E. A. Lysenko

Polymer Micelles with Hydrophobic Core and Ionic Amphiphilic Corona. 1. Statistical Distribution of Charged and Nonpolar Units in Corona

Polymer micelles with hydrophobic polystyrene (PS) core and ionic amphiphilic corona from charged N-ethyl-4-vinylpyridinium bromide (EVP) and uncharged 4-vinylpyridine (4VP) units spontaneously self-assembled from PS-block-poly(4VP-stat-EVP) macromolecules in mixed dimethylformamide/methanol/water solvent. The fraction of statistically distributed EVP units in corona-forming block is β = [EVP]/([EVP]+[4VP]) = 0.3-1. Micelles were transferred into water via dialysis technique, and pH was adjusted to 9, where 4VP is insoluble. Structural characteristics of micelles were investigated both experimentally and theoretically as a function of corona composition β. Methods of dynamic and static light scattering, electrophoretic mobility measurements, sedimentation velocity, transmission electron microscopy, and UV spectrophotometry were applied. All micelles possessed spherical morphology. The aggregation number, structure, and electrophoretic mobility of micelles changed in a jumplike manner near β ~ 0.6-0.75. Below and above this region, micelle characteristics were constant or insignificantly changed upon β. Theoretical dependencies for micelle aggregation number, corona dimensions, and fraction of small counterions outside corona versus β were derived via minimization the micelle free energy, taking into account surface, volume, electrostatic, and elastic contributions of chain units and translational entropy of mobile counterions. Theoretical estimations also point onto a sharp structural transition at a certain corona composition. The abrupt reorganization of micelle structure at β ~ 0.6-0.75 entails dramatic changes in micelle dispersion stability in the presence of NaCl or in the presence of oppositely charged polymeric (sodium polymethacrylate) or amphiphilic (sodium dodecyl sulfate) complexing agents.

Promoter-specific regulation of PPARGC1A gene expression in human skeletal muscle

The goal of this study was to identify unknown transcription start sites of the PPARGC1A (PGC-1α) gene in human skeletal muscle and investigate the promoter-specific regulation of PGC-1α gene expression in human skeletal muscle. Ten amateur endurance-trained athletes performed high- and low-intensity exercise sessions (70  min, 70% or 50% o2max). High-throughput RNA sequencing and exon-exon junction mapping were applied to analyse muscle samples obtained at rest and after exercise. PGC-1α promoter-specific expression and activation of regulators of PGC-1α gene expression (AMPK, p38 MAPK, CaMKII, PKA and CREB1) after exercise were evaluated using qPCR and western blot. Our study has demonstrated that during post-exercise recovery, human skeletal muscle expresses the PGC-1α gene via two promoters only. As previously described, the additional exon 7a that contains a stop codon was found in all samples. Importantly, only minor levels of other splice site variants were found (and not in all samples). Constitutive expression PGC-1α gene occurs via the canonical promoter, independent of exercise intensity and exercise-induced increase of AMPK(Thr172) phosphorylation level. Expression of PGC-1α gene via the alternative promoter is increased of two orders after exercise. This post-exercise expression is highly dependent on the intensity of exercise. There is an apparent association between expression via the alternative promoter and activation of CREB1.

Mixed Micelles Based on Cationic and Anionic Amphiphilic Diblock Copolymers Containing Identical Hydrophobic Blocks

Through the use of the methods of turbidimetry, UV spectrophotometry, fluorescence spectroscopy, dynamic light scattering, and ultracentrifugation, micelle formation is studied for cationic (polysty-rene-poly-N-ethyl-4-vinylpyridium bromide) and anionic (polystyrene-sodium polyacrylate) diblock copolymers containing identical polystyrene blocks in dilute aqueous saline solutions. Mixing of aqueous dispersions of individual micelles is accompanied by the formation of only insoluble products, which likely are intermicellar interpolyelectrolyte complexes. At the same time, mixing of diblock copolymers in a nonselective solvent and its subsequent gradient replacement with water during suppressed interpolyelectrolyte interactions yields mixed diblock copolymer micelles, which are found to be dispersionally stable in an excess of charged units of any polymer component. The micelles are composed of an insoluble polystyrene core and a mixed interpolyelectrolyte corona, and their hydrodynamic characteristics are controlled by the ratio of charged units in the mixed diblock copolymers. The mixed micelles are found to be able to interact with the macromolecules of a homopolyelectrolyte, sodium poly(styrene sulfonate), in aqueous solutions and form ternary complexes. In this case, depending on the composition of the mixed micelles, ternary complexes can be dispersionally stable or can aggregate and precipitate.

