Cardiac morphometry was assayed by planimetry in an image analysis system. mRNA and protein expression were quantified by real time RT-PCR and Western blotting. Receptors were localized by immunocytochemistry. Trypan blue staining, TUNEL, and MTT cell viability assays were employed to study the cytoprotective activity of cardiotrophin-1 (CT-1) in isolated caridomyocytes.
Compared to non-failing SHR, failing SHR exhibited enhanced myocardial cell death (p < 0.01) demonstrated by the increase in Bax/Bcl-2 ratio, caspase-3 activation and poly (ADP-ribose) polymerase (PARP) fragmentation. Failing SHR had a 7-fold diminished expression (p < 0.01) of LIFR, no changes in gp130, and 1.6-fold increased myocardial expression (p < 0.01) of CT-1. In cardiomyocytes isolated from non-failing SHR, recombinant CT-1 inhibited apoptotic and non-apoptotic cell death induced by angiotensin II or hydrogen peroxide. LIFR protein was entirely absent in cardiomyocytes isolated from failing SHR, which were resistant to the cytoprotective effects of CT-1. Finally, stimulation of non-failing SHR cardiomyocytes with angiotensin II, aldosterone, norepinephrine or endothelin-1 significantly decreased (p < 0.01) LIFR expression.
These data suggest that loss of CT-1-dependent survival mechanisms may contribute to the increase of cell death associated with HF in SHR. Neurohumoral activation may contribute to this alteration via suppression of LIFR.