We investigated the myocardial localization and expression of tissue factor (TF) and alternatively spliced human tissue factor (asHTF) in patients with dilated cardiomyopathy (DCM).

Tissue factor is expressed in cardiac muscle and may play a role in maintaining myocardial structure.

Myocardial biopsies were obtained from patients with a normal or mildly impaired ejection fraction (EF) (≥50%) and moderate to severely reduced EF (<50%). Explanted DCM hearts were also examined. Myocardial TF expression level was assessed by real-time polymerase chain reaction, TF protein by enzyme-linked immunosorbent assay, and localization by immunohistochemistry.

We report the identification of asHTF in the human myocardium: it was located in cardiomyocytes and endothelial cells. Quantification of myocardial TF messenger ribonucleic acid in DCM revealed a decrease in the TF/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) ratio (1.76 × 10⁻¹± 6.08 × 10⁻²for EF ≥50% [n = 19] vs. 1.06 × 10⁻¹± 5.26 × 10⁻²for EF <50% [n = 27]; p < 0.001) and asHTF/GAPDH ratio (13.91 × 10⁻⁵± 11.20 × 10⁻⁵for EF ≥50% vs. 7.17 × 10⁻⁵± 3.82 × 10⁻⁵for EF <50%; p = 0.014). Tissue factor isoform expression level was also decreased in explanted DCM hearts (p < 0.01; n = 12). Total TF protein was reduced by 26% in DCM (p < 0.05). The TF/GAPDH ratio correlated positively with the EF (r = 0.504, p < 0.0001). Immunohistochemistry showed TF localized to the sarcolemma and Z-bands of the cardiomyocytes in patients with normal EF, whereas TF was found in the cardiomyocytic cytosol around the nucleus in DCM.

Tissue factor was down-regulated in the myocardium of DCM patients. The reduction in TF expression and change in localization may influence cell-to-cell contact stability and contractility, thereby contributing to cardiac dysfunction in DCM.