KLF7 Regulates Satellite Cell Quiescence in Response to Extracellular Signaling.

Retaining muscle stem satellite cell (SC) quiescence is important for the maintenance of stem cell population and tissue regeneration. Accumulating evidence supports the model where key extracellular signals play crucial roles in maintaining SC quiescence or activation, however, the intracellular mechanisms that mediate niche signals to control SC behavior are not fully understood. Here, we reported that KLF7 functioned as a key mediator involved in low-level TGF-ß signaling and canonical Notch signaling-induced SC quiescence and myoblast arrest. The data obtained showed that KLF7 was upregulated in quiescent SCs and nonproliferating myoblasts. Silence of KLF7 promoted SCs activation and myoblasts proliferation, but overexpression of KLF7 induced myogenic cell arrest. Notably, the expression of KLF7 was regulated by TGF-ß and Notch3 signaling. Knockdown of KLF7 diminished low-level TGF-ß and canonical Notch signaling-induced SC quiescence. Investigation into the mechanism revealed that KLF7 regulation of SC function was dependent on p21 and acetylation of Lys227 and/or 231 in the DNA binding domain of KLF7. Our study provides new insights into the regulatory network of muscle stem cell quiescence. Stem Cells 2016;34:1310-1320.

Histone acetyltransferase inhibitors antagonize AMP-activated protein kinase in postmortem glycolysis.

OBJECTIVE: The purpose of this study was to investigate the influence of AMP-activated protein kinase (AMPK) activation on protein acetylation and glycolysis in postmortem muscle to better understand the mechanism by which AMPK regulates postmortem glycolysis and meat quality. METHODS: A total of 32 mice were randomly assigned to four groups and intraperitoneally injected with 5-Aminoimidazole-4-carboxamide1-ß-D-ribofuranoside (AICAR, a specific activator of AMPK), AICAR and histone acetyltransferase inhibitor II, or AICAR, Trichostatin A (TSA, an inhibitor of histone deacetylase I and II) and Nicotinamide (NAM, an inhibitor of the Sirt family deacetylases). After mice were euthanized, the Longissimus dorsi muscle was collected at 0 h, 45 min, and 24 h postmortem. AMPK activity, protein acetylation and glycolysis in postmortem muscle were measured. RESULTS: Activation of AMPK by AICAR significantly increased glycolysis in postmortem muscle. At the same time, it increased the total acetylated proteins in muscle 45 min postmortem. Inhibition of protein acetylation by histone acetyltransferase inhibitors reduced AMPK activation induced increase in the total acetylated proteins and glycolytic rate in muscle early postmortem, while histone deacetylase inhibitors further promoted protein acetylation and glycolysis. Several bands of proteins were detected to be differentially acetylated in muscle with different glycolytic rates. CONCLUSION: Protein acetylation plays an important regulatory role in postmortem glycolysis. As AMPK mediates the effects of pre-slaughter stress on postmortem glycolysis, protein acetylation is likely a mechanism by which antemortem stress influenced postmortem metabolism and meat quality though the exact mechanism is to be elucidated.

Extraocular muscle satellite cells are high performance myo-engines retaining efficient regenerative capacity in dystrophin deficiency.

