Allgemeines,Genetik, Cytologie,Physiologie

Ohne Zusammenfassung     

Energy storage in the primary photochemical events of rhodopsin and isorhodopsin

The energetics associated with the photoequilibrium (Formula: see text) are measured at 77 K by using pulsed-laser photocalorimetry and a range of excitation wavelengths and relative starting concentrations. Enthalpies for the photochemical transformations R hv----B and I hv----B are measured to be delta HRB = 32.2 +/- 0.9 kcal mol-1 and delta HIB = 27.1 +/- 3.2 kcal mol-1, respectively. Although the value of delta HRB is slightly lower than that reported previously by Cooper of 34.7 +/- 2.2 kcal mol-1 [Cooper, A. (1979) Nature (London) 282, 531-533], the two values are in agreement within experimental error. The energy difference delta HRB - delta HIB = 5.1 +/- 3.3 kcal mol-1 is identical within experimental error with the difference in enthalpies of isorhodopsin and rhodopsin [5.2 +/- 2.3; Cooper, A. (1979) FEBS Lett. 100, 382-384]. We suggest that this result is consistent with the theory that bathorhodopsin is a single, common photochemical intermediate connecting rhodopsin and isorhodopsin.     

High visceral fat mass and high liver fat are associated with resistance to lifestyle intervention

Objective: High visceral adipose tissue (VAT) and high liver fat (LF) are associated with the metabolic syndrome and diabetes. We studied changes in these two fat depots during weight loss and analyzed whether VAT and LF at baseline predict the response to lifestyle intervention. Research Methods and Procedures: One hundred twelve subjects (48 men and 64 women; age, 46 ± 11 years; BMI, 29.2 ± 4.4 kg/m²) were studied after a follow up‐time of 264 ± 60 (SD) days. Insulin sensitivity was estimated from the oral glucose tolerance test. Body fat depots were quantified using magnetic resonance imaging and spectroscopy. Results: Cross‐sectionally high VAT (r = ?0.22, p = 0.02) and high LF (r = ?0.36, p < 0.0001) were independently associated with low insulin sensitivity. With intervention, BMI (?3.0%), VAT (?12.0%), and LF (?33.0%) were reduced (all p < 0.001). Insulin sensitivity was improved (+17%, p < 0.01). The changes in BMI (r = ?0.41), VAT (r = ?0.28), and LF (r = ?0.39) were associated with the increase in insulin sensitivity (all p < 0.01). High VAT (r = ?0.28, p = 0.01) and high LF (r = ?0.38, p < 0.01) at baseline were associated with a lesser increase in insulin sensitivity. Discussion: Baseline values and changes in BMI, VAT, and LF are related to changes in insulin sensitivity during lifestyle intervention. Subjects with high VAT and LF have a lower chance of profiting from lifestyle intervention and may require intensified lifestyle prevention strategies or even pharmacological approaches to improve insulin sensitivity.     

Adiponectin Oligomers and Ectopic Fat in Liver and Skeletal Muscle in Humans

We aimed at determining which circulating forms of the adipokine adiponectin that increases lipid oxidation in liver and skeletal muscle are related to ectopic fat in these depots in humans. Plasma total‐, high‐molecular weight (HMW)‐, middle‐molecular weight (MMW)‐, and low‐molecular weight (LMW) adiponectin were quantified by an enzyme‐linked immunosorbent assay. Their relationships with liver‐ and intramyocellular fat, measured using ¹H magnetic resonance spectroscopy, were investigated in 54 whites without type 2 diabetes. Liver fat, adjusted for gender, age, and total body fat, was associated only with HMW adiponectin (r = ?0.35, P = 0.012), but not with total‐, MMW‐, or LMW adiponectin. In addition, subjects with fatty liver (liver fat ≥5.56%, n = 15) had significantly lower HMW‐ (P = 0.04), but not total‐, MMW‐, or LMW adiponectin levels, compared to controls (n = 39). Similarly, intramyocellular fat correlated only with HMW (r = ?0.32, P = 0.039), but not with the other circulating forms of adiponectin. These data indicate that, among circulating forms of adiponectin, HMW is strongly related to ectopic fat, thus possibly representing the form of adiponectin regulating lipid oxidation in liver and skeletal muscle.     

Dissection of genomewide-scan data in extended families reveals a major locus and oligogenic susceptibility for age-related macular degeneration

