Abstract 575: Human Stro1 Mesenchymal Precursor Cells Induce Proliferative Effects on Vascular Smooth Muscle Cells and Endothelium via PI3 Kinase Dependent Pathways
Background: We have previously shown that immunoselected and culture-expanded Stro1+ human bone marrow (BM) derived-mesenchymal precursor cells (MPCs) produce various soluble factors. Injection of these factors into rat hearts after acute myocardial infarction (MI) results in induction of angiogenesis and arteriogenesis, and functional cardiac recovery. Here, we sought to examine the mechanisms and activation pathways by which such MPC-derived factors may exert their effects on vascular smooth muscle cells (SMC) and endothelial cells (EC).
Methods: Human Stro1+ MPC were immunoselected and bulk expanded to passages 3– 4. Conditioned medium (CM) from 106 cells was generated by replacing growth medium with serum-free medium (SF) for 48h. Concentrated CM or SF was added to cultures of human pulmonary artery endothelial cells (PAEC) and aortic smooth muscle cells (AoSMC) for analysis of cellular survival, growth, proliferation and intracellular signaling.
Results: In cultures of PAEC, CM-treatment for 24h promoted the progression of cells from G to S phase as determined by BrDU incorporation (38% vs 2% for resting cells, p<0.01) whereas SF had no effect (2%). Similar results were observed following culture of AoSMC with CM, but not SF. Culturing PAEC or SMC with CM, but not SF, resulted in over 3– 4 fold greater levels of phosphorylated PI3 kinase than was seen in either resting cells or SF (p<0.01). PI3 kinase phosphorylation induced by CM was significantly reduced by neutralizing MAbs against either MCP-1 and TNF-alpha. Moreover, anti-TNF MAb reduced the proportion of CM-mediated PAEC cycling from 38.4% to 11.3% (p<0.05 vs CM), and both anti-TNF and anti-MCP-1 MAbs reduced CM-mediated SMC cycling.
Conclusion: MPC-derived soluble factors induce proliferative effects on vascular smooth muscle and endothelial cell lineages. These effects appear to be due in large part to cytokine-mediated PI3 kinase phosphorylation in these cell types, with MCP-1 and TNF-alpha being lead contributors. Cytokine-mediated PI3 kinase-dependent activation of these cell types may be responsible for the observed angiogenic and arteriogenic effects of MPC and derived soluble factors in the MI heart in vivo.