Cardiac myosin motor deficits are associated with left ventricular dysfunction in human ischemic heart failure.

During ischemic heart failure (IHF), cardiac muscle contraction is typically impaired, though the molecular changes within the myocardium are not fully understood. Thus, we aimed to characterize the biophysical properties of cardiac myosin in IHF. Cardiac tissue was harvested from 10 age-matched males, either with a history of IHF or nonfailing (NF) controls that had no history of structural or functional cardiac abnormalities. Clinical measures before cardiac biopsy demonstrated significant differences in measures of ejection fraction and left ventricular dimensions. Myofibrils and myosin were extracted from left ventricular free wall cardiac samples. There were no changes in myofibrillar ATPase activity or calcium sensitivity between groups. Using isolated myosin, we found a 15% reduction in the IHF group in actin sliding velocity in the in vitro motility assay, which was observed in the absence of a myosin isoform shift. Oxidative damage (carbonylation) of isolated myosin was compared, in which there were no significant differences between groups. Synthetic thick filaments were formed from purified myosin and the ATPase activity was similar in both basal and actin-activated conditions (20 µM actin). Correlation analysis and Deming linear regression were performed between all studied parameters, in which we found statistically significant correlations between clinical measures of contractility with molecular measures of sliding velocity and ELC carbonylation. Our data indicate that subtle deficits in myosin mechanochemical properties are associated with reduced contractile function and pathological remodeling of the heart, suggesting that the myosin motor may be an effective pharmacological intervention in ischemia.NEW & NOTEWORTHY Ischemic heart failure is associated with impairments in contractile performance of the heart. This study revealed that cardiac myosin isolated from patients with ischemic heart failure had reduced mechanical activity, which correlated with the impaired clinical phenotype of the patients. The results suggest that restoring myosin function with pharmacological intervention may be a viable method for therapeutic intervention.

[Clinical characteristics of SLC35A2 gene variants related congenital disorders of glycosylation typeâ ¡].

Objective: To summarize the clinical characteristics of children with SLC35A2 gene variants related congenital disorders of glycosylation (SLC35A2-CDG), so as to improve the clinicians' understanding of this disease. Methods: Clinical data and gene detection results of 6 epilepsy children with SLC35A2 gene variants were treated in the Department of Pediatrics Peking University First Hospital from April 2019 to February 2020 were analyzed retrospectively. Results: Six children with SLC35A2 gene variants were identified, including 1 male and 5 females. The onset age of seizure was 5.5 (ranged from 2 to 20) months. All 6 cases had epileptic spasms, 2 cases had focal seizures, 2 cases had myoclonic seizures, 1 case had tonic seizures and 1 case had generalized tonic-clonic seizures. All patients with SLC35A2 gene variants were diagnosed as infantile spasm with developmental delay. Four cases had microcephaly, 4 cases had micro skeletal abnormalities, 3 cases had hypotonia and facial dysmorphism, 2 cases had inverted nipples. Visual abnormality, auditory anomaly, congenital cardiac disease and feeding difficulty were observed in one patient. The electroencephalography showed hypsarrhythmia in 6 patients. The brain magnetic resonance imaging (MRI) showed thinning of corpus callosum in 3 patients, delayed myelination in 2 patients and normal brain MRI in 3 patients. There were 2 cases of in-frame deletions, 1 case of missense variant, 1 case of splice site variant, 1 case of 2.14 kb deletion in Xp11.23 (only containing SLC35A2 gene) and 1 case of SLC35A2 gene mosaicism. All 6 cases had de novo variants. The last follow-up age ranged from 18 to 52 months. One patient was seizure free and 5 patients still had frequent seizures after treatment with antiepileptic drugs. Conclusions: SLC35A2 gene variants are mainly de novo variants. The characteristics of patients with SLC35A2-CDG are seizures and developmental delay, infantile spasms are most common diagnosis, micro skeletal anomaly, microcephaly, hypotonia, facial dysmorphism were accompanied features.

Effects of phytonutrients alone or in combination with monensin on productivity in lactating dairy cows.

