Troponin (Tn) is a critical regulator of muscle contraction in cardiac muscle. Mutations in Tn subunits are associated with hypertrophic, dilated and restrictive cardiomyopathies. Improved diagnosis of cardiomyopathies as well as intensive investigation of new mouse cardiomyopathy models has significantly enhanced this field of research. Recent investigations have showed that the physiological effects of Tn mutations associated with hypertrophic, dilated and restrictive cardiomyopathies are different. Impaired relaxation is a universal finding of most transgenic models of HCM, predicted directly from the significant changes in Ca(2+) sensitivity of force production. Mutations associated with HCM and RCM show increased Ca(2+) sensitivity of force production while mutations associated with DCM demonstrate decreased Ca(2+) sensitivity of force production. This review spotlights recent advances in our understanding on the role of Tn mutations on ATPase activity, maximal force development and heart function as well as the correlation between the locations of these Tn mutations within the thin filament and myofilament function.
"The increased expression of MLC2 gene and protein under healthy, static conditions can explain a critical symptom of DCM, most notably a diminished systolic function accompanied by an inability to generate the necessary contractile force. Therefore, this result supports the idea that CM structure and function are affected by a pathological status (altering cellular mechanism) related to DCM (Marian and Roberts, 1994; Morita et al., 2005; Willott et al., 2010). A previous study reported reduced beating rates and contractility with altered sarcomere structures in iPSC-CMs derived from DCM patients (Sun et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: Primary dilated cardiomyopathy (DCM) is a non-ischemic heart disease with impaired pumping function of the heart. In this study, we used human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from a healthy volunteer and a primary DCM patient to investigate the impact of DCM on iPSC-CMs׳ responses to different types of anisotropic strain. A bioreactor system was established that generates cardiac-mimetic forces of 150kPa at 5% anisotropic cyclic strain and 1Hz frequency. After confirming cardiac induction of the iPSCs, it was determined that fibronectin was favorable to other extracellular matrix protein coatings (gelatin, laminin, vitronectin) in terms of viable cell area and density, and was therefore selected as the coating for further study. When iPSC-CMs were exposed to three strain conditions (no strain, 5% static strain, and 5% cyclic strain), the static strain elicited significant induction of sarcomere components in comparison to other strain conditions. However, this induction occurred only in iPSC-CMs from a healthy volunteer ("control iPSC-CMs"), not in iPSC-CMs from the DCM patient ("DCM iPSC-CMs"). The donor type also significantly influenced gene expressions of cell-cell and cell-matrix interaction markers in response to the strain conditions. Gene expression of connexin-43 (cell-cell interaction) had a higher fold change in healthy versus diseased iPSC-CMs under static and cyclic strain, as opposed to integrins α-5 and α-10 (cell-matrix interaction). In summary, our iPSC-CM-based study to model the effects of different strain conditions suggests that intrinsic, genetic-based differences in the cardiomyocyte responses to strain may influence disease manifestation in vivo.
Journal of Biomechanics 10/2015; DOI:10.1016/j.jbiomech.2015.09.028 · 2.75 Impact Factor
"While FHC mutations have been identified across a wide range of proteins, more than half of all mutations that cause hypertrophy occur in proteins of the sarcomere . As of 2010, 68 mutations in the troponin complex had been linked to FHC . The first mutation associated with FHC in cTnC was L29Q (cTnC(L29Q)), which was identified in a patient suffering from left ventricular hypertrophy . "
"Strong evidence links the disease phenotypes with the increased Ca 2? -sensitivity (Jagatheesan et al. 2007; Pinto et al. 2008) thereby strengthening the rationale of using reconstituted mutated systems to model the phenotype. There have been several recent studies and reviews of sarcomeric proteins whose mutations are linked to HCM and RCM (Robinson et al. 2007; Parvatiyar et al. 2010; Gomes et al. 2004; Tardiff 2005; Marston 2011; Ohtsuki and Morimoto 2008; Willott et al. 2009; Tardiff 2011; Redwood and Robinson 2013; Spudich 2014). In this review, we will mainly focus on some mutations in cardiac troponin I (cTnI) and briefly discuss some of the studies with the other thin filament proteins Tm, cTnC and cardiac troponin T (cTnT) that provide evidence of increased contribution of the M 2 state. "
[Show abstract][Hide abstract] ABSTRACT: This review proposes a link between the hypertrophic (HCM) and restrictive cardiomyopathies caused by mutations in several sarcomeric thin filament proteins, and the open state of the three-state muscle regulation theory. The three characteristics of various muscle systems reconstituted from HCM mutated proteins (increased Ca2+-sensitivity, increased basal activity in the absence of Ca2+, and decreased cooperativity) can be explained by the contribution of a myosin-induced open state (M−
), which elevates the basal activity and competes with the normal Ca2+-activated pathway. A model based on the three-state theory of regulation, shows how a change in the closed/blocked equilibrium caused by a mutation that weakens the binding of troponin I to tropomyosin-actin can produce the characteristics of HCM. This review also shows that in the M−
state, Ca2+ can shift the closed–open equilibrium of the N-terminal hydrophobic region of troponin C without affecting activity.
Journal of Muscle Research and Cell Motility 04/2014; 35(2). DOI:10.1007/s10974-014-9383-z · 2.09 Impact Factor
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