Excessive cardiac insulin signaling exacerbates systolic dysfunction induced by pressure overload in rodents - PubMed (original) (raw)

. 2010 May;120(5):1506-14.

doi: 10.1172/JCI40096. Epub 2010 Apr 19.

Tohru Minamino, Haruhiro Toko, Sho Okada, Hiroyuki Ikeda, Noritaka Yasuda, Kaoru Tateno, Junji Moriya, Masataka Yokoyama, Aika Nojima, Gou Young Koh, Hiroshi Akazawa, Ichiro Shiojima, C Ronald Kahn, E Dale Abel, Issei Komuro

Affiliations

Excessive cardiac insulin signaling exacerbates systolic dysfunction induced by pressure overload in rodents

Ippei Shimizu et al. J Clin Invest. 2010 May.

Abstract

Although many animal studies indicate insulin has cardioprotective effects, clinical studies suggest a link between insulin resistance (hyperinsulinemia) and heart failure (HF). Here we have demonstrated that excessive cardiac insulin signaling exacerbates systolic dysfunction induced by pressure overload in rodents. Chronic pressure overload induced hepatic insulin resistance and plasma insulin level elevation. In contrast, cardiac insulin signaling was upregulated by chronic pressure overload because of mechanical stretch-induced activation of cardiomyocyte insulin receptors and upregulation of insulin receptor and Irs1 expression. Chronic pressure overload increased the mismatch between cardiomyocyte size and vascularity, thereby inducing myocardial hypoxia and cardiomyocyte death. Inhibition of hyperinsulinemia substantially improved pressure overload-induced cardiac dysfunction, improving myocardial hypoxia and decreasing cardiomyocyte death. Likewise, the cardiomyocyte-specific reduction of insulin receptor expression prevented cardiac ischemia and hypertrophy and attenuated systolic dysfunction due to pressure overload. Conversely, treatment of type 1 diabetic mice with insulin improved hyperglycemia during pressure overload, but increased myocardial ischemia and cardiomyocyte death, thereby inducing HF. Promoting angiogenesis restored the cardiac dysfunction induced by insulin treatment. We therefore suggest that the use of insulin to control hyperglycemia could be harmful in the setting of pressure overload and that modulation of insulin signaling is crucial for the treatment of HF.

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Figures

Figure 1

Figure 1. Upregulation of cardiac insulin signals by pressure overload.

(A) Mice were subjected to TAC or sham operation (sham), and heart samples were obtained 2 weeks later. Mice were starved for 6 hours, and insulin or PBS was injected before sacrifice. pIrs1 and pAkt levels in the heart were examined by Western blot analysis. The graphs indicate relative expression levels of pIrs1 and pAkt. n = 3. TAC2w, 2 weeks after TAC. (B) Mice were subjected to TAC or sham operation and were sacrificed 2 weeks later. Components of the insulin signaling pathway in the heart were examined by Western blot analysis. The graphs indicate relative expression levels of these signaling molecules. n = 3. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01.

Figure 2

Figure 2. Depletion of plasma insulin attenuates systolic dysfunction induced by pressure overload.

(A) STZ- or vehicle-treated mice were subjected to TAC or sham operation. The heart weight/body weight (HW/BW) ratio was measured 2 weeks after operation. In the insulin-treated group, daily i.p. injection of insulin (0.1 IU/g/d) was performed from 9 weeks (2 weeks after STZ treatment) to 13 weeks of age (2 weeks after TAC). n = 22–24. (B) Cardiac hypertrophy and systolic function of the animals prepared for A were estimated by echocardiography at 1 week (IVST) or 2 weeks (FS and LVDs) after operation. Photographs show representative results of echocardiography (M-mode). n = 6–10. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01. IVST, intraventricular septal thickness; FS, fractional shortening.

Figure 3

Figure 3. Reduction of plasma insulin inhibits cardiac hypoxia due to pressure overload.

