When human skeletal muscle is exposed to exercise training, the outcomes, in terms of physiological adaptation, are unpredictable. The significance of this fact has long been underappreciated, and ...only recently has progress been made in identifying some of the molecular bases for the heterogeneous response to exercise training. It is not only of great medical importance that some individuals do not substantially physiologically adapt to exercise training, but the study of the heterogeneity itself provides a powerful opportunity to dissect out the genetic and environmental factors that limit adaptation, directly in humans. In the following review I will discuss new developments linking genetic and transcript abundance variability to an individual's potential to improve their aerobic capacity or endurance performance or induce muscle hypertrophy. I will also comment on the idea that certain gene networks may be associated with muscle "adaptability" regardless the stimulus provided.
Physical activity and molecular ageing presumably interact to precipitate musculoskeletal decline in humans with age. Herein, we have delineated molecular networks for these two major components of ...sarcopenic risk using multiple independent clinical cohorts. We generated genome-wide transcript profiles from individuals (n = 44) who then undertook 20 weeks of supervised resistance-exercise training (RET). Expectedly, our subjects exhibited a marked range of hypertrophic responses (3% to +28%), and when applying Ingenuity Pathway Analysis (IPA) up-stream analysis to ~580 genes that co-varied with gain in lean mass, we identified rapamycin (mTOR) signaling associating with growth (P = 1.4 × 10(-30)). Paradoxically, those displaying most hypertrophy exhibited an inhibited mTOR activation signature, including the striking down-regulation of 70 rRNAs. Differential analysis found networks mimicking developmental processes (activated all-trans-retinoic acid (ATRA, Z-score = 4.5; P = 6 × 10(-13)) and inhibited aryl-hydrocarbon receptor signaling (AhR, Z-score = -2.3; P = 3 × 10(-7))) with RET. Intriguingly, as ATRA and AhR gene-sets were also a feature of endurance exercise training (EET), they appear to represent "generic" physical activity responsive gene-networks. For age, we found that differential gene-expression methods do not produce consistent molecular differences between young versus old individuals. Instead, utilizing two independent cohorts (n = 45 and n = 52), with a continuum of subject ages (18-78 y), the first reproducible set of age-related transcripts in human muscle was identified. This analysis identified ~500 genes highly enriched in post-transcriptional processes (P = 1 × 10(-6)) and with negligible links to the aforementioned generic exercise regulated gene-sets and some overlap with ribosomal genes. The RNA signatures from multiple compounds all targeting serotonin, DNA topoisomerase antagonism, and RXR activation were significantly related to the muscle age-related genes. Finally, a number of specific chromosomal loci, including 1q12 and 13q21, contributed by more than chance to the age-related gene list (P = 0.01-0.005), implying possible epigenetic events. We conclude that human muscle age-related molecular processes appear distinct from the processes regulated by those of physical activity.
Mainly from cell culture studies, a series of genes that have been suggested to be characteristic of different types of adipocytes have been identified. Here we have examined gene expression patterns ...in nine defined adipose depots: interscapular BAT, cervical BAT, axillary BAT, mediastinic BAT, cardiac WAT, inguinal WAT, retroperitoneal WAT, mesenteric WAT, and epididymal WAT. We found that each depot displayed a distinct gene expression fingerprint but that three major types of depots were identifiable: the brown, the brite, and the white. Although differences in gene expression pattern were generally quantitative, some gene markers showed, even in vivo, remarkable depot specificities: Zic1 for the classical BAT depots, Hoxc9 for the brite depots, Hoxc8 for the brite and white in contrast to the brown, and Tcf21 for the white depots. The effect of physiologically induced recruitment of thermogenic function (cold acclimation) on the expression pattern of the genes was quantified; in general, the depot pattern dominated over the recruitment effects. The significance of the gene expression patterns for classifying the depots and for understanding the developmental background of the depots is discussed, as are the possible regulatory functions of the genes.
Serious and underappreciated sources of bias mean that extreme caution should be applied when using or interpreting functional enrichment analysis to validate findings from global RNA- or ...protein-expression analyses.
