Exploring the microstructure of hydrated collagen hydrogels under scanning electron microscopy.

Collagen hydrogels are a rapidly expanding platform in bioengineering and soft materials engineering for novel applications focused on medical therapeutics, medical devices and biosensors. Observations linking microstructure to material properties and function enables rational design strategies to control this space. Visualisation of the microscale organisation of these soft hydrated materials presents unique technical challenges due to the relationship between hydration and the molecular organisation of a collagen gel. Scanning electron microscopy is a robust tool widely employed to visualise and explore materials on the microscale. However, investigation of collagen gel microstructure is difficult without imparting structural changes during preparation and/or observation. Electrons are poorly propagated within liquid-phase materials, limiting the ability of electron microscopy to interrogate hydrated gels. Sample preparation techniques to remove water induce artefactual changes in material microstructure particularly in complex materials such as collagen, highlighting a critical need to develop robust material handling protocols for the imaging of collagen hydrogels. Here a collagen hydrogel is fabricated, and the gel state explored under high-vacuum (10-6  Pa) and low-vacuum (80-120 Pa) conditions, and in an environmental SEM chamber. Visualisation of collagen fibres is found to be dependent on the degree of sample hydration, with higher imaging chamber pressures and humidity resulting in decreased feature fidelity. Reduction of imaging chamber pressure is used to induce evaporation of gel water content, revealing collagen fibres of significantly larger diameter than observed in samples dehydrated prior to imaging. Rapid freezing and cryogenic handling of the gel material is found to retain a porous 3D structure following sublimation of the gel water content. Comparative analysis of collagen hydrogel materials demonstrates the care needed when preparing hydrogel samples for electron microscopy.

Point-of-care Analysis for Non-invasive Diagnosis of Oral cancer (PANDORA): A technology-development proof of concept diagnostic accuracy study of dielectrophoresis in patients with oral squamous cell carcinoma and dysplasia.

BACKGROUND: Delays in the identification and referral of oral cancer remain frequent. An accurate and non-invasive diagnostic test to be performed in primary care may help identifying oral cancer at an early stage and reduce mortality. Point-of-care Analysis for Non-invasive Diagnosis of Oral cancer (PANDORA) was a proof-of-concept prospective diagnostic accuracy study aimed at advancing the development of a dielectrophoresis-based diagnostic platform for oral squamous cell carcinoma (OSCC) and epithelial dysplasia (OED) using a novel automated DEPtech 3DEP analyser. METHODS: The aim of PANDORA was to identify the set-up of the DEPtech 3DEP analyser associated with the highest diagnostic accuracy in identifying OSCC and OED from non-invasive brush biopsy samples, as compared to the gold standard test (histopathology). Measures of accuracy included sensitivity, specificity, positive and negative predictive value. Brush biopsies were collected from individuals with histologically proven OSCC and OED, histologically proven benign mucosal disease, and healthy mucosa (standard test), and analysed via dielectrophoresis (index test). RESULTS: 40 individuals with OSCC/OED and 79 with benign oral mucosal disease/healthy mucosa were recruited. Sensitivity and specificity of the index test was 86.8% (95% confidence interval [CI], 71.9%-95.6%) and 83.6% (95% CI, 73.0%-91.2%). Analysing OSCC samples separately led to higher diagnostic accuracy, with 92.0% (95% CI, 74.0%-99.0%) sensitivity and 94.5% (95% CI, 86.6%-98.5%) specificity. CONCLUSION: The DEPtech 3DEP analyser has the potential to identify OSCC and OED with notable diagnostic accuracy and warrants further investigation as a potential triage test in the primary care setting for patients who may need to progress along the diagnostic pathway and be offered a surgical biopsy.

Physiological and pathophysiological concentrations of fatty acids induce lipid droplet accumulation and impair functional performance of tissue engineered skeletal muscle.

