Sarcomeric and nonmuscle α-actinin isoforms exhibit differential dynamics at skeletal muscle Z-lines

Engineering a robust and anisotropic cardiac-specific extracellular matrix scaffold for cardiac patch tissue engineering

Extracellular matrix (ECM) fabricated using human induced pluripotent stem cells (hiPSCs)-derived cardiac fibroblasts (hiPSC-CFs) could serve as a completely biological scaffold for an engineered cardiac patch, leveraging the unlimited source and outstanding reproducibility of hiPSC-CFs. Additionally, hiPSC-CF-derived ECM (hiPSC-CF-ECM) holds the potential to enhance maturation of exogenous cardiomyocytes, such as hiPSC-derived cardiomyocytes (hiPSC-CMs), by providing a microenvironment rich in cardiac-specific biochemical and signaling cues. However, achieving sufficient robustness of hiPSC-CF-ECM is challenging. This study aims to achieve appropriate ECM deposition, scaffold thickness, and mechanical strength of an aligned hiPSC-CF-ECM by optimizing the culture period, ranging from 2 to 10 weeks, of hiPSC-CFs grown on micro-grated substrates, which can direct the alignment of both hiPSC-CFs and their secreted ECM. The hiPSC-CFs demonstrated a production rate of 13.5 µg ECM per day per 20,000 cells seeded. An anisotropic nanofibrous hiPSC-CF-ECM scaffold with a thickness of 20.0 ± 2.1 µm was achieved after 6 weeks of culture, followed by decellularization. Compositional analysis through liquid chromatography-mass spectrometry (LC-MS) revealed the presence of cardiac-specific fibrillar collagens, non-fibrillar collagens, and matricellular proteins. Uniaxial tensile stretching of the hiPSC-CF-ECM scaffold indicated robust tensile resilience. Finally, hiPSCs-CMs cultured on the hiPSC-CF-ECM exhibited alignment following the guidance of ECM nanofibers and demonstrated mature organization of key structural proteins. The culture duration of the anisotropic hiPSC-CF-ECM was successfully refined to achieve a robust scaffold containing structural proteins that resembles cardiac microenvironment. This completely biological, anisotropic, and cardiac-specific ECM holds great potential for cardiac patch engineering.

Proposal for considerations during human iPSC-derived cardiac organoid generation for cardiotoxicity drug testing

Human iPSC-derived cardiac organoids (hiPSC-COs) for cardiotoxicity drug testing via the variety of cell lines and unestablished protocols may lead to differences in response results due to a lack of criteria for generation period and size. To ensure reliable drug testing, it is important for researchers to set optimal generation period and size of COs according to the cell line and protocol applied in their studies. Hence, we sought to propose a process to establish minimum criteria for the generation duration and size of hiPSC-COs for cardiotoxic drug testing. We generated hiPSC-COs of different sizes based on our protocol and continuously monitored organoids until they indicated a minimal beating rate change as a control that could lead to more accurate beating rate changes on drug testing. Calcium transients and physiological tests to assess the functionality of hiPSC-COs on selected generation period, which showed regular cardiac beating, and immunostaining assays to compare characteristics were performed. We explained the generation period and size that exhibited and maintained regular beating rate changes on hiPSC-COs, and lead to reliable response results to cardiotoxicity drugs. We anticipate that this study will offer valuable insights into considering the appropriate generation period and size of hiPSC-COs ensuring reliable outcomes in cardiotoxicity drug testing.

Detergent-Based Decellularization for Anisotropic Cardiac-Specific Extracellular Matrix Scaffold Generation

Cell-derived extracellular matrix (ECM) has become increasingly popular in tissue engineering applications due to its ability to provide tailored signals for desirable cellular responses. Anisotropic cardiac-specific ECM scaffold decellularized from human induced pluripotent stem cell (hiPSC)-derived cardiac fibroblasts (hiPSC-CFs) mimics the native cardiac microenvironment and provides essential biochemical and signaling cues to hiPSC-derived cardiomyocytes (hiPSC-CMs). The objective of this study was to assess the efficacy of two detergent-based decellularization methods: (1) a combination of ethylenediaminetetraacetic acid and sodium dodecyl sulfate (EDTA + SDS) and (2) a combination of sodium deoxycholate and deoxyribonuclease (SD + DNase), in preserving the composition and bioactive substances within the aligned ECM scaffold while maximumly removing cellular components. The decellularization effects were evaluated by characterizing the ECM morphology, quantifying key structural biomacromolecules, and measuring preserved growth factors. Results showed that both treatments met the standard of cell removal (less than 50 ng/mg ECM dry weight) and substantially preserved major ECM biomacromolecules and growth factors. The EDTA + SDS treatment was more time-efficient and has been determined to be a more efficient method for generating an anisotropic ECM scaffold from aligned hiPSC-CFs. Moreover, this cardiac-specific ECM has demonstrated effectiveness in supporting the alignment of hiPSC-CMs and their expression of mature structural and functional proteins in in vitro cultures, which is crucial for cardiac tissue engineering.