Extraocular muscles (EOMs) are highly specialized skeletal muscles that originate from the head mesoderm and control eye movements. EOMs are uniquely spared in Duchenne muscular dystrophy and animal models of dystrophin deficiency. Specific traits of myogenic progenitors may be determinants of this preferential sparing, but very little is known about the myogenic cells in this muscle group. While satellite cells (SCs) have long been recognized as the main source of myogenic cells in adult muscle, most of the knowledge about these cells comes from the prototypic limb muscles. In this study, we show that EOMs, regardless of their distinctive Pax3-negative lineage origin, harbor SCs that share a common signature (Pax7(+), Ki67(-), Nestin-GFP(+), Myf5(nLacZ+), MyoD-positive lineage origin) with their limb and diaphragm somite-derived counterparts, but are remarkably endowed with a high proliferative potential as revealed in cell culture assays. Specifically, we demonstrate that in adult as well as in aging mice, EOM SCs possess a superior expansion capacity, contributing significantly more proliferating, differentiating and renewal progeny than their limb and diaphragm counterparts. These robust growth and renewal properties are maintained by EOM SCs isolated from dystrophin-null (mdx) mice, while SCs from muscles affected by dystrophin deficiency (i.e., limb and diaphragm) expand poorly in vitro. EOM SCs also retain higher performance in cell transplantation assays in which donor cells were engrafted into host mdx limb muscle. Collectively, our study provides a comprehensive picture of EOM myogenic progenitors, showing that while these cells share common hallmarks with the prototypic SCs in somite-derived muscles, they distinctively feature robust growth and renewal capacities that warrant the title of high performance myo-engines and promote consideration of their properties for developing new approaches in cell-based therapy to combat skeletal muscle wasting.

Phosphorylation of myofibrillar proteins in post-mortem ovine muscle with different tenderness.

BACKGROUND: Tenderness is one of the most important quality attributes especially for beef and lamb. As protein phosphorylation and dephosphorylation regulate glycolysis, muscle contraction and turnover of proteins within living cells, it may contribute to the conversion of muscle to meat. The changes of myofibrillar protein phosphorylation in post-mortem ovine muscle with different levels of tenderness were investigated in this study. RESULTS: The protein phosphorylation level (P/T ratio) of the tender group increased from 0.5 to 12 h post mortem and then decreased. The P/T ratio of tough group increased during 24 h post mortem, increasing faster from 0.5 to 4 h post mortem than from 4 to 24 h post mortem.The global phosphorylation level of tough meat was significantly higher than tender meat at 4, 12 and 24 h post mortem (P < 0.05). Protein identification revealed that most of the phosphoproteins were proteins with sarcomeric function; the others were involved in glycometabolism, stress response, etc. The phosphorylation levels of myofibrillar proteins, e.g. myosin light chain 2 and actin, were significantly different among groups of different tenderness and at different post-mortem time points (P < 0.05). CONCLUSION: Protein phosphorylation may influence meat rigor mortis through contractile machinery and glycolysis, which in turn affect meat tenderness.

Different actions of salt and pyrophosphate on protein extraction from myofibrils reveal the mechanism controlling myosin dissociation.

BACKGROUND: Myosin is the major functional protein in muscle foods for water retention, protein binding/gelation and fat holding/emulsification. To maximize its functionality, myosin needs to be released from thick filaments. Understanding of the mechanism controlling myosin extraction will help improve quality traits of meat products. RESULTS: The data obtained show that actomyosin binding is the rate-limiting constraint for myosin release in rigor condition. Magnesium pyrophosphate (MgPPi) increased myosin extraction by weakening actomyosin interaction and maximized myosin extraction at 0.4 mol L(-1) NaCl, which was not attained at 1.0 mol L(-1) NaCl in the absence of PPi. Interaction between myosin rod domains is another critical constraint for myosin extraction, which is, rather than PPi, salt dependent. Further, our data suggest that MyBP-C (myosin binding protein C) and M-line might not be of significance in the process of NaCl-induced myosin extraction, though further study was needed. CONCLUSION: Our study provides new insight into the mechanism that controls myosin extraction from intact sarcomere, which could be applied to maximize myosin function and to improve meat quality in practice.

microRNA-151-3p regulates slow muscle gene expression by targeting ATP2a2 in skeletal muscle cells.

