Cardiac-specific IGF-1 receptor transgenic expression protects against cardiac fibrosis and diastolic dysfunction in a mouse model of diabetic cardiomyopathy

Abstract

Objective: Compelling epidemiological and clinical evidence has identified a specific cardiomyopathy in diabetes, characterized by early diastolic dysfunction and adverse structural remodeling. Activation of the insulin-like growth factor 1 (IGF-1) receptor (IGF-1R) promotes physiological cardiac growth and enhances contractile function. The aim of the present study was to examine whether cardiac-specific overexpression of IGF-1R prevents diabetes-induced myocardial remodeling and dysfunction associated with a murine model of diabetes.

Research design and methods: Type 1 diabetes was induced in 7-week-old male IGF-1R transgenic mice using streptozotocin and followed for 8 weeks. Diastolic and systolic function was assessed using Doppler and M-mode echocardiography, respectively, in addition to cardiac catheterization. Cardiac fibrosis and cardiomyocyte width, heart weight index, gene expression, Akt activity, and IGF-1R protein content were also assessed.

Results: Nontransgenic (Ntg) diabetic mice had reduced initial (E)-to-second (A) blood flow velocity ratio (E:A ratio) and prolonged deceleration times on Doppler echocardiography compared with nondiabetic counterparts, indicative markers of diastolic dysfunction. Diabetes also increased cardiomyocyte width, collagen deposition, and prohypertrophic and profibrotic gene expression compared with Ntg nondiabetic littermates. Overexpression of the IGF-1R transgene markedly reduced collagen deposition, accompanied by a reduction in the incidence of diastolic dysfunction. Akt phosphorylation was elevated approximately 15-fold in IGF-1R nondiabetic mice compared with Ntg, and this was maintained in a setting of diabetes.

Conclusions: The current study suggests that cardiac overexpression of IGF-1R prevented diabetes-induced cardiac fibrosis and diastolic dysfunction. Targeting IGF-1R-Akt signaling may represent a therapeutic target for the treatment of diabetic cardiac disease.

FIG. 1.

Cardiomyocyte width is increased by diabetes and IGF-1R overexpression on histological analysis of ventricular cross-sections stained with H-E. A: Representative sections from the LV of sham and diabetic Ntg and IGF-1R mice (H-E stain; magnification ×400). Scale bars show 20 μm. B: Cardiomyocyte width pooled data. n = 8–12 in each group; *P < 0.001 vs. Ntg sham; †P < 0.001 vs. Ntg diabetes. (A high-quality digital representation of this figure is available in the online issue.)

FIG. 2.

A: Gene expression of β-myosin heavy chain (hypertrophic marker) was analyzed on real-time PCR and normalized against 18S expression. n = 8–11 for each group. B: Representative Northern blot showing total RNA. GAPDH was used to normalize for RNA loading (insert). Gene expression of ANP (n = 9–10 per group) and BNP (n = 4–5 per group) was assessed. Mean values for Ntg sham were normalized to 1. *P < 0.05 vs. Ntg sham; †P < 0.05 vs. Ntg diabetic. Sh, sham; D, diabetes.

FIG. 3.

A: Representative sections from the LV of sham and diabetic Ntg and IGF-1R mice. Collagen deposition appears red (sirius red stain; magnification ×200). Scale bars show 40 μm. B: Quantitation of collagen area/total ventricular area pooled data. n = 8–12 in each group; *P < 0.05 vs. Ntg sham; †P < 0.05 vs. Ntg diabetic. A high-quality digital representation of this figure is available in the online issue.)

FIG. 4.

Impact of cardiac-specific IGF-1R overexpression on diabetes-induced diastolic dysfunction. A: Representative mitral flow patterns from pulsed wave Doppler echocardiography. Diabetes (B) tends to decrease E velocity and (C) increases peak A velocity, with (D) net reduction in E:A wave ratio in both Ntg and IGF-1R diabetic mice. IGF-1R (E) reduces incidence of diastolic dysfunction, (F) restores normal deceleration time, and (G) tends to improve LV end diastolic pressure. n = 7–12 in each group; *P < 0.05 vs. sham of the same genotype; †P < 0.05 vs. Ntg counterpart.

FIG. 5.

A: Representative Western blot showing phosphorylation of Akt and total Akt in sham (Sh) and diabetic (D) mice (insert), and quantitative analysis of Akt phosphorylation normalized to total Akt (left panel). Mean values for Ntg sham were normalized to 1. n = 4–6 in each group; *P < 0.05 vs. Ntg sham; †P < 0.05 vs. Ntg counterpart. B: Representative Western blot showing protein levels of IGF-1R and GAPDH protein (insert) and quantitative analysis of IGF-1R normalized to GAPDH (n = 3/group).