Mild Type 2 Diabetes Mellitus Reduces the Susceptibility of the Heart to Ischemia/Reperfusion Injury: Identification of Underlying Gene Expression Changes

Abstract

Despite clinical studies indicating that diabetic hearts are more sensitive to ischemia/reperfusion injury, experimental data is contradictory. Although mild diabetes prior to ischemia/reperfusion may induce a myocardial adaptation, further research is still needed. Nondiabetic Wistar (W) and type 2 diabetic Goto-Kakizaki (GK) rats (16-week-old) underwent 45 min occlusion of the left anterior descending coronary artery and 24 h reperfusion. The plasma glucose level was significantly higher in diabetic rats compared to the nondiabetics. Diabetes mellitus was associated with ventricular hypertrophy and increased interstitial fibrosis. Inducing myocardial infarction increased the glucose levels in diabetic compared to nondiabetic rats. Furthermore, the infarct size was smaller in GK rats than in the control group. Systolic and diastolic functions were impaired in W + MI and did not reach statistical significance in GK + MI animals compared to the corresponding controls. Among the 125 genes surveyed, 35 genes showed a significant change in expression in GK + MI compared to W + MI rats. Short-term diabetes promotes compensatory mechanisms that may provide cardioprotection against ischemia/reperfusion injury, at least in part, by increased antioxidants and the upregulation of the prosurvival PI3K/Akt pathway, by the downregulation of apoptotic genes, proinflammatory cytokine TNF-α, profibrogenic TGF-β, and hypertrophic marker α-actin-1.

Figure 1

Histological analysis (hematoxylin and eosin staining). (a) Hematoxylin and eosin staining micrographs of transverse sections of myocardium (magnification ×400, scale bar: 50 μm) and (b) quantitative analysis of cardiomyocyte cross-sectional area using measurements of ~20 cardiomyocytes in each group. Data is presented as mean ± SEM. ^∗ P < 0.05 versus W; GK; ^$ P < 0.05 versus W + MI. MI indicates myocardial infarction; GK: Goto-Kakizaki; W: Wistar.

Figure 2

Histological analysis (Masson's trichrome staining). Histological examination of the myocardium stained with Masson's trichrome (magnification ×100, scale bar: 100 μm). Data is presented as mean ± SEM. ^∗ P < 0.05 versus W; ^# P < 0.05 versus GK; ^$ P < 0.05 versus W + MI. MI indicates myocardial infarction; GK: Goto-Kakizaki; W: Wistar. Masson's trichrome staining (grade 0 indicates normal tissue showing no fibrotic region; grade 1 indicates mild fibrosis; grade 2 indicates moderate fibrosis, and grade 3 indicates severe fibrosis).

Figure 3

Left-ventricular systolic and diastolic function. Assessment of (a) ejection fraction, (b) maximal slope of the systolic pressure increment dP/dt _max, (c) maximal slope of the diastolic pressure decrement dP/dt _min, and (d) time constant of left-ventricular pressure decay Tau-g. Data is expressed as mean ± SEM. ^∗ P < 0.05 versus W + sham. MI indicates myocardial infarction; GK: Goto-Kakizaki; W: Wistar.

Figure 4

PCR array gene expression clustergrams: (a) GK + sham versus W + sham, (b) GK + MI versus GK + sham, (c) GK + MI versus W + MI, and (d) W + MI versus W + sham. MI indicates myocardial infarction; GK: Goto-Kakizaki; W: Wistar.