141 research outputs found
Extrinsic noise passing through a Michaelis-Menten reaction: A universal response of a genetic switch
The study of biochemical pathways usually focuses on a small section of a
protein interactions network. Two distinct sources contribute to the noise in
such a system: intrinsic noise, inherent in the studied reactions, and
extrinsic noise generated in other parts of the network or in the environment.
We study the effect of extrinsic noise entering the system through a nonlinear
uptake reaction which acts as a nonlinear filter. Varying input noise intensity
varies the mean of the noise after the passage through the filter, which
changes the stability properties of the system. The steady-state displacement
due to small noise is independent on the kinetics of the system but it only
depends on the nonlinearity of the input function.
For monotonically increasing and concave input functions such as the
Michaelis-Menten uptake rate, we give a simple argument based on the
small-noise expansion, which enables qualitative predictions of the
steady-state displacement only by inspection of experimental data: when weak
and rapid noise enters the system through a Michaelis-Menten reaction, then the
graph of the system's steady states vs. the mean of the input signal always
shifts to the right as noise intensity increases.
We test the predictions on two models of lac operon, where TMG/lactose uptake
is driven by a Michaelis-Menten enzymatic process. We show that as a
consequence of the steady state displacement due to fluctuations in
extracellular TMG/lactose concentration the lac switch responds in an
asymmetric manner: as noise intensity increases, switching off lactose
metabolism becomes easier and switching it on becomes more difficult.Comment: 25 pages, 9 figures, changed content, added figures, accepted for
publication in Journal of Theoretical Biolog
Structure-Function Correlation of the Human Central Retina
The impact of retinal pathology detected by high-resolution imaging on vision remains largely unexplored. Therefore, the aim of the study was to achieve high-resolution structure-function correlation of the human macula in vivo.To obtain high-resolution tomographic and topographic images of the macula spectral-domain optical coherence tomography (SD-OCT) and confocal scanning laser ophthalmoscopy (cSLO), respectively, were used. Functional mapping of the macula was obtained by using fundus-controlled microperimetry. Custom software allowed for co-registration of the fundus mapped microperimetry coordinates with both SD-OCT and cSLO datasets. The method was applied in a cross-sectional observational study of retinal diseases and in a clinical trial investigating the effectiveness of intravitreal ranibizumab in macular telangietasia type 2. There was a significant relationship between outer retinal thickness and retinal sensitivity (p<0.001) and neurodegeneration leaving less than about 50 ”m of parafoveal outer retinal thickness completely abolished light sensitivity. In contrast, functional preservation was found if neurodegeneration spared the photoreceptors, but caused quite extensive disruption of the inner retina. Longitudinal data revealed that small lesions affecting the photoreceptor layer typically precede functional detection but later cause severe loss of light sensitivity. Ranibizumab was shown to be ineffective to prevent such functional loss in macular telangietasia type 2.Since there is a general need for efficient monitoring of the effectiveness of therapy in neurodegenerative diseases of the retina and since SD-OCT imaging is becoming more widely available, surrogate endpoints derived from such structure-function correlation may become highly relevant in future clinical trials
The Role of Mislocalized Phototransduction in Photoreceptor Cell Death of Retinitis Pigmentosa
