Starvation leads to decreased levels of mRNA for myofibrillar proteins

Characterization and expression of a myosin heavy-chain isoform in juvenile walleye Sander vitreus

In this study, myosin, the major component of myofibrillar protein in the skeletal muscle, was characterized and its expression was monitored during growth in juvenile walleye Sander vitreus. First, the coding region of myosin heavy chain (MyHC) from the fast skeletal muscle of walleye was amplified by long-distance PCR using a full-length cDNA. Phylogenetic analysis was used to determine the evolutionary relationship of this S. vitreus myosin sequence to other vertebrate myosin sequences. Next, it was established that the myosin isoform was most prevalent in the white muscle, compared with the red and cardiac muscle. Myosin expression was monitored over a series of experiments designed to influence growth. Specifically, change in MyHC mRNA was monitored after acute changes in feeding. Fish exposed to a one-week fasting period showed significant decreases in MyHC mRNA levels by the end of the fast. The effect of feeding was also examined more closely over a 24 h period after feeding, but results showed no significant change in myosin expression levels through this time period. Finally, fish with higher growth rates had higher MyHC mRNA and protein expression levels. This study indicates that MyHC mRNA expression is sensitive to the factors that may influence growth in juvenile S. vitreus.

Patterns of gene expression in atrophying skeletal muscles: response to food deprivation

During fasting and many systemic diseases, muscle undergoes rapid loss of protein and functional capacity. To define the transcriptional changes triggering muscle atrophy and energy conservation in fasting, we used cDNA microarrays to compare mRNAs from muscles of control and food-deprived mice. Expression of >94% of genes did not change, but interesting patterns emerged among genes that were differentially expressed: 1) mRNAs encoding polyubiquitin, ubiquitin extension proteins, and many (but not all) proteasome subunits increased, which presumably contributes to accelerated protein breakdown; 2) a dramatic increase in mRNA for the ubiquitin ligase, atrogin-1, but not most E3s; 3) a significant suppression of mRNA for myosin binding protein H (but not other myofibrillar proteins) and IGF binding protein 5, which may favor cell protein loss; 4) decreases in mRNAs for several glycolytic enzymes and phosphorylase kinase subunits, and dramatic increases in mRNAs for pyruvate dehydrogenase kinase 4 and glutamine synthase, which should promote glucose sparing and gluconeogenesis. During fasting, metallothionein mRNA increased dramatically, mRNAs for extracellular matrix components fell, and mRNAs that may favor cap-independent mRNA translation rose. Significant changes occurred in mRNAs for many growth-related proteins and transcriptional regulators. These transcriptional changes indicate a complex adaptive program that should favor protein degradation and suppress glucose oxidation in muscle. Similar analysis of muscles atrophying for other causes is allowing us to identify a set of atrophy-specific changes in gene expression.

Semi-starvation alters myofibrillar mRNA concentrations to expedite rapid recovery of muscle protein stores following feeding

BACKGROUND

Protein synthesis in skeletal muscle is reduced following starvation and restored by feeding. The mediators and mechanisms are incompletely understood. The aim of this study was to evaluate whether prolongation of undernutrition induced changes in muscle gene expression at the level of mRNA and protein.

MATERIALS AND METHODS

The changes in myosin heavy-chain 2X mRNA in adult partially starved (50% of ad libitum standard rodent chow intake for 4 or 7 days) C57BL mice or subsequently refed mice were studied. Ad libitum-fed mice were used as controls. Protein synthesis, total RNA and myosin heavy-chain 2X mRNA concentrations were determined. Plasma concentrations of amino acids were measured by high-performance liquid chromatography.

RESULTS

Partial starvation of 4 and 7 days reduced bodyweight by 15.6 +/- 1% and 17.1 +/- 2.1% (P < or = 0.05) vs. ad libitum fed controls. Protein synthesis was reduced by 32 +/- 9% and protein content by 20 +/- 4% (P < or = 0.05) following 7 days of partial starvation. Plasma amino acid concentrations were increased (6297 +/- 853) in refed animals vs. ad libitum-fed controls (3057 +/- 141, P < or = 0.05). Total RNA concentration (micrograms RNA micrograms(-1) DNA) in skeletal muscle was unchanged. Myosin heavy-chain 2X mRNA concentration did not change following 4 days of partial starvation but increased by 24 +/- 5% (P < or = 0.05) following 7 days of partial starvation, hence suggesting that expression of myosin mRNA was nutritionally altered.

CONCLUSION

Postprandial stimulation of protein synthesis following starvation may thus be a combination of increased mRNA availability and increased translation. This effect may be activated by peak concentrations of amino acids in plasma following feeding.

