Intravenous glial growth factor 2 (GGF2) isoform of neuregulin-1β improves left ventricular function, gene and protein expression in rats after myocardial infarction.

Recombinant Neuregulin (NRG)-1β has multiple beneficial effects on cardiac myocytes in culture, and has potential as a clinical therapy for heart failure (HF). A number of factors may influence the effect of NRG-1β on cardiac function via ErbB receptor coupling and expression. We examined the effect of the NRG-1β isoform, glial growth factor 2 (GGF2), in rats with myocardial infarction (MI) and determined the impact of high-fat diet as well as chronicity of disease on GGF2 induced improvement in left ventricular systolic function. Potential mechanisms for GGF2 effects on the remote myocardium were explored using microarray and proteomic analysis.Rats with MI were randomized to receive vehicle, 0.625 mg/kg, or 3.25 mg/kg GGF2 in the presence and absence of high-fat feeding beginning at day 7 post-MI and continuing for 4 weeks. Residual left ventricular (LV) function was improved in both of the GGF2 treatment groups compared with the vehicle treated MI group at 4 weeks of treatment as assessed by echocardiography. High-fat diet did not prevent the effects of high dose GGF2. In experiments where treatment was delayed until 8 weeks after MI, high but not low dose GGF2 treatment was associated with improved systolic function. mRNA and protein expression analysis of remote left ventricular tissue revealed a number of changes in myocardial gene and protein expression altered by MI that were normalized by GGF2 treatment, many of which are involved in energy production.This study demonstrates that in rats with MI induced systolic dysfunction, GGF2 treatment improves cardiac function. There are differences in sensitivity of the myocardium to GGF2 effects when administered early vs. late post-MI that may be important to consider in the development of GGF2 in humans

Echocardiographic Measurements and Tissue Weight Ratios.

<p><i>FS%</i> fractional shortening, <i>LVIDd</i> left ventricular inner diameter at diastole, and <i>Heart/Body</i> heart weight to body weight ratio. Values are shown as predicted means with its 95% confidence interval. Groups are stratified by treatment and diet as follows: Normal Diet-Vehicle (n = 10), Normal Diet-Low Dose GGF2 (n = 9), Normal Diet-High Dose GGF2 (n = 9), Fatty Diet-Vehicle (n = 9), and Fatty Diet-High Dose GGF2 (n = 9). ^†FS % changes over time were analyzed using the generalized least squares linear regression method, and estimated means were fit using restricted maximum likelihood. Week 1 pre-treatment values were adjusted by adding a restricted cubic spline to the model. *Indicates significance with p<0.05 compared to vehicle animals. ^‡LVIDd changes over time were also analyzed using GLS regression fit by REML, and week 1 pre-treatment values were adjusted by restricted cubic spline. No significant difference was found between groups at each time point. ^§Heart/Body weight ratios were analyzed using ordinary least squares and one-way ANOVA. Heart/Body weight ratio comparison was found to be non-significant between groups.</p

Comparison of effects of GGF2 in rats early and late after MI.

<p>Data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055741#pone-0055741-g001" target="_blank">Figures 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055741#pone-0055741-g002" target="_blank">2</a> are shown for direct comparison of effects of A) low dose and B) high dose GGF2 (mean +/− S.D.).</p

Examination of the effect of GGF2 on the myocardial proteome.

<p>Representative 2D gel image of total protein stain from the 5-gel coordinated DIGE experiment. A total of 300 µg of protein was loaded onto each DIGE gel. Altered proteins are indicated by numbers which correspond to line entries for identified proteins listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055741#pone-0055741-t003" target="_blank">Table 3</a>.</p

Effect of GGF2 treatment on cardiac function early after MI.

<p>Serial measurements of fractional shortening (FS) were acquired from post-MI rats at baseline (1 week post-MI), 2 weeks after GGF2 treatment, and 4 weeks after GGF2 treatment. Echocardiographic assessment revealed that residual left ventricular (LV) FS% values were significantly higher (p = 0.0001) in GGF2 treated animals compared to those in the vehicle groups at the end of the study. The estimated mean FS% and range at 35 days post MI was 43.6 (41.0, 46.3) for the high dose treated group (n = 9), 42.0 (39.1, 45.0) for the low dose treated group (n = 9), and 36.6 (34.2, 39.1) for the vehicle group (n = 10. Individual rat FS % values trended downwards in the vehicle animals with time, whereas a progressive increase in FS % was observed in both the low dose and high dose GGF2 treatment groups. Moreover, the results indicate that high-fat feeding did not impair the effects of high dose GGF2 treatment on cardiac function.</p