Optimized Langendorff perfusion system for cardiomyocyte isolation in adult mouse heart

Activation of the nonneuronal cholinergic cardiac system by hypoxic preconditioning protects isolated adult cardiomyocytes from hypoxia/reoxygenation injury

Activation of the vagus nerve mediates cardioprotection and attenuates myocardial ischemia/reperfusion (I/R) injury. In response to vagal activation, acetylcholine (ACh) is released from the intracardiac nervous system (ICNS) and activates intracellular cardioprotective signaling cascades. Recently, however, a nonneuronal cholinergic cardiac system (NNCCS) in cardiomyocytes has been described as an additional source of ACh. To investigate whether the NNCCS mediates cardioprotection in the absence of vagal and ICNS activation, we used a reductionist approach of isolated adult rat ventricular cardiomyocytes without neuronal cells, using hypoxic preconditioning (HPC) as a protective stimulus. Adult rat ventricular cardiomyocytes were isolated, the absence of neuronal cells was confirmed, and HPC was induced by 10/20 min hypoxia/reoxygenation (H/R) before subjection to 30/5 min H/R to simulate I/R injury. Cardiomyocyte viability was assessed by trypan blue staining at baseline and after HPC+H/R or H/R. Intra- and extracellular ACh was quantified using liquid chromatography-coupled mass spectrometry at baseline, after HPC, after hypoxia, and after reoxygenation, respectively. In a subset of experiments, muscarinic and nicotinic ACh receptor (m- and nAChR) antagonists were added during HPC or during H/R. Cardiomyocyte viability at baseline (69 ± 4%) was reduced by H/R (10 ± 3%). With HPC, cardiomyocyte viability was preserved after H/R (25 ± 6%). Intra- and extracellular ACh increased during hypoxia; HPC further increased both intra- and extracellular ACh (from 0.9 ± 0.7 to 1.5 ± 1.0 nmol/mg; from 0.7 ± 0.6 to 1.1 ± 0.7 nmol/mg, respectively). The addition of mAChR and nAChR antagonists during HPC had no impact on HPC's protection; however, protection was abrogated when antagonists were added during H/R (cardiomyocyte viability after H/R: 23 ± 5%; 13 ± 4%). In conclusion, activation of the NNCCS is involved in cardiomyocyte protection; HPC increases intra- and extracellular ACh during H/R, and m- and nAChRs are causally involved in HPC's cardiomyocyte protection during H/R. The interplay between upstream ICNS activation and NNCCS activation in myocardial cholinergic metabolism and cardioprotection needs to be investigated in future studies.NEW & NOTEWORTHY The intracardiac nervous system is considered to be involved in ischemic conditioning's cardioprotection through the release of acetylcholine (ACh). However, we demonstrate that hypoxic preconditioning (HPC) protects from hypoxia/reoxygenation injury and increases intra- and extracellular ACh during hypoxia in isolated adult ventricular rat cardiomyocytes. HPC's protection involves cardiomyocyte muscarinic and nicotinic ACh receptor activation. Thus, besides the intracardiac nervous system, a nonneuronal cholinergic cardiac system may also be causally involved in cardiomyocyte protection by ischemic conditioning.

An Optimized Langendorff-free Method for Isolation and Characterization of Primary Adult Cardiomyocytes

Isolation of adult mouse cardiomyocytes is an essential technique for advancing our understanding of cardiac physiology and pathology, and for developing therapeutic strategies to improve cardiac health. Traditionally, cardiomyocytes are isolated from adult mouse hearts using the Langendorff perfusion method in which the heart is excised, cannulated, and retrogradely perfused through the aorta. While this method is highly effective for isolating cardiomyocytes, it requires specialized equipment and technical expertise. To address the challenges of the Langendorff perfusion method, researchers have developed a Langendorff-free technique for isolating cardiomyocytes. This Langendorff-free technique involves anterograde perfusion through the coronary vasculature by clamping the aorta and intraventricular injection. This method simplifies the experimental setup by eliminating the need for specialized equipment and cannulation of the heart. Here, we introduce an updated Langendorff-free method for isolating adult mice cardiomyocytes that builds on the Langendorff-free protocols developed previously. In this method, the aorta is clamped in situ, and the heart is perfused using a peristaltic pump, water bath, and an injection needle. This simplicity makes cardiomyocyte isolation more accessible for researchers who are new to cardiomyocyte isolation or are working with limited resources. In this report, we provide a step-by-step description of our optimized protocol. In addition, we present example studies of analyzing mitochondrial structural and functional characteristics in isolated cardiomyocytes treated with and without the acute inflammatory stimuli lipopolysaccharide (LPS).

