INCREASED EXPRESSION OF FIBRONECTIN ISOFORMS AFTER MYOCARDIAL-INFARCTION IN RATS

Fibronectin is a known chemoattractant for several cell types which pl ay a role in the wound healing process, like fibroblasts, endothelial cells and macrophages. In addition, fibronectin generates a scaffold t o which other extracellular matrix components can attach. The possible involvement of fibronectin in the wound healing process after myocard ial infarction (MI) was investigated by studying the expression of fib ronectin isoforms after induction of a MI in the rat, Deposition of pl asma (pFN) and cellular fibronectin (cFN) protein was determined immun ohistochemically, using monoclonal antibodies specific for cFN and pol yclonal anti-human total FN (tFN antibodies). Expression of the mRNAs of total cFN and the embryonic isoforms EIIIA and EIIIB was investigat ed, using ill situ hybridization (ISH). The ratio between EIIIA contai ning fibronectin (EIIIA(+)-FN) mRNA and total cFN mRNA was determined using a semi-quantitative reverse transcription polymerase chain react ion (RT-PCR), cFN protein Mras present from day 4 until day 35 after i nfarction and was located around the area of infarction, in the epi-an d endomyocardium and in the wall of larger vessels. pFN was found in t he infarcted cardiomyocytes 1 day after the induction of the MI, From day 4 on pFN protein deposition was Found in the border zone of the in farction and in the wall of larger vessels. pFN immunoreactivity remai ned present at high levels around the area of infarction and in the ve ssel wall throughout the entire period of investigation (90 days), Fro m day 35 after the infarction pFN protein was detected in cardiomyocyt es of the right ventricle and septum. cFN mRNA, determined by ii situ hybridization, was present in the border zone of the infarcted area as early as 1 day after MI, and its expression peaked at 4 days after MI . Four days after MI the mRNA's coding for both the embryonic isoforms EIIIA and EIIIB could also be detected in the same area. Because expr ession of the EIIIA isoform was more abundant than the EIIIB isoform w e only determined the percentage of the EIIIIA containing isoform from total FN. EIIIA(+) mRNA was elevated 1 day after MI. We conclude that various fibronectin isoforms including the embryonic isoforms accumul ate in the heart after MI. This suggests that these isoforms may play a role in the wound healing process in the left ventricle of the infar cted heart. (C) 1997 Academic Press Limited.