Determinants of bronchial responsiveness to methacholine at school age in twin pairs

The methacholine inhalation challenge test (MIC) was used to evaluate bronchial responsiveness in 67 children who were the products of multiple pregnancies when they were 7-15 years old. At birth, 30 (45%) infants had intrauterine growth retardation (IUGR; birth weight <2 SD below normal birth weight, or birth weight difference >1.3 SD between twin-pairs), and 59 (88%) were born before 37 weeks of gestation. None of the children had doctor-diagnosed asthma. The provocative dose of methacholine causing a 20% fall in Wright's peak expiratory flow (WPEF) (PD20) was below 1,000 microg in 10 (15%) children, and they were classified as MIC responders. There were no differences in perinatal or neonatal factors between MIC responders and nonresponders; in particular, MIC responses did not differ between IUGR infants, and children with appropriate growth for gestational age (AGA) at birth. There were seven discordant pairs in which one child was a MIC responder and the other was not; 5 responders were IUGR, and 2 were AGA children (ns). Respiratory tract infections after the neonatal period were equally common in IUGR and AGA children. However, these infections were associated with later bronchial hyperresponsiveness. Doctor-diagnosed respiratory infections, numbers of antibiotic courses, episodes of otitis media, and the need for adenoidectomy, tonsillectomy, and tympanostomy were more common in MIC responders than in nonresponders. We conclude that IUGR was not associated with subsequent bronchial hyperresponsiveness in twin pairs assessed by the MIC test. A significant relationship was seen between bronchial hyperresponsiveness and infections after the neonatal period.     

Hemostatic factors as predictors of coronary events and total mortality: The FINRISK '92 Hemostasis Study

The role of hemostatic factors as predictors of coronary heart disease (CHD) and total mortality is poorly understood. Therefore, we carried out a prospective cohort study in Finland. In 1992, a random population sample of 2378 men and women aged 45 to 64 years was investigated and then followed up until December 31, 1998. During the follow-up, 133 CHD events were observed; 73 were among participants free of CHD at baseline. The total number of deaths was 124. After adjustment for traditional risk factors and prevalent CHD at baseline and correction for regression dilution bias, a 1-SD increase in plasminogen was associated with a 1.41-fold (95% CI 1.09 to 1.81) increase in CHD risk. The predictive power of plasminogen depended significantly on the level of total cholesterol being stronger for persons with high cholesterol. A 1-SD increase in fibrinogen was associated with a 1.23-fold (95% CI 1.05 to 1.44) increase in all-cause mortality, but its association with CHD events did not reach statistical significance. Factor VII antigen or coagulant activity or lipoprotein(a) were not independent predictors of CHD risk. These findings support the role of plasminogen as a risk factor for CHD events.     

Prediction of Blood Pressure and Blood Pressure Change With a Genetic Risk Score

The authors investigated whether a genetic risk score (GRS) constructed of 32 single nucleotide polymorphisms would predict incident hypertension and blood pressure (BP) change over time in a population cohort during an 11‐year follow‐up (n=5402 at baseline, 3266 at follow‐up). In multivariable models, GRS was associated with higher systolic/diastolic BP values at baseline (β±standard error [SE], 1.04±0.14/1.11±0.13 mm Hg; P<.0001 for both) and at reinvestigation (β±SE, 0.84±0.18/0.79±0.16 mm Hg; P<.0001 for both). Among participants who were normotensive at baseline (n=2045), GRS was not independently associated with systolic/diastolic BP change over time (β±SE, 0.16±0.18/0.20±0.18 mm Hg; P≥.28 for both). In participants in the top tertile of the GRS, as compared with the bottom tertile, the predicted increase in systolic/diastolic BP was 1.18±0.78/0.70±0.49 mm Hg (P=.046/.15) greater and the odds ratio for incident hypertension was 33% higher (P=.03). These data show that GRS is strongly associated with BP but weakly associated with BP increase and incident hypertension in a late middle‐aged population.     

