Neonatal Apex Resection Triggers Cardiomyocyte Proliferation, Neovascularization and Functional Recovery Despite Local Fibrosis

So far, opposing outcomes have been reported following neonatal apex resection in mice, questioning the validity of this injury model to investigate regenerative mechanisms. We performed a systematic evaluation, up to 180 days after surgery, of the pathophysiological events activated upon apex resection. In response to cardiac injury, we observed increased cardiomyocyte proliferation in remote and apex regions, neovascularization, and local fibrosis. In adulthood, resected hearts remain consistently shorter and display permanent fibrotic tissue deposition in the center of the resection plane, indicating limited apex regrowth. However, thickening of the left ventricle wall, explained by an upsurge in cardiomyocyte proliferation during the initial response to injury, compensated cardiomyocyte loss and supported normal systolic function. Thus, apex resection triggers both regenerative and reparative mechanisms, endorsing this injury model for studies aimed at promoting cardiomyocyte proliferation and/or downplaying fibrosis. In this article, Nascimento and colleagues demonstrate that neonatal apex resection stimulates cardiomyocyte proliferation and permanent scarring in the apex. Newly formed cardiomyocytes compensate muscle loss by resection, and resected hearts recover functional competence in adulthood. These findings endorse this model for studies aiming to block cardiac fibrosis and/or favoring CM proliferation

Assessing the influence of perfusion on cardiac microtissue maturation: A heart-on-chip platform embedding peristaltic pump capabilities

Heart-on-chip is an unprecedented technology for recapitulating key biochemical and biophysical cues in cardiac pathophysiology. Several designs have been proposed to improve its ability to mimic the native tissue and establish it as a reliable research platform. However, despite mimicking one of most vascularized organs, reliable strategies to deliver oxygen and substrates to densely packed constructs of metabolically demanding cells remain unsettled. Herein, we describe a new heart-on-chip platform with precise fluid control, integrating an on-chip peristaltic pump, allowing automated and fine control over flow on channels flanking a 3D cardiac culture. The application of distinct flow rates impacted on temporal dynamics of microtissue structural and transcriptional maturation, improving functional performance. Moreover, a widespread transcriptional response was observed, suggesting flow-mediated activation of critical pathways of cardiomyocyte structural and functional maturation and inhibition of cardiomyocyte hypoxic injury. In conclusion, the present design represents an important advance in bringing engineered cardiac microtissues closer to the native heart, overcoming traditional bulky off-chip fluid handling systems, improving microtissue performance, and matching oxygen and energy substrate requirements of metabolically active constructs, avoiding cellular hypoxia. Distinct flow patterns differently impact on microtissue performance and gene expression program

A new role of AMP-activated protein kinase in regulating proliferation of mesenchymal stem cells

Purpose: Natriuretic peptides (NPs) administered during early reperfusion are protective in models of myocardial infarction. A previous study examining the endogenous components of B-type natriuretic peptide (BNP) protection of reperfused myocardium, implicated both sarcolemmal (s) KATP and mitochondrial (m) KATP channels. The indirect evidence characterising the relationship between BNP signalling and KATP was obtained using sulphonylurea receptor inhibitors in a rat isolated heart model of ischaemia-reperfusion injury. Here we seek to further examine the relationship between NPs and sKATP openings using single channel electrophysiology. Given our previous findings and the overarching consensus that cardioprotective autacoids open KATP channels, it was hypothesised that NPs elicit sKATP opening. Methods: Cardiomyocyte isolation. Left ventricular cardiomyocytes were isolated from male Sprague-Dawley rat hearts subjected to enzymatic digestion with Liberase Blendzyme DL. Cardiomyocytes were cultured overnight in Medium 199, prior to patch clamp. Single channel patch clamp. Single channel recordings at room temperature (22°C) were made from cell attached patches bathed in Na+ Locke, pH 7.2. The recording pipette contained high KCl (140 mM), pH 7.2. Recordings (45 sec) were made over a range of patch potentials (0, -30, -60, -90, -120 mV), in the absence (control) and in the presence of bath applied BNP (10, 100 nM and 1 µM), pinacidil (200 µM) or pinacidil vehicle (DMSO, 0.25%). Recordings were also made with BNP and pinacidil applied concomitantly. Data are mean ± S.E.M. Results: The current voltage relationship of sKATP under control conditions was linear at –ve patch potentials, the mean conductance being 52.9 ± 1.8 pS (n = 18 hearts, n = 35 cells). Pinacidil caused a four fold increase in sKATP open probability compared to control. Mean channel conductance in the presence of pinacidil was 59.9 ± 1.9 pS (n = 16 hearts, n = 44 cells). Interestingly BNP at all concentrations had negligible effects on sKATP open probability and unitary conductance. However, BNP at all concentrations and patch potentials inhibited pinacidil induced sKATP openings, restoring channel open probability to baseline. Conclusion: These data illustrate the inhibitory effect of NP signalling on sKATP function in the cardiomyocyte under normoxia. They are concordant with the inhibitory effect of atrial NP on KATP in the pancreatic beta cell, but are in apparent conflict with the current cardioprotection paradigm. However, differential effects on sKATP and mKATP and the effects of hypoxia-reoxygenation require further exploration