Effect of concentration regime on rheological properties of sodium polymethacrylate and its complexes with polystyrene-poly(N-ethyl-4- vinylpyridinium bromide) block copolymer in aqueous salt solution

The effect of concentration on the behavior of high-molecular-mass sodium polymethacrylate (M w = 3.9 × 105) in a 0.1 M NaCl aqueous solution was studied by the methods of dynamic and static light scattering, and capillary and rotational viscometry. It was shown that the concentration corresponding to the formation of fluctuation network of polyelectrolyte entanglements (6.4%) is substantially higher than the crossover concentration (0.25%). This fact indicates the existence of a wide concentration interval for a semidilute unentangled polyanion solution. The introduction of minor amounts of micelles of cationic amphiphilic polystyrene-poly(N-ethyl-4-vinylpyridinium bromide) diblock copolymer is accompanied by the development of the network of an interpolyelectrolyte complex. The junctions of this network are diblock copolymer micelles that are linked to polyanion macromolecules via salt bonds. The formation of interpolyelectrolyte network leads to the additional structuring of the sodium polymethacrylate solution and an increase in its viscosity. The growth in viscosity is most pronounced in the concentration region above the concentration corresponding to the formation of entanglement network of the free polyanion.

Self-Assembly of an Amphiphilic Diblock Copolymer in Aqueous Solutions: Effect of Linear Charge Density of an Ionogenic Block

The effect of linear charge density of the ionogenic block on the selfassembly of the amphiphilic diblock copolymer based on polystyrene and poly(4�vin ylpyridine) partially alkylated by ethyl bromide in aqueous solutions at pH 9 is studied by UV spectrophotometry and dynamic and static light scattering. Dur� ing dispersion in water, the diblock copolymer forms micelles composed of the hydrophobic polystyrene core and the amphiphilic lyophilizing corona consisting of Nethyl�4�vinylpyridinium bromide ionic units and uncharged units of 4�vinylpyridine. It is shown that with a change in the fraction of charged units in the lyo� philizing block from 30 to 90 mol %, the thermodynamic quality of the solvent with respect to micelles is slightly monotonically improved and the hydrodynamic sizes of micelles in 0.05 M NaCl are increased. At the same time, such properties as the weightaverage deg ree of aggregation of macromolecules in a micelle, the dimensions of the corona in 0.05 M NaCl, and the dispersion stability of micelles in aqueous-saline solution abruptly change when the content of charged units in the lyophilizing block is 60-70 mol %. After addition of oppositely charged polyelectrolytes or lowmolecu larmass surfactants into the micellar solution, poly� electrolyte complexes form and the solubility of these complexes in an excess oppositely charged component likewise changes abruptly with variation in the fraction of charged units in the range from 60 to 70 mol %. A qualitative description is advanced to explain the effect of linear charged density of the lyophilizing block on the selfassembly and complexing behavior of diblock copolymers in aqueous solutions.

Regulation of PPARGC1A gene expression in trained and untrained human skeletal muscle

Promoter‐specific expression of the PPARGC1A gene in untrained and trained human skeletal muscle was investigated. Ten untrained males performed a one‐legged knee extension exercise (for 60 min) with the same relative intensity both before and after 8 weeks of cycling training. Samples from the m. vastus lateralis of each leg were taken before and after exercise. Postexercise PPARGC1A gene expression via the canonical promoter increased by ~100% (P < 0.05) in exercised and nonexercised untrained muscles, but did not change in either leg after training program. In untrained and trained exercised muscle, PPARGC1A gene expression via the alternative promoter increased by two orders of magnitude (P < 0.01). We found increases in postexercise content of dephosphorylated (activated) CRTC2, a coactivator of CREB1, in untrained exercised muscle and in expression of CREB1‐related genes in untrained and trained exercised muscle (P < 0.01–0.05); this may partially explain the increased expression of PPARGC1A via the alternative promoter. In addition, comparison of the regulatory regions of both promoters revealed unique conserved motifs in the alternative promoter that were associated with transcriptional repressors SNAI1 and HIC1. In conclusion, in untrained muscle, exercise‐induced expression of the PPARGC1A gene via the canonical promoter may be regulated by systemic factors, while in trained muscle the canonical promoter shows constitutive expression at rest and after exercise. Exercise‐induced expression of PPARGC1A via the alternative promoter relates to intramuscular factors and associates with activation of CRTC2‐CREB1. Apparently, expression via the alternative promoter is regulated by other transcription factors, particularly repressors.

