Persistent Fibrosis and Left Ventricular Chamber Stiffening Despite Cessation of Repetitive Pressure Overload in Swine

Figures

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  Figure 1. RPO-Induced Elevations in LV Chamber Stiffness Persist After Cessation of Intermittent Hemodynamic Overload Admittance catheter-derived left ventricular (LV) pressure-volume (PV) loops collected during rapid inferior vena cava occlusion revealed a steeper LV end-diastolic pressure-volume relationship (EDPVR) and an increase in the LV diastolic chamber stiffness coefficient (ß) after repetitive pressure overload (RPO) (red) that persisted 2-weeks after cessation of RPO (post-RPO green) compared to the initial study (blue). Values are mean ± SEM; ∗P < 0.05 vs initial study. Analyzed via repeated measures analysis of variance with post hoc Holm-Sidak test.

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  Figure 2. Persistent Cardiomyocyte Loss, Cellular Hypertrophy, and Interstitial Fibrosis After Cessation of RPO Example periodic acid–Schiff–stained (first row) and picrosirius red–stained (second row) myocardial tissue sections from representative animals in each group illustrate repetitive pressure overload (RPO)-induced changes in myocyte morphometry and interstitial fibrosis, respectively. The reduction in myocyte nuclear density (third row, left), increase in myocyte diameter (third row, right), and increase in interstitial and total collagen (fourth row) observed after RPO (red bars) vs normal control animals (blue bars) persisted 2 weeks after cessation of RPO (green bars). Values are mean ± SEM. ∗P < 0.05 vs normal control animals. Analyzed via unpaired t-test.

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  Figure 3. Persistence of the RPO-Induced Increase in LV Chamber Stiffness Is Associated With Continued Protection Against Acute Stretch-Induced Stunning and Myocyte Injury At the initial study (blue bars), LV distension caused by acute pressure overload persisted 1 hour after phenylephrine (PE) infusion was discontinued and LV pressure had normalized. The initial episode of pressure overload was associated with a significant reduction in LV ejection fraction (left panel, blue bars). This was accompanied by a significant rise in circulating cardiac troponin I (cTnI) concentrations within the 24-hour period following PE infusion (right panel, blue bars). These responses were attenuated after 2 weeks of RPO (red) as well as 2 weeks after cessation of RPO (green), demonstrating that RPO-induced elevations in LV chamber stiffness provide sustained protection against stretch-induced stunning and myocyte injury during acute pressure overload. Values are mean ± SEM. ∗P < 0.05 vs baseline. Analyzed via repeated measures analysis of variance with post hoc Holm-Sidak test. Abbreviations as in Figure 1.

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  Figure 4. Persistent Elevations in LV Chamber Stiffness Attenuate the Transcriptional Response to Acute Pressure Overload Expression of natriuretic peptides (atrial natriuretic peptide [ANP], B-type natriuretic peptide [BNP]), proinflammatory genes (C-C chemokine receptor type-2 [CCR2], CD68) and profibrotic genes (collagen I, fibronectin, lysyl oxidase-like 2 [LOXL2]) was significantly elevated 24 hours after a single episode of transient pressure overload (SPO) (gray bars) vs normal myocardium (blue). After the development of increased LV chamber stiffness (RPO, red), the transcriptional response to transient pressure elevation was abolished. Despite cessation of pressure overload for 2 weeks, the transcriptional response to transient pressure overload remained attenuated (post-RPO, green). Values are mean ± SEM. ∗P < 0.05 vs normal control animal. Analyzed via unpaired t-test. Abbreviations as in Figure 1.

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  Figure 5. Dynamic Changes in ECM Proteins Following Cessation of RPO Heat map showing individual extracellular matrix (ECM) proteins (left) and quantitative data for selected ECM proteins of interest (right). There was a delayed increase in ECM proteins after cessation of pressure overload (post-repetitive stress overload [RPO] green bars), including fibrillar and basement membrane collagens, lamins, and other extracellular matrix proteins. ∗P-adjusted <0.05 vs control animals. Please see Supplemental Table 2 for additional summary data.

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  Figure 6. Increased LV Chamber Stiffness and Interstitial Fibrosis Persist Following Prolonged Cessation of RPO Two-point diastolic PV curves created via echocardiographic analysis of the hemodynamic response to PE (top) revealed a significant increase in LV chamber stiffness (LV end-diastolic pressure [ΔEDP]/LV end-diastolic volume [ΔEDV]) after RPO that was maintained 2 weeks and 4 weeks after cessation of RPO (A). This was accompanied by a persistent increase in interstitial collagen (B), demonstrating that the diastolic chamber stiffening and fibrosis produced by 2 weeks of RPO persist for at least 4 weeks following cessation of intermittent hemodynamic overload. This was not associated with anatomical hypertrophy (C) but was accompanied by concentric LV remodeling (D). Values are mean ± SEM. ∗P < 0.05 vs initial study or normal control animal. Analyzed via repeated measures analysis of variance with post-hoc Holm-Sidak test. Abbreviations as in Figures 1 and 3.