Developing cardiac and skeletal muscle share fast-skeletal myosin heavy chain and cardiac troponin-I expression

Random cellulose acetate nanofibers: a breakthrough for cultivated meat production

Overcoming the challenge of creating thick, tissue-resembling muscle constructs is paramount in the field of cultivated meat production. This study investigates the remarkable potential of random cellulose acetate nanofibers (CAN) as a transformative scaffold for muscle tissue engineering (MTE), specifically in the context of cultivated meat applications. Through a comparative analysis between random and aligned CAN, utilizing C2C12 and H9c2 myoblasts, we unveil the unparalleled capabilities of random CAN in facilitating muscle differentiation, independent of differentiation media, by exploiting the YAP/TAZ-related mechanotransduction pathway. In addition, we have successfully developed a novel process for stacking cell-loaded CAN sheets, enabling the production of a three-dimensional meat product. C2C12 and H9c2 loaded CAN sheets were stacked (up to four layers) to form a ~300-400 μm thick tissue 2 cm in length, organized in a mesh of uniaxial aligned cells. To further demonstrate the effectiveness of this methodology for cultivated meat purposes, we have generated thick and viable constructs using chicken muscle satellite cells (cSCs) and random CAN. This groundbreaking discovery offers a cost-effective and biomimetic solution for cultivating and differentiating muscle cells, forging a crucial link between tissue engineering and the pursuit of sustainable and affordable cultivated meat production.

Intermolecular And Dynamic Investigation of The Mechanism of Action of Reldesemtiv on Fast Skeletal Muscle Troponin Complex Toward the Treatment of Impaired Muscle Function

Muscle weakness as a secondary feature of attenuated neuronal input often leads to disability and sometimes death in patients with neurogenic neuromuscular diseases. These impaired muscle function has been observed in several diseases including amyotrophic lateral sclerosis, Charcot-Marie-Tooth, spinal muscular atrophy and Myasthenia gravis. This has spurred the search for small molecules which could activate fast skeletal muscle troponin complex as a means to increase muscle strength. Discovered small molecules have however been punctuated by off-target and side effects leading to the development of the second-generation small molecule, Reldesemtiv. In this study, we investigated the impact of Reldesemtiv binding to the fast skeletal troponin complex and the molecular determinants that condition the therapeutic prowess of Redesemtiv through computational techniques. It was revealed that Reldesemtiv binding possibly potentiates troponin C compacting characterized by reduced exposure to solvent molecules which could favor the slow release of calcium ions and the resultant sensitization of the subunit to calcium. These conformational changes were underscored by conventional and carbon hydrogen bonds, pi-alkyl, pi-sulfur and halogen interactions between Reldesemtiv the binding site residues. Arg113 (-3.96 kcal/mol), Met116 (-2.23 kcal/mol), Val114 (-1.28 kcal/mol) and Met121 (-0.63 kcal/mol) of the switch region of the inhibitory subunit were among the residues that contributed the most to the total free binding energy of Reldesemtiv highlighting their importance. These findings present useful insights which could lay the foundation for the development of fast skeletal muscle small molecule activators with high specificity and potency.

Overexpression of GATA binding protein 4 and myocyte enhancer factor 2C induces differentiation of mesenchymal stem cells into cardiac-like cells

BACKGROUND

Heart diseases are the primary cause of death all over the world. Following myocardial infarction, billions of cells die, resulting in a huge loss of cardiac function. Stem cell-based therapies have appeared as a new area to support heart regeneration. The transcription factors GATA binding protein 4 (GATA-4) and myocyte enhancer factor 2C (MEF2C) are considered prominent factors in the development of the cardiovascular system.

AIM

To explore the potential of GATA-4 and MEF2C for the cardiac differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs).

METHODS

hUC-MSCs were characterized morphologically and immunologically by the presence of specific markers of MSCs via immunocytochemistry and flow cytometry, and by their potential to differentiate into osteocytes and adipocytes. hUC-MSCs were transfected with GATA-4, MEF2C, and their combination to direct the differentiation. Cardiac differentiation was confirmed by semiquantitative real-time polymerase chain reaction and immunocytochemistry.

