Syringaldehyde Alleviates Cardiac Hypertrophy Induced by Hyperglycemia in H9c2 Cells Through GLP-1 Receptor Signals

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  Figure 1. Syringaldehyde (SA) increases the expression of the GLP-1 receptor in H9c2 cells with hypertrophy. (a) Changes in GLP-1 receptor protein levels induced via SA administration at concentrations of 0.1 μM (low), 0.5 μM (medium), and 1 μM (high). (b) Changes in calcium influx induced via SA administration at different concentrations. (c) Levels of cellular cyclic AMP (cAMP) in cells subjected to different concentrations of SA. (d) The cellular cAMP level induced by SA at 1 μM was inhibited, following 30 min pretreatment with Ex 9 at concentrations of 0.1 μM or 0.5 μM. The sample size was 6 except for the Western blotting analysis (n = 4). Statistical significance was indicated as follows: * p < 0.05 vs. control (Con); # p < 0.05 vs. vehicle (Veh).

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  Figure 2. Syringaldehyde (SA) ameliorated the hyperglycemia-induced hypertrophy of H9c2 cells. (a) Changes in the size of the hypertrophic cells treated with syringaldehyde at different concentrations of 0.1 μM (low), 0.5 μM (medium), and 1 μM (high). * p < 0.05 vs. control (Con). # p < 0.05) vs. vehicle (Veh). Gene expression levels of (b) the gene expression levels of ANP (Con: 1 ± 0.2; Veh: 2.1 ± 0.2; SA Med: 1.3 ± 0.1; SA High: 1.2 ± 0.1), BNP (Con: 1 ± 0.2; Veh: 1.9 ± 0.1; SA Med: 1.4 ± 0.2; SA High: 1.1 ± 0.1) and (c) β-MHC (Con: 1 ± 0.1; Veh: 1.9 ± 0.1; SA Med: 1.3 ± 0.2; SA High: 1 ± 0.1) in hypertrophic cells administered various concentrations of SA or without treatment. * p < 0.05 vs. control (Con). # p < 0.05) vs. vehicle (Veh). (d) The size of the H9c2 cells was observed using light microscopy (scale bar: 100 μm). Control cells in a normal culture (Con) were not modified with SA at 1 μM (Con + SA), as indicated in the upper panel. * p < 0.05 vs. normal cells (Con). # p < 0.05) vs. high glucose-induced hypertrophic cell (HG). Values for each indicator are expressed as fold changes in gene expressions of ANP, BNP, and β-MHC, relative to the control group. Fold change is…

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  Figure 3. The signaling pathway for syringaldehyde (SA) alleviated cardiac hypertrophy in H9c2 cells. (a) Changes in cell size in hypertrophic cardiomyocytes with GLP-1 resistance. Cells were treated with or without SA at 1 μM (high dose), exendin-4 (EX-4) at 0.5 μM, and metformin at 5 μM, respectively. (b) SA and EX-4 failed to stimulate cAMP levels in H9c2 cells with GLP-1 resistance, whereas dopamine at 5 μM elevated cAMP levels in these cells. (c) A decrease in hypertrophic cell size due to SA at 0.5 μM (a medium dose) was reversed via pretreatment with H-89 at doses of 0.5 μM (low) or 1 μM (high). (d) Changes in cellular ROS levels in high glucose-induced hypertrophic cells with or without SA treatment. The inhibition of PKA by H-89 (1 μM) reversed the ROS-lowering effect of SA. Values for each indicator are expressed as fold changes in cell size, gene expressions of ANP, BNP, and β-MHC, relative to the control group. Results are presented as the mean ± SE from independent experiments, n = 6. Statistical significance: * p < 0.05 vs. normal control (Con). # p < 0.05 vs. vehicle (Veh). † p < 0.05 vs. hypertrophic cells treated with SA at 0.5 μM (Blank).

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  Figure 4. The role of AMPK in syringaldehyde (SA)-alleviated cardiac hypertrophy in H9c2 cells. H9c2 cells were treated with a high glucose medium for 48 h. siRNA was used to ablate the expression of AMPK and H9c2 cells that received with same volume of scramble. (a) Changes in cell size due to SA at 1 μM (high) were, like the effect of EX-4, reversed by AMPK ablation. Additionally, the effects of metformin were also removed in AMPK-silenced cells. (b) The changes in gene expression levels of ANP (Con: 1 ± 0.2; Veh: 2.6 ± 0.4; SA High + scramble: 1.2 ± 0.2; SA High + siRNA: 2.2 ± 0.3; EX4+ scramble: 1.4 ± 0.1; EX4 + siRNA: 2.2 ± 0.3), and BNP (Con: 1 ± 0.3; Veh: 2.4 ± 0.3; SA High + scramble: 1.3 ± 0.4; SA High + siRNA: 2.3 ± 0.4; EX4+ scramble: 1.6 ± 0.2; EX4 + siRNA: 2.2 ± 0.4). (c) The changes in gene expression levels of β-MHC (Con: 1 ± 0.2; Veh: 1.9 ± 0.2; SA High + scramble: 1.2 ± 0.1; SA High + siRNA: 1.7 ± 0.2; EX4+ scramble: 1.3 ± 0.1; EX4 + siRNA: 1.7 ± 0.3). (d) The expression of O-linked b-N-acetylglucosamine transferase (OGT) was promoted by high glucose levels and reduced by SA at a 1 μM (high) dose. The effect of SA was reversed by compound C (CpC) at doses of 5 μM (low) and…

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  Figure 5. The schematic diagram that presents how syringaldehyde alleviates cardiac hypertrophy.