Protocol for Isolation of Viable Adult Rat Cardiomyocytes with High Yield

Isolation of high-quantity and high-quality ventricular cardiomyocytes from adult rats is critical to study heart physiology and pathology and for drug toxicity screening. It remains challenging to produce a high yield of viable cardiomyocytes from rats. Here, we present our modified enzymatic digestion protocol that relies on the Langendorff device to generate large numbers of viable cardiomyocytes consistently. The most critical parts of this protocol are the selection of rat age and digestion time to obtain viable cardiomyocytes. For complete details on the use and execution of this protocol, please refer to Liu et al. (2019) and Qin et al. (2020).

Optimization of ellagic acid production from ellagitannins by co-culture and correlation between its yield and activities of relevant enzymes

Aspergillus oryzae was co-cultured with Trichoderma reesei using acorn cups extract containing up to 62% ellagitannins as substrate to produce ellagic acid with relatively high levels of ellagitannin acyl hydrolase, cellulase and xylanase. Ellagitannins concentration, initial pH, T. reesei and A. oryzae during the fermentation were identified as important process parameters effecting ellagic acid accumulation and the enzymes syntheses. These parameters were optimized by uniformity design to determine the optimum condition for ellagic acid production. Under optimum operational condition, ellagic acid yield could be arrived at 24%, when the fermentation run lasted 96h with an initial pH of 4.5, an ellagitannins concentration of 4gl(-1), T. reesei of 3ml and A. oryzae of 3ml. Meanwhile, it was found that the three enzymes activities correlated very well with ellagic acid yield, resulting in model with high coefficient of determination (R(2)=0.98). The results indicate that the mixed culture of T. reesei and A. oryzae is an effective approach to produce an enzyme system of degrading ellagitannins for ellagic acid production.

Confocal imaging of single mitochondrial superoxide flashes in intact heart or in vivo

Mitochondrion is a critical intracellular organelle responsible for energy production and intracellular signaling in eukaryotic systems. Mitochondrial dysfunction often accompanies and contributes to human disease. Majority of the approaches that have been developed to evaluate mitochondrial function and dysfunction are based on in vitro or ex vivo measurements. Results from these experiments have limited ability in determining mitochondrial function in vivo. Here, we describe a novel approach that utilizes confocal scanning microscopy for the imaging of intact tissues in live aminals, which allows the evaluation of single mitochondrial function in a real-time manner in vivo. First, we generate transgenic mice expressing the mitochondrial targeted superoxide indicator, circularly permuted yellow fluorescent protein (mt-cpYFP). Anesthetized mt-cpYFP mouse is fixed on a custom-made stage adaptor and time-lapse images are taken from the exposed skeletal muscles of the hindlimb. The mouse is subsequently sacrificed and the heart is set up for Langendorff perfusion with physiological solutions at 37 °C. The perfused heart is positioned in a special chamber on the confocal microscope stage and gentle pressure is applied to immobilize the heart and suppress heart beat induced motion artifact. Superoxide flashes are detected by real-time 2D confocal imaging at a frequency of one frame per second. The perfusion solution can be modified to contain different respiration substrates or other fluorescent indicators. The perfusion can also be adjusted to produce disease models such as ischemia and reperfusion. This technique is a unique approach for determining the function of single mitochondrion in intact tissues and in vivo.

Mitoflash lights single mitochondrial dynamics events in mature cardiomyocytes

Mitochondria, the powerhouse of eukaryotic cells, are highly dynamic organelle. Mitochondrial fission, fusion, kissing and contraction have been reported over and over again in non-static cells, such as fibroblast, with tubular mitochondrial networks. Even though the fluorescence propagation among mitochondria of mature cardiomyocytes had been captured using mitochondrial matrix targeted photoactivatable GFP (PAGFP) or MitoDendra proteins, there are no direct evidence that single real time mitochondrial dynamics events exist in mature cardiomyocytes with ball-like mitochondria. Here we first time revealed the visualizable single mitochondrial dynamics events in adult mature cardiomyocytes by the mitochondrial flash (mitoflash). We found fission, fusion, contraction and kissing were accompanied by a mitoflash event. Metabolism could increase mitochondrial contraction. Fusion and Kissing mediated inter-mitochondrial communication with higher frequency than fission. These results demonstrate that mitochondria of static mature cardiomyocytes are undergoing the rare, but real dynamics change.

Comparative study on isolation and mitochondrial function of adult mouse and rat cardiomyocytes

BACKGROUND

Cultured adult mouse and rat cardiomyocytes are the best and low-cost cell model for cardiac cellular physiology, pathology, drug toxicity screening, and intervention. The functions of mouse cardiomyocytes decline faster than rat cardiomyocytes in culture conditions. However, little is known about the difference of mitochondrial function between cultured mouse and rat myocytes.

