Atrial fibrillation-associated electrical remodelling in human induced pluripotent stem cell-derived atrial cardiomyocytes: a novel pathway for antiarrhythmic therapy development

AIMS

Atrial fibrillation (AF) is associated with tachycardia-induced cellular electrophysiology alterations which promote AF chronification and treatment resistance. Development of novel antiarrhythmic therapies is hampered by the absence of scalable experimental human models that reflect AF-associated electrical remodelling. Therefore, we aimed to assess if AF-associated remodelling of cellular electrophysiology can be simulated in human atrial-like cardiomyocytes derived from induced pluripotent stem cells in the presence of retinoic acid (iPSC-aCM), and atrial-engineered human myocardium (aEHM) under short term (24 h) and chronic (7 days) tachypacing (TP).

METHODS AND RESULTS

First, 24-h electrical pacing at 3 Hz was used to investigate whether AF-associated remodelling in iPSC-aCM and aEHM would ensue. Compared to controls (24 h, 1 Hz pacing) TP-stimulated iPSC-aCM presented classical hallmarks of AF-associated remodelling: (i) decreased L-type Ca2+ current (ICa,L) and (ii) impaired activation of acetylcholine-activated inward-rectifier K+ current (IK,ACh). This resulted in action potential shortening and an absent response to the M-receptor agonist carbachol in both iPSC-aCM and aEHM subjected to TP. Accordingly, mRNA expression of the channel-subunit Kir3.4 was reduced. Selective IK,ACh blockade with tertiapin reduced basal inward-rectifier K+ current only in iPSC-aCM subjected to TP, thereby unmasking an agonist-independent constitutively active IK,ACh. To allow for long-term TP, we developed iPSC-aCM and aEHM expressing the light-gated ion-channel f-Chrimson. The same hallmarks of AF-associated remodelling were observed after optical-TP. In addition, continuous TP (7 days) led to (i) increased amplitude of inward-rectifier K+ current (IK1), (ii) hyperpolarization of the resting membrane potential, (iii) increased action potential-amplitude and upstroke velocity as well as (iv) reversibly impaired contractile function in aEHM.

CONCLUSIONS

Classical hallmarks of AF-associated remodelling were mimicked through TP of iPSC-aCM and aEHM. The use of the ultrafast f-Chrimson depolarizing ion channel allowed us to model the time-dependence of AF-associated remodelling in vitro for the first time. The observation of electrical remodelling with associated reversible contractile dysfunction offers a novel platform for human-centric discovery of antiarrhythmic therapies.

Endothelial CaSR is involved in the induction of atherosclerosis by promoting cell adhesion and local inflammation

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Humboldt foundation

Background

Calcium-Sensing Receptor (CaSR) is a cell surface G-protein coupled receptor that senses calcium in the extracellular environment. This receptor is widely studied in mineral homeostasis due to its presence in varied calcitropic tissues. However, CaSR is also present on the surface of vascular and hematopoietic cells and recent studies suggest that this receptor can also have pathological consequences related to cardiovascular diseases, like atherosclerosis. Since endothelial cells are crucial players in atherogenesis, we aimed to investigate which role endothelial CaSR plays in the development and progression of atherosclerosis.

Methods

We cross-bred CaSRflox/flox Apoe-/- mice with BmxCreERT2 Apoe-/- (endothelial cell specific Cre driver) mice to obtain tamoxifen-inducible mice which have an endothelial cell specific deletion of CaSR. The mice were then fed with a high fat diet (HFD) for 4 or 12 weeks, reflecting early and late atherosclerosis, respectively. We used histological and immuno-fluorescent stainings to analyse the atherosclerotic lesion size and its cellular and acellular composition. Systemic effects on leukocytes were evaluated using flow-cytometry, while intra-vital microscopy was used to study leukocyte adhesion to activated endothelium in-vivo. Further mechanistic studies were performed in human coronary artery endothelial cells (HCAECs) in-vitro.

Results

Endothelial CaSR deficiency in mice resulted in significantly smaller lesion size in early atherosclerotic stages (4 weeks HFD), whereas late atherosclerotic lesions (12 weeks HFD) were not affected by the lack of endothelial CaSR. Moreover, the phenotype of atherosclerotic plaques, characterized by macrophage, smooth muscle cell, collagen and necrotic core content remained unaltered between wild-type and endothelial cell specific CaSR knockout mice. Interestingly, leukocyte adhesion in-vivo, especially neutrophil adhesion, was significantly reduced in endothelial cell CaSR deficient mice. In line with this, overexpression of CaSR in HCAECs in-vitro increased the production of inflammatory cytokines and expression of adhesion molecules ICAM and VCAM.

Conclusion

Our results indicate that while endothelial cell specific CaSR is involved in the induction of atherosclerosis, it does not play a major role in its progression. CaSR has a major influence on endothelium-leukocyte interaction and endothelial inflammation. The increased expression of ICAM/VCAM suggest that CaSR mainly mediates such adhesive effects by modulating integrin expression. Thereby this study highlights that CaSR plays a crucial role in atherosclerosis development, rendering it a novel, so far unexplored therapeutic target.

Micromanaging atherosclerosis: myeloid cell-specific microRNA-26b attenuates atherosclerosis development

Funding Acknowledgements

Type of funding sources: None.

Increasing evidence has shown that microRNAs (miRs) are fundamental players in atherosclerosis, but the exact role of various miRs remains elusive. Preliminary data showed that, with a 5-fold increase, miR-26b was the most highly expressed miR in human atherosclerotic plaques compared to healthy vessels. Therefore, we aimed to determine its cell-specific effects on atherosclerosis development.

We examined the role of miR-26b in atherosclerosis by using full-body knockout (KO) mice on a 4 weeks and 12 weeks Western type diet (WTD) and myeloid cell-specific miR-26b KO (LysM-Cre) mice on 12 weeks WTD on an apolipoprotein E-deficient background. Atherosclerotic plaque size and phenotype were analyzed via immunohistochemical and immunofluorescent stainings. The phenotype and function of bone marrow-derived macrophages (BMDMs) from full body KO mice were analyzed via PCR, ELISA and gelatinase assays. Lipid nanoparticles (LNPs) served as vehicles for miR-26b mimics to restore miR-26b levels in knockout BMDMs.

A full-body miR-26b-KO on a 12 weeks WTD resulted in a striking 3.5-fold increase in atherosclerotic lesion size, compared to control. Consistent with a more advanced plaque phenotype, collagen content, smooth muscle cell percentage and relative necrotic core area were all significantly increased in plaques from miR-26b KO mice whilst the relative macrophage content was significantly reduced. Interestingly, the full-body KO mice on a 4 weeks WTD showed a remarkable 10-fold increase in plaque size and the respective plaques also had a reduced macrophage percentage, showing that miR-26b has very strong effects on both atherogenesis as well as atherosclerosis progression. Intriguingly, relative plaque size in the arches of miR-26b LysM-Cre mice were increased by 3-fold and collagen content was also increased significantly, suggesting a role for myeloid-specific miR-26b in atherosclerosis development. Further highlighting its myeloid-specific effects, miR-26b KO BMDMs showed an increase in IL-6 and TNFα secretion, which could be rescued by LNPs containing miR-26b mimics. Additionally, these miR-26b KO BMDMs showed a reduction in collagen breakdown.

Overall, our results clearly demonstrate an atheroprotective role of myeloid cell-specific miR-26b by attenuating lesion initiation as well as progression, mainly by suppressing inflammation and stimulating collagen breakdown. Our study leads to exciting new insights into the role of miR-26b in atherosclerosis development, providing an important back-bone for future research and potential new treatment options.