RESULTS

hUC-MSCs expressed specific cell surface markers CD105, CD90, CD44, and vimentin but lack the expression of CD45. The transcription factors GATA-4 and MEF2C, and their combination induced differentiation in hUC-MSCs with significant expression of cardiac genes i.e., GATA-4, MEF2C, NK2 homeobox 5 (NKX2.5), MHC, and connexin-43, and cardiac proteins GATA-4, NKX2.5, cardiac troponin T, and connexin-43.

CONCLUSION

Transfection with GATA-4, MEF2C, and their combination effectively induces cardiac differentiation in hUC-MSCs. These genetically modified MSCs could be a promising treatment option for heart diseases in the future.

Whole-genome resequencing of three Coilia nasus population reveals genetic variations in genes related to immune, vision, migration, and osmoregulation

Background

Coilia nasus is an important anadromous fish, widely distributed in China, Japan, and Korea. Based on morphological and ecological researches of C. nasus, two ecotypes were identified. One is the anadromous population (AP). The sexually mature fish run thousands of kilometers from marine to river for spawning. Another one is the resident population which cannot migrate. Based on their different habitats, they were classified into landlocked population (LP) and sea population (SP) which were resident in the freshwater lake and marine during the entire lifetime, respectively. However, they have never been systematically studied. Moreover, C. nasus is declining sharply due to overfishing and pollution recently. Therefore, further understandings of C. nasus populations are needed for germplasm protection.

Results

Whole-genome resequencing of AP, LP, and SP were performed to enrich the understanding of different populations of C. nasus. At the genome level, 3,176,204, 3,307,069, and 3,207,906 single nucleotide polymorphisms (SNPs) and 1,892,068, 2,002,912, and 1,922,168 insertion/deletion polymorphisms (InDels) were generated in AP, LP, and SP, respectively. Selective sweeping analysis showed that 1022 genes were selected in AP vs LP; 983 genes were selected in LP vs SP; 116 genes were selected in AP vs SP. Among them, selected genes related to immune, vision, migration, and osmoregulation were identified. Furthermore, their expression profiles were detected by quantitative real-time PCR. Expression levels of selected genes related to immune, and vision in LP were significantly lower than AP and SP. Selected genes related to migration in AP were expressed significantly more highly than LP. Expression levels of selected genes related to osmoregulation were also detected. The expression of NKAα and NKCC1 in LP were significantly lower than SP, while expression of NCC, SLC4A4, NHE3, and V-ATPase in LP was significantly higher than SP.

Conclusions

Combined to life history of C. nasus populations, our results revealed that the molecular mechanisms of their differences of immune, vision, migration, and osmoregulation. Our findings will provide a further understanding of different populations of C. nasus and will be beneficial for wild C. nasus protection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08182-0.

Effect of a dianthin G analogue in the differentiation of rat bone marrow mesenchymal stem cells into cardiomyocytes

Loss of cardiomyocytes due to myocardial infarction results in ventricular remodeling which includes non-contractile scar formation, which can lead to heart failure. Stem cell therapy aims to replace the scar tissue with the functional myocardium. Mesenchymal stem cells (MSCs) are undifferentiated cells capable of self-renewal as well as differentiation into multiple lineages. MSCs can be differentiated into cardiomyocytes by treating them with small molecules and peptides. Here, we report for the first time, the role of a cyclic peptide, an analogue of dianthin G, [Glu²]-dianthin G (1) in the in vitro cardiac differentiation of rat bone marrow MSCs. In this study, [Glu²]-dianthin G (1) was synthesized using solid-phase total synthesis and characterized by NMR spectroscopy. MSCs were treated with two different concentrations (0.025 and 0.05 mM) of the peptide separately for 72 h and then incubated for 15 days to allow the cells to differentiate into cardiomyocytes. Treated cells were analyzed for the expression of cardiac-specific genes and proteins. Results showed significant upregulation of cardiac-specific genes GATA4, cardiac troponin T (cTnT), cardiac troponin I (cTnI), cardiac myosin heavy chain, and connexin 43 in the treated MSCs compared to the untreated control. For cardiac-specific proteins, GATA4, cTnT, and Nkx2.5 were analyzed in the treated cells and were shown to have significant upregulation as compared to the untreated control. In conclusion, this study has demonstrated the cardiac differentiation potential of [Glu²]-dianthin G (1)-treated rat bone marrow MSCs in vitro both at the gene and at the protein levels. Transplantation of pre-differentiated MSCs into the infarcted myocardium may result in the efficient regeneration of cardiac cells and restoration of normal cardiac function.