MicroRNAs (miRNAs) are a group of small noncoding RNAs that regulate the stability or translation of cognate mRNAs at the post-transcriptional level. Accumulating evidence indicates that miRNAs play important roles in many aspects of muscle function, including muscle growth and development, regeneration, contractility, and muscle fiber type plasticity. In the current study, we examined the function of miR-151-3p in myoblast proliferation and differentiation. Results show that overexpression of miR-151-3p not only upregulates myoblast proliferation, but also decreases slow muscle gene expression (such as MHC-ß/slow and slow muscle troponin I) in both C2C12 myotubes and in primary cultures. Alternatively, inhibition of miR-151-3p by antisense RNA was found to upregulate MHC-ß/slow expression, indicating that miR-151-3p plays a role in muscle fiber type determination. Further investigation into the underlying mechanisms revealed for the first time that miR-151-3p directly targets ATP2a2, a gene encoding for a slow skeletal and cardiac muscle specific Ca(2+) ATPase, SERCA2 thus downregulating slow muscle gene expression. Mechanisms by which the alteration in SERCA2 expression induces changes in other slow muscle gene expression levels needs to be defined in future research.

Muscle-selective knockout of AMPKα2 does not exacerbate diet-induced obesity probably related to altered myokines expression.

Dysregulation of lipid metabolism has been believed to be central in the development of skeletal muscle insulin resistance. Since first being described in 1989, the role of AMPK in energy metabolism, especially its role in lipid metabolism in skeletal muscle has been well studied. However, some recent literature report that fatty acid oxidation in skeletal muscle is not directly associated with AMPK activation and ACC phosphorylation. To further understand the role of AMPK in lipid metabolism and the development of induced obesity and insulin resistance, muscle specific AMPKα2 knockout mice (mAMPKα2-KO) was employed in this study. The results showed that AMPKα2 ablation in muscle did not exacerbate high fat diet induce obesity in mice. On the contrary, it improved animal glucose tolerance and insulin sensitivity, with reduced triglyceride content in skeletal muscle and fat mass in various adipose tissues, when mice were fed high fat diet for 14 weeks. Gene expression analysis revealed that AMPKα2 knockout up-regulated the expression of genes related to lipid catabolism and down-regulated that of genes related to triglyceride synthesis. More importantly, ablation of AMPKα2 altered the expression of several myokines related to adipogenesis and muscle regeneration. Our data suggest that defect in AMPKα2 signaling does not necessarily lead to the development of muscle insulin resistance and obesity. AMPKα2 may regulate whole body lipid metabolism by regulating myokine secretion.

KLF15 regulates slow myosin heavy chain expression through NFATc1 in C2C12 myotubes.

A comprehensive understanding of genetic and environmental factors that control skeletal muscle fiber type specification and transformation is essential not only in sports science, but also in myopathy and metabolic disorders. Krüppel-like factors (KLFs) are a subfamily of the zinc-finger class of transcription factors, which are involved in the development, homeostasis, and pathology of cardiovascular systems. Compared to cardiac and smooth muscles, the role of KLFs in skeletal muscle is much less understood. In this study, the endogenous expression of KLF15 was analyzed in differentiating C2C12 muscle cells and mouse skeletal muscle. Our data indicated that Klf15 was upregulated during myogenic differentiation and higher levels of Klf15 mRNA were detected in mouse slow, oxidative soleus muscle (SL) compared to that in fast, glycolytic tibialis anterior muscle (TA), indicating that KLF15 may play a role in myogenesis or myofiber typing. Additional studies revealed that KLF15 regulated the expression of MHC-ß/slow rather than muscle cell differentiation. Gene silencing, overexpression, and luciferase reporter assay showed that KLF15 regulated MHC-ß/slow by binding to Nfatc1 promoter, inducing its activity, therefore mediating calcineurin/NFAT signaling. Our study contributed to the current knowledge on KLFs in skeletal muscle, and it indicated a need for further intensive studies on the redundant and divergent functions of KLFs.

Antemortem Stress Regulates Postmortem Glycolysis in Muscle by Deacetylation of Pyruvate Kinase M1 at K141.