Fatty acids (FA) exert physiological and pathophysiological effects leading to changes in skeletal muscle metabolism and function, however, in vitro models to investigate these changes are limited. These experiments sought to establish the effects of physiological and pathophysiological concentrations of exogenous FA upon the function of tissue engineered skeletal muscle (TESkM). Cultured initially for 14 days, C2C12 TESkM was exposed to FA-free bovine serum albumin alone or conjugated to a FA mixture (oleic, palmitic, linoleic, and α-linoleic acids [OPLA] [ratio 45:30:24:1%]) at different concentrations (200 or 800 µM) for an additional 4 days. Subsequently, TESkM morphology, functional capacity, gene expression and insulin signaling were analyzed. There was a dose response increase in the number and size of lipid droplets within the TESkM (p < .05). Exposure to exogenous FA increased the messenger RNA expression of genes involved in lipid storage (perilipin 2 [p < .05]) and metabolism (pyruvate dehydrogenase lipoamide kinase isozyme 4 [p < .01]) in a dose dependent manner. TESkM force production was reduced (tetanic and single twitch) (p < .05) and increases in transcription of type I slow twitch fiber isoform, myosin heavy chain 7, were observed when cultured with 200 µM OPLA compared to control (p < .01). Four days of OPLA exposure results in lipid accumulation in TESkM which in turn results in changes in muscle function and metabolism; thus, providing insight ito the functional and mechanistic changes of TESkM in response to exogenous FA.

Mechanical loading of tissue engineered skeletal muscle prevents dexamethasone induced myotube atrophy.

Skeletal muscle atrophy as a consequence of acute and chronic illness, immobilisation, muscular dystrophies and aging, leads to severe muscle weakness, inactivity and increased mortality. Mechanical loading is thought to be the primary driver for skeletal muscle hypertrophy, however the extent to which mechanical loading can offset muscle catabolism has not been thoroughly explored. In vitro 3D-models of skeletal muscle provide a controllable, high throughput environment and mitigating many of the ethical and methodological constraints present during in vivo experimentation. This work aimed to determine if mechanical loading would offset dexamethasone (DEX) induced skeletal muscle atrophy, in muscle engineered using the C2C12 murine cell line. Mechanical loading successfully offset myotube atrophy and functional degeneration associated with DEX regardless of whether the loading occurred before or after 24 h of DEX treatment. Furthermore, mechanical load prevented increases in MuRF-1 and MAFbx mRNA expression, critical regulators of muscle atrophy. Overall, we demonstrate the application of tissue engineered muscle to study skeletal muscle health and disease, offering great potential for future use to better understand treatment modalities for skeletal muscle atrophy.

Mechanical loading stimulates hypertrophy in tissue-engineered skeletal muscle: Molecular and phenotypic responses.

Mechanical loading of skeletal muscle results in molecular and phenotypic adaptations typified by enhanced muscle size. Studies on humans are limited by the need for repeated sampling, and studies on animals have methodological and ethical limitations. In this investigation, three-dimensional skeletal muscle was tissue-engineered utilizing the murine cell line C2C12, which bears resemblance to native tissue and benefits from the advantages of conventional in vitro experiments. The work aimed to determine if mechanical loading induced an anabolic hypertrophic response, akin to that described in vivo after mechanical loading in the form of resistance exercise. Specifically, we temporally investigated candidate gene expression and Akt-mechanistic target of rapamycin 1 signalling along with myotube growth and tissue function. Mechanical loading (construct length increase of 15%) significantly increased insulin-like growth factor-1 and MMP-2 messenger RNA expression 21 hr after overload, and the levels of the atrophic gene MAFbx were significantly downregulated 45 hr after mechanical overload. In addition, p70S6 kinase and 4EBP-1 phosphorylation were upregulated immediately after mechanical overload. Maximal contractile force was augmented 45 hr after load with a 265% increase in force, alongside significant hypertrophy of the myotubes within the engineered muscle. Overall, mechanical loading of tissue-engineered skeletal muscle induced hypertrophy and improved force production.

Development of tissue-engineered skeletal muscle manufacturing variables.