Most of inherited retinal diseases such as retinitis pigmentosa (RP) cause photoreceptor cell death resulting in blindness. RP is a large family of diseases in which the photoreceptor cell death can be caused by a number of pathways. Among them, light exposure has been reported to induce photoreceptor cell death. However, the detailed mechanism by which photoreceptor cell death is caused by light exposure is unclear. In this study, we have shown that even a mild light exposure can induce ectopic phototransduction and result in the acceleration of rod photoreceptor cell death in some vertebrate models. In ovl, a zebrafish model of outer segment deficiency, photoreceptor cell death is associated with light exposure. The ovl larvae show ectopic accumulation of rhodopsin and knockdown of ectopic rhodopsin and transducin rescue rod photoreceptor cell death. However, knockdown of phosphodiesterase, the enzyme that mediates the next step of phototransduction, does not. So, ectopic phototransduction activated by light exposure, which leads to rod photoreceptor cell death, is through the action of transducin. Furthermore, we have demonstrated that forced activation of adenylyl cyclase in the inner segment leads to rod photoreceptor cell death. For further confirmation, we have also generated a transgenic fish which possesses a human rhodopsin mutation, Q344X. This fish and rd10 model mice show photoreceptor cell death caused by adenylyl cyclase. In short, our study indicates that in some RP, adenylyl cyclase is involved in photoreceptor cell death pathway; its inhibition is potentially a logical approach for a novel RP therapy
Effects of Anacetrapib in Patients with Atherosclerotic Vascular Disease
BACKGROUND:
Patients with atherosclerotic vascular disease remain at high risk for cardiovascular events despite effective statin-based treatment of low-density lipoprotein (LDL) cholesterol levels. The inhibition of cholesteryl ester transfer protein (CETP) by anacetrapib reduces LDL cholesterol levels and increases high-density lipoprotein (HDL) cholesterol levels. However, trials of other CETP inhibitors have shown neutral or adverse effects on cardiovascular outcomes.
METHODS:
We conducted a randomized, double-blind, placebo-controlled trial involving 30,449 adults with atherosclerotic vascular disease who were receiving intensive atorvastatin therapy and who had a mean LDL cholesterol level of 61 mg per deciliter (1.58 mmol per liter), a mean non-HDL cholesterol level of 92 mg per deciliter (2.38 mmol per liter), and a mean HDL cholesterol level of 40 mg per deciliter (1.03 mmol per liter). The patients were assigned to receive either 100 mg of anacetrapib once daily (15,225 patients) or matching placebo (15,224 patients). The primary outcome was the first major coronary event, a composite of coronary death, myocardial infarction, or coronary revascularization.
RESULTS:
During the median follow-up period of 4.1 years, the primary outcome occurred in significantly fewer patients in the anacetrapib group than in the placebo group (1640 of 15,225 patients [10.8%] vs. 1803 of 15,224 patients [11.8%]; rate ratio, 0.91; 95% confidence interval, 0.85 to 0.97; P=0.004). The relative difference in risk was similar across multiple prespecified subgroups. At the trial midpoint, the mean level of HDL cholesterol was higher by 43 mg per deciliter (1.12 mmol per liter) in the anacetrapib group than in the placebo group (a relative difference of 104%), and the mean level of non-HDL cholesterol was lower by 17 mg per deciliter (0.44 mmol per liter), a relative difference of -18%. There were no significant between-group differences in the risk of death, cancer, or other serious adverse events.
CONCLUSIONS:
Among patients with atherosclerotic vascular disease who were receiving intensive statin therapy, the use of anacetrapib resulted in a lower incidence of major coronary events than the use of placebo. (Funded by Merck and others; Current Controlled Trials number, ISRCTN48678192 ; ClinicalTrials.gov number, NCT01252953 ; and EudraCT number, 2010-023467-18 .)
Radical pluralism and free speech in online public spaces: the case of North Belgian extreme right discourses
Progressive political movements and activists are not the only ones appropriating Web 2.0 as a way to construct independent public spaces and voice counterhegemonic discourses. By looking at the other extreme of (post-)fascist movements, it will be shown that the internet also gives rise to anti-public spaces, voicing hatred and essentialist discourses. In this article, discourses of hate produced by North-Belgian (post-)fascist movements and activists will be analysed. Theoretically the analysis is informed by radical pluralism and the limits of freedom of speech in a strong democracy. The cases presented challenge the limits of freedom of speech and of radical pluralism and bring us to question whether being a racist is a democratic right, whether freedom of speech includes opinions and views that challenge basic democratic values
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