Tyrone A. Washington

Diet-induced obesity alters anabolic signalling in mice at the onset of skeletal muscle regeneration

Obesity is classified as a metabolic disorder that is associated with delayed muscle regeneration following damage. For optimal skeletal muscle regeneration, inflammation along with extracellular matrix remodelling and muscle growth must be tightly regulated. Moreover, the regenerative process is dependent on the activation of myogenic regulatory factors (MRFs) for myoblast proliferation and differentiation. The purpose of this study was to determine how obesity alters inflammatory and protein synthetic signalling and MRF expression at the onset of muscle regeneration in mice.

Translational machinery of mitochondrial mRNA is promoted by physical activity in Western diet-induced obese mice.

Mitochondria‐encoded proteins are necessary for oxidative phosphorylation; however, no report has examined how physical activity (PA) and obesity affect mitochondrial mRNA translation machinery. Our purpose was to determine whether Western diet (WD)‐induced obesity and voluntary wheel running (VWR) impact mitochondrial mRNA translation machinery and whether expression of this machinery is dictated by oxidative phenotype.

Mitochondrial degeneration precedes the development of muscle atrophy in progression of cancer cachexia in tumour-bearing mice

Cancer cachexia is largely irreversible, at least via nutritional means, and responsible for 20–40% of cancer‐related deaths. Therefore, preventive measures are of primary importance; however, little is known about muscle perturbations prior to onset of cachexia. Cancer cachexia is associated with mitochondrial degeneration; yet, it remains to be determined if mitochondrial degeneration precedes muscle wasting in cancer cachexia. Therefore, our purpose was to determine if mitochondrial degeneration precedes cancer‐induced muscle wasting in tumour‐bearing mice.

Codelivery of Infusion Decellularized Skeletal Muscle with Minced Muscle Autografts Improved Recovery from Volumetric Muscle Loss Injury in a Rat Model.

Skeletal muscle is capable of robust self-repair following mild trauma, yet in cases of traumatic volumetric muscle loss (VML), where more than 20% of a muscles mass is lost, this capacity is overwhelmed. Current autogenic whole muscle transfer techniques are imperfect, which has motivated the exploration of implantable scaffolding strategies. In this study, the use of an allogeneic decellularized skeletal muscle (DSM) scaffold with and without the addition of minced muscle (MM) autograft tissue was explored as a repair strategy using a lower-limb VML injury model (n = 8/sample group). We found that the repair of VML injuries using DSM + MM scaffolds significantly increased recovery of peak contractile force (81 ± 3% of normal contralateral muscle) compared to unrepaired VML controls (62 ± 4%). Similar significant improvements were measured for restoration of muscle mass (88 ± 3%) in response to DSM + MM repair compared to unrepaired VML controls (79 ± 3%). Histological findings revealed a marked decrease in collagen dense repair tissue formation both at and away from the implant site for DSM + MM repaired muscles. The addition of MM to DSM significantly increased MyoD expression, compared to isolated DSM treatment (21-fold increase) and unrepaired VML (37-fold) controls. These findings support the further exploration of both DSM and MM as promising strategies for the repair of VML injury.

Cancer cachexia-induced muscle atrophy: evidence for alterations in microRNAs important for muscle size

Muscle atrophy is a hallmark of cancer cachexia resulting in impaired function and quality of life and cachexia is the immediate cause of death for 20-40% of cancer patients. Multiple microRNAs (miRNAs) have been identified as being involved in muscle development and atrophy; however, less is known specifically on miRNAs in cancer cachexia. The purpose of this investigation was to examine the miRNA profile of skeletal muscle atrophy induced by cancer cachexia to uncover potential miRNAs involved with this catabolic condition. Phosphate-buffered saline (PBS) or Lewis lung carcinoma cells (LLC) were injected into C57BL/6J mice at 8 wk of age. LLC animals were allowed to develop tumors for 4 wk to induce cachexia. Tibialis anterior muscles were extracted and processed to isolate small RNAs, which were used for miRNA sequencing. Sequencing results were assembled with mature miRNAs, and functions of miRNAs were analyzed by Ingenuity Pathway Analysis. LLC animals developed tumors that contributed to significantly smaller tibialis anterior muscles (18.5%) and muscle cross-sectional area (40%) compared with PBS. We found 371 miRNAs to be present in the muscle above background levels. Of these, nine miRNAs were found to be differentially expressed. Significantly altered groups of miRNAs were categorized into primary functionalities including cancer, cell-to-cell signaling, and cellular development among others. Gene network analysis predicted specific alterations of factors contributing to muscle size including Akt, FOXO3, and others. These results create a foundation for future research into the sufficiency of targeting these genes to attenuate muscle loss in cancer cachexia.

