Inhibition of pyruvate dehydrogenase accelerates anaerobic glycolysis under postmortem simulating conditions.

This research aimed to explore the potential influence of mitochondria on the rate of anaerobic glycolysis. We hypothesized that mitochondria could reduce the rate of anaerobic glycolysis and pH decline by metabolizing a portion of glycolytic pyruvate. We utilized an in vitro model and incorporated CPI-613 and Avidin to inhibit pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC), respectively. Four treatments were tested: 400 µM CPI-613, 1.5 U/ml Avidin, 400 µM CPI-613 + 1.5 U/ml Avidin, or control. Glycolytic metabolites and pH of the in vitro model were evaluated throughout a 1440-min incubation period. CPI-613-containing treatments, with or without Avidin, decreased pH levels and increased glycogen degradation and lactate accumulation compared to the control and Avidin treatments (P < 0.05), indicating increased glycolytic flux. In a different experiment, two treatments, 400 µM CPI-613 or control, were employed to track the fates of pyruvate using [13C6]glucose. CPI-613 reduced the contribution of glucose carbon to tricarboxylic acid cycle intermediates compared to control (P < 0.05). To test whether the acceleration of acidification in reactions containing CPI-613 was due to an increase in the activity of key enzymes of glycogenolysis and glycolysis, we evaluated the activities of glycogen phosphorylase, phosphofructokinase, and pyruvate kinase in the presence or absence of 400 µM CPI-613. The CPI-613 treatment did not elicit an alteration in the activity of these three enzymes. These findings indicate that inhibiting PDH increases the rate of anaerobic glycolysis and pH decline, suggesting that mitochondria are potential regulators of postmortem metabolism.

Effects of isoenergetic supplementation as water use mitigation strategy on water footprint and health of nursing bull calves.

Sustainable livestock systems focus on mitigating natural resource use such as water. Dietary management strategies can significantly reduce the water footprint of livestock animals; however, animal health is of concern when animals reduce water intake due to subacute dehydration. To evaluate potential consequences of this nutritional management intervention, a total of 23, 60 ±â€…3 days old nursing Holstein bull calves, weighing 94.7 ±â€…12.07 kg, were distributed in a completely randomized design and received one of three diets. Control was a basal diet composed of a non-medicated milk replacer (milk replacer; n = 7), and the additional two diets, were composed of the same non-medicated milk replacer in addition to either lipid [n = 8; milk replacer + menhaden fish oil (3 %)] or soluble carbohydrate [n = 8; milk replacer + corn starch (7%) isoenergetic to fat group] supplements. Animals were offered ad libitum mineral mix and water, as well as 120 g/day of a composite mix of dried microbrewery's spent grains. Data were analyzed as linear and generalized linear mixed models with diet as a fixed effect and animal as random utilizing R studio (R Core Team, 2021, Vienna, Austria; SAS Inst., Cary, NC). Within supplementation groups, lipid supplemented calves had the highest lymphocyte (63.24 vs 57.69 counts/100 lymphocytes; P < 0.033), and lowest neutrophil counts (29.3 vs 35.3 counts/100 lymphocytes; P < 0.047). Supplementation significantly increased total serum protein (P = 0.001) and skin moisture (P < 0.011), with carbohydrate group having the highest skin moisture (5.30 vs 3.99; P < 0.047). Supplementation also decreased fecal fluidity scores (P < 0.001) with no significant change in serum electrolytes (P > 0.256). No significant differences were found amongst treatments for the ingestive behavior (P > 0.338). The carbohydrate-supplemented calves significantly decreased all daily water footprints compared to the control and fat-supplemented groups: blue a 47.55 L decrease, (P < 0.001), green a 265.62 L decrease (P = 0.005), and gray a 55.87 L decrease (P = 0.009) water footprint, as well as total water footprint (369.04 L, P = 0.004). Our results indicate the potential to maintain animal performance while increasing water use efficiency through diet supplementation tailored to mitigate water use, without adverse effects on animal health.