Three-dimensional tissue-engineered structures enable more representative determination of novel drug or material effects on tissue than traditional monolayer cell cultures. This study sought to better understand how key manufacturing variables affect the myotube characteristics of a skeletal muscle model toward reducing resource use and to develop an understanding of scaling on model consistency. C2C12 murine myoblasts were seeded in a tethered collagen scaffold from which directional myotubes form in response to lines of tension and a change in medium. Collagen polymerizing area length-to-width ratios greater than one were found to reduced cell-matrix attachment and remodeling forces significantly (p < .05) correlating to a reduction in cell fusion potential. Following this, utilizing a factorial design of experiment, 4 million C2C12s/ml, with a polymerizing area width 150% of the anchor point, produced the most favorable myotube characteristics and dramatically reduced the incidence of rupture. Scaled constructs showed no significant differences when compared to larger models. Approximately 20 myotubes with a variation in the alignment of <25° in the central region were consistently observed in the final models. This demonstrates the influence of initial manufacturing variables on tissue formation and has produced a benchmark model for consistent production across scaled constructs for future optimization and as a potential cost-effective preclinical testbed.

The effect of chronic high insulin exposure upon metabolic and myogenic markers in C2C12 skeletal muscle cells and myotubes.

Skeletal muscle is an insulin sensitive tissue and accounts for approximately 80% of post-prandial glucose disposal. This study describes the effects of insulin, delivered for 72 h, to skeletal muscle myoblasts during differentiation or to skeletal muscle myotubes. After chronic treatment, cultures were acutely stimulated with insulin and analyzed for total and phosphorylated Akt (Ser473 ), mRNA expression of metabolic and myogenic markers and insulin-stimulated glucose uptake. Skeletal muscle cells differentiated in the presence of insulin chronically, reduced acute insulin stimulated phosphorylation of Akt Ser473 . In addition, there was a reduction in mRNA expression of Hexokinase II (HKII), GLUT4 and PGC-1α. Insulin-stimulated glucose uptake was attenuated when cells were differentiated in the presence of insulin. In contrast, myotubes exposed to chronic insulin showed no alterations in phosphorylation of Akt Ser473 . Both HKII and GLUT4 mRNA expression were reduced by chronic exposure to insulin; while PGC-1α was not different between culture conditions and was increased by acute insulin stimulation. These data suggest that there are differential responses in insulin signalling, transcription, and glucose uptake of skeletal muscle cells when cultured in either the presence of insulin during differentiation or in myotube cultures.

Resolvin E1 (Rv E1 ) attenuates LPS induced inflammation and subsequent atrophy in C2C12 myotubes.

Resolution of inflammation is now known to be an active process which in part is instigated and controlled by specialized pro-resolving lipid mediators (SPM's) derived from dietary omega-3 fatty acids. Resolvin E1 (Rv E1 ) is one of these SPM's derived from the omega-3 fatty acid eicosapentaenoic acid. Using both molecular and phenotypic functional measures we report that in a model of Lipopolysaccharide (LPS) induced inflammation, Rv E1 attenuated mRNA levels of both interlukin-6 and monocyte chemoattractant protein-1 whilst having no effect on tumor necrosis factor-α or interlukin-1ß in C2C12 skeletal muscle myotubes. Findings at the molecular level were transferred into similar changes in extracellular protein levels of the corresponding genes with the greatest attenuation being noted in IL-6 protein concentrations. Rv E1 instigated beneficial morphological changes through the prevention of LPS induced skeletal muscle atrophy, in tandem with attenuation of the LPS induced reduction in contractile force in tissue engineered skeletal muscle. These findings demonstrate, in our model of endotoxin induced inflammation in skeletal muscle, that Rv E1 has pro-resolving properties in this cell type. Our data provides rationale for further investigation into the mechanistic action of Rv E1 in skeletal muscle, with the vision of having potential benefits for the prevention/resolution of in-vivo skeletal muscle atrophy.

Leucine elicits myotube hypertrophy and enhances maximal contractile force in tissue engineered skeletal muscle in vitro.

