A finite element model of the human knee joint for the study of tibio-femoral contact

As a step towards developing a finite element model of the knee that can be used to study how the variables associated with a meniscal replacement affect tibio-femoral contact, the goals of this study were 1) to develop a geometrically accurate three-dimensional solid model of the knee joint with special attention given to the menisci and articular cartilage, 2) to determine to what extent bony deformations affect contact behavior, and 3) to determine whether constraining rotations other than flexion/extension affects the contact behavior of the joint during compressive loading. The model included both the cortical and trabecular bone of the femur and tibia, articular cartilage of the femoral condyles and tibial plateau, both the medial and lateral menisci with their horn attachments, the transverse ligament, the anterior cruciate ligament, and the medial collateral ligament. The solid models for the menisci and articular cartilage were created from surface scans provided by a noncontacting, laser-based, three-dimensional coordinate digitizing system with an root mean squared error (RMSE) of less than 8 microns. Solid models of both the tibia and femur were created from CT images, except for the most proximal surface of the tibia and most distal surface of the femur which were created with the three-dimensional coordinate digitizing system. The constitutive relation of the menisci treated the tissue as transversely isotropic and linearly elastic. Under the application of an 800 N compressive load at 0 degrees of flexion, six contact variables in each compartment (ie., medial and lateral) were computed including maximum pressure, mean pressure, contact area, total contact force, and coordinates of the center of pressure. Convergence of the finite element solution was studied using three mesh sizes ranging from an average element size of 5 mm by 5 mm to 1 mm by 1 mm. The solution was considered converged for an average element size of 2 mm by 2 mm. Using this mesh size, finite element solutions for rigid versus deformable bones indicated that none of the contact variables changed by more than 2% when the femur and tibia were treated as rigid. However, differences in contact variables as large as 19% occurred when rotations other than flexion/extension were constrained. The largest difference was in the maximum pressure. Among the principal conclusions of the study are that accurate finite element solutions of tibio-femoral contact behavior can be obtained by treating the bones as rigid. However, unrealistic constraints on rotations other than flexion/extension can result in relatively large errors in contact variables.     

Programmed death-1 targeting can promote allograft survival

The recently identified CD28 homolog and costimulatory molecule programmed death-1 (PD-1) and its ligands, PD-L1 and PD-L2, which are homologs of B7, constitute an inhibitory regulatory pathway of potential therapeutic use in immune-mediated diseases. We examined the expression and functions of PD-1 and its ligands in experimental cardiac allograft rejection. In initial studies, we found that most normal tissues and cardiac isografts had minimal expression of PD-1, PD-L1, or PD-L2, but intragraft induction of all three molecules occurred during development of cardiac allograft rejection. Intragraft expression of all three genes was maintained despite therapy with cyclosporin A or rapamycin, but was prevented in the early posttransplant period by costimulation blockade using CD154 or anti-inducible costimulator mAb. We prepared PD-L1.Ig and PD-L2.Ig fusion proteins and showed that each bound to activated PD-1(+) T cells and inhibited T cell functions in vitro, thereby allowing us to test the effects of PD-1 targeting on allograft survival in vivo. Neither agent alone modulated allograft rejection in wild-type recipients. However, use of PD-L1.Ig administration in CD28(-/-) recipients, or in conjunction with immunosuppression in fully MHC-disparate combinations, markedly prolonged cardiac allograft survival, in some cases causing permanent engraftment, and was accompanied by reduced intragraft expression of IFN-gamma and IFN-gamma-induced chemokines. PD-L1.Ig use also prevented development of transplant arteriosclerosis post-CD154 mAb therapy. These data show that when combined with limited immunosuppression, or in the context of submaximal TCR or costimulatory signals, targeting of PD-1 can block allograft rejection and modulate T and B cell-dependent pathologic immune responses in vivo.     

Isolation of an Amoeba Naturally Harboring a Distinctive Legionella Species

There are numerous in vitro studies documenting the multiplication of Legionella species in free-living amoebae and other protozoa. It is believed that protozoa serve as host cells for the intracellular replication of certain Legionella species in a variety of environmental settings. This study describes the isolation and characterization of a bacterium initially observed within an amoeba taken from a soil sample. In the laboratory, the bacterium multiplied within and was highly pathogenic for Acanthamoeba polyphaga. Extracellular multiplication was observed on buffered charcoal yeast extract agar but not on a variety of conventional laboratory media. A 16S rRNA gene analysis placed the bacterium within the genus Legionella. Serological studies indicate that it is distinct from previously described species of the genus. This report also describes methods that should prove useful for the isolation and characterization of additional Legionella-like bacteria from free-living amoebae. In addition, the characterization of bacterial pathogens of amoebae has significant implications for understanding the ecology and identification of other unrecognized bacterial pathogens.     

