Mixed Lineage Kinase 3 (MLK3) Prevents Cardiac Dysfunction and Structural Remodeling with Pressure Overload

Background: Myocardial hypertrophy is an independent risk factor for heart failure (HF), yet the mechanisms underlying pathological cardiomyocyte growth are incompletely understood. The c-Jun N- terminal kinase (JNK) signaling cascade modulates cardiac hypertrophic remodeling, but the upstream factors regulating myocardial JNK activity remain unclear. In this study we sought to identify JNK- activating molecules as novel regulators of cardiac remodeling in HF. Methods and Results: We investigated Mixed Lineage Kinase 3 (MLK3), a master regulator of upstream JNK-activating kinases, whose role in the remodeling process has not previously been studied. We observed increased MLK3 protein expression in myocardium from patients with nonischemic and hypertrophic cardiomyopathy and in hearts of mice subjected to transverse aortic constriction (TAC). Mice with genetic deletion of MLK3 (MLK3-/-) exhibited baseline cardiac hypertrophy with preserved cardiac function. MLK3-/- mice subjected to chronic LV pressure overload (TAC, four weeks) developed worsened cardiac dysfunction and increased LV chamber size compared to MLK3+/+ littermates (n=8). LV mass, pathological markers of hypertrophy (Nppa, Nppb), and cardiomyocyte size were elevated in MLK3-/- TAC hearts. Phosphorylation of JNK, but not other MAPK pathways, was selectively impaired in MLK3-/- TAC hearts. In adult rat cardiomyocytes pharmacological MLK3 kinase inhibition using URMC-099 blocked JNK phosphorylation induced by neurohormonal agents and oxidants. Sustained URMC-099 exposure induced cardiomyocyte hypertrophy. Conclusions: These data demonstrate MLK3 prevents adverse cardiac remodeling in the setting of pressure overload. Mechanistically, MLK3 activates JNK which in turn opposes cardiomyocyte hypertrophy. These results support modulation of MLK3 as a potential therapeutic approach in HF.