Postmortem Metabolism and Pork Quality Development Are Affected by Electrical Stimulation across Three Genetic Lines.

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.

O-GlcNAcylation is a gatekeeper of porcine myogenesis.

Although it has long been known that growth media withdrawal is a prerequisite for myoblast differentiation and fusion, the underpinning molecular mechanism remains somewhat elusive. Using isolated porcine muscle satellite cells (SCs) as the model, we show elevated O-GlcNAcylation by O-GlcNAcase (OGA) inhibition impaired SC differentiation (D5 P < 0.0001) but had unnoticeable impacts on SC proliferation. To explore the mechanism of this phenotype, we examined the expression of the transcription factor myogenin, a master switch of myogenesis, and found its expression was downregulated by elevated O-GlcNAcylation. Because insulin/IGF-1/Akt axis is a strong promoter of myoblast fusion, we measured the phosphorylated Akt and found that hyper O-GlcNAcylation inhibited Akt phosphorylation, implying OGA inhibition may also work through interfering with this critical differentiation-promoting pathway. In contrast, inhibition of O-GlcNAc transferase (OGT) by its specific inhibitor had little impact on either myoblast proliferation or differentiation (P > 0.05). To confirm these in vitro findings, we used chemical-induced muscle injury in the pig as a model to study muscle regenerative myogenesis and showed how O-GlcNAcylation functions in this process. We show a significant decrease in muscle fiber cross sectional area (CSA) when OGA is inhibited (P < 0.05), compared to nondamaged muscle, and a significant decrease compared to control and OGT inhibited muscle (P < 0.05), indicating a significant impairment in porcine muscle regeneration in vivo. Together, the in vitro and in vivo data suggest that O-GlcNAcylation may serve as a nutrient sensor during SC differentiation by gauging cellular nutrient availability and translating these signals into cellular responses. Given the importance of nutrition availability in lean muscle growth, our findings may have significant implications on how muscle growth is regulated in agriculturally important animals.

Cells use a variety of post translational modifications (PTMs) as a mechanism to transduce extracellular signals and adapt their behaviors in response to intracellular nutrient abundance. O-GlcNAcylation, the addition of single sugars to a protein's serine/threonine residues, has been established as a nutrient sensing PTM in a wide range of cell types. Here, we show the functional importance O-GlcNAcylation in porcine myogenesis. We used isolated porcine satellite cells as the model and pharmacological inhibitors to O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) as the tool to study the role of O-GlcNAcylation in porcine myogenesis. Our data show that although O-GlcNAcylation does not play a significant role in muscle cell proliferation, low level of O-GlcNAcylation is critical for muscle cell differentiation. We demonstrate that inhibition of OGA leads to higher level of O-GlcNAcylation and inhibition of myoblast fusion even though the growth medium (high nutrients) has been shifted to the differentiation medium (low nutrients). Together, these data show that porcine muscle cells use O-GlcNAcylation to sense the cellular nutrient levels and adjust their fate in accordance with the strength of the O-GlcNAcylation signals.

Exploratory lipidome and metabolome profiling contributes to understanding differences in high and normal ultimate pH beef.

The aim of this work was to compare the lipidome and metabolome profiling in the Longissimus thoracis muscle early and late postmortem from high and normal ultimate pH (pHu) beef. Lipid profiling discriminated between high and normal pHu beef based on fatty acid metabolism and mitochondrial beta-oxidation of long chain saturated fatty acids at 30 min postmortem, and phospholipid biosynthesis at 44 h postmortem. Metabolite profiling also discriminated between high and normal pHu beef, mainly through glutathione, purine, arginine and proline, and glycine, serine and threonine metabolisms at 30 min postmortem, and glycolysis, TCA cycle, glutathione, tyrosine, and pyruvate metabolisms at 44 h postmortem. Lipid and metabolite profiles showed reduced glycolysis and increased use of alternative energy metabolic processes that were central to differentiating high and normal pHu beef. Phospholipid biosynthesis modification suggested high pHu beef experienced greater oxidative stress.

