Effects of radiograph projection parameter uncertainty on TKA kinematics from model-image registration

Model-image registration techniques have been used extensively for the measurement of joint kinematics in vivo. These techniques typically utilize an explicit measurement of X-ray projection parameters (principal distance, principal point), which is easily done for prospective studies. However, there is vast opportunity to derive useful information from previously collected clinical radiographic films where the projection parameters are unknown. The purpose of this study was to determine variation in measured knee arthroplasty kinematics when the X-ray projection parameters were unknown, but bounded. Based on the clinical radiographic protocol, a nominal principal point was chosen and eight additional points ±2 and ±5 cm in the horizontal and vertical directions were defined. Tibiofemoral kinematics were determined for all nine projection parameter sets for a series of 10 lateral radiographs. In addition, the principal distance was varied ±15 cm and tibiofemoral kinematics were determined for these two projection sets. Measured joint kinematics varied less than 0.6° and 0.4 mm for ±2 cm variations in principal point location, and 0.7° and 0.6 mm for ±5 cm variations in principal point location. Measured joint kinematics varied less than 0.6° and 0.7 mm for ±15 cm variations in principal distance. Variation in X-ray principal point and principal distance over clinically bounded ranges has a small effect on knee arthroplasty kinematics computed from model-image registration with high-quality clinical radiographs.     

The conformational and property space of acetylcholine bound to muscarinic receptors: an entropy component accounts for the subtype selectivity of acetylcholine

The conformational behavior of receptor-bound acetylcholine (ACh) was investigated by molecular dynamics simulations. Based on the great similarity among muscarinic receptors, the study was focused on the human M(1), M(2), and M(5) receptors as previously modeled by us. The results showed that receptor-bound ACh was not frozen in a single preferred conformation but preserved an unexpected fraction of its conformational space. However, there were marked differences between the three receptors since the ligand was mostly trans in the M(1) receptor, equally distributed among trans and gauche conformers in M(2), and exclusively gauche in the M(5); the greater flexibility of M(2)-bound ACh was paralleled by the greater flexibility of the occupied M(2) binding site. By contrast, the property space of receptor-bound ACh, and particularly its virtual (computed, conformation-dependent) lipophilicity, was restricted to relatively narrow ranges optimal for successful interaction. Experimental binding investigations to the individual human M(1), M(2), and M(5) muscarinic receptors showed ACh to have a 10-fold higher affinity for the M(2) compared to the M(1) and M(5) receptors. This selectivity was not confirmed by the calculated binding scores, a fact postulated to be caused by the absence of an entropy component in such binding scores. Indeed, the Shannon entropy of all geometric and physicochemical properties monitored were markedly higher in M(2)-bound ACh compared to M(1)-bound and M(5)-bound ACh. This finding suggests that the selectivity profile of acetylcholine for the M(2) receptor is largely entropy-driven, a fact that might explain the intrinsic difficulty to design subtype-selective muscarinic agonists.     

New findings on 3-D microanatomy of cellular structures in human tissues and organs. An HRSEM study

We present here findings obtained on a large number of human tissues over a period of more than ten years, by our modification of the Osmium maceration method for high resolution scanning electron microscopy (HRSEM). Data are documented by original pictures which illustrate both some 3-D intracellular features not previously shown in human tissues, and results obtained in our current studies on mitochondrial morphology and on the secretory process of salivary glands. We have demonstrated that mitochondria of cells of practically all human tissues and organs have usually tubular cristae, and that even the cristae that look lamellar are joined to the inner mitochondrial membrane by tubular connexions similar to the crista junctions later seen by electron tomography. Concerning salivary glands an important result is the development of a morphometric method that allows the quantitative evaluation of the secretory events.     

