Lateral diffusion of cholesterol in monolayers.

The surface diffusion coefficient of cholesterol in cholesterol monolayers has been measured as a function of cholesterol surface concentration. Two different radiochemical methods, one integral and the other differential, were developed which gave comparable results. In the integral method two cholesterol monolayers, one of which is radioactive, are isolated on inert hydrophilic supports and then brought into contact. After some time the supports are separated and the radioactivity of the supports is measured. The differential method is an autoradiographic experiment. Two cholesterol monolayers, one of which is radioactive, are separated by means of a thin barrier. Upon removal of the barrier and at later times, an autoradiographic plate is brought to within a fraction of a mm from the aqueous surface and exposed. The plates are developed and analysed. The data show that the cholesterol surface diffusion coefficient in the dilute monolayers is approximately 10(-6)cm2/s and is nearly independent of surface concentration up to a concentration corresponding to an area of 40 A2/molecule. As the monolayer becomes compressed beyond this surface concentration, the diffusion coefficient decreases ubruptly with the deeply decreasing surface tension to about 10(-7) cm2/s, when a fully condensed surface layer of 38 A2/molecule is reached. This diffusion coefficient is of the same order of magnitude as the diffusion coefficients measured in lipid bilayers and in membranes.     

Differential Effects of Drug Interventions and Dietary Lifestyle in Developing Type 2 Diabetes and Complications: A Systems Biology Analysis in LDLr?/? Mice

Excess caloric intake leads to metabolic overload and is associated with development of type 2 diabetes (T2DM). Current disease management concentrates on risk factors of the disease such as blood glucose, however with limited success. We hypothesize that normalizing blood glucose levels by itself is insufficient to reduce the development of T2DM and complications, and that removal of the metabolic overload with dietary interventions may be more efficacious. We explored the efficacy and systems effects of pharmaceutical interventions versus dietary lifestyle intervention (DLI) in developing T2DM and complications. To mimic the situation in humans, high fat diet (HFD)-fed LDLr−/− mice with already established disease phenotype were treated with ten different drugs mixed into HFD or subjected to DLI (switch to low-fat chow), for 7 weeks. Interventions were compared to untreated reference mice kept on HFD or chow only. Although most of the drugs improved HFD-induced hyperglycemia, drugs only partially affected other risk factors and also had limited effect on disease progression towards microalbuminuria, hepatosteatosis and atherosclerosis. By contrast, DLI normalized T2DM risk factors, fully reversed hepatosteatosis and microalbuminuria, and tended to attenuate atherogenesis. The comprehensive beneficial effect of DLI was reflected by normalized metabolite profiles in plasma and liver. Analysis of disease pathways in liver confirmed reversion of the metabolic distortions with DLI. This study demonstrates that the pathogenesis of T2DM towards complications is reversible with DLI and highlights the differential effects of current pharmacotherapies and their limitation to resolve the disease.     

Evidence for a Turner syndrome locus or loci at Xp11.2-p22.1.

Turner syndrome is the complex human phenotype associated with complete or partial monosomy X. Principle features of Turner syndrome include short stature, ovarian failure, and a variety of other anatomic and physiological abnormalities, such as webbed neck, lymphedema, cardiovascular and renal anomalies, hypertension, and autoimmune thyroid disease. We studied 28 apparently nonmosaic subjects with partial deletions of Xp, in order to map loci responsible for various components of the Turner syndrome phenotype. Subjects were carefully evaluated for the presence or absence of Turner syndrome features, and their deletions were mapped by FISH with a panel of Xp markers. Using a statistical method to examine genotype/phenotype correlations, we mapped one or more Turner syndrome traits to a critical region in Xp11.2-p22.1. These traits included short stature, ovarian failure, high-arched palate, and autoimmune thyroid disease. The results are useful for genetic counseling of individuals with partial monosomy X. Study of additional subjects should refine the localization of Turner syndrome loci and provide a rational basis for exploration of candidate genes.     

Learning combined feedback and feedforward control of a musculoskeletal system

The goal of this paper is the learning of neuromuscular control, given the following necessary conditions: (1) time delays in the control loop, (2) non-linear muscle characteristics, (3) learning of feedforward and feedback control, (4) possibility of feedback gain modulation during a task. A control system and learning methodology that satisfy those conditions is given. The control system contains a neural network, comprising both feedforward and feedback control. The learning method is backpropagation through time with an explicit sensitivity model. Results will be given for a one degree of freedom arm with two muscles. Good control results are achieved which compare well with experimental data. Analysis of the controller shows that significant differences in controller characteristics are found if the loop delays are neglected. During a control task the system shows feedback gain modulation, similar to experimentally found reflex gain modulation during rapid voluntary contraction. If only limited feedback information is available to the controller the system learns to co-contract the antagonistic muscle pair. In this way joint stiffness increases and stable control is more easily maintained. Received: 7 November 1995 / Accepted in revised form: 13 February 1996     

Prenatal diagnosis of 45,X/46,XX mosaicism and 45,X: implications for postnatal outcome.