METHODS AND RESULTS

A large number of adult mouse and rat cardiomyocytes were comparative isolated using a simple perfusion system. Cardiomyocytes mitochondrial functions were measured after 2 h, 1 day, 2 days, 3 days, and 4 days culture by monitoring mitoflashes. We found that the mitochondrial function of mouse myocytes was remarkedly declined on the third day. Then, we focused on the third day cultured mouse and rat myocytes, comparatively analyzing the respiration function and superoxide generation stimulated by pyruvate/malate/ADP and the mitochondrial permeability transition pore (mPTP) opening induction. Mouse myocytes showed lower respiration and mitoflash activity, but without the change of maximum uncoupled respiration when compared with rat myocytes. Although the response to superoxide production stimulated by respiration substrates was slower than rat myocytes, the basal superoxide generation is faster than the rat. The faster mitochondrial reactive oxygen species (ROS) generation of mouse myocytes upon laser stimulation triggered the faster mPTP opening compared with the rat. Finally, antioxidant MitoTEMPO pretreatment preserved the mitochondrial function of mouse myocytes on the third day.

CONCLUSIONS

The mitochondrial function and stability are different between cultured mouse and rat cardiac myocytes beyond 3 days even though they both belong to Muridae. Mitochondrial ROS impairs the mitochondrial functions of mouse cardiomyocytes on the third day. Suppressing superoxide maintained the mitochondrial function of mouse myocytes on the third day.

Individual and combined effects of physicochemical parameters on ellagitannin acyl hydrolase and ellagic acid production from ellagitannin by Aspergillus oryzae

The individual and interactive effects of physicochemical parameters on ellagitannin acyl hydrolase activity and ellagic acid production by Aspergillus oryzae using ellagitannins from acorn fringe of oak as substrate were studied. Ellagitannins concentration, incubation time were identified as important physicochemical parameters influencing the enzyme synthesis and the production accumulation, and the substrate concentration with initial pH was determined to has an interactive effect on the enzyme synthesis, while ellagitannins concentration and initial pH with incubation time were found to have interactions on the production accumulation. Furthermore, the parameters were optimized by quadratic programming. Under optimum condition, the fermentation run lasted 84 h with 4 g L(-1) ellagitannins concentration, yielding 17.7% ellagic acid. However, the maximum enzyme activity was obtained in 96 h with 5 g L(-1) substrate concentration. The research demonstrated a possible way to develop an efficient approach for recovery of higher added-value product (ellagic acid) from forestry byproduct (acorn fringe of oak).

Mitoflash generated at the Qo site of mitochondrial Complex III

The previous research has shown that mitochondrial flash (mitoflash) genesis are functionally and mechanistically integrated with mitochondrial electron transport chain (ETC) energy metabolism. However, the response of mitoflash to superoxide is not entirely consistent with the response of MitoSOX Red. The generation mechanism of mitoflash is still unclear. Here, we investigated mitoflash activities, using the different combinations of ETC substrates and inhibitors, in permeabilized cardiomyocytes or hearts. We found that blocking the complete electron flow, from Complex I to IV, with any one of ETC inhibitors including rotenone (Rot), antimycin A (AntA), myxothiazol (Myxo), stigmatellin, and sodium cyanide, will lead to the abolishment of mitoflashes triggered by substrates in adult permeabilized cardiomyocytes. However, Myxo boosted mitoflashes triggered by the reverse electron of N,N,N',N'-tetramethyl-p-phenylenediamine/ascorbate. Moreover, Rot and AntA furtherly enhanced mitoflash activity rather than depressed it, suggesting that mitoflashes generated at the Complex III Qo site. Meanwhile, the inhibition of Complex III protein expression resulted in the activity of Complex III decrease, which decreased mitoflash frequency. The function defect (no change of protein level) of the Qo site of Complex III in aging hearts augmented mitoflash generation confirmed the Qo site function was critical to mitoflash genesis. Thus, our results indicate that mitoflash detected by circularly permuted yellow fluorescent protein is generated at the Qo site of Complex III.

