Abstract
Background: Type 1 diabetes mellitus (DM) patients surviving myocardial infarction (MI) are at heightened risk for the subsequent development of heart failure (HF). Despite the worse outcomes, investigations into the pathophysiological mechanisms that contribute to the increased frequency of HF after MI in the type 1 DM heart remain scarce. Neuregulin-1 (NRG-1), along with the ErbB family of receptor tyrosine kinases through which NRG-1 ligands signal, have been shown to be intimately involved in mediating cardiac recovery after MI. However, the impact of type 1 DM on this signaling system post-MI remains to be elucidated. Therefore, in the present study, we examined myocardial NRG-1/ErbB signaling during post-MI HF in the presence of type 1 DM. Methods: Type 1 DM was induced in male Sprague-Dawley rats via a single intraperitoneal injection of streptozotocin (STZ) (65 mg/kg). Two weeks after induction of type 1 DM, MI was produced in DM and non-DM rats by ligation of the left anterior descending (LAD) coronary artery. Residual left ventricular (LV) function was assessed by echocardiography at 4 weeks post-MI. Following echocardiographic assessment, NRG-1, ErbB2, and ErbB4 protein expression was assessed in the remote, surviving LV myocardium of DM and non-DM rats using Western blot techniques. Results: LV Fractional Shortening (FS) and LV Ejection Fraction (EF) were significantly lower in the DM + MI group compared to the MI group ([LVFS: DM + MI, 17.9 ± 0.7 (n=6) vs. MI, 25.2 ± 2.2 (n=6), p <0.05; LVEF: DM + MI, 35.5 ± 1.4 (n=6) vs. MI, 47.5 ± 3.5 (n=6), p <0.05]), indicating an increased functional severity of HF in the diabetic post-MI group. The weight of myocardial scar caused by the infarction was not significantly different between the MI groups ([DM + MI, 0.19 ± 0.02 g (n=4) vs. MI, 0.20 ± 0.03 g (n=4), p =0.70]). ErbB2, ErbB4, and NRG-1 protein expression levels were all significantly lower in the DM + MI group compared to the MI group. Conclusions: These findings demonstrate that type 1 DM impairs myocardial NRG-1/ErbB signaling in response to MI, which may contribute to the accelerated progression of subsequent HF. Augmentation of NRG-1 or its downstream signaling pathways may represent a novel therapeutic strategy for ameliorating post-MI HF in the setting of type 1 DM.
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