Right ventricle-pulmonary artery coupling in pulmonary artery hypertension its measurement and pharmacotherapy

The right ventricular (RV) function correlates with prognosis in severe pulmonary artery hypertension (PAH) but which metric of it is most clinically relevant is still uncertain. Clinical methods to estimate RV function from simplified pressure volume loops correlate with disease severity but the clinical relevance has not been assessed. Evaluation of right ventricle pulmonary artery coupling in pulmonary hypertensive patients may help to elucidate the mechanisms of right ventricular failure and may also help to identify patients at risk or guide the timing of therapeutic interventions in pulmonary hypertension. Complete evaluation of RV failure requires echocardiographic or magnetic resonance imaging, and right heart catheterization measurements. Treatment of RV failure in PAH relies on decreasing afterload with drugs targeting pulmonary circulation; fluid management to optimize ventricular diastolic interactions; and inotropic interventions to reverse cardiogenic shock. The ability to relate quantitative metrics of RV function in pulmonary artery hypertension to clinical outcomes can provide a powerful tool for management. Such metrics could also be utilized in the future as surrogate endpoints for outcomes and evaluation of response to therapies. This review of literature gives an insight on RV-PA coupling associated with PAH, its types of measurement and pharmacological treatment.

Screening of anti-atrophic peptides by using photo-cleavable peptide array and 96-well scale contractile human skeletal muscle atrophy models

Skeletal muscle atrophy is characterized by decreases in protein content, myofiber diameter, and contractile force generation. As muscle atrophy worsens the quality of life, the development of anti-atrophic substances is desirable. In this study, we aimed to demonstrate a screening process for anti-atrophic peptides using photo-cleavable peptide array technology and human contractile atrophic muscle models. We developed a 96-well system, and established a screening process with less variability. Dexamethasone-induced human atrophic tissue was constructed on the system. Eight peptides were selected from the literature and used for the screening of peptides for preventing the decrease of the contractile forces of tissues. The peptide QIGFIW, which showed preventive activity, was selected as the seed sequence. As a result of amino acid substitution, we obtained QIGFIQ as a peptide with higher anti-atrophic activity. These results indicate that the combinatorial use of the photo-cleavable peptide array technology and 96-well screening system could comprise a powerful approach to obtaining anti-atrophic peptides, and suggest that the 96-well screening system and atrophic model represent a practical and powerful tool for the development of drugs/functional food ingredients. This article is protected by copyright. All rights reserved.

Contractile Force Measurement of Engineered Cardiac Tissues Derived from Human iPS Cells

Recent advances in stem cell technologies and tissue engineering are enabling the fabrication of dynamically beating cardiac tissues from human induced pluripotent stem cells. These engineered human cardiac tissues are expected to be used for cardiac regenerative therapies, in vitro drug testing, and pathological investigations. Here we describe the method to fabricate engineered cardiac tissues from human induced pluripotent stem cell-derived cardiomyocytes and to measure the contractile force.

Maintenance of contractile force of the hind limb muscles by the somato-lumbar sympathetic reflexes

This study aimed to clarify whether the reflex excitation of muscle sympathetic nerves induced by contractions of the skeletal muscles modulates their contractility. In anesthetized rats, isometric tetanic contractions of the triceps surae muscles were induced by electrical stimulation of the intact tibial nerve before and after transection of the lumbar sympathetic trunk (LST), spinal cord, or dorsal roots. The amplitude of the tetanic force (TF) was reduced by approximately 10% at 20 min after transection of the LST, spinal cord, or dorsal roots. The recorded postganglionic sympathetic nerve activity from the lumbar gray ramus revealed that both spinal and supraspinal reflexes were induced in response to the contractions. Repetitive electrical stimulation of the cut peripheral end of the LST increased the TF amplitude. Our results indicated that the spinal and supraspinal somato-sympathetic nerve reflexes induced by contractions of the skeletal muscles contribute to the maintenance of their own contractile force.

Assessment of human bioengineered cardiac tissue function in hypoxic and re-oxygenized environments to understand functional recovery in heart failure

Introduction

Myocardial recovery is one of the targets for heart failure treatment. A non-negligible number of heart failure with reduced ejection fraction (EF) patients experience myocardial recovery through treatment. Although myocardial hypoxia has been reported to contribute to the progression of heart failure even in non-ischemic cardiomyopathy, the relationship between contractile recovery and re-oxygenation and its underlying mechanisms remain unclear. The present study investigated the effects of hypoxia/re-oxygenation on bioengineered cardiac cell sheets-tissue function and the underlying mechanisms.