This experiment was conducted to investigate the effects of phytonutrients, compared with monensin as a positive control, on productivity, milk fatty acids, fat mobilization, and blood cells in lactating dairy cows. Thirty-six Holstein cows were used in a 9-wk randomized complete block design study. Following a 2-wk covariate period, cows were blocked by days in milk, parity, and milk yield and randomly assigned to 1 of 3 treatments (12 cows/treatment): 450 mg/cow per day of monensin (MO), 250 mg/cow per day of capsicum plus 450 mg/cow per day of MO (MOCAP), and 1,000 mg/cow per day of a mixture of cinnamaldehyde, eugenol, and capsicum (CEC). Dry matter intake and milk yield were not affected by treatment. Supplementation of CEC increased feed efficiency compared with MO, but did not affect feed efficiency on an energy-corrected milk basis. Milk composition (fat, protein, and lactose), milk fatty acid profile, and blood concentrations of nonesterified fatty acids and ß-hydroxybutyrate were also not affected by treatment. The expression of hormone-sensitive lipase in adipose tissues tended to increase for MOCAP compared with MO. Counts of total white blood cell, neutrophils, lymphocytes, eosinophils, and basophils were not affected by treatment, although monocytes count tended to be decreased by CEC. Treatments had no effect on red blood cells, hemoglobin, and platelets. Results indicate that dietary supplementation of CEC and capsicum had no production or other effects in dairy cows, compared with MO, except CEC increased feed efficiency and tended to decrease blood monocytes count.

Effects of slow-release urea and rumen-protected methionine and histidine on mammalian target of rapamycin (mTOR) signaling and ubiquitin proteasome-related gene expression in skeletal muscle of dairy cows.

The mammalian target of rapamycin (mTOR) is a major regulator of protein synthesis, whereas the ubiquitin-proteasome system (UPS) is regarded as the main proteolytic pathway in skeletal muscle. The objective of the current study was to investigate the effects of slow-release urea and rumen-protected (RP) Met and His supplementation of a metabolizable protein (MP)-deficient diet on the abundance of key components of the mTOR pathway and of the UPS in skeletal muscle of dairy cows. Sixty Holstein cows were blocked based on days in milk and milk yield and were randomly assigned within block to 1 of 5 diets in a 10-wk experiment (including the first 2 wk as covariate period) as follows: (1) MP-adequate diet (AMP; 107% of MP requirements, based on the National Research Council requirements); (2) MP-deficient diet (DMP; 95% of MP requirements); (3) DMP supplemented with slow-release urea (DMPU); (4) DMPU supplemented with RPMet (DMPUM); and (5) DMPUM supplemented with RPHis (DMPUMH). Muscle biopsies were collected from longissimus dorsi during the last week of the experiment. The mRNA abundance of key mTOR signaling genes was not affected by the treatments. The phosphorylated (P)-mTOR protein was or tended to be greater for DMP compared with DMPU and AMP, respectively. The P-mTOR protein in DMPUMH was decreased when compared against DMPUM. The P-ribosomal protein S6 tended to be increased by DMPUM compared with DMPU. The abundance of total-S6 was or tended to be greater for DMP compared with AMP and DMPU, respectively. The mRNA abundance of ubiquitin activating and conjugating enzymes was not affected by the treatments, whereas that of muscle ring-finger protein 1 (MuRF-1) was greater in DMP than DMPU. The increased abundance of mTOR-associated signaling proteins and MuRF-1 mRNA abundance indicates a higher rate of protein turnover in muscle of DMP-fed cows. The reduced abundance of P-mTOR by supplementation of RPHis may suggest that His is likely partitioned to the mammary gland in favor of milk protein synthesis rather than to the skeletal muscle in dairy cows fed MP-deficient diets.

Olanzapine promotes fat accumulation in male rats by decreasing physical activity, repartitioning energy and increasing adipose tissue lipogenesis while impairing lipolysis.

