Abstract Body: Background:
We previously generated a mouse model carrying a deletion of exon Mex5 (the penultimate exon) of the titin gene (Ttn^delMex5). These mice develop dilated cardiomyopathy (DCM) characterized by extensive cardiac fibrosis and reduced systolic function. RNA sequencing analysis revealed significant activation of the transforming growth factor-β (TGF-β) pathway, a major driver of fibrosis in cardiomyopathies. Cartilage Intermediate Layer Protein-1 (CILP-1) is a matricellular protein primarily expressed in articular cartilage, and has been described as a negative modulator of TGF-β signaling.
Hypothesis:
We hypothesized that cardiac overexpression of CILP-1 could attenuate fibrosis through modulation of the TGF-β pathway in titinopathy, for which gene replacement strategies are not feasible due to the large size of the gene. In this study we evaluated an AAV-mediated CILP gene delivery strategy in the Ttn^delMex5 mouse model.
Methods:
An AAV9 vector encoding human CILP under the control of the cardiac troponin T promoter was administered intravenously at 4 weeks of age (1E13 vg/kg). Mice were analyzed three months later. Histological, molecular, and functional assessments were performed. Fibrosis was quantified using Sirius Red staining and classified as dense “established fibrosis” or “intermediate fibrosis” characterized by increased fibroblast and myofibroblast cellularity.
Results:
Total cardiac fibrosis was significantly reduced in AAV-treated mice compared with saline-treated controls (17.59±1.27% vs 33.31±4.65%, p=0.028, n=4). Established fibrosis was not significantly different between groups (4.14% vs 4.95%). In contrast, intermediate fibrosis was significantly decreased in treated mice (12.64±2.04% vs 29.17±4.24%, p=0.0126). RT-qPCR analysis showed reduced expression of fibrosis-associated genes including fibronectin (fold change −2.0, p<0.05), vimentin (fold change −1.9, not significant), and collagen 1A1 (fold change −1.75, not significant). Echocardiographic measurements showed no significant changes in ejection fraction or left ventricular diastolic diameter.
Conclusion:
Cardiac overexpression of CILP-1 reduces fibrotic remodeling in a mouse model of titin-related DCM, particularly by limiting intermediate stages of fibrosis. Although cardiac function was not significantly improved at this stage, these findings suggest that targeting the TGF-β pathway through CILP-1 modulation may represent a complementary therapeutic strategy for titinopathies.