Modulation of the phosphoinositide 3-kinase pathway alters innate resistance to polymicrobial sepsis

We examined the effect of modulating phosphoinositide 3-kinase (PI3K) activity in a murine model of cecal ligation and puncture-induced polymicrobial sepsis. Inhibition of PI3K activity with wortmannin increased serum cytokine levels and decreased survival time in septic mice. We have reported that an immunomodulator, glucan phosphate, induces protection in murine polymicrobial sepsis. We observed that glucan stimulated tissue PI3K activity, which positively correlated with increased survival in septic mice. We investigated the effect of PI3K inhibition on survival in septic mice treated with glucan. Treatment of mice with the PI3K inhibitors, wortmannin and LY294002, completely eliminated the protective effect of glucan, indicating that protection against septic mortality was mediated through PI3K. Inhibition of PI3K resulted in increased serum levels of IL1-beta, IL-2, IL-6, IL-10, IL-12, and TNF-alpha in septic mice. Apoptosis is thought to play a central role in the response to septic injury. We observed that inhibition of PI3K activity in septic mice resulted in increased splenocyte apoptosis and a change in the anatomic distribution of splenocyte apoptosis. We conclude that PI3K is a compensatory mechanism that suppresses proinflammatory and apoptotic processes in response to sepsis and/or inflammatory injury. Thus, PI3K may play a pivotal role in the maintenance of homeostasis and the integrity of the immune response during sepsis. We also observed that glucan phosphate decreased septic morbidity and mortality through a PI3K-dependent mechanism. This suggests that stimulation of the PI3K pathway may be an effective approach for preventing or treating sepsis and/or septic shock.     

The Causes of self-sterility in natural populations of the relictual angiosperm, Illicium floridanum (Illiciaceae)

BACKGROUND AND AIMS: Illicium floridanum, a species belonging to the basal extant angiosperm taxon Illiciaceae, reportedly exhibits self-incompatibility (SI). To date, the site and timing of SI within the carpel of this species remains unidentified. Thus, the objective of this research was to determine the cellular and temporal aspects of SI in I. floridanum. METHODS: Following controlled application of cross- and self-pollen in natural populations of I. floridanum, embryo sac development and temporal aspects of stigma receptivity, as well as pollen tube growth, fertilization, and embryo and endosperm development, were investigated with the aid of light and fluorescence microscopy. KEY RESULTS: Flowers of I. floridanum exhibited complete dichogamy whereby stigmas only supported cross- and self-pollen tube growth prior to anther dehiscence. In contrast to earlier reports of SI in this species, a prezygotic SI resulting in rejection of self-pollen tube growth at the stigma was absent and there were no significant differences between cross- versus self-pollen germination and pollen tube growth within the style and ovary during the first 5 d after pollination. Structural development of the four-celled embryo sac was not differentially influenced by pollen type as noted to occur in other angiosperms with late-acting ovarian SI. The ovule micropyle and embryo sac were penetrated equally by cross- and self-pollen tubes. In addition, there were no statistically significant differences in cross- versus self-fertilization. A resting zygote and multicellular endosperm at a variety of developmental stages was present by 30 d after application of cross- or self-pollen. CONCLUSIONS: In the clear absence of a prezygotic SI that was previously reported to result in differential self-pollen tube growth at the stigma, self- sterility in I. floridanum is likely due to early-acting inbreeding depression, although late-acting post-zygotic ovarian SI cannot be ruled out.     

The effect of glycerol on torque, electromyography, and mechanomyography

The purpose of this investigation was to determine the effect of hyperhydration on the electromyographic (EMG) and mechanomyographic (MMG) responses during isometric and isokinetic muscle actions of the biceps brachii. Eight (22.1 +/- 1.8 years, 79.5 +/- 22.8 kg) subjects were tested for maximal isometric, submaximal isometric, and maximal concentric isokinetic muscle strength in either a control (C) or hyperhydrated (H) state induced by glycerol ingestion while the EMG and MMG signals were recorded. Although fluid retention was significantly greater during the H protocol, the analyses indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, or MMG MPF with hyperhydration. These results indicated that glycerol-induced fluid retention does not affect the torque-producing capabilities of a muscle, the impulses (EMG) going to a muscle, or muscular vibrations (MMG). It has been suggested that EMG and MMG can be used as direct electrical/mechanical monitoring, which could be presented to trainers and athletes; however, before determining the utility of these signals, the MMG and EMG responses should be examined under a variety of conditions such as in the present study.     

