The Role of Transcription Factors Snail and Slug in Cardiac Myofibroblasts

Abstract

CCardiac fibrosis is a major facet contributing to cardiac dysfunction following a myocardial infarction. Persistent and excessive collagen deposition via cardiac myofibroblasts is the hallmark of cardiac fibrosis. Cardiac myofibroblasts, absent in the normal heart, appear after a myocardial infarction and are an invasive and pathological cell type. Excessive collagen produced by these cells reduces the flexibility of the cardiac muscle and contributes to the progression of heart failure. Cardiac myofibroblasts are a major source of proremodeling factors, expressing Angiotensin II (angII), Transforming Growth Factor-[beta]1 (tgf-[beta]1), and Endothelin-1, which facilitate the remodeling of the heart after MI. At the site of myocardial infarction, thirty-percent of the recruited myofibroblasts are of epithelial origin and arise by the process of epithelial to mesenchymal transition (EMT). It is well documented that the process of EMT is required and dependent on the transcription factors SNAI1 (snail) and SNAI2 (slug). Snail and slug contribute to fibrosis through the process of EMT or generation of the myofibroblast population; however, a continued regulatory role of snail and slug in cardiac myofibroblasts has not been investigated. The present investigation began by evaluating the gene expression of snail and slug in Sprague-Dawely rat myocardial infarction (MI) models, in which we found snail and slug to be differentially expressed in MI tissue relative to non-MI tissue. The effects of proremodeling factors angII and tgf-[beta]1 on snail and slug expression in cardiac myofibroblasts was then investigated. After evaluating the influence of angII and tgf-[beta]1 on snail and slug expression, the regulatory role of snail and slug on type I collagen and type III collagen in cardiac myofibroblasts was investigated. The synergistic regulation of collagen turnover by angII and tgf-[beta]1 in cardiac myofibroblasts was also evaluated. The majority of this study determined a role for transcription factors snail and slug in cardiac myofibroblasts and a role in cardiac remodeling. Snail and slug gene expression was found to be inversely regulated in the post-MI rat heart tissue, snail gene expression being elevated and slug abated. Proremodeling factors angII and tgf-[beta]1 demonstrated temporally regulated snail and slug gene expression in cardiac myofibroblasts in early time course experiments. Slug protein expression was found to be elevated in response to tgf-[beta]1 treatment and attenuated in response to angII treatment in cardiac myofibroblasts. Snail protein expression failed to be detected by multiple primary antibodies. Transfections using anti-snail and anti-slug siRNA revealed a regulatory role of snail in the suppression of type III collagen in cardiac myofibroblasts. Furthermore, synergetic regulation of collagen turnover with respect to angII and tgf-[beta]1 in cardiac myofibroblasts was further elucidated. Disruption of angII signaling, via Angiotensin-Converting-Enzyme inhibitor (ACEi), demonstrated that tgf-[beta]1 induced collagen production in cardiac myofibroblasts is dependent on angII and corresponding signaling pathways.