Olanzapine and other atypical antipsychotics cause metabolic side effects leading to obesity and diabetes; although these continue to be an important public health concern, their underlying mechanisms remain elusive. Therefore, an animal model of these side effects was developed in male Sprague-Dawley rats. Chronic administration of olanzapine elevated fasting glucose, impaired glucose and insulin tolerance, increased fat mass but, in contrast to female rats, did not increase body weight or food intake. Acute studies were conducted to delineate the mechanisms responsible for these effects. Olanzapine markedly decreased physical activity without a compensatory decline in food intake. It also acutely elevated fasting glucose and worsened oral glucose and insulin tolerance, suggesting that these effects are adiposity independent. Hyperinsulinemic-euglycemic clamp studies measuring (14)C-2-deoxyglucose uptake revealed tissue-specific insulin resistance. Insulin sensitivity was impaired in skeletal muscle, but either unchanged or increased in adipose tissue depots. Consistent with the olanzapine-induced hyperglycemia, there was a tendency for increased (14)C-2-deoxyglucose uptake into fat depots of fed rats and, surprisingly, free fatty acid (FFA) uptake into fat depots was elevated approximately twofold. The increased glucose and FFA uptake into adipose tissue was coupled with increased adipose tissue lipogenesis. Finally, olanzapine lowered fasting plasma FFA, and as it had no effect on isoproterenol-stimulated rises in plasma glucose, it blunted isoproterenol-stimulated in vivo lipolysis in fed rats. Collectively, these results suggest that olanzapine exerts several metabolic effects that together favor increased accumulation of fuel into adipose tissue, thereby increasing adiposity.

Regulation of muscle growth by pathogen-associated molecules.

Skeletal muscle demonstrates great plasticity in response to environmental and hormonal factors including pathogen-associated molecules, inflammatory cytokines, and growth factors. These signals impinge on muscle by forcing individual muscle fibers to either grow or atrophy. We recently demonstrated that skeletal muscle cells express multiple Toll-like receptors (TLR) that recognize bacterial cell wall components, such as lipopolysaccharide (LPS). Exposure of myocytes to LPS and other TLR ligands initiates an inflammatory response culminating in the autocrine production of cytokines and NO by NO synthase (NOS)2. The TLR signal through protein kinases that phosphorylate and promote the degradation of an inhibitory protein that normally retains the transcription factor, nuclear factor kappaB (NFkappaB), in the cytoplasm. Phosphorylation and degradation of the inhibitor of NFkappaB allows for translocation of NFkappaB to the nucleus and activation of inflammatory genes. Overexpression of a constitutively active inhibitor of NFkappaB kinase in skeletal muscle causes severe wasting, and we found that inhibitors of either the phosphorylation of IkappaB or its proteolytic degradation prevent TLR ligand-induced expression of cytokines and NOS2. The combination of LPS and interferon gamma dramatically enhances the magnitude and duration of LPS-stimulated NOS2 expression and reduces protein translation. Lipopolysaccharide and interferon gamma also downregulates signaling from the mammalian target of rapamycin, a kinase that directs changes in cell size. Inhibitors of NOS block the fall in muscle cell protein synthesis and restore translational signaling, indicating that activation of the NOS2-NO pathway is responsible for the observed decrease in muscle protein synthesis. Our work provides a molecular explanation for reduced muscle growth during infection. Muscle is largely self-sufficient because it expresses receptors, signaling pathways, and effectors to regulate its own size. Prolonged activation of NFkappaB and NOS2 have emerged as detrimental facets of the immune response in muscle. The interplay between inflammatory components and growth factor signaling clearly places muscle at the interface between growth and immunity.

Shear force control for a terahertz near field microscope.

We report on the advancement of apertureless terahertz microscopy by active shear force control of the scanning probe. Extreme subwavelength spatial resolution and a maximized image contrast are achieved by maintaining a tip-surface distance of about 20 nm. The constant distance between scanning tip and surface results in terahertz images that mirror the dielectric permittivity of the surface.

Alteration of somatotropic function by proinflammatory cytokines.

Infections direct amino acids away from growth and skeletal muscle accretion toward the hepatic synthesis of acute-phase proteins. The loss of skeletal muscle protein stores results in both a decrease in muscle function and an increase in mortality. In general, muscle protein synthesis is decreased in rodent models of sepsis, as well as after the injection of components of the bacterial cell wall, such as lipopolysaccharide. Although the overexpression of proinflammatory cytokines is known to hasten the loss of skeletal muscle protein, it is not known whether this represents a direct effect of cytokines or results from secondary changes in the IGF system. Plasma concentrations of IGF-I are dramatically lowered by infection in rats, mice, pigs, and steers. The drop in IGF-I often occurs despite an increase in the plasma concentration of somatotropin. Animals are therefore considered to be GH resistant. The IGF bioactivity is determined not only by the plasma concentration of the ligand, but also by IGFBP; IGFBP-3 is the most abundant of these binding proteins and undergoes proteolysis during some catabolic states. In contrast to IGFBP-3, the plasma concentration of inhibitory IGFBP, such as IGFBP-1, is increased during infection. Insulin-like growth factor-binding protein-1 accumulates in skeletal muscle, where it can potentially inhibit IGF-dependent protein synthesis. Insulin-like growth factor-I and IGFBP-1 are regulated at the level of gene transcription by proinflammatory cytokines. Recent studies demonstrate that bacterial components that activate immune cells also activate the innate immune response in skeletal muscle. Lipopolysaccharide increases proinflammatory cytokine messenger RNA expression in muscle from control mice, but not from mice with a mutation in the lipopolysaccharide receptor. Lipopolysaccharide also increases cytokine expression in human and mouse myoblasts. Local expression of cytokines in skeletal muscle may negatively regulate the autocrine synthesis of IGF-I. Current work is focused on deciphering the mechanism by which muscle becomes GH resistant and the development of therapies to maintain muscle protein stores during infection.

