LOC102549726/miR-760-3p network is involved in the progression of ISO-induced pathological cardiomyocyte hypertrophy via endoplasmic reticulum stress

Pathological cardiac hypertrophy (CH) is featured by myocyte enlargement and cardiac malfunction. Multiple signaling pathways have been implicated in diverse pathological and physiological processes in CH. However, the function of LOC102549726/miR-760-3p network in CH remains unclear. Here, we characterize the functional role of LOC102549726/miR-760-3p network in CH and delineate the underlying mechanism. The expression of LncRNA LOC102549726 and hypertrophic markers was significantly increased compared to the control, while the level of miR-760-3p was decreased. Next, we examined ER stress response in a hypertrophic cardiomyocyte model. The expression of ER stress markers was greatly enhanced after incubation with ISO. The hypertrophic reaction, ER stress response, and increased potassium and calcium ion channels were alleviated by genetic downregulation of LOC102549726. It has been demonstrated that LOC102549726 functions as a competitive endogenous RNA (ceRNA) of miR-760-3p. Overexpression of miR-760-3p decreased cell surface area and substantially mitigated ER stress response; protein levels of potassium and calcium channels were also significantly up-regulated compared to the NC control. In contrast, miR-760-3p inhibition increased cell size, aggravated CH and ER stress responses, and reduced ion channels. Collectively, in this study we demonstrated that the LOC102549726/miR-760-3p network was a crucial regulator of CH development. Ion channels mediate the ER stress response and may be a downstream sensor of the LOC102549726/miR-760-3p network. Therefore, these findings advance our understanding of pathological CH and provide new insights into therapeutic targets for cardiac remodeling.

MicroRNA-34c-5p provokes isoprenaline-induced cardiac hypertrophy by modulating autophagy via targeting ATG4B

Pathological cardiac hypertrophy serves as a significant foundation for cardiac dysfunction and heart failure. Recently, growing evidence has revealed that microRNAs (miRNAs) play multiple roles in biological processes and participate in cardiovascular diseases. In the present research, we investigate the impact of miRNA-34c-5p on cardiac hypertrophy and the mechanism involved. The expression of miR-34c-5p was proved to be elevated in heart tissues from isoprenaline (ISO)-infused mice. ISO also promoted miR-34c-5p level in primary cultures of neonatal rat cardiomyocytes (NRCMs). Transfection with miR-34c-5p mimic enhanced cell surface area and expression levels of foetal-type genes atrial natriuretic factor (Anf) and β-myosin heavy chain (β-Mhc) in NRCMs. In contrast, treatment with miR-34c-5p inhibitor attenuated ISO-induced hypertrophic responses. Enforced expression of miR-34c-5p by tail intravenous injection of its agomir led to cardiac dysfunction and hypertrophy in mice, whereas inhibiting miR-34c-5p by specific antagomir could protect the animals against ISO-triggered hypertrophic abnormalities. Mechanistically, miR-34c-5p suppressed autophagic flux in cardiomyocytes, which contributed to the development of hypertrophy. Furthermore, the autophagy-related gene 4B (ATG4B) was identified as a direct target of miR-34c-5p, and miR-34c-5p was certified to interact with 3' untranslated region of Atg4b mRNA by dual-luciferase reporter assay. miR-34c-5p reduced the expression of ATG4B, thereby resulting in decreased autophagy activity and induction of hypertrophy. Inhibition of miR-34c-5p abolished the detrimental effects of ISO by restoring ATG4B and increasing autophagy. In conclusion, our findings illuminate that miR-34c-5p participates in ISO-induced cardiac hypertrophy, at least partly through suppressing ATG4B and autophagy. It suggests that regulation of miR-34c-5p may offer a new way for handling hypertrophy-related cardiac dysfunction.

