The effect of cardiomyopathy mutation (R97L) in mouse cardiac troponin T on the muscle length-mediated recruitment of crossbridges is modified divergently by α- and β-myosin heavy chain

Abstract

Hypertrophic cardiomyopathy mutations in cardiac troponin T (TnT) lead to sudden cardiac death. Augmented myofilament Ca2+ sensitivity is a common feature in TnT mutants, but such observations fail to provide a rational explanation for severe cardiac phenotypes. To better understand the mutation-induced effect on the cardiac phenotype, it is imperative to determine the effects on dynamic contractile features such as the muscle length (ML)-mediated activation against α- and β-myosin heavy chain (MHC) isoforms. α- and β-MHC are not only differentially expressed in rodent and human hearts, but they also modify ML-mediated activation differently. Mouse analog of human TnTR94L (TnTR97L) or wild-type TnT was reconstituted into de-membranated muscle fibers from normal (α-MHC) and transgenic (β-MHC) mouse hearts. TnTR97L augmented myofilament Ca2+ sensitivity by a similar amount in α- and β-MHC fibers. However, TnTR97L augmented the negative impact of strained crossbridges on other crossbridges (γ) by 22% in α-MHC fibers, but attenuated γ by 21% in β-MHC fibers. TnTR97L decreased the magnitude of ML-mediated recruitment of crossbridges (ER) by 37% in α-MHC fibers, but increased ER by 35% in β-MHC fibers. We provide a mechanistic basis for the TnTR97L-induced effects in α- and β-MHC fibers and discuss the relevance to human hearts.

Cardiomyopathy mutation (F88L) in troponin T abolishes length dependency of myofilament Ca2+ sensitivity

“…Hypertrophic cardiomyopathy (HCM) mutations in the central region (CR; residues 80–180) of cardiac troponin T (TnT) are not well tolerated, perhaps because of their negative impact on thin filament cooperativity and length-dependent activation of cardiac myofilaments. Previous work from our laboratory has demonstrated that the structural integrity of CR is important for thin filament cooperativity and length-dependent activation of cardiac myofilaments ( Ford et al, 2012 ; Gollapudi and Chandra, 2016a , b ). Recent studies have suggested that impairment of length-dependent activation may be one of the primary mechanisms by which HCM mutations lead to altered cardiac phenotype and deleterious complications associated with HCM ( Sequeira et al, 2013 ).…”

Dilated Cardiomyopathy Mutation (R134W) in Mouse Cardiac Troponin T Induces Greater Contractile Deficits against α-Myosin Heavy Chain than against β-Myosin Heavy Chain

“…Therefore, the R131W mutation in TnT may perturb CR-Tm interactions to modulate XB recruitment dynamics. Given that the TnT-mediated function is dependent on the myosin heavy chain (MHC) isoform (Ford et al, 2012 ; Chandra et al, 2015 ; Gollapudi et al, 2015 ; Gollapudi and Chandra, 2016 ), we hypothesized that the effects of DCM-linked mutations in TnT on contractile dynamics would be differently modulated by α- and β-MHC. To better understand the molecular mechanisms that lead to contractile dysfunction, especially in relevance to humans, it is important to consider the differential impact of α- and β-MHC isoforms on contractile dynamics.…”

“…To better understand the molecular mechanisms that lead to contractile dysfunction, especially in relevance to humans, it is important to consider the differential impact of α- and β-MHC isoforms on contractile dynamics. This is because previous studies have demonstrated that the effects of cardiomyopathy mutations in TnT on steady-state and/or dynamic contractile features are differently modulated by α- and β-MHC isoforms (Ford et al, 2012 ; Chandra et al, 2015 ; Gollapudi et al, 2015 ; Gollapudi and Chandra, 2016 ).…”

Myofilament modulation of contraction

“…These findings support the TnC A8V mutation disrupts muscle function by altering the TnC-TnI interaction and provide further support for the significance of this interaction in the myofilament regulation of cardiac contraction. Work from the laboratory of Murali Chandra sought to investigate the myofilament mechanism responsible for differential phenotypes observed for the TnT R97L hypertrophic cardiomyopathy linked mutation (12). Mechanic measurements of R97L TnT muscles containing α- or β-myosin heavy chain (MHC) demonstrated that while the R97L mutation increased calcium sensitivity similarly in the presence of both the α- or β-MHC, cross-bridge recruitment was dependent upon the MCH isoform co-expressed.…”