The prognosis for 45,X/46,XX mosaicism diagnosed prenatally has yet to be established. We report our experience with 12 patients in whom prenatal diagnosis of 45,X/46,XX mosaicism was detected by amniocentesis for advanced maternal age or decreased maternal serum alpha-feto protein and compared them with 41 45,X/46,XX patients diagnosed postnatally. The girls in the prenatal group range in age from 3 mo to 10 years. All have had normal linear growth. Four had structural anomalies including: ASD (n = 1); ptosis and esotropia (n = 1); labial fusion (n = 1); and urogenital sinus, dysplastic kidneys, and hydrometrocolpos (n = 1). Gonadotropins were measured in seven; one had elevated luteinizing hormone/FSH at 3 mo of age. One has developmental delay and seizures as well as ophthalmologic abnormalities. None would have warranted karyotyping for clinical suspicion of Turner syndrome. The prevalence of 45,X/46,XX mosaicism is 10-fold higher among amniocenteses than in series of postnatally diagnosed individuals with Turner syndrome, which suggests that most individuals with this karyotype escape detection and that an ascertainment bias exists toward those with clinically evident abnormalities. The phenomenon of a milder phenotype for the prenatal group is similar to that observed for 45,X/46,XY diagnosed prenatally. Prenatal counseling for 45,X/46,XX in the absence of such ultrasound abnormalities as hydrops fetalis should take into account the expectation of a milder phenotype (except, possibly, with respect to developmental delay) than that of patients ascertained postnatally. The same does not hold true for 45,x diagnosed prenatally.     

Pten Null Prostate Epithelium Promotes Localized Myeloid-Derived Suppressor Cell Expansion and Immune Suppression during Tumor Initiation and Progression

Chronic inflammation is known to be associated with prostate cancer development, but how epithelium-associated cancer-initiating events cross talk to inflammatory cells during prostate cancer initiation and progression is largely unknown. Using the Pten null murine prostate cancer model, we show an expansion of Gr-1⁺ CD11b⁺ myeloid-derived suppressor cells (MDSCs) occurring intraprostatically immediately following epithelium-specific Pten deletion without expansion in hematopoietic tissues. This MDSC expansion is accompanied by sustained immune suppression. Prostatic Gr-1⁺ CD11b⁺ cells, but not those isolated from the spleen of the same tumor-bearing mice, suppress T cell proliferation and express high levels of Arginase 1 and iNOS. Mechanistically, the loss of PTEN in the epithelium leads to a significant upregulation of genes within the inflammatory response and cytokine-cytokine receptor interaction pathways, including Csf1 and Il1b, two genes known to induce MDSC expansion and immunosuppressive activities. Treatment of Pten null mice with the selective CSF-1 receptor inhibitor GW2580 decreases MDSC infiltration and relieves the associated immunosuppressive phenotype. Our study indicates that epithelium-associated tumor-initiating events trigger the secretion of inflammatory cytokines and promote localized MDSC expansion and immune suppression, thereby promoting tumor progression.     

Biophysical properties of membrane lipids of anammox bacteria: I. Ladderane phospholipids form highly organized fluid membranes

Anammox bacteria that are capable of anaerobically oxidizing ammonium (anammox) with nitrite to nitrogen gas produce unique membrane phospholipids that comprise hydrocarbon chains with three or five linearly condensed cyclobutane rings. To gain insight into the biophysical properties of these ‘ladderane’ lipids, we have isolated a ladderane phosphatidylcholine and a mixed ladderane phosphatidylethanolamine/phosphatidylglycerol lipid fraction and reconstituted these lipids in different membrane environments. Langmuir monolayer experiments demonstrated that the purified ladderane phospholipids form fluid films with a relatively high lipid packing density. Fluid-like behavior was also observed for ladderane lipids in bilayer systems as monitored by cryo-electron microscopy on large unilamellar vesicles (LUVs) and epi-fluorescence microscopy on giant unilamellar vesicles (GUVs). Analysis of the LUVs by fluorescence depolarization revealed a relatively high acyl chain ordering in the hydrophobic region of the ladderane phospholipids. Micropipette aspiration experiments were applied to study the mechanical properties of ladderane containing lipid bilayers and showed a relatively high apparent area compressibility modulus for ladderane containing GUVs, thereby confirming the fluid and acyl chain ordered characteristics of these lipids. The biophysical findings in this study support the previous postulation that dense membranes in anammox cells protect these microbes against the highly toxic and volatile anammox metabolites.