CHRNA5/CHRNA3 Locus Associates with Increased Mortality among Smokers

Polymorphisms in the nicotinic acetylcholine receptor gene (CHRNA5/CHRNA3 locus) have been associated with several smoking related traits such as nicotine dependence, cigarette consumption, smoking cessation, lung cancer, and COPD. The aim of this candidate gene study was to study the locus among the Finnish COPD patients and long-term smokers with regard to COPD risk, smoking behavior, cancer, and all-cause mortality. Genotyping of rs1051730, the locus tagging SNP was done in two longitudinal cohorts: Finnish COPD patients (N = 575, 74% men) and long-term smokers, all men (N = 1911). Finnish population sample (N = 1730) was used as controls. The analyses were done using logistic and Cox regression. The main findings were that the minor allele increased the risk of COPD when compared to the Finnish population at large (OR = 1.4, 95% CI 1.2-1.7, p = 3.2 × 10-5). Homozygosity for the risk allele was associated in both cohorts with all-cause mortality (crude HR 2.2, 95% CI 1.2–3.8 and 1.3, 95% CI 1.1–1.5, respectively), with any type of cancer (crude OR 2.3, 95% CI 1.0–5.1) among the COPD patients and with the number of pack-years (crude OR 1.4, 95% CI 1.1–1.9) among the male smokers. CHRNA5/CHRNA3 locus tagged by rs1051730, which has been previously associated with several smoking related diseases was now shown to be associated also with increased all-cause mortality among long-term smokers with or without clinical COPD further emphasizing the clinical importance of the finding.     

Increased plasma N-glycome complexity is associated with higher risk of type 2 diabetes

Aims/hypothesis

Better understanding of type 2 diabetes and its prevention is a pressing need. Changes in human plasma N-glycome are associated with many diseases and represent promising diagnostic and prognostic biomarkers. Variations in glucose metabolism directly affect glycosylation through the hexosamine pathway but studies of plasma glycome in type 2 diabetes are scarce. The aim of this study was to determine whether plasma protein N-glycome is changed in individuals who are at greater risk of developing type 2 diabetes.

Methods

Using a chromatographic approach, we analysed N-linked glycans from plasma proteins in two populations comprising individuals with registered hyperglycaemia during critical illness (increased risk for development of type 2 diabetes) and individuals who stayed normoglycaemic during the same condition: AcuteInflammation (59 cases vs 49 controls) and AcuteInflammation Replication (52 cases vs 14 controls) populations. N-glycome was also studied in individuals from FinRisk (37 incident cases of type 2 diabetes collected at baseline vs 37 controls), Orkney Complex Disease Study (ORCADES; 94 individuals with HbA_1c > 6.5% [47.5 mmol/mol] vs 658 controls) and Southall and Brent Revisited (SABRE) cohort studies (307 individuals with HbA_1c > 6.5% [47.5 mmol/mol] vs 307 controls).

Results

Individuals with increased risk for diabetes type 2 development (AcuteInflammation and AcuteInflammation Replication populations), incident cases of type 2 diabetes collected at baseline (FinRisk population) and individuals with elevated HbA_1c (ORCADES and SABRE populations) all presented with increased branching, galactosylation and sialylation of plasma protein N-glycans and these changes were of similar magnitude.

Conclusions/interpretation

Increased complexity of plasma N-glycan structures is associated with higher risk of developing type 2 diabetes and poorer regulation of blood glucose levels. Although further research is needed, this finding could offer a potential new approach for improvement in prevention of diabetes and its complications.

     

Cell-body rocking is a dominant mechanism for flagellar synchronization in a swimming alga