The amino acid leucine is thought to be important for skeletal muscle growth by virtue of its ability to acutely activate mTORC1 and enhance muscle protein synthesis, yet little data exist regarding its impact on skeletal muscle size and its ability to produce force. We utilized a tissue engineering approach in order to test whether supplementing culture medium with leucine could enhance mTORC1 signaling, myotube growth, and muscle function. Phosphorylation of the mTORC1 target proteins 4EBP-1 and rpS6 and myotube hypertrophy appeared to occur in a dose dependent manner, with 5 and 20 mM of leucine inducing similar effects, which were greater than those seen with 1 mM. Maximal contractile force was also elevated with leucine supplementation; however, although this did not appear to be enhanced with increasing leucine doses, this effect was completely ablated by co-incubation with the mTOR inhibitor rapamycin, showing that the augmented force production in the presence of leucine was mTOR sensitive. Finally, by using electrical stimulation to induce chronic (24 hr) contraction of engineered skeletal muscle constructs, we were able to show that the effects of leucine and muscle contraction are additive, since the two stimuli had cumulative effects on maximal contractile force production. These results extend our current knowledge of the efficacy of leucine as an anabolic nutritional aid showing for the first time that leucine supplementation may augment skeletal muscle functional capacity, and furthermore validates the use of engineered skeletal muscle for highly-controlled investigations into nutritional regulation of muscle physiology.

Hypoxia Impairs Muscle Function and Reduces Myotube Size in Tissue Engineered Skeletal Muscle.

Contemporary tissue engineered skeletal muscle models display a high degree of physiological accuracy compared with native tissue, and therefore may be excellent platforms to understand how various pathologies affect skeletal muscle. Chronic obstructive pulmonary disease (COPD) is a lung disease which causes tissue hypoxia and is characterized by muscle fiber atrophy and impaired muscle function. In the present study we exposed engineered skeletal muscle to varying levels of oxygen (O2 ; 21-1%) for 24 h in order to see if a COPD like muscle phenotype could be recreated in vitro, and if so, at what degree of hypoxia this occurred. Maximal contractile force was attenuated in hypoxia compared to 21% O2 ; with culture at 5% and 1% O2 causing the most pronounced effects with 62% and 56% decrements in force, respectively. Furthermore at these levels of O2 , myotubes within the engineered muscles displayed significant atrophy which was not seen at higher O2 levels. At the molecular level we observed increases in mRNA expression of MuRF-1 only at 1% O2 whereas MAFbx expression was elevated at 10%, 5%, and 1% O2 . In addition, p70S6 kinase phosphorylation (a downstream effector of mTORC1) was reduced when engineered muscle was cultured at 1% O2 , with no significant changes seen above this O2 level. Overall, these data suggest that engineered muscle exposed to O2 levels of ≤5% adapts in a manner similar to that seen in COPD patients, and thus may provide a novel model for further understanding muscle wasting associated with tissue hypoxia. J. Cell. Biochem. 118: 2599-2605, 2017. © 2017 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Creating Interactions between Tissue-Engineered Skeletal Muscle and the Peripheral Nervous System.

Effective models of mammalian tissues must allow and encourage physiologically (mimetic) correct interactions between co-cultured cell types in order to produce culture microenvironments as similar as possible to those that would normally occur in vivo. In the case of skeletal muscle, the development of such a culture model, integrating multiple relevant cell types within a biomimetic scaffold, would be of significant benefit for investigations into the development, functional performance, and pathophysiology of skeletal muscle tissue. Although some work has been published regarding the behaviour of in vitro muscle models co-cultured with organotypic slices of CNS tissue or with stem cell-derived neurospheres, little investigation has so far been made regarding the potential to maintain isolated motor neurons within a 3D biomimetic skeletal muscle culture platform. Here, we review the current state of the art for engineering neuromuscular contacts in vitro and provide original data detailing the development of a 3D collagen-based model for the co-culture of primary muscle cells and motor neurons. The devised culture system promotes increased myoblast differentiation, forming arrays of parallel, aligned myotubes on which areas of nerve-muscle contact can be detected by immunostaining for pre- and post-synaptic proteins. Quantitative RT-PCR results indicate that motor neuron presence has a positive effect on myotube maturation, suggesting neural incorporation influences muscle development and maturation in vitro. The importance of this work is discussed in relation to other published neuromuscular co-culture platforms along with possible future directions for the field.