Comparative Analysis of Heart Regeneration: Searching for the Key to Heal the Heart-Part I: Experimental Injury Models to Study Cardiac Regeneration

Cardiovascular diseases are the leading cause of death worldwide, among which, ischemic heart disease is the most prevalent. Myocardial infarction results from occlusion of a coronary artery, which leads to an insufficient blood supply to the myocardium. As is well known, the massive loss of cardiomyocytes cannot be solved due the limited regenerative ability of the adult mammalian heart. In contrast, some lower vertebrate species can regenerate the heart after injury; their study has disclosed some of the involved cell types, molecular mechanisms and signaling pathways during the regenerative process. In this two-part review, we discuss the current state of the principal response in heart regeneration, where several involved processes are essential for full cardiac function in recovery.

Omentin-1 drives cardiomyocyte cell cycle arrest and metabolic maturation by interacting with BMP7

Mammalian cardiomyocytes (CMs) undergo maturation during postnatal heart development to meet the increased demands of growth. Here, we found that omentin-1, an adipokine, facilitates CM cell cycle arrest and metabolic maturation. Deletion of omentin-1 causes mouse heart enlargement and dysfunction in adulthood and CM maturation retardation in juveniles, including delayed cell cycle arrest and reduced fatty acid oxidation. Through RNA sequencing, molecular docking analysis, and proximity ligation assays, we found that omentin-1 regulates CM maturation by interacting directly with bone morphogenetic protein 7 (BMP7). Omentin-1 prevents BMP7 from binding to activin type II receptor B (ActRIIB), subsequently decreasing the downstream pathways mothers against DPP homolog 1 (SMAD1)/Yes-associated protein (YAP) and p38 mitogen-activated protein kinase (p38 MAPK). In addition, omentin-1 is required and sufficient for the maturation of human embryonic stem cell-derived CMs. Together, our findings reveal that omentin-1 is a pro-maturation factor for CMs that is essential for postnatal heart development and cardiac function maintenance.

Nogo-A reduces ceramide de novo biosynthesis to protect from heart failure

AIMS

Growing evidence correlate the accrual of the sphingolipid ceramide in plasma and cardiac tissue with heart failure (HF). Regulation of sphingolipid metabolism in the heart and the pathological impact of its derangement remain poorly understood. Recently, we discovered that Nogo-B, a membrane protein of endoplasmic reticulum, abundant in the vascular wall, down-regulates the sphingolipid de novo biosynthesis via serine palmitoyltransferase (SPT), first and rate liming enzyme, to impact vascular functions and blood pressure. Nogo-A, a splice isoform of Nogo, is transiently expressed in cardiomyocyte (CM) following pressure overload. Cardiac Nogo is up-regulated in dilated and ischaemic cardiomyopathies in animals and humans. However, its biological function in the heart remains unknown.

METHODS AND RESULTS

We discovered that Nogo-A is a negative regulator of SPT activity and refrains ceramide de novo biosynthesis in CM exposed to haemodynamic stress, hence limiting ceramide accrual. At 7 days following transverse aortic constriction (TAC), SPT activity was significantly up-regulated in CM lacking Nogo-A and correlated with ceramide accrual, particularly very long-chain ceramides, which are the most abundant in CM, resulting in the suppression of 'beneficial' autophagy. At 3 months post-TAC, mice lacking Nogo-A in CM showed worse pathological cardiac hypertrophy and dysfunction, with ca. 50% mortality rate.

CONCLUSION

Mechanistically, Nogo-A refrains ceramides from accrual, therefore preserves the 'beneficial' autophagy, mitochondrial function, and metabolic gene expression, limiting the progression to HF under sustained stress.

Current approaches for the recreation of cardiac ischaemic environment in vitro

Myocardial ischaemia is one of the leading dead causes worldwide. Although animal experiments have historically provided a wealth of information, animal models are time and money consuming, and they usually miss typical human patient's characteristics associated with ischemia prevalence, including aging and comorbidities. Generating reliable in vitro models that recapitulate the human cardiac microenvironment during an ischaemic event can boost the development of new drugs and therapeutic strategies, as well as our understanding of the underlying cellular and molecular events, helping the optimization of therapeutic approaches prior to animal and clinical testing. Although several culture systems have emerged for the recreation of cardiac physiology, mimicking the features of an ischaemic heart tissue in vitro is challenging and certain aspects of the disease process remain poorly addressed. Here, current in vitro cardiac culture systems used for modelling cardiac ischaemia, from self-aggregated organoids to scaffold-based constructs and heart-on-chip platforms are described. The advantages of these models to recreate ischaemic hallmarks such as oxygen gradients, pathological alterations of mechanical strength or fibrotic responses are highlighted. The new models represent a step forward to be considered, but unfortunately, we are far away from recapitulating all complexity of the clinical situations.