Tight gene co-expression in BCB positive cattle oocytes and their surrounding cumulus cells.

BACKGROUND: Cytoplasmic and nuclear maturation of oocytes, as well as interaction with the surrounding cumulus cells, are important features relevant to the acquisition of developmental competence. METHODS: Here, we utilized Brilliant cresyl blue (BCB) to distinguish cattle oocytes with low activity of the enzyme Glucose-6-Phosphate Dehydrogenase, and thus separated fully grown (BCB positive) oocytes from those in the growing phase (BCB negative). We then analyzed the developmental potential of these oocytes, mitochondrial DNA (mtDNA) copy number in single oocytes, and investigated the transcriptome of single oocytes and their surrounding cumulus cells of BCB positive versus BCB negative oocytes. RESULTS: The BCB positive oocytes were twice as likely to produce a blastocyst in vitro compared to BCB- oocytes (P < 0.01). We determined that BCB negative oocytes have 1.3-fold more mtDNA copies than BCB positive oocytes (P = 0.004). There was no differential transcript abundance of genes expressed in oocytes, however, 172 genes were identified in cumulus cells with differential transcript abundance (FDR < 0.05) based on the BCB staining of their oocyte. Co-expression analysis between oocytes and their surrounding cumulus cells revealed a subset of genes whose co-expression in BCB positive oocytes (n = 75) and their surrounding cumulus cells (n = 108) compose a unique profile of the cumulus-oocyte complex. CONCLUSIONS: If oocytes transition from BCB negative to BCB positive, there is a greater likelihood of producing a blastocyst, and a reduction of mtDNA copies, but there is no systematic variation of transcript abundance. Cumulus cells present changes in transcript abundance, which reflects in a dynamic co-expression between the oocyte and cumulus cells.

Molecular and biochemical regulation of skeletal muscle metabolism.

Skeletal muscle hypertrophy is a culmination of catabolic and anabolic processes that are interwoven into major metabolic pathways, and as such modulation of skeletal muscle metabolism may have implications on animal growth efficiency. Muscle is composed of a heterogeneous population of muscle fibers that can be classified by metabolism (oxidative or glycolytic) and contractile speed (slow or fast). Although slow fibers (type I) rely heavily on oxidative metabolism, presumably to fuel long or continuous bouts of work, fast fibers (type IIa, IIx, and IIb) vary in their metabolic capability and can range from having a high oxidative capacity to a high glycolytic capacity. The plasticity of muscle permits continuous adaptations to changing intrinsic and extrinsic stimuli that can shift the classification of muscle fibers, which has implications on fiber size, nutrient utilization, and protein turnover rate. The purpose of this paper is to summarize the major metabolic pathways in skeletal muscle and the associated regulatory pathways.

Skeletal muscle is a heterogenous population of cells that are classified into muscle types based on contractile speed and metabolism. The various types of muscle cells utilize different biochemical pathways to produce energy to support cellular functions. These complex biochemical pathways are unique in their subcellular localization, substrate source, energy production capacity, and regulatory mechanisms. The purpose of this review is to describe the major metabolic pathways in skeletal muscle and the associated regulatory mechanisms.

Proteome basis for the biological variations in color and tenderness of longissimus thoracis muscle from beef cattle differing in growth rate and feeding regime.