The unicellular green alga Chlamydomonas swims with two flagella that can synchronize their beat. Synchronized beating is required to swim both fast and straight. A long-standing hypothesis proposes that synchronization of flagella results from hydrodynamic coupling, but the details are not understood. Here, we present realistic hydrodynamic computations and high-speed tracking experiments of swimming cells that show how a perturbation from the synchronized state causes rotational motion of the cell body. This rotation feeds back on the flagellar dynamics via hydrodynamic friction forces and rapidly restores the synchronized state in our theory. We calculate that this “cell-body rocking” provides the dominant contribution to synchronization in swimming cells, whereas direct hydrodynamic interactions between the flagella contribute negligibly. We experimentally confirmed the two-way coupling between flagellar beating and cell-body rocking predicted by our theory.Eukaryotic cilia and flagella are long, slender cell appendages that can bend rhythmically and thus present a prime example of a biological oscillator (1). The flagellar beat is driven by the collective action of dynein molecular motors, which are distributed along the length of the flagellum. The beat of flagella, with typical frequencies ranging from 20–60 Hz, pumps fluids, for example, mucus in mammalian airways (2), and propels unicellular microswimmers such as Paramecia, spermatozoa, and algae (3). The coordinated beating of collections of flagella is important for efficient fluid transport (2, 4, 5) and fast swimming (6). This coordinated beating represents a striking example for the synchronization of oscillators, prompting the question of how flagella couple their beat. Identifying the specific mechanism of synchronization can be difficult because synchronization may occur even for weak coupling (7). Further, the effect of the coupling is difficult to detect once the synchronized state has been reached.Hydrodynamic forces were suggested to play a significant role for flagellar synchronization already in 1951 by Taylor (8). Since then, direct hydrodynamic interactions between flagella were studied theoretically as a possible mechanism for flagellar synchronization (9–12). Another synchronization mechanism that is independent of hydrodynamic interactions was recently described in the context of a minimal model swimmer (13–15). This mechanism crucially relies on the interplay of swimming motion and flagellar beating.Here, we address the hydrodynamic coupling between the two flagella in a model organism for flagellar coordination (16–19), the unicellular green alga Chlamydomonas reinhardtii. Chlamydomonas propels its ellipsoidal cell body, which has typical diameter of 10 μm, using a pair of flagella, whose lengths are about 10 μm (16). The two flagella beat approximately in a common plane, which is collinear with the long axis of the cell body. In that plane, the two beat patterns are nearly mirror-symmetric with respect to this long axis. The beating of the two flagella of Chlamydomonas can synchronize, that is, adopt a common beat frequency and a fixed phase relationship (16–19). In-phase synchronization of the two flagella is required for swimming along a straight path (19). The specific mechanism leading to flagellar synchrony is unclear.Here, we use a combination of realistic hydrodynamic computations and high-speed tracking experiments to reveal the nature of the hydrodynamic coupling between the two flagella of free-swimming Chlamydomonas cells. Previous hydrodynamic computations for Chlamydomonas used either resistive force theory (20, 21), which does not account for hydrodynamic interactions between the two flagella, or computationally intensive finite element methods (22). We employ an alternative approach and represent the geometry of a Chlamydomonas cell by spherical shape primitives, which provides a computationally convenient method that fully accounts for hydrodynamic interactions between different parts of the cell. Our theory characterizes flagellar swimming and synchronization by a minimal set of effective degrees of freedom. The corresponding equation of motion follows naturally from the framework of Lagrangian mechanics, which was used previously to describe synchronization in a minimal model swimmer (13, 15). These equations of motion embody the key assumption that the flagellar beat speeds up or slows down according to the hydrodynamic friction forces acting on the flagellum, that is, if there is more friction and therefore higher hydrodynamic load, then the beat will slow down. This assumption is supported by previous experiments that showed that the flagellar beat frequency decreases when the viscosity of the surrounding fluid is increased (23, 24). The simple force–velocity relationship for the flagellar beat employed by us coarse-grains the behavior of thousands of dynein molecular motors that collectively drive the beat. Similar force–velocity properties have been described for individual molecular motors (25) and reflect a typical behavior of active force generating systems.Our theory predicts that any perturbation of synchronized beating results in a significant yawing motion of the cell, reminiscent of rocking of the cell body. This rotational motion imparts different hydrodynamic forces on the two flagella, causing one of them to beat faster and the other to slow down. This interplay between flagellar beating and cell-body rocking rapidly restores flagellar synchrony after a perturbation. Using the framework provided by our theory, we analyze high-speed tracking experiments of swimming cells, confirming the proposed two-way coupling between flagellar beating and cell-body rocking.Previous experiments restrained Chlamydomonas cells from swimming, holding their cell body in a micropipette (17–19). Remarkably, flagellar synchronization was observed also for these constrained cells. This observation seems to argue against a synchronization mechanism that relies on swimming motion. However, the rate of synchronization observed in these experiments was faster by an order of magnitude than the rate we predict for synchronization by direct hydrodynamic interactions between the two flagella in the absence of any motion. In contrast, we show that rotational motion with a small amplitude of a few degrees only, which may result from either a residual rotational compliance of the clamped cell or an elastic anchorage of the flagellar pair, provides a possible mechanism for rapid synchronization, which is analogous to synchronization by cell-body rocking in free-swimming cells.     