Volcano-Shaped Scanning Probe Microscopy Probe for Combined Force-Electrogram Recordings from Excitable Cells

Atomic force microscopy based approaches have led to remarkable advances in the field of mechanobiology. However, linking the mechanical cues to biological responses requires complementary techniques capable of recording these physiological characteristics. In this study, we present an instrument for combined optical, force, and electrical measurements based on a novel type of scanning probe microscopy cantilever composed of a protruding volcano-shaped nanopatterned microelectrode (nanovolcano probe) at the tip of a suspended microcantilever. This probe enables simultaneous force and electrical recordings from single cells. Successful impedance measurements on mechanically stimulated neonatal rat cardiomyocytes in situ were achieved using these nanovolcano probes. Furthermore, proof of concept experiments demonstrated that extracellular field potentials (electrogram) together with contraction displacement curves could simultaneously be recorded. These features render the nanovolcano probe especially suited for mechanobiological studies aiming at linking mechanical stimuli to electrophysiological responses of single cells.

Shengmai injection alleviates H2O2‑induced oxidative stress through activation of AKT and inhibition of ERK pathways in neonatal rat cardiomyocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Shengmai injection (SMI) is a classical traditional Chinese medicine (TCM) officially recorded in Pharmacopoeia of the People's Republic of China (version 2015) and has long been used to treat heart failure in China. However scientific evidence for the anti-oxidative stress potential of SMI used in traditional medicine is lacking.

AIM OF STUDY

The present study aimed to evaluate the efficacy of SMI in alleviating H₂O₂‑induced Oxidative Stress the underlying mechanisms MATERIALS AND METHODS: H₂O₂-induced oxidative stress model of cardiomyocytes was established with primary cultured neonatal rat cardiomyocytes. CCK8 cell viability assay and lacatate dehydrogenase cytotoxicity assay were performed to ensure the safety dose and lowest effective dose for the mode employing CCK-8 cell viability assay kit and lactate dehydrogenase cytotoxicity assay kit. ROS levels were determined using CM-H2DCFDA fluorescent probe in cardiomyocytes with H₂O₂-induced oxidative stress. The change of NAD(P)H level in cardiomyocytes was evaluated during the process of oxidative stress. The content of myocardial cytosolic Ca²⁺ and Ca²⁺ was determined using Fura-2/AM and Rhod 2-AM fluorescent probe in mitochondrial in the process of oxidative stress. Annexin V-FITC/PI double staining was applied to examine the apoptotic cells in cardiomyocytes with oxidative stress. To identify the apoptosis after oxidative stress myocardial cells with the application of Annexin V-FITC/PI double staining apoptosis detection kit. Quantitative polymerase chain reaction (RT-PCR) was applied to measure the expression of antioxidant enzymes: catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GSR). Western blot was performed to observe the phosphorylation of AKT and ERK1/2.

RESULTS

SMI was shown to significantly attenuate oxidative stress-induced cell proliferation arrest and apoptosis in neonatal rat cardiomyocytes. In addition, SMI treatment could decrease the production of reactive oxygen species (ROS), nicotinamide adenine dinucleotide (NADH) and malondialdehyde (MDA), and reduce the overloads of cytoplasmic Ca²⁺ and mitochondrial Ca²⁺ induced by H₂O₂. SMI could also restore the mRNA expression and activities of SOD, GSR, and CAT suppressed by H₂O₂. Mechanistically, SMI upregulated intracellular AKT phosphorylation and downregulate ERK1/2 phosphorylation in H₂O₂-treated cardiomyocytes. Pretreatment with LY294002, an AKT phosphorylation inhibitor, suppressed the protective role of SMI in cardiomyocytes, while pretreatment with PD98059, an ERK1/2 phosphorylation inhibitor, enhanced the effect of SMI.

CONCLUSIONS

In conclusion, SMI may attenuate oxidative stress-induced damage in cardiomyocytes potentially through the AKT and ERK1/2 pathway and can function as a promising injectable traditional Chinese medicine to treat oxidative stress-induced injury.

Regulation of Ca2+ signaling by acute hypoxia and acidosis in rat neonatal cardiomyocytes

Ischemic heart disease is an arrhythmogenic condition, accompanied by hypoxia, acidosis, and impaired Ca²⁺ signaling. Here we report on effects of acute hypoxia and acidification in rat neonatal cardiomyocytes cultures.

