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Biomedical subjects

Thomas Nyström

Publications and source records attributed to Thomas Nyström.

At least 19 recordsLinked to original sources
PubMed2006

Conditional and replicative senescence in Escherichia coli.

Analysis of the molecular mechanisms underlying the cellular degeneration of bacteria in stationary phase (known as conditional senescence) reveals interesting similarities with the aging process of higher organisms. These similarities include the role of self-inflicted oxidative damage and the importance of protein quality control systems in retarding senescence. In addition, recent data suggests that Escherichia coli cells display signs of replicative senescence, or loss of fitness, during exponential growth and that this phenomenon targets the 'older' cells. Thus, bacterial physiology might entail both conditional and mandatory aging processes.

Adaptation, Physiological↗
PubMed2006

A microfluidic system in combination with optical tweezers for analyzing rapid and reversible cytological alterations in single cells upon environmental changes.

We report on the development of an experimental platform where epi-fluorescence microscopy and optical tweezers are combined with a microfluidic system to enable the analysis of rapid cytological responses in single cells. The microfluidic system allows two different media to be merged in a Y-shaped channel. Microscale channel dimensions ensure purely laminar flow and, as a result, an environmental gradient can be created between the two media. Optical tweezers are used to move a single trapped cell repeatedly between the different environments. The cell is monitored continuously by fluorescence microscopy during the experiment. In a first experiment on yeast (Saccharomyces cerevisiae) we observed changes in cell volume as the cell was moved between environments with different osmolarity. This demonstrated that the platform allowed analysis of cytological alterations on a time scale shorter than 0.2 s. In a second experiment we observed the spatial migration of the Yap1p transcription factor fused to GFP as a cell was moved from an environment of low to high oxidative capacity. The system is universal allowing the response to numerous environmental changes to be studied on the sub second time scale in a variety of model cells. We intend to use the platform to study how the age of cells, their progression through the cell cycle, or their genetic landscape, alter their capacity (kinetics and amplitude) to respond to environmental changes.

Culture Media↗
PubMed2006

Elimination of damaged proteins during differentiation of embryonic stem cells.

During mammalian aging, cellular proteins become increasingly damaged: for example, by carbonylation and formation of advanced glycation end products (AGEs). The means to ensure that offspring are born without such damage are unknown. Unexpectedly, we found that undifferentiated mouse ES cells contain high levels of both carbonyls and AGEs. The damaged proteins, identified as chaperones and proteins of the cytoskeleton, are the main targets for protein oxidation in aged tissues. However, the mouse ES cells rid themselves of such damage upon differentiation in vitro. This elimination of damaged proteins coincides with a considerably elevated activity of the 20S proteasome. Moreover, damaged proteins were primarily observed in the inner cell mass of blastocysts, whereas the cells that had embarked on differentiation into the trophectoderm displayed drastically reduced levels of protein damage. Thus, the elimination of protein damage occurs also during normal embryonic development in vivo. This clear-out of damaged proteins may be a part of a previously unknown rejuvenation process at the protein level that occurs at a distinct stage during early embryonic development.

Aging↗
PubMed2006

Increased levels of tumour necrosis factor-alpha (TNF-alpha) in patients with Type II diabetes mellitus after myocardial infarction are related to endothelial dysfunction.

