed using flow cytometry. Sca-1+ cells from the heart were isolated using magnetic sorting and lectin binding and acetylated low-density lipoprotein (ac-LDL) uptake were assessed. To assess the effect of RV pressure overload, male and female Fischer CDF rats were subjected to 3 weeks of hypoxia (10% O2) and cardiac structure and function were assessed using echocardiography. Heart samples were collected, and Fulton index was measured to assess RV hypertrophy. Immunofluorescence straining of RV and LV samples was performed to assess abundance and localization of Sca-1+ cells were quantified using immunofluorescence staining of the heart sections.
Results: Most (>95%) of Sca-1+ cells in the heart expressed CD31 and demonstrate lectin binding and ac-LDL uptake. In response to hypoxia, RV systolic pressure was increased significantly in male and female rats (64.4 and 58.2 mmHg) compared to controls (29.3 and 28 mmHg). Significant elevation in the RV hypertrophy was observed in male (47%) and female (45.6%) rats compered to controls (27.6 and 26%, respectively). Importantly, these rats demonstrated adaptive RV remodelling and preserved RV function in response to chronic hypoxia as indicated by similar RV fractional shortening and cardiac index in hypoxia treated rats compared to controls. Adaptive RV remodelling in hypoxia treated rats was associated with an increase in the abundance of Sca-1+ cells in the RV of male (14.4%) and female (14.6%) rats compared to control rats (7.98% and 12.2%, respectively). Immunofluorescence staining demonstrated localization of Sca-1+ cells to vascular endothelium in the RV.
Conclusion: The cardiac Sca-1+ cells in the heart may be the resident endothelial stem/progenitor cells may contribute to angiogenesis and RV adaptation.