The proteome basis for the biological variations in color and tenderness of longissimus thoracis muscle from ½ Angus (Bos taurus taurus) × ½ Nellore (Bos taurus indicus) crossbred steers was evaluated in a completely randomized experimental design consisting of four treatments (n = 9 per treatment): 1) feedlot finished, high growth rate (FH); 2) feedlot finished, low growth rate (FL); 3) pasture finished, high growth rate (PH); and 4) pasture finished, low growth rate (PL). The following comparisons were made to evaluate the effects of finishing systems and growth rates on muscle proteome: 1) FH × PL; 2) FL × PH; 3) FH × FL; and 4) PH × PL. Sixteen protein spots were differentially abundant among these comparisons (P ≤ 0.05), which were distinguished in two major clusters, energy metabolism- and muscle structure-related proteins that impacted glycolysis, carbon metabolism, amino acid biosynthesis and muscle contraction pathways (FDR ≤ 0.05). For FH × PL comparison, triosephosphate isomerase (TPI), phosphoglucomutase-1 (PGM1) and phosphoglycerate kinase 1 (PGK1) were overabundant in FH beef whereas troponin T (TNNT3), α-actin (ACTA1) and myosin regulatory light chain 2 (MYLPF) were overabundant in PL beef. For the FL × PH comparison, PGM1, phosphoglycerate mutase 2 (PGAM2) and annexin 2 (ANXA2) were overabundant in PH beef. For the FH × FL comparison, AMP deaminase (AMPD1) and serum albumin (ALB) were overabundant in FH beef whereas glycogen phosphorylase (PYGM) was overabundant in FL beef. For the PH × PL comparison, myoglobin (MB) was overabundant in PH beef whereas PYGM and MYLPF were overabundant in PL beef. In non-aged beef, L* was positively correlated with PGM1 (r = 0.54) while tenderness was negatively correlated with PGAM2 (r = -0.74) and ANXA2 (r = -0.60). In 7-d aged beef, color attributes (L*, a* and b*) were positively correlated with PGM1 (r = 0.67, 0.64 and 0.64, respectively) while tenderness was negatively correlated with TNNT3 (r = -0.57), PGK1 (r = -0.52) and MYLPF (r = -0.66). Therefore, finishing systems and growth rate affected the muscle proteome profile, which was related to beef color and tenderness. Additionally, these results suggest potential biomarkers for beef color (PGM1 and PGAM2) and tenderness (ANXA2, MYLPF, PGK1 and TNNT3).

Feeding strategies impact animal growth and beef color and tenderness.

The impact of growth rate (GR) and finishing regime (FR) on growth and meat quality traits of Angus x Nellore crossbred steers, harvested at a constant body weight (530 ± 20 kg) or time on feed (140 days), was evaluated. Treatments were: 1) feedlot, high GR; 2) feedlot, low GR; 3) pasture, high GR and 4) pasture, low GR. Live body composition, carcass and meat quality traits were evaluated. High GR had greater impact on muscle and fat deposition in feedlot-finished, but not in pasture-finished animals. Feedlot animals had higher Longissimus muscle area, backfat thickness, meat luminosity and tenderness when compared to pasture groups. Moreover, pasture- and feedlot-finished animals with similar GR did not differ in the chromatic attributes of non-aged meat, regardless of endpoint. Thus, GR appeared to be the main factor driving beef chromatic parameters, while FR had a major impact on achromatic attributes and tenderness of meat.

Metabolomic signature of genetic potential for muscularity in beef cattle.

The aim of this study was to investigate the serum and meat metabolomic changes according to the genetic potential for muscularity of non-castrated Nellore males and its association with phenotypic traits. Forty-eight non-castrated Nellore males were separated into two groups based on their genetic potential for post-weaning muscularity: high (HM) and low (LM). Selection for muscularity did not cause noticeable differences in the traits evaluated during the finishing phase and after slaughter. However, several metabolites in meat and serum, have changed according to the muscularity group. HM animals presented an over-abundance of glycerol, glutamine, choline, methylhistidine, betaine, creatinine and methionine in serum, compared with their LM counterparts. Similarly, the meat samples of HM animals were rich in glucose-6-phosphate, lactate, pyruvate, creatinine, betaine, choline, glycerol and arginine relative to LM bulls. Inosine monophosphate was the only metabolite over-abundant in LM animals. In conclusion, the genetic potential for post-weaning muscularity did not affect performance during the finishing phase, carcass traits and meat quality. However, multivariate analysis shows that the genetic potential of muscularity can be correlated with serum lipid and protein metabolites, and with energy metabolism in meat, providing a footprint of cattle muscularity metabolism.

