Abstract 18372: Bone Marrow Beta-Arrestin 1 and 2 in Outcomes of Myocardial Ischemic Injury: A Novel Role in Cardiac Regeneration
Background: Bone marrow (BM) derived hematopoietic stem cells (HSCs) show potential to differentiate and regenerate myocardium after ischemic injury. Stem cell mobilization, egress from BM, and homing to the site of injury can be regulated by signals through G protein-coupled receptors (GPCRs). β-arrestins (βarr's) are downstream regulators of GPCR desensitization and endocytosis and can initiate novel signaling pathways due to kinase scaffolding. We hypothesized that βarr1 and βarr2 would modulate the regenerative capacity of HSCs and tested this in a model of myocardial ischemic injury in vivo.
Methods: The proliferative capacity of whole BM mononuclear cells (BMMCs) was tested using a colony-forming unit (CFU) assay. To assess the regenerative capacity of these cells, Wild-type (WT) mice were irradiated and subsequently reconstituted with control (WT), βarr1 knockout (KO) or βarr2 KO BMMCs. Four weeks after BM transplant, mice were subjected to myocardial infarction (MI). At 8 weeks we conducted in vivo echocardiography and at 12 weeks obtained hemodynamic measurements of cardiac function and used flow cytometry to isolate the lin−/c-kit+/sca-1+ HSCs from all mice.
Results: Proliferation of BMMCs was markedly reduced in βarr1 and βarr2 KO cells compared to WT (13.6±3.8 and 10.2±2.8 vs 18.7±4.5 CFU resp, p<0.05, n=4). At 12 weeks post-MI the % of c-kit+/sca-1+ HSCs were significantly decreased in mice that received the βarr1 KO BM (0.93±0.07% vs 0.37±0.08%, p<0.01, n=4). Mice that were transplanted with either βarr1 KO or βarr2 KO BM showed significantly reduced survival (47% and 29% resp) vs. WT (73%) at 3 weeks post-MI (n=15/group). Functional assessment showed lower ejection fraction in βarr1 and βarr2 KO vs. WT transplanted mice 8 weeks post-MI. Hemodynamic measurements of left ventricular (LV) function paralleled these findings. Interestingly, mice transplanted with βarr1 and βarr2 KO BM had larger infarctions and more remodeling.
Conclusion: barr1 and βarr2 appear to be the critical molecules for normal BM cardiac precursor/stem cell proliferation and homing, presumably by facilitating normal modulation of key GPCR signals. Importantly, the lack of βarr1 and βarr2 in BM leads to impaired functional recovery after myocardial ischemic injury.
- © 2010 by American Heart Association, Inc.