Abstract Wed053: Cardiomyocyte-Specific Mixed Lineage Kinase 3 Deletion Leads to Adverse Left Ventricular Remodeling and Dysfunction Independent of Blood Pressure Effects

Introduction: Heart failure (HF) is a leading cause of mortality. Protein kinase G1 (PKG1) activation improves HF outcomes but often causes hypotension. Identifying blood pressure (BP)-independent PKG1 effectors could offer new therapeutic targets. Mixed lineage kinase 3 (MLK3) is a novel PKG1a substrate, and whole-body MLK3 knockout mice develop more severe left ventricular (LV) dysfunction after transaortic constriction but also have hypertension. The cardiac myocyte (CM) and BP-independent effects of MLK3 remain unclear. Hypothesis: MLK3 kinase function in the CM opposes basal pathological LV remodeling and dysfunction independent of BP. Methods: Male and female 3- and 6-month-old CM-specific MLK3 deletion (CMKO, n=12) and control MLK3 intact (MLK3 fl/fl Cre-, n=11) littermate mice were studied. Wild type (WT) mice were injected with MLK3 kinase inhibitor URMC-099 or vehicle for 2 weeks (10mg/kg 2x/day, n=4 per group). Echocardiography, organ masses, and LV hemodynamics were measured. We performed phosphoproteomics from the above groups to examine MLK3 kinase-dependent and CM-specific signaling. Results: At 3 months, LV dP/dt was reduced in CMKO males, while dP/dt and dP/dt min were reduced in females, compared with MLK3 intact. At 6 months, CMKO mice exhibited increased LV/tibia length, heart weight/tibia length , and end-diastolic dimension, along with reduced ejection fraction, dP/dt, dP/dt min, and contractile index in females. Notably, BP was not increased in MLK3 CMKO mice. MLK3 kinase inhibition decreased ejection fraction in females, compared with vehicle. MLK3 protein expression was unchanged between WT males and females at 3 and 6 months. Principal component analysis of phosphoproteomic data revealed distinct protein expression and phosphorylation patterns between MLK3 CMKO and MLK3-inhibited groups. Conclusion: CM-specific MLK3 deletion and systemic MLK3 kinase inhibition lead to pathological LV remodeling and dysfunction independent of BP effects, particularly in females, supporting a requirement of intact MLK3 kinase function for normal cardiac function. These findings, combined with the observed phosphoproteomic changes suggest that modulating MLK3 or MLK3-dependent signaling could improve LV function in HF.