Fig. 1.

Sca-1+ CPCs expand in the hearts of mice acutely infected with T. cruzi in a tissue parasitism-dependent manner. (A) Sca-1 transcript is preferentially elevated in the heart during acute T. cruzi infection in parallel with blood parasitemia. Mice were infected with T. cruzi by intraperitoneal injection and euthanized at the time points indicated. Left axis: Cardiac transcripts of stem-cell markers Sca-1, c-Kit, and Musashi-1 were quantified by quantitative PCR. Results are the mean ± S.E.M. of fold-change expression relative to control mice (n = 3–5 mice; two independent experiments). **P < 0.01. Right axis: Blood parasitemia over the course of acute T. cruzi infection was measured by optical microscopy. (B) Elevated Sca-1 transcript at the peak of acute T. cruzi infection indicates an expansion of the progenitor cell population. Mice infected with T. cruzi (Acute, n = 4) express more cardiac Sca-1 mRNA than uninfected mice (Uninf, n = 5). Mice were infected with 1000 parasites and euthanized 18 days later. Cardiac mRNA was quantified by quantitative PCR and plotted after normalization to hypoxanthine-guanine phosphoribosyltransferase. Results are the mean ± S.D.; ***P < 0.001. (C) An increased cardiac Sca-1⁺ progenitor cell population in acute T. cruzi infection mirrors the elevation in Sca-1 transcript. Mice were infected with 3000 parasites and euthanized 20 days later. Sca-1⁺ cells were quantified by flow cytometry. Results are the mean ± S.D.; **P < 0.01. (D) Isolated Sca-1⁺ cells can be reliably characterized as CPCs. Sca-1⁺ cells (passage 2) isolated from murine hearts were induced to differentiate into endothelial cells expressing von Willebrand factor (vWF) upon treatment with 20 ng/ml VEGF, or into cardiomyocytes expressing myosin heavy chain (MyHC) upon treatment with 10 mM 5-azacytidine. (E) Sca-1⁺ cells also exhibit clonogenicity, the ability to grow from a single cell into a colony. Representative image of a Sca-1⁺ colony expanded from a single cell plated by limiting dilution.