Myocardial infarction from a tissue engineering and regenerative medicine point of view: A comprehensive review on models and treatments

In the modern world, myocardial infarction is one of the most common cardiovascular diseases, which are responsible for around 18 million deaths every year or almost 32% of all deaths. Due to the detrimental effects of COVID-19 on the cardiovascular system, this rate is expected to increase in the coming years. Although there has been some progress in myocardial infarction treatment, translating pre-clinical findings to the clinic remains a major challenge. One reason for this is the lack of reliable and human representative healthy and fibrotic cardiac tissue models that can be used to understand the fundamentals of ischemic/reperfusion injury caused by myocardial infarction and to test new drugs and therapeutic strategies. In this review, we first present an overview of the anatomy of the heart and the pathophysiology of myocardial infarction, and then discuss the recent developments on pre-clinical infarct models, focusing mainly on the engineered three-dimensional cardiac ischemic/reperfusion injury and fibrosis models developed using different engineering methods such as organoids, microfluidic devices, and bioprinted constructs. We also present the benefits and limitations of emerging and promising regenerative therapy treatments for myocardial infarction such as cell therapies, extracellular vesicles, and cardiac patches. This review aims to overview recent advances in three-dimensional engineered infarct models and current regenerative therapeutic options, which can be used as a guide for developing new models and treatment strategies.

LPA2 Contributes to Vascular Endothelium Homeostasis and Cardiac Remodeling After Myocardial Infarction

RATIONALE

Myocardial infarction (MI) is one of the most dangerous adverse cardiovascular events. Our previous study found that lysophosphatidic acid (LPA) is increased in human peripheral blood after MI, and LPA has a protective effect on the survival and proliferation of various cell types. However, the role of LPA and its receptors in MI is less understood.

OBJECTIVES

To study the unknown role of LPA and its receptors in heart during MI.

METHODS AND RESULTS

In this study, we found that mice also had elevated LPA level in peripheral blood, as well as increased cardiac expression of its receptor LPA₂ in the early stages after MI. With adult and neonate MI models in global Lpar2 knockout (Lpar2-KO) mice, we found Lpar2 deficiency increased vascular leak leading to disruption of its homeostasis, so as to impaired heart function and increased early mortality. Histological examination revealed larger scar size, increased fibrosis, and reduced vascular density in the heart of Lpar2-KO mice. Furthermore, Lpar2-KO also attenuated blood flow recovery after femoral artery ligation with decreased vascular density in gastrocnemius. Our study revealed that Lpar2 was mainly expressed and altered in cardiac endothelial cells during MI, and use of endothelial-specific Lpar2 knockout mice phenocopied the global knockout mice. Additionally, adenovirus-Lpar2 and pharmacologically activated LPA₂ significantly improved heart function, reduced scar size, increased vascular formation, and alleviated early mortality by maintaining vascular homeostasis owing to protecting vessels from leakage. Mechanistic studies demonstrated that LPA-LPA₂ signaling could promote endothelial cell proliferation through PI3K-Akt/PLC-Raf1-Erk pathway and enhanced endothelial cell tube formation via PKD1-CD36 signaling.

CONCLUSIONS

Our results indicate that endothelial LPA-LPA₂ signaling promotes angiogenesis and maintains vascular homeostasis, which is vital for restoring blood flow and repairing tissue function in ischemic injuries. Targeting LPA-LPA₂ signal might have clinical therapeutic potential to protect the heart from ischemic injury.

Protocol to record and quantify the intracellular pH in contracting cardiomyocytes

Intracellular pH (pHi) plays critical roles in the regulation of cardiac function. Methods and techniques for cardiac pHi measurement have continued to evolve since early 1960s. Fluorescent microscopy is the most recently developed technique with several advantages over other techniques including higher spatial and temporal resolutions, and feasibility for contracting cell measurement. Here, we describe detailed methods for mouse cardiomyocyte isolation, and simultaneous measurement and quantification of pHi and sarcomere length in contracting cardiomyocytes. For complete details on the use and execution of this protocol, please refer to Lyu et al. (2022).