RESULTS

Two populations of neonatal cardiomyocyte were identified based on inactivation kinetics of L-type I_Ca: rapidly-inactivating I_Ca (τ~20ms) myocytes (prevalent in 3-4-day cultures), and slow-inactivating I_Ca (τ≥40ms) myocytes (dominant in 7-day cultures). Acute hypoxia (pO₂<5mmHg for 50-100s) suppressed I_Ca reversibly in both cell-types to different extent and with different kinetics. This disparity disappeared when Ba²⁺ was the channel charge carrier, or when the intracellular Ca²⁺ buffering capacity was increased by dialysis of high concentrations of EGTA and BAPTA, suggesting critical role for calcium-dependent inactivation. Suppressive effect of acute acidosis on I_Ca (~40%, pH6.7), on the other hand, was not cell-type dependent. Isoproterenol enhanced I_Ca in both cell-types, but protected only against suppressive effects of acidosis and not hypoxia. Hypoxia and acidosis suppressed global Ca²⁺ transients by ~20%, but suppression was larger, ~35%, at the RyR2 microdomains, using GCaMP6-FKBP targeted probe. Hypoxia and acidosis also suppressed mitochondrial Ca²⁺ uptake by 40% and 10%, respectively, using mitochondrial targeted Ca²⁺ biosensor (mito-GCaMP6).

CONCLUSION

Our studies suggest that acute hypoxia suppresses I_Ca in rapidly inactivating cell population by a mechanism involving Ca²⁺-dependent inactivation, while compromised mitochondrial Ca²⁺ uptake seems also to contribute to I_Ca suppression in slowly inactivating cell population. Proximity of cellular Ca²⁺ pools to sarcolemmal Ca²⁺ channels may contribute to the variability of inactivation kinetics of I_Ca in the two cell populations, while acidosis suppression of I_Ca appears mediated by proton-induced block of the calcium channel.

Ghrelin protected neonatal rat cardiomyocyte against hypoxia/reoxygenation injury by inhibiting apoptosis through Akt-mTOR signal

Reducing reperfusion period myocardial cell damage is efficient to reduce myocardial ischemia-reperfusion injury. Ghrelin can increase myocardial contractility, improve heart failure caused by myocardial infarction. This study aimed to investigate the protective effect of Ghrelin on myocardial hypoxia/reoxygenation (H/R) injury of neonatal rat cardiomyocytes (NRCMs) and to explore the mechanisms. We isolated the NRCMs, established myocardial H/R model, blocked growth hormone secretagogue receptor (GHSR) by siRNA technique, examined cell activity by MTT and LDH assay, detected apoptosis by Hoechst 33258 staining and flow cytometry and determined the expression levels of apoptosis related proteins and signaling pathway proteins by western blot. We found that Ghrelin can significantly improve cell activity and decrease apoptosis after H/R, however this effect was abolished by GHSR-siRNA. In addition, we found that Ghrelin can significantly increase the expression of Bcl-2 but inhibit the level of Bax and caspase-3. Further mechanism study found that the phosphorylation level of signaling pathway protein Akt and mTOR in Ghrelin treated group were significantly higher than that in other groups. In conclusion, Ghrelin can reduce the H/R damage on NRCMs and inhibit the apoptosis by activating Akt-mTOR signaling pathway.

cUMP hydrolysis by PDE3A

As previously reported, the cardiac phosphodiesterase PDE3A hydrolyzes cUMP. Moreover, cUMP-degrading activity was detected in cow and dog hearts several decades ago. Our aim was to characterize the enzyme kinetic parameters of PDE3A-mediated cUMP hydrolysis and to investigate whether cUMP and cUMP-hydrolyzing PDEs are present in cardiomyocytes. PDE3A-mediated cUMP hydrolysis was characterized in time course, inhibitor, and Michaelis-Menten kinetics experiments. Intracellular cyclic nucleotide (cNMP) concentrations and the mRNAs of cUMP-degrading PDEs were quantitated in neonatal rat cardiomyocytes (NRCMs) and murine HL-1 cardiomyogenic cells. Moreover, we investigated cUMP degradation in HL-1 cell homogenates and intact cells. Educts (cNMPs) and products (NMPs) of the PDE reactions were detected by HPLC-coupled tandem mass spectrometry. PDE3A degraded cUMP (measurement of UMP formation) with a K _M value of ~143 μM and a V _max value of ~42 μmol/min/mg. PDE3A hydrolyzed cAMP with a K _M value of ~0.7 μM and a V _max of ~1.2 μmol/min/mg (determination of AMP formation). The PDE3 inhibitor milrinone inhibited cUMP hydrolysis (determination of UMP formation) by PDE3A (K _i = 57 nM). Significant amounts of cUMP as well as of PDE3A mRNA (in addition to PDE3B and PDE9A transcripts) were detected in HL-1 cells and NRCMs. Although HL-1 cell homogenates contain a milrinone-sensitive cUMP-hydrolyzing activity, intact HL-1 cells may use additional PDE3-independent mechanisms for cUMP disposal. PDE3A is a low-affinity and high-velocity PDE for cUMP. Future studies should investigate biological effects of cUMP in cardiomyocytes and the role of PDE3A in detoxifying high intracellular cUMP concentrations under pathophysiological conditions.