The pathophysiology of insulin resistance and atherosclerosis may share a common inflammatory basis, maintaining endothelial dysfunction, suggesting why patients with T2DM (Type II diabetes mellitus) have an impaired prognosis after an MI (myocardial infarction), but it remains unclear how these parameters are inter-related. Forty patients with an MI (20 patients with and 20 patients without T2DM) took part in this cross-sectional study. Endothelium-dependent [FMD (flow-mediated dilation)] and -independent [NTG (nitroglycerine)] vasodilatation (determined by ultrasound), S(I) (insulin sensitivity index; determined by isoglycaemic-hyperinsulinaemic clamp) and serum levels of CRP (C-reactive protein), TNF-alpha (tumour necrosis factor-alpha), IL-6 (interleukin 6), resistin and adiponectin (determined by ELISA) were measured. Associations between FMD/NTG and S(I), and CRP, TNF-alpha, IL-6, adiponectin, resistin, lipids, blood pressure, BMI (body mass index) and brachial artery diameter were then assessed. FMD (2.1 compared with 4.7%; P<0.05), NTG (14.9 compared with 21.2%; P<0.05) and S(I) [4.3 compared with 6.6 10(-4) dl.kg(-1) of body weight.min(-1).(mu-units/ml)(-1); P<0.05], and adiponectin levels (3.1 compared with 6.4 microg/ml; P<0.01) were all lower in patients with T2DM. TNF-alpha (6.9 compared with 1.8 pg/ml; P<0.01) and IL-6 (2.3 compared with 1.2 pg/ml; P<0.01) levels were higher in patients with T2DM, whereas differences in CRP and resistin levels did not attain statistical significance between the two groups. TNF-alpha concentrations and brachial artery diameter were negatively, whereas S(I) was positively, correlated with FMD. Adjustment for age weakened the association for S(I), whereas TNF-alpha and brachial artery diameter remained significantly associated with FMD after adjustment for group, age and BMI. Endothelial dysfunction and low-grade inflammation co-exist in T2DM after MI. These results suggest that the endothelium is negatively impacted in multiple ways by the diabetic state after an MI.

Adiponectin↗
PubMed2006

Intravenous hydration with a 2.5% glucose solution in Type II diabetes.

Physicians are often unclear about how fast intravenous glucose solutions should be administered to adequately hydrate patients with Type II diabetes while avoiding hyperglycaemia and excessive plasma volume expansion. The aim of the present study was to analyse the disposition of a 2.5% glucose solution and create a nomogram which could serve as a guide to fluid therapy in these patients. Twelve males (mean body mass index, 29 kg/m(2)) with Type II diabetes due to insulin resistance, as quantified by an euglycaemic hyperinsulinaemic glucose clamp, received an infusion of iso-osmotic 2.5% glucose solution with electrolytes (70 mmol/l sodium, 45 mmol/l chloride and 25 mmol/l acetate) at individual rates over 30 and 60 min respectively. Blood glucose and haemoglobin levels were measured repeatedly over 3.5 h to estimate the kinetics of glucose and fluid volume. Mean insulin sensitivity was 4.2x10(-4) dlxkg(-1)xmin(-1)x(micro-units/ml)(-1). The individualized infusion rates reached the predetermined blood glucose level of 12 mmol/l with a mean difference of 0.2 mmol/l. The disposition of glucose was an important factor governing fluid distribution. The volume of distribution of exogenous glucose averaged 19.8 litres, but for the fluid volume it was only 3.7 litres. The clearance was 0.37 litre/min for glucose and 0.10 litre/min for the fluid volume, and the results of the 30-min and 60-min infusions agreed reasonably well. It is concluded that kinetic analysis can be used to guide the infusion time and infusion rate of 2.5% glucose to reach any predetermined glucose level and volume expansion.

Aged↗
PubMed2006

Induction of the heat shock regulon in response to increased mistranslation requires oxidative modification of the malformed proteins.

The Escherichia coli rpsD12 allele, which reduces translational fidelity and elevates expression of heat shock protein (Hsp) genes, only enhanced Hsp gene expression in the presence of oxygen. Similarly, the rpsL141 allele, which reduces mistranslation and Hsp gene expression, failed to affect the Hsp regulon in cells grown anaerobically. Increased production of Hsps in response to starvation is associated with increased mistranslation and was demonstrated to likewise require the presence of oxygen. Thus, mistranslation triggered by starvation or mutations in the accuracy centre of the ribosome appear to elevate Hsp gene expression via an oxidative modification of mistranslated proteins. In contrast, Hsp gene induction during temperature upshifts was independent of oxygen availability. The data further suggest that it is the oxidative modification of mistranslated DnaK substrates rather than oxidation of DnaK itself that triggers Hsp gene expression upon starvation.

Chaperonin 60↗
PubMed2005

Genomic buffering mitigates the effects of deleterious mutations in bacteria.

The relationship between the number of randomly accumulated mutations in a genome and fitness is a key parameter in evolutionary biology. Mutations may interact such that their combined effect on fitness is additive (no epistasis), reinforced (synergistic epistasis) or mitigated (antagonistic epistasis). We measured the decrease in fitness caused by increasing mutation number in the bacterium Salmonella typhimurium using a regulated, error-prone DNA polymerase (polymerase IV, DinB). As mutations accumulated, fitness costs increased at a diminishing rate. This suggests that random mutations interact such that their combined effect on fitness is mitigated and that the genome is buffered against the fitness reduction caused by accumulated mutations. Levels of the heat shock chaperones DnaK and GroEL increased in lineages that had accumulated many mutations, and experimental overproduction of GroEL further increased the fitness of lineages containing deleterious mutations. These findings suggest that overexpression of chaperones contributes to antagonistic epistasis.

