Modeling the mitochondrial cardiomyopathy of Barth syndrome with induced pluripotent stem cell and heart-on-chip technologies

Abstract

Studying monogenic mitochondrial cardiomyopathies may yield insights into mitochondrial roles in cardiac development and disease. Here, we combine patient-derived and genetically engineered iPSCs with tissue engineering to elucidate the pathophysiology underlying the cardiomyopathy of Barth syndrome (BTHS), a mitochondrial disorder caused by mutation of the gene Tafazzin (TAZ). Using BTHS iPSC-derived cardiomyocytes (iPSC-CMs), we defined metabolic, structural, and functional abnormalities associated with TAZ mutation. BTHS iPSC-CMs assembled sparse and irregular sarcomeres, and engineered BTHS “heart on chip” tissues contracted weakly. Gene replacement and genome editing demonstrated that TAZ mutation is necessary and sufficient for these phenotypes. Sarcomere assembly and myocardial contraction abnormalities occurred in the context of normal whole cell ATP levels. Excess levels of reactive oxygen species mechanistically linked TAZ mutation to impaired cardiomyocyte function. Our study provides new insights into the pathogenesis of Barth syndrome, suggests new treatment strategies, and advances iPSC-based in vitro modeling of cardiomyopathy.

Contractility of single cardiomyocytes differentiated from pluripotent stem cells depends on physiological shape and substrate stiffness

“…Microfabrication techniques can engineer hPSC-CMs to develop systems in which cell properties and function match physiological properties (10,11). Engineered multicellular cultures of hPSCCMs can model cardiac contractility (10,11) but are limited by cellto-cell variations in myocyte type (atrial, ventricular, and nodal), cell size, shape, and myofibril alignment, which can lead to inaccurate measurements of contractile output (12).…”

“…Engineered multicellular cultures of hPSCCMs can model cardiac contractility (10,11) but are limited by cellto-cell variations in myocyte type (atrial, ventricular, and nodal), cell size, shape, and myofibril alignment, which can lead to inaccurate measurements of contractile output (12).…”

“…Matrigel is an extracellular matrix mixture (14), and CMs assume the shape of micropatterns of extracellular proteins printed on surfaces (11,15,16). A rectangular shape of hPSC-CMs with a physiological aspect ratio of 7:1 and area of 2,000 μm 2 engineers a physiological organization of sarcomeres (11), with myofibrils aligned along the main cell axis, as in primary adult murine CMs (17). Culturing primary neonatal murine CMs on substrates with a physiological stiffness (∼10 kPa) leads to mature myofibril organization and cell function (13,18).…”

Myostatin deficiency is associated with lipidomic abnormalities in skeletal muscles

“…CL is also involved in the β-oxidation of fatty acids, as a reduction of mature CL impairs skeletal muscle FA oxidation [27,28] and a positive correlation has been demonstrated between mitochondrial COX activity and CL content [29]. Patients with Barth Syndrome (a X-linked disorder resulting from mutations in the gene encoding for tafazzin) or mice models which lack mature CL, have shown exercise intolerance, cardiac and skeletal muscle dysfunction, mitochondrial dysfunction, ATP deficiency and premature mortality [30,31,32] In vitro, mitochondrial respiration has been shown to be impaired in inducible pluripotent stem cell (iPSC)-derived human cardiomyocytes from Barth Syndrome patients [33]. Possible mechanisms for this disease-associated mitochondrial dysfunction include mitochondrial supercomplex destabilization [34], higher reduced levels of mitochondrial cardiolipin [35] and abnormal mitochondrial morphology [30].…”

Updated summary of genome editing technology in human cultured cells linked to human genetics studies

“…These indel mutations in protein-coding regions cause frameshifts to generate a null-mutant cell. To date, many disease-model cells generated by this strategy have been reported [53][54][55][56][57]. In the field of human genetics, these null-mutant cells are also used in complementary tests for the candidate variants underlying a genetic disorder called by forward genetics approach.…”