A comparative study of the efficiency of mitochondria-targeted antioxidants MitoTEMPO and SKQ1 under oxidative stress

MitoTEMPO (MT) and Visomitin (SKQ1) are regareded as mitochondria-targeted antioxidants, which inhibit production of mitochondrial reactive oxygen species (ROS). However, the differences in function between MT and SKQ1 remain unexplored. Herein, we investigated the differential potency of MT and SKQ1 in mitigating oxidative stress under different conditions. The results indicated that high levels of SKQ1 induced cell death. The appropriate concentrations of MT and SKQ1 can prevent or rescue cell damage triggered by hydrogen peroxide (H2O2) and menadione (MEN). MT and SKQ1 reduced ROS levels and reversed the down-regulation of antioxidant defence genes and enzymes. These effects can alleviate the damage to lipids, proteins, and deoxyribonucleic acid (DNA) caused by oxidative stress and restore adenosine 5' triphosphate (ATP) generation. Subsequently, we found that MT administration in ischemic reperfusion kidney injury in mice provided superior renal protection compared to SKQ1, as evidenced by reduced plasma levels of kidney injury markers, improved renal morphology, decreased apoptosis, restored mitochondrial function, and enhanced antioxidant capacity. Overall, our findings suggest that MT is safer and has greater potential than SKQ1 as a therapeutic agent to mitigate oxidative stress damage or oxidative renal injury.

Inhibition of mitochondrial superoxide promotes the development of hiPS-CMs during differentiation

The redox state is a crucial determinant of the maturation transition of cardiomyocytes in vivo. Mitochondria, the primary site of superoxide generation, are very sensitive to various stimulations, including oxygen and nutrient supply. How mitochondrial superoxide affects the differentiation and development of induced pluripotent stem cell (iPSC)-derived cardiac myocytes (iPS-CMs) is not completely clear. To address the questions, we monitored the superoxide level during the differentiation and development of human iPS-CMs using MitoSOX. Mitochondria-targeted antioxidant Mito-TEMPO was used to treat hiPS-CMs in the differentiation period. We found that mitochondrial superoxide generation was dramatically enhanced during the differentiation and early development of iPS-CMs. Increased oxidative stress induced oxidative damage to macromolecules in iPS-CMs, such as lipids, proteins, and DNA. Mito-TEMPO protected mitochondrial functions, alleviated oxidative damage to lipids, proteins, and DNA and improved cellular structure and fatty acid utilization. Our findings confirmed that iPS-CM suffered from oxidative stress during differentiation and that mitochondrial-targeted antioxidant is beneficial for the maturation of iPS-CMs.

Protocol for Imaging of Mitoflashes in Live Cardiomyocytes

We describe a protocol for imaging a mitochondrial fluorescence transient increase event (Mitoflash) in live cardiomyocytes using a confocal microscope. Mitoflash, detected by mitochondria-targeted circularly permuted fluorescent protein (mt-cpYFP), can be used to assess mitochondrial respiration function in situ. The protocol is also suitable for live-cell imaging of other adherent cells, including fibroblasts and hepatocytes. For complete details on the use and execution of this protocol, please refer to Gong et al. (2014) and Gong et al. (2015).

Thrombospondin 1 and Reelin act through Vldlr to regulate cardiac growth and repair

Adult mammalian cardiomyocytes have minimal cell cycle capacity, which leads to poor regeneration after cardiac injury such as myocardial infarction. Many positive regulators of cardiomyocyte cell cycle and cardioprotective signals have been identified, but extracellular signals that suppress cardiomyocyte proliferation are poorly understood. We profiled receptors enriched in postnatal cardiomyocytes, and found that very-low-density-lipoprotein receptor (Vldlr) inhibits neonatal cardiomyocyte cell cycle. Paradoxically, Reelin, the well-known Vldlr ligand, expressed in cardiac Schwann cells and lymphatic endothelial cells, promotes neonatal cardiomyocyte proliferation. Thrombospondin1 (TSP-1), another ligand of Vldlr highly expressed in adult heart, was then found to inhibit cardiomyocyte proliferation through Vldlr, and may contribute to Vldlr's overall repression on proliferation. Mechanistically, Rac1 and subsequent Yap phosphorylation and nucleus translocation mediate the regulation of the cardiomyocyte cell cycle by TSP-1/Reelin-Vldlr signaling. Importantly, Reln mutant neonatal mice displayed impaired cardiomyocyte proliferation and cardiac regeneration after apical resection, while cardiac-specific Thbs1 deletion and cardiomyocyte-specific Vldlr deletion promote cardiomyocyte proliferation and are cardioprotective after myocardial infarction. Our results identified a novel role of Vldlr in consolidating extracellular signals to regulate cardiomyocyte cell cycle activity and survival, and the overall suppressive TSP-1-Vldlr signal may contribute to the poor cardiac repair capacity of adult mammals.