Skeletal Muscle O-GlcNAc Transferase Action on Global Metabolism Is Partially Mediated Through Interleukin-15.

Besides its roles in locomotion and thermogenesis, skeletal muscle plays a significant role in global glucose metabolism and insulin sensitivity through complex nutrient sensing networks. Our previous work showed that the muscle-specific ablation of O-GlcNAc transferase (OGT) led to a lean phenotype through enhanced interleukin-15 (IL-15) expression. We also showed OGT epigenetically modified and repressed the Il15 promoter. However, whether there is a causal relationship between OGT ablation-induced IL-15 secretion and the lean phenotype remains unknown. To address this question, we generated muscle specific OGT and interleukin-15 receptor alpha subunit (IL-15rα) double knockout mice (mDKO). Deletion of IL-15rα in skeletal muscle impaired IL-15 secretion. When fed with a high-fat diet, mDKO mice were no longer protected against HFD-induced obesity compared to wild-type mice. After 22 weeks of HFD feeding, mDKO mice had an intermediate body weight and glucose sensitivity compared to wild-type and OGT knockout mice. Taken together, these data suggest that OGT action is partially mediated by muscle IL-15 production and provides some clarity into how disrupting the O-GlcNAc nutrient signaling pathway leads to a lean phenotype. Further, our work suggests that interfering with the OGT-IL15 nutrient sensing axis may provide a new avenue for combating obesity and metabolic disorders.

Using TD-NMR relaxometry and 1D 1H NMR spectroscopy to evaluate aging of Nellore beef.

The aim of this study was to explore the use of TD-NMR relaxometry and 1H NMR spectroscopy-based for detecting differences in meat quality attributes. There was limited association between various TD-NMR signals and any physicochemical parameters of fresh and aged meat differing in tenderness ratings. Samples were then divided into three groups based on statistical changes in metabolite concentration. Group A samples possessed near linear increases in metabolite concentration over aging time; whereas samples assigned to Groups B and C were characterized by increases in metabolites that peaked between 7 and 14 days, and up to 14 days aging, respectively. 1H NMR spectroscopy discriminated meat quality using changes in metabolites reflective of glycolysis, the citric acid cycle, protein degradation, amino acid generation and purine metabolisms. These data suggest segregation of meat quality is possible using both NMR technologies but additional work is necessary to understand fully their utility in a commercial industry setting.

O-GlcNAc transferase is required to maintain satellite cell function.

O-GlcNAcylation is a posttranslational modification considered to be a nutrient sensor that reports nutrient scarcity or surplus. Although O-GlcNAcylation exists in a wide range of cells and/or tissues, its functional role in muscle satellite cells (SCs) remains largely unknown. Using a genetic approach, we ablated O-GlcNAc transferase (OGT), and thus O-GlcNAcylation, in SCs. We first evaluated SC function in vivo using a muscle injury model and found that OGT deficient SCs had compromised capacity to repair muscle after an acute injury compared with the wild-type SCs. By tracing SC cycling rates in vivo using the doxycycline-inducible H2B-GFP mouse model, we found that SCs lacking OGT cycled at lower rates and reduced in abundance with time. Additionally, the self-renewal ability of OGT-deficient SCs after injury was decreased compared to that of the wild-type SCs. Moreover, in vivo, in vitro, and ex vivo proliferation assays revealed that SCs lacking OGT were incapable of expanding compared with their wild-type counterparts, a phenotype that may be explained, at least in part, by an HCF1-mediated arrest in the cell cycle. Taken together, our findings suggest that O-GlcNAcylation plays a critical role in the maintenance of SC health and function in normal and injured skeletal muscle.