Common missense variant in the glucokinase regulatory protein gene is associated with increased plasma triglyceride and C-reactive protein but lower fasting glucose concentrations

OBJECTIVE—Using the genome-wide association approach, we recently identified the glucokinase regulatory protein gene (GCKR, rs780094) region as a novel quantitative trait locus for plasma triglyceride concentration in Europeans. Here, we sought to study the association of GCKR variants with metabolic phenotypes, including measures of glucose homeostasis, to evaluate the GCKR locus in samples of non-European ancestry and to fine- map across the associated genomic interval.RESEARCH DESIGN AND METHODS—We performed association studies in 12 independent cohorts comprising >45,000 individuals representing several ancestral groups (whites from Northern and Southern Europe, whites from the U.S., African Americans from the U.S., Hispanics of Caribbean origin, and Chinese, Malays, and Asian Indians from Singapore). We conducted genetic fine-mapping across the ∼417-kb region of linkage disequilibrium spanning GCKR and 16 other genes on chromosome 2p23 by imputing untyped HapMap single nucleotide polymorphisms (SNPs) and genotyping 104 SNPs across the associated genomic interval.RESULTS—We provide comprehensive evidence that GCKR rs780094 is associated with opposite effects on fasting plasma triglyceride (P_meta = 3 × 10⁻⁵⁶) and glucose (P_meta = 1 × 10⁻¹³) concentrations. In addition, we confirmed recent reports that the same SNP is associated with C-reactive protein (CRP) level (P = 5 × 10⁻⁵). Both fine-mapping approaches revealed a common missense GCKR variant (rs1260326, Pro446Leu, 34% frequency, r² = 0.93 with rs780094) as the strongest association signal in the region.CONCLUSIONS—These findings point to a molecular mechanism in humans by which higher triglycerides and CRP can be coupled with lower plasma glucose concentrations and position GCKR in central pathways regulating both hepatic triglyceride and glucose metabolism.Recently, in the genome-wide association Diabetes Genetics Initiative (DGI) Study for 19 traits, including plasma lipids, we provided evidence that the glucokinase (GCK) regulatory protein gene (GCKR) region was a novel quantitative trait locus associated with plasma triglyceride concentration (1). Of all single nucleotide polymorphisms (SNPs) tested, an intronic SNP at GCKR (rs780094) explained the greatest proportion of interindividual variability in plasma triglycerides (1).GCKR regulates GCK, which functions as a glucose sensor responsible for glucose phosphorylation in the first step of glycolysis. The discoveries that inactivating mutations in GCK cause maturity onset diabetes of the young type 2 (2) and activating GCK mutations lead to permanent hyperinsulinemic hypoglycemia (3) emphasize that GCK plays a major role in glucose metabolism. GCKR-deficient mice have reduced GCK expression but maintain nearly normal GCK activity and show impaired glucose clearance (4). Furthermore, adenoviral-mediated overexpression of GCKR in mouse liver increased GCK activity and lowered fasting blood glucose (5) and overexpression of GCK in liver led to lowered blood glucose and increased triglyceride concentrations (6,7). Thus, experimental evidence suggests that perturbation of the GCKR pathway has opposing effects of triglyceride and glucose metabolism.In our original report, SNP rs780094 in GCKR was associated with fasting triglyceride levels in two independent samples, each of Northern European ancestry (P = 3.7 × 10⁻⁸ and 8.7 × 10⁻⁸, respectively) (1). After initial identification and replication of a chromosomal region associated with a trait, key next steps include extension of the association finding to related phenotypes, validation of the association finding in different ethnicities, and fine- mapping to identify the putative causal variant. Recently, our initial finding was replicated in a Danish study in which a strong association was found between the rs780094 T allele and elevated fasting triglyceride levels but also lower insulin levels, better insulin sensitivity, and a moderately decreased risk of type 2 diabetes (8). In addition, recent genome-wide association studies identified an association between the same GCKR intronic SNP and C-reactive protein (CRP) levels (9,10).Hereby, we sought to examine the effect of SNP rs780094 on triglycerides and related metabolic traits, including fasting glucose concentrations, in 12 samples representing a range of ancestral groups and including a large prospective study with a mean follow-up time of 23 years. In addition, we performed fine-mapping in one of these samples to identify the strongest association signal in the region.