Murine Isolated Heart Model of Myocardial Stunning Associated with Cardioplegic Arrest.
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ABSTRACT:
SUBMITTER: Cordeiro B
PROVIDER: S-EPMC4545146 | biostudies-other | 2015 Aug
REPOSITORIES: biostudies-other
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Project description:We have demonstrated that scar formation after myocardial infarction (MI) is associated with an endogenous pool of CD44(pos)CD45(neg) multipotential mesenchymal stem cells (MSC). MSC differentiate into fibroblasts secreting collagen that forms a scar and mature into myofibroblasts that express alpha smooth muscle actin (α-SMA) that stabilizes the scar. In the aging mouse, cardiac repair after MI is associated with impaired differentiation of MSC; MSC derived from the aged hearts form dysfunctional fibroblasts that deposit less collagen in response to transforming growth factor beta-1 (TGF-β1) and poorly mature into myofibroblasts. We found in vitro that the defect in myofibroblast maturation can be remedied by AICAR, which activates non-canonical TGF-β signaling through AMP-activated protein kinase (AMPK). In the present study, we injected aged mice with AICAR and subjected them to 1h occlusion of the left anterior descending artery (LAD) and then reperfusion for up to 30days. AICAR-dependent AMPK signaling led to mobilization of an endogenous CD44(pos)CD45(neg) MSC and its differentiation towards fibroblasts and myofibroblasts in the infarct. This was accompanied by enhanced collagen deposition and collagen fiber maturation in the scar. The AICAR-treated group has demonstrated reduced adverse remodeling as indicated by improved apical end diastolic dimension but no changes in ejection fraction and cardiac output were observed. We concluded that these data indicate the novel, previously not described role of AMPK in the post-MI scar formation. These findings can potentially lead to a new therapeutic strategy for prevention of adverse remodeling in the aging heart.
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Project description:BackgroundTraditional preclinical echocardiography (ECHO) modalities, including 1-dimensional motion-mode (M-Mode) and 2-dimensional long axis (2D-US), rely on geometric and temporal assumptions about the heart for volumetric measurements. Surgical animal models, such as the mouse coronary artery ligation (CAL) model of myocardial infarction, result in morphologic changes that do not fit these geometric assumptions. New ECHO technology, including 4-dimensional ultrasound (4D-US), improves on these traditional models. This paper aims to compare commercially available 4D-US to M-mode and 2D-US in a mouse model of CAL.Methods37 mice underwent CAL surgery, of which 32 survived to a 4 week post-operative time point. ECHO was completed at baseline, 1 week, and 4 weeks after CAL. M-mode, 2D-US, and 4D-US were taken at each time point and evaluated by two separate echocardiographers. At 4 weeks, a subset (n = 12) of mice underwent cardiac magnetic resonance (CMR) imaging to serve as a reference standard. End systolic volume (ESV), end diastolic volume (EDV), and ejection fraction (EF) were compared among imaging modalities. Hearts were also collected for histologic evaluation of scar size (n = 16) and compared to ECHO-derived wall motion severity index (WMSI) and global longitudinal strain as well as gadolinium-enhanced CMR to compare scar assessment modalities.Results4D-US provides close agreement of ESV (Bias: -2.55%, LOA: - 61.55 to 66.66) and EF (US Bias: 11.23%, LOA - 43.10 to 102.8) 4 weeks after CAL when compared to CMR, outperforming 2D-US and M-mode estimations. 4D-US has lower inter-user variability as measured by intraclass correlation (ICC) in the evaluation of EDV (0.91) and ESV (0.93) when compared to other modalities. 4D-US also allows for rapid assessment of WMSI, which correlates strongly with infarct size by histology (r = 0.77).Conclusion4D-US outperforms M-Mode and 2D-US for volumetric analysis 4 weeks after CAL and has higher inter-user reliability. 4D-US allows for rapid calculation of WMSI, which correlates well with histologic scar size.
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Project description:RationalePost-ischemic changes in cellular metabolism alter myocardial and neurological function. Pyruvate dehydrogenase (PDH), the limiting step in mitochondrial glucose oxidation, is inhibited by increased expression of PDH kinase (PDK) during ischemia/reperfusion injury. This results in decreased utilization of glucose to generate cellular ATP. Post-cardiac arrest (CA) hypothermia improves outcomes and alters metabolism, but its influence on PDH and PDK activity following CA are unknown. We hypothesized that therapeutic hypothermia (TH) following CA is associated with the inhibition of PDK activity and increased PDH activity. We further hypothesized that an inhibitor of PDK activity, dichloroacetate (DCA), would improve PDH activity and post-CA outcomes.Methods and resultsAnesthetized and ventilated adult female C57BL/6 wild-type mice underwent a 12-minute KCl-induced CA followed by cardiopulmonary resuscitation. Compared to normothermic (37°C) CA controls, administering TH (30°C) improved overall survival (72-hour survival rate: 62.5% vs. 28.6%, P<0.001), post-resuscitation myocardial function (ejection fraction: 50.9±3.1% vs. 27.2±2.0%, P<0.001; aorta systolic pressure: 132.7±7.3 vs. 72.3±3.0 mmHg, P<0.001), and neurological scores at 72-hour post CA (9.5±1.3 vs. 5.4±1.3, P<0.05). In both heart and brain, CA increased lactate concentrations (1.9-fold and 3.1-fold increase, respectively, P<0.01), decreased PDH enzyme activity (24% and 50% reduction, respectively, P<0.01), and increased PDK protein expressions (1.2-fold and 1.9-fold, respectively, P<0.01). In contrast, post-CA treatment with TH normalized lactate concentrations (P<0.01 and P<0.05) and PDK expressions (P<0.001 and P<0.05), while increasing PDH activity (P<0.01 and P<0.01) in both the heart and brain. Additionally, treatment with DCA (0.2 mg/g body weight) 30 min prior to CA improved both myocardial hemodynamics 2 hours post-CA (aortic systolic pressure: 123±3 vs. 96±4 mmHg, P<0.001) and 72-hour survival rates (50% vs. 19%, P<0.05) in normothermic animals.ConclusionsEnhanced PDH activity in the setting of TH or DCA administration is associated with improved post-CA resuscitation outcomes. PDH is a promising therapeutic target for improving post-CA outcomes.
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