The effects of intraperitoneal clenbuterol injection on protein degradation and myostatin expression differ between the sartorius and pectoral muscles of neonatal chicks

Effects of Amino Acid Supplementation to a Low-Protein Diet on the Growth Performance and Protein Metabolism-related Factors in Broiler Chicks

A low-protein (LP) diet may alleviate the environmental impact of chicken meat production by reducing nitrogen excretion and ammonia emissions. Thus, this study investigated the effect of a 15% reduced protein diet with or without amino acid (AA) supplementation on the growth performance of broiler chicks from 10 to 35 days of age and the underlying mechanism for loss of skeletal muscle mass. Thirty-six male broiler chicks were allocated to three experimental groups based on body weight: control, LP, and essential AA-supplemented LP (LP+AA). The body weight gain, feed conversion ratio, and weight of breast muscles and legs significantly decreased only in the LP group at the end of the feeding period. Plasma uric acid levels were significantly lower in the LP+AA group than those of the other groups. In the LP group, mRNA levels of microtubule-associated protein 1 light chain 3 isoform B were significantly higher in the pectoralis major, whereas those of atrogin-1, muscle RING-finger protein-1, and myoblast determination protein 1 were significantly higher in the biceps femoris compared to those in the control group. There were no significant differences in insulin-like growth factor 1 mRNA levels in the liver or skeletal muscle between groups. These findings suggested that supplementation with essential AAs ameliorated the impaired effects of an LP diet on growth performance in broiler chicks, and that the transcriptional changes in proteolytic genes in skeletal muscles might be related to the impaired effects of the LP diet.

Suppression of FoxO1 mRNA by β2 -adrenoceptor-cAMP signaling through miR-374b-5p and miR-7a-1-3p in C2C12 myotubes

β₂ -Adrenoceptor (β₂ -AR) signaling decreases the transcriptional activity of forkhead box O (FoxO), but the underlying mechanisms remain incompletely understood. Here, we investigated how β₂ -AR signaling regulates the protein abundance of FoxO and its transcriptional activity in skeletal muscle. We observed that stimulation of β₂ -AR with its selective agonist, clenbuterol, rapidly decreased FoxO1 mRNA expression, and this was accompanied by a decrease in either FoxO1 protein level or FoxO transcriptional activity. We subsequently observed that miR-374b-5p and miR-7a-1-3p were rapidly upregulated in response to β₂ -AR stimulation. Transfection with mimics of either miRNA successfully decreased FoxO1 mRNA. Moreover, because β₂ -AR stimulation increased cAMP concentration, pretreatment with an adenylyl cyclase inhibitor canceled out these effects of β₂ -AR stimulation. These results suggest that β₂ -AR stimulation results in rapid upregulation of miR-374b-5p and miR-7a-1-3p in myotubes, which in turn results in a decrease in FoxO1 mRNA expression via the β₂ -AR-cAMP signaling pathway.

Insight View on the Role of in Ovo Feeding of Clenbuterol on Hatched Chicks: Hatchability, Growth Efficiency, Serum Metabolic Profile, Muscle, and Lipid-Related Markers

Simple Summary

This study examined the effects of ovo injection of clenbuterol on fat deposition and growth performance in chickens, which is prejudicial to poultry consumers and muscle growth-related genes, egg hatchability, and fertility. The achieved result showed a definite effect of clenbuterol on body gain and hatchability. It decreased fat deposition and upregulation of muscle growth-related gene expressions accompanied by modulation of fatty and amino acid composition, reflecting a new insight into the intracellular pathways of clenbuterol supplementation on chicks.

Abstract

The present study aimed to assess the in ovo administration of clenbuterol on chick fertility, growth performance, muscle growth, myogenic gene expression, fatty acid, amino acid profile, intestinal morphology, and hepatic lipid-related gene expressions. In this study, 750 healthy fertile eggs from the local chicken breed Dokki-4 strain were analyzed. Fertile eggs were randomly divided into five experimental groups (150 eggs/3 replicates for each group). On day 14 of incubation, in addition to the control group, four other groups were established where 0.5 mL of worm saline (30 °C) was injected into the second group of eggs. In the third, fourth, and fifth groups, 0.5 mL of worm saline (30 °C), 0.9% of NaCl, and 10, 15, and 20 ppm of clenbuterol were injected into the eggs. Results suggested that clenbuterol increased growth efficiency up to 12 weeks of age, especially at 15 ppm, followed by 10 ppm, decreased abdominal body fat mass, and improved hatchability (p < 0.01). Clenbuterol also modulated saturated fatty acid levels in the breast muscles and improved essential amino acids when administered at 10 and 15 ppm. Additionally, clenbuterol at 15 ppm significantly decreased myostatin gene expression (p < 0.01) and considerably increased IGF1r and IGF-binding protein (IGFBP) expression. Clenbuterol administration led to a significant upregulation of hepatic PPARα, growth hormone receptor, and Lipoprotein lipase (LPL) mRNA expression with a marked decrease in fatty acid synthase (FAS) and sterol regulatory element-binding protein 1 (SREBP-1c) expression. In conclusion, the current study revealed that in ovo injection of clenbuterol showed positive effects on the growth of hatched chicks through reduced abdominal fat deposition, improved intestinal morphology, and modulation of hepatic gene expressions in myogenesis, lipogenesis, and lipolysis.