Our core timekeeping mechanism, the circadian clock, plays a vital role in immunity. Although the mechanics of circadian control over the immune response is generally explained by transcriptional ...activation or repression derived from this clock's transcription-translation negative-feedback loop, research suggests that some regulation occurs beyond transcriptional activity. We comprehensively profiled the transcriptome and proteome of murine bone marrow-derived macrophages and found that only 15% of the circadian proteome had corresponding oscillating mRNA, suggesting post-transcriptional regulation influences macrophage clock regulatory output to a greater extent than any other tissue previously profiled. This regulation may be explained by the robust temporal enrichment we identified for proteins involved in degradation and translation. Extensive post-transcriptional temporal-gating of metabolic pathways was also observed and further corresponded with daily variations in ATP production, mitochondrial morphology, and phagocytosis. The disruption of this circadian post-transcriptional metabolic regulation impaired immune functionality. Our results demonstrate that cell-intrinsic post-transcriptional regulation is a primary driver of circadian output in macrophages and that this regulation, particularly of metabolic pathways, plays an important role in determining their response to immune stimuli.
Septic patients treated in the intensive care unit (ICU) often develop multiple organ failure including persistent skeletal muscle dysfunction which results in the patient's protracted recovery ...process. We have demonstrated that muscle mitochondrial enzyme activities are impaired in septic ICU patients impairing cellular energy balance, which will interfere with muscle function and metabolism. Here we use detailed phenotyping and genomics to elucidate mechanisms leading to these impairments and the molecular consequences.
Utilising biopsy material from seventeen patients and ten age-matched controls we demonstrate that neither mitochondrial in vivo protein synthesis nor expression of mitochondrial genes are compromised. Indeed, there was partial activation of the mitochondrial biogenesis pathway involving NRF2alpha/GABP and its target genes TFAM, TFB1M and TFB2M yet clearly this failed to maintain mitochondrial function. We therefore utilised transcript profiling and pathway analysis of ICU patient skeletal muscle to generate insight into the molecular defects driving loss of muscle function and metabolic homeostasis. Gene ontology analysis of Affymetrix analysis demonstrated substantial loss of muscle specific genes, a global oxidative stress response related to most probably cytokine signalling, altered insulin related signalling and a substantial overlap between patients and muscle wasting/inflammatory animal models. MicroRNA 21 processing appeared defective suggesting that post-transcriptional protein synthesis regulation is altered by disruption of tissue microRNA expression. Finally, we were able to demonstrate that the phenotype of skeletal muscle in ICU patients is not merely one of inactivity, it appears to be an actively remodelling tissue, influenced by several mediators, all of which may be open to manipulation with the aim to improve clinical outcome.
This first combined protein and transcriptome based analysis of human skeletal muscle obtained from septic patients demonstrated that losses of mitochondria and muscle mass are accompanied by sustained protein synthesis (anabolic process) while dysregulation of transcription programmes appears to fail to compensate for increased damage and proteolysis. Our analysis identified both validated and novel clinically tractable targets to manipulate these failing processes and pursuit of these could lead to new potential treatments.
Recently, a method for the recycling polyurethane (PU), the acidolysis, was reported in which dicarboxylic acids (DA) were used as cleavage agents. Yet, the effect of reaction conditions on the ...properties of the recovered polyol (RP) was not discussed. Therefore, aiming at achieving in-depth knowledge of acidolysis, in this work, the effect of the recycling conditions on the properties of RP was statistically evaluated. Temperature and PU/DA ratio were found to be the predominant factors with influence of 62.4% and 31.5% on the hydroxyl number (OHnumber), respectively. In turn, the acid value (AV) proved to be dependent on several factors and their interactions. Yet, the major influence on AV, the combination of PU/DA ratio and temperature, has 39.7% of influence. Using linear regression to predict the properties of the RP, both the experimental and the predicted values presented high correlation. Afterwards, flexible polyurethane foams (PUF) were produced using up to 30% (w/w) of RP as partial substitute of virgin polyol. It was observed that all foams present similar density, although the presence of the RP enhances their stiffness, which was attributed to the higher content of aromatic moieties of RP. Therefore, the suitability of this recycling method and the subsequent use of the reaction products in the production of new foams was demonstrated. This is fully in line with the principles of circular economy.