Regulation of insulin-like growth factor-I in skeletal muscle and muscle cells.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are potent regulators of muscle mass. Transgenic mice that over-express these proteins exhibit dramatically enlarged skeletal muscles. In contrast, malnutrition, critical illness, sepsis, and aging are all associated with a dramatic reduction in muscle mass and function. The circulating concentration of IGF-I and the expression of IGF-I in skeletal muscle are also reduced during catabolic states. Consequently, GH has been used clinically to increase lean body mass in patients with muscle wasting. Likewise, delivery of IGF-I specifically into muscle has been proposed as a genetic therapy for muscle disorders. A better understanding of the regulation of IGF-I expression in skeletal muscle and muscle cells is therefore of importance. Yet, our knowledge in this area has been limited by a lack of GH responsive muscle cells. In addition the IGF-I gene spans over 90 kb of genomic DNA and it exhibits a very complex regulatory pattern. This review will summarize our knowledge of the control of muscle mass by GH, IGF-I, anabolic steroids, exercise and other growth enhancing hormones. We will also highlight recent advances in the regulation of IGF-I and signal transducers and activators of transcription (Stats) by GH. A special emphasis will be placed on the interaction of IGF-I and proinflammatory cytokines in skeletal muscle and muscle cells.

Tissue-specific regulation of IGF-I and IGF-binding proteins in response to TNFalpha.

The circulating concentration of insulin-like growth factor-I (IGF-I) is regulated by both its rate of synthesis and its ability to form stable complexes with IGF-binding proteins (IGFBPs). An equilibrium between IGF-I and IGFBPs is thought to help maintain muscle protein balance. In contrast, catabolic conditions disrupt the IGF system and result in the loss of skeletal muscle protein. We have examined the mechanisms by which tumour necrosis factor alpha (TNFalpha), a catabolic cytokine, alters the IGF system. Conscious rats were infused intravenously with recombinant human TNFalpha or vehicle for 24 h. TNFalpha decreased the concentration of both total and free IGF-I in the plasma (30-40%). This change was associated with a reduction in IGF-I mRNA expression in liver (39%), gastrocnemius (73%), soleus (46%) and heart (63%), but a 2.5-fold increase in the whole kidney. In contrast, TNFalpha did not alter IGF-II mRNA expression in skeletal muscle. TNFalpha also increased IGFBP-1 in the blood (4-fold) and this response was associated with an increase in IGFBP-1 mRNA expression in both liver (3-fold) and kidney (9-fold). In contrast, IGFBP-3 levels in the blood were reduced 38% in response to the infusion of TNFalpha. This change was accompanied by a 60-80% reduction of IGFBP-3 mRNA in liver and kidney but no significant change in muscle. Hepatic mRNA levels of the acid-labile subunit were also reduced by TNFalpha (46%). Finally, tissue expression of mac25 (also referred to IGFBP-related protein-1) mRNA was increased in gastrocnemius (50%) but remained unchanged in liver and kidney. These results more fully characterize the changes in various elements of the IGF system and, thereby, provide potential mechanisms for the alterations in the circulating IGF system as well as for changes in tissue metabolism observed during catabolic insults associated with increased TNFalpha expression.

Alcohol impairs protein synthesis and degradation in cultured skeletal muscle cells.

