Abstract Body: Introduction: Mixed-lineage kinase 3 (MLK3) is a cGMP-dependent protein kinase 1α (PKG1α) substrate, preserving left ventricular (LV) function without affecting blood pressure (BP). MLK3 kinase-dependent effects maintain LV function, while kinase-independent signalling regulates BP. Thus, enhancing MLK3 kinase activity may improve LV function in heart failure (HF) while circumventing PKG1-induced hypotension. No MLK3-activation strategies exist currently, thus hindering progress in MLK3 research and potential therapeutics.
Hypothesis: Augmenting MLK3 after pressure overload by transaortic constriction (TAC) would prevent LV hypertrophy and dysfunction in mice.
Goal: To test the effect of adeno-associated virus 9 (AAV9)-mediated MLK3 overexpression on LV function, when administered in the setting of pre-existing LV hypertrophy and dysfunction.
Methods: Male mice 12 weeks of age underwent 26G TAC or sham surgery. At day 5 post-TAC we administered by retro-orbital injection AAV9 encoding MLK3 or TdTomato negative control, each under control of the CM-specific cTNT promoter (AAV-MLK3: n=12 TAC, 7 sham; AAV-TdTomato: n=10 Tac, 8 sham. At day 28 post-AAV9 injection, we measured cardiac structure and function by echocardiography, invasive LV hemodynamics, and organ weights.
Results: Echocardiography 5 days post-TAC confirmed TAC-induced LV hypertrophy and reduced systolic function prior to AAV9 treatment. At day 28, AAV-MLK3-treated TAC mice demonstrated improved LV ejection fraction and fractional shortening compared with TAC-AAV-Td controls, indicating improved systolic function. MLK3-treated TAC mice maintained higher LV systolic pressure post-TAC vs. Td controls, further indicating improved cardiac performance. Diastolic indices, including ratio of mitral E/A inflow velocities, tau, and LV relaxation rate were also improved in AAV-MLK3 TAC versus AAV-Td controls. AAV9-MLK3 administration had no effect on LV wall thickness or on LV or whole heart mass normalized to tibia length. MLK3 expression was increased 3-fold in AAV9-MLK3 TAC LVs compared with AAV9-Td controls.
Conclusion: AAV9-mediated MLK3 overexpression after the onset of LV hypertrophy and dysfunction improves LV function in mice.