Hypertrophic cardiomyopathy associated E22K mutation in myosin regulatory light chain decreases calcium‐activated tension and stiffness and reduces myofilament Ca²⁺ sensitivity

Abstract

We investigated the mechanisms associated with E22K mutation in myosin regulatory light chain (RLC), found to cause hypertrophic cardiomyopathy (HCM) in humans and mice. Specifically, we characterized the mechanical profiles of papillary muscle fibers from transgenic mice expressing human ventricular RLC wild‐type (Tg‐WT) or E22K mutation (Tg‐E22K). Because the two mouse models expressed different amounts of transgene, the B6SJL mouse line (NTg) was used as an additional control. Mechanical experiments were carried out on Ca2+‐ and ATP‐activated fibers and in rigor. Sinusoidal analysis was performed to elucidate the effect of E22K on tension and stiffness during activation/rigor, tension‐pCa, and myosin cross‐bridge (CB) kinetics. We found significant reductions in active tension (by 54%) and stiffness (active by 40% and rigor by 54%). A decrease in the Ca2+ sensitivity of tension (by ∆pCa ~ 0.1) was observed in Tg‐E22K compared with Tg‐WT fibers. The apparent (=measured) rate constant of exponential process B (2πb: force generation step) was not affected by E22K, but the apparent rate constant of exponential process C (2πc: CB detachment step) was faster in Tg‐E22K compared with Tg‐WT fibers. Both 2πb and 2πc were smaller in NTg than in Tg‐WT fibers, suggesting a kinetic difference between the human and mouse RLC. Our results of E22K‐induced reduction in myofilament stiffness and tension suggest that the main effect of this mutation was to disturb the interaction of RLC with the myosin heavy chain and impose structural abnormalities in the lever arm of myosin CB. When placed in vivo, the E22K mutation is expected to result in reduced contractility and decreased cardiac output whereby leading to HCM. Sub‐Discipline Bioenergetics. Database The data that support the findings of this study are available from the corresponding authors upon reasonable request. Animal protocol BK20150353 (Soochow University). Research governance School of Nursing: Hua‐Gang Hu: seuboyh@163.com; Soochow University: Chen Ge chge@suda.edu.cn.

Variants identify sarcomere inter-protein contacts distinguishing inheritable cardiac muscle diseases

“…The destabilization potentially mimics the native mechanism for disrupting SRX by RN phosphorylation. RLC has several variants implicated in FHC disease [30][31][32] including one in R1 that stabilizes SRX in mice [33]. The latter implies there are other molecular mechanisms for inheritable FHC.…”

A perspective on Notch signalling in progression and arrhythmogenesis in familial hypertrophic and dilated cardiomyopathies

“…A cogent example of this role is the linkage of mutations in genes expressing sarcomere proteins linked to DCM and HCM. As summarized by Viola & Hool [19], thin filament sarcomere mutations linked to DCM and HCM induce altered myofilament response to Ca 2+ as do mutations in cardiac myosin binding protein C (cMyBP-C) [20] and myosin regulatory light chain [21]. On the other hand a prevalent HCM-linked mutation in myosin heavy chain (R403Q) was reported not to modify myofilament Ca 2+ -sensitivity [22].…”

Critical Evaluation of Current Hypotheses for the Pathogenesis of Hypertrophic Cardiomyopathy

“…Some of these, which are associated with the β-MHC mutations, were considered above. Another example of a mutation that has been found to decrease calcium-activated tension and stiffness and reduce myofilament Ca 2+ sensitivity is the E22K mutation in the RLC of myosin [172]. This mutation causes HCM in both mice and humans.…”

“…Whereas the mentioned study was performed in skinned papillary muscles from transgenic mice, the RLC was of human type, and similar HCM disease phenotypes are seen in mice and humans. However, it is important to note that there are variable results for the effect of the RLC E22K mutation on Ca 2+ sensitivity [198,199], with one of the studies [198,199] even showing an increased Ca-sensitivity (discussed by Zhang et al [172]). One further example of hypocontractility in cell and myofibril studies has been seen with the HCM-causing actin mutation A331P that decreased both the maximum isometric tension and calcium sensitivity in skinned bovine muscle fibers that were reconstituted with actin expressed in insect cells [164].…”