Leukotrienes cause eosinophil emigration into conjunction tissue

The ability of LTB₄, LTC₄, the 5S,6R and 5R,6S LTD₄ stereoisomers, and LTE₄ to evoke leukocyte infiltration into the conjunctiva was demonstrated in the guinea pig by histological andl ight microscopy techniques. LTD₄ and LTE₄ demonstrated a dose-dependent and predominantly eosinophilic infiltrate over the selected dose range (10ng to 1000ng), while there was only a minimal response to LTC₄. LTB₄ produced marked eosinophil inflitrates only at the highest dose; scattered neutrophil infiltrates were also noted at the high dose of LTB₄. The 5R,6S LTD₄ stereoisomer did not evoke any leukocyte infiltrantion. The SRS-A antagonist, FPL 55712, abolished pre-treatment had no inhibitory effect, indicating direct mediation of this response by LTs. Histamine caused a comparable eosinophilia over a dose range of 10μg to 1000μg. LT-induced eosinophil emigration was directed to the conjunctival epithelium; the cells appeared intact and no tissue damage was observed. These results may have relevance in the areas of allergic conjunctivitis and asthma research.     

Skeletal muscle respiratory capacity is enhanced in rats consuming an obesogenic Western diet

Obesity-induced lipid oversupply promotes skeletal muscle mitochondrial biogenesis. Previous investigations have utilized extreme high-fat diets (HFD) to induce such mitochondrial perturbations despite their disparity from human obesogenic diets. Here, we evaluate the effects of Western diet (WD)-induced obesity on skeletal muscle mitochondrial function. Long-Evans rats were given ad libitum access to either a WD [40% energy (E) from fat, 17% protein, and 43% carbohydrate (30% sucrose); n = 12] or a control diet (CON; 16% of E from fat, 21% protein, and 63% carbohydrate; n = 12) for 12 wk. Rats fed the WD consumed 23% more E than CON (P = 0.0001), which was associated with greater increases in body mass (23%, P = 0.0002) and adiposity (17%, P = 0.03). There were no differences in fasting blood glucose concentration or glucose tolerance between diets, although fasting insulin was increased by 40% (P = 0.007). Fasting serum triglycerides were also elevated in WD (86%, P = 0.001). The maximal capacity of the electron transfer system was greater following WD (37%, P = 0.02), as were the maximal activities of several mitochondrial enzymes (citrate synthase, β-hydroxyacyl-CoA dehydrogenase, carnitine palmitoyltransferase). Protein expression of citrate synthase, UCP3, and individual respiratory complexes was greater after WD (P < 0.05) despite no differences in the expression of peroxisome proliferator-activated receptor (PPAR)α, PPARδ, or PPARγ coactivator-1 mRNA or protein abundance. We conclude that the respiratory capacity of skeletal muscle is enhanced in response to the excess energy supplied by a WD. This is likely due to an increase in mitochondrial density, which at least in the short term, and in the absence of increased energy demand, may protect the tissue from lipid-induced impairments in glycemic control.     

Differential proteomic analysis of human erythroblasts undergoing apoptosis induced by epo-withdrawal

The availability of Erythropoietin (Epo) is essential for the survival of erythroid progenitors. Here we study the effects of Epo removal on primary human erythroblasts grown from peripheral blood CD34(+) cells. The erythroblasts died rapidly from apoptosis, even in the presence of SCF, and within 24 hours of Epo withdrawal 60% of the cells were Annexin V positive. Other classical hallmarks of apoptosis were also observed, including cytochrome c release into the cytosol, loss of mitochondrial membrane potential, Bax translocation to the mitochondria and caspase activation. We adopted a 2D DIGE approach to compare the proteomes of erythroblasts maintained for 12 hours in the presence or absence of Epo. Proteomic comparisons demonstrated significant and reproducible alterations in the abundance of proteins between the two growth conditions, with 18 and 31 proteins exhibiting altered abundance in presence or absence of Epo, respectively. We observed that Epo withdrawal induced the proteolysis of the multi-functional proteins Hsp90 alpha, Hsp90 beta, SET, 14-3-3 beta, 14-3-3 gamma, 14-3-3 epsilon, and RPSA, thereby targeting multiple signaling pathways and cellular processes simultaneously. We also observed that 14 proteins were differentially phosphorylated and confirmed the phosphorylation of the Hsp90 alpha and Hsp90 beta proteolytic fragments in apoptotic cells using Nano LC mass spectrometry. Our analysis of the global changes occurring in the proteome of primary human erythroblasts in response to Epo removal has increased the repertoire of proteins affected by Epo withdrawal and identified proteins whose aberrant regulation may contribute to ineffective erythropoiesis.     

A structure-function analysis of NOD, a kinesin-like protein from Drosopbila melanogaster

We have analyzed a collection of 12 mutations in the Drosophila melanogaster nod locus, which encodes a kinesin-like protein involved in female meiotic chromosome segregation. The kinesin-like domain is at the N-terminus of the protein, while the C-terminal portion of the protein is unique. Four of the mutations are missense and affect highly conserved domains of the kinesin-like portion of the predicted protein, and thus demonstrate that the sequence conservation is biologically relevant. Surprisingly, two other mutations, which behave genetically as null alleles, are the result of mutations in the last exon of the nod gene. Thus, these two mutations affect the most C-terminal residues in the unique portion of the predicted protein. Based on these mutations, we suggest that this part of the protein may also be essential for wild-type function. The mutations were induced by either gamma-rays or ethyl methanesulfonate (EMS). All of the gamma-ray induced mutations were small or large chromosomal rearrangements, while all of the EMS mutations were G A transitions. These findings are consistent with the biochemical basis of the mode of action of each mutagen.     