Integrative transcriptomic and metabolomic analysis reveals alterations in energy metabolism and mitochondrial functionality in broiler chickens with wooden breast

This integrative study of transcriptomics and metabolomics aimed to improve our understanding of Wooden Breast myopathy (WB). Breast muscle samples from 8 WB affected and 8 unaffected male broiler chickens of 47 days of age were harvested for metabolite profiling. Among these 16 samples, 5 affected and 6 unaffected also underwent gene expression profiling. The Joint Pathway Analysis was applied on 119 metabolites and 3444 genes exhibiting differential abundance or expression between WB affected and unaffected chickens. Mitochondrial dysfunctions in WB was suggested by higher levels of monoacylglycerols and down-regulated genes involved in lipid production, fatty acid beta oxidation, and oxidative phosphorylation. Lower levels of carnosine and anserine, along with down-regulated carnosine synthase 1 suggested decreased carnosine synthesis and hence impaired antioxidant capacity in WB. Additionally, Weighted Gene Co-expression Network Analysis results indicated that abundance of inosine monophosphate, significantly lower in WB muscle, was correlated with mRNA expression levels of numerous genes related to focal adhesion, extracellular matrix and intercellular signaling, implying its function in connecting and possibly regulating multiple key biological pathways. Overall, this study showed not only the consistency between transcript and metabolite profiles, but also the potential in gaining further insights from analyzing multi-omics data.

Interaction of MyoD and MyoG with Myoz2 gene in bovine myoblast differentiation

This study aims to explore the functional role of Myoz2 in myoblast differentiation, and elucidate the potential factors interact with Myoz2 in promoter transcriptional regulation. The temporal-spatial expression results showed that the bovine Myoz2 gene was highest expressed in longissimus dorsi, and in individual growth stages and myoblast differentiation stages. Knockdown of Myoz2 inhibited the differentiation of myoblast, and negative effect of MyoD, MyoG, MyH and MEF2A expression on mRNA levels. Subsequently, the promoter region of bovine Myoz2 gene with 1.7 Kb sequence was extracted, and then it was set as eight series of deleted fragments, which were ligated into pGL3-basic to detect core promoter regions of Myoz2 gene in myoblasts and myotubes. Transcription factors MyoD and MyoG were identified as important cis-acting elements in the core promoter region (-159/+1). Also, it was highly conserved in different species based on dual-luciferase analysis and multiple sequence alignment analysis, respectively. Furthermore, a chromatin immunoprecipitation (ChIP) analysis combined with site-directed mutation and siRNA interference and overexpression confirmed that the combination of MyoD and MyoG occurred in region -159/+1, and played an important role in the regulation of bovine Myoz2 gene. These findings explored the regulatory network mechanism of Myoz2 gene during the development of bovine skeletal muscle.

Musculoskeletal Biomarkers Response to Exercise in Older Adults

Exercise is an essential component of any good health style, being particularly important for older adults to counteract the effects of aging, including sarcopenia and osteoporosis, which can result in lower fall probability. Exercise programs for older adults are especially designed for that population. A rigorous evaluation of those programs is necessary to assure most benefit is achieved. Serum biomarkers of proteins intrinsic to musculoskeletal homeostasis could contribute objectively to the assessment of the benefits of exercise. In this work, in addition to the usual physical fitness and balance tests, ELISA assays quantified the serum levels of six proteins and one polysaccharide important for the homeostasis of muscle (troponin T and alpha-actinin), tendon/ligament (tenomodulin), cartilage (cartilage oligomeric matrix protein and hyaluronan) and bone (osteocalcin and sclerostin), before and after 8 weeks of an exercise program tailored to older adults, Stay Strong Stay Healthy, offered at a Community Center and at an Independent Senior Living facility. Statistical significance was determined by non-parametric tests (Wilcoxon Signed Ranks and Mann-Whitney U). Physical fitness and balance improved as expected along with a significant decrease in sclerostin, pointing to less inhibition of bone deposition. However, when considering each type of dwelling separately, older adults always saw a significant decrease of the isoform of troponin T associated with fast-twitch muscles, suggesting that daily levels of physical activity may also have a role in the benefit of older adults from exercise.