Susceptibility genes for age-related maculopathy on chromosome 10q26

On the basis of genomewide linkage studies of families affected with age-related maculopathy (ARM), we previously identified a significant linkage peak on 10q26, which has been independently replicated by several groups. We performed a focused SNP genotyping study of our families and an additional control cohort. We identified a strong association signal overlying three genes, PLEKHA1, LOC387715, and PRSS11. All nonsynonymous SNPs in this critical region were genotyped, yielding a highly significant association (P < .00001) between PLEKHA1/LOC387715 and ARM. Although it is difficult to determine statistically which of these two genes is most important, SNPs in PLEKHA1 are more likely to account for the linkage signal in this region than are SNPs in LOC387715; thus, this gene and its alleles are implicated as an important risk factor for ARM. We also found weaker evidence supporting the possible involvement of the GRK5/RGS10 locus in ARM. These associations appear to be independent of the association of ARM with the Y402H allele of complement factor H, which has previously been reported as a major susceptibility factor for ARM. The combination of our analyses strongly implicates PLEKHA1/LOC387715 as primarily responsible for the evidence of linkage of ARM to the 10q26 locus and as a major contributor to ARM susceptibility. The association of either a single or a double copy of the high-risk allele within the PLEKHA1/LOC387715 locus accounts for an odds ratio of 5.0 (95% confidence interval 3.2-7.9) for ARM and a population attributable risk as high as 57%.     

Overexpression of TLR2 and TLR4 susceptibility to serum deprivation-induced apoptosis in CHO cells

We examined the effect of overexpression of TLR2 and TLR4 on apoptosis. TLR2 and TLR4 transfected CHO cells were subjected to serum deprivation for 0, 24, and 48 h. CHO cells served as control. The survival was 80.4% and 66.8% in CHO cells, 73.8% and 47.6% in TLR2/CHO, and 70.5% and 53.0% in TLR4/CHO, respectively. Flow cytometry examination suggested that apoptotic cells were 7.17% and 32.91% in control CHO cells, 29.0% and 64.6% in TLR2/CHO, and 41.4% and 64.6% in TLR4/CHO, respectively. The levels of FasL and caspase-8 activity in TLR2/CHO and TLR4/CHO cells were significantly higher than that of CHO cells. Transfection of dominant negative FADD into TLR2/CHO and TLR4/CHO cells significantly reduced apoptosis. Our results suggest that overexpression of TLR2 and TLR4 in CHO cells sensitizes the cells to serum deprivation-induced apoptosis and that the mechanisms are involved in the death receptor-mediated signaling pathway.     

Farnesylation is involved in meristem organization in Arabidopsis

 Although studies in plant and animal cell culture systems indicate farnesylation is required for normal cell cycle progression, how this lipid modification of select proteins translates into whole-organism developmental decisions involving cell proliferation or differentiation is largely unknown. The era1 mutant of the higher plant Arabidopsis thaliana (L.) Heynh. offers a unique opportunity to understand the role farnesylation may play in regulating various processes during the development of a multicellular organism. Loss of farnesylation affects many aspects of Arabidopsis growth and development. In particular, apical and axillary meristem development is altered and these phenotypes are contingent on the growth conditions. Received: 25 October 1999 / Accepted: 22 December 1999     

LIF and BMP signaling generate separate and discrete types of GFAP-expressing cells

Bone morphogenetic protein (BMP) and leukemia inhibitory factor (LIF) signaling both promote the differentiation of neural stem/progenitor cells into glial fibrillary acidic protein (GFAP) immunoreactive cells. This study compares the cellular and molecular characteristics, and the potentiality, of GFAP(+) cells generated by these different signaling pathways. Treatment of cultured embryonic subventricular zone (SVZ) progenitor cells with LIF generates GFAP(+) cells that have a bipolar/tripolar morphology, remain in cell cycle, contain progenitor cell markers and demonstrate self-renewal with enhanced neurogenesis - characteristics that are typical of adult SVZ and subgranular zone (SGZ) stem cells/astrocytes. By contrast, BMP-induced GFAP(+) cells are stellate, exit the cell cycle, and lack progenitor traits and self-renewal--characteristics that are typical of astrocytes in the non-neurogenic adult cortex. In vivo, transgenic overexpression of BMP4 increases the number of GFAP(+) astrocytes but depletes the GFAP(+) progenitor cell pool, whereas transgenic inhibition of BMP signaling increases the size of the GFAP(+) progenitor cell pool but reduces the overall numbers of astrocytes. We conclude that LIF and BMP signaling generate different astrocytic cell types, and propose that these cells are, respectively, adult progenitor cells and mature astrocytes.