A perspective on the determination of mitochondrial biogenesis

The measurement of mitochondrial biogenesis is important in the determination of aging and disease processes and the assessment of countermeasurements to them. We argue that the frequently used assessments of cell signaling, mitochondrial protein mRNA, mitochondrial protein expression or enzyme activity, and mitochondrial density are not measurements that can lead to conclusions about mitochondrial biogenesis. Instead, we propose that only measurements of mitochondrial synthesis are indicative of biogenesis. Clarification of this issue will hopefully result in further differentiation of the processes important for morphological and functional changes of mitochondria.     

High-level production of amorpha-4,11-diene in a two-phase partitioning bioreactor of metabolically engineered Escherichia coli

Reconstructing synthetic metabolic pathways in microbes holds great promise for the production of pharmaceuticals in large-scale fermentations. By recreating biosynthetic pathways in bacteria, complex molecules traditionally harvested from scarce natural resources can be produced in microbial cultures. Here we report on a strain of Escherichia coli containing a heterologous, nine-gene biosynthetic pathway for the production of the terpene amorpha-4,11-diene, a precursor to the anti-malarial drug artemisinin. Previous reports have underestimated the productivity of this strain due to the volatility of amorphadiene. Here we show that amorphadiene evaporates from a fermentor with a half-life of about 50 min. Using a condenser, we take advantage of this volatility by trapping the amorphadiene in the off-gas. Amorphadiene was positively identified using nuclear magnetic resonance spectroscopy and determined to be 89% pure as collected. We captured amorphadiene as it was produced in situ by employing a two-phase partitioning bioreactor with a dodecane organic phase. Using a previously characterized caryophyllene standard to calibrate amorphadiene production and capture, the concentration of amorphadiene produced was determined to be 0.5 g/L of culture medium. A standard of amorphadiene collected from the off-gas showed that the caryophyllene standard overestimated amorphadiene production by approximately 30%.     

Multiple receptor states are required to describe both kinetic binding and activation of neutrophils via N-formyl peptide receptor ligands

It is well-established that the binding of N-formyl peptides to the N-formyl peptide receptor on neutrophils can be described by a kinetic scheme that involves two ligand-bound receptor states, both a low affinity ligand-receptor complex and a high affinity ligand-receptor complex, and that the rate constants describing ligand-receptor binding and receptor affinity state interconversion are ligand-specific. Here we examine whether differences due to these rate constants, i.e. differences in the numbers and lifetimes of particular receptor states, are correlated with neutrophil responses, namely actin polymerization and oxidant production. We find that an additional receptor state, one not discerned from kinetic binding assays, is required to account for these responses. This receptor state is interpreted as the number of low affinity bound receptors that are capable of activating G proteins; in other words, the accumulation of these active receptors correlates with the extent of both responses. Furthermore, this analysis allows for the quantification of a parameter that measures the relative strength of a ligand to bias the receptor into the active conformation. A model with this additional receptor state is sufficient to describe response data when two ligands (agonist/agonist or agonist/antagonist pairs) are added simultaneously, suggesting that cells respond to the accumulation of active receptors regardless of the identity of the ligand(s).     

Public vaccination policy using an age-structured model of pneumococcal infection dynamics

Public health professionals are charged with the task of designing prevention programs for the effective control of biologically intricate infectious diseases at a population level. The effective vaccination of a population for pneumococcal diseases (infections caused by Streptococcus pneumoniae) remains a relevant question in the scientific community. It is complicated by heterogeneity in individuals' responses to exposure to the bacterium and their responses to vaccination. Due to these complexities, most modelling efforts in this area have been on the cellular/bacteria level. Here, we introduce an age-structured SEIS-type model of pneumococcal diseases and their vaccination. We discuss the use of this framework in predicting the impact of vaccine strategies, with pneumococcal diseases as an example. Using parameter values reasonable for a developed country, we discuss the effects of targeting the colonization and/or infection stages on the age profiles of morbidity in a population.     

Molecular diversity studies of bacterial communities of oil polluted microbial mats from the Etang de Berre (France)

The biodiversity of microbial mats inhabiting the oil-contaminated lagoon Etang de Berre was determined by molecular approaches. The fingerprint of denaturing gradient gel electrophoresis (DGGE) and automatic ribosomal intergenic spacer analysis (ARISA) of mats exposed to different pollution levels showed specific microbial communities for each site but similar diversity richness. Species composition of the mats were compared by constructing 16S rRNA libraries. Amplified rDNA restriction analysis (ARDRA) of clone libraries confirmed their similar level of diversity richness. Phylogenetic analysis of the 16S rRNA sequences showed that the classes gamma and alpha of Proteobacteria were abundantly present in both sites whereas phylotypes related to the delta-Proteobacteria and to the uncultured WS3 group were mainly found in the site with the highest pollution. Identification of the species involved in oil degradation by combining culture-based approaches and DGGE, showed that enrichment cultures were constituted by members of the Rhodobacterales and species related to Rhodococcus, Sphingomonas, Xanthomonas and Microbacterium, all of them known for their ability to degrade hydrocarbons. Our findings suggest that oil pollution has not affected the biodiversity richness of the mats. However, the populations involved in hydrocarbon degradation represent a minor fraction of the mat communities in the Etang de Berre.     