It is well known that preslaughter (antemortem) stress such as rough handling, transportation, a negative environment, physical discomfort, lack of consistent routine, and bad feed quality has a big impact on meat quality. The antemortem-induced poor meat quality is characterized by low pH, a pale and exudative appearance, and a soft texture. Previous studies indicate that antemortem stress plays a key role in regulating protein acetylation and glycolysis in postmortem (PM) muscle. However, the underlying molecular and biochemical mechanism is not clearly understood yet. In this study, we investigated the relationship between antemortem and protein acetylation and glycolysis using murine longissimus dorsi muscle isolated from ICR mice and murine muscle cell line C2C12 treated with epinephrine hydrochloride. Because adrenaline secretion increases in stressed animals, epinephrine hydrochloride was intraperitoneally injected epinephrine into mice to simulate pre-slaughter stress in this study to facilitate experimental operations and save experimental costs. Our findings demonstrated that protein acetylation in pyruvate kinase M1 (PKM1) form is significantly reduced by antemortem, and the reduced acetylation subsequently leads to an increase in PKM1 enzymatic activity which causes increased glycolysis in PM muscle. By using molecular approaches, we identified lysine 141 in PKM1 as a critical residue for acetylation. Our results in this study provide useful insight for controlling or improving meat quality in the future.

Dietary supplementation of Eucommia leaf extract to growing-finishing pigs alters muscle metabolism and improves meat quality.

OBJECTIVE: The objective of this study was to investigate the influence of dietary supplementation of Eucommia ulmoides leaf extract (ELE) on muscle metabolism and meat quality of pigs with and without pre-slaughter transportation. METHODS: In a 43-day feeding experiment, a total of 160 pigs with an initial body weight 60.00±2.00 kg were randomly assigned into four groups in a completely randomized design with 10 replicates. Pigs in groups A and C were fed a basal diet and pigs in groups B and D were fed a basal diet supplemented with 0.5% ELE. Pigs were slaughtered with (group B and D) or without (group A and C) pre-slaughter transport. Muscle chemical composition, postmortem glycolysis, meat quality and muscle metabolome were analyzed. RESULTS: Dietary ELE supplementation had no effect on the proximate composition of porcine muscle, but increased free phenylalanine, proline, citruline, norvaline, and the total free amino acids in muscle. In addition, dietary ELE increased decanoic acid and eicosapentaenoic acid, but decreased heptadecanoic acid, oleic acid, trans-oleic acid, and monounsaturated fatty acids in muscle. Meat quality measurement demonstrated that ELE improved meat water holding capacity and eliminated the negative effects of pre-slaughter transport on meat cooking yield and tenderness. Dietary ELE reduced muscle glycolytic potential, inhibited glycolysis and muscle pH decline in the postmortem conversion of muscle to meat and increased the activity of citrate synthase in muscle. Metabolomics analysis by liquid chromatographic tandem mass spectrometric showed that ELE enhanced muscle energy level, regulated AMP-activated protein kinase (AMPK) signaling, modulated glycogenolysis/glycolysis, and altered the metabolism of carbohydrate, fatty acids, ketone bodies, amino acids, purine, and pyrimidine. CONCLUSION: Dietary ELE improved meat quality and alleviated the negative effect of preslaughter transport on meat quality by enhancing muscle oxidative metabolism capacity and inhibiting glycolysis in postmortem muscle, which is probably involved its regulation of AMPK.

Low-protein diets supplemented with glycine improves pig growth performance and meat quality: An untargeted metabolomic analysis.

For the purpose to improve meat quality, pigs were fed a normal diet (ND), a low protein diet (LPD) and a LPD supplemented with glycine (LPDG). Chemical and metabolomic analyses showed that LPD increased IMF deposition and the activities of GPa and PK, but decreased glycogen content, the activities of CS and CcO, and the abundance of acetyl-CoA, tyrosine and its metabolites in muscle. LPDG promoted muscle fiber transition from type II to type I, increased the synthesis of multiple nonessential amino acids, and pantothenic acid in muscle, which should contributed to the improved meat quality and growth rate. This study provides some new insight into the mechanism of diet induced alteration of animal growth performance and meat quality. In addition, the study shows that dietary supplementation of glycine to LPD could be used to improved meat quality without impairment of animal growth.