Testosterone enables growth and hypertrophy in fusion impaired myoblasts that display myotube atrophy: deciphering the role of androgen and IGF-I receptors.

We have previously highlighted the ability of testosterone (T) to improve differentiation and myotube hypertrophy in fusion impaired myoblasts that display reduced myotube hypertrophy via multiple population doublings (PD) versus their parental controls (CON); an observation which is abrogated via PI3K/Akt inhibition (Deane et al. 2013). However, whether the most predominant molecular mechanism responsible for T induced hypertrophy occurs directly via androgen receptor or indirectly via IGF-IR/PI3K/Akt pathway is currently debated. PD and CON C2C12 muscle cells were exposed to low serum conditions in the presence or absence of T (100 nM) ± inhibitors of AR (flutamide/F, 40 µm) and IGF-IR (picropodophyllin/PPP, 150 nM) for 72 h and 7 days (early/late muscle differentiation respectively). T increased AR and Akt abundance, myogenin gene expression, and myotube hypertrophy, but not ERK1/2 activity in both CON and PD cell types. Akt activity was not increased significantly in either cell type with T. Testosterone was also unable to promote early differentiation in the presence of IGF-IR inhibitor (PPP) yet still able to promote appropriate later increases in myotube hypertrophy and AR abundance despite IGF-IR inhibition. The addition of the AR inhibitor powerfully attenuated all T induced increases in differentiation and myotube hypertrophy with corresponding reductions in AR abundance, phosphorylated Akt, ERK1/2 and gene expression of IGF-IR, myoD and myogenin with increases in myostatin mRNA in both cell types. Interestingly, despite basally reduced differentiation and myotube hypertrophy, PD cells showed larger T induced increases in AR abundance vs. CON cells, a response abrogated in the presence of AR but not IGF-IR inhibitors. Furthermore, T induced increases in Akt abundance were sustained despite the presence of IGF-IR inhibition in PD cells only. Importantly, flutamide alone reduced IGF-IR mRNA in both cell types across time points, with an observed reduction in activity of ERK and Akt, suggesting that IGF-IR was transcriptionally regulated by AR. However, where testosterone increased AR protein content there was no increases observed in IGF-IR gene expression. This suggested that sufficient AR was important to enable normal IGF-IR expression and downstream signalling, yet elevated levels of AR due to testosterone had no further effect on IGF-IR mRNA, despite testosterone increasing Akt abundance in the presence of IGF-IR inhibitor. In conclusion, testosterones ability to improve differentiation and myotube hypertrophy occurred predominately via increases in AR and Akt abundance in both CON and PD cells, with fusion impaired cells (PD) showing an increased responsiveness to T induced AR levels. Finally, T induced increases in myotube hypertrophy (but not early differentiation) occurred independently of upstream IGF-IR input, however it was apparent  that normal AR function in basal conditions was required for adequate IGF-IR gene expression and downstream ERK/Akt activity.

The application of maximal heart rate predictive equations in hypoxic conditions.

