Abstract 12167: Cardiac-Specific Knockout of Myosin Phosphatase Targeting Subunit 2 Prevents Cardiac Fibrosis in a Connective Tissue Growth Factor-Dependent Manner in Mineralocorticoid Receptor-Related Hypertension Mice

Introduction: Myosin phosphatase targeting subunit 2 (MYPT2) is an important subunit of cardiac myosin light chain phosphatase (MLCP), which plays a crucial role in regulating the phosphorylation of MLC (p-MLC). Recent research has shown that cardiac MLCP plays an important role in cardiac fibrosis as a target of Rho kinase and protein kinase G. However, it is unclear how the loss of MYPT2 affects cardiac function and fibrosis.

Methods: After the knockdown of MYPT2, HL-1 cells (murine cardiomyocytes) were incubated with aldosterone (ALDO) for 24h. Cardiac specific MYPT2 knockout (c-MYPT2 ^-/- ) mice were generated using the Cre lox system (αMHCMerCreMer; MYPT2 ^f/f ). Mineralocorticoid receptor (MR)-related hypertension mice were induced by the subcutaneous infusion of ALDO and 8% NaCl food for 4 weeks after uninephrectomy.

Results: In HL-1 cells, ALDO increased connective tissue growth factor (CTGF) and MYPT2 and decreased the p-MLC in a dose-dependent manner. Knockdown of MYPT2 decreased CTGF. In mice model, the MYPT2 expression in the heart from MYPT2 ^-/- mice was decreased to less than 30% compared with MYPT2 ^+/+ mice. Heart rate, blood pressure, and cardiac systolic function were normal in c-MYPT2 ^-/- mice. Type 1 phosphatase catalytic subunit β was decreased and p-MLC was increased in c-MYPT2 ^-/- mice. Blood pressure elevation and left ventricular hypertrophy were observed in both MR-related hypertension mice, while no difference in heart size and the nuclear localization of MR in cardiomyocytes. However, ejection fraction and fractional shortening in echocardiography were higher in c-MYPT2 ^-/- than in MYPT2 ^+/+ in MR-related hypertension mice. After treatment of ALDO for 28 days, both global radial and longitudinal strain (GRS and DLS) were reduced in both c-MYPT2 ^-/- and MYPT2 ^+/+ mice, but the reduction in systolic and diastolic GRS and GLS strain rates were prevented in c-MYPT2 ^-/- mice compared with MYPT2 ^+/+ mice. Histopathology revealed fibrosis degree in c-MYPT2 ^-/- mice was lower than MYPT2 ^+/+ mice with decreased CTGF and increased p-MLC.

Conclusions: Cardiac-specific deletion of MYPT2 resulted in a decrease of MLCP and an increase of p-MLC. MYPT2 deletion can prevent cardiac fibrosis and dysfunction in a MR-related hypertension model.