Duck breast muscle proteins, free fatty acids and volatile compounds as affected by curing methods.

The aim of this study was to investigate the effects of different curing methods on protein structure, protein and lipid oxidation, lypolysis and volatile compounds in duck breast meat. The results showed that compared to static brining and pulsed pressure salting, the vacuum tumbling curing significantly decreased the oxidation of proteins and lipids, and the surface hydrophobicity of proteins, increased α-helix structure but decreased the proportion of ß-sheet, and increased actomyosin dissociation, liplysis and the free fatty acid content in meat. Meanwhile, vacuum tumbling curing decreased the amount of volatile flavor compounds, hexanal, 2,3-octanone, and off-flavor compounds 1-octen-3-ol and 1-hexanol. This study suggests that concerns on healthiness and the sensory quality of processed meat products should be paid in the selection of curing methods and vacuum tumbling curing is superior in terms of both aspects.

Differences between cardiac and skeletal troponin interaction with the thin filament probed by troponin exchange in skeletal myofibrils.

Troponin (Tn) is the calcium-sensing protein of the thin filament. Although cardiac troponin (cTn) and skeletal troponin (sTn) accomplish the same function, their subunit interactions within Tn and with actin-tropomyosin are different. To further characterize these differences, myofibril ATPase activity as a function of pCa and labeled Tn exchange in rigor myofibrils was used to estimate Tn dissociation rates from the nonoverlap and overlap region as a function of pCa. Measurement of ATPase activity showed that skeletal myofibrils containing >96% cTn had a higher pCa 9 ATPase activity than, but similar pCa 4 activity to, sTn-containing myofibrils. Analysis of the pCa-ATPase activity relation showed that cTn myofibrils were more calcium sensitive but less cooperative (pCa50 = 6.14, nH = 1.46) than sTn myofibrils (pCa50= 5.90, nH = 3.36). The time course of labeled Tn exchange at pCa 9 and 4 were quite different between cTn and sTn. The apparent cTn dissociation rates were approximately 2-10-fold faster than sTn under all the conditions studied. The apparent dissociation rates for cTn were 5 x 10(-3) min(-1), 150 x 10(-3) min(-1), and 260 x 10(-3) min(-1), whereas for sTn they were 0.6 x 10(-3) min(-1), 88 x 10(-3) min(-1), and 68 x 10(-3) min(-1) for the nonoverlap region at pCa 9, nonoverlap region at pCa 4, and overlap region at pCa 4, respectively. Normalization of the apparent dissociation rates gives 1:30:50 for cTn compared with 1:150:110 for sTn (nonoverlap at pCa 9:nonoverlap at pCa 4:overlap at pCa 4) suggesting that calcium has a smaller influence, whereas strong cross-bridges have a larger influence on cTn dissociation compared with sTn. The higher cTn dissociation rate in the nonoverlap region and ATPase activity at pCa 9 suggest that it gives a less off or inactive thin filament. Analysis of the intensity ratio (after a short time of exchange) as a function of pCa showed that cTn had greater calcium sensitivity but lower cooperativity than sTn. In addition, the magnitude of the change in intensity ratio going from pCa 9 to 4 was less for cTn than sTn. These data suggest that the influence of calcium on cTn exchange is less than sTn even though calcium can activate ATPase activity to a similar extent in cTn compared with sTn myofibrils. This may be explained partially by cTn being less off or inactive at pCa 9. Modeling of the intensity profiles obtained after Tn exchange at pCa 5.8 suggest that the profiles are best explained by a model that includes a long-range cross-bridge effect that grades with distance from the rigor cross-bridge for both cTn and sTn.

Principles of gene editing techniques and applications in animal husbandry.

