Context-aware phenotyping of cardiac disease across translational models
TL;DR
It is argued that disease expression depends on the biological context in which genetic susceptibility acts, and that studying this requires experimental models containing the relevant context, and that studying this requires experimental models containing the relevant context.
Abstract
Cardiomyopathies are a leading cause of heart failure, arrhythmia and sudden cardiac death, yet patients sharing a diagnosis, and even a causal variant, follow markedly different clinical courses. This thesis argues that disease expression depends on the biological context in which genetic susceptibility acts, and that studying this requires experimental models containing the relevant context. Each chapter adds a layer. The starting point is genetic. Among nearly 470,000 UK Biobank participants, carriers of TNNT2 p.Arg288Cys showed no excess hypertrophic cardiomyopathy after correction for multiple testing and cumulative penetrance below 1% by age 80, while displaying subtle functional differences on cardiac MRI. Dutch probands presented with more severe disease, consistent with ascertainment bias and enrichment for modifiers. The variant is therefore intermediate in effect, insufficient alone but capable of contributing in a permissive context. The question shifts from whether a variant is pathogenic to under which conditions it becomes so. Cellular identity is the first layer. Endothelial and smooth muscle cells from nine canine macrovessels retained location-associated transcriptional programmes through at least three passages, with embryonic positional transcription factors providing the strongest discrimination. An epigenetic mechanism is plausible. Cell source is thus a design decision rather than a practical detail. Local tissue context was added in a fibrin-based co-culture, where endothelial cells self-assembled into lumenised networks alongside hiPSC-derived cardiomyocytes and remained stable for at least three weeks in a commercially available microfluidic device. The positional identity findings simultaneously define its main limitation, since umbilical vein endothelial cells were used. Environmental context was introduced as lipid overload in an isogenic MYH7 p.Arg403Leu pair. A model providing context is of limited value if the readout averages that context away. Across 44,403 single-cell measurements of calcium handling and contraction, within-well variability accounted for 76 to 96% of total variance, and clustering identified a lipid-enriched subpopulation invisible in well averages. Model complexity and measurement resolution are two sides of the same problem. Some layers cannot be engineered. Lifelong exposure, genetic diversity and spontaneous progression are inherent to naturally occurring disease in companion animals. Canine dilated cardiomyopathy returns genetic susceptibility to the foreground with full context attached, with breed-level uniformity supporting bidirectional discovery. In 37 cats with hypertrophic cardiomyopathy, digital pathology combined with Nanopore sequencing revealed structure only after outcome-based reclassification, distinguishing arterial thromboembolism from congestive heart failure. The same morphometric approach across 46 vertebrate species established a physiological reference frame, since a tenfold increase in body mass corresponded to roughly 8% greater cardiomyocyte diameter and no species approached dimensions reported in hypertrophic cardiomyopathy. The contribution is both methodological, favouring continuous measurement analysed with models matched to nested data structures, and conceptual, in showing that genetic findings acquire meaning only within their spatial, metabolic and species-specific context. No single model suffices, but complementary models each supply a different layer.