PURPOSE: Peak heart rate (HRpeak) is a common tool used in exercise prescription for groups in which maximal exercise intensity is contraindicated; however, the application of this method in normobaric hypoxia is unknown. Therefore, this study investigated the response of HRpeak and the application of predictive HRpeak equations to prescribe exercise intensity in acute normobaric hypoxia. Results were used to examine whether age-derived HRpeak predictive equations are valid in hypoxic conditions. METHODS: Fifteen untrained (eight men) volunteers (age 22 ± 2 years; peak rate of oxygen consumption 46.3 ± 7.0 ml kg(-1) min(-1)) completed incremental cycle ergometer tests (randomised order) to measure HRpeak at sea-level (SL (ambient inspiratory oxygen fraction (FIO2) 0.209)) and four normobaric hypoxic conditions FIO2: 0.185, 0.165, 0.142, 0.125 (≈1,000-4,000 m). RESULTS: HRpeak was similar across all conditions (SL, 182 ± 13; 0.185, 178 ± 11; 0.165, 177 ± 9; 0.142, 178 ± 9; 0.125, 175 ± 10 b min(-1)) despite a reduction in oxygen saturation with increasing hypoxia (SL, 95 ± 5; 0.185, 95 ± 2; 0.165, 92 ± 2; 0.142, 88 ± 3; 0.125, 82 ± 4 %; P ≤ 0.05). The HRpeak was overestimated by all equations compared to the measured value (P < 0.05). Four equations overestimated HRpeak in all conditions (P < 0.01); two in four conditions (0.185, 0.165, 0.142, 0.125; P < 0.01); and two in three conditions (0.165, 0.142, 0.125; P < 0.01). CONCLUSION: The overestimation of HRpeak by commonly used age-derived predictive equations in normobaric hypoxic conditions suggests that despite possible contraindications researchers should directly measure HRpeak whenever possible if it is to be used to prescribe exercise intensities.

Epithelial cancer cells exhibit different electrical properties when cultured in 2D and 3D environments.

BACKGROUND: Many drug development and toxicology studies are performed using cells grown in monolayers in well-plates and flasks, despite the fact that these are widely held to be different to cells found in the native environment. 3D, tissue engineered, organotypical tissue culture systems have been developed to be more representative of the native tissue environment than standard monolayer cultures. Whilst the biochemical differences between cells grown in 2D and 3D culture have been explored, the changes on the electrophysiological properties of the cells have not. METHODS: We compared the electrophysiological properties of primary normal oral keratinocytes (nOK) and cancerous abnormal oral keratinocytes (aOK), cultured in standard monolayer and reconstituted 3D organotypical tissue cultures. The electrophysiological properties of populations of the cells were analysed using dielectrophoresis. The intracellular conductivity of aOK was significantly increased when grown in organotypical cultures compared to counterpart cells grown in monolayer cultures. RESULTS: 3D cultured aOK showed almost identical intracellular conductivity to nOK also grown in organotypical cultures, but significantly different to aOK grown in monolayers. The effective membrane capacitance of aOK grown in 3D was found to be significantly higher than nOK, but there was no significant difference between the electrophysiological properties of nOK grown in 2D and 3D cultures. GENERAL SIGNIFICANCE: This work suggests that factors such as cell shape and cytoplasmic trafficking between cells play an important role in their electrophysiology, and highlights the need to use in vitro models more representative of native tissue when studying cell electrophysiological properties.

Effect of acute normobaric hypoxia on the ventilatory threshold.

PURPOSE: This study investigated the response of the ventilatory threshold (VT) to acute normobaric hypoxia and compared the agreement between software-based algorithms which use automatic detection to identify the VT. Results were used to examine whether the VT can be used as a physiological parameter to prescribe and monitor exercise intensity in hypoxic exercise training programs. METHODS: Fourteen untrained individuals (7 women, 7 men; age 22 ± 2 years, [Formula: see text]O2peak 46 ± 7 mL kg(-1) min(-1)) completed five identical graded exercise tests (randomized order) on a cycle ergometer to measure VT at sea-level (SL) and in response to four normobaric hypoxic conditions (FIO2: 0.185, 0.165, 0.142, 0.125) equivalent to 1,000, 2,000, 3,000 and 4,000 m. Data were analyzed using a one-way analysis of variance (ANOVA) with repeated measures. RESULTS: The VT was similar across all conditions (SL = 1.98 ± 0.46, 1,000 m = 2.03 ± 0.61, 2,000 m = 2.27 ± 0.62, 3,000 m = 1.84 ± 0.50, 4,000 m = 2.29 ± 0.58 L min(-1)) for all algorithms used despite a reduction in arterial oxygen saturation at 3,000 (P ≤ 0.01) and 4,000 m (P ≤ 0.01) compared with SL values. CONCLUSION: The VT appears to be a suitable physiological parameter for exercise prescription in normobaric hypoxia up to an altitude of 4,000 m.

