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

EFFECTS OF CONTUSION AND EXHAUSTIVE EXERCISE ON MURF1 AND MAFBX IN THE SKELETAL MUSCLE OF RATS

ABSTRACT Objective To study the effects of contusion and exhaustive exercise on the expression of degradation-related factors MuRF1 and MAFbx in the skeletal muscle of rats and describe the repair mechanism of skeletal muscle injury. Methods Forty-two male SD rats were randomly divided into 7 groups. The rats in each group were killed at different time points (0h, 24h, 48h) after exhaustive exercise (E0, E24, E48) and contusion (D0, D24, D48), respectively, and in the resting state in control group (C). The right gastrocnemius muscles were resected and divided into two parts, one for the mRNAs of MuRF1 and MAFbx by real-time PCR, and the other for protein measurement by Western blotting. Results Compared with the control group, the MuRF1 mRNA and protein expression of the skeletal muscle in the E0 group was markedly increased (P <0.05) and followed by a downward trend in E24 the E48 groups. On the other hand, MuRF1 mRNA expression of the skeletal muscle in the D24 group was significantly upregulated (P <0.01), then decreased in the D48 group (P <0.01). Meanwhile, compared with the C group, MAFbx mRNA gene expression continued to be upregulated in D24 and D48 (P <0.05), but decreased in E24 and E48 (p<0.01). On the other hand, the NF-κB protein contents of the skeletal muscle in the D0, D24, and D48 groups, as well as in the E48 group, were markedly downregulated (P <0.05), and the one in E48 was also remarkably downregulated (P <0.05). Conclusion NF-κB may negatively regulate the process of protein degradation by the NF-κB / MuRF1 signal pathway. Level of evidence III; Therapeutic studies investigating the results of treatment.

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.

Adrenal stress hormone action in skeletal muscle during exercise training: An old dog with new tricks?

Exercise is a key component of a healthy lifestyle as it helps maintain a healthy body weight and reduces the risk of various morbidities and co-morbidities. Exercise is an acute physiological stress that initiates a multitude of processes that attempt to restore physiological homeostasis and promote adaptation. A component of the stress response to exercise is the rapid release of hormones from the adrenal gland including glucocorticoids, the catecholamines and aldosterone. While each hormone targets several tissues throughout the body, skeletal muscle is of interest as it is central to physical function and various metabolic processes. Indeed, adrenal stress hormones have been shown to elicit specific performance benefits on the muscle. However, how the acute, short-lived release of these stress hormones during exercise influences adaptations of skeletal muscle to long-term training remains largely unknown. Thus, the objective of this review was to briefly highlight the known impact of adrenal stress hormones on skeletal muscle metabolism and function (Old Dog), and critically examine the current evidence supporting a role for these endogenous hormones in mediating long-term training adaptations in skeletal muscle (New Tricks).

Feeding the Outer Bran Fraction of Rice Alters Hepatic Carbohydrate Metabolism in Rats

Dietary intake of fiber-rich food has been reported to contribute to multiple health benefits. The aim of the current study is to investigate the effects of a diet containing the outer bran fraction of rice (OBFR), which is rich in insoluble fiber, on the intestinal environment and metabolite profiles of rats. Fourteen 8-week-old male Sprague–Dawley rats were divided into a control group and an OBFR group. For a period of 21 days, the control group was fed a control diet, while the OBFR group was fed a diet containing 5% OBFR. Metabolomics analysis revealed drastic changes in the cecal metabolites of the rats fed the OBFR diet. Furthermore, in the plasma and liver tissue, the concentrations of metabolites involved in pyruvate metabolism, the pentose phosphate pathway, gluconeogenesis, or valine, leucine, isoleucine degradation were changed. Concordantly, the OBFR diet increased the expression of genes encoding enzymes involved in these metabolic pathways in the livers of the rats. Collectively, these results suggest that the OBFR diet altered the concentrations of metabolites in the cecal contents, plasma, and liver, and the hepatic gene expressions of rats, and that this may have mainly contributed to carbohydrate metabolism in the liver.

Insulin acutely increases glucose transporter 1 on plasma membranes and glucose uptake in an AKT-dependent manner in chicken adipocytes

Avian glucose transporters (GLUT) responsible for insulin-responsive glucose uptake into adipocytes remain poorly characterized. We aimed to identify the insulin-responsive GLUT using primary culture of chicken adipocytes. Acute stimulation with 1 μM insulin for 20 min increased 2-deoxyglucose uptake, AKT protein phosphorylation, and GLUT1 protein levels on the plasma membrane of the chicken adipocytes, whereas pretreatment with 10 μM triciribine, an AKT inhibitor, canceled these effects. Furthermore, the insulin stimulation did not affect GLUT12 protein levels on the plasma membrane of the chicken adipocytes. Our results suggest that GLUT1 is an insulin-responsive GLUT in chicken adipocytes.