Driving an Oxidative Phenotype Protects Myh4 Null Mice From Myofiber Loss During Postnatal Growth.

Postnatal muscle growth is accompanied by increases in fast fiber type compositions and hypertrophy, raising the possibility that a slow to fast transition may be partially requisite for increases in muscle mass. To test this hypothesis, we ablated the Myh4 gene, and thus myosin heavy chain IIB protein and corresponding fibers in mice, and examined its consequences on postnatal muscle growth. Wild-type and Myh4 -/- mice had the same number of muscle fibers at 2 weeks postnatal. However, the gastrocnemius muscle lost up to 50% of its fibers between 2 and 4 weeks of age, though stabilizing thereafter. To compensate for the lack of functional IIB fibers, type I, IIA, and IIX(D) fibers increased in prevalence and size. To address whether slowing the slow-to-fast fiber transition process would rescue fiber loss in Myh4 -/- mice, we stimulated the oxidative program in muscle of Myh4 -/- mice either by overexpression of PGC-1α, a well-established model for fast-to-slow fiber transition, or by feeding mice AICAR, a potent AMP kinase agonist. Forcing an oxidative metabolism in muscle only partially protected the gastrocnemius muscle from loss of fibers in Myh4 -/- mice. To explore whether traditional means of stimulating muscle hypertrophy could overcome the muscling deficits in postnatal Myh4 -/- mice, myostatin null mice were bred with Myh4 -/- mice, or Myh4 -/- mice were fed the growth promotant clenbuterol. Interestingly, both genetic and pharmacological stimulations had little impact on mice lacking a functional Myh4 gene suggesting that the existing muscle fibers have maximized its capacity to enlarge to compensate for the lack of its neighboring IIB fibers. Curiously, however, cell signaling events responsible for IIB fiber formation remained intact in the tissue. These findings further show disrupting the slow-to-fast transition of muscle fibers compromises muscle growth postnatally and suggest that type IIB myosin heavy chain expression and its corresponding fiber type may be necessary for fiber maintenance, transition and hypertrophy in mice. The fact that forcing muscle metabolism toward a more oxidative phenotype can partially compensates for the lack of an intact Myh4 gene provides new avenues for attenuating the loss of fast-twitch fibers in aged or diseased muscles.

Mitochondria influence glycolytic and tricarboxylic acid cycle metabolism under postmortem simulating conditions.

The purpose of this study was to test mitochondrial functionality under conditions simulating postmortem metabolism. Isolated mitochondria from porcine longissimus lumborum (LLM) and masseter (MM) muscles were incorporated into an in vitro model that mimics postmortem metabolism. pH and 13C-enrichment of glycolytic and tricarboxylic acid (TCA) cycle intermediates were evaluated at 0, 15, 30, 120, 240, and 1440 min. Addition of mitochondria to the in vitro model lowered its pH at 240 min compared with control. Reactions containing mitochondria had lower pyruvate and lactate [M + 2] and [M + 3] isotopomers at 240 and 1440 min than controls. Furthermore, LLM lowered the enrichment of [M + 2], [M + 3], and [M + 4]α-ketoglutarate at 1440 min compared with MM and control. Succinate [M + 2] and [M + 3] were greater in MM than the control and LLM. [M + 3]fumarate was greater in control at 240 and 1440 min than LLM and MM treatments. Our data indicated that mitochondria are capable of mobilizing pyruvate generated though glycolysis under conditions simulating muscle postmortem metabolism.

New Insights in Muscle Biology that Alter Meat Quality.

Fresh meat quality is greatly determined through biochemical changes occurring in the muscle during its conversion to meat. These changes are key to imparting a unique set of characteristics on fresh meat, including its appearance, ability to retain moisture, and texture. Skeletal muscle is an extremely heterogeneous tissue composed of different types of fibers that have distinct contractile and metabolic properties. Fiber type composition determines the overall biochemical and functional properties of the muscle tissue and, subsequently, its quality as fresh meat. Therefore, changing muscle fiber profile in living animals through genetic selection or environmental factors has the potential to modulate fresh meat quality. We provide an overview of the biochemical processes responsible for the development of meat quality attributes and an overall understanding of the strong relationship between muscle fiber profile and meat quality in different meat species.

