The structural basis of alpha-tropomyosin linked (Asp230Asn) familial dilated cardiomyopathy

Abstract

Recently, linkage analysis of two large unrelated multigenerational families identified a novel dilated cardiomyopathy (DCM)-linked mutation in the gene coding for alpha-tropomyosin (TPM1) resulting in the substitution of an aspartic acid for an asparagine (at residue 230). To determine how a single amino acid mutation in α-tropomyosin (Tm) can lead to a highly penetrant DCM we generated a novel transgenic mouse model carrying the D230N mutation. The resultant mouse model strongly phenocopied the early onset of cardiomyopathic remodeling observed in patients as significant systolic dysfunction was observed by 2 months of age. To determine the precise cellular mechanism(s) leading to the observed cardiac pathology we examined the effect of the mutation on Ca2+ handling in isolated myocytes and myofilament activation in vitro. D230N-Tm filaments exhibited a reduced Ca2+ sensitivity of sliding velocity. This decrease in sensitivity was coupled to increase in the peak amplitude of Ca2+ transients. While significant, and consistent with other DCMs, these measurements are comprised of complex inputs and did not provide sufficient experimental resolution. We then assessed the primary structural effects of D230N-Tm. Measurements of the thermal unfolding of D230N-Tm vs WT-Tm revealed an increase in stability primarily affecting the C-terminus of the Tm coiled-coil. We conclude that the D230N-Tm mutation induces a decrease in flexibility of the C-terminus via propagation through the helical structure of the protein, thus decreasing the flexibility of the Tm overlap and impairing its ability to regulate contraction. Understanding this unique structural mechanism could provide novel targets for eventual therapeutic interventions in patients with Tm-linked cardiomyopathies.

Cardiomyopathy phenotypes in human-induced pluripotent stem cell-derived cardiomyocytes—a systematic review

“…The relation between intracellular Ca 2+ concentrations and force development of the myofilaments is a highly regulated biological constant with half-maximal force development (of skinned myofibers) at a pCa of ~ 5.8 (~ 1.6 μM). Numerous studies reported increased Ca 2+ sensitivity on HCM [ 3 , 13 , 19 , 23 , 67 , 95 , 96 ] and decreased in DCM [ 19 , 20 , 56 ]. The shift in the pCa/force relation leads to more force development at lower Ca 2+ concentrations in case of HCM and less force development in DCM.…”

“…Mutations (or full deletion) of MYBPC3 or cardiac troponin T ( TNNT2 , TnT) have been associated with a shallow pCa-force relationship (lower Hill coefficient) and residual force development at very low or nominal absence of Ca 2+ [ 3 , 56 , 75 ]. In the case of cMyBPC, the effect may be explained by mutations (or its absence) disturbing its normal role in stabilizing the super-relaxed, inactive state (SRX) of myosin heads [ 63 ].…”

Modulating the tension-time integral of the cardiac twitch prevents dilated cardiomyopathy in murine hearts

“…This mutation has been found in at least 2 unrelated families with DCM ( 12 ). In vitro studies have shown that D230N-Tm decreases the calcium (Ca 2+ ) sensitivity of filament sliding and ATPase rates in motility assays ( 13 , 14 ), decreases the Ca 2+ affinity of troponin (Tn) C (TnC) ( 12 ), and increases the affinity of Tm for actin by nearly 5-fold ( 14 ). Moreover, transgenic mice expressing D230N-Tm have significant systolic dysfunction and eccentric hypertrophy by 2 months of age ( 13 ).…”

“…In vitro studies have shown that D230N-Tm decreases the calcium (Ca 2+ ) sensitivity of filament sliding and ATPase rates in motility assays ( 13 , 14 ), decreases the Ca 2+ affinity of troponin (Tn) C (TnC) ( 12 ), and increases the affinity of Tm for actin by nearly 5-fold ( 14 ). Moreover, transgenic mice expressing D230N-Tm have significant systolic dysfunction and eccentric hypertrophy by 2 months of age ( 13 ). We demonstrate here that the D230N-Tm mutation also significantly decreased the twitch T of intact cardiac muscle, thus producing a large, negative TI that correlates well with the DCM phenotype found in these mice ( 13 ).…”

“…Moreover, transgenic mice expressing D230N-Tm have significant systolic dysfunction and eccentric hypertrophy by 2 months of age ( 13 ). We demonstrate here that the D230N-Tm mutation also significantly decreased the twitch T of intact cardiac muscle, thus producing a large, negative TI that correlates well with the DCM phenotype found in these mice ( 13 ). Using multiscale computational modeling as a guide, we investigate approaches to modulate the TI of sarcomeres with D230N-Tm.…”