Background: Genetic cardiomyopathies show clinical overlap with acute myocarditis, often caused by viral infections. Variants in TTN, encoding sarcomeric titin, and PKP2, encoding desmosomal plakophilin-2, are common in myocarditis and are associated with dilated (DCM) and arrhythmogenic (ACM) cardiomyopathy, respectively. Cytomegalovirus (CMV), a common β-herpesvirus that can cause lifelong latency and thereby immune responses, may interact with genetic factors, but its specific role in specific genetic settings remains unclear.
Methods: We infected heterozygous genetic mouse models of Pkp2+/- and Ttn+/- with murine CMV (MCMV) at 3 or 12 months (mo) to study age- and/or infection-related effects on cardiac phenotype. Cohorts were examined up to 3-6 months post-infection (mpi) for cardiac function, remodeling, and immune activation using echocardiography, histology, flow cytometry, immunostaining, cytokine and kinome profiling. In the younger cohorts, 3mo+6mpi, single-cell RNA sequencing of cardiac leucocytes provided detailed insight into inflammatory cell types.
Results: MCMV infection at 3mo selectively induced progressive systolic dysfunction in Pkp2+/- MCMV mice, while cardiac function remained preserved in all control (Ctr) groups and Ttn+/- cohorts. On the cellular level, effector-memory CD8+ T-cells expanded in response to MCMV in all infected groups. In Pkp2+/- MCMV hearts, however, this was accompanied by recruitment of pro-inflammatory monocytes and Trem2+Spp1+ macrophages with pro-fibrotic signatures. Remarkably, a subclinical accumulation of these myeloid subsets was already present in phenotypically silent non-infected Pkp2+/- mice, together with upregulation of Ccr2 in cardiac leucocytes and elevated CCL2 levels in heart lysates, indicating mutation-driven activation of the CCL2/CCR2 axis. In Ttn+/- mice infected at 3mo, cardiac function and tissue architecture remained normal, with only the MCMV-typical CD8+ T-cell response observed.
In aged Pkp2+/- mice (12mo), kinome profiling revealed upregulated kinases linked to NF-κB and immune signaling, as well as the PI3K-AKT-mTOR pathway promoting survival, indicating compensatory signaling. After MCMV infection (12mo+3mpi), a more severe cardiac phenotype developed, marked by fibrosis, reduced ejection fraction, left ventricular dilation, and further elevated cytokine levels. No difference was seen between infected and non-infected mice at that age, suggesting infection accelerates disease but doesn't worsen severity once established. In contrast, aged Ttn+/- mice remained phenotypically silent even after 6mpi, suggesting that other triggers are required for induction of Ttn-linked disease.
Conclusions: MCMV acts as a genotype- and age-dependent modifier of cardiomyopathy. In Pkp2-linked disease, it acts as a second hit, accelerating the onset of dysfunction in young mice but not contributing to established remodeling. Findings highlight inflammation as a key driver in desmosomal cardiomyopathy and suggest infection prevention and early anti-inflammatory treatment to delay disease in PKP2 mutation carriers.
