Browsing by Author "Shi, Tim Hao"
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- Postmortem Metabolism and Pork Quality Development Are Affected by Electrical Stimulation across Three Genetic LinesSpires, Matthew D.; Bodmer, Jocelyn S.; Beline, Mariane; Wicks, Jordan C.; Zumbaugh, Morgan D.; Shi, Tim Hao; Reichert, Brian T.; Schinckel, Allan P.; Grant, Alan L.; Gerrard, David E. (MDPI, 2023-08-11)Variations in postmortem metabolism in muscle impact pork quality development. Curiously, some genetic lines are more refractile to adverse pork quality development than others and may regulate energy metabolism differently. The aim of this study was to challenge pork carcasses from different genetic populations with electrical stimulation (ES) to determine how postmortem metabolism varies with genetic line and explore control points that reside in glycolysis in dying muscle. Three genetic populations (GP) were subjected to ES (100 V or 200 V, 13 pulses, 2 s on/2 s off) at 15- or 25-min post-exsanguination, or no stimulation (NS). Genetic population affected relative muscle relative abundance of different myosin heavy chains, glycogen, G6P, and lactate concentrations. Genetic lines responded similarly to ES, but a comparison of ES treatment groups revealed a trend for an interaction between voltage, time of ES, and time postmortem. Higher voltage accelerated pH decline at 20 min up to 60 min postmortem. Trends in color and firmness scores and L* values were consistent with pH and metabolite data. These data show that genetic populations respond differently to postmortem perturbation by altering glycolytic flux and suggest differences in postmortem glycolysis may be partially responsible for differences in meat quality between genetic populations, though not entirely.
- Signaling pathways regulating skeletal muscle metabolism and growthZumbaugh, Morgan Daughtry (Virginia Tech, 2021-01-05)Skeletal muscle can perceive cellular energy status and substrate availability and demonstrates remarkable plasticity in response to environmental changes. Nonetheless, how skeletal muscle and its resident stem cells (satellite cells; SCs) sense and respond to nutrient flux remains largely undefined. The dynamic post-translational modification O-GlcNAcylation has been shown to serve as a cellular nutrient sensor in a wide range of cells and tissues, yet its role in skeletal muscle and SCs remains unexplored. Here, we ablated skeletal muscle O-GlcNAc transferase (OGT), and thus O-GlcNAcylation, and found the knockout mice exhibited enhanced glucose uptake, insulin sensitivity, and resistance to high-fat diet induced obesity. Additionally, mKO mice had a 3-fold increase in circulating levels of interleukin-15 (IL-15), a potent anti-obesity cytokine, potentially through epigenetic regulation of Il15 by OGT. To further investigate if there was a causal relationship between OGT ablation and the lean phenotype, we generated muscle specific OGT and interleukin-15 receptor alpha (IL-15ra) double knockout mice (mDKO). As a result, mDKO mice had blunted IL-15 secretion and minimal protection against HFD-induced obesity. Together, these data indicate the skeletal muscle OGT-IL15 axis plays an essential role in the maintenance of skeletal muscle and whole-body metabolic homeostasis. As satellite cells (SCs) play an indispensable role in postnatal muscle growth and adult regenerative myogenesis, we investigated the role of O-GlcNAcylation in SC function. To this end, we conditionally ablated OGT in SCs (cKO) and found cKO mice had impaired SC proliferation, in vivo cycling properties, population stability, metabolic regulation, and adult regenerative myogenesis. Together these findings show that SCs require O-GlcNAcylation, presumably to gauge nutritional signals, for proper function and metabolic homeostasis. Another critical yet often neglected player in myogenesis are mitochondria. Traditionally depicted as a power plant in cells, mitochondria are critical for numerous nonconventional, energy-independent cellular process. To investigate the role of both mitochondrial energy production and alternative mitochondrial functions in myogenic regulation, we ablated ATP synthase subunit beta (ATP5b) and ubiquinol-cytochrome c reductase (UQCRFS1) in C2C12 myoblasts to disrupt mitochondrial ATP production and mitochondrial membrane potential, respectively. Ablation of UQCRFS1, but not ATP5b, impaired myoblast proliferation, although lack of either gene compromised myoblast fusion. Interestingly, addition of the potent myogenic stimulator IGF-1 rescued ATP5b fusion but could not override UQCRFS1 knockout effects on proliferation or differentiation. These data demonstrate mitochondrial ATP production is not the "metabolic switch" that governs myogenic progression but rather an alternative mitochondrial function. In summary, skeletal muscle and their resident stem cell population (SCs) both use O-GlcNAcylation, feasibly to sense and respond to nutritional cues, for the maintenance of metabolic homeostasis and normal physiology. A deeper understand of both muscle and SC metabolic regulation may provide therapeutic targets to improve global metabolism and muscle growth.
