Molecular mechanisms of diastolic heart failure: a study of myosin phosphatase regulatory subunit deficiency
M Mccauley, A Aboonabi, K S Lizama, S J Ahn, J A Keefe, S Zhao, T A Patel, F J Gonzalez-Gonzalez, B Bozkurt, L Miller, I Levitan, J Kirk, X H T WehrensAbstract
Background and Aims
Diastolic heart failure (DHF) is a growing clinical challenge with limited therapeutic options. Myosin light chain phosphatase (MLCP), a key regulator of cardiac relaxation, plays a central role in diastolic function. However, the specific contributions of MLCP subunits to cardiac muscle relaxation and DHF pathology remain unclear. This study aims to investigate these mechanisms to address critical gaps in understanding and advance the potential for targeted interventions.
Methods
This study determined the role of the regulatory protein phosphatase 1 subunit 12C, a MLCP protein subunit encoded by the Ppp1r12c gene in mice (human ortholog: PPP1R12C), in cardiac physiology and pathology using a Ppp1r12c knockout (12C-KO) mouse model. Through a combination of physiological assessments, echocardiography, electron microscopy, and multi-omics analyses, we delineate the effects of Ppp1r12c gene ablation upon cardiac structure and function.
Results
12C-KO mice develop hypertension starting at 1-2 months of age, resulting in severe diastolic dysfunction versus wild type controls at six months of age including echo Doppler parameters showing: decreased E velocity (372±126 vs. 590±156, P = 0.03, n = 5 per group), decreased E′ velocity (9.37±2.30 vs. 15.58±3.53, P = 0.01), increased isovolumetric relaxation time (21.40±2.76 vs. 15.05±2.61, P = 0.02), decreased mitral valve acceleration time (263±120 vs. 482±124, P = 0.02), and decreased mitral valve deceleration time (11.39±2.92 vs. 18.80±4.30, P = 0.03). Ultrastructural analyses show sarcomere elongation and Z-line irregularities, consistent with sarcomere remodeling. Transcriptomic and proteomic profiling indicates disrupted gene and protein expression patterns commonly seen in cardiomyopathy and decreased oxidative phosphorylation without compensatory upregulation of other MLCP subunits.
Conclusions
The protein phosphatase 1 regulatory subunit 12C (Ppp1r12c) plays a significant role in regulating blood pressure and cardiac relaxation. Genetic ablation of Ppp1r12c in mice leads to early onset of hypertension and progressive diastolic dysfunction, which is related to sarcomere remodeling and mitochondrial dysfunction. The 12C-KO mouse is associated with sarcomeric remodeling and impaired energetic homeostasis.