Identification and regulation of Sprouty1, a negative inhibitor of the ERK cascade, in the human heart.

We screened a compendium of gene profiles from 19 paired human heart samples harvested at the time of implant and explant of a left ventricular assist device (LVAD) for novel genes regulating the Ras/MEK/ERK cascade. From this analysis we identified Sprouty1, an evolutionally conserved gene that acts as an intrinsic inhibitor of the Ras/MEK/ERK pathway. Sprouty1 mRNA and protein were significantly upregulated in the heart in response to mechanical unloading with a LVAD. The upregulation of Sprouty1 in the heart following mechanical unloading was accompanied by a significant decrease in phosphorylated ERK1/2. Gain of function experiments demonstrated that upregulation of Sprouty1 in isolated cardiac myocytes led to a significant decrease and altered kinetics of ERK1/2 phosphorylation. Immunohistochemistry of human hearts revealed that Sprouty1 was also expressed in the microvasculature. Upregulation of Sprouty1 in endothelial cells led to a significant decrease in VEGF-induced endothelial cell proliferation. To our knowledge, these findings are the first to define Sprouty expression in the heart and suggest that Sprouty1 may serve as an intrinsic mediator governing ventricular remodeling through a coordinated coupling of both myocyte and vascular alterations in response to mechanical load.

Genomic profiling of the human heart before and after mechanical support with a ventricular assist device reveals alterations in vascular signaling networks.

Mechanical unloading of the heart with a left ventricular assist device (LVAD) significantly decreases mortality in patients with heart failure. Moreover, it provides a human model to define the critical regulatory genes governing myocardial remodeling in response to significant reductions in wall stress. Statistical analysis of a gene expression library of 19 paired human heart samples harvested at the time of LVAD implant and again at explant revealed a set of 22 genes that were downregulated and 85 genes that were upregulated in response to mechanical unloading with a false discovery rate of less than 1%. The analysis revealed a high percentage of genes involved in the regulation of vascular networks including neuropilin-1 (a VEGF receptor), FGF9, Sprouty1, stromal-derived factor 1, and endomucin. Taken together these findings suggest that mechanical unloading alters the regulation of vascular organization and migration in the heart. In addition to vascular signaling networks, GATA-4 binding protein, a critical mediator of myocyte hypertrophy, was significantly downregulated following mechanical unloading. In summary, these findings may have important implications for defining the role of mechanical stretch and load on autocrine/paracrine signals directing vascular organization in the failing human heart and the role of GATA-4 in orchestrating reverse myocardial remodeling. This unbiased gene discovery approach in paired human heart samples has the potential to provide critical clues to the next generation of therapeutic treatments aimed at heart failure.

Total left ventricular outflow tract obstruction due to left ventricular assist device-induced sub-aortic thrombosis in 2 patients with aortic valve bioprosthesis.

This report describes 2 patients with an aortic bioprosthesis. Both patients developed total thrombotic occlusion of the sub-aortic left ventricular outflow tract consequent to insertion of a left ventricular assist device (LVAD). Replacing a mechanical valve with a bioprosthesis in patients receiving a left ventricular assist device offers no additional protection against thrombosis of the aortic prosthesis. Pericardial patching below the aortic prosthesis at the time of LVAD implantation may be performed, but will significantly impede or prohibit the native ventricle from ejecting blood and demonstrating any degree of recovery.

Myocardial creatine kinase expression after left ventricular assist device support.

OBJECTIVES: We examined whether unloading of the left ventricle with a ventricular assist device (LVAD) can result in normalization of the creatine kinase (CK) abnormalities in the failing human heart. BACKGROUND: Left ventricular failure is associated with a decrease of myocardial total CK activity and a fetal shift in CK isoform expression that results in an increase in the cytosolic brain type homodimeric-creatine kinase (CK-B) subunit and decreases of the cytosolic muscle-creatine kinase (CK-M) and CK-mitochondrial (CK-Mt) isoforms. The mechanisms of this abnormality are not known. METHODS: Total CK activity and CK protein isoform expression (Western blotting) were examined in 11 patients with end-stage cardiomyopathy. In 7 patients, myocardial tissue was also obtained after 4.1 +/- 1.1 months of left ventricular assist device (LVAD) support. RESULTS: Left ventricular unloading produced by LVAD implantation resulted in a 270% +/- 114% increase in total CK activity (p < 0.01) that was associated with a 69% +/- 18% increase in CK-M protein expression (p < 0.01) and a 121% +/- 69% increase in CK-Mt protein expression (p < 0.01), but no significant change in CK-B expression. CONCLUSIONS: Systolic and diastolic unloading provided by the LVAD resulted in increases of total CK activity as well as CK-Mt and CK-M protein expression. The failure of CK-B expression to decrease suggests that abnormalities other than increased loading are responsible for the increase in CK-B expression in the failing heart.