Cardiomyocyte Specific MLK3 Deletion Opposes LV Dysfunction and Cardiac Fetal Gene Re-Expression
Authors: Burke Anna , Pande Suchita , Lin Weiyu , Kreutz Lennart , Martin Gregory , Blanton Robert 
Published: May 2024

Study Objective: To determine the cardiac myocyte (CM) and blood pressure-independent effects of Mixed lineage kinase 3 (MLK3) in the regulation of left ventricular (LV) function at baseline and in response to pathological stress. Background: MLK3 functions as a direct substrate effector of cGMP-dependent protein kinase 1α (PKG1α). Whole-body MLK3 deletion in mice increases cardiac dysfunction and remodeling after pressure overload and prevents the therapeutic effect of cGMP augmentation on LV function. However, MLK3 deletion also causes hypertension, which may confound these findings. Hypothesis: MLK3 opposes LV dysfunction through a blood pressure-independent function in the cardiac myocyte (CM). Methods: We generated mice harboring LoxP sites flanking the MAP3K11 gene encoding MLK3 (MLK3fl/fl) and crossed them with αMHC-Cre transgenic mice, enabling constitutive postnatal cardiac myocyte-specific MLK3 deletion (CMKO). Male and female 3- and 6-month-old MLK3 CMKO and control MLK3 intact (MLK3fl/fl Cre-) littermates were studied in the basal state. We also performed transaortic constriction (TAC) or sham surgery for 4 weeks on 3-month-old male mice. We assessed LV structure and function by organ mass, echocardiography, pressure volume loop analysis, qPCR, and immunoblot. In basal and TAC studies, we used age-matched αMHC-Cre x MLK3+/+ (non-floxed) mice as additional controls. Results: MLK3 gene excision in CMs was confirmed by PCR. By 6 months of age, MLK3 CMKO mice displayed: progressive reduction in LV ejection fraction; increase in LV internal diameter; and LV hypertrophy, indicating LV dysfunction and pathological remodeling, compared with littermate controls or with αMHC-Cre x MLK3+/+ non-floxed mice. This effect was more prominent in females than in males. LV fetal gene expression did not differ between genotypes at 3 months. At 6 months of age, however, the fetal genes nppa, RCAN, and CTGF were significantly upregulated in both male and female MLK3 CMKO mice, compared with MLK3 intact, indicating pathological remodeling. After 4-week TAC, MLK3 CMKO LVs developed more severe reduction in LV systolic function compared with MLK3 intact littermates as assayed by echocardiographic measures of LV ejection fraction; and invasive hemodynamic indices of preload recruitable stroke work, maximum LV pressure and LV developed pressure. The MLK3 CMKO LVs also demonstrated a more eccentric remodeling phenotype in which LV mass/tibia length, LV end diastolic and end systolic diameters increased more severely in CMKO mice, with corresponding reduced LV wall thicknesses. Finally, lung mass/tibia length was elevated in the MLK3 CMKO TAC mice compared to MLK3 intact TAC littermates, indicating overt heart failure. Conclusion: (1) MLK3 functions as a tonic inhibitor of LV dysfunction and pathological remodeling through a role in the CM, possibly through sex-specific mechanisms. (2) Intact MLK3 is required for normal LV compensation and concentric remodeling in response to pressure overload. These findings have important clinical implications, as drugs which activate PKG1 in heart failure improve outcomes but are limited by excess hypotension. As a myocardial PKG1 substrate which opposes pathological LV remodeling through blood pressure-independent mechanisms, MLK3 may represent a candidate therapeutic target for heart failure. NIH 1R01HL162919. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.