Direct injection and expression in vivo of full-length cDNA of the cardiac isoform of alpha-2 macroglobulin induces cardiac hypertrophy in the rat heart.

Earlier studies from this laboratory have shown that the serum protein of molecular weight of 182 kDa, which plays an indispensable role in the development of cardiac hypertrophy, may be a cardiac isoform of alpha-2 macroglobulin belonging to macroglobulin family (36). Furthermore, reports on the stable expression in vivo of several reporter genes injected directly into the myocardium of rat and the approach of direct gene transfer into adult mammalian heart to characterize the activity of a cellular gene and to modulate overall cardiac function in vivo prompted us to evaluate the hypertrophy inducing potential of a full-length cDNA for the 182 kDa protein upon direct injection. The full-length cDNA of the cardiac isoform of alpha-2 M obtained from hypertrophied rat heart mRNA and cloned in an eukaryotic expression vector namely pcDNA 3.1(-) was injected directly into the rat heart; the protein whose expression was constitutively triggered by the cytomegaloviral promoter could be detected in the serum of the injected animals and it could exert its function of inducing the hypertrophy, by a highly plausible way, by which the cardiac specific 182 kDa protein may bind to many growth modulating factors in the serum, and then be targeted to cardiomyocytes by a receptor mediated mechanism (36). The development of cardiac hypertrophy was monitored by determining the heart weight-body weight ratio. This ratio along with Northern blot analysis of muscle specific marker genes such as beta-MHC, MLC-2 and ANF, and the induction of promoter activity of beta-MHC and c-fos genes monitored using chloramphenicol acetyl transferase as a reporter gene confirmed the induction of cardiac hypertrophy upon direct injection of the full-length cDNA of 182 kDa protein.