Aims: 

Although a reduction in eNOS expression and an induction of TGF-ß1 expression are commonly found in the myocardium and in myocytes of failing hearts, eNOS deficient mice, specifically those with the loss of only one allele, and TGF-ß1 overexpressing mice do not develop a cardiomyopathic phenotype. We therefore challenged the hypothesis that a combination of eNOS deficiency and and TGF-ß1 overexpression is required to induce heart failure. Heterozygous eNOS mice allow us to investigate this topic in the absence of chronic pressure overload.

Methods: 

Mice with a constitutive hepatic release of active TGF-ß1 were crossed with eNOS knock out mice resulting in eNOS heterozygous mice either without a corresponding overexpresion of TGF-b1 (eNOS+/­) or with overexpression of TGF-ß1 (eNOS+/­XTGF-ß1-TG). Heart and lung weight to body weight ratios were calculated (HW/BW; LW/BW). The left ventricular mRNA expression of genes linked to fibrosis, apoptosis, hypertrophy, and calcium handling proteins were quantified by real time RT-PCR. All parameters were evaluated at the age of 6 months.

Results: 

TGF-ß1 had no impact on blood pressure and heart rate in eNOS+/­ mice and both parameters were not different to eNOS wild type mice either. 27 eNOS+/­ mice were analyzed. 6 of them (22%) developed mild disease stages (mean distress score: 4.0). eNOS+/­ developed a moderate myocardial hypertrophy irrespectively of the disease stage (HW/BW: eNOS +/­: 5.200.34 mg/g and 5.250.29 mg/g. eNOS+/+: 4.440.07 mg/g). They had a moderate increase in wet lung weights, too. In sick eNOS+/­ mice we found the following changes in stedy state mRNA expression in left ventricles compared to healthy eNOS+/­: an increase in elastin, elastin/collagen ratio, ornithine decarboxylase, and bax and a decrease in collage-1, UCP-2, bcl-2 to bax ratio, and SERCA2A. 24 eNOS+/­XTGF-ß1-TG were analyzed. 7 of them (29%) developed strong disease (distress score 5.7), significant myocardial hypertrophy (HW/BW: 9.180.61) and increased lung weights.Compared to the healthy eNOS+/­XTGF-ß1-TG mice sick mice had an elevated expression of elastin, ornithine decarboxylase, UCP-2, bax, and biglycan and a reduced bcl-2 to bax ratio. Thus, the main difference between the moderate disease in eNOS+/­ mice and that of the strong disease in eNOS+/­XTGF-ß1-TG mice was the up-regulation of UCP-2 and biglycan as an additive factor on top of heterozygous eNOS genotype that was associated with more sever heart failure.

Conclusion: 

Although the loss of only one allele of eNOS is sufficient to induce a moderate disease at the age of 6 months a co-induction of TGF-ß1 accelrates the dieseae state probably by an induction of UCP-2 and biglycan.