Atrioventricular node dysfunction in pressure overload-induced heart failure—Involvement of the immune system and transcriptomic remodelling

Figures

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  FIGURE 1. HF model with AV node dysfunction. (A), percentage survival of control (n = 9; subject to sham surgery) and HF (n = 11; subject to TAC surgery) mice in the days following surgery. (B–F), body weight (B), heart weight (C), heart weight:body weight ratio (D), lung weight:body weight ratio (E) and in vivo heart rate ((F); measured using the ECGenie) of the two cohorts of mice (n = 9 and 11) at the end of the experiment. (G–J), PR interval (G), QRS duration (H), QT interval (I) and corrected QT interval (J) of the two cohorts of mice (n = 9 and 10) measured in the anaesthetised animals at the end of the experiment. In B-J, means ± SEM as well as individual data points shown. *p < 0.05.

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  FIGURE 2. Transcriptomic remodelling of the AV node in HF. (A), principal component analysis (PCA) of all six replicates based on the 500 most highly expressed transcripts. The x-axis shows the PCA 1 score, which represents the maximum variance direction in the data set. This is principal component 1 (PC1) and it accounts for 64% of the variance in the samples and can be attributed to the variance between the control and HF cohorts. The y-axis shows the PCA 2 score, which represents the second highest variance direction in the data set. This is principal component 2 (PC2) and it accounts for 19% of the variance in the samples and can be attributed to the variance among all samples. The red symbols (1, 2 and 3) represent the three HF technical replicates and the blue symbols (4, 5 and 6) represent the three control technical replicates. Each technical replicate contained three pooled AV node biopsies. (B), volcano plot showing -log10 adjusted p-value plotted against log2 fold change for each transcript measured. Dashed line corresponds to adjusted p = 0.05. The red and blue symbols show the 3,077 transcripts significantly upregulated (red symbols; 1,740 transcripts) or downregulated (blue…

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  FIGURE 3. Downregulation of many key ion channel transcripts in the AV node in HF. (A–D), expression of transcripts for Na+ and Ca2+ channels (A and B) and K+ channels (C and D) in control (black bars) and HF (red bars). Highly expressed ion channel transcripts are shown in the upper panels (A and C) and more poorly expressed ion channel transcripts are shown in the lower panels (B and D). The data for Scn10a are also shown in a zoomed panel. Gene names and more common names are shown. Means ± SEM as well as individual data points shown *p < 0.05.

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  FIGURE 4. Evidence of a shift from fatty acid to glucose metabolism in the AV node in HF. (A), schematic diagram of glycolysis, fatty acid beta-oxidation, the tricarboxylic acid cycle, and the electron transport chain. For glycolysis, fatty acid beta-oxidation, and the tricarboxylic acid cycle, key enzymes and metabolic intermediaries (in light blue) are shown. Transcripts of enzymes highlighted in red were significantly upregulated in HF and transcripts of enzymes highlighted in dark blue were significantly downregulated. For the electron transport chain, ATP synthase and complexes I to IV are shown. Transcripts associated with complexes I and IV were significantly upregulated and are highlighted in red. (B–E), expression of transcripts associated with glycolysis (B), fatty acid beta-oxidation (C), the tricarboxylic acid cycle (D) and the electron transport chain (E) in HF mice as a percentage of that in control mice. All transcripts changed significantly in HF. Significantly upregulated transcripts highlighted in A are shown in red and significantly downregulated transcripts highlighted in A are shown in blue. Red dotted lines correspond to 100%.

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  FIGURE 5. Changes in MAP kinase pathway transcripts in the AV node in HF. (A), significant changes in the expression of MAP kinase pathway transcripts. Expression in HF mice is shown as a percentage of that in control mice. Red dotted line corresponds to 100%. (B), mean (+SEM) expression (as well as individual data points) of p38 pathway transcripts in control (black bars) and HF (red bars) mice. The data for Mapk11 are also shown in a zoomed in panel. *p < 0.05.

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  FIGURE 6. Transcriptomic remodelling of the extracellular matrix of the AV node in HF. (A), expression of all collagen transcripts in HF mice as a percentage of that in control mice. Red dotted line corresponds to 100%. (B and C), expression of highly expressed collagen transcripts (B) and more poorly expressed collagen transcripts (C) in control (black bars) and HF (red bars) mice. Only means + SEM shown (individual data points not shown for clarity). *p < 0.05.

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  FIGURE 7. Evidence of infiltration of the AV node by immune cells in HF. (A), schematic diagram of the cells of the immune system. (B), expression of immune cell markers (transcripts) in HF mice as a percentage of that in control mice. (C), expression of cytokine transcripts in HF mice as a percentage of that in control mice. Red dotted lines correspond to 100%.

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  FIGURE 8. Pathways involved in AV node dysfunction in HF. (A–C), summary of canonical pathways (identified by Ingenuity Pathway Analysis) associated with the cytokines (A), protein kinases (B) and transcription factors (C) changing significantly in the AV node in HF. Details of the pathways are given in the Supplementary File, Canonical pathways. xlsx. 81, 262 and 134 pathways associated with the cytokines, protein kinases and transcription factors, respectively, were identified in total and the area of the pie chart for each group of pathways reflects the number of pathways in each group. (D), Venn diagram of the pathways associated with the cytokines, protein kinases and transcription factors; there is substantial overlap of the pathways and 30 pathways were common to the cytokines, protein kinases and transcription factors. (E), schematic diagram showing a potential chain of events in the AV node during HF leading to AV node dysfunction. Although the schema is based on the results of this study, it remains hypothetical. Although unidirectional arrows are drawn, they could be bidirectional.