Abstract 2970: Gr-1 Positive Cells-secreted Growth Hormone is the Major Paracrine Factor for the Improved Cardiac Function of Dilated Cardiomyopathy Models in Bone Marrow Mononuclear Cell Transplantation
Bone marrow-derived mononuclear cells (BMMNC) are thought to be the promising source of paracrine factors, but the precise mechanisms remains unknown. Recently we observed that intravenous transplantation of BMMNC isolated from wild mice improved cardiac function of several kinds of DCM mice, including doxorubicin-induced DCM mice and mice with dominant-negative mutant of epidermal growth factor receptor driven by αMHC promoter (EGFRdn), via the secreting factor derived from Gr-1(+) cells in BMMNC. Furthermore, since Gr-1(+) cells-derived conditioned medium from wild mice (W-CM) significantly improved percentage of cell shortening (%CS) and beating rate (BR) in neonatal rat cardiomyocytes compared with Gr-1(+) cell-derived CM from EGFRdn mice, we explored the secreted factors highly expressed in Gr-1+) cells from wild mice by DNA microarray analysis and identified growth hormone (GH) was more expressed in Gr-1(+) cells in wild mice compared with Gr-1(+) cells in EGFRdn mice. GH and W-CM induced phosphorylation of Akt, Erk, Jak2, Stat5, PKA, and upregulated the cyclic AMP level in cardiomyocytes, possible downstream-related molecules of GH receptor, and the activation of these kinases was inhibited by pegvisomant treatment, an antagonist of GH receptor. W-CM-mediated improvement of %CS and BR of cardiomyocytes was also inhibited by the treatment with pegvisomant, but not anti-IGF-1 antibody in vitro. Finally we examined the relationship between BMMNC transplantation-mediated improved cardiac function in DCM mice and GH. When W-CM was injected intravenously to DCM mice, the improvement of FS and +dp/dt was observed 3 days after treatment as well as BMMNC transplantation. However, these improvements were inhibited by the treatment with pegvisomant, but not anti-IGF-1 antibody (FS: W-CM, 0.34±0.01; pegvisomant, 0.27±0.01; p<0.01, n=8, +dp/dt: W-CM, 9143.6±320.4; pegvisomant, 6712.2±274.6; p<0.05, n=8). These findings suggest that the improvement of cardiac function of DCM by BMMNC transplantation might be mainly mediated by Gr-1(+) cells-secreted GH. Understanding of the precise molecular mechanisms of GH downregulation in Gr-1(+) cells in heart failure might contribute to the improved effects of cell therapy.