Intensified exercise training does not alter AMPK signaling in human skeletal muscle

The AMP-activated protein kinase (AMPK) cascade has been linked to many of the acute effects of exercise on skeletal muscle substrate metabolism, as well as to some of the chronic training-induced adaptations. We determined the effect of 3 wk of intensified training (HIT; 7 sessions of 8 x 5 min at 85% Vo2 peak) in skeletal muscle from well-trained athletes on AMPK responsiveness to exercise. Rates of whole body substrate oxidation were determined during a 90-min steady-state ride (SS) pre- and post-HIT. Muscle metabolites and AMPK signaling were determined from biopsies taken at rest and immediately after exercise during the first and seventh HIT sessions, performed at the same (absolute) pre-HIT work rate. HIT decreased rates of whole body carbohydrate oxidation (P < 0.05) and increased rates of fat oxidation (P < 0.05) during SS. Resting muscle glycogen and its utilization during intense exercise were unaffected by HIT. However, HIT induced a twofold decrease in muscle [lactate] (P < 0.05) and resulted in tighter metabolic regulation, i.e., attenuation of the decrease in the PCr/(PCr + Cr) ratio and of the increase in [AMPfree]/ATP. Resting activities of AMPKalpha1 and -alpha2 were similar post-HIT, with the magnitude of the rise in response to exercise similar pre- and post-HIT. AMPK phosphorylation at Thr172 on both the alpha1 and alpha2 subunits increased in response to exercise, with the magnitude of this rise being similar post-HIT. Acetyl-coenzyme A carboxylase-beta phosphorylation was similar at rest and, despite HIT-induced increases in whole body rates of fat oxidation, did not increase post-HIT. Our results indicate that, in well-trained individuals, short-term HIT improves metabolic control but does not blunt AMPK signaling in response to intense exercise.     

Effect of carbohydrate ingestion on metabolism during running and cycling.

The effects of carbohydrate or water ingestion on metabolism were investigated in seven male subjects during two running and two cycling trials lasting 60 min at individual lactate threshold using indirect calorimetry, U-14C-labeled tracer-derived measures of the rates of oxidation of plasma glucose, and direct determination of mixed muscle glycogen content from the vastus lateralis before and after exercise. Subjects ingested 8 ml/kg body mass of either a 6.4% carbohydrate-electrolyte solution (CHO) or water 10 min before exercise and an additional 2 ml/kg body mass of the same fluid after 20 and 40 min of exercise. Plasma glucose oxidation was greater with CHO than with water during both running (65 +/- 20 vs. 42 +/- 16 g/h; P < 0.01) and cycling (57 +/- 16 vs. 35 +/- 12 g/h; P < 0.01). Accordingly, the contribution from plasma glucose oxidation to total carbohydrate oxidation was greater during both running (33 +/- 4 vs. 23 +/- 3%; P < 0.01) and cycling (36 +/- 5 vs. 22 +/- 3%; P < 0.01) with CHO ingestion. However, muscle glycogen utilization was not reduced by the ingestion of CHO compared with water during either running (112 +/- 32 vs. 141 +/- 34 mmol/kg dry mass) or cycling (227 +/- 36 vs. 216 +/- 39 mmol/kg dry mass). We conclude that, compared with water, 1) the ingestion of carbohydrate during running and cycling enhanced the contribution of plasma glucose oxidation to total carbohydrate oxidation but 2) did not attenuate mixed muscle glycogen utilization during 1 h of continuous submaximal exercise at individual lactate threshold.     

Methylarginine metabolites are associated with attenuated muscle protein synthesis in cancer-associated muscle wasting

Cancer cachexia is characterized by reductions in peripheral lean muscle mass. Prior studies have primarily focused on increased protein breakdown as the driver of cancer-associated muscle wasting. Therapeutic interventions targeting catabolic pathways have, however, largely failed to preserve muscle mass in cachexia, suggesting that other mechanisms might be involved. In pursuit of novel pathways, we used untargeted metabolomics to search for metabolite signatures that may be linked with muscle atrophy. We injected 7-week–old C57/BL6 mice with LLC1 tumor cells or vehicle. After 21 days, tumor-bearing mice exhibited reduced body and muscle mass and impaired grip strength compared with controls, which was accompanied by lower synthesis rates of mixed muscle protein and the myofibrillar and sarcoplasmic muscle fractions. Reductions in protein synthesis were accompanied by mitochondrial enlargement and reduced coupling efficiency in tumor-bearing mice. To generate mechanistic insights into impaired protein synthesis, we performed untargeted metabolomic analyses of plasma and muscle and found increased concentrations of two methylarginines, asymmetric dimethylarginine (ADMA) and N^G-monomethyl-l-arginine, in tumor-bearing mice compared with control mice. Compared with healthy controls, human cancer patients were also found to have higher levels of ADMA in the skeletal muscle. Treatment of C2C12 myotubes with ADMA impaired protein synthesis and reduced mitochondrial protein quality. These results suggest that increased levels of ADMA and mitochondrial changes may contribute to impaired muscle protein synthesis in cancer cachexia and could point to novel therapeutic targets by which to mitigate cancer cachexia.