Ppp1r1b-lncRNA inhibits PRC2 at myogenic regulatory genes to promote cardiac and skeletal muscle development in mouse and human

Long noncoding RNAs (lncRNAs) have emerged as critical epigenetic regulators and play important roles in cardiac development and congenital heart disease. In a previous study, we identified a novel lncRNA, Ppp1r1b, with expression highly correlated with myogenesis. However, the molecular mechanism that underlies Ppp1r1b-lncRNA function in myogenic regulation is unknown. By silencing Ppp1r1b-lncRNA, mouse C2C12 and human skeletal myoblasts failed to develop fully differentiated myotubes. Myogenic differentiation was also impaired in PPP1R1B-lncRNA deficient human-induced pluripotent stem cell-derived cardiomyocytes (hiPSCs-CMs). The expression of myogenic transcription factors, including MyoD, Myogenin, and Tbx5, as well as sarcomere proteins, was significantly suppressed in Ppp1r1b-lncRNA inhibited myoblast cells and neonatal mouse heart. Histone modification analysis revealed increased H3K27 tri-methylation at MyoD1 and Myogenin promoters in GapmeR treated C2C12 cells. Furthermore, Ppp1r1b-lncRNA was found to bind to Ezh2, and chromatin isolation by RNA purification (ChIRP) assay revealed enriched interaction of Ppp1r1b-lncRNA with Myod1 and Tbx5 promoters, suggesting that Ppp1r1b-lncRNA induces transcription of myogenic transcription factors by interacting with the polycomb repressive complex 2 (PRC2) at the chromatin interface. Correspondingly, the silencing of Ppp1r1b-lncRNA increased EZH2 binding at promoter regions of myogenic transcription factors. Therefore, our results suggest that Ppp1r1b-lncRNA promotes myogenic differentiation through competing for PRC2 binding with chromatin of myogenic master regulators during heart and skeletal muscle development.

Pyruvate Dehydrogenase Phosphatase Regulatory Gene Expression Correlates with Exercise Training Insulin Sensitivity Changes

PURPOSE

Whole body insulin sensitivity (Si) typically improves after aerobic exercise training; however, individual responses can be highly variable. The purpose of this study was to use global gene expression to identify skeletal muscle genes that correlate with exercise-induced Si changes.

METHODS

Longitudinal cohorts from the Studies of Targeted Risk Reduction Intervention through Defined Exercise were used as Discovery (Affymetrix) and Confirmation (Illumina) of vastus lateralis gene expression profiles. Discovery (n = 39; 21 men) and Confirmation (n = 42; 19 men) cohorts were matched for age (52 ± 8 vs 51 ± 10 yr), body mass index (30.4 ± 2.8 vs 29.7 ± 2.8 kg·m), and V˙O2max (30.4 ± 2.8 vs 29.7 ± 2.8 mL·kg·min). Si was determined via intravenous glucose tolerance test pretraining and posttraining. Pearson product-moment correlation coefficients determined relationships between a) baseline and b) training-induced changes in gene expression and %ΔSi after training.

RESULTS

Expression of 2454 (Discovery) and 1778 genes (Confirmation) at baseline were significantly (P < 0.05) correlated to %ΔSi; 112 genes overlapped. Pathway analyses identified Ca signaling-related transcripts in this 112-gene list. Expression changes of 1384 (Discovery) and 1288 genes (Confirmation) after training were significantly (P < 0.05) correlated to %ΔSi; 33 genes overlapped, representing contractile apparatus of skeletal and smooth muscle genes. Pyruvate dehydrogenase phosphatase regulatory subunit expression at baseline (P = 0.01, r = 0.41) and posttraining (P = 0.01, r = 0.43) were both correlated with %ΔSi.