To examine the genetic basis of age-related macular degeneration (ARMD), a degenerative disease of the retinal pigment epithelium and neurosensory retina, we conducted a genomewide scan in 34 extended families (297 individuals, 349 sib pairs) ascertained through index cases with neovascular disease or geographic atrophy. Family and medical history was obtained from index cases and family members. Fundus photographs were taken of all participating family members, and these were graded for severity by use of a quantitative scale. Model-free linkage analysis was performed, and tests of heterogeneity and epistasis were conducted. We have evidence of a major locus on chromosome 15q (GATA50C03 multipoint P=1.98x10-7; empirical P< or =1.0x10-5; single-point P=3.6x10-7). This locus was present as a weak linkage signal in our previous genome scan for ARMD, in the Beaver Dam Eye Study sample (D15S659, multipoint P=.047), but is otherwise novel. In this genome scan, we observed a total of 13 regions on 11 chromosomes (1q31, 2p21, 4p16, 5q34, 9p24, 9q31, 10q26, 12q13, 12q23, 15q21, 16p12, 18p11, and 20q13), with a nominal multipoint significance level of P< or =.01 or LOD > or =1.18. Family-by-family analysis of the data, performed using model-free linkage methods, suggests that there is evidence of heterogeneity in these families. For example, a single family (family 460) individually shows linkage evidence at 8 loci, at the level of P<.0001. We conducted tests for heterogeneity, which suggest that ARMD susceptibility loci on chromosomes 9p24, 10q26, and 15q21 are not present in all families. We tested for mutations in linked families and examined SNPs in two candidate genes, hemicentin-1 and EFEMP1, in subsamples (145 and 189 sib pairs, respectively) of the data. Mutations were not observed in any of the 11 exons of EFEMP1 nor in exon 104 of hemicentin-1. The SNP analysis for hemicentin-1 on 1q31 suggests that variants within or in very close proximity to this gene cause ARMD pathogenesis. In summary, we have evidence for a major ARMD locus on 15q21, which, coupled with numerous other loci segregating in these families, suggests complex oligogenic patterns of inheritance for ARMD.     

Field theoretic study of bilayer membrane fusion. I. Hemifusion mechanism

Self-consistent field theory is used to determine structural and energetic properties of metastable intermediates and unstable transition states involved in the standard stalk mechanism of bilayer membrane fusion. A microscopic model of flexible amphiphilic chains dissolved in hydrophilic solvent is employed to describe these self-assembled structures. We find that the barrier to formation of the initial stalk is much smaller than previously estimated by phenomenological theories. Therefore its creation it is not the rate-limiting process. The relevant barrier is associated with the rather limited radial expansion of the stalk into a hemifusion diaphragm. It is strongly affected by the architecture of the amphiphile, decreasing as the effective spontaneous curvature of the amphiphile is made more negative. It is also reduced when the tension is increased. At high tension the fusion pore, created when a hole forms in the hemifusion diaphragm, expands without bound. At very low membrane tension, small fusion pores can be trapped in a flickering metastable state. Successful fusion is severely limited by the architecture of the lipids. If the effective spontaneous curvature is not sufficiently negative, fusion does not occur because metastable stalks, whose existence is a seemingly necessary prerequisite, do not form at all. However if the spontaneous curvature is too negative, stalks are so stable that fusion does not occur because the system is unstable either to a phase of stable radial stalks, or to an inverted-hexagonal phase induced by stable linear stalks. Our results on the architecture and tension needed for successful fusion are summarized in a phase diagram.     

A new mechanism of model membrane fusion determined from Monte Carlo simulation

We have carried out extensive Monte Carlo simulations of the fusion of tense apposed bilayers formed by amphiphilic molecules within the framework of a coarse-grained lattice model. The fusion pathway differs from the usual stalk mechanism. Stalks do form between the apposed bilayers, but rather than expand radially to form an axial-symmetric hemifusion diaphragm of the trans leaves of both bilayers, they promote in their vicinity the nucleation of small holes in the bilayers. Two subsequent paths are observed. 1) The stalk encircles a hole in one bilayer creating a diaphragm comprised of both leaves of the other intact bilayer, which ruptures to complete the fusion pore. 2) Before the stalk can encircle a hole in one bilayer, a second hole forms in the other bilayer, and the stalk aligns and encircles them both to complete the fusion pore. Both pathways give rise to mixing between the cis and trans leaves of the bilayer and allow for transient leakage.     

Expression of VASP and zyxin in cochlear pillar cells: indication for actin-based dynamics?

Vasodilator-stimulated phosphoprotein (VASP) is a member of the ENA/VASP-protein family. VASP is considered to be a crucial factor in the regulation of actin dynamics, which involves processes such as motility and cell adhesion, e.g. in filopodia or growth cones. In these processes zyxin acts as an important partner of VASP and is particularly concentrated at sites where VASP-dependent actin dynamics occur. Based on indirect evidence that actin-mediated dynamics may effect the mechanical properties of the cochlea, we have investigated expression of VASP and zyxin in the postnatal and adult rat cochlea using polymerase chain reaction and Western blot approaches, as well as immunohistochemistry and confocal microscopy. Besides an expected expression in vessels and fibroblasts, VASP and zyxin expression was also observed in pillar cells. Here, the staining was restricted to the head and foot plate of the pillar cells. Onset of VASP expression in pillar cells coincided with the beginning of hearing. In pillar cells, VASP and zyxin were co-localised with pan-actin, suggesting actin-based dynamics in these cochlear cells, which until now were rather presumed to form a highly rigid bridge between the inner and outer sensory cells. Thus, pillar cells may be more dynamically involved in controlling longer-lasting mechanical properties of the cochlea as hitherto presumed.