Extracellular vesicles may provide an alternative detoxification pathway during skeletal muscle myoblast ageing.

Skeletal muscle (SM) acts as a secretory organ, capable of releasing myokines and extracellular vesicles (SM-EVs) that impact myogenesis and homeostasis. While age-related changes have been previously reported in murine SM-EVs, no study has comprehensively profiled SM-EV in human models. To this end, we provide the first comprehensive comparison of SM-EVs from young and old human primary skeletal muscle cells (HPMCs) to map changes associated with SM ageing. HPMCs, isolated from young (24 ± 1.7 years old) and older (69 ± 2.6 years old) participants, were immunomagnetically sorted based on the presence of the myogenic marker CD56 (N-CAM) and cultured as pure (100% CD56+) or mixed populations (MP: 90% CD56+). SM-EVs were isolated using an optimised protocol combining ultrafiltration and size exclusion chromatography (UF + SEC) and their biological content was extensively characterised using Raman spectroscopy (RS) and liquid chromatography mass spectrometry (LC-MS). Minimal variations in basic EV parameters (particle number, size, protein markers) were observed between young and old populations. However, biochemical fingerprinting by RS highlighted increased protein (amide I), lipid (phospholipids and phosphatidylcholine) and hypoxanthine signatures for older SM-EVs. Through LC-MS, we identified 84 shared proteins with functions principally related to cell homeostasis, muscle maintenance and transcriptional regulation. Significantly, SM-EVs from older participants were comparatively enriched in proteins involved in oxidative stress and DNA/RNA mutagenesis, such as E3 ubiquitin-protein ligase TTC3 (TTC3), little elongation complex subunit 1 (ICE1) and Acetyl-CoA carboxylase 1 (ACACA). These data suggest SM-EVs could provide an alternative pathway for homeostasis and detoxification during SM ageing.

Molecular changes in detrained & retrained adult jaw muscle.

A hypofunctional masticatory system was developed in 21-day-old male rats by feeding them a soft diet for 27 weeks. Retraining of a parallel group for 6 weeks was achieved by switching back to a hard diet after 21 weeks. A control group was fed a hard diet for 27 weeks. At the end of the experimental period, the expression levels of the myosin heavy chain isoform genes MYH 1 and 2 (fast), 3 (embryonic) and 7 (slow) in the deep masseter were compared using qRT-PCR analysis. The gene expressions of MYH 3 and MYH 7 were significantly higher in the rehabilitation group compared with the normal and hypofunctional group, but no significant differences were found in regards to the gene expression of MYH 1 and 2. Retraining made it possible for the slow (MYH 7) isoform levels to adapt to the increased mechanical load. The increased level of embryonic (MYH 3) isoform could be due to the need of creation of new MYH isoforms.

A survey to evaluate parameters governing the selection and application of extracellular vesicle isolation methods.

Extracellular vesicles (EVs) continue to gain interest across the scientific community for diagnostic and therapeutic applications. As EV applications diversify, it is essential that researchers are aware of challenges, in particular the compatibility of EV isolation methods with downstream applications and their clinical translation. We report outcomes of the first cross-comparison study looking to determine parameters (EV source, starting volume, operator experience, application and implementation parameters such as cost and scalability) governing the selection of popular EV isolation methods across disciplines. Our findings highlighted an increased clinical focus, with 36% of respondents applying EVs in therapeutics and diagnostics. Data indicated preferential selection of ultracentrifugation for therapeutic applications, precipitation reagents in clinical settings and size exclusion chromatography for diagnostic applications utilising biofluids. Method selection was influenced by operator experience, with increased method diversity when EV research was not the respondents primary focus. Application and implementation criteria were indicated to be major influencers in method selection, with UC and SEC chosen for their abilities to process large and small volumes, respectively. Overall, we identified parameters influencing method selection across the breadth of EV science, providing a valuable overview of practical considerations for the effective translation of research outcomes.

