Abstract 183: Small Molecule Gβ? Inhibition Reduces Pathologic Activation of Cardiac Fibroblasts

Abstract

Heart failure (HF) is a devastating disease characterized by cardiac hypertrophy, fibrosis and inflammation. Excess signaling through Gβγ subunits leads to chronic β-adrenergic receptor (β-AR) downregulation, mediated predominantly by GRK2 in complex with PI3Kγ. Our recent work has demonstrated the therapeutic potential of the small molecule Gβγ-GRK2 inhibitor Gallein in limiting HF progression. Chronic activation of cardiac fibroblasts (CF), critical yet underappreciated myocardial cells, is a key contributor to pathologic cardiac remodeling. We hypothesized that Gβγ-GRK2 inhibition may limit pathologic CF activation. CFs were stimulated with Isoproterenol (Iso, β-AR agonist), AngII, or vehicle (V), +/- Gβγ inhibition for 24hr. Gallein treatment attenuated the induction of αSMA expression, a marker of pathologic CF activation, and two inflammatory cytokines, IL-1β and IL-6 in response to these pathologic stimuli (Iso, AngII), as assessed by real time PCR. This data suggest that Gallein treatment may reduce pathologic CF activation. Iso stimulation also enhances the phosphorylation of Akt, a kinase downstream of PI3Kγ known to be involved in cellular proliferation. Gβγ inhibition mitigated this induction, decreasing Akt phosphorylation >60% in response to Iso. This phenomenon was also observed in failing human CFs, in which Gallein decreased Akt phosphorylation >70%. We have recently demonstrated that the protease-activated receptor 1 (PAR1), a GPCR we have implicated in cardiac hypertrophy, is transactivated via chronic β-AR stimulation by induction of MMP-13, a protease we have found to be elevated in HF. Recent data from our lab and others have demonstrated that PAR1 is the most abundantly expressed GPCR in CFs, and that its stimulation in CFs may be pathologic. Interestingly, Gβγ inhibition treatment reduced PAR1 cleavage and activation in response to chronic Iso. In summary, small molecule Gβγ inhibition appears to reduce pathologic CF activation. The reduction in β-AR-mediated PAR1 cleavage reveals an alternative role for Gβγ inhibition in preventing CF activation and proliferation. These data suggest a potential therapeutic role for small molecule Gβγ inhibition in limiting pathologic CF activation and cardiac hypertrophy.