Methods

Bioengineered cardiac cell sheets-tissue was fabricated with human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) using temperature-responsive culture dishes. Cardiac tissue functions in the following conditions were evaluated with a contractile force measurement system: continuous normoxia (20% O₂) for 12 days; hypoxia (1% O₂) for 4 days followed by normoxia (20% O₂) for 8 days; or continuous hypoxia (1% O₂) for 8 days. Cell number, sarcomere structure, ATP levels, mRNA expressions and Ca²⁺ transients of hiPSC-CM in those conditions were also assessed.

Results

Hypoxia (4 days) elicited progressive decreases in contractile force, maximum contraction velocity, maximum relaxation velocity, Ca²⁺ transient amplitude and ATP level, but sarcomere structure and cell number were not affected. Re-oxygenation (8 days) after hypoxia (4 days) was associated with progressive increases in contractile force, maximum contraction velocity and relaxation time to the similar extent levels of continuous normoxia group, while maximum relaxation velocity was still significantly low even after re-oxygenation. Ca²⁺ transient magnitude, cell number, sarcomere structure and ATP level after re-oxygenation were similar to those in the continuous normoxia group. Hypoxia/re-oxygenation up-regulated mRNA expression of PLN.

Conclusions

Hypoxia and re-oxygenation condition directly affected human bioengineered cardiac tissue function. Further understanding the molecular mechanisms of functional recovery of cardiac tissue after re-oxygenation might provide us the new insight on heart failure with recovered ejection fraction and preserved ejection fraction.

Helical structure of actin stress fibers and its possible contribution to inducing their direction-selective disassembly upon cell shortening

Mechanisms of the assembly of actin stress fibers (SFs) have been extensively studied, while those of the disassembly-particularly cell shortening-induced ones-remain unclear. Here, we show that SFs have helical structures composed of multi-subbundles, and they tend to be delaminated upon cell shortening. Specifically, we observed with atomic force microscopy delamination of helical SFs into their subbundles. We physically caught individual SFs using a pair of glass needles to observe rotational deformations during stretching as well as ATP-driven active contraction, suggesting that they deform in a manner reflecting their intrinsic helical structure. A minimal analytical model was then developed based on the Frenet-Serret formulas with force-strain measurement data to suggest that helical SFs can be delaminated into the constituent subbundles upon axial shortening. Given that SFs are large molecular clusters that bear cellular tension but must promptly disassemble upon loss of the tension, the resulting increase in their surface area due to the shortening-induced delamination may facilitate interaction with surrounding molecules to aid subsequent disintegration. Thus, our results suggest a new mechanism of the disassembly that occurs only in the specific SFs exposed to forced shortening.

In-vitro examination of the positive inotropic effect of caffeine and taurine, the two most frequent active ingredients of energy drinks

Background

Our study aimed to evaluate changes in the contractile behavior of human myocardium after exposure to caffeine and taurine, the main active ingredients of energy drinks (EDs), and to evaluate whether taurine exhibits any inotropic effect at all in the dosages commonly used in EDs.

Methods

Myocardial tissue was removed from the right atrial appendages of patients undergoing cardiac surgery and prepared to obtain specimens measuring 4 mm in length. A total of 92 specimens were exposed to electrical impulses at a frequency of 75 bpm for at least 40 min to elicit their maximum contractile force before measuring the isometric contractile force (ICF) and duration of contraction (CD). Following this, each specimen was treated with either taurine (group 1, n = 29), or caffeine (group 2, n = 31) or both (group 3, n = 32). After exposure, ICF and CD measuring were repeated. Post-treatment values were compared with pre-treatments values and indicated as percentages.

Results

Exposure to taurine did not alter the contraction behavior of the specimens. Exposure to caffeine, in contrast, led to a significant increase in ICF (118 ± 03%, p < 0.01) und a marginal decrease in CD (95 ± 1.6%, p < 0.01). Exposure to a combination of caffeine and taurine also induced a statistically significant increase in ICF (124 ± 4%, p < 0.01) and a subtle reduction in CD (92 ± 1.4%, p < 0.01). The increase in ICF achieved by administration of caffeine was similar to that achieved by a combination of both caffeine and taurine (p = 0.2).

The relative ICF levels achieved by administration of caffeine and a combination of taurine and caffeine, respectively, were both significantly higher (p < 0.01) than the ICF resulting from exposure to taurine only.

Conclusion

While caffeine altered the contraction behavior of the specimen significantly in our in-vitro model, taurine did not exhibit a significant effect. Adding taurine to caffeine did not significantly enhance or reduce the effect of caffeine.