Adaptation, Physiological↗
PubMed2005

Role of oxidative carbonylation in protein quality control and senescence.

Proteins can become modified by a large number of reactions involving reactive oxygen species. Among these reactions, carbonylation has attracted a great deal of attention due to its irreversible and unrepairable nature. Carbonylated proteins are marked for proteolysis by the proteasome and the Lon protease but can escape degradation and form high-molecular-weight aggregates that accumulate with age. Such carbonylated aggregates can become cytotoxic and have been associated with a large number of age-related disorders, including Parkinson's disease, Alzheimer's disease, and cancer. This review focuses on the generation of and defence against protein carbonyls and speculates on the potential role of carbonylation in protein quality control, cellular deterioration, and senescence.

Age Factors↗
PubMed2005

Glucagon-like peptide-1 relaxes rat conduit arteries via an endothelium-independent mechanism.

A lot of interest has engendered in glucagon-like peptide-1 (GLP-1) as an emerging new drug in the treatment of type 2 diabetes. GLP-1 exerts several effects that reduce glycemia in type 2 diabetes patients. We recently also demonstrated that GLP-1 ameliorates endothelial dysfunction in type 2 diabetes mellitus patients with established coronary heart disease, suggesting a new important cardioprotective role for GLP-1. Because hypertension is overrepresented in diabetes and is adversely influencing survival, we have now investigated direct GLP-1 effects on vascular beds in a rat organ bath model. It was found that GLP-1 relaxed femoral artery rings in a dose-response manner. The relaxant effect from GLP-1 was completely inhibited by the specific GLP-1 receptor antagonist, exendin(9-39). Neither the specific nitric oxide (NO) synthase inhibitor, N-nitro-L-arginine, nor removing of endothelium, affected the GLP-1 relaxant effect. In conclusion, we now report a direct vascular action of GLP-1, relaxing conduit vessels independently of NO and the endothelium.

Acetylcholine↗
PubMed2005

ppGpp: a global regulator in Escherichia coli.

The small nucleotide ppGpp acts as a global regulator of gene expression in bacteria. Proteomic analysis of cells lacking ppGpp has shown that this nucleotide might affect many more genes than previously anticipated. These findings and others suggest that ppGpp causes a redirection of transcription so that genes important for starvation survival and virulence are favoured at the expense of those required for growth and proliferation. In addition, new insights into the mechanism by which ppGpp affects gene expression have been achieved owing to in vitro studies of ppGpp function, complemented by structural studies of the ppGpp-RNA polymerase complex.

DNA-Directed RNA Polymerases↗
PubMed2005

Persistent endothelial dysfunction is related to elevated C-reactive protein (CRP) levels in Type II diabetic patients after acute myocardial infarction.

The atherosclerotic process is an ongoing dynamic and progressive state arising from endothelial dysfunction and inflammation. Although suffering from an acute coronary artery disease, patients with Type II diabetes have a poor outcome compared with non-diabetic patients, which may only partly be explained by traditional risk factors. Our purpose was to compare non-traditional risk factors, such as endothelial function, C-reactive protein (CRP) and adiponectin, in Type II diabetic and non-diabetic patients following AMI (acute myocardial infarction). Twenty Type II diabetic patients were compared with 25 non-diabetic patients at baseline (1-3 days from the onset of chest pain) and at 60 days follow-up after an AMI. Using high-resolution ultrasound, brachial artery responses to FMD (flow-mediated vasodilatation; endothelium-dependent vasodilatation) and NTG (nitroglycerine-induced vasodilatation; endothelium-independent vasodilatation) were measured. Plasma levels of CRP and adiponectin were measured by ELISA. At baseline, FMD (1.9 compared with 3.2%; P=0.22) and CRP levels (6.95 compared with. 5.51 mg/l; P=0.40) did not differ between Type II diabetic and non-diabetic patients, whereas adiponectin levels were lower in Type II diabetic patients (2.8 compared with 5.0 ng/ml; P<0.05). At 60 days follow-up, there were significant differences in FMD (1.5 compared with 4.1%; P<0.02), CRP (4.23 compared with 1.46 mg/ml; P<0.01) and adiponectin (3.3 compared with 5.3 ng/ml; P<0.05) levels between Type II diabetic and non-diabetic patients. In contrast, NTG responses improved in both groups between baseline and follow-up (Type II diabetic patients, 9.7 compared with 13.2% respectively, P<0.05; non-diabetic patients, 7.9 compared with 12.4% respectively, P<0.01). These results show a persistent endothelium-dependent dysfunction and inflammatory activity in patients with Type II diabetes, but not in non-diabetic patients, after AMI. These findings may, in part explain, the poor outcome in coronary artery disease seen in Type II diabetes.