TRPC1 Contributes to Endotoxemia-induced Myocardial Dysfunction via Mediating Myocardial Apoptosis and Autophagy

Cardiac dysfunction is a vital complication of endotoxemia (ETM) with limited therapeutic options. Transient receptor potential canonical channel (TRPC)1 was involved in various heart diseases. While, the role of TRPC1 in ETM-induced cardiac dysfunction remains to be defined. In this study, we found that TRPC1 protein expression was significantly upregulated in hearts of lipopolysaccharide (LPS)-challenged mice. What's more, TRPC1 knockdown significantly alleviated LPS-induced cardiac dysfunction and injury. Further myocardial mRNA-sequencing analysis revealed that TRPC1 might participate in pathogenesis of ETM-induced cardiac dysfunction via mediating myocardial apoptosis and autophagy. Data showed that knockdown of TRPC1 significantly ameliorated LPS-induced myocardial apoptotic injury, cardiomyocytes autophagosome accumulation, and myocardial autophagic flux. Simultaneously, deletion of TRPC1 reversed LPS-induced molecular changes of apoptosis/autophagy signaling pathway in cardiomyocytes. Moreover, TRPC1 could promote LPS-triggered intracellular Ca²⁺ release, subsequent calpain activation and caveolin-1 degradation. Either blocking calpain by PD150606 or enhancing the amount of caveolin-1 scaffolding domain that interacts with TRPC1 by cell-permeable peptide cavtratin significantly alleviated the LPS-induced cardiac dysfunction and cardiomyocytes apoptosis/autophagy. Furthermore, cavtratin could inhibit LPS-induced calpain activation in cardiomyocytes. caveolin-1 could directly interact with calpain 2 both in vivo and in vitro. Importantly, cecal ligation and puncture-stimulated cardiac dysfunction and mortality were significantly alleviated in Trpc1^-/- and cavtratin-treated mice, which further validated the contribution of TRPC1-caveolin-1 signaling axis in sepsis-induced pathological process. Overall, this study indicated that TRPC1 could promote LPS-triggered intracellular Ca²⁺ release, mediate caveolin-1 reduction, and in turn activates calpain to regulate myocardial apoptosis and autophagy, contributing to ETM-induced cardiac dysfunction of mice.

Molecular Changes in Prepubertal Left Ventricular Development Under Experimental Volume Overload

Background

Left ventricular (LV) volume overload (VO), commonly found in patients with chronic aortic regurgitation (AR), leads to a series of left ventricular (LV) pathological responses and eventually irreversible LV dysfunction. Recently, questions about the applicability of the guideline for the optimal timing of valvular surgery to correct chronic AR have been raised in regard to both adult and pediatric patients. Understanding how VO regulates postnatal LV development may shed light on the best timing of surgical or drug intervention.

Methods and Results

Prepubertal LV VO was induced by aortocaval fistula (ACF) on postnatal day 7 (P7) in mice. LV free walls were analyzed on P14 and P21. RNA-sequencing analysis demonstrated that normal (P21_Sham vs.P14_Sham) and VO-influenced (P21_VO vs. P14_VO) LV development shared common terms of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) in the downregulation of cell cycle activities and the upregulation of metabolic and sarcomere maturation. The enriched GO terms associated with cardiac condition were only observed in normal LV development, while the enriched GO terms associated with immune responses were only observed in VO-influenced LV development. These results were further validated by the examination of the markers of cell cycle, maturation, and immune responses. When normal and VO-influenced LVs of P21 were compared, they were different in terms of immune responses, angiogenesis, percentage of Ki67-positive cardiomyocytes, mitochondria number, T-tubule regularity, and sarcomere regularity and length.

Conclusions

A prepubertal LV VO mouse model was first established. VO has an important influence on LV maturation and development, especially in cardiac conduction, suggesting the requirement of an early correction of AR in pediatric patients. The underlying mechanism may be associated with the activation of immune responses.

Metabolic maturation during postnatal right ventricular development switches to heart-contraction regulation due to volume overload

BACKGROUND

Metabolic maturation is one of the primary processes of postnatal cardiomyocyte development. How volume overload (VO), a pathological state of the right ventricle (RV) in children with congenital heart disease (CHD) and patients with heart failure, affects cardiomyocyte metabolic maturation is unclear.