Differential regulation of protein synthesis by skeletal muscle type in chickens

In mammalian skeletal muscles, protein synthesis rates vary according to fiber types. We herein demonstrated differences in the regulatory mechanism underlying the protein synthesis in the pectoralis major (a glycolytic twitch muscle), adductor superficialis (an oxidative twitch muscle), and adductor profound (a tonic muscle) muscles of 14-day-old chickens. Under ad libitum feeding conditions, protein synthesis is significantly higher in the adductor superficialis muscle than in the pectoralis major muscle, suggesting that protein synthesis is upregulated in oxidative muscles in chickens, similar to that in mammals. In the pectoralis major muscle, fasting significantly inhibited the Akt/S6 pathway and protein synthesis with a corresponding decrease in plasma insulin concentration. Conversely, the insulin like growth factor-1 (IGF-1) mRNA levels significantly increased. These findings suggest that the insulin/Akt/S6 pathway plays an important role in the regulation of protein synthesis in the pectoralis major muscle. Interestingly, protein synthesis in the adductor superficialis muscle appears to be regulated in an Akt-independent manner, because fasting significantly decreased S6 phosphorylation and protein synthesis without affecting Akt phosphorylation. In the adductor profound muscle, IGF-1 expression, phosphorylation of Akt and S6, and protein synthesis were decreased by fasting, suggesting that insulin and/or skeletal IGF-1 appear contribute to protein synthesis via the Akt/S6 pathway. These findings revealed the differential regulation of protein synthesis depending on skeletal muscle types in chickens.

The β2-adrenergic receptor is involved in differences in the protein degradation level of the pectoral muscle between fast- and slow-growing chicks during the neonatal period

The aim of this study was to investigate whether β₂-AR mRNA expression is involved in either atrogin-1/MAFbx mRNA expression or protein degradation in chicken skeletal muscle by comparing fast- and slow-growing chicks during the neonatal period. Based on their body weight gain from 1 to 5 days of age, 5-day-old chicks (Gallus gallus domestics) were divided into a slow-growing and a fast-growing group, the mean weight gains of which were 6.3 ± 1.3 g/day and 11.3 ± 0.9 g/day, respectively. The ratio of pectoral muscle weight to total body weight was higher in the fast-growing group of chicks than in the slow-growing group. In addition, the plasma 3-methylhistidine concentration, an index of protein degradation in skeletal muscle, was significantly lower in the fast-growing than in the slow-growing chicks. The mRNA expression of β₂-AR, which we previously found is involved in decreasing muscle protein degradation by suppression atrogin-1/MAFbx mRNA expression, was significantly higher in the pectoral muscle of the fast-growing group compared with that of the slow-growing group. Concordantly, lower mRNA expression of atrogin-1/MAFbx was observed in the pectoral muscle of the fast-growing chicks. However, in the sartorius muscle, which is a muscle in the thigh, the ratio of the muscle weight to total body weight was not significantly different between the two groups of chicks at 5 days of age. In addition, there was no significant difference in the mRNA expressions of β₂-AR and atrogin-1/MAFbx in the sartorius muscle between these two groups. These results suggest that β₂-AR expression levels might be physiologically significant in the control of protein degradation in the pectoral muscle of neonatal chicks.

Identification of transcriptional biomarkers by RNA-sequencing for improved detection of β2-agonists abuse in goat skeletal muscle

In this paper, high-throughput RNA-sequencing (RNA-seq) was used to search for transcriptional biomarkers for β₂-agonists. In combination with drug mechanisms, a smaller group of genes with higher detection accuracy was screened out. Unknown samples were first predicted by this group of genes, and liquid chromatograph tandem mass spectrometer (LC-MS/MS) was applied to positive samples to validate the biomarkers. The results of principal component analysis (PCA), hierarchical cluster analysis (HCA) and discriminant analysis (DA) indicated that the eight genes screened by high-throughput RNA-seq were able to distinguish samples in the experimental group and control group. Compared with the nine genes selected from an earlier literature, 17 genes including these nine genes were proven to have a more satisfactory effect, which validated the accuracy of gene selection by RNA-seq. Then, six key genes were selected from the 17 genes according to the variable importance in projection (VIP) value of greater than 1. The test results using the six genes and 17 genes were similar, revealing that the six genes were critical genes. By using the six genes, three positive samples possibly treated with drugs were screened out from 25 unknown samples through DA and partial least squares discriminant analysis (PLS-DA). Then, the three samples were verified by a standard method, and mapenterol was detected in a sample. Therefore, the six genes can be used as biomarkers to detect β₂-agonists. Compared with the previous study, accurate detection of β₂-agonists abuse using six key genes is an improvement method, which show great significance in the monitoring of β₂-agonists abuse in animal husbandry.