BACKGROUND: Acute and chronic alcohol intoxication decreases skeletal muscle protein synthesis under in vivo conditions. We investigated whether ethanol (EtOH) and its major metabolites, acetaldehyde and acetate, can directly modulate protein balance under in vitro conditions. METHODS: Human myocytes were incubated with different doses of EtOH for varying periods of time (i.e., 4-72 hr). Alternatively, cells were incubated with acetaldehyde, acetate, insulin, insulin-like growth factor-I (IGF-I), or with a combination of EtOH plus insulin or IGF-I. Rates of protein synthesis or degradation were determined by 35S-methionine/cysteine incorporation into or release from cellular protein. RESULTS: A significant, 15% to 20%, decrease in basal protein synthesis was observed after 24 hr, but not at earlier time points, in response to 80 mM EtOH. Incubation of myocytes for 72 hr decreased synthesis in cells incubated with EtOH ranging between 60 and 120 mM. The ability of IGF-I or insulin to stimulate protein synthesis was impaired by 30% and 60%, respectively, in cells incubated with 80 mM EtOH for 72 hr. Exposure of cells to 200 microM acetaldehyde or 5 mM Na-acetate also decreased basal protein synthesis. In contrast, neither EtOH, acetaldehyde, nor acetate altered the basal rate of protein degradation. However, EtOH completely impaired the ability of insulin and IGF-I to inhibit proteolysis. Finally, EtOH did not impair IGF-I receptor autophosphorylation, but inhibited the ability of insulin to phosphorylate its own receptor. EtOH also did not alter the number of insulin or IGF-I receptors or the formation of insulin/IGF-I hybrid receptors. CONCLUSIONS: We have demonstrated that EtOH can directly inhibit muscle protein synthesis under in vitro conditions. Neither EtOH nor its metabolites altered basal protein degradation, although EtOH did compromise the ability of both insulin and IGF-I to slow proteolysis. This impairment seems to be mediated by different defects in signal transduction.

Effects of chronic alcohol consumption on regulation of myocardial protein synthesis.

Heart disease represents an important etiology of mortality in chronic alcoholics. The purpose of the present study was to examine potential mechanisms for the inhibitory effect of chronic alcohol exposure (16 wk) on the regulation of myocardial protein metabolism. Chronic alcohol feeding resulted in a lower heart weight and 25% loss of cardiac protein per heart compared with pair-fed controls. The loss of protein mass resulted in part from a diminished (30%) rate of protein synthesis. Ethanol exerted its inhibition of protein synthesis through diminished translational efficiency rather than lower RNA content. Chronic ethanol administration decreased the abundance of eukaryotic initiation factor (eIF)4G associated with eIF4E in the myocardium by 36% and increased the abundance of the translation response protein (4E-BP1) associated with eIF4E. In addition, chronic alcohol feeding significantly reduced the extent of p70S6 kinase (p70(S6K)) phosphorylation. The decreases in the phosphorylation of 4E-BP1 and p70(S6K) did not result from a reduced abundance of mammalian target of rapamycin (mTOR). These data suggest that a chronic alcohol-induced impairment in myocardial protein synthesis results in part from inhibition in peptide chain initiation secondary to marked changes in eIF4E availability and p70(S6K) phosphorylation.

In vitro and In vivo inhibition of LPS-stimulated tumor necrosis factor-alpha secretion by the gallotannin beta-D-pentagalloylglucose.

The naturally occurring gallotannin beta-D-pentagalloylglucose (beta-PGG) decreases tumor necrosis factor-alpha (TNF-alpha) output from human peripheral blood mononucleocytes exposed to lipopolysaccharide (LPS) by as much as 90% (vs control) at approximately 5 microM concentration. A qualitatively similar but less pronounced effect ( approximately 50% decrease) was observed in the serum of rats dosed with both LPS and beta-PGG. These results may have relevance to therapies that target disease states characterized by an overproduction of TNF-alpha.

Immunization against IGF-I prevents increases in protein synthesis in diabetic rats after resistance exercise.

These studies examined whether passive immunization against insulin-like growth factor I (IGF-I) would prevent increases in rates of protein synthesis in skeletal muscle of diabetic rats after resistance exercise. Male Sprague-Dawley rats were pancreatectomized and randomly assigned to either an exercise or a sedentary group. Animals in each of these groups received either an IGF-I antibody or a nonspecific IgG from a subcutaneous osmotic pump. Exercise did not change plasma or gastrocnemius IGF-I concentrations in nondiabetic rats. However, plasma and muscle IGF-I concentrations were higher in IgG-treated diabetic rats that exercised compared with respective sedentary groups (P < 0.05). Passively immunized diabetic rats did not exhibit the same exercise-induced increase in IGF-I concentrations. In nondiabetic rats, protein synthesis rates were higher after exercise in both control and immunized groups. In diabetic rats, exercise increased protein synthesis in the IgG-treated animals but not in those treated with IGF-I antibody. There was also a significant positive correlation between both plasma and gastrocnemius IGF-I concentrations and rates of protein synthesis in diabetic (P < 0.01), but not nondiabetic, rats. These results suggest that IGF-I is compensatory for insulin in hypoinsulinemic rats by facilitating an anabolic response after acute resistance exercise.

