Greater than normal expression of the collagen-binding stress protein heat-shock protein-47 in the infarct zone in rats after experimentally-induced myocardial infarction.

Abstract

The heat-shock protein with relative molecular mass 47,000 (HSP47) can bind to procollagen molecules in the endoplasmic reticulum, and acts as a molecular chaperone during the processing and secretion of procollagen. To test our hypothesis that HSP47 is expressed in the myocardial infarct zone. We induced myocardial infarction in male Sprague-Dawley rats by ligation of left coronary artery. The expression of HSP47 was examined by Northern blotting, in-situ hybridization, Western blotting and immunohistochemistry. The time-dependent change in the distribution of HSP47 messenger RNA (mRNA) signal was compared with the changes in expression of alpha 1(I) and alpha 1(III) collagen mRNA by in-situ hybridization. The hypoxic induction of HSP47 in cultured cardiac fibroblasts was examined by Northern-blot analysis. Northern blotting demonstrated that the expression of HSP47 mRNA had increased on day 2, reaching a maximum level around day 14 (induced 3.5-fold compared with the preligation hearts) and was maintained at a high level up to day 28. In-situ hybridization analysis revealed HSP47 mRNA signals in spindle-shaped mesenchymal cells located between surviving myocytes in the infarct's peripheral zone 24 h after the ligation, and in the entire infarct zone on day 14. The sequential changes in distribution of HSP47 mRNA signal were identical to those of the alpha 1(I) and alpha 1(III) collagen mRNA. Western blotting demonstrated that expression of HSP47 protein in the infarct zone had increased. Immunofluorescent staining revealed positivity for HSP47 in the infarct's peripheral zone on day 2 and in the entire infarct zone on day 14. Northern blotting revealed that the expression of HSP47 mRNA in cultured cardiac fibroblasts in hypoxic cultures was greater than that in normoxic cultures. The present data demonstrated that an increase in expression of HSP47 is produced by spindle-shaped mesenchymal cells in the infarct zone. Expression of HSP47 mRNA was concurrent with the expression of collagen mRNA of types I and III. Hypoxia is one of the factors which induces expression of HSP47.