β1- and β2-adrenergic receptor stimulation differ in their effects on PGC-1α and atrogin-1/MAFbx gene expression in chick skeletal muscle

Adrenaline changes expression of the genes encoding peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), which is known as a regulator of muscle size, and atrogin-1/muscle atrophy F-box (MAFbx), which is a muscle-specific ubiquitin ligase. However, the subtype of β-adrenergic receptor (β-AR) involved in regulating these genes in skeletal muscle is not yet well defined. In this study, the effects of intraperitoneal injection of adrenaline and three β_1-3-AR selective agonists on chick skeletal muscle metabolism were examined, to evaluate the functions of β-AR subtypes. Adrenaline decreased atrogin-1/MAFbx mRNA levels accompanied by an increase in PGC-1α mRNA and protein levels. However, among the three selective agonists, only the β₁-AR agonist, dobutamine, increased PGC-1α mRNA and protein levels, while the β₂-AR agonist, clenbuterol, suppressed atrogin-1/MAFbx mRNA levels. In addition, preinjection of the β₁-AR antagonist, acebutolol, and the β₂-AR antagonist, butoxamine, inhibited the adrenaline-induced increase in PGC-1α mRNA levels and the decrease in atrogin-1/MAFbx mRNA levels, respectively. Compared with adrenaline administration, the β₃-AR agonist, BRL37344, decreased PGC-1α mRNA levels and increased atrogin-1/MAFbx mRNA levels. These results suggest that, in chick skeletal muscle, PGC-1α is induced via the β₁-AR, while atrogin-1/MAFbx is suppressed via the β₂-AR.

Clenbuterol changes phosphorylated FOXO1 localization and decreases protein degradation in the sartorius muscle of neonatal chicks

To investigate the intracellular signaling mechanisms by which clenbuterol reduces muscle protein degradation, we examined the phosphorylation level and intracellular localization of FOXO1 in the sartorius muscle of neonatal chicks. One-day-old chicks were given a single intraperitoneal injection of clenbuterol (0.1 mg/kg body weight). Three hours after injection, AKT protein was phosphorylated in the sartorius muscle by clenbuterol injection. Coincidentally, clenbuterol increased cytosolic level of phosphorylated FOXO1 protein, while it decreased nuclear level of FOXO1 protein in the sartorius muscle. Furthermore, clenbuterol decreased the expression of mRNAs for muscle-specific ubiquitin ligases (atrogin-1/MAFbx and MuRF1) in the sartorius muscle accompanied by decreased plasma 3-methylhistidine concentration, an index of muscle protein degradation, at 3 h after injection. These results suggested that, in the sartorius muscle of the chicks, clenbuterol changed the intracellular localization of phosphorylated FOXO1, and consequently decreased protein degradation via suppressing the expression of genes encoding muscle-specific ubiquitin ligases.

Time-course changes in muscle protein degradation in heat-stressed chickens: Possible involvement of corticosterone and mitochondrial reactive oxygen species generation in induction of the ubiquitin-proteasome system

Heat stress (HS) induces muscle protein degradation as well as production of mitochondrial reactive oxygen species (ROS). In the present study, to improve our understanding of how protein degradation is induced by HS treatment in birds, a time course analysis of changes in the circulating levels of glucocorticoid and N(τ)-methylhistidine, muscle proteolysis-related gene expression, and mitochondrial ROS generation, was conducted. At 25 days of age, chickens were exposed to HS conditions (33 °C) for 0, 0.5, 1 or 3 days. While no alteration in plasma N(τ)-methylhistidine concentration relative to that of the control group was observed in the 0.5 day HS group, the concentration was significantly higher in the 3-d HS treatment group. Plasma corticosterone concentrations increased in response to 0.5-d HS treatment, but subsequently returned to near-normal values. HS treatment for 0.5 days did not change the levels of μ-calpain, cathepsin B, or proteasome C2 subunit mRNA, but increased the levels of mRNA encoding atrogin-1 (P<0.05) and its transcription factor, forkhead box O3 (P=0.09). Under these hyperthermic conditions, mitochondrial superoxide production was significantly increased than that of thermoneutral control. Here, we show that HS-induced muscle protein degradation may be due to the activation of ubiquitination by atrogin-1, and that this process may involve mitochondrial ROS production as well as corticosterone secretion.

