Abstract Body: Introduction: Drugs which activate cGMP-dependent protein kinase 1 (PKG1) improve LV function and outcomes in heart failure (HF) but are limited by excessive PKG1-induced hypotension. Mixed lineage kinase 3 (MLK3) is a PKG1α substrate required for PKG1 preservation of cardiac function in experimental HF models. In mice, global MLK3 deletion leads to cardiac dysfunction and remodeling after pressure overload, but also causes systemic hypertension. The blood pressure-independent role of MLK3 in the cardiac myocyte (CM) remains poorly understood.

Hypothesis: MLK3 opposes LV dysfunction through a blood pressure-independent function in the CM.

Methods: We generated mice with lox-P sites flanking exons 4-10 of the Map3k11 gene encoding MLK3, and crossed them with αMHC-Cre transgenic mice to generate CM-specific deletion (MLK3 CMKO) mice. We subjected 12-week-old male MLK3 CMKO and control MLK3fl/fl Cre- (MLK3 intact) littermates to transaortic constriction (TAC) or sham surgery for 4 weeks. To control for Cre effects we also studied non-floxed, Cre+ age matched mice.

Results: We confirmed CM specific MLK3 deletion by PCR. At 4 weeks post-TAC, MLK3 CMKO mice exhibited more severe abnormalities in LV ejection fraction, isovolumetric relaxation time, maximum and developed LV pressure, preload recruitable stroke work, and end diastolic/systolic pressure volume relations. Both genotypes developed LV hypertrophy after TAC, but relative wall thickness decreased selectively in the MLK3 CMKO mice, indicating a more eccentric remodeling phenotype. MLK3 CMKO TAC mice also displayed excess LV interstitial fibrosis, as well as increased expression of ANP and CTGF mRNA. Systolic blood pressure did not differ between sham MLK3 CMKO and MLK3 intact sham groups. MLK3 CMKO TAC mice displayed more severe LV dysfunction and eccentric remodeling than control aMHC-Cre+ no-flox TAC mice, indicating an effect of MLK3 deletion rather than Cre toxicity.

Conclusions: CM-specific MLK3 opposes LV dysfunction, eccentric remodeling, and interstitial fibrosis after pressure overload without affecting blood pressure. This suggests future investigation of MLK3 augmentation in HF to promote PKG1 therapeutic effects on LV function but avoid excess hypotension.