Adiponectin↗
PubMed2005

Defense against protein carbonylation by DnaK/DnaJ and proteases of the heat shock regulon.

Protein carbonylation is an irreversible oxidative modification that increases during organism aging and bacterial growth arrest. We analyzed whether the heat shock regulon has a role in defending Escherichia coli cells against this deleterious modification upon entry into stationary phase. Providing the cell with ectopically elevated levels of the heat shock transcription factor, sigma32, effectively reduced stasis-induced carbonylation. Separate overproduction of the major chaperone systems, DnaK/DnaJ and GroEL/GroES, established that the former of these is more important in counteracting protein carbonylation. Deletion of the heat shock proteases Lon and HslVU enhanced carbonylation whereas a clpP deletion alone had no effect. However, ClpP appears to have a role in reducing protein carbonyls in cells lacking Lon and HslVU. Proteomic immunodetection of carbonylated proteins in the wild-type, lon, and hslVU strains demonstrated that the same spectrum of proteins displayed a higher load of carbonyl groups in the lon and hslVU mutants. These proteins included the beta-subunit of RNA polymerase, elongation factors Tu and G, the E1 subunit of the pyruvate dehydrogenase complex, isocitrate dehydrogenase, 6-phosphogluconate dehydrogenase, and serine hydroxymethyltranferase.

Cell Cycle↗
PubMed2005

Differential roles of the universal stress proteins of Escherichia coli in oxidative stress resistance, adhesion, and motility.

The universal stress protein (UspA) superfamily encompasses a conserved group of proteins that are found in bacteria, archaea, and eukaryotes. Escherichia coli harbors six usp genes--uspA, -C, -D, -E, -F, and -G--the expression of which is triggered by a large variety of environmental insults. The uspA gene is important for survival during cellular growth arrest, but the exact physiological role of the Usp proteins is not known. In this work we have performed phenotypic characterization of mutants with deletions of the six different usp genes. We report on hitherto unknown functions of these genes linked to motility, adhesion, and oxidative stress resistance, and we show that usp functions are both overlapping and distinct. Both UspA and UspD are required in the defense against superoxide-generating agents, and UspD appears also important in controlling intracellular levels of iron. In contrast, UspC is not involved in stress resistance or iron metabolism but is essential, like UspE, for cellular motility. Electron microscopy demonstrates that uspC and uspE mutants are devoid of flagella. In addition, the function of the uspC and uspE genes is linked to cell adhesion, measured as FimH-mediated agglutination of yeast cells. While the UspC and UspE proteins promote motility at the expense of adhesion, the UspF and UspG proteins exhibit the exact opposite effects. We suggest that the Usp proteins have evolved different physiological functions that reprogram the cell towards defense and escape during cellular stress.

Bacterial Adhesion↗
PubMed2004

Effects of glucagon-like peptide-1 on endothelial function in type 2 diabetes patients with stable coronary artery disease.