The methyltransferase Set7/9 (Setd7) is dispensable for the p53-mediated DNA damage response in vivo

p53 is the central regulator of cell fate following genotoxic stress and oncogene activation. Its activity is controlled by several posttranslational modifications. Originally defined as a critical layer of p53 regulation in human cell lines, p53 lysine methylation by Set7/9 (also called Setd7) was proposed to fulfill a similar function in?vivo in the mouse, promoting p53 acetylation, stabilization, and activation upon DNA damage (Kurash et?al., 2008). We tested the physiological relevance of this circuit in an independent Set7/9 knockout mouse strain. Deletion of Set7/9 had no effect on p53-dependent cell-cycle arrest or apoptosis following sublethal or lethal DNA damage induced by radiation or genotoxic agents. Set7/9 was also dispensable for p53 acetylation following irradiation. c-myc oncogene-induced apoptosis was also independent of Set7/9, and analysis of p53 target genes showed that Set7/9 is not required for the p53-dependent gene expression program. Our data indicate that Set7/9 is dispensable for p53 function in the mouse.     

Variation, natural selection, and information content--a simulation

In Neo-Darwinism, variation and natural selection are the two evolutionary mechanisms that propel biological evolution. Variation implies changes in the gene pool of a population, enlarging the genetic variability from which natural selection can choose. But in the absence of natural selection, variation causes dissipation and randomization. Natural selection, in contrast, constrains this variability by decreasing the survival and fertility of the less-adapted organisms. The objective of this study is to propose a highly simplified simulation of variation and natural selection, and to relate the observed evolutionary changes in a population to its information content. The model involves an imaginary population of individuals. A quantifiable character allows the individuals to be categorized into bins. The distribution of bins (a histogram) was assumed to be Gaussian. The content of each bin was calculated after one to twelve cycles, each cycle spanning N generations (N being undefined). In a first study, selection was simulated in the absence of variation. This was modeled by assuming a differential fertility factor F that increased linearly from the lower bins (F<1.00) to the higher bins (F>1.00). The fertility factor was applied as a multiplication factor during each cycle. Several ranges of fertility were investigated. The resulting histograms became skewed to the right. In a second study, variation was simulated in the absence of selection. This was modeled by assuming that during each cycle each bin lost a fixed percentage of its content (variation factor Y) to its two adjacent bins. The resulting histograms became broader and flatter, while retaining their bilateral symmetry. Different values of Y were monitored. In a third study, various values of F and Y were combined. Our model allows the straightforward application of Shannon's equation and the calculation of a Shannon-entropy (SE) values for each histogram. Natural selection was, thus, shown to result in a progressive decrease in SE as a function of F. In other words, natural selection, when acting alone, progressively increased the information content of the population. In contrast, variation resulted in a progressive increase in SE as a function of Y. In other words, variation acting alone progressively decreased the information content of a population. When both factors, F and Y, were applied simultaneously, their relative weight determined the progressive change in SE.     

Rapid modification of bacterial artificial chromosomes by ET-recombination

We present a method to modify bacterial artificial chromosomes (BACs) resident in their host strain. The method is based on homologous recombination by ET-cloning. We have successfully modified BACs at two distinct loci by recombination with a PCR product containing homology arms of 50 nt. The procedure we describe here is rapid, was found to work with high efficiency and should be applicable to any BAC modification desired.     

Supramaximal exercise mobilizes hematopoietic progenitors and reticulocytes in athletes