Absence of the Z-disc protein α-actinin-3 impairs the mechanical stability of Actn3KO mouse fast-twitch muscle fibres without altering their contractile properties or twitch kinetics

BACKGROUND

A common polymorphism (R577X) in the ACTN3 gene results in the complete absence of the Z-disc protein α-actinin-3 from fast-twitch muscle fibres in ~ 16% of the world's population. This single gene polymorphism has been subject to strong positive selection pressure during recent human evolution. Previously, using an Actn3KO mouse model, we have shown in fast-twitch muscles, eccentric contractions at L₀ + 20% stretch did not cause eccentric damage. In contrast, L₀ + 30% stretch produced a significant ~ 40% deficit in maximum force; here, we use isolated single fast-twitch skeletal muscle fibres from the Actn3KO mouse to investigate the mechanism underlying this.

METHODS

Single fast-twitch fibres are separated from the intact muscle by a collagenase digest procedure. We use label-free second harmonic generation (SHG) imaging, ultra-fast video microscopy and skinned fibre measurements from our MyoRobot automated biomechatronics system to study the morphology, visco-elasticity, force production and mechanical strength of single fibres from the Actn3KO mouse. Data are presented as means ± SD and tested for significance using ANOVA.

RESULTS

We show that the absence of α-actinin-3 does not affect the visco-elastic properties or myofibrillar force production. Eccentric contractions demonstrated that chemically skinned Actn3KO fibres are mechanically weaker being prone to breakage when eccentrically stretched. Furthermore, SHG images reveal disruptions in the myofibrillar alignment of Actn3KO fast-twitch fibres with an increase in Y-shaped myofibrillar branching.

CONCLUSIONS

The absence of α-actinin-3 from the Z-disc in fast-twitch fibres disrupts the organisation of the myofibrillar proteins, leading to structural weakness. This provides a mechanistic explanation for our earlier findings that in vitro intact Actn3KO fast-twitch muscles are significantly damaged by L₀ + 30%, but not L₀ + 20%, eccentric contraction strains. Our study also provides a possible mechanistic explanation as to why α-actinin-3-deficient humans have been reported to have a faster decline in muscle function with increasing age, that is, as sarcopenia reduces muscle mass and force output, the eccentric stress on the remaining functional α-actinin-3 deficient fibres will be increased, resulting in fibre breakages.

Electroactive nano-Biohybrid actuator composed of gold nanoparticle-embedded muscle bundle on molybdenum disulfide nanosheet-modified electrode for motion enhancement of biohybrid robot

There have been several trials to develop the bioactuator using skeletal muscle cells for controllable biobybird robot. However, due to the weak contraction force of muscle cells, the muscle cells could not be used for practical applications such as biorobotic hand for carrying objects, and actuator of biohybrid robot for toxicity test and drug screening. Based on reported hyaluronic acid-modified gold nanoparticles (HA@GNPs)-embedded muscle bundle on PDMS substrate, in this study for augmented actuation, we developed the electroactive nano-biohybrid actuator composed of the HA@GNP-embedded muscle bundle and molybdenum disulfide nanosheet (MoS₂ NS)-modified electrode to enhance the motion performance. The MoS₂ NS-modified Au-coated polyimide (PI) electrode to be worked in mild pH condition for viable muscle cell was utilized as supporting- and motion enhancing- substrate since it was electrochemically active, which caused the movement of flexible PI electrode. The motion performance of this electroactive nano-biohybrid actuator by electrical stimulation was increased about 3.18 times compared with that of only HA@GNPs embedded-muscle bundle on bare PI substrate. The proposed electroactive nano-biohybrid actuator can be applied to the biorobotic hand and biohybrid robot.

Cullin-3 dependent deregulation of ACTN1 represents a new pathogenic mechanism in nemaline myopathy

Nemaline myopathy is a congenital neuromuscular disorder characterized by muscle weakness, fiber atrophy and presence of nemaline bodies within myofibers. However, the understanding of underlying pathomechanisms is lacking. Recently, mutations in KBTBD13, KLHL40 and KLHL41, three substrate adaptors for the E3-ubiquitin ligase Cullin-3, have been associated with early-onset nemaline myopathies. We hypothesized that deregulation of Cullin-3 and its muscle protein substrates may be responsible for the disease development. Using Cullin-3 knockout mice, we identified accumulation of non-muscle alpha-Actinins (ACTN1 and ACTN4) in muscles of these mice, which we also observed in KBTBD13 patients. Our data reveal that proper regulation of Cullin-3 activity and ACTN1 levels is essential for normal muscle and neuromuscular junction development. While ACTN1 is naturally downregulated during myogenesis, its overexpression in C2C12 myoblasts triggered defects in fusion, myogenesis and acetylcholine receptor clustering; features that we characterized in Cullin-3 deficient mice. Taken together, our data highlight the importance for Cullin-3 mediated degradation of ACTN1 for muscle development, and indicate a new pathomechanism for the etiology of myopathies seen in Cullin-3 knockout mice and nemaline myopathy patients.