Myocardial
hypertrophy is an independent risk factor for development of
heart failure. The intracellular
calcium homeostasis is altered in myocardial
hypertrophy, and recent studies in animal models have confirmed an interaction between the Ca2+/
calmodulin-dependent
calcineurin signaling cascade and development of
cardiac hypertrophy. There is evidence for the involvement of various pathways in development of
hypertrophy. A transgenic rat model overexpressing the mouse
renin gene, TGR(mREN2)27 has been shown to progress profound
cardiac hypertrophy, possibly due to a monogenetic disorder. However, the exact mode of action is not known. To study a possible involvement of
calcineurin and its downstream pathway in development of
cardiac hypertrophy in this transgenic rat model we measured the
protein expression of marker
proteins of the
calcineurin cascade (calcineurin, NFAT-3, GATA-4) and
calcineurin phosphatase activity and GATA-4
DNA binding in TGR ( n=10) compared to age-matched Sprague-Dawley rats ( n=10). In our study there was no significant difference in
calcineurin activity between the transgenic hearts and the hearts of Sprague-Dawley rats. Furthermore, we found neither an increase in
protein expression of
calcineurin B nor a rise in nuclear translocated NFAT-3 DU. Interestingly, the
protein expression of GATA-4 and its
DNA binding activity were significantly higher in hypertrophied myocardium than in control hearts. In transgenic rats overexpressing the mouse
renin gene and thereby developing pronounced
cardiac hypertrophy [TGR(mREN2)27] we thus found no activation of
calcineurin or its downstream pathway. However, the expression of the transcriptional factor GATA-4 and its
DNA binding activity were significantly increased in hearts of transgenic rats. Thus GATA-4 seems to be a marker of
hypertrophy independently of
calcineurin activation, possibly activated by various pathways.