AMPK does not play a requisite role in regulation of PPARGC1A gene expression via the alternative promoter in endurance-trained human skeletal muscle

What is the central question of this study? This study was designed to investigate the role of AMPK in the regulation of PGC‐1α gene expression via the alternative promoter through a cAMP response element‐binding protein‐1‐dependent mechanism in human skeletal muscle. What is the main finding and its importance? Low‐intensity exercise markedly increased the expression of PGC‐1α mRNA via the alternative promoter, without increases in ACCSer79/222 (a marker of AMPK activation) and AMPKThr172 phosphorylation. A single dose of the AMPK activator metformin indicated that AMPK was not involved in regulating PGC‐1α mRNA expression via the alternative promoter in endurance‐trained human skeletal muscle.

Intensity-dependent gene expression after aerobic exercise in endurance-trained skeletal muscle

We investigated acute exercise-induced gene expression in skeletal muscle adapted to aerobic training. Vastus lateralis muscle samples were taken in ten endurance-trained males prior to, and just after, 4 h, and 8 h after acute cycling sessions with different intensities, 70% and 50% V˙O2max. High-throughput RNA sequencing was applied in samples from two subjects to evaluate differentially expressed genes after intensive exercise (70% V˙O2max), and then the changes in expression for selected genes were validated by quantitative PCR (qPCR). To define exercise-induced genes, we compared gene expression after acute exercise with different intensities, 70% and 50% V˙O2max, by qPCR. The transcriptome is dynamically changed during the first hours of recovery after intensive exercise (70% V˙O2max). A computational approach revealed that the changes might be related to up- and down-regulation of the activity of transcription activators and repressors, respectively. The exercise increased expression of many genes encoding protein kinases, while genes encoding transcriptional regulators were both up- and down-regulated. Evaluation of the gene expression after exercise with different intensities revealed that some genes changed expression in an intensity-dependent manner, but others did not: the majority of genes encoding protein kinases, oxidative phosphorylation and activator protein (AP)-1-related genes significantly correlated with markers of exercise stress (power, blood lactate during exercise and post-exercise blood cortisol), while transcriptional repressors and circadian-related genes did not. Some of the changes in gene expression after exercise seemingly may be modulated by circadian rhythm.

Emulsifier-Free Polymerization of n-Butyl Acrylate Involving Trithiocarbonates Based on Oligomer Acrylic Acid

The effect of the chain length of oligomer acrylic acid obtained in the presence of a low-molecularmass trithiocarbonate and the position of trithiocarbonate fragment (within the chain or at the chain end) on the process of emulsion polymerization of n-butyl acrylate and characteristics of the resulting dispersions has been studied for the first time. It has been found that, when using an oligomer with trithiocarbonate group located within the chain in the emulsion polymerization of n-butyl acrylate in a wide range of monomer–water phase compositions, triblock copolymers self-organizing in aqueous medium to give stable particles with the core–shell structure are formed. Oligomers with M n ∼ (5–10) × 103 are optimal for synthesis of stable dispersions. In this case, block copolymers with the controlled length of hydrophobic block and a rather narrow MWD may be obtained. Thin films formed from these copolymers retain the structure of the initial dispersions on solvent removal. If the trithiocarbonate group in the oligomer is located at the chain end, the main polymerization product is a diblock copolymer. In this case, the formation of polymer–monomer particles occurs during a longer period of time, the control of MWD is weakened, and the dispersions of particles lose the aggregative stability after thin film formation.

Ternary copolymers of acrylic acid, N-isopropylacrylamide, and butyl acrylate: Synthesis and aggregative behavior in dilute solutions

Narrowly dispersed hydrophilic block and random copolymers of acrylic acid and N-isopropylacrylamide of various compositions and molecular masses are synthesized for the first time by controlled radical polymerization via the reversible addition-fragmentation chain-transfer mechanism. The copolymers are used for the synthesis of ternary copolymers with n-butyl acrylate. As shown by dynamic light scattering, the resulting amphiphilic copolymers can form stable dispersions in diluted aqueous solutions. It is found that the effective hydrodynamic radii of dispersion particles may be controlled via variation both in the primary structure of the ternary copolymer, i.e., the amount and sequence of hydrophilic and hydrophobic units, and in the external stimuli, i.e., the temperature and pH of a solution.