Marathon runners show increased circulating CD34+ cell counts and postexercise release of interleukin-6 (IL-6), granulocyte-colony stimulating factor (G-CSF) and flt3-ligand (Bonsignore MR, Morici G, Santoro A, Pegano M, Cascio L, Bonnano A, Abate P, Mirabella F, Profita M, Insalaco G, Gioia M, Vignola AM, Majolino I, Testa U, and Hogg JC. J Appl Physiol 93: 1691-1697, 2002). In the present study we hypothesized that supramaximal ("all-out") exercise may acutely affect circulating progenitors and reticulocytes and investigated possible mechanisms involved. Progenitor release was measured by flow cytometry (n = 20) and clonogenic assays (n = 6) in 20 young competitive rowers (13 M, 7 F, age +/- SD: 17.1 +/- 2.1 yr, peak O2 consumption: 56.5 +/- 11.4 ml.min(-1).kg(-1)) at rest and shortly after 1,000 m "all-out." Release of reticulocytes, cortisol, muscle enzymes, neutrophil elastase, and several cytokines/growth factors was measured. Supramaximal exercise doubled circulating CD34+ cells (rest: 7.6 +/- 3.0, all-out: 16.3 +/- 9.1 cells/mul, P < 0.001), and increased immature reticulocyte fractions; AC133+ cells doubled, suggesting release of angiogenetic precursors. Erythrocyte burst forming units and colony forming units for granulocytes-monocytes and all blood series increased postexercise by 3.4-, 5.5-, and 4.8-fold, respectively (P < 0.01 for all). All-out rowing acutely increased plasma cortisol, neutrophil elastase, flt3-ligand, hepatocyte growth factor, VEGF, and transforming growth factor-beta1, and decreased erythropoietin; K-ligand, stromal-derived factor-1, IL-6, and G-CSF were unchanged. Therefore, all-out exercise is a physiological stimulus for progenitor release in athletes. Release of reticulocytes and proangiogenetic cells and mediators suggests tissue hypoxia as possibly involved in progenitor mobilization.     

The NF2 tumor suppressor gene product, merlin, inhibits cell proliferation and cell cycle progression by repressing cyclin D1 expression

Inactivation of the NF2 tumor suppressor gene has been observed in certain benign and malignant tumors. Recent studies have demonstrated that merlin, the product of the NF2 gene, is regulated by Rac/PAK signaling. However, the mechanism by which merlin acts as a tumor suppressor has remained obscure. In this report, we show that adenovirus-mediated expression of merlin in NF2-deficient tumor cells inhibits cell proliferation and arrests cells at G1 phase, concomitant with decreased expression of cyclin D1, inhibition of CDK4 activity, and dephosphorylation of pRB. The effect of merlin on cell cycle progression was partially overridden by ectopic expression of cyclin D1. RNA interference experiments showed that silencing of the endogenous NF2 gene results in upregulation of cyclin D1 and S-phase entry. Furthermore, PAK1-stimulated cyclin D1 promoter activity was repressed by cotransfection of NF2, and PAK activity was inhibited by expression of merlin. Interestingly, the S518A mutant form of merlin, which is refractory to phosphorylation by PAK, was more efficient than the wild-type protein in inhibiting cell cycle progression and in repressing cyclin D1 promoter activity. Collectively, our data indicate that merlin exerts its antiproliferative effect, at least in part, via repression of PAK-induced cyclin D1 expression, suggesting a unifying mechanism by which merlin inactivation might contribute to the overgrowth seen in both noninvasive and malignant tumors.     

Rate-control or rhythm-control: where do we stand?

Atrial fibrillation is the most common sustained rhythm disturbance and its prevalence is increasing worldwide due to the progressive aging of the population. Current guidelines clearly depict the gold standard management of acute symptomatic atrial fibrillation but the best-long term approach for first or recurrent atrial fibrillation is still debated with regard to quality of life, risk of new hospitalizations, and possible disabling complications, such as thromboembolic stroke, major bleeds and death. Some authors propose that regaining sinus rhythm in all cases, thus re-establishing a physiologic cardiac function not requiring a prolonged antithrombotic therapy, avoids the threat of intracranial or extracranial haemorrhages due to Vitamin K antagonists or aspirin. On the contrary, advocates of a rate control approach with an accurate antithrombotic prophylaxis propose that such a strategy may avoid the risk of cardiovascular and non cardiovascular side effects related to antiarrhythmic drugs. This review aims to explore the state of our knowledge in order to summarize evidences and issues that need to be furthermore clarified.