Expression of Protein Kinase G I Alpha and Its Downstream Anti-Remodeling Substrates in Nonischemic Cardiomyopathy and Hypertrophic Cardiomyopathy

Background: The syndrome of heart failure (HF) arises from the pathologic process of cardiac remodeling. We have recently shown that the cGMP-dependent protein kinase I alpha (PKGIα) inhibits pathologic cardiac remodeling in vivo, and this effect requires the PKGIα leucine zipper LZ protein interaction domain. We have begun to explore PKGIa LZ-interacting proteins as potential novel anti-remodeling molecules. To this end, we recently identified that in the LV, PKGIα, through interactions mediated by the LZ domain, regulates a number of cardiovascular signaling molecules, including JNK and mixed lineage kinase 3 (MLK3). However, the expression of PKGIα, JNK, and MLK3 in different phenotypes of human heart failure remains incompletely understood. Methods and Results: In the current study, we tested the hypothesis that expression of PKGIα and its downstream effectors JNK and MLK3 become dysregulated in two phenotypes of remodeling and heart failure: nonischemic cardiomyopathy (NICM) and hypertrophic cardiomyopathy (HCM). We examined LV tissue from: 1) normal control hearts obtained through the national disease research interchange program (n = 4); 2) left ventricular assist device core tissue from patients with NICM (n = 7); and 3) surgical septal ablation tissue from patients with symptomatic HF from HCM (n = 9). We measured protein expression by Western blot and normalized expression to GAPDH. Data were expressed in arbitrary densitometric units (ADU). Compared with normal control LV tissue, normalized PKGIα expression increased significantly in both NICM and HCM LVs (fold increase vs. control: NICM 34.1 + /- 4.3; HCM 53.5 + /- 11.3; P < .05 NICM and HCM vs. control). Similarly, JNK expression increased in NICM and HCM compared with control (fold increase vs control: NICM 10.6 + /- 1.6; HCM 10.5 + /- 1.3; P < .05 NICM and HCM vs. control). Further, phosphorylated JNK increased in failing LVs (fold increase vs control: NICM 20.7 + /- 6.0; HCM +/- 19.9 + /- 4.6; P < .05 NICM and HCM). MLK3 expression increased in NICM and HCM patients compared with control (fold increase vs control: NICM 6.3 + /- 0.9; HCM 7.0 + /- 1.4; P < .05 NICM and HCM vs. control). Conclusions: These data identify that PKGIα, JNK, and MLK3 are expressed in the human heart and become highly upregulated in the setting of pathological hypertrophy both in NICM and HCM. We therefore interpret our results to support that the PKGIα-MLK3-JNK signaling system may function as an anti-remodeling mechanism in humans, which becomes upregulated in the failing human LV but ultimately may become overwhelmed by pathologic pro-remodeling signals. Augmenting PKGIα and its downstream substrates may represent a novel therapeutic strategy for certain types of heart failure.