Alcohol myopathy: impairment of protein synthesis and translation initiation.

Alcohol consumption leads to numerous morphological, biochemical and functional changes in skeletal and cardiac muscle. One such change observed in both tissues after either acute alcohol intoxication or chronic alcohol consumption is a characteristic decrease in the rate of protein synthesis. A decrease in translation efficiency appears to be responsible for at least part of the reduction. This review highlights advances in determining the molecular mechanisms by which alcohol impairs protein synthesis and places these observations in context of earlier studies on alcoholic myopathy. Both acute and chronic alcohol administration impairs translational control by modulating various aspects of peptide-chain initiation. Moreover, this alcohol-induced impairment in initiation is associated with a decreased availability of eukaryotic initiation factor (eIF) 4E in striated muscle, as evidenced by an increase in the amount of the inactive eIF4E.4E-BP1 complex and decrease in the active eIF4E.eIF4G complex. In contrast, alcohol does not produce consistent alterations in the control of translation initiation by the eIF2 system. The etiology of these changes remain unresolved. However, defects in the availability or effectiveness of various anabolic hormones, particularly insulin-like growth factor-I, are consistent with the alcohol-induced decrease in protein synthesis and translation initiation.

Effect of hyperthyroidism on insulin-like growth factor-I (IGF-I) and IGF-binding proteins in adolescent children.

A study was performed on adolescent hyperthyroid patients to determine the effects of hyperthyroidism on insulin-like growth factor (IGF)-I and its binding proteins. Serum concentrations of immunoreactive total and free IGF-I, and IGF binding protein (IGFBP)-2 and IGFBP-3 were determined before and after correction of hyperthyroidism in eight patients with Grave's disease and compared to control patients matched for age, sex and pubertal stage. The concentration of serum total IGF-I was not significantly different in the hyperthyroid state and euthyroid state, and did not differ significantly from euthyroid controls. IGFBP-2 levels were elevated three-fold in hyperthyroid patients at the time of diagnosis of hyperthyroidism compared to control subjects, and fell significantly during treatment. There was also a significant positive correlation between serum IGFBP-2 concentrations and thyroxine (T4) concentrations in all subjects. Serum IGFBP-3 concentrations were also elevated in hyperthyroid subjects and normalized with correction of the hyperthyroidism. There was also a positive correlation between serum T4 and IGFBP-3 concentrations in all subjects. Despite the hyperthyroid-induced elevations in IGFBP-2 and -3, no significant difference in the serum concentration of free IGF-I before or after correction of the hyperthyroid condition was observed. We conclude that hyperthyroidism does not cause alterations in the serum concentrations of either free or total IGF-I. However, both serum IGFBP-2 and IGFBP-3 concentrations were elevated during hyperthyroidism and correlated with serum T4 levels. These abnormalities reversed with normalization of thyroid function.

Impaired myocardial protein synthesis induced by acute alcohol intoxication is associated with changes in eIF4F.

The purpose of the present study was to examine potential mechanisms for the known inhibitory effect of acute alcohol exposure on myocardial protein synthesis. Rats were injected intraperitoneally with either ethanol (75 mmol/kg) or saline, and protein synthesis was measured in vivo 2.5 h thereafter by use of the flooding-dose L-[(3)H]phenylalanine technique. Rates of myocardial protein synthesis and translational efficiency in alcohol-treated rats were decreased compared with control values. Free (nonpolysome bound) 40S and 60S ribosomal subunits were increased 50% after alcohol treatment, indicating an impaired peptide-chain initiation. To identify mechanisms responsible for this impairment, several eukaryotic initiation factors (eIF) were analyzed. Acute alcohol intoxication did not significantly alter the myocardial content of eIF2 alpha or eIF2B epsilon, the extent of eIF2 alpha phosphorylation, or the activity of eIF2B. Acute alcohol exposure increased the binding of 4E-binding protein 1 (4E-BP1) to eIF4E (55%), diminished the amount of eIF4E bound to eIF4G (70%), reduced the amount of 4E-BP1 in the phosphorylated gamma-form (40%), and decreased the phosphorylation of p70S6 kinase and the ribosomal protein S6. There was no significant difference in either the plasma insulin-like growth factor (IGF) I concentration (total or free) or expression of IGF-I or IGF-II mRNA in heart between the two groups. These data suggest that the acute alcohol-induced impairment in myocardial protein synthesis results, in part, from an inhibition in peptide-chain initiation, which is associated with marked changes in eIF4E availability and p70S6 kinase phosphorylation but is independent of changes in the eIF2/2B system and IGFs.