Comparison of extracellular vesicle isolation processes for therapeutic applications.

While extracellular vesicles (EVs) continue to gain interest for therapeutic applications, their clinical translation is limited by a lack of optimal isolation methods. We sought to determine how universally applied isolation methods impact EV purity and yield. EVs were isolated by ultracentrifugation (UC), polyethylene glycol precipitation, Total Exosome Isolation Reagent, an aqueous two-phase system with and without repeat washes or size exclusion chromatography (SEC). EV-like particles could be detected for all isolation methods but varied in their purity and relative expression of surface markers (Alix, Annexin A2, CD9, CD63 and CD81). Assessments of sample purity were dependent on the specificity of characterisation method applied, with total particle counts and particle to protein (PtP) ratios often not aligning with quantitative measures of tetraspanin surface markers obtained using high-resolution nano-flow cytometry. While SEC resulted in the isolation of fewer particles with a relatively low PtP ratio (1.12 × 107 ± 1.43 × 106 vs highest recorded; ATPS/R 2.01 × 108 ± 1.15 × 109, p ⩽ 0.05), EVs isolated using this method displayed a comparatively high level of tetraspanin positivity (e.g. ExoELISA CD63⁺ particles; 1.36 × 1011 ± 1.18 × 1010 vs ATPS/R 2.58 × 1010 ± 1.92 × 109, p ⩽ 0.001). Results originating from an accompanying survey designed to evaluate pragmatic considerations surrounding method implementation (e.g. scalability and cost) identified that SEC and UC were favoured for overall efficiency. However, reservations were highlighted in the scalability of these methods, which could potentially hinder downstream therapeutic applications. In conclusion, variations in sample purity and yield were evident between isolation methods, while standard non-specific assessments of sample purity did not align with advanced quantitative high-resolution analysis of EV surface markers. Reproducible and specific assessments of EV purity will be critical for informing therapeutic studies.

Defining the influence of size-exclusion chromatography fraction window and ultrafiltration column choice on extracellular vesicle recovery in a skeletal muscle model.

Extracellular vesicles (EVs) have the potential to provide new insights into skeletal muscle (SM) physiology and pathophysiology. However, current isolation protocols often do not eliminate co-isolated components such as lipoproteins and RNA binding proteins that could confound outcomes and hinder downstream clinical translation. In this study, we validated an EV isolation protocol that combined size-exclusion chromatography (SEC) with ultrafiltration (UF) to increase sample throughput, scalability and purity, while providing the very first analysis of the effects of UF column choice and fraction window on EV recovery. C2C12 myotube conditioned medium was pre-concentrated using either Amicon® Ultra 15 or Vivaspin®20 100 KDa UF columns and processed by SEC (IZON, qEV 70 nm). The resulting thirty fractions obtained were individually analysed to identify an optimal fraction window for EV recovery. The EV marker TSG101 could be detected from fractions 5 to 14, while CD9 and Annexin A2 only up to fraction 6. ApoA1+ lipoprotein co-isolates were detected from fraction 6 onwards for both protocols. Strikingly, Amicon and Vivaspin UF concentration protocols led to qualitative and quantitative variations in EV marker profiles and purity. Eliminating lipoprotein co-isolation by reducing the SEC fraction window resulted in a net loss of particles, but increased measures of sample purity and had only a negligible impact on the presence of EV marker proteins. In conclusion, our study developed an effective UF+SEC protocol for the isolation of EVs based on sample purity (fractions 1-5) and total EV abundance (fractions 2-10). We provide evidence to demonstrate that the choice of UF column can affect the composition of the resulting EV preparation and needs to be considered when being applied in EV isolation studies in SM. The resulting protocols will be valuable in isolating highly pure EV preparations for applications in a range of therapeutic and diagnostic studies.