Familial Hypertrophic Cardiomyopathy-Linked Mutation (K104E) in the Myosin Regulatory Light Chain Affects Sarcomeric Structure and Function in Tg-Mice

Abstract

Structural and functional effects of the familial hypertrophic cardiomyopathy (FHC)-linked mutation (Lysine 104-to-Glutamic Acid, K104E) in the human ventricular regulatory light chain (RLC) were studied in transgenic (Tg) mice. Small angle X-ray diffraction measurements on freshly skinned papillary muscle fibers demonstrated a mutation-induced increase in the interfilament lattice spacing at both short (2.3 µm) and long (2.5 µm) sarcomere lengths (SL) compared with Tg-WT. The intensity ratio (I1,1/I1,0) in WT fibers increased upon stretch (from SL=2.3 to SL=2.5 µm) indicating a shift in the cross-bridge mass distribution toward the thin filaments. In contrary, the K104E fibers demonstrated no change in I1,1/I1,0 on stretch. In line with X-ray data, K104E fibers developed higher passive tension at pCa 8 when consecutively stretched by 10%, 20%, 30% and 40% of their length compared to WT. Furthermore, the K104E mutation significantly decreased the endogenous RLC phosphorylation (∼2-fold) compared to WT myocardium. Histopathological changes included signs of hypertrophy and severe fibrotic lesions in Tg-K104E hearts. The higher mitochondrial content seen in the left ventricles of K104E mice by electron microscopy was supported by significantly increased myosin ATPase activity in Tg-K104E mice indicating higher energy demand and ATP consumption by the mutant hearts. Studies using single molecule detection demonstrated significantly decreased cross-bridge dissociation rates with lower duty cycle (indicative of lower force production) in Tg-K104E cardiac myofibrils compared to WT. Our results in Tg-K104E mice demonstrated cardiomyocyte hypertrophy and fibrosis, and significant alterations in sarcomere structure and function. Morphological abnormalities, increased passive stiffness and a slower cross bridge dissociation rate in Tg-K104E mice mirror the diastolic dysfunction phenotype observed in K104E positive patients. Supported by AHA12PRE12030412 (to WH), and NIH HL-071778 and HL-108343 (to DSC).