Cardiotrophin-1 stimulation of cardiac fibroblast growth: Roles for glycoprotein 130/leukemia inhibitory factor receptor and the endothelin type A receptor

Cardiotrophin-1 (CT-1), a member of the interleukin-6 superfamily, and endothelin-1 (ET-1) are potent hypertrophic factors in cardiomyocytes. Although CT-1 and ET-1 gene expression in the heart is upregulated in experimental heart failure, their role in the activation of the cardiac fibroblast is unknown. This study was designed to identify the presence and action of CT-1 and its receptor complex, glycoprotein130 (gp130) and leukemia inhibitory factor (LIF) receptor, on cardiac fibroblast growth in cultured adult canine cardiac fibroblasts. In addition, we investigated the interaction between CT-1/gp130/LIF receptor and ET-1/endothelin type A (ET_A) receptor axis. Immunohistochemistry was performed using the indirect immunoperoxidase method, while we assessed the cell cycle of cardiac fibroblasts by flow cytometry, DNA synthesis by [³H]thymidine incorporation, and collagen synthesis by [³H]proline incorporation, respectively. CT-1 and gp130/LIF receptor were widely present in the cytoplasm of the cardiac fibroblasts. Exogenous CT-1 markedly stimulated [³H]thymidine and [³H]proline incorporations (P<0.01), with accumulation of cells in the S phase. Blockade of gp130 or LIF receptor inhibited basal growth as well as CT-1- or ET-1-stimulated cardiac fibroblast growth. The specific ET_A receptor antagonist, BQ123, significantly inhibited CT-1-stimulated DNA synthesis. This study demonstrates that CT-1 and its receptors are present in cardiac fibroblasts. In addition, growth of these cells stimulated by endogenous and exogenous CT-1 requires gp130/LIF receptor as well as ET_A receptor activation. We conclude that gp130/LIF receptor and ET_A receptor activation are essential for cardiac fibroblast growth by CT-1 and that there is synergism with ET-1/ET_A receptor axis.