Neurotoxin 6-aminonicotinamide affects levels of soluble proteins and enzyme activities in various tissues of golden hamsters

The effects of neurotoxin 6-aminonicotinamide (6-AN) on the levels of soluble proteins and enzyme activities in various tissues of golden hamsters were investigated. SDS-polyacrylamide gel electrophoresis showed that a soluble spinal cord protein with molecular mass 75.0 kDa was present at a higher concentration in the treated group compared to that in the control while that of a molecular mass 64.8 kDa appeared to be missing. However, there were no noticeable differences in protein concentrations observed with the cerebrum, brain stem, and cerebellum. Similarly, treatment with 6-AN decreased the concentration of a soluble protein in pectoral muscle having molecular mass 97.2 kDa and increased those having molecular masses 207.4 and 32.1 kDa. In the kidney, soluble proteins with molecular masses 176.6 kDa was missing and those of molecular masses 97.6, 49, 43.3, and 33.8 kDa were decreased whereas those of molecular masses 64.7 and 33.1 kDa were increased. In the testis the soluble proteins with molecular masses 125.4, 88.7, 69.0, 31.2, 19.1, and 17.4 kDa were missing and those of molecular masses 97.0, 51.3, 42.0, 33.0, 27.2, and 22.6 kDa were present in lower amounts whereas those of molecular masses 311.5, 75.0, 64.0, 54.1, and 53.2 kDa were present in higher amounts. The specific activity of 6-phosphogluconate dehydrogenase was markedly increased in the liver but that of other tissues was not affected. Acetylcholinesterase activity was markedly reduced in the spleen but was enhanced in the intestine. Monoamine oxidase activity was markedly reduced in the brain stem, cerebrum, kidney, and liver. The results suggest that the changes in levels of soluble proteins and enzyme activities shown with golden hamster tissues by 6-AN administration were quite different from those shown with quail tissues.

Provision of rhIGF-I/IGFBP-3 complex attenuated development of cancer cachexia in an experimental tumor model

Tumor growth is associated with development of cachexia which includes progressive wasting and anorexia. Our previous studies have indicated that insulin like growth factor-I (rhIGF-I) in complex with its binding protein 3 (IGFBP 3), but not free IGF-I, was a potent stimulator of muscle protein synthesis in rats with chronic undernutrition. The aim of the present study was to evaluate the effect of rhIGF-I/IGFBP-3 on the development of cancer cachexia, and to assess safety data on net tumor growth and progression during treatment.

METHODS

A methylcholantrene induced sarcoma was implanted s.c. in C 57 bl mice. The animals were provided with rhIGF-I/rhIGFBP-3 (5 microg/g bw) i.v. twice daily (n= 18). Controls were provided with saline (n= 20). Body weight and food intake were registered daily. Net tumor growth was measured over 10 days. Protein synthesis in liver and muscle, as well as plasma concentrations of glucose, insulin, IGF-I and amino acids were measured at the end of the study.

RESULTS

tumor size did not differ between control mice and rhIGF-I/rhIGFBP-3 treated mice (1.5 +/- 0.1 g wet tumor weight vs 1.6 +/- 0.2 g respectively). Saline treated tumor bearing controls lost 9.1 +/- 1.3 % body weight over 10 days due to rapid tumor growth while rhIGF-I/rhIGFBP-3 provision attenuated weight loss to 5.6 +/- 1.3% of body weight in study mice (P< 0.05). Food intake was improved and blood glucose concentration was reduced from 7.1 +/- 0.5 to 5.8 +/- 0.2 (P< 0.05) in response to treatment.

CONCLUSION

Our results demonstrate that rhIGF-I/rhIGFBP-3 complex did not affect net tumor growth. Moreover rhIGF-I/rhIGFBP-3 complex improved tumor-host nutritional state by improving food intake, attenuating weight loss and improving glucose metabolism.

Postprandial resynthesis of myofibrillar proteins is translationally rather than transcriptionally regulated in human skeletal muscle

