Aims Dilated cardiomyopathy (DCM), a myocardial disorder that can result in progressive
heart failure and arrhythmias, is defined by ventricular chamber enlargement and dilatation,
and systolic dysfunction. Despite extensive research, the pathological mechanisms
of DCM are unclear mainly due to numerous mutations in different gene families resulting
in the same outcome-decreased ventricular function. Titin (TTN) a giant protein, expressed
in cardiac and skeletal muscles, is an important part of the sarcomere, and thus TTN
mutations are the most common cause of adult DCM. To decipher the basis for the cardiac
pathology in titin-mutated patients, we investigated the hypothesis that induced Pluripotent
Stem Cell (iPSC)-derived cardiomyocytes (iPSC-CM) generated from patients, recapitulate
the disease phenotype. The hypothesis was tested by 3 Aims: (1) Investigate key features
of the excitation-contraction-coupling machinery; (2) Investigate the responsiveness
to positive inotropic interventions; (3) Investigate the proteome profile of the AuP
cardiomyocytes using mass-spectrometry (MS). Methods and results iPSC were generated
from the patients' skin fibroblasts. The major findings were: (1) Sarcomeric organization
analysis in mutated iPSC-CM showed defects in assembly and maintenance of sarcomeric
structure. (2) Mutated iPSC-CM exhibited diminished inotropic and lusitropic responses
to beta-adrenergic stimulation with isoproterenol, increased [Ca2+](out) and angiotensin-II.
Additionally, mutated iPSC-CM displayed prolonged recovery in response to caffeine.
These findings may result from defective or lack of interactions of the sarcomeric
components with titin through its kinase domain which is absent in the mutated cells.
Conclusions These findings show that the mutated cardiomyocytes from DCM patients
recapitulate abnormalities of the inherited cardiomyopathies, expressed as blunted
inotropic response.