Protocol for Measurement of Oxygen Consumption Rate In Situ in Permeabilized Cardiomyocytes

Analysis of mitochondrial respiration function represented by the oxygen consumption rate is necessary for assessing mitochondrial respiration function. This protocol describes steps to evaluate the respiration function of mitochondria in situ in saponin-permeabilized cardiomyocytes. In permeabilized cells, mitochondria are in a relatively integrated cellular system, and mitochondrial respiration is more physiologically relevant than isolated mitochondria. For complete details on the use and execution of this protocol, please refer to Gong et al. (2015a) and Gong et al. (2015b).

The Changes of Mitochondria during Aging and Regeneration

Aging and regeneration are opposite cellular processes. Aging refers to progressive dysfunction in most cells and tissues, and regeneration refers to the replacement of damaged or dysfunctional cells or tissues with existing adult or somatic stem cells. Various studies have shown that aging is accompanied by decreased regenerative abilities, indicating a link between them. The performance of any cellular process needs to be supported by the energy that is majorly produced by mitochondria. Thus, mitochondria may be a link between aging and regeneration. It should be interesting to discuss how mitochondria behave during aging and regeneration. The changes of mitochondria in aging and regeneration discussed in this review can provide a timely and necessary study of the causal roles of mitochondrial homeostasis in longevity and health.

Modified Protocol for A Mouse Heart Failure Model Using Minimally Invasive Transverse Aortic Constriction

Here, we present a modified protocol for a mouse heart failure (HF) model using minimally invasive transverse aortic constriction (miTAC). miTAC is a more effective method in mice than the standard open-chest transverse aortic constriction (TAC) to generate an HF model. miTAC does not require the cutting of the ribs or tracheal intubation with artificial ventilation; it also has a higher survival rate. The successful outcome of the HF model can be verified using transthoracic echocardiography and histology. For complete details on the use and execution of this protocol, please refer to Hu et al. (2003) and Richards et al. (2019).

Calibration and measurement of mitochondrial pH in intact adult rat cardiomyocytes

Mitochondrial pH is a vital parameter of the mitochondrial environment, which determines the rate of many mitochondrial functions, including metabolism, membrane potential, fate, etc. Abnormal mitochondrial pH is always closely related to the health status of cells. Analyzing mitochondrial pH can serve as a proxy for mitochondrial and cellular function. This protocol describes the use of SNARF-1 AM, a pH-sensitive fluorophore, to measure mitochondrial pH. This protocol details the steps to evaluate mitochondrial pH in live adult cardiomyocytes using confocal microscopy. The protocol can be adapted to other adherent cell types. For complete details on the use and execution of this protocol, please refer to Wei-LaPierre et al. (2013).

Functions of FGF21 and its role in cardiac hypertrophy

BACKGROUND

FGF21 is a stress-inducible hormone that operates in the autocrine or paracrine manner. Recent reports have revealed that FGF21 is highly expressed in cardiac hypertrophy to protect against heart injury and dysfunction. FGF21 is used to treat cardiac hypertrophy in mouse models. However, preclinical and clinical trials are restricted.

AIM OF REVIEW

This review mainly elucidates the diverse functions of FGF21 and explores the relationship between these functions and cardiac hypertrophy. It also discusses challenges and future perspectives in treating cardiac hypertrophy with FGF21.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review first illustrates the functions of FGF21, including energy metabolism, inflammation, oxidative stress, apoptosis, and autophagy. We also summarize vital functions and the underlying mechanisms through which FGF21 regulates the initiation and development of cardiac hypertrophy, connecting energy metabolism, inflammation, oxidative stress, apoptosis, and autophagy. Finally, we propose that FGF21 may be a potential therapeutic strategy for cardiac hypertrophy.

Visualizing Mitophagy with Fluorescent Dyes for Mitochondria and Lysosome

Mitochondria, being the powerhouses of the cell, play important roles in bioenergetics, free radical generation, calcium homeostasis, and apoptosis. Mitophagy is the primary mechanism of mitochondrial quality control and is generally studied using microscopic observation, however in vivo mitophagy assays are difficult to perform. Evaluating mitophagy by imaging live organelles is an alternative and necessary method for mitochondrial research. This protocol describes the procedures for using the cell-permeant green-fluorescent mitochondria dye MitoTracker Green and the red-fluorescent lysosome dye LysoTracker Red in live cells, including the loading of the dyes, visualization of the mitochondria and the lysosome, and expected outcomes. Detailed steps for the evaluation of mitophagy in live cells, as well as technical notes about microscope software settings, are also provided. This method can help researchers observe mitophagy using live-cell fluorescent microscopy. In addition, it can be used to quantify mitochondria and lysosomes and assess mitochondrial morphology.