Ractopamine-induced fiber type-specific gene expression in porcine skeletal muscles is independent of growth.

Feeding ractopamine (RAC), a ß-adrenergic agonist (BAA), to pigs increases type IIB muscle fiber type-specific protein and mRNA expression. However, increases in the abundance of these fast-twitch fiber types occur with other forms of muscle hypertrophy and thus BAA-induced changes in myosin heavy chain (MyHC) composition may simply be associated with increased muscle growth known to occur in response to BAA feeding. The objective of this study was to determine whether RAC feeding could change the MyHC gene expression in the absence of maximal muscle growth. Pigs were fed either an adequate diet that supported maximal muscle hypertrophy or a low nutrient diet that limited muscle growth. RAC was included in diets at 0 or 20 mg/kg for 1, 2, or 4 wk. Backfat depth was less (P < 0.05) in pigs fed the low nutrient diet compared with the adequate diet but was not affected by RAC. Loin eye area was greater (P < 0.05) in pigs fed an adequate diet plus RAC at 1 wk but did not differ among remaining pigs. At 2 and 4 wk, however, pigs fed the adequate diet had greater loin eye areas (P < 0.05) than pigs fed the low nutrient diet regardless of RAC feeding. Gene expression of the MyHC isoforms, I, IIA, IIX, and IIB, as well as glycogen synthase, citrate synthase, ß 1-adrenergic receptor (AR), and ß 2-AR were determined in longissimus dorsi (LD) and red (RST) and white (WST) portions of the semitendinosus muscles. MyHC type I gene expression was not altered by RAC or diet. Feeding RAC decreased (P < 0.01) MyHC type IIA gene expression in all muscles, but to a greater extent in WST and LD. MyHC type IIX gene expression was lower (P < 0.05) in WST and LD muscles in response to RAC but was not altered in RST muscles. RAC increased (P < 0.05) MyHC type IIB gene expression in all muscles, but to a greater extent in RST. ß 1-AR gene expression was unaffected by RAC or diet, whereas the expression of the ß 2-AR gene was decreased (P < 0.001) by RAC. No significant RAC * diet interactions were observed in gene expression in this study, indicating that RAC altered MyHC and ß 2-AR gene expression in porcine skeletal muscles independent of growth.

Dual effects of obesity on satellite cells and muscle regeneration.

Obesity is a complex metabolic disorder that often leads to a decrease in insulin sensitivity, chronic inflammation, and overall decline in human health and well-being. In mouse skeletal muscle, obesity has been shown to impair muscle regeneration after injury; however, the mechanism underlying these changes has yet to be determined. To test whether there is a negative impact of obesity on satellite cell (SC) decisions and behaviors, we fed C57BL/6 mice normal chow (NC, control) or a high-fat diet (HFD) for 10 weeks and performed SC proliferation and differentiation assays in vitro. SCs from HFD mice formed colonies with smaller size (p < .001) compared to those from NC mice, and this decreased proliferation was confirmed (p < .05) by BrdU incorporation. Moreover, in vitro assays showed that HFD SCs exhibited diminished (p < .001) fusion capacity compared to NC SCs. In single fiber explants, a higher ratio of SCs experienced apoptotic events (p < .001) in HFD mice compared to that of NC-fed mice. In vivo lineage tracing using H2B-GFP mice showed that SCs from HFD treatment also cycled faster (p < .001) than their NC counterparts. In spite of all these autonomous cellular effects, obesity as triggered by high-fat feeding did not significantly impair muscle regeneration in vivo, as reflected by the comparable cross-sectional area (p > .05) of the regenerating fibers in HFD and NC muscles, suggesting that other factors may mitigate the negative impact of obesity on SCs properties.