Feeding stimulates protein synthesis in skeletal muscles, although the regulatory mechanisms are incompletely understood. The aim of this study was to determine whether this could be detected at the gene transcription level for postprandial stimulation of the synthesis of muscle proteins. Healthy male volunteers were investigated after an overnight fast. Open muscle biopsies were performed in the starved state and 3 h after meal intake, consisting of 0.15 gN/kg, 12 kcal/kg. Blood samples were drawn every 15 to 30 min for 5 h. Myosin mRNA and insulin growth factor-I (IGF-I) mRNA were measured by solution hybridization assay in homogenized muscle specimens. After food intake, plasma glucose concentrations increased from 5.0 +/- 0.1 to 7.3 +/- 0.3 (P < or = 0.001), and insulin concentration rose from 3.8 +/- 0.5 mU/L before to 75.3 +/- 11.4 15 min after the meal (P < or = 0.001). Plasma concentration of free fatty acids declined after food intake (P < or = 0.001). Plasma concentrations of amino acids increased from basal values (2864 +/- 128 microM) to 4419 +/- 262 microM (P < or = 0.05) 90 min after meal ingestion. Myosin mRNA concentration in the biopsied muscle tissue was higher during starvation and was reduced by 20% after food intake: 10.8 +/- 1.3 amol mRNA/microgram DNA in the starved state and 8.5 +/- 1.3 amol mRNA/microgram DNA after food intake (P < or = 0.05). Feeding did not alter IGF-I mRNA concentrations in muscle: 0.51 +/- 0.05 and 0.55 +/- 0.06 amol/microgram DNA in the starved and fed state, respectively (P < or = 0.48). Improved protein balance by stimulation of protein synthesis has been related to increased plasma amino acids. Interestingly, in the short term, this was not related to increases in gene transcription of either myofibrillar proteins (myosin) or muscle IGF-I. Thus, postprandial stimulation of protein synthesis appears not to be regulated by increased gene transcription but by increased translation using the increased concentrations of amino acids. In contrast, as far as the 2X myosin mRNA level is concerned, this is enhanced during starvation, which facilitates rapid recovery once the availability of substrate is resumed.

Effects of 6-aminonicotinamide on levels of soluble proteins and enzyme activities in various tissues of Japanese quail

The effects of 6-aminonicotinamide (6-AN) on the levels of soluble proteins and enzyme activities in various tissues of Japanese quail were investigated. SDS-polyacrylamide gel electrophoresis showed that the soluble proteins with molecular masses corresponding to 160.4 and 52.5 kDa were either missing or present at lower concentrations in the brain of the 6-AN treated group compared to those in the control group. The soluble liver proteins with molecular masses 200, 120 and 70.5 kDa were missing in the treated group compared to those in the control while those of a molecular mass 15.1 kDa were found to be present at higher concentrations. Similarly, treatment with 6-AN decreased the concentration of soluble proteins in pectoral muscle with molecular masses 92.3, 54.5, 43.5, 41.2, 34.5, 27.5, 20.1 and 17.5 kDa and increased those with molecular masses 96.5, 37.7, 25.0, 19.3, 16.6, 13.8 and 10.8 kDa. In the heart, soluble proteins with molecular mass 84.6 kDa were increased. There was a marked reduction in the treatment group in the concentration of NAD in pectoral muscle but not in other tissues. A similar observation was also made with total RNA levels. The specific activity of malic enzyme was markedly increased by 6-AN treatment in the kidney and pectoral muscle but reduced in the liver. 6-Phosphogluconate dehydrogenase and lactate dehydrogenase activities were markedly reduced in the liver. Glyceraldehyde-3-phosphate dehydrogenase activity was significantly decreased in liver and pectoral muscle. NAD glycohydrolase activity was markedly decrease in pectoral muscle. Acetylcholinesterase activity was markedly reduced in liver but was enhanced in pectoral muscle. The results suggest that the metabolic actions of 6-AN are specific for certain proteins in the liver and muscle with the effect being most pronounced in muscle. The effects are also quite distinct from those by its analogue 3-acetylpyridine.

The effect of endotoxin on skeletal muscle protein gene expression in the rat

Sepsis is associated with net breakdown of skeletal muscle protein, mediated partly by reduced rates of muscle protein synthesis. This study investigated the role of altered gene expression for specific muscle proteins in mediating reduced protein synthesis in a rat model of acute severe sepsis. Adult rats were given a single sublethal intraperitoneal dose of endotoxin (bacterial lipopolysaccharide). Protein, RNA and DNA contents of muscle were measured and changes in expression of mRNA in tibialis anterior and extensor digitorum longus muscles were detected by quantification of Northern blots at 6, 24, 48 and 72 hr after endotoxin and in animals starved for 24 hr. Results showed that at 24 hr after endotoxin there was a loss of about 14% of muscle protein content. No reduction in mRNA was found at any time point for beta-myosin heavy chain (MHC), fast-MHC, alpha-actin, skeletal muscle troponin or carbonic anhydrase III (CA III); rather, at 48 hr there was increased expression of beta-MHC (224 +/- 123% control) and CA III (202 +/- 56%). Blocking TNF-alpha by pre-treatment with a monoclonal antibody did not appear to influence this. Total RNA content of muscle was reduced to 67% of the control values 24 hr after LPS, although this was no different to pair-fed animals starved for 24 hr. It is concluded that reduced protein synthesis in skeletal muscle in early acute sepsis is not primarily associated with reduced muscle protein gene expression.