CONCLUSIONS

Exercise-induced adaptations in skeletal muscle Si are related to baseline levels of Ca-regulating transcripts, which may prime the muscle for adaptation. Relationships between %ΔSi and pyruvate dehydrogenase phosphatase regulatory, a regulatory subunit of the pyruvate dehydrogenase complex, indicate that the Si response is strongly related to key steps in metabolic regulation.

Deep RNA sequencing of pectoralis muscle transcriptomes during late-term embryonic to neonatal development in indigenous Chinese duck breeds

Pectoral muscle (PM) comprises an important component of overall meat mass in ducks. However, PM has shown arrested or even reduced growth during late embryonic development, and the molecular mechanisms underlying PM growth during the late embryonic to neonatal period in ducks have not been addressed. In this study, we characterized potential candidate genes and signaling pathways related to PM development using RNA sequencing of PM samples selected at embryonic days (E) 21 and 27 and 5 days post-hatch (dph) in two duck breeds (Gaoyou and Jinding ducks). A total of 393 differentially expressed genes (DEGs) were identified, which showed higher or lower expression levels at E27 compared with E21 and 5 dph, reflecting the pattern of PM growth rates. Among these, 43 DEGs were common to all three time points in both duck breeds. These DEGs may thus be involved in regulating this developmental process. Specifically, KEGG pathway analysis of the 393 DEGs showed that genes involved with different metabolism pathways were highly expressed, while genes involved with cell cycle pathways showed lower expression levels at E27. These DEGs may thus be involved in the mechanisms responsible for the phenomenon of static or decreased breast muscle growth in duck breeds during the late embryonic period. These results increase the available genetic information for ducks and provide valuable resources for analyzing the mechanisms underlying the process of PM development.

Enhancement of Anti-Hypoxic Activity and Differentiation of Cardiac Stem Cells by Supernatant Fluids from Cultured Macrophages that Phagocytized Dead Mesenchymal Stem Cells

Background: Most mesenchymal stem cells (MSCs) die shortly after transplantation into a myocardial infarcted area. Dead MSCs (dMSCs) are phagocytized by macrophages (pMΦ) in vivo and in vitro; however, the effects of pMΦ on cardiac stem cells (CSCs) remain unknown. Methods: MSCs, CSCs, and macrophages were obtained from bone marrow, hearts, and peritoneal cavity of mice, respectively. dMSCs were harvested after hypoxia for 24 h, and incubated with macrophages (2:1) for another 2 days with or without lipopolysaccharide (LPS, 50 ng/mL) and sorted by flow cytometry to obtain pMΦ. Viability and apoptosis of CSCs were respectively evaluated with the cell counting kit-8 (CCk-8) assay and Annexin V-PE/7-AAD staining at 0, 6, 12, and 24 h of culture with supernatant fluids from macrophages (MΦ), LPS-stimulated macrophages (LPS-pMΦ), pMΦ, and MSCs. GATA-4 and c-TnI expression was measured by flow cytometry on the seventh day. Expression of inflammation and growth factors was assessed by real-time polymerase chain reaction (RT-PCR) in MΦ, LPS-pMΦ, and pMΦ cells. Results: pMΦ expressed higher levels of interleukin-10 (IL-10) and transforming growth factor-β (TGF-β)and lower levels of tumor necrosis factor-α(TNF-α)and IL-6 than LPS-pMΦ, higher levels of growth factors and of GATA-4 and c-TnI at the 7th day, which were similar to those in MSCs. CSCs cultured with supernatant fluids of pMΦ exhibited higher proliferative, anti-hypoxic, and differentiation activities. Conclusion: The supernatant fluids of macrophages that had phagocytized dead MSCs encouraged changes in phenotype and growth factor expression, enhanced proliferation, differentiation, and anti-hypoxic activity of CSCs, which is relevant to understanding the persistent therapeutic effect of MSCs after their massive demise upon transplantation in myocardial infarction. Furthermore, some miRNAs or proteins which were extracted from the supernatant fluids may give us a new insight into the treatment of myocardial infarction in the future.