- Understanding Beef Quality Development and Different Feeding RegimesWicks, Jordan C. (Virginia Tech, 2023-09-06)Understanding Beef Quality Development and Different Feeding Regimes Jordan Christie Wicks ABSTRACT Consumption of beef is expected to increase as the world approaches nearly 9 billion inhabitants by the year 2050, adding unprecedented challenges to the future beef industry. Even so, maintaining quality will still be of utmost importance for producers for two reasons. First, the majority of US cattle are sold on the "grid", which offers both premiums and financial penalties based on quality grades. Second, consumers demand quality. Herein, we explored alternative, cost-saving feeding strategies that impact muscle biochemistry and ultimate meat quality in an effort to determine the most feasible management responses during times of sporadic markets. Our results show that reducing feed inputs from intensive feeding (grain-finished) regimes to maintenance diets of forage or grain up to 60 d had minimal effect on metabolic properties of muscle, thus preserving both quality and yield grades. Specifically, muscle metabolism remained largely unchanged, as indicated by lack of significance in oxidative and glycolytic proteins such as succinate dehydrogenase (SDH), citrate synthase (CS), lactate dehydrogenase (LDH), and phosphofructokinase-1 (PFK-1). Additionally, because maintenance rations were fed, we found no difference in non-esterified fatty acid (NEFA) concentration, or O-linked- β-N-acetylglucosamine (O-GlcNAc) protein abundance suggesting a longer or more aggressive feeding approach may be required to evoke such nutrient based muscle and quality differences. Because quality is important and is a factor for optimal pricing at market, intensive feeding practices are often needed to meet such standards. Still, as the cost of feeding increases, producers struggle to balance quality and profitability. To that end, we evaluated carcass quality of cattle subjected to a reduction of time on feed by 30 d, and found quality, yield and color were similar to that of cattle intensively fed for 120 days. Although, little differences were noted between indicators of postmortem metabolism, short-fed (SF) cattle showed a trend for greater adenosine monophosphate deaminase 1 (AMPD1), and significant difference in the expression of myosin heavy chain isoform (MyHC) IIX suggesting muscle of SF cattle is transiting away from that of grass-fed (CON) cattle. Even so, SF cattle proved to have similar color and quality to cattle fed for 120 days, or more traditionally fed. While we failed to detect differences in muscle between days on feed compared to that of CON (grass-fed), we observed differences in quality and yield between long fed and grass-fed cattle. These data suggest variances in quality may be a result of underlying mechanisms yet to be explained. Therefore, we explored the hallmark biomarkers credited for beef quality development. Despite significant differences in quality and yield grades, data resulted in no differences in myoglobin, oxidative or glycolytic proteins, or calpain-1 and calpastatin between varying phases of growth. However, based on our complementary transcriptomics data, we found linear trends in gene expression related to adipogenesis and muscle hypertrophy, implying these differences may simply be a result of growth rather than muscle function. When taken together, our data suggests severe nutrient restrictions may be required to evoke such a shift in muscle that leads to exacerbated differences in quality. A greater understanding of those mechanisms that drive meat quality development from a conventional grain feeding perspective may prove impactful for the future of our industry.