We investigated the effect of 7 Hypertrophic Cardiomyopathy (HCM)-
causing mutations in troponin T (TnT) on troponin function in thin
filaments reconstituted with actin and human cardiac tropomyosin. We
used the quantitative in vitro motility assay to study Ca2+-regulation of
unloaded movement and its modulation by troponin I phosphorylation.
Troponin from a patient with the K280N TnT mutation showed no
difference in Ca2+-sensitivity when compared with donor heart troponin
and the Ca2+-sensitivity was also independent of the troponin I
phosphorylation level (uncoupled). The recombinant K280N TnT mutation
increased Ca2+-sensitivity 1.7-fold and was also uncoupled. The R92Q TnT
mutation in troponin from transgenic mouse increased Ca2+-sensitivity and
was also completely uncoupled. Five TnT mutations (∆14, ∆28+7, ∆E160,
S179F and K273E) studied in recombinant troponin increased Ca2+-
sensitivity and were all fully uncoupled. Thus, for HCM-causing mutations
in TnT, Ca2+-sensitisation together with uncoupling in vitro is the usual
response and both factors may contribute to the HCM phenotype. We also
found that Epigallocatechin-3-gallate (EGCG) can restore coupling to all
uncoupled HCM-causing TnT mutations. In fact the combination of Ca2+-
desensitisation and re-coupling due to EGCG completely reverses both the
abnormalities found in troponin with a TnT HCM mutation suggesting it
may have therapeutic potential.