Cardiac troponin testing in idiopathic inflammatory myopathies and systemic sclerosis-spectrum disorders: biomarkers to distinguish between primary cardiac involvement and low-grade skeletal muscle disease activity

Primary cardiac involvement, an under-recognised manifestation of the idiopathic inflammatory myopathies (IIM) and systemic sclerosis (SSc)-spectrum disorders, is associated with significant mortality. Within these two conditions, traditional skeletal muscle enzyme testing may not effectively distinguish between skeletal and cardiac muscle involvement, especially in patients with subclinical cardiac disease. Accurate biomarkers are thus required to screen for cardiac disease, to better inform both therapeutic decision-making and treatment response. The widespread uptake of cardiac troponin testing has revolutionised the management of acute coronary syndromes. While cardiac troponin I (cTnI) appears specific to the myocardium, cardiac troponin T (cTnT) is also expressed by skeletal muscle, including regenerating skeletal muscle tissue. There is increasing interest about the role of cardiac troponins as a putative biomarker of primary cardiac involvement in IIM and SSc-spectrum disorders. Herewith we discuss subclinical cardiac disease in IIM and SSc-spectrum disorders, the respective roles of cTnI and cTnT testing, and the re-expression of cTnT within regenerating skeletal muscle tissue. There remains wide variation in access to cardiac troponin testing nationally and internationally. We propose two pragmatic clinical pathways using cardiac troponins, preferably measuring concomitant cTnT followed by confirmatory (cardiac) cTnI to screen patients for subclinical cardiac disease and/or low-grade skeletal muscle disease activity, and also an agenda for future research.

Combined biophysical and soluble factor modulation induces cardiomyocyte differentiation from human muscle derived stem cells

Cellular cardiomyoplasty has emerged as a novel therapy to restore contractile function of injured failing myocardium. Human multipotent muscle derived stem cells (MDSC) can be a potential abundant, autologous cell source for cardiac repair. However, robust conditions for cardiomyocyte (CM) differentiation are not well established for this cell type. We have developed a new method for CM differentiation from human MDSC that combines 3-dimensional artificial muscle tissue (AMT) culture with temporally controlled biophysical cell aggregation and delivery of 4 soluble factors (microRNA-206 inhibitor, IWR-1, Lithium Chloride, and BMP-4) (4F-AG-AMT). The 4F-AG-AMT displayed cardiac-like response to β-adrenergic stimulation and contractile properties. 4F-AG-AMT expressed major cardiac (NKX2-5, GATA4, TBX5, MEF2C) transcription factors and structural proteins. They also express cardiac gap-junction protein, connexin-43, similar to CMs and synchronized spontaneous calcium transients. These results highlight the importance of temporal control of biophysical and soluble factors for CM differentiation from MDSCs.

Astragaloside IV inhibits doxorubicin-induced cardiomyocyte apoptosis mediated by mitochondrial apoptotic pathway via activating the PI3K/Akt pathway

Doxorubicin (DOX) is a widely used antitumor drug whose application is seriously limited by its cardiotoxicity. Mitochondria-mediated cardiomyocyte apoptosis plays a critical role in DOX-induced cardiotoxicity (DIC). The aim of the present study was to investigate the protective effect of astragaloside IV (3-O-beta-D-xylopyranosyl-6-O-beta-D-glucopyranosyl-cycloastragenol, AS-IV), a pure saponin isolated from Astragalus membranaceus, against DOX-induced cardiomyocyte apoptosis in primary cultured neonatal rat cardiomyocytes. Immunocytochemistry and Microculture Tetrazolium (MTT) assays showed that AS-IV significantly reduced DOX-induced cardiomyocyte loss. Additionally, AS-IV markedly ameliorated DOX-caused cardiomyocyte dysfunction via restoring the beating cell ratio and beating rate in cardiomyocytes. Furthermore, AS-IV substantially reduced the mitochondrial reactive oxygen species (ROS) production and lactate dehydrogenase (LDH), creatine kinase-MB isoenzyme (CK-MB) and cytochrome c (CytC) release, and restored the reduced ATP level, succinate dehydrogenase (SDH) and ATP synthase activities induced by DOX, suggesting that AS-IV significantly attenuated DOX-induced mitochondrial damage and dysfunction. It was further observed that DOX-induced cardiomyocyte apoptosis, as qualitatively evaluated by Hoechst 33258 staining and accurately quantified by flow cytometry, was markedly inhibited by AS-IV. Western blot analysis manifested that AS-IV significantly inhibited the activation of mitochondrial apoptotic pathway (MAP) via inducing the phosphorylation of Akt and Bad. Furthermore, phosphatidylinositol 3-kinase (PI3K) inhibitor 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) remarkably inhibited the anti-apoptotic effect of AS-IV. Moreover, AS-IV didn't compromise the antitumor activity of DOX. Taken together, our findings indicate that AS-IV ameliorates DIC, and this beneficial effect appears to be dependent on the activation of the PI3K/Akt pathway. Thus, AS-IV may hold promise as an efficient cardioprotective agent against DIC.