GLP-1 stimulates insulin secretion, suppresses glucagon secretion, delays gastric emptying, and inhibits small bowel motility, all actions contributing to the anti-diabetogenic peptide effect. Endothelial dysfunction is strongly associated with insulin resistance and type 2 diabetes mellitus and may cause the angiopathy typifying this debilitating disease. Therefore, interventions affecting both endothelial dysfunction and insulin resistance may prove useful in improving survival in type 2 diabetes patients. We investigated GLP-1's effect on endothelial function and insulin sensitivity (S(I)) in two groups: 1) 12 type 2 diabetes patients with stable coronary artery disease and 2) 10 healthy subjects with normal endothelial function and S(I). Subjects underwent infusion of recombinant GLP-1 or saline in a random crossover study. Endothelial function was measured by postischemic FMD of brachial artery, using ultrasonography. S(I) [in (10(-4) dl.kg(-1).min(-1))/(muU/ml)] was measured by hyperinsulinemic isoglycemic clamp technique. In type 2 diabetic subjects, GLP-1 infusion significantly increased relative changes in brachial artery diameter from baseline FMD(%) (3.1 +/- 0.6 vs. 6.6 +/- 1.0%, P < 0.05), with no significant effects on S(I) (4.5 +/- 0.8 vs. 5.2 +/- 0.9, P = NS). In healthy subjects, GLP-1 infusion affected neither FMD(%) (11.9 +/- 0.9 vs. 10.3 +/- 1.0%, P = NS) nor S(I) (14.8 +/- 1.8 vs. 11.6 +/- 2.0, P = NS). We conclude that GLP-1 improves endothelial dysfunction but not insulin resistance in type 2 diabetic patients with coronary heart disease. This beneficial vascular effect of GLP-1 adds yet another salutary property of the peptide useful in diabetes treatment.

Adult↗
PubMed2004

Tetrahydrobiopterin increases insulin sensitivity in patients with type 2 diabetes and coronary heart disease.

Tetrahydrobiopterin (BH(4)) is an essential cofactor of nitric oxide synthase that improves endothelial function in diabetics, smokers, and patients with hypercholesterolemia. Insulin resistance has been suggested as a contributing factor in the development of endothelial dysfunction via an abnormal pteridine metabolism. We hypothesized that BH(4) would restore flow-mediated vasodilation (FMD, endothelial-dependent vasodilation), which may affect insulin resistance in type 2 diabetic patients. Thirty-two subjects (12 type 2 diabetic subjects, 10 matched nondiabetic subjects, and 10 healthy unmatched subjects) underwent infusion of BH(4) or saline in a random crossover study. Insulin sensitivity index (S(I)) was measured by hyperinsulinemic isoglycemic clamp. FMD was measured using ultrasonography. BH(4) significantly increased S(I) in the type 2 diabetics [3.6 +/- 0.6 vs. 4.9 +/- 0.7 x 10(-4) dl.kg(-1).min(-1)/(microU/ml), P < 0.05], while having no effects in nondiabetics [8.9 +/- 1.1 vs. 9.0 +/- 0.9 x 10(-4) dl.kg(-1).min(-1)/(microU/ml), P = 0.92] or in healthy subjects [17.5 +/- 1.6 vs. 18 +/- 1.8 x 10(-4) dl.kg(-1).min(-1)/(microU/ml), P = 0.87]. BH(4) did not affect the relative changes in brachial artery diameter from baseline FMD (%) in type 2 diabetic subjects (2.3 +/- 0.8 vs. 1.8 +/- 1.0%, P = 0.42), nondiabetic subjects (5.3 +/- 1.1 vs. 6.6 +/- 0.9%, P = 0.32), or healthy subjects (11.9 +/- 0.6 vs. 11.0 +/- 1.0%, P = 0.48). In conclusion, BH(4) significantly increases insulin sensitivity in type 2 diabetic patients without any discernible improvement in endothelial function.

Biopterins↗
PubMed2004

Progression and specificity of protein oxidation in the life cycle of Arabidopsis thaliana.

Protein carbonylation is an irreversible oxidative process leading to a loss of function of the modified proteins, and in a variety of model systems, including worms, flies, and mammals, carbonyl levels gradually increase with age. In contrast, we report here that in Arabidopsis thaliana an initial increase in protein oxidation during the first 20 days of the life cycle of the plant is followed by a drastic reduction in protein carbonyls prior to bolting and flower development. Protein carbonylation prior to the transition to flowering targets specific proteins such as Hsp70, ATP synthases, the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and proteins involved in light harvesting/energy transfer and the C2 oxidative photosynthetic carbon cycle. The precipitous fall in protein carbonyl levels is due to the specific reduction in the levels of oxidized proteins rather than an overall loss of chlorophyll and Rubisco associated with the senescence syndrome. The results are discussed in light of contemporary theories of aging in animals.

ATP Synthetase Complexes↗