(A) Animals were prepared as described for Figure 2A. Immuno­histo­chemistry using antibodies against platelet and endothelial cell adhesion molecule (dark brown) and dystrophin (light brown) was performed at 2 weeks after operation. Scale bars: 20 μm. (B and C) CSA of cardiomyocytes (B) and relative vascular density (C) were estimated as described in Methods. n = 4–5. (D) Cardiac ischemia (brown) in mice prepared as described for Figure 2A was estimated with a Hypoxyprobe-1. Scale bars: 1 mm. (E) Number of TUNEL-positive cells per 1 × 104 cardiomyocytes. n = 4–6. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01.

Figure 4

Figure 4. Cardiomyocyte-specific reduction of Insr expression attenuates systolic dysfunction due to pressure overload.

(A) Western blot analysis of Insr expression in the hearts of CIRKO mice (_Insrflox/+_Cre+) and their littermate controls (control). Graphs indicate relative expression levels of Insr. n = 3. (B) CIRKO mice (_Insrflox/+_Cre+) or littermate controls were subjected to TAC or sham operation, and components of the insulin signaling pathway in the heart were examined by Western blot analysis at 2 weeks after operation. Graphs indicate relative expression levels of these signaling molecules. n = 3. (C) The heart weight/body weight ratio of animals prepared as described in A was measured at 2 weeks after operation. n = 7–9. (D) Cardiac hypertrophy and systolic function of animals prepared as described in A were assessed by echocardiography at 1 week (IVST) or 2 weeks (FS and LVDs) after operation. Photographs show representative results of echocardiography (M-mode). n = 8–13. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01.

Figure 5

Figure 5. Cardiomyocyte-specific reduction of Insr expression attenuates cardiac hypoxia due to pressure overload.

(A) CIRKO mice (_Insrflox/+_Cre+) or littermate controls were subjected to TAC or sham operation. Immuno­histochemistry using antibodies against platelet and endothelial cell adhesion molecules (dark brown) and dystrophin (light brown) was performed at 2 weeks after operation. Scale bars: 20 μm. (B and C) CSA of cardiomyocytes (B) and relative vascular density (C) were estimated as described in Methods. n = 4–5. (D) Number of TUNEL-positive cells per 1 × 104 cardiomyocytes. n = 4–5. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01.

Figure 6

Figure 6. Reduced activation of Akt attenuates systolic dysfunction due to pressure overload.

(A) _Akt1_-deficient (Akt1+/–) mice and WT littermates were subjected to TAC or sham operation. Cardiac hypertrophy and systolic function were assessed by echocardiography at 2 weeks after operation. n = 4–6. (B) Immunohistochemistry using antibodies against platelet and endothelial cell adhesion molecules (dark brown) and dystrophin (light brown) was performed at 2 weeks after operation. Scale bars: 20 μm. (C) CSA of cardiomyocytes and relative vascular density were estimated as described in Methods. n = 3. (D) pAkt and Akt levels in the heart at 2 weeks after operation were examined by Western blot analysis. Graphs indicate relative expression levels of pAkt and Akt. n = 3. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01.

Figure 7

Figure 7. Mechanism of enhanced insulin signaling in the heart during pressure overload.

(A) CIRKO mice (_Insrflox/flox_Cre+) or littermate controls were subjected to TAC or sham operation, and heart samples were obtained at the indicated times. pIrs1 levels were examined by Western blot analysis. The graphs indicate relative expression levels of pIrs1. n = 3. (B) Cardiomyocytes were subjected to mechanical stretch and pIrs1 levels were examined by Western blot analysis. n = 3. (C) siRNA targeting Insr (siInsr) or negative control RNA (siNC) was introduced into cardiomyocytes, after which the cells were subjected to mechanical stretch. pIrs1 levels were examined by Western blot analysis. n = 3. (D) Plasma glucose and insulin levels were examined at 2 weeks after TAC. n = 7–8. (E) Insulin-induced phosphorylation of Akt (pAkt) in the liver was examined after TAC or sham operation. n = 3. Data are shown as mean ± SEM. *P < 0.05; **P < 0.01.

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