The R21C Mutation in Cardiac Troponin I Imposes Differences in Contractile Force Generation between the Left and Right Ventricles of Knock-In Mice

Abstract

We investigated the effect of the hypertrophic cardiomyopathy-linked R21C (arginine to cysteine) mutation in human cardiac troponin I (cTnI) on the contractile properties and myofilament protein phosphorylation in papillary muscle preparations from left (LV) and right (RV) ventricles of homozygous R21C+/+ knock-in mice. The maximal steady-state force was significantly reduced in skinned papillary muscle strips from the LV compared to RV, with the latter displaying the level of force observed in LV or RV from wild-type (WT) mice. There were no differences in the Ca2+ sensitivity between the RV and LV of R21C+/+ mice; however, the Ca2+ sensitivity of force was higher in RV-R21C+/+ compared with RV-WT and lower in LV- R21C+/+ compared with LV-WT. We also observed partial loss of Ca2+ regulation at low [Ca2+]. In addition, R21C+/+-KI hearts showed no Ser23/24-cTnI phosphorylation compared to LV or RV of WT mice. However, phosphorylation of the myosin regulatory light chain (RLC) was significantly higher in the RV versus LV of R21C+/+ mice and versus LV and RV of WT mice. The difference in RLC phosphorylation between the ventricles of R21C+/+ mice likely contributes to observed differences in contractile force and the lower tension monitored in the LV of HCM mice.

Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility

“…[145] reported that cTnI R145G decreased maximal ATPase in the presence of Ca 2+ , and reduced inhibition of actomyosin ATPase activity in the absence of Ca 2+ . cTnI R21C is the only identified HCM-associated mutation located at the cardiac-specific N-terminus of cTnI [30, 157-159]. Using transgenic mice, Wang el al .…”

Exploring Functional Differences between the Right and Left Ventricles to Better Understand Right Ventricular Dysfunction

“…However, two previous studies found no changes in sarcomere shortening in rats [ 41 , 42 ]. Furthermore, at the molecular level, actin interacts differently with myosin cross-bridges in the LV, allowing greater mobility of actin monomers and, hence, greater contractility [ 44 , 45 ], without changes in troponin I and T, myosin-binding protein C (MyBP-C), or the myosin regulatory light chain phosphorylation, between LV and RV [ 46 ]. On the other hand, the maximal shortening velocity is also slower in RV myocytes [ 29 ], which is related to decreased Ca 2+ sensitivity in RV myofilaments [ 46 – 48 ].…”

“…Furthermore, at the molecular level, actin interacts differently with myosin cross-bridges in the LV, allowing greater mobility of actin monomers and, hence, greater contractility [ 44 , 45 ], without changes in troponin I and T, myosin-binding protein C (MyBP-C), or the myosin regulatory light chain phosphorylation, between LV and RV [ 46 ]. On the other hand, the maximal shortening velocity is also slower in RV myocytes [ 29 ], which is related to decreased Ca 2+ sensitivity in RV myofilaments [ 46 – 48 ]. However, greater myosin ATPase activity [ 49 , 50 ] and a faster cellular contraction in the RV have also been reported due to a larger proportion of heavy α -chain-containing myosin isozyme in the RV compared to the LV, which has a larger proportion of the slower β -chain [ 49 ].…”

The Molecular Mechanisms of Mutations in Actin and Myosin that Cause Inherited Myopathy

“…Recently myosin heavy chain has been successfully expressed in small quantities in C2C12 myoblasts and the effects of mutation has been studied [ 30 , 31 ]. Transgenic and knock-in mouse models have been extensively used for actin [ 18 , 32 , 33 , 34 , 35 ], myosin heavy chain [ 36 , 37 ] and myosin light chain mutation studies [ 38 , 39 , 40 ]. Actin has the same sequence in man and mouse and light chain sequences are similar but mouse heart predominantly expressed α-myosin heavy chain ( MYH6 gene) rather than β-myosin ( MYH7 ) which predominates in human heart so the mutations have to be studied in an α-myosin heavy chain background which may significantly impact upon the effects of the mutation [ 41 ].…”