Pitx2c is reactivated in the failing myocardium and stimulates myf5 expression in cultured cardiomyocytes

BACKGROUND

Pitx2 (paired-like homeodomain 2 transcription factor) is crucial for heart development, but its role in heart failure (HF) remains uncertain. The present study lays the groundwork implicating Pitx2 signalling in different modalities of HF.

METHODOLOGY/PRINCIPAL FINDINGS

A variety of molecular, cell-based, biochemical, and immunochemical assays were used to evaluate: (1) Pitx2c expression in the porcine model of diastolic HF (DHF) and in patients with systolic HF (SHF) due to dilated and ischemic cardiomyopathy, and (2) molecular consequences of Pitx2c expression manipulation in cardiomyocytes in vitro. In pigs, the expression of Pitx2c, physiologically downregulated in the postnatal heart, is significantly re-activated in left ventricular (LV) failing myocardium which, in turn, is associated with increased expression of a restrictive set of Pitx2 target genes. Among these, Myf5 was identified as the top upregulated gene. In vitro, forced expression of Pitx2c in cardiomyocytes, but not in skeletal myoblasts, activates Myf5 in dose-dependent manner. In addition, we demonstrate that the level of Pitx2c is upregulated in the LV-myocardium of SHF patients.

CONCLUSIONS/SIGNIFICANCE

The results provide previously unrecognized evidence that Pitx2c is similarly reactivated in postnatal/adult heart at distinct HF phenotypes and suggest that Pitx2c is involved, directly or indirectly, in the regulation of Myf5 expression in cardiomyocytes.

Concise review: skeletal muscle stem cells and cardiac lineage: potential for heart repair

Valuable and ample resources have been spent over the last two decades in pursuit of interventional strategies to treat the unmet demand of heart failure patients to restore myocardial structure and function. At present, it is clear that full restoration of myocardial structure and function is outside our reach from both clinical and basic research studies, but it may be achievable with a combination of ongoing research, creativity, and perseverance. Since the 1990s, skeletal myoblasts have been extensively investigated for cardiac cell therapy of congestive heart failure. Whereas the Myoblast Autologous Grafting in Ischemic Cardiomyopathy (MAGIC) trial revealed that transplanted skeletal myoblasts did not integrate into the host myocardium and also did not transdifferentiate into cardiomyocytes despite some beneficial effects on recipient myocardial function, recent studies suggest that skeletal muscle-derived stem cells have the ability to adopt a cardiomyocyte phenotype in vitro and in vivo. This brief review endeavors to summarize the importance of skeletal muscle stem cells and how they can play a key role to surpass current results in the future and enhance the efficacious implementation of regenerative cell therapy for heart failure.