Protective effects of acacetin isolated from Ziziphora clinopodioides Lam. (Xintahua) on neonatal rat cardiomyocytes

BACKGROUND

The total flavonoids from ethanol extract of the aerial part of Ziziphora clinopodioides Lam. (Lamlaceae) (Xintahua) showed protective activities against rat acute myocardial ischemia in rats. This study aims to isolate acacetin, a flavonoid, from the aerial part of Z. clinopodioides, to develop an HPLC method for its detection, and to evaluate its protective effects on neonatal rat cardiomyocytes.

METHODS

Sephadex LH-20 silicagel and pillar layer chromatography silica gel were applied for the isolation and purification of acacetin and its structure was elucidated on the basis of (1)H and (13)C NMR spectroscopy. The content of acacetin in Z. clinopodioides collected from three different origins was determined by HPLC. The neonatal rat cardiomyocytes were isolated and cultured in vitro to establish a hypoxia/reoxygenation injury model. The viability of cardiomyocytes was measured by the MTT method. Changes of malondialdehyde (MDA) content in the medium were also determined.

RESULTS

The acacetin content in various batches of Z. clinopodioides ranged from 45.50 to 47.41 μg/g. Acacetin of 25, 10, 5 μg/mL significantly decreased the MDA content in a model of hypoxia/reoxygenation injury (P < 0.001, P < 0.001 and P = 0.033, respectively).

CONCLUSIONS

Acacetin protects neonatal cardiomyocytes from the damage induced by hypoxia/reoxygenation stress through reduction of lipid peroxidation and enhancement of the antioxidant activity.

Mesenchymal stem cell secreted platelet derived growth factor exerts a pro-migratory effect on resident Cardiac Atrial appendage Stem Cells

Mesenchymal stem cells (MSCs) modulate cardiac healing after myocardial injury through the release of paracrine factors, but the exact mechanisms are still unknown. One possible mechanism is through mobilization of endogenous cardiac stem cells (CSCs). This study aimed to test the pro-migratory effect of MSC conditioned medium (MSC-CM) on endogenous CSCs from human cardiac tissue. By using a three-dimensional collagen assay, we found that MSC-CM improved migration of cells from human cardiac tissue. Cell counts, perimeter and area measurements were utilized to quantify migration effects. To examine whether resident stem cells were among the migrating cells, specific stem cell properties were investigated. The migrating cells displayed strong similarities with resident Cardiac Atrial appendage Stem Cells (CASCs), including a clonogenic potential of ~21.5% and expression of pluripotency associated genes like Oct-4, Nanog, c-Myc and Klf-4. Similar to CASCs, migrating cells demonstrated high aldehyde dehydrogenase activity and were able to differentiate towards cardiomyocytes. Receptor tyrosine kinase analysis and collagen assays performed with recombinant platelet derived growth factor (PDGF)-AA and Imatinib Mesylate, a PDGF receptor inhibitor, suggested a role for the PDGF-AA/PDGF receptor α axis in enhancing the migration process of CASCs. In conclusion, our findings demonstrate that factors present in MSC-CM improve migration of resident stem cells from human cardiac tissue. These data open doors towards future therapies in which MSC secreted factors, like PDGF-AA, can be utilized to enhance the recruitment of CASCs towards the site of myocardial injury.