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.

Regulation of Autophagy in Chick Myotubes: Effects of Insulin, Insulin-Like Growth Factor-I, and Amino Acids

Autophagy, an intracellular bulk protein degradation system in skeletal muscle, is increased under catabolic conditions resulting in muscle atrophy. This study aimed to investigate the effects of insulin, insulin-like growth factor (IGF)-I, and amino acids on autophagy (LC3-II content and expression of autophagy-related genes) in chick myotubes. Chick myotubes were incubated with insulin (1 µg/ml), IGF-I (100 ng/ml), and amino acids for 3 h. The LC3-II content, an index of autophagosome formation, and mRNA expression of LC3B and GABARAPL1 were significantly decreased by insulin. The LC3-II content, but not mRNA expression of autophagy-related genes, was also significantly decreased by IGF-I. The LC3-II content and LC3B mRNA level were also significantly decreased by amino acids. The mRNA expression of atrogin-1/MAFbx, a muscle-specific ubiquitin ligase, was also significantly decreased by insulin, IGF-I, and amino acids in chick myotubes. These results indicated that insulin, IGF-I, and amino acids regulate autophagy as well as the ubiquitin-proteasome proteolytic pathway in chick myotubes.

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.

Proteomic profiling reveals crucial retinal protein alterations in the early phase of an experimental glaucoma model

PURPOSE

Clinical glaucoma is difficult to assess in terms of molecular pathophysiology, prompting studies in experimental models of glaucoma. The purpose of this study was to investigate quantitative changes in retinal protein expression at the onset of experimental glaucoma in rats. Analyzing the proteome provides a suitable tool to decipher the pathophysiological processes in glaucomatous degeneration.

METHODS

Thermic cauterization of episcleral veins was utilized to elevate the intraocular pressure in Sprague Dawley rats. Morphological changes were surveyed on a cellular level with a staining of Brn3a-positive cells. The retinal nerve fiber layer was investigated using optical coherence tomography (OCT, Heidelberg Engineering) and the optic nerve was analyzed by an axonal grading system. Mass spectrometry-featured quantitative proteomics and immunohistochemical staining was used to identify specifically altered proteins in the course of intraocular pressure elevation and initial neurodegeneration. Proteomic data were further analyzed with Ingenuity Pathway Analysis and Cytoscape to analyze further molecular associations.

RESULTS

The intraocular pressure rose significantly (p < 0.001) for the follow-up period of 3 weeks after which animals were sacrificed. Eyes exposed to an elevated intraocular pressure showed an initial decrease of retinal ganglion cells, retinal nerve fiber layer (p < 0.05) and an impairment of the optic nerve (p < 0.01). Mass spectrometry led to the identification and quantification of 931 retinal proteins, whereas 32 were considerably altered. Bioinformatics-assisted clustering revealed that a majority of these proteins are functionally associated with cell differentiation, apoptosis and stress response. The creation of an interactive protein network showed that numerous altered proteins are connected regarding their cellular function. Protein kinase b, mitogen-activated protein kinase 1 and the NF-κB complex seem to be essential molecules in this context.

CONCLUSIONS

In conclusion, these results provide further lines of evidence that substantial molecular changes occur at the onset of the disease, identifying potential key players, which might be useful as biomarkers for diagnostics and development of medical treatment in the future.

Effects of Insulin-Like Growth Factor-I on the Expression of Atrogin-1/MAFbx in Chick Myotube Cultures

The expression of atrogin-1/MAFbx, a muscle-specific E3 ubiquitin ligase, is increased in catabolic conditions that result in muscle atrophy. The expression of atrogin-1/MAFbx mRNA is also decreased by the insulin-like growth factor-I (IGF-I) in mammalian skeletal muscle cell cultures. This study investigated the effect of IGF-I on the expression of atrogin-1/MAFbx in chicken skeletal muscle cell cultures. Chick myotubes were incubated with IGF-I for 1, 6, or 24 h. Protein content was increased by IGF-I (100 ng/ml) and incubated for 24 h in chick myotubes. The expression of atrogin-1/MAFbx mRNA decreased in the presence of IGF-I (1, 10, and 100 ng/ml) for 6 h in chick myotubes. The expression of the m-calpain large subunit and cathepsin B mRNA was not decreased by IGF-I. Phosphorylation of Akt and FOXO1 increased in the presence of IGF-I (100 ng/ml) for 1 h in chick myotubes. These results indicate that IGF-I suppresses atrogin-1/MAFbx mRNA expression by phosphorylation of Akt and FOXO1, resulting in an increase in muscle growth in chick myotube cultures.