Single injection of clenbuterol into newly hatched chicks decreases abdominal fat pad weight in growing broiler chickens

The aim of the current study was to examine the effects of clenbuterol injection into newly hatched chicks on both the abdominal fat pad tissue weight and the skeletal muscle weight during subsequent growth. Twenty-seven 1-day-old chicks were divided into two groups, receiving either a single intraperitoneal (i.p.) injection of clenbuterol (0.1 mg/kg body weight) or phosphate-buffered saline (PBS). Body weight gain, feed intake and feed conversion ratio were not affected by clenbuterol injection during the 5-week experimental period, while the abdominal fat pad tissue weight of the clenbuterol-injected chicks was lower than that of the control chicks at 5 weeks post-injection. Plasma non-esterified fatty acid concentrations were significantly increased in the clenbuterol-injected chicks, while plasma triacylglycerol concentrations did not differ. Additionally, the enzymatic activity of fatty acid synthase was lower in the liver of the clenbuterol-injected chicks. Conversely, the skeletal muscle weights were not affected by clenbuterol injection. These results suggest that a single clenbuterol injection into 1-day-old chicks decreases the abdominal fat pad tissue weight, but may not affect skeletal muscle weights during growth. © 2015 Japanese Society of Animal Science.

Mechanisms underlying enhancements in muscle force and power output during maximal cycle ergometer exercise induced by chronic β2-adrenergic stimulation in men

The study was a randomized placebo-controlled trial investigating mechanisms by which chronic β2-adrenergic stimulation enhances muscle force and power output during maximal cycle ergometer exercise in young men. Eighteen trained men were assigned to an experimental group [oral terbutaline 5 mg/30 kg body weight (bw) twice daily (TER); n = 9] or a control group [placebo (PLA); n = 9] for a 4-wk intervention. No changes were observed with the intervention in PLA. Isometric muscle force of the quadriceps increased ( P ≤ 0.01) by 97 ± 29 N (means ± SE) with the intervention in TER compared with PLA. Peak and mean power output during 30 s of maximal cycling increased ( P ≤ 0.01) by 32 ± 8 and 25 ± 9 W, respectively, with the intervention in TER compared with PLA. Maximal oxygen consumption (V̇o2max) and time to fatigue during incremental cycling did not change with the intervention. Lean body mass increased by 1.95 ± 0.8 kg ( P ≤ 0.05) with the intervention in TER compared with PLA. Change in single fiber cross-sectional area of myosin heavy chain (MHC) I (1,205 ± 558 μm2; P ≤ 0.01) and MHC II fibers (1,277 ± 595 μm2; P ≤ 0.05) of the vastus lateralis muscle was higher for TER than PLA with the intervention, whereas no changes were observed in MHC isoform distribution. Expression of muscle proteins involved in growth, ion handling, lactate production, and clearance increased ( P ≤ 0.05) with the intervention in TER compared with PLA, with no change in oxidative enzymes. Our observations suggest that muscle hypertrophy is the primary mechanism underlying enhancements in muscle force and peak power during maximal cycling induced by chronic β2-adrenergic stimulation in humans.

Single injection of the β2-adrenergic receptor agonist, clenbuterol, into newly hatched chicks alters abdominal fat pad mass in growing birds

Excessive energy is stored in white adipose tissue as triacylglycerols in birds as well as in mammals. Although β2-adrenergic receptor agonists reduce adipose tissue mass in birds, the underlying mechanism remains unclear. The aim of the current study was to examine the effects of a single intraperitoneal injection of the β2-adrenergic receptor agonist, clenbuterol, on the abdominal fat pad tissue development. Thirty-three chicks at 1-day-old were given a single intraperitoneal injection of clenbuterol (0.1mg/kg body weight) or phosphate-buffered saline. At 2 weeks post-dose, the weight of the abdominal fat tissue was decreased in the clenbuterol-injected chicks, and small adipocyte-like cells were observed in the abdominal fat pad tissue of the clenbuterol-injected chicks. Then, the expression of mRNAs encoding genes related to avian adipogenesis was examined in the abdominal fat pat tissue. The expression of mRNAs encoding Krüppel-like zinc finger transcription factor 5 (KLF-5), KLF-15, and zinc finger protein 423 in the abdominal fat pad tissue of the clenbuterol-injected chicks was significantly lower (P<0.05) than that of the control chicks, while the expression of mRNA encoding peroxisome proliferator-activated receptor-gamma was not affected. In addition, both mRNA expression (P<0.05) and enzymatic activity (P<0.05) of fatty acid synthase (FAS) were decreased in the abdominal fat pad tissue of the clenbuterol-injected chicks, while clenbuterol injection did not affect FAS activity in liver. These results suggested that a single injection with clenbuterol into newly hatched chicks reduces their abdominal fat pad mass possibly via disrupting adipocyte development during later growth stages.