Exercise-induced HSP-72 elevation and cardioprotection against infarct and apoptosis.

Successive bouts of endurance exercise are associated with both increased cardiac levels of heat shock protein-72 (HSP-72) and improved cardioprotection against ischemia-reperfusion (I/R)-induced cardiac cell death. Although overexpression of HSP-72 has been shown to be cardioprotective in transgenic animals, it is unclear whether increased levels of HSP-72 are essential for exercise-induced cardioprotection against I/R-mediated cell death. We tested the hypothesis that exercise-induced increases in myocardial levels of HSP-72 are required to achieve exercise-mediated protection against I/R-induced cardiac cell death. To test this postulate, we investigated the effect of preventing the exercise-induced increase in cardiac HSP-72 on myocardial infarction and apoptosis after 50 min of in vivo ischemia and 120 min of reperfusion. Adult male rats remained sedentary or performed successive bouts of endurance exercise in cold (8 degrees C) or warm (22 degrees C) environments. We found that, compared with sedentary control animals, exercise in a warm environment significantly increased myocardial HSP-72 content. In contrast, exercise in the cold environment prevented the exercise-induced increase in myocardial HSP-72 levels. After in vivo myocardial I/R, infarct size was reduced in both exercised groups compared with sedentary animals. Furthermore, compared with sedentary rats, I/R-induced myocardial apoptosis (as indicated by terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling-positive nuclei and caspase-3 activity) was attenuated in both groups of exercised animals. Therefore, although HSP-72 has cardioprotective properties, our results reveal that increased myocardial levels of HSP-72 (above control) are not essential for exercise-induced protection against I/R-induced myocardial infarction and apoptosis.     

Metformin inhibits mitochondrial adaptations to aerobic exercise training in older adults

Metformin and exercise independently improve insulin sensitivity and decrease the risk of diabetes. Metformin was also recently proposed as a potential therapy to slow aging. However, recent evidence indicates that adding metformin to exercise antagonizes the exercise‐induced improvement in insulin sensitivity and cardiorespiratory fitness. The purpose of this study was to test the hypothesis that metformin diminishes the improvement in insulin sensitivity and cardiorespiratory fitness after aerobic exercise training (AET) by inhibiting skeletal muscle mitochondrial respiration and protein synthesis in older adults (62 ± 1 years). In a double‐blinded fashion, participants were randomized to placebo (n = 26) or metformin (n = 27) treatment during 12 weeks of AET. Independent of treatment, AET decreased fat mass, HbA1c, fasting plasma insulin, 24‐hr ambulant mean glucose, and glycemic variability. However, metformin attenuated the increase in whole‐body insulin sensitivity and VO₂max after AET. In the metformin group, there was no overall change in whole‐body insulin sensitivity after AET due to positive and negative responders. Metformin also abrogated the exercise‐mediated increase in skeletal muscle mitochondrial respiration. The change in whole‐body insulin sensitivity was correlated to the change in mitochondrial respiration. Mitochondrial protein synthesis rates assessed during AET were not different between treatments. The influence of metformin on AET‐induced improvements in physiological function was highly variable and associated with the effect of metformin on the mitochondria. These data suggest that prior to prescribing metformin to slow aging, additional studies are needed to understand the mechanisms that elicit positive and negative responses to metformin with and without exercise.     

Dynamic progression of antisocial behavior in childhood and adolescence: A three-wave longitudinal study from Germany

This longitudinal study from Germany examined the dynamic progression of antisocial behavior in childhood and adolescence based on the social interactional model by Patterson, DeBaryshe, and Ramsey. It examined the link between antisocial behavior, social rejection, academic failure, and affiliation with deviant peers in a sample of 1,657 children and youths aged between 6 and 15 years who were studied at three measurement waves (T1 to T3) over a time period of about 5 years. Teachers rated the children on all variables, parents additionally provided ratings of antisocial behavior and social rejection. Latent structural equation modeling yielded the predicted positive paths from antisocial behavior at T1 to social rejection and academic failure at T2. As predicted, affiliation with deviant peers at T2 was positively associated with social rejection and academic failure at the same measurement point. Finally, affiliation with deviant peers at T2 significantly predicted antisocial behavior at T3.