Background: Anthracycline chemotherapy is an effective and widely used treatment for solid tumors and hematological malignancies regardless of its known cardiotoxicity. The mechanisms of the cardiotoxicity are not fully understood and methods to protect the heart during or following anthracycline chemotherapy are currently unclear. In order to examine the efficacy of human cell based therapy in anthracycline-induced injury, we characterized a mouse model using an immune compromised strain of mice capable of accepting human cells.Methods: Immune compromised mice (NOD.Cg-Prkdc scid Il2rg tm1Wjl /SzJ) were repeatedly exposed to pharmaceutical grade doxorubicin (0.5 mg/kg -4 mg/kg). Cardiotoxicity was assessed by echocardiography and μCT imaging of the coronary vascular bed as well as by flow cytometry and by histological assessments of anthracycline-induced cardiac tissue damage. Results: The immune compromised mice were highly susceptible to doxorubicin treatment. Doxorubicin induced both systemic and cardiac toxicities. Gastrointestinal and hepatic injury occurred at 4 mg/kg and 1.5 mg/kg dosing while mice receiving 0.5 mg/kg weekly only displayed hepatic damage. Repeated exposure to 0.5 mg/kg anthracyclines resulted in cardiac toxicity. Flow cytometric analysis of hearts indicated a loss in endothelial and cardiac progenitor cells after doxorubicin treatment. This endothelial loss is corroborated by the lack of small vessels detected by μCT in the hearts of mice exposed to doxorubicin. Histological assessment shows no overt cardiomyocyte injury but livers from mice treated with doxorubicin show marked hepatic plate atrophy with intracytoplasmic and canalicular cholestasis, rare pericentral hepatocellular necrosis and significant zone 3 iron accumulation, likely an indication of metabolic injury due to doxorubicin toxicity. Conclusions: Immune compromised mice are sensitive to doxorubicin therapy resulting in systemic complications in addition to cardiovascular toxicity. Anthracycline-induced cardiotoxicity is observed at very low doses in NOD.Cg-Prkdc scid Il2rg tm1Wjl /SzJ mice.

To determine whether hepatic depletion of vitamin A (VA) stores has an effect on the postnatal heart, studies were carried out with mice lacking liver retinyl ester stores fed either a VA-sufficient (LRVAS) or VA-deficient (LRVAD) diet (to deplete circulating retinol and extrahepatic stores of retinyl esters). There were no observable differences in the weights or gross morphology of hearts from LRVAS or LRVAD mice relative to sex-matched, agematched, and genetically matched wild-type (WT) controls fed the VAS diet (WTVAS), but changes in the transcription of functionally relevant genes were consistent with a state of VAD in LRVAS and LRVAD ventricles. In silico analysis revealed that 58/67 differentially expressed transcripts identified in a microarray screen are products of genes that have DNA retinoic acid response elements. Flow cytometric analysis revealed a significant and cell-specific increase in the number of proliferating Sca-1 cardiac progenitor cells in LRVAS animals relative to WTVAS controls. Before myocardial infarction, LRVAS and WTVAS mice had similar cardiac systolic function and structure, as measured by echocardiography, but, unexpectedly, repeat echocardiography demonstrated that LRVAS mice had less adverse remodeling by 1 wk after myocardial infarction. Overall, the results demonstrate that the adult heart is responsive to retinoids, and, most notably, reducing hepatic VA stores (while maintaining circulating levels of VA) impacts ventricular gene expression profiles, progenitor cell numbers, and response to injury.heart; lecithin retinyl acyl transferase; postnatal; retinoic acid; vitamin A NEW & NOTEWORTHYWe demonstrate heart-wide expression of retinoic acid receptor-␥, a retinoic acid-activated nuclear receptor, and report that ventricles from adult mice with depleted hepatic vitamin A stores have altered gene expression, a significant increase in proliferating progenitor cells, and improved response to acute myocardial injury.

The adult human heart contains a subpopulation of highly proliferative cells. The role of ErbB receptors in these cells has not been studied. From human left ventricular (LV) epicardial biopsies, we isolated highly proliferative cells (eHiPC) to characterize the cell surface expression and function of ErbB receptors in the regulation of cell proliferation and phenotype. We found that human LV eHiPC express all four ErbB receptor subtypes. However, the expression of ErbB receptors varied widely among eHiPC isolated from different subjects. eHiPC with higher cell surface expression of ErbB2 reproduced the phenotype of endothelial cells and were characterized by endothelial cell-like functional properties. We also found that EGF/ErbB1 induces VEGFR2 expression, while ligands for both ErbB1 and ErbB3/4 induce expression of Tie2. The number of CD31CD45 endothelial cells is higher in LV biopsies from subjects with high ErbB2 (ErbB2) eHiPC compared to low ErbB2 (ErbB2) eHiPC. These findings have important implications for potential strategies to increase the efficacy of cell-based revascularization of the injured heart, through promotion of an endothelial phenotype in cardiac highly proliferative cells.

No abstract

Podocalyxin (Podxl) is a CD34 orthologue and cell surface sialomucin with reported roles in renal podocyte diaphragm slit development, vascular cell integrity, and the progression of blood, breast, and prostate cancers. Roles for Podxl during non-malignant hematopoiesis, however, are largely undefined. Presently we have developed a Vav-Cre Podxl knockout mouse model, and report on novel roles for Podxl in governing stress myelopoiesis. At steady-state, Podxl expression among hematopoietic progenitor cells was low-level but was induced by GCSF (granulocyte colony stimulating factor) in myeloid progenitors, and by TPO (thrombopoietin) in HSCs. In keeping with low level Podxl expression at steady-state, Vav-Cre deletion of Podxl did not markedly alter peripheral blood cell levels. G-CSF challenge in Podxl-KO mice, in contrast, hyper-elevated peripheral blood neutrophil and monocyte levels. Podxl-KO also substantially heightened neutrophil levels following 5-fluorouracil myeloablation. These LOF phenotypes were selective, and Podxl-KO did not alter lymphocyte, basophil or eosinophil levels. Within bone marrow (and following G-CSF challenge), Podxl deletion moderately decreased CFU-GEMM and CD16/32posCD11bpos progenitors but did not affect Gr-1pos cell populations. Notably, Podxl-KO did significantly heighten peripheral blood neutrophil migration capacities. To interrogate Podxl’s action mechanisms, a co-immunoprecipitation plus LC-MS/MS (liquid chromatography – mass spectrometry) approach was applied using hematopoietic progenitors from G-CSF-challenged mice. Rap1a, a Ras-related small GTPase, was a predominant co-retrieved Podxl partner. In bone marrow HPC’s, Podxl-KO led to heightened GCSF activation of Rap1aGTP, and Rap1aGTP inhibition attenuated Podxl-KO neutrophil migration. Studies reveal novel roles for Podxl as an important modulator of neutrophil and monocyte formation, and of Rap1a activation, during stress hematopoiesis.