Display omitted
•Polyurethane foams were recycled via acidolysis using succinic acid.•The effect of the recycling conditions was statistically evaluated.•Temperature and polyurethane/dicarboxylic acid ratio are the predominant factors.•Polyurethane foams were produced using recovered polyol.•The foams are suitable for its use in automotive and domestic applications.
This work intends to provide a preliminary approach concerning the preparation of 3D printed products derived from recycled raw-materials. In that sense, recycled polyurethane foam (PUF) particles ...were added (up to 10% wt/wt) to thermoplastic polyurethane (TPU) to prepare 3D printed products. From the results, it was observed that the presence of PUF particles reduces the density of filaments. Moreover, even though filler and matrix are polyurethane (PU) polymers, the fact that PUF scraps consists of crosslinked PU, it affects inter-layer adhesion, reducing the mechanical performance of the 3D printed specimens, especially when high PUF particles contents were used. Nonetheless, despite of the limitations identified, the addition of PUF particles did not affect the thermal stability of the composites, meaning that these composites can be processed at high temperatures. Therefore, PUF scraps were successfully reused which proved to be a low cost additive for the production 3D printed composites (when using low content), with the advantage of being an alternative to the disposal of PUF.
Attainment of a brown adipocyte cell phenotype in white adipocytes, with their abundant mitochondria and increased energy expenditure potential, is a legitimate strategy for combating obesity. The ...unique transcriptional regulators of the primary brown adipocyte phenotype are unknown, limiting our ability to promote brown adipogenesis over white. In the present work, we used microarray analysis strategies to study primary preadipocytes, and we made the striking discovery that brown preadipocytes demonstrate a myogenic transcriptional signature, whereas both brown and white primary preadipocytes demonstrate signatures distinct from those found in immortalized adipogenic models. We found a plausible SIRT1-related transcriptional signature during brown adipocyte differentiation that may contribute to silencing the myogenic signature. In contrast to brown preadipocytes or skeletal muscle cells, white preadipocytes express Tcf21, a transcription factor that has been shown to suppress myogenesis and nuclear receptor activity. In addition, we identified a number of developmental genes that are differentially expressed between brown and white preadipocytes and that have recently been implicated in human obesity. The interlinkage between the myocyte and the brown preadipocyte confirms the distinct origin for brown versus white adipose tissue and also represents a plausible explanation as to why brown adipocytes ultimately specialize in lipid catabolism rather than storage, much like oxidative skeletal muscle tissue.
The molecular pathways that are activated and contribute to physiological remodeling of skeletal muscle in response to endurance exercise have not been fully characterized. We previously reported ...that ∼800 gene transcripts are regulated following 6 wk of supervised endurance training in young sedentary males, referred to as the training-responsive transcriptome (TRT) (Timmons JA et al. J Appl Physiol 108: 1487-1496, 2010). Here we utilized this database together with data on biological variation in muscle adaptation to aerobic endurance training in both humans and a novel out-bred rodent model to study the potential regulatory molecules that coordinate this complex network of genes. We identified three DNA sequences representing RUNX1, SOX9, and PAX3 transcription factor binding sites as overrepresented in the TRT. In turn, miRNA profiling indicated that several miRNAs targeting RUNX1, SOX9, and PAX3 were downregulated by endurance training. The TRT was then examined by contrasting subjects who demonstrated the least vs. the greatest improvement in aerobic capacity (low vs. high responders), and at least 100 of the 800 TRT genes were differentially regulated, thus suggesting regulation of these genes may be important for improving aerobic capacity. In high responders, proangiogenic and tissue developmental networks emerged as key candidates for coordinating tissue aerobic adaptation. Beyond RNA-level validation there were several DNA variants that associated with maximal aerobic capacity (Vo(₂max)) trainability in the HERITAGE Family Study but these did not pass conservative Bonferroni adjustment. In addition, in a rat model selected across 10 generations for high aerobic training responsiveness, we found that both the TRT and a homologous subset of the human high responder genes were regulated to a greater degree in high responder rodent skeletal muscle. This analysis provides a comprehensive map of the transcriptomic features important for aerobic exercise-induced improvements in maximal oxygen consumption.
PDF