Gene editing techniques were developed chronologically, which include zinc finger nuclease, transcription activator-like effector nuclease and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas 9). In this review, the working principles of these techniques were first introduced, their advantages and disadvantages were then discussed, their application in animal husbandry were elaborated, and finally human concerns about gene editing were presented. Compared to the two former techniques, the third-generation gene editing technique CRISPR/Cas9 has higher targeting efficiency and accuracy, less off-target effect, lower cytotoxicity and lower costs for being easier for vector design and manipulation. Although some people may concern about social or ethical issues, the benefits of gene editing certainly overweigh its demerits. The three gene editing techniques have been successfully used to improve the production and quality of livestock products, animal fertility, resistance to diseases, and welfare in animal husbandry. With legislation and the development of gene editing technology per se, it anticipatable that gene editing will have a broader utilization and make our lives happier.

Fatty Acid Content, Flavor Compounds, and Sensory Quality of Pork Loin as Affected by Dietary Supplementation with l-arginine and Glutamic Acid.

To investigate the effect of functional amino acid on meat flavor and eating quality, 60 growing-finishing pigs (Duroc × Large White × Landrace) were dietarily supplemented with or without 1.0% l-arginine, glutamic acid, or l-arginine plus glutamic acid for 2 months. After animals were slaughtered, the muscle fatty acid profile, flavor compounds, and meat sensory quality were comparatively investigated. The results showed that dietary supplementation with arginine, glutamic acid, or arginine plus glutamic acid had little effect on free amino acids, no effect on 5'-nucleotides and meat sensory taste traits, but supplementation with arginine plus glutamic acid significantly increased (P < 0.05) fat accumulation and fatty acid content in muscle, increased (P < 0.05) the formation of multiple fatty acid oxidation-derived volatile compounds, and improved the tenderness, juiciness, and overall eating quality of meat. This study revealed that dietary supplementation with 1.0% l-arginine and glutamic acid could be used to improve meat eating quality in pork production.

Proteomic analysis reveals that lysine acetylation mediates the effect of antemortem stress on postmortem meat quality development.

To explore the involvement of protein lysine acetylation in the conversion of muscle to meat, a quantitative analysis of the acetylome in postmortem porcine muscle with or without antemortem stress was conducted. In total, 771 acetylpeptides containing 681 lysine acetylation sites mapping to 176 acetylproteins were identified. Acetylproteins were enriched in muscle contraction, carbohydrate metabolism, cell apoptosis and calcium signaling. Bioinformatic analysis suggests that preslaughter handling may be associated with glycolysis in postmortem muscle and the overall meat quality, via acetylation of multiple enzymes of glycogenolysis/glycolysis, regulate rigor mortis via acetylation of contractile, ATP production and calcium signaling-related proteins, and regulate stress response, cell apoptosis and meat tenderization via regulating the functions of heat shock proteins and permeability transition pore complex. This study provides the first overview of the acetylome in postmortem muscle as affected by preslaughter handling and broadens knowledge of the biochemistry regulating meat quality development.

Acetylome profiling reveals extensive involvement of lysine acetylation in the conversion of muscle to meat.

Protein lysine acetylation is an post-translational modification that regulates gene expression, metabolism, cell signaling, and diseases, but its implication in the postmortem (PM) meat quality development is basically unclear. In the present study, a quantitative proteomic analysis was conducted to profile acetylome in porcine muscle within 24 h PM. In total 595 acetylation sites assigned to 163 proteins were identified in porcine muscle, of which 460 sites distributing to 110 proteins significantly changed in acetylation levels in the conversion of muscle to meat. The dynamic acetylation/deacetylaion of muscle proteins was closely associated with critical chemical-biophysical changes in PM muscle. Bioinformatic analysis revealed that protein lysine acetylation likely regulated postmortem meat quality development by regulating glycolysis and muscle pH, cell stress reponse and apoptosis, muscle contraction and rigor mortis, calcium signaling and proteolysis, IMP synthesis and meat flavor development, and even the stability of pigment proteins and meat color. This study provided the first overview of protein lysine acetylation in PM muscle and revealed its significance in the conversion of muscle to meat. Future exploration of the exact role of protein lysine acetylation at specific sites will further our understanding regarding the underlying mechanisms and be helpful for meat quality control. SIGNIFICANCE: This is the first analysis of acetylome in farm animal and postmortem muscle. Our data showed that the dynamic acetylation/deacetylation of muscle proteins was closely related to the postmortem changes of muscle that affect the final quality of raw meat. Proteins related to glucose metabolism and muscle contraction were the two largest clusters of acetylproteins identified in postmortem porcine muscle. Networks of acetylproteins involved in apoptosis, calcium signaling and IMP synthesis were identified in postmortem porcine muscle at the same time. Our results revealed that protein lysine acetylation regulated the conversion of muscle to meat. It likely regulated meat quality development by regulating postmortem glycolysis, mitochondrion initiated cell apoptosis, calcium signaling, rigor mortis, meat flavor compound sysnthesis and meat tenderization. Our study broadened our understanding of the biochemistry regulating the postmortem conversion of muscle to meat and final meat quality development, which may be helpful for future meat quality control.