Exploring the Factors Contributing to the High Ultimate pH of Broiler Pectoralis Major Muscles Affected by Wooden Breast Condition.

The elevated ultimate pH (pH u ) found in wooden breast (WB) meat suggests an altered muscular energetic status in WB but also could be related to a prematurely terminated post-mortem pH decline. The aims of this study were to explore the factors contributing to the elevated pH u and establish whether the occurrence of WB defect alters muscle post-mortem carbohydrate metabolism and determine if the contractile apparatus reflects such changes. A total of 24 carcasses from Ross 308 male chickens were obtained from a commercial producer and harvested using commercial processing procedures. Carcasses were categorized into unaffected (NORM) and WB groups (n = 12 each), and samples were collected from cranial bone-in pectoralis major (PM) muscles at 15 min and 24 h post-mortem for the determination of pH, glycolytic metabolites, adenonucleotides, buffering capacity, phosphofructokinase (PFK) activity, and in vitro pH decline. Twenty-four additional deboned PM samples (12 NORM and 12 WB) were collected from the same processing plant to assess muscle histology and sarcomere length at four different locations throughout the PM muscle. Data show that the reduced glycolytic potential of WB muscles only partially explains the higher (P < 0.001) pH u of WB meat, as residual glycogen along with unaltered PFK activity suggests that neither glycogen nor a deficiency of PFK is responsible for arresting glycolysis prematurely. The dramatic reduction in ATP concentrations in the early post-mortem period suggests a defective ATP-generating pathway that might be responsible for the reduced pH decline in WB samples. Further, the addition of excess of ATPase extended post-mortem glycolysis of WB meat in an in vitro glycolytic system. WB-affected samples have longer (P < 0.001) sarcomeres compared to NORM, indicating the existence of compromised energy-generating pathways in myopathic muscles that may have had consequences on the muscle contraction and tension development, as in vivo, also during the post-mortem period. Considering the overall reduced glycolytic potential and the myodegenerative processes associated with WB condition, we speculate that the higher pH u of WB meat might be the outcome of a drastically impaired energy-generating pathway combined with a deficiency and/or a dysfunction of muscle ATPases, having consequences also on muscle fiber contraction degree.

Metabolite profile and consumer sensory acceptability of meat from lean Nellore and Angus × Nellore crossbreed cattle fed soybean oil.

Thirty each Nellore (NEL) and crossbred Angus × Nellore (AxN) were used to evaluate the effect of feeding soybean oil (SBO) and breed on meat sensory acceptability and its relation to muscle metabolite profiles. Cattle were fed for 133 d on two different diets: 1) basal feedlot diet (CON) and 2) CON diet with 3.5% added SBO. No interactions between diet and genetic group were detected for any traits measured. Meat from animals fed SBO diet had lower overall liking, flavor, tenderness and juiciness scores compared to meat from animals fed CON diet. The four most important compounds differing between animals fed CON and SBO diets were betaine, glycerol, fumarate, and carnosine, suggesting that metabolic pathways such as glycerolipid metabolism; glycine, serine and threonine metabolism; glutamine and glutamate metabolism; valine, leucine and isoleucine biosynthesis; and alanine, aspartate and glutamate metabolism were affected by diets. Nellore beef had a higher overall liking and meat flavor scores than AxN beef. The four most important compounds differing between breeds were glycine, glucose, alanine, and carnosine, which may indicate that metabolic pathways such as glutathione metabolism; primary bile acid biosynthesis; alanine, aspartate and glutamate metabolism; and valine, leucine and isoleucine biosynthesis were affected by genetic groups. Meat carnosine, inosine monophosphate, glutamate, betaine, glycerol and creatinine levels were correlated with sensory acceptability scores. Meat metabolite profiles and sensory acceptability were differentially impacted by diet and breed.