Roles of adherent myogenic cells and dynamic culture in engineered muscle function and maintenance of satellite cells

Highly functional engineered skeletal muscle constructs could serve as physiological models of muscle function and regeneration and have utility in therapeutic replacement of damaged or diseased muscle tissue. In this study, we examined the roles of different myogenic cell fractions and culturing conditions in the generation of highly functional engineered muscle. Fibrin-based muscle bundles were fabricated using either freshly-isolated myogenic cells or their adherent fraction pre-cultured for 36 h. Muscle bundles made of these cells were cultured in both static and dynamic conditions and systematically characterized with respect to early myogenic events and contractile function. Following 2 weeks of culture, we observed both individual and synergistic benefits of using the adherent cell fraction and dynamic culture on muscle formation and function. In particular, optimal culture conditions resulted in significant increase in the total cross-sectional muscle area (- 3-fold), myofiber size (- 1.6-fold), myonuclei density (- 1.2-fold), and force generation (- 9-fold) compared to traditional use of freshly-isolated cells and static culture. Curiously, we observed that only a simultaneous use of the adherent cell fraction and dynamic culture resulted in accelerated formation of differentiated myofibers which were critical for providing a niche-like environment for maintenance of a satellite cell pool early during culture. Our study identifies key parameters for engineering large-size, highly functional skeletal muscle tissues with improved ability for retention of functional satellite cells.

Hypertrophic cardiomyopathy associated Lys104Glu mutation in the myosin regulatory light chain causes diastolic disturbance in mice

We have examined, for the first time, the effects of the familial hypertrophic cardiomyopathy (HCM)-associated Lys104Glu mutation in the myosin regulatory light chain (RLC). Transgenic mice expressing the Lys104Glu substitution (Tg-MUT) were generated and the results were compared to Tg-WT (wild-type human ventricular RLC) mice. Echocardiography with pulse wave Doppler in 6month-old Tg-MUT showed early signs of diastolic disturbance with significantly reduced E/A transmitral velocities ratio. Invasive hemodynamics in 6month-old Tg-MUT mice also demonstrated a borderline significant prolonged isovolumic relaxation time (Tau) and a tendency for slower rate of pressure decline, suggesting alterations in diastolic function in Tg-MUT. Six month-old mutant animals had no LV hypertrophy; however, at >13months they displayed significant hypertrophy and fibrosis. In skinned papillary muscles from 5 to 6month-old mice a mutation induced reduction in maximal tension and slower muscle relaxation rates were observed. Mutated cross-bridges showed increased rates of binding to the thin filaments and a faster rate of the power stroke. In addition, ~2-fold lower level of RLC phosphorylation was observed in the mutant compared to Tg-WT. In line with the higher mitochondrial content seen in Tg-MUT hearts, the MUT-myosin ATPase activity was significantly higher than WT-myosin, indicating increased energy consumption. In the in vitro motility assay, MUT-myosin produced higher actin sliding velocity under zero load, but the velocity drastically decreased with applied load in the MUT vs. WT myosin. Our results suggest that diastolic disturbance (impaired muscle relaxation, lower E/A) and inefficiency of energy use (reduced contractile force and faster ATP consumption) may underlie the Lys104Glu-mediated HCM phenotype.

Tri-iodo-l-thyronine promotes the maturation of human cardiomyocytes-derived from induced pluripotent stem cells

BACKGROUND

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) have great potential as a cell source for therapeutic applications such as regenerative medicine, disease modeling, drug screening, and toxicity testing. This potential is limited, however, by the immature state of the cardiomyocytes acquired using current protocols. Tri-iodo-l-thyronine (T3) is a growth hormone that is essential for optimal heart growth. In this study, we investigated the effect of T3 on hiPSC-CM maturation.

METHODS AND RESULTS

A one-week treatment with T3 increased cardiomyocyte size, anisotropy, and sarcomere length. T3 treatment was associated with reduced cell cycle activity, manifest as reduced DNA synthesis and increased expression of the cyclin-dependent kinase inhibitor p21. Contractile force analyses were performed on individual cardiomyocytes using arrays of microposts, revealing an almost two-fold higher force per-beat after T3 treatment and also an enhancement in contractile kinetics. This improvement in force generation was accompanied by an increase in rates of calcium release and reuptake, along with a significant increase in sarcoendoplasmic reticulum ATPase expression. Finally, although mitochondrial genomes were not numerically increased, extracellular flux analysis showed a significant increase in maximal mitochondrial respiratory capacity and respiratory reserve capability after T3 treatment.

CONCLUSIONS

Using a broad spectrum of morphological, molecular, and functional parameters, we conclude that T3 is a driver for hiPSC-CM maturation. T3 treatment may enhance the utility of hiPSC-CMs for therapy, disease modeling, or drug/toxicity screens.