Differential effects of leucine supplementation in young and aged mice at the onset of skeletal muscle regeneration

Aging decreases the ability of skeletal muscle to respond to injury. Leucine has been demonstrated to target protein synthetic pathways in skeletal muscle thereby enhancing this response. However, the effect of aging on leucine-induced alterations in protein synthesis at the onset of skeletal muscle regeneration has not been fully elucidated. The purpose of this study was to determine if aging alters skeletal muscle regeneration and leucine-induced alterations in markers of protein synthesis. The tibialis anterior of young (3 months) and aged (24 months) female C57BL/6J mice were injected with either bupivacaine or PBS, and the mice were given ad libitum access to leucine-supplemented or normal drinking water. Protein and gene expression of markers of protein synthesis and degradation, respectively, were analyzed at three days post-injection. Following injury in young mice, leucine supplementation was observed to elevate only p-p70S6K. In aged mice, leucine was shown to elicit higher p-mTOR content with and without injury, and p-4EBP-1 content post-injury. Additionally in aged mice, leucine was shown to elicit higher content of relative p70S6K post-injury. Our study shows that leucine supplementation affects markers of protein synthesis at the onset of skeletal muscle regeneration differentially in young and aged mice.

PGC‐1α4 gene expression is suppressed by the IL‐6—MEK—ERK 1/2 MAPK signalling axis and altered by resistance exercise, obesity and muscle injury

PGC‐1α4 is a novel regulator of muscle hypertrophy; however, there is limited understanding of the regulation of its expression and role in many (patho)physiological conditions. Therefore, our purpose was to elicit signalling mechanisms regulating gene expression of Pgc1α4 and examine its response to (patho)physiological stimuli associated with altered muscle mass.

Development of an infusion bioreactor for the accelerated preparation of decellularized skeletal muscle scaffolds.

The implantation of decellularized tissue has shown effectiveness as a strategy for the treatment of volumetric muscle loss (VML) injuries. The preparation of decellularized tissue typically relies on the diffusion driven removal of cellular debris. For bulky tissues like muscle, the process can be lengthy, which introduces opportunities for both tissue contamination and degradation of key ECM molecules. In this study we report on the accelerated preparation of decellularized skeletal muscle (DSM) scaffolds using a infusion system and examine scaffold performance for the repair of VML injuries. The preparation of DSM scaffolds using infusion was dramatically accelerated. As the infusion rate (1% SDS) was increased from 0.1 to 1 and 10ml/hr, the time needed to remove intracellular myoglobin and actin decreased from a maximum of 140 ± 3hrs to 45 ± 3hrs and 10 ± 2hrs respectively. Although infusion appeared to remove cellular debris more aggressively, it did not significantly decrease the collagen or glycosaminoglycan composition of DSM samples when compared to un‐infused controls. Infusion prepared DSM samples retained the aligned network structure and mechanical integrity of control samples. Infusion prepared DSM samples supported the attachment and in‐vitro proliferation of myoblast cells and was well tolerated by the host when examined in‐vivo.

Potential Roles of mTOR and Protein Degradation Pathways in thePhenotypic Expression of Feed Efficiency in Broilers

The cost of feed represents as much as 70% of the total cost of raising a meat producing animal to market weight. Thus, feed efficiency (FE; g gain: g feed) is a very important genetic trait in animal agriculture. We have observed that a hallmark of low feed efficiency in a highly selected male broiler (meat chicken) line was extensive protein oxidation that probably resulted from increased reactive oxygen species being produced by the mitochondria. Repair or resynthesis of damaged proteins would therefore represent a considerable energetic drain and contribute to the phenotypic expression of low feed efficiency. In the present study, a software program (Ingenuity Pathway Analysis, IPA) facilitated the analysis and interpretation of data from a 4 x 44k chicken oligo array on breast muscle along with data from previous studies obtained from broilers individually phenotyped for FE. The findings support a hypothesis that differential expression of genes associated with the Akt/mTOR, protein ubiquitination, and proteasome pathways through modulation of transcription and protein turnover could play an important role in the phenotypic expression of feed efficiency. Confirmation of this hypothesis will require a thorough assessment of protein expression as well as protein and enzyme activity measurements associated with these pathways in the low and high FE broiler phenotypes.

Skeletal muscle insulin resistance as a precursor to Diabetes: Beyond glucoregulation.

BACKGROUND Prevalence of Type 2 Diabetes Mellitus (T2DM) has reached pandemic levels in the Western societies. T2DM begins with the development of peripheral insulin resistance which prior research suggests may commonly originate within the skeletal muscle. A number of mechanisms have been proposed for the development of muscle insulin resistance including those of classical glucose handling, and also other cellular derangements observed in this disease which include mitochondrial degeneration, alterations in muscle protein turnover and early evidences for dysregulation of the microRNAs. The purpose of the current review is to examine the current findings on these latter aspects of mitochondrial maintenance, protein turnover and microRNA dysregulation along with the potential implications for these derangements in the development of insulin resistance and hence T2DM. We summarize multiple evidences for the degeneration of mitochondria and known elements of the processes regulating mitochondrial quality. Subsequently, we examine current findings of the alterations in muscle protein synthesis and autophagic protein degradation in T2DM and potential feedback of these systems onto canonical insulin signaling. Finally, evidences have emerged for the dysregulation of microRNAs in muscle insulin resistance. Of note early data point to several microRNAs altered by the insulin resistant state which exhibit relations to classic insulin signaling and the other processes discussed here. CONCLUSION Considering that T2DM may be initiated with muscle insulin resistance, improved understanding of the dysregulation of these metabolic parameters of skeletal muscle in the pathogenesis of T2DM may be key to developing efficacious therapeutic modalities to prevent and treat this condition.