METHODS AND RESULTS

A fistula between the abdominal aorta and inferior vena cava on postnatal day 7 (P7) was created in a mouse model to induce a young-aged RV VO. RNA sequencing revealed that the most enriched gene ontology (GO) terms of the upregulated transcriptome had been changed from metabolic maturation to heart contraction by VO. Transmission electron microscopy imaging showed that metabolic maturation marker-mitochondria were converted into the maturation style in the sham group while remaining unchanged in VO group. Calcium imaging showed that the calcium handling ability had slightly increased in the sham group but dramatically increased in the VO group, even with irregular contraction. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the top three enriched KEGG pathways for the upregulated transcriptome during normal RV development were the citrate cycle, cardiac muscle contraction, and protein processing in the endoplasmic reticulum. VO changed those to arrhythmogenic RV cardiomyopathy, dilated cardiomyopathy, and hypertrophic cardiomyopathy.

CONCLUSIONS

Metabolic maturation of postnatal RV development was partly interrupted by VO, and the underlining mechanism was associated with the activation of cardiomyopathy pathways.

Postnatal Right Ventricular Developmental Track Changed by Volume Overload

Background Current right ventricular (RV) volume overload (VO) is established in adult mice. There are no neonatal mouse VO models and how VO affects postnatal RV development is largely unknown. Methods and Results Neonatal VO was induced by the fistula between abdominal aorta and inferior vena cava on postnatal day 7 and confirmed by abdominal ultrasound, echocardiography, and hematoxylin and eosin staining. The RNA-sequencing results showed that the top 5 most enriched gene ontology terms in normal RV development were energy derivation by oxidation of organic compounds, generation of precursor metabolites and energy, cellular respiration, striated muscle tissue development, and muscle organ development. Under the influence of VO, the top 5 most enriched gene ontology terms were angiogenesis, regulation of cytoskeleton organization, regulation of vasculature development, regulation of mitotic cell cycle, and regulation of the actin filament-based process. The top 3 enriched signaling pathways for the normal RV development were PPAR signaling pathway, citrate cycle (Tricarboxylic acid cycle), and fatty acid degradation. VO changed the signaling pathways to focal adhesion, the PI3K-Akt signaling pathway, and pathways in cancer. The RNA sequencing results were confirmed by the examination of the markers of metabolic and cardiac muscle maturation and the markers of cell cycle and angiogenesis. Conclusions A neonatal mouse VO model was successfully established, and the main processes of postnatal RV development were metabolic and cardiac muscle maturation, and VO changed that to angiogenesis and cell cycle regulation.

Proteome characterisation of extracellular vesicles isolated from heart

Cardiac intercellular communication is critical for heart function and often dysregulated in cardiovascular diseases. While cardiac extracellular vesicles (cEVs) are emerging mediators of signalling, their isolation remains a technical challenge hindering our understanding of cEV protein composition. Here, we utilised Langendorff-collagenase-based enzymatic perfusion and differential centrifugation to isolate cEVs from mouse heart (yield 3-6 μg/heart). cEVs are ∼200 nm, express classical EV markers (Cd63/81/9⁺ , Tsg101⁺ , Pdcd6ip/Alix⁺ ), and are depleted of blood (Alb/Fga/Hba) and cardiac damage markers (Mb, Tnnt2, Ldhb). Comparison with mechanically-derived EVs revealed greater detection of EV markers and decreased cardiac damage contaminants. Mass spectrometry-based proteomic profiling revealed 1721 proteins in cEVs, implicated in proteasomal and autophagic proteostasis, glycolysis, and fatty acid metabolism; essential functions often disrupted in cardiac pathologies. There was striking enrichment of 942 proteins in cEVs compared to mouse heart tissue - implicated in EV biogenesis, antioxidant activity, and lipid transport, suggesting active cargo selection and specialised function. Interestingly, cEVs contain marker proteins for cardiomyocytes, cardiac progenitors, B-cells, T-cells, macrophages, smooth muscle cells, endothelial cells, and cardiac fibroblasts, suggesting diverse cellular origin. We present a method of cEV isolation and provide insight into potential functions, enabling future studies into EV roles in cardiac physiology and disease.

Establishment and characterization of an immortalized epicardial cell line

Recently, the increasing significance of the epicardium in cardiac development and regeneration is beginning to be recognized. However, because of the small proportion of primary epicardial cells and the limited cell culture time, further research on the mechanism of epicardial cells is hindered. Here, we transfected simian virus 40 Large T (SV40-LT) into primary epicardial cells to establish an immortalized cell line, named EpiSV40. We further demonstrated that EpiSV40 can be easy to culture and has the proliferation, migration and differentiation capacities comparable to primary epicardial cells. EpiSV40 can serve as an ideal in vitro model for epicardial cell research, which will booster the study of the epicardium in cardiac development and heart regeneration.