IGF-I/IGFBP-3 binary complex modulates sepsis-induced inhibition of protein synthesis in skeletal muscle.

The present study evaluated the ability of insulin-like growth factor I (IGF-I) complexed with IGF binding protein-3 (IGFBP-3) to modulate the sepsis-induced inhibition of protein synthesis in gastrocnemius. Beginning 16 h after the induction of sepsis, either the binary complex or saline was injected twice daily via a tail vein, with measurements made 3 and 5 days later. By day 3, sepsis had reduced plasma IGF-I concentrations approximately 50% in saline-treated rats. Administration of the binary complex provided exogenous IGF-I to compensate for the sepsis-induced diminished plasma IGF-I. Sepsis decreased rates of protein synthesis in gastrocnemius relative to controls by limiting translational efficiency. Treatment of septic rats with the binary complex for 5 days attenuated the sepsis-induced inhibition of protein synthesis and restored translational efficiency to control values. Assessment of potential mechanisms regulating translational efficiency showed that neither the sepsis-induced change in gastrocnemius content of eukaryotic initiation factor 2B (eIF2B), the amount of eIF4E associated with 4E binding protein-1 (4E-BP1), nor the phosphorylation state of 4E-BP1 or eIF4E were altered by the binary complex. Overall, the results are consistent with the hypothesis that decreases in plasma IGF-I are partially responsible for enhanced muscle catabolism during sepsis.

Stimulation of insulin-like growth factor binding protein-1 synthesis by interleukin-1beta: requirement of the mitogen-activated protein kinase pathway.

Insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) is a 28-kDa plasma protein that binds to IGF-I and IGF-II with high affinity. IGFBP-1 is elevated in the blood as a result of sepsis, AIDS, excessive alcohol consumption, and diabetes and may, in part, be responsible for the wasting observed during these pathophysiological conditions. The liver is the principal site of IGFBP-1 synthesis, and we have previously shown that proinflammatory cytokines can directly stimulate IGFBP-1 secretion in a human hepatoma cell line (HepG2). The purpose of the present study was to investigate the role of the MAP kinase pathway in regulating IGFBP-1 synthesis by IL-1beta. We show that IL-1beta stimulates the phosphorylation of ERK-1 and -2 in a time- and dose-dependent manner. In addition, the MAP kinase-kinase MEK-1 and the ribosomal S6-kinase RSK-1 are also phosphorylated in response to IL-1beta. The transcription factor CREB, a potential substrate of both protein kinase A (PKA) and RSK-1, is phosphorylated in response to IL-1beta and cAMP in HepG2 cells. The ability of IL-1beta to stimulate the expression of IGFBP-1 and the phosphorylation of the above kinases was specifically inhibited by PD98059, a MEK-1 inhibitor. cAMP also stimulated IGFBP-1 synthesis, but PD98059 failed to block the cAMP effect. Conversely, a PKA inhibitor (H-89) inhibited the ability of cAMP, but not IL-1beta to stimulate IGFBP-1 synthesis. The effect of IL-1beta and cAMP on IGFBP-1 messenger RNA (mRNA) accumulation was additive. IL-1beta, cAMP, PD98059, and H-89 had similar effects on the accumulation of IGFBP-1 protein and mRNA. IL-1beta and cAMP did not change the half-life of IGFBP-1 mRNA, but PD98059 and SB202190, a p38 MAP kinase inhibitor, destabilized IGFBP-1 mRNA and blocked the phosphorylation of RSK-1 in response to IL-1beta. Our data demonstrate that the MAP kinase signal transduction pathway plays an important role in the regulation of IGFBP-1 synthesis by IL-1beta.