Role of leptin in the regulation of growth and carbohydrate metabolism in the ovine fetus during late gestation.

Leptin is an important regulator of appetite and energy expenditure in adulthood, although its role as a nutritional signal in the control of growth and metabolism before birth is poorly understood. This study investigated the effects of leptin on growth, carbohydrate metabolism and insulin signalling in fetal sheep. Crown-rump length-measuring devices and vascular catheters were implanted in 12 sheep fetuses at 105-110 days of gestation (term 145 +/- 2 days). The fetuses were infused i.v. either with saline (0.9% NaCl; n = 6) or recombinant ovine leptin (0.5-1.0 mg kg(-1) day(-1); n = 6) for 5 days from 125 to 130 days when they were humanely killed and tissues collected. Leptin receptor mRNA and protein were expressed in fetal liver, skeletal muscle and perirenal adipose tissue. Throughout infusion, plasma leptin in the leptin-infused fetuses was 3- to 5-fold higher than in the saline-infused fetuses, although plasma concentrations of insulin, glucose, lactate, cortisol, catecholamines and thyroid hormones did not differ between the groups. Leptin infusion did not affect linear skeletal growth or body, placental and organ weights in utero. Hepatic glycogen content and activities of the gluconeogenic enzymes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase in the leptin-infused fetuses were lower than in the saline-infused fetuses by 44, 48 and 36%, respectively; however, there were no differences in hepatic glycogen synthase activity or insulin signalling protein levels. Therefore, before birth, leptin may inhibit endogenous glucose production by the fetal liver when adipose energy stores and transplacental nutrient delivery are sufficient for the metabolic needs of the fetus. These actions of leptin in utero may contribute to the development of neonatal hypoglycaemia in macrosomic babies of diabetic mothers.

Compound C, an inhibitor of AMP-activated protein kinase, inhibits glycolysis in mouse longissimus dorsi postmortem.

Pale, soft, and exudative (PSE) meat has been recognized for decades and causes huge economic loss to the meat industry due to its inferior quality. Although it has been well established that fast and excessive glycolysis combined with high temperature in muscle early postmortem is the cause of PSE meat, the molecular mechanisms associated with this abnormal glycolysis remain poorly defined. Our previous studies with mice and pigs suggest that AMPK regulates muscle glycolysis postmortem. To confirm further the role of AMPK in the regulation of postmortem glycolysis, we investigated the effects of intraperitoneal injection of compound C, a specific AMPK inhibitor, on AMPK activation and glycolysis in postmortem longissimus dorsi (LD) muscle of mice. Data showed that intraperitoneal injection of compound C inhibited AMPK activation in postmortem mouse LD muscle. Simultaneously, injection of compound C inhibited glycolysis and increased muscle pH corroborating of our previous observations that postmortem glycolysis is inhibited in AMPK knockout mice. This study firmly supports that AMPK regulates glycolysis in postmortem skeletal muscle and suggests that AMPK can be a target to control postmortem glycolysis, preventing incidence of PSE meat.