Abstract 104: Protein Kinase GIα Functions in the Cardiac Myocyte as a Tonic Inhibitor of Pathologic Cardiac Hypertrophy In Vivo

Abstract

Objectives: We and others previously demonstrated that activation of the NO-cGMP-Protein Kinase G (PKG) pathway inhibits cardiac hypertrophy and remodeling in vivo. However, it remains untested whether PKG specifically in the cardiac myocyte (CM) mediates these effects. We therefore tested the hypothesis that PKGIα inhibits pathologic cardiac hypertrophy through a specific role in the CM. Methods and Results: We created and characterized mice with CM-restricted excision of PKGIα. Mice were generated in which the PKGI exon 1 (specific for the Iα isoform) was flanked by loxP sites. We crossed these PKGIα fl/fl mice with αMHC-Cre mice which constitutively express Cre recombinase selectively in the CM. The resultant PKGIα fl/fl / αMHC-Cre+/- mice were compared with PKGIα fl/fl / αMHC-Cre-/- littermate controls (termed PKG CMKO and Ctrl, respectively). By age 3 months (n=5 per genotype), male PKG CMKO mice developed atrial and LV hypertrophy compared with Ctrl littermates PKG CMKO atrial weight/tibia length 0.33 ± 0.03 mg/mm vs 0.22 ± .01 in Ctrl, P <0.05; PKG CMKO LV/TL 5.0 ± 0.2 mg/mm vs 4.1 ± 0.4 in Ctrl, P <0.05). LV CM cross sectional area also increased in the 3 month old PKG CMKO mice (9445 ± 282 pixels PKG CMKO vs 8273 ± 213 in Ctrl, n>400 cells/genotype, 5 hearts per genotype; P <0.001). The systolic index end systolic elastance was decreased in 3 month old PKG CMKO mice (PKG CMKO 3.1 ± 0.4 mmHg/μ l vs 6.1 ± 1.0 in Ctrl-; P <0.05). Importantly, blood pressure did not differ between genotypes. By age 6 months, PKG CMKO mice developed early mortality (3 of 4 PKG CMKO males died at 6 months of age vs 0 of 4 Ctrl males). Total heart and atrial weights of male mice (n=3 PKG CMKO , 4 Ctrl) increased in PKG CMKO mice (heart weight/tibia length 10.8 ± 1.7 mg/mm in PKG CMKO vs 7.1 ± 0.6 in Ctrl; P <0.05; atrial weight/tibia length 2.3 ± 1.1 mg/mm in PKG CMKO vs 0.30 ± 0.1 Ctrl, P <0.05). LV fractional shortening percentage, recorded at 6 months age, trended lower in the PKG CMKO mice as well (35 ± 3% PKG CMKO vs 44 ± 4% Ctrl, P 0.09). Conclusions: These data provide the first evidence that PKGIα functions in the CM as a tonic inhibitor of age-dependent pathologic hypertrophy, supporting further study of PKGIα as a therapeutic target in the prevention and treatment of LV remodeling and congestive heart failure.