Increased expression of dermatopontin mRNA in the infarct zone of experimentally induced myocardial infarction in rats: comparison with decorin and type I collagen mRNAs.

Objectives: Dermatopontin, a 22 kDa extracellular matrix (ECM) protein, has been shown to interact with other ECM components, especially decorin, and to regulate ECM formation. We examined dermatopontin mRNA expression in the myocardial infarct zone.

Methods: The cDNA encoding the rat dermatopontin was cloned by RT-PCR based on screening results from the Expressed Sequence Tag database. The dermatopontin mRNA expression was examined in the infarct zone after experimentally induced myocardial infarction in rats by the methods of Northern blotting and in situ hybridization. The expression of dermatopontin mRNA was compared to that of decorin and type I collagen mRNAs.

Results: The isolated clone contained a 609 bp cDNA insert containing a complete open reading frame encoding 202 amino acids. The rat dermatopontin cDNA showed high homology to human and mouse counterparts (>96 %). Northern blotting demonstrated that dermatopontin mRNA expression did not markedly increase on day 2, but was increased on days 7, 14 and 28 by 2.4-, 4.1- and 4.2-fold, respectively, compared to that in preligation hearts. Dermatopontin mRNA expression was regulated almost in parallel with decorin mRNA expression. In situ hybridization demonstrated mRNA signals for dermatopontin in macrophages and spindle-shaped mesenchymal cells (fibroblasts and myofibroblasts) located in the infarct interior zone around infarcted necrotic tissue on day 7. Coexpression of dermatopontin mRNA with decorin and type I collagen mRNAs was observed in spindle-shaped mesenchymal cells.

Conclusions: The present results demonstrated the time-dependent increase in the expression of dermatopontin mRNA in parallel with that of decorin mRNA in the infarct zone. Coexpression of dermatopontin mRNA with decorin and type I collagen mRNAs suggests that dermatopontin plays a role in ECM (fibrillar collagen matrix) reformation in the infarct along with decorin and type I collagen.