Engineered Human Muscle Tissue from Skeletal Muscle Derived Stem Cells and Induced Pluripotent Stem Cell Derived Cardiac Cells

During development, cardiac and skeletal muscle share major transcription factors and sarcomere proteins which were generally regarded as specific to either cardiac or skeletal muscle but not both in terminally differentiated adult cardiac or skeletal muscle. Here, we investigated whether artificial muscle constructed from human skeletal muscle derived stem cells (MDSCs) recapitulates developmental similarities between cardiac and skeletal muscle. We constructed 3-dimensional collagen-based engineered muscle tissue (EMT) using MDSCs (MDSC-EMT) and compared the biochemical and contractile properties with EMT using induced pluripotent stem (iPS) cell-derived cardiac cells (iPS-EMT). Both MDSC-EMT and iPS-EMT expressed cardiac specific troponins, fast skeletal muscle myosin heavy chain, and connexin-43 mimicking developing cardiac or skeletal muscle. At the transcriptional level, MDSC-EMT and iPS-EMT upregulated both cardiac and skeletal muscle-specific genes and expressed Nkx2.5 and Myo-D proteins. MDSC-EMT displayed intracellular calcium ion transients and responses to isoproterenol. Contractile force measurements of MDSC-EMT demonstrated functional properties of immature cardiac and skeletal muscle in both tissues. Results suggest that the EMT from MDSCs mimics developing cardiac and skeletal muscle and can serve as a useful in vitro functioning striated muscle model for investigation of stem cell differentiation and therapeutic options of MDSCs for cardiac repair.

Gene expression profiles in engineered cardiac tissues respond to mechanical loading and inhibition of tyrosine kinases

Engineered cardiac tissues (ECTs) are platforms to investigate cardiomyocyte maturation and functional integration, the feasibility of generating tissues for cardiac repair, and as models for pharmacology and toxicology bioassays. ECTs rapidly mature in vitro to acquire the features of functional cardiac muscle and respond to mechanical load with increased proliferation and maturation. ECTs are now being investigated as platforms for in vitro models for human diseases and for pharmacologic screening for drug toxicities. We tested the hypothesis that global ECT gene expression patterns are complex and sensitive to mechanical loading and tyrosine kinase inhibitors similar to the maturing myocardium. We generated ECTs from day 14.5 rat embryo ventricular cells, as previously published, and then conditioned constructs after 5 days in culture for 48 h with mechanical stretch (5%, 0.5 Hz) and/or the p38 MAPK (p38 mitogen-activated protein kinase) inhibitor BIRB796. RNA was isolated from individual ECTs and assayed using a standard Agilent rat 4 × 44k V3 microarray and Pathway Analysis software for transcript expression fold changes and changes in regulatory molecules and networks. Changes in expression were confirmed by quantitative-polymerase chain reaction (q-PCR) for selected regulatory molecules. At the threshold of a 1.5-fold change in expression, stretch altered 1559 transcripts, versus 1411 for BIRB796, and 1846 for stretch plus BIRB796. As anticipated, top pathways altered in response to these stimuli include cellular development, cellular growth and proliferation; tissue development; cell death, cell signaling, and small molecule biochemistry as well as numerous other pathways. Thus, ECTs display a broad spectrum of altered gene expression in response to mechanical load and/or tyrosine kinase inhibition, reflecting a complex regulation of proliferation, differentiation, and architectural alignment of cardiomyocytes and noncardiomyocytes within ECT.

Comparison of Myosin Heavy Chain mRNAs, Protein Isoforms and Fiber Type Proportions in the Rat Slow and Fast Muscles

We studied the expression of myosin heavy chain isoforms at mRNA and protein levels as well as fiber type composition in the fast extensor digitorum longus (EDL) and slow soleus (SOL) twitch muscles of adult inbred Lewis strain rats. Comparison of the results from Real Time RT-PCR, SDS-PAGE and fiber type analysis showed corresponding proportions of MyHC transcripts (MyHC-1, -2a, -2x/d, -2b), protein isoforms (MyHC-1, -2a, -2x/d, -2b) and fiber types (type 1, 2A, 2X/D, 2B) in both muscles. Furthermore, we found that slow MyHC-1 mRNA expression in the SOL was up to three orders higher than that of fast MyHC transcripts. This finding can explain the predominance of MyHC-1 isoform and fiber type 1 and the absence of pure 2X/D and 2B fibers in the SOL muscle. Based on our data presenting quantitative evidence of corresponding proportions between mRNA level, protein content and fiber type composition, we suggest that the Real Time RT-PCR technique can be used as a routine method for analysis of muscle composition changes and could be advantageous for the analysis of scant biological samples such as muscle biopsies in humans.