Effect of prolonged starvation on the activities of malic enzyme and acetylcholinesterase in tissues of Japanese quail

During starvation muscle protein degradation is increased but the mechanism for this is uncertain. In this study Japanese quail were starved for 5 days and the activities of malic enzyme and acetylcholinesterase were determined in various tissues. SDS-polyacrylamide gel electrophoresis showed that the soluble proteins with molecular weights corresponding to 160, 120, 108, 99 and 38 kDa were absent in the liver of the starved group. In the pectoral muscle the soluble proteins with molecular weights corresponding to 69, 41 and 34 kDa were missing. The activity of malic enzyme in the liver, heart and pectoral muscle of the starved group decreased markedly whereas that of acetylcholinesterase increased markedly in the pectoral muscle (P < 0.005). It is concluded that in prolonged starvation acetylcholinesterase synthesis may be induced in tissues being subjected to protein catabolism and that this enzyme may be involved as a protease in protein degradation.

Sepsis-induced myofibrillar protein catabolism in rat skeletal muscle

This study evaluated sepsis-induced changes in myosin heavy chain (Mhc) protein breakdown and synthesis in rat soleus muscles. Rats were anesthetized and their external jugular veins were cannulated. After 12-16 h, rats were implanted intraabdominally with a sterile fecal pellet, or a pellet containing bacteria (Escherichia coli, 150 CFU and Bacteroides fragilis 10(4) CFU). Thirty hours after implantations, rats were infused with 14C-Leu (60 x 10(3) Bq/h) through the jugular cannula for 4 h. Protein fractional synthetic rate coefficient (FSRC) was determined in muscles of different rat groups. In separate experiments, intact soleus muscles were removed from the three rat groups on days 1 and 2 after implantations, and processed for their wet weight, total protein and Mhc contents. No mortality occurred in sterile-implanted rats. Approximately 40-45% of all septic-implanted rats died on days 1-3, post-implantation. Whereas an approximately 15% (P < 0.01, days 1 or 2) decrease occurred in Mhc content in sterile-implanted rats compared to unoperated controls, septic insult resulted in a greater Mhc loss (a 27% decrease, P < 0.001). Rats' body weight, soleus wet weight and tolat muscle protein changes with sepsis relative to controls were also greater than in the sterile groups. The FSRC value in the septic-implanted rats was significantly lower (P < 0.05) than in non-septic rat muscle. TNF-alpha administration to the septic animals or their treatment with diltiazem did not have a significant effect on FSRC. Overall, these results indicate myosin as a major muscle protein subjected to net catabolism during sepsis, and that the net catabolic response was related to a more pronounced increased in Mhc degradation than the decrease in Mhc synthesis.

Experimental and clinical applications of molecular cell biology in nutrition and metabolism

Rapid advances in molecular biology have yielded important new techniques for understanding the cellular mechanisms of normal homeostasis and disease. In particular, molecular laboratory methodologies have become important investigative tools for nutritional studies. Detection techniques for specific DNAs, RNAs, and proteins allow direct examination of cellular regulation of protein expression in health and illness. Construction of transgeneic models by recent techniques of inserting foreign genes into experimental animals has provided novel models for studies of cellular metabolism. In addition, molecular biology has had impact on clinical nutrition and therapy. Molecular techniques not only allow for early diagnosis of many inborn genetic errors of metabolism, recombinant technology has also provided for large-scale production of proteins and hormones of potential therapeutic value. The possibility for direct gene therapies is also nearing reality. Hence, understanding the language of molecular biology and the recent developments in this field is not only of research interest, but is also of clinical relevance.

Can protein-calorie malnutrition cause dysphagia?

Nutrient deprivation has previously been shown to cause alterations in muscle and nerve function. Although an effect has never been studied in the neuromusculature of deglutition, the authors argue that an effect is likely. The proposed result is an increase in swallowing impairment in dysphagic individuals and associated risk of aspiration. Research studying the relationship between malnutrition and dysphagia is needed to verify clinical significance. Until controlled studies are completed, the authors suggest alternative alimentation in repleting severely malnourished dysphagic patients prior to attempting oral diet. A review of nutritional status indices is included to aid in identifying dysphagic patients at nutritional risk. Early identification of nutritional compromise and intervention can prevent malnutrition and its deleterious effects.

Reduced levels of mRNA for myofibrillar proteins in skeletal muscle from septic rats

The influence of sepsis on transcription of myofibrillar proteins in skeletal muscle was studied in rats. Sepsis was induced by cecal ligation and puncture (CLP); control rats were sham-operated. Sixteen hours later, muscle levels of mRNA for myofibrillar proteins were determined by using cDNA probes specific for transcripts for alpha actin and myosin heavy chain. Sepsis resulted in a 2-6 fold decrease in alpha actin mRNA levels and an even more pronounced reduction in myosin heavy chain mRNA levels. Results suggest that sepsis-induced reduction of muscle protein synthesis is at least partly regulated at the transcriptional level.