Chronic heart failure after myocardial injury (MI) is characterized by an extensive loss of myocytes due to considerable cell death. Bone marrow derived stem cells (BMSCs) can transdifferentiate and show potential for regenerating the myocardium after MI. Stem cell mobilization, egress from the bone marrow and recruitment to the site of injury can be regulated by signals through G protein coupled receptors (GPCRs). βArrestins have signalling and scaffolding functions and act as downstream regulators of GPCR desensitization and endocytosis. We explored the potential role for βArrestins in cardiac precursor cell function, concentrating on BMSCs. Using knockout (KO) mice, we investigated the role βArrestin1 (βArr1) and βArrestin2 (βArr2), their modulation of regenerative competence of BMSCs and their contribution to cardiac repair after ischemic injury. in vitro, we observed that BM derived cells devoid of either βArr1 or βArr2 are slower to proliferate, colonize and migrate, compared to wild type (WT) BM cells. We also observed elevated cell death in βArr2 deficient cells following oxidative stress. Additionally, the number of cKit+ stem cells, thought to be potential cardiac precursor cells, was significantly lower in the BM and blood of βArr KO vs WT. Similarly, BM and blood of the chimeras contained fewer and less viable cardiac stem/precursor cells pre and post MI, compared to WT transplanted controls. In our in vivo study, we carried out BM transplants to determine whether the βArrs may be involved in cardiac repair. WT mice were irradiated and received BM transplants from WT, βArr1 KO or βArr2 KO mice. Following BM reconstitution, mice underwent MI and their recovery was monitored. Interestingly, chimeric mice with βArr1 and βArr2 KO BM had significantly inferior outcomes, including significantly decreased post MI survival with βArr2 KO BM and both βArr chimeras had significantly lower cardiac function post MI than mice receiving WT BM. Histology revealed that both chimeras developed larger infarcts and hypertrophy at an faster rate. We conclude that βArrs play a novel role downstream of GPCR desensitization in cardiac progenitor cells in BM and appear to be critically involved in the heart’s response to ischemic injury via cardiac repair and regeneration.
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